Development of Natural Fibre-Reinforced Polymer Composites Ballistic Helmet Using Concurrent Engineering Approach: A Brief Review

Round 1

Reviewer 1 Report

Excellent dissertation on concurrent engineering applied to fiber composites. I have no further comments and my sincere congratulations to the authors. 

Author Response

Dear editor,

Thanks for your letter and the thoughtful comments from the referees about our paper entitled “Development of Natural Fibre Reinforced Polymer Composites Ballistic Helmet Using Concurrent Engineering Approach: A Brief Review” sustainability-1657191. We carefully analysed all the comments and these comments are very valuable and helpful for perfecting and modifying our manuscript, and also have important guiding significance for our research. Therefore, we carefully checked the manuscript and revised it according to each comment. Consequently, we feel that our manuscript is substantially strengthened. Revised portion are marked using yellow background in the revised manuscript. The detailed corrections in the paper and the responses to the reviewer’s comments are as the following list of revisions. We also had sent this manuscript to be proofread by well-known proof-reader, in order to achieve the high quality of the journal. The certificate of proofreading is attached below:

 

We look forward to your positive response. If you have any question about this paper, please don’t hesitate to let us know. We hope these revisions will make it more acceptable for publication. Thank you.

Sincerely yours,

R.A. Ilyas

School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

Centre for Advanced Composite Materials (CACM), Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

 

Reviewer 1

Excellent dissertation on concurrent engineering applied to fiber composites. I have no further comments and my sincere congratulations to the authors.

Dear reviewers, thanks a lot for your support.

 

Reviewer 2

1. I think that the title is not well appropriated because only small paragraphs (paragraphs 4 and 5) deal with natural fibre composites.

Dear reviewer, thanks for your constructive comment. The tittle is well developed as we considered natural fibre composite as potential materials for ballistic helmet. Besides that, we have revised the section 4, 5 and 6. Thus we think that the information that provided by us is enough.

4. Implementation of Natural Fibre Composites Toward Sustainable Development

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix). The reinforcement material is made from natural fibres obtained from animal, mineral and plant by-products [43–46], as shown in Figure 4. For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51]. The reinforcement can exist in several shapes and sizes which include as laminate, particles, and continuous or short fibres [52–54]. Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48,55]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5. Some of the advantages and disadvantages of natural fibres and synthetic fibres are explained in Table 3. The polymer matrix which is known as continuous phase was in form of thermosetting and thermoplastics polymers [56,57]. To produce products with natural fibre composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [58,59].

 

 

Figure 4. Schematic representations of natural fibres and synthetic fibres [59].

 

 

Figure 5. Schematic diagram of components of lignocellulosic fibre [59].

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends. For instance, Ishak et al. [60] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties. Later on, Misri et al. [61] had developed sugar palm fibre reinforced polymer composite as a life boat due to its excellent mechanical and water resistant performances. This shows that selection of appropriate fibre with its matrix would exhibit significant functionality. Another important aspect in developing optimized biocomposites is to apply appropriate fibre arrangement and layering sequence. The fibre  usually were arranged in a many techniques such as multi-directional, randomly distribution of short or continuous fibres, bi-directional, unidirectional [62–64].

 

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included. The choice of matrix is extensive, covering a range of thermoplastics and thermosetting polymers. Recently, natural fibre-composites have been implement in wide spectrum of engineering usage such as aerospace [70,71], automotive [72,73], civil [74,75], safety appliances [9,76] marine [61,77], and medical [78–80] applications. It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [81,82]. Additionally, the upsurge of competition among industrial players in the global market for lightweight products has accelerate the application of natural fibre-composites in many sectors [83,84].

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

5. Development Natural Fibre Hybrid Composite to Apply for Ballistic Helmet

The US Army initiated a design research programme to replace the M1 steel ballistic helmet design in the early 1960s. As a result of the programme, a single-walled ballistic helmet with improved protection and reduced weight has been developed. After that, more research was done on the resulting PASGT manufactured with Kevlar fibres. The US Army then continued its new ballistic helmet development programme, specifically the Modular Integrated Communications Helmet (MICH) and Advanced Combat Helmet, to reduce the weight of the PASGT ballistic helmet (ACH). ACH is a continuation of MICH's design evolution, and it's built of K129 Kevlar fibre, which has a density area of 185g/m2 versus 270g/m2 for K29 Kevlar fibre. Kevlar fibre K129 is 40% stronger than Kevlar fibre K29 (used for PASGT) [35]. According to Kadir Bilisik & Turhan [86], Kevlar K129 has a higher energy absorption rate than Kevlar K29.

There are two phases to the in development of novel materials for ballistic helmets. Part one: chemistry, metallurgical science, and polymer science contribute to the invention of wholly new materials. The second section features a mix of new and classic materials and geometric and architectural elements [87]. Concerns about the usage of finite resources (synthetic fibre) and their environmental impact have encouraged researchers to look into alternative uses of natural fibres in composite hybrids [88–90]. A composite of two or more types of fibres will provide an advantage in overcoming the components' current weaknesses [91]. A study conducted by Wambua et al., [42], on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

Studies on natural fibres on ballistic properties have been performed on jute, hemp and textile hemp reinforced polypropylene composites produced using hot compression molding. According to a paper by Yahaya et al., [92] woven natural fibre composites offer outstanding mechanical behavioural qualities. The natural fibre has advantages such as biodegradable, recyclable, better energy recovery, high strength and specific modulus, lower health risks, low density, low cost, less skin irritation, available in large quantities, low production costs, lightweight materials, less abrasion of equipment, reduced tool wear, improved energy recovery, and reduced skin irritation and respiration are all advantages of natural fibre development in developing countries [93–97].

6. CE for Natural Fibre-Composite Product Development

All aspects in natural fibre-composite product developments such as customer needs, product design specification (PDS), concept generation, and detail design [96,98–100] have to be fully considered. Specifically for detail design, the elements such as component design and process design are essential for this stage [101–103]. According to Strong [104], component designs usually covered the sub-activities such as drawing or layout, constraints, analysis and material selection. For process design, the sub-activities under this element are such as manufacturing method selection, sequencing, machine/tool selection, system layout, integration of system and manufacturing procedures. Other research by  Pugh [105], the CE is also covered in other processes of the total design including product design specification, market investigation and conceptual design besides relevant in detail design. Even though there are two distinct of philosophy in total design process, both Strong [104] and Pugh [105] entail simultaneous consideration of the manufacturing process at the product design stage. In this manner, the designers should embed design features in order to facilitate the fabrication process with lesser complexity especially the manufacturing process is applied with hand lay-up technique [7,106,107]. For composite which fabricate using hand lay-up process, the labour cost is a key cost element for lesser cost and produce large volume of product batch. Figure 7 depicts main activities during CE process which also recognized as CE wheel that may lead to a ‘wheel of fortune’.

 

Figure 7. Concurrent engineering wheel [13].

 

 

2. Maybe the manuscript should be reorganized in order to highlight the natural fibre composites.

Dear reviewer, we have revised the manuscript as your comments. Thanks a lot.

 

3. Particularly, there are some imprecisions in paragraphs 4 and 5 and these paragraphs should be improves and more precise.

Thanks a lot for the constructive comment. We have revised this manuscript accordingly. Thank you.

4. line 198: which are

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix).

5. line 202: "such as" is repeated 2 times

For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51].

6. line 206: which are obtained

Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

7. line 208: "the fibre formed into usually in form" please change

The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

8. line 212: explain compositions

To produce products with natural fiber composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [57,58].

 

9. line 221: what is a "good" treatment?

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends.

10. line 223: what are "good" properties?

For instance, Ishak et al. [59] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties.

11. line 225: performances

Later on, Misri et al. [60] had developed sugar palm fibre reinforced polymer compo-site as a life boat due to its excellent mechanical and water resistant performances.

12. line 235: explain "good"

It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [75,76].

13. line 252: there 2 phases IN the development

There are two phases to the in development of novel materials for ballistic helmets.

14. line 260: ramie and not remie

A study conducted by Wambua et al., [42] on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

15. line 260: a verb is missing in order to understand the sentence

Done revised. Thank you.

 

16. line 268: the word advantages is repeated

Done revised. Thank you.

 

17. Paragraph 6:
18. line 310: is design not designed

Done revised. Thank you.

 

Reviewer 3

Dear authors, this publication describes an important approach to the development of a ballistic helmet made of natural fiber-reinforced polymer composites. The topic is very interesting in the context of the current trend of popularizing polymer composites with a filler of natural fibers. However, I have two comments:

Thanks a lot for your support.

1. The text should be expanded with information on the use of modern computational techniques related to the modeling and forecasting of the microstructure of composite materials with natural fillers. Such programs are, among others DIGIMAT, Autodesk Helium Composites - they use homogenization models to predict the properties of composite materials. Data from these programs may be necessary material data for simulation, e.g. in ABAQUS, LS-DYNA, NASTRAN, PRONTO 3D programs (Table 5).

Dear reviewer, thanks for your comment. We have revised this section as follows:

“The contribution of computational modelling begins in the early stages of concept design. When a designer develops some sketch ideas into three-dimensional (3D) drawings. The computational techniques such as modelling and forecasting of the microstructure of composite materials with natural fillers are essential in development of natural fibre composite products. This was due to these tools act as data-driven multi-physical modeling, leading to unexpected insights and exploration of the system properties [122]. The superior multi-functional behavior of natural fibre composites lead to an extensive examination of their physical, mechanical and thermal properties under various exposure conditions [123]. Generally, this type of analysis is called as machine learning (ML) which functioned to analyze the behavior of ballistic helmet under certain circumstances to be safely used for user. The usage of ML in designing stage of natural fibre composites to link the findings of the large volume of relevant literature and highlight the broad spectrum potential of ML in applications such as prediction, optimization, feature identification, uncertainty quantification, reliability and sensitivity analysis [124]. Table 5 shows the computational applications and contributions in the development process.”

 

2. The literature review should clearly compare the properties of natural and synthetic fibers and their influence on the properties of composites. This will allow a clear comparative analysis (advantages and disadvantages) of natural fibers.

Dear reviewer, thanks for your comment. We have included the advantages and disadvantages of natural fibre and synthetic fibre.

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

I am waiting for corrections / replies and good luck.

 

Reviewer 4

1. In the abstract section: some developed natural reinforced composite for using in helmet be introduced.

Dear reviewer, thanks for your comment. We have revised the manuscript accordingly.

2. In the page 2, line 75-77 some synthetic fibers reinforced composites as examples be added.

Researchers have developed new composite materials incorporating natural fibres to reduce reliance on synthetic composite materials such as kevlar due to production costs, ease of supply, sustainability, and low weight [6–9].

 

3. Figure 4 is uncompleted. For example, the date based natural fibers has not mentioned. Also, the mineral and animal based natural fibers be completed.

Figure 4 has been revised. Thank you for your suggestion.

 

4. A comparative view section between synthetic fibers reinforced composites and natural fibers reinforced composites for using as helmet be added.
5.  
6. Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

7.  

 

 

8. A comparative view section by using the mechanical test for various natural fibers reinforced composites be added.

We have include the mechanical test for various natural fibers reinforced composites. Thanks a lot for your suggestion.

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included.

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

 

 

9. Which kinds of natural fibers have great potential for using into the helmets? Be mentioned in the conclusion section.

Thanks a lot. We have mentioned in the conclusion section. It is well-known that natural fibre-composites have excellent physico-mechanical per-formance due to the cellulose component provide good shape and structural integrity for the fibres. Most common natural fibres used in composite products are such as flax, coir, hemp and jute, meanwhile, roselle, sugar palm and kenaf are those emerging fibres. However, there are three natural fibres that have high potential in the development of ballistic helmets, namely kenaf, bamboo and sugar palm.

 

10. The number of used references is too much. Be summarized.

 

Dear reviewer, this is review paper. Thus we have to cite many related paper and summarized it. Thank you.

Author Response File: Author Response.docx

Reviewer 2 Report

I think that the title is not well appropriated because only small paragraphes (paragraphes 4 and 5) deal with natural fibre composites.

Maybe the manuscript should be reorganized in order to highlight the natural fibre composites.

Particularly, there are some imprecisions in paragraphes 4 and 5 and these paragraphes should be improves and more precise.

line 198: which are

line 202: "such as" is repeated 2 times

line 206: which are obtained

line 208: "the fibre formed into usually in form" please change

line 212: explain compositions

line 221: what is a "good" treatment?

line 223: what are "good" properties?

line 225: performances

line 235: explain "good" 

line 252: there 2 phases IN the development

line 260: ramie and not remie

line 260: a verb is missing in order to understand the sentence

line 268: the word advantages is repeated

Paragraph 6:

line 310: is design not designed

Author Response

Dear editor,

Thanks for your letter and the thoughtful comments from the referees about our paper entitled “Development of Natural Fibre Reinforced Polymer Composites Ballistic Helmet Using Concurrent Engineering Approach: A Brief Review” sustainability-1657191. We carefully analysed all the comments and these comments are very valuable and helpful for perfecting and modifying our manuscript, and also have important guiding significance for our research. Therefore, we carefully checked the manuscript and revised it according to each comment. Consequently, we feel that our manuscript is substantially strengthened. Revised portion are marked using yellow background in the revised manuscript. The detailed corrections in the paper and the responses to the reviewer’s comments are as the following list of revisions. We also had sent this manuscript to be proofread by well-known proof-reader, in order to achieve the high quality of the journal. The certificate of proofreading is attached below:

 

We look forward to your positive response. If you have any question about this paper, please don’t hesitate to let us know. We hope these revisions will make it more acceptable for publication. Thank you.

Sincerely yours,

R.A. Ilyas

School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

Centre for Advanced Composite Materials (CACM), Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

 

Reviewer 1

Excellent dissertation on concurrent engineering applied to fiber composites. I have no further comments and my sincere congratulations to the authors.

Dear reviewers, thanks a lot for your support.

 

Reviewer 2

1. I think that the title is not well appropriated because only small paragraphs (paragraphs 4 and 5) deal with natural fibre composites.

Dear reviewer, thanks for your constructive comment. The tittle is well developed as we considered natural fibre composite as potential materials for ballistic helmet. Besides that, we have revised the section 4, 5 and 6. Thus we think that the information that provided by us is enough.

4. Implementation of Natural Fibre Composites Toward Sustainable Development

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix). The reinforcement material is made from natural fibres obtained from animal, mineral and plant by-products [43–46], as shown in Figure 4. For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51]. The reinforcement can exist in several shapes and sizes which include as laminate, particles, and continuous or short fibres [52–54]. Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48,55]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5. Some of the advantages and disadvantages of natural fibres and synthetic fibres are explained in Table 3. The polymer matrix which is known as continuous phase was in form of thermosetting and thermoplastics polymers [56,57]. To produce products with natural fibre composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [58,59].

 

 

Figure 4. Schematic representations of natural fibres and synthetic fibres [59].

 

 

Figure 5. Schematic diagram of components of lignocellulosic fibre [59].

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends. For instance, Ishak et al. [60] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties. Later on, Misri et al. [61] had developed sugar palm fibre reinforced polymer composite as a life boat due to its excellent mechanical and water resistant performances. This shows that selection of appropriate fibre with its matrix would exhibit significant functionality. Another important aspect in developing optimized biocomposites is to apply appropriate fibre arrangement and layering sequence. The fibre  usually were arranged in a many techniques such as multi-directional, randomly distribution of short or continuous fibres, bi-directional, unidirectional [62–64].

 

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included. The choice of matrix is extensive, covering a range of thermoplastics and thermosetting polymers. Recently, natural fibre-composites have been implement in wide spectrum of engineering usage such as aerospace [70,71], automotive [72,73], civil [74,75], safety appliances [9,76] marine [61,77], and medical [78–80] applications. It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [81,82]. Additionally, the upsurge of competition among industrial players in the global market for lightweight products has accelerate the application of natural fibre-composites in many sectors [83,84].

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

5. Development Natural Fibre Hybrid Composite to Apply for Ballistic Helmet

The US Army initiated a design research programme to replace the M1 steel ballistic helmet design in the early 1960s. As a result of the programme, a single-walled ballistic helmet with improved protection and reduced weight has been developed. After that, more research was done on the resulting PASGT manufactured with Kevlar fibres. The US Army then continued its new ballistic helmet development programme, specifically the Modular Integrated Communications Helmet (MICH) and Advanced Combat Helmet, to reduce the weight of the PASGT ballistic helmet (ACH). ACH is a continuation of MICH's design evolution, and it's built of K129 Kevlar fibre, which has a density area of 185g/m2 versus 270g/m2 for K29 Kevlar fibre. Kevlar fibre K129 is 40% stronger than Kevlar fibre K29 (used for PASGT) [35]. According to Kadir Bilisik & Turhan [86], Kevlar K129 has a higher energy absorption rate than Kevlar K29.

There are two phases to the in development of novel materials for ballistic helmets. Part one: chemistry, metallurgical science, and polymer science contribute to the invention of wholly new materials. The second section features a mix of new and classic materials and geometric and architectural elements [87]. Concerns about the usage of finite resources (synthetic fibre) and their environmental impact have encouraged researchers to look into alternative uses of natural fibres in composite hybrids [88–90]. A composite of two or more types of fibres will provide an advantage in overcoming the components' current weaknesses [91]. A study conducted by Wambua et al., [42], on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

Studies on natural fibres on ballistic properties have been performed on jute, hemp and textile hemp reinforced polypropylene composites produced using hot compression molding. According to a paper by Yahaya et al., [92] woven natural fibre composites offer outstanding mechanical behavioural qualities. The natural fibre has advantages such as biodegradable, recyclable, better energy recovery, high strength and specific modulus, lower health risks, low density, low cost, less skin irritation, available in large quantities, low production costs, lightweight materials, less abrasion of equipment, reduced tool wear, improved energy recovery, and reduced skin irritation and respiration are all advantages of natural fibre development in developing countries [93–97].

6. CE for Natural Fibre-Composite Product Development

All aspects in natural fibre-composite product developments such as customer needs, product design specification (PDS), concept generation, and detail design [96,98–100] have to be fully considered. Specifically for detail design, the elements such as component design and process design are essential for this stage [101–103]. According to Strong [104], component designs usually covered the sub-activities such as drawing or layout, constraints, analysis and material selection. For process design, the sub-activities under this element are such as manufacturing method selection, sequencing, machine/tool selection, system layout, integration of system and manufacturing procedures. Other research by  Pugh [105], the CE is also covered in other processes of the total design including product design specification, market investigation and conceptual design besides relevant in detail design. Even though there are two distinct of philosophy in total design process, both Strong [104] and Pugh [105] entail simultaneous consideration of the manufacturing process at the product design stage. In this manner, the designers should embed design features in order to facilitate the fabrication process with lesser complexity especially the manufacturing process is applied with hand lay-up technique [7,106,107]. For composite which fabricate using hand lay-up process, the labour cost is a key cost element for lesser cost and produce large volume of product batch. Figure 7 depicts main activities during CE process which also recognized as CE wheel that may lead to a ‘wheel of fortune’.

 

Figure 7. Concurrent engineering wheel [13].

 

 

2. Maybe the manuscript should be reorganized in order to highlight the natural fibre composites.

Dear reviewer, we have revised the manuscript as your comments. Thanks a lot.

 

3. Particularly, there are some imprecisions in paragraphs 4 and 5 and these paragraphs should be improves and more precise.

Thanks a lot for the constructive comment. We have revised this manuscript accordingly. Thank you.

4. line 198: which are

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix).

5. line 202: "such as" is repeated 2 times

For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51].

6. line 206: which are obtained

Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

7. line 208: "the fibre formed into usually in form" please change

The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

8. line 212: explain compositions

To produce products with natural fiber composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [57,58].

 

9. line 221: what is a "good" treatment?

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends.

10. line 223: what are "good" properties?

For instance, Ishak et al. [59] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties.

11. line 225: performances

Later on, Misri et al. [60] had developed sugar palm fibre reinforced polymer compo-site as a life boat due to its excellent mechanical and water resistant performances.

12. line 235: explain "good"

It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [75,76].

13. line 252: there 2 phases IN the development

There are two phases to the in development of novel materials for ballistic helmets.

14. line 260: ramie and not remie

A study conducted by Wambua et al., [42] on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

15. line 260: a verb is missing in order to understand the sentence

Done revised. Thank you.

 

16. line 268: the word advantages is repeated

Done revised. Thank you.

 

17. Paragraph 6:
18. line 310: is design not designed

Done revised. Thank you.

 

Reviewer 3

Dear authors, this publication describes an important approach to the development of a ballistic helmet made of natural fiber-reinforced polymer composites. The topic is very interesting in the context of the current trend of popularizing polymer composites with a filler of natural fibers. However, I have two comments:

Thanks a lot for your support.

1. The text should be expanded with information on the use of modern computational techniques related to the modeling and forecasting of the microstructure of composite materials with natural fillers. Such programs are, among others DIGIMAT, Autodesk Helium Composites - they use homogenization models to predict the properties of composite materials. Data from these programs may be necessary material data for simulation, e.g. in ABAQUS, LS-DYNA, NASTRAN, PRONTO 3D programs (Table 5).

Dear reviewer, thanks for your comment. We have revised this section as follows:

“The contribution of computational modelling begins in the early stages of concept design. When a designer develops some sketch ideas into three-dimensional (3D) drawings. The computational techniques such as modelling and forecasting of the microstructure of composite materials with natural fillers are essential in development of natural fibre composite products. This was due to these tools act as data-driven multi-physical modeling, leading to unexpected insights and exploration of the system properties [122]. The superior multi-functional behavior of natural fibre composites lead to an extensive examination of their physical, mechanical and thermal properties under various exposure conditions [123]. Generally, this type of analysis is called as machine learning (ML) which functioned to analyze the behavior of ballistic helmet under certain circumstances to be safely used for user. The usage of ML in designing stage of natural fibre composites to link the findings of the large volume of relevant literature and highlight the broad spectrum potential of ML in applications such as prediction, optimization, feature identification, uncertainty quantification, reliability and sensitivity analysis [124]. Table 5 shows the computational applications and contributions in the development process.”

 

2. The literature review should clearly compare the properties of natural and synthetic fibers and their influence on the properties of composites. This will allow a clear comparative analysis (advantages and disadvantages) of natural fibers.

Dear reviewer, thanks for your comment. We have included the advantages and disadvantages of natural fibre and synthetic fibre.

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

I am waiting for corrections / replies and good luck.

 

Reviewer 4

1. In the abstract section: some developed natural reinforced composite for using in helmet be introduced.

Dear reviewer, thanks for your comment. We have revised the manuscript accordingly.

2. In the page 2, line 75-77 some synthetic fibers reinforced composites as examples be added.

Researchers have developed new composite materials incorporating natural fibres to reduce reliance on synthetic composite materials such as kevlar due to production costs, ease of supply, sustainability, and low weight [6–9].

 

3. Figure 4 is uncompleted. For example, the date based natural fibers has not mentioned. Also, the mineral and animal based natural fibers be completed.

Figure 4 has been revised. Thank you for your suggestion.

 

4. A comparative view section between synthetic fibers reinforced composites and natural fibers reinforced composites for using as helmet be added.
5.  
6. Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

7.  

 

 

8. A comparative view section by using the mechanical test for various natural fibers reinforced composites be added.

We have include the mechanical test for various natural fibers reinforced composites. Thanks a lot for your suggestion.

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included.

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

 

 

9. Which kinds of natural fibers have great potential for using into the helmets? Be mentioned in the conclusion section.

Thanks a lot. We have mentioned in the conclusion section. It is well-known that natural fibre-composites have excellent physico-mechanical per-formance due to the cellulose component provide good shape and structural integrity for the fibres. Most common natural fibres used in composite products are such as flax, coir, hemp and jute, meanwhile, roselle, sugar palm and kenaf are those emerging fibres. However, there are three natural fibres that have high potential in the development of ballistic helmets, namely kenaf, bamboo and sugar palm.

 

10. The number of used references is too much. Be summarized.

 

Dear reviewer, this is review paper. Thus we have to cite many related paper and summarized it. Thank you.

Author Response File: Author Response.docx

Reviewer 3 Report

Dear authors,
this publication describes an important approach to the development of a ballistic helmet made of natural fiber-reinforced polymer composites. The topic is very interesting in the context of the current trend of popularizing polymer composites with a filler of natural fibers. However, I have two comments:

1. The text should be expanded with information on the use of modern computational techniques related to the modeling and forecasting of the microstructure of composite materials with natural fillers. Such programs are, among others DIGIMAT, Autodesk Helium Composites - they use homogenization models to predict the properties of composite materials. Data from these programs may be necessary material data for simulation, e.g. in ABAQUS, LS-DYNA, NASTRAN, PRONTO 3D programs (Table 1).
2. The literature review should clearly compare the properties of natural and synthetic fibers and their influence on the properties of composites. This will allow a clear comparative analysis (advantages and disadvantages) of natural fibers.

I am waiting for corrections / replies and good luck.

Author Response

Dear editor,

Thanks for your letter and the thoughtful comments from the referees about our paper entitled “Development of Natural Fibre Reinforced Polymer Composites Ballistic Helmet Using Concurrent Engineering Approach: A Brief Review” sustainability-1657191. We carefully analysed all the comments and these comments are very valuable and helpful for perfecting and modifying our manuscript, and also have important guiding significance for our research. Therefore, we carefully checked the manuscript and revised it according to each comment. Consequently, we feel that our manuscript is substantially strengthened. Revised portion are marked using yellow background in the revised manuscript. The detailed corrections in the paper and the responses to the reviewer’s comments are as the following list of revisions. We also had sent this manuscript to be proofread by well-known proof-reader, in order to achieve the high quality of the journal. The certificate of proofreading is attached below:

 

We look forward to your positive response. If you have any question about this paper, please don’t hesitate to let us know. We hope these revisions will make it more acceptable for publication. Thank you.

Sincerely yours,

R.A. Ilyas

School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

Centre for Advanced Composite Materials (CACM), Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

 

Reviewer 1

Excellent dissertation on concurrent engineering applied to fiber composites. I have no further comments and my sincere congratulations to the authors.

Dear reviewers, thanks a lot for your support.

 

Reviewer 2

1. I think that the title is not well appropriated because only small paragraphs (paragraphs 4 and 5) deal with natural fibre composites.

Dear reviewer, thanks for your constructive comment. The tittle is well developed as we considered natural fibre composite as potential materials for ballistic helmet. Besides that, we have revised the section 4, 5 and 6. Thus we think that the information that provided by us is enough.

4. Implementation of Natural Fibre Composites Toward Sustainable Development

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix). The reinforcement material is made from natural fibres obtained from animal, mineral and plant by-products [43–46], as shown in Figure 4. For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51]. The reinforcement can exist in several shapes and sizes which include as laminate, particles, and continuous or short fibres [52–54]. Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48,55]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5. Some of the advantages and disadvantages of natural fibres and synthetic fibres are explained in Table 3. The polymer matrix which is known as continuous phase was in form of thermosetting and thermoplastics polymers [56,57]. To produce products with natural fibre composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [58,59].

 

 

Figure 4. Schematic representations of natural fibres and synthetic fibres [59].

 

 

Figure 5. Schematic diagram of components of lignocellulosic fibre [59].

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends. For instance, Ishak et al. [60] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties. Later on, Misri et al. [61] had developed sugar palm fibre reinforced polymer composite as a life boat due to its excellent mechanical and water resistant performances. This shows that selection of appropriate fibre with its matrix would exhibit significant functionality. Another important aspect in developing optimized biocomposites is to apply appropriate fibre arrangement and layering sequence. The fibre  usually were arranged in a many techniques such as multi-directional, randomly distribution of short or continuous fibres, bi-directional, unidirectional [62–64].

 

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included. The choice of matrix is extensive, covering a range of thermoplastics and thermosetting polymers. Recently, natural fibre-composites have been implement in wide spectrum of engineering usage such as aerospace [70,71], automotive [72,73], civil [74,75], safety appliances [9,76] marine [61,77], and medical [78–80] applications. It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [81,82]. Additionally, the upsurge of competition among industrial players in the global market for lightweight products has accelerate the application of natural fibre-composites in many sectors [83,84].

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

5. Development Natural Fibre Hybrid Composite to Apply for Ballistic Helmet

The US Army initiated a design research programme to replace the M1 steel ballistic helmet design in the early 1960s. As a result of the programme, a single-walled ballistic helmet with improved protection and reduced weight has been developed. After that, more research was done on the resulting PASGT manufactured with Kevlar fibres. The US Army then continued its new ballistic helmet development programme, specifically the Modular Integrated Communications Helmet (MICH) and Advanced Combat Helmet, to reduce the weight of the PASGT ballistic helmet (ACH). ACH is a continuation of MICH's design evolution, and it's built of K129 Kevlar fibre, which has a density area of 185g/m2 versus 270g/m2 for K29 Kevlar fibre. Kevlar fibre K129 is 40% stronger than Kevlar fibre K29 (used for PASGT) [35]. According to Kadir Bilisik & Turhan [86], Kevlar K129 has a higher energy absorption rate than Kevlar K29.

There are two phases to the in development of novel materials for ballistic helmets. Part one: chemistry, metallurgical science, and polymer science contribute to the invention of wholly new materials. The second section features a mix of new and classic materials and geometric and architectural elements [87]. Concerns about the usage of finite resources (synthetic fibre) and their environmental impact have encouraged researchers to look into alternative uses of natural fibres in composite hybrids [88–90]. A composite of two or more types of fibres will provide an advantage in overcoming the components' current weaknesses [91]. A study conducted by Wambua et al., [42], on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

Studies on natural fibres on ballistic properties have been performed on jute, hemp and textile hemp reinforced polypropylene composites produced using hot compression molding. According to a paper by Yahaya et al., [92] woven natural fibre composites offer outstanding mechanical behavioural qualities. The natural fibre has advantages such as biodegradable, recyclable, better energy recovery, high strength and specific modulus, lower health risks, low density, low cost, less skin irritation, available in large quantities, low production costs, lightweight materials, less abrasion of equipment, reduced tool wear, improved energy recovery, and reduced skin irritation and respiration are all advantages of natural fibre development in developing countries [93–97].

6. CE for Natural Fibre-Composite Product Development

All aspects in natural fibre-composite product developments such as customer needs, product design specification (PDS), concept generation, and detail design [96,98–100] have to be fully considered. Specifically for detail design, the elements such as component design and process design are essential for this stage [101–103]. According to Strong [104], component designs usually covered the sub-activities such as drawing or layout, constraints, analysis and material selection. For process design, the sub-activities under this element are such as manufacturing method selection, sequencing, machine/tool selection, system layout, integration of system and manufacturing procedures. Other research by  Pugh [105], the CE is also covered in other processes of the total design including product design specification, market investigation and conceptual design besides relevant in detail design. Even though there are two distinct of philosophy in total design process, both Strong [104] and Pugh [105] entail simultaneous consideration of the manufacturing process at the product design stage. In this manner, the designers should embed design features in order to facilitate the fabrication process with lesser complexity especially the manufacturing process is applied with hand lay-up technique [7,106,107]. For composite which fabricate using hand lay-up process, the labour cost is a key cost element for lesser cost and produce large volume of product batch. Figure 7 depicts main activities during CE process which also recognized as CE wheel that may lead to a ‘wheel of fortune’.

 

Figure 7. Concurrent engineering wheel [13].

 

 

2. Maybe the manuscript should be reorganized in order to highlight the natural fibre composites.

Dear reviewer, we have revised the manuscript as your comments. Thanks a lot.

 

3. Particularly, there are some imprecisions in paragraphs 4 and 5 and these paragraphs should be improves and more precise.

Thanks a lot for the constructive comment. We have revised this manuscript accordingly. Thank you.

4. line 198: which are

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix).

5. line 202: "such as" is repeated 2 times

For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51].

6. line 206: which are obtained

Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

7. line 208: "the fibre formed into usually in form" please change

The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

8. line 212: explain compositions

To produce products with natural fiber composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [57,58].

 

9. line 221: what is a "good" treatment?

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends.

10. line 223: what are "good" properties?

For instance, Ishak et al. [59] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties.

11. line 225: performances

Later on, Misri et al. [60] had developed sugar palm fibre reinforced polymer compo-site as a life boat due to its excellent mechanical and water resistant performances.

12. line 235: explain "good"

It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [75,76].

13. line 252: there 2 phases IN the development

There are two phases to the in development of novel materials for ballistic helmets.

14. line 260: ramie and not remie

A study conducted by Wambua et al., [42] on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

15. line 260: a verb is missing in order to understand the sentence

Done revised. Thank you.

 

16. line 268: the word advantages is repeated

Done revised. Thank you.

 

17. Paragraph 6:
18. line 310: is design not designed

Done revised. Thank you.

 

Reviewer 3

Dear authors, this publication describes an important approach to the development of a ballistic helmet made of natural fiber-reinforced polymer composites. The topic is very interesting in the context of the current trend of popularizing polymer composites with a filler of natural fibers. However, I have two comments:

Thanks a lot for your support.

1. The text should be expanded with information on the use of modern computational techniques related to the modeling and forecasting of the microstructure of composite materials with natural fillers. Such programs are, among others DIGIMAT, Autodesk Helium Composites - they use homogenization models to predict the properties of composite materials. Data from these programs may be necessary material data for simulation, e.g. in ABAQUS, LS-DYNA, NASTRAN, PRONTO 3D programs (Table 5).

Dear reviewer, thanks for your comment. We have revised this section as follows:

“The contribution of computational modelling begins in the early stages of concept design. When a designer develops some sketch ideas into three-dimensional (3D) drawings. The computational techniques such as modelling and forecasting of the microstructure of composite materials with natural fillers are essential in development of natural fibre composite products. This was due to these tools act as data-driven multi-physical modeling, leading to unexpected insights and exploration of the system properties [122]. The superior multi-functional behavior of natural fibre composites lead to an extensive examination of their physical, mechanical and thermal properties under various exposure conditions [123]. Generally, this type of analysis is called as machine learning (ML) which functioned to analyze the behavior of ballistic helmet under certain circumstances to be safely used for user. The usage of ML in designing stage of natural fibre composites to link the findings of the large volume of relevant literature and highlight the broad spectrum potential of ML in applications such as prediction, optimization, feature identification, uncertainty quantification, reliability and sensitivity analysis [124]. Table 5 shows the computational applications and contributions in the development process.”

 

2. The literature review should clearly compare the properties of natural and synthetic fibers and their influence on the properties of composites. This will allow a clear comparative analysis (advantages and disadvantages) of natural fibers.

Dear reviewer, thanks for your comment. We have included the advantages and disadvantages of natural fibre and synthetic fibre.

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

I am waiting for corrections / replies and good luck.

 

Reviewer 4

1. In the abstract section: some developed natural reinforced composite for using in helmet be introduced.

Dear reviewer, thanks for your comment. We have revised the manuscript accordingly.

2. In the page 2, line 75-77 some synthetic fibers reinforced composites as examples be added.

Researchers have developed new composite materials incorporating natural fibres to reduce reliance on synthetic composite materials such as kevlar due to production costs, ease of supply, sustainability, and low weight [6–9].

 

3. Figure 4 is uncompleted. For example, the date based natural fibers has not mentioned. Also, the mineral and animal based natural fibers be completed.

Figure 4 has been revised. Thank you for your suggestion.

 

4. A comparative view section between synthetic fibers reinforced composites and natural fibers reinforced composites for using as helmet be added.

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

 

 

5. A comparative view section by using the mechanical test for various natural fibers reinforced composites be added.

We have include the mechanical test for various natural fibers reinforced composites. Thanks a lot for your suggestion.

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included.

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

 

 

6. Which kinds of natural fibers have great potential for using into the helmets? Be mentioned in the conclusion section.

Thanks a lot. We have mentioned in the conclusion section. It is well-known that natural fibre-composites have excellent physico-mechanical per-formance due to the cellulose component provide good shape and structural integrity for the fibres. Most common natural fibres used in composite products are such as flax, coir, hemp and jute, meanwhile, roselle, sugar palm and kenaf are those emerging fibres. However, there are three natural fibres that have high potential in the development of ballistic helmets, namely kenaf, bamboo and sugar palm.

 

7. The number of used references is too much. Be summarized.

 

Dear reviewer, this is review paper. Thus we have to cite many related paper and summarized it. Thank you.

Author Response File: Author Response.docx

Reviewer 4 Report

1. In the abstract section: some developed natural reinforced composite for using in helmet be introduced.
2. In the page 2, line 75-77 some synthetic fibers reinforced composites as examples be added. 
3. Figure 4 is uncompleted. For example, the date based natural fibers has not mentioned. Also, the mineral and animal based natural fibers be completed.
4. A comparative view section between synthetic fibers reinforced composites and natural fibers reinforced composites for using as helmet be added.
5. A comparative view section by using the high-speed impact test for various natural fibers reinforced composites be added.
6. Which kinds of natural fibers have great potential for using into the helmets? Be mentioned in the conclusion section.
7. A future trend section be added.
8. The number of used references is too much. Be summarized.   

Author Response

Dear editor,

Thanks for your letter and the thoughtful comments from the referees about our paper entitled “Development of Natural Fibre Reinforced Polymer Composites Ballistic Helmet Using Concurrent Engineering Approach: A Brief Review” sustainability-1657191. We carefully analysed all the comments and these comments are very valuable and helpful for perfecting and modifying our manuscript, and also have important guiding significance for our research. Therefore, we carefully checked the manuscript and revised it according to each comment. Consequently, we feel that our manuscript is substantially strengthened. Revised portion are marked using yellow background in the revised manuscript. The detailed corrections in the paper and the responses to the reviewer’s comments are as the following list of revisions. We also had sent this manuscript to be proofread by well-known proof-reader, in order to achieve the high quality of the journal. The certificate of proofreading is attached below:

 

We look forward to your positive response. If you have any question about this paper, please don’t hesitate to let us know. We hope these revisions will make it more acceptable for publication. Thank you.

Sincerely yours,

R.A. Ilyas

School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

Centre for Advanced Composite Materials (CACM), Universiti Teknologi Malaysia, 81310, UTM Johor Bahru, Johor, Malaysia

 

Reviewer 1

Excellent dissertation on concurrent engineering applied to fiber composites. I have no further comments and my sincere congratulations to the authors.

Dear reviewers, thanks a lot for your support.

 

Reviewer 2

1. I think that the title is not well appropriated because only small paragraphs (paragraphs 4 and 5) deal with natural fibre composites.

Dear reviewer, thanks for your constructive comment. The tittle is well developed as we considered natural fibre composite as potential materials for ballistic helmet. Besides that, we have revised the section 4, 5 and 6. Thus we think that the information that provided by us is enough.

4. Implementation of Natural Fibre Composites Toward Sustainable Development

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix). The reinforcement material is made from natural fibres obtained from animal, mineral and plant by-products [43–46], as shown in Figure 4. For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51]. The reinforcement can exist in several shapes and sizes which include as laminate, particles, and continuous or short fibres [52–54]. Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48,55]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5. Some of the advantages and disadvantages of natural fibres and synthetic fibres are explained in Table 3. The polymer matrix which is known as continuous phase was in form of thermosetting and thermoplastics polymers [56,57]. To produce products with natural fibre composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [58,59].

 

 

Figure 4. Schematic representations of natural fibres and synthetic fibres [59].

 

 

Figure 5. Schematic diagram of components of lignocellulosic fibre [59].

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends. For instance, Ishak et al. [60] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties. Later on, Misri et al. [61] had developed sugar palm fibre reinforced polymer composite as a life boat due to its excellent mechanical and water resistant performances. This shows that selection of appropriate fibre with its matrix would exhibit significant functionality. Another important aspect in developing optimized biocomposites is to apply appropriate fibre arrangement and layering sequence. The fibre  usually were arranged in a many techniques such as multi-directional, randomly distribution of short or continuous fibres, bi-directional, unidirectional [62–64].

 

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included. The choice of matrix is extensive, covering a range of thermoplastics and thermosetting polymers. Recently, natural fibre-composites have been implement in wide spectrum of engineering usage such as aerospace [70,71], automotive [72,73], civil [74,75], safety appliances [9,76] marine [61,77], and medical [78–80] applications. It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [81,82]. Additionally, the upsurge of competition among industrial players in the global market for lightweight products has accelerate the application of natural fibre-composites in many sectors [83,84].

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

5. Development Natural Fibre Hybrid Composite to Apply for Ballistic Helmet

The US Army initiated a design research programme to replace the M1 steel ballistic helmet design in the early 1960s. As a result of the programme, a single-walled ballistic helmet with improved protection and reduced weight has been developed. After that, more research was done on the resulting PASGT manufactured with Kevlar fibres. The US Army then continued its new ballistic helmet development programme, specifically the Modular Integrated Communications Helmet (MICH) and Advanced Combat Helmet, to reduce the weight of the PASGT ballistic helmet (ACH). ACH is a continuation of MICH's design evolution, and it's built of K129 Kevlar fibre, which has a density area of 185g/m2 versus 270g/m2 for K29 Kevlar fibre. Kevlar fibre K129 is 40% stronger than Kevlar fibre K29 (used for PASGT) [35]. According to Kadir Bilisik & Turhan [86], Kevlar K129 has a higher energy absorption rate than Kevlar K29.

There are two phases to the in development of novel materials for ballistic helmets. Part one: chemistry, metallurgical science, and polymer science contribute to the invention of wholly new materials. The second section features a mix of new and classic materials and geometric and architectural elements [87]. Concerns about the usage of finite resources (synthetic fibre) and their environmental impact have encouraged researchers to look into alternative uses of natural fibres in composite hybrids [88–90]. A composite of two or more types of fibres will provide an advantage in overcoming the components' current weaknesses [91]. A study conducted by Wambua et al., [42], on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

Studies on natural fibres on ballistic properties have been performed on jute, hemp and textile hemp reinforced polypropylene composites produced using hot compression molding. According to a paper by Yahaya et al., [92] woven natural fibre composites offer outstanding mechanical behavioural qualities. The natural fibre has advantages such as biodegradable, recyclable, better energy recovery, high strength and specific modulus, lower health risks, low density, low cost, less skin irritation, available in large quantities, low production costs, lightweight materials, less abrasion of equipment, reduced tool wear, improved energy recovery, and reduced skin irritation and respiration are all advantages of natural fibre development in developing countries [93–97].

6. CE for Natural Fibre-Composite Product Development

All aspects in natural fibre-composite product developments such as customer needs, product design specification (PDS), concept generation, and detail design [96,98–100] have to be fully considered. Specifically for detail design, the elements such as component design and process design are essential for this stage [101–103]. According to Strong [104], component designs usually covered the sub-activities such as drawing or layout, constraints, analysis and material selection. For process design, the sub-activities under this element are such as manufacturing method selection, sequencing, machine/tool selection, system layout, integration of system and manufacturing procedures. Other research by  Pugh [105], the CE is also covered in other processes of the total design including product design specification, market investigation and conceptual design besides relevant in detail design. Even though there are two distinct of philosophy in total design process, both Strong [104] and Pugh [105] entail simultaneous consideration of the manufacturing process at the product design stage. In this manner, the designers should embed design features in order to facilitate the fabrication process with lesser complexity especially the manufacturing process is applied with hand lay-up technique [7,106,107]. For composite which fabricate using hand lay-up process, the labour cost is a key cost element for lesser cost and produce large volume of product batch. Figure 7 depicts main activities during CE process which also recognized as CE wheel that may lead to a ‘wheel of fortune’.

 

Figure 7. Concurrent engineering wheel [13].

 

 

2. Maybe the manuscript should be reorganized in order to highlight the natural fibre composites.

Dear reviewer, we have revised the manuscript as your comments. Thanks a lot.

 

3. Particularly, there are some imprecisions in paragraphs 4 and 5 and these paragraphs should be improves and more precise.

Thanks a lot for the constructive comment. We have revised this manuscript accordingly. Thank you.

4. line 198: which are

Natural fibre-composites or biocomposites are composite materials composed of reinforcement material distributed within a continuous phase (polymer matrix).

5. line 202: "such as" is repeated 2 times

For natural fibres, they can be extracted from the sources such as (1) plants including oil palm, sugar palm, kenaf, pineapple leaf, banana pseudo-stem, coir, rice husk, wood, and bamboo [47–49], or even from (2) animal by-products including shells, skins and feathers [50,51].

6. line 206: which are obtained

Generally, the natural fibres obtained from plant lignocellulosic fibre have three main constituents: cellulose, lignin, and hemicellulose, which influence its mechanical and physical performance [48]. The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

7. line 208: "the fibre formed into usually in form" please change

The fibre usually exists in the form of a cellulose reinforced lignin matrix along with hemicellulose component as shown in Figure 5.

 

8. line 212: explain compositions

To produce products with natural fiber composite performance at optimum levels with the optimum natural fibre composite performance possible, it is essential to determine the properties of the composite, its chemical composition, synthesis and mechanical performance [57,58].

 

9. line 221: what is a "good" treatment?

To develop an optimum natural fibre-composites, a good selection of fibres, matrices natural fibre treatment, layering sequences and fabrication techniques could tally with the design intends.

10. line 223: what are "good" properties?

For instance, Ishak et al. [59] reported that sugar palm fibres have superior properties to resist the seawater and act as excellent water barrier properties.

11. line 225: performances

Later on, Misri et al. [60] had developed sugar palm fibre reinforced polymer compo-site as a life boat due to its excellent mechanical and water resistant performances.

12. line 235: explain "good"

It can be noted that the natural fibre-composite have been widely used due to its excellent in mechanical performance and remarkable awareness among the publics toward environmental sustainability [75,76].

13. line 252: there 2 phases IN the development

There are two phases to the in development of novel materials for ballistic helmets.

14. line 260: ramie and not remie

A study conducted by Wambua et al., [42] on the ballistic properties of jute, ramie, hemp, and hemp textiles reinforced polypropylene composites produced using hot compression molding, shows that the hybrid structures have a clear advantage over mild steel and the plain composites. Mild steel alone performs better than hemp and jute composites but slightly less than flax composites. In addition, it was found that the ballistic properties of the hemp composites increased significantly when a mild steel plate was used as facing and backing.

 

15. line 260: a verb is missing in order to understand the sentence

Done revised. Thank you.

 

16. line 268: the word advantages is repeated

Done revised. Thank you.

 

17. Paragraph 6:
18. line 310: is design not designed

Done revised. Thank you.

 

Reviewer 3

Dear authors, this publication describes an important approach to the development of a ballistic helmet made of natural fiber-reinforced polymer composites. The topic is very interesting in the context of the current trend of popularizing polymer composites with a filler of natural fibers. However, I have two comments:

Thanks a lot for your support.

1. The text should be expanded with information on the use of modern computational techniques related to the modeling and forecasting of the microstructure of composite materials with natural fillers. Such programs are, among others DIGIMAT, Autodesk Helium Composites - they use homogenization models to predict the properties of composite materials. Data from these programs may be necessary material data for simulation, e.g. in ABAQUS, LS-DYNA, NASTRAN, PRONTO 3D programs (Table 5).

Dear reviewer, thanks for your comment. We have revised this section as follows:

“The contribution of computational modelling begins in the early stages of concept design. When a designer develops some sketch ideas into three-dimensional (3D) drawings. The computational techniques such as modelling and forecasting of the microstructure of composite materials with natural fillers are essential in development of natural fibre composite products. This was due to these tools act as data-driven multi-physical modeling, leading to unexpected insights and exploration of the system properties [122]. The superior multi-functional behavior of natural fibre composites lead to an extensive examination of their physical, mechanical and thermal properties under various exposure conditions [123]. Generally, this type of analysis is called as machine learning (ML) which functioned to analyze the behavior of ballistic helmet under certain circumstances to be safely used for user. The usage of ML in designing stage of natural fibre composites to link the findings of the large volume of relevant literature and highlight the broad spectrum potential of ML in applications such as prediction, optimization, feature identification, uncertainty quantification, reliability and sensitivity analysis [124]. Table 5 shows the computational applications and contributions in the development process.”

 

2. The literature review should clearly compare the properties of natural and synthetic fibers and their influence on the properties of composites. This will allow a clear comparative analysis (advantages and disadvantages) of natural fibers.

Dear reviewer, thanks for your comment. We have included the advantages and disadvantages of natural fibre and synthetic fibre.

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

I am waiting for corrections / replies and good luck.

 

Reviewer 4

1. In the abstract section: some developed natural reinforced composite for using in helmet be introduced.

Dear reviewer, thanks for your comment. We have revised the manuscript accordingly.

2. In the page 2, line 75-77 some synthetic fibers reinforced composites as examples be added.

Researchers have developed new composite materials incorporating natural fibres to reduce reliance on synthetic composite materials such as kevlar due to production costs, ease of supply, sustainability, and low weight [6–9].

 

3. Figure 4 is uncompleted. For example, the date based natural fibers has not mentioned. Also, the mineral and animal based natural fibers be completed.

Figure 4 has been revised. Thank you for your suggestion.

 

4. A comparative view section between synthetic fibers reinforced composites and natural fibers reinforced composites for using as helmet be added.

 

Table 3: Advantages and disadvantages of natural fibres and synthetic fibres

	Advantages	Disadvantages
Natural Fibre	Lightweight	Flammable
	Recyclable	Dimensional instability
	Improved specific mechanical properties	High moisture absorption
	Eco-friendly, carbon dioxide neutrality	Anisotropic behavior
	Do not generate any harmful gases during processing, low energy requirements during production	Limited processing temperature (~200-230 oC)
	Good thermal properties	Sensitive to UV
	Good acoustic properties	Fugal attack and microbial
	Low cost, availability, renewable resources, disposal by composting	Low strength than synthetic fibres, especially impact strength
	Non-abrasive and great formability	Variable quality, influenced by weather
	No dermal issue for their handling	Low durability
	Safer crash behavior in tests	Poor fibre/matrix adhesion
Synthetic fibres	Long lasting	Flammable
	Readily pick-up to various dyes	Prone to heat damage
	Stretchable	Melt easily
	Waterproofing	Not eco-friendly
	Non biodegradability	Cause for microplastic pollution
	Moisture resistance	Not suitable for hot washing
	Strain and wear resistance	Poor insulation capacity
	High production	Moderate recyclability

 

 

 

5. A comparative view section by using the mechanical test for various natural fibers reinforced composites be added.

We have include the mechanical test for various natural fibers reinforced composites. Thanks a lot for your suggestion.

NFPCs are composites whose mechanical efficiency is determined by the interface of fiber-matrix adhesion with the stress transfer function, which transfers stress from the matrix to the fibre. Many researchers have reported on this in various studies [65–69]. Natural fibre characteristics such as volume fraction, physical qualities, impurities, moisture absorption and orientation play an important role in the determination of NFPC mechanical properties. Mechanical properties of PLA, epoxy, PP, and polyester matrices can be affected by many types of natural fibers and to show some of them, Figure 6 is included.

 

 

 

Figure 6. Some of mechanical properties of natural fiber reinforced polymer composite [85].

 

 

6. Which kinds of natural fibers have great potential for using into the helmets? Be mentioned in the conclusion section.

Thanks a lot. We have mentioned in the conclusion section. It is well-known that natural fibre-composites have excellent physico-mechanical per-formance due to the cellulose component provide good shape and structural integrity for the fibres. Most common natural fibres used in composite products are such as flax, coir, hemp and jute, meanwhile, roselle, sugar palm and kenaf are those emerging fibres. However, there are three natural fibres that have high potential in the development of ballistic helmets, namely kenaf, bamboo and sugar palm.

 

7. The number of used references is too much. Be summarized.

 

Dear reviewer, this is review paper. Thus we have to cite many related paper and summarized it. Thank you.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

It's ok for me