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A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Bioactive Coatings and Biointerfaces".

Deadline for manuscript submissions: closed (1 June 2021) | Viewed by 52780

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Special Issue Editor

Dr. Philippe Evon

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Guest Editor

Laboratoire de Chimie Agro-industrielle (LCA), Université de Toulouse, INRA, Toulouse INP, Toulouse, France
Interests: biorefinery; twin-screw extrusion; biopolymers; biocomposites; molding processes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Entitled “Natural Fiber-Based Composites”, this Special Issue has the objective to give an inventory of the latest research in the area of composites reinforced with natural fibers. Fibers of renewable origin have many advantages. They are abundant and cheap, they have a reduced impact on the environment, and they are also independent from fossil resources. Their ability to mechanically reinforce thermoplastic matrices is well known, as their natural heat insulation ability.

In the last twenty years, the use of cellulosic and lignocellulosic agricultural byproducts for composite applications has been of great interest, especially for reinforcing matrices. The latter can themselves be of renewable origin (e.g., proteins, starch, PLA, PHAs), thus contributing to the development of 100% bio-based composites with a controlled end of life.

In this way, original manuscripts presenting the last developments in the field of natural fiber-based composites are welcome. In addition to the use of natural fibers, that of renewable matrices is strongly recommended but not mandatory. Structured as original experimental works, papers will focus on the preparation and molding processes of such materials (e.g., extrusion, injection-molding, hot pressing, 3D printing) and their thermomechanical characterization. New data dealing with their aging behavior, recyclability, biodegradability, and life cycle assessment will be highly appreciated.

The Special Issue will be of interest for producers of natural fibers, polymer matrices of renewable origin and composite materials, with the aim of future marketing of more environment-friendly materials.

In particular, the topic of interest includes but is not limited to:

Cellulosic and lignocellulosic fibers
Composite materials reinforced with renewable fibers
Preparation and molding processes of natural fiber-based composites
Thermo-mechanical characterization of natural fiber-based composites
Aging behevior of natural fiber based composites
Recyclability of natural fiber based composites
Biodegradability of natural fiber based composites at end of life
Life cycle assessment

Dr. Philippe Evon
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (22 papers)

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Editorial

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Open AccessEditorial

Special Issue “Natural Fiber Based Composites”

Philippe Evon

Coatings 2021, 11(9), 1031; https://doi.org/10.3390/coatings11091031 - 27 Aug 2021

Viewed by 1211

Abstract

In the last twenty years, the use of cellulosic and lignocellulosic agricultural by-products for composite applications has been of great interest, especially for reinforcing matrices [...] Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

Research

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Open AccessArticle

Coffee Wastes as Sustainable Flame Retardants for Polymer Materials

and

Coatings 2021, 11(9), 1021; https://doi.org/10.3390/coatings11091021 - 26 Aug 2021

Cited by 18 | Viewed by 3594

Abstract

Development of green flame retardants has become a core part of the attention of material scientists and technologists in a paradigm shift from general purpose to specific sustainable products. This work is the first report on the use of coffee biowastes as sustainable flame retardants for epoxy, as a typical highly flammable polymer. We used spent coffee grounds (SCG) as well as SCG chemically modified with phosphorus (P-SCG) to develop a sustainable highly efficient flame retardant. A considerable reduction in the peak of heat release rate (pHRR) by 40% was observed in the pyrolysis combustion flow calorimeter analysis (PCFC), which proved the merit of the used coffee biowastes for being used as sustainable flame retardants for polymers. This work would open new opportunities to investigate the impact of other sorts of coffee wastes rather than SCG from different sectors of the coffee industry on polymers of different family. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Sound-Absorption Performance and Fractal Dimension Feature of Kapok Fibre/Polycaprolactone Composites

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Coatings 2021, 11(8), 1000; https://doi.org/10.3390/coatings11081000 - 22 Aug 2021

Cited by 4 | Viewed by 1578

Abstract

This article introduces a kind of composite material made of kapok fibre and polycaprolactone by the hot-pressing method. The effects of volume density, mass fraction of kapok fibre, and thickness on the sound-absorption performance of composites were researched using a single-factor experiment. The sound-absorption performance of the composites was investigated by the transfer function method. Under the optimal process parameters, when the density of the composite material was 0.172 g/cm³, the mass fraction of kapok was 40%, and the thickness was 2 cm, the composite material reached the maximum sound-absorption coefficient of 0.830, and when the sound-absorption frequency was 6300 Hz, the average sound-absorption coefficient was 0.520, and the sound-absorption band was wide. This research used the box dimension method to calculate composites’ fractal dimensions by using the Matlab program based on the fractal theory. It analysed the relationships between fractal dimension and volume density, fractal dimension and mass fraction of kapok fibre, and fractal dimension and thickness. The quantitative relations between fractal dimension and maximum sound-absorption coefficient, fractal dimension, and resonant sound-absorption frequency were derived, which provided a theoretical basis for studying sound-absorption performance. The results showed that kapok fibre/polycaprolactone composites had strong fractal characteristics, which had important guiding significance for the sound-absorption performance of kapok fibre composites. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Enhanced Antibacterial Efficiency of Cellulosic Fibers: Microencapsulation and Green Grafting Strategies

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Coatings 2021, 11(8), 980; https://doi.org/10.3390/coatings11080980 - 18 Aug 2021

Cited by 8 | Viewed by 2364

Abstract

We report an analysis of chemical components of essential oils from barks of Ceylon cinnamon and cloves of Syzygium aromaticum and an investigation of their antibacterial activity. The components of oils were determined by using Gas Chromatography/Mass Spectrometry (GC-MS) analysis, and the antimicrobial activity was assessed by the disk diffusion test. The synergic effect of essential oils mixture (cinnamon oil and clove oil) was evaluated. Antimicrobial properties were conferred to cellulosic fibers through microencapsulation using citric acid as a green binding agent. Essential oil mixture was encapsulated by coacervation using chitosan as a wall material and sodium hydroxide as a hardening agent. The diameter of the produced microcapsules varies between 12 and 48 μm. Attachment of the produced microcapsules onto cotton fabrics surface was confirmed by Attenuated Total Reflectance-Fourier Transformed Infrared (ATR-FTIR) spectroscopy, optical microscopy and Scanning Electron Microscopy (SEM) analysis. The results show that microcapsules were successfully attached on cotton fabric surfaces, imparting antibacterial activity without significantly affecting their properties. The finished cotton fabrics exhibited good mechanical properties and wettability. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Continuous Mechanical Extraction of Fibres from Linseed Flax Straw for Subsequent Geotextile Applications

and

Coatings 2021, 11(7), 852; https://doi.org/10.3390/coatings11070852 - 15 Jul 2021

Cited by 3 | Viewed by 2197

Abstract

Linseed flax is a multipurpose crop. It is cultivated for its seeds and particularly for its oil. The main contributors for this crop are Canada, France and Belgium. In general, straws of linseed flax are buried in the fields or burnt. However, these solutions are not good practices for the environment and from an economical point of view. In this study, straws of linseed flax (six batches in total) with different dew retting durations and harvesting techniques were studied to possibly use them for producing innovative geotextiles. Two different fibre extraction processes were investigated. A first process (A) involved horizontal breaker rollers and then a breaking card. A second one (B) consisted in using vertical breaker rollers, and an “all fibre” extraction device (fibre opener) followed by sieving. The chemical composition of fibres in parietal constituents appeared to be globally equivalent to the one of textile flax with a pectic content decreasing as a function of the dew retting duration. This contributed to an increase in the cellulose content. The fibre content was situated in a range from 29% to 33%, which corresponds to a good yield for linseed flax fibre. The level of purity can reach values of up to 90% for method A (without extra-sieving) and 96% for method B (with extra-sieving), and the length of the fibres (larger for method A than for method B) and their tensile properties make them suitable for structural geotextile yarn manufacturing. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Fibre Individualisation and Mechanical Properties of a Flax-PLA Non-Woven Composite Following Physical Pre-Treatments

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Coatings 2021, 11(7), 846; https://doi.org/10.3390/coatings11070846 - 14 Jul 2021

Cited by 3 | Viewed by 2368

Abstract

Pre-treatments for plant fibres are very popular for increasing the fineness of bundles, promoting individualisation of fibres, modifying the fibre-matrix interface or reducing water uptake. Most pre-treatments are based on the use of chemicals and raise concerns about possible harmful effects on the environment. In this study, we used physical pre-treatments without the addition of chemical products. Flax tows were subjected to ultrasound and gamma irradiation to increase the number of elementary fibres. For gamma pre-treatments, a 20% increase in the number of elementary fibres was quantified. The biochemical composition of pre-treated flax tows exhibited a partial elimination of sugars related to pectin and hemicelluloses depending on the pre-treatment. The hygroscopic behaviour showed a comparable decreasing trend for water sorption-desorption hysteresis for both types of pre-treatment. Then, non-woven composites were produced from the pre-treated tows using poly-(lactid) (PLA) as a bio-based matrix. A moderate difference between the composite mechanical properties was generally demonstrated, with a significant increase in the stress at break observed for the case of ultrasound pre-treatment. Finally, an environmental analysis was carried out and discussed to quantitatively compare the different environmental impacts of the pre-treatments for composite applications; the environmental benefit of using gamma irradiation compared to ultrasound pre-treatment was demonstrated. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Preparation and Application of Efficient Biobased Carbon Adsorbents Prepared from Spruce Bark Residues for Efficient Removal of Reactive Dyes and Colors from Synthetic Effluents

Glaydson Simões dos Reis

Helinando Pequeno de Oliveira

and

Guilherme L. Dotto

Coatings 2021, 11(7), 772; https://doi.org/10.3390/coatings11070772 - 27 Jun 2021

Cited by 46 | Viewed by 2314

Abstract

Biobased carbon materials (BBC) obtained from Norway spruce (Picea abies Karst.) bark was produced by single-step chemical activation with ZnCl₂ or KOH, and pyrolysis at 800 °C for one hour. The chemical activation reagent had a significant impact on the properties of the BBCs. KOH-biobased carbon material (KOH-BBC) had a higher specific surface area (S_BET), equal to 1067 m² g⁻¹, larger pore volume (0.558 cm³ g⁻¹), more mesopores, and a more hydrophilic surface than ZnCl₂-BBC. However, the carbon yield for KOH-BBC was 63% lower than for ZnCl₂-BBC. Batch adsorption experiments were performed to evaluate the ability of the two BBCs to remove two dyes, reactive orange 16 (RO-16) and reactive blue 4 (RB-4), and treat synthetic effluents. The general order model was most suitable for modeling the adsorption kinetics of both dyes and BBCs. The equilibrium parameters at 22 °C were calculated using the Liu model. Upon adsorption of RO-16, Q_max was 90.1 mg g⁻¹ for ZnCl₂-BBC and 354.8 mg g⁻¹ for KOH-BBC. With RB-4, Qmax was 332.9 mg g⁻¹ for ZnCl₂-BBC and 582.5 mg g⁻¹ for KOH-BBC. Based on characterization and experimental data, it was suggested that electrostatic interactions and hydrogen bonds between BBCs and RO-16 and RB-4 dyes played the most crucial role in the adsorption process. The biobased carbon materials showed high efficiency for removing RO-16 and RB-4, comparable to the best examples from the literature. Additionally, both the KOH- and ZnCl₂-BBC showed a high ability to purify two synthetic effluents, but the KOH-BBC was superior. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Elaboration by Wrapping Process and Multiscale Characterisation of Thermoplastic Bio-Composite Based on Hemp/PA11 Constituents

Chaimae Laqraa

Manuela Ferreira

Ahmad Rashed Labanieh

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Damien Soulat

Coatings 2021, 11(7), 770; https://doi.org/10.3390/coatings11070770 - 26 Jun 2021

Cited by 2 | Viewed by 1579

Abstract

The present work investigates the potential of developing bio-composites based on thermoplastic polymers reinforced with natural fibres by using hybrid yarns. The hybrid yarns were produced by the wrapping technique, in which a multifilament of polyamide 11 (PA11) was wrapped around an untreated low-twisted hemp roving to produce a yarn with sufficient tenacity and stiffness for the next step of weaving. The tensile behaviour of the wrapped yarns was identified both in the dry- and thermo-state. Then, two different fabrics were woven and tested to study the influence of yarn densities and weave diagrams on the tensile and flexural properties. At this fabric scale, properties of fabrics made from hybrid yarns were compared with those of fabrics from a previous study made from 100% hemp roving. Composites made from these fabrics, with stacking of two cross-plies, were produced by thermocompression and characterised regarding mechanical strength. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessFeature PaperArticle

Development of Electrospun Films from Wastewater Treatment Plant Sludge

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Urška Vrabič-Brodnjak

Coatings 2021, 11(6), 733; https://doi.org/10.3390/coatings11060733 - 18 Jun 2021

Cited by 1 | Viewed by 1890

Abstract

Electrospinning is a versatile method for producing continuous polymer nanofibers, including from wastewater treatment plant sludge (WTPS). In this context, purified WTPS was successfully used to produce electrospun fibers. The main objective of our research was to produce new, local, circular, renewable and environmentally friendly packaging material. The aim of the research was to purify and treat WTPS to make it suitable for the electrospinning process, thus producing a new material and chemically characterizing it in the first step. One of the major advantages of our process was that the electrospinning process could be carried out with water and ethylenediaminetetraacetic acid. The optimal viscosity was determined to be 20,000 mPas in order to produce sufficient nanofibers. Analyses such as Fourier-Transform Infrared Spectroscopy (FTIR) and ¹H-NMR (proton nuclear magnetic resonance) were used to determine the substances of unpurified and purified WTPS. The tensile properties, contact angle, surface properties and differential scanning calorimetry of the final material were determined and used. The ¹H-NMR analysis confirmed the presence of a small quantity of polyhydroxyalkanoates in the samples. Based on the properties, the final material was brittle and less stretchable compared to electrospun packaging films available in the market. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Preparation of Nanochitin/Polystyrene Composite Particles by Pickering Emulsion Polymerization Using Scaled-Down Chitin Nanofibers

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Coatings 2021, 11(6), 672; https://doi.org/10.3390/coatings11060672 - 01 Jun 2021

Cited by 8 | Viewed by 2253

Abstract

In this study, we investigate the Pickering emulsion polymerization of styrene using scaled-down chitin nanofibers (SD-ChNFs) as stabilizers to produce nanochitin/polystyrene composite particles. Prior to emulsion polymerization, an SD-ChNF aqueous dispersion was prepared by disintegrating bundles of the parent ChNFs with an upper hierarchical scale in aqueous acetic acid through ultrasonication. After styrene was added to the resulting dispersions, the mixtures at the desired weight ratios (SD-ChNFs to styrene = 0.1:1–1.4:1) were ultrasonicated to produce Pickering emulsions. Radical polymerization was then conducted in the presence of potassium persulfate as an initiator in the resulting emulsions to fabricate the composite particles. The results show that their average diameters decreased to a minimum of 84 nm as the weight ratios of SD-ChNFs to styrene increased. The IR and ¹H-NMR spectra of the composite particle supported the presence of both chitin and polystyrene in the material. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Study on the Grafting of Chitosan-Essential Oil Microcapsules onto Cellulosic Fibers to Obtain Bio Functional Material

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Coatings 2021, 11(6), 637; https://doi.org/10.3390/coatings11060637 - 27 May 2021

Cited by 9 | Viewed by 2868

Abstract

The purpose of this work was to prepare chitosan–essential oil microcapsules using the simple coacervation method and to graft them onto cellulosic fibers to obtain bio functional textile. The microcapsules morphology was characterized by optical microscopy. The 2D dimethyloldihydroxyethylene urea resin (DMDHEU) was used as a binding agent to graft microcapsules on the surface of cellulosic fibers. Scanning Electron Microscopy (SEM) photographs and Attenuated Total Reflectance-Fourier Transformed Infrared (ATR-FTIR) analyses were performed to prove the interaction between cellulosic fibers and microcapsules. Furthermore, the properties of the different fabrics such as mechanical strength and air permeability were investigated. Furthermore, washing durability was evaluated. Finally, the antibacterial activity of the finished fibers against the strains Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was evaluated. The results evidence the ability of treated fabrics to induce bacteria growth inhibition. The coacervation method is a simple process to incorporate cinnamon essential oil on the cellulosic fiber’s surface. The use of essential oils as active agents seems to be a promising tool for many protective textile substrates such as antimicrobial masks, bacteriostatic fabrics and healthcare textiles. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Electrospun Sericin/PNIPAM-Based Nano-Modified Cotton Fabric with Multi-Function Responsiveness

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Coatings 2021, 11(6), 632; https://doi.org/10.3390/coatings11060632 - 25 May 2021

Cited by 8 | Viewed by 2012

Abstract

There is a significant interest in developing environmentally responsive or stimuli-responsive smart materials. The purpose of this study was to investigate multi-function responsive cotton fabrics with surface modification on the nanoscale. Three technologies including electrospinning technology, interpenetrating polymer network technology, and cross-linking technology were applied to prepare the multi-function sericin/poly(N-isopropylacrylamide)/Poly(ethylene oxide) nanofibers, which were then grafted onto the surfaces of cotton textiles to endow the cotton textiles with outstanding stimuli-responsive functionalities. The multi-function responsive properties were evaluated via SEM, DSC, the pH-responsive swelling behavior test and contact angle measurements. The results demonstrate that with this method, multi-function responsive, including thermo- and pH-responsiveness, cotton fabrics were fast formed, and the stimuli-responsiveness of the materials was well controlled. In addition, the antimicrobial testing reveals efficient activity of cotton fabrics with the sericin/PNIPAM/PEO nanofiber treatments against Gram-positive bacteria and Gram-negative bacteria such as Staphylococcus aureus and Escherichia coli. The research shows that the presented strategy demonstrated the great potential of multi-function responsive cotton fabrics fabricated using our method. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessFeature PaperArticle

Life Cycle Assessment of Olive Pomace as a Reinforcement in Polypropylene and Polyethylene Biocomposite Materials: A New Perspective for the Valorization of This Agricultural By-Product

Gabriela Espadas-Aldana

Priscila Guaygua-Amaguaña

Claire Vialle

Jean-Pierre Belaud

Philippe Evon

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Caroline Sablayrolles

Coatings 2021, 11(5), 525; https://doi.org/10.3390/coatings11050525 - 29 Apr 2021

Cited by 8 | Viewed by 2922

Abstract

The main environmental impact of olive oil production is the disposal of residues such as pomace and water vegetation. During the olive oil extraction process, the olive stone is milled and discharged within the olive pomace. However, olive stone flour can be valorized as filler for polymeric composites. A life cycle assessment of the olive pomace valorization was carried out by focusing on the manufacturing process of a biocomposite made of two different thermoplastic matrices, i.e., polyethylene and polypropylene. The functional unit is the production of 1 m² of a lath made of an olive pomace-based biocomposite. The analysis was carried out with the SimaPro PhD 9.1.1.1 software, and the database used for the modeling was Ecoinvent 3.6. The obtained results reveal that the hotspot of the whole process is the twin-screw compounding of the olive stone fraction, with the polymeric matrix and coupling agent, and that human health is the most affected damage category. It represents 89% for both scenarios studied: olive stone fraction/polypropylene (OSF/PP) and olive stone fraction/polyethylene (OSF/PE). Further research directions include the use of biosourced polymer matrices, which could reduce the impact of olive pomace-based composite manufacturing. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Printing with Natural Dye Extracted from Impatiens glandulifera Royle

Maja Klančnik

Coatings 2021, 11(4), 445; https://doi.org/10.3390/coatings11040445 - 13 Apr 2021

Cited by 5 | Viewed by 2279

Abstract

Invasive alien plants that damagingly overgrow native ecosystems can be beneficially used to produce natural dyes. Natural dyes are healthier and more environmentally friendly than synthetic dyes, so their use on textiles and other products that come into contact with humans is desirable. In this study, the possibility of using a natural dye extracted from the purple petals of the invasive plant Impatiens glandulifera Royle (Himalayan balsam) for screen printing on various substrates; woven fabrics and different papers made from virgin fibers, recycled fibers, and from fibers of Japanese knotweed, was investigated. The prints were evaluated by color measurements and fastness properties. With the violet dye extract, purple-brown prints were obtained on papers made from Japanese knotweed, and more brown prints on other substrates. They had excellent rub fastness but faded significantly when exposed to light. The wash fastness of the prints on cotton fabrics was moderate and poor on polyester fabrics, but the prints had good resistance to wet ironing. The addition of acid to the printing paste resulted in a lighter violet color, the addition of alkali caused a drastic color change to green, both additives increased the light fastness of the prints but reduced the fastness on fabrics to wet treatments. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

Open AccessArticle

Green Sound-Absorbing Composite Materials of Various Structure and Profiling

Eulalia Gliscinska

Javier Perez de Amezaga

Marina Michalak

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Izabella Krucinska

Coatings 2021, 11(4), 407; https://doi.org/10.3390/coatings11040407 - 31 Mar 2021

Cited by 6 | Viewed by 1911

Abstract

This article presents thermoplastic sound-absorbing composites manufactured on the basis of renewable raw materials. Both the reinforcing material and the matrix material were biodegradable and used in the form of fibers. In order to mix flax fibers with polylactide fibers, the fleece was fabricated with a mechanical system and then needle-punched. The sound absorption of composites obtained from a multilayer structure of nonwovens pressed at different conditions was investigated. The sound absorption coefficient in the frequency ranging from 500 Hz to 6400 Hz was determined using a Kundt tube. The tests were performed for flat composites with various structures, profiled composites, and composite/pre-pressed nonwoven systems. Profiling the composite plate by convexity/concavity has a positive effect on its sound absorption. It is also important to arrange the plate with the appropriate structure for the incident sound wave. For the composite layer with an added pre-pressed nonwoven layer, a greater increase in sound absorption occurs for the system when a rigid composite layer is located on the side of the incident sound wave. The addition of successive nonwoven layers not only increases the absorption but also extends the maximum absorption range from the highest frequencies towards the lower frequencies. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessEditor’s ChoiceArticle

Low-Density Insulation Blocks and Hardboards from Amaranth (Amaranthus cruentus) Stems, a New Perspective for Building Applications

Philippe Evon

Guyonne de Langalerie

and

Coatings 2021, 11(3), 349; https://doi.org/10.3390/coatings11030349 - 18 Mar 2021

Cited by 2 | Viewed by 2665

Abstract

Nowadays, amaranth appears as a promising source of squalene of vegetable origin. Amaranth oil is indeed one of the most concentrated vegetable oils in squalene, i.e., up to 6% (w/w). This triterpene is highly appreciated in cosmetology, especially for the formulation of moisturizing creams. It is almost exclusively extracted from the liver of sharks, causing their overfishing. Thus, providing a squalene of renewable origin is a major challenge for the cosmetic industry. The amaranth plant has thus experienced renewed interest in recent years. In addition to the seeds, a stem is also produced during cultivation. Representing up to 80% (w/w) of the plant aerial part, it is composed of a ligneous fraction, the bark, on its periphery, and a pith in its middle. In this study, a fractionation process was developed to separate bark and pith. These two fractions were then used to produce renewable materials for building applications. On the one hand, the bark was used to produce hardboards, with the deoiled seeds acting as natural binder. Such boards are a viable alternative to commercial wood-based panels. On the other hand, the pith was transformed into cohesive and machinable low-density insulation blocks revealing a low thermal conductivity value. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Contribution of Different Pretreatments to the Thermal Stability and UV Resistance Performance of Cellulose Nanofiber Films

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Coatings 2021, 11(2), 247; https://doi.org/10.3390/coatings11020247 - 19 Feb 2021

Cited by 3 | Viewed by 1470

Abstract

Hot water (HW), green liquor (GL), and sodium chlorite (SC) pretreatments were used to pretreat sugarcane bagasse (SCB) and spruce (SP) and then to prepare cellulose nanofibers (CNFs) through high-pressure homogenization to explore the effect of physicochemical properties on the thermal stability and ultraviolet (UV) resistance performance of CNF films. The results indicated that the lignin content of HW-pretreated CNFs was higher than that of GL- and SC-pretreated CNFs, and the hemicellulose content of HW-pretreated CNFs was lower than that of GL- and SC-pretreated CNFs. The synergy of lignin and hemicellulose impacted the thermal stability of CNF films. The thermal stability of all the SP CNF films was higher than that of all the SCB CNF films. Hot water pretreatment improved the thermal stability of CNF films, and green liquor and sodium chlorite pretreatment decreased the thermal stability of CNF films. The highest thermal stability of SP-HW CNF films reached 392 °C, which was 5.4% higher than that of SP-SC CNF films. Furthermore, the ultraviolet resistance properties of different CNF films were as follows: SCB-HW > SCB-GL > SCB-SC and SP-HW > SP-GL > SP-SC. Green liquor pretreatment is an effective method to prepare CNFs. Conclusively, this research provides a basic theory for the preparation of CNFs and allows the improvement of CNF films in the application of thermal stability management and UV resistance fields. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

An Experimental Study for the Improvement of the Stain Resistance for Exterior Wall Paints in a Western City in China

Xiao Huang

Caixia Wang

and

Dengling Zhu

Coatings 2021, 11(2), 220; https://doi.org/10.3390/coatings11020220 - 12 Feb 2021

Cited by 4 | Viewed by 1801

Abstract

In recent years, with the rapid development of the building industry in western cities during the period of “Western Development” in China, the paints industry has developed rapidly and become more mature. In addition, waterborne inorganic exterior wall paints have been a great choice in the building industry because of their reduced volatile organic compounds (VOCs) and less toxicity and odor. However, the problem of stain resistance for exterior wall paints in western cities has not been solved, which has become a major obstacle to the application and promotion of exterior wall paints in western cities in China. Therefore, effective measures should eventually be carried out for improving the stain resistance of exterior wall paints in western cities in China. In this paper, an experimental study on improving stain resistance for exterior wall paints in a typical western city in China, Chongqing, is reported. In the three defined designs, the effects of the paint structure type, the pigment volume concentration (PVC), thickeners, cosolvents and wetting and dispersing agents on the stain resistance of exterior wall paints in a typical western city in China, Chongqing, were examined. The experimental results suggest that the stain resistance of silicone–acrylic paint was the most suitable among the three kinds of tested paints (silicone–acrylic paint, styrene–acrylic paint and pure acrylic paint). In addition, the PVC had a great influence on the stain resistance of the exterior wall paints. The compactness, water absorption and stain resistance of the paint’s film were the most suitable when the PVCs of the paints reached 45%. Furthermore, the tested wetting and dispersing agents made the same contributions to the paints’ stain resistance, as their decline rates for reflectivity were similar. The reflectivity of the film significantly decreased when the ratio of associating thickener to non-associating thickener reached 4:1, and also significantly declined when the content of propylene glycol reached 5%. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Enhancing Flame Resistance of Cellulosic Fibers Using an Ecofriendly Coating

Riadh Zouari

and

Sondes Gargoubi

Coatings 2021, 11(2), 179; https://doi.org/10.3390/coatings11020179 - 03 Feb 2021

Cited by 4 | Viewed by 1939

Abstract

Among the various advanced materials, flame-retardant cellulosic textiles are important as they directly relate to human health and hazards. The use of environmentally friendly flame-retardant coatings is currently one of the major concerns in the textile coating industry. In this work, acrylic acid was grafted onto the surface of cotton using plasma technology to enhance the attachment of acrylate phosphate monomer. Surface analyses, such as scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and attenuated total reflectance Fourier-transform infrared (ATR-FTIR), were carried out to characterize the coating. Textile properties such as wettability and mechanical properties of untreated and treated cotton samples were investigated. A laundering test was also performed to predict the durability of the finishing. The outcomes revealed that acrylic acid-grafted samples treated with acrylate phosphate monomer have good flame-retardant properties. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessArticle

Mucilages from Different Plant Species Affect the Characteristics of Bio-Mortars for Restoration

Maria Fernanda Falcon Martinez

Alejandro Meza Orozco

and

Coatings 2021, 11(1), 75; https://doi.org/10.3390/coatings11010075 - 11 Jan 2021

Cited by 9 | Viewed by 2155

Abstract

The need for compatible materials for the preservation of cultural heritage has resulted in the revival of lime-based mortar technology and other applications. This work investigates the cohesion and integrity of lime mortars added with fresh mucilage extracted from five plants and evaluates their bioreceptivity for long-term durability. Specimens of lime mortars added with 2.5% of fresh mucilage extracted from Aloe vera, Cylindropuntia californica, Opuntia engelmannii, Opuntia ficus-indica and Salvia hispanica mucilages were analyzed for color change (colorimetry), cohesion (ultrasound measurements), integrity (X-rays) and bioreceptivity (microbiological tests).The internal structure of the specimens added with Cacti mucilages shows better compactness, and no color change was noticed in the bio-mortars also after aging. The bioreceptivity response of mortars inoculated with bacteria, fungi and a photosynthetic biofilm was quite different. Specimens added with Aloe and Cylindropuntia mucilages showed a higher extent of bioreceptivity than the control; the specimens of bio-mortars added with Opuntia engelmannii, Opuntia ficus-indica and Salvia hispanica mucilages did not appear, up to threemonths after the contamination, any microbial growth. These results indicate that the addition of mucilage improves the mortar qualities, but the choice of the plant mucilage must be carefully evaluated since it can be responsible for changes in the bioreceptivity of the mortar. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessFeature PaperArticle

A New Composite Biomaterial Made from Sunflower Proteins, Urea, and Soluble Polymers Obtained from Industrial and Municipal Biowastes to Perform as Slow Release Fertiliser

and

Coatings 2021, 11(1), 43; https://doi.org/10.3390/coatings11010043 - 02 Jan 2021

Cited by 12 | Viewed by 2866

Abstract

Controlled-release fertilizers (CRF) are needed under current agriculture practice to decrease the environmental impact caused by fertilizer doses applied in excess of plants’ uptake rate. Commercial CRF are available. They are manufactured from mineral fertilizers encapsulated into a synthetic polymer matrix or coated by a polymer layer. However, substitution of fossil sourced organic polymers with biopolymers is a major environmental concern. In the present paper, we describe the manufacture by a continuous twin-screw extrusion process, and the mechanical and chemical properties of injection-molded composite pellets containing 90% sunflower protein concentrate (SPC) matrix, and 5–10% of a biopolymer (BP) obtained from municipal biowastes (MBW), and/or urea (U). The reported results show that SPC-BP-U behaves as an efficient eco-friendly CRF. BP contributes to several benefits to the performance of the composite pellets, upon increasing surface hardness, and controlling the formation of ammonia from urea hydrolysis and the release of organic nitrogen. The SPC-BP-U appears a powerful eco-friendly CRF to supply organic C and the three major N, P, and K nutrients to soil and plants. It offers worthwhile scope for being tested in the cultivation of specific plants under the real operational conditions of agriculture practices. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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Open AccessReview

Developments in Chemical Treatments, Manufacturing Techniques and Potential Applications of Natural-Fibers-Based Biodegradable Composites

Muhammad Yasir Khalid

and

Fausto Pedro García Márquez

Coatings 2021, 11(3), 293; https://doi.org/10.3390/coatings11030293 - 04 Mar 2021

Cited by 57 | Viewed by 4461

Abstract

The utilization of synthetic materials stimulates environmental concerns, and researchers worldwide are effectively reacting to environmental concerns by transitioning towards biodegradable and sustainable materials. Natural fibers like jute and sisal have been being utilized for ages in several applications, such as ropes, building materials, particle boards, etc. The absence of essential information in preparing the natural-fiber-reinforced materials is still a challenge for future applications. Chemical treatments and surface modifications can improve the quality of the natural fibers. Natural-fiber-based composites are a potential candidate for many lightweight engineering applications with significant mechanical properties. In the view of the progressive literature reported in the field, this work aims to present the significance of natural fibers, their composites, and the main factors influencing these materials for various applications (automotive industry, for instance). Secondly, we aim to address different surface modifications and chemical treatments on natural fibers and finally provide an overview of natural fiber reinforced polymer composites’ potential applications. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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