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Special Issue "Green Composites"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Composites".

Deadline for manuscript submissions: closed (30 September 2015)

Special Issue Editor

Guest Editor
Prof. Dr. Marco Morreale

Faculty of Engineering and Architecture, Kore University of Enna, 94100– Enna, Italy
Website | E-Mail
Interests: green composites; biocomposites; nanocomposites; biodegradable polymers; polymer blends; polymer processing; mechanical behaviour of polymer-based systems; rheological behaviour of polymer-based systems; aging of polymer-based systems; asphalts

Special Issue Information

Dear Colleagues,

The recent concerns in terms of environmental protection and the search for more and more versatile and polymer-based materials has led to an increasing interest in the use of polymer composites filled with natural-organic fillers (biodegradable and/or coming from renewable resources) as a replacement for traditional mineral-inorganic fillers, with the aim to reduce the use of petroleum-derived, non-renewable resources and to achieve a more intelligent utilization of environmental and financial resources. These “green composites” are very promising, can find applications in several fields (automotive, construction, furnishing, etc.) and a further degree of environmental friendliness is achieved when also the polymer matrix is biodegradable and/or coming from renewable sources. On the other hand, some issues may occur regarding ductility, dimensional stability, and processability. This requires an effort from the research community in order finding the best solutions (which can rely on a suitable choice of the components and their amounts, chemical modifications, use of adhesion promoters, and additives) and it is of fundamental importance to investigate new formulations and to refine the processing techniques. The market for these composites is currently increasing its volumes, and this trend will certainly go on, leading to further reduction of costs and improvements of the quality of the composites, as well as a broadening of the application range.

In this Special Issue, we aim at providing a comprehensive overview of recent developments in this field. Reviews, full papers, short communications, covering the many aspects of the current research on green composites are all welcome.

Dr. Marco Morreale
Guest Editor

Manuscript Submission Information

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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. Materials 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 1500 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.

Keywords

  • processing of green composites
  • rheology of green composites
  • characterization and structure-property relationships of green composites
  • chemical modification of natural-organic fillers
  • synthesis and characterization of biodegradable polymer matrices for application in green composites
  • polymer-natural organic filler adhesion promoters
  • environmental impact and LCA of green composites
  • industrial and commercial applications of green composites
  • testing of green composites

Published Papers (12 papers)

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Research

Open AccessArticle Effects of Wet/Dry-Cycling and Plasma Treatments on the Properties of Flax Nonwovens Intended for Composite Reinforcing
Materials 2016, 9(2), 93; doi:10.3390/ma9020093
Received: 27 November 2015 / Revised: 23 December 2015 / Accepted: 25 January 2016 / Published: 3 February 2016
Cited by 3 | PDF Full-text (4347 KB) | HTML Full-text | XML Full-text
Abstract
This research analyzes the effects of different treatments on flax nonwoven (NW) fabrics which are intended for composite reinforcement. The treatments applied were of two different kinds: a wet/dry cycling which helps to stabilize the cellulosic fibers against humidity changes and plasma treatments
[...] Read more.
This research analyzes the effects of different treatments on flax nonwoven (NW) fabrics which are intended for composite reinforcement. The treatments applied were of two different kinds: a wet/dry cycling which helps to stabilize the cellulosic fibers against humidity changes and plasma treatments with air, argon and ethylene gases considering different conditions and combinations, which produce variation on the chemical surface composition of the NWs. The resulting changes in the chemical surface composition, wetting properties, thermal stability and mechanical properties were determined. Variations in surface morphology could be observed by scanning electron microscopy (SEM). The results of the X-ray photoelectron spectroscopy (XPS) showed significant changes to the surface chemistry for the samples treated with argon or air (with more content on polar groups on the surface) and ethylene plasma (with less content of polar groups). Although only slight differences were found in moisture regain and water retention values (WRV), significant changes were found on the contact angle values, thus revealing hydrophilicity for the air-treated and argon-treated samples and hydrophobicity for the ethylene-treated ones. Moreover, for some of the treatments the mechanical testing revealed an increase of the NW breaking force. Full article
(This article belongs to the Special Issue Green Composites)
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Open AccessFeature PaperArticle Evaluation of Castor Oil Cake Starch and Recovered Glycerol and Development of “Green” Composites Based on Those with Plant Fibers
Materials 2016, 9(2), 76; doi:10.3390/ma9020076
Received: 14 December 2015 / Accepted: 13 January 2016 / Published: 27 January 2016
PDF Full-text (2062 KB) | HTML Full-text | XML Full-text
Abstract
Continuous efforts are being made in some countries for the recovery of crude glycerin (RG/CG) and castor oil cake (COC), the two byproducts of biodiesel production. These are expected to help, not only in addressing environmental safety, but also in adding value to
[...] Read more.
Continuous efforts are being made in some countries for the recovery of crude glycerin (RG/CG) and castor oil cake (COC), the two byproducts of biodiesel production. These are expected to help, not only in addressing environmental safety, but also in adding value to those byproducts, which otherwise may go to waste. Finding ways to utilize those byproducts underlines the main objective of this study. This paper presents the evaluation of (i) COC, glycerin and banana and sugarcane fibers for moisture content; (ii) COC for structural and thermal properties; and (iii) CG for its chemical characteristics. The possibility of using COC and CG with the selected fibers as reinforcement in the development of bio-composites is attempted through thermo-molding. Results revealed enhanced mechanical properties for these composites. The obtained results are discussed in terms of the observed morphology. Full article
(This article belongs to the Special Issue Green Composites)
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Open AccessFeature PaperArticle Biodegradable Nanocomposite Films Based on Sodium Alginate and Cellulose Nanofibrils
Materials 2016, 9(1), 50; doi:10.3390/ma9010050
Received: 30 September 2015 / Revised: 30 December 2015 / Accepted: 11 January 2016 / Published: 14 January 2016
Cited by 8 | PDF Full-text (3600 KB) | HTML Full-text | XML Full-text
Abstract
Biodegradable nanocomposite films were prepared by incorporation of cellulose nanofibrils (CNF) into alginate biopolymer using the solution casting method. The effects of CNF content (2.5, 5, 7.5, 10 and 15 wt %) on mechanical, biodegradability and swelling behavior of the nanocomposite films were
[...] Read more.
Biodegradable nanocomposite films were prepared by incorporation of cellulose nanofibrils (CNF) into alginate biopolymer using the solution casting method. The effects of CNF content (2.5, 5, 7.5, 10 and 15 wt %) on mechanical, biodegradability and swelling behavior of the nanocomposite films were determined. The results showed that the tensile modulus value of the nanocomposite films increased from 308 to 1403 MPa with increasing CNF content from 0% to 10%; however, it decreased with further increase of the filler content. Incorporation of CNF also significantly reduced the swelling percentage and water solubility of alginate-based films, with the lower values found for 10 wt % in CNF. Biodegradation studies of the films in soil confirmed that the biodegradation time of alginate/CNF films greatly depends on the CNF content. The results evidence that the stronger intermolecular interaction and molecular compatibility between alginate and CNF components was at 10 wt % in CNF alginate films. Full article
(This article belongs to the Special Issue Green Composites)
Open AccessArticle Processing and Characterization of Cellulose Nanocrystals/Polylactic Acid Nanocomposite Films
Materials 2015, 8(12), 8106-8116; doi:10.3390/ma8125447
Received: 30 September 2015 / Revised: 30 October 2015 / Accepted: 23 November 2015 / Published: 1 December 2015
Cited by 14 | PDF Full-text (2836 KB) | HTML Full-text | XML Full-text
Abstract
The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization
[...] Read more.
The focus of this study is to examine the effect of cellulose nanocrystals (CNC) on the properties of polylactic acid (PLA) films. The films are fabricated via melt compounding and melt fiber spinning followed by compression molding. Film fracture morphology, thermal properties, crystallization behavior, thermo-mechanical behavior, and mechanical behavior were determined as a function of CNC content using scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, dynamic mechanical analysis, and tensile testing. Film crystallinity increases with increasing CNC content indicating CNC act as nucleating agents, promoting crystallization. Furthermore, the addition of CNC increased the film storage modulus and slightly broadened the glass transition region. Full article
(This article belongs to the Special Issue Green Composites)
Open AccessArticle New Polylactic Acid Composites Reinforced with Artichoke Fibers
Materials 2015, 8(11), 7770-7779; doi:10.3390/ma8115422
Received: 28 September 2015 / Revised: 5 November 2015 / Accepted: 10 November 2015 / Published: 16 November 2015
Cited by 12 | PDF Full-text (5346 KB) | HTML Full-text | XML Full-text
Abstract
In this work, artichoke fibers were used for the first time to prepare poly(lactic acid) (PLA)-based biocomposites. In particular, two PLA/artichoke composites with the same fiber loading (10% w/w) were prepared by the film-stacking method: the first one (UNID) reinforced
[...] Read more.
In this work, artichoke fibers were used for the first time to prepare poly(lactic acid) (PLA)-based biocomposites. In particular, two PLA/artichoke composites with the same fiber loading (10% w/w) were prepared by the film-stacking method: the first one (UNID) reinforced with unidirectional long artichoke fibers, the second one (RANDOM) reinforced by randomly-oriented long artichoke fibers. Both composites were mechanically characterized in tensile mode by quasi-static and dynamic mechanical tests. The morphology of the fracture surfaces was analyzed through scanning electron microscopy (SEM). Moreover, a theoretical model, i.e., Hill’s method, was used to fit the experimental Young’s modulus of the biocomposites. The quasi-static tensile tests revealed that the modulus of UNID composites is significantly higher than that of the neat PLA (i.e., ~40%). Moreover, the tensile strength is slightly higher than that of the neat matrix. The other way around, the stiffness of RANDOM composites is not significantly improved, and the tensile strength decreases in comparison to the neat PLA. Full article
(This article belongs to the Special Issue Green Composites)
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Open AccessArticle Mechanical, Thermomechanical and Reprocessing Behavior of Green Composites from Biodegradable Polymer and Wood Flour
Materials 2015, 8(11), 7536-7548; doi:10.3390/ma8115406
Received: 30 September 2015 / Revised: 30 October 2015 / Accepted: 2 November 2015 / Published: 11 November 2015
Cited by 8 | PDF Full-text (5971 KB) | HTML Full-text | XML Full-text
Abstract
The rising concerns in terms of environmental protection and the search for more versatile polymer-based materials have led to an increasing interest in the use of polymer composites filled with natural organic fillers (biodegradable and/or coming from renewable resources) as a replacement for
[...] Read more.
The rising concerns in terms of environmental protection and the search for more versatile polymer-based materials have led to an increasing interest in the use of polymer composites filled with natural organic fillers (biodegradable and/or coming from renewable resources) as a replacement for traditional mineral inorganic fillers. At the same time, the recycling of polymers is still of fundamental importance in order to optimize the utilization of available resources, reducing the environmental impact related to the life cycle of polymer-based items. Green composites from biopolymer matrix and wood flour were prepared and the investigation focused on several issues, such as the effect of reprocessing on the matrix properties, wood flour loading effects on virgin and reprocessed biopolymer, and wood flour effects on material reprocessability. Tensile, Dynamic-mechanical thermal (DMTA), differential scanning calorimetry (DSC) and creep tests were performed, pointing out that wood flour leads to an improvement of rigidity and creep resistance in comparison to the pristine polymer, without compromising other properties such as the tensile strength. The biopolymer also showed a good resistance to multiple reprocessing; the latter even allowed for improving some properties of the obtained green composites. Full article
(This article belongs to the Special Issue Green Composites)
Open AccessArticle Thermo-Mechanical Behaviour of Flax-Fibre Reinforced Epoxy Laminates for Industrial Applications
Materials 2015, 8(11), 7371-7388; doi:10.3390/ma8115384
Received: 30 September 2015 / Accepted: 28 October 2015 / Published: 3 November 2015
Cited by 5 | PDF Full-text (6832 KB) | HTML Full-text | XML Full-text
Abstract
The present work describes the experimental mechanical characterisation of a natural flax fibre reinforced epoxy polymer composite. A commercial plain woven quasi-unidirectional flax fabric with spun-twisted yarns is employed in particular, as well as unidirectional composite panels manufactured with three techniques: hand-lay-up, vacuum
[...] Read more.
The present work describes the experimental mechanical characterisation of a natural flax fibre reinforced epoxy polymer composite. A commercial plain woven quasi-unidirectional flax fabric with spun-twisted yarns is employed in particular, as well as unidirectional composite panels manufactured with three techniques: hand-lay-up, vacuum bagging and resin infusion. The stiffness and strength behaviours are investigated under both monotonic and low-cycle fatigue loadings. The analysed material has, in particular, shown a typical bilinear behaviour under pure traction, with a knee yield point occurring at a rather low stress value, after which the material tensile stiffness is significantly reduced. In the present work, such a mechanism is investigated by a phenomenological approach, performing periodical loading/unloading cycles, and repeating tensile tests on previously “yielded” samples to assess the evolution of stiffness behaviour. Infrared thermography is also employed to measure the temperature of specimens during monotonic and cyclic loading. In the first case, the thermal signal is monitored to correlate departures from the thermoelastic behaviour with the onset of energy loss mechanisms. In the case of cyclic loading, the thermoelastic signal and the second harmonic component are both determined in order to investigate the extent of elastic behaviour of the material. Full article
(This article belongs to the Special Issue Green Composites)
Open AccessArticle Damage Characterization of Bio and Green Polyethylene–Birch Composites under Creep and Cyclic Testing with Multivariable Acoustic Emissions
Materials 2015, 8(11), 7322-7341; doi:10.3390/ma8115382
Received: 6 August 2015 / Accepted: 14 October 2015 / Published: 2 November 2015
Cited by 3 | PDF Full-text (4099 KB) | HTML Full-text | XML Full-text
Abstract
Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green
[...] Read more.
Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green and biocomposites. Thus, this article investigates the behavior of two comparable green and biocomposites with tests that better reflect real-life applications, i.e., load-unloading and creep testing, to determine the evolution of the damage process. Comparing the mechanical results with the AE, it can be concluded that the addition of a coupling agent (CA) markedly reduced the ratio of AE damage to mechanical damage. CA had an extremely beneficial effect on green composites because the Kaiser effect was dominant during cyclic testing. During the creep tests, the use of a CA also avoided the transition to new damaging phases in both composites. The long-term applications of PE green material must be chosen carefully because bio and green composites with similar properties exhibited different damage processes in tests such as cycling and creep that could not be previously understood using only monotonic testing. Full article
(This article belongs to the Special Issue Green Composites)
Open AccessArticle Effect of Extrusion on the Mechanical and Rheological Properties of a Reinforced Poly(Lactic Acid): Reprocessing and Recycling of Biobased Materials
Materials 2015, 8(10), 7106-7117; doi:10.3390/ma8105360
Received: 21 August 2015 / Revised: 2 October 2015 / Accepted: 12 October 2015 / Published: 19 October 2015
Cited by 3 | PDF Full-text (4114 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this research paper is to study the behaviour of a common used biopolymer (Poly(Lactic Acid) (PLA)) after several reprocesses and how two different types of additives (a melt strength enhancer and a nanoadditive) affect its mechanical and rheological properties. Systematic
[...] Read more.
The aim of this research paper is to study the behaviour of a common used biopolymer (Poly(Lactic Acid) (PLA)) after several reprocesses and how two different types of additives (a melt strength enhancer and a nanoadditive) affect its mechanical and rheological properties. Systematic extraction of extrudate samples from a twin-screw compounder was done in order to study the effect in the properties of the reprocessed material. Detailed rheological tests on a capillary rheometer as well as mechanical studies on a universal tensile machine after preparation of injected specimens were carried out. Results evidenced that PLA and reinforced PLA materials can be reprocessed and recycled without a remarkable loss in their mechanical properties. Several processing restrictions and specific phenomena were identified and are explained in the present manuscript. Full article
(This article belongs to the Special Issue Green Composites)
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Open AccessArticle Rice Husk Ash to Stabilize Heavy Metals Contained in Municipal Solid Waste Incineration Fly Ash: First Results by Applying New Pre-treatment Technology
Materials 2015, 8(10), 6868-6879; doi:10.3390/ma8105346
Received: 26 August 2015 / Revised: 25 September 2015 / Accepted: 29 September 2015 / Published: 9 October 2015
Cited by 5 | PDF Full-text (2669 KB) | HTML Full-text | XML Full-text
Abstract
A new technology was recently developed for municipal solid waste incineration (MSWI) fly ash stabilization, based on the employment of all waste and byproduct materials. In particular, the proposed method is based on the use of amorphous silica contained in rice husk ash
[...] Read more.
A new technology was recently developed for municipal solid waste incineration (MSWI) fly ash stabilization, based on the employment of all waste and byproduct materials. In particular, the proposed method is based on the use of amorphous silica contained in rice husk ash (RHA), an agricultural byproduct material (COSMOS-RICE project). The obtained final inert can be applied in several applications to produce “green composites”. In this work, for the first time, a process for pre-treatment of rice husk, before its use in the stabilization of heavy metals, based on the employment of Instant Pressure Drop technology (DIC) was tested. The aim of this work is to verify the influence of the pre-treatment on the efficiency on heavy metals stabilization in the COSMOS-RICE technology. DIC technique is based on a thermomechanical effect induced by an abrupt transition from high steam pressure to a vacuum, to produce changes in the material. Two different DIC pre-treatments were selected and thermal annealing at different temperatures were performed on rice husk. The resulting RHAs were employed to obtain COSMOS-RICE samples, and the stabilization procedure was tested on the MSWI fly ash. In the frame of this work, some thermal treatments were also realized in O2-limiting conditions, to test the effect of charcoal obtained from RHA on the stabilization procedure. The results of this work show that the application of DIC technology into existing treatment cycles of some waste materials should be investigated in more details to offer the possibility to stabilize and reuse waste. Full article
(This article belongs to the Special Issue Green Composites)
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Open AccessArticle Effects of Fiber Reinforcement on Clay Aerogel Composites
Materials 2015, 8(8), 5440-5451; doi:10.3390/ma8085258
Received: 2 July 2015 / Revised: 2 August 2015 / Accepted: 4 August 2015 / Published: 21 August 2015
Cited by 4 | PDF Full-text (2042 KB) | HTML Full-text | XML Full-text
Abstract
Novel, low density structures which combine biologically-based fibers with clay aerogels are produced in an environmentally benign manner using water as solvent, and no additional processing chemicals. Three different reinforcing fibers, silk, soy silk, and hemp, are evaluated in combination with poly(vinyl alcohol)
[...] Read more.
Novel, low density structures which combine biologically-based fibers with clay aerogels are produced in an environmentally benign manner using water as solvent, and no additional processing chemicals. Three different reinforcing fibers, silk, soy silk, and hemp, are evaluated in combination with poly(vinyl alcohol) matrix polymer combined with montmorillonite clay. The mechanical properties of the aerogels are demonstrated to increase with reinforcing fiber length, in each case limited by a critical fiber length, beyond which mechanical properties decline due to maldistribution of filler, and disruption of the aerogel structure. Rather than the classical model for reinforced composite properties, the chemical compatibility of reinforcing fibers with the polymer/clay matrix dominated mechanical performance, along with the tendencies of the fibers to kink under compression. Full article
(This article belongs to the Special Issue Green Composites)
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Open AccessArticle Correlation between Mechanical Properties with Specific Wear Rate and the Coefficient of Friction of Graphite/Epoxy Composites
Materials 2015, 8(7), 4162-4175; doi:10.3390/ma8074162
Received: 12 May 2015 / Revised: 19 June 2015 / Accepted: 26 June 2015 / Published: 8 July 2015
Cited by 3 | PDF Full-text (1637 KB) | HTML Full-text | XML Full-text
Abstract
The correlation between the mechanical properties of Fillers/Epoxy composites and their tribological behavior was investigated. Tensile, hardness, wear, and friction tests were conducted for Neat Epoxy (NE), Graphite/Epoxy composites (GE), and Data Palm Fiber/Epoxy with or without Graphite composites (GFE and FE). The
[...] Read more.
The correlation between the mechanical properties of Fillers/Epoxy composites and their tribological behavior was investigated. Tensile, hardness, wear, and friction tests were conducted for Neat Epoxy (NE), Graphite/Epoxy composites (GE), and Data Palm Fiber/Epoxy with or without Graphite composites (GFE and FE). The correlation was made between the tensile strength, the modulus of elasticity, elongation at the break, and the hardness, as an individual or a combined factor, with the specific wear rate (SWR) and coefficient of friction (COF) of composites. In general, graphite as an additive to polymeric composite has had an eclectic effect on mechanical properties, whereas it has led to a positive effect on tribological properties, whilst date palm fibers (DPFs), as reinforcement for polymeric composite, promoted a mechanical performance with a slight improvement to the tribological performance. Statistically, this study reveals that there is no strong confirmation of any marked correlation between the mechanical and the specific wear rate of filler/Epoxy composites. There is, however, a remarkable correlation between the mechanical properties and the friction coefficient of filler/Epoxy composites. Full article
(This article belongs to the Special Issue Green Composites)

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