New environmentally friendly composite laminates with epoxidized linseed oil (ELO) and slate fiber fabrics

This work focuses on the development of new composite laminates based on the use of epoxidized linseed oil (ELO) as matrix and reinforcement fabrics from slate fibers with different silane treatments. The curing behavior of the ELO resin is followed by differential scanning calorimetry (DSC) and the gelation is studied by oscillatory rheometry and gel-time. Composite laminates of ELO matrix and slate fabrics are manufactured by Resin Transfer Molding (RTM) and the mechanical properties of the composite laminates are tested in tensile, flexural and impact conditions. The effects of different silane coupling agents on fiber-matrix interface phenomena are studied by scanning electron microscopy (SEM). As in other siliceous fibers, silane treatment leads to improved mechanical performance but glycidyl silane treatment produces the optimum results as the interactions between silanized slate fiber and epoxidized linseed oil are remarkably improved as observed by scanning electron microscopy (SEM).     

Effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites

The effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites was evaluated. Alkali treatment of the fibers and reaction with organosilanes as coupling agents were applied to improve fiber–matrix adhesion. Fiber loadings of 1, 3, 5, and 7 wt% were incorporated to the phenolic matrix and tensile, flexural, morphological and thermal properties of the resulting composites were studied. In general, mechanical properties of the composites showed a maximum at 3% of fiber loading and a uniform distribution of the fibers in such composites was observed. Silane treatment of the fibers provided derived composites with the best thermal and mechanical properties. Meanwhile, NaOH treatment improved thermal and flexural properties, but reduced tensile properties of the materials. Therefore, the phenolic composite containing 3% of silane treated cellulose fiber was selected as the material with optimal properties.     

Developing rigid gliadin based biocomposites with high mechanical performance

We aim to produce unidirectional fiber composites with high mechanical performance based on flax fibers and a rigid gliadin matrix. As a fraction from wheat gluten, gliadin is soluble in alcohol containing media. The fabrication process did not involve any further solvents or plasticizers. Finally, samples were cooled at different rates. Overall, the cooling rate does not strongly affect the mechanical properties although slowly cooled materials contain a higher amount of non-disulfide cross-links, next to disulfide bonds within the gliadin matrix. At 40% fiber volume fraction, flax/gliadin composites with a flexural modulus and strength of respectively 21.5 GPa and 240 MPa were obtained when loaded in the longitudinal direction. These high values demonstrate that in this composite fabrication process, a good impregnation of the polymer matrix in between the fiber bundles has been achieved. However, the fiber–matrix adhesion, as measured by transverse flexural and tensile tests, was still relatively modest.     

The effect of alkaline and silane treatments on mechanical properties and breakage of sisal fibers and poly(lactic acid)/sisal fiber composites

The main goals of this work were to study the effect of different chemical treatments on sisal fiber bundles tensile properties as well as on tensile properties of composites based on poly(lactic acid) (PLA) matrix and sisal fibers. For this purpose, sisal fibers were treated with different chemical treatments. After treating sisal fibers the tensile strength values decreased respect to untreated fiber ones, especially when the combination of NaOH + silane treatment was used. Taking into account fiber tensile properties and fiber/PLA adhesion values, composites based on silane treated fibers would show the highest tensile strength value. However, composites based on alkali treated and NaOH + silane treated fibers showed the highest tensile strength values. Finally, experimental tensile strength values of composites were compared with those values obtained using micromechanical models.     

Synergistic effect of coupling agents and fiber treatments on mechanical properties and moisture absorption of polypropylene–rice husk composites and their foam

Rice husks and polypropylene were applied as the fibers and matrix, respectively, to make composites. Polypropylene-grafted maleic anhydride (PP-g-MA) and styrene ethylene butadiene styrene-grafted maleic anhydride (SEBS-g-MA) were used as coupling agents. The rice husks were also treated with NaOH, silane, or NaOH + HCl + silane to enhance the effect of the coupling agents. Using a combination of 2 wt% PP-g-MA and 1 wt% SEBS-g-MA, the impact strength of the composite increased, but the tensile strength and modulus were not reduced relative to the use of PP-g-MA alone. The three treatments – NaOH, silane and NaOH + HCl + silane – and added coupling agents improved the impact strength and decreased the moisture absorption rate of the composites except for those subjected to the alkaline treatments. The foaming results showed that adding coupling agents improved the cell structure and reduced the density of the foam.     

The effect of interfacial interactions on the mechanical properties of polypropylene/natural zeolite composites

The effect of interfacial interactions on the mechanical properties of polypropylene (PP)/natural zeolite composites was investigated under dry and wet conditions. Interfacial interactions were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of natural zeolite with a non-ionic surface modifier; 3 wt% polyethylene glycol (PEG) and three different types of silane coupling agents; 3-aminopropyltriethoxysilane (AMPTES), methyltriethoxysilane (MTES) and 3-mercaptopropyltrimethoxysilane (MPTMS), at four different concentrations (0.5–2 wt%). PP composites containing (2–6 wt%) zeolite were prepared by an extrusion technique. The tensile properties of the composites determined as a function of the filler loading and the concentration of the coupling agents were found to vary with surface treatment of zeolite. Silane treatment indicated significant improvements in the mechanical properties of the composites. According to the dry and wet tensile test results, the maximum improvement in the mechanical properties was obtained for the PP composites containing 1 wt% AMPTES treated zeolite. The improvement in the interfacial interaction was confirmed using a semi-empirical equation developed by Pukanszky. Good agreement was obtained between experimental data and the Pukanszky model prediction. Scanning electron microscopy studies also revealed better dispersion of silane treated filler particles in the PP matrix.     

A study of the mechanical properties of short natural-fiber reinforced composites

The degree of fiber–matrix adhesion and its effect on the mechanical reinforcement of short henequen fibers and a polyethylene matrix was studied. The surface treatments were: an alkali treatment, a silane coupling agent and the pre-impregnation process of the HDPE/xylene solution. The presence of Si–O–cellulose and Si–O–Si bonds on the lignocellulosic surface confirmed that the silane coupling agent was efficiently held on the fibres surface through both condensation with cellulose hydroxyl groups and self-condensation between silanol groups.

The fiber–matrix interface shear strength (IFSS) was used as an indicator of the fiber–matrix adhesion improvement, and also to determine a suitable value of fiber length in order to process the composite with relative ease. It was noticed that the IFSS observed for the different fiber surface treatments increased and such interface strength almost doubled only by changing the mechanical interaction and the chemical interactions between fiber and matrix.

HDPE-henequen fiber composite materials were prepared with a 20% v/v fiber content and the tensile, flexural and shear properties were studied. The comparison of tensile properties of the composites showed that the silane treatment and the matrix-resin pre-impregnation process of the fiber produced a significant increase in tensile strength, while the tensile modulus remained relatively unaffected. The increase in tensile strength was only possible when the henequen fibers were treated first with an alkaline solution. It was also shown that the silane treatment produced a significant increase in flexural strength while the flexural modulus also remained relatively unaffected. The shear properties of the composites also increased significantly, but, only when the henequen fibers were treated with the silane coupling agent. Scanning electron microscopy (SEM) studies of the composites failure surfaces also indicated that there is an improved adhesion between fiber and matrix. Examination of the failure surfaces also indicated differences in the interfacial failure mode. With increasing fiber–matrix adhesion the failure mode changed from interfacial failure and considerable fiber pull-out from the matrix for the untreated fiber to matrix yielding and fiber and matrix tearing for the alkaline, matrix-resin pre-impregnation and silane treated fibers.     

Influence of the process parameters on the mechanical properties of engineering biocomposites using a twin-screw extruder

The utilization of bio-based engineering polymers as a matrix material for cellulosic fiber reinforced composites has become an important focus in materials research. This is due to a rising demand for sustainable materials from renewable resources. In addition to this aspect, the bio-based materials provide an advantage for lightweight applications with their lower density. In this investigation, the completely bio-based polyamide 10.10, with a melting point above 200 °C, was used as a polymer matrix. Chopped man-made cellulose fibers (Cordenka CR-Type) were investigated as reinforcement for use in injection molded applications. A co-rotating twin-screw extruder with a screw-diameter of 18 mm was used for compounding. It was verified that reinforcing polyamide 10.10 with 20 wt% and 30 wt% cellulosic fibers is possible, resulting in an increase of impact and tensile properties. Furthermore, it was shown that the temperatures and screw-configurations of the twin-screw extruder only result in different fiber length distributions but in minor differences of the morphological structure and mechanical properties of PA 10.10 with 20 wt% fibers. Compounds with 30 wt% cellulose fibers show significant higher impact properties that those with 30 wt% glass fibers.     

Ductile unidirectional continuous rayon fibre-reinforced hierarchical composites

Endless rayon fibres (Cordenka®) were used to reinforce polyhydroxybutyrate (PHB) nanocomposites containing 2.5 wt.% nanofibrillated cellulose (NFC) to create truly green hierarchical composites. Unidirectional (UD) composites with 50–55% fibre volume fraction were produced using a solvent-free continuous wet powder impregnation method. The composites exhibit ductile failure behaviour with a strain-to-failure of more than 10% albeit using a very brittle matrix. Improvements at a model composite level were translated into higher mechanical properties of UD hierarchical composites. The Young’s moduli of rayon fibre-reinforced (NFC-reinforced) PHB composites were about 15 GPa. The tensile and flexural strength of hierarchical PHB composites increased by 15% and 33% as compared to the rayon fibre-reinforced neat PHB composites. This suggests that incorporation of NFC into the PHB matrix binds the rayon fibres, which does affect the load transfer between the constituents resulting in composites with better mechanical properties.     

柔性非织造布和玻璃纤维布叠层热压制备玻璃纤维布/聚苯硫醚复合板材

为改善玻璃纤维增强聚苯硫醚（PPS）复合板材的力学性能,分别以柔性的玻璃纤维布和PPS非织造布作为增强体和基体,采用叠层热压成型法制备出刚性的复合板材,采用力学性能测试、XRD、PLM、SEM研究了热压温度、热压时间、玻璃纤维含量和处理玻璃纤维布的硅烷偶联剂种类对复合板材的力学性能、结晶度、结晶形态和微观形貌的影响。结果表明,在无硅烷偶联剂处理玻璃纤维布时,控制热压温度为320℃,热压时间为30 min,压力为30 MPa,玻璃纤维质量分数为50%,复合板材的拉伸强度和弯曲强度最佳,分别为286.0 MPa和175.0 MPa,缺口冲击强度达到61.6 MPa。使用硅烷偶联剂KH560处理玻璃纤维布,在最佳成型工艺条件下,复合板材力学性能改善最明显,其弯曲强度为394.9 MPa,弯曲模量为23.6 GPa,层间剪切强度为16.4 MPa,缺口冲击强度为81.0 MPa。通过优化实验条件和使用硅烷偶联剂处理玻璃纤维表面,复合板材的力学性能得到了明显提高。     

Additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling

Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of the most popular AM techniques, is the most widely used method for fabricating thermoplastic parts those are mainly used as rapid prototypes for functional testing with advantages of low cost, minimal wastage, and ease of material change. Due to the intrinsically limited mechanical properties of pure thermoplastic materials, there is a critical need to improve mechanical properties for FDM-fabricated pure thermoplastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form thermoplastic matrix carbon fiber reinforced plastic (CFRP) composites those could be directly used in the actual application areas, such as aerospace, automotive, and wind energy. This paper is going to present FDM of thermoplastic matrix CFRP composites and test if adding carbon fiber (different content and length) can improve the mechanical properties of FDM-fabricated parts. The CFRP feedstock filaments were fabricated from plastic pellets and carbon fiber powders for FDM process. After FDM fabrication, effects on the tensile properties (including tensile strength, Young's modulus, toughness, yield strength, and ductility) and flexural properties (including flexural stress, flexural modulus, flexural toughness, and flexural yield strength) of specimens were experimentally investigated. In order to explore the parts fracture reasons during tensile and flexural tests, fracture interface of CFRP composite specimens after tensile testing and flexural testing was observed and analyzed using SEM micrograph.     

Environmental effects on the mechanical and thermomechanical properties of aspen fiber–polypropylene composites

The mechanical properties of newly developed aspen fiber–polypropylene composites (APC) were experimentally explored and numerically predicted at the temperatures and humidity that are typical for domestic housing applications. The mechanical properties of APCs with five different fiber-loadings were evaluated at the room temperature, 4 °C, and 40 °C. Environmental effects on the mechanical properties of APCS were experimentally quantified after conditioning the APCs with two different fiber-loadings in the following temperature and humidity for over 7000 h: (1) hot/dry at 40 °C and 30% relative humidity (RH), (2) hot/wet at 40 °C and 82% RH, (3) cold/dry at 4 °C and 30% RH, and (4) cold/wet at 4 °C and 82% RH. The tensile moduli, flexural moduli, and the flexural strength increased as the woodfiber content increased in the composites. However, the tensile strength decreased as the fiber content increased. The tensile strength was shown to slightly improve with an addition of a coupling agent between the aspen fibers and polypropylene. The simple empirical micromechanics Halpin–Tsai model for randomly distributed short fiber reinforced composites was employed to predict the homogenized elastic moduli of APC, by optimizing the interfacial model parameter. Scanning electron microscopy (SEM) micrographs confirmed that an addition of the adhesion promoter maleated anhydride polypropylene (MAPP) between the aspen fibers and polymeric matrix improved the interfacial bonding.     

Experimental study on the mechanical properties and microstructure of chopped basalt fibre reinforced concrete

With high ductility and sufficient durability, fibre reinforced concrete (FRC) is widely used. In this study, the effects of the volume fraction and length of basalt fibre (BF) on the mechanical properties of FRC were analyzed. Coupling with the scanning electron microscope (SEM) and mercury intrusion porosimeter (MIP), the microstructure of BF concrete was studied also. The results show that adding BF significantly improves the tensile strength, flexural strength and toughness index, whereas the compressive strength shows no obvious increase. Furthermore, the length of BF presents an influence on the mechanical properties. Compared with the plain concrete, the compressive, splitting tensile and flexural strength of concrete reinforced with 12 mm BF increase by −0.18–4.68%, 14.08–24.34% and 6.30–9.58% respectively. As the BF length increasing to 22 mm, corresponding strengths increase by 0.55–5.72%, 14.96–25.51% and 7.35–10.37%, separately. A good bond between the BF and the matrix interface is observed in the early age. However, this bond shows degradation to a certain extent at 28 days. Moreover, the MIP results indicate that the concrete containing BF presents higher porosity.     

Uniaxially aligned electrospun fibers for advanced nanocomposites based on a model PVOH-epoxy system

This work demonstrates the potential of aligned electrospun fibers as the sole reinforcement in nanocomposite materials. Poly(vinyl alcohol) and epoxy resin were selected as a model system and the effect of electrospun fiber loading on polymer properties was examined in conjunction with two manufacturing methods. A proprietary electrospinning technology for production of uniaxially aligned electrospun fiber arrays was used. A conventional wet lay-up fabrication method is compared against a novel, hybrid electrospinning–electrospraying approach. The structure and thermomechanical properties of resulting composite materials were examined using scanning electron microscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and tensile testing. The results demonstrate that using aligned electrospun fibers significantly enhances material properties compared to unreinforced resin, especially when manufactured using the hybrid electrospinning–electrospraying method. For example, tensile strength of such a material containing only 0.13 vol% of fiber was increased by ∼700%, and Young’s modulus by ∼250%, with concomitant increase in ductility.     

Binderless all-cellulose fibreboard from microfibrillated lignocellulosic natural fibres

Fully biobased all-cellulose fibreboards are produced without the use of additional bonding agents such as polymer resins or binders as in the case of e.g. medium density fibreboard (MDF) or natural fibre reinforced plastic (NFRP). These materials make use of the self-binding capability of cellulose, exploiting the enhanced hydrogen bonded network present in micro- and nanofibrillated cellulose, resulting in good mechanical performance. After the optimisation of refinement, drying and hot-pressing conditions, binder-free panels from microfibrillated flax fibres with excellent mechanical properties of around 17 GPa and 120 MPa for flexural modulus and strength, and relatively low water sorption are achieved, making these materials competitive with conventional cellulose based composite materials. The work shows the potential of creating all-cellulose engineering materials using only the intrinsic bonding capacity of microfibrillated lignocellulose, potentially leading to environmentally friendly panel board materials, which are entirely based on renewable resources, recyclable and biodegradable.     

Utilization of natural montmorillonite modified with dimethyl,dehydrogenated tallow quaternary ammonium salt as reinforcement in almond shell flour–polypropylene bio-nanocomposites

The main goal of this work was to evaluate the technical feasibility of almond shell flour (ASF) as wood substitute in the production of wood–plastic composites (WPCs). The effects of organically modified montmorillonite (OMMT), as reinforcing agent, on the mechanical and physical properties were also investigated. In order to improve the poor interfacial interaction between the hydrophilic Lignocellulosic material and hydrophobic polypropylene matrix, maleic anhydride grafted polypropylene (MAPP) was added as a coupling agent to all the composites studied. In the sample preparation, OMMT and ASF contents were used as variable factors. The morphology of the specimens was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results of mechanical properties measurements indicated that when 3 wt.% OMMT were added, tensile and flexural properties reached their maximum values. At high level of OMMT loading (5 wt.%), increased population of OMMT lead to agglomeration and stress transfer gets blocked. The addition of OMMT filler decreased the water absorption and thickness swelling of composites. SEM study approved the good interaction of the almond shell flour with the polymer as well as the effectiveness of OMMT in improvement of the interaction. TEM study revealed better dispersion of silicate layers in WPCs loaded with 3 wt.% of OMMT. The improvement of physico-mechanical properties of composites confirmed that OMMT has good reinforcement and the optimum synergistic effect of OMMT and ASF was achieved at the combination of 3 and 50 wt.%, respectively. The findings indicated that almond shell as agro-waste material is a valuable renewable natural resource for composite production and could be utilized as a substitute for wood in composite industries.     

Assessment of three oxide/oxide ceramic matrix composites: Mechanical performance and effects of heat treatments

Mechanical performance of three oxide/oxide ceramic matrix composites (CMCs) based on Nextel 610 fibers and SiOC, alumina, and mullite/SiOC matrices respectively, is evaluated herein. Tensile strength and stiffness of all materials decreased at 1000 °C and 1200 °C, probably because of degradation of fiber properties beyond 1000 °C. Microstructural changes in the composites during exposure at 1000 °C and 1200 °C for 50 h reduce their flexural strength, fracture toughness and work of fracture. A literature review regarding mechanical properties of several oxide/oxide CMCs revealed lower influence of fiber properties on composite strength compared with elastic modulus. The tested composites exhibit comparable stiffness and strength but higher fracture toughness compared with average values determined from a literature review. Considering CMCs with different compositions, we observed an interesting linear trend between strength and fracture toughness. The validity of the linear relationship between fracture strength and flexural toughness for CMCs is discussed.     

Biocomposites from Musa textilis and polypropylene: Evaluation of flexural properties and impact strength

Abaca (Musa textilis)-reinforced polypropylene composites have been prepared and their flexural mechanical properties studied. Due to their characteristic properties, M. textilis has a great economic importance and its fibers are used for specialty papers. Due to its high price and despite possessing very distinctive mechanical properties, to date abaca fibers had not been tested in fiber-reinforced composites. Analysis of materials prepared showed that, in spite of reduced interface adhesion, flexural properties of the PP composites increased linearly with fiber content up to 50 wt.%. Addition of a maleated polypropylene coupling agent still enhanced the stress transfer from the matrix to the reinforcement fiber. As a result, composites with improved flexural properties were obtained. The mechanical properties of matrix and reinforcing fiber were evaluated and used for modelling both the flexural strength and modulus of its composites. In addition, the impact strength of materials was evaluated. Comparison with mechanical properties of composites reinforced with fiberglass points out the potentiality of abaca-reinforced polypropylene composites as suitable substitutes in applications with low impact strength demands.     

Greatly enhanced cryogenic mechanical properties of short carbon fiber/polyethersulfone composites by graphene oxide coating

In order to employ polyethersulfone (PES) in cryogenic engineering field, its cryogenic mechanical performance should be examined and should also be improved to meet the high requirement for cryogenic engineering application. In this work, pure PES, graphene oxide (GO)/PES, short carbon fiber (SCF)/PES, GO/SCF/PES and GO-coated SCF/PES composites are prepared using the extrusion compounding and injection molding techniques. The tensile and flexural properties of these composites are systematically investigated at a typical cryogenic temperature (77 K). It is shown that the cryogenic mechanical properties are enhanced by the addition of GO, SCFs and coated-SCFs. In particular, the GO-coated SCF/PES composites display the greatly enhanced cryogenic mechanical properties with the highest values compared to other PES composites. In addition, it is exhibited that the cryogenic mechanical properties at 77 K of PES and its composites are far higher than those at room temperature (RT).     

Effects of environmental aging on the mechanical properties of bamboo–glass fiber reinforced polymer matrix hybrid composites

Short bamboo fiber reinforced polypropylene composites (BFRP) and short bamboo–glass fiber reinforced polypropylene hybrid composites (BGRP) were fabricated using a compression molding method. Maleic anhydride polypropylene (MAPP) was used as a compatibilizer to improve the adhesion between the reinforcements and the matrix material. By incorporating up to 20% (by mass) glass fiber, the tensile and flexural modulus of BGRP were increased by 12.5 and 10%, respectively; and the tensile and flexural strength were increased by 7 and 25%, respectively, compared to those of BFRP. Sorption behavior and effects of environmental aging on tensile properties of both BFRP and BGRP systems were studied by immersing samples in water for up to 1200 h at 25°C. Compared to BFRP, a 4% drop in saturated moisture level is seen in BGRP. After aging in water for 1200 h, reduction in tensile strength and modulus for BGRP is nearly two times less than that of BFRP. Use of MAPP as coupling agent in the polypropylene matrix results in decreased saturated moisture absorption level and enhanced mechanical properties for both BFRP and BGRP systems. Thus it is shown that the durability of bamboo fiber reinforced polypropylene can be enhanced by hybridization with small amount of glass fibers.