Mechanical properties of rigid polyurethane composites reinforced with surface treated ultrahigh molecular weight polyethylene fibers

The mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE) fibers reinforced rigid polyurethane (PU) composites were studied, and the effects of the fiber surface treatment and the mass fraction were discussed. Chromic acid was used to treat the UHMWPE fibers, and polyurethane composites were prepared with 0.1 to 0.6 wt% as‐received and treated UHMWPE fibers. Attenuated total reflection Fourier transform infrared demonstrated that oxygen‐containing functional groups were efficiently grafted to the fiber surface. The mechanical performance tests of the UHMWPE fibers/PU composites were conducted, and the results revealed that the treated UHMWPE fibers/PU composites had better tensile, compression, and bending properties than as‐received UHMWPE fibers/PU composites. Thermal gravimetric analyzer showed that the thermal stability of the treated fiber composites were improved. The interface bonding of PU composites were investigated by scanning electron microscopy and dynamic mechanical analysis, and the results indicated that the surface modification of UHMWPE fiber could improve the interaction between fiber and PU, which played a positive role in mechanical properties of composites.     

High reinforcing capability cellulose nanocrystals extracted from <Emphasis Type="Italic">Syngonanthus nitens</Emphasis> (Capim Dourado)

The chemical composition and morphology of Syngonanthus nitens (Capim Dourado) fibers were investigated. An unusual low lignin content and high holocellulose content have been observed. High aspect ratio cellulose whiskers were prepared from these lignocellulosic fibers by an acid hydrolysis treatment. The average diameter and length were 4.5 nm and 300 nm, respectively, giving rise to an aspect ratio around 67. Natural Rubber nanocomposite films reinforced with cellulose whiskers extracted from capim dourado were prepared by film casting. The mechanical properties of the ensuing nanocomposite films were investigated in both the linear and the non-linear range using dynamical mechanical analysis and tensile tests, respectively. The reinforcing effect observed above the glass transition temperature of the matrix was higher than the one observed for other polysaccharide nanocrystals and cellulose whiskers extracted from other sources.     

Effects of cellulose whiskers on properties of soy protein thermoplastics

Environmentally-friendly SPI/cellulose whisker composites were successfully prepared using a colloidal suspension of cellulose whiskers, to reinforce soy protein isolate (SPI) plastics. The cellulose whiskers, having an average length of 1.2 microm and diameter of 90 nm, respectively, were prepared from cotton linter pulp by hydrolyzing with sulfuric acid aqueous solution. The effects of the whisker content on the morphology and properties of the glycerol-plasticized SPI composites were investigated by scanning electron microscopy, dynamic mechanical thermal analysis, differential scanning calorimetry, ultraviolet-visible spectroscopy, water-resistivity testing and tensile testing. The results indicated that, with the addition of 0 to 30 wt.-% of cellulose whiskers, strong interactions occurred both between the whiskers and between the filler and the SPI matrix, reinforcing the composites and preserving their biodegradability. Both the tensile strength and Young's modulus of the SPI/cellulose whisker composites increased from 5.8 to 8.1 MPa and from 44.7 to 133.2 MPa, respectively, at a relative humidity of 43%, following an increase of the whisker content from 0 to 30 wt.-%. Furthermore, the incorporation of the cellulose whiskers into the SPI matrix led to an improvement in the water resistance for the SPI-based composites.     

Synergistic modification by mercapto hyperbranched polysiloxane and functionalized graphene oxide on the surface of aramid fiber

With the purpose of improving the interfacial properties of aramid fibers reinforced rubber composites and enhancing the tensile strength of aramid fibers simultaneously, mercapto hyperbranched polysiloxane (HPSi) and functionalized graphene oxide (GO) were used to modify the surface of aramid fibers. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and other characterization methods were performed to confirm the process of synergistic modification. Judging from the results of mechanical property tests, it could be acquired that the tensile strength of modified aramid fiber was increased by 16.8%, which could be ascribed to the wrapping effect of GO sheets. The interfacial properties were assessed by the pull-out tests of composites, and the results showed that the maximum pull-out force after synergistic surface modification was increased by 99.3%, which could be mainly related to additive reaction between double bonds and mercapto groups and the promotion of surface energy. More critically, during pull-out test, aramid fiber bundles might bring a part of shear stress into the grafted GO sheets, namely, GO sheets could convert fracture energy into interfacial energy, which would improve interfacial properties dramatically.     

PREPARATION AND MECHANICAL PROPERTIES OF T-ZnOw/PS COMPOSITES

The main subject of this work is about the preparation of T-ZnOw/PS composites through different methods and the evaluation of mechanical properties of the composites.Different surface modification methods of T-ZnOw whiskers,the so called wet-type modification and dry-type modification,and different molding processing methods of T-ZnOw/PS composites,namely compression molding and injection molding,have been employed.Two different coupling agents, titanate coupling agent (NDZ105) and silane coupling agent...     

Surface modification of carbon fiber via electron‐beam irradiation grafting

In this paper, the surface properties of polyacrylonitrile‐based carbon fibers is improved by electron‐beam (EB) irradiation in maleic anhydride/acetone solution at 100, 150, 200 and 150 KGy. Experimental study of this paper is carried out to identify surface topography, surface chemical composition and functional groups, adsorption ability and interface properties of CF/epoxy composites. The results reveal that the roughness of carbon fiber surface is increased obviously after modification by EB irradiation grafting technology. The ratio value of O/C and the relative content of oxygen functional groups on fiber surface are improved effectively, comparing with the unmodified carbon fiber. Besides, adsorption of carbon fiber on epoxy and the mechanical performance of CF/epoxy composites are clearly enhanced after irradiation grafting modification. Copyright © 2012 John Wiley & Sons, Ltd.     

Behavior of biodegradable composites based on starch reinforced with modified cellulosic fibers

The aims of this study were to develop composite films based on potato starch and cellulose modified with toluenediisocyanate, to investigate their morphology and structure, and to evaluate their behavior to enzymatic hydrolysis and their potential use to manufacture of biodegradable seedling pots. The effects of modified cellulosic fibers upon mechanical properties and biodegradability of composite materials based on starch matrix were investigated by tensile strength tests, Fourier infrared spectroscopy, X‐ray diffraction, and dynamic vapor sorption. The behavior of the films to enzymatic hydrolysis with amylase and cellulase was studied; the kinetic of enzymatic hydrolysis and characterization of materials are reported. Chemical modification of cellulose improves tensile strength with about 47%, and decreases the biodegradability of composites making them more resistant to microbial attack, thus prolonging their shelf life. Copyright © 2015 John Wiley & Sons, Ltd.     

Rheological,morphological and mechanical properties of flax fiber polypropylene composites: influence of compatibilizers

In this work, the rheological, mechanical and morphological properties of flax fiber polypropylene composites were investigated. The effect of incorporating a polypropylene grafted acrylic acid or a polypropylene grafted maleic anhydride on these properties has been studied as well. According to scanning electron microscopic observations and tensile tests, the addition of a compatibilizer improved the interfacial adhesion between the flax fibers and the polymer matrix. The tensile modulus of composite containing 30 wt% flax fibers was improved by 200 % and the tensile strength improved by 60 % in comparison with the neat PP. Plasticizing effect of the compatibilizers as a result of their lower melt flow index was also shown to decrease the rheological properties of the composites, even though the effect was not pronounced on the mechanical properties.     

Biodegradable polyesters reinforced with surface-modified vegetable fibers

Flax fibers are investigated as reinforcing agents for biodegradable polyesters (Bionolle and poly(lactic acid) plasticized with 15 wt.-% of acetyltributyl citrate, p-PLLA). The composites are obtained either by high temperature compression molding fiber mats sandwiched between polymer films, or by batch mixing fibers with the molten polymer. Fibers in composites obtained by the latter method are much shorter (140-200 microm) than those of the mats (5,000 microm). Flax fibers are found to reinforce both p-PLLA and Bionolle (i.e. tensile modulus and strength increase) when composites based on fiber mats are investigated. Conversely, analogous composites obtained by batch mixing show poor mechanical properties. The observed behavior is attributed to the combined effect of fiber length and fiber-matrix adhesion. If flax fibers with a modified surface chemistry are used, the strength of short fiber composites is seen to improve significantly because the interface strengthens and load is more efficiently transferred. Appropriate surface modifications are performed by heterogeneous acylation reactions or by grafting poly(ethylene glycol) chains (PEG, molecular weight 350 and 750). The highest tensile strength of p-PLLA composites is reached when PEG-grafted flax fibers are used, whereas in the case of Bionolle the best performance is observed with acylated fibers.     

Investigation into hemp fiber- and whisker-reinforced soy protein composites

Whiskers, designated as W, were prepared from hemp fibers. Both fibers and whiskers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis. Scanning electron microscopy and transmission electron microscopy were used to evaluate the dimensions of the fibers and whiskers, respectively. By incorporating different weight fraction of the fibers and whiskers into soy protein isolate, we prepared two different composites designated as SC and SC-W, respectively. Thiodiglycol was used as a plasticizer for the preparation of composites. The SC and SC-W composites were characterized and compared in terms of mechanical properties, volume fraction of porosity, and water uptake. The results indicated that there was not much significant difference in the properties of the composites. In fact, mechanical properties of fiber-reinforced composites were higher than whisker-reinforced composites at optimum weight fractions. This study can give us the idea about the judicious use of fibers or whiskers as reinforcement materials.     

A new study on effect of various chemical treatments on Agave Americana fiber for composite reinforcement: Physico-chemical,thermal, mechanical and morphological properties

This research is focused to fundamentally understand the benefits of using Agave Americana C. plant as potential reinforcement in polymeric composites. The fibers were extracted from the external part of the bark of the plant, which grows worldwide in pastures, grasslands, open woodlands, coastal and riparian zones. In order to use the natural fiber as reinforcement it is paramount important to probe their chemical composition, microstructural behavior and mechanical properties. Hence, firstly the extracted fibers were chemically treated with NaOH, stearic acid, benzoyl peroxide and potassium permanganate. The chemical composition in terms of cellulose, hemicellulose, lignin and other waxy substances were determined using a standard TAPPI method. FT-IR technique was used to understand the character of molecular bonds, crystallinity and their correlations with various bonds in fiber structure. The thermal stability was investigated through thermogravimetric and differential scanning calorimetric analysis, and the mechanical characterization was performed by applying standard tensile test. The surface morphology of fibers was examined through scanning electron microscopy (SEM) and finally reliability scrutiny of all the analysis was carried out. The results of chemical modification techniques applied on the surfaces of natural fibers allows to produce superior fibers used to form the novel composite materials for light-weight application.     

Morphology control of poly(lactic) acid/polypropylene blend composite by using silanized cellulose fibers extracted from coir fibers

The objective of this work is the use of cellulose fibers extracted from coir fibers as Janus nanocylinders to suppress the phase retraction and coalescence in poly(lactic) acid/polypropylene bio-blend polymers via prompting the selective localization of cellulose fibers at the interface using chemical modification. The untreated and modified cellulose fibers extracted from coir fibers using a silane molecule (tetraethoxysilane) were used as reinforcement and as Janus nanocylinder at two weight contents (2.5 wt% and 5 wt%) to manipulate the morphology of the bio-blends. Their bio-composites with PLA-PP matrix were prepared via melt compounding (at PLA/PP: 50/50). The treatment effect on component interaction and the bio-composites properties have been studied via Scanning electron microscopy, infrared spectroscopy, and differential calorimetry analysis. The mechanical and rheological properties of nanocomposites were similarly assessed. Young's modulus and tensile strength of PLA-PP nanocomposites reinforced by silanized cellulose fibers show a great enhancement as compared to a neat matrix. In particular, there was a gain of 18.5% in Young's modulus and 11.21% in tensile strength for silanized cellulose fiber-based bio-blend composites at 5 wt%. From the rheological point of view, it was found that the silanized cellulose fibers in PLA-PP at both fibers loading enhances the adhesion between both polymers leading to tuning their morphology from sea-island to the continuous structures with the appearance of PLA microfibrillar inside of bio-composites. This change was reflected in the relaxation of the chain mobility of the bio-blend composites.

     

Smart modification of inorganic fibers and flammability mechanical and radiation shielding properties of their rubber composites

Facile and smart method for the modification of inorganic fibers has been developed. The polyaniline was synthesized on basalt fiber surface presenting an organic polymer shell to the inorganic fibers. The modified basalt fibers were dispersed in rubber-producing well-dispersed rubber composites. Various mass loadings of modified basalt fibers were dispersed and optimized. The effect of radiation on the properties of developed rubber composites was investigated by exposure to different gamma radiation doses. The flammability, thermal and mechanical properties were studied. The flammability of developed composites was improved achieving 62 and 16% reduction in the peak heat release rate compared to blank rubber and unmodified basalt fiber-based rubber composite, respectively. This is in addition to significant reduction in emission of CO and CO₂ gases by 65 and 58%, respectively. Also, the tensile strength property was enhanced by 38 and 53% compared to blank and unmodified basalt composite, respectively. The role of polyaniline layer on inorganic fiber surface and their effect on the properties of the produced composites was studied. The organic polymer shell achieved good compatibility and interfacial adhesion of basalt fibers with rubber matrix and radiation protection effect for the developed composites.     

接枝改性木纤维对聚氯乙烯／木纤维复合材料力学性能的影响

接枝改性木纤维对聚氯乙烯／木纤维复合材料力学性能的影响廖兵，黄玉惠，赵树录，林果，丛广民（中国科学院广州化学研究所广州５１０６５０）关键词木纤维，聚氯乙烯／木纤维复合材料，接枝木纤维可作塑料的增强填料，但它与塑料的界面亲合性差，须进行改性，改善表面亲...     

Mechanical Behavior of Unidirectional Curaua Fiber and Glass Fiber Composites

Summary: This work intends to promote the use of natural fibers by comparing the behavior of isophthalic polyester matrix composites reinforced with unidirectional curaua fibers with that of unidirectional glass fiber composites. The composites were produced varying the reinforcement angle (0°, 15°, 30°, 45°, 60°, 75° and 90°) with the aim of studying the fiber orientation effect on composite strength. Composites were also made varying the fiber volume fraction (10%, 20%, 30%, 40% and 50%). The efficiency of an alkaline (5% NaOH) surface treatment of the curaua fiber was also evaluated. The unidirectional composites were characterized using tensile, flexural and short beam tests as per ASTM standards. The properties of a lamina reinforced with either glass or curaua fibers were also studied using theoretical micromechanical approach available in commercial software. The curaua fiber alkaline treatment produced higher tensile strength results compared with untreated fibers. The increase in reinforcement angle significantly decreased strength and modulus of the composites, as expected, and the glass fiber composites showed a more pronounced dependence with fiber orientation. Although the glass fiber laminas showed the best mechanical performance, the results obtained with the curaua fibers were considered similar for angles greater than 45°.     

Property correlations for composites based on ethylene propylene diene rubber reinforced with flax fibers

EPDM composites filled with short flax fibers were prepared by melt blending procedure. The effects of fiber loading on the mechanical, thermal and water uptake characteristics were studied. The physico-mechanical, morphological thermal properties and water absorption behavior were discussed using tensile testing, differential scanning calorimetry, thermogravimetrical analysis and scanning electron microscopy. Scanning electron microscopy revealed that the flax fibers were well dispersed in the polymer matrix. The tensile strength and hardness of the composites were found to be improved at higher fiber loading. The water absorption pattern of EPDM/fiber composites at room temperature follows a Fickian behavior for composites with 10, 15 and 20 phr flax fiber.     

Effect of fiber length and composition on mechanical properties of carbon fiber‐reinforced polybenzoxazine

The mechanical strength and modulus of chopped carbon fiber (CF)‐reinforced polybenzoxazine composites were investigated by changing the length of CFs. Tensile, compressive, and flexural properties were investigated. The void content was found to be higher for the short fiber composites. With increase in fiber length, tensile strength increased and optimized at around 17 mm fiber length whereas compressive strength exhibited a continuous diminution. The flexural strength too increased with fiber length and optimized at around 17 mm fiber length. The increase in strength of composites with fiber length is attributed to the enhancement in effective contact area of fibers with the matrix. The experimental results showed that there was about 350% increase in flexural strength and 470% increase in tensile strength of the composites with respect to the neat polybenzoxazine, while, compressive properties were adversely affected. The composites exhibited an optimum increase of about 800% in flexural modulus and 200% in tensile modulus. Enhancing the fiber length, leads to fiber entanglement in the composites, resulted in increased plastic deformation at higher strain. Multiple branch matrix shear, debonded fibers and voids were the failures visualized in the microscopic analyses. Defibrillation has been exhibited by all composites irrespective of fiber length. Fiber debonding and breaking were associated with short fibers whereas clustering and defibrillation were the major failure modes in long fiber composites. Increasing fiber loading improved the tensile and flexural properties until 50–60 wt% of fiber whereas the compressive property consistently decreased on fiber loading. Copyright © 2008 John Wiley & Sons, Ltd.     

Polymer matrix influence on stability of wood polymer composites

The aim of the presented work is to show the influence of the various polymer matrices and the different amounts of the cellulose filler on the composites properties. Samples based on polypropylene, polystyrene, polyoxymethylene, acrylonitrile butadiene styrene, polyester resin, and polylactic acid with different contents of cellulose fibers were prepared by injection molding process. The mechanical and dielectric properties of these composites were studied in order to check whether investigated wood polymer composites fulfill requirements for their application in electrical devices. For all tested composites, a linear increase of modulus with cellulose content was observed. Addition of cellulose to the tested polymers significantly reduces strain at break. In the case of polypropylene and polyoxymethylene composites, the tensile strength increases with the content of the filler. For other materials, there is an inverse relationship, namely the addition of cellulose decreases the tensile strength. The electrical strength decrease was observed with increased cellulose content for the majority of the investigated composites. Polar groups incorporated by cellulose fibers have led to dielectric constant increase. Furthermore, aging of composites in mineral oil and evaluation of water uptake for wood–plastic samples were performed. Wood polymer composites have changed significantly after aging. The water diffusion coefficients were determined, and the significant influence of the amount of cellulose on the water absorption was shown. Copyright © 2015 John Wiley & Sons, Ltd.     

The effect of fiber content on the mechanical and thermal expansion properties of biocomposites based on microfibrillated cellulose

A new method to obtain composites of phenolic resin reinforced with microfibrillated cellulose with a wide fiber content was established and the mechanical properties were evaluated by tensile test. A linear increase in Young’s modulus was observed at fiber contents up to 40 wt%, with a stabilizing tendency for higher fiber percentages. These results were ratified by measurements of the coefficient of thermal expansion (CTE) relative to fiber content, which indicated a strong thermal expansion restriction rate below 60 wt% fiber content, indicating the effective reinforcement attained by the cellulose microfibrils. The low CTE achieved of 10 ppm/K is one of the important properties of cellulose composites.     

Continuous cellulose fiber-reinforced cellulose ester composites. II. Fiber surface modification and consolidation conditions

We prepared thermoplastic composite panels using solution impregnation of continuous lyocell (regenerated cellulose) fibers with a cellulose mixed-ester (cellulose acetate butyrate) matrix. We examined both fiber-matrix adhesion and melt consolidation in an effort to produce uniform panels having low void content and high mechanical strength. We characterized the effect of surface modification by acetylation on interfacial adhesion between the cellulose fiber and cellulose ester. Whereas wood fiber acetylation had previously been observed to result in significant strength gains in (discontinuous) wood fiber- reinforced composites (with the same matrix material), we did not observe a similar increase in strength in the continuous lyocell cellulose fiber system. This suggests that interfacial stress transfer is not a limitation in this system. This was confirmed by microscopic examination of the fracture surfaces, which indicated that fiber-matrix adhesion was considerable in the absence of fiber surface modification. We then systematically varied melt consolidation conditions (temperature, pressure and time) in an attempt to define optimum consolidation parameters by using design of experiments (DOE) methodology. We measured both interlaminar shear strength (ILSS) and composite void volume. We found that a minimal void content (ca. 2.83 vol. %) occurred at moderate temperatures (200°C), low consolidation pressures (81.4kPa) and long press times (13min). This was also where we maximized the interlaminar shear strength (ILSS) at a value of 16.3MPa. This agrees with the regression model predictions. We observed the highest tensile properties at the ILSS and void-volume optimal-consolidation condition: a tensile modulus of 22GPa and tensile strength of 246MPa were obtained.