Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. II. Chemical modification

The effect of chemical modification of both fiber and matrix on melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variations of melt viscosity with different shear rate and shear stress values for different temperatures were studied. A temperature range of 130 to 150°C and shear rates of 16.4 to 5468 s^?1 were chosen for the analysis. Chemical modifications with stearic acid, maleic anhydride, silane, and peroxides were tested for their ability to improve the interaction between the matrix and fiber. The viscosity of the hybrid composites increases with every chemical modification. In the case of peroxide‐treated composites, the increase can be attributed to the peroxide‐induced grafting of the polyethylene matrix to the fiber surface and to the crosslinking of the polyethylene matrix. These phenomena are both activated by temperature, whereas temperature causes a reverse effect for all other chemical modifications. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 443–450, 2003     

Mechanical properties of plasma-treated sisal fibre-reinforced polypropylene composites

In recent years, sisal fibres have become a promising reinforcement for composites because of their low cost, low density, high specific strength, high specific modulus, easy availability and renewability. However, the poor adhesion between the hydrophilic sisal fibre and the hydrophobic thermoplastic matrices has adversely affected the widespread use of these composites. In this study, argon and air-plasma treatments have been used to modify the fibre surfaces under suitable treatment parameters to improve the compatibility between sisal fibres and polypropylene (PP). Sisal fibres and PP fibres are blended together to form a random mat which is then vacuum hot-pressed into a preimpregnated composite sheet. Mechanical properties such as tensile strength and modulus, flexural strength and modulus, and the storage modulus of the composite sheets improve after the incorporation of plasma-treated fibres. Furthermore, scanning electron microscopy analyses reveal the increased surface roughness of sisal fibre. Surface characterisation has been performed by X-ray photoelectron spectroscopy, showing an increase in oxygen/carbon ratio of sisal fibres after plasma treatment.     

Flax fibre physical structure and its effect on composite properties: Impact strength and thermo-mechanical properties

Earlier investigations by the authors showed that the tensile modulus of flax fibre mat polypropylene composites (NMT) could surpass the values of glass mat reinforced thermoplastic (GMT) on fibre weight basis. The tensile and flexural strength could reach values of up to 65% of the GMT strength values, however, very much dependent on the fibre physical structure. This study deals with the Charpy impact and the thermo-mechanical properties of flax NMT materials. The trend is that the Charpy impact strength decreases with increasing fibre internal bonding and enhanced fibre-matrix adhesion, which is opposite to the trend for the tensile and flexural properties. The impact strength of the NMT materials is lower than generally reported for GMT materials. Dynamic mechanical thermal analysis reveals that with increasing temperature the storage modulus of the NMT materials reduces more slowly when the fibre internal bonding and the fibre-matrix adhesion are improved. In order to approach the tensile, flexural and impact strength of GMT materials, composites should be based on the strong elementary flax fibres. The axial tensile strength of elementary fibres approaches the strength of glass fibres and the lateral strength of the elementary fibres is higher than the technical flax fibres lateral strength. The thermo-mechanical properties can probably be improved when non-cellulosic material can be removed from the flax fibre surface without damaging the fibre.     

The effect of fibre sizing and compatibilizer of polypropylene/poly(butylene terephthalate) blends on the mechanical and interphase properties of basalt fibre reinforced composites

The effect of basalt fibre sizing on the mechanical and interphase properties of fibre‐reinforced composites was studied. Two different chemical preparations of the fibre surface (PBT‐compliant and PP‐compliant) were used. The polymer matrix was prepared from polypropylene/poly(butylene terephthalate) (PP/PBT) immiscible polymer blend and the effect of different compatibilizers on the composite properties was evaluated. SEM hints at improved fibre adhesion to the polymer matrix when a PP‐compliant sizing is applied. SEM also reveals improved compatibilization effects when block copolymer instead of multiblock copolymer is used for the PP/PBT blend preparation. The pull‐out test was applied to quantitatively evaluate the interface adhesion between the fibres and matrices. It showed a high value of the interfacial shear strength between basalt fibres modified with PP‐compliant sizing and polymer blend compatibilized by block copolymer, thus confirming good adhesion. One possible explanation of such good mechanical properties can be related to the chemical interactions between functional groups, mainly maleic anhydride on basalt fibres and the polyolefin component (PP) of the polymer matrix. © 2017 Society of Chemical Industry     

Carbon fibre reinforcement of cement

Despite their high cost, carbon fibres are an attractive choice as reinforcement for reactive matrices such as cement because of their chemical inertness at ambient temperatures. Since these fibres have very high specific strength and elastic modulus, only a small volume per cent of the fibre is required for producing composites having strengths similar to those of commercial asbestos cement sheets. A 3 vol % addition of the high-modulus carbon fibre to cement results in a two-fold increase in the modulus of elasticity and a five-fold increase in the tensile strength over the values of the unreinforced matrix. But no significant improvement in impact strength has been observed at these low levels of fibre addition.     

Effect of alkali treatment on properties of unidirectional isora fibre reinforced epoxy composites

Abstract

Unidirectional isora fibre reinforced epoxy composites were prepared by compression moulding. Isora is a natural bast fibre separated from Helicteres isora plant by retting process. The effect of alkali treatment on the properties of the fibre was studied by scanning electron microscopy (SEM), IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical properties such as tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali treated fibres have been studied as a function of fibre loading. The optimum fibre loading for tensile properties of the untreated fibre composite was found to be 49% by volume and for flexural properties the loading was optimised at ～45%. Impact strength of the composite increased with increase in fibre loading and remained constant at a fibre loading of 54·5%. Alkali treated fibre composite showed improved thermal and mechanical properties compared to untreated fibre composite. From dynamic mechanical analysis (DMA) studies it was observed that the alkali treated fibre composites have higher E' and low tan δ maximum values compared to untreated fibre composites. From swelling studies in methyl ethyl ketone it was observed that the mole percentage of uptake of the solvent by the treated fibre composites is less than that by the untreated fibre composites. From these results it can be concluded that in composites containing alkalised fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Tensile properties and creep response of polypropylene fibre composites with variation of fibre diameter

The mechanical properties and morphology of polypropylene (PP) long‐fibre reinforced random poly(propylene‐co‐ethylene) (PPE) composites (50/50 % vol/vol) have been investigated with reference to the fibre diameter with constant length. There is an improvement in the mechanical properties of PPE matrix by incorporation of long PP fibres into the matrix. The elastic modulus of the composite increased with decrease in the fibre diameter to 50 µm, to 0.91 GPa, which was 5 times higher than for pure PPE. However, composite stiffness decreased with decreasing fibre diameter of less than 50 µm and this is discussed in term of the fibre stiffness, packing, stress concentration and aspect ratio. Creep resistance of the composites showed the same behaviour. Morphology of the composites was investigated using scanning electron microscopy. This showed that there was a thin layer of matrix on the reinforcement, which was attributed to good impregnation and wetting of the fibres. Moreover, prediction of tensile modulus using the Cox model correlated well with experimental data. Copyright © 2004 Society of Chemical Industry     

Nanocomposite matrix for increased fibre composite strength

A new type of three-phase thermoplastic composite has been made, consisting of a main reinforcing phase of woven glass or carbon fibres and a PA6 nanocomposite matrix. Nanocomposites have the potential to improve the matrix dominated flexural and compressive strength by increasing the matrix modulus. Good quality fibre composites have been made with several types of PA6 nanocomposite and unfilled PA6 in combination with glass and carbon fibre reinforcement. Flexural tests on commercial PA6 fibre composites have shown the decrease of the flexural strength upon increasing temperature and this has been compared with the decrease of the matrix modulus. The nanocomposites used in this research have moduli that are much higher than unfilled PA6, also above T_g and in moisture conditioned samples. The strength of glass fibre composites can be increased by more than 40% at elevated temperatures and the temperature range at which a certain minimum strength is present can be increased by 40-50 °C. Carbon fibre composites also show significant improvements at elevated temperatures, although not at room temperature. The advantage of the use of nanocomposites instead of other polymers to improve the fibre composite properties is that the properties can be improved without any change in the processing conditions.     

Studies on recyclable composites: nylon fibre reinforced high density polyethylene composites

Abstract

A commercial grade of high density polyethylene (HDPE) matrix reinforced with nylon fibre up to 30 wt-% of HDPE was studied as a potential candidate for recyclable composites. These composite materials show improvement in mechanical properties such as tensile strength and flexural strength. Modification using styrene maleic anhydride – grafted HDPE significantly improved the mechanical and thermal properties. The HDPE/nylon composites/blends obtained by recycling of the composites also show good mechanical properties.     

Effect of reprocessing on mechanical properties of short glass fibre reinforced styrene maleic anhydride

Abstract

The effect of reprocessing by injection moulding on the mechanical properties of styrene maleic anhydride composites reinforced with 10, 20, and 30 wt-% short glass fibres has been studied. The study revealed that matrix properties related to the breaking point were significantly reduced by reprocessing. The observed reduction in the property values of the matrix material was attributed to the reduction in ductility caused by the molecular weight degradation. For the composites, almost all measured properties were reduced as a consequence of reprocessing. The strength and modulus of the composite were found to be linear functions of both the average length and the concentration of the fibres in the composite. The reduction in composite property values was attributed mainly to the degradation of fibres during each reprocessing cycle. Using a modified rule of mixtures, values of the overall efficiency parameter for strength and modulus were estimated and found to decrease as the number of reprocessing cycles was increased. This reduction in the overall efficiency parameters was mainly due to fibre breakage, occurring at each reprocessing cycle.     

Characterization of fibre/resin bonding in composites using a pull-out test

From the early use of glass fibres in an organic matrix to that of high strength and high modulus fibres such as carbon and Kevlar, the subject of fibre/matrix bonding has received considerable attention. This paper gives details of a pull-out test has been used to measure the adhesion between fibres and matrix. A summary of results obtained with the test technique, over a period of some ten years, is also given. Despite operational difficulties the method gave interesting results regarding the mechanical aspects of the interaction between fibres and matrix.     

Processability,morphology and mechanical properties of wood flour reinforced high density polyethylene composites

Abstract

Wood flour reinforced high density polyethylene (HDPE) composites have been prepared and their rheological properties measured. The melt viscosity decreased as the processing temperature increased and the wood flour content decreased. A power law model was used to describe the pseudoplasticity of these melts. Adding wood flour to HDPE produced an increase in tensile strength and modulus. Composites compounded in a twin screw extruder and treated with a coupling agent (vinyltrimethoxysilane) or a compatibliser (HDPE grafted with maleic anhydride) exhibited better mechanical properties than the corresponding unmodified composites because of improved dispersion and good adhesion between the wood fibre and the polyalkene matrix. Scanning electron microscopy of the fracture surfaces of these composites showed that both the coupling agent and compatibiliser gave superior interfacial strength between the wood fibre and the polyalkene matrix.     

Bonding of air-formed wood fibre/polypropylene fibre composites

The effectiveness of a maleated polypropylene (MAPP) as a coupling agent in wood fibre/polypropylene fibre composites made by non-woven web technology has been evaluated. The composite panels were made with 70 or 85% wood fibre, wiht the MAPP being incorporated in the panels at a level of 1 or 3% by spraying an emulsified form on the wood fibres. Both levels of MAPP significantly increased bending and tensile strength and moduli, and dynamic modulus. At the 70% wood fibre level, impact energy was increased significantly in panels with 3% MAPP. At the 85% wood fibre level, both 1% and 3% MAPP significantly increased impact energy. The MAPP also led to small improvements in water resistance for composites containing 85% wood fibre. The effectiveness of MAPP is believed to be the result of efficient incorporation at the wood/polypropylene interface, thus providing effective coupling of the polar wood component to the non-polar polymer matrix.     

剑麻/含红土聚乙烯基复合材料制备与性能

针对废旧地膜资源化利用过程中出现的高成本和低性能问题,本文提出了废旧地膜免清洗和剑麻纤维边角料增强的废旧地膜资源化利用技术。采用挤出造粒和注塑成型工艺,制备了剑麻边角料填充含红土废旧聚乙烯复合材料,分析了红土和剑麻纤维边角料对废旧地膜的填充作用。结果表明,红土颗粒使废旧地膜注塑试样的拉伸模量、硬度和耐热温度分别提高了34.4%、41.3%、和33.1%。红土颗粒难以和塑料基体形成良好的界面粘结,导致含红土废旧地膜注塑试样的拉伸强度、弯曲性能和冲击强度轻微降低,表明红土颗粒不能对废旧地膜进行增韧增强,但可以提高模量和耐热温度。剑麻纤维边角料对含红土废旧地膜具有明显的增强增韧作用,随着剑麻纤维添加量的增加,剑麻纤维填充的含红土废旧地膜复合材料的力学性能增加。剑麻纤维填充量超过一定值后,会在复合材料中引入气孔,同时会降低剑麻纤维的分散程度,出现剑麻聚集体,导致复合材料的力学性能降低。     

Curing Characteristics and Mechanical Properties of Oil Palm Wood Flour Reinforced Epoxidized Natural Rubber Composites

Abstract

The paper reports on the curing characteristics and mechanical properties of oil palm wood flour (OPWF) reinforced epoxidized natural rubber (ENR) composites. Three sizes of OPWF at different filler loadings were compounded with a two roll mill. The cure (t ₉₀) and scorch times of all filler size decrease with increasing OPWF loading. Increasing OPWF loading in ENR compound resulted in reduction of tensile strength and elongation at break but increased tensile modulus, tear strength and hardness. The composites filled with smaller OPWF size showed higher tensile strength, tensile modulus and tear strength. Scanning electron microscope (SEM) micrographs showed that at lower filler loading the fracture of composites occurred mainly due to the breakage of fibre with minimum pull-out of fibres from the matrix. However as the filler loading is increased, the fibre pull-out became very prominent due to the lack of adhesion between fibre and rubber matrix.     

Functional interphases with multi-walled carbon nanotubes in glass fibre/epoxy composites

The interphase between reinforcing fibre and matrix is a controlling element in composite performance. We deposited multi-walled carbon nanotubes (MWCNTs) onto electrically insulating glass fibre surfaces leading to the formation of semiconductive MWCNT-glass fibres and in turn multifunctional fibre/polymer interphases. The deposition process of MWCNTs onto glass fibre surfaces involved both electrophoretic deposition (EPD) and conventional dip coating methods. The EPD coating method produces a more homogeneous and continuous nanotube distribution on the glass fibre surface compared with the dip coating. According to fragmentation test results, the interphase with a small number of heterogeneous MWCNTs in the EPD fibre/epoxy composites, mimicking a biological bone structure, can remarkably improve the interfacial shear strength. We found that the semiconductive interphase results in a high sensitivity of the electrical resistance to the tensile strain of single glass fibre model composites. This material provides a possible in situ mechanical load sensor and early warning of fibre composite damage.     

Resonant frequency study of tensile and shear elasticity moduli of carbon fibre reinforced composites (CFRC)

The dynamic elastic properties are important characteristics of composite materials. They control the vibrational behaviour of composite structures and are also an ideal tool for monitoring of the development of CFRCs’ mechanical properties during their processing (heat treatment, densification). The present studies have been performed to explore relations between the dynamic tensile and shear moduli and some structural features (viz., fibre fraction, fibre type, porosity, weave pattern of woven reinforcement) of various unidirectional or bi-directional fibre reinforced carbon/carbon composites, made out of PAN- or pitch-based fibres as reinforcements and phenolic resin or coal tar pitch as matrix precursors. The dynamic tensile and in-plane shear moduli were determined from resonant frequencies of a beam with free ends. The longitudinal dynamic Young’s modulus of unidirectional CFRC composites – besides its dependence on the original fibre modulus and fibre volume contents – also reflects changes induced in matrix and fibres by heat treatment. The in-plane shear modulus does not depend on the fibre type but there exists its distinct tendency to increase with increasing fibre fraction. For bi-directionally reinforced composites, the longitudinal tensile modulus is more sensitive to the fabric weave pattern than to the fibre type. Tensile modulus of diagonally cut specimens and in-plane shear modulus of longitudinally cut ones are mutually correlated and, therefore, simultaneously controlled by densification steps and graphitisation heat treatment.     

Behavior of polyolefin blends with acetylated sisal fibers

The influence of acetylation on the mechanical, thermal and thermodegradative behavior of sisal fiber‐reinforced PP, PP/HDPE and PP/HDPE with functionalized and non‐functionalized EPR composites was studied. Acetylation of the fiber improves adhesion of the fiber to the polyolefin matrix. In general, acetylation of the sisal fiber was found to enhance the tensile strength and modulus of the resulting composites, except in some cases. Thermal properties suggest that the mixing and molding temperatures are between 160 and 230 °C and that when acetylated fiber is mixed with polyolefins, greater polymer‐fiber interactions takes place, which slightly favor stability of these composite materials. The results allow us to suggest that a satisfactory profit/cost relation justifies the addition of acetylated fiber to PP, PP/HDPE, and PP/HDPE/EPR. © 2000 Society of Chemical Industry     

Reinforcing high density polyethylene with cellulosic fibers. I: The effect of additives on fiber dispersion and mechanical properties

High density polyethylene (HDPE) was reinforced with 0-40 wt% of wood flour (aspen). The effects of: stearic acid, mineral oil, maleated polyethylene wax, and sodium silicate on the tensile and impact strength of the composite were studied. The comparison of tensile properties of the composites showed that the addition of maleated polyethylene wax produced a significant increase in tensile strength, with the increase in filler concentration, while the tensile modulus remained relatively unaffected. Microscopic studies of the composites indicate a better dispersion of the fibers in the polymer matrix when stearic acid was used.     

Preparation and characterization of poly(vinyl chloride)/virgin and treated sisal fiber composites

Mechanical property changes, thermal stability, and water absorption capacity of poly(vinyl chloride) (PVC)/sisal fiber composites were assessed with respect to the effect of maleic anhydride chemical treatments of the sisal fiber, for five different sisal fiber contents, varying from 0 to 30% by weight in the composite. The composites prepared with the untreated sisal exhibited higher tensile modulus and hardness than the unloaded resin, while elongation and tensile strength were reduced. The deterioration in the mechanical properties of PVC blended with sisal fiber is attributed to the presence of moisture, interfacial defects at the fiber and polymer interface, and fiber dispersion in the PVC matrix. The amount of absorbed water is a function of the amount of fiber in the composite (F0 = 0 phr, F5 = 0.77 phr, and F20 = 4.83 phr). The comparison of the results of characterization of F5, F20, and F30 formulations prepared with the untreated fibers and the treated ones showed a reduction in absorbed water after the chemical treatment of fiber with maleic anhydride (F0 = 0 phr, F5 = 0.28 phr, and F20 = 2.99 phr), thus improving the mechanical properties of composites prepared with the treated sisal. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3630–3636, 2007