Mechanical properties of natural fibre reinforced polymer composites

During the last few years, natural fibres have received much more attention than ever before from the research community all over the world. These natural fibres offer a number of advantages over traditional synthetic fibres. In the present communication, a study on the synthesis and mechanical properties of new series of green composites involving Hibiscus sabdariffa fibre as a reinforcing material in urea-formaldehyde (UF) resin based polymer matrix has been reported. Static mechanical properties of randomly oriented intimately mixed Hibiscus sabdariffa fibre reinforced polymer composites such as tensile, compressive and wear properties were investigated as a function of fibre loading. Initially urea-formaldehyde resin prepared was subjected to evaluation of its optimum mechanical properties. Then reinforcing of the resin with Hibiscus sabdariffa fibre was accomplished in three different forms: particle size, short fibre and long fibre by employing optimized resin. Present work reveals that mechanical properties such as tensile strength, compressive strength and wear resistance etc of the urea-formaldehyde resin increases to considerable extent when reinforced with the fibre. Thermal (TGA/DTA/DTG) and morphological studies (SEM) of the resin and biocomposites have also been carried out.     

Chemical modification of flax reinforced polypropylene composites

This paper presents an experimental study on the static and dynamic mechanical properties of nonwoven based flax fibre reinforced polypropylene composites. The effect of zein modification on flax fibres is also reported. Flax nonwovens were treated with zein coupling agent, which is a protein extracted from corn. Composites were prepared using nonwovens treated with zein solution. The tensile, flexural and impact properties of these composites were analysed and the reinforcing properties of the chemically treated composites were compared with that of untreated composites. Composites containing chemically modified flax fibres were found to possess improved mechanical properties. The viscoelastic properties of composites at different frequencies were investigated. The storage modulus of composites was found to increase with fibre content while damping properties registered a decrease. Zein coating was found to increase the storage modulus due to enhanced interfacial adhesion. The fracture mechanism of treated and untreated flax reinforced polypropylene composites was also investigated from scanning electron microscopic studies.     

Natural fibres-based polymers: Part I—Mechanical analysis of <Emphasis Type="Italic">Pine needles</Emphasis> reinforced biocomposites

Lack of resources and increasing environmental pollution has evoked great interest in the research of materials that are friendly to our health and environment. Polymer composites fabricated from natural fibres is currently the most promising area in polymer science. Keeping in view the various advantages of natural fibres, in current series of green composites a study on natural fibre reinforced polymer composites has been made. This paper presents the results of an experimental series designed to assess the possibility of Pine needles as reinforcing material in polymer composites. First of all, urea-formaldehyde resin was synthesized and optimized by evaluating its mechanical properties. Optimized resin was reinforced with employing Pine needles of different dimensions such as particle reinforcement, short fibre reinforcement and long fibre reinforcement. Experimental results obtained shows that mechanical properties such as tensile strength, compressive strength and wear resistance of UF resin increases to a considerable extent when reinforced with Pine needles. Further it has been observed that particle reinforcement is more effective as compared to short fibre and long fibre reinforcement. These results suggest that Pine needles can be potential candidates for use in natural fibre reinforced polymer composites. Thermal and morphological studies of these composites have also been carried out.     

Atmospheric plasma fluorination as a means to improve the mechanical properties of short-carbon fibre reinforced poly (vinylidene fluoride)

The impact of fluorination of carbon fibres on the properties of short fibre reinforced polyvinylidene fluoride (PVDF) composites was studied. As received and continuously atmospheric plasma fluorinated (APF) carbon fibres were cut to an average fibre length of 2 mm. Short fibre composites (SFC) containing 5, 10 and 15 wt.% carbon fibres were manufactured using a twin-screw mixer. Test specimens were produced by injection moulding. The mechanical properties of the SFC were studied using tensile and compression testing. As expected, the incorporation of short-carbon fibres into PVDF led to an increase in strength and stiffness. The tensile strength and Young’s modulus of the SFC containing APF-treated carbon fibres increased by up to 17% and 190%, respectively. Furthermore, the compressive strength and modulus of the SFC containing APF-treated carbon fibres also increased by 19% and 35%, respectively. APF of carbon fibres results only in a marginal increase in the bulk matrix crystallinity of PVDF as determined by DSC. Scanning electron micrographs of fracture surfaces from tensile tested specimens exhibited a typical brittle failure mode with low fibre loading fraction. Despite the presence of up to 5% of voids and visible resin rich regions at fracture surface, SFC containing APF-treated fibres suggest better bonding at the fibre/matrix interface which led to the much enhanced mechanical properties.     

Dental application of various kinds of fibres in heat curing acrylic resin

The effect of the type of fibres on bending behaviour and impact energy in reinforced acrylic resin was examined. Reinforcing materials such as inorganic glass fibre and cloth and organic polyester and Kevlar fibres were coated with a silane coupling treatment, whereas Co-Cr wire was directly used for the reinforcement. After silane coupling treatment each fibre was added to the heat curing base resin, except polyester fibre. It is concluded that the inclusion of glass linear fibre provides an effective improvement on plain acrylic base resin. An additional way to reinforce the resin matrix was given by the combined use of glass and Kevlar fibres.     

The mechanical properties of oxyfluorinated hybrids of glass fibre and polypropylene fibre

The mechanical properties of a low-cost system comprising orthophthalic polyester resin reinforced with hybrids of glass and polypropylene fibres were investigated. The fibres were oxyfluorinated to overcome the poor surface adhesion properties of polypropylene. Interlaminar shear tests, Izod-type impact tests and tensile tests were considered. It would be expected that increasing polypropylene fibre content corresponds with a decrease in mechanical properties due to the poor properties of polypropylene. Oxyfluorinated laminates containing approximately 25% and 50% polypropylene in the warp direction were, however, found to exhibit significant improvements in interlaminar shear strength, in peak shear stress under impact loading as well as in impact resistance over untreated glass fibre laminates. Scanning electron microscope images show that the reason for this improvement is that the interfacial bond between the polypropylene fibres and the resin is strengthened to such an extent that failure occurs within the polypropylene fibres rather than at the interface.     

Effects of Gear-Shape Fibre on the Transverse Mechanical Properties of Unidirectional Composites: Virtual Material Design by Computational Micromechanics

This paper aims to study the effect of fibre cross-section shape on the mechanical properties of unidirectional fibre reinforced composites. First, the specific surface area of different cross-section shape is compared, and the gear-shape fibre is selected for further study, which has the largest specific surface area. The effect of gear-shape fibre with various tooth number on the transverse mechanical properties of unidirectional composites is investigated by computational micromechanics, comparing with the traditional round fibre. It is found that all the gear-shape fibre reinforced composites have higher transverse stiffness and strength than the round fibre reinforced composite, and the gear-shape fibre with fewer tooth number has greater reinforcing effect on the mechanical properties of the composite. The mechanism of this phenomenon is revealed by examine the damage initiation and evolution process of the composite, and suggestion is made on the optimal cross-section shape of the reinforcing fibre for the composites.     

Jute-reinforced polyester composites

Raw jute fibre has been incorporated in a polyester resin matrix to form uniaxially reinforced composites containing up to 60 vol% fibre. The tensile strength and Young's modulus, work of fracture determined by Charpy impact and inter-laminar shear strength have been measured as a function of fibre volume fraction. These properties all follow a Rule of Mixtures relationship with the volume fraction of jute. Derived fibre strength and Young's modulus were calculated as 442 MN m^–2 and 55.5 GN m^–2 respectively. Polyester resin forms an intimate bond with jute fibres up to a volume fraction of 0.6, above which the quantity of resin is insufficient to wet fibres completely. At this volume fraction the Young's modulus of the composite is approximately 35 GN m^–2, the tensile strength is 250 MN m^–2, the work of fracture is 22 kJ m^–2 and the inter-laminar shear strength is 24 MN m^–2. The properties of jute and glass fibres are compared, and on a weight and cost basis jute fibres are seen in many respects to be superior to glass fibres as a composite reinforcement.     

Evaluation of mechanical and thermal properties of banana–flax based natural fibre composite

Hybrid materials of any kind are the keynote for today’s demands. This paper deals with one of such hybrid composite made of natural fibres namely, banana and flax fibres. The structural build-up is such that one layer of banana fibre is sandwiched between two layers of flax fibres by hand layup method with a volume fraction of 40% using Epoxy resin and HY951 hardener. Glass fibre reinforcement polymer (GFRP) is used for lamination on both sides. This lamination also increases the overall mechanical properties along with better surface properties. The properties of this hybrid composite are determined by testing its tensile, impact, and flexural loads using a Universal testing machine. Thermal properties are analysed and hybrid composites of flax and banana with GFRP have better thermal stability and flame resistance over flax, banana with GFRP single fibre hybrid composites. Morphological analysis is done using Scanning Electron Microscope (SEM). The result of test shows that hybrid composite has far better properties than single fibre glass reinforced composite under impact and flexural loads. However it is found that the hybrid composite have better strength as compared to single fibre composites.     

Viscoelastic behaviour of novel commingled biocomposites based on polypropylene/jute yarns

Jute yarn reinforced polypropylene commingled composites were prepared by an environmentally benign technique called commingling method in which the matrix fibres and reinforcing fibres are intermingled together with good alignment. The dynamic mechanical properties or viscoelastic behaviour of these commingled composites were studied with reference to fibre content and various chemical treatments. The storage and loss modulus increased with fibre content where as tan δ decreased. KMnO₄ and MAPP treated composites showed much higher storage and loss modulus values at all temperatures compared to untreated one. The glass transition temperature showed a marginal increasing tendency with fibre content and chemical treatments. The surface treatment mechanisms were supported by FT-IR spectra and the increase in interfacial adhesion after chemical treatments were supported by SEM images. Theoretical modelling was used to predict the values of storage modulus and tan δ and was found to be comparable with that of experimentally obtained results.     

Natural-fibre-reinforced polyurethane microfoams

Polyurethane-based composites reinforced with woven flax and jute fabrics were prepared with an evenly distributed microvoid foam structure. The relationship between the resin-filled grade and the microvoid content and the density was described. The influence of the type of reinforcing fibre, fibre and microvoid content on the mechanical properties was studied. The investigation results for the static mechanical properties of the composites were described by approximate formulae. It was found that the specific data were only slightly dependent on microvoid content. Increasing the fibre content induces an increase in the shear modulus and impact strength. However, increasing the microvoid content in the matrix results in a decreased shear modulus and impact strength. The woven flax fibre results in composites with better mechanical strength than the woven jute fibre composites.     

Influence of the Physical Structure of Flax Fibres on the Mechanical Properties of Flax Fibre Reinforced Polypropylene Composites

This study investigates the influence of the physical structure of flax fibres on the mechanical properties of polypropylene (PP) composites. Due to their composite-like structure, flax fibres have relatively weak lateral bonds which are in particular present in flax fibres that are often used in natural fibre mat reinforced thermoplastics (NMT). These weak bonds can be partly removed by combing the fibres. In order to study the influence of the physical structure of flax fibres on NMT tensile and flexural properties, uncombed and combed flax fibre reinforced PP composites were manufactured via a wet laid process. The influence of improved fibre-matrix adhesion was studied using maleic-anhydride grafted PP. Results indicated that the flax physical structure has a significant effect on flax-PP composite properties and that the flax fibre reinforced PP properties are similar to values predicted with existing micromechanical models. The tensile modulus of flax-PP composites can fairly compete with commercial glass mat reinforced thermoplastic (GMT) modulus, the strength, however, both tensile and flexural, can not. In order to rise the strength of flax fibre reinforced PP composites to the level of GMT strength, the flax fibres have to be further isolated to elementary flax fibres.     

玻璃纤维增强灌注型聚氨酯泡沫塑料的拉伸、压缩性能和破坏机理

研究了用短切玻璃纤维对硬质聚氨酯泡沫体的增强效果及拉伸、压缩的破坏行为。结果表明当纤维长为12 mm 时, 6 w t% 纤维含量的增强效果为最好, 可以使泡沫体的拉伸强度提高75% , 压缩强度提高25% , 压缩模量增加约30%。纤维增强的泡沫体拉伸产生的裂纹扩展时, 遇到纤维可能终止扩展(应力不大时) , 也可能发生偏转(应力较大时) ; 泡沫破坏时, 可能出现纤维拉出、拉断等不同的破坏形式。增强泡沫体在压缩破坏时, 主要是泡沫结构的支柱弯曲、扭转变形引起泡壁破裂和支柱失稳, 并导致材料的破坏。      

A step-by-step method of rule-of-mixture of fiber- and particle-reinforced composite materials

A new method of rule-of-mixture is presented for predicting the mechanical properties of fiber- and particle-reinforced composite materials. The composite material is composed through a hypothetical process in which the matrix is reinforced one-by-one with reinforcing materials (fibers or particles). The mechanical properties of the composed material are obtained step-by-step using the cylinder model for fiber-reinforced materials and the sphere model for particle-reinforced materials. Results obtained by the present method are compared with those of other methods and experimental results. It is found that, for the longitudinal modulus, the present method gives equally good prediction as other methods. For the transverse modulus and shear modulus, the results obtained by the present method show better agreement with experimental results.     

Could biopolymers reinforced by randomly scattered flax fibre be used in structural applications?

Thermoplastics reinforced by natural fibres are mainly used for fitting-up products in the automotive industry. The aim of this work is to study the tensile properties of natural fibre-biopolymer composites in order to determine whether or not, biocomposites may replace glass fibre reinforced unsaturated polyester resins. The materials used are flax fibre, polylactic acid (PLA), l-polylactide acid (PLLA), poly(3-hydroxylbutyrate) (PHB), polycaprolactone and starch thermoplastic (MaterBi® Z), poly(butylene succianate) (PBS) and poly(butylene adipate-co-terephtalate) (PBAT). The tensile properties of the flax fibres have already been determined [C. Baley, Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase, Comp Part A 2002;33:939–948]. The composites are manufactured using a film stacking technique. After studying the processing parameters, these are then adapted to each thermoplastic composites. Test samples are cut out from the composites to test their mechanical properties under tensile loading conditions. These tensile properties are then compared to those of similar polypropylene flax composites. Preliminary results show that the tensile properties are improved with the fibre volume fraction. The tensile strength and Young’s modulus of PLLA and PLA flax composites are greater than those of similar PP/flax fibre composites. The specific tensile strength and modulus of flax fibre/PLLA composite have proved to be very close to those of glass fibre polyester composites.     

Kohlenstoff-Fäden und deren Verwendung in Verbundwerkstoffen

Carbon fibres and carbon fibre composite materials. Carbon fibres are a new reinforcement for high performance composite materials. Their most interesting property is the high Young's modulus. The tensile strength of carbon fibres exceeds 200 kp/mm², the Young's modulus 50,000 kp/mm². Carbon fibre reinforced plastics are mainly used where high stiffness is needed. In most cases, carbon fibre composite components are manufactured by filament winding burt also by lamination and moulding. Data about the different processes for the production of carbon fibres as well as mechanical properties are given. In addition to the different manufacturing methods of composite materials a survey about the today applications is given.     

Different ageing conditions on cementitious roofing tiles reinforced with alternative vegetable and synthetic fibres

This paper discusses the effects of different ageing conditions on the mechanical and physical characteristics of cementitious roofing tiles reinforced with sisal and newsprint pulps, sisal strand fibre and polypropylene (PP) fibre. Roofing tiles with undulate shape were produced by a slurry de-watering and pressing technique. They were subjected to three distinct ageing conditions: fast carbonation, accelerated ageing cycles and fast carbonation plus accelerated ageing cycles. Fast carbonation did not improve the maximum load (ML), limit of proportionality (LOP), toughness and maximum deflection but did decrease their water absorption, apparent porosity and air permeability; however, after 50 heat and rain accelerated ageing cycles, it was ineffective in maintaining the mechanical properties (ML, LOP, toughness and deflection) of the tiles reinforced with vegetable fibres. The refined sisal pulp fibres led to roofing tiles with slightly higher LOP, toughness and maximum deflection than those reinforced with newsprint pulp fibres. PP fibres significantly improved the mechanical performance (ML, LOP, toughness and deflection) of the roofing tiles in relation to sisal strand fibres. The accelerated ageing cycles were effective in promoting severe degradation on the roofing tiles with sisal strand fibres, while the tiles reinforced with PP fibres were practically unaffected.     

Influence of alkali treatment and fibre length on mechanical properties of short Agave fibre reinforced epoxy composites

Composites based on short Agave fibres (untreated and alkali treated) reinforced epoxy resin using three different fibre lengths (3 mm, 7 mm and 10 mm length) are prepared by using hand lay up and compression mould technique. The materials were characterized in terms of tensile, compressive, flexural, impact, water absorption properties and machinability behaviour. All mechanical tests showed that alkali treated fibre composites withstand more fracture strain than untreated fibre composites. As evidenced by the dynamic mechanical analysis (DMA) tests, the thermo-mechanical properties of the composite with alkali treated Agave fibre were considerably good as alkali treatment had facilitated more sites of fibre resin interface. The machinability and atomic force microscope (AFM) studies were carried out to analyze the fibre–matrix interaction in untreated and alkali treated Agave fibre–epoxy composites.     

Polyoxymethylene composites with natural and cellulose fibres: Toughness and heat deflection temperature

Cellulose and abaca fibre reinforced polyoxymethylene (POM) composites were fabricated using an extrusion coating (double screw) compounding followed by injection moulding. The long cellulose or abaca fibres were dried online with an infrared dryer and impregnated fibre in matrix material by using a special extrusion die. The fibre loading in composites was 30 wt.%. The tensile properties, flexural properties, Charpy impact strength, falling weight impact strength, heat deflection temperature and dynamic mechanical properties were investigated for those composites. The fibre pull-outs, fibre matrix adhesion and cracks in composites were investigated by using scanning electron microscopy. It was observed that the tensile strength of composites was found to reduce by 18% for abaca fibre and increase by 90% for cellulose fibre in comparison to control POM. The flexural strength of composites was found to increase by 39% for abaca fibre and by 144% for cellulose fibre. Due to addition of abaca or cellulose fibre both modulus properties were found to increase 2-fold. The notched Charpy impact strength of cellulose fibre composites was 6-fold higher than that of control POM. The maximum impact resistance force was shorted out for cellulose fibre composites. The heat deflection temperature of abaca and cellulose fibre composites was observed to be 50 °C and 63 °C higher than for control POM respectively.     

三维编织CF/KF混杂复合材料力学性能研究

考察了三维编织碳纤维/芳纶纤维混杂增强铸型尼龙(简称HF/MCPA)复合材料的力学性能,着重分析了复合材料的冲击、剪切和弯曲性能。试验结果表明:碳纤维和芳纶纤维混杂复合材料不仅有较好的弯曲强度、剪切强度,同时冲击强度也很好。随着碳纤维体积分数的增加,混杂复合材料的冲击强度降低;横向剪切强度先增大后降低;纵向剪切强度逐渐增大,出现最大值;弯曲强度和模量随之提高,达到最大值后开始下降,最大值时CF∶KF为3∶2。