Sisal Fiber Reinforced Polypropylene Composites Research Articles

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.

An investigation on the processing of sisal fibre reinforced polypropylene composites

In this paper, a pre-impregnation technique has been introduced for the injection moulding of sisal fibre reinforced polypropylene (PP/SF) composites. The major advantasge of the pre-impregnation technique is that the PP/SF composites can be injection moulded with relatively lower barrel temperature, and therefore significant thermal degradation of the sisal fibres could be avoided. The resulting injection mouldings possessed lighter colour and no odor.

Environmental effects on the degradation behaviour of sisal fibre reinforced polypropylene composites

The environmental degradation behaviour on the physical and mechanical properties of short sisal/PP composites has been studied with special reference to the influence of ageing conditions like treatment with water and UV radiation. The dependence of water uptake on the sorption characteristics of sisal/PP composites was evaluated by immersion in distilled water with respect to fibre loading, temperature and chemical treatment. It is found that water uptake increases with increase of fibre loading due to the increase in cellulose content. The raise of temperature up to 70 °C is accompanied by an increase of the rate and extent of sorption. Chemical treatments such as urethane derivative of PPG, PMPPIC and MAPP were given to sisal fibre. All chemically modified fibre composites showed lower uptake than the unmodified composites. This is because all chemical treatments given to sisal fibre reduce its hydrophilicity thereby favouring strong interfacial adhesion between the fibre and PP matrix. The influence of water uptake on the tensile properties of sisal/PP composites was studied. Tensile properties decreased with water uptake, time of immersion and fibre loading. The behaviour was strongly dependent on the chemical treatment and fibre orientation. The influence of the tensile properties of sisal/PP composites exposed to UV radiation was studied. The tensile properties were found to decrease with increase in the time of exposure to UV radiation. The reduction in properties is due to chain scission and degradation occurring to PP molecules as a result of photooxidation promoted by ultraviolet radiation. As a result of UV irradiation, surface cracks can be seen on neat PP and PP composites which can be evidenced from SEM photos. The retention of tensile properties increased with increase of fibre loading.

Dynamic mechanical properties of short sisal fibre reinforced polypropylene composites

Abstract The dynamic mechanical properties of short sisal fibre reinforced polypropylene composites containing both untreated and treated fibres have been studied with reference to fibre loading, fibre length, chemical treatments, frequency and temperature. By the incorporation of short sisal fibre into polypropylene, the storage moduli ( E ′)and loss moduli ( E ″) have been found to be increasing whereas the mechanical loss factor (tan δ ) decreasing. The storage modulus decreases with increase in temperature. The treated fibre composites show better properties compared to untreated system. The Arrhenius relationship has been used to calculate the activation energy for the glass transition. The use and limitations of various theoretical equations to predict the tan δ and storage modulus of the fibre reinforced plastic composites have been discussed. Cole–Cole analysis has been carried out to understand the phase behaviour of the composite samples. A master curve for the modulus of the blend is drawn by applying the time–temperature super position principle.

Melt Rheological Behaviour of Short Sisal Fibre Reinforced Polypropylene Composites

The melt rheological properties of short sisal fibre reinforced polypropylene composites have been studied using a capillary rheometer. The dependence of the relative composition of component reinforcements and their aspect ratio and also the extent of chemical modification on the overall rheological behaviour have been studied. Incorporation of sisal fibre into polypropylene results in an increase in melt viscosity and a decrease in melt elasticity. The melt viscosity was found to have increased with fibre loading. Incorporation of fibres decreased the extrudate deformation and die-swell and this improvement was more prominent at higher fibre loading. A comparison was made between the two techniques employed for the preparation of the composites, i.e. melt mixing in a Haake Rheocord and solution mixing using toluene-xylene mixture as the solvent. It is found that composites prepared by solution mixing showed a higher viscosity as compared to melt mixed composites. Various chemical modifications using chemicals such as isocyanate, maleic anhydride and permanganate treatment have been carried out to improve the interaction between the matrix and fibre. The influence of chemical treatment on the viscosity of the system has been analysed. The fibre breakage analysis during extrusion was carried out using optical microscopy. The morphology of extrudate has been studied by optical and scanning electron microscopes. Master curves have been generated using modified viscosity and shear rate functions that contain the melt flow index (MFI) as a parameter. A comparison was made between theoretical and experimental viscosity values and it was found that experimental viscosity is slightly higher than theoretical viscosity because of the misalignment of fibres.

Thermal Expansion Anisotropy in Injection-Moulded Natural-Fibre Composites

Recently much effort has been devoted to the development of natural-fibre composites produced via injection moulding. Although several processing-cost benefits may be associated with the injection moulding process, the microstructures of injection-moulded composites can be quite complex and anisotropic. In this study, the thermal expansion anisotropy that may develop in injection moulded natural-fibre composites has been investigated. A thermal mechanical analyser (TMA) has been employed to determine the thermal expansion properties of jute and sisal-fibre reinforced polypropylene composites injection-moulded into the form of tensile bars and disks. Measurements indicated that thermal expansion coefficients of tensile bars in the melt-flow direction may be 5 to 7 times less than thermal expansion coefficients in the cross-flow direction.