M. G. Kumaran

Oil palm fibers: Morphology, chemical composition, surface modification, and mechanical properties

Oil palm fiber is an important lignocellulosic raw material for the preparation of cost-effective and environment-friendly composite materials. The morphology and properties of these fibers have been analyzed. The properties of two important types of fibers, the oil palm empty fruit bunch fiber and the oil palm mesocarp fiber (fruit fiber) have been described. The surface topology of the fibers has been studied by scanning electron microscopy. Thermogravimetry and differential thermal analysis were used to determine the thermal stability of the fibers. Fiber surface modifications by alkali treatment, acetylation, and silane treatment were tried. The modified surfaces were characterized by infrared spectroscopy and scanning electron microscopy. The chemical constituents of the fibers were estimated according to ASTM standards. Mechanical performance of the fibers was also investigated. Microfibrillar angle of the fibers was theoretically predicted. The theoretical strength of the fibers was also calculated and compared with the experimental results.

The mechanical performance of hybrid phenol-formaldehyde-based composites reinforced with glass and oil palm fibres

Oil palm fibre was hybridised with glass fibre in order to achieve superior mechanical performance. The reinforcing effect of glass in phenol formaldehyde resin is evaluated at various glass fibre loadings. Tensile strength, tensile modulus and flexural strength increase with an increase in fibre loading. However, elongation at break and flexural modulus are found to decrease beyond 40 wt.% fibre loading. Impact strength and the density of the composites showed similar trends. Compared to the gum sample, hardness of the composites decreased by glass fibre reinforcement. The hybrid effect of glass fibre and oil palm empty fruit bunch (OPEFB) fibre on the tensile, flexural and impact response of the composites was investigated. Randomly oriented glass and OPEFB fibre mats were arranged as interlayers to enhance the hybrid effect. The overall performance of the composites was improved by the glass fibre addition. Impact strength shows great enhancement by the introduction of a slight amount of glass fibre. Density of the hybrid composite decreases as the volume fraction of the OPEFB fibre increases. Hardness of the composites also showed a slight decrease on an increased volume fraction of OPEFB fibre. Scanning electron micrographs and optical photographs of the fractured surfaces were taken to study the failure mechanism and fibre/matrix interface adhesion. The experimental results were compared with theoretical predictions. The hybrid effect of glass and OPEFB fibre was also calculated.

Oil Palm Fibre Reinforced Phenol Formaldehyde Composites: Influence of Fibre Surface Modifications on the Mechanical Performance

Oil palm fibres have been used as reinforcement in phenol formaldehyde resin. In order to improve the interfacial properties, the fibres were subjected to different chemical modifications such as mercerisation, acrylonitrile grafting, acrylation, latex coating, permanganate treatment, acetylation, and peroxide treatment. The effect of fibre coating on the interface properties has also been investigated. Morphological and structural changes of the fibres were investigated using scanning electron microscopy and IR spectroscopy. Mechanical properties of untreated and treated fibres were studied. Changes in stress–strain characteristics, tensile strength, tensile modulus and elongation at break of the fibres upon various modifications were studied and compared. The incorporation of the modified fibres resulted in composites having excellent impact resistance. Fibre coating enhanced the impact strength of untreated composite by a factor of four. Tensile and flexural performance of the composites were also investigated. Finally, inorder to have an insight into the failure behaviour, the tensile and impact fracture surfaces of the composites were analysed using scanning electron microscope.

Thermoplastic elastomers from blends of polystyrene and natural rubber: morphology and mechanical properties

Abstract Thermoplastic elastomers (TPEs) from blends of natural rubber and polystyrene (NR/PS) have been prepared. Morphology and properties of these blends have been studied with special reference to the effect of blend ratio, processing conditions and vulcanising systems. The mechanical properties and morphology of the blends are dependent on the processing conditions, i.e. whether the samples are prepared by the melt mixing technique or by the solution casting technique. Three different solvents namely chloroform, benzene and carbon tetrachloride were used as the casting solvents. Differences in mechanical and morphological properties were observed in each case which in turn depend upon the interaction of the solvent with the constituent homopolymers. Attempts have been made to correlate the morphology with properties. Experimental values were compared with different theoretical models. The effects of dynamic crosslinking using sulphur, peroxide and mixed systems on morphology and mechanical properties of NR/PS blends have also been studied.

Thermal behaviour of natural rubber/polystyrene blends : thermogravimetric and differential scanning calorimetric analysis

Abstract The thermal behaviour of natural rubber (NR)/polystyrene (PS) blends has been studied by thermogravimetry and differential scanning calorimetry. NR PS blends are immiscible and incompatible and the compatibility can be improved by the addition of a suitable compatibilizer (NR-g-PS). The effects of the compatibilizer loading and blend ratio on the thermal properties were evaluated. It was found that the weight loss of the blend at any temperature is lower than that of the homopolymers. This suggests that blending improves the overall thermal behaviour of the blend. Addition of the compatibilizer was also found to improve the thermal stability. The initial decomposition temperature increased with the addition of the graft copolymer. The weight loss was found to decrease on the introduction of the compatibilizer. DSC studies revealed that even with the addition of a technological compatibilizer, the NR PS blends were thermodynamically incompatible. This is evident from the presence of two glass transitions, corresponding to PS and NR phases for the compatibilised and uncompatibilised blends.

Transport of styrene monomer through natural rubber

The diffusion and transport of inhibitor-free styrene through crosslinked natural rubber (NR) have been studied at various temperatures. NR has been vulcanized by conventional, efficient, peroxide and mixed vulcanization techniques. The dependence of diffusion coefficient on the crosslinking system has been studied for all the systems. The influence of temperature on the sorption and the activation energies of sorption have been calculated. The interaction parameter, permeability, sorption coefficient and molecular weight between crosslinks have been evaluated using the diffusion data. The effect of degree of crosslinking on the sorption characteristics of styrene through NR has also been investigated for the different crosslinking systems. The peroxide system showed lowest uptake and the conventional system showed highest uptake.

The Technological Compatibilization of Natural Rubber/Polystyrene Blends by the Addition of Natural Rubber-graft-Polystyrene

Abstract Compatibility of natural rubber (NR)/polystyrene (PS) blend is poor and can be enhanced by the addition of a graft copolymer of natural rubber and polystyrene (NR-graft-PS). The effects of homopolymer molecular weight, copolymer molecular weight, copolymer concentration, processing conditions and mode of addition on the morphology of the dispersed phase have been investigated by means of optical microscopy. The addition of a small percentage of the compatibilizer decreases the domain size of the dispersed phase. The effect levels off at higher concentrations. The leveling off could be an indication of interfacial saturation. The experimental results were compared with the theoretical predictions of Noolandi and Hong. The addition of the graft copolymer improves the mechanical properties of the blend and attempts were made to correlate the mechanical properties with the morphology of the system. Attempts were also made to understand the conformation of the graft copolymer at the interface.

Stress-relaxation behaviour in composites based on short oil-palm fibres and phenol formaldehyde resin

The stress relaxation in phenol-formaldehyde composites reinforced with short oil-palm empty fruit bunch fibres has been studied as a function of fibre loading, fibre treatment, physical ageing and strain level. Maximum stress relaxation was observed for 30 wt.% fibre loading. Treated composites showed higher relaxation except in composites treated with alkali and toluene 2, 4 diisocyanate (TDI). Water ageing increased the rate of relaxation. The effect of hybridisation of the oil-palm fibres with glass fibres on the relaxation behaviour was examined. The stress-relaxation rate of the composite was lowered upon hybridisation. The rate of relaxation for different time intervals and crossover time was calculated in order to explain the relaxation mode of the composites. Master stress-relaxation curves were drawn to explain the long-term behaviour of the composites by superimposing the stress values at different strains by a horizontal shift along the logarithmic time axis. The relaxation modulus values for the composite show a trend similar to that of relaxation of stress in the composites.

Environmental effects in oil palm fiber reinforced phenol formaldehyde composites: Studies on thermal, biological, moisture and high energy radiation effects

Accelerated weathering studies of untreated and treated oil palm fiber reinforced phenol formaldehyde composites and oil palm/glass hybrid fiber reinforced phenol formaldehyde composites were conducted. Thermal, water, biological and γ radiation effects on the composite properties were analysed. Mechanical properties such as tensile, flexural and impact properties of thermal and water aged samples were investigated. The extent of biodegradation and γ irradiation effects was estimated from variations in tensile and impact properties. The tensile and impact fracture mechanism and changes in fiber-matrix adhesion were studied using scanning electron microscopic analysis. The changes in the tensile and flexural stress-strain characteristics as well as deformation behaviour of aged composites are well explained by respective stress-strain curves. Mechanical performance of the composites decreased upon thermal ageing. Marked decrease in these properties of the composites is observed upon radiation ageing. However water immersion leads to an increase in strength properties in some treated composites such as on acetylation, silane, acrylonitrile grafting, isocyanate, permanganate treatment, alkali treatment etc. It is found that oil palm fiber increases the biodegradability of the composites.

Characterization of EVA/clay nanocomposite membranes and its pervaporation performance.

Pervaporation separation of chlorinated hydrocarbon/acetone mixtures has been investigated using nanoclay modified poly(ethylene-co-vinyl acetate) films. The results have been compared with the unfilled poly(ethylene-co-vinyl acetate) films. The nanoclay modified membranes were characterized by X-ray diffraction technique. The dispersion of layered silicates in the polymer matrix was analyzed using transmission electron microscopy. The nanoclay showed excellent dispersion in the polymer matrix. The effect of free volume on the pervaporation performance was investigated by positron annihilation lifetime spectroscopy. Poly(ethylene-co-vinyl acetate) nanocomposite membrane showed high selectivity because of the plateletlike morphology and high aspect ratio of layered silicates. The nano clay content and the swelling effects on pervaporation performance of nano composite membranes have been investigated in detail.