S. S. Bhagawan

Mechanical Properties of Pineapple Leaf Fiber-Reinforced Polyester Composites

Pineapple leaf fiber (PALF) which is rich in cellulose, relatively inexpen- sive, and abundantly available has the potential for polymer reinforcement. The present study investigated the tensile, flexural, and impact behavior of PALF-reinforced polyes- ter composites as a function of fiber loading, fiber length, and fiber surface modification. The tensile strength and Youngs modulus of the composites were found to increase with fiber content in accordance with the rule of mixtures. The elongation at break of the composites exhibits an increase by the introduction of fiber. The mechanical proper- ties are optimum at a fiber length of 30 mm. The flexural stiffness and flexural strength of the composites with a 30% fiber weight fraction are 2.76 GPa and 80.2 MPa, respec- tively. The specific flexural stiffness of the composite is about 2.3 times greater than that of neat polyester resin. The work of fracture (impact strength) of the composite with 30% fiber content was found to be 24 kJ m 02 . Significant improvement in the tensile strength was observed for composites with silane A172-treated fibers. Scanning electron microscopic studies were carried out to understand the fiber-matrix adhesion, fiber breakage, and failure topography. The PALF polyester composites possess superior mechanical properties compared to other cellulose-based natural fiber composites. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1739-1748, 1997

Effects of environment on the properties of low-density polyethylene composites reinforced with pineapple-leaf fibre

Abstract The influence of water environment on the sorption characteristics of low-density polyethylene composites reinforced with short pineapple-leaf fibers (PALF/LDPE) has been studied by immersion in distilled water at 28, 50 and 70°C. The effects of fiber loading, temperature and chemical treatment on the sorption behavior are also evaluated. Water uptake is found to increase with fiber loading owing to the increased cellulose content. Weight change profiles for the composites at high temperature indicated that the diffusion is close to Fickian. All of the treated composites showed lower uptake than the unmodified composites. Parameters like diffusion, sorption and permeability coefficients were determined and activation energies were calculated. The thermodynamic constants such as entropy, enthalpy and first-order kinetic rate constant have been evaluated. A correlation between theoretical and experimental sorption results was evaluated. The effect of water uptake on uniaxial tensile properties has also been studied. Mechanical properties decreased after exposure to water, depending on time of immersion, fiber loading and chemical treatment. Finally, studies were carried out on the flexural properties of PALF/LDPE composites exposed to ultraviolet radiation.

Melt rheological behaviour of short pineapple fibre reinforced low density polyethylene composites

Abstract The melt theological behaviour of short pineapple fibre reinforced low density polyethylene composite has been studied using a capillary rheometer. The influence of fibre loading, fibre length, and fibre treatment on the theology of composites was investigated. Studies were carried out in the temperature range of 125 to 145°C and shear rate of 016.4 to 5468 s−1. The melt viscosity was found to be increased with fibre loading. Various chemical treatments were made to improve fibre—matrix interfacial adhesion. Treatments based on poly(methylene)—poly(phenyl)isocyanate (PMPPIC), silane and peroxide increased the viscosity of the system due to high fibre—matrix interfacial interaction. Viscosity of the system decreased with increase of temperature. However, in peroxide treated composites viscosity is increased due to the crosslinking of composite at higher temperature. The fibre breakage during extrusion was analysed using optical microscopy. The morphology of the extrudates has been studied by optical and scanning electron microscopies. Master curves were generated using modified viscosity and shear rate functions that contain melt flow index as a parameter.

Morphology, mechanical and viscoelastic behaviour of blends of nitrile rubber and ethylene-vinyl acetate copolymer

Nitrile rubber/ethylene-vinyl acetate copolymer (NBR/EVA) blends with different ratios were prepared by using a two roll mixing mill. The morphology of the blends was studied using optical and electron microscopies. The morphology of the blends indicated a two phase structure in which the minor phase is dispersed as domains in the major continuous phase. However, between 40 and 50 wt% of NBR content both NBR and EVA exist as continuous phases and generate a co-continuous morphology. The viscoelastic properties have been determined using a Rheovibron Viscoelastometer at 35 Hz over a wide range of temperatures. The effect of blend ratio on the mechanical properties such as tensile strength, elongation at break, stress-strain behaviour and hardness has been investigated. The mechanical properties increase with the increase of EVA content in the blend. Attempts have been made to correlate the variation of properties with morphology of the blend. Various composite models have been used to fit experimental mechanical and viscoelastic data.

Influence of short pineapple fiber on the viscoelastic properties of low-density polyethylene

Abstract Viscoelastic properties of low-density polyethylene reinforced with short pineapple fibers, extracted from pineapple leaves, have been studied as a function of temperature at different fiber orientations. It was found that longitudinally oriented fiber composites show the maximum value of storage modulus. The effects of fiber loading and fiber length on the viscoelastic properties have been assessed.

Effects of blend ratio, crosslinking systems and fillers on the morphology, curing behavior, mechanical properties, and failure mode of acrylonitrile butadiene rubber and poly(ethylene-co-vinyl acetate) Blends

Blends of acrylonitrile butadiene rubber (NBR) and poly(ethylene-co-vinyl acetate) (EVA), with varying proportions of the components, were vulcanized using different crosslinking systems, namely, sulfur (S), dicumyl peroxide (DCP), and a mixed system (S + DCP). Mechanical properties, such as stress–strain behavior, tensile strength, elongation at break, Youngs modulus, tensile set, and tear strength, were studied. The mixed system exhibited better mechanical performance than other systems. The tensile and tear fracture surfaces were analyzed under the scanning electron microscope in order to understand the failure mechanism. The variation in properties was correlated with the morphology of the system. The effect of high-abrasion furnace black (HAF), semireinforcing furnace black (SRF), silica, and clay on the mechanical properties and failure mechanism of 50/50 blend of NBR–EVA (N50P) has also been studied. The Kraus equation has been applied to analyze the extent of polymer–filler interaction. Applicability of various theoretical models has been investigated to predict the properties of the blend systems.

THERMOGRAVIMETRIC ANALYSIS AND THERMAL AGEING OF CROSSLINKED NITRILE RUBBER/POLY- (ETHYLENE-CO-VINYL ACETATE) BLENDS

The thermal behaviour of nitrile rubber (NBR)/poly(ethylene-co-vinyl acetate) (EVA) blends was studied by thermogravimetry. The effects of blend ratio, different crosslinking systems (sulphur, peroxide and mixed), various fillers (silica, clay and carbon black) and filler loading on the thermal properties were evaluated. It was found that the initial decomposition temperature increased with the addition of NBR to EVA. Among the various crosslinking systems studied, the peroxide cured system showed the highest initial decomposition temperature. This is associated with the high bond dissociation energy of C–C linkages. The addition of fillers improved the thermal stability of the blend. The mass loss at different temperatures and activation energy of degradation were also studied. The thermal ageing of these blends was carried out at 50 and 100°C for 72 h. It was seen that the properties are not affected by the mild ageing condition. Also, the peroxide cured system was found to exhibit better retention in properties, than other crosslinking systems.

Processability characteristics and physico-mechanical properties of natural rubber modified with cashewnut shell liquid and cashewnut shell liquid–formaldehyde resin

Abstract Natural rubber (NR) has been modified with 5–15 phr each of cashewnut shell liquid (CNSL) and cashewnut shell liquid–formaldehyde (CNSLF) resin with a view to studying the processability characteristics of the mixes and physicomechanical properties of their vulcanizates. The plasticizing effect of these additives in NR was shown by the reduction in melt viscosity and power consumption during mixing in a Brabender Plasticorder compared to that of unmodified NR. Despite the reduction in chemical crosslink density, the vulcanizates containing 15 phr of CNSL and 5–10 phr of CNSLF showed higher tensile and tear strengths and elongation at break. The higher values of activation energy for thermal decomposition of the vulcanizates containing 15 phr each of CNSL (301 kJ/mol) and CNSLF (372 kJ/mol) than that of the unmodified NR vulcanizate (177 kJ/mol) indicate improvement in thermal stability of NR vulcanizates in presence of the modifiers.

Tearing behavior and recyclability of nitrile rubber/poly(ethylene-co-vinyl acetate) blends

The tear strength of nitrile rubber/poly(ethylene-co-vinyl acetate) (NBR/EVA) blends was measured as a function of blend composition in an Instron universal testing machine. An increase in tear strength was observed with increasing EVA content. The variation in this property was correlated with the microstructural morphology of the system. The tear failure mechanism of these blends as a function of blend composition was studied by examining the failure surfaces and the fracture patterns correlated with the strength and failure of these materials. Various models such as parallel model, series model and the Halpin-Tsai equation were used to fit the experimental tear strength values. In order to analyze the reprocessability of these blends, the blends were recycled up to three times and the mechanical properties were measured. It was found that the properties of the blends were little affected by recycling.

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3-dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass-transition temperatures, indicating that the system is immiscible. It was also found that the glass-transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time-temperature superposition and Cole-Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism.