This paper describes the tensile, impact, flexural properties and aging behavior of short banana fiber reinforced polyester composites with special reference to the effect of fiber length and fiber content. Maximum tensile strength was observed at 30 mm fiber length while impact strength gave the maximum value for 40 mm fiber length. Incorporation of 40% untreated fibers gave a 20% increase in the tensile strength and a 341% increase in impact strength. On treatment with silane coupling agent, composites showed a 28% increase in tensile strength and a 13% increase in flexural strength. Aging studies showed a decrease in tensile strength of the composites. The experimental tensile strength values were compared with theoretical predictions according to Piggot equation. Scanning electron microscopy studies were carried out to understand the morphology of the fiber surface, fiber pullout and interface bonding. Water absorption studies showed an increase in water uptake with increase in fiber content. Finally, the properties of banana fiber reinforced polyester composites have been compared with other natural fiber reinforced composites.

ABSTRACT:The mechanical performance of short randomly oriented banana and sisal hybrid fiber reinforced polyester composites was investigated with reference to the relative volume fraction of the two fibers at a constant total fiber loading of 0.40 volume fraction (V f ), keeping banana as the skin material and sisal as the core material. A positive hybrid effect is observed in the flexural strength and flexural modulus of the hybrid composites. The tensile strength of the composites showed a positive hybrid effect when the relative volume fraction of the two fibers was varied, and maximum tensile strength was found to be in the hybrid composite having a ratio of banana and sisal 4 : 1. The impact strength of the composites was increased with increasing volume fraction of sisal. However, a negative hybrid effect is observed when the impact strength of the composites is considered. Keeping the relative volume fraction of the two fibers constant, that is, banana : sisal ϭ 0.32 : 0.08 (i.e., 4 : 1), the fiber loading was optimized and different layering patterns were investigated. The impact strength of the composites was increased with fiber loading. Tensile and flexural properties were found to be better at 0.40 V f . In the case of different layering patterns, the highest flexural strength was observed for the bilayer composites. Compared to other composites, the tensile properties were slightly higher for the composite having banana as the skin material and sisal as the core material. Scanning electron micrographs of the tensile and impact fracture surfaces of the hybrid composites having volume fraction 0.20 and 0.40 V f were studied. The experimental tensile strength and tensile modulus of hybrid composites were compared with those of theoretical predictions.

The effect of blend ratio and compatibilization on dynamic mechanical properties of PP/NBR blends was investigated at different temperatures. The storage modulus of the blend decreased with increase in rubber content and shows two Tg's indicating the incompatibility of the system. Various composite models have been used to predict the experimental viscoelastic data. The Takayanagi model fit well with the experimental values. The addition of phenolic modified polypropylene (Ph‐PP) and maleic modified polypropylene (MA‐PP) improved the storage modulus of the blend at lower temperatures. The enhancement in storage modulus was correlated with the change in domain size of dispersed NBR particles. The effect of dynamic vulcanization using sulfur, peroxide, and mixed system on viscoelastic behavior was also studied. Among these peroxide system shows the highest modulus. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2309–2327, 1997

Hybrid composites of low density polyethylene (LDPE) reinforced with intimately mixed short sisal and glass fibers were prepared by solution mixing technique. The mechanical properties of these composites have been investigated with reference to the effects of orientation and composition of fibers in them. It has been observed that the composites contining longitudinally oriented fibers exhibit better mechanical properties than those with randomly oriented ones. Also it is seen that the mechanical properties increase with increase in the volume fraction of glass fibers in the hybrid composites. The effict of chemical modification of sisal fibers on the properties of 50:50 sisal/glass fiber composites has also been studied. The hybrid effect was calculated by the additive rule of hybrid mixtures using the mechanical properties of individual composites. A positive hybrid effect was echibited by the composites for all the mechanical properties except for elongation at break.

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