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in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: Tensile and impact properties of Neem bark flour (BF) containing high density polyethylene (HDPE) composites were studied at 0-0.26 volume fraction of filler. Tensile modulus and strength and breaking elongation decreased with increase in BF concentration. The decrease in tensile modulus and strength was attributed to the decrease in crystallinity of the polymer compared to the imposed mechanical restraint by the BF. Analysis of tensile strength data indicated formation of stress concentration in the interphase. Because of this stress concentration and the mechanical restraint, the elongation-at-break and Izod impact strength decreased. Use of a coupling agent, HDPE-g-MAH, brings about enhanced phase adhesion, increasing the tensile modulus and strength. Enhanced adhesion marginally lowers composite ductility at higher filler contents and aids stress transfer increasing the Izod impact strength inappreciably. Scanning electron microscopic studies indicated better dispersion of BF particles and enhanced interphase adhesion in presence of the coupling agent.

Mechanical properties such as tensile and impact strength behavior of teak wood flour (TWF)-filled high-density polyethylene (HDPE) composites were evaluated at 0-0.32 volume fraction (U f ) of TWF. Tensile modulus and strength initially increased up to U f ¼ 0.09, whereas a decrease is observed with further increase in the U f . Elongation-at-break and Izod impact strength decreased significantly with increase in the U f . The crystallinity of HDPE also decreased with increase in the TWF concentration. The initial increase in the tensile modulus and strength was attributed to the mechanical restraint, whereas decrease in the tensile properties at U f > 0.09 was due to the predominant effect of decrease in the crystallinity of HDPE. The mechanical restraint decreased the elongation and Izod impact strength. In the presence of coupling agent, maleic anhydride-grafted HDPE (HDPE-g-MAH), the tensile modulus and strength enhanced significantly because of enhanced interphase adhesion. However, the elongation and Izod impact strength decreased because of enhanced mechanical restraint on account of increased phase interactions. Scanning electron microscopy showed a degree of better dispersion of TWF particles because of enhanced phase adhesion in the presence of HDPE-g-MAH.

The nonisothermal crystallization behavior and melting characteristics of high-density polyethylene (HDPE) in HDPE/teak wood flour (TWF) composites have been studied by differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) methods. Composite formulations of HDPE/TWF were prepared by varying the volume fraction (U f ) of TWF (filler) from 0 to 0.32. Various crystallization parameters evaluated from the DSC exotherms were used to study the nonisothermal crystallization behavior. The melting temperature (T m ) and crystallization temperature (T p ) of the composites were slightly higher than those of the neat HDPE. The enthalpy of melting and crystallization (%) decrease with increase in the filler content. Because the nonpolar polymer HDPE and polar TWF are incompatible, to enhance the phase interaction maleic anhydride grafted HDPE (HDPE-g-MAH) was used as a coupling agent. A shift in the crystallization and melting peak temperatures toward the higher temperature side and broadening of the crystallization peak (increased crystallite size distribution) were observed whereas crystallinity of HDPE declines with increase in U f in both DSC and WAXD. Linear correlations were obtained between crystallization parameters and tensile and impact strength.

ABSTRACT:The melt rheological behavior of neem bark flour (BF) filled high density polyethylene (HDPE) has been studied at varying volume fraction (U f ) from 0 to 0.26 at 180, 190, and 200 C in the shear rate range from 100 to 5000 s À1 using extruded pellets of the composites. The melt viscosity of HDPE increases with U f because the BF particles obstruct the flow of HDPE. With the incorporation of the coupling agent HDPE-g-MAH, the viscosity decreased compared to the corresponding compositions in the HDPE/BF systems due to a plasticizing/lubricating effect by HDPE-g-MAH. The composites obeyed power law behavior in the melt flow. The power law index decreases with increase in the filler content and increases with temperature for the corresponding systems while the consistency index showed the opposite trend. The activation energy for viscous flow exhibited inappreciable change with either U f or inclusion of the coupling agent, however, the pre-exponential factor increased with filler concentration.