Transcrystalline interphases in natural fiber-PP composites: effect of coupling agent

Abstract

The interest in lignocellulosic fiber composites has been growing in recent years because of their high specific properties. In this work, a new technique was used to prepare specimen to observe the transcrystalline zones in kenaf fiber-polypropylene composites. A maleated polypropylene (MAPP) coupling agent was used to improve the stress-transfer efficiency in the composites. Transcrystallinity was observed for both the uncoupled and coupled composites, although the rate of growth was higher for the coupled composites. Dynamic mechanical spectroscopy was used to observe the relaxations of the composites. The peak temperature of the β-relaxation, associated with the glass-rubber transition of the amorphous molecules, of the coupled composites was higher than that of the uncoupled composites. Restricted molecular mobility due to covalent interactions between the MAPP and the lignocellulosic surface may account for the shift to higher temperatures. It appears that during compounding the extractives sheared from the fiber surface is an important factor in determining the β-relaxation of these composites. The intensities of the α-transition, related to molecular mobility associated with the presence of crystals, is proportional to the fiber volume fraction. Thus it is possible that the molecules responsible for the α-transition are predominantly in the transcrystalline zone. These 'rigid' amorphous molecules in the transcrystalline zone do play a role in composite behavior and need to be considered when tailoring interphases.

Keywords:

• Transcrystallinity
• kenaf fiber
• natural fiber composites
• fiber-reinforced PP composite
• dynamic mechanical analysis
• coupling agents