Investigating the effects of water absorption and rubber toughening in sisal fiber reinforced polypropylene composites

Abstract

The objective of this research project is to investigate the properties of sisal fiber reinforced polypropylene (SFRPP) composites. The toughening effect due to the incorporation of a styrene-ethylene-butylene-styrene triblock copolymer (SEBS) into the SFRPPs was also investigated. The maximum sisal fiber and SEBS content employed in this work was 30 and 20 wt% respectively. In this work, a number of tests have been conducted. They include single fiber tensile test, fiber length and orientation measurements, water absorption test, conventional pendulum impact tests, instrumented drop weight impact test and instrumented drop weight plate impact test. According to the single fiber tensile test, heat treatment can greatly reduce the tensile strength of the sisal fibers. The value of tensile strength is significantly reduced as the single fibers are heat treated to a temperature of 200℃ for 30 min. As the sisal fiber is exposed to such high temperatures for such longer period, severe degradation would occur. Therefore, the sisal fibers should only be exposed to the high temperature condition for brief duration during melt processing of reinforced composites. Water absorption treatment was conducted by immersing injection molded SFRPP tensile bars containing different weight percentage of sisal fibers into a water bath at 90 oC for different durations. The moisture up-take (measured by percentage of weight-gain) initially increased with immersion time until a maximum was reached. For longer immersion time beyond the maximum value, the percentage of weight-gain was found to decrease. Other than weight-gain measurements, tensile and impact tests were also performed on the composites after subjected to different stages of water absorption treatment. It has been found that the mechanical properties of the composites are sensitive to the water absorption treatment as well as to the sisal fiber content. The water absorption treatment has the effect of weakening the sisal fiber/polypropylene interface significantly. In order to modify the impact fracture behaviour of SF/PP, a styrene-ethylene- butylene-styrene triblock (SEBS) rubber has been added to SF/PP. It was found that a pronounced toughening effect would be achieved as 20 wt% of SEBS was added into the SF/PP. The impact resistance of the fiber reinforced composites with rubber toughening were significantly better than the fiber reinforced composites without rubber.

Date of Award	15 Feb 2005
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kwok Yiu Robert LI (Supervisor)