Flexural properties of macadamia nutshell particle reinforced polyester composites

A study on the flexural properties of macadamia nutshell particle reinforced polyester composites is presented in this paper. The macadamia nutshell/polyester composites were made as per the hand layup procedure and the instructions provided by the manufacturers. These specimens were then tested in the three point bend configuration in accordance with ASTM D790-07 at a span to depth ratio of 16. Four weight fractions of macadamia nutshell particles 10%, 20%, 30% and 40% were chosen to be studied. The process-induced voids were studied and it is shown that voids play an important role in flexural properties. When voids exist, flexural modulus was calculated using a micromechanical model. It is shown from both the experimental results and calculation that flexural modulus increases with the weigh fraction of macadamia nutshell particles, while decreases with increasing void content. Adding macadamia nutshell particles does not improve the flexural strength of polyester. It is shown flexural strength decreases with increasing void content.