Recent interest in environmental sustainability has resulted in growing interest in the development of biodegradable plastics to replace conventional plastics. The aims of this thesis are to provide a testing method that successfully demonstrates fracture toughness of biodegradable starch-based polymer materials provided by Plantic® Technologies. In particular, the response of fracture toughness to moisture content for three Plantic® sheet materials is investigated (denoted XE1, R1 and HP1). Plantic® speculates that, based on qualitative testing, the XE1 and HP1 sheets are more resistive to fracture than the R1 material and the XE1 material exhibits less sensitivity to moisture than the other two.
The proposed testing method is the Trouser Tear Test which exhibits Mode III fracture (out-of-plane tearing) of the specimen. Prior to testing, the Plantic® materials were conditioned at various relative humidity (RH). The results indicate that there is a relationship between moisture content and fracture toughness, by which fracture toughness of the materials peaks at between 52.0-75.5%RH. It was also observed that the materials generally exhibited decreasing fracture toughness in the order of: R1>HP1>XE1. This appears to contradict with the Plantic® results.
To further investigate the material behaviour behind fracture, optical microscope images of the fracture paths were taken. Scanning electron microscopy (SEM) was used to view the fracture surface of the specimens subjected to trouser tear testing. The following thesis outlines the observations made from the SEM images to provide insight into the fracture toughness results.
The thesis concludes with observations that trouser tear testing produced consistent results amongst the tested specimens however these results appeared to contradict with the expected behaviour. The SEM results revealed little in the way of the fracture mechanisms occurring under mode III fracture. Therefore, the report recommends a broader range of testing to be conducted to better represent the behaviour of the Plantic® materials with varying moisture content.