Pproperties of injection moulded starch/synthetic polymer blends - II. Evaluation of mechanical properties

The effect of the composition, starch type, inclusion of fibers, and the presence or absence of weldline on the mechanical properties of injection moulded starch and synthetic polymer blends were studied as a function of time. In addition, the effect on the mechanical properties after mixing a fraction of reground starch/EVAMA and starch/EMA materials generated from runners and sprues with the respective virgin blended material have been studied. We have also investigated the effects of annealing, and soaking in water on the tensile properties of these blend compositions. Scanning electron microscopy has been used to study the morphology of selected blends. Statistical analyses were done to delineate the significant effects of the above compositions on the tensile and flexural properties of the blends. A small amount of functionalized polymer has stabilized the phase morphology and led to enhanced properties. Corn starch yielded better tensile properties that wheat starch or wheat flour. Weldline (knitline) strength ranged from 55 to 95% of nonweldline values and was dependent on composition. Up to 25% of reground materials can be used without any detrimental effect on properties. Addition of fibers increased the tensile but not flexural strengths, though the weldline properties of samples containing fiber were poor. Fibers with medium aspect ratios (3-3.5) were found to give better properties. Soaking in water reduced the tensile properties significantly. The tensile properties for most compositions were invariant with time.