Preparation, processing and characterization of biodegradable wood flour/starch-cellulose acetate compounds

A novel biodegradable material was prepared by compounding, in different proportions, pine wood flour (WF) and a commercial starch-cellulose acetate blend on a configurable co-rotating twin screw extruder. After pelletizing, the compounds were injection moulded and the mechanical and rheological properties of the mouldings determined. As the content of wood flour increases up to 50% (wt/wt), the tensile strength and the modulus improve significantly, whereas the toughness drops gradually. The effect of the wood flour content on the shear viscosity is complex, being impossible to establish a linear relationship between the two. The shear viscosity decreases with shear rate, but for a level of 40% and 50% of WF there is evidence for a quasi-Newtonian behaviour, irrespective of the test temperature. Compounds with 50% WF present the highest tensile and strength and modulus but are difficult to process. However, the processability can be improved by using glycerol as plasticizer, without paying a too severe penalty in mechanical properties. In fact, by adding 15% glycerol (wt/wt), compounds with 50% WF can be successfully injection moulded into specimens with good mechanical properties.