(433a) Developing a Novel Preparation Method for Residual Biomass Polymer Blends

There is a growing interest in polymeric materials from renewable resources. Nevertheless, in facing a society where petroleum-based plastic products are almost ubiquitous, the challenge for the emerging biobased polymer materials is twofold: being cost effective and performance competitive while lowering the environmental footprint.

Soy protein meal, a residue after oil crush, has being explored as a new resource for plastics. However, owing to some obstacles such as water/moisture sensitivity, high melt viscosity, narrow process window and brittleness, neat soy protein (SP) plastics have little practical values. To overcome these disadvantages, blending SP with other biodegradable polymers has received increasing attention. Sugar beet pulp (SBP) is another agricultural residue which has received similar attention for plastic applications as SP. In the current study of SP or SBP polymer blends, SP and SBP are merely used as organic fillers in most cases. Although certain processing and end use properties can be improved with respect to that of neat SP and SBP plastics, the mechanical properties of the blends are often not satisfactory and even lower than that of both the neat polymer and the neat SP (or SBP) plastics.

In this work, we introduced a novel method to prepare polymer blends of residual biomass and biodegradable thermoplastic polymer. SP and SBP were used as plastic components during the compounding of the blends. The polymers used were poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT), respectively. The mixing of the blends was carried out in a twin screw extruder and the test specimens were prepared by injection molding. Plasticization of SP and SBP by water during compounding played a critical role in determining SP (or SBP) to be a plastic component or filler in the mixing and hence the morphological structure of the resulting blends. When extra water was added, SP (or SBP) behaved like a melt during the compounding, consequently the resulting blends demonstrated significant different properties and morphological structures from those made of dry SP (or SBP). Because water evaporated during mixing and after drying, the resulting blends actually became in situ formed thermoplastic composites.  Percolation network structure of SP (or SBP) was noted in some of these blends. Different effects of SP (or SBP) as a plastic component and filler on phase structure and mechanical properties of the resulting blends were investigated. Molecular weight changes of the thermoplastic PLA and PBAT after processing were examined. The change of SP molecular structure caused by melt processing was also evaluated by protein solubility test. Effects of various compatibilizers on the properties of the blends were also studied. The results suggest that when SP and SBP were used as plastic components in mixing, the resulting blends demonstrated an overall superior performance than when they are used as fillers.