Biobased products from starch using extrusion processing and chemical modifications.

摘要

Biobased products from starch have shown great potential to replace petroleum based products and they are also environmentally friendly and biodegradable. Starch foams are one of the product forms obtained from starch and are a possible replacement for petroleum-based foams. Such foams have been prepared in the past but their sensitivity to humidity has remained a problem. Extensive research over the last few years has been focused on resolving the collapse of the foam at high humidity, improving the cushioning protection and developing an economical foaming process. However, these issues are still problematic and need to be resolved before such biobased foams can gain widespread entry into the marketplace.;Initially, the effects of starch feed rate, the addition of a nucleating agent, and the extruder screw configuration were studied. It was demonstrated that screw configuration plays an important role in the extrusion process and the nucleating agent talc is an effective component with which to control the cell size. An annular die was used to extrude tubular starch foams which were then sliced to yield foam sheets suitable for cushioning protection and insulation of shipping containers. A Box-Behnken statistical design of experiment (DOE) was used to optimize the properties of the foams extruded with various additives. It was found that the density, cell structure and water sensitivity of these foams were affected by the feed rates (e.g. foam composition) of the water, talc and polyhydroxy ether (PHE). The use of PHE was found to be extremely effective in minimizing water sensitivity.;Because PHE contains Bisphenol A, a suspected endocrine disrupter, another alternative polymer additive - Polyvinyl buytral (PVB) was studied. It was shown that PVB minimizes the moisture sensitivity of the foam and provided a more hydrophobic character. A statistical design experiment was used again to identify the composition and process parameters affecting the physical properties of the foams and to optimize the feed rates of the various additives. The foam extrusion process to make foam sheet was scaled down to a lab scale extruder in order to provide a more convenient technique for exploring different raw materials and formula variations.;The performance (moisture adsorption, cushion curve, and thermal insulation) of the starch foam sheets under different processing conditions and compositions were evaluated. The results indicate that these foams are classified in the moderate fragile level, implying that these foams are suitable as protective packaging of network hardware equipment, personal computers and medical diagnostic apparatus. The starch sheets have similar thermal resistance, R value, compared with polystyrene foams.;Finally, starch phosphate was synthesized using sodium trimetaphosphate and glycerol phosphoric acid by an extrusion method to examine its use as a possible electrorheological fluid or as a flame retardant additive.;The main accomplishment of this research is a starch foam sheet with a significantly high moisture resistance that can be prepared by extrusion using readily available and affordable resin additive. The process and the composition have been used to scale up the manufacturing of these foam sheets for commercial production.