In situ Plasticization of Starch and Coblending with Bio-based Polyesters: An Investigation into The Process Parameters for Continuous Thermoplastic Starch Co-Polyester Manufacturing

Abstract

Today’s industry seeks to engage in change which provides both environmentally and economically sustainable manufacturing solutions. The plastic industry’s current challenge is to produce bio-based polymers which offer ease of processing, excellent stability as well as mechanical and physical properties similar to those found in olefinic polymers. The objective of this research is to determine the parameters under which specific starches could be destructured (plasticized), chemically modified, and transesterified in the presence of polyester resins to produce stable starch copolyester polymers. The goal is to provide insight about the variables controlling the process, as well as develope a technology to enable sustainable thermoplastics.

The starch-resin copolymer produced in patent WO 2013116945A1 Wolff (Wolff, 2016), while viable in a batch reactor process, was not viable on a commercial scale. Examinations were performed using CW Brabender (CWB) 60cc internal mixer and associated software, which allowed for the capture of stock (material) temperatures, torque, and specific energy, in real time. The information gathered offers insight into migration from batch reactor to extrusion processing.

The ideal parameters required for the gelatinization and plasticization of Dent cornstarch (the control) were found to have a correlation between moisture, temperature, mechanical energy and the presence of alternative plasticizers, depending on processing temperature. These parameters were used to evaluate several different starches, with various levels of chemical modification and/or ratio of amylose:amylopectin, and found three starches which quickly destructured and plasticized. Results determined that commercial viability required the addition of free radical initiators (peroxide) and a grafting agent (maleic anhydride), in tandem with the specific moisture levels within the starches.

It was concluded that reaction mechanisms can be driven by the relationship between free radical initiators and the amylose:amylopectin ratio within the starch, as well as the levels of maleic anhydride (MAH) added, while taking into consideration the starch’s initial level of moisture. Further analysis of the samples produced, with respect to their physical and chemical properties, could offer further insight into achieving properties similar to olefinic polymers, yet on a commercial scale.