Background: Starch-based plastics can replace fossil-based plastics in the production of one-time-use items such as plastic bags. However, the production of plastic film from starch is challenged by the formation of bubbles and uneven drying patterns, which decrease the strength and flexibility of the film.

Purpose: The objective of this research is to understand the cause of film imperfections in potato starch-based plastic (PSBP) and develop a processing protocol for the production of PSBP bags.

Methods: PSBP films are prepared by mixing potato starch (5.0 g), acetic acid (1.5 g), glycerin (1.5 g), and distilled water (100.0 g) at a temperature of 60 to 65 C for 2 to 4 minutes. Two methods for eliminating bubbles are studied: film drying under a vacuum desiccator pump (30 minutes to 24 hours) and centrifuging before drying (30, 120, and 300 seconds). Tensile strength and elongation at yield were measured according to the ASTM (American Society of Testing and Materials) standard D882.

Results: Contact angle testing to determine the surface tension of the ingredients in various combinations demonstrated use of a plasticizer and initiator together significantly increased hydrophobicity. The use of the vacuum desiccator pump was effective at reducing bubble formation but did not fully eliminate it. Centrifuging before drying for 120 seconds or more successfully produced a bubble-free film. To fabricate substantially large films, the plastic was dried over a flat metal surface coated with Teflon (polytetrafluoroethylene) for 24 hours at room temperature and natural air convection. This slow drying method produced film without uneven drying patterns. The edges of the drying platform were covered with a thin layer of coconut oil to reduce warping and cracking. The resulting film had a tensile strength of 1.57 MPa (SD = 0.24), percent of elongation at yield of 80.0% (SD = 33.0%), and a density of 1.53 g/cm3 (SD = 0.047). Plastic bags were successfully produced by ironing the edges at 165 C for 3 seconds.

Amanda Siegel

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