Influence of Choline Chloride/Urea and Glycerol Plasticizers on the Mechanical Properties of Thermoplastic Starch Plastics

Jacob Staker; Sydney Schott; Riya Singh; Kourtney Collier; Gregory Druschel; Amanda P Siegel; Andres Tovar

doi:10.3390/polym16060751

Influence of Choline Chloride/Urea and Glycerol Plasticizers on the Mechanical Properties of Thermoplastic Starch Plastics

Polymers (Basel). 2024 Mar 9;16(6):751. doi: 10.3390/polym16060751.

Authors

Jacob Staker¹, Sydney Schott¹, Riya Singh², Kourtney Collier², Gregory Druschel³, Amanda P Siegel¹, Andres Tovar²

Affiliations

¹ Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA.
² Department of Mechanical and Energy Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA.
³ Department of Earth and Environmental Sciences, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202, USA.

Abstract

Bio-based plastics made of food-safe compostable materials, such as thermoplastic starch (TPS), can be designed into films that have potential to replace many non-biodegradable single-use plastic (SUP) items. TPS film characteristics, such as elongation at break and tensile strength, are largely affected by the choice of the plasticizers used in formulation. Our work identifies the mechanical properties and the chemical structural differences between TPS films made with two different plasticizer mixtures that have not yet been compared alongside one another: deep eutectic solvent choline chloride/urea (1:2) (CC:U) and glycerol with an acetic acid catalyst (AA:G). Potato-based TPS samples were formed by mixing each plasticizer with a consistent amount of potato starch and distilled water with heat. After gelation formation, the viscous TPS mixture was centrifuged to degas and extruded. Films were dried at controlled room temperature. Characterization included the tensile testing of coupons according to ASTM (American Society of Testing and Materials) standard D638, attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, X-ray diffraction (XRD), melting point (MP), and scanning electron microscopy (SEM). The AA:G films displayed significantly higher tensile strength (M = 2.04 ± 1.24 MPa) than the CC:U films (M = 0.18 ± 0.08 MPa); however, the CC:U films had higher elongation at break (M = 47.2 ± 3.6%) than the AA:G films (M = 31.1 ± 12.6%). This can be explained by the difference in functional groups, composition, and the degree of crystallinity evidenced by the FTIR, XRD, MP, and SEM results. Our findings suggest that potato-based TPS films with an AA:G plasticizer mixture hold promise for SUP applications that require more strength, while CC:U films may be more suited for wraps and bags that require flexibility. These innovations can aid to mitigate the environmental impact of harmful plastic waste.

Keywords: chemical structure; compostable plastic; deep eutectic solvent; film characterization.

Grants and funding

This manuscript is based upon research work funded by the Center for Research and Learning (CRL) MURI Program at Indiana University-Purdue University Indianapolis.