FULLY GREEN STARCH-BASED THERMOCHROMIC COMPOSITES
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Green thermochromic (TC) materials are an emerging field of research. Recently, researchers have sought to develop “greener” alternatives by replacing one or more petroleum-based plastic and toxic chemical components of intrinsic or doped thermochromic materials. In this study, a fully green thermochromic system was developed using coaxial electrospinning to form a nontoxic, binary thermochromic dye-based core and poly (lactic acid) (PLA) sheath composite fibers. These fibers were integrated into a crosslinked waxy maize starch resin to form composite films. Chlorophenol red (CPR), a sulfonephthalein dye, was used to form an aqueous binary dye which was integrated, as core, into PLA fibers for the purpose of shielding the dye from other competing chromic interactions and pre-mature environmental degradation. These thermochromic fibers exhibited a reversible color shift in which the fibers transitioned from a deep red color to a bright yellow color between -5°C and 0°C, respectively. The colorimetric properties of the CPR dye and the fiber were characterized using a colorimetry. The color differences, ∆E, of the TC transition of the CPR dye and the electrospun TC fiber membrane were determined to be 9.68 and 2.17, respectively, with the shielding of PLA attributed to the smaller color difference exhibited in the fiber. The presence of the CPR dye inside the fiber was confirmed using confocal microscopy. The nonporous, wrinkled morphology of the TC fibers was analyzed using SEM and Cryo-FIB SEM. The wide distribution of fiber diameters, a characteristic of electrospinning, in the TC fiber membrane led to a variance in the chemical composition of the fiber which was analyzed using UV-Vis and ATR-FTIR analyses. The thermal properties of the TC fiber membrane and composite were investigated using DSC and TGA. The tensile properties of the composite were investigated. The Young’s Modulus was found to be higher in the composite at 8.01 MPa, while the ultimate tensile stress, elongation, and toughness were higher in the starch resin at 7.11 MPa, 501%, and 2188 kJ/m3, respectively. Future applications for this technology exist in SMART frozen food packaging due to its transition temperature of around 0°C. There are opportunities to adjust the transition temperature and expand this technology to other applications such as biocompatible systems, temperature monitoring systems for infants, and other potentially-ingestible plastics in novelty items.