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Starch acetate nanocomposite foams with four organoclays (Cloisite 30B, 10A, 25A, and 20A) were prepared by melt‐intercalation methods. The structural properties, thermal behaviors, and mechanical properties were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry analyses (TGA), and Instron universal testing machine. XRD results indicated that the intercalation of starch acetate into the nanoclay layers occurred for all four clays. The extent of intercalation depended on the type of organoclay and was exhibited in the sequence of Cloisite 30B >10A >25A >20A. SEM results indicated a decrease in cell size in the starch acetate foam matrix with the addition of nanoclay. Glass transition temperature (Tg) and onset temperatures of thermal degradation increased with the addition of organoclay into the starch acetate matrix. The incorporation of organoclays decreased significantly the compressibilities of starch acetate nanocomposites and did not substantially affect their spring indices.

ABSTRACT:The extrusion of polysaccharide-based polymers, such as starch acetate, is quite different from that of ordinary synthetic polymers. To understand how the physiochemical properties of blowing agents affect plasticization and expansion processes, starch acetate was extruded with water, ethanol, and ethyl acetate. The studied properties and factors were the evaporation rate, surface tension, boiling point, solubility index, latent heat of vaporization of blowing agents, extrusion temperature, and nucleating-and blowing-agent concentrations. The properties of the blowing agents and operating conditions affected the solubility of the matrix polymer, the nucleation process, and cell growth, which affected the foam density and specific volume. A high temperature increased the cell density and specific volume when water and ethanol were used because a high temperature increased the solubility of starch acetate in water and ethanol and promoted nucleation. Ethyl acetate already had high solvency to starch acetate and a high evaporation rate. A high temperature reduced the melting strength, thereby reducing the cell density and specific volume. Water evaporation was greater, despite a high latent heat of evaporation (hr) and boiling point, than the average volumes of ethanol and ethyl acetate that evaporated. The blowing-agent efficiency was a function of the solvency, blowing-agent evaporation rate, and operating conditions.

There are three consecutive processes involved in extrusion foaming: extrusion (mixing and melting), cell initiation and cell growth, and cooling. Extrusion of polysaccharide‐based polymers with a single blowing agent is limited by cost, safety, and the various physicochemical requirements of the three processes in extrusion. Balancing or comprising between requirements of various processes should be maintained in the optimization process. Secondary blowing agents such as pentane, ethyl acetate, and sodium bicarbonate were used in water and ethanol‐based foaming processes. The introduction of secondary blowing agents of low surface tension or, in other words, of high evaporation rate, such as pentane and ethyl acetate, increased cell density while the addition of high surface tension secondary blowing agents reduced cell density. The specific volume of foams can be increased by secondary blowing agents by increasing nuclei density, increasing solvency, and increasing the amount of vaporized blowing agent.

The fabrication of solvent-free ionic conductive elastomers with high stretchability and degradability is highly desired yet challenging now. Here, solvent-free ionic conductive elastomers were fabricated by the polymerization of acrylic acid (AA)/1-vinylimidazole (IM)-type deep eutectic solvent. An ion pair between AA and IM was formed in the deep eutectic solvent during fabrication. Dynamic bonding including hydrogen bonding and ionic bonding between AA and IM attracted the polymeric chain crosslinking into a liquid-free polymer elastomer without extra cross-linkers. As-prepared conductive elastomers exhibit high transparency (91.4%), ultrahigh stretchability (1464%), fast autonomous self-healing, and degradability. Furthermore, the deep eutectic solvent-based elastomers could be easily attached to human skin and human activities could be detected with high sensitivity. The resulting ionic conductive elastomer with transparency, adhesiveness, self-healing ability, and degradation would meet the Sustainable Development Goals and have potential applications for wearable devices.