Molecular Entanglement Facilitated Improvement of Thermal Stability of Cellulose Diacetate

As a renewable and degradable biomass material, cellulose diacetate (CDA) has significant development potential and has gained widespread interest from researchers. However, its poor thermal stability at high temperatures limits its practical use in the extrusion process and restricts its applications in other fields, such as high-heat airflow filters, battery separators and special textile materials. To enhance the thermal stability of CDA, three heat-resistance additives, i.e., polyphenylene sulfide (PPS), polycarbonate (PC) and polyimide (PI), were introduced to synthesize PPS/CDA, PC/CDA and PI/CDA composite materials through melt extrusion. The incorporation of three heat-resistant additives increased the glass transition temperature (T_g), initial melting temperature (T_mⁱ) and final melting temperature (T_m^f) of the composites, and it reduced the heat loss at 195 °C. After conducting the isothermal thermogravimetry test for 3 h at 215 °C in an air atmosphere, the weight loss of PPS/CDA, PC/CDA and PI/CDA composites was 4.6%, 4.1% and 3.7%, respectively, which was 5.1% lower than that of pure CDA. Morphology characterization tests using a 3D digital microscope and a field emission scanning electron microscope (FESEM) revealed the compatibility order with CDA as the following: PC > PPS > PI. Additionally, Fourier transform infrared spectroscopy (FT-IR) disclosed that hydrogen bonds were formed between heat-resistant additives and CDA molecules, and the carbonyl groups in CDA showed conjugation and hyperconjugation effects with the benzene rings in the additives. Therefore, the enhanced thermal stability of CDA composites can be attributed to the molecular entanglement and crosslinking between additives and CDA molecules.