Thermal evaluation of biocomposites made from poly (lactic acid) and cottonseed byproducts

Authors: He, Zhongqi; Nam, Sunghyun; KULKARNI, SOURABH - University Of Massachusetts; BAGHERI KASHANI, MOHAMMAD - University Of Massachusetts; NAGARAJAN, RAMASWAMY - University Of Massachusetts

Submitted to: Macromol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2025
Publication Date: 4/4/2025
Citation: He, Z., Nam, S., Kulkarni, S., Bagheri Kashani, M., Nagarajan, R. 2025. Thermal evaluation of biocomposites made from poly (lactic acid) and cottonseed byproducts. Macromol. 5(2) Article 16. https://doi.org/10.3390/macromol5020016.
DOI: https://doi.org/10.3390/macromol5020016

Interpretive Summary: Biodegradable polyester, poly(lactic acid) (PLA), has attracted considerable research interest in the last couple of decades because of its good processability and properties with other agricultural biomass materials. For valorization of cotton biomass byproducts, PLA composites with some cotton byproducts have been explored by different research groups in the last decade. As a continuation of the PLA-cotton byproducts composite research and assessment of future applications, this work investigated thermal and thermos-oxidative stability and kinetics of the PLA composites with cottonseed-meal and oil. The objectives of this study were to: 1) assess degradation mechanisms based on the activation energy values of degradation derived from the experiments, and 2) monitor the thermal decomposition processes by using thermogravimetric -Fourier transform infrared spectroscopy and analyze the roles of the individual components in thermal and thermo-oxidative degradation. The main gaseous products (i. e., carbonyl compounds, carbon dioxide, carbon monoxide, methane and water) from thermal degradation were similar between neat PLA and PLA-cottonseed byproduct composites. The emission of carbon monoxide and methane was relatively lower in the composite samples than neat PLA. This detailed study on thermal and thermo-oxidative degradation kinetics of PLA-cottonseed materials could be used to estimate the possible management and recycling of the solid waste of these materials after use.

Technical Abstract: Poly(lactic acid) (PLA) is derived from sugar-based materials. While it is a leading sustainable biopolymer, PLA has been integrated with other agricultural coproducts (e. g., lignin, protein, and starch) to reduce its cost and enhance its modulus and biodegradability. Cottonseed oil and meal are the byproducts of cotton fiber industry. In this work, 4 biocomposites were formulated with PLA, cottonseed oil, washed cottonseed meal, and plasticizing reagent glycerol with different formulation ratios. The thermal degradation behaviors were examined by thermogravimetric (TG) analysis under air and nitrogen conditions with neat PLA sample as a control. The thermal decomposition characteristic values were impacted by both the biocomposite formulation and the heating rates of 1, 2, 5 and 10 °C min-1. Results from two kinetic modeling methods that were examined indicated that the activation energy was relatively steady for the neat PLA in the whole degradation process. Generally, the low activation energy values of other biocomposites than the PLA under nitrogen conditions implied that these cottonseed byproduct constituents promote thermal decomposition of these biocomposites. However, the presence of oxygen would confound the thermal decomposition of the biocomposites as shown by variable activation energy curves with higher values under air conditions. TG-FTIR analysis revealed that the major gaseous compounds were carbonyl, carbon dioxide, carbon monoxide, methane and water which were derived from the thermal decomposition of the biocomposites.