(181l) Devitrification and Crystallization of Cellulose-Filled Polylactic Acid Toward Real-World Applications: Solid-State Shear Pulverization (SSSP)

Even though polylactic acid (PLA) continues to be a bio-based and biodegradable polymer of significant interest to both industry and the scientific community, the application range of PLA is limited due to its inherent behavior in practical, commercial production settings. Its glass transition temperature (T_g) is just above the ambient temperature, which leads to drastic changes in properties at higher application temperatures, and its grudgingly slow crystallization kinetics lead to products with inconsistent mechanical properties and appearance. Comonomers, additives, and fillers used to circumvent these inherent issues are often petroleum-based and not sustainable. Solid-state shear pulverization (SSSP) is a continuous, scalable, and environmentally benign polymer processing methodology, which has been used previously to disperse fillers in nanocomposites. This paper presents how neat PLA and PLA/ cellulose composites can be effectively processed with SSSP for real-world, sustainable commodity applications. When applied to neat PLA, SSSP imparts chain defects and branching, which serve as heterogeneous nucleation sites in the polymer and promotes the formation of a rigid amorphous phase. Effects of devitrification and cold-crystallization are suppressed with induced melt-crystallization, thereby minimizing the physical deformation of the material. Compounding cellulose-based nanofillers with SSSP is also found effective due to the tunable nature of the low-temperature shear and compression mechanism involved, showing superior filler dispersion over traditional melt compounding. Microscopy is employed to evaluate the morphology at different length scales. Thermomechanical characterization involve dynamic mechanical analysis and calorimetry. Physical appearance of the specimens is quantified by colorimetry and spectrophotometry. The processing-structure-property investigation gives insight into how an entirely bio-based PLA materials can further replace traditional plastic materials in a wider range of applications.