Novel Green Polymer Composites: Major Enhancements in the Crystallization Kinetics of Poly(lactic acid) and Mechanical Properties of Polypropylene Created via Solid-State Shear Pulverization

P.J. Brunner, J.M. Torkelson, N. Kane
Northwestern University, US

Keywords: poly(lactic acid), polypropylene, microcrystalline cellulose, crystallization, mechanical properties


Hybrids of polylactide (PLA) or polypropylene (PP) with microcrystalline cellulose (MCC) were created using a continuous, industrially scalable, and environmentally benign process called solid-state shear pulverization (SSSP). The PLA composite was subsequently melt-processed (MP) with added polyethylene glycol (PEG). We demonstrate a synergistic effect of MCC and PEG in enhancing the crystallizability of PLA. A sample made by addition of 1 wt% MCC to PLA via SSSP followed by MP with 10 wt% PEG was successfully injection molded into a bottle cap (no distortion in the part) in a cycle time of ~33 seconds, indicating the development of a high level of crystallinity. Differential scanning calorimetry demonstrated the part was ~35% crystalline, which, as far as we know, is the highest level of crystallinity obtained at this cycle time. Additionally, SSSP successfully dispersed MCC in PP leading to major enhancements in the mechanical properties. For example, upon addition of 20 wt% MCC, the tensile strength of PP increased 100%. Furthermore, this SSSP processed material was successfully injection molded into a bottle cap, which showed increased stiffness, excellent dispersion of MCC, and maintenance of the “living hinge” character of PP.