Hybrids of poly(lactic acid) (PLA) or polypropylene (PP) with microcrystalline cellulose (MCC) were created using a novel, continuous, and industrially scalable process called solid-state shear pulverization (SSSP), which exposes polymers to high shear and compressive forces near ambient temperature. For the PLA composite, this was followed with melt processing (MP) with added polyethylene glycol (PEG). We demonstrate a synergistic effect of MCC and PEG in enhancing the crystallization kinetics of PLA. For example, we were able to successfully injection mold a highly crystalline (∼35 %) commerical bottle cap in 33 sec, which as far as we know, is the highest level of crystallinity obtained at this cycle time. Neat PLA took over 10 min to reach similar crystallinity levels. Additionally, an SSSP processed 80/20 wt% PP/MCC composite was successfully injection molded into a bottle cap, which showed excellent MCC dispersion and stiffness, while maintaining of the "living hinge" character of PP.