Improved molecular chain constraint of poly (propylene carbonate) composites by the synergistic effect of poly (vinyl alcohol) and carbon nanotubes

Poly (propylene carbonate) (PPC), an amorphous polymer copolymerized from exhaustless carbon dioxide and propylene epoxide, is attracting more and more interest for its biodegradability and benefit for alleviating the greenhouse effect. However, its low glass transition temperature (T-g), around 20-40. C, and poor mechanical properties limit its industrial application. To enhance its T-g and mechanical properties, based on inter-macromolecular complexation, one-dimensional rigid fillers, hydroxylated carbon nanotube (CNT) and poly (vinyl alcohol) (PVA) with rich hydroxyl groups were separately or simultaneously introduced into PPC to constrain the mobilization of PPC molecular chains via hydrogen bonding in PPC-CNT and PPC-PVA, as well as the physical entanglement of CNT network. The effects of mixing ways on the morphology and performances of the final PPC based composites were studied. When premixed with PPC, CNT particles could disperse quite well in PPC matrix under the powerful ultra-sonic vibration and achieve the uniform distribution after the subsequent melting process, thus effectively decreasing the total free volume fraction of the system, i.e. making CNT particles well exerting their restriction effect on PPC molecular chains. In this way, T-g of the ternary composite with 2% CNT increased to 49.4 degrees C, and the mechanical strength enhanced to 62.7 MPa, both higher than the values of PPC/PVA composite and other ternary composites obtained via other mixing way.