Preparation of poly (propylene carbonate)/graphite nanoplates-spherical nanocrystal cellulose composite with improved glass transition temperature and electrical conductivity

Poly(propylene carbonate) (PPC) is a new attractive biodegradable polymers synthesized from inexhaustible carbon dioxide and propylene epoxide, but shows low glass transition temperature (T-g) and poor mechanical properties, which greatly limits its practical applications and industrialization development. To improve T-g and the practicability of PPC, in this work, graphite nanoplates-spherical nanocrystalline cellulose (GNP-SNCC) hybrids, which were bonded by both physical and chemical forces, were prepared by ball milling from graphite and microfibrillated cellulose, and the structure formation as well as properties of PPC/GNP-SNCC composites were studied. The results showed that the improved interfacial interactions between GNP-SNCC and PPC, and the rigid two-dimensional structure of GNP-SNCC were beneficial for the constraint of PPC molecular chains, thus significantly improving T-g and the mechanical properties of PPC matrix, e.g. T-g increased from 34.0 degrees C of neat PPC to 51.3 degrees C, and the yield strength increased from 27 MPa to 52.8 MPa. Moreover, facilitated by SNCC, a conductive pathway of GNP was effectively constructed, leading to the great increase in the electrical conductivity of PPC/GNP-SNCC composite. The composite with 10 wt% (5.71 vol%) graphite showed 9 orders of magnitude higher than that of PPC/graphite composite with the same graphite content, and the percolation threshold was drastically decreased from 15 to 5 wt% (8.56-2.85 vol%).