The rapid development of petroleum-based plastics has brought great convenience to our life, but the non-biodegradable wastes raised a tremendous effect on the environment. Cellulose is the most abundant renewable natural polymer material with various renewable sources, low price and high mechanical strength, but poor processing property. PLA also has excellent biocompatibility, good mechanical properties, barrier properties, and relatively low price, which owns a wide range of potential industrial applications. While the poor compatibility makes cellulose hard to disperse in PLA matrix, thus hinders the properties of the composites.
The surface modification of nano particles is very important in nanotechnology. Grafting from (GF) and grafting to (GT) are two main methods to prepare surface modified nanoparticles like nanocellulose crystalline (NCC) grafted with polylactic acid (PLA) chains. In the GF method, the NCC can get high grafting degree but short side chains to improve its compatibility with the polymer matrix. The GT method can help obtain long side chains to increase the chain entanglements but owns low grafting density. To take the advantage of both methods, a mixed modification method combining GT and GF methods was put forward to synthesize comb-like NCC-g-PLA (NP) as a macromolecular modifying agent of PLA. Firstly, GT Method was used to obtain long side-chain NP to improve chain entanglement. Secondly, the GF method was applied to obtain NP-g-PLA (NPL) and NP-g-PDLA (NPD) with additional short side chains to improve its dispersion and compatibility in the PLA matrix. The products showed an enhanced nucleation effect, the degree of crystallinity (Xc) of PLA composites increased almost four times with only 1 wt% NPD or NPL. What's more, the storage modulus and loss modulus of the composite melts also increased with 1 wt% NPL or NPD. The NPD/PLA shows a higher effect than NPL/PLA owning to stronger interaction originated from the stereocomplex (SC) network of PLA matrix with PDLA short chains in NPD. The resulted materials are promising for heat-resistant such as injection molded hot-food packaging and coffee/tea cups and normal environmentally friendly packaging applications such as mulching films and disposable containers etc.
 

Nanocellulose crystalline；Polylactic acid; Grafting to; Grafting from