Surface grafting of cellulose nanocrystals with poly(3-hydroxybutyrate-co-3-hydroxyvalerate).

Chemically modified cellulose nanocrystals (CNCs) were synthesized by grafting poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) onto CNCs via homogeneous acylation reaction between N,N-dimethyl formamide (DMF) by using toluene diisocyanate (TDI) as coupling agent and dibutyltin dilaurate as catalyst. The resulting copolymers were studied by using (1)HNMR, FT-IR, WAXD, DSC, TGA and contact angle measurements. Results showed that the copolymers kept their initial morphological integrity. Moreover, it is found that with the increase of the TDI/PHBV fractions, two transition exhibitions occurred in their thermal and hydrophobic properties, which could be modulated through controlling the lengths and grafting densities of PHBV side chains. Compared with those of neat PHBV, the crystallization of PHCN7 became easy while the crystallinity slightly decreased to 55.5%, the maximum decomposition temperature increased by 48.5°C, meanwhile the contact angle increased to 58° as compared to neat CNCs (30°).

Simultaneous improvement of mechanical properties and thermal stability of bacterial polyester by cellulose nanocrystals.

Green nanocomposites were prepared by adding well-dispersed cellulose nanocrystals (CNCs) into bacterial polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) matrix. Simultaneous enhancements on the mechanical property and thermal stability of PHBV after reinforcement of CNCs were achieved. Compared to neat PHBV, a 149% improvement in tensile strength and 250% increase in Young's modulus can be obtained for the resulting nanocomposites with 10 wt.% CNCs, more importantly, the T0, T5%, Tmax and Tf increased by 51.4, 36.5, 47.1 and 52.9°C, respectively. This was due to a combination of CNCs reinforcement in the polymeric matrix, and especially the formation of strong intermolecular hydrogen bonding interactions through achieving the excellent dispersion of CNCs in the PHBV matrix via the solvent exchange procedure, as a result, the formation of six-membered ring ester during the degradation process of PHBV was clearly suppressed.