Cellulose nanocrystal assisted dual-modification of starch and subsequent polyvinyl alcohol blends

A cellulose nanocrystal (CNC) based dual-modification was explored as a means to achieve better film properties. Starch was mixed with 0.5 wt% CNC followed by oxidation with NaClO, then esterified with CNC and vinyl acetate. The dual-modified starch showed an increased degree of substitution, disrupted morphology, and decreased crystallinity. A remarkable catalytic effect of CNC was found with 0.3 wt% CNC in esterification, where the degree of substitution was 2.7 times higher than that of dual-modified starch without CNC. The best modifying condition was selected as 0.3 wt% CNC and 7.0 wt% vinyl acetate. The film generated from dual-modified starch, polyvinyl alcohol (PVOH), and glycerol generated a smooth surface and compact structure. Moreover, the films based on dual-modified starch had improved transparency, thermal stability, and tensile strength compared to that of native starch or oxidized starch. The highest tensile strength of film was obtained at 25.7 MPa with 30 wt% PVOH. The film showed the highest water resistance with a contact angle of 113°.