Toughening of Cellulose Diacetate Through Microphase-Controlled Blending of Poly(ε-Caprolactone)−Poly( N -Vinylpyrrolidone) Block Copolymers

Cellulose diacetate (CDA) is a biobased plastic with high strength and marine biodegradability; however, its applications are limited by intrinsic brittleness. In this study, a series of block copolymers (BCPs) composed of poly(ε-caprolactone) (PCL; A block) as a soft segment and poly(N-vinylpyrrolidone) (PVP; B block) as a CDA-compatible segment were synthesized as toughening additives for CDA. Incorporation of the PVP segment into the BCPs suppressed macrophase separation of PCL, leading to the formation of dispersed PCL domains with radii of 4.4−19.4 nm. The mechanical properties of the CDA films were improved by adding 10 wt % BCPs, with toughness increasing 4.09- to 12.4-fold over neat-CDA depending on BCP architecture. BAB- and AB2-type BCPs were more effective than AB-type BCPs, correlating with their ability to generate smaller domains and reduce the interdomain spacing (ligament thickness). In particular, significant toughness enhancement was observed when the ligament thickness was reduced to <60 nm.