Graft polymerization of ε-caprolactone to cellulose nanocrystals and optimization of grafting conditions utilizing a response surface methodology

The objective of this study was the grafting, statistical polymerization optimization, and subsequent characterization of poly(ε-caprolactone)grafted cellulose nanocrystals (CNCs) obtained by ring opening polymerization.The most significant variables on the grafting ratio of poly(ε-caprolactone) as obtained from the response surface methodology (Box-Behnken design) were monomer content, polymerization temperature, and polymerization time.It was shown that an experimental grafting ratio of 134.23% closely matched the predicted rate of 138.57%, within an R 2 =99.79% under the proposed optimized conditions.The optimum operating conditions obtained from the response surface methodology were the following: εcaprolactone: CNCs mass ratio (monomer content) of 14:1, polymerization temperature of 130°C and polymerization time of 26.5 h.It was shown that poly(εcaprolactone) successfully grafted onto the cellulose nanocrystals while cellulose nanocrystals maintained their original morphology and their native crystallinity.Although, the surface coverage was relatively low, the poly(ε-caprolactone)-grafted nanocellulose was shown to be much more hydrophobic compared to unmodified cellulose nanocrystals.