Graft polymerization of epsilon-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(epsilon-caprolactone)grafted cellulose nanocrystals (CNCs) obtained by ring opening polymerization. The most significant variables on the grafting ratio of poly(epsilon-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: epsilon-caprolactone: CNCs mass ratio (monomer content) of 14: 1, polymerization temperature of 130 degrees C and polymerization time of 26.5 h. It was shown that poly(epsilon-caprolactone) 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(epsilon-caprolactone)-grafted nanocellulose was shown to be much more hydrophobic compared to unmodified cellulose nanocrystals.