Colloidal properties and cytotoxicity of enzymatically hydrolyzed cationic starch-graft-poly(butyl acrylate-co-methyl methacrylate) latex by surfactant-free emulsion polymerization for paper coating application

In this work, graft copolymerization of n-butyl acrylate (BA) with methyl methacrylate (MMA) onto enzymatically hydrolyzed cationic cassava starch (CCS) was carried out in a semi-batch emulsion polymerization and the latexes were used as a binder for paper sizing agent. The purpose of this work was to substitute a portion of the BA/MMA by CCS (from 0 to 20 wt.%) in the copolymer and to investigate the consequent effects on the properties of the latex, films and coated paper (e.g., colloidal properties, cytotoxicity and water absorption). Cytotoxicity of polymer films, CCS and alpha-amylase was evaluated in human keratinocytes cells (HaCaT) for 24 and 96 h. The results show that the grafting efficiency decreased as the concentration of CCS increased. Nuclear magnetic resonance (H-1-NMR) and Fourier transform infrared spectroscopy (FT-IR) analyses revealed successful grafting copolymerization of BA and MMA onto CCS. Polymer films and CCS solutions were not cytotoxic towards HaCaT cells until 24 h of incubation. Nevertheless, after 96 h of incubation, cell viability was below 70 %, which is an indication that the polymer films with 10 and 20 wt. % of CCS were cytotoxic after longer incubation times. The cell viability was lower as the concentration of CCS in the film increased. Water absorption of polymer films and coated paper showed a direct relationship with respect to both the content of CCS employed and the grafting efficiency. These results demonstrate the utility of enzymatically hydrolyzed cationic starch-graft-polymer as coating binders and as sizing agents for the paper and packing industry.