Nano-scale core-shell structural casein based coating latex: Synthesis, characterization and its biodegradability

Nano-scale core-shell type particle of caprolactam-butylacrylate co-modified casein (CA-CPL-BA) bearing poly(butylacrylate) core and casein-caprolactam shell was synthesized via emulsifier-free polymerization, and was applied as the film-former in leather finishing. By utilizing potassium persulfate-sodium hydrogensulfite as a redox pair during preparing CA-CPL-BA, the grafting extent was superior to that initiated by ammonium persulfate-sodium hydrogensulfite, potassium persulfate or ammonium persulfate. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis results demonstrated that the average size of neat casein particle was around 700 nm while the resultant CA-CPL-BA latex particles were significantly decreased to about 80 nm in size. Compared with those of neat casein films, enhanced hydrophobicity and higher thermo-stability of the CA-CPL-BA latex film were confirmed by contact angle test and thermal gravimetric (TG) measurement, respectively. Meanwhile, the application performance of the leather samples finished by CA-CPL-BA was proved to be equivalent to that finished by the commercial leather finishing agent product. A possible mechanism of emulsifier-free polymerization for this system was proposed and then proved. Biodegradability tested by soil burial degradation experiments proved that CA-CPL-BA had preferable biodegradability.