Promotion by copper (II)-modified montmorillonite of the drying property of oriental lacquer sap

Abstract

A series of hybrid lacquer saps were prepared by adding copper(II)-modified montmorillonite (Cu(II)-MMT) into the raw lacquer. Cu(II)-MMT can effectively accelerate the polymerization of urushiol over a wide humidity range. Addition of 5 wt% of Cu(II)-MMT suspension (concentration, 5 wt%) into the raw lacquer sap made its touch-free drying time and hardened drying time decrease from each >36 days and >36 days to 6 days and 9 days at 36 °C and 50% relative humidity and from each >120 h and >120 h to 5 h 40 min and 23 h 30 min at 34 °C and 65% relative humidity, respectively. GPC tests proved the acceleration of the urushiol polymerization. Based on the results from UV–vis, FT-IR and NMR, the urushiol polymerization catalyzed by Cu(II)-MMT is similar to that catalyzed by laccase. However, a distinct difference is that the degree of crosslinking of lacquer films increased due to the formation of SiOC and AlOC bonds between urushiol and MMT in the drying process. Furthermore, addition of Cu(II)-MMT also improves the gloss and thermo-stability of lacquer films.