Coating performance and rheological characteristics of novel soybean oil-based wax emulsions

Abstract

Aqueous emulsions of soybean oil-based coating materials consist of ethylene glycol and propylene glycol mono- and di-esters of stearic acid (EGMD and PGMD, respectively) and compound emulsions (mixtures of EGMD emulsion with four commercial polymer emulsions) were formulated and tested for paperboard coating. Paper coated with compound emulsions had excellent water resistance and grease resistance. With EGMD accounting for as high as 60% of the emulsion’s solid content, 5-min Cobb value of about 1.0 gsm (gram per square meter) was achieved. Increased number of drawdowns (coating) significantly improved water and grease resistance of the coated papers. With three-drawdown and coat weight of 14.93–23.00 gsm, 5-min Cobb value of less than 2 gsm and oil penetration of less than 2% were achieved. Greater heat exposure during drying resulted in better water resistance. Increasing the drying temperature from 100 to 200 °C for 30 s reduced the 5-min Cobb value of papers coated with PGMD compound emulsions from 34.1 to 1.1 gsm. The addition of cross-linking agent, zinc ammonium carbonate (ZAC), in the emulsions improved water repellency but not grease resistance. The effect of different emulsifiers on coating performance, rheology and stability of W/O and W/O/W PGMD emulsions were also investigated. The yield stress of cetyltrimethylammonium bromide (CTAB) based emulsions (1.61–21.32 Pa) were much higher than those of Tween 80 based emulsions (0.023–0.066 Pa). Both the W/O and W/O/W emulsion had higher viscosity than the compound emulsions. The compound emulsions had comparable surface energy but lower gluability compared to the commercial emulsions.