Design of low cost waterborne polyvinyl alcohol coatings using plasticizer polyethylene glycol to minimize the residual solvent and coating defects

Abstract

AbstractWaterborne coatings provide nontoxicity and flame‐retardance but exhibit inefficient drying. The literature on drying enhancers is limited for the want of residual solvent minimization study. Here, we use polyethylene glycol‐6000 (PEG), a low cost biodegradable plasticizer, to minimize the residual solvent in polyvinyl alcohol (PVA)‐water coatings. Coatings were prepared at different PEG loadings (0, 0.50, 1.00, 2.50, 5.00, and 7.50 wt%) and initial conditions. The maximum drop in the residual solvent was 87% at 0.50 wt% PEG loading in the coating of initially 5% PVA and 1000 μm thickness. The effect of doubling the initial wet thickness from 500 to 1000 μm was first examined. The minimum residual solvent significantly reduced from 1.30% to 0.59%, and occurred at the same PEG loading of 0.50 wt%. However, the drying time increased and drying rate slowed down remarkably. SEM results also revealed that at the optimum PEG loading a smooth and dense coating was obtained. Thermogravimetric analysis/derivative thermogravimetric studies showed improved thermal stability and differential scanning calorimetry showed little decrease in Tg at optimized PEG loading. When the initial polymer concentration was doubled from 5% to 10%, the optimum PEG loading lowered from 0.50 to 0 wt%. Simultaneously, a marked increase in the minimum residual solvent from 1.30% to 3.27% occurred, caused by the hydrophilicity of PVA and enhanced solution viscosity. On comparison with a fluorosurfactant (FS) modifier, PEG yields significantly better maximum reduction in residual solvent at substantially lower optimum loading by employing higher wet film thickness. Furthermore, PEG is significantly lower in cost and environmentally friendly than FS.