Effect of Beeswax on hydrophobicity, moisture resistance and transparency of UV curable linseed oil based coating for compostable paper packaging

Abstract

Compostable bio-sourced moisture barrier coating is among the most emerging material alternative to non-degradable single use plastics liner in paper packaging applications. In the current work, highly unsaturated linseed oil is epoxidized and acrylated to form UV curable bio-acrylate resin (Acrylated Linseed Oil) to be used as bio-coating material for paper substrate to improve its barrier properties. Beeswax has been proposed as an excellent barrier to water vapour permeability, the hydrophobicity being imparted by esters of long chain fatty alcohols, acids and long chain alkanes present within. Beeswax is incorporated into AELO resin to enhance the water and moisture barrier property of the coating due to its hydrophobicity and food compatibility. The addition of beeswax has significantly reduced the Water Vapour Transmission Rate (WVTR) to 20 g/m2.day.atm while improving the Water Contact Angle (WCA) to 111° for 10 wt% beeswax loading. Further, the WCA remains above 90° even after 50 cycles of abrasion revealing the durability of the coating. The hydrophobicity is further reinstated by the SEM images which show microscale roughness imparted by uniformly dispersed beeswax. Beeswax thus improves hydrophobicity both by virtue of its composition and the surface roughness imparted. Improved transparency (>95% UV–vis transmittance), higher thermal stability (T5 >250 °C, T10 >300 °C), and reasonable glass transition temperature of the bio-coatings reveals its wide application in the field of packaging. The compostability of the coating in soil and paper repulpability after removal of the coating, both explored its potential in paper-based food packaging by replacing single use plastics.