PHBV coating on biodegradable plastic sheet: Effect of coating on morphological, mechanical and barrier properties

This research compares two coating techniques (dip-coating versus bar-coating) of poly(3-hydroxy butyrate-co-3-hydroxyvalerate) (PHBV) on a biodegradable plastic sheet. A blend of 30% PHBV/70% poly (butylene adipate-co-terephthalate) (PBAT) with and without chain extender was explored as biodegradable plastic sheets, while PHBV coating was used to improve oxygen and water vapor barrier properties of the sheet without affecting the mechanical performance. The PHBV coating thickness was nominally 10-15 μm (dip-coating) and 25–35 μm (bar-coating). Comprehensive characterizations showed that a PHBV/PBAT/Joncryl (30 wt%/70 wt%/0.3phr) bar-coated with PHBV [coating weight: 10–15%] exhibited ~ 48% and ~ 53% improvement in water vapor and oxygen barrier, respectively as compared to the uncoated sheet (PHBV/PBAT/Joncryl (30 wt%/70 wt%/0.3 phr)). The water contact angle of the PHBV-coated (bar-coating) polymer blend sheet (PHBV/PBAT/Joncryl (30 wt%/70 wt%/0.3 phr)) was increased to 106.6 ± 3.53°, showed hydrophobic nature. However, the %elongation at break was reduced from 651.8 ± 69.1% to 196.4 ± 48.4% due to the increased PHBV content. On the other hand, PHBV dip-coating [coating weight: 5–10%] had little effect on the water vapor and oxygen barrier properties as well as the water contact angle, as compared to the uncoated sheet. However, the %elongation at break was reduced from 651.8 ± 69.1% to 501.3 ± 168.7%. These results showed the superiority of bar-coating, mainly due to the higher coating thickness and more uniform coating, over the dip-coating technique in this research. Overall, the PHBV-coated polymer sheet developed in this research can significantly contribute to flexible packaging applications that require good barrier performance against water vapor and oxygen permeation.