Improving the Shear and Tack Strengths of Chlorinated Poly(propylene carbonate) through Chain Extension with Polylactic Acid for Biodegradable Hot Melt Adhesives

Hot melt adhesives are commonly used in packaging and various types of products due to their affordability and convenience. Despite the use of different polymers for preparing hot melt adhesives, achieving both high performance and biodegradability in these adhesives remains a significant challenge. Herein, we fabricate copolymers of chlorinated poly(propylene carbonate) (CPPC) and polylactic acid (PLA) (CPPC-PLA) through a chain extension reaction that involves 4,4′-diphenylmethane diisocyanate (MDI) as the chain extender. By adding PLA to the CPPC chains, the copolymers' molecular weight increases, and their thermal stability improves without compromising their biodegradability. Additionally, CPPC-PLA copolymers with various degrees of chain extension are prepared by modifying the MDI concentration. When more MDI is added, the mechanical properties, storage modulus (G′), and loss modulus (G″) of copolymers are improved. More importantly, the introduction of 7 wt % MDI to CPPC-PLA copolymers results in a significant increase in both tack and shear strengths, with improvements of 108 and 134%, respectively. CPPC-PLA copolymers have the advantage of being biodegradable while also delivering exceptional performance, enriching the category of hot melt adhesives and opening the door for potential applications in other fields.