Sugar-Core Synthesized Multibranched Polylactic Acid and Its Diacrylate Blends as a UV LED-Curable Coating with Enhanced Toughness and Performance

Abstract

Exploring the application of biodegradable/bioplastic coating material for eco-friendly and sustainable packaging is one of the global challenges being tackled. In this context, we propose (i) the synthesis of multibranched polylactic acid (PLA) using table sugar mainly composed of sucrose as a core initiator, and (ii) a model formula for sugar-based PLA (suPLA) and its diacrylate blends as a UV LED-curable coating. The synthesis of suPLA through ring-opening polymerization (ROP) was optimized by sugar: l-lactide (L-LA) molar ratio, temperature, and reaction time. suPLA, with a Mw of ∼1000 g/mol, was obtained with a maximum yield of around 80%. To establish a model UV LED-curable bioplastic-based coating, the suPLA with different content was formulated in tripropylene glycol diacrylate (TPGDA) as a diluent monomer. The influence of curing time (0–60 s) on double bond conversion for turning the liquid coating to a solid film of the suPLA/TPGDA blending system was assessed. Aiming to validate the influence of the curing degree, changes in the chemical function, thermal stability, glass transition temperature, crystallization temperature, and enthalpy were also characterized. By increasing the suPLA content, the tensile tests on the UV LED-cured suPLA-TPGDA films showed significant improvement in terms of toughness. The coating surface morphologies and optical properties (i.e., gloss value, color difference, yellowness, and whiteness indexes) were also determined. It is worth noting that the sugar molecule and multibranched structure play an important role in moisture absorption. The biodegradation test demonstrated that the UV LED-cured suPLA-TPGDA film exhibited biodegradation phenomena, as analyzed from CO2 production, physical appearance, changes of mass, chemical functions, and thermal stability. The current study showed that the suPLA and its diacrylate blends are promising biobased, printable, and UV LED-curable coating prototypes to create a tough film for a sustainable packaging approach in the future.