Biodegradability and thermostability of renewable waterborne polyurethane synthesized from trihydroxyl poly(L-malic acid)/glycol based polyols and polycaprolactone diol

Abstract

Abstract A biodegradable composite polyester-based waterborne polyurethane (L-AWPU) was synthesized by coupling L-malic acid and polyethylene glycol to obtain poly(L-malic acid ethylene glycol ester, PL-A) and polycaprolactone (PCL) as raw materials. The content of PL-A in polymer system was controlled to prepare L-AWPU with excellent biodegradable and thermostability properties. Compared to traditional PCL-WPU, the introduction of PL-A not only taking naturally degradable bio-based molecular chains into WPU, but also improving the branching degree of polyurethane molecular chains and formed intramolecular crosslinking structures due to the trifunctional hydroxyl group in malic acid. When the content of PL-A reached 20 wt%, the temperature of thermal weight loss (T5%) and maximum weight loss rate (Tmax) of polyurethane coating increased from 237.93°C and 259.91°C to 333.86°C and 343.13°C, respectively. The establishment of intramolecular crosslinking structures and increase in molecular weight improved the thermal stability of polyurethane. The tensile strength and elongation at break of L-AWPU showed no significant decrease compared to PCL-WPU at PL-A content of 20 wt%. The influence of PL-A content in polymer system on biodegradability of L-AWPU was specifically analyzed. The degradation rates of L-AWPU in 0.6% lipase PBS buffer solution and soil for 28 days reached 45.95% and 55.55% at PL-A content of 40 wt%, which were 1.71-fold and 1.52-fold increased compared to PCL-WPU. Containing natural bio-based molecular chains and trihydroxy crosslinked structures, L-AWPU showed excellent thermal stability and biodegradability, making it suitable for environmentally friendly and recyclable coatings.