Influence of alkyl side chain length in PLA polyols on the mechanics of bio-based waterborne polyurethane synthetic leather

Sustainability is an important direction for polyurethane synthetic leather, polylactide polyols are favored due to their high bio-based content and biodegradability. However, polyurethanes containing segments formed from polylactide polyols are hard and brittle, which limits their application. To address this, a strategy was proposed to improve mechanical properties of bio-based waterborne polyurethane (BWPU) through introducing alkyl side chains into molecule of polylactide diols (PLA-OH). PLA-OH with molecular weight 1000 g/mol were synthesized by ring opening polymerization (ROP) of l -lactide, initiated by diols with different alkyl side chain lengths (n-butyl, n-hexyl, n-octyl). A series of BWPU with various alkyl side chain lengths were prepared by using PLA-OH, bio-based poly(oxy-1,3-propanediyl) (PO 3 G), isophorone diisocyanate, sodium polyethersulfonate and 1,4-cyclohexanediol as main components. The influence of the alkyl side chains of PLA-OH on the properties of BWPU was studied in detail, including hydrogen bonded, thermal properties, mechanical properties, water contact angle, stress relaxation and creep behavior. The results showed that the introduction of alkyl side chains significantly improved the mobility of polyurethane segments, the relaxation rate of the BWPU was accelerated and the creep recovery rate was significantly increased. When the side chains of polylactide diols is n-hexyl, PLAC6-BWPU achieves an optimal balance of low modulus (16.5 MPa), high elongation at break (1043%), and high strength (10.2 MPa). The synthetic leather surface layer prepared with PLAC6-BWPU exhibits excellent abrasion resistance and flex resistance, enduring over 50,000 rubbing cycles and more than 30,000 flex cycles without surface damage or cracking, making them highly suitable for applying in high-performance synthetic leather manufactures.