UV-curable bio-based castor oil-modified poly(l-lactide) with excellent adhesion and ductility

To improve the inherent brittleness of poly( l -lactide) (PLLA) and obtain a kind of UV-curable bio-based PLLA with excellent adhesion and ductility, castor oil (CO) was used to modify PLLA by a novel and simple pathway. After a series of castor oil-poly( l -lactide) oligomers (COPLLA) were prepared via the ring-opening polymerization of l -lactide (LLA) with CO as the initiator, a kind of bio-based castor oil-modified PLLA with chemical cross-linked network and PLLA branched chain (CCPLLA) was obtained through UV-initiated thiol-ene reaction between COPLLA and pentaerythritol tetra(mercaptoacetate) (PETMA) as the crosslinker. CCPLLA was respectively measured by Fourier transform infrared (FTIR) spectroscopy and extraction, showing the good UV-curing effect. With increasing the molecular weight of PLLA branched chain, the glass transition temperature of CCPLLA rose, meanwhile CCPLLA gradually transformed from an amorphous state to having crystalline behavior, which determined by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The mechanical and adhesive properties of CCPLLA first increased significantly and then slightly decreased with increasing the length of PLLA branched chain. Among them, CCPLLA-18 exhibited the best comprehensive performance such as tensile strength, ductility, adhesive property, water resistance, thermal stability and optical transmittance. Therefore, the UV-curable bio-based castor oil-modified PLLA has application potential in the field of adhesive, particularly for bonding of heat-sensitive substrates and those requiring high transparency.