Functionalized Imidazolium-based Ionomers as Effective Toughening Agents for Poly(lactic acid)

Two kinds of novel functionalized bio-based ionomers (ECO-OH-PF6, ECO-EG-PF6) were successfully synthesized through simple quatemization and ion exchange reactions from commercialized chloroether rubber and 1-(2-hydroxyethyl) imidazole, new designed PEG-based imidazole. The two ionomers were studied as toughening agents for poly(lactic acid) (PLA) by a melt blending method. Due to the different side chain structures, the two ionomers possess completely different physical properties, thus leading to totally different toughening effect for the PLA/ionomers binary blends. DSC and DMA results indicated that the ECO-EG-PF6 mainly played a role of plasticizer for PLA, leading to enhancement in cold crystallization and flexibility of PLA. The PLA/ECO-EG-PF6 (90/10) blend exhibited a high tensile strength of 63.1 MPa, an improved elongation at break up to 135% and impact strength of 4.8 kJ/m(2). However, the transparency of the PLA/ECOEG-PF6 (90/10) blend was decreased because of the unmatching refractive index (RI) of the large PEG segment with PLA and the improved crystallinity. Compared with the ECO-EG-PF6, the ECO-OH-PF6 ionomer endowed PLA with better transparency and tensile ductility. Especially, the PLA/ECO-OH-PF6 (80/20) binary blend achieved the optimal mechanical properties with the tensile strength of 47.8 MPa and high elongation at break (241%). The results of DMA and SEM suggest that ECO-OH-PF6 and PLA had a good interfacial compatibility and adhesion, which is due to the ion-dipole interactions and hydrogen bonding formed between ECO-OH-PF6 and the PLA matrix. Moreover, the PLA/ECO-OH-PF6 (90/10) blend showed a high light transmittance of 77%-87% in the visible light range, which is comparable to that of PLA.