Study On Toughening Poly(Lactic Acid)with Functionalized Elastomeric Ionomers

Increasing concern about global energy shortage and environmental pollution have stimulated intensive research interest in developing eco-friendly plastic materials from renewable feedstocks.Polylactic acid(PLA),a fully renewable and biodegradable polyester,enjoy a great deal of attention in recent years because of its good mechanical strength,high transparency,and suitability for a variety of processing methods etc..PLA has already been used as substitutes for petroleum-based plastics in single-use and disposable applications owing to its sustainable advantages.However,poor toughness of PLA greatly limit its application in wider and high value-added range areas including automotive,electronics and medical products,etc..To effectively broaden the application fields of PLA,it is of great significance to develop effective toughening agents for toughening PLA by designing innovative elastomers with excellent performance poly(lactic acid).In this thesis,we developed a series of novel ionomers with different imidazolium-based cations as effective toughening agents for PLA to achieve high performance PLA-based materials.Moreover,based on the functionalized ionomers,we also proposed an integration strategy combining reactive compatilization,non-covalent interaction and dynamic vulcanization for preparing high-tough PLA blends.The main achievements are shown as followed:1.A series of elastomeric ionomers functionalized with different imidazolium-based cations were synthesized by a facile and effcient quaternization reaction from commercial bromobutyl rubber(BIIR)and different functionalized imidazoles including 1-ethylimidazole,N-(2-hydroxyethyl)imidazole,newly designed 1-(11?-hydroxyundecyl)imidazole,and N-[3-(1H-imidazol-1-yl)propyl]-hexanamide of post-chemical reaction.These i-BIIR ionomers showed balanced physical performance,high thermal stability and adjustable viscosity,which were suitable for using as toughening agent for PLA.2.Blending PLA with the i-BIIR ionomers were prepared by simple melt extrusion method to achieve highly toughened sustainable blends.The influence of the cationic structure of these ionomers and blend ratio on the compatibility and mechanical performance of the blends was thoroughly investigated.The introduction of polar hydroxyl groups with varied alkyl lengths or an amide group into the imidazolium cation of the i-BIIRs markedly improved the compatibility and impact toughness of the PLA/i-BIIRs blends,relative to those of the pure BIIR and the i-BIIR ionomers without functional polar groups.These PLA/i-BIIRs ionomer blends exhibited an excellent flexibility-stiffness balance,in which the highest elongation at break up to 300%was achieved with a slightloss in stiffness.An impressively high impact strength of 17.1k J/m~2 was achieved for the PLA and i-BIIR-11-OH(80/20)blends,and this impact strength was almost 6 times that of the neat PLA.3.Based on these unique functionalized elastomeric ionomers,we developed a novel integration strategy to obtain high-performance PLA based blends by combination of synergistical multiple non-covalent bond interactions(hydrogen bonding and ion-dipole interactions etc.),in-situ reaction blending and melt dynamic vulcanization.can effectively enhance interfacial compatibility,and achieve super toughness PLA-based blend materials.The effects of ionic groups,vulcanizing agents and blending ratios on the compatibility,morphology and mechanics of blends were systematically studied.Dynamic mechanical analysis(DMA)and Fourier infrared spectroscopy(FTIR)results indicated that there were two kinds of synergistic capacity-enhancing effect of mechanism combining in-situ grafting reactions and non-covalent bond interactions(ion-dipole and hydrogen bonding,etc.)in the two-phase interface under the dynamic vulcanization strategy.The morphological structure results exhibited that under the synergistic effect of in situ grafting reaction and non-covalent bond interaction,the particle size of the dispersed phase of the ionomer was significantly reduced,and the phase interface adhesion also was remarkedly enhanced.The blended system greatly improved the toughness of polylactic acid without apparently sacrificing strength:the elongation at break and impact strength are up to 250%and 17.3 k J/m~2,respectively.The interfacial adhesion between the evenly dispersed and suitable size's ionomer and PLA matrix was enhanced because the combination of intermolecular interaction and in-situ grafting reactions was the native mechanism for achieving high-performance sustainable PLA blends.