Efficient Synthesis Strategy Of IPP-g-PLA And Toughening Of Highly Transparent Poly(Lactic Acid)

Poly(lactic acid)(PLA)is a kind of bio-based environmentally friendly material with excellent properties that can be completely decomposed into carbon dioxide and water by microorganisms in nature.The raw material source is sufficient and renewable.The production process is non-polluting and can be recycled in nature.However,PLA is a kind of brittle material.Untoughened PLA material usually has an elongation at break of less than 7%,sensitive to notches and has low impact and tear resistance,which greatly limite its application in many fields.Toughening modification of PLA is the key and hot research topic in PLA research field.Blending tough materials with PLA is the most economical and easy way to modify toughness,but because most tough materials have poor compatibility with PLA,compatibilizers must be added to the blending system to improve the compatibility.Previous studies have confirmed that graft polymers are more likely to form nano-alloys and play a better toughening effect compared with block copolymers.Besides,graft copolymers additives can significantly improve the interfacial adhesion between incompatible components in the binary mixture and achieve a more ideal toughening modification effect.However,the realization of toughening and modification of PLA is often accompanied by a large decrease in mechanical strength or the destruction of transparency.Solving these problems is the core challenge and research hotspot in this research field.To improve the toughness of PLA,a series of well-designed graft copolymers,including ionically modified isotactic polypropylene-graft-Poly(L-lactic acid)(i PP-g-PLLA)copolymers with explicit graft length,graft density and ionic group content,as well as an i PP-g-PLLA copolymer with super high molecular weight and explicit graft density,have been prepared via efficient graft from and graft onto approaches,respectively.The semicrystal or rubbery copolymer backbone originated from i PP was designed to improve the toughness and maintain a relative high strength,while the grafted PLLA branch was to ensure a high level of compatibility with the PLA matrix,and the imidazoliun-based ionic group was expected to promote the interfacial reinforcement.All these graft copolymers were identified with random distributed PLLA branches,bearing very high molecular weight(33-398×10 ~4)and high PLLA content(57.3-89.3 wt%).The modified PLA blends exhibited significantly increased elongation at break(up to about 190%)and simultaneously retained excellent transparency and very high stiffness.The transmittance of PLA at the wavelength of500-700 nm is 91.0-92.5%,and the transmittance of some blends of PLA and 5 wt%modifier can reach more than 90%.The nanometer-scale phase-separated particles with good compatibility and refractive index matching to the PLA matrix were demonstrated to play the crucial role in the excellent performance.In this experiment,a series of graft copolymers were used to study the toughening properties of PLA.The phase interface properties,mechanical properties,and transparency of PLA blends were explored.We also explained the high toughness of the blend from the mechanism.The findings suggested the newly designed i PP-g-PLLA copolymers are very economic,promising and effective modifiying agents for developing highly transparent and tough PLA based sustainable materials.