Study On Toughening Modification Of Poly (lactic Acid) And Its Low Temperature Resistance

In recent years,due to the increasing awareness of environmental protection,the application of biodegradable materials has become more and more extensive.Polylactic acid(PLA)is an important alternative material to reduce and solve the"white pollution"of plastics,but PLA is relatively brittle at room temperature,which greatly limits its application in engineering materials and other fields.In order to improve the performance of PLA,people have conducted a lot of research on PLA.The more commonly used method of toughening modification is blending modification.However,we found that most of the research on the toughening modification of PLA stays at room temperature,while the research on the toughening modification of PLA at low temperature is rarely reported.For PLA,in order to obtain a wider range of applications,it is not enough to have high toughness at room temperature.It should also have excellent mechanical properties at low temperatures.In this paper,aiming at the serious brittleness of PLA,the melt blending method was used to prepare PLA blends with excellent mechanical properties at room temperature and low-temperature.FTIR,GPC,SEM,DSC,DMA,rheology,impact,stretching and other technical means are used to characterize the microstructure and macroscopic properties of PLA blends,and analyze and summarize the relationship between the structure and properties of PLA blends.The results and conclusions obtained in this paper are as follows:(1)The super toughed polylactic acid(PLA)blends with various content of Ethylene/butyl methacrylate/Glycidyl Methacrylate Terpolymer(GEBMA)were prepared by melt compounding.The blend was an immiscible system but had good compatibility due to the chemical reaction between the epoxy groups of GEBMA and the end group of PLA during the blending process.The addition of GEBMA suppressed the cold crystallization and non-isothermal melt crystallization of PLA.GEBMA was a very effective toughening agent for PLA.The addition of only 15 wt%GEBMA,the elongation at break and impact strength of the blend were significantly improved compared to neat PLA,which were 63 and18 times that of neat PLA,respectively.Scanning electron microscopy(SEM)images of the impact fracture surfaces of the blends showed a large amount of cavities and plastic deformation in the blend,which induced energy dissipation and therefore led to the improvement in toughness of the PLA/GEBMA blends.And PLA/GEBMA blends also have relatively high toughness at low-temperature.For the PLA/GEBMA blown films,the addition of GEBMA significantly improved the flexibility of PLA/GEBMA blown film.The tear strength reached a maximum of 143.5 KN/m in the machine direction(MD)and 166.7KN/m in the transverse direction(TD).Moreover,the biodegradation of PLA was enhanced after blends preparation.(2)Poly(lactic acid)(PLA)blends with different toughening agents were prepared by melt compounding,and the effects of toughening agents on the toughness of PLA,especially the low-temperature toughness,were investigated.All blends were immiscible systems,but the rheological Cole-Cole diagram showed that the blends had certain compatibility,and the interfacial bonding of PLA/GEBMA blend was the best.With addition of the toughening agents,all blends showed improvement of the tensile and impact toughness both at room temperature and low temperature.GEBMA was the best toughening agent,the elongation at break and impact strength at room temperature and low temperature were greatly improved.The elongation at break,tensile strength and impact strength of PLA blend with 20 wt%GEBMA at-20°C was 55.8 MPa,195.9%and 18.8 k J/m~2,respectively,which showed the reinforcement and super ductility at low temperature.However,the toughening effect of Poly(propylene carbonate)polyurethane(PPCU)at low temperature was poor.The Tg and interfacial bonding were the main factors affecting the toughness of the blends,especially at low temperature.The lower the Tg and the better the interfacial bonding,the better the toughness of the blends.(3)Polylactic acid(PLA)blends with excellent toughness and strength at both room temperature and low-temperature were prepared by melt compounding with acrylicester based impact resistance agent(AEIR).The morphology,thermal properties,mechanical properties,rheological properties and biodegradability of the blends were investigated.Morphology observations revealed the blend was immiscible but had good compatibility with the dispersed phase size of about 200-300 nm.With the addition of AEIR,dramatic improvement in toughness of PLA was achieved in a wide temperature range,especially at low temperatures the tensile strength was effectively remained.For the blend with 20 wt%AEIR,the tensile strength,elongation at break and impact strength were 51.6 MPa,72%and77.1 KJ/m~2 at-20 ~oC,respectively,much greater than that reported.The calculated T_g of AEIR was lower than the test temperatures,and the brittle-tough transition occurred.The PLA matrix demonstrated obvious shear yielding which induced energy dissipation and therefore lead to excellent toughness of the blends.Moreover,the biodegradation of PLA was enhanced after blends preparation.(4)The PLA/Poly(butylene succinate-butylene terephthalate)(PBST)/ADR blends with excellent toughness and strength at both room temperature and low-temperature were prepared by melt blending method through in-situ compatibilization reaction,and the morphology,thermal properties,rheological properties,mechanical properties,and biodegradability were investigated.The PLA/PBST blend was an immiscible system,and the compatibility of the PLA/PBST blend was improved after adding ADR.FTIR and GPC curves confirmed the chain extension reaction of ADR with PLA and PBST.The formation of the PLA-g-PBST copolymer improves the interfacial bonding of the blend,so that the PLLA/PBST/ADR blend has very good mechanical properties.For the PLLA/PBST/ADR blend with 70/30 PLLA/PBST content,when the ADR content was 0.8 wt%,the impact strength of the blend reached the maximum value of 74.7 KJ/m~2,which was 21.3 times that of neat PLLA.When the ADR content was 1 wt%,the elongation at break of the blend reached the maximum value of 392.7%,which was 93.2 times that of neat PLLA.Surprisingly,the PLLA/PBST/ADR blend exhibited excellent toughness at low temperatures.When the ADR content was 0.8 wt%,the elongation at break of the PLLA/PBST/ADR blend was as high as 93.2%at-20°C,and the impact strength was 12.3 k J/m~2.When the ADR content was 1 wt%,the impact strength of the blend was as high as 18.8 k J/m~2 at-20°C,and the elongation at break was approximately 67.5%.In addition,compared with neat PLLA,the biodegradation rate of PLLA/PBST blends was significantly improved.After adding ADR,the biodegradation rate of the blend gradually decreased.Enhanced low-temperature toughness and biodegradability are of great significance to the wide application of PLLA.And the biodegradability of the blend can be adjusted by adjusting the content of ADR,so as to obtain materials with excellent comprehensive properties.