Regulation Of Crystallization And Mechanical Properties Of Poly (Lactic Acid)

In this paper,a serie blend of different proportions of poly(1-lactic acid)(PLLA)/thermoplastic elastomers(TPEE)blend materials were obtained by melt blending.Nucleating agents(included TMC-210,TMY-4 and TMC-300)were added into PLLA/TPEE blend materials to improve the crystallization behaviors and mechanical properties of PLLA.In addition,we also studied the effect of reuse of waste MTP catalyst on PLLA.The different performance of blend materials were systematically investigated by differential scanning calorimetry(DSC),wide angle X-ray diffraction(WAXD),polarized optical microscopy(POM),scanning electron microscope(SEM)and mechanical test.Firstly,the influence of nucleating agent TMY-4 on the crystallization ability of PLLA was explored.The results showed that with the increase of TMY-4 content,the crystallization temperature of PLLA moved to high temperature and reached 111.2 ℃ when TMY-4 content was 5 wt%.TMY-4 playd the role of heterogeneous nucleation,promoted the crystallization of PLLA,it made the spherulite refinement,the crystal nucleus density increased and the grain more refined.At the same time,TMY-4 can improve the impact strength of PLLA.When TMY-4 content reached 5 wt%,the impact strength of PLLA reached to 4.80 kJ·m-2,an increase of 58.5%.After that,PLLA/TMY-4/TPEE blends were prepared by adding different amounts of TPEE into PLLA/TMY-4 blends.The crystallinity and mechanical toughness of the blends were greatly improved.The impact strength of PLLA/TMY-4/TPEE was 13.68 kJ·m-2 when the addition of TPEE reached 40 wt%,which was 4.51 times higher than pure PLLA.Secondly,different proportions of TPEE were melt into PLLA/TMC-210 blends.The effects of different proportions of TPEE and TMC-210 on the crystallization and mechanical properties of PLLA were investigated.The experimental results showed that compared with PLLA,the crystallization ability of ternary blends PLLA/TMC-210/TPEE have been greatly improved,the nucleation density increased,the crystallinity increased,but the crystal structure has not been changed.The results of mechanical properties test showed that the impact strength of the blends increased with increasing TPEE content.When the content of TPEE reached 50 Wwt%,the impact strength of the blends could reach as high as 20.7 kJ·m-2,6.84 times higher than pure PLLA.Therefore,slow crystallization rate and poor toughness shortcomings of PLLA can simultaneously be solved by TMC-210 and TPEE.Then we added TMC-300 with different mass ratios into the PLLA/TPEE blends to explore the appropriate ratio of TMC-300 into the PLLA/TPEE blends.The results showed that TMC-300 can play a good role in promoting crystallization in PLLA/TPEE blends.With the increase of TMC-300 content,TMC-300 had more obvious heterogeneous nucleation effect on PLLA/TPEE blends.When the content of TMC-300 reached 0.8 wt%,the crystallization temperature reached 124.84 ℃.On mechanically properties,the impact strength of PLLA/TPEE/TMC-300 ternary blend reached 22.64 kJ·m-2 when the content of TMC-300 was 1 wt%,which was 7.47 times higher than pure PLLA.Therefore,at an appropriate ratio,TPEE and TMC-300 can play a synergistic toughening effect on PLLA to improve the toughness of PLLA.Finally,the recycling of MTP-DC in PLLA was studied.It was found that the MTP-DC can act as the nucleating agent and its ability was excellent.The crystallization temperature of PLLA was as high as 112.27 ℃ when the content of MTP-DC was 1 wt%.With the increase of the content of MTP-DC,the strength of the impact strength of PLLA gradually increased,so MTP-DC helped to improve the toughness of PLLA.By reusing MTP-DC,resources can be greatly conserved and the costs can be reduced,and avoiding the use of expensive PLLA-specific nucleating agents.While crystallizing the PLLA nucleates,the flexural modulus of PLLA increased,and the toughness also increased as the spent catalyst content increases.