| Polylactic acid(PLA)is a biodegradable polyester that is expected to replace traditional petroleum-based plastics.PLA has good biocompatibility and high mechanical strength,and has broad application prospects in daily life,packaging and biomedicine.However,the defects of poor toughness and large brittleness limit the development prospects of PLA.By adding polyethylene glycol(PEG),the interaction between PLA molecular chains can be weakened,processing performance can be improved,and PLA can be toughened at the same time.However,PEG as a plasticizer can easily lead to a substantial decrease in the modulus and melt strength of the blend,and the migration of the plasticizer will also cause the material to become brittle again.In this thesis,using dicumyl peroxide(DCP)as initiator and maleic anhydride(MAH)as graft,polylactic acid grafted with maleic anhydride(PLA-g-MAH)was prepared by melt grafting.And PLA-g-MAH is used to prepare high-toughness PLA/PEG/PLA-g-MAH blends,which provides new ideas for improving the migration of plasticizers in PLA plasticizing systems.Multiple groups of PLA-g-MAH were prepared using different amounts of MAH and DCP.The structure and reaction mechanism of PLA-g-MAH were analyzed by proton nuclear magnetic resonance spectroscopy(~1H NMR)and Fourier infrared spectroscopy(FT-IR).DCP can cause the tertiary hydrocarbons of PLA to form free radicals,and it can also aggravate the?chain scission of PLA to form free radicals.With the increase in the amount of MAH and DCP,the double bond of MAH and the?chain scission of PLA form free radicals to compete for the grafting site on the tertiary carbon of PLA.The grafting rate of PLA/DCP/MAH(100/0.5/8)grafts is up to 1.33%.Taking the ratio of PLA/DCP/MAH(100/1/8)(referred to as GPLA,grafting rate 0.85%)as a reference,GPLA-a was prepared by adding DCP step by step.The initial torque of the preparation process is large,the viscosity is high,and the grafting rate of GPLA-a is only 0.74%.GPLA-b was prepared by adding plasticizer ATBC.ATBC reduced the melt viscosity of PLA and improved the dispersibility of MAH and DCP.The grafting rate of GPLA-b was0.88%.PLA/PEG/GPLA blends were prepared by reactive melt blending,and the effects of different PEG molecular weights,PEG dosages,GPLA dosages and grafts prepared by different strategies on the properties of PLA/PEG/GPLA blends were studied.The PLA/PEG plasticizing system has a critical plasticizer concentration,which is about12.5wt%.After adding GPLA,this value shifts to a higher concentration.In the process of melt blending,GPLA reacts with PEG1000 to form branched PLA with short branches,and the number of branched PLA branches formed by reaction with PEG10000 is small,which is not conducive to increasing the entanglement between molecular chains.The molecular weight of PEG6000 is moderate,and the branched PLA formed by the reaction with GPLA has a significant effect on increasing the entanglement between molecular chains.The complex viscosity,modulus and melt strength of PLA/PEG6000/GPLA blends are relatively large.Branched PLA can increase the entanglement between molecular chains in the system,and this entanglement network is beneficial to inhibit the migration of PEG,and can also cooperate with the plasticizing effect of PEG to further toughen PLA.The elongation at break of the PLA/PEG/GPLA(80/20/5)blend is 526.9%and the tensile strength is 30.91MPa. |
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