Study On The Microwave-assisted Synthesis And Mechanism Of Poly(Lactic Acid)

Polylactic acid is an environment-friendly high-molecular material with excellent biodegradability and biocompatibility.It is prepared from lactic acid fermented from renewable crops and has been used in medical care,daily necessities,electronics,Building materials and other fields.In the production and processing of polylactic acid,it is unavoidable that the reaction time is too long,the production conditions are required to be high,and the crystallization rate during the processing is slow,the degradation reaction easily occurs,and the impact resistance is poor.In order to reduce the reaction time and save the production cost,the polylactic acid was prepared by the lactide ring-opening polymerization method and the microwave organic synthesis chemistry technology was introduced into the lactide ring-opening polymerization process.The thermal degradation kinetics of polylactic acid was also studied.The isothermal crystallization kinetics of polylactide and other aspects have been studied in depth and systematically,playing a guiding role in the process parameters of polylactic acid processing.Using L-lactic acid as raw material,the experiment explored the choice of catalyst and the concentration,reaction temperature,time,lactide collection device and other processes,and examined the effect of different solvents on the recrystallization of lactide to prepare a refined lactide.The rate is above 60%,the melting point is 97°C,and it is ready for the lactide ring-opening polymerization of polylactic acid.In the process of synthesizing polylactic acid,microwave radiation was used as the energy source for the ring-opening polymerization of lactide.A new microwave radiation synthesis process was studied and developed.The microwave power was 250W,the reaction time was 40min,and the lactide initiator molar ratio was 1874.:1.Polylactic acid with a viscosity-average molecular weight of about 50,000 can be prepared by using a self-made lactide in a laboratory.Polylactide with a molecular weight of 110,000 can be prepared using lactide obtained by McLean as a raw material,and the polylactic acid can be prepared with a molecular weight of 110,000.More than ten times of work efficiency.The kinetics of microwave-assisted lactide ring-opening polymerization were also studied in this paper.The reaction was in accordance with a three-level kinetics model.The rate constant k was0.875mol^-2.L².min^-1.Under the protection of high-purity argon,using different heating rates,the thermal degradation kinetics and thermal degradation kinetics of different poly?lactic acid?s were studied by TG-DTG technique.The power of different types of poly?lactic acid?was determined by FWO method and IKP method.By studying the parameters and comparing them with the parameters obtained,the activation energy of polylactic acid?P-PLA?and self-made polylactic acid?S-PLA?was determined by screening different models,which were157.6±8.1 and 101.8±16.7 kJ/mol.The thermal degradation process of S-PLA mainly uses nucleation growth?between S3 and S4?and reaction order?S15?.The basic law of P-PLA is consistent with nucleation growth?between S3 and S4?,and the reaction order is degraded.The process is relatively weak.The isothermal crystallization process of commercial polylactic acid and self-made polylactic acid was studied by the hot stage polarizing microscope and dilatometer method.The isothermal crystallization process was analyzed using the Avrami equation.The study showed that the PLA crystal was a spherulite structure and the commercial polylactic acid was obtained.The isothermal crystallization activation energy E values of self-made polylactic acid were-130.1 kJ/mol and-139.7 kJ/mol,respectively.Using POM and hot stage to observe the growth process of two isothermal dynamic crystalline crystals of polylactic acid,the radial growth rates of two polylactic acid spherulites at different temperatures were calculated.It was found that the higher the molecular weight,the lower the radial growth rate and the higher the temperature.The smaller the number of nucleation,the higher the radial growth rate.