Preparation Of Phosphite Functionalized Polysiloxane And Its Stability To Polylactic Acid

In order to improve the processing stability,thermal oxygen stability,hydrolysis resistance and flame retardant properties of poly(lactic acid)(PLA).Firstly,through the functional modification of the polysiloxane chain extender,a phosphite-functionalized polysiloxane chain extender containing both phosphorus and silicon elements was prepared.Then the chain extender was bonded to the molecular chain by the chain extension reaction with PLA.On the one hand,the molecular weight of the polylactic acid are increased by the chain extension reaction,thereby improving the processing thermal stability and thermal oxygen stability of the polylactic acid.On the other hand,using the hydrophobic property of the chain extender itself and the special flame retardant effect of phosphorus and silicon elements,the polylactic acid has higher hydrolysis resistance and flame retardant properties.In addition,the flexibility of the polysiloxane chain extender itself also imparts good mechanical properties to the material.The conclusions are as follows:A polysiloxane microsphere(PSQ)containing both amino and epoxy functional groups was prepared by one-step sol-gel method.Then a phosphite functionalized polysiloxane(PPSQ)was synthesized by two-step esterification.The successful grafting of the phosphite to the polysiloxane was confirmed by infrared spectroscopy,ICP testing,thermogravimetric analysis and 29Si NMR.By adjusting the amount of PPSQ,reaction time and reaction temperature,an optimal processing process(ie,the addition of PPSQ is 2wt%,the reaction temperature is 180? and the reaction time is 10 minutes)was found to carry out the chain extension reaction.The chain-extended polylactic acid obtained at this condition shows the strongest stable ability in melt shear processing.The weight average molecular weight increased from 198.6 kg/mol of blank PLA to 213.0 kg/mol,with an increase of 7.3%compare with Virgin-PLA.And under the optimal processing conditions,the mechanical properties of PLA samples are improved.Compared to Virgin-PLA,the flexural modulus of PLA-PPSQ increased from 2507.2MPa to 2569.9MPa,the tensile strength increased from 47.1 MPa to 55.2MPa,the impact strength increased from 26.3J/m to 49.8J/m,and the impact strength increased as much as 89.4%.Furthermore,the Ozawa method and the Kissinge method were used to calculate the activation energy of the oxidative degradation process from 175kJ/mol to 187kJ/mol compare virgin-PLA with PLA-PPSQ samples.Shows that PLA-PPSQ has good thermal oxygen stability.In addition,a hydrolysis kinetics model was established.The hydrolysis rate of the PLA system was reduced from 4.94×10-3k/h to 2.63×10-3k/h,and the hydrolysis rate was decreased by 46.8%,which confirmed that the hydrolytic stability of PLA after PPSQ chain extension was improved.This is closely related to the increase of the molecular weight caused by the chain extension reaction and the hydrophobic properties of the chain extender itself.Finally,through the cone calorimeter test on the polylactic acid samples,the effect of the synergistic effect of phosphorus or silicon on the combustion performance of PLA was investigated.It is found that when PSQ and PPSQ are added to PLA,the residual carbon content of the PLA system was increased from 3.3%to 24.3%and 11.3%,the total heat release amount decreased from 78.5 MJ/m2 to 69.5 MJ/m2 and 65.5 MJ/m,the total smoke release decreased from 4.0m2/m2 to 3.7 m2/m2 and 2.8 m2/m2.That is,the flame retardant performance of PLA is enhanced by the chain extender containing both phosphorus and silicon.Then the SEM,EDS,ICP and FTIR were used to characterize the surface morphology,elemental content and characteristic structure of the combustion products of PLA samples.Compared to Virgin-PLA and PLA-PSQ,the carbon layer of PLA-PPSQ is uniform,dense,and thick,and the content of silicon on the surface of the combustion products is higher,indicating that the amount of Si-C and Si-O protective layers in PLA-PPSQ is more,so PLA-PPSQ has better flame retardancy than PLA-PSQ.