Studies Of Divinylbenzene-maleic Anhydride Copolymer Hollow Microspheres On The Multifunctional Modification Of Degradable Polyester

With the continuous improvement of environmental protection requirements,the biodegradable polymers are widely used in more and more areas.Poly(lactic acid)(PLA)is an early developed biodegradable material and polyhydroxyalkanoate(PHA)is currently in the stage of development and application.Although these polymers have excellent biodegradability,and can satisfied the requirements of environmental protection materials,they has some inherent structural disadvantages such as slow crystallization rate and serious melt dropping during combustion for PLA,and poor thermal stability and comprehensive performance for PHA,etc.in the processing and molding,it need to further multi-functional modification and optimization of properties to broaden its the application field.Divinylbenzene maleic anhydride copolymer hollow microsphere(DM)is a novel particle with hollow structure and micron size,and the benzene ring structure in the molecular structure endows it strong rigidity.With its special spatial structure and its own maleic anhydride group,DM is expected to be applied in polymer matrix,especially polyester polymer,and improve the comprehensive performance of the matrix,and it has the potential to be used as a polyester modifier.At present,there are few reports about hollow microspheres as modifiers,especially on the modification of degradable polyester are still rarely reported at present.In this work,focusing on the above problems,DM were used as modifiers to multi-functional modification of biodegradable polyester by melt blending.The main research results are as follows:(1)The crystallization behavior of poly(lactic acid)(PLA)was studied by using divinylbenzene maleic anhydride hollow microspheres(DM).It was found that DM could be as a novel organic nucleating agent for PLA.The effect of DM on the crystallization behavior of PLA was studied by DSC,POM and WAXD.The non-isothermal and isothermal processes in DSC showed that DM could change the crystallization behavior of PLA,and the crystallization rate and degree of crystallinity would increase when the loading of DM increased from 0%to 3%.The POM showed that it could improve the nucleation density,while the spherulite size was reduced;WAXD pattern showed that DM could not change the mechanism of crystallization.In addition,adding a small amount of DM can improve the brittleness of PLA,for example,adding of 0.5%DM can increase the elongation at break of PLA by 2.4 times as much as that of pure PLA,and its heat resistance also further improve.(2)In order to solve the problem that traditional intumescent flame retardant(IFR)systems are difficult to effectively flame retardant PLA and anti-dropping of PLA,four kinds of samples PLA/24%APP,PLA/18%APP/6%PER,PLA/20%APP/4%DM and PLA/15%APP/5%PER/4%DM were prepared by blending,the flame retardant of the composites were characterized by LOI,UL-94 and CONE.It was found that adding of DM can anti-dropping of PLA/IFR systems,and the PLA/15%APP/5%PER/4%DM reaches to V-0 without dropping,which is due to that,the maleic anhydride group of DM could capture the hydroxyl group of PLA and have the chemical crosslinking,and could increase the viscosity of systems to anti-dropping.DM could reduce the flame retardant effect of the composites,for example,the LOI value of PLA/15%APP/5%PER/4%DM decreased by 0.6%,and the values of pHRR and THRR increased by 60kW/m2 and 16MJ/m2 respectively,compared with PLA/18%APP/6%PER.In addition,TGA found that DM can promote the carbon residue,because of two methods,its own divinylbenzene group and cross-linked residue,and that also helps to inhibit the dropping.PLA/IFR/DM is characterized by LOI,UL-94 and cone.It is found that the composite contain DM can reduce the serious droplet phenomenon of PLA intumescent flame retardant systems,in which the sample PLA/15%APP/5%PER/5%DM can reach to V-0 without dropping.The mechanism of droplet inhibition is characterized by TG-DSC and viscosity analysis.It is found that the maleic anhydride group of DM can capture the hydroxyl and cross-linking,which can promote the viscosity of matrix.TGA,SEM,FTIR and Raman were used to analyze the mechanism of cross-linking promoting charring.It was found that the crosslinking of DM at high temperature promoted the char matrix and enhanced the strength of carbon layer.But at the same time,it was found that the flammability of DM itself led to the decrease of flame retardancy such as LOI,pHRR and THRR.(3)Resorcinol bis(diphenyl phosphate)(RDP)has the function of thermal stability,plasticization as well as flame retardation on polyester,and it and DM were compounded into P34HB by melting blend.TG and DSC were used to characterize the thermal stability of P34HB its composites under the air and N2.It was found that RDP can delay the initial degradation of P34HB in the low temperature,DM mainly plays a role in the maximum degradation in the middle and high temperature,and they have a synergistic effect;TG-IR test shows that the addition of RDP,DM and their combination can not change the degradation mechanism of P34HB,only delay its degradation process.the thermal conductivity illustrates that DM has a high thermal conductivity.The mechanism that RDP and DM improving the thermal stability of P34HB is that RDP weakens the random chain scission reaction(β-elimination)and intramolecular ester exchange in the degradation process of P34HB by termination,chain extension and space steric effect.DM slows down the degradation process mainly by termination,steric hindrance and its high thermal conductivity.The different mechanism between the RDP and DM is the reason of synergistic effect.In addition,it is found that rigid DM and soft RDP can modify the crystallization,mechanical and processing properties of P34HB,which is of great significance in practical production.