Study On The Preparation And Properties Of Polylactic Acid Composite Foaming Material

Polylactic acid(PLA),as the main biodegradable material,is an ideal substitute for traditional petroleum plastics.Due to PLA excellent properties of high transparency,biodegradability and chemical degradation,it has been widely concerned.However,the disadvantages of PLA are obvious,such as brittleness,inflammable,high price and slow degradation time,which limit its wide application to a great extent.Aiming at the shortcomings of PLA,such as brittleness,high cost and poor flame retardancy,this paper makes corresponding improvement,so as to improve the mechanical properties and flame retardant properties of the material.In order to solve the problem of high cost of PLA,starch with lower cost and similar performance was selected as filler,but the processability of unplasticized starch was not good.In this paper,composite plasticizer was used to plasticize starch.The results showed that the esterification reaction between starch and composite plasticizer occurred in the plasticization process,which destroyed the hydrogen bond between starch molecules and reduced the melting enthalpy of starch.The optimum plasticizing ratio was 0.7,and the melting enthalpy was the lowest,which better improved the processing of starch.The influence of various factors on the mechanical properties was explored through orthogonal experiment,and the results showed that the addition amount of thermoplastic starch(TPS)had the greatest influence on the mechanical properties of materials.By changing the amount of TPS,the results of single factor experiment showed that TPS and PLA were partially compatible and well dispersed by SEM.The addition of TPS reduced the bending strength from 92.57 MPa to 45.75 MPa With the increase of TPS content,the glass transition temperature moved to low temperature,the melting temperature decreased slightly,and the cold crystallization temperature increased somewhat,but it was still lower than that of pure PLA.In order to solve the brittleness problem of PLA,polybutylene terephthalate butylene adipate(PBAT)was selected as toughening material.The molecular chains of PLA and PBAT were entangled under the action of compatibilizer polyethylene glycol(PEG),which enhanced the interfacial bonding and improved the compatibility of the blends.The results showed that the ratio of PLA/PBAT had the greatest influence on the mechanical properties of materials by orthogonal experiment.By changing the ratio of PLA / PBAT,the results of single factor test showed that the surface of continuous phase detected was smooth by SEM,there was no obvious phase interface,showed good compatibility.Compared with pure PLA foaming,the diameter of the foaming pores increased from 99.481μm to 131.34μm.With the increase of PBAT content,the toughness of the material increased,and the tensile elastic modulus decreased from890.20 MPa to 434.20 MPa.For the thermal properties of the materials,the glass transition temperature gradually moved to the lower temperature direction from 61.45℃ to 56.13℃.Melting temperature changed little,and the crystallization peak area and peak height increased gradually.When the mass ratio of PLA/PBAT was 60/40,PBAT crystallized,and two crystallization peaks appeared in DSC.In order to solve the problem that organic matter was easy to burn,the composite flame retardant was prepared in this paper,and the effects of the content of composite flame retardant on the performance of foamed materials was explored.The results showed that the combustion time of composite flame retardants generally decreased or even the material did not ignite with the increase of the content of composite flame retardants.Through the combustion test,when the content of composite flame retardant agent was 17%,the oxygen index of PLA/PBAT/TPS composite flame retardant foaming material was 35.2%,the vertical combustion grade reached V-0,and it had the phenomenon of no droplet and no ignition of absorbable cotton.For the mechanical properties of composite flame retardant foaming materials,the tensile strength decreased with the increase of the amount of composite flame retardant.