Synthesis Of Aliphatic Polyester-copoly (Lactic Acid) And Itsmodification Of Poly (Lactic Acid)

Polylactic acid（PLA）is a renewable,fully bio-based,aliphatic thermoplastic polymer with degradable properties that is widely used in many applications due to its excellent tensile strength（around 45 MPa）,thermal stability and degradability.However,the inherent brittleness of PLA,with an elongation at break of only about 7%,has limited its wider application.In this paper,high molecular weight polyethylene succinate（PES）and polyethylene succinate-co-poly（lactic acid）（PESL）were synthesized by one-pot melt polycondensation using bio-based monomers butyric acid（SA）,ethylene glycol（EG）and lactic acid（LA）as raw materials with different composition ratios and different properties by adjusting the feeding ratio of lactic acid monomers.The synthesized PES-based polymers were blended with different ratios of commercial PLA by melt blending method to obtain a series of composites.After blending the PESL with 85%commercial PLA,the obtained composites have excellent mechanical properties,with elongation at break reaching more than 250%and still maintaining excellent tensile strength（about 50 MPa）;the initial decomposition temperature of the composites,T_d5%is above 320℃and the melting point,T_mis about 160℃,indicating their excellent thermal stability.The toughening mechanism as well as the compatibility were investigated,showing that the introduction of lactic acid units in the copolyester increased the bonding force between the phase interfaces.Then the diol and diacid types were changed,and polybutylene succinate（PBS）and polybutylene succinate-co-polylactic acid（PBSL）with different lactic acid contents were synthesized by the same polymerization method using adipic acid（AA）and butylene glycol（BDO）with ethylene glycol and succinic acid and lactic acid raw materials,respectively,and polyethylene adipate（PEA）and polyethylene adipate-co-polylactic acid（PEA）with different lactic acid contents,respectively.glycol adipate-co-poly（lactic acid）（PEAL）with different lactic acid contents,after which the composites were also prepared by co-blending with commercial PLA with 85%mass fraction.The mechanical properties of the PBS-based composites and PEA-based composites were initially tested,and the PBS-based composites were found to have a tensile strength of about 50 MPa,good toughness,and elongation at break of about 280%;the PEA-based composites also had good mechanical properties（tensile strength of about 45 MPa and elongation at break of about 250%）.The modification effect was analyzed.In general,the PES-based composites meet the index requirements of the disposable plastics industry in terms of thermomechanical properties,and the obtained composites are fully bio-based,which have a very broad application prospect and development potential in the field of plastics industry.