Synthesis Of Poly(Succinic Acid-co-propanet Riol) And Toughening Polylactic Acid With It

Polylactic acid (PLA) has good mechanical properties, high tensile strength,compression modulus, transparency, and can be fully biodegradable; therefore, it has awide range of applications, especially in the packaging filed. But the flexibility ofPLA is very poor, and this defect limits its usage in packaging material. Currently,there are many methods to toughen the PLA, although these methods can improve itstoughness, it also will bring great damage to its other properties.In this paper, we have synthesized one kind of modifier and blend it with PLA toimprove the flexibility of PLA.The dissertation includes three main parts. The first part concentrates on thesynthesis of poly(succinic acid-co-propanetriol)(PGD) by melt polymerization fromglycerol and succinic anhydride. We have studied the effect of reaction time andtemperature on the degree of branching of PGD，gel content and reaction content ofcarboxyl groups by1H-NMR and FTIR. It was found that all of them were increasedwith increasing in reaction time and temperature.The second part is about the effect of the degree of branching and contents ofPGD on the tensile properties and impact properties of PLA/PGD blend. It indicatedthat the flexibility of PLA could be improved dramatically when blended with PGD.When the contents of PGD were from0wt%、3wt%、5wt%、10wt%，it was found thatwhen the content of PGD reached5wt%，the elongation at break of PLA/PGD blendimproved significantly，from3.2%to234.2%，which was72.2times than pure PLA，and the fracture behaviors of blends were from brittle to ductile. Though the tensilestrength decreased，it was still more than30MPa. On the other hand，the maximumimpact strength increased from18.8KJ/m2to53.8KJ/m2，which was increased186.2%compared to the pure PLA. DSC analysis indicated that addition of PGD made the Tg and Xc decreased slightly. From the SEM image it found that the fracture surface ofpure PLA was very smooth，but it was very coarse for the blends. The PGD and PLAformed the sea-island structure in the blends，the average particle size of PGDdispersed in the PLA matrix was from1μm to4μm.And then the last part studied the reaction kinetics of glycerol and succinic acidwith equimolar. The result was that: In the absence of additional acid as a catalyst，thepolycondensation reaction of2-3system was2.5grade，and the critical gel pointstested from the experiment at190℃and200℃were86.21%and86.96%，they wereclosed to the theoretical value，which was86.6%.