Synthesis Of New Plastjcizers And The Plasticizing Effect For Poly(Lactic Acid)

Dipropylene glycol dibenzoate (DPGDB) and Glycercol tribenzoate (GTB) were synthesized from dipropylene glycol, glycerol and benzoic acid by esterification process. The chemical structure of DPGDB and GTB was characterized by 1H-Nuclear magnetic resonance and infrared spectroscopy, and the results show that the expected product was gained.This study chose triacetate (GTA) as a control. GTA, DPGDB and GTB were used for plasticizing PLA via a melt-compounding process. The effect of the addition of plasticizers on the properties of PLA was studied by differential scanning calorimetry apparatus(DSC), a parallel plate rheometer, tensile tests, X-ray diffraction (XRD), thermogravimetric analysis (TGA), migration tests and water vapor permeability tests. The additions of three kinds of plasticizers all could lead the glass transition temperature (Tg) and melting point (Tm) of PLA decreased. With an increase of plasticizer content, Tg and Tm of PLA gradually shifted to a lower temperature and their Shore D hardness were decreased. The rheology of plasticized PLA showed that storage modulus of the material (G’), loss modulus (G"), the apparent viscosity (η) and viscous flow activation energy (ΔEη) reduced significantly. The Softening-plasticizing effect coefficient (K) increased at first and then decreased with the increase of plasticizer content, and the value of K showed a upward tendency on three plasticizers in a sequence:GTA> DPGDB> GTB.The elongation at break of PLA/plasticizer blends improved significantly, while the corresponding tensile stress of PLA/plasticer blends maintained at 10 MPa. The plasticized PLA films crystallized slowly with the increasing of storing time, which was amorphous after 0 day store. After 75 days of storage, only PLA/GTA-25 appeared obvious crystallization peak. After 30 days of storage, PLA plasticized with DPGDB and GTB exhibited good storage stability and mechanical properties while the performance degradation of PLA/GTA was faster. Due to migration, the weight loss of DPGDB and GTB were much lower than GTA. DPGDB and GTB showed a good thermal stability. The water vapor permeability of plasticized PLA increased gradually with the increase of plasticizer content. This study shows that the increase of the molecular weight of plasticizer can effectively improve its stability, the stability of DPGDB and GTB was much higher than that of GTA, but with the increase of the molecular weight of plasticizer will also reduce the compatibility of plasticizer and PLA, the plasticizing efficiency of GTB was much lower than that of GTA. The modification of plasticizer molecular structure could compensate the defect of the decrease compatibility between PLA and plasticizer, which is because of the increase of the molecule weight of plasticizer. Molecular weight of DPGDB is higher than that of GTA, but because the ether bond is introduced into the molecular structure of DPGDB, the plasticizing efficiency of DPGDB is as good as that of GTA.