Study On The Crystallization Behavior Of Poly (L-lactic Acid) Induced By Novel D-Gluconic Acetal Nucleators

Poly(lactic acid)(PLLA)is a polymer material with good biodegradability and biocompatibility,and it is a potential alternative material for petroleum-based plastics.Poly(lactic acid)is a semi-crystallized polymer with defects such as slow crystallization rate and poor thermal stability,which to a large extent limit the application and development of poly(lactic acid).Adding nucleating agents is the most efficient and cost-effective way to improve these defects.In this paper,we designed and synthesized a series of highly efficient PLLA organic nucleators,D-gluconic acetal nucleators(denoted as G-C₁₈(OH),G-C₁₈,G-C₁₆(OH)₃and G-C₁₄,respectively),and the effect of D-gluconic acetal nucleators with 0.5 wt%on crystallization and mechanical properties of PLLA was studied.The experimental results show that the addition of four D-gluconic acetal nucleators can promote the crystallization temperature of PLLA to increase by about12?20°C,and the crystallinity to increase by about 30%,and the half-crystallization time is 81?86%shorter of neat PLLA.Under the condition of rapid cooling,the D-gluconic acetal nucleators still has nucleation effect,in which the nucleation effect of G-C₁₈and G-C₁₄is more remarkable,which can still cause the crystallinity of PLLA to change to about three times the original.In the mechanical properties,the addition of D-gluconic acetal nucleators can increase the stiffness of PLLA and increase the elastic modulus of PLLA.In this paper,through in situ x-ray diffraction analysis,it is determined that the reason why the D-gluconic acetal nucleators can enhance the crystallization thermodynamic properties of PLLA is that the addition of D-gluconic acetal nucleators can induce PLLA to form a form at lower temperature,thus prompting PLLA crystallization to be more complete.Through Fourier time-resolved infrared spectroscopy,the interaction mechanism between D-gluconic acetal nucleators and PLLA was determined:the hydroxyl groups on gluconic acid fragment interacted with C=O on PLLA chain via hydrogen bonds leading to a certain semi-ordered structure in the melt,and the D-gluconic acetal nucleators molecule acted as a bridge to link the polylactic acid molecular chain,thus improving the crystallization behavior of PLLA.Furthermore,the nucleation mechanism of PLLA by D-glucuron nucleation agent can be deduced into three stages:(1)the hydroxyl groups on gluconic acid fragment interacted with C=O on PLLA chain via hydrogen bonds leading to a certain semi-ordered structure in the melt;(2)the semi-structure is further rearranged to a helix configuration during the induction period of crystallization;(3)eutectic crystallization of nucleator molecules and PLLA chain resulted.