Surface Functionalization Of Nano-SiO₂ Based On Polylactic Acid Melt Degradation And Its Application

The excellent properties of biodegradability and biocompatibility of Polylactic acid?PLA?making it show a broad application prospects in biomedical fields,which drawn lots of attention.However the low elongation at break,slow crystallization rate and poor thermal stability of PLA limits its application in a large part.Nano-SiO₂ has the advantage of non-toxic,rigid and high thermal resistance,which is suitable for modification of PLA acted as a kind of a polymer filler.Nevertheless,the agglomeration behavior of nano-SiO₂ in PLA matrix and incompatibility between the two interfaces usually lead to the undesirable enhancement of material performance.Currently this problem can be solved by surface modification of nano-SiO₂.Therefore,in this paper we explored a simple,efficient and low cost method of surface functionalization of nano-SiO₂ based on the degradation of PLA in melt state,and studied the effect of functionalized nano-SiO₂ on mechanical properties,crystalline properties and thermal stability of PLA.Firstly,the functionalized nano-SiO₂ was prepared by long-term melt blending and high-speed centrifugal separation process.Then,the functionaliztion effect of nano-SiO₂ and the mechanism of covalent grafting between PLA and nano-SiO₂ were studied by thermogravimetric analysis,transmission electron microscopy,Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.The research indicate:?1?PLA can react with nano-SiO₂ during melt blending under the condition of high temperature and high shear force,thus PLA chains grafted on the surface of nano-SiO₂ successfully;?2?The melt blending time has a significant effect on the surface functionalization of nano-SiO₂,and the appropriate blending time?10 min?favored more PLA chains grafted on the surface of nano-SiO₂;?3?Transesterification reaction,condensation reaction and esterification reaction occurred between degraded PLA chains and surface silicon hydroxyl group of nano-SiO₂ were considered as the main mechanism of PLA covalent grafted nano-SiO₂.Then,the PLA nanocomposites with different contents?0.5-3 wt%?of pristine nano-SiO₂ and functionalized nano-SiO₂ were prepared by injection molding.The effects of functional nano-SiO₂ on the microstructure,mechanics,crystallization and thermal stability of PLA were studied by scanning electron microscopy,electronic universal testing machine,impact testing machine,differential scanning calorimeter and thermogravimetric analyzer.The results and conclusions are as follows:?1?Functionalized nano-SiO₂ particles can improve the tensile strength,toughness and impact strength of PLA at low content,which attributed to its excellent dispersion and compatibility in PLA matrix,and the reinforcement effect was weakened with the increasing content of functionalized nano-SiO₂ due to agglomeration;?2?Functionalized nano-SiO₂ plays a heterogeneous nucleation effect in PLA matrix which improved crystallinity of PLA.?3?Functionalized nano-SiO₂ can improve PLA's thermal stability in some degree,and the improvement effect is proportional to the content of nano-particles.