Surface Modification Of SiO₂ Nanoparticles Based On Melt Blending And Its Application In PCL Composites

Polycaprolactone(PCL)has been widely used in packaging,biomedical,agroforestry and other fields due to its good biodegradability and biocompatibility,non-toxicity and environmental friendliness.However,the low mechanical strength and poor thermal stability of pure PCL has greatly limited its further development in the above fields.As a kind of rigid inorganic nano-filler,SiO2 nanoparticles are considered as ideal reinforcing filler for PCL due to low price,non-toxic,harmless,non-toxic and high thermal stability.Nevertheless,the agglomeration behavior of nano-SiO2 in PCL matrix and incompatibility between the two interfaces usually lead to the undesirable enhancement of material performance.Based on the surface of the nano-silica is rich in silanol groups,these problems can be solved by surface modification of nano-SiO2.In this paper,PCL is covalently grafted onto the surface of SiO2 nanoparticles by the high temperature and strong shear force in the melt blending process of the extruder.A low-cost,simple operation and batch-scale nethod of modification of nano-SiO2 surface was explored.Based on this,the mechanism and influence of modified SiO2 on the microstructure,mechanical properties,crystallization properties and thermal stability of PCL were studied.Firstly,PCL and nano-SiO2 were melt-blended under orthogonal test conditions,and then nano-SiO2 with covalently grafted PCL molecular chain was prepared by high-speed centrifugal separation process.The optimal scheme was determined by orthogonal experiment,and the reaction mechanism of covalent grafting of nano-SiO2 with PCL was studied by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.The results show that:(1)Under the high temperature and strong shear force of the extruder,PCL is successfully grafted onto the surface of SiO2 nanoparticles,and the optimum process conditions for preparing modified nano-SiO2 are melt blending temperature 120?,melt blending time 20 min and screw speed 40 rpm;(2)Transesterification reaction,esterification reaction and condensation reaction occurred between degraded PCL chains and surface silicon hydroxyl group of nano-SiO2 were considered as the main mechanism of PCL covalent grafted nano-SiO2.Then,PCL/SiO2 nanocomposites with different contents(0.5-3 wt%)of nano-SiO2 before and after modification as fillers were prepared by solution blending and compression molding.The effects of modified nano-SiO2 on the microstructure,mechanics,crystallization and thermal stability of PCL 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)At the same content,the modified nano-silica particles have better dispersibility in the PCL matrix,the size of the agglomerates is smaller,and this phenomenon is more obvious at high contents;(2)Under the low content(0.5 wt%),the modified nano-SiO2 with better dispersibility and interfacial bonding ability has the best toughening effect for PCL.At this time,compared with pure PCL,the tensile strength,elongation at break and impact strength of PCL/modified Si02 composites respectively increased by 18.0%,17.0%and 19.6%.And the reinforcement effect was weakened with the increasing content of modified nano-SiO2 due to agglomeration;(3)Nano-SiO2 before and after modification can increase the storage modulus of PCL,and the strengthening effect of modified nano-SiO2 is more significant;(4)Under the dual effects of heterogeneous nucleation and hindering the movement of PCL molecular chain segments,the crystallinity of PCL/modified nano-SiO2 composites increase first and then decrease;(5)The modified nano-SiO2 can effectively improve the thermal stability of PCL materials,and its thermal stability is continuously improved with the increase of particle content.