Study On P(3HB-CO-4HB)/Nano-ZnO Composite

Poly(3-Hydroxybutyrate-co-4-Hydroxybutyrate)[P (3HB-CO-4HB)] is a thermoplastic copolyester produced by a number of microorganisms. It has been paid much attention for excellent biocompatibility and complete biodegradability. However, poor melt strength, lower crystallization, serious second crystallization and larger spherulites made it difficult to use directly. Nanometer ZnO, as a multifunctional inorganic nanoparticles, can simultaneously improve the mechanical properties, antibacterial property, crystallization rate and UV aging resistance of the polymer matrix.In this article, nano-ZnO was used as modifier to prepare nanocomposites of P (3HB-CO-4HB) with mole fraction5%of4HB. It is expected that the strength, the toughness and processibility of P (3HB-CO-4HB) were improved simultaneously to expand its application aera.According to the mechanism of surface modification for nanoparticles, anionic surfactant (sodium dodecyl sulfonate, SDS), cationic surfactant(cetyltrimethy lammonium bromide, CTAB), polyethylene glycol(PEG), silane coupling agent (KH550) and titanate coupling agent (TMC-980) were selected respectively to modify the surface of the nano-ZnO with different technologies and conditions. By comparing the activity indexs and particle size of modified nano-ZnO, the optimal modifying effect was obtained via grafting reaction of TMC-980on nano-ZnO. Based on the result, P (3HB-CO-4HB)/nano-ZnO composites was prepared via melt blending. Fourier transform infrared spectroscopic(FTIR), dynamic Contact Angle Measurer, Laser Particle Size Analyzer, Scanning electron microscopy(SEM), Polarizing microscope (POM), capillary rheometer, universal Testing Instrument, Computer control heat distortion Vicat softening testing machine etc. were used to characterize the effect of titanate coupling TMC-980on surfacial modification of nano-ZnO, the effects of modified nano-ZnO on the thermal properties, mechanical properties, melt rheological properties, fracture morphologies and crystallization morphologies of composites. Halpin-Tsai equation was used for theoretical analysis and quantitative prediction on the toughening and reinforcing mechanism and modifying effect of zero dimensional nano-ZnO.The results show as follow:(1) Grafting reaction between the stearic long-chain on TMC-980and the superficial-OH groups of nano-ZnO can carry out under proper conditions, which made the nano-ZnO covered with organic segmer, the particle agglomeration prevented and the lipophilicity of modified nano-ZnO improved. The particle size of modified nano-ZnO decreased from 51884nm to256nm. Water contact angle of modified nano-ZnO increased from7°to58°. Activity index increased form0to99.80%.(2) There is an optimum dosage of titanate coupling agent for the modification of nano-ZnO. In this work, the modification effect is optimal at mass fraction3%of TMC-980, corresponding to the predicting value of single layer coated theory.(3) The notched impact strength, tensile strength and break elongation of P (3HB-CO-4HB)/nano-ZnO composites first increase and then decrease with increase of the nono-ZnO content. The notched impact strength, tensile strength and break elongation of P (3HB-CO-4HB)/nano-ZnO composites are higher29.48%,11.23%and64.67%than that of neat P (3HB-CO-4HB) respectively at1wt%～1.5wt%nano-ZnO.(4) Proper modified nano-ZnO can act as nucleating agent to significantly reduce the spherulite size of the composites and make its fracture morphology to be typical ductile failure characteristics. Overdose of nano-ZnO will result in serious agglomeration, large spherulite size and poor mechanical properties.(5) Halpin-Tsai model can be used to evaluate the dispersion effect of nano-ZnO in P (3HB-CO-4HB) matrix and predict the elastic modulus of the composites. It can be used to fit the elastic modulus of composite and perdict the optimum amount of nano-ZnO via calculating the shape factor (ξ) value of nano-ZnO in the composite material, which can provideds theory basis for optimizing formulation and composition of composites.(6) Based on the optimal ξ value from Halpin-Tsai model evaluation and comprehensively considering the various properties of the composites, the best performance of the composites can be obtained at the dosage of nano-ZnO was Vz=0.2-0.3%(1.0wt%～1.5wt%), at which the theoretical predictions are in good agreement with the experimental results.