Surface Modification Of Nano-Sb₂O₃ Particles And Its Effect On The Mechanical Properties Of Poly（butylene Terephthalate） Nanocomposites

Compared with the properties of conventional composites,the nanocomposites have many excellent properties due to the specifical properties of inorganic nanoparticles.The polymer-based nanocomposites,which combined the stiffness,special functionality,thermostability and dimensional stability of nanoparticles with the toughness,excellent processing properties and insulativity of polymer matrix,have been widely used in many fields.In general,t he polymer-based nanocomposites are formed by the matrix phase,nanoparticles phase and interphase.However,the nanoparticles phase and interphase have great influence on the ultimate properties of polymer-based nanocomposites.This is due to the nanoparticles phase is included by the dispersed states and the special functionality of nanoparticles,and the interphase is stand for the union state between the nanoparticles and the matrix.As a semicrystalline thermoplastics polymer,poly（butylene terephthalate）（PBT）has been widely used in engineering applications,such as automobile,biomedical devices,electrical and electronics industries.In this study,the PBT,brominated epoxy（BEO）and nano-Sb₂O₃ particles were selected as materials.First,the nano-Sb₂O₃ particles were modified by different surfactants and the nano-Sb₂O₃/BEO-PBT composite powders were dispersed by high energy ball milling（HEBM）,and than the nano-Sb₂O₃/BEO-PBT composites were prepared by by a twin screw extruder.The effects of milling time and surface modifiction on the aggregation level and interfacial interactions of nano-Sb₂O₃ particles within nano-Sb₂O₃/BEO-PBT composites are qualitatively characterized and quantitatively evaluated.The main results are as follows:（1）The surface of nano-Sb₂O₃ particles was modified with various surfactants（CTAB,PEG and KH550）by using mechanochemical method which endlessly provided fresh surface and energy for causing chemical adsorption.The fourier transform infrared spectroscopy（FTIR）results indicate that the adsorption of ionic surfactants CTAB on the surface of nano-Sb₂O₃ particles originate from the electrostatic interaction,the adsorption of non-ionic surfactants PEG on the surface of nano-Sb₂O₃ particles is hydrogen interaction,while the KH550 molecules are chemically anchored on the surface of nano-Sb₂O₃ particles through the covalent effect of Sb-O-Si.The results of TEM,UV absorbance and particle size distribution show that the dispersion stability of modified nano-Sb₂O₃ particles is significantly improved,and the average particle size and polydispersity index（PI）are reduced.Besides,the nano-Sb₂O₃ particles that were modified by the compounds of CTAB and KH550 not only had best dispersity,but also exhibited the highest hydrophobicity with surface contact angle of 134.7o,which could enhance the dispersion state and interface compatibility of nano-Sb₂O₃ particles within nanocomposites.（2）The BEO-PBT and nano-Sb₂O₃/BEO-PBT composite powders were prepared by using a high energy ball milling（HEBM）process.The effects of the milling time and the nano-Sb₂O₃ particles content on the structure,morphology,particle size distribution and thermal behavior were discussed and the formation mechanism of HEBM was also analyzed.The results of intrinsic viscosity,TGA,DSC and FTIR indicate that the HEBM process and the addition of nano-Sb₂O₃ particles reduce the relative average molecular weight and decrease the crystallinity of BEO-PBT,but did not change the chemical structure of PBT.The results of particle size distribution and SEM backscattered electrons（BSE）images indicate that the average particle size of nano-Sb₂O₃ particles within the nano-Sb₂O₃/BEO-PBT composite powders is changed from 370 nm that milled for 0 h to 180 nm that milled for 10 h.Besides,the interfacial tension between nano-Sb₂O₃ particles and PBT can be significantly reduced by the HEBM process,which consequently formed specific interactions by hydrogen bonds between the hydroxyl groups on the surface of nano-Sb₂O₃ particles and the carbonyl groups of PBT molecules.Therefore,the HEBM process not only improved the dispersion of nano-Sb₂O₃ particles within the nanocomposites,but also obtained a special interaction between PBT and nano-Sb₂O₃ particles.（3）The mechanical properties of nano-Sb₂O₃/BEO-PBT composites which were dispersed by the HEBM were discussed.The effects of milling time on the aggregation level and the interfacial interactions of nano-Sb₂O₃ particles within the nanocomposites were quantitatively analyzed by the tensile strength and Young’s modulus of PBT-BEO and nano-Sb₂O₃/BEO-PBT composites.The results show that the aggregated size(D_agg)of nano-Sb₂O₃ particles within the nanocomposites increase with the increased nano-Sb₂O₃ particles content but the real filling degree(V_re),interfacial adhesion parameters including interfacial compatibility（B）,interfacial strength（σ_i）and interface thickness（r_i）are increased with the milling time increasing.The higher B shows the lower r_i at higherσ_i.When the nano-Sb₂O₃ particles are added,the agglomerates of nano-Sb₂O₃ particles are inevitably presented within nanocomposites.The D_agg of nano-Sb₂O₃ particles had great influence on the aggregated interfacial compatibility(B_agg)and interfacial area(A_ia).The lower the D_agg,the higher the B_agg and the A_ia are.Besides,interfacial strength(σ_agg)and interface thickness（R_i）between the aggregated nano-Sb₂O₃ particles and PBT are mostly depended on the D_agg and the B_agg parameters.The larger the D_agg and the B_agg,the higher theσ_agg and the R_i are.However,the largest D_agg could produce many defects and stress concentration in the nano-Sb₂O₃/BEO-PBT composites,which affected the ultimate mechanical properties of nanocomposites.（4）The effects of the surface modification of nano-Sb₂O₃ particles on the properties of nano-Sb₂O₃/BEO-PBT composites were discussed.The qualitatively characterized results including scanning electron microscopy（SEM）,thermal stability analysis（TGA）,differential scanning calorimetry（DSC）and dynamic thermodynamics（DMA）indicated that the dispersion and the interfacial compatibility of modified nano-Sb₂O₃ particles within nanocomposites are improved.The quantitatively analyzed results indicate the D_agg of modified nano-Sb₂O₃ particles within the nanocomposites is obviously smaller than that of the unmodified nano-Sb₂O₃ particles,whereas the A_ia and V_re of modified nano-Sb₂O₃ particles are higher than that of the unmodified nano-Sb₂O₃ particles.The D_agg of unmodified,CTAB modified,KH550 modified and their compounds modified nano-Sb₂O₃particles within the PBT matrix is 140.3 nm,121.7 nm,99.6 nm and 89.2 nm,respectively.The interfacial compatibility of nano-Sb₂O₃ particles with the PBT matrix was analyzed by two different empirical equation including b and B.The interfacial compatibility b of unmodified,CTAB modified,KH550 modified and their compounds modified nano-Sb₂O₃ particles which evaluate from the DMA is 7.9,11.6,13.3 and 14.5,respectively.The interfacial compatibility B of unmodified,CTAB modified,KH550 modified and their compounds modified nano-Sb₂O₃ particles which evaluate from the tensile strength is 4.31,4.60,4.90 and 5.14,respectively.Besides,theσ_i of CTAB/KH550 mofidied nano-Sb₂O₃/BEO-PBT composites is ranged from60.5 MPa to 110.2 MPa,which can effectively deliver the triaxial stresses to the nano-Sb₂O₃ particles to adsorb more energy.Therefore,the ultimate mechanical properties of nano-Sb₂O₃/BEO-PBT composites can be significantly improved.