| Composite is a kind of novel materials consisted of polymer,nonmetallic or metallic materials.It has better properties than neat materials.People prefer polymer composites because of the excellent performance.They attract many researchers in the materials fields and have been applied in many fields,such as industry,agriculture, aviation and spaceflight,national defence et al.Fillers,especially functional fillers can improve some properties or bring some new properties for composites.Inverse gas chromatography(IGC) is an effective method to obtain the macro thermodynamic properties of the surface of solid materials and study the relationship between the thermodynamic parameters and the composition and conformation of surface.It can be used to characterize the effect of the surface modification of fillers and the influence of the surface modification on the polymer composites, consequently predict the interactions between fillers and polymers.It can be used to characterize the surface activity of materials and provide the theoretical base for the use of the materials and the design of composites.The main research content and results are as follows.(1) Inverse gas chromatography(IGC) was used to characterize the surface properties of pristine multi-walled carbon nanotubes(MWNTs),as well as the poly(acrylic acid) sidewall covalently functionalized MWNTs(PAA-g- MWNTs) and hydroxyl group directly grafted MWNTs(MWNTols).The surface thermodynamic parameters were calculated,including the dispersive component of the surface energy(γSD),the specific free energy(△GAB),the enthalpy(△HAB) of adsorption corresponding to acid-base surface interactions and the acidic(KA) and the basic(KD) parameters.The results show that chemical modification successfully reduces the dispersive component of the surface energy of MWNTs. Furthermore,MWNTs grafted with hydroxyl groups exhibit a more basic character,while MWNTs grafted with poly(acrylic acid) show a more acidic character,which can reduce the agglomeration of CNTs and strengthen the interaction between CNTs and polymer at the same time.IGC can provide useful complementary information on the changes resulted from the chemical modifications of the surface which is difficult for other technologies,such as FTIR et al.(2) Phenolic resin/expanded graphite(EG) composites were synthesized via in situ condensation polymerization of the monomers in the presence of foliated graphite. SEM observation showed that the graphite flakes were well dispersed in the phenolic resin matrix.The electrical conductivity of the composites was investigated as a function of the foliated graphite fraction.The composites containing graphite sheets exhibited an electrical conductivity percolation threshold with 3.2 wt%graphite content in polymer matrix.Inverse gas chromatography measurements were carried out to characterize the surface of the foliated graphite before and after condensation polymerization of phenolic resin using a series of both non-polar and polar acid-base probe gases.The data obtained indicated that the character of graphite surface changed after the polymerization of phenolic resin.The dispersive component of surface free energy decreased greatly.Before polymerization the graphite surface is predominantly acidic while the surface turns to basic after polymerization.The increased polarity of surface contributed to the stronger interactions between graphite and phenolic resin and the fine dispersion of expanded graphite in the matrix,and resulted in the low conductivity percolation threshold.(3) Zeolite loading rhodium(Rh)was prepared by the wet impregnation method using H-β-zeolite as support.Retention time of three n-alkanes(C5-C7),cyclohexane, benzene,trichloroethylene and tetrachloroethylene on the Rh/H-β-zeolite catalysts (0.5-2.0 wt%of Rh) and H-β-zeolite were measured by inverse gas chromatography(IGC) in the 473.2～513.2 K temperature range.Standard free energy of adsorption,dispersive component of surface free energy of adsorbent and specific interaction parameters between polar probes and catalysts were evaluated.The results indicate that the adsorption characteristics of H-β-zeolite can be modified by rhodium.Surface area,enthalpy of adsorption and dispersive component of surface free energy of the zeolite decrease after the impregnation of rhodium.Besides,it was found that rhodium dispersed in the framework of H-β-zeolite had special adsorption for benzene which may be useful for making catalysts for certain reactions and separation engineering involving benzene in the future.(4) Because of the specific interaction between benzene and the zeolite loaded with rhodium(Rh/H-β-zeolite),novel hybrid membranes were prepared by incorporating Rh/H-β-zeolite into polyvinyl chloride(PVC) for the pervaporative separation of benzene and cyclohexane.The characteristics of these membranes for separating benzene/cyclohexane mixtures were investigated by varying zeolite type,zeolite content,feed composition and operating temperature. The results showed that the pervaporation performances for membranes filled with Rh/H-β-zeolite were higher than those for membranes filled with H-β-zeolite which was caused by the special interactions between benzene and Rh/H-β-zeolite proved by IGC previously.And the PVC-RhB-7 membrane exhibited much lower activation energy EJ value compared to PVC-B-7 membrane.The membrane containing 7%of Rh/H-β-zeolite had the highest separation selectivity of benzene at all feed composition.When zeolite content is lower than 7%,the membrane flux decreases and separation factor increases with the increase of zeolite loading. The reason was that the zeolite particles were more resistant to membrane swelling and reduced possibility of loosening of polymeric chains.When zeolite content is higher than 7%,the membrane flux increases and separation factor increases because of the defects on the interface.
|
PDF Full Text Request