Study On Structure And Properties Of Polymer/POSS Composites By Reactive Processing

Organic-inorganic nanocomposites have drawn great attention due to their excel combination of properties of organic polymers and with inorganic systems. Polyhedral oligermeric silsesquioxane (POSS) is a kind of important organic-inorganic hybrid molecular with a formula of (RSiO1.5)n. Nanostructured POSS molecular, with the diameter of 1~3 nm, is thought as"the smallest possible particles of silica". Due to its special structure and properties, POSS (0-D) can be thought as one of the most promising nanofillers which including clay layered silicates (2-D), single and multi-wall carbon nanotubes (1-D), and has drawn great interest.Recently, POSS has been widely introduced into polymers by chemical copolymerization or physical blending. In this study, polymer/POSS composites were prepared through reactive processing method and their structure and properties were studied. There are three parts in this study: (1) The study on structure and properties of epoxycyclohexyl POSS (epoxy-POSS) chain-extended poly(butylene terephthalate) (PBT), (2) The study on structure and properties of octavinyl POSS (OvPOSS) grafted polypropylene (PP) by reactive blending, (3) The study on structure and properties of maleic anhydride-grafted PP (MA-g-PP) reactive compatibilized PP/octaaminophenyl polyhedral oligomeric silsesquioxane (OapPOSS) composites.(1) The study on structure and properties of epoxy-POSS chain-extended PBTEpoxy-POSS chain-extended PBT was prepared by reactive extrusion. The epoxy-POSS chain-extended PBT has higher intrinsic viscosity, lower carboxyl content and melt flow index (MFI) than PBT. PBT had an intrinsic viscosity of 1.1 dL/g, carboxy1 content of 21.6 eq/106g and MFI of 30 g/10min, but the PBT chain-extended with 2 wt% epoxy-POSS had an intrinsic viscosity of 1.7 dL/g, carboxy1 content less than 7 eq/106g and MFI of 7 g/10min. The chain-extended PBT has also improved mechanical properties and thermal properties, indicating it is favorable for storage, processing and application.(2) The study on structure and properties of OvPOSS grafted PP by reactive blendingThe OvPOSS grafted PP was prepared by reactive blending in the presence of dicumyl peroxide (DCP), and the structure and properties of PP/OvPOSS composites were studied. The graft ratio of OvPOSS increased with the increase of DCP or OvPOSS content. The structure and properties of PP/OvPOSS composites prepared by two different processing methods (physical blending and reactive blending) were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and rheological test, respectively. For the physical blending composites, POSS molecules can completely dissolve in PP matrix at OvPOSS content lower than 2 %, and aggregate to crystal with further increasing OvPOSS content. And the dissolved OvPOSS molecules can act asβ-form crystalline nucleating agents. While for the reactive blending composites, OvPOSS had good compatibility and dispersion in PP matrix. Theβ-form crystal disappeared. The reactive blending composites have better mechanical properties than the physical blending ones, and have the best mechanical properties at 2 % OvPOSS content. The impact strength and flexural modulus of PP filled with 2 % POSS and 0.1 % DCP are about 50 % and 20 % higher than that of pure PP, respectively. PP/OvPOSS composites have lower degradation temperature than PP, and the reactive blending composites have better thermal stability than that of the physical blending ones. The heat release rate and mass loss rate decreased whenOvPOSS was added.The rheological behavior of physical and reactive blending composites was compared by using oscillatory rheological measurements and melt flow index. It was found that the viscosity of physical blending composites drops at lower OvPOSS content (0.5~1 wt %) and thereafter increases with increasing OvPOSS content. While the viscosity of the reactive blending composites increases with increasing OvPOSS content and the composites display a solid-like rheological behavior at low frequency region when POSS content is higher than 1 wt %. The deviation of reactive blending composites from the scaling log G′-log G″of linear polymer in Han plot, upturning at high viscosity in Cole-Cole plot and from van Gurp-Palmen plot are related to the gelation behavior when OvPOSS was grafted to PP chains..Isothermal and nonisothermal crystallization behavior was analyzed by DSC test. The crystallize peak temperature (Tp) of physical blending PP/OvPOSS composites is close to that of pure PP and changes little with increasing OvPOSS content. While for the reactive blending composites and OvPOSS-g-PP, Tp is greatly higher than that of PP and changes little with increasing OvPOSS content. It indicates that aggregated OvPOSS crystals have little nucleating effect on PP while grafted OvPOSS has significant nucleating effect and the nucleating effect changes little with increasing the graft ratio of OvPOSS. The Avrami equation was used to study the isothermal crystallization kinetics of PP and PP/OvPOSS composites. The results show that OvPOSS can act as a heterogeneous nucleating agent, especially effective for the reactive blending composites. Addition of OvPOSS accelerates the crystallization of PP, increases the rate of crystallization and decreases the chain folding energy of PP. For the nonisothermal crystallization kinetics of PP/OvPOSS composites, the Ozawa equation is not suitable for these materials while the combination of Avrami and Ozawa equations exhibits great advantages in treating the nonisothermal crystallization kinetics of PP/OvPOSS composites. The activation energies (ΔE) calculated by Kissinger and Takhor methods for the nonisothermal crystallization of phtsical blending and reactive blending PP/OvPOSS composites are slightly higher than PP.(3) The study on structure and properties of MA-g-PP reactive compatibilized PP/OapPOSS composites.OapPOSS was prepared and filled to PP and MA-g-PP was selected as compatibilizer. The addition of MA-g-PP could improve the compatibility between PP and OapPOSS, promote a fine dispersion of OapPOSS particles in PP matrix and improve the mechanical properties of PP due to the reaction of amine groups of OapPOSS with maleic anhtydride groups of MA-g-PP. With increasing OapPOSS content, the Tp of PP/OapPOSS composites decreased while that of PP/MA-g-PP/OapPOSS composites increased, indicating OapPOSS could retard the crystallization of PP in PP/OapPOSS composites, while the nucleating effect compensated and overlapped the retardation effects when MA-g-PP was added. For PP/OapPOSS composites,η* increased with increasing OapPOSS content, while theη* of all the PP/MAPP/OapPOSS composites was lower than that of PP /OapPOSS at the same OapPOSS content and reached the maximum at 5 % OapPOSS content. It is probably due to the lower particle-particle interaction and interface slipping when OapPOSS was encapsulated by PP chain when OapPOSS was reacted with MA-g-PP.The innovations of this dissertation are list as follows:Recently, POSS has been widely introduced into polymers by chemical copolymerization or physical blending. While there are little reports about PP/POSS composites prepared by reactive processing. In this study, POSS was introduced to polymers to improve the properties of polymers. Compared with PP/POSS composites prepared by physical blending, the reactive blending composites had better mechanical properties. Their rheological behavior and thermal properties were different.(1) A method of epoxy-POSS chain-extended PBT was investigated. PBT chain extended by this method has higher viscosity, lower gel content, better thermal stability and lower water absorption, which is advantage for storage, processing and application of PBT.(2) OvPOSS was firstly grafted to PP by reactive blending method. The structure and properties of the composites prepared by the two processing methods (reactive blending and physical blending) was studied. For the reactive blending composites, OvPOSS has goog compatibility and dispersion in PP matrix, significant nucleating effect on the crystallization of PP and improved the mechanical properties of PP. Reactive blending has advantages of simplified technique, short product cycle and no complicated aftertreat including separation, purification and solvent recycle. The properties of reactive blending composites also have better properties than physical blending composites. It provides a new method to prepare polymer/POSS composites.(3) The rheological behavior of reactive blending and physical blending composites was compared, and the structure-property relationship of composites was discussed. The reactive blending composites display solid-like rheological behavior at low frequency region when OvPOSS content is higher than 1 %, while the physical blending composites do not display solid-like rheological behavior even at 10 % OvPOSS content. The difference of rheological behavior of two different methods was explained by the interaction of POSS and polymer, which can provide the reference for investigating the structure-property relationship of other polymer/fillers composites.(4) MA-g-PP was selected as reacitve compatibilizer to PP/OapPOSS composites. The addition of MA-g-PP could improve the compatibility between PP and OapPOSS, and improve the mechanical properties of PP due to the reaction of amine groups of OapPOSS with MA-g-PP. It provides a method for choosing suitable formation of POSS filled polymer and studying the structure-properties relationship.