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Study On Structure And Properties Of PHB/PEN,PEN And Their Reactive Blends

Posted on:2006-01-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:L ZhangFull Text:PDF
GTID:1101360152487440Subject:Materials science
Abstract/Summary:PDF Full Text Request
It has been recently considered as an important subject in the polymer materials field that to improve the compatibility between thermotropic liquid crystalline polymer (TLCP) and thermoplastic polymer (TP) with flexible chain via reactive blending in order to prepare the in-situ composites with better properties.Poly(ethylene naphthalate)(PEN) is a new product of polyesters, which has better mechanical property, thermal stability and gas barred property as compared to poly(ethylene terephthalate)(PET). The 60PHB/PEN synthesized by PEN instead of PET also has better properties than 60PHB/PET, however, there has been little research work concerned. Therefore, to sysmatically study the reactive blending of the two polymer components in the presence of small amount chain extender has not only academic but also potential application significances. In this dissertation a thermotropic liquid crystalline aromatic copolyester 60PHB/PEN was synthesized at first, and the thermal decomposition kinetics of PEN and 60PHB/PEN was analyzed in detail. The dependence of the crystallization and melting behaviors of the reactive blends on the transesterification of PEN/(60PHB/PEN) in the presence of small amount of chain extender, as well as the crystallization kinetics were systematically studied, the compatibility of the blend system and its spinnabilify was preliminarily discussed. The main results obtained are as follows:1. A thermotropic liquid crystalline copolyester containing 60mol% of p-hydroxy benzoic acid(PHB) was synthesized, the structure and the liquid crystalline nature of which were characterized by means of element analysis, FT-IR, 13C NMR, DSC, polarizing microscope with hot stage and WAXD methods. The results indicate that the obtained 60PHB/PEN is random copolyester of PEN and PHB sequences, whichexhibits a typical nematic liquid crystalline character in a range of temperature from 217℃ to 370℃.2. The thermogravimetric behaviors of PEN and 60PHB/PEN under isothermal condition at various temperatures and dynamic condition at various heating rates were examined. The data thus obtained were analyzed by using several kinetic methods. The results show that 60PHB/PEN has better thermal stability than PEN. All data including Td, Tdm, (da/dt)m, E and Ln(Z) derived from single heating rate method are increased with increasing heating rates, while n value still keep constant during the period. The decomposition of the polymer was transformed from decomposition-controlled process into diffusion-controlled process as the heating rate was increased.3. The effect of reactive blending conditions on the thermal behavior, such as glass transition temperature(Tg), cold crystallization temperature(Tcc), melting point(Tm) and crystallization temperature from the melt(Tmc) etc., of the blend system of PEN and 60PHB/PEN in the presence of small amount chain extender was studied by DSC method. The results show that there is little effect on Tg but the Tcc tends to be increased while both Tm and Tmc are decreased as the blending time and the temperature are increased respectively, which are also significantly affected by the addition of chain extender. All these changes are related to the change in sequence structure caused by transesterification reaction between PEN and 60PHB/PEN under melt blending conditions.4. The results from the study of isothermal crystallization kinetics of PEN/(60PHB/PEN) reactive blends reveal that blending time, temperature and chain extender will have an effect on the crystallization process. The Avrami exponential n is closely related to the preparation and testing conditions of the samples, which is changed in a range of 3.1-4.7. Both homogeneous and heterogeneous nucleations may coexist while the crystallites formed may also possess two and three dimensions during the crystallization. The addition of chain extender decreases the crystallization rate of PEN blocks in the reactive blends. It reveals that the effect of chain extenderon transesterification reaction makes to form sho...
Keywords/Search Tags:Poly (ethylene naphthalate), Thermotropic liquid crystalline copolyesters, In-situ composite, Reactive blending, Compatibility, Chain extender, Thermal decomposition, Crystallization
PDF Full Text Request
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