Studies on Miscibility, Morphology and Crystallization Kinetics of PBT/PAr Blend

• Main Authors: Ai-Sen Liu, 劉埃森
• Other Authors: Wen-Bin Liau
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/41072153667376098433

博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 87 === The miscibility, morphology and crystallization kinetics of poly(butylene terephthalate) [PBT] blending with different backbone of polyarylates [PAr] are the subjects in this investigation. The PBT is a crystalline polymer, and PAr can be crystalline or amorphous one by means of structural modification, therefore, they can blend into binary crystalline [PBT/PAr(I-100)] and crystalline/amorphous [including: PBT/PAr(I75-T25), PBT/PAr(I50-T50), PBT/PAr(I25-T75) and PBT/PAr(T-100)] blend systems. From the results of DSC analysis, a single and composition-dependent glass transition temperature was found and characterized the thermodynamically miscible for all the five blend systems. Specifically, the PBT and PAr(I-100) can crystallize sequentially rather than simultaneously in the 50/50 composition by weight. In addition to the dilution effect of PAr(I-100) on PBT, the suppression effect of previously formed PBT crystallites on PAr(I-100) recrystallization are more pronounced. From the WAXD patterns, it can be proved that both crystals coexisted and didn''t alter crystal structure by each other as well as formed cocrystal. From the isothermal crystallization experiments, the interaction parameters, 12, were all negative, and different degree of depression in melting points were obtained, showing that the PBT with five different kinds of PAr blends are miscible but with different degree of miscibility. On the other hand, the miscibility of PBT, PAr(I-100) and PAr(T-100) were qualitatively predicted using the binary interaction model developed by Flory and Huggins'' mean-field theory. It was primarily due to the intramolecular attractive effect of PAr segments. The observation of morphology by POM found that the addition of PAr into PBT caused the spherulites texture more coarse, and the dimension became smaller and nucleation density became more dense with increasing amount of PAr. Similarly, the addition of PBT can improve the mobility of PAr(I-100) segments, and the morphology of PAr(I-100) from sheaf-like switched to spherulite. In contrast to the growth rate depression of PBT, the addition of PAr(I-100) also induced the PBT growth mechanism transition from regime III to II. It was probably due to the reduction in degree of undercooling and change in surface free energy caused by miscibility. Finally, the conformations of PAr simulated by molecular mechanics showed that the PAr(I-100) is helix and the PAr(T-100) is crankshaft type. However, the conformation of -form crystalline PBT is nearly linear. From the difference of packing density in molten state of different PBT/PAr blends analyzed by WAXD, it can infer that the interaction strengths between PBT and PAr segments are by the order of T-100 > I-100 > I25-T75 > I75-T25 > I50-T50. These were in agreement with the magnitude order of different PBT/PAr blends of spherulitic growth rates under the same degree of undercooling and composition.