Dendritic Crystal Morphology and Miscibility in Several Model Polyesters and Their Blends

• Main Authors: Kai-Cheng Yen, 顏凱宸
• Other Authors: Eamor M. Woo
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/27062914527522705610

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 95 === Miscibility and crystal growth kinetics in crystalline/crystalline blends of monomorphic poly(pentamethylene terephthalate) (PPT) with monomorphic poly(heptamethylene terephthalate) (PHepT) were probed using polarized-light optical microscopy (POM), differential scanning calorimetry (DSC). The blends comprising PPT and PHepT of all compositions were proven to be miscible in the melt state or quenched amorphous phase, whose interaction strength was determined (c12 = - 0.57), showing favorable interactions and phase homogeneity. Growth analysis also showed supporting evidence for miscibility between these two crystalline polymers. Regime-II parameters for crystals were compared between neat PPT and PPT blended with PHepT to assess effects on growth kinetics, phase, and spherulite patterns of PPT in the blends. For this system, no coincidence was found between the regime transitions of growth kinetics (from Regime-II to III) and spherulite patterns (transition from ringless to ring-banded). Specific interactions and miscibility are demonstrated in a series of binary miscible blend comprising of bio-compatible/biodegradable polyesters, such as poly(ethylene adipate) (PEA), or poly(butylene adipate) (PBA), and a macomolecular ester with polyphenol groups, tannic acid (TA). Thermal analysis and infrared spectroscopy were used for proving existence of favorable interactions, and polarized-light optical microscopy was used for characterizing the changes in crystal growth. The appearance of a single composition-dependent glass transition temperature (Tg) observed by differential scanning calorimetry (DSC) indicated that TA is miscible with PBA, and PEA, respectively, over the entire range of compositions. Fourier transform infrared (FTIR) spectroscopy confirmed the presence of specific intermolecular hydrogen bonding interactions between the carbonyl groups of polyesters and the phenolic hydroxyl groups of TA. The blend Tg’s generally exhibited various extents of positive-then-negative deviation from linearity with the compositions. The Tg-composition relationships for three blend systems could all be fitted by the Kwei equation with large negative q values of -60~ -70 for different polyesters. Significant effects by TA on the spherulitic crystallization growth in the polyester/TA blends were also discussed to support the miscibility and strong interactions. Overall, the behavior of blends of polyesters with TA is similar to that of blends of polyesters with poly(vinyl p-phenol) (PVPh) that have been more widely studied and reported. However, TA is naturally bio-resourceful, bio-compatible, and bio-degradable but PVPh is not. Synergism of miscibility, natural bio-compatibility, and biodegradability in these blends by introducing naturally biodegradable macromolecules such as TA may offer greater potential in intended applications. The third part of this study deals with the dendritic morphology of PEO/TA blends. Such peculiar morphology has been reported in many miscible PEO/amorphous polymer blends that are with strong intermolecular interactions. The miscibility of PEO/TA blends was determined by DSC, and strong intermolecular interactions were confirmed by FTIR. The crystallization kinetics of PEO/TA was analyzed by Lauritzen-Hoffman model. For this system, no regime transition was found in the crystallization temperatures measured. The crystallographic effect on the feather-like or dendrite morphologies of PEO/TA blend was analyzed by Wide-Angle X-ray Diffraction (WAXD). The intensity of (032) crystal planes decreased with the increase of TA content. It may be due to the constrained growth direction caused by the strong intermolecular interactions. Besides, the surface morphologies observed by AFM showed that the lamellar orientation changed from edge-on to flat-on.