摘要:

A series of copolymers and blends based on polybutylene were characterized using13C NMR and thermal analysis. Optical microscopy techniques were used to measure crystallization rates and examine their morphology, and this behavior was related to their composition. As expected, the highest melting and crystallization temperatures, and the fastest crystallization rates were obtained for the polybutylene homopolymer. Copolymerized ethylene randomly distributed along the chain, even at a level of 1%, significantly reduced the melting temperature and crystallization rate. Increasing the ethylene content to 5% results in a polybutylene which crystallizes with difficulty to produce poorly defined spherulites. Four blends based on a polybutylene containing 1% ethylene were studied. A dispersed crystalline phase could be detected in all cases. Two of the blends contained 6-7% ethylene but differed in molar mass. Their melting and crystallization behavior was similar although the spherulite growth rate for the lower molar mass material was a little higher. A second pair of blends contained 5-6% polypropylene and included a “nucleated” and a “nonnucleated” grade. Results for these suggested that the polypropylene itself was acting as a nucleating agent.

ISSN:0022-2348    

DOI:10.1080/00222349108219478

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A series of previously characterized polybutylenes were compression molded using various cooling conditions. Crystallinity decreased as cooling rate increased. The samples exhibited three types of tensile behavior. The crystallinity of samples containing around 5% ethylene was about 40%. These behaved as elastomers, exhibiting typical entropic elasticity. For the remaining samples, crystallinities between 55% and 70% were observed, depending on grade, and more particularly on cooling conditions. For these, lower crystallinity levels favor sample necking and stress-induced orientation, producing high elongation at break and high tensile strength values, while the higher crystallinity samples show high moduli and elasticity values coupled with uniform deformation. In the former case, significant crystalline deformation—causing alignment of the c axes of the crystallites towards the stretching direction, and thereby reinforcing the sample—is responsible for the high elongations and tensile strength encountered. In the higher-crystallinity case much of the deformation is taken up by interlamellar void generation, with little or noc-axis alignment, this elastic mechanism having been termed “hard elasticity.”

ISSN:0022-2348    

DOI:10.1080/00222349108219479

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Crystallization and melting, heat of fusion, and degree of crystallinity of syndiotactic PP were investigated. The double peak melting behavior was established for the partially crystalline polymer. A Hoffman-Weeks extrapolation resulted in equilibrium melting points of 151°C and 155°C for two polymers with relatively short syndiotactic sequences. The enthalpy of fusion was found to be 200 J/g, which corresponds to the value of isotactic pp. A very close correlation between the syndiotactic IR index and the heat of fusion was found. The melting point dependence on the sequence length was evaluated.

ISSN:0022-2348    

DOI:10.1080/00222349108219480

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Poly(ethylene terephthalate)/poly(butylene terephthalate) blends [xPET/(l-x)PBT] were prepared by ultraquenching of the melt between two metal rolls rotating in a liquid nitrogen bath. Both DSC and WAXS studies indicate that immediately after preparation, the blends are amorphous regardless of the composition. Two glass transition temperatures are found for the as-quenched 0.5 PET/0.5 PBT blend. The activation energies determined from the dependence of each glass transition temperature on the heating rate are approximately the same. Furthermore, they are equal to the mean activation energy for the overall crystallization. This can be explained in terms of the percolation threshold theory.

ISSN:0022-2348    

DOI:10.1080/00222349108219481

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The mechanical properties of miscible poly(butylene terephthalate) (PBT)/poly (hydroxy ether of bisphenol A) (phenoxy) blends obtained by melt mixing have been studied by means of the tensile test. The crystallinity of the blends has been studied by means of DSC and density measurements. A synergistic behavior, principally in the break properties, at high PBT contents in the blends is observed. As can be seen from the torque and density data, this synergistic behavior is related with the high level of miscibility which seems to exist at high PBT contents compared with that of the high phenoxy content region.

ISSN:0022-2348    

DOI:10.1080/00222349108219482

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Phase behavior in binary and ternary mixtures of ethyl cellulose (EC), hydroxypropyl cellulose (HPC), and acrylic acid (AA) was investigated by optical techniques including polarized-light microscopy (POM), refractometry, UV absorption, and circular dichroism (CD) spectrophotometries, and laser-light scattering. Both derivatives of cellulose formed a cholesteric liquid-crystal phase in concentrated solutions in AA. EC and HPC homopolymer solutions in AA showed iridescent colors in the concentration range of 42–50 wt% and 65–80 wt%, respectively. In the 30–50 wt% HPC/AA solutions, an optical image with fingerprint-like patterns was observed between crossed polars. CD revealed that the cholesteric helical sense was right-handed in the HPC/AA mesophase, while the EC/AA mesophase formed left-handed structures. Anisotropic samples of HPC/AA and EC/AA also showed a POM image with a grid-like texture, which was much coarser in the former system compared with that in the latter. A phase diagram constructed for the ternary system EC/HPC/AA was divided into five distinct regions: (1) isotropic (I) monophase, (2) I + HPC mesophase (HLC), (3) I + HLC + EC mesophase (ELC), (4) HLC + ELC, and (5) anisotropic monophase, with the optical appearance changeable depending on polymer composition and concentration. In region 5 the anisotropic system was apparently monophasic in POM observations; however, CD and UV results indicated that the biphasic separation into the two cholesteric structures still occurred. Optical anisotropy and phase behavior were also examined for the EC/ HPC binary blends prepared from solutions and melt.

ISSN:0022-2348    

DOI:10.1080/00222349108219483

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor