摘要:

Studies of polymer degradation over the past decade have increasingly been carried out using thermoanalytical methods. These methods involve the measurement of a convenient variable during a gradual, linear increase in temperature. The most widely used of these techniques are thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The morphology of a polymer sample (i.e., the crystallinity, shape and size of the crystals, the structure of the surface of the crystals, and the strain of amorphous regions) influences the heat content and its dependence on temperature. The latter can be satisfactorily investigated by calorimetry measurement in a differential scanning calorimeter.

ISSN:0360-2559    

DOI:10.1080/03602558908049808

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Most of the research in the field of olefin polymerization is focused on TiC1, catalysts on a specially prepared MgCl, support. In order to combine a high polymer yield with good stereoselectivity, a complexed cocatalyst is used. Most frequently it is a mixture of AIEtzCl or AlEt, with an electron donor such as tetrahydrofuran (THF) or ethyl benzoate for ethylene and propylene polymerization, respectively.

ISSN:0360-2559    

DOI:10.1080/03602558908049809

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

At present many new fluids not obeying the Newtonian laws are being studied by scientists because of their industrial importance [1]. The constitutive equations of these fluids have been given by different researchers, for example, Oldroyd [2] and Walters [3]. Beard and Walters [4] solved the two-dimensional boundary layer flow for an elasticoviscous fluid, near a stagnation point for the case of Walter's liquid B″, when the elasticoviscous parameter is very small. A new method is now proposed for determination of the two-dimensional boundary layer flow near a stagnation point for Walter's liquid B″ I, which is valid not only for very small positive elasticoviscous parameters but also for positive elasticoviscous parameters.

ISSN:0360-2559    

DOI:10.1080/03602558908049810

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The commercial application of polymer blends is undoubtedly the result of extensive research in this field. However, sometimes poor performance results from incompatibility of components in the blends, which in turn affects processibility. Processing is in large part simply flow and forming of compounds. A major problem often encountered in industry is batch-to-batch variation of viscosity and elastic memory of the compound, two characteristics which largely determine the compound's processability and dimensional stability. Efficient and quality production require reproducibility in the processing stages [1–4]. If a polymer melt is sheared mechanically, it can then be processed in a less elastic and less viscous state provided that the recovery of a more fully entangled, equilibrium state is not too fast [5]. Mechanical shear may reduce entanglement density r6–81. Shear modifications are manifested in changes in viscosities, die swell, die entrance pressure losses, melt fracture, etc. Various methods have also been developed over the years for rheological characterisation of polymer melts (9–17).

ISSN:0360-2559    

DOI:10.1080/03602558908049811

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Effects of degree of crosslinking in butyl rubber on the flow behavior and morphology of crosslinkable polyethylene (XLPE) and butyl rubber blends have been studied as a function of shear rate and processing temperature. Viscosity, flow activation energy, and rheological parameters have been studied with reference to the effect of blend compositions. Low-crosslinked butyl rubber showed higher normal stress difference than the highly crosslinked butyl rubber in the blend. As evidenced from extrudate swell, melt compliance, and Reynolds number, phase reversion in low-crosslinked butyl rubber occurred within a narrow composition range whereas in highly crosslinked butyl rubber blends, the change occurred over a wide composition range. Change of phase has also been confirmed by SEM examination. Highly crosslinekd butyl rubber showed higher elastic response than low-crosslinked rubber.

ISSN:0360-2559    

DOI:10.1080/03602558908049812

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Epoxy (DGEBA)-glass fiber laminates were cured with different hardeners. Imide-amine hardeners were synthesized with different chemical groups in their backbone structure. Higher curing and postcuring temperatures were required for epoxy-glass fiber laminates cured with imide-amine hardeners. Compared to epoxy cured with aromatic amine (DADPM), tensile and flexural strength increased by 38.5% and 23.1%, respectively, in the laminates cured with imide-amine with sulfone groups in the backbone structure. Fracture surface of the laminates showed good bonding between the fiber and matrix.

ISSN:0360-2559    

DOI:10.1080/03602558908049813

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Molecular transport of small molecules through polymer films has been widely studied over the past several years [1–8]. In most of these investigations it has been shown that the penetrant solubility and diffusion follow Henry's law and Fick's law, respectively, and that solubility (S), diffusion (D), and permeability coefficients (P) are independent of penetrant concentration. Several theories of diffusion, permeation, and solution have been developed to relate the experimental data to polymer film morphology, chemical structure, and other physical properties [9–14]. From a practical view point, the phenomenon of transport is very useful in the treatment of hazardous waste in landfill areas. In chemical industries, its importance lies in the separation of organic compounds. Additionally, membrane separation techniques have been used in such industrial applications as desalination of brine, salt manufacturing from seawater, oxygen-enriched air, etc. The pervaporation technique wherein the permeate is removed from a mixture at the opposite side of the membrane as a vapor is now very popular [15].

ISSN:0360-2559    

DOI:10.1080/03602558908049814

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Block and graft copolymers with incompatible sequences exhibit characteristic morphological behavior and interesting properties, owing to microdomain formation in the solid state. The thermodynamic approach to the problem of microdomain formation for block copolymers has been worked out [1–5] by demonstrating that the morphology of the domain structure-such as equilibrium size, shape, and interfacial thickness-can be described in terms of a balance of physical factors. It has been established, especially by electron microscopy, small-angle X-ray scattering, and X-ray diffraction, that segregated microphases can be spheres, cylinders, or lamellae. The type of morphology adopted by the copolymer essentially depends on its composition [6]. The morphological changes on AB block copolymer will be observed also by changing the selectivity of the casting solvent for the A component in solution-cast films or in ordered solutions [7–9], simply because selectivity changes the ratio between the effective radii or gyration of A- and B-block chains. More recently, a new morphology named “tetrapod-network” structures were found in a block copolymer [10], a three-component pentablock copolymer [11], and in star- block polymers [12–14]. Generally, physical properties of these multicomponent polymer systems depend strongly on the morphology of domain structure. According to the foregoing results, thc establishment of a synthesis method for well-defined block and graft copolymers will be important in the design of the desired morphology of the domain structure (domain spacing and shape).

ISSN:0360-2559    

DOI:10.1080/03602558908049815

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0360-2559    

DOI:10.1080/03602558908049816

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0360-2559    

DOI:10.1080/03602558908049817

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor