摘要:

The complex permittivities of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends have been measured under variation of temperatureT(20°-60°C), frequencyv(5 Hz-300 kHz), and hydrostatic pressurep(0-260 MPa). The values can be represented by a master curve with the shift factors △p/△log (v/Hz) = −140 MPa at room temperature and △ (1/T) /△ log (v/Hz) = −2. 10−4K−1at atmospheric pressure. The dependence of the activation energy △EAon pressurepis then given by △EA=(100 + 0.02 MPa−1p) kJ/mol. Furthermore, the results indicate that the β-relaxation of PVDF is due to motions in the crystal-amorphous interphase. The interactions between the two polymers, which are miscible at all compositions, disturb the correlations between the PVDF monomer units at that location as well as the mobility of the PMMA side group.

ISSN:0022-2348    

DOI:10.1080/00222349308215523

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Melt-crystallized poly(vinylidene fluoride)s (PVF2) with different crystallization histories were irradiated with γ-rays within the range of irradiation doses 0–83 Mrad. The effects on the crystalline structure and mechanical properties have been measured, compared, and discussed. The degree of crystallinity of the samples was found to increase with radiation dose. The differential scanning calorimeter scans of the quenched samples indicate that there are two melting peaks, and that the area of the lower temperature peak increases while the area of higher temperature peak decreases with increasing dose. Yield stress and breaking stress for all samples are not significantly affected by irradiation but elongation at break is.

ISSN:0022-2348    

DOI:10.1080/00222349308215524

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The tensile drawing of polyethylene terephthalate fibers spun from polymer of high and low molecular weight over a range of windup speeds has been studied. An analysis of the mechanical properties, orientation, and shrinkage behavior for different draw ratios leads to two conclusions. First, the network structure is the same for both polymers and the same as that described for a medium molecular weight polymer in an earlier paper. Secondly, an increase in molecular weight has an effect similar to an increase in the windup speed on the spun fiber molecular structure, which affects the ultimate mechanical properties obtainable by the chosen processing routes.

ISSN:0022-2348    

DOI:10.1080/00222349308215525

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The crystal-liquid crystal and liquid crystal-liquid crystal transitions (Tc-lcandTc-lc) of poly(p-oxybenzoate), nominally at 350° and 430°C, have been followed by electron diffraction (ED) using thin film polymerized single crystals. The ED patterns indicate the transition occurs in both phase I and II individual crystals over a broad temperature range, with high-orderhk0reflections being observable in the ED patterns of some samples. The molecular packing for phase II at room temperature, phase I and II high-temperature forms, and the relationship between the high- and low-temperature forms are proposed. Cooling from above theTc-lctransition temperature results in an apparent memory of the original structure. It is proposed that the high-temperature lattices, between 350° and 430°, should be described as molecular columnar or condis crystals. Above 430°C thehk0ED patterns are consistent with a nematic-type packing of the molecules.

ISSN:0022-2348    

DOI:10.1080/00222349308215526

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Reinforcement of acrylic denture base resin with high-performance polyethylene fiber in various forms (chopped, woven, and continuous parallel) resulted in a significant reduction of both water sorption at saturation and dimensional changes taking place during immersion. Incorporation of the fibers does not decrease the rate of approach to equilibrium, and in some cases, this is increased. The nonsteady state for each system can be described in terms of a “Fickian”-type diffusion process. Diffusion coefficients can be calculated with water uptake or with dimensional changes data, both giving similar values for any given system.

ISSN:0022-2348    

DOI:10.1080/00222349308215527

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor