摘要:

Porous interpolymer anion exchange membranes were prepared from poly-(vinylidene fluoride) and poly(l-vinyl-3-methylimidazolium iodide). Depending on the membrane composition, the hydraulic permeability and the membrane conductance were varied over four orders of magnitude. The rejection of potassium chloride, calcium chloride, and methylene blue solutions was determined during ultrafiltration. A model was developed to account for the observed salt rejection. The membrane porosity and tortuosity parameters for this interpolymer membrane system were compared with an analogous system of cation-exchange membranes derived from poly(styrenesulfonic acid) and poly(vinylidene fluoride).

ISSN:0022-2348    

DOI:10.1080/00222347808212595

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

By simultaneous recording of tensile stress-strain data and the free radicals formed during bond rupture, new knowledge is obtained of the molecular mechanism of deformation and fracture of oriented fibers. To do this, a large variation in molecular morphology was obtained by strain annealing nylon 6 fibers at various temperatures and tensions. The results show that in order to maximize fracture stress, it is necessary to break some chains during the annealing treatment. Tension will overcome the detrimental changes caused by high temperature; if sufficiently high tension is applied, higher strengths are obtained. It is also found that the initial rupture of chains will be later when the chains are more homogeneous and are able to absorb and distribute the stress more uniformly. This homogeneous stress distribution leads to stronger fibers.

ISSN:0022-2348    

DOI:10.1080/00222347808212596

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Experiments are described in which nylon 6 fibers are annealed while subjected to a constant stretch (or slack). Subsequent mechanical and structural measurements are described and analyzed. A paracrystalline structure model is proposed in which folded chains, fully extended chains, partially folded, and partially extended chains coexist in the highly drawn high strength fiber. An explanation of structural changes occurring during the thermal-mechanical treatment is that the folded and partially folded chains are arranged randomly in staggered fashion in small units throughout the structure. During slack annealing, the chains become more folded and shrinkage occurs. Some of the chain refolding will be permanent and may act as new defect sites thereby reducing fracture stress. During annealing in the presence of comparatively high tensile stresses the folded chains are unfolded to some extent, but not completely, and the load-carrying chains in the structure are more uniformly loaded. At the higher applied strains during annealing, chains are broken and may snap back into folds. The tension annealing increases the overall chain orientation, the strained segment uniformity, and the number of load-bearing chains. These factors may contribute to an increased fracture stress.

ISSN:0022-2348    

DOI:10.1080/00222347808212597

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The dynamic mechanical and dielectric β loss peaks in poly(ethylene tereph-thalate) are shown not to be comparable. Only the dielectric data are internally consistent, and these are used to infer which conformational changes occur during commercial processing.

ISSN:0022-2348    

DOI:10.1080/00222347808212598

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Infrared (IR) thermal analysis was used to study the extent, distribution, and the thermal behavior of hydorgen bonding in MDI-based segmented polyurethane elastomers. Two series of polyurethane elastomers were studied; one was based on a polytetrahydrofuran soft segment (ET series), while the second was based on a poly(tetramethylene adipate) soft segment (ES series). The hard segment in these materials was formed form p, p′-diphenylmethane diisocyanate (MDI) extended with butanediol. Bonded and free NH and C=O infrared absorbances were resolved as a function of temperature using a nonlinear least squares analysis for the fitting of Gaussian curve shapes. Results of this analysis revealed that at room temperature, about 80% of the NH groups in the ET and ES polyurethanes formed hydrogen bonds. In the ET polyurethanes, about 65% of the urethane carbonyls were hydrogen-bonded at room temperature. The extent of interurethane hydrogen bonding was found to be higher in the materials having better phase separation. Hard to soft segment hydrogen bonding was found to be weaker and was shown to dissociate first when the polyurethanes were heated from room temperature. A measurable amount of hydrogen bonding (∼35–40%) was found to remain at temperatures as high as 200°. The ΔH of hydrogen bond dissociation calculated from the Van't Hoff equation was used as an indication of hard domain perfection. Hard domain perfection was found to increase with increasing hard and soft segment length in both the ET and ES polyurethanes. Trends of soft segment Tgand ΔH suggest a dispersion of hard segments in the soft segment phase as well as a dispersion of soft segment material in the hard segment domain.

ISSN:0022-2348    

DOI:10.1080/00222347808212599

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Poly(ethylene oxide) fractions with molecular weights in the range from 1.55 × 103to 1.5 × 105were studied. The optical microscopic observations of the morphology of supermolecular structures grown isothermally from the melt were used to determine the dependance of structural-morphological changes on temperature. Two morphological transitions were established: (1) a high temperature transition at 49 [Ptilde] 3° C from hedritic structures to positive spherulitoids and (2) a low temperature transition at 38 [Ptilde] 2° C from positive spherulitoids to negative spherulites. It is supposed that the transition from hedrites to positive spherulitoids proceeds through a transition from b-axis-oriented lamellae with tilted chains to [401] lamellae with chains perpendicular to the lamellar surface.

ISSN:0022-2348    

DOI:10.1080/00222347808212600

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Until recently, linear polyethylene had never been quenched from the melt to the glass due to the ease with which it crystallizes. However, the publication by Hendra and co-workers [1] of IR and Raman spectra of amorphous polyethylene has stimulated renewed interest in the problem. In this note we would like to report preliminary results on a new ultraquenching technique which produces amorphous polyethylene with considerably greater reliability than Hendra's liquid nitrogen quench [2].

ISSN:0022-2348    

DOI:10.1080/00222347808212601

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor