摘要:

A new method using a simple zone drawing technique was suggested for determining optimum initial concentration of polymer solution which has suitable macromolecular entanglements. Ultra high molecular weight (UHMW) polyethylene (PE) gel films were prepared from decalin solutions with concentrations of 0.3, 0.5, 0.7, and 1.0 g/dL, and different gelation/crystallization temperatures. In order to investigate drawing behaviors of UHMW PE gel films with different solution concentrations, those prepared were drawn under various zone drawing conditions. Through a series of experiments, it turned out that the initial concentration of PE solution in decalin caused significant changes in the draw ratio of UHMW PE gel film. That is, the one-step zone draw ratio of the gel film for initial concentration of 0.5 g/dL was at its maximum and gradually decreased at higher or lower concentrations. Moreover, this tendency was similar to the maximum draw ratio data. Thus, it was shown that the initial concentration of 0.5 g/dL is the optimum polymer concentration to produce maximum draw ratio in this work. Based on these results, it may be concluded that the optimum concentration of the initial UHMW PE solution can be determined directly by the zone draw ratio.

ISSN:0022-2348    

DOI:10.1080/00222349708220412

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The sorption and diffusion of water in various types of ethyl cellulose that had a degree of substitution (DS) in the range 1.7–2.6 was investigated and compared to the properties of pure cellulose. The derivatives were characterized by thermal and thermomechanical methods. The water vapor sorption isotherms were analyzed by the Zimm-Lundberg function, which relates the volume fraction activity coefficient, γ1, of the solvent in condensed incompressible systems to the cluster integral,G11, based on the expressions forG11originally introduced by Kirkwood and Buff. Using the Orofino equation, which expresses the tendency of solvent clustering in terms of a formal activity dependence of the Flory interaction parameter χ, the χ(0) parameter at zero solvent concentration was evaluated. Since Flory-Huggins thermodynamics cannot be applied unequivocally to systems exhibiting marked water clustering, χ(0) was identified to be the “true” Flory parameter. The clustering functions obtained and the χ(0) values showed a strong dependence on the DS, both clustering tendency and χ(0) values increasing with increasing DS. The diffusion coefficient of water and the glass transition temperature were discussed as a function of water clustering in the polymers. The results of the cluster analysis confirm Barrer's idea that the unusual concentration dependence of the diffusion coefficient of water in highly substituted ethyl cellulose can be related to a nonrandom molecular distribution of the sorbed water molecules. Accordingly, the effect of water clustering in pure cellulose appeared to be of less consequence than its plasticizing effect, while the opposite is found in highly substituted ethyl cellulose.

ISSN:0022-2348    

DOI:10.1080/00222349708220413

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Some metallocene catalyst synthesized short chain branched polyethylene (SCBPE) samples have been found to possess at least intermolecular heterogeneity in the SCB. As-received SCBPE samples are molecularly homogeneous in the isotropic melt. However, phase separation due to the intermolecular heterogeneity can be found via molecular segregation processes induced by multiple-step isothermal crystallization experiments. When the phase-separated SCBPE samples are reheated above their melting temperatures, the phase-separated (heterogeneous) melt is maintained for an extended period of time (at least 20 h at 150°C). Neither phase mixing in the melt nor significant changes in molecular weight, molecular weight distribution, comonomer content, or sequence have been found during the high-temperature treatment. Comparisons of overall crystallization kinetics and morphology of the SCBPE samples obtained from the homogeneous and heterogeneous melts exhibit substantially different behavior which indicates that the phase-separated melt exists and can be identified.

ISSN:0022-2348    

DOI:10.1080/00222349708220414

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Lamellar single crystals of poly(ethylene terephthalate) (PET) have been prepared by our confined thin film melt polymerization method between glass at polymerization temperatures of 150° to 225°C. (010) twinned crystals are frequently observed among these lamellae, especially for those prepared at higher temperatures. Based on [001] and [101] electron diffraction patterns, with a total of 25 independent reflections, the lattice parameters are determined asa= 4.657,b= 5.836,c= 10.831 Å;α = 96.26°,β = 128.30°, and γ = 106.62° with a calculated density of 1.559 g/cm3for a “perfect” PET single crystal. Chain packing and molecular conformation in the triclinic unit cell (Pì) were simulated by the Cerius2modeling software.

ISSN:0022-2348    

DOI:10.1080/00222349708220415

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The autocorrelation function (ACF) was measured at various temperatures using the dynamic light scattering (DLS) technique for two kinds of toluene solutions of poly(γ-benzyl L-glutamate) (PBLG): one was a semidilute PBLG (Mw= 2.3 × 105) solution far above the critical crossover concentration ø2*(PBLG-23), and the other was also a semidilute PBLG (Mw= 1.0 × 105) solution nearø2*(PBLG-10). Both of the PBLG solutions were sol at elevated temperatures and gelled with decreasing temperature. For PBLG-23, the ACF obtained in the sol phase could be fit well by a double-exponential function: the fast mode was due to a cooperative diffusive motion in a transient entangled PBLG-23 network; the slow mode was considered to be diffusive motion of aggregated PBLG-23 chains. On the other hand, the ACF of PBLG-10 was characteristic and was modulated vibrationally near the gelation threshold. This fact suggested strongly underdamped coupling between aggregated domains of PBLG-10 chains.

ISSN:0022-2348    

DOI:10.1080/00222349708220416

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Strain-induced crystallization (SIC) is studied in blends containing 92 wt% ofcis-l, 4-polyisoprene (hevea rubber) and 8% of synthetictrans-l, 4-polyisoprene (t-PI), for different molecular weights of t-PI. The initial crystallinity (in the unstrained state) is analyzed in terms of the effect of both molecular weight and the microgel content. The SIC of the natural rubber was measured using the wide-angle x-ray scattering technique. Uncrosslinked solution blends were uniaxially stretched at room temperature, and the dependence of the induced crystallinity on elongation and molecular weight of the t-PI component was analyzed. Also, the molecular weight dependence of the induced crystallization rate is discussed.

ISSN:0022-2348    

DOI:10.1080/00222349708220417

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

It is shown that the mathematical law describing the scatter in measurements of the strength of solids, previously obtained by the author, is supported by data obtained on polyamide fibers. It is shown that this law is also applicable for some composite materials.

ISSN:0022-2348    

DOI:10.1080/00222349708220418

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Solution properties of polyaniline (PAn) doped by camphorsulfonic acid (CSA) were examined. PAn-CSA behaves like a poly-electrolyte to different extents depending on the solvent used. In anm-cresol/chloroform solution, PAn-CSA exhibits an expanded chain conformation because of its polyelectrolytic properties. Dilute and concentrated solution properties of PAn-CSA indicate that PAn-CSA is a semirigid polymer which has strong interchain interactions.

ISSN:0022-2348    

DOI:10.1080/00222349708220419

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The technique of time-resolved small-angle x-ray scattering is used to monitor the disorder-order transformation occurring in asymmetric, diblock styrene-butadiene. A rapid thermal quench is applied to drive the system from its initial high-temperature disordered state to a low-temperature ordered structure, a body-centered cubic lattice of styrene spheres characterized by a series of concentric Debye rings in the two-dimensional scattering profile. At relatively late times in the microdomain ordering process, the uniform Debye rings were seen to rapidly develop nonuniformities indicating the existence of preferred orientation with a fiber texture, the 110] axis of the bcc structure defining the fiber axis. These results are interpreted in the context of a developing transformation strain energy during the ordering process and shown to be consistent with accompanying changes in lattice spacing as well as earlier observations of apparent fluctuations in the ordering process.

ISSN:0022-2348    

DOI:10.1080/00222349708220420

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Blends of phenolphthalein poly(ether ether sulfone) (PES-C) with a thermotropic liquid crystalline copolyester (LCP) were prepared. Miscibility, morphology, thermal behavior, and mechanical properties of the PES-C/LCP blends with various compositions were studied by using differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), dynamic mechanical analysis (DMA), tensile tests, and scanning electron microscopy (SEM). Both DSC and DMA studies showed that the blends have two glass transition temperatures (Tg) corresponding to those of the PES-C-and LCP-rich phases, respectively. PES-C and LCP are partially miscible, theTg's varying with composition. Young's modulus increases slightly with increasing LCP content owing to the high modulus of LCP, whereas the tensile strength greatly decreases with increase of LCP content. The interfaces between PES-C and LCP are weakly bonded, with rather poor interaction. SEM observations revealed that the blends have a two-phase structure and that the adhesion between the phases is poor.

ISSN:0022-2348    

DOI:10.1080/00222349708220421

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor