摘要:

AbstractThe packing densities (Van der Waals volume/molar volume) were determined at 293 K for various epoxide–amine stoichiometric networks. They are noticeably higher than those of linear polymers except strongly hydrogen bonded ones [polyamides, poly(vinyl alcohol)]. By extrapolation of the dilatometric data, it was found that the packing densities at the frontiers of the glassy state (0 K andTg) of the epoxy networks are comparable to those of linear polymers having the same theoretical hydrogen bond density (polyamides). However, for a given packing density at 0 K, the packing density atTgis higher for a network than for the corresponding linear polyme

ISSN:0021-8995    

DOI:10.1002/app.1988.070350301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractFollowing our previous work using fibrous biomass byproducts for radiation‐treated composite materials, polypropylene and two different kinds of PVC have been compounded with chopped coconut fiber (coir). Preirradiation of coir has been applied together with some crosslinking additive to achieve chemical bond between thermoplastics and fibrous biopolymer. Effect of addition of 10–50% coir to PVC and PP on the processability was monitored by Brabender plastograph. Dynamical mechanical analysis (DMA) data as well as tensile and impact strength of these coir composites have not been found superior to that of the starting thermoplastics. Considering, however, coconut fiber as a cheap filler, composites with acceptable tensile and impact strength could be produced with coir content as high as

ISSN:0021-8995    

DOI:10.1002/app.1988.070350302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThis paper gives the results of the estimated coagulum content in the final sample of a dispersion based on styrene–butylacrylate–acrylic acid, prepared by semicontinuous emulsion polymerization. The results were gained from experiments on 25 L and 5 m3reactors. The dependence of the amount of coagulum on the agitation intensity was studied. It was found that it is necessary to divide the results into two regions: (a) for specific power input smaller than 80 W/m3; (b) for specific power input greater than 80 W/m3. It was found that polymerization scaling up from the point of constant coagulum content in the system studied is possible under the conditions of constant specific power input. The specific power input varied in the range from 5 to 3000 W/m2. For the first region was gained the empiric correlationY= 2.16(ℰV)−1and for the second region the equationY= 3.5 × 10−5(ℰV)1.5, whereYis the amount of coagulum (wt %). For the existence of two regions we propose the following hypothesis according to which increasing mixing intensity improves the temperature and concentration nonuniformity which results in the decrease of coagulum content. From the certain value of specific power input, which is specific for each system, the amount of coagulum starts to increase due to increasing

ISSN:0021-8995    

DOI:10.1002/app.1988.070350303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effect of the initial temperature of heating on the elongation of syndiotactic‐rich poly(vinyl alcohol) thin films was investigated in water under a load. The elongation ratiosEiafter 4 h at fixed temperatures increased roughly with an increase in the initial temperatureTiand a decrease in the annealing temperature.Eiafter 4 h was the smallest atTi= 45°C for the films annealed at temperatures below 100°C.Eiwas 6.8 atTi= 60°C for the unannealed film and 1.12 atTi= 70°C for the film annealed at 200°C. The elongation at break decreased and the temperature at break increased with an increase in annealing temperature, but those at the annealing temperature of 100°C were the smallest. The films annealed at 200°C did not break even at 98°C (boiling temperature) in water and the elongation ratio was 1.42–1.97 in the initial temperature range of 10–70°C. From these results, the relation between the elongation in water and the state of polymer chains in film

ISSN:0021-8995    

DOI:10.1002/app.1988.070350304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractA series of four TDI–polypropylene oxide (PO) water‐blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of both the foams and plaques was investigated using dynamic mechanical spectroscopy (DMS), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM), swelling, wide angle X‐ray scattering (WAXS), and small angle X‐ray scattering (SAXS). A high degree of microphase separation occurs in these foams, and its degree is nearly independent of water (hard segment) content. In the foam with the lowest water content the morphology possesses many similarities to that of typical linear segmented urethane elastomers. Small hard segment domains are present with a correlation distance of about 7.0 nm. When the water content is increased a binodal distribution of hard segment material appears. There are the small hard segment domains typical of segmented urethane elastomers as well as larger “hard aggregates” greater than 100 nm in size. The larger domains are thought to be aggregates of rich polyurea that develop by precipitation during the foaming reaction. WAXS patterns of the foams suggest urea and possibly hard segment ordering that may be of a paracrystalline nature but certainly lacking in true 3‐dimensional

ISSN:0021-8995    

DOI:10.1002/app.1988.070350305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractPolyacrylonitrile (PAN) fibers pretreated with potassium permanganate have reduced the activation energy of cyclization and the oxidation time, and also improved the properties of the resultant carbon fibers. The activation energy of cyclization is reduced to 24 ± 1 kcal/mol from 30 ± 3 kcal/mol and the tensile strength of the carbon fibers increases by about 20−40%. The method of measuring the “aromatization index” (AI) value is modified and is recommended in checking the oxidation process. All fully stabilized PAN fibers have almost the same AI value. However, the oxidation time is decreases by 30 min when oxidation temperature is raised

ISSN:0021-8995    

DOI:10.1002/app.1988.070350306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe technique of laser interferometry is now used routinely by the microelectronics industry for the measurement of the dissolution rates of thin polymer films. In addition to the rate of dissolution, laser interferometry can also provide quantitative information on the thickness of the transition layer between the dissolving glassy polymer and the liquid solvent. This paper describes how observed patterns of reflected light intensity may be analyzed to calculate the thickness of the transition layer for polymers that dissolve with little or no swelling. The technique requires knowledge of the shape of the concentration profile in the transition layer. However, by assuming various simple model profiles one may obtain a reasonable estimate. Experimental measurements of poly(methyl methacrylate) (PMMA) films dissolving in methylethyl ketone indicate transition layers of thicknesses 0 to 0.1 μm for PMMA of molecular weightsMw= 37,000 to 1,400,000

ISSN:0021-8995    

DOI:10.1002/app.1988.070350307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractImmiscible blends of high density polyethylene (HDPE) and an amorphous glassy phase consisting of either pure polystyrene (PS) or a miscible blend of PS and a polyether copolymer (PEC) were compatibilized with various amounts of a styrene‐hydrogenated butadiene block copolymer (SEBS). PEC is structurally similar to poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO). Using a liquid displacement stress dilatometer, the volume change of samples during uniaxial mechanical straining was determined and related to the various modes of deformation. Blends were fabricated by both injection and compression molding. Miscible PEC and PS blends were found to undergo a craze to shear yielding transition between 40 and 60% PS, which occurred at higher PS concentrations as SEBS was added. Blends with a HDPE matrix and a dispersed glassy phase showed reduced volume dilatation on adding SEBS, indicating better interfacial adhesion between the incompatible blend components. Increases in the sample volume were substantially less in blends with a PEC/PS glassy phase instead of pure PS, suggesting more effective compatibilization by the SEBS copolymer in blends with PEC. This trend is presumed to stem from an exothermic heat of mixing between the PS endblocks of SEBS and the PEC‐rich phases in the blend. Microscopic evidence of the improved adhesion and modes of deformation agrees with the results obtained by dilatometry. The volume dilatation of compression‐molded materials do not seem to be similarly affected by the composition of the glassy phase which may reflect morphological differences between injection‐and compression

ISSN:0021-8995    

DOI:10.1002/app.1988.070350308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe analysis of dielectric loss data is frequently complicated by the presence of ohmic conductivity, especially at lower frequencies. Two simple methods are discussed for locating transition temperatures and for determining activation energies in such cases. In the first method the permittivity derivative [dε′(T)/dT] is used; in the second, permittivity difference spectra ε′(T,v1) – ε′(T,v2) (v1≪v2are used. The latter technique, however, cannot be used for activation energy determination. The theoretical basis of these methodologies and an analysis of representative experimental data are presented. The data set include measurements of pure and filled polyurethanes and of radiation‐cured unsaturated polyester resins. Finally, the advantages of data presentation in the form of ε′ and ε″ instead of

ISSN:0021-8995    

DOI:10.1002/app.1988.070350309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractQuinazolone‐imide copolymers were prepared by polycondensation of 6,6′‐methylenebis(2‐methyl‐3,1‐benzoxazine‐4‐one) and 3,3′,4,4′‐benzophenonetetracarboxlic dianhydride and 4,4′‐oxydianiline. Their thermal properties by TGA and their chemical etching properties by the use of the etchant composed of hydrazine hydrate and ethylenediamine were studied. The copolymers obtained had good solubility and excellent heat resistance and gave flexible and tough films. The chemical etching properties were more subject to influence of the polymer composition than th

ISSN:0021-8995    

DOI:10.1002/app.1988.070350310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY