摘要:

AbstractThe emulsion polymerization of vinyl acetate using some bisulfite adducts of different chain lengths with potassium persulfate as the redox initiation system, in the absence of emulsifier, was studied. The effects of such adducts, which contain the same weight equivalent of bisulfite anion, on the rate of polymerization, maximum conversion, and stability of the produced polymer lattices as well as the morphological characteristics including volume‐average diameters and the number of polymer particles per unit volume of water were investigated. The rate of polymerization was found to be dependent on the concentration of benzaldehyde, acetaldehyde, octyl aldehyde, methyl propyl ketone, and acetone sodium bisulfite adducts to the powers 0.54, 0.66, 0.95, 1.0, and 1.1, respectively. Also, it was found that increasing adduct chain lengths decreases the volume‐average diameter, increases the obtained lattice stability, and improves the morphology of the polymeric particles, where a spherical morphology and extra stability were obtained in the presence of the octyl aldehyde adduct. © 1993 John Wiley&Sons, Inc.This article is a US Government work and, as such, is in the public domain in the United States of Ame

ISSN:0021-8995    

DOI:10.1002/app.1993.070490201

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

年代:1993

数据来源: WILEY

摘要:

AbstractCellulose fibers surface‐coated with butyl benzyl phthalate (BBP)‐plasticized PVC were evaluated as a reinforcement in thermoplastic matrices. Coated fibers were agglomerated during compounding with polypropylene (PP) and polyethylene (PE). However, an excellent dispersion and improved processability were achieved in polystyrene (PS). Melt rheology was also seen to be affected by fiber coating, and viscosity was lower for coated fibers. Fiber coatings seem to lubricate the blending process as well as to protect fiber from damage during processing. Fiber length was unaffected during treatment when coated fibers were used, as shown by microscopic investigation of extracted fibers, whereas the length of untreated fibers was reduced during processing. Introducing surface‐coated fibers into PS resulted in an increased elongation at break and improved impact strength of composites. The pullout of the fibers is suggested to be responsible for both improvements. The interphase achieved in PS with PVC/BBP‐coated fibers was simulated with PS/PVC/BBP blends. From DSC and DMTA, it was shown that BBP is a cosolvent for PS and PVC and that a single‐phase material was achieved at the relevant concentrations, which also was confirmed by optical clarity. © 1993 John Wiley

ISSN:0021-8995    

DOI:10.1002/app.1993.070490202

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

年代:1993

数据来源: WILEY

摘要:

AbstractDense poly (vinyl alcohol) (PVA) membranes of different crystallinities were prepared and studied in pervaporation of water‐ethanol mixtures. High selectivities to water were obtained with all types of membranes. Permeation fluxes increase exponentially with the water content in the liquid mixture. At a given water content, the membrane permeability decreases drastically when its crystallinity increases. When the pervaporation temperature increases, the permeation flux increases according to the Arrheniuslike law, with a permeation acti‐vation energy that depends strongly on the crystallinity of the membrane. A permeation model, in which the volume fraction of amorphous polymer intervenes in both the sorption and the diffusion laws, was proposed and validated by the experimental data. With the obtained values of the parameters, the permeation Olux can be calculated for membranes of a given crystallinity at any temperature and composition of the water‐alcohol mixture. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070490203

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

年代:1993

数据来源: WILEY

摘要:

AbstractMid‐infrared (MIR) and near‐infrared (NIR) spectroscopies have been employed to examine the reactions between phenyl glycidyl ether (PGE) and five aromatic amines. Although MIR spectroscopy can effectively study the kinetics of PGE/aromatic amine cure reactions, the OH and NH stretching bands overlap and the NH in‐plane bending band overlaps with an aromatic ring stretching band of PGE. This significantly reduces the utility of MIR spectroscopy for quantitative studies of PGE cure reactions. In contrast, the absorption bands of these functional groups in the NIR spectrum are well separated from the absorption bands of other functional groups. The utility of NIR spectroscopy for studying the kinetics of epoxy resin cure reactions has been clearly established. Absorbances in the NIR spectra suitable for quantitative studies of epoxy resin reaction kinetics have been identified. The ability ofin situNIR spectroscopy to obtain isothermal kinetic data has been demonstrated. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070490204

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe objective of this study was to improve the durability and stability of urea–formaldehyde‐bonded wood products by decreasing the internal stress developed during the resin cure and by improving the ability of the cured system to withstand cyclic stresses. Urea–formaldehyde resins were modified either by incorporating urea‐capped di‐and trifunctional amines into the resin structure or by using the hydrochloride derivatives of some of these amines as the curing agent, or by both methods. This study supplements our previous work by examining the effects of additional amines and subjecting bonded products to additional testing. Solid wood joints bonded with a variety (7 of 15) of modified adhesives had resistance to cyclic stress superior compared to that of joints bonded with unmodified urea–formaldehyde adhesive; at least three of the modified adhesives approached the behavior of phenol–formaldehyde‐bonded joints. Resistance to moist heat aging, although still inferior to that of phenol–formaldehyde‐bonded joints, was significantly improved for joints bonded with modified adhesives over joints made with unmodified resins. The fracture behavior of joints made with modified adhesives was different from that of joints made with unmodified resins. The fracture energy was greater for joints made with three of four modified adhesives than for joints made with unmodified resins. Modified adhesives produced particleboards made with enhanced cyclic stress resistance. Formaldehyde emission from particleboards made with resins modified with urea‐terminated amines was less than emission from boards made with unmodified resins. However, emissions from particleboards made with amine hydrochlorides were not improved compared to those from boards made with an ammonium chloride curing agent. © 1993 John Wiley&Sons, Inc.This article is a US Government work and, as such, is in the public domain in the Un

ISSN:0021-8995    

DOI:10.1002/app.1993.070490205

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

年代:1993

数据来源: WILEY

摘要:

AbstractSorption and diffusion of dichloromethane vapor were measured in amorphous syndiotactic polystyrene films, obtained with different cooling conditions and after controlled aging times at different temperatures. The diffusional behavior, at the temperature of 25°C, was characterized by three stages, depending on penetrant activity. In the first stage, at low activity, the diffusion coefficient was independent of vapor concentration; the second stage was characterized by concentration‐dependent diffusion, whereas in the third stage, at high activity, the strong interaction solvent–polymer increased the mobility, allowing the polymer crystallization. The different cooling conditions neither have an effect on the diffusional behavior nor on the sorption curve. The aging, both at room temperature and at 70°C, did not change the diffusion parameters, but led to the appearance of more and more anomalous sorption behavior. The sorption curve, as a function of vapor activity, did not show any difference for the fresh and the aged‐at‐room temperature samples, whereas the samples aged at 70°C presented a lower sorption at low activity. The presence of ordered domains, impermeable to the penetrant at low activity, was suggested on the basis of sorption results. The solvent‐induced crystallization was investigated for all the samples. Crystallization was induced at an activity of 0.45 for the fresh and the aged‐at‐room temperature samples; at variance, the samples aged at 70°C crystallize at a slightly higher activity, reaching, nevertheless, a higher level of crystallinity. © 1993 Jo

ISSN:0021-8995    

DOI:10.1002/app.1993.070490206

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

年代:1993

数据来源: WILEY

摘要:

AbstractTransport properties of dichloromethane vapor were measured in atactic polystyrene (aPS) samples, oriented by drawing at 95°C to different draw ratios (3 and 4.5) and analyzed after controlled aging times at different temperatures. The diffusional behavior is characterized by three zones, depending on vapor activity: In Zone I, at low activity, the diffusion coefficient is independent of vapor concentration; Zone II is characterized by concentration‐dependent diffusion and by the appearance of non‐Fickian sorption curves; and in Zone III, the strong interaction polymer‐solvent induces disorientation of the samples. The diffusional behavior is very similar to that of undrawn aPS, and also the extrapolated parameters coincide, showing that in the case of amorphous polymers, the drawing does not influence the diffusion. The aging, both at room temperature and at 70°C, decreases the diffusion parameters and leads to the appearance of anomalous sorption curves. The sorption curve as a function of vapor activity does not show any difference for the fresh and aged at room temperature‐oriented samples; furthermore, it coincides with that of aPS. At variance, the oriented samples aged at 70°C show a lower sorption at low activity. As in the case of aPS, the presence of ordered domains, impermeable to the penetrant at low activity, was suggested for the oriented samples. © 1993 John Wile

ISSN:0021-8995    

DOI:10.1002/app.1993.070490207

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe mechanical and dynamic mechanical properties of short carbon fiber‐filled styrene–isoprene–styrene (S–I–S) block thermoplastic elastomeric composite have been studied. Brabender mixing followed by milling of the fiber–rubber compositions caused about a 30‐fold decrease in the fiber aspect ratio and random fiber orientation. Although low‐strain moduli increased on fiber incorporation, tensile and tear properties dropped and anisotropy in mechanical properties was not observed. Tan δ values at theTgregion decreased on filler incorporation, but at room temperature, the tan δ values increased with filler loading. The variation of storage moduli and tan δ values with frequency followed a pattern similar to the variation of these properties with filler incorporation. © 1993 J

ISSN:0021-8995    

DOI:10.1002/app.1993.070490208

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

年代:1993

数据来源: WILEY

摘要:

AbstractInfrared microspectroscopy was used to determine quantitatively and qualitatively methyl centralite (MC) and dibutyl phthalate (DBP) diffusion profiles in cross sections of nitro‐cellulose‐based monoperforated propellant grains. The absorbance values of the CO peak of DBP at 1717 cm−1and the aromatic CC peak of MC at 1496 cm−1were measured relative to the NO2overtone peak of the nitrocellulose at 2555 cm−1at 10 μm intervals from the outside edge inward (external profile) and the perforation edge inward (internal profile). Infrared microimaging was used to determine the distribution and penetration depth of the DBP and MC using the CO peak of DBP at 1717 cm−1and the aromatic CC peak of MC at 1496 cm−1as diagnostic of the two deterrents to obtain the contour and axonometric displays of the distribution. © 19

ISSN:0021-8995    

DOI:10.1002/app.1993.070490209

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

年代:1993

数据来源: WILEY

摘要:

AbstractNovel cation‐exchange composites were prepared by polymerizing / cross‐linking of mixtures of acrylic acid (AA) andN‐methylolacrylamide (NMA) in the presence of cellulose pulp using ammonium persulfate in conjunction with a sodium thiosulfate, sodium metabisulfite, or glucose initiating redox system. The (NH4)2S2O8/Na2S2O3. 5H2O redox system proved to be efficient for aqueous polymerization/ cross‐linking reactions and/or interactions of cellulose with highly concentrated mixtures of NMA and AA, used as commercially available, at very low polymerization temperature (30°C) and for a very short duration of polymerization (90 s) using a liquor‐to‐cellulose ratio of 6.25 L/kg. Various parameters that affect the synthesis of these composites, such as reaction temperature, concentration of redox system components, and drying temperature as well as AA and NMA concentrations, were reported. Four kinds of cation‐exchange composites of different nitrogen and carboxyl contents were synthesized and characterized by investigating their potentiometric titrations, water solubilities, and swellabilities as well as their durabilities. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070490210

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

年代:1993

数据来源: WILEY