摘要:

AbstractDifferential scanning caiorimetry (DSC) was used to characterize the vulcanization of styrene‐butadiene rubber (SBR). The effect of three different fillers on the vulcanization process was also investigated. The fillers used were carbon black HAF and SRF and silica. The calculated reaction orders, activation energy, reaction energy, and preexponential factor, completed with physical properties, were used to calculate the temperature and extent of reaction inside a mold with time. The mathematical model used yields that are in fair agreement with experimental temperature measurements inside the mol

ISSN:0021-8995    

DOI:10.1002/app.1991.070431001

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

年代:1991

数据来源: WILEY

摘要:

AbstractGelatin was graft copolymerized with poly(glycidyl methacrylate) using potassium peroxydisulfate in aqueous medium. Effect of temperature, time, initiator, monomer, and backbone concentrations were studied. The percent grafting was found to increase initially and then decrease in all the cases except with variation of monomer concentration. The rate of grafting, grafting efficiency, and percent of grafting were calculated. The grafting results have been discussed in the light of the rate of grafting. Mechanical properties, FT IR spectra, percent swelling, and percent dye uptake were carried out on the graft copolymerization and the results discussed.

ISSN:0021-8995    

DOI:10.1002/app.1991.070431002

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

年代:1991

数据来源: WILEY

摘要:

AbstractTo improve the hydrophilicity and enhance the transport flux of nylon 4 membrane for dialysis, this study attempts to utilize blending nylon 4 with poly(vinyl alcohol) (PVA). The instability of PVA in water can be obtained more easily than by other methods, such as chemical, γ‐ray irradiated crosslinking, or high‐temperature treatment used by previous researchers. The effects of maturation time of the casting solution, nylon 4/PVA ratios, and casting solvent compositions on esterification of PVA, salt permeability, water content, partition coefficient, diffusivity, and mechanical strength of membrances are studied. The membrane, prepared by casting solution of nylon 4/PVA = 9/1 wt % formic acid with 24‐h maturation time, possesses permeabilities of NaCl and urea, 33.14 and 19.67 × 10−5cm2/min, res

ISSN:0021-8995    

DOI:10.1002/app.1991.070431003

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of different types of elastomeric matrix (NR, SBR, CR, NBR) and several levels (10, 15, and 20 parts phr) of short fibers on mechanical properties of uncured and cured composites and on swelling behavior of composites in hydrocarbon solvent are studied. The variation of the dynamic properties,E′,E″, and tan δ is determined as a function of deformation amplitude, temperature, and vibration frequency in composite materials subjected to dynamic deformation. The increase of fiber level does not limit the orientation ability of the fibers, which in all materials seemed to be above 70%. The addition of fiber markedly reduces maximum swelling and entails an increase in material stiffness. In addition, the amount of dissipated energy is increased and hence transformable into heat upon fiber incorporation, which can reach up to 16 times the value corresponding to the matrix alone, in addition to an increase with strain amplitude. The effect is most pronounced in the presumed direction of fiber orientation.The marked reduction of elongation at break (up to values of 7–9% of those of unfilled samples) and the shape of stress‐strain curves point to a good fiber‐matrix adhesion. Dynamic glass transition temperature is displaced toward higher values as a consequence of matrix‐fiber interaction, which increases proportionally to fiber level, thus proving a linear relationship between thermal displacement and the number of interactions between the two phases. By the same token, the apparent activation energy of the relaxation process is enhanced for fiber‐containing materials as compared to the fiber‐free. The fiber composites present a less prominent yet broader

ISSN:0021-8995    

DOI:10.1002/app.1991.070431004

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

年代:1991

数据来源: WILEY

摘要:

AbstractFilms obtained from native cellulose synthesized byAcetobacter xylinumand from cellulose obtained from cuproammoniacal solutions (cellulose II) were morphologically characterized by studying thecis‐transisomerization of azo dye Chrysophenine dispersed in their amorphous region. The kinetic measurements of the reaction showed that both films behave as glassy polymers in the temperature range explored (36–66°C). In going from native cellulose to cuproammoniacal cellulose, an increase of the isomerization rate was observed, revealing a more homogeneous distribution and likely larger extent of free volume in the amorphous phase of cellulos

ISSN:0021-8995    

DOI:10.1002/app.1991.070431005

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

年代:1991

数据来源: WILEY

摘要:

AbstractA series of UV‐autocurable epoxy‐multiacrylate resins was synthesized, and the effects of degree of polymerization (DP) and epoxy type on their properties were investigated. These autocurable multiacrylate resins possess good pot life and are cured rapidly when exposed to ultraviolet (UV) without the addition of photoinitiator or photosensitizer. The curing rate of the autocurable resins was probably dependent on the number of abstractable hydrogen in epoxy resins. Stress‐strain, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used to characterize the properties of cured multiacrylate resins. Increased crosslinking density of cured films improved tensile properties. Increasing the molar ratio of epoxy resin in the multiacrylate resins was found to decrease the effective acrylate concentration of resins and to depress crosslinking density of cured resins, which also resulted in an increased elongation at break but a decreased Young's modulus and breaking strength. Furthermore, the different structures of epoxy resins were used to give wide range properties of cured epoxy‐multiacrylate resins with a glass transition temperature (Tgrange from 74 to 102°C. The film properties of the multiacrylate resins coated on steel plates were also inve

ISSN:0021-8995    

DOI:10.1002/app.1991.070431006

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

年代:1991

数据来源: WILEY

摘要:

AbstractChloromethylstyrene1(mixture meta and para; 60/40) can be oxydized in corresponding aldehyde2. Vinylbenzaldehyde2reacts with primary amines such as aniline, benzylamine, 2‐phenylethylamine, 3‐phenylpropylamine, and 2‐aminopyridin to give Schiff bases that are polymerized in bulk with a radical initiator. Poly(vinyl benzaldehyde)6prepared from corresponding monomer2also reacts with primary amines to give polymeric Schiff bases. Hydrolyses of these polymeric imines have been carried out either in heterogeneous acidic medium or basic heterogeneous medium; a suitable percentage of amines has been released after some hours. Finally, a study of hydrolysis and of diffusion of released amines in a dosage form (Eudragit RL) has been also carried out with some polymeric Schiff

ISSN:0021-8995    

DOI:10.1002/app.1991.070431007

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

年代:1991

数据来源: WILEY

摘要:

AbstractA new variation in the bismaleimide (BMI) resin family, maleimide‐terminated poly(oxy‐1,4‐phenylene sulfonyl‐1,4‐phenylene) oligomers, has been synthesized. The preparation of oligomers (n= 1–12) is described in this study. The structure of these oligomers is characterized by FT‐IR and NMR spectroscopy. These oligomers are light yellow to light gray powders that can be melted or dissolved in solvents. Their terminating group bismaleimide has relatively high reactivity. Therefore, these BMI resins can be cured at 250°C to form a crosslinked product. Since the backbone chain is poly(arylene ether sulfone), the cured polymers have highTg's, which increased from 220°C to higher than 340°C as the number of repeating unitsnof the corresponding oli

ISSN:0021-8995    

DOI:10.1002/app.1991.070431008

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe mean length and the indices of long‐chain branches (LCBs) of a high‐pressure lowdensity polyethylene (HPLDPE) as a function of molecular weight have been determined for its molecular‐weight‐tractionated parts by the13C‐NMR analysis and the viscosity measurements. The mean LCB length of the fractions was of the order of 200–300 carbons in length. The size of LCBs increases with increasing molecular weight, but the size of LCBs relative to the overall macromolecular size decreases with increasing molecular weight. The LCB sizes as a function of molecular weight determined for the fractions of one parent HPLDPE are in good agreement with those previously reported for HPLDPE who

ISSN:0021-8995    

DOI:10.1002/app.1991.070431009

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe curing processes of maleimide‐terminated polyether sulfone oligomers (Mnfrom 1100 to 3000) and ethynyl‐terminated polysulfone prepolymers (Mnfrom 2600 to 12000) were investigated by means of DSC. The initial temperature of cure reaction is increased, and the apparent activation energyEaof cure reaction is decreased as theMnof the uncured prepolymer increases. On the basis of theTgchanges during the curing process, the kinetics of cure is proposed to be similar to a stepwise reaction, although the curing reaction is believed to proceed via a free radical chain mechanism. In this proposed reaction some initial reaction products with many branches and one remaining active functional group are formed first. The more these products occur, the more likely they can interreact to form a network. During the curing process the mobility of the active end group is restricted by the rigid polysulfone chain. Therefore, the reaction is mainly controlled by the movement of polymer, i.e., by the kinetics of diffusion. Films of these cured polymers were made by casting from solution. Their β relaxation peaks at low temperatures were examined by dielectric and dynamic mechanical measurements. The films made of the prepolymer withMn>3000 are flexible and fold

ISSN:0021-8995    

DOI:10.1002/app.1991.070431010

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

年代:1991

数据来源: WILEY