摘要:

AbstractThe moisture‐induced plasticization of some amorphous polyamides in pure and blended form has been determined by calorimetric methods. The compositional dependence of the glass transition temperature of these polymer‐diluent systems has been adequately accounted for using an existing predictive expression derived from both a conformational entropy and a thermodynamic treatment of the glass transition phenomenon. The success of this approach to account for the behavior of amorphous polyamide blends containing hydrophobic and hydrophilic constituents exemplifies the importance of compositional parameters in determining the overall response of morphologically complex hydrophilic polymers. The results add further credence to the simple plasticizing action of water in polar polymers irrespective of their chemical and physical constitut

ISSN:0021-8995    

DOI:10.1002/app.1988.070360301

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

年代:1988

数据来源: WILEY

摘要:

AbstractA family of rubber‐toughened, mica‐filled polypropylene materials was developed. The rubber modifier used was an ethylene‐propylene‐diene monomer (EPDM) compound. A unique feature of this rubber‐modified system is that it can be directly molded from a dry blend. This simplifies processing by eliminating the need for melt compounding which, in turn, contributes to greater flexural moduli since attrition of the mica platelets is reduced. In addition, impact measurements were conducted as a function of temperature for EPDM/polypropylene and EPM D/poly(propylene‐ethylene) copolymer blends. The low temperature impact resistance was improved for both systems; however, the modified copolymer system maintained ductile behavior to a far lower temperature than the corresponding homopol

ISSN:0021-8995    

DOI:10.1002/app.1988.070360302

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

年代:1988

数据来源: WILEY

摘要:

AbstractThis work constitutes an indirect verification of a theoretical method that allows the production of polymers with prespecified molecular weight distributions (MWDs), through semibatch living‐anionic homopolymerizations. The chemical system consisted of styrene with sec‐butyllithium, in a solvent mixture of cyclohexane and tetrahydrofurane (THF). The necessary flow profiles were applied by a pair of computer‐controlled pumps, and the produced MWDs were measured by size exclusion chromatography, with correction for nonuniform instrumental spreading. The main difficulty was the estimation of the initial moles of initiator and of the concentration of impurities in the monomer solution. For such estimation, a precalibration experiment was implem

ISSN:0021-8995    

DOI:10.1002/app.1988.070360303

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe series of nylon 612 copolymers was synthesized from caprolactam (C) and laurolactam (L) at 145°C. The 50/50 C/L molar ratio copolymer was found to have the minimum melting temperature (Tm) for the series. The glass transition temperatures (Tg's) of the copolymers were affected by the crystallinity of the copolymers. TheTgwas at a minimum for the 50/50 copolymer for crystalline samples. However, for amorphous samples there was a decrease inTgwith increasing L content. Percent crystallinity was determined by differential scanning calorimetry and X‐ray techniques. It was found that the degree of crystallinity was at a minimum for copolymers of 70/30 to 40/60 C/L ratios. Coefficients of linear thermal expansion (CLTE) were obtained for the copolymers at 10°C intervals from 20 to 70°C for dry and from 20 to 50°C for samples conditioned at 50% relative humidity and 50°C. The dry samples gave lower initial values, but had a greater temperature dependence than the conditioned samples. As expected, the CLTE was found to be lowest for samples exhibiting the highest crystallinity. The tensile strengths and moduli decreased rapidly with increasing L up to the 70/30 C/L ratio after which they remained relatively constant. Elongations reached maximums between 70/30 and 40/60 C/L ratios. An inverse relationship was found between crystallinity and impact st

ISSN:0021-8995    

DOI:10.1002/app.1988.070360304

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe stress relaxation behavior of model silicone room temperature vulcanizing (RTV) elastomers has been used to examine the chemistry of the cured silicone network. It has been shown that the tin crosslinking catalyst, together with water, produces siloxane bond rearrangement which results in chemical stress relaxation. The measurement of the rate of stress relaxation of unfilled model elastomers at various temperatures gave an apparent activation energy of 10.3 kcal/mole−1for the relaxation process. In addition, the effects of some of the constituents of the RTV on relaxation behavior have been examine

ISSN:0021-8995    

DOI:10.1002/app.1988.070360305

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

年代:1988

数据来源: WILEY

摘要:

AbstractAverage advancing and receding contact angles made against cotton and glass fibers by a set of probe liquids are determined using the Wilhelmy technique. The dispersive and polar components of the surface energy are calculated from the measured contact angles using both the geometric and the harmonic mean methods. It is found that these components are similar for untreated cellulose and glass fibers, and that they both have a high polar component, corresponding to a hydrophilic surface. Changes in surface energy caused by treatment of the cellulose fiber surfaces with melamine, polyethyleneimine (PEI), and a silane coupling agent are reported. It is found in particular that polyethyleneimine treatment of cellulose significantly reduces the polar component of its surface energy. While treatment of glass fibers with a silane coupling agent reduces the polar component and increases the dispersive component of the surface energy it shows little effect on the surface energy of cellulose.

ISSN:0021-8995    

DOI:10.1002/app.1988.070360306

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

年代:1988

数据来源: WILEY

摘要:

AbstractCharacterization of styrene‐graftedBombyx morisilk fibroin membrance was investigated. It was revealed from the water sorption and1H nuclear magnetic resonance (NMR) measurements that the amounts of water adsorbed on the silk fibroin membranes decreased by the styrene grafting and the states of water adsorbed on the styrene‐grafted silk fibroin membranes were not homogeneous; the presence of two components of water adsorbed on the membranes at 60% relative humidity was observed. In addition, the fraction of the fast component decreased with increasing styrene grafting. The membrane potentials increased with increasing of the grafting. The KCl permeability of the membrane strongly depends on the degree of styrene graft

ISSN:0021-8995    

DOI:10.1002/app.1988.070360307

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

年代:1988

数据来源: WILEY

摘要:

AbstractEffect of cyanoethylation of starch on the properties of starch xanthide–NR vulcanizates has been studied. Significant improvements in compounding, tensile modulus, tensile strength, and retention of wet strength of the vulcanizates have been recorded. Equilibrium swelling of vulcanizates by water is also greatly suppressed. The role of cyanoethylation of starch in imparting such specific effects has been analyzed in the light of the polarity of the cyanoethyl group and its effect in lowering the critical yield stress of the modified starch for efficient dispersive mixing in NR matri

ISSN:0021-8995    

DOI:10.1002/app.1988.070360308

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

年代:1988

数据来源: WILEY

摘要:

AbstractPolyethers are prepared by condensing, respectively, 2,4‐dichloroquinoline and its 6‐methyl and 6‐methoxy derivatives separately with ethylene, propylene, butylene, diethylene and triethylene glycols. These polyethers are characterized and the electrical conductivity of polyethers is measured at various temperatures up to

ISSN:0021-8995    

DOI:10.1002/app.1988.070360309

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

年代:1988

数据来源: WILEY

摘要:

AbstractTo obtain accurate measurements of the limiting viscosity number (LVN) or the intrinsic viscosity [η] of solutions of ultrahigh molecular weight polyethylene (UHMWPE), a low shear floating‐rotor viscometer of the Zimm‐Crothers type was constructed to measure viscosities at elevated temperatures (135°C) and near zero shear rate. The zero shear rate measurements for UHMWPE whole polymer and UHMWPE fractionated by hydrodynamic crystallization were compared with viscosity measurements at moderate and high shear rates (up to 2000s−1) carried out in a capillary viscometer. The limiting viscosity number of UHMWPE decreases, as expected, with shear rate. The higher shear rate data could not be extrapolated to yield the correct zero‐shear rate viscosities. Fractionation of UHMWPE gave 10 fractions ranging in LVN from 9 to 50 dL/g. A tentative integral molecular weight distribution for the whole polymer was calculated on the basis of the Mark‐Houwink equation, but because it had been previously established only for lower molecular weight polyethylenes, it may not be accurate. A correlation was found between the LVNs for the fractions in the two types of

ISSN:0021-8995    

DOI:10.1002/app.1988.070360310

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

年代:1988

数据来源: WILEY