ISSN:0021-8995    

DOI:10.1002/app.1991.070430501

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis article discusses the phase separation and morphology of ethylcellulose/cellulose acetate phthalate blended films cast from methanol/methylene chloride (50/50 v/v) solvent mixture. The solvent system has been shown to be a cosolvent for CAP and a solvent/nonsolvent for EC. The two polymers have been shown to phase separate for all blend compositions via nucleation and growth. The morphology of these systems consists of a dispersion of broad size distribution of the minor component in a matrix of the major one. The formation of two layers due to coalescence of the dispersed phases and their eventual precipitation has been observed for the middle blend compositions. Finally, the phase separation in this system is discussed in terms of the Flory–Huggins theory and changes in the solvency mechanism during film casting. Enrichment of the solvent system in methanol at relatively early stages of film casting leads to changes in the system viscosity, relative chain conformation in solution, and chain diffusion. The effect of these parameters on the final morphology are discussed in terms of deviations from the equilibrium binodal decompositio

ISSN:0021-8995    

DOI:10.1002/app.1991.070430502

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

年代:1991

数据来源: WILEY

摘要:

AbstractA bending‐beam technique has been used to in situ monitor the diffusion of water in various polyimide films. The polyimides studied are pyromellitic dianhydride‐4.4′‐oxydianiline (PMDA–ODA), pyromellitic dianhydride‐p‐phenylenediamine (PMDA–PDA), and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride‐p‐phenylenediamine (BPDA–PDA), and their blends and random copolymers. The diffusion of water in these films obeys Fick's law. In PMDA–ODA, the mean diffusion constant is 5.2 ± 0.4 × 10−9(cm2/s) for thicknesses ranging from 6.7 to 27.3 μm. In PMDA–PDA, it is 2.0 ± 0.4 × 10−9(cm2/s) for thicknesses ranging from 7.3 to 20.0 μm, and in BPDA–PDA, 0.27 ± 0.02 × 10−9(cm2/s) for thicknesses ranging from 4.8 to 21.0 μm. In the blends and random copolymer with 50 wt % PMDA–ODA and 50 wt % PMDA–PDA, the diffusion constants are slightly smaller than those in the pure PMDA–ODA, but much larger than in the pure PMDA–PDA. On the contrary, in those with 50 wt % BPDA–PDA and 50 wt % PMDA–PDA, the diffusion constants are much smaller than those in the pure PMDA–PDA, but slightly larger than in the pure BPDA–PDA. These diffusion constants are primarily affected by the chemical structure of the imide molecule. The morphology, such as crystallinity, of the films has played a secondary factor. Hygroscopic stresses due to water uptake in all the studied films increase as the film thickness increases. It can be attributed to th

ISSN:0021-8995    

DOI:10.1002/app.1991.070430503

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

年代:1991

数据来源: WILEY

摘要:

AbstractSegmented block copolymers consisting of nylon 6 and polyoxypropylene blocks were prepared and characterized. Pronounced phase separation in the solid phase was deduced from differential calorimetry and from small‐angle X‐ray scattering, as well as from dynamic mechanical measurements. The morphology (from X‐ray diffraction) and anisotropy in mechanical properties strongly suggest phase separation in the melt (which is optically clear). Elastomerlike properties are described and disc

ISSN:0021-8995    

DOI:10.1002/app.1991.070430504

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

年代:1991

数据来源: WILEY

摘要:

AbstractProcessability of thermoplastic elastomer (TPE) prepared by radiation‐induced grafting of methyl methacrylate (MMA) onto radiation vulcanized natural rubber latex (RVNRL) has been evaluated using a kneader and a hot roll mill at 150°C. It was found that mixing time and revolution rate (rpm) of the kneader have significantly affected the processability. The longer mixing time and the higher revolution rate result in better processability. In such processing conditions, however, the mechanical properties were found to be inferior because the molecular chain scissions occurred during the mixing. A considerable improvement of mechanical properties was obtained when the mixing was carried out without added process oils. Blends of the grafted vulcanized natural rubber latex (RVNRL‐g‐PMMA) and MMA grafted on unvulcanized natural rubber latex (NRL‐g‐PMMA) improved processability where the better processability could be achieved at a shorter mixing time and a lower revolution rate. In addition, a comparable value of mechanical properties wa

ISSN:0021-8995    

DOI:10.1002/app.1991.070430505

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe permeability of four structurally related poly(alkoxyphosphazenes), three isomers of poly(dibutoxyphosphazenes) (PBuP), and poly(di‐neopentyloxyphosphazene) (Pneo‐PeP), to 13 gases has been determined by the time‐lag method. Systematic variations in chemical structure have shown a large effect of side chains on permeabilities and permselectivities. The permeability of poly(di‐n‐butoxyphosphazene) (Pn‐BuP) is of the order of 10−8cm3(STP) cm/(cm2s cmHg) for many gases, and the value for a large gas is higher than that for a smaller one. For small gases such as He and H2, poly(di‐sec‐butoxyphosphazene) (Ps‐BuP) is as permeable as Pn‐BuP, but its diffusivities for larger gases such as Xe and C3H8are about one order lower than those of Pn‐BuP. While the permselectivity of Pn‐BuP is determined by the solubility, that of Ps‐BuP depends on both the diffusivity and solubility factors. The property of poly(diisobutoxyphosphazene) (Pi‐BuP) is intermediate between them. These polymers are constitutionally identical, and the only difference is the arrangements of carbons in the side groups. As the side chains become bulky, the permeability decreases, whereas the permselectivity increases. Further decreases of diffusivity and then permeability are observed for Pneo‐PeP, whose side groups have one more methyl group than does Pi‐BuP. But the solubility data are not much different from other three polymers and the diffusivity factor becomes more significant in permselectivity. The diffusivity depends on the polymer structure much more than does the solubility. The relationships between chemical structure and gas diffusi

ISSN:0021-8995    

DOI:10.1002/app.1991.070430506

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe aqueous kinetic swelling properties of a class of cross‐linked hydrophobic polyamine copolymer gels based onn‐alkyl esters of methacrylic acid (nAMA) andN,N‐dimethylaminoethyl methacrylate (DMA) have been studied as a function of solution ionic composition (pH, ionic strength, and buffer content), gel composition, and temperature. Water uptake and swelling in these gels are driven by ionization of the DMA amine groups, which overcomes the hydrophobic tendency of these gels to exclude water in the unionized state. Sorption kinetics in initially glassy gel disks are generally biphasic, characterized by an initial phase of relatively slow water uptake followed by an accelerated phase during which significant volume expansion of the gel occurs. This sorption/swelling behavior strongly suggests a moving penetrant front mechanism. The initial rate of water sorption increases markedly as (1) solution pH decreases, (2) gelnAMA comonomer content decreases, (3) gelnAMA side‐chain length decreases, and (4) temperature increases. Furthermore, the initial phase of sorption in initially glassy gels is generally non‐Fickian and approaches zero‐order behavior as (1) pH increases, (2)nAMA content increases, and (3) temperature decreases. In direct contrast, sorption in initially dry,rubberygels is monophasic, but non‐Fickian, and approaches zero‐order behavior as temperature increases. This behavior is contrary to the Fickian sorption behavior normally observed in polymers above their glass transition temperatures. Finally, sorption kinetics critically depend upon the nature of the ions in solution: Kinetics are significantly faster in the presence of weak electrolytes than that of strong electrolytes. We discuss the importance of the rate of ion transport in determining the overall sorption kinetics and how sorption kinetics can be non‐Fickian in rubbery gels. Also, we propose a mechanism for the observed enhanced kinetics in the presence of

ISSN:0021-8995    

DOI:10.1002/app.1991.070430507

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

年代:1991

数据来源: WILEY

摘要:

AbstractEight types of structural deformities have been identified in cotton fibers by using the SEM, and their incidence has been quantified in four varieties grown in India. Although the total number of deformities per cm was found to be nearly equal in these four varieties, their number showed a wide spread when structural reversals (which constitute one class of deformity) were excluded. The correspondence found between the number of defects other than reversals and the drop in bundle tenacity with increase in gauge length seems to suggest that weak links other than reversals might strongly influence fiber strength.

ISSN:0021-8995    

DOI:10.1002/app.1991.070430508

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

年代:1991

数据来源: WILEY

摘要:

AbstractThree poly(n‐alkyl acrylates), PA‐14, PA‐16, and PA‐18, and three poly(vinyl alcohol) aliphatic acid esters, PVA‐14, PVA‐16, and PVA‐18, have been synthesized. They are white crystalline polymers at room temperature and characterized by IR, DSC, SALLS‐photometer, and polarizing microscope. Both the melting point and heat of fusion of PVA–esters are larger than those of the corresponding PA–esters, and the sizes of spherulites of PVA–esters are also larger. This may be attributed to the different order of linking in the ester group and the OH group residue in PVA–esters. In the testing of the effects on pourpoint depression of some petrolic oils, only PA‐14 and PVA‐14 are effective for 0# diesel oil. The influences of molecular weight and molecular weight distribution of PA–esters and PVA–esters upon the pour‐point depression of oil are negligible. These results show that the length ofn‐alkyl side chain of the polyesters plays the most important role in depressing the pour‐point of petrolic oil and that the order of linking in the esters group se

ISSN:0021-8995    

DOI:10.1002/app.1991.070430509

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

年代:1991

数据来源: WILEY

摘要:

AbstractFunctional Bromothymol Blue dyes containing amino groups in position 3 have been immobilized on the surface of chlorosulfonated polystyrene fibers and characterized by ESCA. Upon laser irradiation, a modified fiber has been used as an antenna fiber in a twisted pair of plastic optical fibers immersed in aqueous solutions having various pH. The light transmitted to the receiving fiber depends on pH values. This device can be used as a pH sensor.

ISSN:0021-8995    

DOI:10.1002/app.1991.070430510

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

年代:1991

数据来源: WILEY