摘要:

AbstractThe performance of acrylic (50:50 MMA/BuA) latexes was investigated as a function of fusion level using high speed tensile testing. The structure of the copolymer was varied via the addition of molecular weight modifiers to the emulsion polymerizations. Chain transfer agent (CBr4) was used to reduce the copolymer modulus, and crosslinker (EGDM, ethylene glycol dimethacrylate) was added to increase the modulus. The resulting materials exhibited a wide range of viscoelastic behavior (G*varied from ∼ 107dyne cm−2to ∼ 109dyne cm−2). Fracture energy and peak force at break were measured as a function of the complex modulus. It was found that both of these parameters showed a maximum with respect toG*that corresponded to intermediate levels of crosslinking. This observation was explained in terms of the degree of coalescence of the films. Fully fused films (excess CBr4) were brittle and performed poorly, conceivably because of insufficient entanglement to support stress. Marginally fused films also exhibited inferior, brittle behavior. The films cast from latexes synthesized with low levels of molecular weight modifiers showed intermediate fusion levels and superior tensile performance. The quantitative results were rationalized using scanning electron microscopy (SEM) of both the virgin films and the fracture surfaces. For comparison, the same materials were tested in a fully fused state following hot pressing. The behavior paralleled that expected for vulcanized rubbers in which lightly crosslinked materials exhibit the highest tensile strength. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070481001

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

年代:1993

数据来源: WILEY

摘要:

AbstractSolid‐state NMR and thermal analysis techniques were used to compare the mobility of poly(vinyl butyral) (PVB) in the presence and absence of both alumina filler particles and plasticizer. The relative mobility of main‐chain and side‐chain carbons increases in the presence of both plasticizer and alumina as seen from an increase in the average cross‐polarization rates, 〈TCH〉, and from a general decrease in the rotating frame spin‐lattice relaxation rates,CT1ρ. Unlike the main‐chain carbons, inversion recovery cross‐polarization (IRCP) data on solution cast composites show that the side‐chain methyl groups in neat PVB samples are best characterized by a monoexponential cross‐polarization model. However, in the presence of alumina, a fraction of the methyl groups becomes less mobile as indicated by the biexponential IRCP behavior. Polymer phase mobility also increases below the critical pigment volume concentration (CPVC) as seen from decreasing transition temperatures using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). This is accompanied by an increase in the rigidity of a portion of the polymer phase above the CPVC as indicated by an increase in the apparentTg, along with an increase in the mobility of another portion as indicated by the appearance of a low‐temperature DMA transition. These trends are consistent with an increase in polymer chain packing heterogeneity in the presence of alumina. ©

ISSN:0021-8995    

DOI:10.1002/app.1993.070481002

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

年代:1993

数据来源: WILEY

摘要:

AbstractSeveral elastomeric sequential interpenetrating polymer networks (IPNs) based on nitrile rubber (NBR) and poly(vinyl acetate) (PVA) have been synthesized. Cross‐linked NBR was swollen in vinyl acetate monomer containing benzoyl peroxide (BPO) as initiator and tetraethylene glycol dimethacrylate (TEGDM) as cross‐linker and then the swollen mass was polymerized. The composition of the IPNs could be varied by varying the swelling time and concentration of BPO and TEGDM. The properties of these IPNs were investigated by tensile test, differential scanning calorimetry (DSC), dynamic mechanical analysis, and swelling measurement. On increasing the PVA content as well as cross‐linking level, the tensile strength increased because of better mixing. DSC showed a singleTgvalue for all the individual IPNs, theTgvalues changing regularly with composition. The tan δ peak for IPNs appeared at higher temperature compared to NBR and was found to be dependent on both the composition of IPNs as well as cross‐linking level. IPNs having 2 and 5% cross‐linker (TEGDM) showed splitting in the tan δ peak. On increasing the cross‐linker concentration to 9% and beyond, the splitting disappeared. The damping capability of the IPNs has been explained in terms of the magnitude of tan δ, area under the tan δ curve, and ½ peak width. The IPNs also showed better solvent‐resistance properties. © 1993 J

ISSN:0021-8995    

DOI:10.1002/app.1993.070481003

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

年代:1993

数据来源: WILEY

摘要:

AbstractPhotografting of acrylonitrile (AN) and methacrylic acid (MAA) on low‐density polyethylene film (thickness 70 μm), on which benzophenone was coated earlier, was investigated at 60°C in water medium under air atmosphere. In the case of AN monomer, where grafted polymer was formed predominantly, oxygen in the system promoted the formation of both grafted polymer and homopolymer. With MAA monomer, in which homopolymer was formed preferentially compared to the formation of grafted polymer, the formation of homopolymer was accelerated by the presence of oxygen while suppressing that of grafted polymer. The formation of polyethylene peroxides by photoirradiation seemed to be a factor for the accelerated polymerization under air atmosphere. It was found that additives such as hydrazine and metallic ions (Fe2+, Cu2+, and Ni2+) are useful for enhancing the photografting under air atmosphere. © 1993 John Wiley&Sons,

ISSN:0021-8995    

DOI:10.1002/app.1993.070481004

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe depression of the glass transition temperature by water was studied in a set of polyurethanes in which the soft segment consisted of polyethylene oxide (sample I) or a block copolymer of poly(propylene oxide) terminated with poly(ethylene oxide) in various proportions (sample set II). DSC measurements were made at two added water contents for each type of sample and at various temperatures. TheTgreduction appeared to be governed solely by the nonfreezing bound water and was much larger in sample I than in samples of set II. The more limited effect on theTgof set II samples is attributed to restricted mobility arising from coupling of the short terminal poly(ethylene oxide) to rigid hard‐segment units. Therefore, the data for sample I are preferred as a test of the predictive relations for theTgdepression. On this basis, it appears that the simple Fox mixing equation is more reliable than is the available free volume approach, which required unrealistically high values of the thermal expansion coefficient for water to fit the data for sample I. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070481005

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe dependence of phase structure on the intensity of mixing was studied for two modified polyamide/[poly(phenylene oxide) + polystyrene] (50/50) blends with different viscosity ratios of components. In these blends, polyamide forms the matrix and the mixture of miscible polymers [poly(phenylene oxide) and polystyrene]forms the disperse phase at all rates of mixing. The average size of the droplets of the disperse phase grows with increasing rate of mixing. This (rather surprising) result is explained as a consequence of the dynamic equilibrium between breakup and coalescence of droplets in a highly concentrated system at the condition of steady mixing. Generally, the dependence of droplet size on rate of mixing is not necessarily a monotonic function for blends with a high content of the disperse phase. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070481006

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

年代:1993

数据来源: WILEY

摘要:

AbstractAromatic polyimides have many advantages such as low thermal expansion coefficient, good electrical insulation, and self‐extinguishing properties. We tried to use polyimide film for honeycomb structure. Polymide honeycomb core and sandwich panel were prepared from polyimide film, i.e., UPILEX R, and adhesive by the expansion method. Mechanical properties, i.e., compressive, crushed, shear, and flexural strengths, were evaluated for this core and panel. Compressive and crushed properties increased largely with the density of the honeycomb, whereas shear and midspan flexural properties did not vary so much with the density, because these failures occured in the adhered interface. Strong adhesion is required for improving the latter properties. © 1993 John Wiley&Sons, I

ISSN:0021-8995    

DOI:10.1002/app.1993.070481007

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe reaction of 2,5‐dimethylpiperazine with a double molar amount of maleic anhydride afforded a new unsaturated dicarboxylic acid that was characterized by IR and1H‐NMR spectroscopy. It was condensed with various aromatic diamines by the phosphorylation method to yield polyamides bearing olefinic bonds. They were readily soluble in polar aprotic solvents and certain acids. The DTA traces of polyamides showed exotherms above 250°C attributable to their cross‐linking through the olefinic bonds and a partial thermal degradation. Evidence for the cross‐linking of polyamides attained during their heat‐curing was obtained from the IR spectra of the uncured and cured samples. Thermal stabilities of cured (at 300°C for 15 h) polyamides were evaluated by TGA and isothermal gravimetric analysis. They were stable up to 321–336°C in N2or air and afforded an anserobic char yield of 61–71% at 800°C. © 1993 Jo

ISSN:0021-8995    

DOI:10.1002/app.1993.070481008

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe kinetics of lignin (ammonium‐based lignosulfonate and sodium‐based lignosulfonate) methylolation were studied in solution by monitoring the rate of disappearance of form‐aldehyde and by using differential scanning calorimetry (DSC) techniques under an iso‐thermal program, at 20, 40, 50, and 60°C, respectively. The kinetic parameters obtained from these two methods agree with each other. The results show that the degree of lignin methylolation depends on the number and availability of reactive sites per C9unit of lignin. Lignin methylolation has a lower activation energy and a lower preexponential factor than that of phenol methylolation. Lignins took a shorter time to reach complete methylolation than did phenol at the low temperatures used here. © 1993 John Wiley&

ISSN:0021-8995    

DOI:10.1002/app.1993.070481009

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe subject of this paper is the extended‐length netted wound composite shells operating in cantilever loading conditions. The winding method that enables the attainment of various thicknesses of the netted shell zonewise is discussed. The distinguishing feature of this formation is the introduction of the sectional expansion mandrel into the production process. The efficiency of the elaborated method is based on the known dependence of the composites' mechanical properties on the tension of the reinforcing filler. On completion of winding, the blank is heated and, with the mandrel sections moved apart in the axial direction, the required level of fiber tension is created in each zone. The improved quality of the material enables increasing of the load‐carrying capacity of the items at the simultaneous reduction of their mass. Use of the procedure is most expedient for the manufacture of items from high‐modulus reinforcing materials. The field of application is the production of vital shell structures, such as helicopter tail booms, masts of vessels, and power transmission line supports. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070481010

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

年代:1993

数据来源: WILEY