摘要:

AbstractStudies were made of the thermal softening and degradation behavior in air of low‐ and high‐density polyethylene (PE) grafted with acrylonitrile (AN) by electron beam prior irradiation in nitrogen. It was found that both LDPE and HDPE were made to exhibit higher softening points by grafting and that this tendency increased with increasing percent graft. The starting temperatures of the thermal degradation and thermogravimetric curves were also found to shift to higher temperatures. On the other hand, in marked contrast to the thermal softening and degradation behavior of grafted PE in air, its behavior in nitrogen showed substantial dependance on oxidative degradation, suggesting that the oxidation of PE was inhibited by polyacrylonitrile (PAN), which forms graft chains. It was considered that the oxidation‐inhibiting mechanism of PAN produced in the amorphous regions prevents oxygen from dissolving and diffusing into the amorphous phase, thus inhibiting the oxidative degradation of PE, and that, when heated, PAN undergoes nitrile oligomerization and the nitrile oligomer end radicals act to trap those radicals which participate in PE oxidative degrad

ISSN:0021-8995    

DOI:10.1002/app.1991.070430201

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

年代:1991

数据来源: WILEY

摘要:

AbstractRoad bitumens, when combined with polymers such as styrene‐butadiene‐styrene (SBS) block copolymers, show improved mechanical properties. The corresponding blends, however, are thermodynamically unstable, and phase separation quickly occurs at higher temperatures. A solution is proposed for improving the thermal stability of these blends: It is based on the formation of reversible, ionic interactions between the bitumen and the SBS, thereby leading to a mixed, ionomeric network. Both compounds are first chemically modified by the grafting of carboxylic acid groups, then mixed, and, finally, the available acid groups are partially or totally neutralized by adding zinc acetate dihydrate to the blends. Comparison of the thermal stability of the resulting ionomeric blends with that of the untreated blends is discussed. The use of ion‐ion interactions to enhance miscibility, which, for the first time, has been extended to bitumen–polymer systems, is shown to be a means of obtaining stable

ISSN:0021-8995    

DOI:10.1002/app.1991.070430202

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

年代:1991

数据来源: WILEY

摘要:

AbstractTwo different phenol–formaldehyde (PF) resole resins are serving as models in a study aimed at establishing the effects of moisture, temperature, pressure, and time on resin cure and bonding during the pressing of wood flakeboard. This phase of the program had two goals: first, to characterize the two resins in terms of their structure and chemistry during synthesis, aging, and cure—using viscosity measurement, gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA); second, to make a preliminary evaluation of the utility of DSC, FTIR, and DMA for measuring the degree of resin cure. The two resins differed significantly in relative amounts of hydroxymethyl groups and methylene linkages (NMR), in molecular weight and its distribution (GPC), and in reaction rate (as measured by viscosity, DSC, FTIR, or DMA). The degree of cure developed during constant heating rate DSC scans was calculated for a series of maximum DSC temperatures from both the loss in hydroxymethyl groups (FTIR) and the decrease in available exothermic heat (DSC). Agreement between the two methods was quite good, considering the inherent difficulties in quantifying infrared data. For comparison, the degree of cure developed during constant heating rate DMA scans was calculated for a series of maximum DMA temperatures from both the increase in storage modulus (DMA) and the decrease in exothermic heat (DSC after rewetting). Samples that apparently achieved complete cure in the DMA still exhibited significant residual cure potential in the DSC. We attribute the lower apparent cure in the DMA to loss of moisture from samples during the DMA scan, with consequent loss in plasticization and molecular mobil

ISSN:0021-8995    

DOI:10.1002/app.1991.070430203

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

年代:1991

数据来源: WILEY

摘要:

AbstractFree radical copolymerization of glycidyl methacrylate (GMA) and N‐vinyl‐2‐pyrrolidone (VPD) was carried out using 2,2′‐azobisisobutyronitrile (AIBN), in chloroform at 60°C. The polymers were characterized by IR and13C‐NMR spectroscopic methods. The percentage composition of the copolymers were established by microelemental analysis and by13C‐NMR spectroscopy. The copolymerization reactivity ratios were computed using the Fineman‐Ross method, the Kelen‐Tudos method, and the extended Kelen‐Tudos method. The molecular weights of the copolymers were obtained by GPC measurements. Thermal properties of the homo‐ and copolymers were also studied by thermogravimetric analysis. The copolymers were tested as adhesives for leather‐to‐leather an

ISSN:0021-8995    

DOI:10.1002/app.1991.070430204

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn this study, the flexible nylon‐6 was reinforced by the wholly rigid aromatic polyamide poly(m‐phenylene isophthalamide) (PmIA) (Nomex) by physical polyblending and chemical copolymerization usingp‐aminophenylacetic acid (P‐APA) as a coupling agent. From DSC measurements, it was shown that Tgof the polyblends increased with the increase of Nomex content. The Tgand Tmof multiblock copolyamides were found to be higher than those of polyblends and triblock copolyamides. Scanning electron microscopy revealed that the polyblends were a dispersed phase structure, although the multiblock copolyamides exhibited a homogeneous texture rather than an aggregated one. From the wide‐angle X‐ray diffraction pattern, it was found that the triblock copolyamides and polyblends had two diffraction peaks, i.e., 2 θ = 20.5 and 24°. However, the multiblock had only one at 2 θ = 20°, indicating a different crystal structure for multiblock copolyamides. For the mechanical properties, it was found that the multiblock copolyamides had a more significant reinforcing effect than those of polyblends and triblo

ISSN:0021-8995    

DOI:10.1002/app.1991.070430205

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

年代:1991

数据来源: WILEY

摘要:

AbstractExperimental results on plasma treatments of polysulfone and polyetherimide to improve the wettability of these polymers are presented. The plasma is characterized by optical emission spectroscopy. The wettability of the polymer surfaces were checked by contact angle measurements and ESCA is used to compare the surfaces before and after plasma treatment. Correlations between contact angle, concentration of oxygen at the surface, and optical emission intensity of the OH radical have been established. Optimization of operational plasma parameters leading to the best wettability of the treated samples is reported.

ISSN:0021-8995    

DOI:10.1002/app.1991.070430206

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

年代:1991

数据来源: WILEY

摘要:

AbstractKinetics of gelation for aqueous solutions of poloxamers 407 and 288 were determined using pulse shearometry. The principle of this method for determining the shear modulus of a semisolid was based on generation of a torsional force that is transmitted through the poloxamer sample at discrete time intervals. Three distinct linear phases were observed for the log dynamic shear modulus (G′) vs. time profiles as poloxamer 407 and 288 solutions of varying concentrations were allowed to passively warm at room temperature to a temperature exceeding the sol‐to‐gel transition temperature,Tm. The beginning of the second exponential phase coincided with the onset of the gelation process as determined by visual observation. Although gelation appeared visually to be complete at the beginning of the third exponential phase of the logG′ vs. time profiles, this last exponential phase may indicate the rate of formation of the polymer network. A comparison of poloxamer 407 [30% (w/w);Tm= 10.9°C] and poloxamer 288 [37% (w/w);Tm= 11.1°C] would suggest that the concentration of poloxamer required to achieve approximately the same gelation temperature for poloxamers having a similar ratio of poly(oxypropylene):poly(oxyethylene) units decreases with increasing molecular weight of the poly(oxypropylene) hydrophobe contained in the copolymer. Results of these preliminary studies suggest that the gelation process was significantly (p<.05) more rapid for poloxamer 407 at a 30% (w/w) concentration compared to a 30% (w/w) solution of poloxamer 288 when the poloxamer solutions were allowed to passively warm at room temperature. In addition, it appears that the rate of gelation for the poloxamer solutions studied was dependent on the rate of heat transfer through the polymer

ISSN:0021-8995    

DOI:10.1002/app.1991.070430207

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe mechanical properties of a system consisting of a bisphenol A diglycidylether (DGEBA) expoxy, cured with a cycloaliphatic diamine (4,4′‐diamino‐3,3 dimethyldicyclohexyl‐methane, 3DCM), in the presence of an epoxy‐terminated butadiene‐acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration. Fracture toughness (KIc) and fracture energy (GIc) were increased, while Young's modulus and yield strength decreased slightly with increasing volume fraction of the dispersed phase. We show that there is no significant influence of the precure schedule and of the various observed particle diameters on the mechanical properties for a constant rubber volume fraction. In our case, the main deformation process in the rubber‐modified epoxy networks is shear yielding while cavitation

ISSN:0021-8995    

DOI:10.1002/app.1991.070430208

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

年代:1991

数据来源: WILEY

摘要:

AbstractNew biscyanamides containingo‐substituted groups or a phenyl‐ether linkage were synthesized. The curing reaction behaviors of the biscyanamides were investigated. All the prepared biscyanamides began to polymerize as soon as they melted after being put on a heated plate beyond a certain temperature. The cured resins of each biscyanamides were prepared on the optimal conditions. Optimal conditions for cured resins were obtained from the curing reaction behaviors of each biscyanamide by differential scanning calorimetry (DSC). The effect of chemical structures of the biscyanamides on the thermal and mechanical properties of the cured resins such as seen by thermal gravimetric analysis (TGA), density, and flexural strength were studied. The introduction of alkyl groups into theorthoposition decreased intermolecular interactions. The introduction of a long phenyl‐ether linkage into the structure gave a broad exothermal peak in the DSC and good workability for the preparation of the cured resins. Moreover, the extension between cross‐linkings improved the flexibility of the cured resins. The cured resins with fluorine‐containing substituent groups also had better thermal stability in the air compared with hydrocarbon gro

ISSN:0021-8995    

DOI:10.1002/app.1991.070430209

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

年代:1991

数据来源: WILEY

摘要:

AbstractPolybutylene terephthalate (PBT) is a commercially successful thermoplastic polyester but has certain drawbacks such as low impact strength and low melt strength. An attempt has been made to modify the properties of PBT by blending it with polyolefin such as highdensity polyethylene (HDPE). Since PBT and HDPE are incompatible, an ionomer has been used as a compatibilizer to form an alloy. Alloys of PBT and HDPE with varying amounts (2‐8%) of ionomer were prepared by melt blending. The ultimate mechanical properties improved significantly on the addition of the ionomer due to an increase in interfacial adhesion between PBT and HDPE. DSC studies show that the presence of ionomer facilitated the crystallization of PBT in the alloy. DMTA studies show that more of PBT (amorphous) is going in to the HDPE‐rich phase in the presence of ionomer. The morphology of the alloys was studied using scanning electron microscopy (SEM), polarizing microscopy (PM), and small‐angle light scattering (SALS). They showed improved dispersion of HDPE domains in PBT matrix with increasing ionomer content and change in the type of superstructure on adding the ionomer. It has been shown that an alloy of PBT and HDPE with improved mechanical properties and homogeneous morphology can be made with use of ionomer as a compatibilizer. Such alloys are cost effective and can find use in several engineering applica

ISSN:0021-8995    

DOI:10.1002/app.1991.070430210

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

年代:1991

数据来源: WILEY