摘要:

AbstractA variety of thermoplastic fully imidized poly(imide siloxane) segmented copolymers with useful thermal and mechanical properties have been prepared. Other interesting properties described are the materials' hydrophobic character, surface domination, UV stability, and atomic oxygen plasma resistance.

ISSN:0032-3888    

DOI:10.1002/pen.760292002

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractPost‐curing of vinyl‐addition cured siloxane networks can take place due to the presence of excess silicon hydride. The reaction of these groups, which leads to increased crosslink density especially at elevated temperatures, can be retarded by treatment with ammonia gas or eliminated by exposure to ethylene gas. There is an interesting correspondence between post‐curing behavior and the gelation process. In both cases, two curing regimes are observed. For low extents of reaction, the mobility of chains is high, even though the post‐curing experiment is performed on samples which have already gelled, and the cure is controlled by reaction kinetics, not by the diffusion of the reactants. At high degrees of cure or post‐cure, both cases behave as crosslinked networks to reduce the probability of interaction between reactants, and the cure is diffusion‐controlled. However, the post‐cured gels do not exhibit ideal network behavior since the last crosslinks formed during post‐curing have a much greater effect on the physical properties than those formed initially. This may be due to the bimodal distribution of chain lengths between crosslinks that is formed dur

ISSN:0032-3888    

DOI:10.1002/pen.760292003

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractWe demonstrate the use of computer vision techniques and optical microscopy to follow the kinetics and microstructure during spinodal decomposition of a polymer blend. Among other features, the mean of the population of the local maxima of the gradients in each image is computed; this global feature is shown to co‐develop with the phase separation of the blend. An algorithm is presented which employs the gradient magnitude technique to analyze optical images of spinodally decomposing polymer blends. This algorithm has been used to extract the Cahn‐Hilliard spinodal growth rates for a binary blend of polystyrene with poly(vinyl methyl ether). We show that the spinodal temperature can be found from the temperature dependence of this growth rate. We also show how additional shape features such as compactness might be used to study, the same binary bl

ISSN:0032-3888    

DOI:10.1002/pen.760292004

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractShear and extensional flows can have a significant effect on the miscibility for a blend of polystyrene with poly(vinyl methyl ether). The cloud point temperature in a planar stagnation flow is elevated by as much as 12 K; the magnitude depends on the extension rate, the strain, and the blend composition. Flow‐induced miscibility is also observed in the shear flow between parallel plates which has been used to test smaller samples and to prepare solid samples for further characterization. At lower temperatures, as much as 30 K below the coexistence temperature, flow‐induced phase separation occurs in both shear flow and extensional flows. The stress, rather than deformation rate, appears to be the most important parameter in flow‐induced phase separ

ISSN:0032-3888    

DOI:10.1002/pen.760292005

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThis study deals with the cold compaction of polyether‐etherketone (PEEK) and nickel powder blends. Four different types of PEEK powders which are commercially available from Imperial Chemical Industries (ICI) were utilized for this investigation. These PEEK powders included fine and coarse size powders of a low viscosity grade (150PF and 150P) and similar powders of a high viscosity grade (450PF and 450P). Each of the four different PEEK powders were blended with about 10 vol−% nickel powder (Novamet) using a dry mixing technique. These PEEK/nickel powder blends were then successfully compacted at room temperature. Green strengths as high as 39.5 MPa and 26.3 MPa were measured on nickel filled 150 grade and 450 grade compacts, respectively. The higher strength values of the nickel filled compacts compared to their respective unfilled ones were attributed to a higher degree of mechanical interlocking and plastic deformation, which was induced in the polymer particles during compaction by the hard nickel filler. These composites also exhibited lower viscoelastic recoveries than their respective unfilled compacts. Electrical resistivities as low as 0.06 ohm‐cm were achieved by compacting 150P/nickel powder blends. This resistivity value agreed well with the calculated value predicted from the liter

ISSN:0032-3888    

DOI:10.1002/pen.760292006

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThis study deals with the characterization and cold compaction of polyetheretherketone (PEEK) powders. Four different types of PEEK powders which are commercially available from Imperial Chemical Industries (ICI) were characterized for density, crystallinity, particle size, particle size distribution, and particle morphology. Fine and coarse size powders of a low viscosity grade (150PF and 150P) and similar powders of a high viscosity grade (450PF and 450P) were processed. Compaction was successful at room temperature using the 150 grade powders but not with the 450 grade powders. Compressibility curves were obtained at room temperature for the 150 grade powders and their post‐compaction viscoelastic recoveries were measured. The coarse and fine size 150 grade powders reached relative plateau densities of 95.8% and 95.1%, respectively, when compacted at pressures exceeding 300 MPa. These high densification values at room temperature were associated with minimal post‐compaction viscoelastic recoveries and as‐compacted strengths as high as 8.9 MPa. A modified densification parameter (DP*) was developed based on the plastic deformation of the crystalline regions alone. This new dimensionless parameter,DP*, demonstrated a better fit of all the compaction data. The transverse rupture strength and the green density data are presented and explained in terms of th

ISSN:0032-3888    

DOI:10.1002/pen.760292007

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractEpoxies toughened with two reactive liquid rubbers, an epoxy‐terminated butadiene acrylonitrile rubber (ETBN) and an amino‐terminated butadiene acrylonitrile rubber (ATBN), were prepared and studied in terms of their structure property relationships. A two‐phase structure was formed, consisting of spherical rubber particles dispersed in an epoxy matrix. A broad distribution of rubber particles was observed in all the materials with most of the particles ranging in size from 1 to 4 μm, but some particles exceeding 20 μm were also found. Impact strength, plane strain fracture toughness (KIC), and fracture energy (GIC) were increased, while Young's modulus and yield strength decreased slightly with increasing rubber content and volume fraction of the dispersed phase. BothGICandKICwere found to increase with increasing apparent molecular weight between crosslinks and decreasing yield strength. The increased size of the plastic zone at the crack tip associated with decreasing yield strength could be the cause of the increased toughness. An ATBN‐toughened system containing the greatest amount of epoxy sub‐inclusion in the rubbery phase demonstrated the best fracture toughness in this series. In the present systems, rubber‐enhanced shear deformation of the matrix is considered to be the major toughening mechanism. Curing conditions and the miscibility between the liquid rubber and the epoxy resin determine the phase morphology of the resulting two‐phase systems. Kerner's equation successfully describes the modulus dependence on volume fraction for the two‐phas

ISSN:0032-3888    

DOI:10.1002/pen.760292008

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractEpoxies containing epoxy‐terminated butadiene acrylonitrile rubber (ETBN) or amino‐terminated butadiene acrylonitrile rubber (ATBN) were prepared and studied in terms of fatigue crack propagation (FCP) resistance and toughening mechanisms. Rubber incorporation improves both impact and FCP resistance, but results in slightly lower Young's modulus andTgAsTgincreases, the degree of toughening decreases. Rubber‐induced shear yielding of the epoxy matrix is believed to be the dominant toughening mechanism. Decreasing fatigue resistance with increasing cyclic frequency is observed for both neat and rubber‐toughened epoxies. This result may be explained by the inability of these materials to undergo possible beneficial effects of hysteretic heating. FCP resistance is linearly proportional toMc1/2, whereMcis the apparent molecular weight between crosslinks determined on the rubber‐toughened material. FCP resistance also increases with increasing static fracture toughnessKIC. ATBN‐toughened epoxies demonstrated better fatigue resistance than ETBN‐toug

ISSN:0032-3888    

DOI:10.1002/pen.760292009

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractGelation phenomenon in thermoset polymers is an area of extreme importance from the processing point of view. Gel point (GP) has traditionally been detected using rheological and mechanical techniques. We wish to report the use of dielectric and especially calorimetric techniques for detecting GP. Using a particular thermoset system, we have compared the calorimetric, dielectric, and mechanical techniques and shown how to define GP in terms of time and temperature. As a matter of convenience, we have briefly defined the gelation phenomenon in thermosets, its significance and measurement, and a critical evaluation of the techniques for detecting GP.

ISSN:0032-3888    

DOI:10.1002/pen.760292010

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760292011

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY