摘要:

AbstractWe present chain structure, phase morphology, and toughness relationships in thermoplastic polymers and polymer/rubber blends. In neat polymers, molecular aspects of craze/yield behavior are controlled by two chain parameters: entanglement density νeand characteristic ratioC∞. The crazing stress is proportional to ν e1/2, and the yield stress is proportional toC∞. The dispersed rubber toughens a polymer/rubber blend mainly by promoting energy dissipation of the matrix. The toughening efficiency correlates with the rubber phase morphology and the chain structure of the

ISSN:0032-3888    

DOI:10.1002/pen.760301302

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe positron annihilation lifetime spectroscopy (PALS) technique is used to measure volume relaxation in physically aged glassy polycarbonate. The relaxation times and activation energy calculated for the isothermal relaxations in the aged polycarbonate are greater than those parameters calculated for unaged polycarbonate. The activation energy of 8.2 kcal/mol in the aged polycarbonate is used to identify the phenyl group motion or the cooperative carbonate‐phenyl interaction as the molecular features responsible for the thermally induced open volume relaxations. It is postulated that the open volume relaxation kinetics as measured by PALS can be used as a nondestructive indication of property differences between aged and unaged polycarbonat

ISSN:0032-3888    

DOI:10.1002/pen.760301303

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effect of added silica on the spherulite radial growth rates of isotactic poly(propylene oxide) (i‐PPrO) has been investigated by optical photomicroscopy. Two different i‐PPrO samples were used of different molecular weights and isotacticity, 87 and 100% as determined by13C NMR. The addition of fine particle silica, an effective nucleating agent, depresses the spherulite growth rates throughout the entire temperature range, but the effect is more dramatic for the i‐PPrO of lower isotacticity. For a given sample, the retardation increases as the quantity of filler increases. The growth rate‐temperature behavior is analyzed in terms of the classical Hoffman‐Lauritzen equation, modified to take into account the polymer‐filler

ISSN:0032-3888    

DOI:10.1002/pen.760301304

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effect of viscous dissipation on solidification onto the inner surface of a straight circular tube of a liquid flowing laminarly with a specified volumetric rate is analytically determined. Steady conditions and a constant tube wall temperature below the solidification temperature of the liquid are assumed. Solutions for the thickness of the solidified shell and for the pressure drop are obtained. The pressure gradient versus volumetric flow rate curve exhibits a minimum, suggesting that it might be possible to design runners for injection molding machines to have a minimum pressure drop if the volumetric flow rate is specified.

ISSN:0032-3888    

DOI:10.1002/pen.760301305

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractLow‐density foam (0.02–0.09 g/cc) was produced from gels of ultrahigh molecular weight (UHMW) polyethylenes in solvents with melting points above ambient. The hot PE solutions were stirred at high speed to induce extended chain crystalline gels. These gels were subsequently cooled to allow the solvent to solidify and then the solvent was extracted with alcohol or sublimed. This resulted in a tough, low density foam or a collapsed mass depending mainly on the concentration of the polymer. Shrinkage was significant until polymer concentrations reached 4–5%. Foam cell size varied between 5–30 μm, or 25–75 μm depending on the method of preparation. Polarizing microscopy revealed both spherulitic and row‐nucleated structures depending on the thermal history followed during the sample preparation. We were also interested in whether or not small particles could be used to influence the nucleation and growth of the solution crystallization process. These particles could be suspended in the gel and stabilized in something like a colloidal necklace as has been proposed recently. We successfully incorporated small (0.5 μm) tungsten particles in UHMWPE gels which remained in the foam on extraction of the solvent. Polyethylene containing carbon black particles produced less successful results. These effects may be related to absorption associated with gela

ISSN:0032-3888    

DOI:10.1002/pen.760301306

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractPoly[2,2'‐(m‐phenylene)‐5,5'‐bibenzimidazole] (PBI) is shown to be miscible with poly(4‐vinyl pyridine) over the entire composition range. Experiments were performed with commercial PBI as well as a lower molecular weight material synthesized by us. Blend miscibility is evidenced by single glass transition temperature intermediate between the pure polymers. Hydrogen bonding between the components was detected by infrared spe

ISSN:0032-3888    

DOI:10.1002/pen.760301307

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760301301

出版商:Society of Plastics Engineers    

年代:1990

数据来源: WILEY