摘要:

AbstractThe structure and properties of the pulp‐like aromatic polyamide PPTA fibers prepared directly from a polymerization medium were studied by scanning electron microscopy (SEM), X‐ray diffractometry, and polarizing light microscopy. The morphology of the fiber appears significantly different from that of Kevlar and does not reveal a skin‐core structure. Regular defect bands and, thus, the regular clustering of the chain ends also could not be obs

ISSN:0032-3888    

DOI:10.1002/pen.760291202

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA previously empirical pressure‐dependent yield criterion for polymeric solids is derived from linear thermoelasticity and equilibrium thermodynamics. The assumption of a critical value of the mechanical component of the internal energy density at the onset of plastic deformation leads to an explicit expression for the yield condition in terms of the stress invariants and thermomechanical properties of the material. Order of magnitude agreement between the linear theory and published experimental data is obtained for a variety of polymers, suggesting a possible physical basis for pressure‐dependent yield

ISSN:0032-3888    

DOI:10.1002/pen.760291203

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe mutual diffusion coefficients for polybutadiene‐ethylbenzene and polybutadiene‐n‐nonane systems were measured by using a sorption apparatus with a quartz spring in the temperature region from 80 to 130°C and for mass fraction of hydrocarbon ranging from 0 to 0.27. The mutual diffusion coefficients were correlated with good agreement by the free‐volum

ISSN:0032-3888    

DOI:10.1002/pen.760291204

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe possibility of a number of halatopolymers forming complexes with pyridine and their ability to produce ketones by pyrolytic decarboxylation have been investigated. Of all the halatopolymer‐forming divalent metal (i.e., Mg2+, Ca2+, Ba2+, Zn2+, Cd2+, Mn2+, and Pb2+) dicarboxylates (i.e., suberate, sebacate, dodecanedioate, and terephthalate) investigated only Cd2+yielded polyalkylene ketone on pyrolysis and formed complexes with pyridine. The polyalkylene ketones were infusible, and no solvents were found for them which suggests a cross‐linked molecular structure. Complexes formed by the cadmium aliphatic dicarboxylates were unstable but highly viscous in solution. Cadmium‐pyridine terephthalate complexes were on the contrary very s

ISSN:0032-3888    

DOI:10.1002/pen.760291205

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractSome model experiments on polymer melt devolatilization (DV) conducted in our laboratories have been previously reported. Here, we examine some theories and propose some mathematical models in pursuit of an explanation of these experimental observations. Included are bubble nucleation and free volume theories as well as continuum models for bubble growth in quiescent fluids and fluid flow in rolling pools without bubbles. A modification of Harvey's cavity model seems to explain the behavior of foam formation in DV, at least qualitatively. Denson's cell model for bubble growth fits the separation data under vacuum. A simple exponential model for overall separation fits the separation data at atmospheric pressure (entrained DV).

ISSN:0032-3888    

DOI:10.1002/pen.760291206

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe structure and the properties of oriented polymer surfaces were studied for three series of uniaxially oriented films of polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET). The surface structure was characterized in terms of relative crystallinity and molecular orientation along with topology and roughness by using FT‐IR‐ATR dichroism technique, optical microscopy and surface profilometer. In all three polymers, the surface orientation function increases with draw ratio. The relative surface crystallinity and the trans con‐former also increases for PP and PET, respectively. In uniaxially drawn PP, the surface becomes rough with increasing draw ratio and the roughness is anisotropic with peaks and valleys elongated along the draw direction. For drawn PP, the equilibrium contact angles for four different liquids all exhibit anisotropy with higher values in perpendicular direction than that in parallel to the draw direction. In contrast, both drawn PET and PS films show smooth surfaces, and the equilibrium contact angles were all isotropic. When roughness is removed from the drawn PP by polishing without altering the molecular orientation, the anisotropy becomes negligible and the contact angles approach the value for undrawn PP. When surface roughness was created deliberately on undrawn PET and PS films, the contact angle anisotropy was clearly observed. Therefore, the anisotropy in surface topology rather than the molecular orientation seems to play a dominant role in developing anisotropic wetting behavior. The equilibrium contact angles for smooth surfaces have been calculated using the experimentally obtained roughness and anisotropic contact angle data from the rough surface. These values are in reasonable agreement with the measured contact angles for smooth surfaces, suggesting that the observed contact angle anisotropy can be attributed entirely to the roughness anisotropy rather than to the molecular orient

ISSN:0032-3888    

DOI:10.1002/pen.760291207

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractAnalysis of the crystallization kinetics of poly(etheretherketone) (PEEK) was achieved with dynamic differential scanning calorimetry results. A new kinetic model for the nonisothermal crystallization was derived and the possibility of its application was investigated. By evaluating the parameters in the model, the crystallization behavior of PEEK was analyzed. The experimental and predicted crystallinity change showed good agreement, which indicated that the model equation was appropriate to describe the nonisothermal crystallization kinetics of PEEK. As the melt temperature was increased the number of heterogeneous nuclei decreased, hence the crystallization was delayed.

ISSN:0032-3888    

DOI:10.1002/pen.760291208

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe technique of Impulse Viscoelasticity was used to characterize the network mechanical properties of amine‐cured epoxies during cure. The effects of amine molecular weight, functionality and stoichiometry were investigated. Among the properties which were obtained were the equilibrium tensile modulus, gelation time, cure and thermal stresses, volumetric changes during cure, glass transition temperature, thermal expansion coefficient, and molecular weight between cress‐links. It was found that these networks cured elastically and agreed closely with the predictions of rubber elasticity theory over a wide range of crosslink densit

ISSN:0032-3888    

DOI:10.1002/pen.760291209

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractViscoelastic measurements were made on test specimens cut from plaques made from milled, compression molded blends of poly(vinyl chloride) (PVC) and methylmethacrylate‐butadiene‐styrene modifier (MBS). The experimental frequency range was from 0.0159 to 79.6 Hz. and the temperature range was from −140 to 20°C. The MBS modifier level studied was 8.26, 10.71, and 13.04 weight percent. This experimental range covers the beta relaxation process of PVC and the alpha relaxation process of the rubbery regions of the modifier. The complex compliance was represented in terms of a function originally proposed by Havriliak and Negami to represent the dielectric relaxation processes in polymers. The parameters of this expression as well as their dependence on temperature were determined by the multi‐response statistical techniques developed by Havriliak and Watts. Addition of MBS modifier to PVC appears to enhance the already present beta relaxation process in PVC. In addition the temperature dependence of the relaxation time has been increased so that the process is faster at room temperature. The α and β parameters of the relaxation function have changed so that the process is narrower at room temperature. There is no significant viscoelastic evidence supporting a second phase. This observation suggests significant impedance matching of the two phases which may be an important criteria for impact modification. Similarity of the two processes suggests a possible mechanism for the PVC be

ISSN:0032-3888    

DOI:10.1002/pen.760291210

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe combination of rubbery and rigid polymers in a multiphase structure using staged emulsion polymerization has yielded materials with properties ranging from reinforced elastomers to high impact plastics. The many different particle morphologies that result from a two‐stage latex (TSL) polymerization include core/shell, domain, interpenetrating polymer networks (IPN), and various combinations thereof. The sequence of polymerization, crosslinking, grafting, and composition are among the significant parameters that determine the particle morphology. Elastomeric TSL with soft polyacrylates (PA) as the seed particles and polystyrene (PS) as the second stage, with each stage lightly crosslinked, may yield IPN‐microdomain particles.The particle morphology has been elucidated through a combination of microscopy and mechanical property analyses. The significant modulus of elastomeric latex interpenetrating polymer networks (LIPN) results from reinforcement by PS intra‐particle microdomains and their significant tensile strength from a strength forming mechanism of PS inter‐particle microdomains. The increase in the PA seed crosslinking increases the crosslinked PS (xPS) level of molecular mixing with, and grafting via residual unsaturation to, the crosslinked PA (xPA) network and decreases particle deformnability. At higher xPS concentrations the formation of an xPS‐rich shell enhances xPS continuity in the molded material through the partial coalescence of the shells, diminishing the PA continuity, and yielding more PS‐like properties.The submicron lightly crosslinked latex particles with these different morphologies flow as a pseudoplastie material through a particle slippage flow mechanism exhibiting neither a Newtonian plateau nor a yield stress at low shear rates. The deformable lightly crosslinked particles with interchangeable PS ties which disintegrate at elevated temperatures retain their identity and regain their shape at the cessation of shear. The LIPN can be processed using standard thermoplastic methods and machinery, with power law constants and shear insensitive flow activation energies that are similar to those of thermoplastics at high levels of shear. Uncrosslinked PS shells around crosslinked PA seed particles, on the other hand, completely coalesce upon molding to form a continuous thermoplastic PS matrix that may essentially flow through molecular

ISSN:0032-3888    

DOI:10.1002/pen.760291211

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY