摘要:

AbstractA model describing the expansion of a polyurethane (PU) foam in a closed mold is developed. An energy balance is stated, together with constitutive equations for the vaporization rate of the foaming agent and the polymerization kinetics. A numerical solution is obtained for an experimentally‐characterized PU formulation. It is shown that in order to avoid premature gelling or undesirable density distributions, the wall temperature must be close to the initial one. The relative fraction of skin in the foam may be increased by decreasing the part thickness or by adding less catalyst or more blowing agent to the formulation. Factors affecting cream, rise, and process times are discusse

ISSN:0032-3888    

DOI:10.1002/pen.760261102

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe incremental response ΔG(t)obtained by superposing a deformation, Δγ, on a large deformation, γ1, has been determined in step shear experiments for a polyisobutylene solution and for a poly(methylmethacrylate) glass in torsion. For both systems ΔG(t)at γ1was found to be smaller than the linear viscoelastic modulus,G(t), at zero prestrain. ΔG(t)was found to increase with increasing time,te, after imposition of the large deformation. It was also observed that the “apparent relaxation spectrum” associated with ΔG(t)narrows and shifts to shorter times when compared to the spectrum associated with the linear viscoelastic modulus, ΔG(t). The results for the solution art‐well described by the nonlinear constitutive equation of the BKZ elastic fluid theory. It is found that ΔG(t)for the glass falls between the behavior predicted by the BKZ theory and the linear viscoe

ISSN:0032-3888    

DOI:10.1002/pen.760261103

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe extent of molecular demixing of poly[cross‐(ethyl acrylate)]‐inter‐poly[cross‐(methyl methacrylate)] interpenetrating polymer networks (PEA/PMMA IPNs), of mid‐range composition was investigated by decrosslinking and/or annealing using dynamic mechanical spectroscopy. A single broad transition characteristic of extensive but incomplete molecular mixing was observed for the PEA/PMMA IPN. The presence of crosslinking in both phases of an IPN enhances the mutual miscibility of the polymers. Through the use of a labile crosslinker, acrylic acid anhydride (AAA), polymer networks may be decross‐linked, allowing the chains to separate and form two distinct phases. Annealing further sharpens the transitions, and phase separation becomes most pronounced when decrosslinking is followed b

ISSN:0032-3888    

DOI:10.1002/pen.760261104

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractAn extensive experimental study of the effect of processing and resin variables on the light transmission of polypropylene tubular blown film is reported. The resin variables investigated include melt flow rate (average molecular weight), molecular weight distribution, and the addition of a nucleating agent. Processing variables studied include blow‐up and draw down ratios, and frost line height (cooling rate). Increasing the draw down and blowup ratios and decreasing the frost line height generally lead to increased light transmission. Decreasing the resin melt flow rate, narrowing the molecular weight distribution, and the addition of a nucleating agent also improve light transmission. The overall light transmission properties of the films are dominated by their surface roughness characteristics, while the internal morphology of the films plays a secondary role. The changes in light transmission of the films in response to changes in processing or resin variables were traced to their effect on the surface texture and internal morpholog

ISSN:0032-3888    

DOI:10.1002/pen.760261105

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe generally accepted kinetic mechanism for free radical copolymerization was simplified by various assumptions and restrictions to give several realistic and easily evaluated models for the simulation of industrial molding. Six assumptions, including conversion‐dependent rate coefficients and constant comonomer concentration ratios, were used to obtain a simplified model. Special cases of this simplified model were obtained by the following additional constraints: (1) RestrictionC, consecutive inhibition and radical generation reactions; (2) RestrictionI, constant initiator decomposition rate; (3) RestrictionZ, zero termination rate for free radicals; and (4) RestrictionKorP, all rate coefficients independent of conversion or only polymerization rate coefficient dependent on conversion. For various combinations of these restrictions, the time and concentration variables in the simplified model are separated and solved; the separate solutions are then combined in various ways to give models capable of predicting a wide variety of behavior. Many of these models have analytical solutions that greatly facilitate the evaluation of rate constants. Models based on restrictionsKCI, PCI, andPCZare shown to give good agreement with isothermal DSC data plotted as reaction rate versus time and, in a more sensitive test, as reaction rate divided by monomer concentration versus fractional conversion. Because of their predictive ability and ease of evaluating constants. ModelsPCIandPCZare recommended for simulating industrial processing; they are particularly well suited for simulating compression molding of sheet molding compoun

ISSN:0032-3888    

DOI:10.1002/pen.760261106

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe use of the J method to characterize fracture is described, and it is noted that smaller specimens may be used to obtain plane strain values than in conventional linear elastic fracture mechanics (LEFM) tests. Various methods of computing J are described, and the extrapolations necessary to define crack initiation are discussed. The various schemes and size criteria are then explored for a polypropylene copolymer, and it is found that the recommended ASTM procedure using energy works well. The method is then used to characterize several toughened polymers, and some discussion of the slope of the resistance curve is given.

ISSN:0032-3888    

DOI:10.1002/pen.760261107

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractThe strength and durability in wet environment of aluminum/epoxy/aluminum joints are investigated as a function of structural changes of γ aminopropyltriethoxy silane (γ‐APS) primer at the interface. Both dry and wet strengths exhibit strong dependencies on both the thickness and the extent of drying of γ‐APS prior to joint formation. Generally, dry strength decreases with increasing thickness of γ‐APS primer, and increases with dehydration of γ‐APS at any given thickness. Strength retention of the joints after exposure to water at 55°C also improves dramatically when the adsorbed γ‐APS is extensively dried. These results are analogous to earlier observations with α‐Al2O3/polyethylene joint system. In aluminum joints, porous oxide substrate facilitates the mechanical interlocking mechanism, and its interplay with both the thickness and the extent of cure of γ‐APS is analyzed by characterizing the fractured surfaces using scanning electron microscopy (SEM) electron spectroscopy for ch

ISSN:0032-3888    

DOI:10.1002/pen.760261108

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

摘要:

AbstractOne of the important aspects in designing polymer structures and predicting their lifetime is the computation of time‐dependent deformation. A tensile creep law for constant uniaxial stress was developed using talc‐filled polypropylene as an example. A simplified finite‐element creep analysis technique for polymer structures was developed with only one time step, an isochronous stress‐stress formulation, and a deformation plasticity‐type analysis, With an elastic analysis and this one‐step nonlinear analysis for a given time and temperature, the displacement of a critical location in the polymer structure can be calculated for any time and temperature without further finite‐element analysis. Comparisons of calculations with this one‐step analysis and with the standard time‐stepping analysis and experimental results for a beam in bending and a plate with a hole demonstrate the usefulness

ISSN:0032-3888    

DOI:10.1002/pen.760261109

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760261101

出版商:Society of Plastics Engineers    

年代:1986

数据来源: WILEY