摘要:

AbstractThere is an increasing body of evidence showing that, for a variety of copolymers, there are significant changes in the copolymer composition over the molecular weight distribution of the polymer. In this work, we have polymerized the copolymer poly(styrene‐methyl methacrylate) using ethylaluminum sesquichloride as the initiator. The copolymers produced were fractionated using a semiprep gel permeation chromatograph. The composition of the fractions was determined using infrared spectroscopy. Results show that the percent methyl methacrylate of the copolymers was higher at both the low‐ and high‐molecular‐weight regions of the p

ISSN:0032-3888    

DOI:10.1002/pen.760230102

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractEquilibrium sorption isotherms were obtained for the sulfur dioxide‐epoxy resin of aliphatic diglycidyl ether system over a temperature range of 1° to 45°C. The sorption isotherms indicated the presence of Langmuir sorption due to specific interaction. This is uncommon for rubbery polymers, though similar behavior was also observed previously. Zimm‐Lundberg's clustering analysis indicated a slight tendency for clustering of the penetrant molecules at low temperatures and higher activities. The number of Langmuir sites for sorption was found to be independent of temperature. The mobilities of the molecules sorbed in Henry's law mode and the Langmuir mode were found to be approximately equal. Predictions of the permeability values for this system are presented and compared with other data from the literature. The temperature dependence of different sorption parameters is presented and discussed in d

ISSN:0032-3888    

DOI:10.1002/pen.760230103

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractUniaxial tension tests to the yield point were performed on a crystalline polymer, poly(4‐methyl pentene‐1) (PMP) as a function of temperature from 21° to 200°C at a strain rate of 2 min−1. After testing, the specimens showed considerable stress whitening as a result of microvoid formation. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (240°C). Thus, the behavior of this crystalline polymer is similar to that of glassy polymers, but with the melting temperature, rather than the glass transition temperature, as the reference point. The ratio of thermal to mechanical energy input to produce yielding is an order of magnitude smaller for PMP than it is for glassy polymers. The ratio of yield stress to Young's modulus is about 0.02, which is typical for polymers. Yield stress is a linear function of log strain rate, which implies that yielding can be described as a segmental flow rate process in which the applied stress biases the activation energy. The activation volume is on the order of 20 monomer unit volumes and increases as the temperature increases. The activation energy is 19

ISSN:0032-3888    

DOI:10.1002/pen.760230104

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThis article analyzes the average residence time distribution of polymer melt across the die width in a common linearly tapered coat‐hanger die, which excells the T die but is a little inferior to the curvilinearly tapered coat‐hanger die in residence time uniformity according to the approximated calculation of ten used. From another point of view, a linearly tapered coat‐hanger die may be designed so that a desired ratio of the residence time through the die far end to that along the die center line may be imposed as one of the design constr

ISSN:0032-3888    

DOI:10.1002/pen.760230105

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractA theoretical and experimental investigation is presented for filling thin cavities of variable gap thickness. The modeling is based upon a finite‐element/finite‐difference formulation for an inelastic power‐law fluid and includes the effects of viscous heating and conduction upon the flow dynamics. Extensive results are presented for polypropylene and polystyrene melts injected into two variable‐gap‐thickness cavities, of which one has an insert. Good agreement is found between the predictions and measurements concerning the shape of the advancing melt front, the location of weld lines, and the temporal pressure trace at various positions in t

ISSN:0032-3888    

DOI:10.1002/pen.760230106

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractDifferential scanning calorimetry is employed to study the crystallization kinetics of two commercial injection‐molding high‐density polyethylene resins. Also, polarized light microscopy has been used to elucidate the morphological structures formed at various crystallization conditions. Corrections and operating procedures are recommended in order to correct for temperature lag in scanning, transient response during isothermal crystallization and for thermal gradients within the polymer sample. As a result of these studies, a modified Avrami equation has been proposed in order to obtain a more extensive and reliable characterization of isothermal crystallization kinetics. Moreover, a procedure is recommended and employed to predict nonisothermal crystallization behavior on the basis of isothermal crystallization kinet

ISSN:0032-3888    

DOI:10.1002/pen.760230107

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractSintering of amorphous polymer particles above their glasstransition temperature is a slow coalescence process in which surface tension is the main driving force, tending to decrease the total surface area, resisted by the polymer viscosity. The shape, and therefore the boundaries of the coalescing particles, change with time. A numerical finite‐element method (FEM) was used to solve the momentum and continuity equations for a coalescing spherical‐particles pair. The solution obtained describes a limited sintering time interval with reasonable agreement. Future modifications of the solution technique are suggested in order to extend its validity to longer sintering peri

ISSN:0032-3888    

DOI:10.1002/pen.760230108

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThis article contends that three distinct physical processes control electron transport in conductor‐filled polymer systems. Percolation is required to explain the macroscopic conduction in the disordered medium. Quantum mechanical tunneling (possibly quantum fluctuation augmented) is needed to describe conduction between adjacent conductive particles at the microscopic level. And, thermal expansion is invoked to deduce constituent volume densities and microscopic tunnel lengths. Each of these mechanisms is given a mathematical form. The ansatz is used to predict resistivityvs.temperature and resistivityvs.conductor‐filling fraction functions. Successes and deficiencies of the theory are discussed with respect to experimental data and theoretical considerati

ISSN:0032-3888    

DOI:10.1002/pen.760230109

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760230101

出版商:Society of Plastics Engineers, Inc.    

年代:1983

数据来源: WILEY