摘要:

AbstractProcessing of polymers is greatly affected by the presence of dissolved gases. Analysis of the effect of dissolved gases requires two types of information: equilibrium thermodynamic data and predictive correlations as well as diffusion rate data and analyses. We review here the state‐of‐the‐art knowledge of the equilibrium thermodynamics of gases dissolved in polymers. The published data are presented and analyzed. Also, we review the latcst theories and predictive correlations for gas solubility in pol

ISSN:0032-3888    

DOI:10.1002/pen.760170202

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractPrior studies of two series of segmented polyurethanes based on 2, 4 toluene cliisocyanate (2, 4 TDI) or 2, 8 TDI, butanediol, and a 1000 molecular weight polytetramethyleneoxide (PTMO‐1000) soft segment revealed a rapid increase in soft segment glass transition temperature (Tg) with increasing urethane content in the 2, 4 TDI series. The change inTgcouldbe correlated with estimates of hard segment‐soft segment phase mixing obtained by infrared analysis of the urethane NH and carbonyl bands. In the present paper, the infrared data have been reevaluated using improved procedures for resolving the carbonyl band into H‐bonded and nonbonded components, and the relation between the estimated extent of phase mixing andTghas been reexamined. The transition behavior in an extensive series of related polymers has also been determined, including 2, 4 TDI arid 2, 6 TDI samples with PTMO2000 as well as polybutyleneadipate (PBA‐1000 and PBA‐2000) soft segments. The results indicate the effectiveness, of increased soft segment molecular weight in promoting phase segregation, imply that much greater phase mixing occurs in polyester than polyether samples, suggest that anchoring the ends of the soft segments has only a small effect onTg, and provide some evidence that H‐bonding not only increasesTgbut can also impede soft segment crys

ISSN:0032-3888    

DOI:10.1002/pen.760170203

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractRestricting the discussion to isothermal transport of a single penetrant in a polymer sample, we define convection and diffusion. We distinguish carefully between diffusion in homogeneous and inhomogeneous samples. In the latter case, the diffusion flux is no longer directly proportional to the gradient of the concentration, i.e., Fick's first law does not hold. We point out, unless an external force responsible for convection can be identified, that diffusion with convection in a homogeneous medium is in many instances indistinguishable mathematically from diffusion in an inhomogeneous medium with microscopic inhomogeneities. Finally, we list a number of exact results available for permeation and sorption parameters for thin slab of a dilute inhomogeneous material. These parameters all yield the same value of the diffusion coefficient if the latter is constant. On the other hand, these parameters provide different functional information about the partition coefficient and diffusion coefficient for an inhomogeneous polymer‐penetrant syste

ISSN:0032-3888    

DOI:10.1002/pen.760170204

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractChemorheological changes in epoxy resins subjected to large strains while heated were observed earlier, but the subject was not treated quantitatively. This paper describes the investigation of an epoxy resin—Epon 826, of known chemical, structure, crosslinked with two different amines. By means of a simple calibrated apparatus, the epoxide samples were subjected to large strains in a non‐oxidizing atmosphere and in air. They were heated to different temperatures for various times; the results were compared with data obtained from unstrained samples kept in otherwise the same conditions. The results show a linear‐logarithmic relation between the torsion modulus,G(10)and the time of applied strain at a certain temperature and also a linear relation betweenG(10), and 1/T°K, both aboveT(10). The results obtained in swelling experiments support the data from 10 sec torsional modulus vs temperature measurements. An increase in the amount of solubles and inMcis observed on extending the time of heating. A clear difference in properties between the strained and unstrained samples, kept in otherwise the sane conditions, is observed and the contribution of the applied strain to chemorheology has been shown. Both systems of crosslinked Epon 826 showed the same general behavior, although the specific data were dif

ISSN:0032-3888    

DOI:10.1002/pen.760170205

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe results of wide angle X‐ray diffraction and, ATR polarization measurements are reported in order to characterize the anisotropy in poly(m‐phenyleneisophthalamide) and poly(p‐phenyleneterephthalamide) (Fiber B) fibers. Additional information on the state of order of the investigated fibers is derived from ATR spectroscopic accessibility measurements by deuterium exc

ISSN:0032-3888    

DOI:10.1002/pen.760170206

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractDuring the injection molding process, moldings undergo shear and elongational stresses. They are also exposed to thermal gradients of varying intensity. Invariably, molded parts, or at least some sections thereof, freeze before the polymer chains can relax to a random, non‐oriented configuration. As a result, injection molded parts contain frozen strains and exhibit anisotropic physical properties. In the present work, a variety of experimental techniques have been employed to determine the three‐dimensional variation of the following properties of injection‐molded, thermoplastic, rectangular parts: density, heat shrinkage, birefringence, and tensile str

ISSN:0032-3888    

DOI:10.1002/pen.760170207

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe theory of deep drawing, which has been developed for metals, is examined critically for thermoplastics. Two special characteristics of thermoplastics, the strong orientation hardening after initial yielding and the ease of crack formation and growth, are shown to vitiate the usual correlation between the drawability of the sheet and the low strain plastic behavior of the material. Attempts to improve the limiting draw ratio of thermoplastics, by biaxially rolling sheet prior to forming, are shown to be effective only if the polymer does not craze easily under tensile stresses.

ISSN:0032-3888    

DOI:10.1002/pen.760170208

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe fluid mechanics of impingement mixing was investigated experimentally, and the design procedure, including scale‐up, for the MIT Liquid Injection Molding System was established. For impingement mixing to be effective, the Reynolds number based on the nozzle diameter must be greater than about 50 and the momentum ratio of the fluid components must he equal to 1 in addition to satisfying the desired mass flow rate rati

ISSN:0032-3888    

DOI:10.1002/pen.760170209

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractA unique liquid injection molding machine for polyurethane was designed and built to process a large quantity of polyurethane in a short period of time. This machine has a continuously variable flow rate. Using inexpensive, low capacity gear pumps, 5 gallon hydraulic accumulators were charged with fluid components. The fluid can be pumped into the accumulators at low pressure followed by nitrogen gas addition to the bladders to raise the fluid pressure, or the charging pumps can pump up the accumulators against an existing pressure. The two components were then discharged under pressure through linkage activated ball valves and mixed together in a mixing chamber. The system provided for a very low pressure loss during discharge, resulting in high fluid velocity. Extremely high flow rates were possible: approximately 1440 lb/min at 2500 psi, a pressure less than the maximum possible system pressure. This system delivers large flow rates of high quality urethane while still maintaining its simplicity, light weight, and relative low cost.

ISSN:0032-3888    

DOI:10.1002/pen.760170210

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractIn an evaluation of low modulus polyurethanes as adhesives, systems based on 1, 4 butanediol‐extended methylene diisocyanate polymer displayed a tendency to crack during cure. Cracking occurred when these systems were gelled at low temperatures in thin layers where adhesion places constraints on dimensional change. A test technique was developed that evaluates the tendency for polyurethane adhesives to develop internal cracks during cure. The test consists of casting the material between the walls of two eccentric beakers and observing the behavior of the system as cure proceeds. The 1, 4 butanediol‐extended methylene diisocyanate system was studied by systematically evaluating the influence of processing variables on cracking. The variables studied included curing agent to prepolymer stoichiometry, moisture content of the curing agent, effect of pre‐evacuating the prepolymer, the inclusion of additives such as silicone antifoam agent and silane coupling agents, and time/temperature cure conditions. The following factors were identified as being primarily responsible for cracking in these polyurethane systems: (1) the stoichiometry of the curing agent to the prepolymer, which must be held within a narrow range; (2) the water content of the curing agent which must be minimized; and (3) additives, particularly silane coupling agents, which enhance adhesion of the urethane to the container walls and also prematurely terminate chain exte

ISSN:0032-3888    

DOI:10.1002/pen.760170211

出版商:Society of Plastics Engineers, Inc.    

年代:1977

数据来源: WILEY