摘要:

AbstractA concentric cyclinder dilatometer was designed and built to study the influence of shear on the crystallization kinetics of polymers. This instrument allows crystallization to be followed at both constant temperature and shear rate. Several samples of polyethylene oxide (Carbowax 4000, Carbowax 20‐M, and WSR‐205) were used. A low molecular weight fraction of the Carbowax 20‐M, as well as the unfractionated material, was crystallized under shear. The WSR‐205 was studied only in a mixture with Carbowax 4000. It was shown that the kinetics of crystallization of uncrosslinked melts of polyethylene oxide are altered by shear. The induction times for the appearance of crystallinity are shorter in the sheared systems than in the quiescent melts. The Avrami exponents are also higher for crystallization in sheared melts than in quiescent systems and increase with decreasing supercooling. The high values of the Avrami exponent are attributed to the disruption of crystalline aggregates into particles larger than the critical sized nucleus. These particles will persist in the melt and continue to grow spontaneously. A continuous infusion of growing particles into the melt occurs.At constant temperature and shear rate, the induction time of the crystallization curve is influenced by polymer molecular weight. In moderate to high molecular weight samples, the effect of shear becomes saturated at very low shear rates. Decreasing the molecular weight separates the crystallization curves. The curves from the higher shear rates appear at the shorter induction times. However, decreasing the molecular weight below that at the critical entanglement molecular weight allows the nucleation rate, strongly dependent upon the supercooling, to influence the relative positions of the sheared crystallization

ISSN:0032-3888    

DOI:10.1002/pen.760140602

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe influence of surface properties on the flow of fluids, including epoxy resin, through aligned glass and other fiber beds has been examined. The observed flow rates were higher than those predicted from the Kozeny‐Carman equation, and were influenced by the surface properties of the fluid used. This is attributed to variations in the distribution of porosities and to the presence of air bubbles trapped during the initial wetting of the bed. The implications of these findings to the preparation of composites are discusse

ISSN:0032-3888    

DOI:10.1002/pen.760140603

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractCrack velocity measurements and fracture toughness tests have been carried out on extruded sheets of bisphenol‐A polycarbonate. Slow bend tests provided quasi‐staticK1cdata while dynamic initiation values were obtained from instrumented Charpy impact tests. In both types of tests high‐speed crack velocity measurements were made using conductive silver grids applied to the specimens. The variation ofK1cwith strain rate and temperature was found to be small and in general agreement with expectations from the relaxation properties of polycarbonate. Notch acuity was found to have little effect in that values ofK1cand crack velocity from specimens having the standard Charpy notch were similar to values obtained from sharp‐cracked specimens. Some anisotropy was present in the material and gave rise to a small variation in K1cvalues with direction of crack propagation. Crack velocity and also the fracture mode transition temperature showed considerable dependence upon orientation. It was thought that dynamic toughnessKd, was influenced more thanK1cby partial orientation of amorphous regions in the material and that the relaxation time for re‐orientation was probably signifi

ISSN:0032-3888    

DOI:10.1002/pen.760140604

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThis study is devoted to the mechanical properties of impregnated asbestos‐cements. We studied the influence of the degree of impregnation and of the nature of the resin on the modulus of elasticity and on the strength of the materials. The impregnation of asbestos‐cement by polymeric resins produces composites of outstanding mechanical properties. The relative increase in flexural and tensile strength is much higher for mortar and concrete but the improvement produced by the polymer on asbestos‐cement is especially significant if one takes into consideration the already high absolute strengths of the mate

ISSN:0032-3888    

DOI:10.1002/pen.760140605

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractTechniques have been developed for measuring the strain and thermal histories of fluid elements as they move from the die lips to the freeze line. Motion pictures were analyzed to determine the rates of extension in the machine and transverse directions. A radiation pyrometer was used to measure the temperature of the film. These techniques were used to study the film blowing of polyethylene; a 2.5‐in. diameter die was used, and blow‐up ratios in the range of 1.8 to 3.4 were employed. Film thickness ranged from 2 to 4 mils. The maximum measured extensional strain rates in both the transverse and machine direction were in the range of 0.15 to 0.6 sec−1. Standard shrinkage and impact tests were performed on the finished films, and an attempt was made to correlate the results with several simple empirical norms of the strain history. No correlation could be discerned. The results of this study are inconsistent with some popular ideas about the origin of orientation in blow films, but they are consistent with some recently published data on the influence of deformation on orientation in melt‐drawn capillary ex

ISSN:0032-3888    

DOI:10.1002/pen.760140606

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe equilibrium sorption of n‐hexane vapor and n‐hexane liquid in solution cast films of polystyrene, poly(phenylene oxide), and blends of these homopolymers was studied over a significant range of penetrant activity and temperature. These equilibrium sorption measurements were supplemented by density determinations, refractive index measurements, differential scanning calorimetry and differential thermal analysis. A seemingly complicated pattern of results emerged when the equilibrium penetrant content was plotted as a function of blend composition. At relatively low activity and temperature the equilibrium concentration of n‐hexane in these films monotonically increased with poly(phenylene oxide) content in the blend. Conversely, at high activities and in unit activity liquid, the equilibrium penetrant concentration exhibited a distinct minimum when plotted as a function of blend composition. At higher activities, solvent induced crazing accompanied the sorption of penetrant. These results were explained consistently by considering the nature of the sorption isotherm over an activity range sufficient to lower the glass transition temperature, of the equilibrated and swollen blend, below the temperature of the sorption experiment. Most importantly, the interpretation and explanation of these data are based upon phenomena common to all glassy polymer‐organic penetrant systems and no special properties of this blend system were included in the analysis. The results, therefore, reflect the apparent homogeneity of polystyrene‐poly (phenylene oxide) blends and are useful in considering the equilibrium of penetrant sorption in glassy polymers as a general class of

ISSN:0032-3888    

DOI:10.1002/pen.760140607

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe kinetics of n‐hexane vapor and n‐hexane liquid sorption in solution cast films of polystyrene, poly(phenylene oxide), and blends of these homopolymers were studied over a significant range of temperature and penetrant activity. The kinetics of concomitant solvent crazing, apparent at high penetrant activities, were also monitored. In all cases the kinetics of sorption and crazing obeyed predominantly Case II or relaxation‐controlled behavior. Although the rates of crazing and sorption at high activities was much more rapid in the homopolymers than in the blends, the sorption rate at lower penetrant activities increased monotonically with increasing poly(phenylene oxide) content.These kinetic results qualitatively superimpose upon the equilibrium relationships reported in Part I of this series. Specifically, at a fixed temperature, the rate of crazing was virtually a unique function of equilibrium n‐hexane content independent of polymer composition and largely independent of penetrant activity. The coupling between rate of sorption and equilibrium penetrant content was dramatic. In limiting cases, the sorption rate increased by a factor of 10,000 apparently due to a twofold increase in equilibrium penetrant concentration. This seemingly complicated kinetic behavior is explained rather simply in terms of the equilibrium relationships between organic penetrants and polymeric glasses developed and interpreted in the first part of this

ISSN:0032-3888    

DOI:10.1002/pen.760140608

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractIn the process of transforming from liquid to crystal, a polymer molecule must assume conformations which cause it to have a higher free energy than either the liquid or the crystal. This free energy barrier to crystallization is minimized if the molecule folds, thus providing both the driving force for folding as well as the assurance that the crystallization behaves as a classical kinetically‐controlled process. This free energy barrier exists equally well for the melting of extended chain crystals accounting for their observed super‐heating. Finally these ideas can be extrapolated to predict some rather unconventional conclusions with regard to polymer conformation in the m

ISSN:0032-3888    

DOI:10.1002/pen.760140609

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

摘要:

AbstractThe general incompatibility and microheterogeneity of polymeric mixtures are discussed. The concepts are extended to elastic polyblends whose polymer constituents are polarizable, non‐conducting and non‐magnetic. A theory is then developed for the interactions of dynamic deformation fields in polyblends with applied electromagnetic fields. It is shown that certain electro‐ and magneto‐acoustical and optical effects are the outcome of the above‐mentioned interactions. Plane elastic as well as electromagnetic waves are shown to be generally dispersive in such media. We have employed an internal scale parameter, commonly called the couple stresses constant, which can be estimated by measuring the speeds of plane waves, thus enabling polymer engineers and scientists to evaluate incompatibility in elastic polyblends. The present work also establishes a generalized Faraday effect by showing that there exist three pairs of left and right circularly polarized plane waves traveling at different speeds in a polyblend. We also discuss a new phenomenon, i.e. “micromagneto‐elastic dragging”, emerging from our analysis. This phenomenon asserts that the more profound the internal incompatibility of polyblends, the more depressed the speed of plane waves below their normal values observed in the absence of incompatibility. For convenience, we have called such materials elastic micro‐dielectric polymers o

ISSN:0032-3888    

DOI:10.1002/pen.760140610

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760140611

出版商:Society of Plastics Engineers, Inc.    

年代:1974

数据来源: WILEY