摘要:

AbstractThe crystallization behavior of three IUPAC low density polyethylene samples has been characterized by thermal analysis. Their rates of crystallization only are directly correlatable with their film forming ability in film blowing technology. The IUPAC samples possessed essentially indistinguishable physical properties, including differential scanning calorimetry (DSC) melting curves and rheological characteristics, but their propensity for crystallization was found readily to parallel their film forming ability and other characteristics associated with end‐use performance. The application of thermal analysis to assess crystallization is a unique diagnostic tool for measuring polymer film processability, which is well illustrated here using a few simple experiments made on the original polymer specimens and a polymer blend. Although all samples exhibit similar small‐angle X‐ray periodicities, the morphological differences assessed, particularly by microtomy‐optical microscopy, correlate with, and complement, the results of phase transformation kinetics responsible for film properties. Fractography‐scanning electron microscopy proves to be inferior to optical methods for revealing the morphology of these low density poly

ISSN:0032-3888    

DOI:10.1002/pen.760210102

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThe oxidative degradation of cold drawn highly oriented high density polyethylene is studied by IR spectroscopy. Both gamma and ultraviolet radiation sources are used. It is found that under gamma radiation the oxidative degradation, as determined from carbonyl formation, is reduced very significantly but that the trans‐vinylene unsaturation in the polymer increases with draw ratio. Similar results are obtained for samples irradiated in vacuum or when the polymer is stabilized with a radical quencher. Annealing (with free‐ends) of the samples restores the rate of carbonyl formation over and above that of the undrawn polymer although restoration after annealing with fixed‐ends is not complete. There, is further increase in trans‐vinylene development after annealing. In stabilized samples, the effect of annealing on carbonyl and trans‐vinylene development appears to depend on draw ratio.Under ultra‐violet radiation, the oxidative degradation of drawn and unannealed samples is also reduced with increasing draw ratio. The same effect is observed in stabilized samples. Annealing, once again, restores the rate of oxidative degradation to that of the undrawn polymer. The main unsaturation product during ultraviolet irradiation is the vinyl end group and its development is suppressed with drawing. During ultraviolet irradiation of unannealed drawn samples, cracks, generally perpendicular to the draw direction (intrafibrillar cracks) appear on the sample and with further irradiation they penetrate into the sample. In the case of stabilized and unannealed drawn samples, cracks parallel to the draw direction (interfibrillar cracks) appear first and continued irradiation results in the appearance of intrafibrillar cracks. These observations may have significance in modelling the fibrous structures obtained by drawing semicrystalli

ISSN:0032-3888    

DOI:10.1002/pen.760210103

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA history dependent solubility model is generalized in accordance with the Dual Mode Sorption Theory to take into account a history dependency of effective water diffusion coefficients in epoxy resins, based on hypothesized microcavitational damage due to the combined effects of temperature and sorbed moisture. Sorption data presented in a different paper are analyzed in the light of a transport model in which part of diffusing molecules are completely immobilized in the formed microcavities. The nature of the hypothesized damaging process is in agreement with the diffusion coefficient depressions and solubility increases experimentally found and theoretically predicted by the model.

ISSN:0032-3888    

DOI:10.1002/pen.760210104

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractAn experimental study was made of single fibers rotating and bending in Couette flow of a Newtonian liquid. A previous result for critical fiber buckling was re‐tested and found satisfactory, and the transition between ‘springy’ and ‘snake’ rotation was delineated. The minimum radius, of curvature achieved during rotation in the “snake orbit” regime was measured as a function of fiber aspect ratio, Young's modulus, and fluid shear stress. Two correlations are presented which are constrained to satisfy limiting conditions for very stiff and very flexible fibers. Together with a result from thin rod theory, these correlations may be used to predict breaking conditions for fibers of known Young's modulus and ultimate tensile strength. Predictions are tested in experiments where two types of glass fiber are broken in suspension and found satisfactory. Results show that several reinforcing materials will probably break within the range of conditions covered by our experiments, or in a region which can be treated by extrapolation fro

ISSN:0032-3888    

DOI:10.1002/pen.760210105

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractFilms of low‐density polyethylene, polypropylene, and rigid poly(vinyl chloride) were exposed for 1700 h to artificial aging in a Weather‐O‐Meter. Photochemical aging was characterized by tensile measurements. We noted that only ultimate properties are affected, whereas properties defined in the low strain range remain unchanged. The kinetics of strain and stress at break depend as much on the polymer's initial rheological characteristics as on the rate of the chemical degradation. The results show that aging results in localized chain breaking leading to defects at the supermolecular level. The average decrease of molecular weight does not seem to influence the mechanical beh

ISSN:0032-3888    

DOI:10.1002/pen.760210106

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractThermoplastic interpenetrating polymer networks, IPN's, are defined as combinations of two physically crosslinked polymers. A styrene‐b‐ethylene‐co‐butylene‐b‐styrene (SEBS) triblock elastomer was combined with an ionomer prepared from a random copolymer of styrene, methacrylic acid, and isoprene (90/10/1 by volume), and subsequently neutralized. Two subclasses of the thermoplastic IPN's were identified. A sequential polymerization method yielded the chemically blended thermoplastic IPN's (CBT IPN's). Melt blending of the separately synthesized polymers produced the mechanically blended thermoplastic IPN's (MBT IPN's). Stress‐strain and Rheovibron characterization revealed that the CBT IPN's exhibited greater tensile strength and higher elongation at break, but lower moduli than the MBT IPN materials of the same overall composition. Analysis of moduli data with the theories of Takayanagi, Davies, Budiansky, and Kerner disclosed more equal dual phase continuity for the MBT IPN's than the CBT IPN's at each composition. The low modulus of the more rubbery CBT IPN compositions was attributed to a decrease in the effective chain end‐to‐end distance between crosslinks in the elastomeric (EB) center block, brought about by the

ISSN:0032-3888    

DOI:10.1002/pen.760210107

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractMixtures of two compatible polymers, poly(vinyl chloride) and poly(acrylonitrile‐co‐butadiene) containing 40 percent acrylonitrile, can be compatible with poly(vinylidene chloride‐co‐vinyl chloride), which is incompatible and partially compatible respectively with these two polymers. The crystalline melting temperature and relative heat of fusion of poly(vinylidene chloride‐co‐vinyl chloride) in blends are higher than those in the pure component. This is attributed to greater ordering of the polymer chains in the crystalline phases of the blends. Replacing the rubber by poly(acrylonitrile‐cobutadiene) containing 30 percent acrylonitrile, shows that these three polymers, in which each pair is incompatible or at most partially compatible, also form compatible ternary blends. The crystalline melting temperature is higher and relative heat of fusion lower than those in the pure component. This is attributed to dissolving of parts of the polymer chains originally located in the crystalline phases in the amorphous phases

ISSN:0032-3888    

DOI:10.1002/pen.760210108

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA study has been carried out on the properties of a fast‐curing two‐part polyurethane sealant, and on its blends with other polymers, such as poly(vinyl acetate), poly(vinyl chloride) and poly(vinyl alcohol). Different substrates, such as Portland cement mortar, wood, and aluminum in three different thermal conditions were used. Tension tests by Universal Testing machine Model 1175 have been made, and stress‐strain curves have been devised and discussed. A two‐component fastcuring polyurethane sealant demonstrates good adhesivity for the supports mentioned. The elasticity of polyurethane sealants may improve even at low temperatures if mixing with other p

ISSN:0032-3888    

DOI:10.1002/pen.760210109

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

摘要:

AbstractA real‐time computer system is described which minimizes the total analysis time in gel permeation chromatography by automatically acquiring the data, performing the necessary calculations and displaying the molecular weight distribution and molecular weight averages as soon as the polymer peak has eluted. The calculation method described here is valid for linear homopolymers only, and does not include corrections for instrumental peak broadening. The experimental results show good reproducibility and precision. On‐line changes of the constants and other parameters may be implemented by means of an auxiliary program which runs in parallel with the data analysis program. A system such as that described here is suitable for utilization as a measurement technique in process control applications. The programs are written in CORAL 66 for a Ferranti Argus 700 E compu

ISSN:0032-3888    

DOI:10.1002/pen.760210110

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760210101

出版商:Society of Plastics Engineers, Inc.    

年代:1981

数据来源: WILEY