摘要:

AbstractThe changes in structure and mechanical properties of melt spun polypropylene filaments were determined as the filaments were successively (i) drawn, (ii) twisted, (iii) annealed, and (iv) untwisted. Filaments spun to two different melt draw down levels were studied. The effects of draw temperature and draw ratio, extent of twist, annealing temperature, and the extent of untwisting were examined. Melt spun and twisted filaments (draw ratio of 1) were also considered. Structural characterization techniques used in this study include wide angle (WAXS) and small angle (SAXS) diffraction, scanning electron microscopy (SEM), birefringence and density measurement. Drawing increased crystalline orientation and at low temperatures disrupted the monoclinic unit. cell existing in the melt spun fibers. The drawing produced considerable fibrillation under all conditions even when carried out at 120°C. The fibrillation quid void formation due to low temperature drawing was more pronounced. The variation of WAXS patterns and mechanical properties of twisted drawn filaments was interpreted by presuming that the fibrils act in a manner analogous to that of the filaments in a continuous filament twisted yarn. In the case of incompletely drawn filaments the effect of additional drawing occurring during twistin must be considered. Twisted fibers annealed at 150°C sowed a drastic reduction in tensile properties, while those annealed at 125°C did not set the twist and caused the fibers to tend to untwist. Annealing at 140°C appeared to give satisfactory heat setting. Annealing of cold drawn and cold drawn and twisted fibers increased the density, removed many defects and reformed a well defined monoclinic crystal structure and a lamellar morphology. Untwisting of heat set filaments tended to give back the properties of hot drawn fibers. In some cases, however, the opening of cracks was no

ISSN:0032-3888    

DOI:10.1002/pen.760191102

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractOne of the major factors of concern in compression molding of fiber‐reinforced thermosets is the mold cycle time which directly affects the processing cost. An ideal system would be the one which cures in a relatively short time resulting in excellent mechanical and physical properties. However, in practice, a compromise has to be made between the mold cycle time and ultimate property requirements. The effects of cure cycle time, temperature, preheating and post‐cooling on mechanical properties of continuous as well as chopped glass fiber reinforced polyester and vinyl ester systems involving 1/4 to 1 in thick sections have been studied. Mold cycle time is strongly influenced by the part thickness and mold temperature. Internal heat generation due to curing reaction causes high thermal gradients across the thickness. Preheating offers advantages of reducing both the mold cycle time and the thermal gradient. The flexural and interlaminar shear strengths are strongly dependent or, the mold cycle time. Maximum strengths are obtained when the mold is opened at the instant when there is no thermal gradient across the thickn

ISSN:0032-3888    

DOI:10.1002/pen.760191103

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractDifferential scanning calorimetry and wide angle X‐ray diffractometry were used to investigate the effects of molecular weight and molecular weight distribution on the crystallization kinetics of oriented, glassy nylon 6. The samples had number average molecular weights ranging from 10,000 to 42,000 and polydispersity indices ranging from 2.0 to 3.1. Noncrystalline films were prepared by quenching molten films between plattens chilled with liquid nitrogen. These films were drawn 4X and 5‐1/3X, and the resultant uniaxial orientation was observed to enhance markedly the room temperature crystallization kinetics. Although macroscopic deformation can be assumed to be affine at the molecular level, it is hypothesized that wholechain molecular relaxation occurs at rates inversely proportional to the square of molecular weight, thereby creating a distribution of extension ratios which reflect the actual molecular weight distribution. Thus, the crystallization rate and the degree of crystallinity depend on the fraction of high molecular weight molecules present in the sample. Given two samples with the same molecular weight, the one with the broader distribution crystallizes more rapidly. Similarly, samples having the larger molecular weight crystallize to a greater extent when two samples have the same molecular weight distribut

ISSN:0032-3888    

DOI:10.1002/pen.760191104

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractContinuous flow reactors are increasingly utilized for polymerization. Two aspects of reactor performance are considered here, with major emphasis on the screw extruder as a reactor. First, the effect of residence time distribution is discussed, and comparative calculations are made for several flow reactors using a simple model for a polycondensation reaction. We conclude that the extruder behaves nearly as a plug flow reactor. Second, the effect of viscous heating in the extruder is accounted for, in the limiting case of adiabatic operation. A model for the effect of heating on conversion is developed, and some implications for scale‐up are note

ISSN:0032-3888    

DOI:10.1002/pen.760191105

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe viscoelastic nature of polymer concrete was investigated utilizing an epichlorohydrin/bisphenol A‐type epoxy resinaggregate system. Compression specimens were tested for linearity of viscoelastic behavior, the effect of size of mass on creep, and for determination of the specific creep compliance and the associated elastic modulus. The creep compliance was determined by least squares curve fitting of the experimental creep data. Collocation, a numerical Laplace transform inversion routine, was used to develop the equation for the relaxation modulu

ISSN:0032-3888    

DOI:10.1002/pen.760191106

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe elongational behavior in constant force experiments has been considered for three samples of commercial polyisobutylene. The results compare favorably with the predictions of two existing non‐linear theories as long as the samples deform homogeneously. Some qualitative observations have been made with reference to the “failure point”, i.e., the point where a non‐homogeneous deformation

ISSN:0032-3888    

DOI:10.1002/pen.760191107

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA new method and apparatus for determining the oxidative stability of molten polymers, especially polyolefins, is described. The apparatus consists of a laboratory scale mixer modified to allow for the continuous determination of the oxygen absorbed by the polymer. The oxygen uptake curve observed for polyolefins is of the type normally associated with the autocatalytic oxidation of hydrocarbons and yields an induction period—a traditional measure of stability. Typical results from experiments concerning the antioxidant type, antioxidant level and temperature on polyethylene stabilization are presented to illustrate the usefulness of the technique in both quality control and research application

ISSN:0032-3888    

DOI:10.1002/pen.760191108

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe effect of bonding temperature on the peel strength of adhesive joints, polyolefin/butyl rubber and polyolefin/ethylene‐vinylacetate copolymer, has been investigated. The peel strength, measured at room temperature, undergoes a sharp transition from its low values to higher values as the bonding temperature is changed from below to above, the melting point of the substrate. This increase in peel strength is accompanied by changes in failure mode from the apparent interfacial failure to cohesive failure through the adhesives. Investigation of the interface using Fourier Transform Infrared Internal Reflection spectroscopy and interference microscopy indicates that the sharp increase in the peel strength at the melting temperature of substrate is associated with the presence of an interdiffused layer at the interfac

ISSN:0032-3888    

DOI:10.1002/pen.760191109

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractMeasured melt viscosities and primary normal stress coefficients are presented for a well‐characterized, rubbermodified polystyrene as a function of shear rate and mineral oil diluent concentration. The logarithmic blending relationship accurately predicts the observed data. Melt relaxation times and shear compliance data are also calculated. The compliance numbers are consistent with molecular models based on a simple dumbbell (appropriately modified for rubber and mineral oil addition

ISSN:0032-3888    

DOI:10.1002/pen.760191110

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA basic theoretical investigation is made of the fluid mechanics of mixing of particulates into a polymer melt in an internal mixer. It is shown how increasing levels of viscoelasticity, especially with non‐linear, strain rate hardening character, should deteriorate mixing. he characteristics of internal mixers are discussed in terms of dimensionless groups. Rational scaling procedures based on considerations of viscoelastic fluid mechanics and energy balances are critically investigated and their limitations considere

ISSN:0032-3888    

DOI:10.1002/pen.760191111

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY