摘要:

The transformation from the orthorhombic to the monoclinic structure has been observed by means of infrared spectroscopy in shaken preparations of single crystals of polyethylene, mixed crystals of polyethylene and perdeuteropolyethylene, and physical mixtures of single crystals of these two polymers. Annealing of such shaken samples results in the conversion of the monoclinic back to the orthorhombic structure, but with an accompanying change from the (110) folding characteristic of single crystals to (200) folding. The monoclinic structure thus appears to be an intermediate state in the fold-plane transformation which can occur upon deformation. Both unannealed and annealed physical mixtures give evidence of ciliary penetration.

ISSN:0022-2348    

DOI:10.1080/00222347008229368

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Infrared spectroscopy is applied to discuss the orientation, the crystallinity, and the conformation of chain segments in the amorphous regions in drawn high-density polyethylene. The orientation of the crystals as well as the crystallinity are derived from the dichroism and the absorbance, respectively, of the band at 1894 cm-1. The orientation and some aspects about the conformation of the chain segments in the amorphous regions can be obtained from the bands in the 1400-1300 cm-1region (gauche) and at 1078 cm-1 (gauche and trans). The dichroic studies show a high degree of orientation increasing with draw ratio λ for the chain segments in the crystals, but a low orientation reaching saturation at λ between 5 and 10 for those in the amorphous regions. The experiments indicate a change in crystallinity during the drawing process which depends on the thermal treatment of the undrawn sample. In the amorphous regions the number of CH2groups in gauche conformations decreases up to λ between 10 and 15 and remains nearly constant with further drawing. Since the sum of gauche and trans conformations remains unchanged, it can be deduced that the number of loops decreases and that of tie molecules increases with draw ratio.

ISSN:0022-2348    

DOI:10.1080/00222347008229369

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Infrared dichroic measurements, refined to apply to Systems of low orientation, have been used to determine the structure of uniplanar and biaxially drawn polyacrylonitrile films. Orientation results in an alignment of the molecular chains with some degree of unkinking of the molecule. Preferential orientation of the nitrile side groups occurs due to the intermolecular dipolar attractions. Contrary to previous work, the results indicate that this dipolar interaction yields nitrile groups less well oriented than the chains with respect to the direction of draw.

ISSN:0022-2348    

DOI:10.1080/00222347008229370

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Crystallization from a stressed polymer melt produces not the familiar randomly nucleated spherulitic structures, but instead a highly oriented “row-nucleated” morphology. We have crystallized films of polyoxymethylene from stressed melts; just as polyethylene, the surfaces are covered with protruding lamellar edges highly oriented in the extrusion direction. There is no evidence for the more familiar spherulitic morphology. Electron microscopy directly revealed for the first time that the row nuclei are fibers, only about 200 to 300 A in diameter, extending for distances up to 10 mU. Although comprising a negligibly small amount of total sample volume, they are of prime importance in influencing how the sample will crystallize. Their presence determines, more than any other single factor, whether the sample will crystallize spherulitically or into a row-nucleated morphology. When deformed in the extrusion direction, the twisted lamellar bundles open up to form a fishnetlike structure. Simultaneously, slip between lamellae also occurs by a mechanism similar to shearing a deck of cards; for elongations up to 50%, there is little evidence of lamellar destruction. In the transverse direction, the film is brittle and fails before 1% elongation. Voids are formed at the largest lamellar “twist points” where two or more bundles are twisted together.

ISSN:0022-2348    

DOI:10.1080/00222347008229371

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Small- and wide-angle X-ray investigation of drawing and annealing of polypropylene quenched films in wide ranges of draw ratio (λ = 1-20) and of temperature (20°-150°C) shows the discontinuity of the elementary act of transformation in the microneck of the original lamella of the microspherulitic into the microfibrils of the final fiber structure. The long period, the orientation, and the crystalline disorder change abruptly. The continuity of macroscopical deformation in the neck is a consequence of superposition of the effects of a great many microneck zones which are more or less randomly scattered over the whole neck area. In the first stages of plastic deformation before the appearance of micronecks the lamellae parallel to the draw direction are compressed and those perpendicular to the draw direction become physically separated. This was checked by noting the drastic reduction of scattering after the introduction of dodecane which fills the holes between lamellae created in the initial stage of drawing. The diagonally oriented lamellae retain their thickness. As a consequence of steady rotation of lamellae from the perpendicular to the parallel orientation to the draw and of the destruction of nearly parallelized lamellae the diagonally oriented lamellae retain their numbers and yield a strong diagonal smallangle X-ray scattering maximum, whereas the equatorial and meridional maxima rapidly decrease in intensity. Annealing at a temperature above that of drawing makes the long period increase very nearly linearly with log tAand concurrently the crystals disorient and the sample shrinks. Clamped samples exhibit a slightly slower increase of L and much less disorientation.

ISSN:0022-2348    

DOI:10.1080/00222347008229372

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

High-density commercial polyethylenes have been crystallized under the combined orientation and pressure effects available in the Instron capillary rheometer. The samples so formed were found to have a high degree of crystal perfection and crystal orientation in combination with the unusual property of transmitting visible light. The samples consisted of fibrils aligned parallel to the axis of flow in the rheometer System. The procedure for forming the crystal structure is elucidated. X-Ray, differential scanning calorimetry,. and stereo-scannig electron microscopy were utilized to initiate a study of the structure. Evidence is presented that indicates the presence of an extended-chain component in the crystal structure.

ISSN:0022-2348    

DOI:10.1080/00222347008229373

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The shrinkage of drawn bulk polyoxymethylene was studied by wide-angle and small-angle X-ray diffraction and electron microscopy as a function of the amount of draw. Upon heating, the drawn material shrinks nearly instantaneously; the rtained strain increases with draw ratio. Small-angle patterns, including circuler, ellipsoidal, four-, six-, and two-point patterns, show various degrees of reversibility which decrease with increasing elongation especially above 100% draw. Wide-angle pole figures indicate changes in chain orientation distribution for samples drawn between 10 and 200% (the maximum examined). Deformation occurs primarily by several micronecking processes as well as lamellar and molecular slip. Morphological changes during shrinkage take place in all of the structural units formed by drawing. In addition to changes in spherulite dimensions, lamellar slip occurs, short fibrils disappear, and large diameter fibrils as well as lamellae normal to the draw direction form.

ISSN:0022-2348    

DOI:10.1080/00222347008229374

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

Observations on the free retraction of cold-drawn polyethylene and polypropylene as functions of time and temperature are reported and discussed in relation to possible origins of long-range retractive forces in crystalline polymers.

ISSN:0022-2348    

DOI:10.1080/00222347008229375

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

In recent years, several electron spin resonance (ESR) studies of mechanical degradation of crystalline polymer solids initiated by grinding [1,2], fracture, and mechanical stresses [3-7] have appeared. Highly oriented fibers or films were used in the mechanical loading experiments. The general consensus is that under high stress the most strained chemical bonds in polymer chains are cleaved and macroradicals are formed. Each chain rupture produces two radicals which under favorable conditions may be observed by ESR. The presence of air (oxygen) or high chain mobility enhanced by high temperature and swelling agents can so efficiently destroy the radicals that the radical population never reaches the sensitivity limit of the ESR spectrometer. In the absence of such scaveging processes the primary radicals produced by chain reupture may still be rather unstable and tend to transfer their energy to other close-by groups. By such transfer, eventually very stable secondary radicals are formed which are easy to observe. Unidentified impurities (most probably antioxidant) in nylon 66 fibers, investigated by Campbell and Peterlin [5], seemed to serve as such secondary radical centers.

ISSN:0022-2348    

DOI:10.1080/00222347008229376

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor

摘要:

The validity of the theory of linear viscoelasticity over the temperature range 20°-13°C has been tested by studying the tensile creep behavior of the amorphous, glassy polycarbonate based on bisphenol A. The stress threshold, beyond which the mechanical properties deviate from the predictions of linear theory by more than 3%, is found to decrease as the temperature approaches the vicinity of the glass transition temperature (149°C). Extension of the experimental time scale from 10 to 1000 sec likewise diminishes the stress level below which the linear theory is applicable. The onset of nonlinear behavior is marked by a clear increase in the isothermal, isochronous compliance with increasing stress. Such an increase in compliance with stress becomes gradually sharper at increasing stress levels until necking or failure of the specimen occurs. The analytical characterization of the transition from linear to nonlinear behavior, as well as certain molecular implications of such a transition, are discussed.

ISSN:0022-2348    

DOI:10.1080/00222347008229377

出版商:Taylor & Francis Group    

年代:1970

数据来源: Taylor