Linear High-density Polyethylene Research Articles

Multiple-pulse proton NMR of pressure-crystallized linear polyethylene

We have been interested recently in exploring relaxation under multiple-pulse NMR as a means of characterizing polymer morphology. For such work it is important to know the effectiveness of homonuclear decoupling for different experimental conditions. One measure of how well the dipolar interactions are averaged is given by the linewidth in the chemical-shift spectrum recorded using multiple-pulse sequences, since the largest error Hamiltonians analyzed using the Magnus expansion are frequently those related to the dipolar interaction (1-3). Pressure-crystallized linear polyethylene (LPE) is a useful sample in this context because it represents one of the most strongly coupled proton spin systems available. An additional advantage is that crystallization of LPE under high pressure (4.86 GPa in this case) results in a material which is roughly 95% crystalline as indicated by density measurements (4). This largely eliminates complications arising from the superposition of crystalline and amorphous lineshapes. Details concerning the preparation of the sample have been published (4). In the spectrum of pressure-crystallized LPE obtained from a free induction decay, the full width at half maximum of the resonance is 80 kHz, or 400 ppm for a ‘H Larmor frequency of 200 MHz. The multiple-pulse spectrum recorded with BR-24 (2) on a Bruker CXP-200 spectrometer is shown in Fig. 1. The methylene ‘H shielding tensor displays axial symmetry, in agreement with reported methylene tensors for several small organic compounds (5). As is also the case with these smaller compounds, uII arises from the most shielded orientation. The observed anisotropy of the shielding tensor is 6.9 f 0.2 ppm. Gerstein (6) has previously reported the multiple-pulse spectrum of a high-density LPE obtained through MREV-8 (7, 8) with a cycle time of 2 1 ps. The reported value of the anisotropy is 4.72 ppm, but the axially symmetric character of the tensor is not as well defined as that in Fig. 1. We ascribe most of the improvement to our use of a spherical sample, which minimizes broadening from bulk magnetic susceptibility effects (9, IO). In addition, BR-24 is generally recognized to be more effective than MREV8 in homonuclear decoupling (3) since the design of BR-24 minimizes contributions from higher order error Hamiltonians. The data in Table 1 illustrate the superiority of BR-24 in analyzing the pressure-crystallized LPE. The cycle-time dependence of linewidth using MREV-8 is considerably stronger than that of BR-24, with the shortest cycle times offering the most effective elimination of dipolar couplings. An

ON THE CONTRIBUTION OF LONG CHAIN BRANCHING TO POLYETHYLENE MELT RHEOLOGY

Abstract The sensitivity of rheological behavior to the presence of long chain branched (LCB) molecules in a matrix of ostensibly linear high density polyethylene (HDPE) is examined. Branching is introduced by gamma irradiation of the HDPE just short of the gel dose. The irradiated and unirradiated polymers are blended to obtain various concentrations of LCB from 1 to 7.2 LCB/10,000 carbon atoms. Dramatic changes in viscoelasticity and temperature dependencies far in excess of those expected from molecular weight changes are detected. While the Mw¯ observed by low angle laser light scattering (LALLS) and size exclusion chromatography (SEC) increases by a factor of only about 1.2, the dynamic viscosity at low frequencies and 190°C increases by a factor of 14. Furthermore, flow activation energy values increase from 8 to 40 kcal/mole.

Determination of chemical structures by 1H‐ and 13C‐NMR for thermally degraded linear high density polyethylene

AbstractChemical structures were determined for polymer residues obtained by thermal degradation of a linear high‐density polyethylene. Terminal methyl, double bonds (terminal vinyl, trans‐vinylene, and vinylidene), and long chain branching were identified by using 1H‐ and 13C‐NMR spectra data. The number of these functional groups per 1000 C was quantified with a relative error of about 10%.

Mechanism for long-chain branching in the thermal degradation of linear high-density polyethylene

Mechanism for long-chain branching in the thermal degradation of linear high-density polyethylene

Effect of container type on pH and alkalinity stability

Errors in pH measurement of 0.1-0.2 units can be propagate large errors in the predicted aqueous speciation. When accurate on-site analyses are impossible to obtain, changes in pH and alkalinity between the time of sampling and after transport to a laboratory must be minimized in many sampling programs. Several container and cap combinations were evaluated for their ability to preserve the pH and alkalinity of test waters that were out of equilibrium with atmospheric carbon dioxide over time periods representative of mail or other surface transport. Provided that no air bubbles were present when the sample bottle was filled and sealed, polyvinyl chloride bottles with caps having a conical polyethylene insert yielded the most satisfactory results. High density linear polyethylene bottles were also generally satisfactory. Cap design was observed to be very important. Guidelines for analysis and preservation are given, and if followed, laboratory measurements can be reliably substituted for field measurements in many instances.

A comparison of the flow behavior of linear polyethylene, poly(butylene terephthalate), and poly(ethylene terephthalate)

The viscous and elastic properties of linear high density polyethylene (HDPE), poly(butylene terephthalate) (PBT), and poly(ethylene terephthalate) (PET) are investigated using an Instron capillary rheometer and the Philippoff–Gaskins–Bagley analysis. The viscous properties studied are the shear viscosity and the constant shear rate activation energy and the elastic properties studied are the entrance pressure drop and the end correction. The variables are shear rate and temperature. The order of decreasing viscosity is HDPE>PET>PBT; the order of decreasing activation energy is PB>PET>HDPE; the order of decreasing entrance pressure drop is HDPE>PET>PBT; and the order of decreasing end correction is PBT>PET>HDPE. As temperature increases, both viscosity and entrance pressure drop decrease. The observed behavior is discussed in terms of the difference in number of terephthalic acid moities in the polymer chains and in terms of oligomer plasticization.

Chlorinated Polyethylene. II. Mechanisms of Chlorination

The present paper deals with the mechanisms of photochlorination and thermal chlorination of polyethylene as influenced by the microtacticity evolution of the polymer under chlorination. The investigations have been carried out on a branched low-density polyethylene and a linear high-density polyethylene, both chlorinated under various conditions which enabled us to study the influences of the chlorination time, the chlorination temperature, the chlorination method, the solvents used, etc., on the mechanisms of chlorination. The high-resolution nuclear magnetic resonance analyses published elsewhere,5,6,12 the infrared spectroscopy,8 the ratios (Cl/C), and (number of CHCl units/number of CH2 units) and the degree of polymerization are the main results discussed.

Transformation of the viscoelastic functions of calcified tissues and interfacial biomaterials into a common representation

Since both connective and calcified tissues are markedly viscoelastic in nature, an understanding of the behavior of these tissues intrinsically as materials on their own, as well as in composite formation with synthetic implants, is of prime importance in order to predict and anticipate materials' design and function. Thus considerable interest has developed in recent years with respect to measurements of the viscoelastic properties of biological materials. However, attempts to characterize the viscoelasticity of calcified tissues have involved many different experimental procedures; hence results appear in terms of different functions, e.g. relaxation modulus, creep compliance. Since this diversity precludes a simple useful comparison of the results, the present study was initiated so that measured functions could be cast into a common representation, and thus compared. Linear viscoelasticity theory implies definite exact relationships between the functions. Using these relations, experimental results on bone, dentin and implant materials presently used to interface to the natural tissues, e.g. polymethyl methacrylate and high density linear polyethylene, were transformed into the complex dynamic modulus representation. Analysis shows that the results of experiments on bone are not in agreement as to dispersion (i.e. change of modulus with frequency) and its variation with strain. Further, analysis of the internal consistency of some experiments demonstrates a violation of the Boltzmann integral which indicates that linear viscoelasticity (almost invariably assumed by workers in the field) fails for bone in compression. It is concluded that the dynamic behavior of bone is not as well understood as has been thought heretofore; direction is given for future experiments.

Interrelationships among the viscoelastic functions for anisotropic solids: Application to calcified tissues and related systems

The Boltzmann superposition integral is applied to the anisotropic solid in order to derive relationships between various viscoelastic functions for orthotropic solids with special emphasis on describing biological systems such as calcified and connective tissues. These relations show that the results of uniaxial tension or compression experiments are rather complicated functions of the stiffness modulus tensor elements; as such the data could not be readily treated in a theoretical manner. On the other hand, torsional type experiments can be used to directly yield the appropriate shear elements of the tensor. Applying these derived relationships, the experimental results on cortical bone in uniaxial compression were transformed by means of computer techniques into a common representation (the complex dynamic modulus). The lack of agreement among these transformed results, based on the data from several different experimenters, as well as the failure of data from individual experiments to satisfy internal consistency tests, lead to the conclusion that the Boltzmann integral fails to describe properly the viscoelastic properties of cortical bone in compression. This implies that linear viscoelasticity theory, invariably assumed for bone, does not apply to bone in compression over the entire frequency range studied. For the purpose of comparison, dynamic moduli for synthetic (PMMA and high density linear polyethylene) and other natural (dentin and cancellous bone) materials are also presented. Fourier analytic techniques similar to those used for the above have been applied to the time-dependence of knee-joint forces obtained from gaiting studies.

Heat Capacities of Polyethylene from 2 to 360 K. II. Two High Density Linear Polyethylene Samples and Thermodynamic Properties of Crystalline Linear Polyethylene.

Heat capacities of two high density linear polyethylene samples were measured from 2 to 360 K. By incorporating the results from the previous work of this series, thermodynamic properties of completely crystalline linear polyethylene may be estimated. C p , H - H0, S and - (G - H0) at 298.15 K for crystalline linear polyethylene are estimated to be 22.60 J K-1 mol-1, 3544 J mol-1, 23.02 J K-1 mol-1 and 3319 J mol-1, respectively. Spontaneous adiabatic temperature drifts were observed in both samples near 240 K. These drifts may be attributed to the enthalpy relaxation phenomena occurring in the glass transformation region.

New Relaxation Phenomena in Linear Polyethylene at Cryogenic Temperatures

The internal friction of linear high-density polyethylene (LPE) at cryogenic temperatures was investigated using an inverted free-oscillating torsion pendulum (1–3 Hz). The results show that LPE is not viscoelastically inactive below its γ peak as had been previously contended. Two new relaxation peaks, δ at 48 °K and ε at 20 °K, were observed. The characteristics of these loss maxima are identical to those of the cryogenic relaxations observed for polyethylene terephthalate and polyoxymethylene. A mechanism consisting of the motions of dislocation jogs and their interactions with specific conformational kink defects is proposed. This mechanism is consistent with all the experimental data in that it accounts for the effects of orientation and thermal histories on the relaxation strength of the δ and ε internal-friction peaks.

Fractionation of polyethylene by gel permeation chromatography

AbstractThe performance of the gel permeation chromatography (GPC) technique was studied with several commercial samples of linear high density polyethylene. A comparison of these data was made with those obtained from the elution column technique based on fractional dissolution. GPC gave reproducible fractionation data in the molecular weight range of 103–106. These data were obtained from two columns in series with nominal capacity of 1–104 and 1–106A. Polyethylene fractions of known molecular weights are required as calibration standards and for many commercial polyethylenes it is necessary to increase sensitivity at molecular weight higher than 106.

Molecular weight and molecular weight distribution of high density linear polyethylene

Journal of Polymer ScienceVolume 26, Issue 112 p. 124-125 Letters to the Editor Molecular weight and molecular weight distribution of high density linear polyethylene H. S. Kaufman, H. S. Kaufman M. W. Kellogg, Company Jersey City, New JerseySearch for more papers by this authorE. K. Walsh, E. K. Walsh M. W. Kellogg, Company Jersey City, New JerseySearch for more papers by this author H. S. Kaufman, H. S. Kaufman M. W. Kellogg, Company Jersey City, New JerseySearch for more papers by this authorE. K. Walsh, E. K. Walsh M. W. Kellogg, Company Jersey City, New JerseySearch for more papers by this author First published: October 1957 https://doi.org/10.1002/pol.1957.1202611217Citations: 17AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume26, Issue112October 1957Pages 124-125 RelatedInformation