Observation of optical modes in polyethylene by neutron scattering

Multiphonon contributions to the directional phonon frequency functions are calculated for crystalline polyethylene. These results are compared to previously calculated one-phonon frequency functions.     

Lattice modes of alkali halides activated by polyatomic impurity ions of various symmetries

Raman and lattice side band spectra of the external modes of ReO⁻₄, NO⁻₃ and NCO⁻ isolated wuthin KI have been recorded at 300K and 77K. Similarities and differences shown by these spectra are interpreted in terms of (i) highly specific properties of the impurity-occupied lattice site (eg. torsional and translational oscillations of the impurity ion), (ii) a very general but weak activation of host lattice modes due to the disorder imposed by the randomly distributed impurity ions and (iii) selective enhancement of specific host lattice modes which, as a result of having the same symmetry properties, can resonate with (and draw intensity from) the modes described in (i) above. It is in order to investigate this third point, (which has been totally ignored in previous work on the external mode spectra of polyatomic impurity ions) that three ions with different symmetries have been used.     

Different combustion modes and flame shapes in massive loads of polyethylene revealed by macro-thermogravimetry

Journal of Thermal Analysis and Calorimetry - While thermogravimetric analysis can reveal the reaction mechanisms that occur during combustions, it cannot be used to study reactions involving large...     

On the use of Raman-active longitudinal acoustic modes in the study of polyethylene lamellar structures

The first-, third-, and fifth-order low-frequency, Raman-active, longitudinal acoustical modes of the n-alkane C₉₄H₁₉₀ and different morphological forms of semicrystalline polyethylene have been obtained. An analysis of the results shows that the correction needed to obtain the extended planar-zigzag ordered sequence length is maximum for the n-alkane and very small for the polymer systems. These represent solution crystals as well as bulk-crystallized material. For the latter, samples were prepared so that the crystallite thickness is either comparable to or very much smaller than the extended chain length. An approximate method is also developed which enables the natural linewidth to be determined.     

Linear and nonlinear excitations in a polyethylene crystal, 1. Vibrational modes and linear equations

Linear excitations in a polyethylene crystal are investigated by a new analytical method from the “first principles”. Elastic moduli are calculated from the parameters of molecular potentials of interaction. High anisotropy allows to derive comparatively simple approximate equations describing the dynamics of the crystal. Approximate expressions for the low-frequency branches of vibrational spectra are obtained. The role of internal degrees of freedom is revealed. Approximate expressions governing the dynamics of all degrees of freedom considered are obtained in analytic form suitable for nonlinear generalizations.     

Surface modification of polyethylene with multi-end-functional polyethylene additives

We have prepared and characterized a series of multifluorocarbon end-functional polyethylene additives, which when blended with polyethylene matrices increase surface hydrophobicity and lipophobicity. Water contact angles of >112° were observed on spin-cast blended film surfaces containing less than 1% fluorocarbon in the bulk, compared to ~98° in the absence of any additive. Crystallinity in these films gives rise to surface roughness that is an order of magnitude greater than is typical for amorphous spin-cast films but is too little to give rise to superhydrophobicity. X-ray photoelectron spectroscopy (XPS) confirms the enrichment of the multifluorocarbon additives at the air surface by up to 80 times the bulk concentration. Ion beam analysis was used to quantify the surface excess of the additives as a function of composition, functionality, and molecular weight of either blend component. In some cases, an excess of the additives was also found at the substrate interface, indicating phase separation into self-stratified layers. The combination of neutron reflectometry and ion beam analysis allowed the surface excess to be quantified above and below the melting point of the blended films. In these films, where the melting temperatures of the additive and matrix components are relatively similar (within 15 °C), the surface excess is almost independent of whether the blended film is semicrystalline or molten, suggesting that the additive undergoes cocrystallization with the matrix when the blended films are allowed to cool below the melting point.     

Characterization and properties of polyethylene blends I. Linear low-density polyethylene with high-density polyethylene

A blend system of linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with high-density (linear) polyethylene (HDPE) is investigated by differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), Raman longitudinal-acoustic-mode spectroscopy (LAM), and light scattering (LS). For slowly cooled or quenched samples, one single endotherm is evident in the DSC curve which depends on the composition. No separate peaks are observed in the WAXD, SAXS, Raman-LAM, and LS studies on the LLDPE/HDPE blends. This observation along with the fact that no peak broadening is observed suggests that these peaks are associated with the presence of a single component. In no case did we see double peaks or a broadened peak that might be associated with two closely spaced unresolved peaks. This suggests that segregation has not taken place at the structural levels of crystalline, lamellar, and spherulitic textures. A single-step drop in the scattered intensity (I_Hv) as a function of temperature is seen in the LS studies. It is therefore concluded that cocrystallization between the LLDPE and HDPE components occurs. The mechanical and optical α, β, and γ relaxations of these blends are explored by dynamic birefringence. The 50/50 blend displays the intermediate relaxation behavior between those of the components in all α, β, and γ regions. This observation is reminiscent of the characteristic of the typical miscible blends.     

Lattice dynamics of tetracyanoethylene

Lattice dynamics calculations for both crystalline forms of tetracyanoethylene are presented. The comparison of the calculated static and dynamical properties with the experimental data, leads us to suggest an improved parameter set for the “6-exp” potential function for crystals with cyano groups.     

Lattice model of glasses

Glass-forming liquids have been extensively studied in recent decades, but there is still no theory that fully describes these systems, and the diversity of treatments is in itself a barrier to understanding. Here we introduce a new simple model that (possessing both liquid-crystal and glass transition) unifies different approaches, producing most of the phenomena associated with real glasses, without loss of the simplicity that theorists require. Within the model we calculate energy relaxation, nonexponential slowing phenomena, the Kauzmann temperature, and other classical signatures. Moreover, the model reproduces a subdiffusive exponent observed in experiments of dense systems. The simplicity of the model allows us to identify the microscopic origin of glassification, leaving open the possibility for theorists to make further progress.     

Lattice oligomer dynamics

Exact results are obtained for the dynamics of short chains on the cubic lattice in the presence of excluded volume. The dynamics is used to evaluate the vector end-to-end length and squared length correlation functions. These functions are compared to those obtained by computer simulation by Kranbuehl and Verdier for longer chains. A coherent picture of the effects of excluded volume and chain length on the system properties sampled is found.     

Deformation band studies of oriented polyethylene and polyethylene terephthalate

Deformation bands formed at the yield point in tensile tests on oriented high-density polyethylene have been studied by optical microscopy and wide-angle x-ray (WAXS) diffraction. The observations of the rotation of the optical extinction direction are shown to obey a simple scheme proposed previously by us: the principal directions of the refractive index ellipsoid within the deformation bands are everywhere parallel to the principal axes of the plastic strain ellipsoid, zero strain referring to the isotropic state. This result is similar to that obtained previously for polyethylene terephthalate (PET) and polypropylene despite the much higher crystallinity obtained with polyethylene. Independent measurements of the molecular reorientation in the deformation bands made using wide-angle x-ray scattering broadly confirm the optical measurements. The results taken together suggest that the material within the band, whether crystalline or not, becomes realigned about the new direction of maximum elongation as if controlled by the deformation of an effective molecular network.     

Adhesive effect of low-density polyethylene gels on polyethylene moldings

Adhesive effect of low density polyethylene (LDPE) gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, electron microscopy, and DSC measurements. When heated at 110°C for 2 h, all of the gels showed strong adhesive strengths around 30 kg/cm², which is sufficiently strong for practical uses. It has been found that the adhesive strength increases with the heating temperature and that the temperature at which the heated gel begins to exhibit the adhesive effect depends upon solvents and is about 30° lower than that of the HDPE gels.     

Adhesion of a pair of polyethylene moldings by polyethylene gels

It was found that polyethylene gels in solvents such as benzene, toluene, xylene, decalin, tetralin, tetrachloroethylene, 1,1,2,2-tetrachloroethane, and chlorobenzene are effective for adhesion of a pair of polyethylene plates. In particular, the adhesion strength of polyethylene gels in decalin, tetralin and tetrachloroethylene was strong enough for practical use.Adhesive effect appears due to local dissolution of the surface of polyethylene plate in contact with the gel with increasing temperature, and subsequent recrystallization.     

Photocrosslinking of polyethylene. II. Properties of photocrosslinked polyethylene

Some properties of photocrosslinked high density polyethylene (2 mm thick sheets) have been studied. The homogeneity of the network is greatly improved by the application of triallylcyanurate (TAC) as crosslinking agent. The role of TAC in promoting the crosslinking is discussed. The crosslinked PE is found to be durable towards immersion in boiling water. Oxygen permeability increases while density and melting point decrease with increasing degree of crosslinking. The network chain density is obtained using conventional swelling method in boiling xylene, which together with data from melting point depression show that contribution of chain entanglement is insignificant to the gel formation of PE in this work.     

Adhesion of polyethylene

Summary Liquid phase oxidation by oxygen gas catalysed with cobalt acetate is employed as effective method for introduction of polar groups to polyethylene. Main polar groups introduced were carbonyl groups in ketone form. Apparent activation energy of liquid phase oxidation 25.6 Kcal/mole is intermediate between these ozone catalyzed oxidation and fuming HNO₃ oxidation. Degradation of polymer during oxidation was also recognized by the decrease of molecular weight.

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Zusammenfassung Die Oxydation durch gasf?rmigen Sauerstoff katalysiert mit Kobalt-Azetat lie? sich als wirksame Methode zur Einführung polarer Gruppen in Poly?thylen anwenden. Die meisten polaren Gruppen wurden als Carbonylgruppen in Ketonform eingeführt. Die scheinbare Aktivierungsenergie der flüssigen Phasen-Oxydation betr?gt 25,6 kcal/mol und liegt etwa zwischen ozon-katalysierter Oxydation und Oxydation durch rauchende Salpeters?ure. Der Abbau der Polymeren w?hrend der Oxydation wurde ebenfalls durch die Abnahme des Molekulargewichts beobachtet.

     

Adhesive effect of linear low-density polyethylene gels on polyethylene moldings

Adhesive effect of linear low density polyethylene (LLDPE) gels in organic solvents such as decalin, tetralin, and o-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, and DSC measurements. For all of the gels the temperature at which the heated gel starts to exhibit the adhesive effect was about 70 °C, which is similar to the result of LDPE gel. In particular, when heated at 110 °C, LLDPE gel in tetralin showed such a strong bond strength that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking. It was found that LLDPE gel behaved as though it added LDPE gel to HDPE gel namely LDPE-like components in LLDPE resin exerted the adhesive effect at lower heating temperature, HDPE-like components exerted the strong adhesive effect at higher heating temperature.     

Adhesive effect of high density polyethylene gels on polyethylene moldings

Adhesive effect of polyethylene moldings by use of high density polyethylene gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene was investigated by shearing tests, electron microscope, and DSC measurements. All of the gels showed such a strong adhesive strength over 36 kg/cm² that polyethylene plates of 3 mm in thickness gave rise to necking sufficient for practical use, when heated at 120 °C for 2 h. In particular, the gel in tetralin showed a strong adhesive strength when heated at 110 °C. It was found that adhesive strength increases with the heating temperature; the temperatures at which adhesive strength begins to increase differ depending on the type of polyethylene sample and solvent. It is apparent that polyethylene gels exhibit an adhesive effect when they are heated at higher temperatures than the gel melting temperatures, and that the closer the SP values of solvents used for the gelation are to the molded polyethylene, the stronger the adhesion of the polyethylene molding.     

Adhesion of molded polyethylene using polyethylene gels by microwave heating

Adhesive effect of polyethylene gels on the molded polyethylene by heating with microwaves has been investigated. Polyethylene gels in polar organic solvents such aso-xylene, chlorobenzene,o-dichlorobenzene,m-dichlorobenzene, 1,1,1,2-tetrachloroethane, and 1,1,2,2-tetrachloroethane were used as adhesives. All of these gels showed adhesive effect when heated with microwaves. In particular, the gels in 1,1,2,2-tetrachloroethane showed such strong adhesion that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking by heating for 8 min in a 500 W (2450 MHz) microwave oven.     

Lattice vibrations of polymethylene crystal

The energy levels of the lattice vibrations of orthorhombic polymethylene crystal was calculated quantum-mechanically. The rotational modes were treated in the same manner as employed for the internal-rotation problem. For the translational modes the energy levels were obtained from perturbation calculations. The results clearly indicated that the anharmonicities have significant effects on the lattice modes, the A_g rotational mode in particular.