Degradation of crosslinked polyethylene in water by gamma-irradiation

The degradation of crosslinked polyethylene by gamma-irradiation in water was studied. Change in the physical properties and the growth of carbonyl group after irradiation showed a good correlation. The degradation observed at 80°C is the least, and that at 60°C is the severest. The distribution of the oxidized layer in the sample was measured and was also calculated from the diffusion model using the observed parameters. Comparison of both results suggest that some products caused by gamma-irradiation of water supress the degradation of XLPE at 80°C.     

Structure formation of fullerene-containing propylene oxide oligomers in deuterium water

Structure formation of propylene oxide oligomers with terminal hydrophobic aliphatic fragment and of oligo(propylene oxides) additionally containing covalently bonded fullerene C₆₀ in deuterium water was studied by small-angle neutron scattering. Propylene oxide chains containing a long hydrophobic fragment undergo organization into spherical micelles, whereas the fullerene(C₆₀)-containing derivatives form rodlike structures (elongated “chains” of cross-linked micelles).     

Characterization and properties of polyethylene blends II. Linear low-density with conventional low-density polyethylene

Melting and crystallization phenomena in blends of a linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with a conventional low-density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light-scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different time scales.     

Long-chain branching in low-density polyethylene

A method is given for the analysis of long-chain branching in polymers by using combined GPC and intrinsic viscosity measurements. A computer program was written to evaluate branching indices by a tabular, iterative method. The method was applied to the evaluation of long-chain branching in low-density polyethylene.     

Determination of deuterium oxide in water by reversed-phase high-performance liquid chromatography

Refractive index detection allows > 0.1% D₂O to be determined in a few microliters of enriched water with a C₁₈ column when pure water is used as the mobile phase.     

Electron trapping in low-density polyethylene

Thermoluminescence (TL) emission from low-density polyethylene has been investigated. The glow curves of gas-free samples x-irradiated at ?190°C and heated to room temperature were found to contain three peaks numbered I, II, and III in order of increasing temperature, in agreement with earlier results. The sites of all traps are accessible to absorbed gases; in the presence of air, O₂, N₂ or Ar, “gas” traps are formed, resulting in the appearance of an additional peak IV in the glow curve at a temperature between peaks I and II, large reductions in the intensities of peaks II and III, and various changes in peak I. The peak I, II, and III traps are formed from particular chain configurations occurring in the chain-fold regions of the samples, these configurations being broken up by different forms of molecular motion within the chains. It is unlikely that the peak IV traps are just the gas molecules themselves; they are probably formed from new chain configurations occurring in the amorphous regions of the samples in the presence of the gas, the properties of the gas influencing the associated TL intensity and emission temperature. These traps are also broken up by molecular motion. The samples can be divided into two main types, differing mainly in the height of peak I relative to peak II, which is of nearly constant intensity in all samples. We suggest that two types of trap which are not interconvertible are associated with peak I, and that the dominant type in a given sample depends on the fine details of the sample fabrication process.     

Characterizing blends of linear low-density and low-density polyethylene by DSC

Summary A two-step isothermal annealing (TSIA) procedure is described that enables the endothermic peaks of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and their blends, to be satisfactorily resolved during analysis by differential scanning calorimetry. A modified form of multistep isothermal annealing, the TSIA procedure produces a highly characteristic profile of the blend components by facilitating the segregation of the phases based on branch density. It is proposed that the TSIA procedure may have significant merit in the identification and quantification of the components in an unknown blend as well as increasing the sensitivity in analytical procedures aimed at blend component quantification.     

Thermoluminescence and chain-fold morphology in low-density polyethylene

Further thermoluminescence data are presented supporting our earlier suggestion that the electron traps associated with the three peaks in the thermoluminescence glow curve of a low-density polyethylene sample from which absorbed air has been removed are formed by the polymer chains themselves in the chain-fold regions of the samples. These traps are shown to be sensitive to heating of the sample to temperature around its melting point; in particular, the lowest temperature peak disappears if the sample is held at 90°C in vacuum for 5 min. If the sample is maintained in vacuum at room temperature after such treatment, its modified glow curve remains unchanged for a period of at least 7 days; however, if the sample is exposed to air, nitrogen, or argon after such treatment, its gas-free glow curve begins to change within 3 days, evolving toward a three-peak form with the same peak temperatures but with relative intensities different from those observed before heating began. This suggests that the gas molecules “lubricate” the polymer chains, which then begin to move toward new equilibrium configurations. Immersion in n-hexane at room temperature has little effect on the luminescence centers but disables the electron traps. Immersion in fuming nitric acid at room temperature for 2 days appears to destroy the electron traps permanently, as would be expected if the chain folds are digested by the acid; its effect on the luminescence centers is still to be determined.     

Study of thermal and dielectric behavior of low-density polyethylene composites reinforced with zinc oxide whisker

Different scanning calorimetry and dynamic mechanical analysis are used to study the thermal behavior of composites by melt-mixing low-density polyethylene (LDPE) matrix and zinc oxide whisker (ZnO_w) fillers. Micrographs of the composites illustrate that needle or wedge shaped ZnO_w are distributed uniformly in the LDPE matrix. Dielectric properties of the composites are measured in a frequency range of 1-10 MHZ. The results show that the addition of ZnO_w does not affect the melting behavior of LDPE, but has an important effect on the heat of fusion, dynamic mechanical behavior, and dielectric behavior of the composites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ionization constants for deuterium oxide in deuterium oxide-organic mixtures

A potentiometric method using a glass electrode has been applied to determination of ionization constants for deuterium oxide (D₂O) in binary mixtures of D₂O with dioxane, tetrahydrofuran, acetone, dimethylsulfoxide, CH₃CH₂OD, and CH₃OD at 25°C. The results are compared with values of ionization constants for H₂O obtained previously in the corresponding H₂O-organic mixtures, and the isotope effect is shown to be small. Further calculations with the D₂O results show that the first five solvents mentioned above are neither appreciably acidic nor basic in D₂O solution, but that CH₃OD shows slightly acidic behavior (pK_a=16.0±0.3).     

Reduction of alkynes into 1,2-dideuterioalkenes with hexamethyldisilane and deuterium oxide in the presence of a palladium catalyst

A combination of hexamethyldisilane and deuterium oxide was found to work as a deuterium transfer reagent for alkynes in the presence of a catalytic amount of a palladium complex to give (E)-1,2-dideuterioalkenes selectively through the corresponding (Z)-isomer.     

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 linear low-density polyethylene and oligomers

A pressure vessel design is put forward taking the form of a two-layer bottle, the inner sealing layer of which is made of linear low density polyethylene by rotational molding and the external power layer of which is made by winding an oligomer impregnated roving or moldable filament on the inner layer. It is shown that, to achieve the highest adhesion strength, it is necessary to preliminarily prepare the surface of the polyethylene sample by obtaining a particular microstructure and to use epoxy or polyester oligomers with a viscosity low enough to provide complete filling of the polyethylene sample surface texture.     

The colloid-structure of semicrystalline low-density polyethylene

The length-distribution of stereoregular sequences in low-density polyethylene (LDPE) is determined by a computer-aided analysis of cp-melting curves within the framework of thermodynamics of eutectoid copolymers. Small-angle x-ray scattering patterns are then described by using the structure data derived. One of the results is that fluctuations of the mean electron-density are increasingly reduced with an increasing degree of crystallinity.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

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.     

The water structure around the chloride ion in aqueous polyethylene oxide solutions

Neutron diffraction and nuclear magnetic relaxation yield complementary information on the interaction of ions and water molecules in solution. In the present study the two techniques are used to investigate the influence of poly (ethyleneoxide) on the Cl⁻ hydration sphere. It is concluded that the important effect of PEO on the ³⁵Cl relaxation rate is due to the occurrence of a long correlation time rather than structural changes.     

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.