Degree of crystallinity and lattice thermal conductivity of polyethylene at low temperatures

The lattice thermal conductivity of a semicrystalline polymer was studied at low temperatures by calculating the total lattice thermal conductivities of four samples of polyethylene with different degrees of crystallinity between 0.43 and 0.81 and temperatures between 0.4 and 20 K. The contributions of the crystalline and noncrystalline natures and their percentage contributions were taken into account. The predicted lattice thermal conductivity of polyethylene was in fairly good quantitative agreement with the experimental value, and showed a strong crystallinity dependence, with a distinctive cross-over point at about 2 K.     

A quantitative electron-microscopic study of a linear polyethylene fraction crystallized at different temperatures

Replica and thin-section electron microscopy was performed on a linear polyethylene fraction (M_w = 1.89 × 10⁵, M_n = 1.79 × 10 ⁵) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographic faults are also discussed.     

Molecular conformations in polyethylene after recrystallization or annealing at high pressures

Information on molecular conformations inside polyethylene lamellas following high pressure treatments is obtained by comparing observed and predicted length distributions of nitrated samples. Three types of conformation are inferred. The commonest is that molecules are folded with chain ends included in lamellas, except that ends are not turned in by less than ～600 Å from a surface. This situation accounts in detail for the previously observed agreement between the number fracture-surface distribution of crystal thicknesses and the gel permeation chromatography (GPC) weight distribution following nitration. The second conformation, found especially for samples of low polydispersity, is also of folded molecules but with chain ends excluded from lamellas. This particular case justifies rigorously the initial assumption of folding. Finally there are examples where the molecular length distribution is substantially lower than the crystal thickness distribution, implying that molecular length is not the upper limit of crystal thickness and that molecules can be fully extended inside lamellas.     

The oxidation of HI at low temperatures and the heat of formation of HO2

The kinetics of the oxidation of hydrogen iodide (HI + O₂) at low temperature (414–499 K) in the gas phase by the method of iodination kinetics is complicated by a heterogeneous reaction between hydrogen iodide and oxygen. Present work leads to an upper limit for the bimolecular rate constant k₁ for the first and rate-determining step (1) These data are combined with an estimated A factor A₁ = 10^9.3±0.2 L/mol·s (assuming a tight linear I···H···O— transition state), to calculate the lower limit of the activation energy for the forward reaction E₁. This leads to a minimum value for the heat of formation of the HO₂ radical, ΔH_f298^°(HO₂) < 3.0 kcal/mol.     

Viscoelastic properties of linear low density polyethylene melts

The importance of linear low density polyethylene (LLDPE) is being rapidly felt. The combination of favourable production economics and excellent product performance characteristics has enabled this new plastic to gain acceptance for a wide variety of applications. No studies on the rheological properties of LLDPE exist to date. The viscous and elastic properties of this new polymer has now been investigated and unified curves for viscosity and normal stress differences are given. The temperature dependence of the rheological properties of LLDPE has also been studied.     

High-precision adiabatic calorimetry and the specific heat of cyclopentane at low temperature

We describe a fully automated adiabatic calorimeter designed for high-precision covering the temperature range 15 to 300 K. Initial measurements were performed on synthetic sapphire (20 g). The statistical error of the apparatus estimated from the scattering of theC _p data of sapphire is about 0.1% and the average absolute error of specific heat between 100 and 300 K was 0.7% compared to values given in the literature. The heat capacity and the three phase transitions of cyclopentane (C₅H₁₀) which is recommended as a standard for the temperature calibration of scanning calorimeters have also been measured. The transition temperatures were determined to be (literature values in parentheses): 122.23 K (122.39 K) 138.35 K (138.07 K) and 178.59 K (179.69 K), with an experimental error of ±40 mK.     

Desorption behavior of a surfactant in a linear low‐density polyethylene blend at elevated temperatures

The desorption behavior of a surfactant in a linear low‐density polyethylene (LLDPE) blend at elevated temperatures of 50, 70, and 80 °C was studied with Fourier transform infrared spectroscopy. The composition of the LLDPE blend was 70:30 LLDPE/low‐density polyethylene. Three different specimens (II, III, and IV) were prepared with various compositions of a small molecular penetrant, sorbitan palmitate (SPAN‐40), and a migration controller, poly(ethylene acrylic acid) (EAA), in the LLDPE blend. The calculated diffusion coefficient (D) of SPAN‐40 in specimens II, III, and IV, between 50 and 80 °C, varied from 1.74 × 10^?11 to 6.79 × 10^?11 cm²/s, from 1.10 × 10^?11 to 5.75 × 10^?11 cm²/s, and from 0.58 × 10^?11 to 4.75 × 10^?11 cm²/s, respectively. In addition, the calculated activation energies (E_D) of specimens II, III, and IV, from the plotting of ln D versus 1/T between 50 and 80 °C, were 42.9, 52.7, and 65.6 kJ/mol, respectively. These values were different from those obtained between 25 and 50 °C and were believed to have been influenced by the interference of Tinuvin (a UV stabilizer) at elevated temperatures higher than 50 °C. Although the desorption rate of SPAN‐40 increased with the temperature and decreased with the EAA content, the observed spectral behavior did not depend on the temperature and time. For all specimens stored over 50 °C, the peak at 1739 cm^?1 decreased in a few days and subsequently increased with a peak shift toward 1730 cm^?1. This arose from the carbonyl stretching vibration of Tinuvin, possibly because of oxidation or degradation at elevated temperatures. In addition, the incorporation of EAA into the LLDPE blend suppressed the desorption rate of SPAN‐40 and retarded the appearance of the 1730 cm^?1 peak. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1114–1126, 2004     

Mechanical properties of blends of low density with linear low density polyethylene

Torque values and mechanical properties are reported for blends of low density with linear low density polyethylene (PE). The torque values show that incompatible mixtures in the molten state are formed when the torques of the pure polymers are almost equal. Semicompatible behaviour is shown in the other cases. The mechanical properties indicate that semicompatible mixtures are formed in the solid state. The mechanical properties of these blends are strongly influenced by the linear low density polyethylene only for contents exceeding 25%.     

The second virial coefficient of argon at low temperatures

We present experimental data of second virial coefficients of argon at temperatures of 77.3, 87.2 and 90.2 K. The results are in excellent agreement with theoretical values.     

Chlorination of lignin at low temperatures

A high reactivity of the olefinic double bonds of the lignin (Lg) macromolecule in the reaction with molecular chlorine has been found which has permitted the chlorination of Lg to be carried out under cryogenic conditions at 150–250 K. The process takes place by a radical-chain mechanism with a length of the kinetic chain of approximately 1000 units. The bulk of the chlorine is consumed in the olefinic chains of the Lg. Other reaction products besides chlorolignin are hydrogen chloride and phenoxyl radicals, which have singlet ESR spectrum (ΔH=1.0−1.2 mT) and are retained in the chlorinated samples of Lg to ∼250 K. Institute of Chemical Physics, Academy of Sciences of the USSR, Chernogolovka, Moscow Province. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 671–676, September–October, 1990.     

Effects of ultrasonic oscillations on linear viscoelastic behaviors of metallocene‐catalyzed linear low density polyethylene and its blends with low density polyethylene

The effects of ultrasonic oscillations on linear viscoelastic behaviors of metallocene‐catalyzed linear low density polyethylene (mLLDPE) and its blends with low density polyethylene (LDPE) were investigated in this article. The experimental results showed that ultrasonic oscillations can increase the cross modulus, characteristic time, plateau modulus, complex viscosity, zero shear viscosity, and flow activation energy of mLLDPE. Molecular weight of mLLDPE increases but molecular polydispersity index decreases in the presence of ultrasonic oscillations. It has been found for mLLDPE/LDPE blends that the addition of LDPE as well as ultrasonic oscillations can decrease the cross modulus but increase the characteristic time of the blends. The complex viscosity, zero shear viscosity, and flow activation energy of the blends increase by the addition of LDPE, but decrease in the presence of ultrasonic oscillations. Shear thinning effect of the blends is improved because of the addition of LDPE. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3030–3043, 2005     

On sample positioning at low temperatures

A method is presented to measure the position of a small solid sample which is suspended by thin copper wires, from a microbalance, in a dewar that has been described earlier [1]. The shrinkage of the wires at low temperatures is reproducible to within ± 0.15 mm.     

Monodisperse CdSe nanorods at low temperatures

A new synthetic method is presented that allows the preparation of highly monodisperse CdSe nanorods (so called quantum rods) at relatively low temperatures (160 degrees C). This method is characterized by a high aspect ratio of the particles and affords good reproducibility. The morphology of the resulting nanorods was examined by means of transmission electron microscopy (TEM) and the electro-optic properties by means of fluorescence spectroscopy. The conditions of the reaction of nanoparticle growth were examined by varying the concentration of the organometallic precursors, the growth temperature, and the growth time. The experimental findings correspond well with previously published semiempirical pseudo-potential calculations.     

低温下生物柴油的胶凝特性研究

利用流变仪在小振幅振荡剪切模式下对地沟油、花生油和大豆油生物柴油的胶凝特性进行了研究。结果表明,低温下生物柴油不仅具有冷却胶凝特性,还表现出明显的等温胶凝特性。分析了冷却速率和剪应力对地沟油生物柴油胶凝特性的影响。结果表明,静态降温时降温速率越大,生物柴油的胶凝温度越低,降温及恒温静置过程中同一温度下的胶凝结构越弱。相同降温速率下,生物柴油的胶凝结构和胶凝温度随剪应力的增加而降低,但经受不同剪应力作用的生物柴油恒温静置后胶凝结构相差不大。降温过程中施加的剪应力较小时,冷却胶凝结构随降温速率的增大而降低;剪应力较大时,冷却胶凝结构随降温速率的增大而加强。不管施加的剪应力多大,等温胶凝结构随降温速率的增大而加强。     

Radiation polymerization of acrolein at low temperatures

Radiation polymerization of acrolein in the presence of the additives such as 2-hydroxyethyl methacrylate, acrylic acid, and water at low temperatures (0–78°C) was studied. The polyacrolein resulting from the polymerization gave a small particlelike microsphere (0.5–5 μm in diameter). The rate of the polymerization reaction of acrolein appeared to be accelerated by the addition of a small amount of 2-hydroxyethyl methacrylate or acrylic acid. The particle size of the polyacrolein particle varied with the condition of the polymerization and increased or decreased with an increase in the addition concentration of 2-hydroxyethyl methacrylate or acrylic acid.     

Vibrational relaxation of DF at low temperatures

Temperature dependence of the probability of the deexcitation process DF(ν = 1) + DF(ν = 0) → DF(ν = 0) + DF(ν = 0) has been investigated near and below room temperature based on the model that the vibrational energy is transferred to the hindered rotational (oscillatory) motion as well as the translational motion. The deexcitation probability increases sharply with decreasing temperature; this inverse temperature dependence is attributed to the important contribution of hydrogen-bond attraction.     

Post-irradiation grafting of tetrafluoroethylene at low temperatures

Low-temperature postirradiation grafting of tetrafluoroethylene (TFE) to polyolefines and silicone elastomers was the subject of study. After preliminary dissolution of TFE in the polymer at 273°K the system was slowly cooled to 77°K. In this process a certain part of TFE in polyolefines (ethylene-propylene copolymer and polypropylene) is retained by the vitreous polymer matrix. When slowly heated after radiolysis at 77°K this system shows graft polymerization of dissolved TFE after T_g. The graft copolymer is soluble and its IR spectra contain absorption bands characteristic of polytetrafluoroethylene. In polydimethylsiloxane rubber (SKT) the dissolved TFE when frozen to 77°K remains sorbed between the SKT crystallites rather than in a separate phase. When these radiolyzed samples are heated the graft-polymerization occurs primarily over the temperature range between the TFE and SKT melting points. The technique provedes for 100–150% grafting of TFE. This method also permits grafting to silicone rubbers and to several other polymers and elastomers.     

Thermodynamic behaviors of polyampholytes at low temperatures

The thermodynamic properties of 6-mer polyampholyte chains were simulated with the multicanonical Monte Carlo method in a three-dimensional off-lattice model. The results demonstrate that the number of the charged monomers on the chain and the sequence significantly affect the transition behaviors of polyampholyte chains. In the case of the random distribution of the charged monomers, two oppositely charged monomers act as two stickers during a collapse process, due to which the movement of monomers is suppressed and the chains can more directly reach their solid state. Interestingly, in a proper arrangement of the charged monomers, the chains may have a proteinlike nondegenerate state, i.e., the chain is designable. The transition of such polyampholyte chains appears to be of a two-state, all-or-none type.     

Solution photochemistry of o-hydroxybenzophenone at low temperatures

The decay of triplet o-hydroxybenzophenone takes place with a lifetime of 24 ns in methanol at 175 K and is proposed to involve the interconversion of the intermolecularly hydrogen bonded (anti) conformer into a short-lived syn species.