Morphology and mechanical properties of blown films of a low‐density polyethylene/linear low‐density polyethylene blend

The morphologies of films blown from a low‐density polyethylene (LDPE), a linear low‐density polyethylene (LLDPE), and their blend have been characterized and compared using transmission electron microscopy, small‐angle X‐ray scattering, infrared dichroism, and thermal shrinkage techniques. The blending has a significant effect on film morphology. Under similar processing conditions, the LLDPE film has a relatively random crystal orientation. The film made from the LDPE/LLDPE blend possesses the highest degree of crystal orientation. However, the LDPE film has the greatest amorphous phase orientation. A mechanism is proposed to account for this unusual phenomenon. Cocrystallization between LDPE and LLDPE occurs in the blowing process of the LDPE and LLDPE blend. The structure–property relationship is also discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 507–518, 2002; DOI 10.1002/polb.10115     

Characterization of an unsaturated low‐density polyethylene

This study concerns a new group of low‐density polyethylenes (LDPEs)—unsaturated LDPE. The new LDPE is a copolymer between ethylene and 1,9‐decadiene and was polymerized in a commerical high‐pressure tubular reactor. The diene copolymerized with one double bond, leaving the other unreacted as a pendant side group. This yielded a copolymer containing a higher number of vinyl groups than ordinary LDPE. Fractionation of the copolymer and determination of the number of unsaturated structures in the different fractions by Fourier transform infrared spectroscopy revealed that the diene is homogeneously incorporated along the molar‐mass distribution curve. It is also possible to obtain copolymers with a varying vinyl content, without drastic changes in molar mass or molar‐mass distribution, by a controlled addition of 1,9‐decadiene to the reactor. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2974–2984, 2003     

Selective oxidation of saturated hydrocarbons at secondary positions

The selectivity in the oxidation of saturated hydrocarbons by oxygen in pyridine-acetic acid in presence of an iron catalyst and zinc is strongly dependant on the oxygenation of the reaction mixture; using air and slow stirring, it is possible to attack adamantane and $\text{trans}$-1,4-dimethylcyclohexane almost exclusively at the secondary positions.     

Chemiluminescence of polyethylene: The comparative antioxidant effectiveness of phenolic stabilizers in low‐density polyethylene

The thermal stabilizing efficiency of a range of phenolic antioxidants (Lowinox CA22, Lowinox WSP, Lowinox TBP6, Irganox 3114, Irganox 1330, and Cyanox 1790) was determined in polyethylene films with chemiluminescence and hydroperoxide analysis and compared with standard systems based on Irganox 1010 and 1076. Under both nitrogen and oxygen conditions, good correlations were obtained between the two methods, confirming the importance and role of the hydroperoxide functionality and its stability in the oxidative process. Chemiluminescence decay rates correlated well with the initial corresponding hydroperoxide contents, which were measures of the antioxidant efficiencies in the polymer. The antioxidant structure and volatility (melting points) were important parameters to consider in any such correlations and related very much to the methodology and conditions of analysis (i.e., the temperature and atmosphere). Some of the antioxidants themselves under nitrogen exhibited strong chemiluminescence, which appeared to be a legacy associated with their manufacturing history and the partial oxidation of their structures, which gave peroxide functionalities. This was more notable for the complex antioxidant structures. Under oxygen, higher levels of chemiluminescence were observed, and this was indicative of some level of oxidation associated with the antioxidant structures. With temperature‐ramping experiments, the chemiluminescence emission was significant and only observed at temperatures close to the melting points of the additives and/or polymer. Mobility was clearly an essential feature of this reaction emission because chemiluminescence was well observed when the molten state was reached. Under normal practical conditions, such levels of chemiluminescence, because of employed stabilizers, do not contribute significantly to the chemiluminescence emissions of stabilized polymer materials. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3312–3326, 2002     

Applicability of the transient plane source method to measure the thermal conductivity of low‐density polyethylene foams

The thermal conductivity at constant pressure of a collection of crosslinked, closed‐cell polyethylene foams were measured at room temperature with the transient plane source (TPS) method. The experimental results were compared with those determined by a standard steady‐state technique. The results showed that the values measured by the TPS method follow the same trends as those measured by a heat‐flow meter. Therefore, with the TPS technique it is possible to observe the influence of structural characteristics such as cell size, black carbon content in foams, density, and so forth on thermal conductivity. However, the values obtained by the transient method were approximately 20% higher than those given by the standard method. Possible reasons for these variations are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1226–1234, 2004     

Modeling of the linear viscoelastic behavior of low‐density polyethylene

We predict the linear viscoelastic behavior of low‐density polyethylene from both the molecular‐weight distribution and the individual structure of each species in the sample. The “structure map” of the samples was derived from SEC measurements. This map is a three‐dimensional representation of the seniority distribution, and represents the probability of existence of a segment with seniority i in a molecule of molecular weight M. Moreover, results from the kinetics of the free radical polymerization of polyethylene show that the molecular weight of the segments increases according to their seniority. Finally, tube dilatation was generalized to the case of polydisperse samples. The solvent behavior of the relaxed segments was included through a continuous function of time that describes the instantaneous state of the entanglement network in the sample. The comparison between the theoretical predictions and the experimental data shows a good agreement over the whole experimental frequency range. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43:1973–1985, 2005     

Products of ozone oxidation of some saturated cyclic hydrocarbons

Low-temperature ozone oxidation of a series of saturated carbocyclic hydrocarbons afforded the corresponding alcohols and/or ketones in high yield through intermediate trioxidanes. exo,endo-Tetracyclo-[6.2.1.0^3,5]undecane-2,7-dione and exo,endo,endo-hexacyclo[9.3.1.0^3,8.0^4,6.0^5,9.0^12,14]pentadecane-2,10-dione were isolated, and exo,endo,exo-pentacyclo[6.3.1.0^2,7.0^3,5.0^9,11]dodecyl-, exo,exo,exo-heptacyclo-[9.3.1.0^2,10.0^3,8.0^4,6.0^5,9.0^12,14]pentadecyl, and 1-methylcyclohexyltrioxidanes were identified and characterized for the first time.     

A low‐temperature polymorph of m‐quinquephenyl

A low‐temperature polymorph of 1,1′:3′,1′′:3′′,1′′′:3′′′,1′′′′‐quinquephenyl (m‐quinquephenyl), C₃₀H₂₂, crystallizes in the space group P2₁/c with two molecules in the asymmetric unit. The crystal is a three‐component nonmerohedral twin. A previously reported room‐temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993). Chem. Commun. pp. 1795–1797] also crystallizes with two molecules in the asymmetric unit in the space group P. The unit‐cell volume for the low‐temperature polymorph is 4120.5 (4) ų, almost twice that of the room‐temperature polymorph which is 2102.3 (6) ų. The molecules in both structures adopt a U‐shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit‐cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C—H...π interactions.     

Kinetics of the thorough oxidation of traces of saturated hydrocarbons in air

Conclusions The kinetics of the thorough oxidation on a platinum-aluminum catalyst of small quantities of n-pentane, h-heptane, and n-nonane has been investigated. Under comparable conditions n-pentane is oxidized considerably more slowly than n-heptane and n-nonane. A kinetic equation has been found which describes the reaction rate in all the systems studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1728–1734, August, 1981.     

The low‐temperature phase of di‐tert‐butylsilanediol

The crystal structure of di‐tert‐butyl­silanediol, C₈H₂₀O₂Si, has a reversible phase transition at 211 (2) K. The orthorhombic high‐temperature structure has space group Ibam, with Z′ = , and shows a disordered hydrogen‐bonding system. The low‐temperature structure, determined at 143 (2) K, has a twinned monoclinic cell, with space group C2/c and Z′ = 2, and shows an ordered hydrogen‐bonding system.     

Morphology,structure, and properties of in situ compatibilized linear low‐density polyethylene/polystyrene and linear low‐density polyethylene/high‐impact polystyrene blends

Blends of linear low‐density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high‐impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl₃), was adopted to initiate the Friedel–Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl₃ blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel–Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE‐g‐PS and LLDPE‐g‐HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m². Scanning electron microscopy micrographs showed that the size of the domains decreased from 4–5 to less than 1 μm, depending on the content of added AlCl₃. The crystallization behavior of the LLDPE/PS blend was investigated with differential scanning calorimetry. Fractionated crystallization phenomena were noticed because of the reduction in the size of the LLDPE droplets. The melt‐flow rate of the blending system depended on the competition of the grafting reaction of LLDPE with PS and the degradation of the blending components. The degradation of PS only happened during the alkylation reaction between LLDPE and PS. Gel permeation chromatography showed that the alkylation reaction increased the molecular weight of the blend polymer. The low molecular weight part disappeared with reactive blending. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1837–1849, 2003     

On the mechanism of the gif system for the oxidation of saturated hydrocarbons

The high selectivity of the Gif system for hydrocarbon oxidation is shown to depend upon the capture of $\text{tert.}$ radicals by pyridine; the mechanism for the secondary oxidation products has only a minor radical component as judged by competitive trapping.     

Branching degree and rheological response correlation in peroxide‐modified linear low‐density polyethylene

Correlations between rheological behavior and degree of long chain branching (LCB) of linear low‐density polyethylene (LLDPE) upon a peroxide (dicumyl peroxide [DCP]) modification process under various conditions are discussed in this paper. The gel content analysis revealed negligible insoluble crosslinked fraction implying that incorporation of DCP to LLDPE predominately leads to branching rather than crosslinking. The slight changes in average molecular weight and molecular weight distribution induced by peroxide modification under various conditions revealed that formation of low‐molecular‐weight fractions due to chain scission is also negligible. The changes in terminal, trans, and pendant double bonds concentration of the modified samples with different amounts of peroxide were well depicted by Fourier transform infrared spectroscopy. Considering insignificant changes in molecular weight and molecular weight distribution during peroxide modification, the deviation observed in zero‐shear‐rate viscosity (η₀) values of the modified LLDPE with that of power‐law equation related to the linear PEs could be reliably attributed to the presence of LCB in the peroxide modified samples. Increasing the DCP content at roughly constant molar mass led to increasing of η₀ values as a result of increased degree of LCB. The increase in η₀ values was ascribed to prolonged relaxation times of the polymer molecules due to the retarded reptation motion‐driven relaxation mechanism. Copyright © 2014 John Wiley & Sons, Ltd.     

Melt grafting of N‐carbamyl maleamic acid onto linear low‐density polyethylene

The grafting of N‐carbamyl maleamic acid (NCMA) onto linear low‐density polyethylene (LLDPE) was carried out with different concentrations of 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy) hexane (DBPH) as an initiator. The modification process was performed in the molten state with a Brabender mixer. All the materials were characterized with Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and melt rheology. The analysis of the FTIR spectra indicated that the grafting efficiency increased with the concentration of both NCMA and DBPH. The calorimetric experiments showed that the modification process did not noticeably alter the enthalpy of fusion of LLDPE, whereas the melting temperature of the modified polymers was slightly lower than that corresponding to the original LLDPE. The rheological response of the molten polymers, determined under dynamic shear flow at small‐amplitude oscillations, indicated that the modification process induced crosslinking of the chains. Both the dynamic viscosity and elastic modulus of the modified LLDPE increased with the concentration of NCMA and DBPH, showing that larger molecules were generated during the modification process. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3950–3958, 2002     

Catalytic air oxidation of ambient temperature hydrocarbons

Catalytic air oxidation of the aliphatic hydrocarbons n-decane, hexanes, gasoline and diesel fuel was conducted at ambient temperature with novel iron catalysts. The concentration of n-decane in water was reduced from 1.42 g in 100 ml to 0.07 g in 100 ml in 5 h at room temperature forming carbon monoxide and water by means of intermediate aldehydes. Results of FT–IR and GC–MS analyses demonstrated formation of aldehydes and unsaturated alcohols. Carbon monoxide was detected on catalyst residues and in the vapor phase. The indicated catalytic reaction mechanisms are discussed.     

Ambient analysis of saturated hydrocarbons using discharge-induced oxidation in desorption electrospray ionization

Saturated nonfunctionalized hydrocarbons can be oxidized in situ by initiating an electrical discharge during desorption electrospray ionization (DESI) to generate the corresponding alchohols and ketones. This form of reactive DESI experiment can be utilized as an in situ derivatization method for rapid and direct analysis of alkanes at atmospheric pressure without sample preparation. Betaine aldehyde was incorporated into the DESI spray solution to improve the sensitivity of detecting the long-chain alcohol oxidation products. The limit of detection for alkanes (C₁₅H₃₂ to C₃₀H₆₂) from pure samples is ∼20 ng. Multiple oxidations and dehydrogenations occurred during the DESI discharge, but no hydrocarbon fragmentation was observed, even for highly branched squalane. Using exact mass measurements, the technique was successfully implemented for analysis of petroleum distillates containing saturated hydrocarbons.     

Modelling of thermal oxidation of phosphite stabilized polyethylene

The thermal oxidation behaviour of polyethylene films stabilized by various weight ratios of organophosphites (Irgafos 168) has been studied at selected temperatures. The duration of the induction period was found to increase proportionally with the stabilizer concentration, even at temperatures as low as 80 °C. Particular attention was paid to the phosphite-phosphate conversion during the induction period. A kinetic model, involving volatile and partially soluble hydroperoxide decomposers, was developed in order to simulate these results. With the use of kinetic parameters that can be at least tentatively justified from theoretical considerations, this model gave simulations in reasonable agreement with the experimental observations for stabilizer depletion and carbonyl formation. Of particular note is the fact that, even for non-trivial results such as the shape of the phosphite versus phosphate concentration plots, or phosphate build-up, there was also a quite good agreement.     

The low‐temperature study of d‐ and dl‐camphoric anhydride

The low‐temperature crystal stuctures of d ‐ and dl ‐camphoric anhydride, C₁₀H₁₄O₃, have been determined by X‐ray diffraction methods. Although the two enantiomers crystallize in different space groups, the cell volumes and densities are essentially the same. The six‐membered rings deviate significantly from planarity, both exhibiting half‐boat conformations. The dihedral angle between the six‐ and five‐membered rings is 80.3 (1)° in both cases. The main difference in the molecular stuctures can be described by two torsion angles associated with the H atoms of the methyl substituents. The packing of the racemic and chiral structures are essentially the same.     

Polymer nanoparticles: their effect on rheological,thermal, and mechanical properties of linear low‐density polyethylene (LLDPE)

Rheological, thermal, and mechanical properties of polymer particle/LLDPE blends were studied in this paper. The blends were prepared individually by incorporating nanoparticles of polystyrene (nPS) of ～60 nm and polymethyl methacrylate (nPMMA) of ～50 nm with different wt% loading (i.e., 0.10–0.5%). It was shown from the experimental results that rheological, thermal and mechanical properties were increased as polymer particles blended with LLDPE. Blends with 0.25 wt% loading of nPS and 0.5 wt% loading of nPMMA exhibited better rheological, thermal, and mechanical properties compared with that of other wt% loadings. The improvements in properties were due to the close packing of LLDPE chains as recorded by improvement in crystallinity of LLDPE with addition of nPS and nPMMA as shown by SEM. Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanical properties of oriented low‐density polyethylene with an oriented lamellar‐stack morphology

A quantitative study was undertaken of the anisotropy of low‐strain mechanical behavior for specially oriented polyethylene with controlled crystalline and lamellar orientation. The samples were prepared by the die drawing of injection‐molded rods of polyethylene and annealing. This produced a parallel lamellar structure for which a simple, three‐dimensional composite laminate model could be used to calculate the expected anisotropy. Experimental data, including X‐ray strain measurements of the lateral crystalline elastic constants, showed good quantitative agreement with the model prediction. The X‐ray strain measurements confirmed that the amorphous regions exert large constraints on the crystalline phase in the lateral directions, where an order of magnitude difference was found between the measured apparent lateral crystalline compliances in the lamellar‐stack sample and the expected values for a perfect crystal. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 755–764, 2000