Characteristics of solid-state extruded polyethylene

This paper describes the properties of solid-state extruded polyethylene as a function of two primary processing variables, extrusion temperature, and area reduction. The polymer was extruded in sheet form, giving a material having an orthotropic mode of orientation. Property data are presented for melting temperature and heat of fusion; sonic modulus, yield stress, and elongation at fracture; small-angle x-ray scattering; optical absorption coefficient; and morphology for material etched by ion bombardment at liquid nitrogen temperature. Combining the present results with data previously reported in the literature, it is found that over the temperature range of about 90–120°C, where polyethylene can be successfully extruded to large area reductions, many properties of the extrudates show a surprisingly small dependence on extrusion temperature. A notable exception to this behavior is the elastic modulus, which increases significantly with increasing extrusion temperatures. In contrast to extrusion temperature, area reduction is found to have a major effect on nearly all properties of solid-state extruded polyethylene. In most cases, the form of this dependence is such that the properties change rapidly at small area reductions and much more slowly at large reductions.     

Deformation structures in solid-state extruded polyethylene

Deformation structures resembling kink bands have previously been reported in a number of oriented semicrystalline polymers which have undergone various modes of deformation. In the present work, such structures have been observed and studied in solid-state extruded polyethylene which has been processed to give a biaxial, “single crystal” texture. Deformation of this material by bending followed by unbending has been observed to lead to shear during the bending stage and to void formation during the unbending stage. The kink bands which form during this treatment exhibit a single morphology regardless of the axis of bending so long as the direction of compression during bending is parallel to the original extrusion direction. Besides intracrystalline slip, which is known to contribute at least in part to the process of kink band formation, mechanisms involving interlamellar slip and interfibrillar slip are also considered. These mechanisms are considered in terms of three distinct experimental observations: the relationship between the kink boundary and the x-ray long period, the process of void formation during unbending, and the single characteristic morphology of the kink bands.     

Pressure crystallized and solid-state extruded poly - ethylene. Precision determination of lattice parameters

Precision determination of high density polyethylene unit-cell dimensions are reported. The crystallographic analysis was carried out on pressure crystallized and subsequently solid-state extruded samples respectively, by means of x-ray photographic and diffractometric procedures. In all cases the crystal data was derived from a large number of independent reflections. It was shown that the unit-cell dimensions and the corresponding crystallographic densities of all the specimens are invariant with respect to either crystallization pressure or nominal draw ratio. The effects of deformation on macroscopic density are attributed, therefore, to changes of the degree of crystallinity and to an increase of the density of the amorphous phase. This interpretation is consistent with the experimental data in the framework of the two-phase model of polymer morphology.     

Isoconversional analysis of solid-state transformations

A key issue in kinetic analysis is the "prediction" of the evolution of a solid state transformation for a particular temperature program. Many methods have been proposed to calculate this evolution from kinetic parameters determined from non-isothermal isoconversional methods. In this study, we will review and compare the most accurate methods. We will then introduce a new method that provides an accurate prediction for an arbitrary temperature program.     

Fire retardancy of a reactively extruded intumescent flame retardant polyethylene system enhanced by metal chelates

A reactive extrusion technology was adopted to synthesize a flame retardant (ER), based on the esterification of melamine phosphate and pentaerythritol. The ER imparts good flame retardancy and non-dripping for polyethylene (PE) when combined with ammonium polyphosphate to yield an intumescent polyethylene (PE-IFR). The performance of this intumescent system has been enhanced by the addition of small amounts (0.2%) chelated copper(II)salicylaldehyde (CuSA) and salicylaldoxime, (CuSAO). The thermal stabilization and burning behaviour of the flame retardant PE system have been investigated by TGA, LOI, the UL-94 test and cone calorimetry. All formulations studied provide good flame retardant behaviour, with LOI ≥ 27.4 and UL-94 V-0 rating. The onset of decomposition in TGA for flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) commences at lower temperature than that of PE with release of blowing agent, but continues to a higher temperature, leaving a greater residue. Significant differences have been observed in burning behaviour using cone calorimetry, between flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) and PE, showing decreases in HRR, PHRR, MLR, FIGRA and CO emission.     

Incorporating multifunctional LiAlSiO_4 into polyethylene oxide for high-performance solid-state lithium batteries

High ionic conductivity,good electrochemical stability,and satisfactory mechanical property are the crucial factors for polymer solid state electrolytes.Herein,fast ion conductor LiAlSiO_4(LASO) is incorporated into polyethylene oxide(PEO)-based solid-state electrolytes(SSEs).The SSEs containing LASO exhibit enhanced mechanical properties performance compared to pristine PEO-LiTFSI electrolyte.A reduced melting transition temperature of 40.57℃ is enabled by introducing LASO in to PEO-based SSE,which is beneficial to the motion of PEO chain and makes it possible for working at a moderate environment.Coupling with the enhanced motion of PEO,dissociation of the lithium salt,and conducting channel of LASO,the optimized composite polymer SSE exhibits a high ionic conductivity of 4.68×10^-4,3.16×10^-4 and 1.62×10^-4 S cm^-1 at 60,50 and 40℃,respectively.The corresponding LiFePO_4//Li solid-state battery exhibits high specific capacities of 166,160 and 139 mAh g^-1 at 0.2 C under 60,40 and 25℃.In addition,it remains 130 mAh g^-1 at 4.0 C,and maintains 91.74% after 500 cycles at 1.0 C under 60℃.This study provides a simple approach for developing ionic conductor-filled polymer electrolytes in solid-state lithium battery application.     

The morphology of gel-spun polyethylene fibers,investigated by solid-state 13C NMR

Gel-spun polyethylene fibers were analyzed at room temperature with ¹³C NMR, using both, CP-MAS and BILEV (Bloch-decay with two-level decoupling). The analysis shows the existence of three different components in the fiber sample—a crystal component, an amorphous component and a third component, named the oriented, mobile component. This latter component has a ¹³ C chemical shift that is similar to the crystalline chemical shift, but with a mobility, expressed by T₁, that is closer to the amorphous component. The chemical shift and T₁ are as follows: 34.06 ppm and 28.1 s for the crystalline part; 31.70 ppm and 0.3 s for the amorphous part; and 34.06 ppm and 1.8 s for the oriented mobile component. The percentages are 63.2% crystalline; 34.0% oriented mobile, 2.8% amorphous component. Using proton spin-diffusion measurements, it was possible to estimate the domain size of the crystalline and oriented mobile components to be 62.8 and 13.2 nm, respectively, in agreement with the results of a full-pattern x-ray study on the same sample. After melting of the fiber at 450 K and recrystallinzation on cooling, the oriented, mobile component is dramatically reduced. © 1994 John Wiley & Sons, Inc.     

Dynamic thermal analysis of solid-state reactions

There are many reactions of interest in which one or more of the reactants belong to some solid phases. Modern thermoanalytical instruments can conveniently provide reaction kinetic data of high precision and accuracy, from which the underlying activation energyE may be derived in principle. Unfortunately, no best method yet exists for the derivation when the data have been collected with a programmed linear increase in sample temperature, unlike the case of isothermal measurements, which however suffer from experimental limitations [1]. Here we propose a method for extractingE from non-isothermal data, that promises general validity.     

Changes in row structure of extruded polyethylene film in grafting with styrene. II. Copolymer morphology

The morphology of extruded high-density polyethylene film grafted with styrene was studied by transmission electron microscopy of thin stained sections. Near the film surface grafted polystyrene was confined to amorphous layers between lamellar crystals of polyethylene. In the film interior separate polystyrene domains were also formed and became predominant in grafting in diluted styrene. The deciding factor for the location of grafted polystyrene is the chain length because only long chains can coalesce in large separate zones. The polystyrene zones expand by cracking the stacks of lamellae along the lamellar normals. Straightening of the twisted crystalline lamellae of polyethylene occurred in grafting. “Bubbles” of styrene homopolymer were formed under conditions of high monomer concentration. The effect of staining the graft by the Kanig method² was also discussed.     

Applications of thermal analysis in some solid-state reactions

TG-DTG-DTA has been used to characterize various isomers of CoCl₂·2(CH₃C₆H₄NH₂). Thermal analysis is further used to analyse the binary mixtures of these isomers. DTA recorded after different elapsed times follows the progress of reaction between cobalt chloride and benzocaine where progressively small endotherms are associated with starting materials. The application of thermal analysis to following the solid-solid reactions between metal acetates and 8-hydroxyquinoline was highlighted. The stoichiometry of such reactions was confirmed from the decrease in intensity of an endotherm as one increases the stoichiometry.Thanks are due to Drs. Keshav Chander, K. Kaur, Rajinder Singh and G. S. Chopra for helpful discussions and experimental work.     

Microstructure and dynamic mechanical analysis of extruded layered silicate PVC nanocomposites

The nanostructure and dynamic mechanical properties of polyvinyl chloride (PVC) and the bentonite nanocomposites have been investigated. Nanocomposites with 5 wt% concentration of bentonite were prepared by melt extrusion followed by two‐roll‐milled processing. Atomic force microscopy (AFM) and wide‐angle X‐ray scattering (WAXS) were utilized to study the micro and nanostructure of the two‐roll‐milled sheets. The nanocomposites were compounded with two types of coupling agents: KZTPP® and Tamol 2001®. Optical microscopy showed that the materials remained optically transparent, i.e. they did not show evidence of nanoclay agglomeration. The WAXS patterns of PVC‐bentonite‐KZTPP nanocomposite were anisotropic, suggesting flow‐induced preferred orientation of the nanoplates. Moreover, the 001 reflection of the bentonite was shifted toward smaller angles, suggesting that the nanoplates were intercalated by the macromolecules. On the other hand, the WAXS patterns of PVC‐bentonite‐Tamol 2001 nanocomposite remained isotropic and did not show evidence of bentonite, suggesting exfoliation of the nanoplates. The nanocomposites showed an increase in glass transition temperature T_g, with the sequence T_g,PVC < T_g,KZTPP < T_{g,Tamol 2001}. Moreover, dynamic mechanical analysis (DMA) showed an increase in mechanical moduli and activation energy (and a decrease in the intensity of the mechanical damping Tan δ) following the same sequence. Interestingly, the improvement in mechanical moduli became more pronounced above the glass transition temperature. Copyright © 2008 John Wiley & Sons, Ltd.     

Mathematical description of the softening temperature of poly(vinyl chloride) blends with solid-state chlorinated polyethylene

Summary Excess molar volumes of methyl tert-butyl ether (MTBE)+1-pentanol+octane and the binary mixtures MTBE+1-pentanol and 1-pentanol+octane, were measured at 298.15 K and atmospheric pressure, using a DMA 4500 Anton Paar densimeter. All the experimental values were compared with the results obtained by empirical expressions for estimating ternary properties from binary results.     

Multi-component analysis of low-density polyethylene oxidative degradation

The oxidative degradation of polyethylene in various conditions has been studied. In order to gain insight into the oxidation process, a method for the curve-fitting analysis of the IR carbonyl band between 1800 cm⁻¹ and 1600 cm⁻¹ in oxidized low-density polyethylene (LDPE) has been developed. Up to 10 components were needed to fit the band envelope, whose assignments and peak positions were based on the literature and on the synthesis of an appropriate model compound. The determination of the other band parameters, such as peak width and peak shape, necessary for reliable best fitting of the absorbance envelopes, was obtained by overall fitting optimization process. By using the available extinction coefficients, the quantitative determinations of the main oxidized species, i.e. ketones, carboxylic acids, esters, γ-lactones and ketoacids, were obtained with a reasonable confidence by rigorous parameter setting. The method was applied to the IR analysis of LDPE samples oxidized in different conditions (under thermal and irradiation stimulation), either as beads or films, as a function of time. Total hydroperoxide concentrations were also quantitatively estimated by a modified iodometric titration procedure. A good linear correlation between concentrations estimated by chemical titration and by intensity analysis of the free hydroperoxide IR band was observed.     

Differential thermal analysis of pressure crystallized polyethylene

Summary The results presented here demonstrate that although medium-density polyethylene in addition to linear polyethylene can crystallize in extended-chain as well as folded-chain crystals, the branches have a significant effect on the ease of forming extended-chain crystals. Besides the two types of crystals having different melting points, as measured by DTA, an endothermic peak assumed to be due to the onset of rotational motion and located just below the respective melting peaks is associated with each type of crystal. Melting itself does not result in a complete disappearance of order; if the sample is held just above the melting point for a short period of time sufficient seed nuclei remain to produce crystallization at a higher temperature than commensurate with the cooling rate employed. This crystallization at atmospheric pressure takes place through chain folding even though the nuclei are remnants of extended-chain crystals. In addition to fractionation and segregation by molecular weight during crystallization under pressure, for which some further evidence is presented, the results obtained here suggest that fractionation by branching content may also occur.

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Zusammenfassung Die wiedergegebenen Daten zeigen für Poly?thylen mittlerer Dichte, das wie lineares Poly?thylen sowohl mit gestreckten Ketten wie mit gefalteten Ketten kristallisieren kann, da? die Verzweigungen einen wesentlichen Einflu? auf die Leichtigkeit der Ausbildung von gestreckten Ketten haben. Au?erdem besitzen beide Typen von Kristallen verschiedene Schmelzpunkte, gemessen mittels DTA. Ein endothermer Pik würde dem Einsetzen von Rotationen zuzuordnen sein und tritt kurz unterhalb des bezüglichen Schmelzpiks der entsprechenden Kristallart auf. Das Schmelzen besteht nicht in einem vollst?ndigen Verschwinden der Ordnung. Wenn eine Probe kurz über dem Schmelzpunkt für nicht zu lange Zeit gehalten wird, verbleiben genügend Keime, um Kristallisation bei h?herer Temperatur zu erzeugen als der angewendeten Abkühlungsgeschwindigkeit entspricht. Diese Kristallisation bei 1 Athmosph?re l?uft ab unter Faltung auch dann, wenn die Keime aus dem Aufschmelzen gestreckter Kristalle stammen. Zus?tzlich zur Fraktionierung und Segregation nach dem Molekulargewicht w?hrend der Kristallisation unter Druck, für welche einige Hinweise pr?sentiert werden, ergeben die Kristalle weitere Hinweise, da? die Fraktionierung durch den Gehalt an Verzweigung eintritt.

     

Crystalline order in polyethylene: A 13C NMR CP/MAS solid-state T1 study

The carbon-13 spin-lattice relaxation times T₁ of the crystalline components of four solid ethylene-octene copolymers have been studied as a function of thermal history, branching number, and branching distribution. Slowly cooled samples (1 deg/min from melt to room temperature) exhibited similar or longer T₁s with respect to the same sample quench cooled (from the melt into 20°C water). The greater the degree of branching and the more homogeneous the branching distribution, the shorter were the observed crystal lattice T₁s. Differences of up to a factor of 3 in T₁ were observed for the same sample undergoing the two thermal treatments. Different degrees of branching homogeneity (for the same total number of branches) resulted in differences approaching a factor of 7 for samples with the same thermal history. These variations were attributed to the differing effects of side-chain disruption of the crystal lattice.     

Systematic analysis for common cations by solid-state spot-tests

Solid-state capillary spot-tests for 17 cations with 16 organic and inorganic reagents have been examined. A comparative study of the colour reactions in solution has also been made. Some new reactions are described. The reactions studied have been systematized.