PE Samples Research Articles

Ethylene homopolymerization by novel Ziegler Natta-type catalytic systems obtained by oxidative addition of salicylaldimine ligands to bis(1,5-cyclooctadiene)nickel(0) and methylalumoxane

A new series of monochelate nickel(II) catalysts, obtained by oxidative addition of salicylaldimine ligands to bis(1,5-cyclooctadiene)nickel(0), was reported for the polymerization of ethylene (E). Almost stoichiometric amounts of MAO as co-catalyst were necessary in order to activate these systems, the productivity being dependent on the Al/Ni molar ratio. The activity and the average molecular weight of the resulting PE were mainly influenced by the nature of the substituents on both the phenolate moiety and on the N-aryl ring. In particular, when two nitro groups are present on the 3,5-positions of phenolate moiety high activity (up to 120,000 g PE/(mol Ni× h)) was observed. The obtained PE samples showed a high linearity and average molecular weight in the 100,000–500,000 Da range. The obtained results seem to suggest that, at least for these catalysts based on salicylaldiminate ligands, the presence of electron withdrawing nitro groups on the phenoxy moiety plays a more important role with respect to the bulkiness of the substituents on both the ortho positions of the N-aryl group in order to prevent chain transfer and thus enhance the molecular weight of the polymer.

Dose rate effects in radiation degradation of polymer-based cable materials

Cable ageing under the nuclear power plant (NPP) conditions must be effectively managed to ensure that the required plant safety and reliability are maintained throughout the plant service life. Ionizing radiation is one of the main stressors causing age-related degradation of polymer-based cable materials in air. For a given absorbed dose, radiation-induced damage to a polymer in air environment usually depends on the dose rate of the exposure. In this work, the effect of dose rate on the degradation rate has been studied. Three types of NPP cables (with jacket/insulation combinations PVC/PVC, PVC/PE, XPE/XPE) were irradiated at room temperature using 60Co gamma ray source at average dose rates of 7, 30 and 100 Gy/h with the doses up to 590 kGy. The irradiated samples have been tested for their mechanical properties, thermo-oxidative stability (using differential scanning calorimetry, DSC), and density. In the case of PVC and PE samples, the tested properties have shown evident dose rate effects, while the XPE material has shown no noticeable ones. The values of elongation at break and the thermo-oxidative stability decrease with the advanced degradation, density tends to increase with the absorbed dose. For XPE samples this effect can be partially explained by the increase of crystallinity. It was tested by the DSC determination of the crystalline phase amount.

Effects of irradiation on the melting and crystallization behavior of ethylene polymers with different thermal history

Ethylene polymers, including HDPE, Ziegler–Natta-catalyzed LLDPE (Z–N LLDPE), metallocene-catalyzed LLDPE (m-LLDPE), and LDPE were thermally treated by different procedures, that is, quenching, slow cooling, and thermal segregation. These PE samples, having different thermal histories, were then irradiated with various doses, that is, 0, 13, 35, and 70 Mrad, by gamma ray using a 60Co radiation source. The melting and crystallization behaviors of these irradiated samples were studied by a differential scanning calorimeter (DSC). The effects of the thermal histories and irradiation on the polymers were evaluated by their melting temperatures (Tm), crystallization temperatures (Tc), and heat enthalpies (ΔH) in the heating and cooling scans. The results indicated that irradiation affects the samples having different thermal histories in different ways. The effects of the dosage on each kind of sample are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 536–544, 2003

Straight‐Chain Segment Length Distribution in Oriented Polyethylene as Revealed by LAM-Raman Spectroscopy

With the help of low-frequency Raman spectroscopy, the peculiarity of structural organization of oriented PE produced by multistage zone drawing of melt-crystallized films was studied. The draw ratios varied from DR=6 to 21 for PEI with Mη=8·104 and from 3.5 to 5.7 for PEII with Mη≈106. The half widths (Δν) of all observed LAM bands were larger than 10–20 cm−1. This means that the bands comprise a continuum of the overlapped elementary bands with Δν≈3 cm−1 because of the wide straight–chain segments (SCS) length distribution. The length (L) of straight segments calculated from LAM-spectra, following a routine procedure, lies in the range from 7–8 to 60 nm. Weight fractions GMW of the SCS, as functions of their length, have a bell-like shape. Comparison of the SCS lengths with the value of the long periods (D) inferred from SAXS data for the same samples indicates that the lengths do not exceed 2D. The structural interpretation of the data obtained is given on the basis of microfibrillar models of oriented polymers. The peculiarity of the microfibrillar structure in PEI and PEII samples such as crystallite sizes and shapes and concentrations of inter- and intrafibrillar tie molecules, manifest themselves as the shape of GMW (L) functions obtained for PE samples of various Mw and DR.

Surface oxidation of UHMWPE for orthopedic use increases apoptosis and necrosis in human granulocytes.

Ultra high molecular weight polyethylene (UHMWPE) used in orthopedic prosthesis is often sterilized with gamma-rays and the subsequent oxidation was suggested to favor the in vivo wear. UHMWPE debries produced by wearing trigger an inflammatory response that can led to the implant failure. To explore direct effects of UHMWPE oxidation on immunocompetent cells and their possible role in the prosthesis failure, peripheral blood cells (PBCs) have been grown for 24 and 48 h onto plastic (Ct), UHMWPE (PE) and heat oxidized UHMWPE (PEOx) discs. PBCs necrosis and apoptosis were assessed in flow cytometry using propidium iodide staining. After 24 h, no statistically significant differences were observed in the amount of apoptotic and necrotic cells between Ct, PE and PEOx samples while, after 48 h, both necrotic and apoptotic cells were strongly increased in PEOx samples where also the granulocytes population appeared strongly reduced (6.3+/-1.1%) compared to PE (10.5+/-1.5%) and Ct (15.1+/-0.9%) samples. We conclude that surface oxidation may interfere with prosthetic failure and/or integration via granulocytes modulation.

Environmental biodegradation of polyethylene

The degradation of a commercial environmentally degradable polyethylene was investigated in two stages. Firstly by abiotic oxidation in an air oven to simulate the effect of the compost environment and secondly in the presence of selected microorganisms. Initial biofilm formation was followed by fluorescence microscopy and the subsequent growth of bacteria on the surface of the plastic was observed by scanning electron microscopy (SEM). It was observed that microbial growth occurred on the presence of PE samples that had been compression moulded to thick sections but had not been deliberately pre-oxidised. Molecular enlargement and broadening of molecular weight distribution occurred after preheating in air at 60 °C but not at ambient temperatures but colonisation of microorganisms occurred on all samples. Erosion of the film surface was observed in the vicinity of the microorganisms and the decay of oxidation products in the surface of the polymer film was measured by FTIR measurements and was found to be associated with the formation of protein and polysaccharides, attributable to the growth of the microorganisms.

Solid-state high-resolution 13C NMR study on the interphase in lamellar semi-crystalline polymers

The 13C spin-lattice relaxation time T 1c, the spin–spin relaxation time T 2c, the chemical shift values as well as mass fractions of the interphase of PE samples crystallized under various conditions were reported mainly in this work. The existence of the interphase is identified by the method of solid-state high-resolution 13C NMR and the thickness of interfacial region has been obtained. Also, a model of chain folding in the interphase region is proposed and compared with Flory's calculations; consequently, the applicable extent of the theory is examined.

Stretched polyethylene (UHMWPE)--a new substance modification for minimizing wear in artificial knee joint replacement

Polyethylene wear is a major cause of aseptic loosening of knee endoprostheses. With the aim of minimizing this mechanical wear, we stretch-modified the structure of polyethylene. From plates of UHMWPE, stretched PE samples were produced under defined conditions, and subsequently submitted to friction tests in a fluid environment (cycles 5 x 10(5), frequency 1.5 Hz, load 500 N, contact stress 10 MPa). After load testing, the stretched samples revealed a 70% reduced wear rate in comparison with non-stretched samples. Microscopic examination (light microscopy, scanning electron microscopy) showed abrasive scratches in all test samples, but only in the non-stretched specimens were signs of pitting found. Translating these results to unidirectional tractive rolling on the tibial plateau in the knee joint suggests that a significant reduction in polyethylene wear can be expected. However, further experimental investigations need to be carried out to confirm this highly promising possibility.

Dynamic mechanical properties of metallocene catalyzed linear polyethylenes

We have examined dynamic mechanical properties of metallocene catalyzed linear polyethylenes (L-PEs) with various molecular weight Mw from ca. 20M to 2.6G and branched linear polyethylenes (B-PEs) having various degree of short-chain branching. The dynamic mechanical relaxation mechanisms of these metallocene catalyzed PE samples were discussed in the terms of the structural factors such as lamellar thickness, amorphous layer thickness, and crystallinity. It was found that the positions of α (crystal) relaxation and melting temperature have similar functional dependence of the inverse of the lamellar thickness 1/Lc. The β relaxation appeared around 250K in the dynamic mechanical spectra for higher molecular weight PEs having more than about 200M of Mw. The molecular mechanism underlying β relaxation for L-PE was found to be different from that for B-PE.

Synthesis and Characterization of Syndiotactic Styrene−Ethylene Block Copolymers

Six samples of styrene−butadiene block copolymers (sPS−B 1−6) containing a range of styrene molar fractions (xS = 0.9−0.16) were prepared using MAO-activated CpTiCl3 and converted to the corresponding styrene-1-butene-ethylene terpolymers (sPS−PE, 1h−6h) through the selective hydrogenation of the unsaturated butadiene segments with p-toluenesulfonhydrazide. The monomer compositions and chemical microstructures of the sPS−PE copolymers were determined by 1H NMR (xS = 0.93−0.1) and 13C NMR, respectively. The chemical shift assignments of the monomer tetrads (SSSS, SSEE, EESE, EEbE, EEEE, SEES, EEES; S = styrene, E = ethylene, b = 1-butene) were also determined by 13C NMR as well as the average monomer block lengths (nS = 72−4; nE = 2−51). The block structure of the sPS−PE copolymers was further confirmed by DSC (differential scanning calorimetry), WAXD (wide-angle X-ray diffraction), and solid-state CP-MAS 13C NMR (cross polarization magic angle spinning) analysis. The sPS−PE samples with high styrene conte...

Degradation of polyethylene containing ferric salt and starch

The degradation of polyethylene containing four different ferric salts was compared, using remaining percentage elongation at break as a parameter; and the degradation process was also evaluated with carbonyl index, or with the formation and concentration of hydroperoxide groups. Starch can act as a synergist during the photodegradation of ferric contained PE film. X-ray photoelectroscopy analysis shows that part of ferric ions turned into ferrous ions during the degradation process because of the redox reaction of ferric ions with oxygen. When stabilizer was added, the changes from ferric ions to ferrous ions decreased. If the PE samples were exposed to high pressure mercury lamp in the atmosphere of nitrogen gas, the absorption peaks of carbonyl group was not found in IR spectra after several days exposure.

Mechanism of the immobilization of surfactants on polymeric surfaces by means of an argon plasma treatment: Influence of UV radiation

The mechanism of the immobilization of the surfactant sodium 10-undecenoate (C11(:)) on poly(ethylene) (PE) by means of an argon plasma treatment has been investigated. In particular, the influence of the vacuum ultraviolet (UV) radiation emitted by the argon plasma on the immobilization was studied. For this purpose, PE samples were coated with C11(:) (PE/C11(:) samples) and treated with an argon plasma under different conditions. PE/C11(:) samples were placed inside (glow) and outside (afterglow) the visible region of the plasma. Additionally, polymer samples that were placed in the glow of the plasma were covered with lithium fluoride or quartz crystals. These materials are transparent for electromagnetic radiation with a wavelength longer than 104 and 150 nm, respectively. Derivatization X-ray Photoelectron Spectroscopy was applied to characterize the modified polymer surfaces. It was demonstrated that vacuum UV radiation with a wavelength shorter than 150 nm made a predominant contribution to the process of immobilization. Under certain conditions it was possible to retain about 30% of the functional groups of the initially coated surfactant layer on PE. Furthermore, the UV radiation accounted for etching of PE and PE/C11(:) surfaces and initiated oxidation of the polymer surfaces.

Coating of Anionic Surfactants onto Poly(ethylene) Surfaces Studied with X-ray Photoelectron Spectroscopy

Poly(ethylene) (PE) samples were immersed in aqueous solutions of different anionic surfactants, viz. sodium dodecane sulfate (SDS), sodium 10-undecene sulfate (S11(:)), and sodium 10-undecenoate (C11(:)). When the PE samples were removed from the solutions, dried, and analyzed with X-ray photoelectron spectroscopy (XPS), surfactant was detected at the surface only if the PE samples were wetted by the surfactant solution. Wetting was accomplished by pretreating the polymer with an argon plasma for 5 s. In this way, a relatively hydrophilic surface was obtained with advancing and receding water contact angles of 89° and 31°, respectively. In a second approach, 1 vol % of hexanol was added to the surfactant solutions, thereby decreasing the surface tension of the solutions to a value below 31 mN/m, allowing direct coating of PE with the surfactants. XPS was performed to estimate the orientation of the molecules in the surfactant layer at the surface. Surfactant molecules were randomly oriented in a homogeneous layer. The thickness of this layer varied from 10 to 60 A and increased with increasing surfactant concentration of the immersion solution.

Análise sensorial de goiabadas de marcas comerciais

Sensory analysis of guava paste was realized by using quantitative descriptive analysis of 9 samples of Brazilian market (6 from the internal market and 3 from the external market) representative of six commercial brands. Guava paste is the product obtained from the processing of the sound desintegrated guavas, with or without water, with jelly like agents, pH adjusters and other ingredients and permitted additives until the appropriate consistency is obtained. The product is thermally processed and packed to ensure the perfect preservation. Judges were selected and trained, and the characteristics and definitions were established developing a glossary, directed by a sensory analyst. The sensory characteristics that described the guava paste were synerisis, presence of air bubbles, small holes and dark points on the surface and the bottom of the sample when removed from the can, brightness, colour, general appearance, firmness, cut type, cut resistance, adhesivity, sandiness, cohesivity, guava aroma, sweetness, acidity, guava flavour, caramelized, off flavour, residual flavour and overall quality. The sensory evaluation results of the guava paste samples analysed allowed the classification of the samples through step-wise discriminant analysis in the 5 groups with distinct sensory characteristic. The samples CE, SF and VE constituted three distinct groups and differed significantly (a = 5%) between them and the rest of the groups. The samples AI and AE constituted the 4th group and the 5th group was constitued of EI, EE, PE and CI samples.

Preparation of heparin-like surfaces by introducing sulfate and carboxylate groups on poly(ethylene) using an argon plasma treatment

Carboxylate and sulfate groups were introduced at the surface of poly(ethylene) (PE) samples.This was accomplished by coating and immobilizing sodium 10-undecenoate (C11(:)) and 10-undecenesulfate (S11(:)) on the polymer by means of an argon plasma treatment. The composition of the coatedsurfactant layer was proportional to the composition of the coating solution. The thickness of the surfactantlayer on the surface of PE samples, which were precoated from an aqueous solution with a total surfactantconcentration of 0.30 M, was about 55 A°. The presence of carboxylate and sulfate groups after plasmatreatment of the precoated surfaces was confirmed by X-ray photoelectron spectroscopy (XPS). About20% of the initial amount of functional groups of the coated surfactants was retained at the PE surface.The ratio of carboxylate/ sulfate groups at the plasma treated surfaces was dependent on the compositionof the precoated surfaces. The minimum surface density of these groups on the resulting samples wasabout one group per 40 A°2.

Polylactides ‐ degradable polymers for fibres and films

AbstractModification of a poly(L‐lactide) (PLLA) base resin, by treatment with peroxides and compounding with plasticisers, yield resins which can be processed by conventional techniques and equipment to thin blown films, fibres and nonwoven fabrics having properties comparable to those of corresponding PP and PE samples. Film samples have tensile strength between 30 and 50 MPa, elongation at break around 250%, and puncture resistance, measured as dart drop values, of 12 g/μm. Fibres can be spun to filaments or directly to nonvowen fabrics by spun‐bond techniques. These fabrics have mechanical properties comparable to polypropylene materials. The polymer products are readily degraded in a compost to carbon dioxide, water and biomass.

Compatibilization of blends of polyethylene with a semirigid liquid crystalline polymer by PE‐g‐LCP copolymers

AbstractThe blends of thermoplastics with liquid crystalline polymers show, in general, poor properties because of the lack of adherence between the two phases. The use of ad hoc synthesized copolymers containing the monomer units of the two polymers has been recently considered by some of us for blend compatibilization, and the results appear promising. In this work, new PE‐g‐LCP copolymers, prepared either by the synthesis of the LCP in the presence of a functionalized PE, or by reactive blending of the latter polymer with preformed LCP, have been employed as compatibilizing additives for blends of PE with a semirigid LCP. The morphology and the rheological and mechanical properties of the ternary blends, compared with those of samples without compatibilizers, or containing conventional maleic anhydride grafted PE, indicate that the PE‐g‐LCP copolymers do in fact lead to an improvement of interfacial adhesion, both in the melt and in the solid state, as well as to a modest enhancement of the mechanical properties. The results may be rationalized considering that the PE‐g‐LCP copolymers used by us consist of fairly short PE backbones with LCP grafts of various length. The molecules with longer LCP branches are thought to become mixed at the surface of the LCP particles and to give rise to fairly weak interaction with the PE matrix. It is argued that new PE‐g‐LCP copolymers synthesized from higher molar mass functionalized PE samples might show much better compatibilizing performance.

Crystal hardness and average distance between stable entanglements in melt crystallized polyethylene

Microhardness of a series of linear PE samples with a wide range of molecular weights has been determined. The influence of the mode of crystallization from the melt on the mechanical properties has been examined. It is shown that crystal hardness is correlated to the thickness of the amorphous layer for each series of samples. A new expression which describes the microhardness (H) of polyethylene as a function of the average distance between stable entanglements (knots) s is proposed. A value of s = 360 A, for the mean length between knots in the network is obtained. Analysis of data reveals that the H value can be expressed in terms of the following morphological parameters: 1) average number of chain folds in a lamellar crystal, 2) the nature of the interface between the crystalline and the amorphous layer and 3) the linear crystallinity.

Immobilization of functionalized alkyl-poly(ethylene oxide) surfactants on poly(ethylene) surfaces by means of an argon plasma treatment

Alkyl-poly(ethylene oxide) (PEO) surfactants containing a terminal hydroxyl, sulfate, or carboxylate group were grafted at the surface of poly(ethylene) (PE) samples to improve their blood compatibility. Grafting was achieved by immobilizing PEO surfactants on PE using an argon plasma treatment. The sulfate group containing PEO surfactant was synthesized by sulfating polyoxyethylene(20)stearylether (Brij78®; B) with chlorosulfonic acid. A carboxylate-terminated surfactant was synthesized by a substitution reaction of the sodium alkoxide form of B with sodium iodoacetate. XPS analysis of the modified PE samples showed that at short plasma treatment times of up to 5 s the structure of the immobilized surfactants is largely retained. When plasma treatment times longer than 30 s were applied, the PEO chains of the surfactants were degraded. The wettability of the modified PE samples was improved compared to the unmodified PE samples. The wettability of the modified samples did not change when they were stored in air at room temperature for at least 12 weeks.

Modification of polyethylene properties by implantation with F + ions and iodination

Polyethylene samples implanted with 150 keV F + ions to the doses 10 11 -10 15 cm -2 were doped with iodine by exposing them to iodine vapors at 90°C for 3 h. The iodine depth profiles, measured by Rutherford back-scattering techniques, evolve dramatically with increasing implanted doses, from bumpy profiles at lower fluences to a depleted one comprising two concentration maxima with no iodine in between observed at highest dose. The areal density of iodine incorporated into the 500-nm-thick surface layer is proportional to the ion dose for the doses ≤ 1 X 10 13 cm -2 and it achieves a saturation or declines at higher doses. The results support the concept of enhanced iodine diffusion in the radiation-damaged surface layer and its trapping on the radiation defects within. The sheet resistivity of as-implanted PE is practically constant, independent of the implanted dose. Iodine doping of the ion-implanted PE samples results in immediate, strong decrease of the sheet resistivity by 3-4 orders of magnitude which, however, is not stable. The measured temperature dependence of the sheet resistance indicates p-semiconducting character of ion-implanted and iodinated samples at the temperatures below the PE melting point. The iodine redistribution and/or escape with increasing temperature is observed.