Matériaux composites à base de graves et de liants polymères—IV. Étude des propriétés mécaniques des matériaux réalisés à base de polyéthylène noble

This study concerns mixtures of calcareous, silica-calcareous, basaltic and sandy granules with polyethylene. The polyethylene (PE) is a low density material or a mixture of recovered PE and PE waxes. The compression resistances (RC) of these composits are related to the kneading temperature, the kneading time, the binder ratio and the fluidity index (I.F.). The two most important factors are the PE ratio and its oxidation rate. On the other hand, I.F. and granules nature are less important factors. In all cases the mechanical performances obtained are always better than those obtained with classical bituminous materials.     

Probing Liquid-Liquid Phase Separation of a Polyethylene Blend with Thermal Analysis

Summary: A series of polyethylene (PE) blends consisting of a high density polyethylene (HDPE) and a linear low density polyethylene (LLDPE) with a butene-chain branch density of 77/1000 carbon was prepared at different concentrations. The LLDPE only crystallized below 50 °C, therefore, above 80 °C and below the melting temperature of HDPE, only HDPE crystallized in the PE blends. A specifically designed multi-step experimental procedure based on thermal analysis technique was utilized to monitor the liquid–liquid phase separation (LLPS) of this set of PE blends. The main step was first to quench the system from the homogeneous temperatures and isothermally anneal them at a prescribed temperature higher than the equilibrium melting temperature of the HDPE for the purpose of allowing the phase morphology to develop from LLPS, and then cool the system at constant rate to record the non-isothermal crystallization. The crystallization peak temperature (T_p) was used to character the crystallization rate. Because LLPS results in HDPE-rich domains where the crystallization rates are increased, this technique provided an experimental measure to identify the binodal curve of the LLPS for the system indicated by increased T_p. The result showed that the LLPS boundary of the blend measured by this method was close to that obtained by phase contrast optical microscopy method. Therefore, we considered that the thermal analysis technique based on the non-isothermal crystallization could be effective to investigate the LLPS of PE blends.     

Interfacial adhesion mechanisms in incompatible semicrystalline polymer systems

The mechanism of adhesion at semicrystalline polymer interfaces between isotactic polypropylene (iPP) and linear low‐density polyethylene (PE) was studied with transmission electron microscopy (TEM) and an asymmetric‐double‐cantilever‐beam test. From the TEM images, both the interfacial width and the lamellar thickness of the polymers were extracted. During annealing, the interfacial width increased with the annealing temperature, and this indicated the accumulation of amorphous polymers at the interface. The interfacial strength, determined from the critical fracture energy (G_c), also increased with the annealing temperature and reached a maximum above the melting temperatures of iPP and PE, whereas the smallest G_c value was obtained below the melting temperatures of the two materials. A mechanism of interfacial strengthening was proposed accounting for the competition between the interdiffusion of PE and crystallization of iPP. As the annealing temperature increased, the rates of PE diffusion and iPP crystallization increased. Although the crystallization of iPP hindered the interdiffusion of PE, both the interfacial width and the fracture energy increased with the temperature, and this indicated that PE interdiffusion dominated iPP crystallization. Below the critical temperature, the fracture surfaces of both iPP and PE were smooth, and chain pullout dominated the fracture mechanism. Above the critical temperature, iPP crystallization still hindered the interdiffusion, and crazes could be seen on the iPP side. Above the melting temperatures of the two materials, ruptured surfaces could also be seen on the PE side, and crazing was the fracture mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2667–2679, 2004     

Blends of normal high density and ultra-high molecular weight polyethylene, γ irradiated at a low dose

The kinetics of a nonisothermal crystallization and melting of irradiated with dose of 6 Mrad blends of an ultra-high molecular-weight polyethylene (UHMWPE) and a high-density polyethylene with normal molecular weight (NMWPE) is investigated by means of DSC. The blends have been prepared at temperature below the flow temperature of UHMWPE: The enthalpies of melting of the polyethylenes increase, while those of their blends decrease after irradiation. The enthalpies of crystallization of the pure polyethylenes are higher, while those of their blends almost do not change or are a bit higher after irradiation. The rates of a nonisothermal crystallization and melting of the polyethylenes increase, while those of the polyethylenes in the blends decrease after irradiation. Thermomechanical measurements under constant load in wide-temperature interval of irradiated polyethylenes and their blends have been made. A high-elastic plateau in viscous-liquid state is established on the thermomechanical curves of UHMWPE, and the blends with high content of UHMWPE. On the basis of results obtained assumptions have been made about the processes taking place in the blends under the action of irradiation, as well as about the character of the mutual influence between the components in the process of irradiation.     

Reversible Melting of Thermally Fractionated Polyethylene

Different grades of linear low density polyethylenes (LLDPEs) have been quenched cooled step-wise and crystallised isothermally at (a series of increasing) temperatures in a DSC (thermal fractionated samples). These samples have been investigated by temperature modulated DSC (MDSC). The heat flow curves of the thermal fractionated materials were compared with those obtained from samples crystallised at a relatively slow cooling rate of 2 K min^-1(standard samples). The melting enthalpy obtained from the total heat flow of the thermal fractionated samples was 0-10 J g^-1higher than those of standard samples. The melting enthalpy obtained from the reversing heat flows was 13-31 J g^-1lower in the thermal fractionated samples than in the standard samples. The ratio of the reversing melting enthalpy to the total melting enthalpy increased with decreasing density of the PE. The melting temperature of the endotherms formed by the step-wise cooling was 9 K higher than the crystallisation temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modeling the Fractionation Process in TREF Systems. III. Model Validation With Low Molecular Weight Homopolymers

Low molecular weight semicrystalline homopolymers are used as a model system for temperature rising elution fractionation (TREF) analysis. An already proposed thermodynamic model for TREF analysis is used to characterize TREF fractions from low molecular weight polyethylenes M?_n = 500 to 3000 and some of their mixtures. In this molecular weight range it is possible, under appropriate crystallization, conditions, to form extended-chain crystals, and therefore lamellar thicknesses become comparable to extended-chain lengths. Lamellar thicknesses calculated from TREF spectra permit calculations of the molecular weights of the fractions, up to a limit of about 142 CH₂, where partially folded-chain crystallites appear under these operating conditions. Also homopolymers blends are fractionated and the TREF spectra analyzed to test model predictions. It is shown that appearance of chain folding may set a resolution limit to the analysis of commercial copolymers by TREF. © 1996 John Wiley & Sons, Inc.     

Non-isothermal crystallization of polyethylene blends with bimodal molecular weight distribution

Non-isothermal crystallization of polyethylene (PE) blends with bimodal molecular weight distribution (MWD) was investigated by differential scanning calorimetry (DSC) at various scanning rates. The bimodal PE blends were prepared by blending two unimodal polyethylenes with large difference in molecular weigh in different ratio in xylene solution. Different kinetic parameters such as the half-time of crystallization (t_1/2), crystallization rate constant (Z_c), F(T) and the effective activation energy were determined. Some complicated relationships between these parameters and the average molecular weight were found. The crystallization rate first increased and reached a maximum then decreased, and also correlated with the MWD. The Avrami index under non-isothermal conditions was analyzed with a method developed by Harnisch and Muschik; the results indicated that homogeneous nucleation and spherulitic growth regimes were present in all samples studied.     

Study on the determination of the molecular weight of polyethylene with ultrahigh temperature GPC

Ultrahigh or high molecular weights of polyethylenes (PE) and their distributions are for the first time determined at 160° or 170°C by gel permeation chromatography (GPC). The thermostability of PE at high temperatures is discussed. In order to calculate the real molecular weight of PE, a new calibration curve is established. For PE with high molecular weight more reliable and accurate results can be obtained by GPC measurements at these temperatures. The application of ultrahigh temperature GPC for polymer characterization is demonstrated in this paper.     

Divinyl‐End‐Functionalized Polyethylenes: Ready Access to a Range of Telechelic Polyethylenes through Thiol–Ene Reactions

Telechelic α,ω‐iodo‐vinyl‐polyethylenes (Vin‐PE‐I) were obtained by catalytic ethylene polymerization in the presence of [(C₅Me₅)₂NdCl₂Li(OEt₂)₂] in combination with a functionalized chain‐transfer agent, namely, di(10‐undecenyl)magnesium, followed by treatment of the resulting di(vinylpolyethylenyl)magnesium compounds ((vinyl‐PE)₂Mg) with I₂. The iodo‐functionalized vinylpolyethylenes (Vin‐PE‐I) were transformed into unique divinyl‐functionalized polyethylenes (Vin‐PE‐Vin) by simple treatment with tBuOK in toluene at 95 °C. Thiol–ene reactions were then successfully performed on Vin‐PE‐Vin with functionalized thiols in the presence of AIBN. A range of homobifunctional telechelic polyethylenes were obtained on which a hydroxy, diol, carboxylic acid, amine, ammonium chloride, trimethoxysilyl, chloro, or fluoroalkyl group was installed quantitatively at each chain end.     

Morphological Changes of Linear,Branched Polyethylenes and their Blends during Crystallization and Subsequent Melting by Synchrotron SAXS and DSC

Summary: The crystalline structure and phase morphology of linear, branched polyethylenes and their blends during crystallization and subsequent melting were investigated, using a combination of differential scanning calorimetry (DSC), and synchrotron small angle X-ray scattering (SAXS). A linear polyethylene (PE1) with weight-average molecular weight (M_w) of 114 000 g/mol, and two branched polyethylene copolymers, containing 4.8 mol% (PE4) and 15.3 mol% (PE10) hexane, with molecular weights of 93 000 g/mol and 46 000 g/mol were used as pure samples. Two blends, PE1-4 and PE1-10, each with a weight ratio of 50/50, were prepared by solution blending. Our results indicate that in PE4 a phase separation within the branched component itself occurred, forming a broad distribution of lamellar thicknesses during the crystallization process. PE10 on the other hand did hardly crystallize because of the high degree of branching. Co-crystallization of both components took place in blend PE1-4 and liquid-liquid phase separation occurred in the melt of PE1-10. Morphological parameters were determined by using Bragg's law and the correlation function, respectively. The detected semicrystalline morphology can be well described by the lamellar insertion mode where thin lamellae develop between thicker primary lamellae. During subsequent heating, lamellae melted in the reversed sequence of their formation. The evolution of the structural parameters as a function of temperature revealed that surface melting began at first, and then the complete melting of stacks occurred until the final melting temperature was reached.     

Mesure des capacites calorifiques et des enthalpies de la solution solide AIN-SiC

The AlN-SiC solid solution was prepared by a reaction of powdered silicon, carbon and aluminium nitride at 2000°C. In the molar ratio range from 1 AlN -0 SiC to about 0.5 AlN -0.5 SiC high purity phases with wurtzite structure were obtained.Heat capacities of some mixtures were measured at constant pressure between 313 and 533 K, and also the enthalpy changes between 298 and 453 K. It was observed that addition of small amounts of silicon carbide to aluminium nitride resultedC _p and H values close to those of silicon carbide.

---

Zusammenfassung Durch die Reaktion von pulverisiertem Silizium, Kohlenstoff und Aluminiumnitrid bei 2000°C wurden AlN-SiC- Mischkristalle hergestellt. Im Molverhältnisbereich von 1 AlN - 0 SiC bis 0.5 A1N - 0.5 SiC erhielt man reine Phasen mit Wurtzit-Struktur. Im Temperaturbereich 313–533 K wurden Wärmekapazitäten bei konstantem Druck und im Temperaturbereich 298–453 K auch die Enthalpieänderungen einiger Gemische gemessen. Es konnte festgestellt werden, daß geringe Zusätze von Siliziumcarbid zu AluminiumnitridC _p und H-Werte verursachen, die denen von Siliziumcarbid sehr nahe stehen.

     

Mutual influence of LDPE and PP in their blends during crystallization

An indication for the mutual influence of LDPE and PP was the change of the morphology parameters of PE and PP at different ratios of the polymers in blends. That influence depends on the blend composition and is different for PE and PP. It is especially interesting in the blend PE75/PP25 where the influence between PE and PP shows dependence also on the sample geometry. Melting parameters, non-isothermal crystallization parameters - crystallization peak temperature T_c, crystallization begin temperature T_onset, half-width w_1/2 of the crystallization peak, degree of crystallinity α and crystallization rate coefficient CRC, as well as the isothermal kinetics parameters showed dependence on the blend composition. It was established that PE is more stable then PP concerning the mutual influence of both polymers on their crystallization. It was established that PE affects the crystal nucleation of PP and causes a decreasing of PP spherulite size.     

Etude des spectres d'absorption infrarouge de l'hydroxyde de strontium et de ses hydrates

Résumé L'étude des spectres d'absorption infrarouge de Sr(OH)₂ et de ses hydrates, jointe à l'analyse par A. T. D. et thermogravimétrie a mis en évidence la formation d'une deuxième forme de monohydrate et les diverses liaisons d'inégale force de l'eau dans ces composés: eau d'insertion, eau de cristallisation.

---

Summary A study of the infrared absorption spectra of Sr(OH)₂ and its hydrates, combined with the analysis by differential thermal analysis and thermogravimetry has indicated the formation of a second form of the monohydrate and the various bonds of unequal strength of the water in these compounds: water of intercalation, water of crystallization.

---

Zusammenfassung Das Studium der IR-Absorptionsspektren des Strontiumhydroxids und seiner Hydrate ergab im Zusammenhang mit der thermischen Differentialanalyse und Thermogravimetrie den Nachweis der Bildung einer zweiten Form des Monohydrats und des Vorhandenseins von Wasserbindungen unterschiedlicher Stärke in diesen Verbindungen, und zwar von nichtstöchio-metrischem und von Kristallwasser.

     

Abiotic and biotic degradation of oxo-biodegradable polyethylenes

Conventional polymeric materials accumulate in the environment due to their low biodegradability. However, an increase in the biodegradation rate of these polymers may be obtained with the addition of pro-degrading substances. This study aimed to evaluate abiotic and biotic degradation of polyethylenes (PEs) using plastic bags of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) formulated with pro-oxidant additives as test materials. These packaging materials were exposed to natural weathering and periodically analyzed with respect to changes in mechanical and structural properties. After a year of exposure, residue samples of the bags were incubated in substrates (compost of urban solid waste, perlite and soil) at 58 °C and at 50% humidity. The biodegradation of the materials was estimated by their mineralization to CO₂. The molar mass of the pro-oxidant-activated PE decreased and oxygen incorporation into the chains increased significantly during natural weathering. These samples showed a mineralization level of 12.4% after three months of incubation with compost. Higher extents of mineralization were obtained for saturated humidity than for natural humidity. The growth of fungi of the genera Aspergillus and Penicillium was observed on PE films containing pro-oxidant additives exposed to natural weathering for one year or longer. Conventional PE films exposed to natural weathering showed small biodegradation.     

Crystallization mechanisms for LLDPE and its fractions

The crystallization behavior of two ethylene/octene copolymers, which differ in hexyl branch concentration, and their fractions were assessed. Fractionation of the crystalline linear low density polyethylenes (LLDPEs) was achieved by temperature rising elution fractionation. As the column temperature was raised, the eluted fractions exhibited a reduction in branch concentration and an increase in molecular weight. This was attributed to the difference in reactivity between ethylene and octene and the subsequent depletion of the ethylene monomer in the solution process. Spherulites formed during the crystallization of the whole polymers were well developed, banded, and displayed a wide distribution of sizes. However, spherulites of the LLDPE fractions were less well developed, more uniform in size, and tended to progressively deteriorate and become smaller as the concentration of branches increased. The ethylene and octene blocks of the copolymer crystallized independently, and it was proposed that the octene portion formed short, curved lamellae in the interfacial region of the lamellae formed from the linear ethylene portion of the molecule. Decreases in d spacing for fractions with increased short chain branching corresponded with similar drops in molecular weight.     

Crystallization behavior and morphology of PE-g-LCP copolymers

 This study presents DSC and optical microscopy investigations on copolymers of semiflexible liquid crystalline polymer SBH 112 grafted to functionalized low molecular mass polyethylene (PEox) obtained by melt polycondensation or reactive blending procedures. The crystallization behavior of the PE-g-SBH copolymers has been studied under non-isothermal measurement conditions carried out at different cooling rates. The crystallization temperature (T _cr) of the PE component of the copolymers decreases steadily upon increasing the concentration of the SBH grafts. It was found that the copolymers prepared by reactive blending crystallize at slightly higher T _cr than those prepared by polycondensation and with a higher rate, confirmed by the determination of the crystallization rate coefficients (CRC). The results have been interpreted by the fact that the PE crystallizable segments and SBH grafts of the copolymers obtained by reactive blending are longer than those of the copolymers prepared by polycondensation. The overall nonisothermal crystallization kinetics has been studied by the Harnisch and Muschik equation. The results show that the mechanism of the crystallization of the PE phase changes only when the SBH content overruns ca.50%, due to the decrease of both nucleation and crystal growth rates. The morphology of the copolymers crystallized nonisothermally from melt has been examined by polarization microscopy. Fairly homogeneous morphology with tiny PE spherulites is observed for PE-g-SBH copolymers prepared by polycondensation with SBH as the minor phase. No sign of the dispersed LCP domains can be recognized. On the contrary, the morphology of the copolymers prepared by reactive blending is distinctly biphasic. The allegedly longer PE segments crystallize into tiny spherulites too, but the LC domains formed by the long SBH branches present in this type of copolymers appear clearly in the micrographs at room temperature. It is concluded that the copolymers prepared by reactive blending would be more effective as compatibilizers for PE/SBH blends than those prepared by polycondensation. Received: 9 October 1996 Accepted: 13 January 1997     

Etude du comportement thermique de la poly(pivalolactone) par diffraction des rayons-x aux petits angles et par calorimetrie dynamique

Poly(α,α-dimethyl-β-propiolactone) (PPL), known as poly(pivalolactone), has been studied by differential scanning calorimetry (DSC) and small-angle X-ray diffraction (SAXR). DSC measurements indicate the presence of two melting endotherms. Peak 1 and Peak 2, the latter at lower temperatures. Peak 1 is relatively unaffected by the crystallization temperature and its relative intensity decreases with heating rate. Peak 2 is greatly influenced by the crystallization temperature of the sample and its relative intensity increases with heating rate. Peak 2 is associated with the true melting of the PPL samples and Peak 1 with a recrystallization process during the heating cycle. SAXR long periods increase with crystallization and annealing temperatures. Similar increases in density, in melting temperature, in lamella thickness, and in degree of crystallinity have been observed. These results lead to a thermodynamic melting temperature of 268 ± 3 for PPL, and to interfacial free energies of, respectively. 13 × 10^?7 J cm^?2 and (43 ± 4) × 10^?7 J cm^?2 for the lateral surface and the fold surface of the PPL crystal.     

Séparation de peptides sur couche mince de poudre de cellulose sans liant. 2ème Partie: Séparation par chromatographie à deux dimensions et par chromato-électrophorèse des composants des mélanges de peptides,peptides plus simples et aminoacides qui en dérivent par hydrolyse

Résumé Nous montrons que la chromatographie selon deux directions et des associations de chromatographie et d'électrophorèse en couche mince de poudre de cellulose sans liant sont des méthodes efficaces pour séparer les composants des mélanges du type «peptide, peptides plus simples et aminoacides qui en dérivent par hydrolyse». Ces résultats sont obtenus par des électrophorèses sous faible gradient de potentiel (environ 10 volts/cm), par des chromatographies de partage avec un certain nombre de nouvelles phases mobiles. Le choix du milieu d'électrophorèse tout comme celui du solvant de chromatographie a une influence capitale sur la qualité des séparations. A cette occasion, on montre l'efficacité de certains nouveaux solvants [1] pour la séparation des composants des mélanges de peptides et d'aminoacides.

---

Separation of peptides on binder-free cellulose thin layers. Part II. Two-dimensional chromatography and chromato-electrophoresis of mixtures of peptides and their hydrolysis products (lower peptides and amino-acids)

Summary It is shown that two-dimensional chromatography and association of chromatography and electrophoresis on thin layers of binder-free cellulose powder are efficient methods for the separation of the components of mixtures of peptides and their hydrolysis products (lower peptides and amino-acids). These results are obtained using low-voltage electrophoresis (ca. 10 volts/cm), partition chromatography and new solvents (mobile phases). Choice of solution for electrophoresis and of solvent for chromatography has a most important bearing on the quality of separations. By way of example, the efficiency of some new solvents [1] for the separation of the components of mixtures of peptides and aminoacids is shown.

     

Photodegradation of polyethylenes: Comparative effect of Fe and Ca-stearates as pro-oxidant additives

The effect of iron and calcium stearates on the degradation of polyethylene (LDPE and LLDPE), under natural and artificial exposure, has been studied. The activity of stearates has been evaluated by chemiluminescence and FTIR of polyethylenes. The analysis of the molecular weight changes and content of degradation products identified by GC-MS during ageing process confirmed their pro-degrading activity. Films containing stearates exhibited lower CL emission, and revealed the higher efficiency of Fe-Stearate compared to Ca-Stearate in decomposing hydroperoxides, leading to higher degradation during processing. The results were confirmed by TGA analysis, where the weight loss onset and T_max shifted to lower temperatures in polyethylenes with incorporation of Fe- and Ca-stearates compared to pure polymers.Polyethylenes were outdoor and accelerated exposed, and CL measured at different period of times. Chemiluminescence temperature-ramping tests under nitrogen showed the formation of a peroxide peak at lower temperature, and a significant increase in carbonyl index for PE containing stearates was found by FTIR. The results were supported by GC-MS, where the concentration of extracted products identified in the polyethylenes containing Fe-stearate was significant, and a much greater decrease in molecular weight was determined by GPC, which confirmed the development of degradation for polyethylenes with Fe-Stearates in comparison to pure or Ca-stearate polyethylenes.     

Non-isothermal crystallization kinetics of exfoliated and intercalated polyethylene/montmorillonite nanocomposites prepared by in situ polymerization

Polyethylene/montmorillonite (PE/MMT) nanocomposites, one intercalated sample with higher MMT content and one exfoliated sample with lower MMT content, were prepared by in situ polymerization using MMT-supported metallocene as catalyst. Non-isothermal crystallization behaviors of these two nanocomposites were investigated and compared. The exfoliated sample exhibits higher crystallization temperature (T_c) than the neat PE, showing nucleation effect of MMT. The intercalated sample has lower T_c than the neat PE due to the confinement of MMT. It is observed that the intercalated sample has longer induction period and faster overall crystallization rate, indicating co-existence of suppression and nucleation effects in this sample. The Avrami plots show that the crystal growth of PE in the intercalated sample is two-dimensional, while it is three-dimensional in the exfoliated sample. The crystallization activation energy of the intercalated sample is slightly smaller than that of the exfoliated sample.