Selective localization of organoclay and effects on the morphology and mechanical properties of LDPE/PA11 blends with distributed and co-continuous morphology

Influence of the molecular structure on the melt strength and extensibility of polyethylenes

Melt strength (MS) and breaking stretching ratio (BSR) data relative to polyethylenes with different molecular structure (high density (HDPE), low density (LDPE), and linear low density (LLDPE)) are shown. HDPE and LLDPE samples show high breaking stretching ratio and low melt strength values. The LDPE samples exhibit very large melt strength values but low breaking stretching ratio values. For the last mentioned samples, differences are shown in the non-isothermal elongational behavior between samples polymerized with tubular and vessel technology. For all the samples, MS decreases with increasing melt index while BSR increases with melt index.

Film Nanocompositi Polimerici

Transient response in nonlinear region of molten polymers subjected to a sudden imposition of constant shear stress or constant electric field

Experimental transient results in the nonlinear region are reported for a commercial polyisobutylene subjected to sudden imposition of either a constant shear stress or a constant electric field. Some steady-state results, eventually obtained in different types of experiments, are also considered. In both cases, a model analysis is presented that accounts for the nonlinear effects through changes in the free volume depending upon the applied stress. The good comparison between theoretical predictions and experimental results seems to indicate that the phenomenological approach advanced here is very promising.

Mechanisms of polymer crystallization from flowing solutions

The recent experimental results on flow-induced crystallization by Pennings and coworkers show that extremely rigid polyethylene fibers can be obtained in a shear flow. On the other hand, the mechanism by which these flow-induced crystals are produced is still open to investigation. In this work a few aspects of fibrous crystal growth are theoretically investigated. The molecular dynamics of chains partly attached to the crystal and partly immersed in the solution is considered. The influence of temperature and of geometrical factors is also discussed.

Dynamic-mechanical and dielectric measurements have been performed with some polycarbonate samples. In one set of experiments care was taken to avoid any absorption of moisture. In other sets of experiments, samples were exposed to atmospheric humidity and to boiling water. The glass transition temperature was found to be highly affected by the absorption of water and by the test conditions. Dynamisch-mechanische und dielektrische Messungen wurden an Polycarbonatproben durchgefuhrt. In einer Versuchsserie wurde die Absorption von Wasser vollstandig vermieden, in weitern Versuchen wurden die Proben der Luftfeuchte bzw. kochendem Wasser ausgesetzt. Die Glasubergangstemperatur wurde durch das …

SHEAR BEHAVIOUR OF MOLTEN LINEAR LOW DENSITY POLYETHYLENE.

The rheological behaviour of molten polyethylene has been widely studied especially with respect to the different structure of the high density and low density samplesI–I0. In particular it is well known that the presence in the LDPE of long chain branching alters dramatically the whole flow curve, the activation energy, the die-swell, the instability phenomena, etc.

Elongational behavior of low density/linear low density polyethylenes

Rheological data have been collected in isothermal elongational flow for three different types of blends, made from one low density polyethylene and three linear low density samples. In addition to the transient curves, elongation at break data are also reported. The influence of the composition and of the molecular weight of the linear low density polyethylene is discussed.

EFFECT OF DRAWING ON THE STRUCTURE AND THE DYNAMIC-MECHANICAL BEHAVIOR OF SALTED POLYCAPROAMIDE.

Abstract Structural determinations, obtained through density, birefringence, and WAXS measurements, are reported for nylon 6/inorganic salt fiber samples as a function of draw ratio. They confirm the possibility of achieving very high amorphous orientation in these systems. Dynamic-mechanical data have also been collected which allow determination of glass transition temperatures. These are also discussed in terms of structural parameters.

Torque-rheometry investigation of model transreactions involving condensation polymers

High barrier properties HDPE/PA6/MMT Films-Preliminary rheological and morphological studies

Model analysis of uniaxial and biaxial stretching of polymer melts

The biaxial extension results byDenson et al. are compared with the predictions of a model of non-linear viscoelasticity. Date of uniaxial extension on the same material (a commercial polyisobutylene) are taken for extending the comparison. The model used seems to adequately describe both types of elongational flow with the same value of the single adjustable parameter.

Transient birefringence of polymer melts in intermittent shear flow: Model analysis of the non-linear viscoelastic behaviour

A non-linear viscoelastic model has been used to interpret transient flow birefringence in changing shear flow for a polymer melt. It is shown how the new model is consistent with the basic hypothesis of the linear stress-optical law. Stress growth in shear flow and relaxation after different amounts of shearing are compared with the predictions of the non-linear model. A good agreement between experimental data and theoretical predictions is found.

Constant stretching rate experiments on low density polyethylene

A simple apparatus for elongational test of molten polymers is presented. Its realiability is demonstrated by means of stress growth in constant stretching rate experiments and relaxation test on a low density polyethylene sample.

The viscoelastic behavior of nylon 6/lithium halides mixtures

Stress-relaxation experiments in the limit of small deformations have been carried out in a wide range of temperatures for pure nylon 6 and its mixtures with LiBr and/or LiCl. Master curves have been constructed, by allowing horizontal shifts only, showing the shape typical for semicrystalline polymers in the case of pure nylon and that of essentially amorphous polymers in the case of salted samples. The glass transition temperatures determined from the plot logaT− 1/T is increased when in the presence of salts. All such effects are considered to reflect the binding action of Li+ and Br− ions.

The rheological behaviour of HDPE/LDPE blends. II. Die swell and normal stresses

Die swell data are presented for different high-density/low-density polyethylene blends. The data relating to samples with frozen-in stresses are represented, collected as a function of the usual operational parameters (L/D ratio, flow rate, temperature). Data obtained with annealed samples are used to derive, through a theoretical approach, normal stresses. Die Strahlaufweitung wurde fur verschiedene Mischungen aus Polyethylenen hoher und niedriger Dichte gemessen. Die an Proben mit eingefrorenen Spannungen erhaltenen Werte wurden in Abhangigkeit von technologischen Parametern (Lange/Durchmesser-Verhaltnis, Fliesgeschwindigkeit, Temperatur) dargestellt. An getemperten Proben gemessene Wert…

The role of organoclay in the morphology modification and in the properties in polyethylene/polyamide blend systems

Extensional flow of HDPE/LDPE blends

Elongational viscosity data, obtained through the converging flow analysis by Cogswell, are presented for two types of HDPE/LDPE blends at various compositions and different temperatures. The results relative to the homopolymer parents compare favourably with literature data obtained also with different and more sophisticated techniques. Those relative to blends show peculiar features for the two cases: when the newtonian viscosity of the LDPE is higher all the blends show a behaviour typical of the LDPE with a maximum in η el /η0 enhanced at small percentage of HDPE; when the newtonian viscosity of the LDPE is similar to that of the HDPE there is only a gradual change in the properties.

Effect of a filler on the dielectric properties of an epoxy resin

The effect of aluminum hydroxide upon the dielectric properties of an epoxy resin has been studied in a wide frequency and temperature range. An interfacial polarization effect, known as the Maxwell–Wagner–Sillars polarization is evidenced for the filled resin, which shows a higher permittivity, a higher dielectric loss, and a β transition with a larger relaxation time. The glass transition temperature is, on the contrary, mostly unaffected by the presence of the filler.

A procedure is described for the preparation of a block copolymer with A-B-A sequences in which ω-ω′-dihydroxy-poly-(ethylene glycol) is inserted between two polymeric monoacidic chains of polycaproamide and bonded to them by means of ester links. The resulting material was characterized. The copolymer is isomorphous with the polycaproamide. Thermal treatments induce a crystalline transition γ α as in polycaproamide. The influence of the moisture content on the glass transition temperature and on the storage modulus is discussed. Ein Verfahren zur Herstellung eines Blockcopolymers mit A-B-A-Sequenzen wird beschrieben. In dem Copolymer ist ω-ω′-Dihydroxy-polyethylenglycol uber Esterbindungen…

The non-isothermal rheological behaviour of molten polymers: Shear and elongational stress growth of polyisobutylene under heating

Data of stress growth under both shear and elongational kinematics have been taken in presence of heating temperature ramps on a commerical polyisobutylene.

THERMOTROPIC HOMOPOLYESTERS. IV. STUDY OF FIBER FORMATION.

We report a melt spinning and viscosity study of two semiflexible homopolyesters containing both rigid and flexible segments in the repeating unit. Single filaments of the polyesters formed from 4,4′-diacetoxybiphenyl and azelaic acid (PB7) and sebacic acid (PB8), and from 4′-hydroxyphenyl-4-hydroxycinnamate and azelaic acid (C7), were spun at temperatures between 205 and 255°C. The temperature dependence of the Newtonian melt viscosity of PB7 and C7 was investigated, and a range of molecular weights was studied for PB7. The spinning parameters, fiber characteristics, and viscosity-temperature behavior are related to the type of mesophase formed. The mechanical properties of fibers spun fro…

Influence of molecular weight on the creep behavior of undiluted polyisobutylenes

The elongational behavior in constant force experiments has been considered for three samples of commercial polyisobutylene. The results compare favorably with the predictions of two existing non-linear theories as long as the samples deform homogeneously. Some qualitative observations have been made with reference to the “failure point”, i.e., the point where a non-homogeneous deformation begins.

Physical and structural characterization of blends made with polyamide 6 and gamma-irradiated polyethylenes

Abstract Morphological, calorimetric and rheological results of blends made with polyamide 6 and polyethylene gamma irradiated in air are presented. The polar oxidized groups grafted in the poliolefin chains through gamma-radiation induce “compatibilization” effects in the blends with a more uniform and finer distribution of the polyethylene “phase” in the polyamide matrix, with respect to blends made with the unirradiated polymer. This effect, observed with polyethylenes of different molecular structure, i.e. low density, linear low density and high density, was attributed to the presence of interactions among the functional oxidized groups of the polyethylene chains and the polyamide. Tes…

Non-Isothermal Effects in the Elongational Flow of Polymer Melts

Non-isothermal histories occur in almost all polymer processing, and however only a few experimental and theoretical studies have been devoted to the rheological response of the polymeric fluids under non-isothermal conditions. A systematic study, which cannot however be considered exhaustive, has been recently carried out in this field by Bogue and coworkers1–3.

Dielectric properties of a filled epoxy resin: Effect of thermal treatments

Dielectric measurements have been performed at several frequencies on samples of a cycloaliphatic epoxy resin filled with aluminum hydroxide. The samples were thermally treated at three different temperatures for times up to 2,000 hours. At low aging temperatures and times an improvement of the characteristics is observed due perhaps to an assessment of the bulk of the polymer and more precisely to a change in the free volume. At high temperatures and times a thermo-oxidation involving layers deeper and deeper becomes the predominant mechanism responsible of the decrease in the properties with respect to the virgin material.

Preparation and mechanical characterization of fibres from a new copoly(ether-ester-amide) are reported. The mechanical characteristics are slightly lower than those of polyamide 6, but satisfactory for textile use, and the fibres have larger moisture absorption. This gives rise to more comfortable fibres preventing the accumulation of electrostatic charges. Die Herstellung und mechanische Charakterisierung von Fasern aus einem neuen Copoly(ether-ester-amid) werden beschrieben. Die mechanischen Eigenschaften sind etwas schlechter als die von Polyamid 6, aber ausreichend fur textile Anwendungen. Die Fasern weisen eine grosere Feuchtigkeitsabsorption auf. Dies fuhrt zu einem angenehmeren Verh…

Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride

Nylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x-ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high-modulus fibers after subsequent crystallization. Also, t…

Macro-oriented network of liquid-crystalline polyesters: crosslinking induced by g-irradiation and thermally activated reaction.

Abstract The synthesis of a macro-oriented network from liquid-crystalline polymers, bearing pendant groups with unsaturations, is reported. Virgin polymers are processable to obtain oriented samples, e.g. fibres, which may be crosslinked through thermal activation and/or exposure to γ-radiation. The liquid-crystalline state is “frozen” and the macroscopic anisotropy is preserved even at high temperatures. Compared to virgin fibres, irradiated samples show an enhancement of tensile performances, thus indicating that the main effect of irradiation is crosslinking without significant degradation phenomena.

The effect of the composition on the properties of?-irradiated ethylenevinyl alcohol copolymers

Two ethylene-vinyl alcohol copolymers (Eval E and Eval F with about 45% and 25% of ethylene respectively) have been irradiated in air in the dose range 0–200 Mrad. The irradiated samples show both crosslinking and degradation; the former effect is more relevant in the copolymer with a larger content of polyethylene. Calorimetric results show that both the crystalline and the amorphous phases are involved in the reactions initiated by the irradiation.

Dilute solution rheology of flexible macromolecules (bead–rod model)

The rheological behavior of dilute solutions of flexible macromolecules is studied by means of a freely jointed multiple bead–rod model. The solution of the equations describing the mechanics of the system is obtained by means of a numerical procedure, which applies to arbitrary flow conditions. The case of the transient stress in uniaxial elongational flow is developed in some detail. A comparison with bead–spring models shows both quantitative and qualitative differences which are briefly discussed.

Optimization of spinning, drawing, and annealing conditions in the production of highly oriented fibers from the polycaprolactam/3.7% LiCl system

A polycaprolactam/3.7% w/w LiCl system, obtained by anionic polymerization of caprolactam directly in the presence of salt, has been employed for the production of highly oriented fibers. More particularly, an optimization of spinning, drawing, and annealing conditions has been performed, finally obtaining fibers which shows very satisfactory mechanical results. Namely, average moduli values up to 12 GPa and strength values up to 1 GPa when fracture is far from clamps, have been observed.

An experimental investigation of the shear behaviour of polyethylenes with different structures

Rheological properties in shear flow are presented for four different polyethylene samples: a high density, a linear low density and two low density polyethylenes manufactured using different techniques. Tests have been performed with the aid of capillary types of instrument equipped with capillaries of various lengths at three different temperatures. End correction factors have been determined and true flow curves obtained. Swelling ratios for both unannealed and annealed samples have been determined as well as the shear rate and shear stress at which irregularities begin. In some cases generalized plots have been prepared and in all cases the rheological response is discussed in terms of …

Structural modifications in an irradiated ethylene-vinyl alcohol copolymer

Extraction experiments and calorimetric measurements have been performed, on a commercial ethylene-vinyl alcohol copolymer irradiated in the dose range 0–20 Mrad.

Dielectric behaviour of a γ-irradiated polycarbonate

Dielectric measurements on a γ-irradiated polycarbonate in a dose range 0–20 Mrad and at test frequencies of 103 and 104 Hz have been carried out. The glass transition temperature shows a maximum at 3.5 Mrad and then decreases at larger doses. This result is in line with other experiments (intrinsic viscosity, dynamic-mechanical measurements, etc) already reported: the Tg values are however larger in the present results. This is probably due to the plasticizing action of the absorbed moisture present in the previous tests. A Tg vs 1/[n]2 plot (1/[n]2 is proportional to 1/m ) allows to find the value of the glass transition point at an infinite molecular weight and the dependency of Tg on mo…

Elongational flow of dilute polymer solutions

In this work, elongational viscosity data obtained for dilute solutions of Separan NP 20 in glycerol, are presented. The data are taken under transient stress conditions with two different experimental techniques.

The role of the clay in morphology modification of the uncompatible polymer blends

EFFECT OF MOISTURE ON THE BULK PROPERTIES OF SALTED POLY(CAPROAMIDE).

The glass-transition temperature (Tg) and the elastic modulus of nylon-6 and its mixtures with 4% w/w LiCl and with 2% LiCl+3% LiBr were investigated. In one set of experiments care was taken to avoid absorption of moisture during the measurements. In another set of experiments, samples were exposed to atmospheric humidity for different lengths of time. Both unoriented and oriented specimens were investigated. The presence of 4% LiCl almost doubles the amount of moisture absorbed at equilibrium by nylon-6. The Tg was found to be greatly affected by the moisture content and by salt type. When strict precautions to exclude moisture are taken, the addition of 4% LiCl raises the Tg of nylon-6 b…

Increasing the elastic modulus of polyamides

Melt Strength and Extensibility of High-Density Polyethylene

The extensional flow of polymer melts has been extensively studied because of its importance in many technological processing operations and, from a more fundamental point of view, because the tensile properties of the polymer melts cannot be correlated directly with shear viscosity behavior.1–5

The rheological behaviour of HDPE/LDPE blends

The rheological behaviour of three types of HDPE/LDPE blends at several compositions (various weight percentages of LDPE) has been studied with the aid of a capillary rheometer and three different capillaries.

Effects Of Adding New Low Molecular Weight Phosphazene Compounds To PBT/Ny Blends

Influenza di argille organomodificate su morfologia e proprietà di miscele polimeriche polietilene/poliammide

Shear behaviour of undiluted polyisobutylenes

Some new data in shear flow are presented for two commercial polyisobutylene samples, namely Vistanex LMMH and L 100. In particular beyond a few steady state results, the tangential stress build-up after a sudden imposition of a shear rate and the decay after cessation of steady shear flow have been collected. The data are used to further test a constitutive equation already advanced by some of the authors. The comparison seems to confirm the validity of the proposed model, whose single adjustable parameter is shown to be independent of molecular weight.

The rheological behavior of HDPE/LDPE blends 4. Instability phenomena in capillary flow

Experimental data, relative to instability phenomena in capillary flow, have been collected for HDPE/LDPE blends already characterized from a rheological viewpoint. The data comprise morphological observations as well as the determination of critical parameters as a function of the blend composition and of the processing conditions.

Testing of a model for the non linear electric behavior of polymeric materials

Some experimental results relative to a molten polymer (a commercial polyisobutylene) in d.c. and a.c. tests are presented.

The glass transition behaviour of salted nylon 6

Glass transition measurements of nylon-6/lithium halides mixtures have been carried out in wide range of frequency with the aid of different experimental techniques. The results show an increase of the glass transition temperature when the salt is present and prove the larger effectiveness of lithium chloride with respect of lithium bromide. This effect, in line with the large reduction of the specific volume caused by the salt, is due to the formation of a pseudo-cross-linking between lithium ions and the carbonyl-oxygen groups of the polyamide.

Theoretical predictions from a non-linear model based on the free volume concept, which were previously tested only with a molten polymer, are presented and compared with literature data of solid polyethylene. The agreement is good both when a steady state is reached in the experimentally explored times and when, on the contrary, the data do not show it. Theoretische Berechnungen des elektrischen Verhaltens von Polymeren anhand eines nichtlinearen Modells, die auf dem Konzept des freien Volumens basieren und bisher lediglich an einem geschmolzenen Polymer getestet wurden, werden vorgestellt und mit Literaturdaten von festem Polyethylen verglichen. Die Ubereinstimmung ist gut, wenn in den ex…

Ruolo della reologia nelle evoluzioni morfologiche di miscele polimeriche immiscibili nano composite

Rheological characterization of polycaprolactam anionically synthesized in the presence of lithium chloride

Melt viscosity and dynamic-mechanical data are reported for samples obtained by anionic polymerization of caprolactam, in the presence of LiCl. The full body of results is essentially in line with those previously reported relative to mixtures of inorganic salts and commercial nylon 6, In particular a drastic-decrease of the melting point and of the rate of crystallization is confirmed as well as an increase of the glass transition temperature and of the melt viscosity. Some quantitative differences exist, which may be attributed to the different molecular weight distribution in the polymers employed in the present work.

Effect of adding new phosphazene compounds in polybutylenetherephtalate/polyamide blends

Photo-degradation behaviour of OMMT-filled PE/PA blends: improvement of the photo-resistance through morphology modification