Monoaxial drawing behaviour of isotactic polypropylene quenched at different temperatures

Quenched films of isotactic polypropylene were obtained in different quenching conditions; the films structure was analyzed in terms of phases composition and gross morphology. The mechanical behaviour, analyzed at room temperature in monoaxial drawing shows that the initial structure strongly affects the drawing behaviour. The drawing occurs by necking propagation in all the samples, but the deformation in the neck depends on the gross morphology while the drawing load depends on crystallinity. The obtianed results are discussed on the basis of the molecular and structural model of the fibers formation by drawing of crystalline polymeric films.     

Drawing behavior of cross-linked isotactic polypropylene

The drawing behavior of cross-linked isotactic polypropylene was analysed. The crystallinity and the composition of the crystalline phase are affected by cross-linking. Structural and topological features play a significant role in the drawing behavior. The yielding, the necking phenomenon, and the ultimate properties, i.e., stress and strain at the fracture, can be correlated with the sample structure. The general picture agrees well with Peterlin's model of cold drawing.     

Melt drawing as a route to high performance polyethylene

Well established routes for obtaining stiff and strong polyethylene (PE) involve solid state drawing either of solution crystallized gel films or melt crystallized spherulitic PE. The aim of this work is to show the potential of melt deformation as an alternative route for obtaining highly oriented products. Our previous work on the melt deformation route showed that oriented PE fibers could be directly extruded under appropriately controlled conditions [8,9]. Here, we show that PE films (or filaments) can also be melt drawn in the temperature window 130–160 °C, thus yielding oriented products. The advantage of melt drawing over direct melt extrusion is that it allows a wider operational latitude and thus does not require such carefully controlled conditions.The morphology produced by melt deformation is different from solid state deformation and consists of extended chain fibrils with platelet overgrowths. The relative amount of fibrils and platelets depends on operating parameters. The temperature window of PE melt drawing is identified with the regime where some flow induced crystallization takes place. The conditions for melt drawability are of wider generality for crystallizable flexible chain polymers. They are: (i) adequate strain rate to overcome entropie resistance to chain extension, (ii) but not high enough to activate the elastic response of the transient networks in the entangled system, (iii) sufficient strain to fully extend the chain, (iv) appropriate temperature for flow-induced crystallization and strain hardening, and (v) cooling to freeze the oriented structure.Ultra high molecular weight PEs were not the most suitable for melt drawing due to their high recoverable elongation in the melt (melt elasticity) in addition to added limitations imposed by their nascent grain systeme. Our work suggests that an optimum molecular weight for melt drawing is¯M _w(400–900)×10³ with further possibilities for improvement through multimodal distributions.     

The spinnability of viscoelastic solutions of tetradecyl- and hexadecyl-trimethylammonium salicylates

The spinnability was measured for aqueous viscoelastic solutions of tetradecyl- and hexadecyltrimethylammonium salicylates (C₁₄TASal, C₁₆TASal) in the absence and presence of sodium salicylate (NaSal) and sodium bromide (NaBr). The spinnability is classified into two types, D and C. While the intrinsic drawing length in type D is proportional to the drawing velocity, the drawing intrinsic length in type C decreases with the drawing velocity or is independent of it. The spinnability changes from type D to C, as the drawing velocity and the surfactant concentration increase, and the temperature lowers. The effect of salt is different between NaSal and NaBr. It can be assumed that a pseudo-network structure composed of rod-like micelles is formed in viscoelastic and spinnable surfactant solutions. Then, the spinnability depends on the balance between the elasticity and the viscosity in which the structure results.     

Drawing and extrusion of semi-crystalline polymers

This review treats mainly the initial transformation of the starting unoriented lamellar material into the final oriented microfibrillar structure and its drawing. If the starting material has partially oriented shish-kebab structure the drawing is a combination of transformation of lamellae into the microfibrils and the drawing of microfibrils. The review article is based on the literature from the last ten years and relys heavily on recent reviewing [1–3]. Older articles are only included if they have contributed to the basic ideas and experiments of drawing.     

Adhesive effect of low-density polyethylene gels on polyethylene moldings

Adhesive effect of low density polyethylene (LDPE) gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, electron microscopy, and DSC measurements. When heated at 110°C for 2 h, all of the gels showed strong adhesive strengths around 30 kg/cm², which is sufficiently strong for practical uses. It has been found that the adhesive strength increases with the heating temperature and that the temperature at which the heated gel begins to exhibit the adhesive effect depends upon solvents and is about 30° lower than that of the HDPE gels.     

Diffusion-based adhesive bonds between phases in fibrous composites

In this paper the mesophase developed between main phases in fibrous composites was studied assuming that it constitutes a diffuse boundary. This type of mesophase is normally developed in polymer-polymer adjacent phases and it it useful for the study of modern composites disposing a coupling agent between main phases. At the high temperature of reaction of phases during the casting process both neighboring phases are partly liquified, allowing a two-way movement of elements of either phase whose intensity and extent depends on the particular diffusion characteristics of either phase and the affinities between them.The characteristics of this diffusion reaction were studied and their influence on the development and the properties of the adhesion between phases were established, especially for fiber composites. Interesting results were derived concerning the extent of the diffusive mesophase and its mechanical properties, as well as its contribution on the global mechanical behavior of the composite. Finally, the results were found to be in agreement with previously established models.     

Thermoplastic elastomers by hydrogen bonding 4. Influence of hydrogen bonding on the temperature dependence of the viscoelastic properties

The temperature dependence of the viscoelastic properties of thermoreversible polybutadiene networks based on hydrogen bond linkages is analyzed from the logarithmic shift factors loga _T . For binary hydrogen bond complexes thermorheologically simple behavior is observed. The temperature dependence of loga _T is described by the Williams-Landel-Ferry (WLF) equation. The thermoreversible linkages cause an increase in the apparent activation enthalpy of flow which is related to the number of complexing sites in the polymer. Thermorheologically complex behavior is observed in a system with more complex association.     

A real-time drawing study on solution-crystallized UHMW-polyethylene — comparison with conventional x-ray results

Solution-crystallized ultra-high molecular weight polyethylene (UHMW-PE) can be drawn in the solid state to very high draw ratios, leading to materials with excellent mechanical properties. Very recently, the drawing process has been studied via different x-ray techniques, on the basis of which a deformation mechanism was proposed which could satisfactorily explain all observations. However, like most deformation studies performed in the past, the measuring conditions were quite different from the actual drawing conditions. Cooling drawn samples to room temperature as well as relieving the stretching force may give rise to the introduction of artefacts, leading to misinterpretation of the results. In order to exclude this possibility an x-ray study was performed on solution-crystallized UHMW-PE in real time, i.e.,during the deformation process, using the benefits of synchrotron facilities. Comparison of these results with x-ray results obtained via the conventional method shows that the latter method can be used without any problems for a qualitative study on the solid state drawing of ultradrawable UHMW-PE. One of the major advantages of the real-time method is the possibility to study the initial elastic deformation region.Presented in part at the Rolduc Polymer Meeting-2, April 1987, Kerkrade, The Netherlands.     

Deformation behavior of oriented UHMW-PE fibers

The mechanical behavior of gel-spun, ultra-drawn, UHMW-PE fibers was investigated as a function of temperature, stress, and time under static and dynamic loading conditions. From a phenomenological point of view, two separate contributions to the deformation behavior could be distinguished, i.e., a reversible (viscoelastic) contribution and an irreversible plastic flow component. It was investigated whether or not this distinction can be rationalized on a molecular basis. The fibers were studied using static (creep) and dynamic mechanical analysis (DMA), dilatometry, and wide-angle x-ray scattering (WAXS). The results of the combined experimental observations are discussed in an attempt to relate the deformation behavior of highly oriented PE fibers to events occurring on a molecular scale.     

SAXS investigation on the influence of oil dilution on morphological changes in a SBS block copolymer during the first draw cycle

Spin-cast films of one pure SBS and two oil-extended SBS samples were observed during first cycle drawing in the synchrotron radiation beam at Hasylab. For evaluation, from a two-dimensional Vidicon scattering picture the scattering curve was extracted by intersecting perpendicular to the observed layer lines. Using a method described in a preceding paper [1], the scattering curve is analyzed by fitting to one-dimensional two-phase models. Essential for a fit with parameters of physical sense is the assumption of at least two components. One of these two main components is identified with fibrils containing PS cylinders, the axes of which are orientated parallel; the other is identified with fibrils containing cylinders transverse to the drawing direction.For the mechanical properties of the thermoplastic rubber this splitting of cylinder orientation in the drawn state seems to be of some importance. Only the cylinders of the longitudinal component turn out to be rigid, while the cylinders of the transversal component appear to yield and even break.The amount of cylinders allotted to each of the two components in the drawn state varies as a function of the diluent. An extrapolation of topological parameters back to the undrawn state indicates a possible reason, a fair variation of the cylindrical particle dimensions within a lattice cell of only slighly varying dimensions. While paraffinic mineral oil dilution causes the cylinders lengths to decrease, thus improving cylinder orientability within the pseudo lattice cell, aromatic oil dilution increases the particles diameters.A remaining faint contribution to the scattering pattern that produces the layer lines is suggested not to be caused by a periodic structure, but by a single and precisely defined polybutadiene matrix length (string) between two PS cylinders with a considerable height variance.     

Effect of coexistent hydrocarbon phase on the volume behavior of adsorbed film and micelle of dodecyltrimethylammonium chloride

Interfacial tension () between aqueous dodecyltrimethylammonium chloride (DTAC) solution and benzene was measured as a function of pressure (p) and concentration. The/p was observed to change discontinuously at the critical micelle concentration; this indicates that the micelle formation of DTAC in the aqueous solution coexisting with benzene can be treated like the appearance of a macroscopic phase. It was shown by drawing the vs.A curves that hydrocarbon, such as benzene, cyclohexane, and hexane, make the adsorbed film of DTAC expand. The volume behavior of the micelle with benzene molecules solubilized was found to bear a strong resemblance to that of the adsorbed film at the water/benzene interface. The difference in the molar volume value of adsorbed DTAC among the coexistent hydrocarbon phases was attributed to the difference in the contribution of the hydrocarbon molecules to the interfacial excess volume; the number of the solubilized hydrocarbon molecules was evaluated to be one or two a micelle.     

Miscibility behavior of ternary lipidphospholipid/water systems

Differential-scanning-calorimetry was applied to study the lyotropic and thermotropic properties of the two ternary systems dimyristoylcephaline (di-(C14:0)-PE)/Palmitic acid (C₁₅COOH)/water (H₂O) and dimyristoylcephaline (di-(C14:0)-PE)/palmitic acid methyl ester (C₁₅COOMe)/water (H₂O) in dispersions with excess water (50 wt.%).The phase diagrams of both systems showed that the two systems differ in their miscibility behavior. The system di-(C14:0)-PE/C₁₅COOH/H₂O is completely miscible in its high-temperature phase. In the low-temperature phase the mixing gap was found within the concentration range of C₁₅COOH and was also indicated by a maximum value of the transition enthalpy of the pseudo-binary mixtures.In the pseudo-binary system di-(C14:0)-PC/C₁₅COOMe/H₂O, the tendency towards demixing is much more pronounced. It was observed that the incorporated C₁₅COOMe melted above its normal melting point, but below the transition temperature of di(C14:0)-PE/H₂O system; therefore, the phase transition started at lower temperature. In the low-temperature phase, both lipids are partially miscible. The demixing range of the phase diagram lies within the concentration region of C₁₅COOMe. Up to the mole fraction ofXC₁₅COOMe=0.43, C₁₅COOMe can be incorporated into theL-phase of the system di-(C14:0)-PE/H₂O.     

Adhesive effect of high density polyethylene gels on polyethylene moldings

Adhesive effect of polyethylene moldings by use of high density polyethylene gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene was investigated by shearing tests, electron microscope, and DSC measurements. All of the gels showed such a strong adhesive strength over 36 kg/cm² that polyethylene plates of 3 mm in thickness gave rise to necking sufficient for practical use, when heated at 120 °C for 2 h. In particular, the gel in tetralin showed a strong adhesive strength when heated at 110 °C. It was found that adhesive strength increases with the heating temperature; the temperatures at which adhesive strength begins to increase differ depending on the type of polyethylene sample and solvent. It is apparent that polyethylene gels exhibit an adhesive effect when they are heated at higher temperatures than the gel melting temperatures, and that the closer the SP values of solvents used for the gelation are to the molded polyethylene, the stronger the adhesion of the polyethylene molding.     

Theoretical study of dielectric behavior of microcapsule suspensions with distributed drug release rate

Theoretical consideration is made concerning the dielectric behavior of aqueous suspensions of W/O-type microcapsules containing aqueous electrolyte solutions, especially concerning distribution effects of the electrolyte release rate on the dielectric behavior.It is shown at first that the distribution of the release rate causes electrical conductivity of the capsule interior. Next, it is deduced, in the light of a theory of the interfacial polarization, that the distribution characteristics of the capsule interior's electrical conductivity are closely related to those of the relaxation time for a dielectric relaxation exhibited by the suspensions. Several formulas are derived to describe the relation between the distribution characteristics of the release rate and those of the relaxation time.     

DSC experiments on gel-spun polyethylene fibers

The tensile strength of gel-spun polyethylene fibers obtained after hot-drawing depends on spinning conditions such as spinning speed, spinning temperature, spinline stretching, polymer concentration, and molecular weight/molecular weight distribution. High deformation rates in the spinline result in shish-kebab structures which after hot-drawing lead to fibers with poor properties. This is in contrast to hot-drawn fibers obtained from gel-spun fibers with a lamellar structure. Lamellar or shish-kebab structures in the gel-spun fibers can be distinguished by means of DSC experiments on strained fibers. On the basis of these experiments a qualitative prediction of the final tensile properties can be made. DSC experiments on (un)strained hot-drawn fibers show that in the case of shish-kebab structures an incomplete transformation into a fibrillar structure takes place which partly explains the low tensile strength. Chain slippage which becomes possible after the orthorhombic-hexagonal phase transition is involved in the fracture mechanism. The shift of the orthorhombic-hexagonal phase transition to higher temperatures with increasing tensile strength indicates that the increase in strength corresponds to an increase in length of the crystal blocks. Consequently, creep failure also occurs at higher stresses. The melting behavior of cold-drawn and hot-drawn fibers is qualitatively similar, but the transformation into a fibrillar structure is more complete in the latter case.     

Interfacial effects on the ageing behavior of high density polyethylene filled with glass spheres

The stress relaxation and creep behavior of unfilled high density polyethylene (HDPE) and HDPE filled with untreated and surface-treated glass spheres were measured at room temperature. A silane-based coupling agent capable of providing a covalent bond between HDPE and the glass spheres was used for the surface-treatment. Two different amounts of the coupling agent were employed giving silane layers on the fillers with different thicknesses. The effect of ageing time at room temperature on the viscoelastic properties after quenching from 100 °C to room temperature in ice water was also investigated. The effects of the surface treatment of the fillers and the ageing time was characterized by means of the internal stress ( _i ) concept. The _i -value increased with the degree of interaction of the filler/matrix interface and the ageing time. It was here not possible to superimpose the different flow curves with regard to the ageing time with sufficient accuracy. This is due to the variation of _i with ageing time. The surface-treatment of the filler had a marked effect on the creep behavior at high applied stress levels and on the ageing behavior of the composites, presumably due to the formation of an interphase region close to the filler surface with different properties and different ageing characteristics than that of the bulk of the matrix.     

Drug-carrying latices for prolonged release of drugs

Dichlorophene was used as a model drug. Drug-carrying latex particles were prepared by soap-free emulsion copolymerization of dichlorophene acrylate with some hydrophilic methacrylate comonomers. The comonomers used affected not only the structure and colloidal stability of particles, but also the drug-activity of particles. Preliminary study of the drug activity revealed that highly hydrophilic latex particles were very stable and too inactive to be engulfed by amoebae and kill them. On the contrary, less hydrophilic particles carrying a large amount of drug can be an effective device to release drugs at a moderate rate to fight against extracelluar targets such as parasites.     

The effect of the N-B transition of bovine and human serum albumins on the binding sites of fluorescent probes

The N(neutral)-B(alkaline) transition of bovine serum albumin (BSA) and human serum albumin (HSA) was investigated with three anionic and one cationic dansyl (dimethylamino-naphthalenesulfonyl, DNS) probes. The N-B transition of the HSA-probe complex was characterized by a large enhancement of the fluorescence intensity of the dansyl group, accompanied by a blue-shift of the maximum wavelength in the emission spectra, and large changes in the thermodynamic parameters of the binding process. Contrary to this, such changes were not observed for the BSA-probe complex. It is suggested that the conformational adaptability of HSA to the probes at the binding site increases in the B conformation, although the nature of the site on BSA is hardly affected by the transition.     

New conducting polymers, 3. Doping,stability, electrical,and optical characteristics of poly-(P-phenylphosphoethynediyl)

Studies on direct-current electrical conductivity and optical properties of a new solution of processable conducting polymer are reported. Electrical conductivity of thin films of the polymer on glass plate at room temperature was 6×10⁻⁶ S/cm. Study of conductivity with variation of temperature does not provide any definite thermal activation energy, which is in accordance with the amorphous nature of polymer. Optical absorption data adopting the Bardeen equation showed that maximum ‘optical gap’ (E _g ) is 3.30 eV. Doping with Br₂-vapor was found to be only partially effective in decreasingE _g by 0.43 eV. The polymer was found to be quite stable under normal atmospheric conditions. Environmental stability of both undoped and doped polymer has been discussed. Part 2: [5]