Investigations of the influence on the phase morphology of PP-EPDM-blends on their mechanical properties

This work covers the dependence of the mechanical properties of polymer blends on their composition and their phase morphology. Blends of EPDM-elastomers and polypropylene were prepared covering the whole concentration range. The phase morphology was varied strongly by employing different mixing techniques and its morphology was characterized by means of electron microscopy and light microscopy, as well as by x-ray scattering and calorimetry.Mechanical properties such as the complex shear modulus, the tensile modulus as well as the stress strain behavior were investigated as a function of the composition of the blends and their phase morphology. The experimental finding is that the complex modulus, the tensile modulus, the yield stress, and the ultimate stress are rather insensitive with respect to the phase morphology and vary continuosly with the composition. The elongation at break, on the other hand, as well as the impact strength were found to depend on the phase morphology and to vary discontinously with the composition. One conclusion to be drawn is that one is not always forced to control the phase morphology tightly during processing in order to obtain materials with sufficiently good mechanical properties. Rather, simple theoretical approaches, neglecting details of the phase morphology are frequently able to satisfactorily predict mechanical properties of multiphase blends.     

Morphology and mechanical properties of ultrahigh molecular weight polypropylene prepared by gelation/crystallization at various temperatures

Films of ultrahigh molecular weight (5.4×10⁶) polypropylene were produced by gelation/crystallization at various temperatures from dilute decalin solutions according to the method of Smith and Lemstra. The temperatures chosen were 20°, 30°, 50°, and 60°C. With increasing the temperature, the long period and crystallinity of the resultant gel film increased. By contrast, when the films were stretched up to 50 } 60 times, the increases in Young's modulus and crystallinity become more significant, as the temperature of the gelation/crystallization became lower. This interesting phenomenon is thought to be due to the dependence of the number of entanglements on the temperatures concerning gelation/crystallization and evaporation of solvent from the gel to form a film.     

Some structural and mechanical properties of bacterially produced poly-β-hydroxybutyrate-co-β-hydroxyvalerate

Some structural and mechanical properties of PHB homopolymer and copolymers containing 17 and 25–30% PHV have been investigated. X-ray scattering, optical microscopy, density measurements and differential scanning calorimetry were used to interpret the results of load-elongation curves and thermomechanical softening measurements.     

Structural changes in solvent-induced crystallization of quenched isotactic polypropylene

Solvent-induced crystallization of quenched isotactic polypropylene (iPP) films in dichloromethane, cyclohexane, carbon tetrachloride, and chloroform has been investigated.WAXD, density, and DSC measurements indicate that smectic iPP films undergo a complex rearrangement of the structure in these liquids, leading to a process of crystallization.Transport properties of the dried samples, after the solvent treatment, show that the first stage of crystallization involves, in addition to the smectic phase, a fraction of amorphous phase, while further crystallization regards only the smectic phase.The morphology of the crystallized samples has been investigated by transmission electron microscopy following permanganic etching. No change in the basic morphology is found, although local organization showing splaying and branching appears clearer in the solvent crystallized samples than in the starting smectic sample.     

Thermo-optical analysis as a complementary method in the study of phase transitions of thermotropic liquid crystalline polymer and its blends with polycarbonate

Differential scanning calorimetry (DSC) and thermo-optical analysis (TOA) were applied to study the phase transitions phenomena of thermotropic liquid crystalline polymer and its blends with polycarbonate. It was found that both methods are complementary. Glass transition temperatures of the blends of polycarbonate with liquid crystalline polymer were measured and discussed.     

Viscoelastic properties of polyacrylonitrile particles stabilised by a poly-2-vinylpyridine/polytert butylstyrene block copolymer

The viscoelastic properties of a dispersion of polyacrylonitrile particles stabilised by a block copolymer poly-2-vinylpyridine/polytert butylstyrene dispersed in solvesso have been measured as a function of particle concentration and frequency at ambient temperatures. At low volume fraction of particles it was found that the loss modulus of the dispersions was larger than the storage modulus, whilst at volume fractions > 0.40 the storage modulus dominates the rheology. This is attributable to there being a steric repulsion between the particles as a result of an increasing concentration of particles and the resultant reduction in interparticle separation in the dispersion. In addition the observed exponential increase of the storage modulus with increasing particle volume fraction mirrors the exponential increase in force with decreasing surface separation of the same type of polymers adsorbed to mica.     

Temperature-dependence of mechanical and morphological properties of ultra-high molecular weight polyethylene cross-linked by electron beam irradiation

Cross-linking of ultra-high molecular weight polyethylene was performed with electron-beam irradiation in the range of radiation dose from 12 to 96 Mrad under nitrogen. Dry gel films and melt films were used as specimens. Two kinds of cross-linked specimens could be kept at 200°C for a prolonged time in an undeformed state and this tendency was independent of radiation dose. The elongation of the gel films hampered the heat-resistant effect and the drawn specimens were broken at temperatures lower than 175 °C. The elongation of the melt films could not be realized, because of a marked fixation of chains in the fiber network, even at a dose of 12 Mrad.     

Influence of crosslinking on mechanical and dielectric properties of nitrile-butadiene-rubber

Several copolymers of acrylonitrile with butadiene (different acrylonitrile content, different molecular weight), uncrosslinked and crosslinked by tetramethylthiuramdisulfide or radiation, are investigated by dynamic mechanical measurements (10^–4 Hz to 100 Hz). The viscoelastic behaviour at very low frequencies is strongly influenced by molecular weight and crosslinking whereas the main relaxation (glass process) remains nearly the same. Stress strain curves (Mullins effect) and some dielectric measurements are also reported.     

Dielectric relaxation in polymer solids Part 2: Application of the new model to polyurethane systems

Measurements of the complex permittivity of crosslinked polyurethanes at different temperatures in the frequency range 1–10⁵ Hz are discussed with respect to shape of relaxation curves. Using a new model (published in preceding paper) the shape parameters are related to small and large scale interaction.     

Preparations and properties of polyurethane aqueous dispersion from uncatalyzed systems of H12MDI,PTAd/bisphenol A polyol,and DMPA

Aqueous dispersions of polyrethane (PU) containing ionic and nonionic hydrophilic segments were prepared in a prepolymer mixing process using substantial amount of solvent. The acid groups were neutralized with tertiary amine, and chain extension in aqueous media was carried out with triethylene tetramine. Average particle size and particle size distribution of the dispersion, and mechanical and viscoelastic properties of the emulsion cast films were determined.     

Physical and chemical cross-linking effects in polyurethane elastomers

A series of polyester-urethane block copolymers of various molecular weights was prepared via a two-step polymerization process. The prepolymer composition was kept constant in all the samples, while the NCO/OH ratio during the chain extension was varied from 0.9 to 1.2. Chemical and physical cross-linking effects were studied by means of F.T.I.R spectroscopy, swelling, and elastic behavior. Equilibrium stress-strain measurements and tensile-retraction tests were carried out to examine the elastomeric behavior of the materials tested. The extent of agreement between microscopic and macroscopic behavior was then evaluated.     

Structure-property relationship of polyurethane ionomer

Polyurethane (PU) ionomers were prepared using various types of polyol (PTAd, PCL, PTMG, and PPG) and isocyanate (MDI, HDI, and IPDI), together with different extender (DMPA) contents, degree of neutralization, and number average molecular weight (M _n) of polyol. Modulus (E), strength (_b), and glass transition temperature (T _g) significantly increased with the increased amount of extender and extender neutralization. Among three of the iocyanate used, PU from MDI gave the highest modulus, strength, andT _g. With regard to theM _n of PTAd (600, 1000, 2000), PU from PTAd 600M _n gave the highest modulus, strength, andT _g, due probably to the highest hard segment content and phase mixing. On the other hand, PU from PTAd 2000M _n gave significantly improved strength over PTAd 1000M _n, and the highest elongation. The results were interpreted in terms of soft-segment crystallization, and soft-hard phase separation, which was concluded from the lowered softT _g.     

Phase diagrams and structures of lecithin/water systems with branched lecithin components

The influence of chain branching on the phase transition parameters and structures of the homologous series of 1-(x-methylpalmitoyl)-2-hexadecyllecithins in the water-saturated two-phase region (50 wt.% water) were studied by differentialscanning-calorimetry as a function of the position x of methyl branching. With increasing x a linear decrease in the enthalpies and alternating temperatures of main transition were observed. The phase diagram of the ternary system 1-(3-methyl-palmitoyl)-2-hexadecyllecithin/1,2-dipalmitoyllecithin/water (50 wt.% water) showed that both components are completely miscible within the high-temperature phase (L -phase). However, in the low-temperature phase (gel phase), the components are partially miscible only. It follows that gel phases with interdigitated chains and those with tilted chains are not completely miscible. The phase diagram of the ternary system 1,2-di-(8-methylpalmitoyl)-lecithin/1,2-dipalmitoyllecithin/water (50 wt.% water) showed that both components are completely miscible within the high-temperature phase and low-temperature phase. Within the concentration range between the mole fraction x=0.91 and x=0.97, a drop-like course in the phase diagram was obtained.     

Association of poly-(L-lysine) homologues in sodium carbonate solution

The molecular weights of isopoly(L-Iysine), poly(L-ornithine), and poly(L-, -diaminobutylic acid), the homologues of poly (L-lysine), were determined by the sedimentation equilibrium method in aqueous solutions of 1.0 M NaCl or 0.1 M Na₂CO₃. In every sample the molecular weights in the presence of carbonate ions was twice that in NaCl solution. In a previous paper we reported that poly(L-lysine) behaved as a dimer at concentrations higher than 0.4 g/dl in the presence of carbonate ions and as a monomer in dilute solution, and these two forms were related by a monomer-dimer equilibrium. The homologues did not have a monomer-dimer equilibrium relationship under the conditions of the measurements that we carried out. The CD spectrum of isopoly(L-lysine) in water showed a uniform increase with a decrease in the wave length in the presence of carbonate ions. However, in the alkaline region in NaOH solution, the spectrum changed and a small minimum at 212 nm was found. When additional carbonate ions were added a large minimum at 205 nm was observed. This result can be explained by a change in the conformation from a random coil to a regular structure. We could not compare isopoly(L-lysine) with other polypeptides, because it does not have peptide bonds. The CD spectra of poly(L-ornithine) and poly(L-, -diaminobutylic acid) in NaOH or Na₂CO₃ solutions showed only slightly regular structures. It was also confirmed that the dimer-structures of the poly (L-lysine) homologues do not have regular structures.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, FRG, February 16–17,1989.     

Changes in electrokinetic properties of natural rubber latex after surface chemical modifications

High-ammonia latex concentrate prepared from doubly-concentrifuged fieldHevea latex was exhaustively dialyzed to remove any residual water-soluble non-rubber constituents. The specially purified latex was then treated with specific chemical reagents to modify the surface ionogenic groupings originally present on the latex particle surface. The electrophoretic mobility of the modified latexes was investigated as a function of pH. The change in electrokinetic properties of the surface-modified latex was explained in terms of chemical modification to the ionogenic groups of the adsorbed layer of proteins and long chain fatty acid soaps on the latex particle surface, the negative charges of which are primarily responsible for the colloidal stability of the latex. For comparison direct extraction of the long-chain fatty acid soaps from the specially purified latex by solvent was also carried out. Present results indicate that the number of carboxyl groups from the adsorbed long-chain fatty acid soaps plays a major role in the stabilization of the latex concentrate. In comparison the contribution of negative charges from the adsorbed proteins towards the stability of the latex is of less importance.     

Scattering function and the dynamics of phase separation in polymer mixtures under shear flow

The phenomenological mean-field theory describing concentration fluctuations and spinodal decomposition of binary mixtures of long flexible macromolecules is generalized to mixtures under steady shear flow. This shear flow leads to a partial orientation and stretching of the coils, as well as to an anisotropic deformation of concentration fluctuations. Generalizing the approach of Onuki and Kawasaki, we obtain the collective scattering function describing these concentration fluctuations in the mixture under shear flow. Both the steady-state situation in the one-phase region and the initial stages of spinodal decomposition for concentrations inside of the spinodal curve are considered.Contributed paper delivered at the Tagung der Deutschen Physikalischen Gesellschaft, Fachausschuß Polymerphysik, Berlin, March 30–April 3, 1987.     

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.     

Phase behavior and elastic properties of a slightly crosslinked liquid crystalline main-chain polymer

A liquid crystalline main-chain polymer was slightly crosslinked by a reaction with, -difunctionalized oligo-siloxanes. Crosslinking does not disturb the liquid crystalline phases, which are identified by x-ray measurements as smecticB and smecticA phases. Measurements of the elastic properties of the crosslinked sample show rubber-like elasticity, even in the liquid crystalline phases. A difference of 7 K was found between cooling and heating for the smecticA/isotropic transition from DSC and mechanical measurements.     

Heat of micelle formation: Effect of counterions with concentrated,diffused, and separated electric charges

Heats of micelle formation were estimated from calorimetric measurements of anionic surfactants to see if there is any effect of the electrical charge of the counterion on micelle formation from the viewpoint of enthalpy change. The cationic counterions used are Na⁺ and Cu²⁺ for the concentrated electric charge, MV²⁺ for the diffused and 1,1-(1,)-alkanediyl)bispyridiniumions n=2, 4, 6, 8, 10, 12, 14 for the separated. The heat of micelle formation was obtained by subtracting an enthalpy change of dissolution of surfactant solid precipitated below the micelle temperature range (MTR or Krafft point) from a heat of complete dissolution of the precipitated surfactant solid around the MTR. The heats thus evaluated were found to be much more temperature-dependent than counterion-dependent. They were compared with the enthalpy change calculated from the CMC change with temperature, and the big difference between them was discussed from a thermodynamic point of view.     

Dynamics of phase separation and critical phenomena in polymer mixtures

The phenomenological mean-field theory for statics and dynamics of polymer mixtures is described, generalizing the approaches of Flory-Huggins, Cahn-Hilliard and de Gennes. Predictions are made for critical behavior, spinodal decomposition and homogeneous nucleation. The validity of the mean-field approximations is discussed with Ginzburg criteria. The results of the theory are compared to computer simulations and recent experiments.Invited talk delivered at the Tagung der Deutschen Physikalischen Gesellschaft, Fachausschu\ Polymerphysik, Kaiserslautern, 12–14 March 1986, and at the Gordon Research Conference on Polymer Physics, Andover, New Hampshire, 14–18 July 1986.The author is grateful to Dieter W. Heermann, Alla Sariban, Harry L. Frisch, Josef JÄckie and Thomas Schichtel for their fruitful collaboration on this research described in this review. He thanks them and Arthur BaumgÄrtner for allowing to present partially unpublished material, and for stimulating discussions. Furthermore the author has benefitted from discussions with P. G. de Gennes, P. Pincus, H. Sillescu and G. R. Strobl. This research is supported in part by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 41.