Wolfram Gronski

Rubber Nanocomposites: Morphology and Mechanical Properties of BR and SBR Vulcanizates Reinforced by Organophilic Layered Silicates

Abstract Rubber compounds based on butadiene rubber (BR) or styrene—butadiene rubber (SBR) containing organophilic layered silicates were prepared. Organophilic silicates were swollen in a rubber/toluene solution. Matrix—filler reactive bonding was performed by adding bis(triethoxysilylpropyl)-tetrasulfan (TESPT) during swelling. Excellent dispersion of organoclay nanofillers in rubber matrices was demonstrated by transmission electron microscopy (TEM) and atomic force microscopy (AFM) exhibiting intercalated and partially exfoliated silicate layers. Matrix—filler interfacial coupling by TESPT led to reduced strain at break and reduced hysteresis for both organoclay and silica-based vulcanizates as expected for successful matrix filler coupling. Organoclay vulcanizates exhibited enhanced hysteresis when compared to silica compounds. This is related to orientation and sliding of anisotropic silicate layers, as determined by online wide-angle X-ray scattering (WAXS) measurements during cyclic tensile testing.

Cocontinuous polymer blends: influence of viscosity and elasticity ratios of the constituent polymers on phase inversion

Abstract The morphological properties of melt-mixed blends with cocontinuous phase morphology composed of poly(methyl methacrylate) and polystyrene or poly(styrene– co –acrylonitrile) are studied. By means of digital image analysis of two-dimensional TEM pictures the mean form factor ff irr was established as a classificator. For 11 blend systems phase inversion concentrations were determined in this way. We studied the influence of viscosity and/or elasticity ratios on the phase inversion concentration. Most theories based on viscosity ratio disagree with our experimental data. The analysis of corresponding phase inversion concentrations based on elasticity ratio determined at a constant shear stress leads to a simple and good correlation.

Structure and Density of Crosslinks in Natural-Rubber Vulcanizates. A Combined Analysis by NMR Spectroscopy, Mechanical Measurements, and Rubber-Elastic Theory

Abstract 13C-NMR MAS solid-state spectroscopy and 1H-NMR relaxation measurements have been applied for quantitative determination of crosslink density in sulfur-accelerated NR vulcanizates. It is shown that the 13C-NMR method is able to distinguish between monosulfidic crosslinks and polysulfldic structures; therefore a quantitative determination of chemical crosslinks was possible. An analysis of 13-NMR transversal relaxation measurements provided the network densities which were in good agreement with the results of the 13C-NMR measurements. Comparing stress-strain data with the spectroscopically determined crosslink density of the NR vulcanizates and calculated crosslink densities of peroxide-cured vulcanizates, it is shown that the same relation between low-strain modulus and crosslink density is valid independent of the structure of the vulcanizates. The chemical crosslink density determined by a theoretical approach based on the tube concept was in approximate agreement with the NMR results.

Blockpolymers of styrene and isoprene with variable interphase: Morphology and dynamic viscoelastic behaviour

A method is described to prepare poly[isoprene-b-(isoprene-co-styrene)-b-styrene] threeblock polymers with variable interphase thickness by anionic polymerization. At constant overall molecular weight the total interlayer content multiply exceeds that of normal blockpolymers. At high copolymer content three-phase systems are obtained. The morphology is examined by electron microscopy under various staining conditions. The dynamic viscoelastic behaviour, determined with torsion pendulum experiment, has been simulated for lamellar two-and three-phase systems with different contents of copolymer material. A new interpretation of theTg depression of the hard phase is given in terms of a cooperative softening of the pure hard phase and surface interlayer material.

A melt rheometer with integrated small angle light scattering

A stress-controlled commercial rheometer has been equipped with small-angle light scattering (SALS) instrument working in a range of wave-vectors between 0.5 and 4.2 μm−1 By a specially designed optical system the scattered light is focused directly on the square chip of a CCD-detector with high dynamical range allowing quantitative two-dimensional (2 D) intensity measurements of polarized and depolarized scattering. The rheo SALS system is suited for simultaneous fast measurements of 2D SALS and rheological material functions of polymer melts and liquid crystals. As a first application results on the influence of shear rate on the late stage of spinodal decomposition of a polybutadiene/polyisoprene blend are reported. A second application concerns a creep experiment in the liquid crystalline phase of a lyotropic non-ionic surfactant with simultaneous measurement of the time-dependent compliance and associated changes of the 2D intensity patterns of the polarized and depolarized scattering.

Shear-induced coalescence in polymer blends—simulations and rheo small angle light scattering

The kinetics of shear-induced coalescence of polystyrene(PS)/poly(methyl methacrylate) (PMMA) blends containing 1 and 5% PMMA were studied as a function of shear rate with rheo-SALS (small angle light scattering). The growth of the average particle size is shown to be a function of total strain independent of shear rate, the growth rate being controlled by the volume fraction of the dispersed phase. The experimental behavior is quantitatively described by the simulation of the evolution of particle size distribution on the basis of non-linear rate equations including hydrodynamic interactions.

Morphology and grafting of oxazoline‐functional polymer particles with various carboxylic acids

Oxazoline-functionalized, crosslinked PMMA-particles, prepared by free radical nonaqueous dispersion polymerization, were grafted with n-decanoic acid and carboxylic acid-terminated polystyrene. Oxazoline groups, separated by an alkylspacer from the PMMA backbone, showed enhanced mobility with respect to the backbone, as evaluated by solid-state NMR spectroscopy using a dipolar filter. As a function of molecular mass of the carboxylic acid, the oxazoline conversion varied from 70 mol % for n-decanoic acid to 1% for monocarboxylate-terminated polystyrene CT-PS with Mn: 15,900 g/mol. Morphological studies, performed by TEM, showed that reaction with acid terminated polystyrene results exclusively in interfacial grafting at the particle surface. At low grafting levels a raspberry-like morphology was obtained, whereas grafting levels exceeding 14 wt % CT-PS resulted in core-shell morphology. Core-shell morphology was also verified by static light scattering using toluene solvent, which is isorefractive to the PMMA core.

Conductive radical anion salts of poly(butadiene-b-4-vinylpyridine) blockcopolymers

SummaryPoly (1,4-butadiene-b-4-vinylpyridine) blockcopolymers are made conductive by formation of the complex salt of the 4-VP-block with tetracyanoquinodimethane (TCNQ). Microphase separated morphologies are obtained where the conductive 4-VP phase is continous or forms a network on a submicron scale in a continous elastomer phase. While the absolute value of the conductivity of 10-3–10-4 Scm-1 depends on the morphology the activation energy typical for an electron hopping process is approximately the same as in the low molecular weight complex with ethylpyridine.

Direct comparison of the segmental orientations of free oligomer and network chains in polybutadiene model networks

The segmental orientation in a semi-interpenetrating polymer network based on crosslinked polybutadiene swollen to different degrees by free butadiene oligomers (of molar masses below the entanglement limit) is studied as a function of uniaxial strain for both the oligomer chains and the network chains by using 2H nuclear magnetic resonance (n.m.r.) spectroscopy. While the second moment of the orientation distribution function, P2, is usually obtained from the quadrupolar splitting of the maxima of the spectra, herein we obtain the averaged P2 from the whole spectrum. For high volume fractions of the network chains (φ > 0.8) the untangled oligomer shows the same degree of orientation as the network, while for larger degrees of swelling the oligomer orientation is smaller than that of the network chains. Strain birefringence measurements performed on the same materials show a similar strain dependence as the orientation parameter obtained from 2H n.m.r. spectroscopy.

Structure development under shear flow during spinodal decomposition of a polymer blend observed by simultaneous measurement of small angle light scattering and rheological functions

Abstract The structure development of the late stage of the spinodal decomposition of a binary polymer blend under shear flow has been studied by simultaneous measurement of rheological functions and the 2-dimensional light scattering pattern obtained by small angle light scattering (SALS). During the structure development at constant shear rate the viscosity passes through maxima which are related to the onset of the structure deformation. In a creep recovery experiment an unusual reversal of the recovery is observed which is related to the relaxation of the anisotropic non-equilibrium morphology.