Measuring and predicting the dynamics of linear monodisperse entangled polymers in rapid flow through an abrupt contraction. A small angle neutron scattering study

Small-angle neutron scattering measurements on a series of monodisperse linear entangled polystyrene melts in nonlinear flow through an abrupt 4:1 contraction have been made. Clear signatures of melt deformation and subsequent relaxation can be observed in the scattering patterns, which were taken along the centerline. These data are compared with the predictions of a recently derived molecular theory. Two levels of molecular theory are used: a detailed equation describing the evolution of molecular structure over all length scales relevant to the scattering data and a simplified version of the model, which is suitable for finite element computations. The velocity field for the complex melt flow is computed using the simplified model and scattering predictions are made by feeding these flow histories into the detailed model. The modeling quantitatively captures the full scattering intensity patterns over a broad range of data with independent variation of position within the contraction geometry, bulk flow rate and melt molecular weight. The study provides a strong, quantitative validation of current theoretical ideas concerning the microscopic dynamics of entangled polymers which builds upon existing comparisons with nonlinear mechanical stress data. Furthermore, we are able to confirm the appreciable length scale dependence of relaxation in polymer melts and highlight some wider implications of this phenomenon.

Layered silicate nanocomposites based on various high-functionality epoxy resins. Part II: The influence of an organoclay on the rheological behavior of epoxy prepolymers

The effect of an organically surface modified layered silicate on the viscosity of various epoxy resins of different structures and different functionalities was investigated. Steady and dynamic shear viscosities of the epoxy resins containing 0-10 wt% of the organoclay were determined using parallel plate rheology. Viscosity results were compared with those achieved through addition of a commonly used micron-sized CaCO3 filler. It was found that changes in viscosities due to the different fillers were of the same order, since the layered silicate was only dispersed on a micron-sized scale in the monomer (prior to reaction), as indicated by X-ray diffraction measurements. Flow activation energies at a low frequency were determined and did not show any significant changes due to the addition of organoclay or CaCO3. Comparison between dynamic and steady shear experiments showed good agreement for low layered silicate concentrations below 7.5 wt%, i.e. the Cox-Merz rule can be applied. Deviations from the Cox-Merz rule appeared at and above 10 wt%, although such deviations were only slightly above experimental error. Most resin organoclay blends were well predicted by the Power Law model, only concentrations of 10 wt% and above requiring the Herschel-Buckley (yield stress) model to achieve better fits. Wide-angle X-ray measurements have shown that the epoxy resin swells the layered silicate with an increase in the interlayer distance of approximately 15 Angstrom, and that the rheology behavior is due to the lateral, micron-size of these swollen tactoids.

Layered silicate nanocomposites based on various high-functionality epoxy resins: The influence of an organoclay on resin cure

The influence of an organically modified clay on the curing behavior of three epoxy systems widely used in the aerospace industry and of different structures and functionalities, was studied. Diglycidyl ether of bisphenol A (DGEBA), triglycidyl p-amino phenol (TGAP) and tetraglycidyl diamino diphenylmethane (TGDDM) were mixed with an octadecyl ammonium ion modified organoclay and cured with diethyltoluene diamine (DETDA). The techniques of dynamic mechanical thermal analysis (DMTA), chemorheology and differential scanning calorimetry (DSC) were applied to investigate gelation and vitrification behavior, as well as catalytic effects of the clay on resin cure. While the formation of layered silicate nanocomposite based on the bifunctional DGEBA resin has been previously investigated to some extent, this paper represents the first detailed study of the cure behavior of different high performance, epoxy nanocomposite systems.

The plasticisation effect of glycerol and water on the gelatinisation of wheat starch

In the extrusion manufacture of starch-based thermoplastics, such as biodegradable packaging materials, glycerol is an effective additive as a plasticiser, that is, to diminish the brittle nature of the product and provide the desired extent of flexibility. However, the addition of glycerol may also affect the gelatinisation behaviour of the starch-water mixture, and hence the required processing conditions for producing a homogeneously gelatinised starch-based material. The effect of glycerol on the gelatinisation of wheat starch was studied using differential scanning calorimetry (DSC). Mixtures of starch, water and glycerol were investigated with a water content ranging from 12 - 40% and a glycerol concentration up to 75%. Dependent on composition, the enthalpy of gelatinisation ranged from 1.7 - 12.6 J/g (on a dry starch basis), while the onset and peak temperatures varied from 54 to 86 degreesC and 60 to 90 degreesC, respectively. As expected, water acted as a plasticiser in that the onset temperature for gelatinisation (TO) decreased with increasing moisture content. Glycerol, however, increased To. It is shown that the T-0 of starch-glycerol-water mixtures may be predicted on the basis of the effective moisture content of the starch fraction of these mixtures resulting from the relative speed of moisture absorption by glycerol and starch, respectively. Moisture sorption kinetics of wheat starch and glycerol in 100% relative humidity were determined and used to predict the preferential water absorption by glycerol in starch-glycerol-water mixtures and hence the resulting T-0 of the system.

Yield behaviour of a melt-compounded polyethylene-intercalated montmorillonite nanocomposite

The yield behaviour of a series of melt-mixed polyethylene-modified montmorillonite nanocomposites has been studied as a function of temperature and strain rate and compared to the behaviour of the base polymer. The processing conditions used gave an intercalated structure as assessed by X-ray diffraction. Although there was a modest improvement in stiffness with clay content, the yield behaviour was insensitive to the addition of the clay. Both the base polymer and the nanocomposites showed double yield points. These were analysed as activated rate processes, with the activation energies consistent with the low strain yield point being associated with the alpha(2) molecular relaxation and the higher strain yield point with W axis slip. (C) 2003 Society of Chemical Industry.

Phase behavior, crystallization, and morphology in thermosetting blends of a biodegradable poly(ethylene glycol)-type epoxy resin and poly(ε-caprolactone)

Thermosetting blends of a biodegradable poly(ethylene glycol)-type epoxy resin (PEG-ER) and poly(epsilon-caprolactone) (PCL) were prepared via an in situ curing reaction of poly(ethylene glycol) diglycidyl ether (PEGDGE) and maleic anhydride (MAH) in the presence of PCL. The miscibility, phase behavior, crystallization, and morphology of these blends were investigated. The uncured PCL/PEGDGE blends were miscible, mainly because of the entropic contribution, as the molecular weight of PEGDGE was very low. The crystallization and melting behavior of both PCL and the poly(ethylene glycol) (PEG) segment of PEGDGE were less affected in the uncured PCL/PEGDGE blends because of the very close glass-transition temperatures of PCL and PEGDGE. However, the cured PCL/PEG-ER blends were immiscible and exhibited two separate glass transitions, as revealed by differential scanning calorimetry and dynamic mechanical analysis. There existed two phases in the cured PCL/PEG-ER blends, that is, a PCL-rich phase and a PEG-ER crosslinked phase composed of an MAH-cured PEGDGE network. The crystallization of PCL was slightly enhanced in the cured blends because of the phase-separated nature; meanwhile, the PEG segment was highly restricted in the crosslinked network and was noncrystallizable in the cured blends. The phase structure and morphology of the cured PCL/PEG-ER blends were examined with scanning electron microscopy; a variety of phase morphologies were observed that depended on the blend composition. (C) 2004 Wiley Periodicals, Inc.

Mode II delamination testing in uniaxially oriented PVC pipes

The mode II fracture toughness of an oriented PVC pipe was measured using an End Notched Flexure test geometry. A relatively low value of G(IIC) was found of 1.07 kJ m(-2) and this indicates that it is energetically more favorable for a crack to propagate in the tangential direction rather than radially through the wall of the pipe. Examination of the mechanism of crack advanced showed that although the crack was propagating globally in mode II, micro-cracks were opening ahead of the crack in mode I or in mixed mode. Growth of the crack occurred by linking up of these micro-cracks. This is similar to the mechanism found for mode II cracking in carbon fibre epoxy composites. (C) 2004 Kluwer Academic Publishers.

Determination of domain sizes in blends of poly(ethylene) and poly(styrene) formed in the presence of supercritical carbon dioxide

Well-mixed blends of poly(ethylene) and poly(styrene) have been synthesized using supercritical carbon dioxide as a solvent. The morphology of the blends has been conclusively characterized using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), Raman microprobe microscopy, and C-13 solid-state cross-polarization magic angle spinning NMR (C-13 CPMAS NMR). DSC measurements demonstrate that poly(styrene) in the blends resides solely in the amorphous regions of the poly(ethylene) matrix; however, corroborative evidence from the SAXS experiments shows that poly(styrene) resides within the interlamellar spaces. The existence of nanometer-sized domains of poly(styrene) was shown within a blend of poly(styrene) and poly(ethylene) when formed in supercritical carbon dioxide using Raman microprobe microscopy and C-13 CPMAS NMR spectroscopy coupled with a spin diffusion model. This contrasts with blends formed at ambient pressure in the absence of solvent, in which domains of poly(styrene) in the micrometer size range are formed. This apparent improved miscibility of the two components was attributed to better penetration of the monomer prior to polymerization and increased swelling of the polymer substrate by the supercritical carbon dioxide solvent.

Miscibility and phase separation in blends of phenolphthalein poly(aryl ether ketone) and poly(ethylene oxide): a differential scanning calorimetric study

Miscibility and phase separation in the blends of phenolphthalein poly(aryl ether ketone) (PPAEK) and poly(ethylene oxide) (PEO) were investigated by means of differential scanning calorimetry (DSC). The PPAEK/PEO blends prepared by solution casting from N,N-dimethylformamide (DMF) displayed single composition-dependent glass transition temperatures (T-g), intermediate between those of the pure components, suggesting that the blend system is miscible in the amorphous state at all compositions. All the blends underwent phase separation at higher temperatures and the system exhibited a lower critical solution temperature (LCST) behavior. A step-heating thermal analysis was designed to determine the phase boundaries with DSC. The significant changes in the thermal properties of blends were utilized to judge the mixing status for the blends and the phase diagram was thus established. (C) 2004 Elsevier B.V. All rights reserved.

Thermosetting Blends of Polybenzoxazine and Poly(ε-caprolactone): Phase Behavior and Intermolecular Specific Interactions

Polybenzoxazine (PBA-a)/poly(epsilon-caprolactone) (PCL) blends were prepared by an in situ curing reaction of benzoxazine (BA-a) in the presence of PCL. Before curing, the benzoxazine (BA-a)/PCL blends are miscible, which was evidenced by the behaviors of single and composition-dependant glass transition temperature and equilibrium melting point depression. However, the phase separation induced by polymerization was observed after curing at elevated temperature. It was expected that after curing, the PBA-a/PCL blends would be miscible since the phenolic hydroxyls in the PBA-a molecular backbone have the potential to form inter- molecular hydrogen-bonding interactions with the carbonyls of PCL and thus would fulfil the miscibility of the blends. The resulting morphology of the blends prompted an investigation of the status of association between PBA-a and PCL under the curing conditions. Although Fourier-transform infrared spectroscopy (FT-IR) showed that there were intermolecular hydrogen-bonding interactions between PBA-a and PCL at room temperature, especially for the PCL-rich blends, the results of variable temperature FT-IR spectroscopy by the model compound indicate that the phenolic hydroxyl groups could not form efficient intermolecular hydrogen-bonding interactions at elevated temperatures, i.e., the phenolic hydroxyl groups existed mainly in the non-associated form in the system during curing. The results are valuable to understand the effect of curing temperature on the resulting morphology of the thermosetting blends. SEM micrograph of the dichloromethane-etched fracture surface of a 90:10 PBA-a PCL blend showing a heterogeneous morphology.

Dynamic and steady-state rheology of Australian honeys at subzero temperatures

The rheology of 10 Australian honeys was investigated at temperatures -15C to 0C by a strain-controlled rheometer. The honeys exhibited Newtonian behavior irrespective of the temperature, and follow the Cox-Merz rule. G/G' and omega are quadratically related, and the crossover frequencies for liquid to solid transformation and relaxation times were obtained. The composition of the honeys correlates well (r(2) > 0.83) with the viscosity, and with 24 7 data sets (Australian and Greek honeys), the following equation was obtained: mu = 1.41 x 10(-17) exp [-1.20M + 0.01F - 0.0G + (18.6 X 10(3)/T)] The viscosity of the honeys showed a strong dependence on temperature, and four models were examined to describe this. The models gave good fits (r(2) > 0.95), but better fits were obtained for the WLF model using T-g of the honeys and mu(g) = 10(11) Pa.s. The WLF model with its universal values poorly predicted the viscosity, and the implications of the measured rheological behaviors of the honeys in their processing and handling are discussed.

Water diffusion in methacrylate based copolymer hydrogels of 2-hydroxyethyl methacrylate

The diffusion of water into cylinders of polyHEMA and copolymers of HEMA with THFMA, BMA and CHMA were studied over a range of copolymer compositions. The diffusion of water into the polymers was found to follow a Fickian, or case I mechanism. The diffusion coefficients of water were determined from mass measurements and NMR imaging studies. They were found to vary from 1.7 +/- 0.2 x 10(-11) m(2) s(-1) for polyHEMA at 37 degreesC to lower values for the copolymers. The mass of water absorbed at equilibrium relative to the mass of dry polymer varied from 52-58 wt% for polyHEMA to lower values for the copolymers.

Gelatinisation of starch in mixtures of sugars. II. Application of differential scanning calorimetry

Differential scanning calorimetry was used to investigate the effect of mixtures of glucose and fructose, and five types of honeys on starch gelatinisation. At a 1:1 starch:water ratio, glucose generally increased the enthalpy (DeltaH(gel)) and temperatures (T-onset, T-peak and T-end) of gelatinisation more than fructose. Upon mixing, DeltaH(gel) of the low-temperature endotherm decreased in comparison to the sole sugars, but was fairly constant (7.7 +/- 0.33 J/g dry starch). DeltaH(gel) of the high-temperature endotherm increased with the fructose content. For both endotherms, the gelatinisation temperatures were unchanged (CV less than or equal to 3%) for the mixtures. With the honeys (moisture, 14.9-18.0%; fructose, 37.2-44.0%; glucose, 28.3-31.9%) added at 1.1-4.4 g per g dry starch, the enthalpy and temperatures of gelatinisation did not vary significantly (CV less than or equal to 6%). Typical thermograms are presented, and the results are interpreted in the light of the various proposed mechanisms for starch gelatinisation in sugar-water systems, total sugar content and possible sugar-sugar interactions. The thermograms were broader in the presence of the sugars and honeys, and a biphasic character was consistently exhibited. The application of an exponential equation to the gelatinisation temperatures of the starch-honey mixtures revealed an opposing influence of fructose and glucose during gelatinisation. The mechanism of starch gelatinisation may be better understood if techniques could be perfected to quantify breakage and formation of hydrogen bonds in the starch granules, and suggested techniques are discussed. (C) 2004 Elsevier Ltd. All rights reserved.

Investigation of the starch gelatinisation phenomena in water-glycerol systems: application of modulated temperature differential scanning calorimetry

The use of modulated temperature differential scanning calorimetry (MTDSC) has provided further insight into the gelatinisation process since it allows the detection of glass transition during gelatinisation process. It was found in this work that the glass transition overlapped with the gelatinisation peak temperature for all maize starch formulations studied. Systematic investigation on maize starch gelatinisation over a range of water-glycerol concentrations with MTDSC revealed that the addition of glycerol increased the gelatinisation onset temperature with an extent that depended on the water content in the system. Furthermore, the addition of glycerol promoted starch gelatinisation at low water content (0.4 g water/g dry starch) and the enthalpy of gelatinisation varied with glycerol concentration (0.73-19.61 J/g dry starch) depending on the water content and starch type. The validities of published gelatinisation models were explored. These models failed to explain the glass transition phenomena observed during the course of gelatinisation and failed to describe the gelatinisation behaviour observed over the water-glycerol concentrations range investigated. A hypothesis for the mechanisms involved during gelatinisation was proposed based on the side chain liquid crystalline polymer model for starch structure and the concept that the order-disorder transition in starch requires that the hydrogen bonds (the major structural element in the granule packing) to be broken before the collapse of order (helix-coil transition) can take place. (C) 2004 Elsevier Ltd. All rights reserved.

Rheological Properties of Organoclay Suspensions in Epoxy Network Precursors

This paper deals with the evolution of the state of dispersion of organically modified montmorillonites in epoxy or amine precursors. The epoxy prepolymer is a diglycidyl ether of bisphenol A (DGEBA) and the curing agent is an aliphatic diamine with a polyoxypropylene backbone (Jeffamine D2000). The clay dispersion is evaluated at the platelet scale (nanoscopic scale) from X-ray spectrometry [wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS)] and at the aggregates scale (microscopic scale) from rheological analysis. The organoclays used form gels in the monomers above the percolation threshold if no shear is applied and present a mechanical gel/sol transition when shear stress increases. Gel strength and viscosity at high shear rates are linked to the nanometric state of dispersion and reveal the existence of two different organizations depending on organoclay/monomer interactions: (i) When the clay shows good interactions with the monomer, a significant swelling of the clay galleries by the monomer is obtained. These swollen particles lead to formation of weak gels which after shearing give high relative viscosity fluids. (ii) When the clay develops poor interactions with the monomer, the clay tends to reduce its exchange surface with the monomer and leads to a strongly connected gel. Shear breaks down this physical network leading to a very low relative viscosity fluid composed of nonswollen particles keeping a high aspect ratio. (C) 2003 Elsevier B.V All rights reserved.