A. Santamaría

Influence of the processing conditions on the rheological behaviour of polymer-modified bitumen☆☆

Abstract Mixing polymers into bitumen has important consequences on the engineering properties of bituminous binders. Thus, structural and chemical changes may be observed during processing of polymer-modified bitumens. Chemical compatibility and processing conditions are crucial to obtain suitable properties. Most polymers occur to be insoluble, in some degree, in the bitumen matrix, and phase separation may result. Polymer stabilization can be achieved by mechanical dispersion of the modifier and swelling by compatible components in the maltene fraction. This paper deals with the influences that processing variables exert on the rheological properties of polymer-modified bitumens. From the experimental results obtained we may conclude that a rotor–stator mixer device enhances the rheological properties of binders prepared with high-density polyethylene, low-density polyethylene, ethylene–propylene–diene monomer, and their blends, as compared to a stirred tank device.

Facile Synthesis of Supramolecular Ionic Polymers That Combine Unique Rheological, Ionic Conductivity, and Self‐Healing Properties

A new family of supramolecular ionic polymers is synthesized by a simple method using (di-/tri-)carboxylic acids and (di-/tri-)alkyl amines. These polymers are formed by carboxylate and ammonium molecules that are weakly bonded together by a combination of ionic and hydrogen bonds, becoming solid at room temperature. The supramolecular ionic polymers show a sharp rheological transition from a viscoelastic gel to a viscous liquid between 30 and 80 °C. This sharp viscosity decrease is responsible for an unprecedented jump in ionic conductivity of four orders of magnitude in that temperature range. As a potential application, this chemistry can be used to develop polymeric materials with self-healing properties, since it combines properties from supramolecular polymers and ionomers into the same material.

Rheological behaviour of metallocene catalysed high density polytheylene blends

Abstract Dynamic and steady state flow measurements and shrinkage experiments have been carried out to investigate the influence of blend composition on viscous and elastic properties of a new type of polyolefin: high density polyethylenes of high and low molecular weight obtained via metallocene catalysts. The polyethylenes are characterized by narrow molecular weight distribution and absence of branching. A model based on the additivity of molecular weight and free volume has been used to fit the complex and steady state viscosities vs composition data, at constant frequency or shear rate, which show a large positive deviation from linearity. The single correlation between G′ and G″ and the small effect of blend composition on dimensional stability correspond to the behaviour expected for a miscible blend. ‘Sharkskin’ and ‘slip-stick’ effects observed in extrusion process of the high molecular weight sample disappear for blends of 50% and higher content of low molecular weight polyethylene.

Chemical and Rheological Properties of the β-Glucan Produced by Pediococcus parvulus 2.6

Some physicochemical and rheological properties of the exopolysaccharide (EPS) produced by Pediococcus parvulus 2.6 were examined. Structural characterization by NMR ((1)H and 2D-COSY) showed that the same EPS, a 2-substituted (1,3)-beta-D-glucan, was synthesized irrespective of sugar source used for growth (glucose, fructose, or maltose). The molecular masses of these beta-glucans were always very high (>10(6) Da) and influenced by the culture medium or sugar source. The steady shear rheological experiments showed that all concentrations of the beta-glucan aqueous solutions exhibited a pseudoplastic behavior at high shear rates. Viscoelastic behavior of beta-glucan solutions was determined by dynamic oscillatory analysis. A critical concentration of 0.35% associated with the appearance of entanglements was calculated. The beta-glucan adopts an ordered hydrogen bond dependent helical conformation in neutral and slightly alkaline aqueous solutions, which was partly denatured under more alkaline conditions.

Thermorheological analysis of PVC blends

The effect of temperature on dynamic viscoelastic measurements of miscible poly (vinyl chloride) (PVC)/ethylene-vinyl acetate–carbon monoxide terpolymer (EVA-CO) and immiscible PVC/high-density polyethylene (HDPE) and PVC/chlorinated polyethylene (CPE) molten blends is discussed. PVC plasticized with di(2 ethyl hexyl) phthalate (PVC/DOP) and CaCO3 filled HDPE (HDPE/CaCO3) are also considered for comparison purposes. Thermorheological complexity is analyzed using two time–temperature superposition methods: double logarithmic plots of storage modulus, G′, vs. loss modulus, G″, and loss tangent, tan δ, vs. complex modulus, G*, plots. Both methods reveal that miscible PVC/EVA-CO and PVC/DOP systems are thermorheologically complex, which is explained by the capacity of PVC to form microdomains or crystallites during mixing and following cooling of the blends. For immiscible PVC/HDPE and PVC/CPE blends the results of log G′ vs. log G″ show temperature independence. However, when tan δ vs. log G* plots are used, the immiscible blends are shown to be thermorheologically complex, indicating that the morphology observed by microscopy and constitued by a PVC phase dispersed in a HDPE or CPE matrix, is reflected by this rheological technique.

The effect of a miscible and an immiscible polymeric modifier on the mechanical and rheological properties of PVC

Abstract PVC/copoly(ester-urethane) (Baymod PU®) and PVC/EVA copolymer blends have been analysed from the point of view of the effect of miscibility on the mechanical and rheological properties. The FTIR and NMR analysis of Baymod PU modifier leads to the conclusion that its miscibility with PVC (determined by dynamic mechanical analysis) is due to the presence of 31.9% poly(e-caprolactone) and 38.4% adipates in the main chain of the copoly(ester-urethane) polymer. However the PVC/EVA system considered in this work results in an immiscible blend, due to the low content of vinyl acetate, 33 wt%. The comparison of the mechanical and rheological properties of both blends with those of a PVC plasticised with a low molecular weight common plasticiser (PVC/DOP system), reveals that compatibility is not a determinant point in what some ultimate properties are concerned. The molecular weight (related to the viscosity of pure polymers, which is similar for both polymeric modifiers) seems to play a more important role than the miscibility. The stress–strain curves of both PVC/copoly(ester-urethane) (PU) miscible blends and PVC/EVA immiscible blends resemble each other and are very different with respect to PVC/DOP curves. The PVCs plasticised with DOP show a considerably higher elongation at break and a lower Young’s modulus than PVC mixed with polymeric modifiers. Miscible systems, PVC/PU and PVC/DOP, show similar values of the stress at break, slightly higher than those of immiscible PVC/EVA blends. The results of the latter two-phase system are well fitted to a two-parameter equivalent box model developed by Kolarik, considering a value very close to zero for the parameter, which accounts for the adhesion in between the phases. The reduction of the viscosity, induced by PU and EVA polymeric modifiers, with respect to that of pure PVC, is remarkable at shear rates such as those involved in calendering and milling, but is less significant at shear rates above 1000 s −1 which correspond to injection moulding processes. A better performance is obtained with DOP plasticiser at such high shear rates. For immiscible PVC/EVA blends the variation of the viscosity with composition has been adjusted using an adaptation of the Kolarik model, being this a novel approach to relate the viscous and mechanical behaviour of immiscible but in some way compatible blends [1] . As expected miscible PVC/PU blends viscosity data follow a free volume additivity model.

Postponing sharkskin of metallocene polyethylenes at low temperatures: the effect of molecular parameters

Abstract The effect of temperature on extrusion rheometry of single site metallocene-catalyzed polyethylenes and polyethylene copolymers is investigated. Samples of molecular weight, Mw, ranging from 90,000 to 330,000 and short-chain branching degree (SCB) from 0 to 21.2 CH3/1000C, as well as samples with a small amount of long-chain branching, are analyzed. It is observed that all the samples display a low temperature region, limited by induced crystallization and gross melt fracture, in which smooth extrudates are produced at shear rates similar to those of industrial extrusion. A characteristic temperature of this region, Ts, is defined as the highest temperature at which sharkskin disappears. Clear symptoms of non-slip conditions at the capillary wall, are detected in this low temperature region. We assume that the necessary slip–stick conditions to produce sharkskin, would only be produced at shear rates above those involved in gross melt fracture. The analysis of the effect of the molecular parameters, leads to the conclusion that only SCB has a direct effect on Ts. A linear correlation between Ts and SCB level is established, showing the decrease of the former as the latter is increased. Considering the wide spectrum of the molecular characteristics of our samples, we claim that decreasing temperature is a sound route to postpone sharkskin of any polyethylene.

A striking hydrodynamic phenomenon: Split of a polymer melt in capillary flow

We present experimental results, acquired during capillary flow of very elastic polymer melts, showing a double extrudate at the exit of the die. The initial extrusion conditions give rise to an extrudate with very severe sharkskin instability, but when a certain critical shear stress is exceeded a second extrudate emerges from a scission of the first one. When the process is stabilized both branches become identical, with a sharkskin characterized by a double wavelength rather than the initial extrudate, but with the ridges out of phase. A tentative simple model, based on stick–slip hydrodynamic effect, is presented.

Ionic Supramolecular Networks Fully Based on Chemicals Coming from Renewable Sources

New supramolecular ionic networks are synthesized by proton transfer reaction between a bio-based fatty diamine molecule (Priamine 1074) and a series of naturally occurring carboxylic acids such as malonic acid, citric acid, tartaric acid, and 2,5-furandicarboxylic acid. The resulting solid soft material exhibits a thermoreversible transition becoming a viscoelastic liquid at high temperatures. All the networks show an elastic behavior at low temperatures/high frequencies, with elastic modulus values ranging from 4.5 × 10(6) to 4.5 × 10(7) Pa and soft network to liquid transitions T(nl) between -10 and 60 °C. The supramolecular ionic network based on cationic Priamine 1074 and anionic citrate shows promising self-healing properties at room temperature as well as relatively high ionic conductivity values close to 10(-6) S cm(-1).

New supramolecular ionic networks based on citric acid and geminal dicationic ionic liquids

A new family of supramolecular ionic networks was synthesized by a straightforward method using citric acid and germinal dicationic ionic liquids. The networks were formed by the ionic boding of multi carboxylate and cationic molecules. The resulting networks are solid soft material at room temperature, which exhibited a thermoreversible transition, becoming a viscoelastic liquid at high temperatures. Thus, each supramolecular ionic network was characterized by an elastic modulus, Ge, and a network-liquid transition temperature, Tnl. The glass transition temperature, Tg, of the systems was evaluated by differential scanning calorimetry (DSC) measurements, which, however, were not able to detect the Tnl. Considering the effect of the employed dicationic ionic liquids, the three characteristic parameters of the networks, Ge, Tnl and Tg, followed the same trend, as they increased following the sequence: citrate-1,3-propanedipyridinium > citrate-1,3-propanedimethylimidazolium > citrate/1,3-propanedimethylpyrrolidinium and citrate/1,3-propanedibenzylimidazolium. The nature of the dication and its substituents determined the basic parameters of the elastic network, Ge and Tnl. The observed effect of the chemical structure on Tg was assumed to be due to a reduction of the free volume as Ge augments.