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Rheology is proposed as a tool to explore plasticized poly(vinyl chloride) (PVC) formulations to be used in the fused filament fabrication (FFF) 3D printing process and so manufactures flexible and ductile objects by this technique. The viscoelastic origin of success/failure in FFF of these materials is investigated. The analysis of buckling of the filament is based on the ratio between compression modulus and viscosity, but for a correct approach the viscosity should be obtained under the conditions established in the nozzle. As demonstrated by small amplitude oscillatory shear (SAOS) measurements, PVC formulations have a crystallites network that provokes clogging in the nozzle. This network restricts printing conditions, because only vanishes at high temperatures, at which thermal degradation is triggered. It is observed that the analysis of the relaxation modulus G(t) is more performing than the G&Prime, /G&prime, ratio to get conclusions on the quality of layers welding. Models printed according to the established conditions show an excellent appearance and flexibility, marking a milestone in the route to obtain flexible objects by FFF.

A review on the rheological features of polymer blend nanocomposites (PBNANOs) is presented. The role played by nanoparticles to fine-tune the morphology of immiscible blends, substituting conventional compatibilizers, is highlighted. Most of the reviewed papers center their attention on the dynamic (oscillatory) viscoelastic properties in the linear regime, in which the structure of these complex systems remains unaffected. It is seen that the authors have been able to link the linear rheological results to the morphology of PBNANOs and establish viscoelastic models to calculate the interfacial tension between polymer phases. The suitability of the oscillatory techniques, in the linear and nonlinear regime, to detect the coalescence of the droplets of the dispersed polymer phase is presented, even when the works referred to the nonlinear regime are scarce. Regarding to these latter rheological measurements, continuous extrusion flow and extensional flow results on PBNANOs are also reviewed.

Selective reduction of hydrogen bonds of a phenoxy resin gave samples particularly suitable to investigate specific interactions in associative polymers. The glass transition temperature decreased when reducing hydrogen bonds, but dielectric results indicated that α and β relaxations are rather affected by steric hindrances (bulky groups). A model accounting for the combined effect of entanglements and secondary interactions on viscosity, which can be generalised for other associative polymers, is proposed and hydrogen bonds/entanglements rate is determined. Dynamic viscoelastic results at T = 170 °C and T - T = 80 °C, showed that hydrogen bonds did not constitute a network and were weakened by temperature. The non-linear viscoelastic parameter Q decreased as the amount of hydrogen bonds was reduced. LAOS (Large Amplitude Oscillatory Shear) experiments constitute a new rheological tool to investigate associative polymers. Strain hardening in extensional flow was probed to be a consequence of the long relaxation times associated to hydrogen bonds and obtained from viscoelastic data., The authors are grateful to the financial support from the Basque Government (GIC IT-618-13 and GIC IT-586-13). L. Sangroniz and A. Sangroniz thank the Spanish Ministry (FPU) and Basque Government, respectively, for their PhD grants

This work presents novel findings on the rheological properties of self-nucleated polymer melts. Different polycaprolactones (PCL) with varying molar masses were investigated with shear rheometry, assessing the viscoelastic functions at different temperatures, reached either from the melt or from the semi-crystalline state. The latter condition produces a self-nucleated melt, in which residual clusters of unclear nature enhance the re-crystallization process, while a homogeneous melt is obtained with the first protocol. Striking differences are observed in melts with or without self-nuclei. The Newtonian viscosity and flow activation energy increase up to one order of magnitude with respect to the fully equilibrated melt. The plateau modulus also shows a remarkable increment, indicating an apparent decrease of the molecular weight between entanglements. The results demonstrate the existence of an additional attractive intermolecular interaction between chain segments in self-nucleated PCL melts, able to provide “extra” physical entanglements which progressively dissolve as the temperature is raised. Self-nucleated propene/ethylene copolymers analyzed in previous work display much weaker effects. The apparent discrepancy is discussed in light of the differences in intermolecular interactions and melting enthalpies between the two polymers.

Compounds based on PVC, typically employed to elaborate profiles, films, sheets and pond membranes by calendering, extrusion or injection processing methods, have been reformulated to obtain flexible materials apt to Fused Filament Fabrication (FFF) 3D Printing. Suitable filaments were obtained in Haake MiniLab extruder (Thermo Fisher Scientific) at a temperature of 140 °C. Since the occurrence of filament buckling depends on the ratio of the compression modulus, K, to the viscosity, η, the compounds were characterized under the premises of the printing temperatures and velocities. From the low K values found for the filaments it was inferred that buckling would arise during 3D Printing. However, FFF process was found to be perfectly feasible for selected samples. A rheological explanation of this unexpected and positive result was proposed considering the hypothesis of a plug flow in the nozzle.

Homemade graphene based polyurethane composites elaborated using a facile melt mixing method were studied. The polyurethane (PUR) was a hot-melt adhesive and the research was carried out considering the perspective of electrically conductive adhesive composites. The crystallization of PUR was significantly modified by graphene; for instance the crystallization temperature was shifted to higher temperatures. Avrami equation results indicated that the composites constituted nucleated axialites, instead of espherulites. These results were used to explain the initial decrease of conductivity, followed by a recovery, observed during the crystallization process. The observed huge conductivity enhancement, together with the increase of the crystallization temperature, opens interesting perspectives in the development of electrically conductivity adhesives which offer a rapid welding.

Melt memory effects on polymer crystallization are commonly reported in the literature, even when they are not completely understood. In particular, the exact nature of the melt heterogeneities that cause an enhanced nucleation (i.e., the >self-nuclei>) is unknown. This is partly due to sensitivity limitations of the experimental techniques employed to study melt memory. In this work, the melt memory effect of semicrystalline polymers is studied for the first time by dielectric measurements. Polycaprolactones of two different molecular weights have been investigated. Isotropic or self-nucleated melt states are obtained, at a given experimental temperature, by cooling from the isotropic melt or heating from the semicrystalline solid, respectively. A detectable decrease in electrical permittivity is obtained for a self-nucleated melt, consistent with the presence of molecular dipoles with restricted mobility in the case of samples displaying crystalline memory. The volume fraction of repeating units involved in the formation of self-nuclei is estimated to be lower than 0.4%. The relative difference in dielectric permittivity between self-nucleated and isotropic melt state shows excellent correlation with rheological measurements that detect an increase in Newtonian viscosity and with the enhancement of nucleation density, measured by DSC. Each of these measured parameters showed a different sensitivity to the presence of self-nuclei, which is linked both to their nature and to the features of the specific measurements. It is suggested that the relatively strong memory effect displayed by PCL, which can be evidenced by different techniques, is related to the presence of weak intermolecular hydrogen-bonding interactions., R.G.A. acknowledges support by the USA National Science Foundation, Grant DMR 1607786. The UPV/EHU team acknowledges funding from the following projects: Mineco MAT2014-53437-C2-P, MAT2017-83014-C2-1-P, and Basque Government IT586-13. L.S. gratefully acknowledges a FPU thesis grant from Spanish Government.

For the first time PVC–PBA random copolymers were prepared by Single Electron Transfer–Degenerative Chain Transfer Living Radical Polymerization giving rise to homogeneous chains, in terms of PVC/PBA proportion. Dynamic viscoelastic measurements in the terminal zone allowed evaluating the entanglement plateau modulus value, G N 0 , for each composition. An equation based on a model that correlates G N 0 to melt chain dimensions was used to fit the variation of G N 0 with PBA concentration. Correspondingly, the entanglements number, the characteristic ratio and the packing length values of each copolymer were obtained. As a corollary, the characteristic ratio of PBA, never reported before, was also evaluated.

Dynamic viscoelastic measurements were combined with differential scanning calorimetry (DSC) and atomic force microscopy (AFM) analysis to investigate the rheology, phase structure, and morphology of poly(l-lactide) (PLLA), poly(e-caprolactone) (PCL), poly(d,l-lactide) (PDLLA) with molar composition l-LA/d-LA = 53:47, and poly(l-lactide-co-e-caprolactone) (PLAcoCL) with molar composition l-LA/CL = 67:33. After melt conformation, both copolymers PDLLA and PLAcoCL were found to be amorphous whereas PLLA and PCL presented partial crystallinity. The copolymers and PCL were considered as thermorheologically simple according to the rheological methods employed. Therefore, data from different temperatures could be overlapped by a simple horizontal shift (a T) on elastic modulus, G′, and loss modulus, G′, versus frequency graph, generating the corresponding master curves. Moreover, these master curves showed a dependency of G″≈ω and G′≈ω 2 at low frequencies, which is a characteristic of homogeneous melts. For the first time, fundamental viscoelastic parameters, such as entanglement modulus G N 0 and reptation time τ d, of a PLAcoCL copolymer were obtained and correlated to chain microstructure. PLLA, by contrast, was unexpectedly revealed as a thermorheologically complex liquid according to the failure observed in the superposition of the phase angle (δ) versus the complex modulus (G*); this result suggests that the narrow window for rheological measurements, chosen to be close to the melting point centered at 180 °C thus avoiding thermal degradation, was not sufficient to assure an homogeneous behavior of PLLA melts. The understanding of the melt rheology related to the chain microstructural aspects will help in the understanding of the complex phase structures present in medical devices.

Isothermal crystallization of two nanocomposites composed of multiwalled carbon nanotubes (MWCNT) and graphene dispersed in a hot melt adhesive polyurethane (PUR) is investigated. Rheological percolation is reached for PUR/MWCNT, but not for PUR/Graphene nanocomposites. Analysis of the elastic modulus versus time indicates that the crystallization process is more hastened by MWCNTs than by graphene, favouring the welding process of the corresponding adhesives. Correlative AFM images show that the crystal size follows the order: Crystals in neat PUR > Crystals in PUR/Graphene > Crystals in PUR/MWCNT. The nucleation density is higher in the case of MWCNTs due to the poorer dispersion of graphene in the PUR matrix. Analysis of DSC results by the Avrami equation and the fitting of G′-time results to a rheological equation adapted from the Avrami equation, show that the parameter n decreases from n = 3 for neat PUR to n = 2 for both nanocomposites. The coherence between the value n = 2 and AFM images is demonstrated: The lamellae organization in two dimensional growth, that brings about nucleated axialites, as expected for n = 2, is confirmed by AFM microscopy.

The properties of multiwall carbon nanotubes (MWCNT)/polyurethane (PUR) nanocomposites after being submitted to flow, i.e., in conditions similar to their application as electrically conductive adhesives (ECA), are investigated. A decrease of the elastic modulus is observed after flow is stopped, compatible with a rearrangement of the MWCNT/PUR network during flow. The implications of the viscoelastic results on probe-tack data are elucidated and a slightly higher energy of adhesion is observed for sheared samples. Dynamic viscoelastic measurements reveal that crystallization of PUR is fastened with MWCNTs, shortening the solidification process for samples submitted to flow or not. Electrical conductivity results show that the 4 wt% MWCNT/PUR nanocomposite can be submitted to flow and give, on cooling to room temperature, values of the electrical conductivity between 10−2 and 10−1 Siemens /m. 2 wt% MWCNT/PUR sample presents a shear induced semiconductor to insulator transition and a temperature-induced isolator to semiconductor transition. We conclude that MWCNT/PUR nanocomposites are good candidates to develop Hot Melt ECAs, since they display satisfactory viscosity, tack, crystallization (linked to permanent adhesion), and electrical conductivity. POLYM. COMPOS., 36:704–712, 2015. © 2014 Society of Plastics Engineers

Novel results on the thermomechanical and rheological properties of poly (Styrene-b-Ethylene-co-Butylene-b-Styrene) (SEBS) copolymers of molecular weight close to Mw = 200,000 g/mol, with varying styrene content and ethylene/butylene proportion, are presented. DSC and DMTA tests reveal that only the sample which contains more ethylene than butylene in PEB midblock chains is able to crystallize. Small amplitude oscillatory flow measurements show evidence of PEB entanglements, although the chains are anchored to PS cylinder domains. Increasing butylene proportion in PEB leads to a decrease of the entanglement density. Entanglements and microphase segregation bring about a very elastic behaviour which produces “plug-flow”, leading to smooth extrudates, in extrusion flow experiments.

Novel rheological features and conductivity results of irradiated PP/MWCNT nanocomposites are presented. Elongational flow measurements reveal a strain hardening behaviour which is compatible with the creation of long chain branched macromolecules provoked by irradiation. However, oscillatory shear flow results suggest that irradiation does not affect interactions of MWCNTs with PP chains. The addition of carbon nanotubes brings about conductivities of the order of 10 −2 S/cm, but its scavenger effect reduces the number of radicals generated by irradiation, lessening the strain hardening effect. The employed mixing method provides a dispersion of MWCNTs in a PP matrix, which followed by an ad hoc irradiation, allows obtaining an electrical conductive polypropylene with a strain hardening behaviour. The obtained results open novel routes to conductive nanocomposites apt to be processed using methods discarded for linear PPs, such extrusion-blowing and others.

The preparation procedure of epoxy and benzoxazine multi-walled carbon nanotube buckypaper composites is described. The morphology of the buckypaper is characterized by scanning electron microscopy and porosimetry, revealing a non-uniform porous structure. The wetting behavior of epoxy and benzoxazine resins in the buckypaper surface is studied by contact angle measurements. Scanning electron microscopy photographs of the composites obtained by infiltration of the buckypaper with epoxy and benzoxazine resins and subsequent curing reveal that a good impregnation is achieved. Thermal conductivity results reveal higher values for pristine buckypaper than for the composites, which is explained by the extremely small thermal conductance of the nanotube–polymer interface. The thicker resin layer surrounding the nanotubes observed in the buckypaper/epoxy composite justifies its lower conductivity, as compared with the buckypaper/benzoxazine composite.

A combined analysis of Pressure–Volume–Temperature (PVT), Dynamic Mechanical Thermal Analysis (DMTA) and oscillatory flow measurements for blends of a polypropylene (PP) with a commercial liquid crystalline polymer (Rodrun LC3000) is presented. This analysis allows the determination of the pressure–viscosity coefficient b = ∂lnη 0 /∂P. This coefficient depends on the Rodrun LC3000 content, increasing with it and is of the same order of magnitude as values reported for several commercial polymers showing a similar dependence of the viscosity on pressure. The analysis of the pressure dependence of Tg (related to b ) leads to the conclusion that the number of segments involved in the glass transition of PP increases with the Rodrun LC3000 content, thus demonstrating that the polymers are not totally immiscible. As far as the authors know, this is the first time that the dependence of the viscosity on the pressure has been reported for thermoplastic/liquid crystalline polymer blends.

Results of the loss tangent, tan δ, at low frequencies, obtained for a SEBS copolymer and carbon nanotube (CNT)/polyurethane (PUR) nanocomposites, are analysed. The hindering effect of nanostructures (i.e. ordered domains or nanoparticles) on the motion of polymer chains is revealed by the occurrence of a mechanical relaxation at low frequencies. In the case of SEBS copolymer, the effect of domains orientation and extender oil on a characteristic time associated with the relaxation is investigated. For CNT/PUR nanocomposites, the variation of the frequency at which the relaxation takes place, with CNT concentration and temperature, reveals that the interactions between the nanotubes and the polymer chains are improved with temperature

A study of the requirements necessary to fabricate novel MWCNT buckypaper/benzoxazine nanocomposites, based on rheological results, is presented. Best conditions to infiltrate the resin, without any diluents, in the buckypaper are selected from viscosity data obtained under time–temperature cycles. Infiltration results are analyzed using SEM microphotographs. The nanocomposite is obtained after an adequate curing process of the benzoxazine impregnated buckypaper. The mechanical and electrical properties of the nanocomposite are investigated. The obtained electrical conductivity values are several orders of magnitude larger than the values reported for conventional CNT/polymer nanocomposites.

The combined analyses of pressure–volume–temperature tests and oscillatory flow measurements for three thermotropic liquid crystalline cellulose derivatives, one acetoxypropylcellulose and two hydroxypropylcelluloses, are presented. This combined analysis allows for the determination of the pressure–viscosity coefficient b = ∂lnη0/∂P. It was observed that the activation energy of flow, dT g /dP, the compressibility coefficient and the pressure–viscosity coefficient obtained for the investigated thermotropic systems lie within the range of the values of these parameters reported for conventional polymers. However, the values of the thermal expansion coefficient below T g are considerably lower, reflecting the effect of the liquid crystalline order. The differences found between the three systems are explained considering microstructural factors, such as (average molar substitution), length of branching and hydrogen bonds.

The electrical conductivity of a nanocomposite constituted of multiwalled carbon nanotubes (MWCNT) dispersed in a semicrystalline polyurethane matrix, is investigated during cooling from the melt to the solid state. The same percolation threshold, ϕ c = 0.85 wt.%, is obtained in the molten and in the solid state, although the exponent t of the percolation equation is significantly higher in the solid state. A remarkable increase of the conductivity during crystallization is observed for nanocomposites of MWCNT content above ϕ c , but for contents below ϕ c the conductivity decreases. Combined conductivity and PVT results, lead us to discard the hypothesis of an increase of the density of the conductive network (associated with volume shrinkage) as being the cause of the conductivity enhancement during crystallization. Instead, the analysis of the parameters of the percolation equation for the molten and the solid state, suggests a transition from a less effective conductive network to a more performing three dimensional network.

A melt-mixing procedure has been used to disperse multi-walled carbon nanotubes (MWCNT) in an epoxy matrix. According to dynamic viscoelastic results, a physical network is formed for carbon nanotube concentrations of 0.3 weight per cent (wt%) and above. The temperature activated curing process is followed analyzing the evolution of the dynamic viscoelastic functions and the dielectric loss with time. Curing process from a physical to a chemical network is monitored. The presence of MWCNT accelerates curing, even when the rheological percolation is not reached (absence of physical network). Several hypotheses are considered to explain this result. Electrical conductivity decreases during cure, so lower electrical conductivities are found for cured MWCNT/epoxy samples than for dispersions: this is explained by a distortion of nanotubes physical network and a reduction of the ionic conductivity contribution of the liquid phase. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Electrically conducting adhesive nanocomposites are obtained dispersing multiwall carbon nanotubes (MWCNT) in a thermoplastic polyurethane (TPU) by a melt mixing method. The liaison between the viscoelastic properties of the nanocomposites and their tackiness is investigated. Probe-tack results obtained at a low strain rate obey a polymer/nanotube interaction mechanism that favours tackiness, since maximum stress, strain at failure and adhesion energy increase with MWCNT concentration. However, in experiments at a high strain rate, the polymer entanglement network plays the principal role and MWCNTs only act diminishing the deformabilty of the network and reducing strain at failure and adhesion energy.

Novel nanocomposites prepared by melt mixing of MWCNTs in a hot-melt adhesive PCL-based polyurethane are investigated. The nucleating effect of MWCNTs and the confinement they cause to polymer chains are considered. The broadening of the glass transition is indicative of a growth of the immobilized amorphous fraction adhered to MWCNTs. In the molten state the formation of a combined polymer/MWCNT network is observed. Practical requisites of hot melt adhesives, such as adequate melting temperature, crystallization degree, and viscosity are preserved when MWCNTs are added. Improvement of strength at room temperature and welding rate during cooling, are observed.

Solutions of a binaphthoxy phosphazene copolymer (containing chiral 2,2'-dioxy-1,1'-binaphthyl units with 50% R and S configurations distributed along the chains) in N-methyl pyrrolidone were studied by means of continuous flow experiments and small amplitude oscillatory flow tests. A sudden viscosity decrease was observed in the polymer concentration range (39-40 wt %), evidencing a liquid-crystalline polymer behavior. This has been confirmed by other rheological methods which have demonstrated that, for a sufficiently high concentration, the solutions of the binaphthoxy phosphazene copolymer give rise to a lyotropic system with formation of rigid rods (axial ratio of 10) stacked parallel to each other. The lyotropic properties of our binaphthoxy phosphazene copolymer are compatible with a regular helical structure, similar to that found for a homoleptic binaphthoxy phosphazene, which contains only S configuration. This suggests that the chains of 50% R/S binaphthoxy phosphazene copolymer are, in average, close to the strictly alternating R-S copolymeric structure of the syndiotactic isomer.

The rheological analysis of epoxy pre-polymer/MWCNT dispersions indicates that a physical network is formed. This is destroyed with an imposed shear, giving a viscoplastic and shear thinning behavior. Such destruction is not reflected in dynamic viscoelastic experiments, due to the very rapid recovery of the MWCNT network in the pre-polymer matrix. This responds to the observed lower electrical than rheological percolation threshold. Electrical conductivity results fulfill electron hopping/tunnelling mechanism, which implies a tube–tube distance close to 5 nm. However, rheological percolation requires nanotubes should touch each other, since no polymer chains are implied in the network.

Microphase-separated poly(styrene-b-ethylene-co-butylene-b-styrene) copolymers of different molecular weights with polystyrene (PS) volume fraction φ = 0.30 are investigated. Linear dynamic viscoelastic data reveal the blocking effect of the ordered PS microdomains, which produces a predominantly elastic response at low frequencies, associated with a mechanical relaxation. These results are correlated with tack and extrusion flow measurements, which involve polymer/metal adhesion processes. Nonlinearity implied in some experiments alters the ordered morphology of low molecular weight samples producing a viscous dominant behavior. Dissipation is reflected in viscous-like adhesion and lack of viscoplastic response in extrusion flow experiments. For the highest molecular sample, only a rubbery or entangled state (G' > G" and G' > 10 Pa) is observed in the linear viscoleastic regime. This is associated with the lack of adhesion seen in both, probe tack experiments and capillary flow measurements. This lack of adhesion gives rise to a plug-flow as the polymers slips in the capillary wall. POLYM. ENG. SCI., 50:1449-1456, 2010. © 2010 Society of Plastics Engineers.

The relation between Pressure–Volume–Temperature (PVT) and rheological behaviour of several polymers including polypropylene, poly(methyl methacrylate), polyamide, polycarbonate, polystyrene and polystyrene/polycarbonate blends was studied. Pressure–viscosity coefficient b = ( ∂ ln η 0 / ∂ P ) was calculated by means of a revisited version of the Miller equation that accounts for pressure and temperature effect on Newtonian viscosity through the activation energy of flow and PVT parameters. Pressure–temperature dependent viscosities experimentally determined using pressure chamber capillary rheometry allow us to check the approach of the Miller equation. Incorporating the pressure effect in the Carreau–Yasuda model for η ( γ ˙ ) allows establishing the viscosity curves of thermoplastics over a wide range of shear rates and pressures.

Bitumen phases separated from 5% and 12% EVA/bitumen blends are investigated. Basic characterization is carried out using a peculiar thin layer chromatographer, the Iatroscan. The rheological and technical analysis lead us to conclude that these macromolecular materials, obtained from physical distillation of the blends, constitute new bitumens of unique properties.

Poly(styrene)-poly(ethylene-co-butylene)-poly(styrene) (SEBS) triblock copolymers with a PS volume fraction ϕ = 0.30 are investigated. The analysis of the loss tangent at low frequencies leads to define a mechanical relaxation associated to the blocking effect of ordered PS cylinders on PEB chains motion. Submitting SEBS to a shear flow at 250 °C an orientation of the cylinders is observed. The effect of the molecular weight and the cylinder alignment on the relaxation is studied. Continuous flow experiments, in torsion and capillary mode, reveal the presence of very severe surface cracks which cause the phenomenon called “flow split”. The correlation between dynamic viscoelastic results and flow split is investigated, concluding that this is related to an entanglement–disentenglement process, rather to an alignment effect of PS cylinders.

A set of amorphous poly[ethylene-co-(1,4-cyclohexanedimethylene terephthalate)] (PECT) copolymers containing 25 and 30% of 1,4-cyclohexane dimethylene (CHDM) units and small amounts of branching agent pentaerythritol (PER) is investigated. The level of long chain branching was estimated by analyzing the positive deviation from η 0 M w 3.54 law. Branching also produced melt elasticity enhancement which is desirable for certain processing methods. Capillary extrusion experiments at 180°C generated flow-induced crystallization in PECT containing 25% of CHDM. Crystallization increased with the amount of PER added, which was explained by the favorable effect of branching to increase elongational rate at the entrance of the capillary. Linear and branched PECTs containing 30% of CHDM did not crystallize.

The fractional free volume f of polycarbonate (PC), polystyrene (PS) and poly(methyl methacrylate) (PMMA) is determined by pressure-volume-temperature (PVT) measurements using the Simha-Somcynsky equation of state. Results are compared with the free volume obtained by viscoelastic measurements. Temperature and pressure dependent viscosity and free volume results are correlated using the characteristic ratio C ∞ and the parameter B of the monomeric friction factor ζ = ζ exp B/f. This leads to obtain new results on the temperature and pressure dependence of C ∞ , as well as on the pressure dependence of B parameter.

Extrusion flow experiments of linear and branched syndiotactic poly(propylene)s were carried out. The work was focused on flow instabilities. Ionized radiation was employed to induce long chain branching in linear samples. Sharkskin and melt fracture were postponed in the case of slightly long branched samples, which possess an enhanced melt elasticity compared to linear samples. For the most elastic samples the nature of the flow instability changed: sharkskin disappeared and melt fracture was observed instead. The correlation between sharkskin and melt strength results is discussed.

Novel oscillatory flow results of phenoxy/organoclay nanocomposites are analysed considering the blocking effect of nanostructure on polymer chain mobility. The modification provoked by this hindering effect on loss tangent spectrum is investigated. The study of three different systems, involving a pristine montmorillonite and two montmorillonites modified with one alkyl tail and two alkyl tails, respectively, leads to conclude that polymer–alkyl repulsive interactions play the most important role in the chain mobility obstruction process. Our results suggest that polymer–alkyl interactions increase with temperature.

Dynamic viscoelastic functions of bitumen/polymer waterproofing membranes are investigated. Analyses of the effect of polymer concentration on the height of the loss tangent peak observed around 20 °C reveals the existence of a continuous polymer phase. The variation of the elastic modulus and the loss modulus with frequency leads to define a Relaxation Spectrum Index which is used to determine the polymer concentration for the phase inversion. This is related to the Spanish UNE 104281 technical norm on bitumen/polymer blends for roofing. The results of the elastic modulus as a function of temperature and frequency were employed to evaluate the bonding capacity of the membranes to the roof surface. New perspectives on the characterization of bitumen/polymer membranes, similar to the Strategic Highway Research Program (SHRP) used in road pavement, are open.

A series of polyurethane multiblock copolymers with different proportions of hard segments (urethane) to soft segments (polyadipate of hexane-1,6-diol), are investigated. Dynamic viscoelastic functions of homogeneous melts in the terminal zone are determined. For the first time, entanglement modulus values of such copolymers are reported, which allows estimation of the packing length. These parameters do not vary with changing the hard-to-soft segment ratio, a result that is explained by a compensating effect of the chain architecture. For samples of similar molecular weight, the relaxation time of the terminal zone increases as the hard-to-soft segment ratio augments. The adhesives obtained from PUR solutions show a correlation between the elastic modulus and the debonding stress-strain curves in tack experiments.

Pressure–Volume–Temperature ( PVT ) data of an isotactic and a syndiotactic PP are fitted to a modification of the Simha–Somcynsky equation of state (S–S), to calculate characteristic parameters, such as V ∗ , T ∗ , P ∗ and the solubility parameter δ . The hole fraction of the S–S model and the free volume are deduced from these parameters. The application of a modified Doolittle equation and a modified Berry–Fox equation to estimate viscosity, leads to extract novel conclusions on the differences between both types of PPs. An equation which accounts for the effect of temperature on the characteristic ratio of syndiotactic PP is presented.

Summary: Melt elasticity of a series of conventional and metallocene-catalyzed PEs is investigated. The samples show very noticeable differences in their molecular architecture, including a variable degree of LCB and MWD. Four parameters (De, RSI, recoverable shear and steady state compliance), determined through dynamic viscoelastic measurements, are correlated with molecular architecture and blown film properties. RSI parameter shows a particular capacity to discern the LCB effect from the MWD effect on PE melt elasticity. Enhancing melt elasticity improves bubble stability, but provokes more haze and poorer impact properties in the film. Dart impact values vs. relaxation spectrum index.

Rheological techniques are used to investigate the rejuvenation of aged bitumen. The thermal transition associated with the collapse of the compact structure constituted by asphaltene is determined by Dynamic Mechanical Thermal Analysis. For aged bitumen, this transition shifts to a higher temperature but when rejuvenating agents are added, the transition returns to its original value. The “rutting factor,” G*/sin δ allows to define the maximum temperature the binder can reach without permanent deformation. The employed rejuvenating agents are suitable because permanent deformation is postponed. Viscosity results reveal that aged bitumen needs a high mixing temperature (>200°C) to behave like a fluid material able to wet, adhere, and envelop aggregates. The addition of rejuvenating agents considerably reduces mixing and compaction temperatures. The mixture of 80% aged bitumen—20% recycled motor oil, obtained exclusively from waste materials is an apt binder that can compete satisfactorily with new 60/70 bitumen.

The linear viscosity of m-LLDPE/LDPE blends is adjusted to a free volume model, conceived for miscible blends. A deviation from the model is observed at 47.5% m-LLDPE/52.5% LDPE blend, suggesting immiscibility in the molten state at this composition. Time–temperature superposition method is used to confirm miscible and immiscible cases. The effect of miscibility on practical rheological features is analysed using extrusion rheometry. The results indicate a core-sheet morphology in the immiscible blend, as the less viscous LDPE encircles the m-LLDPE phase. Miscible blends with a high LDPE content and immiscible 47.5% m-LLDPE/52.5% LDPE blend, show ‘melt fracture’, but not ‘sharkskin’. The latter is observed in miscible blends of a high m-LLDPE content. ‘Sharkskin’ is postponed in 87.5% m-LLDPE/12.5% LDPE blend, a result which is associated to the elongational viscosity enhancement, due to the presence of long chain branches. The correlation between melt spinning and blown film extrusion results is investigated, showing evidences of the technical limitations caused by immiscibilty.

Metallocene-catalysed linear low density polyethylenes (mLLDPEs) of different molecular weights are mixed with a base mLLDPE to obtain a pre-determined grade and a suitable extrusion processability. Complex viscosity results are revealed as a very suitable tool to tailor the properties of the prepared binary and ternary blends, The investigated blends show symptoms of miscibility like time-temperature superposition and observance of Cox-Merz rule. This allows to evaluate the molecular weight distribution, supplying also practical data related to the polyethylene grade and 'sharkskin' instability. The complex viscosity curve of a model sample that would have both, a suitable grade and processability, is created; blends are prepared to match the model curve. The blend with a low molecular weight mLLDPE shows a parallel shift of the complex viscosity to lower values (molecular weight distribution is not broadened), postponing sharkskin, but changing the polymer grade. Satisfactory results are neither obtained with blends of a high molecular weight mLLDPE. Best results are obtained with ternary blends, which combine the modifications provided by low and high molecular weight mLLDPEs, approaching the complex viscosity and molecular weight distribution of the model.

Three block polyurethane samples [differing in hard (urethane) to soft (macroglycol) segments ratio] dissolved in 2-butanone, are investigated. Rheological results obtained in the range 10–25 °C led to the hypothesis of an order-disorder transition associated with H bonds being discarded. The critical concentration and the characteristic molecular weight for entanglements, Mc, are estimated approximately from linear viscosity results. Mc decreases as the percent of hard segments in the polyurethane increases, a result which is correlated with short-distance chain parameters such as length and molecular weight per bond and characteristic ratio. Annealing clear solutions at temperatures around 0 °C causes haziness; on heating, a clearing temperature is detected at Tc≈15 °C. This transition coincides with a maximum observed in complex viscosity η* versus temperature curves. These results are probably due to incipient crystallization of soft segments domains. This hypothesis is compatible with differential sc...

Rheological measurements reveal that the viscoelastic properties of a 60/70 penetration grade bitumen are improved when either a virgin EVA or a recycled EVA copolymer of similar vinyl acetate content are mixed with it. Risk of cracking at low temperatures and rutting at high temperatures, are both reduced. Better viscoelastic features are obtained with the bitumen modified with recycled EVA, probably due to the presence of carbon black, which acts like a filler in this material. Stability tests performed combining oscillatory flow and microscopy results disclose that blends with the higher polymer proportion (3%) are susceptible of phase separation after 24 h of storage at 165 °C, but 1% blends are stable for at least 4 days. A general evaluation of the results indicates that the performance of this bitumen as a binder for road pavement, is particularly improved when 1% of recycled EVA or virgin EVA is added.

Dynamic mechanical thermal analysis (DMTA) and oscillatory flow measurements are carried out to investigate the rheological properties of 70/30 blends of a bitumen with metallocene catalyzed atactic polypropylenes. DMTA results indicate that saturated liquid resins of the bitumen act as a plasticizer on polypropylene. The glass transition temperature of polypropylene decreases, and the pure bitumen broad relaxation disappears, which signifies that a polypropylene-saturated resin mixture constitutes the continuous phase. Such results are not obtained when a conventional atactic polypropylene is used in the blend. Oscillatory flow measurements show a viscosity reduction of the blends with respect to pure polypropylene, beyond what could be expected from a simple additive rule, reflecting the plasticization of polypropylene. One of the blends displays a viscoplastic behavior at low frequency, which is attributed to the presence of small crystals, formed on cooling from the mixing temperature. Some viscoelastic properties related to the use of these materials as roofing membranes are analyzed. Polym. Eng. Sci. 44:1792–1799, 2004. © 2004 Society of Plastics Engineers.

New rheological results with molten polypropylenes of different degrees of syndiotacticity are presented. The temperature dependence of their dynamic viscoelastic functions is correlated with the characteristic ratio. Relaxation time and Newtonian viscosity values are plotted as a function of molecular weight. The very high values of both rheological parameters found for the most syndiotactic polypropylenes are explained considering the reptation model, which links conformational parameters with the viscoelastic response in the molten state.

Binary and ternary blends of PVC mixed with α-methylstyrene/acrylonitrile-butadiene-styrene copolymer (AMS-ABS) and ethylene/vinyl acetate/carbon monoxide terpolymer (EVA-CO) are investigated, with the aim to obtain a new PVC based material with an improved heat distortion temperature and good processability. Dynamic Mechanical Thermal Analysis (DMTA) reveals that ternary PVC/AMS-ABS/EVA-CO blends exhibit two glass transition temperatures: the lower T g corresponds to a PVC/EVA-CO phase and the higher one to a PVC/AMS-ABS phase. An analysis of PVC respective interactions with AMS-ABS and EVA-CO leads to assert that the distribution of PVC in the ternary PVC/AMS-ABS/EVA-CO system is basically controlled by the binary immiscible blend composition, taken as Φ AMS-ABS/Φ EVA-CO ratio. The inclusion of AMS-ABS and EVA-CO to form ternary blends based on PVC, allows to improve heat distortion temperature (owed to the presence of AMS-ABS), maintaining a low viscosity in the molten state, due to the plasticizing effect of EVA-CO.

Polyaniline doped with camphorsulfonic acid 'PANI-CSA) and ethylcellulose (EC), constitutes the basis of the investigated binary PANI(CSA) 0.5 /m-cresol and ternary PANI(CSA) 0.5 /EC/m-cresol solutions. Ternary solutions give rise to gels with a lower elastic modulus and electrical conductivity than binary PANI(CSA) 0.5 /m-cresol gels. However, the dimensional stability is considerably improved, since warping observed in binary gels is eliminated or lessened. These results are explained considering the role played by ethylcellulose, which interacts with the hydroxyl group of m-cresol, skimping PANI(CSA) 0.5 /m-cresol specific interactions and retarding solvent evaporation.

A blend of random ethylene-vinyl acetate copolymer (EVA) and triblock styrene-butadiene-styrene copolymer (SBS) was dissolved in a recycled engine oil to obtain ternary thermoreversible gels. As the temperature was increased, first a network associated with EVA disappeared, and a second one associated with SBS dominated, maintaining the elastic response of the system. The principal advantage of these ternary systems is that their mechanical properties and thermal stability are better than that of binary gels. These gels, made from waste, can be used as bitumen modifiers to obtain binders of improved properties and good stability, which are useful for road surfacing.

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.

Viscosity results of a solution of poly(2-hydroxyethyl methacrylamide) in glycerine, obtained from a continuous increase of shear rate and under steady state (constant shear rate) conditions, reveal the existence of a shear thickening region. The analysis of normal stresses shows that the first normal stress coefficient exhibits the same shear-thickening effect as the viscosity. The increase of the solution elasticity during shear thickening is also noticed by an enhancement of the storage modulus, measured in experiments using parallel superposition of oscillations on steady flows, as the shear stress is increased. Thermorheological simplicity, observed in dynamic measurements in absence of steady flow, is broken when shear stresses corresponding to the shear thickening region are applied. The results are explained by the presence of shear-induced hydrogen bonds, which provoke a reinforcement of the plateau modulus and an enlargement of the relaxation time spectrum.

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.