P. Partal

Rheological characterisation of synthetic binders and unmodified bitumens

Abstract This paper deals with the characterisation of the linear viscoelastic and steady-state flow properties of commercial pigmentable synthetic binders and unmodified bitumens. From the experimental results obtained, we may conclude that both types of materials show a thermorheologically simple linear viscoelastic behaviour in the temperature range studied (5°C–50°C), although synthetic binders are thermorheologically complex materials in steady-state flow. Both of them display a predominant viscous behaviour within the linear viscoelasticity region. Synthetic binders are characterised by an apparent shift of the terminal zone of the relaxation spectrum to lower frequencies, probably related to the development of entanglements among macromolecule components, and by the highest values of the zero-shear-rate limiting viscosity.

Development of highly-transparent protein/starch-based bioplastics

Striving to achieve cost-competitive biomass-derived materials for the plastics industry, the incorporation of starch (corn and potato) to a base formulation of albumen and glycerol was considered. To study the effects of formulation and processing, albumen/starch-based bioplastics containing 0-30 wt.% starch were prepared by thermo-plastic and thermo-mechanical processing. Transmittance measurements, DSC, DMTA and tensile tests were performed on the resulting bioplastics. Optical and tensile properties were strongly affected by starch concentration. However, DMTA at low deformation proved to be insensitive to starch addition. Thermo-mechanical processing led to transparent albumen/starch materials with values of strength at low deformation comparable to commodity plastics. Consequently, albumen biopolymers may become a biodegradable alternative to oil-derived plastics for manufacturing transparent packaging and other plastic stuffs.

Linear viscoelastic properties of sucrose ester-stabilized oil-in-water emulsions

This paper deals with the influence of composition [sucrose ester SE and oil O concentrations] and temperature on the linear viscoelasticity properties of highly concentrated oil-in-water emulsions, using a hydrophilic sucrose palmitate as emulsifier. Different oil-in-water emulsions were prepared using a sucrose palmitate (SE=1–5 wt %) with a hydrophilic–lipophilic balance of 15, sunflower oil (O=60–80 wt %) and water. Oscillatory measurements were carried out in the linear viscoelasticity region. The relaxation time spectra of the emulsions were calculated using regularization techniques and were fitted to an empirical model proposed by Reference 1996. The results obtained are explained on the basis of the relationship among linear viscoelasticity properties, droplet size distribution, and characteristics of the continuous phase. Thus, an increase in sucrose palmitate concentration produces higher values of the linear viscoelasticity functions and a broader plateau region in the relaxation time spectrum...

Wheat gluten-based materials plasticised with glycerol and water by thermoplastic mixing and thermomoulding

BACKGROUND Gluten has been investigated as a source for biodegradable polymeric materials because it is a renewable, available and low-cost raw material. The aim of this study was to evaluate the influence of some variables involved in the two stages of protein/plasticiser thermo-mechanical processing, where a mixture of glycerol and water was used as the plasticiser. RESULTS Gluten/glycerol/water blends mixed under different thermal conditions (adiabatic starting at 25 °C and isothermal at 60 and 90 °C) exhibited shear thinning capillary flow behaviour, where a marked increase in flow properties was obtained at the highest temperature. Two thermal events, glass transitions related to the plasticiser blend and gluten, were detected by Modulated Differential Scanning Calorimetry (MDSC) and Dynamic Mechanical Analysis (DMA) tests. Moderate moulding temperature led to less resistant materials showing higher ductility, whereas higher mixing and moulding temperatures led to bioplastics with higher mechanical properties. CONCLUSION A moulding temperature of 130 °C (close to the denaturation temperature) was found to be suitable for the thermomoulding process. In addition, the use of moderate mixing temperature seems to be convenient for those applications that required materials exhibiting high water absorption behaviour and suitable mechanical properties. Protein extractability results reflect the benefits of combining high shear and high temperature during processing to improve cross-linking reactions.

Transient flow of o/w sucrose palmitate emulsions

Abstract This paper deals with the characterisation and modelling of the nonlinear viscoelasticity properties of concentrated oil-in-water emulsions containing sunflower oil (60–80 wt%), water and a hydrophilic sucrose palmitate (1–5 wt%). With this aim, transient shear flow and nonlinear stress relaxation tests were carried out. Oscillatory shear measurements were also performed to calculate the linear relaxation modulus of the emulsions studied. The transient flow behaviour of all the emulsions studied is qualitatively similar, showing always a stress overshoot followed by a stress decay which tends to a steady-state value. However, at a critical shear rate, which depends on temperature and disperse phase concentration, a stress undershoot may be found. This behaviour has been attributed to optically observed shear-induced microstructural changes. A factorable nonlinear viscoelastic constitutive equation, the Wagner model with Soskey–Winter’s damping function, predicts the transient flow of these emulsions, in a range of shear rates, fairly well. However, a lack of concordance is found as shear rate increases, fact that has been explained on the basis of wall-slip phenomena and shear-induced microstructural changes.

Thermo-mechanical and hydrophilic properties of polysaccharide/gluten-based bioplastics.

The influence of adding different polysaccharides (locust bean gum, LBG; methyl cellulose, MC; and carboxymethyl cellulose, CMC) to gluten-based biodegradable polymeric materials was assessed in this work. Gluten/polysaccharide/plasticiser bioplastics were prepared at different polysaccharide concentrations (0-4.5%) and pH values by mixing in a two-blade counter-rotating batch mixer (at 25 °C under adiabatic conditions) and thermomoulding at 9MPa and 130 °C. Bioplastic probes were evaluated through dynamic mechanical thermal analysis, tensile strength and water absorption capacity tests. Results pointed out that a moderate enhancement of the network structure may be achieved by adding polysaccharide at a pH close to the protein isoelectric point (pH 6), which also conferred a further thermosetting capacity to the system. Moreover, the addition of MC and CMC was found to significantly enhance material elongation properties. However, the presence of charges induced by pH leaded to a higher incompatibility between the polysaccharide and protein domains forming the composite. The pH value played a relevant role in the material water absorption, which significantly increased under acidic or basic conditions (particularly at pH 3).

Effect of Salt on the Rheological Properties of Low-in-Fat O/W Emulsions Stabilised with Polysaccharides

The droplet size distribution, stability, flow and viscoelastic properties of 35% oil-in-water emulsions stabilised with 1% w/w Tween 60 and: (i) 5% potato starch (PS), (ii) 5% potato starch and 0.5% xanthan gum (PS + XG), or (iii) 1% xanthan gum (XG), with and without the addition of 0.5M NaCl were studied. Visual inspection of the emulsions that contained XG and PS + XG, with and without NaCl, showed that they remained stable after 6 months. Emulsions stabilised with PS (without salt) showed an incipient interface after four months storage, while those containing 0.5 M NaCl destabilised within a month. The presence of NaCl did not affect droplet size distribution. Microscopic observations showed that all the emulsions flocculated. The rheological properties of these emulsions were characterised on a controlled-stress rheometer. The linear viscoelasticity was determined by oscillatory measurements that revealed the systems that exhibited weak gel-like properties. The addition of NaCl to the systems caused a decrease of viscosity, storage modulus and of loss modulus for emulsions containing PS and PS + XG while it did not affect emulsions prepared with XG alone. The viscoelastic linear behaviour was described according to the Maxwell generalised model and the discrete relaxation time spectra of the emulsions by means of the BSW-CW model.

Steady-state flow behaviour of synthetic binders

This paper deals with the influences that mineral oil, resin and polymer concentrations, and temperature, exert on the steady-state viscous flow of model synthetic binders. With this aim, both binary (oil/resin and oil/polymer) and ternary systems have been studied. All the systems show a Newtonian region in a shear rate range that depends on binder concentration and temperature. The temperature dependence of the zero-shear-rate-limiting viscosity is described by an Arrhenius-like equation, in a temperature range that depends on binder composition. This limiting viscosity, at any concentration and temperature within the experimental range studied, can be estimated from the values of activation energies and viscosities of the binary oil/resin systems and the polymer concentration used. These results have been discussed on the basis of the development, depending on the polymer/resin ratio, of both a polymer-rich phase and a resin-rich phase in the bulk binder and its influence on the microstructure of the system.

Modelling of pyrolysis and combustion of gluten–glycerol-based bioplastics

Non-isothermal thermogravimetric analysis, under nitrogen and air atmospheres, has been applied to study the thermal degradation of wheat gluten and gluten-glycerol-based bioplastics. In order to explain experimental data, thermal degradation has been simulated using the so-called pseudo-components, which are related to protein fraction (mainly gliadin and glutenin), residual starch and plasticiser. Thus, the proposed models have been used to shed some light on the thermal decomposition of these materials, which have been found affected by their compositions and microstructures. Modelling confirms the experimental bioplastic and gluten isolate compositions, e.g. bioplastic moisture content, starch concentration and the expected gliadin/glutenin ratio. According to the simulation, the glycerol volatilisation is affected by bioplastic moisture content and hindered by the protein matrix. A fact pointing out that glycerol/water blend plays relevant plasticizing roles in the protein matrix through diverse physicochemical interactions.

End-performance evaluation of thiourea-modified bituminous binders through viscous flow and linear viscoelasticy testing

Straight-run bitumens are no longer suitable in new asphalt mixtures. Consequently, the use of modified bitumens has become more important. In order to both improve binders’ mechanical properties and prevent it from phase separation whilst stored at high temperature, the paving industry is currently developing new modification routes based on reactive agents. This work studies the use of thiourea, which has proven to efficiently broaden the temperature interval over which the binder demonstrates an adequate performance. On the one hand, viscous flow and dynamic shear tests indicate an enhancement in the high in-service temperature strength, along with a reduced thermal susceptibility. On the other hand, results of dynamic flexural tests reveal a significant decrease in the binder glass transition temperature. Finally, the use of master curves and a further frequency/temperature conversion are proposed, in order to attain a suitable viscoelastic characterisation of bituminous binders at low temperatures.