Starch-based polyurethane foams were synthesized by reacting a mixture of starch and polycaprolactone triol with an aliphatic diisocyanate, in the presence of water as blowing agent. Some foams were also prepared by adding a certain amount of polyethyleneglycol. The reaction kinetics is affected by the presence of starch due to the higher viscosity related to the presence of the high molecular weight polysaccharide. Starch-based polyurethanes show higher glass transition temperatures and lower thermal stability. Cellular materials with different mechanical properties can be obtained by varying the amount of starch and by controlling the relative amount of polycaprolactone triol and polyethyleneglycol in the composition.
A detailed rheological study of aqueous solutions of methylhydroxyethylcellulose has been carried out in the presence of different acrylate-based graft polymer used as additive contents. Both polymer components are used in cement formulations to improve the flow performances of the concretes, but no physicochemical studies can be easily found in the literature. The content of the graft polymer has been varied between 0.1 and 2.7 wt% in an aqueous solution with a fixed content of 6.5 wt% of methylhydroxyethylcellulose. Creep curves were performed at different stresses in order to build up the flow curves for the various solutions. We found that the addition of the graft polymer triggers a phase transition, which is made more dramatic by the presence of an external flow. A "flow-phase diagram" has been obtained, which could be used as a guide for determining the critical conditions for the onset of the flow-induced instability
In this paper, the rheological properties of an extrudable cement-based paste are investigated by means of an original ram extrusion apparatus (capillary rheometer). The experimental results indicate that a careful measurement of the die pressure is necessary to obtain a realistic viscosity vs shear rate curve, as required in extrusion technology. In particular, it is shown that the optimal test configuration is when the pressure measurement is made directly inside the rheometer die. By applying this rheological methodology in steady-state conditions, it has been observed that the extrudable cement-based material here evaluated obeys to a simple power–law equation, in the range of shear rates investigated, which are suitable for an industrial extrusion proces
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