MECHANICAL PROPERTIES OF RIGID POLYURETHANE FOAMS MODIFIED WITH WOOD SAWDUST

P.M. STEFANI; R. SPERONI; A. VAZQUEZ

Alicante

Workshop; 2nd Workshop on Polymer Analysis & Biopolymer Degradation & Stabilization; 2003

Eucalyptus grandis sawdust as modifier. Two systems were analyzed: foams obtained with different amounts of moist sawdust with a constant water contentRigid polyurethane foams (PUFs) are materials used by several industries (construction, automotive, nautical, etc,) with a great number of applications. PUFs are obtained from the reaction of di-isocyanate with polyol. This is an exothermic reaction, and the released heat can be used to form a cellular structure by evaporation of physical blowing agents such as chlorofluorocarbons (CFCs). However, nowadays the use of CFCs is considered undesirable for the environment and so they have been partially replaced by other types of foaming agents as water, which reacts with di-isocyanate, releasing carbon dioxide yielding bubbles. Since some years ago, the interest in the study of additon of biomass as fibers or fillers to polymer, has increased. The main advantage of using biomass is its ecological character and the low cost because the biomass is generally obtained as a residue in agriculture. However, there are some disadvantages, such as high sensitivity to moisture, and tendency to form aggregates during processing make their use still limited. The present work examines the effect of increasing fractions of wood sawdust on the foaming process and final properties of a commercial polyurethane system, with the aim to obtain foams with at least similar properties, but achieving lower costs and valorizing a natural residue with the clear positive effect to the environment. With this purpose, PUFs were prepared from a commercial system (supplied by BASF –Argentina) and about 13 wt% and foams unmodified using water as blowing agent. The effect ofincreasing fractions of moist sawdust or water, on the foaming process, mechanicalproperties and structure of the PUFs were analyzed by different techniques. The opticalMicroscopy analysis during the formation of PUFs modified with sawdust showed that bubbles are generated on the surface of sawdust particles as result of the reaction betweenisocyanate and the impregnated water in the particles. Density and mechanical properties ofthe foams decrease as the amount of moist sawdust or water increase in the formulation.However, in the range of low density, the presence of the sawdust improved slightly themechanical properties respect to the unmodified system. foams obtained with different amounts of moist sawdust with a constant water content about 13 wt% and foams unmodified using water as blowing agent. The effect of increasing fractions of moist sawdust or water, on the foaming  process, mechanical properties and structure of the PUFs were analyzed by different techniques. The optical microscopy analysis during the formation of PUFs modified with sawdust showed thatbubbles are generated on the surface of sawdust particles as result of the reaction between isocyanate and the impregnated water in the particles. Density and mechanical properties of the foams decrease as the amount of moist sawdust or water increase in the formulation. However, in the range of low density, the presence of the sawdust improved slightly the mechanical properties respect to the unmodified system. foams obtained with different amounts of moist sawdust with a constant water content about 13 wt% and foams unmodified using water as blowing agent. The effect of increasing fractions of moist sawdust or water, on the foaming process, mechanical properties and structure of the PUFs were analyzed by different techniques.