ABSTRACT
Rigid polyurethane foam (PUP) having different fillers such as precipitated silica (Si[O.sub.2]), precipitated calcium carbonate (CaC[O.sub.3]) and glass powder (GP) were prepared by blowing with distilled water. The effect of filler loading on different properties of P UP was studied. In this investigation, the filler content was varied from 5 to 50 parts per hundred of polyol (phr) by weight. The properties such as density, mechanical, morphological, water absorption, thermal conductivity and thermal properties of the filled PUP were compared with the neat PUF. The density of silica filled PUP decreases with an increase in the filler loading. In case of calcium carbonate and glass powder the density initially decreases with filler loading, but after a certain concentration of fillers there is an increase in density with filler content. The mechanical properties such as compressive stress at 10% strain, compressive modulus and hardness of the filled PUF decrease in comparison with the neat PUF due to the reaction between isocyanate and surface functional group present in filler.
In all cases, the water absorption of the PUP increases with the increase in filler loading, due to the decrease in the closed cell content. The thermal conductivity analysis of PUP shows that the insulation properties decrease with the increase in silica as well as CaC[O.sub.3] loading. This is mainly due to formation of open and damaged cell structure. However, when glass powder is used as filler the thermal conductivity first decreases, but later increases with filler loading.
INTRODUCTION
Rigid polyurethane foams (PUFs) are very useful materials due to their wide range of properties. They have huge range of applications both as insulating and structural materials (1). As structural materials, they have very good strength and toughness. Generally the properties of polyurethane foams depend on the structure and geometry of the foam and their density. Addition of different fillers influences the ultimate properties of PUF (1, 2). Fillers may simply be used to lower the material cost and/or to improve the mechanical properties like tensile/compressive strength, modulus, and abrasion resistance. In general fillers may be classified into two types such as reinforcing/active (e.g. carbon black, precipitated silica, calcium silicate) and non-reinforcing fillers (e.g. clay, calcium carbonate). The average particle size and particle shape of the fillers have profound influence on the properties of the polymer. The reinforcing fillers provide greater mechanical strength and non-reinforcing fillers minimize the cost. Mineral fillers are sometimes treated with different chemicals to improve polymer-filler interaction and filler dispersion, which aid in wetting or attachment of polymers to fillers. Stearic acid-treated calcium carbonate or amine, hydroxyl amine and glycol silicate treated clays may be cited as examples of treated fillers. Reinforcing filler like precipitated silica, calcium silicate may be treated with coupling agent such as silanes, titanates whereby more effective wetting and better polymer-filler interaction may be achieved via the coupling agent (3). The effect of some fillers on the mechanical properties of PUF has been reported in the literature. Michel et al. studied the effect of filler size on the mechanical properties of high density PUP (4). Zhen et al. reported the mechanical properties of PUF filled with hybrid reinforced fibers (5). Goods et al. studied the mechanical properties of aluminum powder filled particle that strengthened the properties of PUF (6). Jang et al. reported on the physical properties of garnet filled PUF composite (7). Li Chang et al. reported on the physical properties of soy flour filled PU foam (8). Cunningham et al. studied the properties of jet-cooked starch-oil composite on PUP (9). Badri et al. reported the properties of polyurethane composites from palm oil resources (10). The present investigation reports the effect of different fillers like precipitated silica, calcium carbonate and glass powder on the mechanical, morphological, water absorption, thermal conductivity and thermal properties of the water blown rigid PUF and compares these properties with the properties of neat foam.
EXPERIMENTAL
Materials
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