Composite material including rigid foam with inorganic fillers

#This invention relates generally to composite materials, and more particularly, to composite materials based on rigid polyurethane foams and reinforcing mineral fillers.

#Polyurethane foams are commonly prepared by reacting isocyanate with hydrogen-containing compounds having reactive hydroxyl groups, for example, polyester or polyether polyols. The reaction occurs in the presence of a catalyst, and a blowing agent is provided in order to produce an expanded, cellular product. The blowing agent can be produced chemically by the interaction of the isocyanate with water to generate CO2 gas. In low density, high expanding systems, a blowing agent such as trichlorofluoromethane is added which vaporizes at the outset of the reaction. Polyurethane foam systems are commonly prepared as two components, the isocyanate component being maintained separate from the polyol-catalyst-blowing agent component until the time of use.

#Structural articles formed from polyurethane foams usually include fillers to increase the strength of the polyurethane foam. U.S. Pat. No. 4,661,533 to Stobby describes a rigid polyurethane modified polyisocyanurate foam containing fly ash as a filler that is used for building insulation. However, structural building products, for example synthetic lumber, require higher density foams than those taught by Stobby.

#A composite material that is formed from a thermosetting polyurethane binder and a plurality of inorganic fillers dispersed therein is described in detail below. The polyurethane foam binder is formed from the reaction of two or more polyether polyols with aromatic isocyanates. The mineral fillers can be particulate materials, for example, fly ash, bottom ash, fine sand, ceramic particles, and glass particles, and/or mineral fibers, for example, glass fibers, graphite fibers, carbon fibers, ceramic fibers, vermiculite fibers, basalt fibers, and vallostonite fibers, as well as inorganic fibers. The composite material can be formed into any shape and be used for a replacement of natural wood as an artificial or synthetic lumber. For example, the composite material is suitable for use as railroad ties, roof shingles, siding for homes, fence posts, window and door frames, and also a replacement for some ceramic and concrete building materials. The composite material exhibits high flexural strength and impact resistance along with low thermal expansion and contraction compared to natural and known synthetic wood. The composite material also exhibits higher fire resistance and lower water absorption compared to natural and known synthetic wood.

#The composite material, in an exemplary embodiment, is formed from a reaction mixture containing liquid and solid components. The liquid components include two or more polymeric and/or oligomeric polyether polyols, polymeric, oligomeric, or monomeric polyisocyanates, amine catalysts, organometallic catalysts, and a blowing agent. The liquid components can also include surfactants, wetting agents, plasticizers, light and heat stabilizers and antioxidants, flame retardants, mold release agents, and antistatic agents. Solid components of the reaction mixture include particulate and/or filament mineral and/or organic fillers, chopped and/or milled reinforcing fibers, and pigments. The solid components can also include light and heat stabilizers and antioxidants, antistatic agents, mold release agents, and flame retardants.

#Polyether polyols used to form the composite material include low-viscosity polyether polyols having a first molecular weight and a functionality of about 3 or less, and in one embodiment, a functionality from about 2 to about 3. Also, polyether polyols having a second molecular weight lower than the first molecular weight and a functionality of about 3 or greater are used in the reaction mixture where greater than 50 weight percent of the polyols in the mixture has a functionality of 3 or less. Particularly, in one embodiment, the ratio of the weight of polyether polyols having a functionality of about 3 or less to the weight of polyether polyols having a functionality of about 3 or greater is about 1:1 to about 5:1, and in another embodiment from about 1.5:1 to about 3.0:1. Polyether polyols with a functionality of about 3 or less provide flexibility to the composite material while polyether polyols with a functionality of greater than about 3 provide rigidity to the composite material.