OPEN-PORE POLYURETHANE FOAM AND FELT
November 25, 1964
OPEN-PORE POLYURETHANE FOAM AND FELT - [DESIGN NEWS REPORT pamphlet page 5] inch by the ratio of the other thickness to 1/2 inch. In filtering applications, the in-depth-loading allowed by the open 3-dimensional structure and the high percentage of void volume provide an unusually large contaminant collecting capacity. For example, a 20 by 1-inch-thick filter of the open-pore foam will arrest and hold approximately 365 grams, more than twice the weight of the filter. for comparison, mechanical filters of the same size are capable of holding from 140 to 300 grams.Filtering characteristics of the felted material have not yet been fully evaluated. Felted materials will arrest smaller particles than standard foam because of the structure's smaller-sized air cells; their capacity, however, will be less. Typical flow characteristics of the felt range from 175 fpm at 0.5 inch of water for 1/8 inch of firmness, 3[sic] to 6 fpm at 0.5 inch of water for 1/8 inch of firmness 15.Physical PropertiesLike other polyurethane materials, open-pore foam is relatively strong, has good flex resistance and has high resistance to tear abrasion and impact. Tensile strength varies with porosity and is higher for the smaller-pore-sized materials, ranging from an average of 15 psi for 10 ppi foam to an average of 35 psi for 100 ppi foam. Tear strength averages around 3.5 to 4 lb. for all pore sizes. Elongation is approximately 450 percent for grades of 60 to 100 ppi. Below 60 ppi, elongation is somewhat less. Resiliency is also good and recovery of the material is virtually completed in 1 minute. The felted material provides high mechanical properties. Depending on initial pore size and firmness, tensile strength varies from 50 to 270 psi while tear strengths of 7 to 35 psi are achieved.Environmental ResistanceChemically, the material is an ester-type polyurethane and has good resistance to most chemical solutions, cleaning solvents and biological agents. Exceptions are chlorine, strong acids and strong caustics. Aliphatic and aromatic hydrocarbons are also problems, since they can cause the material to swell and lose strength. Protection against these agents can be provided by coatings. The material is also color fast; however, light colors tend to fade when subjected to ultraviolet light. In regard to aging, samples have shown no signs of deterioration after 5 years of normal use. However, prolonged exposure to sunlight and weather will cause serious loss of physical properties. The foam can be used without ill effects at temperatures to 250F. It can thus be washed in hot water and even sterilized with boiling water or steam without deterioration. Low-temperature properties are also good. Although the material slightly stiffens at very low temperatures, it can be used to -50F with out danger of embrittlement.Design and FabricationOpen-pore foam and felt may be shaped by reciprocating or rotary saws and knives, shearing, die-cutting and hot-wire cutting devices. Foams and felts also may be nailed, stapled, sewn, glued, laminated, taped and, in some cases, heat-sealed. Small areas of the material can be made self-supporting while large areas require only minimum support (i.e., a 2-ft square filter may only require diagonal wires to prevent displacement under airflow). It can also be made self-gasketing when clamped in compression between adjacent surfaces. Because of its good tear strength, it can be edge-fastened.Applications and AvailabilityTypical applications of foam materials are shown in illustrations. Both felts and foams are produced by proprietary processes. The foam is available in a number of porosity grades in thicknesses from 1/4 to 12 inches (in 1/16-inch increments) under the registered trade name of "SCOTT Industrial Foam". Standard grades and thicknesses of foam are available compressed to firmnesses of 3, 5, 10 and 15 under the registered trade name of "SCOTTFELT". Technical information for this article was provided by the Foam Div., Scott Paper Co., Chester, Pa.