Heat polyurethane foam

Siace the pores ia an aerogel are comparable to, or smaller than, the mean free path of molecules at ambient conditions (about 70 nm), gaseous conduction of heat within them is iaefficient. Coupled with the fact that sohd conduction is suppressed due to the low density, a siUca aerogel has a typical thermal conductivity of 0.015 W/(m-K) without evacuation. This value is at least an order of magnitude lower than that of ordinary glass and considerably lower than that of CFC (chloro uorocarbon)-blown polyurethane foams (54). 

Laboratory experiments using rodents, or the use of gas analysis, tend to be confused by the dominant variable of fuel—air ratio as well as important effects of burning configuration, heat input, equipment design, and toxicity criteria used, ie, death vs incapacitation, time to death, lethal concentration, etc (154,155). Some comparisons of polyurethane foam combustion toxicity with and without phosphoms flame retardants show no consistent positive or negative effect. Moreover, data from small-scale tests have doubtful relevance to real fine ha2ards. 

Foams prepared from phenol—formaldehyde and urea—formaldehyde resins are the only commercial foams that are significantly affected by water (22). Polyurethane foams exhibit a deterioration of properties when subjected to a combination of light, moisture, and heat aging polyester-based foam shows much less hydrolytic stabUity than polyether-based foam (50,199). 

The foams, marketed by Rohm as Rohacell, are stable at room temperature to hydrocarbons, ketones, chlorinated solvents and 10% sulphuric acid. They may be used under load at temperature up to 160°C. Uses quoted for these materials include bus engine covers, aircraft landing gear doors, radar domes, domes, ski cores and tennis racket cores. Their potential is in applications demanding a level of heat deformation resistance, solvent resistance and stiffness not exhibited by more well-known cellular polymers such as expanded polystyrene and the polyurethane foams. 

Chlorofluorocarbon-blown foam blocks are used to insulate the walls and roofs of some buildings, thus reducing heat losses and helping to conserve fossil fuels. In this area, polyurethane foam competes with polystyrene foam, which until recently was blown with dichlorodifluoromethane (CFC 12) but is now blown with a mixture of chlorodifluoromethane (HCFC 22) and 1 -chloro-l,l-difluoroethane (HCFC 142b). 

This low pressure process, also known as elastic reservoir molding, consists of making basically a sandwich of plastic-impregnated open-celled flexible polyurethane foam between the face layers of fibrous reinforcements. When this plastic composite is placed in a mold and squeezed, the foam is compressed, forcing the plastic outward and into the reinforcement. The elastic foam exerts sufficient pressure to force the plastic-impregnated reinforcement into contact with the heated mold surface. Other plastics are used. 

Example 5. Glycolysis of Polyurethanes with Propylene Oxide after Pretreatment with Ethanolamine.55 A rigid polyurethane foam (ca. 100 g) was dissolved in 30 g ethanolamine by heating. Excess ethanolamine was stripped, leaving a clear solution. Infrared and GPC analysis indicated that the clear solution obtained contained some residual polyurethane, aromatic polyurea, aliphatic polyols, aromatic amines, and N,N -bis(f -hydroxyethyljurea. Next the mixture was dissolved in 45 g propylene oxide and heated at 120°C in an autoclave for 2 h. The pressure increased to 40 psi and then fell to 30 psi at the end of the 2-h heating period. The product was a brown oil with a hydroxyl number of485. 

Rigid polyurethane foams were prepared at room temperature using eommercial polyols and polymerie 4,4 -diphenyl methane diisoeyanate, and used to study their reeyeling by aminolysis. The reaction products obtained by treatment with diethylene triamine at 180 C were evaluated as hardeners for epoxy resins. The exothermie heats of euring were determined over the temperature range 60-80 C by differential scanning calorimetry. A reaction order of 2.2-2.4 was obtained. 8 refs. 

Paraffin gauze dressing Perforated film absorbent dressing Polyurethane foam Burns, scaids, grafts Postoperative wounds Burns, ulcers, grafts. Any combination of dry heat, gamma-radiation and ethylene oxide... 

Polyurethane foams are widely used for carpet backing. In the direct coating method, the pre-heated carpet passes direcdy underneath spray heads, which deliver the required amount... 

POLYETHYLENE OUTER PIPE AND POLYURETHANE FOAM PROTECT STEEL HOT STEAM PIPE IN MOSCOW DIRECT HEATING SYSTEM... 

While unaffected by water, styrofoam is dissolved by many organic solvents and is unsuitable for high-temperature applications because its heat-distortion temperature is around 77°C. Molded styrofoam objects are produced commercially from expandable polystyrene beads, but this process does not appear attractive for laboratory applications because polyurethane foams are much easier to foam in place. However, extruded polystyrene foam is available in slabs and boards which may be sawed, carved, or sanded into desired shapes and may be cemented. It is generally undesirable to join expanded polystyrene parts with cements that contain solvents which will dissolve the plastic and thus cause collapse of the cellular structure. This excludes from use a large number of cements which contain volatile aromatic hydrocarbons, ketones, or esters. Some suitable cements are room-temperature-vulcanizing silicone rubber (see below) and solvent-free epoxy cements. When a strong bond is not necessary, polyvinyl-acetate emulsion (Elmer s Glue-All) will work. 

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