Polyurethane foams development

The insulating value and mechanical properties of rigid plastic foams have led to the development of several novel methods of buUding constmction. Polyurethane foam panels may be used as unit stmctural components (220) and expanded polystyrene is employed as a concrete base in thin-sheU constmction (221). 

Polyurethane foams do, however, suffer from one serious disadvantage. Unless modified they bum with copious evolution of smoke and toxic by-products, which has led to a number of fatal fires, particularly in domestic accommodation. To some extent the problem may be reduced by suitable upholstery covering, but as mentioned on p. 775 a number of countries have now made mandatory the use of fire retardent additives. At the time of writing there is considerable activity in the development of new safer systems, particularly in the use of amino materials such as melamine as additives. Further developments may also be expected in the near future. 

The RIM process was originally developed for the car industry for the production of bumpers, front ends, rear ends, fascia panels and instrument housings. At least one mass-produced American car has RIM body panels. For many of these products, however, a number of injection moulding products are competitive, including such diverse materials as polycarbonate/PBT blends and polypropylene/EPDM blends. In the shoe industry the RIM process has been used to make soling materials from semi-flexible polyurethane foams. 

To meet the 2001 U.S. energy standards and the 2003 phase-out of HCFCs, there is a great incentive to develop a significantly better thermal insulation. The most dramatic approach would use vacuum panels for insulating the cabinet. A number of U.S. and Japanese manufacturers have developed such panels and placed these kinds of refrigerators in homes. The panels consist of multilayer plastic envelopes filled with precipitated (fumed) silica. The claimed thermal conductivity is one-fourth that of polyurethane foam. The two major obstacles are cost and the maintenance of vacuum for twenty years. 

The tank is typically about sixteen inches in diameter and about four to five feet tall. The top of the tank is domed upward and the bottom of the tank is also domed upward in a concave manner. The outside of the tank is insulated with a polyurethane foam insulation that is squirted into the gap between the tank and a thinner sheet metal jacket. The polyurethane is made of two different components that react and harden when mixed. Included in the mixture is a blowing agent that causes the polyurethane to expand in a foam-like manner. Prior to about 1980, water heaters were insulated with fiberglass insulation. The foam insulation process was developed to allow automation and increased manufacturing speed and reduced costs. A side benefit was improved insulating ability leading to a slight increase in efficiency. 

The next major improvement was the development of combustion modified PU foam. The original CMHR polyurethane foam was developed in the USA (26) and contained hydrated alumina and halogenated flame retardants but was made in a single operation. It was used in institutions, public buildings, hotels etc. but its high density and less than optimum physical properties... 

These criteria were developed by the UK PU foam industry and were intended to differentiate the melamine or exfoliated graphite containing combustion modified PU foams from the standard, high resilience and flame retarded (chloro and bromo phosphate) containing PU foams (Table IV). This distinction was required because large scale burning tests of real arm chairs and furnished rooms had demonstrated the superiority of the combustion modified polyurethane foams. 

This support matrix is coated with PAC using a proprietary procedure that maintains the carbon in an activated state. Use of this porous polyurethane foam overcomes a difficulty that technology developers have had in identifying materials that are suitable support for the biomass when used to remove organic pollutants from the vapor phase. 

The one-shot process was developed in the 1950s. It is a technique by which the polyol and the isocyanate are mixed together. Without help, however, the reaction would be too slow to be useful. For this reason, the key to the process is the development of a formulation that accelerates tlie isocyanate reaction. We will discuss the design of a formulation to meet a specific end use in the next chapter. To complete our discussion of the processes by which polyurethane foams are made, consider the formulation for a conventional foam used for furniture cushions (Table 2.3). 

Sun et al. studied the immobilization of Rhizopus orzae in polyurethane foam cubes. The growth rates of the cells, the effectiveness of the immobilization process, and the ability to produce lactic acid were investigated. Although the study was not an attempt to remediate a wastewater stream, the paper presents an excellent review of the surface effects that hampered the development. The size of the cube defines... 

Around that time, Taku Matsushita and coworkers began work on the use of conventional polyurethane foams (we used hydrophilic polyurethanes) as scaffolds for the propagation of hepatic cells. Using a rat rnodel, they were able to demonstrate the development of the hepatic spheroids necessary in the development of a functional artificial liver. 

It is useful to examine reticulated foams in the context of their suitability as scaffolds for artificial organ development. Reticulated foams are made in a postprocessing step after polyurethane foams are made. Polyether and polyester polyurethanes are made for reticulation. The major use of the materials is in air filtration where resistance to flow (a mass transport property) is an important requirement. 2005 by CRC Press LLC... 

Prospective, multisite, uncontrolled clinical studies were conducted to study the effectiveness of the formulations and the acceptability of the polym ethane delivery system. The formulation was imbibed into 2.5-in. hydrophilic polyurethane foam discs (LMI, St. Charles, MI). Each disc contained 2.4 g of the formulation. The method of application was developed in tests that limited the active ingredient to the same amount or less than the monograph specifications for the formulation ingredients. Fourteen volunteers were given boxes containing 42 individually wrapped foam pads impregnated with the fonnulation and were asked to complete the questionnaire weekly. 

Work at the EPA Gulf Breeze Laboratory has demonstrated the potential usefulness of encapsulation in the bioremediation of PAHs. A model system has been developed in which a pure culture capable of degrading fluoranthene (strain EPA505) has been successfully encapsulated in polyurethane foam and polyvinyl alcohol (Baker et al., 1988). The capsules can be stored for several months at 4 °C with only minimal loss of viability. Upon addition of the capsules to moist soil, fluoranthene mineralization commenced in approximately the same way as observed when fresh bacterial cells were added to the soil. These results are shown in Figure 5.7a. Since the same inoculation size was used in all flasks during this experiment, the results suggest that the immobilization process does not significantly affect microbial activity. 

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