Foam products

Foam-injection molding Foam plastic sheathing Foam products Foam regulators Foam rheology... 

Low deasity polyethyleae foam products (thin sheets, planks, rounds, tubes) ia the range of 32—160 kg/m (2—10 lbs/ft ) have beea prepared by an extmsion technique usiag various gaseous fluorocarboa blowiag ageats (100,101). The techniques are similar to those described earlier for produciag extmded polystyreae foam planks and foam sheets. 

In the low pressure process, a short shot of a resia containing a blowiag ageat is forced iato the mold where the expandable material is aUowed to expand to fiU the mold under pressures of 690—4140 kPa (100—600 psi). This process produces stmctural foam products with a characteristic surface swid pattern produced by the coUapse of ceUs on the surface of molded articles. 

In the high pressure process, a resia melt containing a chemical blowiag ageat is iajected iato an expandable mold under high pressure. Foaming begias as the mold cavity expands. This process produces stmctural foam products with very smooth surfaces siace the skin is formed before expansion takes place. 

There are three basic types of polyethylene foams of importance (/) extmded foams from low density polyethylene (LPDE) (2) foam products from high density polyethylene (HDPE) and (J) cross-linked polyethylene foams. Other polyolefin foams have an insignificant volume as compared to polyethylene foams and most of their uses are as resia extenders. 

Foam Products. Latices are made into foams for use in cushioning appHcations. The latices are frothed with air and then chemically coagulated for thick appHcations, or heated to induce coagulation for thinner appHcations. The latter method allows for infinite pot life during production (see Foamed plastics). 

The Hquid monomers are suitable for bulk polymerization processes. The reaction can be conducted in a mold (casting, reaction injection mol ding), continuously on a conveyor (block and panel foam production), or in an extmder (thermoplastic polyurethane elastomers and engineering thermoplastics). Also, spraying of the monomers onto the surface of suitable substrates provides insulation barriers or cross-linked coatings. 

In more recent years, molded flexible foam products are becoming more popular. The bulk of the molded flexible urethane foam is employed in the transportation industry, where it is highly suitable for the manufacture of seat cushions, back cushions, and bucket-seat padding. TDI prepolymers were used in flexible foam mol ding ia conjunction with polyether polyols. The introduction of organotin catalysts and efficient siHcone surfactants faciHtates one-shot foam mol ding, which is the most economical production method. 

The polyurethane industry is dominated by the multinational isocyanate producers. Several of the principal isocyanate producers, including BASF, Bayer, Dow, ICI, and Olin, also manufacture polyols, the other significant building block for polyurethanes. Annual production capacities of the global aromatic isocyanate producers are Hsted in Table 11. Polyols, mainly used for flexible foam production, account for 65 wt % in a flexible foam formulation, 35% in rigid polyurethane foams, and even less in PUIR foams. 

In addition to chemical synthesis and enhanced oil recovery, gaseous carbon dioxide is used in the carbonated beverage industry. Carbon dioxide gas under pressure is introduced into mbber and plastic mixes, and on pressure release a foamed product is produced. Carbon dioxide and inert gas mixtures rich in carbon dioxide are used to purge and fiH industrial equipment to prevent the formation of explosive gas mixtures. 

The alloys can be processed into parts requiring hydrolytic and autoclave stabiHty, such as desalinization filter frames and medical devices. Foamed products are used in cabinets for business machines, computers, and copiers. Automotive seat backs are made by blow mol ding and replacements for metal parts by injection mol ding. 

Foam Production This is important in froth-flotation separations in the manufac ture of cellular elastomers, plastics, and glass and in certain special apphcations (e.g., food products, fire extinguishers). Unwanted foam can occur in process columns, in agitated vessels, and in reactors in which a gaseous product is formed it must be avoided, destroyed, or controlled. Berkman and Egloff (Emulsions and Foams, Reinhold, New York, 1941, pp. 112-152) have mentioned that foam is produced only in systems possessing the proper combination of interfacial tension, viscosity, volatihty, and concentration of solute or suspended solids. From the standpoint of gas comminution, foam production requires the creation of small biibbles in a hquid capable of sustaining foam. 

Chlorofluoro- Used in refrigeration and production of Refrigeration, plastic foam production, Attacks stratospheric ozone layer green-... 

In the absence of solvents and with suitable catalysts the evolution of carbon dioxide simultaneously with the polycarbodi-imide formation gives rise to a foamed product. These foams are cross-linked because of reactions between carbodi-imide groups and free isocyanate groups. Raw materials for such foams are now available from Bayer (Baymid). 

High-pressure structural foam products have generally been found to require little or no postfinishing. Although high-pressure foam products may exhibit visual splay, their surface smoothness is maintained and no sanding or filling is required. 

Fig. 6-19 Composite cross-section of a structural foam product.

There are many ways in which foams can be processed and used as slabs, blocks, boards, sheets, molded shapes, sprayed coatings, extruded profiles, foamed in place in existing cavities, in which the liquid material is poured and allowed to foam, and as structural foams (Chapter 6, STRUCTURAL FOAM). Conventional equipment such as extruders, injection, or compression machines is used. However specially designed machines are available to just produce foamed products. 

Polyurethane materials are extremely versatile in that it is possible to produce a large variety of structures which range in properties from linear and flexible to crosslinked and rigid. The crosslinked PURs are thermosets, which are insoluble and infusible and therefore cannot be reprocessed by extrusion without suffering extensive thermal degradation. At present, the main sources of recyclable waste are flexible PUR foams and automobile waste. Waste and scraps of these materials may consist of 15-25% by weight of total PUR foam production. 

Gafa and Lattanzi [6] determined the foaming power of commercial surfactants including AOS, LAS, AS, and SAS in 1 g/L solutions at 40°C according to a modified Ross-Miles method [66]. Their data, shown in Table 24, show that the best foaming products are the AOS and AS compounds followed by LAS and SAS. 

The rapid rise in the industrial (catalyst in PVC and foam production), agricultural (fungicides and acaricides), and biological applications (wood, stone, and glass preservatives) of organotin(IV) compounds during the last few decades has led to their accumulation in the environment and, consequently, in biological systems. 

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