Foam producers

There are five basic types of polystyrene foams produced in a wide range of densities and employed in a wide variety of apphcations (/) extmded polystyrene board (2) extmded polystyrene sheet (2) expanded bead mol ding (4) injection molded stmctural foam and (5) expanded polystyrene loose-fiU packaging. 

Fig. 2. Problems in wetting A, Hquids that wet the exterior before displacing gas from pores leave gas trapped in the submerged clump B, fully wetted clumps of buoyant particles do not sink C, nonwetting Hquids do not penetrate and displace gas from pores, so clump remains buoyant and caimot submerge and D, foam produced from air is drawn under the surface, sheared into small bubbles, and stabilized by the wetting agent.

Most low density rigid polyurethane foams have a closed-ceU content of >90%. Above 0.032 g/cm, closed-ceU content increases rapidly and is generally >99% above 0.192 g/cm. Bun foam, produced under controlled conditions, has a very fine-cell stmcture, with cell sizes of 150—200 lm. 

Most flexible foams produced are based on polyether polyols ca 8—10% (15—20% in Europe) of the total production is based on polyester polyols. Elexible polyether foams have excellent cushioning properties, are flexible over a wide range of temperatures, and can resist fatigue, aging, chemicals, and mold growth. Polyester-based foams are superior in resistance to dry cleaning and can be flame-bonded to textiles. 

Pour Methods. The Hquid is poured or drained from one vessel iato another. This approach is best limited to foams produced from dissolved gases ia the Hquid. 

For materials of equivalent density water-blown polyurethanes and the hydrocarbon-blown polystyrene foams have similar thermal conductivities. This is because the controlling factor determining the conductivity is the nature of the gas present in the cavities. In both of the above cases air, to all intents and purposes, normally replaces any residual blowing gas either during manufacture or soon after. Polyurethane foams produced using fluorocarbons have a lower thermal conductivity (0.12-0.15 Btu in fr h °F ) (0.017-0.022 W/mK) because of the lower conductivity of the gas. The comparative thermal conductivities for air, carbon dioxide and monofluorotrichloromethane are given in Table 27.3. 

Sodium bicarbonate (baking soda) is added for taste and mouth feel. It combines with acids to release carbon dioxide gas, adding to the foam produced by brushing. It is a mild abrasive. It may reduce the numbers of acid-loving bacteria in the mouth, although this effect lasts only as long as the mouth stays alkaline. 

The glycolysis of rigid polyurethane foams produces polyol products which can be reintroduced into the production cycle of PUR insulation materials to form materials with properties practically equivalent to dtose of materials produced using virgin polyols. Aromatic amines produced as by-products in die glycolysis process are toxic and therefore undesired side products. The most frequently observed side product is diphenylmedianediamine (DMDA), which is formed... 

The foam volume and stability of alcohol sulfates is relatively increased in hard water compared to soft water. The amount and quality of foam is dependent on the alkyl length. Sulfates with C12-C,4 alkyl chains produce the richest creamy foam with small bubbles. C8-C10 alcohol sulfates are foam depressants and C16-C18 alcohol sulfates are poor foaming surfactants. Foams produced by alcohol sulfates are also relatively stable in the presence of sebum. Sodium and ammonium alcohol sulfates foam better than triethanolamine alcohol sulfates. Alcohol ether sulfates produce lighter foams than those of alcohol... 

Alcohol ether sulfates with different number of moles of ethylene oxide are also used in emulsion polymerization and in the paint industry as dispersing agents. A particular use of alcohol ether sulfates is as foamers in low- and medium pressure drilling for water, oil, and gas. The foam produced by the surfactant reduces the pressure of the water column as water is replaced by air. 

Figure 6.2. (a). Colloidal silica network on the surface of spores from Isoetes pantii (quill wort). Scale = 20 pm. (b). Polystyrene networks and foams produced as a biproduct of colloidal latex formation. Both types of colloidal system are typical of the diversity of patterns that can be derived from the interactions of minute particles. Scale (in (a)) = 50pm. 

This is an insoluble gelatin foam produced by whisking warm gelatin solution to a uniform foam, wtiieh is then dried. It ean be cut into suitable shapes, paeked in metal or paper containers and sterilized by dry heat (150°C for 1 hour). Moist heat destroys the physical properties of the material. Immediately before use, it ean be moistened with normal saline eontaining thrombin. It behaves as a meehanieal haemostat providing the ftamewoik on wtiieh blood elotting ean oeeur. 

In the manufacturing of crosslinked polyolefin foam, the foam expansion and cell stabilization highly dependent on the degree of crosslinking. It has been reported that at higher crosslinking level the foam produce have higher density [1, 2]. 

M or Plant water system Foam produced in ACE cascade evaporator during water-washing carried out into furnace through primary air system... 

The foam produced with Aqueous Film Forming Foam (AFFF) concentrate is dry-chemical compatible. Protein and fluoroprotein foam concentrates and AFFF concentrates are incompatible and should not be mixed although foams separately generated with these concentrates are compatible and can be applied to a fire in sequence or simultaneously. AFFF is available in various liquid concentrate percentages. 

The aromatic polyols resulting from the reaction can be mixed with commercial polyols, blowing agents, surfactants, catalysts, and polymeric isocyanates to produce a rigid polyurethane foam. n compared w control foams produced from commercially available polyester polyols, the foams produced from reclaimed materials were found to have essentially the same properties. 

Harden s (27) market survey of the growth of polyolefin foams production and sales shows that 114 x 10 kg of PE was used to make PE foam in 2001. The growth rate for the next 6 years was predicted as 5-6% per year, due to recovery in the US economy and to penetration of the automotive sector. In North America, 50% of the demand was for uncrosslinked foam, 24% for crosslinked PE foams, 15% for EPP, 6% for PP foams, 3% for EVA foams and 2% for polyethylene bead (EPE) foam. As protective packaging is the largest PE foam use sector, PE foam competes with a number of other packaging materials. Substitution of bead foam products (EPP, EPE, ARCEL copolymer) by extruded non-crosslinked PE foams, produced by the metallocene process was expected on the grounds of reduced costs. Compared with EPS foams the polyolefin foams have a lower yield stress for a given density. Compared with PU foams, the upper use temperature of polyolefin foams tends to be lower. Eor both these reasons, these foams are likely to coexist. 

EFFECT OF CELL SIZE ON THE PHYSICAL PROPERTIES OF CROSSLINKED CLOSED CELL POLYETHYLENE FOAMS PRODUCED BY A HIGH PRESSURE NITROGEN SOLUTION PROCESS... 

Blends of poly (ethylene terephthalate) (PETP) and polypropylene (PP) with different rheological properties were dry blended or compounded, and extrusion foamed using both physical blowing and chemical agents, and the foam properties compared with those of foam produced from the individual components in the absence of compatibilisers and rheology modifiers. The foams were characterised by measurement of density, cell size and thermal properties. Low density foam with a fine cell size was obtained by addition of a compatibiliser and a co-agent, and foamed using carbon dioxide. The presence of PP or a polyolefin-based compatibiliser did not effect... 

No.4, July 2001, p.333-52 INVESTIGATION OF THE RADIATION CROSSLINKED FOAMS PRODUCED FROM METALLOCENE POLYOLEFIN ELASTOMERS/ POLYETHYLENE BLEND Kim D W Kim K S... 

---