Structural Foam Preparation

Chapter 3 on Thermoplastic Foams discusses structural foams in general and considers the properties of individual structural-foam types. This discussion is concerned solely with methods of manufacturing these foams. 

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The content of the gas is called quality therefore a 70 quality contains 70% gas. Recently, foams with 95% gas have been examined. For such foam types, only foam prepared from 2% of an anionic surfactant with plain water had uniform, fine-bubble structure [782]. 

In the present study DSC and TGA data were run on DuPont 910 and DuPont 951 instruments, respectively. Arapahoe Smoke Chamber results were obtained on a commercial apparatus. Coated samples used were commercially prepared zinc arc spray samples on Noryl FN 215 Structural Foam. 

The high hydrophobicity of silicones can complicate their use in some applications. For example, proteins can undergo denaturation in contact with silicones [1]. In such cases, the siloxane can be modified to include a hydrophilic domain. This is typically accomplished by functionalizing the silicone with a hydrophilic polymer such as poly(ethylene oxide)(PEO). Silicone surfactants of this type have found widespread use as stabilizers for polyurethane foams, and have been investigated as a structurant to prepare siloxane elastomers for biomaterials... 

Cell shape is governed predominantly by final foam density and the external forces exerted on the cellular structure before its stabilization in the expanded state. In a foam prepared without such external forces, the cells tend to be spherical or ellipsoidal at gas volumes less than 70-80% of the total volume, and the shape of packed regular dodecahedra at greater gas volumes. These shapes are consistent with surface chemistry [26,28,29]. 

Other coco-based surfactants are sulfosuccinates formed by the reaction of coco fatty alcohol with maleic anhydride and further reaction with sodium sulfite or bisulfite. This product possesses good foaming properties, is compatible with soap, and is a good lime dispersant. It is used in toilet soap formulation, shampoos, hand cleaning pastes, and for scouring raw wool. Its ether variant, with 2-4 moles ethylene oxide, forms intense, finely structured foam and is used in combination with ether sulfate in baby shampoos and bath preparations. 

Two-component premix systems are widely used for different foam systems because these systems can be supplied in two kinds of drums. In addition, the machines for foam preparation can be of simple structure, and their handling and maintenance are easy. 

In the case of using aromatic polyisocyanate in making polyimide foams, crosslinking is increased by adding a highly functional polyol to react with part of the isocyanate so that the foam contains some urethane structure. A typical foam prepared in this way would have a density of 3.97 Ib/ft (63.5 kg/m ) and a K-factor of 0.26 Btu/(h) (fP) ( F/in). Foams of this type have been prepared in a range of densities of 2.5 to 18.5 Ib/ft (40 to 296 kg/m ) with compressive strengths of 25 to 1340 psi (172 to 9239 kPa) (8). 

The word "surfactant" is a widely used contraction of "surface-active agent," a compound that alters the surface tension of a liquid in which it is dissolved (1). Surfactants impart stability to polymers during the foaming process. They help control cell structure by regulating the size, and to a large degree, the uniformity of the cells. In urethane foams the choice of surfactant is governed by factors such as polyol type and method of foam preparation (13). 

Chapter 3 and all subsequent chapters were prepared by the editor, A.H. Landrock. Chapter 3 covers all types of thermoplastic foams, including rigid, semi-rigid, and structural foams. Chapter 4 briefly discusses elastomeric foams. Chapter 5 discusses a number of miscellaneous and specialty foams, many of which were also covered in Chapter 2. 

The problem of ozone depletion considered in the Montreal Protocol is discussed in detail. Qiapter 8 considers methods of manufacture, including molding methods, spraying, frothing, laminating, structural foam molding, syntactic foam preparations, and foam-in-place techniques. Chapter 9 on sources of information covers journals, manufacturers bulletins, technical conferences and their published proceeding, seminars and workshops, standardization activities, trade associations, consultants, and information centers, and books. 

Styrenic Resins Styrenic resins are thermoplastics prepared by firee-radical polymerization of styrene alone or with other unsaturated monomers. The properties of styrenic resins vary widely with molecular structure, attaining the high performance level of engineering plastics. Processed by blow and injection molding, extrusion, thermoforming, film techniques, and structural foam molding. Used heavily for the manufacture of automotive parts. 

J-29 is a structural foam adhesive-ribbon (tape) (18) specifically prepared for honeycomb structure. The epoxy resin is foamed by a diazo compound, and metallic powder filler is used to increase the thermal conductivity.,... 

Surfactants are necessary in the RIM urethane elastomer process where some degree of foaming is desired in the final moulding. They are added to the foam formulation to decrease the surface tension of the system and facilitate the dispersion of water in the hydrophobic medium, aid in nucleation, stabilize the foam and regulate cell structure. The choice of surfactant depends upon the type of foam preparation (polyester, prepolymer or one-shot polyether). Both ionic and non-ionic surface-active agents have been employed. 

The most suitable polyols are prepared via a coinitiator technique whereby optimal functionality (4-5), hydroxyl number (330-430), use viscosity (2,500 cps max) and reactivity are achieved. Comparative letbora-tory evaluations have shown that sucrose amine-based polyols are inherently more compatible with polymeric isocyanates than other polyols. They have also demonstrated excellent flow and demolding characteristics and produce hard but not brittle structural foams. 

The traditional antioxidant, BHT, was among the best performers. Foams prepared with AO-2 showed a sUghtly higher level of discoloration as compared with BHT. This small difference in performance may be structurally related. AO-2 is similar to BHT, differing only in the substitution of the para methyl group with a nonyl hydrocarbon chain. This substitution results in over a 50% increase in molecular weight with no increase in active substituents. The dilution effect of the alkyl chain may contribute to the observed marginal decrease in performance. 

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