Thermoplastic structural foam

In a properly foamed molding the foam cells are roughly spherical and the cell walls have no particular directional alignment. They are essentially randomly oriented. The local orientation and anisotropic reinforcement effect of the fibers around individual cell walls are integrated into, and become additional factors in, a general enhanced reinforcing effect that is isotropic in the molding considered as a whole (50). 

Stabilizers are agents used in compounding some plastics to assist in maintaining the physical and chemical properties of the compounded materials at satisfactory values throughout the processing and service life of the material and the parts made from the material. Some additives that function as stabilizers include the following 

The term stabilizer is obviously a general term covering a wide range of additives intended to maintain certain properties at desired levels. 

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). 

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Throne, J.L. Mechanical properties of thermoplastic structural foams, in Wendle, B.C. (ed.) Engineering Guide to Structural Foams, Technomic, Lancaster, PA, USA (1976) pp. 91 -114. 

Thermoplastic structural foams with bulk densities not less than 50% of the solid resin densities are considered. Cellular morphology, uniform-density cell behaviour, the I-beam concept in designing, core-density profile and the role of the skin, mechanical properties, and ductile-brittle transitions are discussed. 63 refs. 

Table 3-1 suimnarizes the physical properties of typical thermoplastic structural foams of 1/8" wall thickness with a 20% density reduction over solid plastics (6). 

Table 3.1 Physical Properties of Thermoplastic Structural Foam (Reprinted from Reference 6, Courtesy of Van Nostrand Reinhold) N) 4s- X 9 O. CT O O PT O -h... 

Brewer, G.W., "Properties of Thermoplastic Structural Foams," pp., 508-513 in Engineering Materials Handbook, Vol. 2 -Engineered Plastics, ASM International, Materials Park, Ohio (1988). 

Foam-Kon. [LNP ICI Advanced Materials] Thermoplastic structural foam cone. for high pressure foam systems, inj. molding compds. 

Table 7.18 Properties of fV thick thermoplastic structural foam (20% weight reduction)... 

Hobbs S.Y., 1975, Bubble growth in thermoplastic structural foams, G.E.P. technical information series, nr. 75CRD210... 

Solvent cements are usually preferable to conventional adhesives for thermoplastic structural foams. Some solvent cements and solvent-containing, pressure-sensitive adhesives will collapse thermoplastic foams. Water-based adhesives based on SBR, polyvinyl acetate, or neoprene are frequently used. Solvent cementing is not effective on polyethylene foams because of their inertness. Recommendations for adhesives for thermoplastic foams are ... 

Permanent Gases. Air can be whipped into liquid plastisol or used to froth liquid polyurethane formulations. In hot processing, where air could cause oxidative degradation, nitrogen alone is used typically, it is compressed into molten polymer during molding or extrusion to make thermoplastic structural foam. 

Supercritical CO2. This is liquefied at high pressure, forced into the molten polymer, and then allowed to expand and form gas bubbles. This process has been successful in thermoplastic structural foams. 

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