Foamed rigidity

The plastic insulants are rigid, homogeneous materials, suitable as the core of sandwich panels. Such a method of fahrication is facilitated when using foamed rigid polyurethane, since the liquids can he made to foam between the inner and outer panel skins and have a good natural adhesion, so making a stiff structural component [40]. 

The difference between rigid and flexible foams, from a simplified view, is the nature of the cells that make up the foam. Rigid foams are made up of... 

Structural foams. Rigid foams made from thermosets. See polymer foams. 

One of the great benefits of polyurethane is versatility. With only slight changes in chemistry, one can make products ranging from soft furniture cushions to automobile bumpers and infinite numbers of other products. Depending on the application, a polyurethane chemist can vary density and stiffness to achieve acceptable product performance. The chemistry is in fact much more versatile than is required. Figure 2.19 covers soft foams, rigid foams, and other polyurethanes. We will provide more details later in this chapter, particularly as to how the independent properties of density and stiffness relate to end uses. 

Many choices of surfactants are commercially available for use in various foams such as flexible foams, HR foams, rigid foams, etc. 

Foam Rigid Foam Semi-Rigid Foam Flexible Foam... 

As opposed to flexible urethane foams, rigid urethane foams have a highly cross-linked chemical structure and a high percent of closed cells, e.g., over 90%. Rigid urethane foams can be classified as follows unmodified (or pure) rigid urethane foams and modified rigid urethane foams, which include isocyanurate-modified, epoxy-modified, amide-modified and oxazolidone-modified rigid urethane foams. 

Production Technolt es of Rigid Urethane Foam. Rigid urethane foams can be produced by different methods, as shown below. 

Polyurethane Foams. Rigid polyurethane foam can be prepared by the reaction of a polyisocyanate, a polyol, a blowing agent, a catalyst and a surfactant. Detailed explanation of these foams are described in the sections on Rigid Urethane Foams and Miscellaneous Urethane Foams earlier in this chapter. 

Polyvinyl Chloride (PVQ Foams. Rigid PVC foam is inherently fire retardant because of the high chlorine content (56.7%). Flexible PVC foams present increased fire hazards because of the plasticizers they contain. Flammable plasticizers used include alkyl phthalates, as dioctyl phthalate. Non-burning types include alkyl aryl phosphates (phosphate esters). The latter types should improve resistance to ignition and reduce flame spread when compared to the usual phthalate plasticizers (38) (41). 

MIL-P-26514F Polyurethane Foam, Rigid or Flexible, for Packaging, 18 December 1987, 24 pp (FSC 8135) (69)... 

MIL-F-46194 Foam, Rigid, Structural, Closed Cell Polymediacrylimide (PMI), 18 July 1988, 10 pp (AREA CMPS) (MR)... 

Flexible Foam Rigid Foam Elastomers Surface Coatings Adhesives Sealants... 

Z-Thane. [UTl] Polyurethane systems compds., elastomers, foams, rigid and flexible grades. 

The dielectric constant of rigid PU foams Rigid polyurethane foam (PUF) preinsulated pipes for district heating systems need measuring systems to detect leakage in a pipeline network while it is in use. One of such systems measures the absorption of a reflected pulse, transmitted via a copper wire embedded in the PUF insulation. Information about the dielectric constant and loss factor of these foams as a function of the foam density and the MDI index (see 4.1.3) was necessary to calibrate such a system. 

Flexible polyurethane foam, rigid polyurethane foam, unsaturated polyesters... 

---