Urethane-polyisocyanuric foams

Urethane - polyisocyanuric foams (PU/PIR) foams) contain isocyanuric rings. Isocyanuric rings are glycolysed at lower reaction rates than the urea or urethane groups, with the formation of hydroxyalkyl carbamates and an amine (reaction 20.7) [11] ... 

Foamed plastics (qv) were developed in Europe and the United States in the mid-to-late 1930s. In the mid-1940s, extmded foamed polystyrene (XEPS) was produced commercially, foUowed by polyurethanes and expanded (molded) polystyrene (EPS) which were manufactured from beads (1,2). In response to the requirement for more fire-resistant ceUular plastics, polyisocyanurate foams and modified urethanes containing additives were developed in the late 1960s urea—formaldehyde, phenoHc, and other foams were also used in Europe at this time. 

Urethane structures decompose at around 200 °C, giving around 20% char yield, but isocyanuric structures are much more thermostable and are decomposed at 325 °C, with a char yield of around 50% [4, 5]. Due to this high char yield, polyisocyanuric foams have an intrinsic fire resistance [6-9]. 

Though closed-cell rigid polyurethane foams are excellent thermal insulators, they suffer form the drawback of unsatisfactory fire resistance even in the presence of phosphorus- and halogen-based fire retardants. In this context, polyisocyanurates, which are also based on isocyanates, have shown considerable promise. Isocyanurate has greater flame resistance then urethane. Although rigid polyurethane is specified for the temperatures up to 200°F (93°C), rigid polyisocyanurate foams, often called trimer foams, withstand use temperatures to 300°F (149°C). Physical properties and insulation efficiency are similar for both types. 

Morimoto, T., Mori, T. and Enomoto, S. Ignition properties of polymers evaluated from ignition temperature and ignition limiting oxygen index. J. Appl. Polym. Sci., 22, 1911 (1978) Imai, Y. and Inukai, T. Studies on general properties of urethane-modified polyisocyanurate foams. J. Cellular Plast., 19, No. 5, 312 (1983)... 

PIR foams are produced by using standard PU foaming equipment. Unmodified PIR foams have a highly crosslinked structure, and therefore are extremely brittle. What did prove successful was to lower the crosslinking density of the foams by adding modifiers, which led to, modified polyisocyanurate foams such as [40] urethane-modified PIR foam, amide-modified PIR foam, imide-modified PIR foam, carbodiimide-modified PIR foam and oxazolidone-modified PIR foam. 

This book series presents in-depth reports on the most important new developments in urethane technology. Volumes 2-5 contain papers written only by Japanese specialists. A number of these papers concern rigid and flexible foams. Polyurethanes and polyisocyanurates are widely used in Japan. The papers cover recent developments in chemistry, processing, properties and applications. 

Frisch, Patel, and Marsh [28] also reported on the preparation of isocyanurate-urethane foams and briefly reviewed the early developments in the field of polyisocyanurates. 

The trimerization of isocyanates to form isocyanurate rings is particularly important in producing iire-resistant rigid foams, and a large volume of work has appeared on this topic. Much of it has been done by Kresta and co-workers, who have discussed the general mechanism, the co-catalytic effect of urethane groups, and the use of cyclic sulphonium zwitterions and aminimides as catalysts. Model systems have been used for these studies, but attention has also been paid to the kinetics and mechanism of commercial polyisocyanurate systems. ... 

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