Polyurethanes in the Construction Industry

MDI [4,4 -methylenebis (phenylisocyanate)] accounted for almost 85% of the worldwide demand for aniline in 2000. MDI is used primarily to make rigid polyurethane foam and polyurethane elastomers. MDI growth is expected to be 6% to 8% per year during the 2000 s as its use continues to increase in the construction industry (the largest user of rigid polyurethane foam) and the auto industry (the largest user of reaction-injection molding plastics). The aniline uses are shown in Table 20.3255. 

More than 50% of the rigid polyurethane foams manufactured in the United States in 1994 are used in the construction industry (Table 10). About 60% of the total rigid foam is used in laminated boards and insulation panels about 30% is poured in place. Insulated appliances is another important use of rigid insulation foam. 

In this book I have confined discussion to those polymeric materials which are cured by chemical reaction and which have found widespread application in the construction industry. As such, the book covers materials based on epoxies, polyurethanes, silicones, polysulphides, alkyds and polyesters. In addition, there is a chapter on hybrid polymer systems and one on acrylics. It is true that acrylic emulsions are not strictly thermosetting polymer systems, but their widespread use and importance made their exclusion difficult. These materials find use as coatings, sealants, adhesives, grouts, flooring compounds, repair compounds and waterproofing agents. 

Several other polymers such as polyurethanes, alkyds, acrylics, polyesters, silicones, etc. can be hybridised to improve the performance or to obtain desired end-results. The growth of hybrid polymer technology is giving rise to considerable improvements, and many hybrid systems have been introduced to the market. Most of the work reported in this field is for coatings, but at the same time it is useful for other products used in the construction industry. Research is under way by many polymer manufacturers and universities, and innovations are continuously being reported. In this chapter we shall be dealing with those combinations which are useful, or may be useful, for the construction industry. 

To produce polyether polyols (PEP), sorbitol is reacted in the presence of a catalyst with propylene or ethylene oxide (see Figure 9.2.12). The reaetion is aimed at achieving polyols with a hydroxyl number of between 350 and 550. Sorbitol-based PEPs are then used to manufacture rigid or semi-rigid polyurethane foams by reaction with a suitable polyisocyanate. These foams are typically used in the construction industry and in packaging, industrial insulation, appliances and transport applications. 

Of the 687 kt/a of rigid foam produced in the United States and Canada in 1998, more than 50% was used in the construction industry. About 60% of this total was used in laminated boards and insulation panels abont 30% was poured at construction site. Insulated appliances (132 kt/a) and tank and pipe insulation (79 kt/a) are other important uses of rigid insulation foam. Rigid polyurethane foam is produced from PMDI. Another important application of PMDI is particle board binder resins. A total of 160 kt/a of PMDI was used in this application in the United States and Canada in 1998. 

Sealants are used to seal cracks and joints in window frames or between panels, to prevent rain, air and dust from passing through the joint and even to improve the thermal performance of a wall. Sealants are available in a non-cured, pourable or extrudable state for easy application. Upon curing, they are transformed into a solid elastomeric material. Sealants must be deformable, have good recovery properties and should have good overall elastic properties. They should be durable and should not be affected by the environment to which they wiU be subjected. The general composition of a sealant consists of a base polym and additives. Sealants can be classified based on their chemical conq)osition. Two of the most widely used groups in the construction industry, are siliccmes and polyurethanes (i). 

Synthetic polymers suitable as binders for the production of caulks and sealants include silicones, polyurethanes, polysulfides, and aqueous polymer emulsions. The importance of these sealants in the construction industry has also increased considerably through the increased use of prefabricated elements. The movement of components must be absorbed and compensated by the joint sealant. These movements can be expansion, contraction, or shear. 

In 2002, the world production of polymers (not including synthetic libers and rubbers) was ca. 190 million metric tons. Of these, the combined production of poly(ethylene terephthalate), low- and high-density polyethyelene, polypropylene, poly(vinyl chloride), polystyrene, and polyurethane was 152.3 milhon metric tons [1]. These synthetic, petroleum-based polymers are used, inter alia, as engineering plastics, for packing, in the construction-, car-, truck- and food-industry. They are chemically very stable, and can be processed by injection molding, and by extrusion from the melt in a variety of forms. These attractive features, however, are associated with two main problems ... 

Structural adhesives based on polyurethanes are used widely in the transport industry, especially for bonding plastics reinforced with glass or other fibres. They are used also as sealants in glazing for motor vehicles—most notably following the introduction in recent years of front and rear windows bonded as elements in the construction. 

Adipic acid is mainly used to produce nylon-6,6, a synthetic polyamide used in clothing, in the automobile industry, and in construction it also finds application in polyurethanes, plasticizers, and synthetic lubricants. Manufacture of nylon accounts for 89% of adipic acid consumption in North America, and 55-65% in Western Europe and Japan. 

Among the countless number of applications of polymers, the construction industry is one which utilises several polymeric materials. In this book I cover those polymeric materials which are single or bicomponent systems and are cured at ambient temperature either with the aid of curing agents or atmospheric moisture. The various polymers used in manufacturing such products include epoxies, polyurethanes, acrylics, silicones, polysulphides, alkyds and polyesters. As a result of innovation, new technologies exist which utilise more than one polymer in a single product. Such systems are discussed in Chapter 10, on hybrid polymers. 

Polyurethane sealants have taken a good share in today s sealant market. Polysulphide sealants are in greater use for water-retaining structures, and silicone sealants for structural glazing purposes but polyurethanes have a greater market share as construction sealants. These sealants were first introduced to the construction industry in the early 1970s as two-component materials. 

Organic isocynate [8,85,91] compounds have been known for a long time, but first became commercially interesting in the last decades based on the development work by Bayer. The reaction of di- and polyisocyanates with di- and polyols forms polyurethanes (PUR) with many uses. The preferred use of PUR in the automobile industry, in construction, and in refrigeration technology led to a considerable increase in the production capacity for feedstock diisocyanates. 

Flexible and rigid foams are the most popular types of polyurethane made in the United States. Flexible foams are used for cushioning, as in mattresses, upholstered furniture, and automobile seats. Semiflexible foams are component of carpet pads, sponges, packaging, and door panels for automobiles. Rigid polyurethane foams are used to produce insulation for roofs, refrigerators, and freezers. The construction industry accounted for more than half of all the rigid polyurethane foam made in 2002, primarily for... 

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