Silicones in the Construction Industry

The applications of silicon in the electronics industry are so important that the major part of this report will be devoted to the electrochemistry of the elemental silicon crystals used as semiconductors. In fact, the extremely efficient surface treatment of Si wafers needed for the construction of ultra large-scale... 

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. 

Today, silicones have become virtually irreplaceable materials worldwide and have an extremely wide range of applications. The use of silicone room-temperature vulcanising (RTV) elastomers in the construction industry originated in the early 1960s. The value of silicone RTV elastomers is based on important properties such as their thermal stability, unusual surface properties, water repellency, high permeability, oxidative stability and ultraviolet (UV) resistance (Cash, 1970). 

Table 6.1 Specific properties and applications of silicone systems in the construction industry...

Silicone coatings used in the construction industry are one-component silicone rubber dispersions. They cure at room temperature, vulcanisation being effected by the influence of atmospheric humidity. The process evolves various primary aliphatic amines and the solvent evaporates. 

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. 

In this group of products, foaming takes place at the same time with the chemical reaction (polycondensation) between the initial starting materials in view to produce the polymer. The most common are made of PU, PIR, PF, UF, EP, and silicone polymers. The most versatile and most used in the construction industry are the foams based on PU and more recently on PIR. 

We will try to place each Chemical type chapter near to the chapter dealing with the Industry using these types of adhesives and sealants, so that each volume will focus on one main field for instance, in Volume 3 that will be devoted to Construction, we will study the adhesives for construction, civil engineering, the silicone sealants, the woodworking and furniture adhesives, acrylic adhesives and sealants. Those working in the construction industry can then get fairly complete information from that volume. However, construction... 

Room temperature vulcanizing (RTV) systems with outstanding resistance to weathering together with good adhesion to a wide variety of substrates form the basis of families of coatings, sealants and adhesives which find much use in exposed applications particularly in the construction Industry and this is one of the most Important applications of silicones today. 

RTV silicone adhesive is a rubberlike polymer called polydimethsiloxane. RTV stands for room temperature vulcanizing, or simply a rubber that cures at room temperature. Silicone rubber adhesives are made using a complicated process that turns elemental silicon metal made from sand (silica) into a rubbery polymer. When cured, silicone rubber adhesives/sealants have excellent resistance to heat (500—600 °F) and moisture that makes them exceptionally suited for outdoor weathering applications such as sealant and caulking compounds in the construction industry. Because of its exceptional properties, silicone adhesive has been used in some exotic applications such as the soles of the boots worn by the first astronauts to walk on the moon. Silicone adhesive/sealants are used to seal windows, doors, and portholes on the space shuttle and many satellite missiles. A special silicone adhesive is used to bond the heat shield tiles on space shuttles. 

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. 

Another important application area for PSAs in the electronic industry focuses on the manufacturing, transport and assembly of electronic components into larger devices, such as computer disk drives. Due to the sensitivity of these components, contamination with adhesive residue, its outgassing products, or residue transferred from any liners used, needs to be avoided. Cleanliness of the whole tape construction becomes very critical, because residuals like metal ions, surfactants, halogens, silicones, and the like can cause product failures of the electronic component or product. Due to their inherent tackiness, acrylic PSAs are very attractive for this type of application. Other PSAs can be used as well, but particular attention has to be given to the choice of tackifier or other additives needed in the PSA formulation. The choice of release liner also becomes very critical because of the concern about silicone transfer to the adhesive, which may eventually contaminate the electronic part. 

Conveyor systems are applied in a number of areas in the rubber industry. The types used can range from simple canvas belt conveyors used for haul-off from conventional extruders, to systems used for transport and cooling of profile products, both in and emerging from continuous vulcanisation units. The latter types have to be resistant to the temperatures used in such systems and are variously constructed from glass fibre-reinforced polytetrafluoroethylene or a silicone rubber covered belt. 

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