Formaldehyde polymers, production volume

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

The main thermoplastic polymer types are actylic, cellulosic, ethylene vinyl acetate (EVA), polyethylene terephthalate (PET), polyamides (nylons), polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polycarbonate and polypropylene (PP). PET, PVC, HOPE, LDPE, PS and PP have a higher production volume and relatively low cost. The main thermosetting polymer types are aminoplastics, epoxies, phenolics (phenol formaldehyde), polyesters and silicones. These polymers have a wide range of applications and their features are very different. 

The first plastic was a mixture of cellulose nitrate and camphor invented in the 1860s by John Wesley Hyatt it was given the TM Celluloid. In 1899 Spit-teler developed a method of hardening casein with formaldehyde and thus founded the casein plastics industry, e.g., small items such as buttons. The earliest high-volume plastic, a condensation product of phenol and formaldehyde, was introduced by Leo Baekeland in 1907. Trademarked Bakelite, it was the first truly synthetic high polymer. Its chief use was as engineering material since its dark color limited its application to items in which color was not a factor. 

Thermosetting polymers can be made using either step growth or chain polymerization procedures. To obtain a crosslinked polymer, at least one of the monomers used must be trifunctional. A condensation production process is used to produce phenolic polymers which have the highest volume usage of all thermosets. The reaction between phenol and formaldehyde to form a thermoset phenolic polymer is shown in Fig. 4.54. Three... 

The greatest volume of wood adhesives for structural applications are thermosetting phenol-formaldehyde (PF) or urea-formaldehyde (UF) polymers or their derivatives. PFs are the commodity for exterior applications, while UFs are the commodity for interior applications. Because each composite product and the associated process may require a somewhat different resin, many variations of PF and UF resins are available. Isocyanate crosslinking resins are used to a lesser extent than PFs or UFs in manufactured board. Although these resins impart a durable, water resistant bond suitable for exterior application, the cost per pound of adhesive is greater than for PFs or UFs. 

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