Polyurethane phenolic isocyanate

This process is used to a minor extent for moulding and core-making, with restrictions for steel casting, as cracks or pinholes may occur. These can be prevented however, by the addition of iron oxide and by dr3dng the moulds and cores. In some countries (e g. Sweden) this type of binder has not been used for 25 years, mainly because of its effect on the working environment. 

This process is based on a polyaddition reaction between a phenolic resin and an isocyanate (mostly MDI), catalysed by a pyridine derivative with the result being a polyurethane stmcture. All the components are in solution in aromatic and/or polar solvent (i.e. aliphatic solvent) with a high boiling point. Contamination by water must be strictly avoided since water reacts strongly with the isocyanate. 

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Polyurethane (phenolic isocyanate) The sand temperature is kept between 15 and 25 C, to maintain process control and to minimise emissions. Best practice is to work with three pumps and to mix the catalyst and the phenolic resin with isocyanate and sand directly in the mixer [202, TWG, 2002]... 

TG-MS is ideally suited to reveal differences in pressure behaviour during thermal decomposition of materials. This has been illustrated by Mol [144] in TG-MS analysis of toluene diisocyanate (TDI) and methylene bis-4-phenol isocyanate (MDI)-based polyurethanes, where the observed greater increase in pressure for the TDI polyurethane than for the MDI derivative indicates a higher loss of low molecular weight fragments. This is not possible to deduct from the TG curves alone. Such indications are of great... 

Polyurethane Vapours of formaldehyde, phenol, isocyanate and aromatic solvents may be emitted because of the vapour pressure of these constituents. As the polymerisation occurs at ambient temperature, the vapour pressures of the components are low and given the consumption rates, the emissions are insignificant. Obnoxious odours may be generated in the moulding area but are not likely to cause external nuisance... 

As discussed in the Introduction, in addition to hot-melt adhesives, one of the most important forms of adhesives for the future is the waterborne system. In general, an advantage of the waterborne system is that it is free from the solvent-pollution problem. For this reason, we shall describe several new waterborne systems in detail acrylics, modified ethylene-vinyl acetate, polyurethanes, phenolics, epoxies, isocyanates, and tackifiers. Applications of these systems range from PSA s contact adhesives, and laminating adhesives to wood adhesives. 

The chief outlets are for polyurethane (di-isocyanates) 40%, rubber chemicals, herbicides minor users include dye makers (approx. 5%) and pharmaceutical manufacturers. Benzene is the feedstock and the traditional route is to nitrate this and then to reduce the nitrobenzene to aniline. Catalytic hydrogenation has displaced iron/ferrous chloride reduction in this and analogous reductions e.g. in the manufacture of toluidines. Amination of phenol manufactured from cumene (Vol. I, p. 366) has been patented (Figure 2.8). The yield claimed is 99% though the economic viability is uncertain. 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryHc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenoHc thermosetting resins (see Phenolic resins). Toluene 2,4-cHisocyanate (TDI), employed in the production of polyurethane foam, indirectly consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

An emulsion polymer-isocyanate adhesive, a crosslinked polyvinyl acetate adhesive, a resorcinol-formaldehyde adhesive, a phenol-resorcinol-formalde-hyde adhesive, and an acid-catalyzed phenolic-formaldehyde adhesive developed bonds of high shear strength and wood failure at all levels of acetylation in the dry condition. A neoprene contact bond adhesive and a moisture-curing polyurethane hot-melt adhesive performed as well on acetylated wood as untreated wood in tests of dry strength. Only a cold-setting resorcinol-formal-... 

Since polyurethanes are frequently used in household objects, their thermal degradation and products generated during burning were studied frequently [3-5]. Among these can be included studies on polyester-urethanes [6], polyether-urethanes [7], phenol-formaldehyde urethane [8], studies on the influence of fire retardants on polyurethane decomposition [9, 10], generation of isocyanates during decomposition [11], and other studies [12-17]. Some reports on thermal decomposition of polyurethanes are summarized in Table 14.1.1. 

Example 4. Polyurethane formation, in which the alcohol adds across the carbon nitrogen double bond of the isocyanate function (0 = C = N-R) to form the urethane (-0-C0-NH-) link without loss of a small molecule, represents an exception to this general recognition feature of polycondensations. Bakelite is one of several possible products from phenol-formaldehyde resins, and these may or may not involve loss of a small molecule. This more complicated process will be discussed in further detail later. 

Phenol blocked isocyanates also have been used to prepare hyperbranched polyurethanes by a step-growth polycondensation mechanism, using DBTDL as a catalyst. 4... 

Ho et al (1996) examined polyol or polysiloxane thermoplastic polyurethanes (TPUs) as modifiers in cresol-formaldehye novolac epoxy resins cured with phenolic novolac resin for computer-chip encapsulation. A stable sea-island dispersion of TPU particles was achieved by the epoxy ring-opening with isocyanate groups of the urethane prepolymer to form an oxazolidone. The flexural modulus was reduced by addition of TPU and also the Tg was increased due to the rigid oxazolidone structure. Mayadunne et al (1999) extended this work to a series of phenol- and naphthol-based aralkyl epoxy resins. 

Similarly, an aqueous treatment for wool uses an isocyanate blocked with a bisulfite. In this case, the by-product bisulfite salt can be removed, and possibly recycled, by washing the fabric with water at the end. The dissociation temperature decreases in the following order alcohol > lactam > phenol > ketoxime > active methylene compound. e-Caprolactam is a typical lactam, ethyl acetoacetate a typical active methylene compound. This thermal reversibility has been used to prepare a polyurethane from 1,4-butanediol, 4,4 -diphenyldiiso-cyanate, and 4,4 -isopropylidenediphenol (bisphenol A) (2.30) that can be recycled just by remolding.76... 

Polyurethanes (single-component system) Block polyisocyanates and hydroxyl polymers Phenol-blocked isocyanates and hydroxyl groups Unblocking or removal of phenol to form a free isocynate followed by addition of hydroxyl groups to form urethane linkages 8 ... 

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