Phenoplast resins

Amino and phenoplast resins (like melamine, urea, and phenolic) can also be used for elevated temperature curing. They are cross-linked through the hydroxyl group of the epoxy and produce products with good chemical resistance. 

UF precursors can be mixed with MF precursors to give copolymer networks. Due to the difference in reactivity, melamine methylols are consumed first, thus inducing a certain heterogeneity in composition of the resulting network. It is even possible to mix MF resins with phenoplast resins however, there is no evidence for the existence of covalent bonding between the two networks. The fields of... 

Cross-linking with aminoplasts and phenoplasts constitutes an important class of hardeners for high molecular-weight epoxy resins that require elevated temperature cures (see Amino resins). 

Phenolic resins are also widely known as phenol-formaldehyde resins, PF resins and phenoplasts. The trade name Bakelite has in the past been widely and erroneously used as a common noun and indeed is noted as such in many English dictionaries. 

Carswell. T.S., Phenoplasts their structure, properties, and chemical technology. In Mark. H. and Melville, H.W. (Eds.), High Polymers. Interscience, New York, 1947, Chapter 1. Knop, A. and Pilato, L.A., Phenolic Resins. Springer-Verlag, Berlin, 1985, p. 3. 

Another POLIDCASYR extension ensures that structural features of the backbone can be distinguished from those occurring in side chains. The system furthermore augments structure codes for polymers using a controlled vocabulary of keywords, such as epoxy resin , aminoplast or phenoplast . 

In far too many instances trade-name polymer nomenclature conveys very little meaning regarding the structure of a polymer. Many condensation polymers, in fact, seem not to have names. Thus the polymer obtained by the step polymerization of formaldehyde and phenol is variously referred to a phenol-formaldehyde polymer, phenol-formaldehyde resin, phenolic, phenolic resin, and phenoplast. Polymers of formaldehyde or other aldehydes with urea or melamine are generally referred to as amino resins or aminoplasts without any more specific names. It is often extremely difficult to determine which aldehyde and which amino monomers have been used to synthesize a particular polymer being referred to as an amino resin. More specific nomenclature, if it can be called that, is afforded by indicating the two reactants as in names such as urea-formaldehyde resin or melamine-formaldehyde resin. 

Phenoplasts manufactured on tlie basis of thermoreactive phenolformalde-hyde resin, harden on heating up to 120-170°C and then become insoluble. They are usually reinforced witli asbestos fiber. 

Soils stabilized with urea-formaldehyde have strengths comparable to the phenoplasts and like those materials are less sensitive to testing strain rate than other chemical grouts. (For optimum mechanical properties and to keep free formaldehyde levels low, one molecule of urea should be provided with three molecules of formaldehyde.) Little data are available, but it is probable that aminoplasts break down comparatively quickly under cyclic wet iry and freeze thaw conditions. The creep endurance limit is probably a relatively high percentage of the UC. Except as noted above, the resins have good stability and are considered permanent. 

Formaldehyde is employed in the production of aminoplasts and phenoplasts, which are two different but related classes of thermoset polymers. Aminoplasts are products of the condensation reaction between either urea (urea-formaldehyde or UF resins) or melamine (melamine-formaldeliyde or MF resins) with formaldehyde. Phenoplasts or phenolic (phenol-formaldehyde or PF) resins are prepared from the condensation products of phenol or resorcinol and formaldehyde. 

The principal feature that distinguishes thermosets and conventional elastomers from thermoplastics is the presence of a cross-linked network structure. As we have seen from the above discussion, in the case of elastomers the network structure may be formed by a limited number of covalent bonds (cross-linked rubbers) or may be due to physical links resulting in a domain structure (thermoplastic elastomers). For elastomers, the presence of these cross-links prevents gross mobility of molecules, but local molecular mobility is still possible. Thermosets, on the other hand, have a network structure formed exclusively by covalent bonds. Thermosets have a high density of cross-links and are consequently infusible, insoluble, thermally stable, and dimensionally stable under load. The major commercial thermosets include epoxies, polyesters, and polymers based on formaldehyde. Formaldehyde-based resins, which are the most widely used thermosets, consist essentially of two classes of thermosets. These are the condensation products of formaldehyde with phenol (or resorcinol) (phenoplasts or phenolic resins) or with urea or melamine (aminoplastics or amino resins). 

Nitrile butadiene rubber (NBR), which is formaldehyde-resistant, is the predominantly used elastifying component for phenoplastics. The resin and rubber interreact during the curing process. Natural rubber is incompatible with phenolic resins. At a rubber content of 25 %, the modulus of elasticity, at 1,000 N mm , has already fallen into the middle range of unreinforced thermoplastics. The impact strength reaches the values of type 74 (fabric chips, reinforced). Their form stability when exposed to heat is below that of type 31 at temperatures below 100 °C. 

Whereas natural fibers, mainly in the form of short fibers and fabric chips, have foimd application above all in the curable phenoplast and aminoplast molding compounds, it was more than anything else the development of the polyesters and epoxy resins that made it necessary to develop new kinds of reinforcing fibers to optimize the properties of these products as well. Modem, high-strength, synthetic organic fibers are the results of these efforts [112]. 

The most important resin types used in production of curable molding compounds are phenolic, urea, melamine, unsaturated polyester, epoxide and diallyl phthalate resins. Curable molding compounds built up with these bonding agents are described in DIN 7708" (Phenoplasts and Aminoplasts), DIN 16911 and 169132 (Polyester Molding Compounds and Polyester Resin Mats), and DIN 16912 (Epoxy resin Molding Compounds). There is as yet no standard for diallyl phthalate masses, for the test method see ISO 1385 - 1.02.1977. 

In dry-compounded polyester resin molding compounds and the moldings made out of them, modification with melamine resins results in a reduced processing rate similar to what is seen with phenoplasts and aminoplasts. It is possible to improve the surface quality [79]. 

Phenoplast n. Another name for phenol-formaldehyde resin. 

Phenolic resins are among the oldest and best-known general purpose molding materials. They were among the very first commercial polymers to be introduced at the turn of the twentieth century under the tradename Bakelite. These polymers are also known as phenoplasts. 

Phenol resins are generally identified by liberating phenol om ttie thermosetting sample by heat or hydrolysis and then applying rapid tests for it 24,9i) J ov, ever, detailed information about the presumed type of phenoplast can be obtained only by its thermal breakdown into the structural units and their separation and identification by or This led to the discovery fliat the pyrolysis... 

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