Phenol-formaldehyde polymers applications

Unlike phenol-formaldehyde polymers, the amino resins are not themselves deeply coloured, but are of a naturally light appearance. They can be easily pigmented to give a variety of shades, which leads to application in uses where good appearance is highly valued, for example in decorative tableware, laminated resins for furniture, and modem white electrical plugs and sockets. 

Copolymers of furfural with phenol or phenol-formaldehyde polymers have been available commercially for many years. Since the acid-catalyzed reaction of furfural and phenol has been difficult to control, most industrial applications involve the use of alkaline catalysts. Furfural-phenol resins are used for their alkali resistance, enhanced thermal stability, and good electrical properties compared to phenol-formaldehyde resins. 

Novolak diazonaphthoquinone positive-tone resists, the most important imaging system of semiconductor production today1510,1511 is an archetypal example of the industrial applications of photochemistry. Novolak is a phenol formaldehyde polymer (Bakelite) that dissolves in aqueous hydroxide, but the addition of a small amount of the diazonaphthoquinone 585 dramatically decreases the solubility. When irradiated, 585 undergoes the photo-Wolff rearrangement (see also Scheme 6.171), leading to ring contraction and subsequently to carboxylic acid formation (Scheme 6.284). Such a photochemically altered site is readily soluble and can be removed with a basic developer solution. 

Phenol-formaldehyde polymers, phenolics, were not only one of the first commercially available plastics, but they were the first commercially used thermosets. Normally one does not think of thermosetting polymers as useful for packaging applications because of the need to reshape the material. Phenolics were commonly used for closure manufacture in the past, because of their excellent chemical resistance. Phenolic closures have nearly disappeared from the market today. 

Phenol-formaldehyde polymers, including novolaks and resoles, have a number of applications in coatings, finishes, adhesives, composites, laminates and related areas. Concerns have been raised regarding the continued use of phenol-formaldehyde resins due to the various toxic effects of formaldehyde. Consequently, there has been active investigation for alternative sources of these types of oligomers and polymers with a consideration for environmental compatibility. 

Sulfonated phenol-formaldehyde polymer is the first hydrocarbon-based polymer membrane in the literature. The phenolic polymer membrane was prepared by condensation polymerization of sulfonated phenol with formaldehyde, but the sulfonated phenolic polymer had low chemical and mechanical stability for fuel cell applications. 

Cellulose fibers in the form of papers and cotton had been used in combination with phenol-formaldehyde polymer as one of the earUest fiber-polymer composites [12]. Glass fibers later came on the scene and contributed to the commerciahzation of fiber-reinforced plastics [13]. The technical appHcations of fiber-reinforced plastic composites are shown in Figure 13.2. At least 50% of the fiber-reinforced plastics is used for automotive and construction applications. 

General Properties. Phenolic resins generally are aqueous solutions of alkaline-catalyzed phenol-formaldehyde polymers. A typical resin would be about 40% solids, containing phenol, formaldehyde, and sodium hydroxide in molar ratios of about 1 2 0.75, and might average 10-50 phenol units linked together. These can be spray dried for application as a dried powder. Phenol-formaldehyde resins are cured with heat under pressure. The resultant bond is highly water resistant and heat resistant. The durability and weatherability of phenolic-bonded wood composites enables them to be rated for exterior use. 

The term aminoplastics has been coined to cover a range of resinous polymers produced by interaction of amines or amides with aldehydes. Of the various polymers of this type that have been produced there are two of current commercial importance in the field of plastics, the urea-formaldehyde and the melamine-formaldehyde resins. There has in the past also been some commercial interest in aniline-formaldehyde resins and in systems containing thiourea but today these are of little or no importance. Melamine-phenol-formaldehyde resins have also been introduced for use in moulding powders, and benzoguanamine-based resins are used for surface coating applications. 

Thermosets differ molecularly from thermoplastics in that their individual chains are anchored to one another through crosslinks. The resulting network creates cohesive materials that demonstrate better thermal stability, rigidity, and dimensional stability than thermoplastics. Some examples of traditional thermosets are melamine-formaldehyde resins, which are used to treat fabrics to make them wrinkle-free, and Bakelite (a phenol-formaldehyde resin), a historically important polymer used in many applications, such as costume jewelry, electrical switches, and radio casings. 

In general, the acid-sorbing resins may be classified as high molecular weight polyamines or polyimines. Thus, the original Adams and Holmes material was a polymer of m-phenylenediamine. Cation Exchange materials include synthetic resins, such as sulfonated phenol-formaldehyde or polystyrene types, and sulfonated coal. Some manufacturers have a variety of sub-types which are considered superior for particular applications. 

The polymerization of phenols or aromatic amines is applied in resin manufacture and the removal of phenols from waste water. Polymers produced by HRP-catalyzed coupling of phenols in non-aqueous media are potential substitutes for phenol-formaldehyde resins [123,124], and the polymerized aromatic amines find applications as conductive polymers [112]. Phenols and their resins are pollutants in aqueous effluents derived from coal conversion, paper-making, production of semiconductor chips, and the manufacture of resins and plastics. Their transformation by peroxidase and hydrogen peroxide constitutes a convenient, mild and environmentally acceptable detoxification process [125-127]. 

Spent resins are generally compatible with the polymer matrix material. Generally, the polymer and the resin do not interact chemically. The immobilization of spent ion-exchange resins in polymers is a common application all over the world. Epoxy resins, polyesters, polyethylene, polystyrene and copolymers, polyurethane, phenol-formaldehyde, and polystyrene are among the polymers used (IAEA, 1988). Inorganic materials are generally not immobilized using polymers because they are more acceptable to other immobilization matrices such as cement. 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

In the case of phenolics, it is possible to make linear thermoplastic polymers called novolaks, but this is done by reaction of less than one mole of formaldehyde with one mole of phenol the resulting resin has a large excess of free phenol Usually in application hexamethylene tetramine (HEXA) is added to the novolak. When heated, the HEXA breaks down into ammonia and formaldehyde and enters the reaction to form a light degree of cross-links in the final product. 

The disadvantages of the urea-formaldehyde adhesives lie in their lack of durability and in their characteristic pungent formaldehyde odor. For particleboard applications subject to high temperature and moisture exposure, phenol-formaldehyde adhesives are required, since the urea-formaldehyde polymer is hydrolyzable and hydrolysis is enhanced with moisture and heat. 

Usually, phenolphthalein-derived polymers are polymerized through the hydroxyl groups, thus destroying their well-known indicator properties. There is one example in which phenolphthalein and o-cresolphthalein 284 have been polymerized with formaldehyde to form phenol/formaldehyde type polymers, for example, 285. These polymers retain the indicating properties of the monomers with potential application in pFl test strips and optical pH sensors <2005PSA1019>. 

Treatment of solid wood over the years for increased utility included many chemical systems that affected the cell wall and filled the void spaces in the wood. Some of these treatments found commercial applications, while some remain laboratory curiosities. A brief description of the earlier treatments is given for heat-stabilized wood, phenol-formaldehyde-treated veneers, bulking of the cell wall with polyethylene glycol, ozone gas-phase treatment, ammonia liquid- and gas-phase treatment, and p- and y-radiation. Many of these treatments led to commercial products, such as Staybwood, Staypak, Im-preg, and Compreg. This chapter is concerned primarily with wood-polymer composites using vinyl monomers. Generally, wood-polymers imply bulk polymerization of a vinyl-type monomer in the void spaces of solid wood. 

Most of the formaldehyde produced is consumed in the production of urea-formaldehyde resins and phenol-formaldehyde resins. These cross-linked polymer products are in turn used in adhesive and laminate applications. 

Historically, the reaction of phenol with formaldehyde was of vital importance to the polymer industry, being one of the first totally synthetic commercial polymer resin systems developed. In 1907, Leo H. Baekeland commercialized, under the tradename Bakelite , a range of cured phenol-formaldehyde resins, which were useful in producing heat-resistant molded products . Since this early work, phenol-formaldehyde resins have been used in many applications, including refractory compounds, adhesives, thermal insulation and electrical industries ". ... 

This entry will provide an overview of the classical phenol-formaldehyde system. The fundamentals of this system will be described. The current applications of this classical system will be discussed. Resins prepared from structurally modified phenols will be examined and labeled as modified-classical phenol-formaldehyde systems. The effect of these modifications on the mechanical, thermal, and other properties will be examined. Finally, the considerable work on polymers that can be classified as nonclassicaf phenolic resins will be presented and the area of nanocomposites utilizing phenolic resins will be examined. 

MAJOR POLYMER APPLICATIONS PVC, rubber, urea formaldehyde, phenol formaldehyde... 

The development of ACF and AC cloths is closely related to that of carbon fibers (CFs). This makes that the raw materials used for the preparation of ACFs be, chronologically, the same as for CFs. Thus, in 1966, viscose and acetate cloths were, like for CFs, the first materials used to obtain ACFs [4, 5]. The low yield of the ACFs, and CFs, obtained from the above precursors, oriented the research towards the seek of other raw materials for the preparation of cheaper CFs and ACFs with a higher yield. In this way, ACFs were prepared from 1970 using lignin (with the brand of Kayacarbon ALF), polyvinylchloride [6] (i.e., Saran polymer, already used to obtain ACs) and phenolic precursors [7]. The high yield and the good mechanical properties of the ACFs obtained make these precursors very useful for this application. In fact. Economy and Lin [8] developed ACFs from a phenol formaldehyde precursor, which are commercialized since 1976 under the name of Novolak. In 1980, Kuray Chemical Co. Ltd commercialized ACFs from phenolic resin under the name of Kynol. ... 

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