Phenol-formaldehyde resin applications

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. 

Phenolics are also used in a variety of other applications such as adhesives, paints, laminates for building, automobile parts, and ion exchange resins. Global production of phenol-formaldehyde resins exceeded 5 billion pounds in 1997. 

From this brief discussion it is clear that crosslinking in phenol-formaldehyde resins is complicated and no individual specimen of these materials can be characterised well at the molecular level. Crosslinking is irregular and variable, though it gives rise to a material having sufficiently acceptable properties that it became the first commercially important plastic material indeed, as mentioned in Chapter 1, these resins continue to retain some commercial importance in certain specialised 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. 

James Swinburne also discovered phenol-formaldehyde resins at the same time, but he was one day late in his application for patent than Baekeland. 

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]. 

In the development of a reactive non-chrome post-treatment, a variety of phenolic resins were synthesized and commercial phenolic resins evaluated. It was found that phenol-formaldehyde resins, creso1-forma1dehyd e condensates, ortho-novo 1 ak resins, and phenol-formaldehyde emulsions gave positive results when employed as post-treatments over zinc and iron phosphate conversion coatings. The above materials all possessed drawbacks. The materials in general have poor water solubility at low concentrations used in post-treatment applications and had to be dried and baked in place in order to obtain good performance. The best results were obtained with poly-4-vinylphenol and derivatives thereof as shown in the following structure (8,9,10)... 

Since the days of Bakeland many varieties and applications of phenol-formaldehyde resins have been found (1). In this paper we are concerned only with recent applications of functionally substituted phenol-formaldehyde-Novolak resins as applied to lithographic uses for micro-image fabrication. 

Urea-formaldehyde resins are used for applications in which the panel is not in contact with water. For applications with high level of humidity, the phenol-formaldehyde resins are required. In all cases, free formaldehyde constitutes a dangerous pollutant that is slowly released and can be particularly toxic in confined rooms. Recent research has been done to substitute this type of resin by natural binders, such as cross-linkable proteins (Silvestre et al., 2000 Yang et al., 2006). 

Phenol-formaldehyde resins find numerous applications in such areas as wood composites, fiber bonding, laminates, foundry resins, abrasives, friction and molding materials, coatings and adhesives, and flame retardants (JL). From a specialty chemicals standpoint, they are also used as developer resins in carbonless papers (2.). Conventional methods of preparation involve condensation of a phenol with formaldehyde under either acidic (novolak) or basic (resole) conditions (2). Their typical molecular weight range is from 800-4000 daltons (D) and includes a wide variety of alkyl or aryl substituted phenols (A)- The... 

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. 

This copolymer can be obtained from a polydimethylsiloxane that has aminoalkyl end groups in a reaction with the polyetherimide formed from the reaction of a bis(ether anhydride) with diaminobenzene. The material is fire resistant and is used in cable insulations. Among other more complex copolymers with practical applications are poly[2,2-propanebis(4-phenyl)-carbonate]-b/ock-poly(dimethylsiloxane)] and a silicone phenol formaldehyde copolymer obtained in two steps, the first being the heating of a polydimethylsiloxane that has reactive end groups with glycerol, and the second step being the reaction with a phenol formaldehyde resin. 

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. 

The single largest use for the phenol-formaldehyde resins is in adhesive applications for the production of plywood, chipboard, and particle board. The resin can comprise as much as one-third of the weight of the board, particularly of particle boards, which contributes to a total demand for phenolics in the U.S.A. of over half a million metric tonnes per year. They are also used as the matrix adhesives for the production of several types of grindstones. In combination with paper, woven cotton, glass fiber, etc., components, phenolics contribute to the production of engineering and decorative laminates in the form of rods, tubes, and sheets. The sheet products Arborite and Formica are familiar as the finished surfaces of furniture, bathroom, and kitchen counter tops and other areas where attractive patterns and water resistance are important characteristics. Molded products from phenolics are also important where heat or electrical resistance is required, such as saucepan and toaster handles, switches, and the printed circuit boards used in computers. Recent phenolics production in the U.S.A. has totaled over 500,000 metric tonnes per year, not including fillers [38]. 

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 ". ... 

The commercial importance of phenol-formaldehyde resins has resulted in extensive studies of these systems, with the aim of identifying the reaction mechanisms and intermediates that occur during subsequent polymerization reactions. However, the complexity of Novolac-type systems has made a detailed understanding of the subsequent chemical processes and their relationship to the physical properties of the final polymerized product difficult. Thus, it is necessary to simplify the system in order to more readily unravel this complexity. Model compounds are frequently used to understand complicated chemical systems and their application to phenol-formaldehyde systems has been well documented . ... 

These resins (Resole or Novolac) are used as curing agents or hardeners for epoxy molding compounds for electronics applications such as computer components. 0-cresol-formaldehyde resins have heen also used to modify phenol-formaldehyde resins, and in laminates. 

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