Louis A. Pilato

Phenolic Resins: Chemistry, Reactions, Mechanism

The chemistry of phenolic resins involves a variety of key factors which are critical in the design of the desired phenolic resin. These include: Molar ratio of F to P Mode of catalysis: acid, base, metal salt, enzyme Liquid, solid, dispersion Thermoplastic or thermosetting resin

Phenol–Formaldehyde Polymers

In 1872, von Bayer1 obtained a colorless noncrystallizing resinous product from the reaction of phenol with formaldehyde, while he was investigating phenol-based dyes. The occurrence of similar intractible materials in an acidic medium was also reported by ter Mer,2 Claus and Trainer,3 Claisen4 and others. The reaction between formaldehyde and phenol in the alkaline pH range was first recorded in 1894 by Lederer5 and Manasse.6 This reaction is generally referred to as the Lederer–Manasse reaction. These early investigators did not perceive any practical use for the ill-defined products. Speyer7 and Luft8 were the first to recognize the technical significance and practical use of curable phenolic resins.

Modified and Thermal-Resistant Resins

Polymers are considered to be moderately thermally stable, if they survive incremental increases in temperature in an inert atmosphere without a significant change in properties (Table 9.1).

Thermosets: Overview, Definitions, and Comparisons

The history of thermosets [1–6] and their application began around 125 years ago (Table 5.1) with phenolic resins, and is thus, historically speaking, closely linked with the name “Baekeland”.

Economic Significance, Survey of Applications, and Six Bonding Functions

The following remarks will review the uses of phenolic resins and their distribution throughout the various areas of application, making reference to the six “bonding functions” that phenolic resins mainly assume in applications. The organization of the application-related chapters of this book is oriented toward these bonding functions. Tables 6.1 and 6.2 summarize the main types of resins — resoles and novolaks — that are commercially available and are used for various applications (solid and liquid resoles, solid and solution novolaks).

Structure (Methods of Analysis)

Structure property relationships provide a description of the many resin characteristics which guide the resin designer in the selection of phenolic resins for the intended application. Resin characteristics such as hydrodynamic volume or size, functionality and/or molecular configuration, solution properties describing the structural attributes of the phenolic resin in various solvents, mechanical property guidelines and fire behavior of phenolics especially fire/smoke/toxicity (FST) criteria are described.

Composite Wood Materials

Phenol resin bonded wood materials — particle boards (PB), plywood, fiber boards (FB) and glued wood construction products — are used for outdoor construction and in high humidity regions because of the high moisture and weathering resistance of the phenolic adhesive bond and its high specific strength.

High Technology and New Applications

In the 80’s the wave of high technology has fostered the active participation of phenolic resins in “high tech” areas ranging from electronics, computers, communication, outer space, aerospace, biomaterials, biotechnology and advanced composites. From the sophistication of microchip technology in communication systems, or the delicate heart beat maintained by a pacemaker to the excessive temperature environment of outer space, phenolic resin chemistry plays an indispensable role in these burgeoning high technology areas.

Phenolic Resins in Rubbers and Adhesives

Generally, phenolic resins exhibit adhesive characteristics in virtually every type of application1, 2). They are always used in conjunction with fillers or reinforcing fibers. Their adhesion to most materials is very good due to the marked polarity of the phenolic structure. Disadvantages, however, are their brittleness in non-modified composition combined with high cure temperature and pressure requirements.

Conclusion: Guidelines for Future Developments in Phenolic Resins and Related Technologies

The impression sometimes arises that development, production, and con sumption of phenolic resins and other thermosets — particularly amino and furan resins — are stagnant or in decline. However, this is not, in fact, the case. It is safe to assume that this group of products will always be required for many end-use applications due to its performance characteristics. The reader of this publication will recognize that phenolic resins still have a bright future as adhesives for industrial applications and thermosetting molding compounds. Pertinent examples are matrix resins for high performance fiber composites, applications in the transportation industry, components for carbonbased materials and refractories that afford a high carbon yield in the caebonization process, and giass fiber-reinforced phenolic molding compounds exhibiting high, constant thermal resistance.