Phenol-formaldehyde thermal properties

Phenol—formaldehyde resins are used as mol ding compounds (see Phenolic resins). Their thermal and electrical properties allow use in electrical, automotive, and kitchen parts. Other uses for phenol—formaldehyde resins include phenoHc foam insulation, foundry mold binders, decorative and industrial laminates, and binders for insulating materials. 

Phenol-formaldehyde resins using prepolymers such as novolaks and resols are widely used in industrial fields. These resins show excellent toughness and thermal-resistant properties, but the general concern over the toxicity of formaldehyde has resulted in limitations on their preparation and use. Therefore, an alternative process for the synthesis of phenolic polymers avoiding the use of formaldehyde is strongly desired. 

Recently, several reports of the flame-retardant properties of boron-containing bisphenol-A resins have appeared from Gao and Liu.89 The synthesis of a boron-containing bisphenol-A formaldehyde resin (64 and 65) (Fig. 42) from a mixture of bisphenol-A, formaldehyde, and boric acid, in the mole ratio 1 2.4 0.5, has been reported.893 The kinetics of the thermal degradation and thermal stability of the resins were determined by thermal analysis. The analysis revealed that the resin had higher heat resistance and oxidative resistance than most common phenol-formaldehyde resins. 

Of all organic polymers used to produce insulation materials, glyptal and phenol-formaldehyde polymers are the most thermal resistant. They can function for a long time in electrotechnical devices at temperatures up to 130 °C. At higher temperatures insulation from organic polymers bums. Its dielectric properties considerably decrease, because the carbon formed is a good conductor. 

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. 

Blending of inert materials with ion-exchange resins to an extent that the desirable properties such as thermal stability and exchange capacity are not affected can partially replace the polymer content thereby reducing the production cost. Vasudevan et al. reported the preparation of phenol-formaldehyde composite ion-exchange... 

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. 

The novolacs are another class of epoxy resins. They are produced by reacting a novolac resin, usually formed by the reaction of o-cresol or phenol and formaldehyde with epichlorohydrin. Figure 3.5 shows the general structure. These materials are used as transfer molding powders, electrical laminates, and parts where superior thermal properties and high resistance to solvents and chemicals are required. 

Phenol-formaldehyde resins are widely used in industry and, consequently, studies on their thermal properties are of great technical importance [1]. Phenol-formaldehyde polymers heated for 1 hour up to 300, 430 and 840 °C lose 7%, 10% and 50% of their mass, respectively. 

Epoxy group functionalized polyphenylsilsesquioxane oligomers were used for modification of phenol-formaldehyde oligomer (novolac resin -SF-0112) for increasing their flexibility, their hydrophobic surface properties, thermal stability and flame-retardant properties. Novolac resin - SF-0112 contains a little amount of free phenols (0.9%) compared with other phenol-formaldehyde oligomers. 

However, the introduction of stabilizers is essential, since processes of thermal and thermooxidative destruction develop extremely intensively during the use and reprocessing of such polymers, leading to a sharp deterioration of their physicomechanical and dielectric properties. Thus, an extremely urgent problem at the present time is a detailed investigation of the processes of decomposition of condensation polymers for developing a theory of their stabilization. Works in the field of the study of the thermal and thermooxidative destruction of certain condensation polymers (epoxide, phenol-formaldehyde resins, polycarbonate, and polyarylates) are outlined below. 

Alkanolamines are used as cross-linking and hardener accelerators in epoxy resins applications. Improved thermal and oxidative stability of polyvinyl alcohol, poly(phenylene ether), polystyrene, polypropylene, and polyethylene polymers are achieved by the addition of small amounts of the alkanolamines. Diethanolamine and morpholine act as initiators for the preparation of poly (alkyl methacrylate) in bulk or solution polymerization. The ethanolamines are efficient initiators for the preparation of polyvinyl chloride. Alkanolamines promote cross-linking of styrene copolymers with polystyrene or polyvinyl alcohol. Addition of alkanolamines to phenolic formaldehyde or urea formaldehyde resins affords improved electrical properties and increased water solubility. 

There are two types of phenol-formaldehyde resin (a) novo-lac, the uncrosslinked acid-catcilyzed phenol formald yde resin, and (b) resole, a beise-cateilyzed jhenol-foritalddiyde resin. Both of these resins are cheap and readily available. In the uncured stage both of these resins have poor thermal properties and brittleness, vhich are the major limitations to their application in various industries including cable insulation. 

Pine needles reinforced polymer composites using phenol-formaldehyde and urea-formaldehyde resins as polymer matrix were obtained through compression molding technique and investigated for mechanical properties and thermal behavior (Thakur and Singha 2011 Singha and Thakur 2010a, b, c). 

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