Phenol formaldehyde resins 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. 

Moulding powders based on melamine-phenol-formaldehyde resins were introduced by Bakelite Ltd, in the early 1960s. Some of the principal physical properties of mouldings from these materials are given in Table 24.1. 

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. 

Diene rubbers can be vulcanized by the action of phenolic compounds like phenol-formaldehyde resin (5-10 phr). Resin-cured NR offers good set properties and low hysteresis [54]. 

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. 

Some satisfactory results were also obtained by modification of properties of phenol-formaldehyde resin (PFR) composites with the synthesized diallylsilazanes (scheme 1). Thas, addition of diallylsilazanes (1-3 mass %) to this composition has improved some of essential characteristics of hardened PFR (table 3). It should be noted that other important physical and mechanical properties of the composites have remained safe (table 3). 

Finally, it is important to note that it is possible to produce carbon sorbents with dehganding properties from different materials. In Table 29.4 this is demonstrated for granulated activated carbon Novocarb (MAST Carbon International, US Patent 20020176840A1, Nov. 2002) prepared by pyrolysis of phenol-formaldehyde resins, and coconut shell derived activated carbon ZL-150 (Huzhou Beigang Enterprises Group Corp., P.R. China). 

It has been demonstrated that red oak OSL could be used to replace 35% to 40% of the phenol (or phenolic resin solids) in phenol-formaldehyde resins used to laminate maple wood and to bond southern pine flake boards (wafer-board and/or strandboard) without adversely affecting the physical bond properties. While this pulping process and by-product lignin do not commercially exist at this time in the United States, lignins from such processes are projected to cost 40% to 50% less than phenol as a polymer raw material. 

The importance of crosslinked polymers, since the discovery of cured phenolic formaldehyde resins and vulcanized rubber, has significantly grown. Simultaneously, the understanding of the mechanism of network formation, the chemical structure of crosslinked systems and the motional properties at the molecular level, which are responsible for the macroscopic physical and mechanical properties, did not accompany the rapid growth of their commercial production. The insolubility of polymer networks made impossible the structural analysis by NMR techniques, although some studies had been made on the swollen crosslinked polymers. 

Important parameters were varied over relatively wide ranges producing particleboards with acceptable properties i.e., properties similar to those obtained using a phenol-formaldehyde resin as the control. Conditions used in both the liquid and gas phase reaction systems gave results shown by the examples in Table II. 

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. 

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