Cure, phenol-formaldehyde

Cured phenol-formaldehydes are resistant to attack by most chemicals. Organic solvents and water have no effect on them, though they will swell in boiling phenols. Simple resins are readily attacked by sodium hydroxide solutions, but resins based on phenol derivatives, such as cresol, tend to be less affected by such solutions. Simple phenol-formaldehyde polymers are resistant to most acids, though formic and nitric acids will tend to attack them. Again, cresol-based polymers have resistance to such attack. 

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. 

Fig. 3. 2H NMR spectra of uncured (A) and (B, C) cured phenol/formaldehyde resins (I) deuterated [DJformaldehyde containing resin and (II) deuterated [3,5-DJphenol containing resin (adapted from Ref. )...

Manley [32] examined a cured phenolic formaldehyde (PF) resin by means of TG-DTA-MS observing a lower sensitivity of TG relative to DTA. However, new TGA instrumental developments have been reported since. The TG curve shows loss of phenol (MS evidence m/z 94) DTA observes water (MS m/z 18), ammonia (MS m/z 17) and formaldehyde... 

Van Beek, L. K. H. Dielectric behavior of curing phenolic-formaldehyde resins, J. Appl. Polym. Sci., 8,2843 (1964)... 

In general, these groups of cellulose ethers have been used for their innate adhesive properties and to provide thickening to adhesive formulations. They are used for plywood adhesives, industrial adhesives, wallpaper paste, library paste, and latex adhesives. For example, methylcellulose is used in some adhesives as an additive to control viscosity, especially in the heat-cure phenol-formaldehyde glues and other hot-pressing adhesives. Hydroxyethylcellulose is used as an ingredient in polyvinyl acetate emulsions, where it acts as a thickener and protective colloid. 

Pyrolysis Products of Cured Phenol-Formaldehyde Resin... 

Figure 12.12 Py-GC/MS chromatogram of cured phenol-formaldehyde resin at 600°C...

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 ". ... 

Cured phenol—formaldehyde resin is less stable towards radiation than is polystyrene. About 108 rad reduce the tensile strength to about 80% of its original value. If the polymers are filled with inorganic materials, their stability is considerably improved. 

Table 12.1. Typical values for various properties of cured phenol-formaldehyde polymers, unfilled and filled [13]. 

Stripping [59]. A practical application embodying these concepts has led to the preparation of self-curing phenol-formaldehyde resins [60]. 

Since the discovery of cured phenolic formaldehyde resins and vulcanized rubbers, interest has grown in such areas as the mechanisms of network formation, the chemical structures of crosslinked systems, and the dynamics of networks. Although the vast majority of polymers used industrially are crosslinked to a greater or lesser degree, the ability to characterize these systems is highly limited. Traditional tech-... 

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