Phenol-formaldehyde resin, pyrolysis products

There is a common feature of the polymer composition in PC, PPO, epoxy and phenol-formaldehyde resin, all contain phenoxy moieties in their repeating unit. Hence, it is not unexpected that the major pyrolysis products of these plastics are phenols. The reason of the production of phenolic compounds is the higher bonding energy of the C-0 linkage in the phenoxy moiety related to that of other bonds along the polymer chain. 

Pyrolysis Products of Cured Phenol-Formaldehyde Resin... 

The carbonaceous products were obtained by pyrolysis at temperature of AN Tp (acenaphthene) and PH (phenol-formaldehyde resin) those from were nongraphitizable. 

The mixture of organic compounds in bio oil from pyrolysis of different feedstock is shown in Table 5. It can be seen that the amount of phenols is very high in HPL-oil in comparison to others. More than 97 wt, /o of these phenols originate from phenol-formaldehyde resins from the HPL production process. Normally the phenol components have an amount below 1 wt.% in the oil. On the other hand Table 5 demonstrates a large variation in the total amount of each chemical class. 

Carbon molecular sieves, or carbogoric sieves are amorphous materials made by pyrolyz-ing coal, coconut shells, pitch, phenol-formaldehyde resin, or other polymers. EKslocations of aromatic microdomains in a glassy matrix give their porosity. Pores are slit-shaped. Pore structure is controlled by the temperature of the pyrolysis. Pore widths range from 3 A to 10 A. Acarbogenic sieve made from polyfurfuryl alcohol and combined with silica-alumina was selective for monomethylamine production from methanol and ammonia [54]. 

Phenol-formaldehyde resins are relatively resistant to heat. They start decomposing at about 250° C still maintaining some mechanical resistance, the decomposition rate increasing significantly around 300° C. In an inert atmosphere at 750° C, phenol-formaldehyde resins form more than 50% char [2, 3]. The volatile materials consist of xylene (76%). traces of phenol, cresol, and benzene [4]. The heating in air above 300° C leads to the oxidation of the carbonaceous char and complete volatilization of the polymer [5], More information regarding pyrolysis products of phenol-formaldehyde... 

FIGURE 1. Schematic representation of the pyrolysis of a phenol-formaldehyde resin, showing possible fragmentation sites leading to simple aromatic products... 

It should be emphasized that Py-GC is often very sensitive to structural differences in polymers. Depending on the similarity of the chemical structure and selection of the pyrolysis and chromatographic separation conditions, the chromatograms of the pyrolysis products (pyrograms) from test substances may feature qualitative and in some instances only quantitative differences. For example, pyrograms of phenol—formaldehyde resins obtained on the basis of 3-methylphenol and 3,5-dimethylphenol differed widely in the qualitative composition of the pyrolysis products [19], whereas with low-density (Marlex 6002) and high-density (Okiten G-03) polycthylenes, only quantitative differences in the ratios of individual products were found [20]. 

Py-GC has also been applied in studying the structures of some phenol—formaldehyde resins. The main pyrolysis products were found to correspond to individual fragments of the initial polymer molecule [254]. 

During the thermal decomposition of phenol-formaldehyde resins, considerable quantities of volatiles (up to 50% of the initial mass) having a rather diverse composition are liberated. At temperatures up to 360 °C one may observe release of considerable quantities of propanols (up to 11% mass), acetone (6.7% mass), propylene (4.0% mass) and butanols (3.0% (mass). The non-volatile products of decomposition at temperatures up to 400 °C cause an increase in the quantity of acetone (17.6% mass) while, carbon dioxide, carbon monoxide and methane which are the major products of decomposition also begin to be released. The quantity of non-volatile pyrolysis products (molecular mass about 350) is gradually reduced to about 37% (mass) at elevated temperatures. 

Information about the composition of the sample material can be significantly increased if the paints have been derivatized during pyrolysis. Tetramethyl-ammonium hydroxide (TMAH) is used as a derivat-izing reagent for structure elucidation of alkyd, unsaturated polyester, epoxy, and phenol-formaldehyde resins. The derivatization of paints, whose pyrolysis products elute at very low retention times (such as formulations based on polyvinylacetate... 

TABLE 22. Composition of Gaseous Products of the Pyrolysis of Hardened Phenol-Formaldehyde Resin... 

Fast pyrolysis of biomass provides a method for the production of phenolics that has the potential to replace at least 50% or more of the phenol in phenol-formaldehyde thermosetting resins. The gel tests indicate that the P/N fractions from pine sawdust pyrolysis with paraformaldehyde have shorter gel times than commercial plywood resins such as Cascophen 313, even without prepolymer formation. A novolak formulation has been prepared using 1 1 by volume of phenol and P/N fraction and about half of the amount of formaldehyde that would be used than if phenol alone were employed. Very promising resols have also been made with a similar substitution of the P/N fraction for phenol. Wood testing and resin formulation development are ongoing activities. The projected economics suggest that additional research and development of this process are fully warranted. 

Other variations of the condensation reaction are utilized, such as condensation of a phenol, a substituted benzaldehyde, and formaldehyde. Pyrolysis studies on ion exchange resins are common in literature [21-25]. Depending on the nature of the attached group, as well as on the proportion of the polymer that is derivatized, pyrolysis products originating from these groups can be seen in pyrolysates. 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryhc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenolic thermosetting resins (see Phenolic RESINS). Toluene 2,4-diisocyanate (TDI), employed in the production of polyurethane foam, indirectiy consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

---