Phenolic resins thermal decomposition

One such process involves the thermal decomposition of a diazo compound to give an acid that cross-links phenol formaldehyde resins upon heating, similar to the conventional UV initiated plates used in the industry (Figure 4.3), but other sensitisation methods are also used (see section 4.5). It is also possible to produce plates in a dry resin process by ablation or phase change methods. 

Electrical and electronic devices are made utilizing several various types of plastic materials, thus when discarded their waste is difficult to recycle. The plastics employed in housing and other appliances are more or less homogeneous materials (among others PP, PVC, PS, HIPS, ABS, SAN, Nylon 6,6, the pyrolysis liquids of which have been discussed above). However, metals are embedded in printed circuit boards, switches, junctions and insulated wires, moreover these parts contain fire retardants in addition to support and filler materials. Pyrolysis is a suitable way to remove plastics smoothly from embedded metals in electrical and electronic waste (EEW), in addition the thermal decomposition products of the plastics may serve as feedstock or fuel. PVC, PBT, Nylon 6,6, polycarbonate (PC), polyphenylene ether (PPO), epoxy and phenolic resins occur in these metal-containing parts of EEW. 

Carbonaceous materials (CMs) are sometimes also named polymeric carbons. They are mostly prepared by thermal decomposition of organic precursors. One strategy is pyrolysis of gaseous or vaporized hydrocarbons at the surface of heated substrates, a second is heating (pyrolysis) of natural or synthetic polymers, both in an inert atmosphere. The latter is of special interest, and according to Miyabayashi et al. [374], precursors such as condensed polycyclic hydrocarbons, polymeric heterocyclic compounds, phenol-formaldehyde resins, polyacrylonitrile or polyphenylene are heated to 300-3000 °C for 0.15-20 h. Sometimes, a temperature/time profile is run. The temperature range must be divided into two domains, namely... 

BSH is used for foaming rubbers, polystyrene, epoxy resins, polyamides, PVC, polyesters, phenol-formaldehyde resins, and polyolefins. However, the thermal decomposition of BSH yields not only nitrogen but also a nontoxic residue (disulfide and thiosulfone) which may degrade to give thiophenol and thus an unpleasant odor to the foams. 

Thermal analysis is applied to get information about transition temperatures, decomposition characteristics, and the crosslinking process of phenolic resins. Solid, liquid or gelled phenolics can be investigated by thermal analysis because of a variety of different sample vessels or attachments. 

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. 

Prokai [2] used pulse probe mass spectroscopy (MS) and pyrolysis-gas chromatography-mass spectroscopy (Py-GC-MS) to study the thermal decomposition of high molecular weight phenol-formaldehyde resins. He showed that degradation occurred by cleavage of the phenol-methylene bond and subsequent hydrogen abstraction to form phenol and methyl substituted phenols. 

The effect of carbon nanofibres on the thermal behavior of phenolic resins was studied by Bafekrpour et al. [96]. The presence of carbon nanofibres produced an increase in the thermal stability of the nanocomposites, compared to the neat phenolic resin. Thus, the decomposition temperature was shifted to higher values with an increase of the nanofibres content. The same trend was obtained for the nanocomposites char yield. 

Thermal decompositions have been studied most effectively by mass spectroscopic thermal analysis, thermogravimetric analysis, and electrical conductivity. Several analytical characterizations of phenolic resins have recently been reported, making use of a variety of properties, including expansion coefficients, " specific heat capacity, ultrasonic properties, dipole moments, and laser light scattering. Recently, high-temperature properties of reinforced phenolic components have been studied by Goetzel. ... 

Figure 146 [5] shows the relative stability of hardened phenol-formaldehyde and epoxide resins to thermal decomposition. In [14] the oxidative destruction and destruction in an inert medium of a hardened phenol-formaldehyde resin of the resol type were investigated by a ther-mogravimetric method. The volatile destruction products were studied by the method of direct chromatography. It was found that the initial activation energy of the process of oxidation of the resin within the temperature range 300-380°C corresponds to 15 kcal/mole (S. Madorsky and... 

Phenol formaldehyde Resins, nickel, copper, and cobalt [95-97] all cause thermal decomposition of polymers. 

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