Phenol formaldehyde precursor

The development of ACF and AC cloths is closely related to that of carbon fibers (CFs). This makes that the raw materials used for the preparation of ACFs be, chronologically, the same as for CFs. Thus, in 1966, viscose and acetate cloths were, like for CFs, the first materials used to obtain ACFs [4, 5]. The low yield of the ACFs, and CFs, obtained from the above precursors, oriented the research towards the seek of other raw materials for the preparation of cheaper CFs and ACFs with a higher yield. In this way, ACFs were prepared from 1970 using lignin (with the brand of Kayacarbon ALF), polyvinylchloride [6] (i.e., Saran polymer, already used to obtain ACs) and phenolic precursors [7]. The high yield and the good mechanical properties of the ACFs obtained make these precursors very useful for this application. In fact. Economy and Lin [8] developed ACFs from a phenol formaldehyde precursor, which are commercialized since 1976 under the name of Novolak. In 1980, Kuray Chemical Co. Ltd commercialized ACFs from phenolic resin under the name of Kynol. ... 

Weight Loss and Dimensional Changes. The weight loss resulting from the elimination of non-carbon constituents tapers off afterthe temperature reaches 1000°C, 6is shown in Fig. 6.2. The phenol formaldehyde precursor has a total weight loss approaching 40% with a carbon yield of 85%.f l... 

Glassy, or vitreous, carbon is a black, shiny, dense, brittle material with a vitreous or glasslike appearance (10,11). It is produced by the controUed pyrolysis of thermosetting resins phenol—formaldehyde and polyurethanes are among the most common precursors. Unlike conventional artificial graphites, glassy carbon has no filler material. The Hquid resin itself becomes the binder. 

In contrast to gas-phase carbonization, most thermosetting resins, such as phenol-formaldehyde and furfuryl alcohol, and also cellulose can be converted to carbon materials by solid-phase carbonization. When the carbonization of most of these precursors proceeds rapidly, the resultant carbon materials become porous. If the carbonization is performed so slowly that the resultant carbonaceous solids can shrink completely, the so-called glass-like carbons are produced, which contain a large number of closed pores. 

Glass-like carbons (glassy carbons) are produced by the pyrolysis of different precursors, such as phenol-formaldehyde resin, poly(furfuryl alcohol), cellulose, etc., through an exact control of the heating process [88,89], They are characterized by an amorphous structure and also by... 

The carbons in Fig. 24 are also compared with SNU2, which is a carbon produced by a Korean research group [6] using a similar template, but a different carbon precursor (phenol formaldehyde) intercalated in the gas phase. The comparison between these templated carbons indicates that the choice of precursor does not significantly alter the replication in this route. 

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... 

We will not discuss here models for pores in carbons, as this topic is treated in Chapter 5, and elsewhere in specialist [15] or general reviews [106, 107]. For similar reasons, we will not discuss porosity control [44, 108] in detail. However, porous carbons prepared by the template technique, especially the ordered ones, deserve special attention. Ordered mesoporous carbons have been known to scientists since 1989 when two Korean groups independendy reported their synthesis using mesoporous silicas as templates [109, 110]. Further achievements have been described in more recent reports [111, 112]. One might have expected that the nanotexture of these materials would merely reflect the nature of the precursor used, namely phenol-formaldehyde [109] or sucrose [110] in the two first ordered mesoporous carbon syntheses (as is well known, these two precursors would have yielded randomly oriented, isotropic carbon had they been pyrolyzed/activated under more conventional conditions). However, the mesopore walls in some ordered mesoporous carbons exhibited a graphite-like, polyaromatic character [113, 114], as described in Chapter 18. This information was obtained by nitrogen adsorption at low relative pressures, as in classical... 

The commonest of these occur in industrialized and urban areas where discharges from indnstry canse the snrface water (and groundwater to a lesser extent) to be contaminated with phenol or its derivatives, like cresol. Examples include the manufacture of certain herbicides or their precursors, the pulp and paper industry, the manufacture of phenol for use in plastics, such as phenol-formaldehyde, the manufacture and use of pentachlorophenol as a wood preservative, use of phenol derivatives (cresol, etc.) in hospitals, etc. The runoff of these compounds to surface waters and seepage to the groundwater are enlarged in rainy seasons in many Asian cities. 

Thermosets, on the other hand, are polymers formed by the mixing and chemical reaction of fluid precursors into a mold once the precursors react, a crosslinked network that cannot flow anymore under heating is created therefore, reaction and molding into the final shape usually take place at the same time (by the RIM or reaction injection molding process). Examples of common thermosets are some polyesters, phenol-formaldehyde resins, epoxy resins, and polyurethanes, among others. Chapter 28 of this handbook elaborates on this topic. 

One of the oldest group of polymers, still widely used in the electrical industry as Bakelite , is the phenol-formaldehyde (PF) resins formed in situ by reaction of phenol with formaldehyde. Owing to the polyfunc-tionahty of phenol which can react with three difunctional formaldehyde molecules, the result is a highly cross-linked structure which can be formed in one step from the low precursors. 

In the case of thermosets, deliberate and extensive orientation is virtually unknown. This appears to be the result of the practical difficulties involved, rather than from any theoretical obstacle. For example, it is possible that the fibre Kynol produced by the Carborundum Corporation is oriented to some extent. This is produced from a melt-spun Novolak phenol-formaldehyde resin, which is later further cross-linked with formaldehyde. It is, of course, legitimate to consider carbon fibres as extreme examples of thermosets. Formed by the cyclisation and subsequent graphitisation of polyacrylonitrile (or other suitable precursors), they are highly oriented. 

SiC nanofibers by melt-spinning of polymer blends have been prepared from PCS as a SiC ceramic precursor and a novolac-type phenol-formaldehyde resin [121]. These nanofibers were amorphous, about 100 nm in diameter, more than 100 (un long, and were rich in oxygen. 

Fabrication of glassy carbon materials is a relatively straightforward, but time consuming process. A preformed polymeric precursor such as phenol-formaldehyde, polyfurfuryl alcohol, polyvinyl alcohol or oxidized polystyrene is slowly heated in an inert atmosphere to a high temperature in excess of 2000 °C. Heating times may be as short as a day or as long as one month. It is not unusual to encounter exothermic temperature regions that must be traversed very slowly (i.e., 1 °C temperature increase per hour) to avoid the nucleation of bubbles. 

Zeolites are microporous crystalline aluminosilicates with a channel-like or cagelike pore structure with pore-opening sizes in the range of 0.3 to 1.5 nm [13]. The spatially periodic pore structure and well-defined nanospaces of zeolites offer opportunities to control the nanostructure and morphology of microporous carbon materials at the nanometer level. As schematically illustrated in Figure 2.1, zeolite pores can be filled wifh a carbon precursor such as furfuryl alcohol (FA). After a proper treatment, followed by removal of the zeolite framework, a carbon nanostructure with pores replicated from the zeolite framework is obtained. Over the past decade, many zeolite templates (e.g., zeolite Y, zeolite (3, and ZSM-5) and carbon precursors (e.g., FA, phenol-formaldehyde, and sucrose) have been... 

The earliest preparation of CMS was based on the decomposition of a Saran co-polymer (90/10 mixture of vinylidene chloride and vinyl chloride) today CMS with a wide range of physical properties are made from a variety of natural and synthetic precursors. These include coal, coconut shell, phenol-formaldehyde resin, polyfurfuryl-alcohol, polyacrylonitrile, polyvinyl-alcohol, and cellulose, with coal tar pitch used in most cases as a binder [30-33],... 

The representative carbon precursor is the phenol formaldehyde resin, polyacrylonitrile, pitch, coke, coconut shell, wood, etc. In most cases, these precursors are activated after carbonizing (pyrolysis in inert gas). The activation process for preparing the activated carbons is classified as gas activation (physical activation) and chemical activation. These activation characteristics are summarized in Table 1. In the former, the starting carbon materials are gasified using steam or carbon dioxide gas at... 

For completeness, after discussing the histories of carbon fibers derived from cellulose, PAN, and pitch, the category of "other precursors" should be covered. The tremendous activity in carbon fiber research and development is reflected in the large number of precursors which have been converted into carbon fibers. Besides the "big three", the list [34] includes phenolic polymers, phenol formaldehyde resin, furan resins [35], polyacenaphthalene, polyacrylether, polyamide, polyphenylene, polyacetylene, polyimide, polybenzimidazole, polybenzimidazonium salt, polytriazoles, modified... 

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