Novolak resin precursors

Fibers. The principal type of phenoHc fiber is the novoloid fiber (98). The term novoloid designates a content of at least 85 wt % of a cross-linked novolak. Novoloid fibers are sold under the trademark Kynol, and Nippon Kynol and American Kynol are exclusive Hcensees. Novoloid fibers are made by acid-cataly2ed cross-linking of melt-spun novolak resin to form a fuUy cross-linked amorphous network. The fibers are infusible and insoluble, and possess physical and chemical properties that distinguish them from other fibers. AppHcations include a variety of flame- and chemical-resistant textiles and papers as weU as composites, gaskets, and friction materials. In addition, they are precursors for carbon fibers. 

It may be noted that pol)aner is often also used to refer to the massive state. Then the term refers to a material whose molecules are polymers, i.e., a polymeric material. Likewise, the term resin is sometimes used to refer to any material whose molecules are polymers. Originally this term was restricted to natural secretions, usually from coniferous trees, used mainly in surface coatings later, similar synthetic substances were included. Now the term is generally used to indicate a precursor of a cross-linked polymeric material, e.g., epoxy resin and novolak resin. (See later.)... 

Specialty Epoxy Resins. In addition to bisphenol, other polyols such as aUphatic glycols and novolaks are used to produce specialty resins. Epoxy resins may also include compounds based on aUphatic, cycloaUphatic, aromatic, and heterocycHc backbones. Glycidylation of active hydrogen-containing stmctures with epichlorohydrin and epoxidation of olefins with peracetic acid remain the important commercial procedures for introducing the oxirane group into various precursors of epoxy resins. 

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. ... 

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. 

Fuertes and co-woikers [12, 46 8, 78] investigated intensively the preparation of caibon membranes from PR precursors. According to Centeno and Fuertes [12], they coated a small quantity of liquid phenohc resin (Novolak type) on the finely polished surface of a porous carbon disk by means of a spin coating technique. The supported phenolic resin film was cured in air at 150°C for 2 h, and then carbonization was carried out in a vertical tubular furnace (Carbolite) at different temperatures (between 500 and 1,000°C) under vacuum. Figure 4.6 shows the SEM micrograph of the membranes. The polymeric film (Fig. 4.6a) coated on top of the porous substrate is dense and has a thickness of around 2 pm. The thickness of the carbon membrane shown in Fig. 4.6b is also about 2 pm. Figure 4.6c shows the top view of the fractured membrane. The top smface is veiy smooth. Helium gas permeance of membranes carbonized at different temperatures is shown in Fig. 4.7. 

NMR studies include spectral assignments in PF resins,benzylphenols" and cresol novolaks," reaction curing,and phenolic precursors.Several very useful chemical shifts for novolaks dissolved in pyridine are for the methylene protons, p-p at 3.8 ppm, o-o at 4.1 ppm, and the o-p substitution at 4.5 ppm. The areas under the absorption peaks allow the percentage distribution of isomers to be evaluated. The analogous signals are in the regions of 41.0, 30.8-31.4, and 35.5-35.9 ppm, respectively. 

Fuertes and Menendez (2002) and Centeno and Fuertes (1999, 2001) have published a series of studies using this precursor. Centeno and Fuertes (1999) have spin coated a small amount of a novolak-type phenolic resin on the surface of carbon supports. The membranes were then carbonized in a tubular furnace from 500 to 1000°C in vacuum. The resulting membranes had O2/N2 selectivity of around 10 and CO2/CH4 selectivity of 160. This work was later extended and in that case (Centeno and Fuertes, 2001 Fuertes and Menendez, 2002) a novalak-type phenolic resin was deposited on the inner face of a ceramic tubular membrane used for ultrafiltration. The membrane was subsequently pyro-lyzed to 700°C. In some cases an oxidative pretreatment was used before pyrolysis or an oxidative posttreatment after pyrolysis. The resulting membranes had O2 permeabilities around 100 Barrers and O2/N2 selectivities around 12 at 25°C. Films dip coated with resin three times had lower permeability and only slightly higher selectivities than those dipped only once. For hydrocarbon mixtures, the separation performance was increased by several treatments air oxidation of the resin, air oxidation of the carbon, or chemical vapor deposition (CVD) posttreatment of the carbon. 

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