Celcon

Throughout the remainder of this article the term homopolymer refers to Delrin acetal resin manufactured and sold by Du Pont the term copolymer refers to Celcon acetal copolymer resins (registered trademark of Hoechst Celanese Corporation). 

Nominal MI, g/10 min Hoechst Celanese Celcon Du Pont Delrin BASF Ultraform... 

Grades of acetal resins specifically designed to enhance the excellent lubricity of the material, without sacrifice in other properties, are known. These include Delrin AF, Ultraform N2311, and Celcon LW materials. Antistatic grades, particularly useful in electronic appHcations, have been developed. At least one recendy introduced new grade, Celcon SR90, claims good scuff resistance. 

The copolymeis, eg, Celcon M 90 [95327 3-8] aie pioduced by the cationic catalyzed reaction of 1,3,5-tiioxane [110-88-3J and an ethylene oxide. 

Property ASTM method Delrin 500 homopolymer resin Celcon M90 copolymer resin ... 

The first commercially available acetal resin was marketed by Du Pont in 1959 under the trade name Delrin after the equivalent of ten million pounds had been spent in research or polymers of formaldehyde. The Du Pont monopoly was unusually short lived as Celcon, as acetal copolymer produced by the Celanese Corporation, became available in small quantities in 1960. This material became commercially available in 1962 and later in the same year Farbwerke Hoechst combined with Celanese to produce similar products in Germany (Hostaform). In 1963 Celanese also combined with the Dainippon Celluloid Company of Osaka, Japan and Imperial Chemical Industries to produce acetal copolymers in Japan and Britain respectively under the trade names Duracon and Alkon (later changed to Kematal). In the early 1970s Ultraform GmbH (a joint venture of BASF and Degussa) introduced a copolymer under the name Ultraform and the Japanese company Asahi Chemical a homopolymer under the name Tenal. 

Formaldehyde is also produced by the oxidation of light petroleum gases, a process which also yields methanol and acetaldehyde. This process is currently used in the Celanese Corporation plant for the production of Celcon. 

An alternative approach to the production of thermally stable polyoxy-methylenes was made by chemists of the Celanese Corporation of America and the commercial products were marketed as Celcon. Hostaform and Duracon. The principle of thermal stability in this case is the copolymerisation of formaldehyde with a second monomer which is a cyclic ether of the general form shown in Figure 19.3 (I). 

Oxidative attack at random along the chain leading to chain scission and subsequent depolymerisation. Initial chain scission is reduced by the use of antioxidants (see Chapter 7) and in recent formulations hindered phenols seemed to be preferred. It is reported that 2,2 -methylenebis-(4-methyl-6-t-butylphenol) is present in Celcon and 4,4 -butylidene bis-(3-methyl-6-t-butylphenol) in Derlin. The copolymerisation helps to reduce the rate of depolymerisation where initiation of depolymerisation is not completely prevented. 

The electrical insulation properties of the acetal resins may be described as good but not particularly outstanding. There are available alternative materials which are better insulators and are also less expensive. There are, however, applications where impact toughness and rigidity are required in addition to good electrical insulation characteristics, and in these instances acetal resins would be considered. Table 19.3 lists some of the more important electrical characteristics of Delrin acetal resin. Data for the trioxane-based copolymer resin (e.g. Celcon) are virtually identical. 

Celcon, Delrin, Duracon, Hostaform, lupital Acetal, Kematal, Lucel, Sniatal, Ultraform... 

Celanese came out a year later with a similar product under the trade name Celcon. Celanese circumvented DuPont s patent on the basis of employing a copolymer variation that allowed enhanced stabilization against thermal depolymerization (structure 4.74). The copolymer has a of 170°C ... 

Another stable polyacetal (POM Celcon) is produced by the cationic copolymerization of a mixture of trioxane and dioxolane (structure 5.23). 

Celcon Trade name of copolymer of formaldehyde and dioxolane. 

For example, Celanese announced Celcon acetal copolymer in February 1961. By the last half of 1962 and the first half of 1963 we carried through on a specific advertising and promotion program which consisted of ... 

The case history approach was also used to interest design engineers in end use companies by highlighting successful applications of Celcon. The case histories spelled out reasons why the material was selected over another plastic or a metal and emphasized performance requirements of the material in the application. 

Based on knowledge of relative properties and costs, it appeared to us that Celcon had some advantages to offer in the application. We quickly learned that people making tubing from nylon were extruding at rates up to 150 feet per minute. At the time, our company had very little experience with the extrusion properties of Celcon and we learned that under conditions which were being used... 

The potential volume involved and our assessment of the property benefit of Celcon in the application were sufficient to justify a lab program whose objective was to develop a polymer or modify the extrusion process so that Celcon would extrude at comparable or faster speeds than the material being used. After some nine months of effort an extrusion die was designed that permitted extrusion speeds of 450 feet per minute while making tubing with the tolerance specifications established by the customer. The foregoing is an example of a type of process development work described in the preceding paper. 

At this point the information accumulated over the years was presented to the Celanese affiliates in Germany, Japan, and the U. K. They were able to develop the use of Celcon for hot and cold water faucets. As a result of this experience there has been renewed interest... 

FA.. Marion H.J. McSpadden, Feasibility Study of Thermoplastic Gun Propellant , AFATL-TR—73-142 (1973) [The report describes an attempt to use an acetal resin (Celanese Corp Celcon ) and HMX to form a proplnt. The use of this mixt in proportions of 30—80% HMX was found not to be feasible because of lower than expected impetus, low burning rates and high burning rate exponents. However, the authors recommend the thermoplastic material as a candidate for use as cartridge case or closure material because of the high temp... 

Polyoxymethylene (POM) is, again, a crystalline polymer, with a melting point of about 180 °C. Its mechanical properties enable it to gradually replace metals in a number of applications. Many technical parts are being made from POM, such as gear wheels, bars, automotive accessories, parts of several apparatuses and machines. The polymer is used as such (e.g. Delrin ), but also as a copolymer with a small amount of ethylene oxide (e.g. Celcon and Hostaform ). 

Polyformaldehyde. Polyformaldehyde or polyacetal is made by two different processes. Delrin is made from formaldehyde by anionic polymerization catalyzed by a tertiary amine. The homopolymer is end-capped with acetic anhydride. Celcon is made from trioxane cationic copolymerization using boron trifluoride catalyst and ethylene oxide (2-3%) as the comonomer. Boron trifluoride is a Lewis acid that associates with trioxane and opens up the six-membered ring. Ethylene oxide provides the end capping. Without an end cap, polyformaldehyde is thermally unstable and loses formaldehyde units. 

Acetal translucent crystalline polymer is one of the stiffest TPs available. It provides excellent hardness and heat resistance, even in the presence of solvents and alkalies. Its low moisture sensitivity and good electrical properties permit direct competition with die-cast metal in a variety of applications. In addition, acetal has extremely high creep resistance and low permeability. Acetal is also available as a copolymer (Hoechst Celanese Corp. s Celcon) for improved processability. The homopolymer (DuPont s Delrin) has a very low coefficient of friction and its resistance to abrasion is second only to nylon 6/6. Acetals are frequently blended with fibers such as glass or fluorocarbon to enhance stiffness and friction properties. Acetal is not particularly weather-resistant, but grades are available with UV stabilizers for improved outdoor performance. Acetal, whether homopolymer or copolymer, is not used to any significant degree in forming structural foams. 

Acetal Copolymer (CELCON ) As with DELRIN , this is a highly crystalline polymer with excellent solvent resistance. It is somewhat more amenable to solvent cementing than the homopolymer, however. The solvent cement recommended by the manufacturer, Hoechst Celanese, is hexafluoroacetone sesquihydrate, available from Allied Signal, Inc. This solvent is a severe eye and skin irritant, however, and should be handled with care (7). 

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