Chemical cure linings

In the past chemical cure linings have been employed on a wide scale. These linings, usually based on natural rubber or acrylonitrile-butadiene rubber consist of a standard lining compound with a chemical activator such as dibenzylamine incorporated in the formulation. Prior to the application of the lining to the substrate, the individual sheets of rubber are dipped or brush coated with carbon disulphide or a solution of a xanthogen disulphide in a solvent. The carbon disulphide or xanthogen disulphide permeates the rubber and combines with the dibenzylamine to form an ultra-fast dithiocar-bamate accelerator in situ, and thus the rubber rapidly vulcanises at ambient temperature. 

With older vessels requiring repairs, one has to make a judgment as to how to repair the vessel. Basically, there are two options for repair. One is to use a chemically curable lining that is appropriate to match the lining in the vessel. Chemical cure linings may have high leech-able sulfite levels, even when cured with steam. Therefore, chemical cure linings are only considered acceptable on minor repairs. 

In order to increase the capacity of a production line especially by reducing the necessary press times, adhesive resins with a reactivity as high as possible should be used. This includes two parameters (1) a short gelation time and (2) a rapid bond strength increase, and this even at a low degree of chemical curing. 

Such chemical cure methods have been used for many years but, due to the inherent hazards of flammability and toxicity of the system, are not accepted in several countries. Also, if all the exposed working surfaces have not been properly treated, unvulcanised areas may occur which would rapidly deteriorate when the lining is put into service. 

Increase in dimensions of an elastomer due to the absorption of any organic liquid with which it may come in contact or in which it may be immersed. Measurement of the swelling of vulcanised rubber in solvents can be used to determine state of cure and to assess the suitability of elastomers for such uses as chemical plant lining or oil seals. 

The calendering process and its conditions are developed or modified according to the requirements of subsequent operations and the purpose for which the sheet is used. Thus for sheets which are to be open cured, such as in chemical plant lining and custom built items such as inflatables and ebonite pipes, roll coverings for paper and steel mills, the calendering needs to be more exact than the sheets which are used for blank preparation for molding of... 

Chemical cure - A tank lining system which can cure at low temperatures by topically applying a liquid curing agent. 

Vulcanizing agent-Any material that can produce in rubber the change in physical properties known as vulcanization, such as Chemcure applied to chemical cure rubber linings. 

Like any new field, chemotherapy of plant disease has its semantic problems. When we helped initiate it in 1940, we called it chemotherapy in line with our medical confreres. Literally it means, of course, chemical cure, but it is given a connotation of internal therapy as well. There is a strong tendency, particularly in Britain to label it "systemic fungicide/ The semantic problem here is that not all chemotherapeutants are systemic fungicides. Even benomyl, the leading contender, is not a true fungicide. It is a fungistat. 

Selfelastomeric materials may be compounded and calendered with a chemical curing agent which will, over a period of time, slowly cure the sheet at ambient temperatures. This type of curing is primarily noted in natural rubber and neoprene sprayed and troweled coatings, and has not, in recent years, been, to the writer s knowledge, employed for total cure of sheet linings. 

Among materials available for thin linings are those based on epoxy and phenolic resins that are 0.15-0.30 mm (0.006-0.12 in.) thick. They are either chemically cured or heat baked. Baked phenolic linings are used to protect railroad tank cars transporting sulfonic acid. Tanks used to store caustic soda (sodium hydroxide) have a polyamide cured epoxy lining. 

Resorcinol additions just prior to use provide acceleration, though they are still not the most cost effective nor technically effective use of resorcinol. In-line addition of a PRF resin Just before application of the resin to the adherend achieves better results at less than half the cost of resorcinol chemical, in most cases and it is easier to handle. A variant of this concept is application of the resorcinol and PF resins to the substrate separately but in a way that permits them to come into contact during the curing process. Such methods are sometimes called honeymoon systems. 

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