Plastic and nonmetallic article shaping or treating: processes – With step of cooling to a temperature of zero degrees c. or...
Patent
1998-11-04
2000-10-10
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
With step of cooling to a temperature of zero degrees c. or...
264 453, 264 49, 264 54, B29C 6720
Patent
active
061298670
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel process for preparing alveolar cellulosic products. It also relates to alveolar cellulosic products which can be obtained from said process.
Alveolar cellulosic products are sponge or sponge-cloth type artificial products; i.e., consisting of sponges, sponge-cloths, foamed sponges or the like. Such materials can be used alone or integrated into a composite structure for hygiene and cleaning purposes, in particular for domestic cleaning. The expression "sponge-cloth" means an alveolar cellulosic material with two substantially parallel faces and of small thickness, generally less than one centimeter. Such a material may comprise a reinforcing scrim in its structure.
To date, such alveolar cellulosic materials have been produced by a process known as the viscose process which is known to the skilled person and has been described in French patent FR-A-812 502. That process comprises: action of an alkaline solution on the basic cellulosic dough; the cellulosic dough is thus transformed into alkali-cellulose, which reacts with carbon disulfide to form a cellulose xanthate which is soluble in soda-containing water); mechanical strength of the finished product; soluble and/or fusible crystalline materials which form pores after coagulating the dough by digestion and/or fusion; side of at least one scrim or depositing onto a carrier strip; to act and to regenerate the cellulose. Heating can be either by passing an alternating electrical current between electrodes in contact with the dough, or by bringing the dough into contact with an acidic medium (pH less than 1) at temperatures close to 70.degree. C. for a few minutes (acid regeneration, which advantageously employs a mixture of sulfuric acid and sodium sulfate, to produce sponge-cloths), or bringing the dough into contact with a basic medium (pH close to 12) at temperatures close to 100.degree. C. for a few hours (basic regeneration, which advantageously employs a basic sodium sulfate solution, to produce sponges).
In the conventional process, the products obtained--alveolar cellulosic materials--are then rinsed, optionally bleached, dried, and plasticized before being cut and packaged.
That process is based on chemical modification of the cellulose in the cellulosic raw material. (The cellulose, firstly transformed into alkali-cellulose, reacts with carbon disulfide to produce cellulose xanthate which is soluble in the medium). The modified cellulose (transformed into one of its derivatives) must be regenerated at the end of the process. Such chemical modification of cellulose uses carbon disulfide. Carbon disulfide is a pollutant per se. Further, it is the cause of the appearance of by-products which are also pollutants: sulfides, polysulfides and thiosulfates in aqueous solution ; hydrogen sulfide as a gas. a high chemical oxygen demand (COD); category of volatile organic compounds (VOC), and hydrogen sulfide which is malodorous in very low concentrations and obviously is a nuisance in the surrounding area.
A great deal of research has been carried out to reduce or overcome those disadvantages. Work on optimizing and improving the viscose process has been carried out with a view to minimizing the quantity of carbon disulfide used. Thus in a nearby field, that of producing cellulosic fibers by spinning viscose, the most advanced companies currently prepare viscose with about 28% of carbon disulfide with respect to the alpha-cellulose used. Simultaneously, discharge treatment technologies have been developed. The most sophisticated technologies currently enable all of the pollutants in the aqueous phase to be recycled and no polluted water is discharged into the natural surroundings. Gas treatment technologies can recycle up to 70% of the carbon disulfide used to produce viscose by adsorption on activated charcoal and can convert two thirds of the residual emissions to sulfuric acid by catalytic oxidation. Sulfuric acid is itself used in the process. Atmospheric discharges can thus currently be limited to about 10% of
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Chanzy Henri
Chevalier Christophe
Wertz Jean-Luc
Financiere Elysees Balzac
Kuhns Allan R.
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