Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Patent
1997-05-19
1999-11-30
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
526 67, 526 68, 526 69, 528491, 528493, 528497, C08J 1104, C08J 600, C08F 200
Patent
active
059944161
DESCRIPTION:
BRIEF SUMMARY
The "material recycling" of polyarylene sulfide waste for reuse has hitherto been limited to the melting of puregrade, uncontaminated production waste or off-specification batches. In this case it is possible to use only polyarylene sulfide waste of identical or similar composition, in particular with identical additions and filler contents, since otherwise an alteration in the properties of the polymer material must be accepted. Repeated thermal stressing in the course of reuse lead in general to a loss of quality in the polymer material.
DE-C-34 33 978 reports that the repeated thermal stressing of polyarylene sulfide produces deficient or excessive crosslinking, which in linear polyarylene sulfide starting materials signifies an impairment of the flow properties and viscoelastic properties.
In general, a large number of fillers in plastics, such as glass fibers or mineral substances, are damaged when processed a subsequent time. In the case of fiber-rein-forced plastics, for example, repeated extrusion in the course, for example, of an injection molding process severely reduces the average fiber length of reinforcing fibers, so that the mechanical properties of a plastic worsen with each processing step (so-called downgrading).
EP 0 461 655 A1 describes how polyarylene sulfide particles having a low content of oligomer and ash are obtained from a liquid reaction mixture which comprises polyarylene sulfide, polar organic solvent and water, by cooling the mixture. The method is part of a preparation process for polyarylene sulfide.
The object of the invention is the recovery of polyarylene sulfide from materials comprising it, especially waste materials, where the content and the nature of fillers or additives, impurities or contamination and the age of the material should be irrelevant and the recovered polyarylene sulfide should also be suitable for recompounding.
The invention provides a process for obtaining polyarylene sulfide from polyarylene sulfide-containing material, in which the polyarylene sulfide-containing material is treated with a solvent, the polyarylene sulfide dissolving and being subsequently precipitated.
The invention also provides for the purification of polyarylene sulfide-containing material, where the polyarylene sulfide-containing material is dissolved, undissolved polyarylene sulfide oxidation products, polyarylene sulfide ageing products, degradation products, composition products, additives or fillers are separated off, and the polyarylene sulfide is precipitated from the resulting solution.
The polyarylene sulfide is precipitated by cooling the polyarylene sulfide solution, spontaneously evaporating the solvent (flashing) ot, preferably, by mixing with a liquid medium. The term liquid medium refers here to water and/or an organic or inorganic solvent in which polyarylene sulfide has little or no solubility. It is advantageous if the liquid medium dissolves oligomers and/or other impurities. Solvents suitable for this purpose are those having an aldehyde or keto group, such as acetone, or aromatic solvents such as toluene. A liquid medium which is miscible with water, for example acetone, can contain water. It is advantageous if the liquid medium is miscible with the solvent for dissolving PAS. The liquid medium can also be composed of a mixture of solvents. A mixture can comprise, for example, the solvent used for dissolving PAS.
The use of acetone or of acetone-containing solvent mixtures as the liquid medium is particularly advantageous in precipitating PAS, since acetone has a good take-up capacity for soluble constituents, such as impurities of the polyarylene sulfide used for the purification. Acetone has also proved to be favorable for washing the precipitated polyarylene sulfide. Soluble constituents or impurities are, for example, unconverted reactants in the preparation of PAS, soluble oligomers formed during the preparation, soluble additives, amine compounds and sulfide compounds.
The dissolution of the polyarylene sulfide-containing materials or of polyarylene su
REFERENCES:
patent: 5039788 (1991-08-01), Bobsein et al.
Bruck Martin
Schleicher Andreas
Foelak Morton
Ticona GmbH
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