Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1996-12-19
1998-09-15
Yoon, Tae
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528487, 521 48, 524126, 525420, C08G 6387, C08G 6948
Patent
active
058079661
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for increasing the molecular weight of polycondensates and to the polycondensates obtainable by said process.
Polycondensates as exemplified by polyester, polyamide and polycarbonates are important engineering plastics having many different utilities, e.g. as foils, bottles, fibres and injection moulding parts. These polymers have in common that they are prepared by polycondensation reactions. The damage done to such polycondensates by processing and use results mainly in polymer fragments containing functional end groups, as a consequence of chain cleavage reactions.
The mechanical and physical properties depend essentially on the molecular weight of the polymer. Reduced molecular weight makes possible only a limited high-quality recycling of used polyesters, polyamides, polycarbonates and production waste, typically generated from fibre production and injection moulding, without carrying out an aftertreatment.
It is generally known to enhance the material properties of used polycondensates, i.e. polyamides damaged by heat or hydrolysis. Typically these polycondensates can be postcondensated in the solid state (S. Fakirov, Kunststoffe 74 (1984), 218 and R. E. Grutzner, A. Koine, Kunststoffe 82 (1992), 284). However, this method is time consuming and is, moreover, highly sensitive to the impurities that may be present in waste material.
EP-0 410 230 also proposes the use of phosphoric acid, phosphorous acid or phosphonous acid as catalyst for the solid phase condensation of polyamides .
F. Mitterhofer describes investigations using a diphosphonite as processing stabiliser for polymer recyclates (C.A. 91, 124534).
It is also commonly known to obtain crosslinked polyamides by using an epoxy resin and a standard polyamide catalyst, preferably sodium hypophosphite (EP-A-0 295 906). The crosslinked polyamides obtainable in this manner typically have a melt viscosity which is the four times higher than that of the starting polyamide.
Accordingly, it is the object of this invention to provide a process that makes it possible to increase the molecular weight of polycondensates, e.g. polyesters, polyamides and polycarbonates as well as the corresponding copolymers and blends in a relatively short time. In this process, the increase of the molecular weight shall essentially be effected without crosslinking.
Surprisingly, it has been found possible to increase the molecular weight of the polycondensate substantially by fusing and adding at least one diphosphonite or a mixture of at least one diphosphonite and at least one difunctional compound to a polycondensate. This molecular weight increase effects an enhancement of the properties of the polycondensates, e.g. in injection moulding and, in particular, of recyclates. With the process of this invention it is possible to achieve an increase in the molecular weight of, in particular, polycondensate recyclates originating from the collection of used technical parts, as from automotive and electric utilities, which makes it possible to employ the recyclates for their original utilities. Such recyclates originate also from, inter alia, industrial or domestic useful material collections, production wastes or obligatory returnables.
Accordingly, the invention relates to a process for increasing the molecular weight of polyamides, essentially without crosslinking, which comprises heating a polyamide or a copolymer or a blend thereof, with the addition of at least one diphosphonite to above the melting point (in the case of crystalline polyamides) or to above the glass transition temperature (in the case of amorphous polyamides) of the polymer.
Another aspect of the invention is a process for increasing the molecular weight of polycondensate recyclates, essentially without crosslinking, which comprises heating a polyamide recyclate, a polyester recyclate or a copolymer or a blend recyclate of these polymers, with the addition of at least one diphosphonite to above the melting point (in case of crystalline polycondensate types) or to
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Chem Abst. 91,124534.
Kunststaffe 74 (1984), 218 ff.
Kunstrstaffe 82 (1992), 284 ff.
Herbst Heinz
Hoffmann Kurt
Pfaendner Rudolf
Ciba Specialty Chemicals Corporation
Hall Luther A. R.
Malia Victoria M.
Yoon Tae
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