Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Patent
1996-08-28
1997-12-02
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
525437, 525439, 524115, 524123, 524174, 524323, C08J 1104
Patent
active
056936818
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP95/00541 filed Dec. 15, 1995.
The present invention relates to a process for increasing the molecular weight of polyesters and to the polyesters obtainable by said process.
Polyesters as exemplified by polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), as well as polyester copolymers and polyester blends with e.g. polycarbonate (PBT/PC), are important thermoplastics belonging to the group of engineering plastics. Partially crystalline polyesters are used for injection moulding compounds and have superior strength and rigidity, high dimensional stability and good wear properties. Amorphous polyesters have high transparency, superior toughness and very good resistance to stress-cracking, and can be processed to hollow objects. A further utility of PET is fibre production.
The mechanical and physical properties depend essentially on the molecular weight of the polymer. Owing to reduced molecular weight, it is only possible to achieve a limited high-quality recycling of used polyesters and production waste without carrying out an aftertreatment.
It is generally known to enhance the material properties of used polyesters, i.e. polyesters damaged by heat or hydrolysis, which damage is typically accompanied by a molecular weight reduction. As polycondensates, polyesters are obtained by a postcondensation in the solid state (S. Fakirov, Kunststoffe 74 (1984), 218 and R. E. Grutzner, A. Koine, Kunststoffe 82 (1992), 284). However, this method is troublesome and, moreover, is highly sensitive to the impurities that may be present in waste material. A typical method of regenerating waste PET is disclosed in DE 40 34 459. To increase the melt viscosity in this method a residence time of up to 4 hours under vacuum in the temperature range from 270.degree. to 310.degree. C. is necessary.
It is therefore the object of this invention to provide a process that makes it possible to increase the molecular weight of polyesters, especially PET, in a relatively short time.
Surprisingly, it has been found possible to increase the molecular weight of polyesters substantially by fusing the polyester and blending it with a mixture of at least one tetracarboxylic dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester. This molecular weight increase effects an enhancement of the properties of the polyesters, preferably of those used for injection moulding and of recyclates, especially PET bottle scrap material.
Accordingly, the invention relates to a process for increasing the molecular weight of polyesters, polyester copolymers or polyester blends, which comprises heating a polyester blended with a tetracarboxylic dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester to above the melting point (in the case of crystalline polyesters) or to above the glass transition temperature (in the case of amorphous polyesters) of said polyester.
The polyesters, i.e. virgin polyesters as well as polyester recyclate, may be homo- or copolyesters that are derived from aliphatic, cycloaliphatic or aromatic dicarboxylic acids and diols or hydroxycarboxylic acids. In addition, mixtures of these polyesters are also suitable. Their composition will depend essentially on the desired properties for a specific end use.
The aliphatic dicarboxylic acids may contain from to 2 to 40 carbon atoms, the cycloaliphatic dicarboxylic acids from 6 to 10 carbon atoms, the aromatic dicarboxylic acids from 8 to 14 carbon atoms, the aliphatic hydrocarboxylic acids from 2 to 12 carbon atoms and the aromatic and cycloaliphatic hydroxycarboxylic acids from 7 to 14 carbon atoms.
The aliphatic diols may contain from 2 to 12 carbon atoms, the cycloaliphatic diols from 5 to 8 carbon atoms and the aromatic diols from 6 to 16 carbon atoms.
Aromatic diols will be understood as meaning those in which two hydroxyl groups are bonded to one or to different aromatic hydrocarbon radicals.
The polyesters may also be branched with minor amounts, typically 0.1 t
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Kunststoffe 74, (1984), pp. 218-221.
Kunststoffe 82, (1992), pp. 284-288.
Herbst Heinz
Hoffmann Kurt
Pfaendner Rudolf
Acquah Samuel A.
Ciba Specialty Chemicals Corporation
Crichton David R.
Malia Victoria M.
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