Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1997-08-14
1999-03-02
Hoke, Veronica P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524128, 524151, C08K 534
Patent
active
058772421
DESCRIPTION:
BRIEF SUMMARY
Many polymeric materials are subject to ageing phenomena which have an undesirable effect during preparation, storage, processing or use and in the widest sense are caused by oxidation. The olefinically unsaturated polymers formed by polymerization of dienes, eg. natural or synthetic rubber, or thermoplastics toughened with such polymers, are particularly sensitive.
As a result of oxidation, the polymers change their outward appearance (loss of transparency, yellowing, cracking, etc) and more or less simultaneously lose their good mechanical properties (impact resistance, elongation at break, tensile strength). In extreme cases, the utility article becomes completely useless.
Among various possible stabilization methods, the addition of antioxidants is generally the usual and most widely used method. Antioxidants are chemical compounds which can inhibit oxidation and the resulting ageing phenomena, typically they themselves undergoing a change. They are generally effective even in small amounts and are advantageously added to the polymer at a very early stage (R. Gachter and H. Muller, Taschenbuch der Kunststoff-Additive, 2nd edition, 1983, page 2, Carl Hanser Verlag Munich).
In addition to the polyolefins, the acrylonitrile/butadiene/styrene copolymers (ABS) and high impact polystyrene (SB) have the highest consumption of antioxidants.
A distinction is made between primary and secondary antioxidants on the basis of their action mechanism. The most important primary antioxidants are the sterically hindered phenols, and also secondary aromatic amines. The latter play only a minor role especially in thermoplastics, owing to their tendency to discolor the products.
Primary antioxidants act as free radical acceptors, while secondary antioxidants (phosphites, thioethers) decompose hydroperoxides. Synergistic mixtures of primary and secondary antioxidants, ie. mixtures in which the components reinforce one another in their action, are frequently used in practice.
The commercially available sterically hindered phenols have a wide range of structures: thiobisphenols, alkylidenebisphenols, alkylphenols, hydroxybenzyl compounds, acylaminophenols and hydroxyphenylpropionates (R. Gachter and H. Muller, Taschenbuch der Kunststoff-Additive, 2nd edition, 1983, page 9 et seq., Carl Hanser Verlag Munich).
For the stabilization of polymers which come into contact with foods, it is necessary to use stabilizers which do not present a health hazard, preferably those which also occur in natural foods.
Vitamin E (.alpha.-tocopherol), which is one of the sterically hindered phenols, has already been described as an efficient stabilizer. EP 384 472 describes the use of Vitamin E for polystyrene packaging materials, in conjunction with light stabilizers.
EP 408 693 describes stabilizer mixtures comprising Vitamin E and mono/di/triglycerides for styrene polymers.
Cylindrical and lamellar morphology is found in particular in block copolymers, for example those comprising styrene and butadiene. In contrast to the morphologies derived from a spherical shape (cellular particle, capsular particle, drop particle or filament particle morphologies; in conventional impact-resistant polystyrene or acrylonitrile/butadiene/styrene polymers), the rubber phase in block copolymers is exposed to a substantially higher load during processing. As a result of the direct chemical bonding to the hard phase, stresses in the rubber phase are more poorly eliminated and hence thermal oxidative damage is greatly facilitated.
Such block copolymers are readily obtainable by anionic polymerization and have long been known (cf. for example M. Szwarc: Carbanions, Living Polymers and Electron Transfer Processes, John Wiley Publishers 1968).
These block copolymers include the novel star styrene/butadiene block copolymers predominantly containing styrene, as described, for example, in U.S. Pat. No. 3,639,517 (from 70 to 95% of styrene and from 5 to 30% of butadiene), German Patent 2,550,227 and German Laid-Open Application DOS 2,550,226 (from 60 to 95% of styrene an
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patent: 4584346 (1986-04-01), Kitchen
patent: 5384349 (1995-01-01), Trepka et al.
J.R. Chipault-"Antioxidants for use in Foods" Autoxidation and Antioxidants-vol. 11, W.O. Lunberg, Ed., pp. 486-491 (1962), Interscience Publishers.
R. Gaechter et al., Taschenbuch der Kunststoff-Additive, 2. Auflage, 1893, S 2ff.
R. Gaechter et al., Taschenbuch der Kunststoff-Addivitve 2. Auflage, 1983 S 9ff.
Guntherberg Norbert
Knoll Konrad
Loth Wolfgang
Naegele Paul
Niessner Norbert
BASF - Aktiengesellschaft
Hoke Veronica P.
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