Synergistic combinations of phenolic antioxidants

Details Synergistic combinations of phenolic antioxidants Synergistic combinations of phenolic antioxidants

2002-08-22

2003-11-11

Sanders, Kriellion A. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C252S404000

Reexamination Certificate

active

06646035

ABSTRACT:

The invention relates to synergistic combinations of phenolic antioxidants in polyolefine pipes and other thermoplastic molding materials especially those which are in contact with water.
The usability and lifetime of—often partially crosslinked—polyolefin pipes and other thermoplastic materials which are in prolonged contact with water such as geotextiles, water pipes, tubing for heating equipment etc. is influenced by numerous parameters such as mechanical properties, density, molar mass and mass distribution of the polymer. Depending on the final use and the local conditions (temperature, stress, and environmental influences) during the use time, a lifetime of up to several decades should be guaranteed. New trends for lifetime expectancy are more than 50 years. In case of their use for water transportation, special requirements must be fulfilled which can be reached by addition of appropriate stabilizers and stabilizer conditions. Their contribution can be determined under accelerated test conditions at elevated temperatures by hot water storage. As important technical criteria oxidation induction time (OIT) and mechanical stability are used to assess the stabilization of polyolefin pipes or other polyolefin-based molding materials. OIT-tests are still established and are used as technically important criteria despite the fact that extrapolations of OIT-data are since a long time discussed to be often too optimistic compared to conventional oven aging results. Effects in the polymer matrix e.g. change in cristallinity, free volume, morphology, and coefficient of diffusion and reaction kinetics cause changes in the degradation mechanism. Nevertheless, especially in the PE-MD- and PE-HD-sector OIT-limits of at least 30 minutes at T=210° C. are required. Another technical criterion which must fulfill certain technical requirements is color determined as yellowness index (YI).
Further technical criteria to judge the quality of resins used for contacts with water is the remaining stabilizer content after hot water storage (95° C.) which is part of the standard test program of the involved resin producers and manufacturers of finished articles.
The following publications refer to the above mentioned problems:
1) Higuchi, Y.; Nishimura, H.; Tamamura, H.; Harada, T. Osaka Gas Co., Ltd., Japan. Proc. Int. Gas Res. Conf. (1998), (Vol. 3), 67-75.
2) Advanced extraction resistant long-term thermal stabilizers for polyolefin pipes. Schmutz, T h.; Kramer, E.; Zweifel, H.; Dörner, G. Ciba Specialty Chemicals, Inc., Basel, Switz. J. Elastomers Plast. (1998), 30(1), 55-67.
One of the decisive criteria preventing rapid oxidative degradation of polyolefin pipes or other molding articles based on thermoplastic polymers is the use of long-term stabilizers. The efficiency is depending on the compatibility, the solubility, the mobility and the migration of additives in the pipe resin.
Phenolic antioxidants have been used in combination with phosphites or phosphonites and sometimes with alpha-tocopherol for the stabilization of polyethylene-based thermoplastic polymers (WO-A-97/49758). Stabilization of polyolefins with phenolic antioxidants has also been described in R. Gächter, H. Müller; Handbook “Plastic Additives” (“Kunststoffadditive”), 3. German Edition, Carl Hanser Publishers, Munich, Vienna 1990; pp 68.
There is a certain technical need to improve stabilizer systems used in polymer substrates for extended contact with extracting media with regard to long term stability of the system (problems with migration, stability to hydrolysis).
It has now been found that combinations of certain phenolic antioxidants lead to a synergistic effect for long-term thermal stabilization in thermoplastic, especially polyolefin articles to be utilized under extractive conditions of water before and after hot water storage. The instant stabilizer combinations offer surprisingly the possibility to outperform the state of the art with regard to resistance against oxidative degradation, color and other parameters.
Object of the instant invention are stabilizer compositions for thermoplastic polymers, especially for polyolefins, comprising
a) at least one phenolic antioxidant selected from the compounds (I) to (VI):
bis-[3,3-bis-(4′-hydroxy-3′-tert.butylphenyl)-butanoic acid]-glycolester (I),
4,4′,4″-[(2,4,6-trimethyl-1,3,5-benzenetriyl)tris(methylene)]-tris[2,6-bis(1,1-dimethylethyl)phenol] (II),
1,3,5-triazine-2,4,6(1H,3H ,5H)-trione, 1,3,5-tris[[4-(1,1-dimethylethyl)-3-hydroxy-2,6-dimethylphenyl]methyl] (III),
phenol, 4,4′,4″-(1-methyl-1-propanyl-3-ylidene)tris[2-(1,1-dimethylethyl)-5-methyl (IV),
phenol, 2,6-bis[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]octahydro-4,7-methano-1H-indenyl]-4-methyl (V), or
benzenepropanoic acid, 3-(1,1-dimethylethyl)-4-hydroxy-5-methyl-, 2,4,8,10-tetraoxa-spiro[5.5]undecane-3,9-diyl-bis(2,2-dimethyl-2,1-ethanediyl) ester (VI), and
b) at least one phenolic antioxidant selected from the compounds (VII) or (VIII):
tetrakismethylene(3,5-di-tert.butyl-4-hydroxyphenyl)-hydrocinnamate (VII) or
octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate (VIII),
wherein the weight ratio of component a) to component b) is from 1:10 to 10:1, preferably from 1:2to 2:1.
The compounds (I) to (VIII) are commercially available products of the following chemical structure:
Special preference is given to a stabilizer composition, wherein component a) is compound (I), (II) or (III) or any mixture thereof. Especially preferred is compound (I).
Further suitable phenolic antioxidants of group a) are 1,4-bis(3,5-di-tert-butyl-4-hydroxybenzyl)-2,3,5,6-tetramethylbenzene; 2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)phenol; 2,4-bisoctylmercapto-6-(3,5di-tert-butyl-4-hydroxyanilino)-1,3,5-triazine; 2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyanilino)1,3,5-triazine; 2-octylmercapto-4,6-bis(3,5di-tert-butyl-4-hydroxyphenoxy)-1,3,5-triazine; 2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenoxy)-1,2,3-triazine; 1,3,5-tris(3,5di-tert-butyl-4-hydroxybenzyl) isocyanurate; 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate; 2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenylethyl)-1,3,5-triazine; 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexahydro-1,3,5-triazine; or 1,3,5-tris(3,5-dicyclohexyl-4-hydroxybenzyl) isocyanurate.
All phenolic components are used in a range between 0.001 and 2.000% weight-percent, preferentially in concentrations between 0.020 and 0.200 weight-percent, related to the thermoplastic polymer to be stabilized, for the long term use especially in polyethylene-HD- and polyethylene-MD articles in contact with water before, during and after water storage.
A further object of the instant invention therefore is a method of use of said stabilizer compositions for the stabilization of thermoplastic polymers, especially polyolefins, which are in prolonged contact with extracting media like water, in concentrations of 0.001% to 2.000%, preferably 0.020% to 0.20% by weight, based on the polymer.
Another object of the instant invention is a process of stabilizing thermoplastic polymers, especially polyolefins, which are in prolonged contact with extracting media like water, by incorporating 0.001% to 2.000%, preferably 0.020% to 0.20% by weight, based on the polymer, of said stabilizer compositions.
Suitable thermoplastic polymers to be stabilized according to the instant invention are for example the following ones:
1. Polymers of monoolefins and diolefins, for example polypropylene, polyisobutylene, polybut-1-ene, poly-4-methylpent-1-ene, polyisoprene or polybutadiene, as well as polymers of cycloolefins, for example of cyclopentene or norbornene; furthermore polyethylene (which optionally can be crosslinked); for example, high density polyethylene (HDPE), polyethylene of high density and high molar mass (HDPE-HMW), polyethylene of high density and ultrahigh molar mass (HDPE-UHMW), medium density polyethylene (HMDPE), low density polyethylene (LDP

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