ANTIOXIDANTS FOR PLASTICS

Abstract: A polar phenolic compound consisting of an alkyl chain with two end groups, the first being an optionally-substituted phenyl group and the other a trinitrophenyl group. A preferred example is 3-(3,5 di-tertiary-butyl-4-hydroxy phenyl) propyl 2,4,6 trinitrophenyl ether. These compounds are useful as antioxidants in plastics materials for food packaging.

Description: ANTIOXIDANTS FOR PLASTICS The present invention relates to antioxidants for plastics materials. The processing of plastics materials necessitates the presence of antioxidants mainly to capture peroxides, especially for thermal and light stabilisation. These additives are used in plastics materials for food packaging. During prolonged contact between foodstuff and packaging material, extraction of low molecular weight components can occur. Consequently, additives will migrate from the packaging material into packed foods, creating a health hazard for consumers and leading to a loss of stabilising properties in the plastics material. Both features are undesirable and there is a need for additives, such as antioxidants, which do not have this tendency to migrate to the surface of the plastics materials. The migration behaviour of phenolic antioxidants is influenced by molecular shape and size. In a first approximation, migration rates depend on the molecular weight of the migrating species. However, increasing the molecular weight is limited by the requirement that the additive be capable of diffusing slowly through the plastics material in order to exert its function. In German Patent Application No 2.544.014 the use of polar phenolic antioxidants-to stabilise plastics materials has been described. We have found that an improved result can be obtained with polar phenolic antioxidants consisting of molecules, having an alkyl chain with two end groups, the first being an optionally-substituted phenyl group and the other a trinitrophenyl group. One example of these compounds is 3-(3,5 di-tertiarybutyl-4-hydroxy phenyl)propyl 2,4,6 trinitrophenyl ether, which in this specification will be referred to as TNPP. If these substances are added to a polymer matrix with electron-donating properties (for instance a polyamide or a polyvinylpyrrolidone), a charge-transfer complex will be formed. However, the equilbrium between complex and "free" species allows sufficient "mXobile'l antioxidant to be available to capture peroxides in the plastics material. Consumption of the antioxidant will shift the equilibrium gradually towards the release of "free" antioxidant species and maintain a functional behaviour for an extended service life. The formation of charge-transfer complexes considerably reduces the spontaneous migration of the additive. Losses due to extraction by the packed foodstuffs will diminish, resulting in a lower contamination of the food and an extended life-time of the plastics material. The additives have been tested in plastics materials, such as High Density Polyethylene (HDPE) and Polyamide (PA). The following antioxidants have been synthesised and tested in different polymers: EMI3.1 EMI3.2 <SEP> NO <tb> HO <SEP> g <SEP> 2 <SEP> 2 <SEP> CH2 <SEP> <SEP> ss <SEP> N02 <tb> <SEP> NO2 <SEP> (see <SEP> Table <SEP> I) <tb> in which the crosses in the phenyl group mean tertiary butyl groups. Normally the amount of additive in the plastics material is less than 1% by weight. The migration values of the antioxidants used are represented in Tables I and II; in which BHT means the conventional 2,6 di-tertiary-butyl-4 methyl phenol and DMD means 5,5 dimethyl-2-(3,5-di-tertiary butyl-4 hydroxyphenyl) -1, 3-dioxane. TABLE I Migration values (as percentage of the initial concentration in the plastic) of 4 additives from pressed High Density Polyethylene into 3 test liquids after different storage conditions Migrated Amount (weight %) in: HB307 Heptane Water/Ethanol (90/10) Storage time 2 hrs 10 days 2 hrs 10 days 2 hours 10 days Storage temp. 70 C 40 C 70 C 40 C 70 C 40 C Plastic/Additive HDPE-BHT 15.62 32.54 95.38 100.00 1.16 1.84 HDPE-DMD 9.15 32.54 95.38 100.00 2.27 2.98 HDPE-TNPP 5.99 12.01 73.95 56.62 0.62 0.38 TABLE II Migration values of 3 additives from pressed Polyamide into 3 test liquids after different storage conditions Migrated Amount (weight %) in: : HB307 Heptane Water/Ethanol (90/10) Storage time 2 hrs 10 days 2 hrs 10 days 2 hours 10 days Storage temp. 70 C 40 C 70 C 40 C 70 C 40 C Plastic/Additive PA-BHT 5.09 PA-DMD 0.09 0.16 0.12 0.25 6.24 20.89 PA-TNPP n.d. n.d. n.d. n.d. 0.41 0.54 n.d. = not detected

Claims: CLAIMS: 1. A polar phenolic compound consisting of an alkyl chain with two end groups, the first being an optionallysubstituted phenyl group and the other a trinitrophenyl group. 2. A compound as claimed in claim 1 wherein the alkyl chain is a lower alkylene group, optionally including a divalent linking group other than alkylene. 3. A compound as claimed in claim 2 wherein the alkylene group contains up to 3 carbon atoms and the linking group is an ester or ether group. 4. A compound as claimed in any one of the preceding claims wherein the phenyl group is substituted with at least one tertiary butyl group. 5. A compound as claimed in any one of the preceding claims wherein the phenyl group is substituted with at least one hydroxyl group. 6. 3-(3,5 di-tertiary-butyl-4-hydroxy phenyl) propyl 2,4,6 trinitrophenyl ether. 7. A plastics material including, as an antioxidant, at least one compound as claimed in any one of the preceding claims. 8. A high density polyethylene including, as an antioxidant at least one compound as claimed in any one of the preceding claims. 9. A polyamide including, as an antioxidant, at least one compound as claimed in any one of the preceding claims. 10. Food when packaged using a plastics material as claimed in any one of claims 7 to 9

Inventors: LE GOFF, BERNARD
Applicants: EUROPEAN ATOMIC ENERGY COMMUNITY (EURATOM)
Application year: 1983
Main classification: C08K5
IPC codes: C07C205, C08K5