Aging retardant

Antioxidant agent Also called aging retardants. AOAs are of major importance to the plastic industry because they extend the plastic s (that are effected by oxygen) useful temperature range and service life during processing and/or product use. The variety of AOAs available and their specific uses are extensive. 

Gomi, F., Utsumi, H., Hamada, A, and Matsuo, M. (1993). Aging retards spin clearance from mouse brain and food restriction prevents its age-dependent retardation. Life Sci. 52, 2027-2033. 

Thyroid hormone also plays a major role in the maturation of bone. A deficiency of thyroid hormone in early life leads to both delay in and abnormal development of epiphyseal centers of ossification (epiphyseal dysgenesis). Hypothyroidism-induced impairment of linear growth can lead to dwarfism in which the Umbs are disproportionately short in relation to the trunk with the apparent bone age retarded in relation to chronological age. 

The commercial significance of the ingredients used in rubber compounding to improve resistance to ageing accelerated work on the discovery, development, use and manufacture of new products. The development efforts were competitive in nature, each manufacturer claiming superiority of their products over the others. Some of the age retardants are listed below. 

Mechanism of stabilization of pro pints by Centr 1 and its gelatinizing and stabilizing powers are discussed in Refs 3,5,9,12,13,14,18, 20,21,23,26,27,28,30,31 Sc 33. Formation of complexes of Centr 1 with-various substances are given in Refs 7,10,32,35 38. Recovery of Centr 1 and of other compds from double-base propints is described in Ref 36. Synthesis of various compds which are formed from Centr 1 during the aging of double-base proplnts is described in Ref 29. Binary mixts and molecular combinations of Centr 1 with various compds are discussed in Refs 7,10,11 35-Addnl information on Centr 1 may be found in Refs 4,8,16,17,19 24 Uses After WWI it was manufd in Ger under the name of Mollit 1 for use as a plasticizer (Ref 1, p[ 238] Sc Ref 4). Its use as gelatinizer-stabilizer-flash reducer in smokeless proplnts was already mentioned under CENTRALITES, Introduction. It has also been used as an age-retarder in vulcanized rubber (Ref 39)... 

Vitamin E (a-tocopherol) occurs naturally in most vegetable oils. The highest concentrations are found in corn, soybean oils, sunflower seed, wheat germ, rapeseed, alfalfa, and lettuce. It is claimed to have age-retardant properties. May produce erythema-multiforme-like eruptions... 

Uses intermediate for mtg. of detergents, aging retardants for rubber, phenoiic UV absorbers, and flame retardants in cosmetics and personai care creams and iotions mfg. of househoid and industriai deaners, personai care prods., textiie auxs., piasticizers, ore flotation, oii weii driiiing, metai iubricants, agric. additives Features Low carbonyi content heips maintain coior in sensitive appiics. avaii. in kosher grade... 

Filtration of viscose is not a straightforward chemical engineering process. The solution of cellulose xanthate contains some easy-to-deal-with undissolved pulp fibers, but also some gel-like material which is retarded rather than removed by the filters. The viscose is unstable and tends to form more gel as it ages. Its flow characteristics make the material close to the walls of any vessel or pipe move more slowly, get older, and gel more than the mainstream viscose. So while filtration can hold back gels arising from incomplete mixing, new gels can form in the pipework after the filters. 

The drawbacks of cellular materials include limited temperature of appHcations, poor flammabiUty characteristics without the addition of fire retardants, possible health ha2ards, uncertain dimensional stabiUty, thermal aging and degradation, friabiUty, and embrittlement due to the effects of uv light (3,6,15). 

Nickel dialkyldithiocarbamates stabili2e vulcani2ates of epichlorhydrinethylene oxide against heat aging (178). Nickel dibutyldithiocarbamate [56377-13-0] is used as an oxidation inhibitor in synthetic elastomers. Nickel chelates of substituted acetylacetonates are flame retardants for epoxy resins (179). Nickel dicycloalkyldithiophosphinates have been proposed as flame-retardant additives for polystyrene (180—182) (see Flame retardants Heat stabilizers). 

Amine Cross-Linking. Two commercially important, high performance elastomers which are not normally sulfur-cured are the fluoroelastomers (FKM) and the polyacrylates (ACM). Polyacrylates typically contain a small percent of a reactive monomer designed to react with amine curatives such as hexamethylene-diamine carbamate (Diak 1). Because the type and level of reactive monomer varies with ACM type, it is important to match the curative type to the particular ACM ia questioa. Sulfur and sulfur-beating materials can be used as cure retarders they also serve as age resistors (22). Fluoroelastomer cure systems typically utilize amines as the primary cross-linking agent and metal oxides as acid acceptors. 

Monomer conversion (79) is followed by measuring the specific gravity of the emulsion. The polymerization is stopped at 91% conversion (sp gr 1.069) by adding a xylene solution of tetraethylthiuram disulfide. The emulsion is cooled to 20°C and aged at this temperature for about 8 hours to peptize the polymer. During this process, the disulfide reacts with and cleaves polysulfide chain segments. Thiuram disulfide also serves to retard formation of gel polymer in the finished dry product. After aging, the alkaline latex is acidified to pH 5.5—5.8 with 10% acetic acid. This effectively stops the peptization reaction and neutralizes the rosin soap (80). 

LEE c-K, KLOPP R G, WEINDRUCH R and PROLLA T A (1999) Gene expression profile of aging and its retardation by caloric restriction. Science 285 1390-93. 

The addition of STPP (1-7%) acted as a retarder and increased compressive strength (mortar II). Less heat and ammonia were evolved and the cement set more slowly in 10 minutes. The paste hardened in 30 to 60 minutes. Traces of ADP persisted for 30 minutes but no STPP was detected in the reaction products. Struvite, the main hydration product, schertelite and dittmarite all appeared within 5 minutes. Struvite continued to increase in amount as the cement aged schertelite disappeared after 3 hours and dittmarite after a week. Stercorite was found only during the first 7 hours. 

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