Oxidative aging polymers

Li, K., Wang, K., Zhan, M., Xu, W. The change of thermal-mechanical properties and chemical structure of ambient cured DGEBA/TEPA under accelerated thermo-oxidative aging. Polym. Degrad. Stab. 98, 2340-2346 (2013)... 

There are no known practical peroxide cure systems for the PO—AGE polymers. Apparentiy the peroxide attacks the polymer backbone at a rate that is unfavorably competitive with the cross-linking rate. A typical sulfur cure system consists of zinc oxide [1314-13-2] tetramethylthiuram mono sulfide (TMTM), 2-2-mercaptobenzothiazole [149-30-4] (MBT), and sulfur. A sulfur donor cure system is zinc oxide, di-o-tolylguanidine [97-39-2] (DOTG) and tetramethylthiuram hexasulftde. 

Chemiluminescence is the emission of light in the 300-500 nm region due to exothermic chemical reactions. With a suitable detection system this can be used to monitor the chemical reactions that occur when materials age. This technique is sensitive enough to produce results more rapidly and at lower temperatures. Chemiluminescence has been used to investigate the effect of different additives on the oxidation of polymers as well as to determine oxidation induction times which are more meaningful than those obtained from the DSC method. 

These polar transformation products and sulfur oxides (SO2, SO3) arising in the ultimate stages of the transformation process are formed in trace amounts in the aged polymer matrix. Volatile products may be sources of undesirable organoleptic problems. This limits the use of organic thiocompounds in odor-sensitive applications. Organic S-proto-nic acids 85, 86 deactivate basic stabilizers (HAS). The peroxidolytic effect of 85, 86 is reduced in the presence of some antiacids or fillers, e.g., calcium carbonate. 

Relating Kinetic Models to Embrittlement in Polymer Oxidative Aging... 

Determination of the residual antioxidant content in polymers by HPLC and MAE is one way to determine the amoimt needed for reasonable stabilization of a material, and also to compare different antioxidants and their individual efficiencies. During ageing and oxidation of PE, carboxyhc acids, dicarboxylic acids, alcohols, ketones, aldehydes, n-alkanes and 1-alkenes are formed [86-89]. The carboxyhc acids are formed as a result of various reactions of alkoxy or peroxy radicals [90]. The oxidation of polyolefins is generally monitored by various analytical techniques. GC-MS analysis in combination with a selective extraction method is used to determine degradation products in plastics. ETIR enables the increase in carbonyls on a polymer chain, from carboxylic acids, dicarboxyhc acids, aldehydes, and ketones, to be monitored. It is regarded as one of the most definite spectroscopic methods for the quantification and identification of oxidation in materials, and it is used to quantify the oxidation of polymers [91-95]. Mechanical testing is a way to determine properties such as strength, stiffness and strain at break of polymeric materials. 

The acrylic core-shell polymers are considered to offer superior ultraviolet-light and thermal-oxidative aging properties than does the more conventional reactive liquid polymeric toughener, CTBN. Hence, there is current interest in the use of acrylic core-shell polymers as tougheners for adhesives and composite matrices that possess a relatively high glass-transition temperature. 

The ozone concentration in the troposphere during the daytime is typically about 1 pphm (parts per hundred million parts of air by volume) [20], Values up to 100 pphm were measured in some photochemical smog areas. The molecular mechanism of the ozone aging of diene based elastomers was studied in detail and is well understood [19,21], Products or intermediates different from those arising in autoxidation or photo-oxidation of polymers were identified ozonides (3), zwitterions (4), diperoxides (5), polyperoxides (6), polymeric ozonides (7) and terminal aldehydes (8). Reactivity of aminic antiozonants (AOZ) with these species accounts for the protection of rubbers against atmospheric 03. AOZ must also possess antioxidant properties, because the free radical processes are concerted with ozonation due to the permanent presence of oxygen. 

In contrast, the presence of Cl based on low-molecular amines of NDA or G-2 type hampers gas-penetrability of the polymer films as a result of atmospheric aging [114]. Vapor-penetrability of PE films increases by 1.5-2 times after exposure to UV radiation for 200 hours or to climatic factors for two months. Under the same conditions, the vapor-penetrability of inhibited films grows, but by only 10-20%. Apparently, Cl of the named type function in this case like a stabilizer that hampers photo and thermal-oxidative aging of PE. 

H2 release and crosslinking macrochains during oxidation at relatively low temperature is untypical for methylene chains of aliphatic polymers, but this phenomenon accompanies oxidative ageing of fully aromatic PI and PPQ. 

J. Verdu, Oxidative Ageing of Polymers (Wiley, Hoboken, 2012)... 

Oxidative aging, elastomers n. Breaking down of an elastomer through the action of oxygen on the polymer itself or on other ingredients of the compound. The process may be signaled by change of color, visible deterioration of the part surface, or lowered performance in service. 

Key words chemical degradation, biochemical degradation, oxidative degradation, hydrolytic degradation, enzymatic degradation, calcification, accelerated ageing, polymer implants. 

Other earlier applications include those of Bletsos and co-workers [47] who produced time-of-flight ion MS of additives in polydimethylsiloxane and polytetrafluoroethylene, MS of organic additives in carbon black filled styrene-butadiene rubber [48] and oxidative ageing of antioxidants present on polymer surfaces [49, 36]. 

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