Antioxidants packages

R. A. Hill, "New Antioxidant Package for Polyether Polyols, with Reduced Fogging Behaviour," 34thMnnualPolyurethane Technical Marketing Conference, New Odeans, La., Oct. 21—24,1992. 

One key consideration in developing radiation curable adhesive systems is the thermal stability and volatility of any photoinitiators used. These chemicals are designed for liquid systems where these issues do not arise. Few of the commercial photoinitiators have adequate thermal stability at the highest hot melt temperatures (180-200°C) and many are too volatile. Reduced application temperatures and special antioxidant packages are often required. 

Low molar mass antioxidants are known to suffer from physical loss and research in recent years has, therefore, focused on finding substantive alternatives. For example, reactive antioxidants, which can be chemically anchored on the polymer backbones to prevent physical loss during processing or in-service, have been explored as nonmigratory antioxidants. Clearly, there are many factors that need to be considered before choosing antioxidants in end-use applications. The success of an antioxidant package is critically dependent on the underlying chemical and physical factors that influence antioxidant performance in different substrates and environments. 

Antioxidants and stabilizers are chosen for target applications on the basis of chemical, physical, toxicological, and economic factors. The final selection of an antioxidant package must take into consideration the performance requirements of the end-use polymer article including toxicity, compatibility, appearance, and color. Issues of efficacy and safety have been the driving force behind much of the recent progress made in the areas of biological, reactive, and macromole-cular antioxidants. 

These two steps remove the intermediates which propagate the chain reaction and stop the chain. Inhibition chemistry is the centerpiece of the application of antioxidant packages in lubricants. 

Because primary and secondary antioxidants differ in their mechanism of attack to prevent oxidative degradation, in practice both type of antioxidants are often used together to obtain the best results. Often such combinations provide a synergistic effect, where the combined antioxidant package provides greater protection than the sum of the two alone. However, antioxidants can also interact in an antagonistic fashion, so proper pairing is needed. 

Antioxidants are usually in the form of antioxidant packages, combining two or more antioxidants (one of these, in general, is the primary antioxidant while the other is the secondary antioxidant, and both are expected to work together synergistically). The primary antioxidant helps to prevent or to terminate oxidative reactions. The secondary antioxidant helps to neutralise reactive materials that can create new cycles of oxidation. Antioxidants are also regarded as anti-ageing additives [15]. 

Only a few articles have been published examining the effects of various antioxidant packages on the thermo-oxidative degradation of aromatic polyesters [3-19]. 

A combination chain extender and antioxidant package known as Irgamod RA20, which is a masterbatch consisting of 75.5% polyester carried resin, 20.5% pyromellitic dianhydride, 2% pentaerythritol and 2% Irganox 1425 [47]. 

Antioxidant substances are used to reduce the deterioration of food products caused by the contact with atmospheric oxygen. Natural antioxidants have been incorporated into polymer blend films at various levels of loadings. The blend films are from two or more polymers in various ratios mixed homogenously. Various polymers of LDPE, LDPE-PP, and EVA-LDPE have been used in polymer blended combinations of antioxidant packaging films containing mixed active compounds of tocophaol-sesamol (3,4-methylenedioxyphenol) and tocophaol-quacetin... 

Oxidative degradation and the importance of antioxidant additives have already been discussed in detail in Sect. 5.2.2. T q)ically, phosphite and a hindered phenol are used as the main components of the antioxidant package for most of the HDPE geomembranes available on the market. Normally, carbon black is added as UV stabiliser. The concentration of the antioxidant components is t3 ically in the range of a few thousand ppm (mg/kg). Depletion of these antioxidants was identified as the relevant... 

What conclusion about service lifetimes can be drawn from these longterm test results For our discussion it is crucial that the change in OIT value provides at least a rough estimation for the depletion time t2. This assumption was established for the antioxidant package commonly used in HOPE geomembranes and it explains the oxidation behaviour in the OIT measurement itself as described in Sect. 3.2.7. In the following we will show that a consistent explanation of all our experimental results is possible within this interpretation scheme. 

Overall, all aspects of environmental effects, antioxidant safety, optimum concentration levels and antioxidant permanence under the specified service conditions have to be considered and balanced with the initial cost of the antioxidant the cost effectiveness of antioxidant packages is a decisive factor in all industrial apphcations. 

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