Ageing stabilisers

Grades of PP of melt index 3 were employed in these studies of general-purpose polymers and special high heat ageing stabilisation. Additional studies are discussed involving pigmented materials incorporating various UV stabilisers. In these latter studies these PP... 

After ageing stabilisation to convert anhydride appr. 1% H2O, LAB-SA, stable product... 

N. B. Neiman, Aging and Stabilisation of Polymers, Consultants Bureau, New York, 1965, p. 236. 

Such structural changes are a consequence of chemical reactions of which the most common are oxidation, ozone attack, dehydrochlorination and ultraviolet attack. (Reactions due to high-energy radiation or to high temperature are not considered here as causing natural aging.) Over the years many materials have been introduced as antioxidants, antiozonants, dehydrochlorination stabilisers and ultraviolet absorbers—originally on an empirical basis but today more and more as the result of fundamental studies. Each of these additive types will be eonsidered in turn. 

KuzMiNSKir, A. s. (Ed.), The Ageing and Stabilisation of Polymers (English translation by leyland, B. N.), Elsevier, Amsterdam (1971)... 

There are a number of occasions where a transparent plastics material which can be used at temperatures of up to 150°C is required and in spite of its relatively high cost, low impact strength and poor aging properties poly-(4-methylpent-1 -ene) is often the answer. Like poly(vinyl chloride) and polypropylene, P4MP1 is useless without stabilisation and as with the other two materials it may be expected that continuous improvement in stabilising antioxidant systems can be expected. 

Apart from routine quality control actions, additive analysis is often called upon in relation to testing additive effectiveness as well as in connection with food packaging and medical plastics, where the identities and levels of potentially toxic substances must be accurately known and controlled. Food contact plastics are regulated by maximum concentrations allowable in the plastic, which applies to residual monomers and processing aids as well as additives [64-66]. Analytical measurements provide not only a method of quality control but also a means of establishing the loss of stabilisers as a function of material processing and product ageing. 

Obviously, use of such databases often fails in case of interaction between additives. As an example we mention additive/antistat interaction in PP, as observed by Dieckmann et al. [166], In this case analysis and performance data demonstrate chemical interaction between glycerol esters and acid neutralisers. This phenomenon is pronounced when the additive is a strong base, like synthetic hydrotalcite, or a metal carboxylate. Similar problems may arise after ageing of a polymer. A common request in a technical support analytical laboratory is to analyse the additives in a sample that has prematurely failed in an exposure test, when at best an unexposed control sample is available. Under some circumstances, heat or light exposure may have transformed the additive into other products. Reaction product identification then usually requires a general library of their spectroscopic or mass spectrometric profiles. For example, Bell et al. [167] have focused attention on the degradation of light stabilisers and antioxidants... 

For the copolymers, the stabiliser is less affected during accelerated ageing due to the presence of the comonomer units. 

J. Rychly and L. Rychla, Chemiluminescence from polymers. In M. Strlic and J. Kolar (Eds.), Ageing and Stabilisation of Paper, National and University Library, Ljubljana, Slovenia, 2005, p. 71. 

The resin composition was indeed found to influence the ageing processes in mastic, the polymer fraction was shown to reduce the oxidation of triterpenoids (Figure 5.8). This was found for both natural ageing [33, 36] and artificial ageing. Because the polymer, a polymyrcene, contains many double bonds that can easily be oxidised [42], it might act as a radical stabiliser. The mastic samples shown in Figure 5.8 were obtained from three aliquots of the same mastic solution, the polymer part of the first aliquot was removed and added to the third. 

A report (37) on the effect of different types of radiation on the elongatlon-at-break of certain commercial cable Insulating materials pointed to several aspects requiring fundamental Investigations on well-characterised materials under defined conditions. It showed the Importance of antl-oxldant stabilisers, particularly In relation to long term ageing. It was concluded that the differences observed could be attributed to dose rate effects rather than to the types of radiation studied. The Irradiated samples were standard dumb hell shaped tensile samples. 

Nugent noted that caustic soda broke a benzene water emulsion stabilised with gelatine, and that the breaking was preceded by an inhibition period which increased with the age of the emulsion as instanced by the following figures. 

Global opiate abuse has stabilised at an estimated 15.6 million people, or 0.4 per cent of the worlds population aged 15-64. Opiates continue to be the main problem drug worldwide, accounting for some 60 per cent of treatment demand in Asia and in Europe. 

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