Thermal stabilisers

Polymers are subject to unsaturation, which leads to a colour change during processing, as a result of temperature and pressnre [1, 2]. The use of stabilisers should ensure adequate stability of polymers during processing. Repeated processing with additional heat steps 

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High-MW hindered amine thermal stabiliser (HATS) formulations are designed for advanced extraction resistant long-term stabilisation, i.e. for use in extractive environments such as polyolefin pipes, fulfilling the stringent requirement of guaranteeing product lifetime of more than 50 years [565], These systems offer much better gas and hot water resistance than the low-MW phenolic antioxidant systems. Ethanox 330... 

The commercial evolution of hindered amine stabilisers is best illustrated by the sequence of the monomeric Tinuvin 770, oligomeric Tinuvin 622, Chimassorb 944 and Chimassorb 119, and most recently Chimassorb 2020 (Figure 3.25) with increased control on volatility, migration, extractability and co-additive interactions [597]. The hindered amine thermal stabilisers Chimassorb 944 and Chimassorb 119, outperform Cyasorb UV3346 as to extraction resistance [565]. 

For samples that meet the solubility requirements of the SEC approach, analyses were also reported for additives in polymers such as PVC and PS [28,29]. Direct SEC analysis of PVC additives such as plasticisers and thermal stabilisers in dissolution mode has been described [28,30,31 ]. In the analysis of a dissolved PS sample using a SEC column of narrow pore size, the group of additives was separated on a normal-phase column after elution of the polymer peak [21]. Column-loading capacity of HPSEC for the analysis of additives, their degradation products and any other low-MW compounds present in plastics has been evaluated for PS/HMBT, PVC/TNPP and PVC/TETO (glyceryl tri[l-14C] epoxyoleate) [31]. It was shown that HPSEC can be used to separate low-MW compounds from relatively large amounts of polymers without serious loss of resolution of the additives the technique has also been used for the group analysis of chlorohydrin transformation products of the TETO model compound [32]. 

Additives with new functions (e.g. UVAs as FRs, or FRs as thermal stabilisers)... 

Flame retardant Thermal stabiliser Light stabihser... 

Thermal stabilisers for PVC are often heavy metal stearates (lead, barium), tin thiolates (R2Sn(SR2) = MZ2), and work by reacting the allylic... 

W.O. Drake, Hindered amine stabilisers as thermal stabilisers or HAS as HATS not just HALS, Proceedings of the 14th International Stability Controlled Degradation, Luzern, Switzerland, 1992, p. 57. 

H. Schaper, E.B.M. Doesburg, P.H.M. de Korte, L.L. van Reijen, Thermal Stabilisation of High Surface Area Alumina , Solid State Ionics, 16 261-66 (1985). 

Four different polyester plasticisers for PVC, having moderate acid numbers (11.5 to 20.5 mg KOH/g resin), were synthesised. These polyesters were modified by converting the terminal COOH group to Ba(II) and Cd(II) carboxylate salts in order to introduce the capability of heat stabilisation for PVC. The modified polyesters were applied as dual function polyesters, i.e. as plasticisers and stabilisers at the same time. The thermal stabilisation efficiency of the plasticised PVC films formed was tested photometrically and the data obtained were compared with that afforded by Irgastab BZ 556. The efficiencies of these modified polyesters as heat stabilisers for PVC were found to be comparable with those of Irgastab BZ 556. 38 refs. CIBA-GEIGY CO. 

AUen NS, Edge M (1992) Thermal Stabilisation of Polymers. In Allen NS, Edge M (eds) Fimdamentals of Polymer Degradation and Stabilisation. Elsevier Applied Science, London, p 22... 

One of the few areas where the properties of the top monolayer is crucial to economic success is catalysis. In such technology, reactions are performed at the outermost atomic layer, by direct interaction with the incoming molecules, and submonolayer amounts of impurities can severely affect the rates of reaction either positively or negatively. A schematic illustration of the catalytic event is presented in fig. 2, which shows a catalytically active component (a metal particle in this case) supported on a relatively inert material, such as alumina, which is used to thermally stabilise the metal with respect to loss of surface area ( sintering — which results in an increase in particle size and decrease in particle number density per unit area). The events which occur during the catalytic cycle are illustrated. 

Consequently inter-laboratory comparisons of uv stability of polymers and the effects of uv stabilisers is normally difficult if not impossible. There is evidence that in some cases the role of photostabilisers has been confused with that of thermal stabilisers since the two are mechanistically related (11). Just how important can be the prior thermal history of polyethylene on its uv stability is shown in Figure 1 which relates the processing time under standard conditions to the time to embrittlement in a standard sunlamp / blacklamp (S/B) environmental simulator. Figure 1 also shows the... 

By contrast, the copper salt [M = Cu(ll)] of the monomeric phosphorodithioate has been employed with 4-t-octyldiphenylamine as an antioxidant system and thermal stabiliser for lubricants and hydraulic fluids (ref.45). 

By impregnating y-Al203 with cerium/zirconium citrate solutions and subsequent calcination nanostructured CemZri.n,02 mixed oxides supported on AI2O3 are obtained, which feature remarkably high oxygen stor e even after a calcination at 1373 K for 24 h. Mutual thermal stabilisation between alumina and solid solutions has been observed, which prevents formation of a-alumina and sintering effects after a severe ageing. 

One typical composition for a blood bag is 59 wt.% PVC, 12% Vitamin E, 6% citrate plasticiser, 14% TEHTM and 9% epoxidised soya oil. Vitamin E suppresses haemolysis of red blood cells, while the soya oil is a thermal stabiliser for PVC processing which also has some plasticising effect. Thus, plasticised PVC can act as a reservoir for additives of a preservative nature. 

PVC is one of the lowest-cost commodity resins, used extensively today due to its excellent chemical and mechanical properties. However, the thermal decomposition temperature of PVC is close to its processing temperature, and hence use of proper heat stabilisers during its processing is essential. In addition, PVC-wood composites (plastic lumber) discolour with time during outdoor use, and this can be improved by use of proper thermal stabilisers [16]. 

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