Polymers light stabilisation

Additives used include plasticisers such as diphenyl diethyl ether, ultraviolet light absorbers such as 5-chloro-2-hydroxybenzophenone (1-2% on the polymer) and stabilisers such as phenoxy propylene oxide. 

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... 

Oligomeric hindered amine light stabilisers, such as Tinuvin 622 and Chimassorb 944, resist satisfactory analysis by conventional HPLC and have required direct UV spectroscopic analysis of a polyolefin extract [596], PyGC of an extract [618,648], or SEC of an extract [649]. Freitag et al. [616] determined Tinuvin 622 in LDPE, HDPE and PP by saponification of the polymer dissolution in hot toluene via addition of an... 

David et al. [184] have shown that cool on-column injection and the use of deactivated thermally stable columns in CGC-FID and CGC-F1D-MS for quantitative determination of additives (antistatics, antifogging agents, UV and light stabilisers, antioxidants, etc.) in mixtures prevents thermal degradation of high-MW compounds. Perkins et al. [101] have reported development of an analysis method for 100 ppm polymer additives in a 500 p,L SEC fraction in DCM by means of at-column GC (total elution time 27 min repeatability 3-7 %). Requirements for the method were (i) on-line (ii) use of whole fraction (LVI) and (iii) determination of high-MW compounds (1200 Da) at low concentrations. Difficult matrix introduction (DMI) and selective extraction can be used for GC analysis of silicone oil contamination in paints and other complex analytical problems. 

An excellent and comprehensive review has covered HPLC analysis of AOs and light stabilisers up to 1990 [576]. Normal vs. reversed-phase and isocratic vs. gradient-elution HPLC separation of synthetic mixtures of additives and of solvent extracts from polymers were discussed. 

The anti-oxidant itself is often consumed in performing its function, although hindered amine light stabilisers (HALS) are self-regenerating. Depending on the polymer, their concentration in the polymer may vary from a few parts per million (e.g., in PE) to several per cent (e.g., in ABS, natural rubber). Because it is impossible to determine all the polymer down-stream end uses, nearly all have food contact approval. 

These compounds are excellent PVC thermostabilisers. They have less smell, leach less out of the polymer and have higher light-stabilising properties than alkyltinmercaptides. 

Here we report the use of a readily prepared polymer immobilised TEMPO as a catalyst for alcohol oxidations.15 It was derived from a commercially available oligomeric, sterically hindered amine, poly[[6-[(l,l,3,3-tetramethylbutyl)amino]-l,3,5-triazine-2,4-diyl] [2,2,6,6-teramethyl-4-piperidinyl)-imino]-1,6-hexane-diyl[(2,2,6,6-tetramethyl-4-piperidinylimino]], better known as Chimassorb 944 (MW 3000 see figure 3 for structure). This compound is used as an antioxidant and a light stabiliser for plastics. It contributes significantly to the long-term heat stability of polyolefins and has broad approval for use in polyolefin food packaging.16... 

Light stabilisers also prevent photodegradation. UV absorbers such as hydroxybenzophenone or hydroxyphenyl triazole types, operate by absorbing and dissipating UV radiation prior to potential degradation of the polymer. No permanent chemical change occurs, so activity is retained. Hindered amine light stabilisers (HALS) are also used but their activity is not particularly well understood (80). 

The mechanistic behaviour of absorbers based on 2-hydroxybenzo-phenone, 2-hydroxyphenylbenzotriazole and salicylates continues to attract much interest. Salicyloyl(3 5-di-tert-butyl-4-hydroxy-benzyDamine is claimed to be the most effective light stabiliser to date for polyethylenewhile effective polymer bound stabilisers based on 2-(2-hydroxyphenyl)-2H-benzotriazole have been made... 

---