Synergists with HALS

A number of beneficial effects can be obtained by using other light stabilizers in conjunction with a HALS system. Specific cyanoacrylate-based UV absorbers offer particular benefits, for example in ABS and PA, and as individual components in rigid or plasticized PVC, polyurethane foams, and SB rubber. Broadband absorbers based on benzophenone can be used, for example, in sunshading sheet. 

Ferro s UV-Chek AM 340 is a hydroxybenzoate ester light stabilizer that is used in conjunction with a HALS. It functions initially as a radical-free 

New patented polyfunctional additives from Ciba are claimed to act as both primary and secondary anti-oxidants. Based on hydroxylamines, functioning as free radical scavengers, peroxide decomposers, and reducing agents, they have low colour and act synergistically with HALS UV stabilizers. Coded FS, they are designed to replace blends of phenolic, a phosphite, or thioester and a HALS, and are aimed initially at PP fibres, but early trials show similar benefits in PP films and thick-section parts. 

BASF has developed HALSs and UV absorbers in the Univul range three HALS grades are especially suitable for ABS, PA. PP, HDPE, and PMMA and include a grade with outstanding light fastness at high temperature (for automobile applications, for example). 

Schulmann has introduced a new HALS UV stabilizer with good resistance to pesticides. For greenhouse and agricultural films, a HALS offering excellent clarity and outstanding UV resistance and an alternative nickel quencher have been introduced by Colortech for applications where conventional stabilizers may be exposed to chemical deactivation (as when exposed to halogenated or sulphur-based pesticides or fumigants). 

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Features Low volatility high permanence strong UV-B absorber synergistic with HALS... 

Costabilizers enhancing light stability can be used synergistically with HALS products to provide processing and long-term stability ... 

As a partially hindered amine, 3 showed light-stabilizing activity lower than that of piperazine or piperidine HALS, but comparable to commercial benzophenones. Like HALS, they are strongly synergistic with benzophenones and benzotriazoles in polyolefins. 

Coatings exposed to sunlight for extended periods are also subjected to degradation. Combinations of HALS and ultraviolet light absorbers (UVAs) are used to obtain a synergistic effect. A 1 1 combination of a UVA of the benzotriazole class with HALS has been used [13], Figures 4.7 and 4.8 show the benzotriazole and HALS combination. 

Features Nondiscoloring, nonstaining synergistic with benzophenone, benzotriazole, HALS... 

Low-molecular-weight HALS, a hydroperoxide inhibitor, has been shown to considerably reduce photooxidation of PBT [107]. It can be expected that the combination of a UV absorber with HALS will be particularly effective. There is little data on stabihzation of thermoplastic polyester elastomers, but the stabilizers used to protect polymers that degrade by free-radical chain oxidations should also be efficient for these types. Thus, UV absorbers of the benzotriazole and benzophenone types may be used for their screening capabihties, and synergistic effects can be expected with the addition of HALS to reduce the rate of chain oxidations. 

For example, a high MW hindered amine (eg, CYASORB UV-3346 Light Stabilizer) combined with CYASORB UV-2908 provides synergistic performance in PP slit tape applications during Xenon ARC WOM exposure (Fig. 11) (64). The use of this combination also allows improved processability in production of the slit tapes because of reduction in water carryover compared with HALS alone. It has also been demonstrated that, in thick section PP, long-term stability can be dramatically improved with CYASORB UV-3346 combined with CYASORB UV-2908. 

Thioethers such as DSTDP have been used in combination with primary antioxidants to provide extended lifetimes to polyolefins exposed to elevated temperatures. Unfortunately, the mechanism by which these thio-synergists function has been shown to produce sulfenic and sulfonic acids which are capable of further reacting with HALS. Figure 5 shows the effect of DSTDP on HALS performance. While both HALS-1 and HALS-3 show a strong negative interaction with DSTDP, HALS-5 is relatively imaffected. 

The Good-rite 3125 was also combined with the Chimassorb 944LD and Cyanox STDP to evaluate possible synergistic effects between combinations of a hindered phenol stabilizer with first a thioester and then a hindered amine light stabilizer (HALS). 

Two groups of anti-oxidants are of practical importance hindered phenol light stabilisers (HPLS) and hindered amine light stabilisers (HALS). Examples are shown in Fig. 13.7 and the mechanism of the radical trapping reaction is shown in Fig. 13.8. They are often combined with UV absorbents (for partly synergistic effects) and mostly used for the fibre protection. 

HALS exhibit a complex behavior when present in combination with other antioxidants and stabilizers. Effective synergism in both melt and thermal stabilization has been achieved when secondary and tertiary HALS were used in combination with both aromatic and aliphatic phosphites the synergistic optimum depends on the structure of the phosphite. HALS also synergize the action of UV-absorbers, e.g., benzo-triazoles, in different polymers such as polypropylene, polystyrene, and ABS. " ... 

Outstanding properties very low color contribution, broad UV absorbance, synergistic performance with hindered amine light stabilizers (HALS) in styrenic polymers ... 

Another way to reduce the alkalinity of a HALS is to form a polymeric molecule through the active amine groups as Lowilite 62, shown in Fig. 4.18. With flame-retarded polypropylene, a combination of stabilizers is often found to be synergistic. Later, common commercial systems and some next-generation systems are discussed. 

In comparison with PP sulphur-containing synergists are used only occasionally for the stabilization of HDPE. Preference is given to dilauryl thiodipropionate over distearyl thiodipropionate because the latter is less compatible with HDPE [2]. Long-term heat stability of HDPE can be improved considerably by the addition of high molecular weight HALS [6 8]. 

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