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How Does UV absorber Work?
The primary function of UV absorbers is to soak up UV radiation in the presence of a chromophore (Ch) found in the polymer, the purpose is to filter out the UV light that is dangerous to the polymer before chromophore free radical Ch* has had an opportunity of forming. Above all, a UV absorber must function within the 290 and 350 nm range. The effectiveness of UV absorbers is decided not only by their absorption characteristics but additionally, above all, by the Lambert-Beer Law.
Extinction depends on wavelength and might be considered a measure of the stabilizing or screening impact of the UV absorber. In different words, the higher the extinction, the higher the UV light screening and the larger the stabilizing effect – always assuming that the UV absorber shouldn't be itself destroyed by the absorption of the light. Extinction thus is determined by the extinction coefficient, the concentration, "c", of the UV absorber within the polymer, and on the film thickness, "d", of the unpigmented polymers.
For a UV absorber to be effective, it must take up UV light higher and faster than the polymer it is supposed to stabilize and dissipate the absorbed energy before unwelcome side reactions are triggered. This means that transformation of the energy absorbed within the form of UV light should take place within the singlet state. Inter-system crossing (transition S1 to T1) and therefore phosphorescence have to be excluded.
Common Rules to Follow When Selecting Antioxidant and UV Stabilizers
1. Stability & Extraction
Uv Stabilizers and antioxidant hydrolysis resistance are ok，it are the colour stability must pay attention. Additionally, there additives shall not react with other ingredients in the system, neither corrosion equipment nor extract by the substance on the article surface.
Hindered amine light stabilizer usually shows low alkalinity, no acidic additives shall be used together, and remaining article shall not apply in an acidic environment.
2. Solubility & Compatibility
Most polymers are non-polar while antioxidant, UV stabilizer are somewhat polar. Solubility is a matter must concern. Antioxidant and UV stabilizers shall dissolve while not decompose in polymers processing temperature which most UV stabilizer might meet this requirement.
3. Migration
When potential, high molecule weight and relatively high melting point antioxidants and UVA shall be chosen, every dosage shall decide based on most stringent processing and end-user environment.
4. Processing
When antioxidant and UV stabilizer melting range quite differ from resins’. Bias current or stick to screwing may occur. When this hole exceeds one hundred, UV stabilizer and antioxidant shall add in masterbatch form then combine with resin to process.
5. Dealing with and Safety
Antioxidant and UV stabilizer shall non or low toxic. No or low dust. Not dangerous to human throughout plastic process and lifetime. Not dangerous to animal or plates. No air pollution to air，earth and water.
For agriculture file, food packing, toys, disposable infusion set or direct meals, drug, medical device, medical units, human contact plastics. Only FDA or EU approval antioxidant and UV stabilizer observe maximum focus is allowed.
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