How Does UV absorber Work?
The main operate of UV absorbers is to absorb UV radiation within the presence of a chromophore (Ch) found within the polymer, the aim is to filter out the UV light that is dangerous to the polymer earlier than chromophore free radical Ch* has had a chance of forming. Above all, a UV absorber should operate within the 290 and 350 nm range. The effectiveness of UV absorbers is decided not only by their absorption traits but in addition, above all, by the Lambert-Beer Law.
Extinction relies on wavelength and may be considered a measure of the stabilizing or screening impact of the UV absorber. In other words, the higher the extinction, the higher the UV light screening and the greater the stabilizing effect – always assuming that the UV absorber is just not itself destroyed by the absorption of the light. Extinction thus is dependent upon the extinction coefficient, the concentration, "c", of the UV absorber in the polymer, and on the film thickness, "d", of the unpigmented polymers.
For a UV absorber to be efficient, it should take up UV light better and faster than the polymer it is supposed to stabilize and dissipate the absorbed energy before unwelcome side reactions are triggered. This implies 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 due to this fact phosphorescence should be excluded.
General Guidelines to Follow When Choosing Antioxidant and UV Stabilizers
1. Stability & Extraction
Uv Stabilizers and antioxidant hydrolysis resistance are ok，it are the color stability must pay attention. Additionally, there two additives shall not react with other ingredients within 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 collectively, and closing 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 have to concern. Antioxidant and UV stabilizers shall dissolve while not decompose in polymers processing temperature which most UV stabilizer might meet this requirement.
When possible, high molecule weight and comparatively high melting level antioxidants and UVA shall be selected, each dosage shall determine based mostly on most stringent processing and end-consumer environment.
When antioxidant and UV stabilizer melting range quite differ from resins’. Bias present or stick to screwing could occur. When this gap exceeds 100, UV stabilizer and antioxidant shall add in masterbatch form then mix with resin to process.
5. Dealing with and Safety
Antioxidant and UV stabilizer shall non or low toxic. No or low dust. Not harmful to human throughout plastic process and lifetime. Not dangerous to animal or plates. No pollution to air，earth and water.
For agriculture file, meals 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 most concentration is allowed.
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