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Acrylated urethane oligomers are typically abrasion resistant, tough, and flexible, making ideal coatings for floors, paper, printing plates, and packaging materials. Acrylated polyethers and polyesters result in very hard solvent resistant films, however, polyethers are prone to UV degradation and therefore are rarely used in UV curable material.
In the past, UVA was considered not harmful or less harmful than UVB, but today it is known to contribute to skin cancer via indirect DNA damage (free radicals such as reactive oxygen species). [69] UVA can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA.
In chemistry, a photoinitiator is a molecule that creates reactive species (free radicals, cations or anions) when exposed to radiation (UV or visible). Synthetic photoinitiators are key components in photopolymers (for example, photo-curable coatings, adhesives and dental restoratives).
Photochemical immersion well reactor (50 mL) with a mercury-vapor lamp.. Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible (400–750 nm), or infrared radiation (750–2500 nm).
Organic photochemical reactions are explained in the context of the relevant excited states. [8] [9]Parallel to the structural studies described above, the role of spin multiplicity – singlet vs triplet – on reactivity was evaluated.
The reactive chlorine radical develops a transition state resembling the reactant with little radical character. When the alkyl radical is fully formed in the transition state, it can benefit fully from any resonance stabilization present thereby maximizing selectivity.
Depending upon substitution, the UV absorption spectrum is changed to match the application. Concentrations normally range from 0.05% to 2%, with some applications up to 5%. Frequently, glass can be a better alternative to polymers when it comes to UV degradation. Most of the commonly used glass types are highly resistant to UV radiation ...
The glass remains transparent at this stage, but its ability to absorb UV light increases. This increased absorption is only detectable using UV transmission spectroscopy and is caused by an oxidation reduction reaction that occurs inside the glass during exposure. This reaction causes cerium ions to oxidize to a more stable state, and silver ...