Groundwork for Non Intentionally Added Photoinitiator Identification in Polyolefin Streams
Groundwork for identifying non-intentionally added photoinitiators in polyolefins requires high-resolution mass spectrometry and toxicological screening.
Norrish Type I Cleavage
Meaning
Photochemical reaction mechanism where a carbonyl group breaks into two radical fragments upon absorbing ultraviolet radiation during ink curing. It measures the efficiency of radical generation and stops applying once the source of radiation is removed.
Fragment Generation
Splitting of the chemical bond occurs at the alpha position relative to the carbon atom of the carbonyl group. Norrish type I cleavage is a common pathway for the initiation of uv curing in industrial inks used on plastics. The resulting radicals are highly reactive and quickly start the solidification of the coating.
This reaction is independent of temperature but highly dependent on light intensity.
Material Stability
Exposure to sunlight can trigger this same reaction in the polymer backbone of the finished part. If the plastic contains many carbonyl groups, it will become brittle and crack over time. Moulders add light stabilizers to absorb the uv energy and prevent this degradation.
The rate of cleavage determines the useful outdoor life of the product.
Product Safety
Breakdown products from this reaction can be volatile and contribute to the odour of the recycled plastic. Monitoring the concentration of these small molecules is a priority for companies making food grade containers. Understanding the reaction allows for better ink formulations that produce fewer byproducts.