Pretty much from the moment the Almighty said “Let there be light!” human beings have considered a sunny day to be a good thing. When you’re dealing with polymers, however, sunlight — specifically the ultra-violet portion of it — can be a bad thing.
Ultra-violet radiation accounts for a tiny portion of sunlight, but it can cause a variety of polymers, both natural and created, to degrade. Exposure to too much sunlight can cause products made from these polymers to break, crack, disintegrate, shatter or otherwise stop working — unless you add light stabilizers to the polymer during manufacturing.
Light stabilizers help your tires stay black, keep road cones from cracking in the hot sun, and ensure plastic safety goggles stay clear instead of turning yellow over time. Without these important polymer additives, many everyday products simply couldn’t do their job. They would change color, lose flexibility, become more prone to shattering and even undergo chemical transformations.
Three basic types of light stabilizers work in a range of polymers to help prevent UV damage: UV absorbers, quenchers and hindered amine light stabilizers (HALS).
As their name suggests, absorbers soak up the UV radiation that would otherwise get absorbed by other components in the polymer, transforming it into heat that can be harmlessly dissipated. Remember our friend carbon black from an earlier blog? It’s a very effective and widely used light absorber … because it’s black! Absorbers are generally a low-cost additive, but may not be effective for long-term protection in all products.
UV degradation occurs when certain components in a polymer, known as chromophores, absorb UV radiation. Quenching light stabilizers transfer the energy generated by this absorption, and allow those over-excited molecules to go back to whatever it is they’re supposed to be doing in a given polymer. Quenchers, however, are generally considered less effective than other types of light stabilizers.
For the long haul, HALS are often a better choice. When a polymer begins to degrade in the light, free radicals are formed. HALS trap those free radicals so they can’t do any damage. HALS have been hugely helpful in some industries, such as the auto industry (thank HALS for fade-resistant dashboards).
Since all three types of light stabilizers work differently, they’re often added in combination to help protect a polymer in multiple ways.
Look into the light stabilizer
Of course in the world of polymers, things don’t always go as planned. That’s when additives analysis — which can test for the presence, absence, function and performance of components like light stabilizers — comes in handy. Through testing such as thermogravimetric analysis, we can confirm that a product is conforming to a formula, reverse engineer a product, compare a product to a competitor, guide product development and even unearth why a product failed. In the case of light stabilizers, we might be called on to explain why a plastic faded or changed color or why a product made from PVC shattered.
By shedding light on how effective UV stabilizers are in a client’s product, we can tell them if they need to adjust their formulation, or if they’re OK to say “Let there be light! We can take it!”