Ultra Violet radiation is destructive to polymeric materials so the choice of an appropriate and efficient UV package is critical to ensure good performance and longevity of the polymer.
Wells Plastics have over twenty years experience in this complex area, producing highly concentrated and end application specific formulations. All polymer types are considered from olefins through styrenics to ETPs.
Careful selection of hindered amines and conjugated ring systems ensures the best possible performance and co-inclusions of antioxidants further enhance the stabilisation package.
Tapes, Fibres, Geotextiles, Films, Extrusions and Injection Mouldings.
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The first UV protection of polymers was offered through the use of UV absorbers. These are conjugated organic systems which “absorb” UV radiation due to the double bonds within the molecules absorbing light energy in the UV region and re-emitting it in the IR region. Such compounds include benzophenones and benzotriazoles.
UV absorbers are only really effective in thicker sections as the thicker the section then the greater the chance of the light energy falling on an absorber molecule rather than a polymer molecule. Also relatively large amounts of absorber have to be added to the polymer to ensure there is enough present to scavenge all of the light energy that falls onto the polymer substrate.
These systems have the advantage that they can be used to protect whatever is being covered or packaged by the treated polymer as well as the polymer itself.
The most effective and important stabilisers are the hindered amine light stabilisers, the so called HALS. Rather than simply absorbing the light energy these work by interrupting the photodegradation process before it can get destructively underway. The mechanisms used include “free radical scavenging”, “peroxide decomposition” as well as a little energy absorption.
There are a number of types of HALS available, with an important variation being molecular weight. Monomeric HALS are small molecules which migrate readily and rapidly to the polymer surface. Oligomeric HALS by contrast are large almost polymeric molecules and as such remain relatively well fixed within the polymer substrate and do not readily move to the surface. As a result of this difference in migration oligomeric HALS tend to be recommended for food contact applications. Selecting the formulation you need
Within both groups there is a wide range of compounds with varying chemistries rendering the molecules more (or less) effective when challenged with UV light of a specific wavelength. UV light is normally defined as being within the region of 280-400nm, while visible light is found within 400- 800nm. UV light is then subdivided further into UV-A (the lower wavelengths, peaking around 310nm) and UV-B (slightly higher wavelengths peaking at around 350nm).
Sunlight intensity and composition varies according to latitude, atmospheric effects etc. so it is important that the additive (or more normally the combination of additives) is selected to suit the exact application. It is therefore important to identify where in the world a final product will be used and the required life span. Other factors that affect the choice of UV stabilisation package include product dimensions, type and colour of pigments present and application information such as food or pesticide contact.
Wells has many years of experience in developing the correct formulation for precise requirements and we are able to offer a product from our large range of standard grades or produce a carefully formulated “special” to meet even the most demanding application.
Cherry wood veneer darkens significantly on exposure to UV light. A furniture supplier wanted to change from packaging cherry veneered tables in cardboard to using a translucent plastic instead. However with the films tried so far the cherry wood veneer darkened on storage but the corners, which were protected by cardboard, did not. This resulted in customer complaints of a “two-tone” table once they were unpacked.
Wells Plastics recommended the use of UV91690 in the packing film at trial addition levels of 4% and 6%. UV91690 contains a carefully selected mixture of UV absorbers to impart wideband protection.
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This information is correct to the best of our knowledge, but we would recommend that users make their own assessment to confirm that the material meets their requirements. We accept no liability for any damage, loss or injury resulting from the use of this information. Freedom from patent rights must not be assumed.
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