Polycarbonate sheet that has no UV absorbers will only block wavelengths below 290 nm. Unfortunately wavelengths below 385 nm will cause the Polycarbonate to weather and become brittle and yellow. Manufacturers therefore add UV absorbers to the Polycarbonate resin to give it some protection against the UV light. Some outdoor grades of Polycarbonate also have an additional cap layer or coating heavily loaded with additional UV absorbers to further protect the sheet against the affect of UV light.
There are some grades of Polycarbonate, that are often known as FDA or NSF Standard 51 compliant grades that have no UV absorbers. The reason that no UV absorbers are added is that these grades are designed to be used in the Food Processing environment and the UV absorbers are not approved by the FDA to be used in Food Processing areas. The manufacturers therefore produce grades without the UV absorbers. Because these FDA grades of Polycarbonate sheet have no UV absorbers, they should not be used outside as they will yellow very quickly.
One question that we are often asked is are the FDA approved grades safe to be used in food contact applications? The FDA grades of Polycarbonate sheet do not have UV absorbers in them because they are not approved for materials used in Food Processing environments. However, the Polycarbonate itself does still have Bisphenol A or BPA in it and there is currently a great deal of debate about whether BPA is safe in food contact applications such as baby feeding bottles. As a result of this debate, at HighLine Polycarbonate we do not sell any Polycarbonate sheet that will be used in applications where it comes into regular, direct contact with food. However, FDA grades of Polycarbonate sheet can be used as machine guards to protect operators on food packaging lines when the machine guards do not come into contact with food that will be eaten.
One un-intended market for FDA approved grades of Polycarbonate sheet is to customers who bond Polycarbonate sheet to other materials using a UV cured adhesive. The adhesive requires light from a UV lamp to pass through the sheet in order to bond it to another material. The UV absorbers in Standard Polycarbonate sheet block the UV light from the lamp preventing the adhesive from curing. By using an FDA grade of Polycarbonate sheet, the adhesive is able to be cured effectively. After bonding, the sheet can be protected against UV light by adding a coating with UV absorbers.