Weathering and deterioration are some of the most common chemical reactions which affect polycarbonate sheets. When these products are used in outdoor applications, after sometime they begin to turn yellow. This makes ultraviolet stabilization an important procedure during the manufacturing process to obtain a non-yellowing polycarbonate products.
During this chemical reaction; some of the most common properties which are greatly affected include:
- A decrease in light transmission which is as a result of the yellow color and haziness of the polycarbonate sheet since UV alters the polymer chain structure.
- Bleaching may occur more so for those sheets which have been tinted with either colored or clear grade tints.
- The surface properties also deteriorate since the polycarbonate sheet may begin to have micro-cracks which affect the light transmission properties.
- Mechanical properties such as stiffness and impact strength also reduces significantly which is as result if decomposition.
To save the end users from these devastating situations, there are a number of manufacturing approaches which have been adopted in an attempt to get non-yellowing polycarbonate sheets. Some of the most common ultraviolet protection approaches include:
- The use of ultraviolet absorber which is embedded on the surface.
- A hard coating which has been concentrated with the ultraviolet absorbers
- A coextruded layer which has been concentrated with the ultraviolet radiation absorbers.
In certain scenarios, the manufacturing company may opt for a combination of either of the two or more strategies depending on the nature of the non-yellowing polycarbonate sheet they would wish to produce.
Polycarbonates sheets are resistant to the fluctuating environmental temperature however; for an extended exposure to high temperatures, polycarbonate sheets tend to degrade at a faster rate. It is important to note that when polycarbonates are exposed to high temperature for a long period of time; they do not lose their mechanical properties such as the high impact strength.
The non-yellowing polycarbonate sheets have an anti-UV layer which is basically designed to prolong the lifespan of the polycarbonate sheets. This layer bars the ultraviolet radiation from reaching the polycarbonate sheets surface. In an attempt to achieve an excellent transparency surface, the twin-wall polycarbonate sheets are apparently being used for a number of applications. A number of greenhouses are constructed using the twin-wall polycarbonate sheets.
The sun is not the only source of UV radiations; there are other artificial sources of light with emit UV radiations. The term “non-yellowing polycarbonate sheets” does not imply that the polycarbonate sheet will remain clear without any defects for the entire lifespan. Depending on the nature of precaution which has been taken; this coating may remain effective for more than ten years.
Once the polymer’s chain structure has been distorted by the UV radiation; the only viable option is always to replace the polycarbonate sheet. However, this will be after a long period of time. The non-yellowing polycarbonate sheet are more economical than other materials such as glass which are used in the construction industry. The polycarbonate manufacturers will indicate the time frame within which these sheets can be able to maintain all their desirable chemical and mechanical properties.