Ultra-Violet Radiation Testing
Composite materials can rapidly change when exposed to UV light. A photochemical degradation can occur in these materials, unless they have been stabilized.
● Ultra violet degradation may be indicated by the softening of the material, so that the outer surface may be rubbed off or plucked off, and in extreme cases, the outer surface may become powdered.
● Certain types of UV stabilising additives are rapidly leached out, especially in an alkaline environment, which should be taken into consideration in applicable situation.
● The performance of UV stabilised additives may be affected by colour and the type of pigment used. Therefore, each combination of UV stabilising additive and pigment should be tested separately.
The test apparatus shall be in accordance with ASTM G53/96 using a fluorescent UV-B lamb.
The specimens are alternately exposed to UV light alone and to condensation alone in a repetitive cycle for at least 200 h using a test cycle of 8 h at 60 C with UV radiation alternating with 4 h at 50 C with condensation.
After exposure is complete, the specimens are checked for breaking force and elongation at break in accordance with ISO 5081
and the values are compared with results performed on simultaneously cut test specimens that have been stored under dark and cool conditions.
All load bearing materials of the FIBC shall, after tested retain at least 50% of the original values of the breaking force and elongation of the materials.
The most obvious way to mitigate the degradation of FIBC due to UV radiation and other weather impacts is to physically protect the big bags from the elements.
Chemical alternatives are available and widely used to help polymers like polypropylene maintain their properties longer against degradation through environmental influences. To counter the harmful effects of UV light on FIBC, two main methods are used: UV light absorbers, e.g. Triazine or Benzotriazole, and light stabilisers, i.e. HALS (Hindered Amine Light Stabilisers).
These additives, which absorb or stabilise UV light respectively, are often introduced to the base formula for the polypropylene material out of which the FIBC are woven.