Big bags are most commonly made of woven polypropylene, a polymer that, like other materials, is damaged by exposure to sunlight over time. This degradation process can ultimately cause the fabric to tear when exposed to strain and put both content and personnel at risk. Fortunately, through the use of UV stabilizers in the polymer and the proper handling of FIBCs, the risk of photochemical damage can be reduced to a minimum. It is, however, vital that FIBCs are covered or stored away from the sunlight during usage, transport and storage.
Standardized tests to demonstrate the UV resistance of FIBC have been in existence since 1989. The UV resistance test according to Annex A of ISO 21898: 2004 is currently the prevailing standard. However, standardized test conditions inevitably vary from the real life conditions that FIBC are exposed during use. Not only does the spectrum and intensity of UV radiation vary in different climate zones, but also other weather factors like temperature, humidity or frost play a role. Furthermore, substances in contact with the polymer, like pigments and even the goods filled into the FIBC, may also have an influence on the UV stability of the bag. The combination will influence the speed of photochemical degration. Ultraviolet light is harmful to plastics because it attacks the carbon bonds in the chemical structure, releasing free radicals that inturn react with oxygen in the air, destabilizing the plastics’ chemical structure and degrading it.
The aim of testing is to recreate enviornm,ental strains in a controlled laboratory environment and examine the durability of samples against a batter of tests. The governing international regulation is the UV resistance Annex to ISO 21898:2004. Once the exposure is complete, the samples are to be tested for their breaking force and the elongation of the fibre at the breaking point. The results are then compared to a control sample.
The UV resistance tests under ISO 21898:2004 give a common set of accelerated laboratory testing procedures that are repeatable and require the results of the tests to be expressed in terms that are comparable. Still, the International Standards Organization concedes that “a number of factors of uncertainty are inherent in the procedure, so comparisons should be available between the method used and exposures in the environment in which the product is to be used”.
The most obvious way to mitigate the degradation of an FIBC due to UV radiation and other weather impacts is physically to protect the bags from the elements. Although FIBC handling instructions routinely advise against outdoor exposture, this is not always practical for users and certainly not controllable by FIBC producers and traders.
To counter the harmful effects of UV light on FIBCs, two main methods are used: UV light absorber and light stabilisers. Both methods can retard the damaging effects of UV light but cannot stop it altogether. We cannot predict how well that test correlates to real life exposure to light, temperature and other environmental influences in different climates from the artic to the tropics where FIBCs are being used.
Capro Industries has been dedicated to promoting end-user safety and the correct handling and use of FIBC since the beginning. Access our safe handling guidelines atwww.capro.net/resources.
Also, if you are curious to find out if your FIBCs meet the current UV safety standards, contact our packaging experts today at 1-800-935-3422 and ask about our complimentary UV test. - a $1,200.00 value.
By Allison Bouchat