While FIBCs are incredible products, they do have some downfalls that science and technology are trying to address to make these bags the safest and most useful product in existence. One of the biggest issues with FIBCs is what they are constructed of. FIBCs are generally made from polypropylene tapes that are weaved into panels and the panels are then sewn together with thread to create the FIBCs everyone recognizes. One major issue the FIBC industry is working to improve is the break down of polypropylene tapes, causing the product to weaken and leading to safety concerns.
Polypropylene has a natural tendency to break down if exposed to sunlight for long periods of time. The industry currently adds certain chemicals to help increase the amount of time it takes for the polypropylene tapes to break down when exposed to sunlight. While this industry standard is widely practiced, Global-Pak is always looking for ways to advance the industry and make the FIBCs we produce and sell the best on the market. One advancement we researched is how different color FIBCs can affect the longevity of the polypropylene tapes in the product. After thorough investigation, we determined black bags (and sometimes grey) generally last longer in the sunlight. Generally, darker colors absorb more heat which presumably would cause the plastic tapes to weaken. In fact, the black color does absorb more heat, but we have found this to be less detrimental versus having a cooler white FIBC left out in the sun. This phenomenon can be traced back to the production of the tapes used in FIBC manufacturing.
When the plastic is melted and extruded, it is generally a transparent color. To get the different color tapes according to the customers requirements, additions must be made during the master batch melting process to change the extruded plastic tapes from transparent to the desired color. For example, when a black bag is requested, the addition of carbon black to the preproduction mix would result in black polypropylene. The concentrations of any additions to the polypropylene can change the physical properties drastically, so industry standards are set based on prior experience and testing.
So, what is so interesting about black bags and why do they seem to last longer in direct sunlight? This can mostly be traced back to carbon black additive during the melting and extrusion process. We educated ourselves on why plastics without any additions are destroyed by UV light and why the carbon black causes longevity in the product to answer this question.
When UV light encounters plastic, the energy given off by the light (known as photons) excites the electrons in the plastic. Pure plastics can’t absorb the UV radiation, but due to living in an imperfect world there are almost always impurities and catalytic residues that act as receptors for the photons within the plastic. When enough of the photons are absorbed by the plastic via its impurities, the molecules in the plastic start to produce free radicals. Free radicals are defined as “an atom, molecule, or ion that has unpaired valence electrons,” and when enough of them are produced a chain reaction within the material can cause degradation of the material. In the presence of oxygen, which is readily available, the free radicals form hydrogen peroxides that can break the double bonds of the polymers causing degradation. The process that forms the hydrogen peroxides is known as photo-oxidation.
The carbon black added during the manufacturing process helps preserve the bag because the dark color absorbs energy from the light and converts it to thermal energy. (Thermal energy is why black items tend to be hotter than other items when left in sunlight.) When the energy is converted to thermal energy, it transforms the energy from the photons to heat energy. The conversion of energy caused by the black color is why they last longer in outdoor environments compared to other colors of FIBCs.
While researching this topic, it was found that carbon black can provide additional benefits outside of increasing bag longevity. According to one study presented at a Conference on Manufacturing and Electronic Technology the addition of carbon black can increase the tensile strength of the polypropylene as well. During the study it was noted that the addition of certain percentages of carbon black improved the tensile strength by up to 23%. Additional scientific studies and testing are required to find the ideal addition percentage of carbon black, but there are benefits to using black FIBCs.
Carbon black is a relatively cheap material that can be added to many products for color. The addition of carbon black can also change the physical properties of the bag’s material, creating unintended positive effects on the strength and longevity. If you are looking to use a FIBC in an outdoor environment with exposure to elements, a black bag may be the best option.