Customers decide to color their polyethylene chemical storage tanks for a number of reasons. Tanks may be colored for aesthetics, branding, chemical identification and to reduce transmission of radiant heat through the plastic.
There are three ways to change the color of polyethylene tanks: inserting color pigments directly into the mold with raw resin, using a compounded resin that is produced in a controlled environment by a resin manufacturer, or by painting the exterior of the chemical storage tank.
Let’s take a closer look at the advantages and disadvantages of each option for coloring polyethylene chemical tanks.
Adding a Pigment to Resin: Potential for Issues
Coloring a polyethylene tank by adding a pigment into a virgin poly resin can cause unintended negative results. Pigments are contaminants at some level and often require heavy metals to discolor resin past its natural color. Pigment also affects other compounds in resin, such as UV inhibitors or antioxidants. Therefore, any time you add a pigment post-production to a resin you effectively compromise the overall performance of the end product.
Also, different colors affect the processing of polyethylene tanks. For example, certain colors will absorb more heat or reflect more heat in the manufacturing process. Without a way to properly measure the internal temperature of the cooking cycle, you could potentially vary the manufacturing temperature significantly. Overcooking or undercooking now becomes a distinct possibility. This can alter the tank’s performance by affecting the brittleness of the plastic as well as how the plastic responds to environmental factors.
Compounded Resins: A Better Solution
Another option for coloring polyethylene plastic tanks is by using a compounded resin. Compounded resins arrive colored directly from the supplier with the pigment introduced in an earlier phase so it doesn’t compromise the structure of the polyethylene. Poly Processing only uses compounded resins to color polyethylene tanks as they preserve the reaction and don't affect the catalyst, or peroxide, that allows for cross-linking in XLPE tanks.
Painting a Tank vs. Compounded Resin
Another option for changing the color of a polyethylene tank is by painting the exterior. Painted tanks have an advantage in that the exterior paint 100% blocks the UV. A latex paint is recommended and will prevent UV from degrading the polymer over time. This may be a good option for outside tanks storing chemicals that are highly sensitive to UV and heat, like sodium hypochlorite.
Check out our tank painting guide to learn how to paint your polyethylene tank.
What Color Should I Choose?
Polyethylene has the positive trait of being a poor conductor of heat. Therefore, with large polyethylene tanks, such as tanks over 6,000 gallons, it will take a lot of energy to raise the temperature of the chemical just from exposure to UV. Since heat is not a big issue in this case, a black tank might make most sense to block UV rays. With small tanks or in warmer environments where ambient temperature is high, a few degrees difference may create off-gassing issues with temperature sensitive chemicals. In that case, a white or lighter colored compounded resin polyethylene tank would make most sense to deflect heat. With a high ambient temperature and UV exposure, painting a tank, or insulating and painting the insulation would likely be the best solution. The insulation will provide temperature stability while the mastic paint coating will block all UV exposure to the polyethylene tank.
A Study on the Effects of Adding Pigment
Poly Processing commissioned a thorough study with the Pennsylvania College of Technology on the impact of blending pigment with polyethylene. To view technical details and results from this comprehensive study, click the button below.