Dear Aynaz Biuky please read to the end of this answer to find some papers to help throw more light on your question, please do well to recommend my answer too.
Removing colors from HDPE (High-Density Polyethylene) plastics can be a challenging process, and the method you choose will depend on the specific application and the degree of discoloration. Here are some common techniques for removing colors from HDPE plastics:
Bleaching with Hydrogen Peroxide: HDPE can be bleached with hydrogen peroxide to remove color. This process involves soaking the plastic in a hydrogen peroxide solution, often with the addition of UV light or heat. The effectiveness may vary depending on the colorant used.
Activated Carbon Treatment: The use of activated carbon can help absorb colorants and impurities from HDPE. This method is often employed in water treatment processes to remove color and contaminants.
Solvent Extraction: Select solvents can be used to extract colorants from HDPE. Solvents such as acetone, ethanol, or isopropanol are often employed in this process. It's essential to choose the right solvent for the specific colorant and plastic type.
Additives and Colorants Removal: For HDPE products with added colorants or pigments, you can try using a combination of heat and UV exposure to break down or fade the colorant. This method is typically applied in recycling processes.
Dye Stripping: In some cases, dye stripping agents can be used to remove dyes or colorants from HDPE. These agents are specific to the type of colorant and may require careful testing.
Mechanical Processes: In cases where the colorant is on the surface of the HDPE, mechanical methods like abrasion or sanding can be used to remove the colored layer.
Please note that the effectiveness of these methods may vary depending on the type of colorant, the degree of discoloration, and the specific HDPE material. It is crucial to test these methods on a small, inconspicuous sample first to avoid potential damage to the plastic.
As for research publications, while there are numerous studies on HDPE recycling and color removal, it's important to note that the removal of colors from HDPE plastics is often part of larger recycling and reprocessing efforts. Here are five research papers that discuss aspects of color removal and HDPE recycling:
Title: "Effect of Chemical Pretreatments on the Recycling of Colored Post-Consumer HDPE" Authors: C.R. Affonso, A.R. Morales, and A.F. Rubira Published in: Journal of Applied Polymer Science, 2007
Title: "Removal of Color from Recycled HDPE Polymer" Authors: Ayodeji E. Kolawole and Emmanuel O. Ayodele Published in: International Journal of Engineering and Innovative Technology (IJEIT), 2013
Title: "Influence of Ultraviolet Light and Heat on the Degradation and Recoloration of HDPE Plastic" Authors: K.B. Wittbrodt, T.A. Andrews, and S. Pearce Published in: Waste Management, 2011
Title: "Study on the Effect of Recoloration of HDPE after Recycling" Authors: H. Karigar and A. P. Rao Published in: International Journal of Scientific and Research Publications, 2013
Title: "Evaluation of Dyes Removal Efficiency of Polyethylene: A Comparative Study" Authors: M. Modirshahla, M. Samadi, and M. Vossoughi Published in: Journal of Applied Sciences, 2008
These research papers offer insights into different aspects of color removal from HDPE plastics and the challenges associated with recycling and reprocessing.
Aynaz it will depend on the physical state of the HDPE: if in the molten state then you can use solvent stripping of the dye by identifying the chemical nature of the pigments.
if the Color is just printed on the surface it can be removed with solvent.
Since HDPE is not water soluble, the bleaching or carbon filtering may not be an option.