Why did my epoxy hardener turn yellow in the container?

Yellow Epoxy Resin Hardener

Color Change in Epoxy Curing Agent and Prevention Techniques

An epoxy curing agent or "hardener" can change in color over time due to several factors, including the shelf life, chemical reactions, exposure to light, temperature, and moisture, and the presence of impurities. These different factors can cause the epoxy hardener to become yellow, orange, and even brown over time. Here is a detailed explanation of the primary reasons for the color change:

  • Shelf Life: The shelf life of an epoxy hardener plays a crucial role in maintaining its effectiveness and preventing color changes. Our recommended shelf life for the epoxy hardener is 12 months unopened from the date of purchase. Once opened, we recommend using it within 6 months for best results.
  • Chemical Reactions: The curing agent, or epoxy hardener, can undergo oxidation or other side reactions, leading to a change in color.
  • Exposure to Light: Ultraviolet (UV) light from the sun or other sources can cause the epoxy and the curing agent to degrade, a process known as photodegradation. This degradation can lead to the formation of chromophoric (color-producing) structures within the epoxy matrix. Prolonged exposure to UV light can result in the yellowing or browning of the epoxy, depending on the specific formulation and the curing agent used.
  • Temperature: High temperatures can accelerate chemical reactions within the epoxy, including those responsible for color changes. In most cases this is more of an issue during curing, but it is important to properly store the epoxy resin and hardener.
  • Moisture: Exposure to moisture can cause the epoxy and the curing agent to react with water molecules, forming hydrolyzed products. This hydrolysis can lead to the formation of chromophoric groups, which may result in discoloration of the epoxy. Furthermore, moisture can promote the growth of mold or mildew, which can cause staining or color changes on the epoxy surface.
  • Impurities: The presence of impurities, either in the epoxy resin, curing agent, or the substrate, can cause a change in color. For example, contaminants like metal ions or organic substances can react with the curing agent and create colored compounds. Additionally, the presence of air bubbles or dust particles can affect the final appearance and color of the epoxy.

Is there anything that can be done to mask the yellow color of the hardener?

In most cases, the yellow hue of the hardener is not going to be noticeable unless applied over light colors or poured in thick layers. Once the epoxy resin and hardener are mixed together the mixture will appear more clear, and then when applied as a coating it typically is completely clear.

If you do notice that the color of the applied epoxy resin still has a yellow hue you can add a small amount of Deep Sea Blue Liquid Resin Dye to mask the color of the yellow hardener.

Otherwise, it's probably best to replace the product if you have any concerns of your projects final clarity.

Factors Affecting Epoxy Curing Agent Discoloration and Prevention Measures.

In summary, the color change in an epoxy curing agent over time can be attributed to several factors, including chemical reactions, exposure to light and temperature, moisture, and the presence of impurities. To minimize discoloration, it is essential to follow proper storage and handling procedures.