Why does color vary in natural polyurethanes?
Natural polyurethanes vary from a light tan (almost yellow) to a medium-dark amber (almost greenish). This variation is noticed from supplier to supplier, and even within a given supplier’s production. Black or other colored (pigmented) polyurethanes do not typically exhibit this variability in color. It is important to note that these color variations have no impact on the chemical or physical properties of the polyurethane.
This variation in appearance is most often due to inherent variations in the prepolymer or amine curative components, durometer of the finished polyurethane, or the conditions during the storage, handling and processing of the components into polyurethanes. The appearance will further change with exposure to ambient UV radiation and with age.
Variations in appearance may be attributed to one or more of the following variables:
- Color contributions from the base urethane raw materials- prepolymer, curative and other additives
- Shape of the polyurethane part: thickness and geometry
- Durometer of the urethane
- Processing conditions of the components into polyurethane
- Exposure to UV light as the part ages
Given that appearance is a function of so many variables, it becomes impractical to establish a specific color specification.
If inherent variation in polyurethane’s natural color may be a concern, Harkness recommends utilizing black polyurethane, which is provided at no additional cost.
If you have any further questions regarding color or any other technical matter related to cast polyurethanes, please do not hesitate to contact us here at Harkness Industries.