Meaning
Thermal or chemical breakdown of colorant molecules during high-temperature polymer processing causes shifts in color and loss of aesthetic appeal. Preventing pigment degradation requires selecting colorants that can withstand both the melt temperature of the polymer and the shear forces generated within the extruder. This protective choice prevents plastic parts from changing color or fading during production and subsequent outdoor exposure.
Processing Heat
Extruding resins at temperatures above their recommended limits can break the chemical bonds of organic colorants. When pigment degradation occurs, it does not just alter the shade of the plastic, it can also release volatile compounds that cause voids or surface defects in the molded part. Moulders must monitor melt temperatures closely to ensure that the colorants remain stable throughout the entire molding cycle.
In processes like injection molding of engineering plastics, even a brief spike in heater band temperatures can destroy the pigment structure, turning a vibrant color into a dull grey.
Chemical Interactions
Antioxidants and other additives can sometimes react with colorants at high temperatures, accelerating the breakdown of both compounds. This form of pigment degradation is particularly common in formulations containing acidic residues or active primary stabilizers. Testing additive compatibility beforehand ensures that the colorant will not lose its stability or interfere with the thermal protection of the polymer.
Product Performance
Color fading and loss of mechanical strength in finished products are often accelerated by the breakdown of the coloring agents under ultraviolet light. When pigment degradation is triggered by sunlight, it can generate free radicals that attack the polymer matrix, leading to cracking and premature part failure. Adding ultraviolet absorbers protects both the color and the mechanical integrity of the plastic.
