Yellowing of by-product polyethylene wax is a result of the combined action of multiple dimensions including production process, storage environment and inherent properties, with core inducements coming from multiple levels. When the molecular chains of by-product polyethylene wax are in long-term contact with oxygen, oxidation reactions will occur, the molecular chains break to generate carbonyl compounds, and unsaturated double bonds are oxidized to form chromophoric groups. Yellowing usually starts from the edge of the wax block and presents a light yellow gradient feature, which is also the most common inducement for yellowing of by-product wax. Compared with refined polyethylene wax, by-product wax has a weaker antioxidant system and a faster oxidation rate. High temperature is a key catalyst for accelerating yellowing. When the ambient temperature exceeds 70°C, molecular motion intensifies and the oxidation rate increases significantly. After reaching the critical point of 120°C, part of the carbon chains begin to undergo thermal decomposition, directly generating colored impurities. Uneven temperature of drying equipment and local overheating during the production process will lead to spot-like yellowing of wax products. Relevant experimental data shows that for every 10°C increase in ambient temperature, the oxidation rate of by-product wax increases by 1.8 times. The production source characteristics of by-product wax determine that it is more likely to be mixed with various yellowing-promoting impurities. Fe³⁺ remaining in iron production containers and pipelines is a powerful oxidation catalyst, which will greatly accelerate yellowing. Sulfides brought in from the upstream production process, incompletely removed catalyst residues, and pigment components that have not been thoroughly cleaned remaining in the recycled materials mixed in some by-product waxes are all high-risk yellowing factors unique to by-product wax, which will be deeply removed in refined polyethylene wax. Improper storage and use environments will further aggravate yellowing. Long-term outdoor storage under ultraviolet radiation may cause obvious color difference in about half a year. Long-term open storage will make the wax continuously contact with air, constantly consuming the limited antioxidant components. Humid environments or those with corrosive gases will also destroy the molecular structure of the wax and accelerate the color change process.
