The hardness or softness of polyethylene wax (PE wax) is fundamentally determined by its internal molecular structure, a characteristic that profoundly influences its pricing and performance in practical applications. Hard polyethylene wax typically features higher molecular weight, density, and crystallinity. Its molecular chains are orderly and tightly packed, resulting in a higher melting point and a rigid texture. Soft polyethylene wax, on the other hand, generally has lower molecular weight, higher degrees of branching, and a disrupted crystalline structure, granting it greater flexibility and plasticity. The most common type of soft wax is oxidized polyethylene wax.
Regarding price, there is a notable difference between hard and soft waxes. Typically, soft oxidized polyethylene wax, produced through an oxidation process that introduces polar groups, involves more complex manufacturing. Consequently, it often commands a higher price than non-polar hard waxes produced via simple cracking or polymerization. Of course, factors like raw material purity, molecular weight distribution, and brand also affect pricing, and some high-quality homopolymer hard waxes can also be expensive. However, the functionalization achieved through modification (like oxidation) generally adds cost.
In practical application, the difference between hard and soft wax directly impacts processing and final product quality. A key concern is "exudation" or "migration." Hard polyethylene wax, due to its non-polar nature and high crystallinity, has poorer compatibility with many polar resins (like PVC, PA). This makes it more prone to migrating to the product's surface, forming visible "bloom" or "haze," which can affect subsequent printing, coating, or aesthetics. Soft oxidized polyethylene wax, with its improved polarity, offers better resin compatibility and a significantly reduced tendency to migrate, allowing it to remain more stably within the product matrix.
Another common concern is "blockage" during processing, often related to the lubricant's dispersibility and melting point. Hard polyethylene wax has a higher melting point. If its particles are too coarse or dispersion is poor, it can accumulate and cause stagnation in the extruder or die, especially at insufficient processing temperatures, potentially leading to flow channel blockage over time. Soft polyethylene wax, with its lower melting point, melts and disperses more easily, presenting a relatively lower risk of blockage. However, it's crucial to note that any waxy additive, if overdosed, can cause excessive lubrication, leading to material slippage in the screw, which reduces conveying efficiency and plastification—this is also a form of process abnormality or "blockage." Furthermore, excessive use of soft wax at very high temperatures might sometimes lead to melt fracture due to over-lubrication, affecting the surface smoothness of the extrudate.
Therefore, selecting polyethylene wax requires a systematic approach. Hard wax is preferred for applications demanding high dispersibility, high gloss, and abrasion resistance, but attention must be paid to its compatibility with the base material to prevent exudation. For polar resin systems requiring good compatibility, internal lubrication to improve processing flow, and avoidance of surface bloom, soft oxidized polyethylene wax is more suitable. In many cases, blending both types in an appropriate ratio can synergistically combine external and internal lubrication effects, striking an optimal balance between cost, performance, and process stability. Ultimately, pilot testing to determine the correct type and dosage is the key step to avoiding issues like exudation or blockage, ensuring smooth production and final product quality.
