Short answer: lubricant exudation is usually a formulation-balance problem, not a mystery. Get the dosage, the lubricant type, the internal/external balance and the extrusion conditions right, and the surface stays clean.
Wood-plastic composites (WPC) combine polyethylene (PE) with wood flour or other lignocellulosic fillers. They are widely used for outdoor decking, wall cladding, fencing and decorative profiles. These products need lubricants, because highly filled PE melts are viscous and rub hard against the screw, barrel and die.
The trouble starts when part of that lubricant does not stay in the material. Lubricant exudation (also called blooming or bleeding) means the additive migrates to the profile surface. Typical signs are a greasy feel, visible residue, white or glossy patches, or uneven deposits that show up after cooling or storage.
Why it matters:
The core question for formulators and buyers is simple: how can you reduce exudation risk through formulation and lubricant selection? The sections below walk through the causes, fixes and tests. For a product overview, see Joysun's PE WPC composite lubricant page.
Every polymer matrix can hold only so much lubricant. When the dosage goes beyond what the formulation needs, the surplus has nowhere to go and tends to migrate, leave surface residue or cause other processing issues. The right level depends on resin type, wood flour content and processing conditions, so a number copied from another formula is only a starting point.
PE is non-polar. Wood flour is polar and hygroscopic. A lubricant that fits poorly with the PE phase will disperse badly and migrate more easily. Different lubricant chemistries (for example amide waxes, ester waxes, polyolefin waxes) behave differently in the same melt. That is why lubricant systems should be chosen for the specific formulation, not by name alone.
If a line shows die buildup, the quick fix is often more external lubricant. That can backfire, because external components are less compatible with the matrix and are the first to migrate. Too much internal lubricant has its own cost: slower fusion and possible loss of mechanical strength.
Barrel temperature, screw speed, residence time and cooling all influence how lubricant disperses and where it ends up. Overheating or unstable running can worsen surface defects in some formulations. Before blaming the lubricant, rule out look-alikes: moisture from wood flour, pigment bloom, or other additives can produce spots that resemble exudation. A wipe test and a check of the raw materials usually tell them apart.
Match the lubricant to your PE grade, wood flour loading and target product. Compare lubrication efficiency, dispersion and long-term surface stability. A composite (multi-component) lubricant is designed to cover several functions in one package, which can simplify dosing and batch consistency. Even so, do not assume it beats a single-component system in every formula. Test both in your own recipe.
Joysun's technical team shares extrusion and formulation support through its R&D center. Related reading on the whole system is on the PE wood-plastic composite technical solutions page.
| Test | What to do |
|---|---|
| Visual inspection | Look for oil film, spots or residue under consistent lighting. |
| Surface wiping | Use the same wipe material, pressure and conditions each time; compare residue. |
| Thermal aging | Hold samples at a set temperature and time, then compare the surface. |
| Extrusion stability | Record torque, die buildup, continuity and profile appearance. |
| Long-term storage | Compare surface state after production, after cooling and after storage. |
Test temperature, time and pass criteria should follow the end use and customer requirements. One test result does not equal long-term outdoor performance. For finished decking, product standards such as ASTM D7031 (guide to properties of wood-plastic composite products) and ASTM D7032 (performance ratings for WPC deck boards and guardrail systems) are common references. Please check the current edition before use.
Zhejiang Joysun Advanced Material Co., Ltd. (founded in 2005, based in Pinghu, Zhejiang) offers a range of PE WPC composite lubricants. According to its product page, the grades include:
| Grade | Positioning | Dosage listed |
|---|---|---|
| H101L | Ultra-high anti-exudation | 2.2–3.2% |
| H838L | Premium anti-exudation | 2.2–3.2% |
| H201L | Mid-to-high-end anti-exudation | 1.5–2.5% |
| H771L | Mid-to-low-end general purpose | 1.0–1.8% |
| H912L | Flame-retardant WPC systems | 2.0–3.0% |
The page also lists POE01, a compatibilizer (3–6%), which improves bonding between the PE or PP matrix and wood flour and can be used alongside the lubricants. Anti-exudation results (such as 72-hour hot-water immersion tests) are given per grade by the manufacturer, so please confirm exact performance, dosage and suitable formulations in the official technical data before you commit. Foamed profiles? Joysun also supplies chemical foaming agents, and flooring producers can look at the SPC/WPC floor one-pack additive range.
Need samples, a TDS or formulation advice?
Browse the PE WPC composite lubricant range, read the full WPC technical solution, or contact Joysun (sale@joysunsh.com). More updates are in company news.
