White masterbatch yellowing: causes and how to specify TiO2 grade
White masterbatch turns yellow for four distinct reasons, and only two of them are fixed by changing the grade. Here is how to tell them apart before you pay for a trial.
1. Anatase vs rutile TiO2 — the #1 grade choice
White masterbatch uses titanium dioxide. Two crystal forms exist, and they behave very differently:
| Crystal form | Refractive index | Whiteness | UV resistance | Typical use |
|---|---|---|---|---|
| Rutile (R-type) | 2.71 | ≥ 97 | Good | Film, fibres, injection, outdoor |
| Anatase (A-type) | 2.55 | 94–96 | Poor — chalking | Indoor, paper coating, low-cost applications |
The cheaper mistake is to accept anatase TiO2 masterbatch for outdoor film or pipe. Anatase chalks under UV and yellows noticeably in 6–12 months. Rutile grades cost more per kg, but anatase simply does not satisfy outdoor specifications.
2. Sulphur-induced yellowing
When TiO2 masterbatch is processed with any material containing sulphur compounds — recycled resin, pigment blends, or certain UV stabilisers — the titanium dioxide reacts to form titanium sulphide. The symptom is: yellowing appears inside the barrel or shortly after extrusion, at the same machine position, and disappears when you switch to virgin resin.
Fix: Specify a surface-treated rutile TiO2 grade. Alumina- or silica-coated grades resist sulphur reaction far better than untreated grades. Ask the supplier which surface treatment is used.
3. Thermal degradation — processing temperature is the real issue
Above about 260 °C, some white masterbatch carrier resins begin to degrade, producing yellow oxidation products that the TiO2 cannot mask. The symptom is: yellowing only on thick sections or on the surface that runs hot, and yellowness increases with barrel temperature.
This is not a TiO2 grade problem — it is a processing problem. Lower the barrel temperature by 10–15 °C or switch to a masterbatch with a higher-temperature carrier (EVA or a more stable PP grade rather than standard LDPE).
4. Photo-yellowing of the polymer, not the TiO2
The fourth cause is the polymer itself yellowing under UV, not the TiO2. The symptom is: the whole part yellows evenly, over weeks or months of outdoor exposure, and the film loses gloss.
This is a UV stabiliser problem, not a white masterbatch problem. Either add a UV stabiliser to the virgin resin, or specify a white masterbatch that already contains one. The TiO2 alone is not a UV stabiliser — it scatters light but does not absorb harmful UV wavelengths.
How to specify white masterbatch — four questions
Before you compare prices, ask for these on the TDS:
- TiO2 crystal form — rutile or anatase (rutile only for outdoor use)
- TiO2 content in % — typical range is 50–70% by weight
- Surface treatment — alumina, silica or mixed coating (required for sulphur resistance)
- Whiteness value — rutile should quote ≥ 97 (Hunter L-value)
Typical addition rates
| Application | Typical addition rate |
|---|---|
| Blown film, PE | 4–8% |
| Cast film | 5–10% |
| Injection molding | 2–5% |
| Fibres / raffia | 5–10% |
| Woven sacks | 3–6% |
Common questions
Can I tell anatase from rutile on the TDS?
Look for "crystal form" or "TiO2 type". "R-type" or "rutile" is what you want. If it says nothing, ask — anatase is cheaper and some suppliers sell it as premium.
Does higher TiO2 content mean better whiteness?
Only up to about 70%. Above that you hit diminishing returns and the masterbatch becomes harder to disperse. 50–70% is the standard range.
What is "blue-white" vs "yellow-white"?
Rutile TiO2 with a slight blue undertone is preferred. Anatase tends toward a yellow-white. The Hunter b-value on the TDS tells you: negative b = blue, positive b = yellow.
Does white masterbatch fade in sunlight?
Rutile TiO2 masterbatch used with a UV stabiliser will not fade. Without a UV stabiliser the polymer itself can yellow, making the masterbatch look as if it faded.
Related: how to read a masterbatch TDS · addition rate by process · White masterbatch specifications