Titanium dioxide is the whitest, most opaque pigment available at industrial scale, and it is the reason white plastic is white. It is also, in one of its two crystal forms, capable of actively destroying the polymer it is sitting in.
Knowing which form you are buying is the most valuable thing a purchaser of white masterbatch can know.
Why titanium dioxide hides so well
Opacity is about bending light, not absorbing it.
A pigment particle scatters light when its refractive index differs sharply from the medium around it. Polyethylene has a refractive index around 1.5. Rutile titanium dioxide sits at approximately 2.7 – one of the largest gaps available in any commercially usable white pigment.
That mismatch is what makes a thin white film opaque. Light entering the film is scattered repeatedly by the particles and reflected back out before it can pass through.
Two consequences follow directly:
Particle size is optimised, not minimised. Maximum scattering happens when the particle is roughly half the wavelength of the light being scattered – in practice around 0.2 to 0.3 microns for visible light. Particles much finer than that scatter poorly and start to look transparent or blue-toned; particles much coarser waste material. Pigment producers control this tightly, which is part of what separates grades.
Past a certain loading, more TiO₂ stops adding opacity. Particles crowd each other, their scattering fields overlap, and efficiency drops. You keep paying and stop hiding. This is why a well-formulated 60% white can outperform a badly formulated 70%.
Rutile versus anatase – the difference that matters
Titanium dioxide crystallises in two commercially relevant forms.
| Rutile | Anatase | |
| Refractive index | ~2.7 | ~2.5 |
| Opacity / hiding power | Higher | Lower |
| Photocatalytic activity | Low, especially when surface treated | High |
| Tone | Slightly warm | Slightly blue |
| Outdoor durability | Good | Poor – causes chalking |
| Typical cost | Higher | Lower |
Anatase is photocatalytic. Under ultraviolet light it generates highly reactive species at the particle surface – the same property that makes anatase useful in self-cleaning surfaces and air purification. Inside a polymer, those reactive species attack the polymer chains touching the pigment.
The result is chalking: the polymer at the surface is eaten away, leaving loose pigment that rubs off as a powder. The part fades, roughens, and loses surface strength. And because the reaction produces radicals, it directly consumes the UV stabiliser you paid for.
Put anatase into an outdoor product and you have added an accelerant, not a pigment. The part degrades faster than the same part with no white pigment at all.
This is the single most common cause of “our white grade fails faster than our natural grade” – in woven sacks, in agricultural film, in outdoor furniture, in profiles.
Anatase is not useless. It is cheaper, it has a cleaner blue tone, and for indoor, short-life or non-durable applications it is a legitimate choice. It should simply never see sunlight.
Surface treatment is not a detail
Even rutile has some residual photoactivity. Pigment producers suppress it by coating the particle – typically with alumina and silica, sometimes with an organic treatment on top.
That inorganic coating does three separate jobs:
- Passivates the surface, so photocatalytic reactions cannot reach the polymer
- Improves dispersion, by making the particle easier to wet out and harder to re-agglomerate
- Improves durability, which is why weatherable grades carry heavier treatment than general-purpose ones
So “rutile” alone is not a specification. A lightly treated rutile intended for indoor use will not deliver the outdoor life of a heavily treated weatherable grade, and both are legitimately called rutile.
Ask for the grade name and the intended durability class, not just the crystal form.
Chloride process and sulphate process
Two manufacturing routes exist, and the distinction shows up in Indian supply.
Chloride process grades are generally purer, brighter and more consistent, with a cleaner tone. Almost all high-durability weatherable rutile is chloride-route.
Sulphate process grades can be perfectly good and are often more economical, and the route is capable of producing both anatase and rutile.
Neither route is automatically right or wrong. But if you are buying a weatherable white for a ten-year outdoor product, you should know which you are getting.
How the cost gets taken out of a white masterbatch
TiO₂ is by a wide margin the most expensive component of a white masterbatch. Which means every route to a cheaper price per kilo runs through the pigment.
The four common ones, in rough order of how visible they are:
1. Lower TiO₂ loading. Honest if declared. A 50% white is not a defective 70% white – it just needs a higher addition rate. Compare on cost in use, not price per kilo. Our let-down ratio calculator does that arithmetic.
2. Extenders. Calcium carbonate or talc partially replacing TiO₂. These are cheap and white, but their refractive index is close to the polymer’s, so they contribute very little opacity. A white with heavy extender needs a higher dosage to hide, and can look grey or dull rather than bright.
3. Anatase substituted for rutile. Cheaper, and undetectable by eye indoors. Shows up as chalking, fading and premature failure, months or years later, in the field.
4. Lower-durability rutile. Lightly treated grades priced against weatherable ones.
None of these are visible in a quote. All are visible in a test.
What to test, and how to specify
Specify:
- Crystal form – rutile, stated explicitly, for anything with sun exposure
- Surface treatment and durability class
- TiO₂ content in the masterbatch, as a percentage
- Carrier resin and MFI
- Recommended dosage to hit your opacity target at your wall thickness
- Whether extenders are present, and at what loading
Test:
- Opacity or contrast ratio at your actual gauge, against a black-and-white chart – this is what you are actually buying
- Tinting strength against a reference, to catch loading changes between lots
- Ash content, which will reveal total inorganic loading and expose heavy extension
- Accelerated weathering with ΔE and yellowness index measured – this is what catches anatase
- Yellowness index after heat ageing, for anything processed hot
The weathering test is the one that matters. Everything else can be argued about; a chalked panel cannot.
The food contact question
Titanium dioxide as a food additive has been the subject of significant regulatory attention internationally in recent years. That is a question about eating the pigment.
TiO₂ as a pigment in a plastic article that contacts food is a different regulatory question, governed by food-contact material rules and migration limits rather than food-additive rules.
If you are making food packaging, do not rely on general commentary either way – ask your supplier for the specific food-contact compliance documentation for the grade, for the jurisdiction you are selling into, and confirm it is current.
FAQs
What is the difference between rutile and anatase titanium dioxide? Rutile has a higher refractive index, so it hides better, and it is far more stable outdoors. Anatase is cheaper with a bluer tone, but it is photocatalytic – under UV it generates radicals that attack the surrounding polymer, causing chalking and accelerated failure.
Can I use anatase titanium dioxide in outdoor plastic products? No. Anatase actively accelerates degradation under UV, so an outdoor part pigmented with anatase will typically fail sooner than the same part with no white pigment at all. Use surface-treated rutile.
Why does adding more titanium dioxide stop improving opacity? Because scattering efficiency falls when particles crowd each other and their scattering fields overlap. Past the optimum loading you add cost without adding hiding power.
What does surface treatment do to titanium dioxide? An alumina and silica coating passivates the particle surface so photocatalytic reactions cannot reach the polymer, improves dispersion, and raises outdoor durability. Weatherable grades carry heavier treatment than indoor grades.
How much titanium dioxide is in a white masterbatch? Commonly 50% to 75%. A lower loading is not a defect provided it is declared – compare suppliers on cost in use at your required opacity, not on price per kilogram.
How can I tell if a white masterbatch has been extended with cheap filler? Measure ash content and compare it against the declared TiO₂ loading, and check contrast ratio at your actual gauge. Heavily extended whites need a higher dosage to hide and often look dull rather than bright.
Which test detects anatase substitution? Accelerated weathering, with ΔE and yellowness index measured before and after, and a visual check for chalking. Indoors and on day one, anatase and rutile can look almost identical.