What Is White Masterbatch, and Why Does Titanium Dioxide Define Its Quality?

The blow molding plant had been supplying white HDPE bottles to a dairy company for two years with the same white masterbatch. A new supplier offered a white that was cheaper per kilogram, purchasing approved it based on a sample that looked identical in pellet form, and the supervisor programmed it into the feeder at the usual percentage. The bottles came out of the machine white. In the customer's laboratory, held up against the lamp, the shoulders and the base let light through, and next to the label the white looked yellowish. The lot was held for insufficient opacity, the plant raised the let-down ratio to reach the standard and, at the new percentage, each bottle ended up costing more than with the previous white.

White masterbatch is a titanium dioxide concentrate that provides opacity, whiteness and hiding power to the part. Its quality depends on the TiO2 grade (crystal form, surface treatment and particle size), on its loading and on its dispersion.

Two whites at the same percentage and a bottle that lets light through

White masterbatch is one of the most widely consumed families in plastics processing. It carries a high loading of titanium dioxide (TiO2) dispersed in a carrier resin and is dosed over natural resin for three jobs: making the part opaque, giving it a clean white and covering the base shade of the resin, especially when the resin is recycled. It also serves as a background for light and pastel shades, which look translucent or dirty on a resin without white.

In our article on masterbatch families, we placed it alongside black and color concentrates. Here we examine the component that determines its performance, because two whites with the same percentage on the data sheet can produce very different parts, as in the opening case.

What the let-down percentage leaves unsaid

The let-down percentage indicates how much concentrate enters the machine; opacity depends on how much titanium dioxide reaches the part and how much light each particle manages to scatter. Those two figures change from one white to another for three reasons: the actual pigment loading, the TiO2 grade used and the quality of its dispersion. An economy white can cut costs on any of the three, and the difference shows up in the part, rarely in the pellet.

Titanium dioxide: the pigment that gives white its hiding power

Refractive index: the origin of opacity

A white part looks opaque because the pigment particles scatter light in all directions before it can pass through. That ability depends on the difference between the refractive index of the pigment and that of the surrounding resin. Titanium dioxide has the highest refractive index among commonly used white pigments, well above that of polyolefins, which is why a small amount is enough to cover. White minerals such as calcium carbonate have an index close to that of the resin: they lighten the part and lower its cost, provide little opacity and serve as fillers in plastics.

Rutile and anatase: two forms of the same pigment

Titanium dioxide is sold in two crystal forms. Rutile has the higher refractive index and, with the appropriate treatment, better weather resistance; it is the form that dominates in masterbatch for plastics. Anatase covers somewhat less, has a bluer undertone and is less abrasive, although its greater activity under ultraviolet light makes it less suitable for outdoor parts. Its use is concentrated in specific applications, such as some fibers and indoor parts. For most polyolefin parts, the practical question is which rutile grade the concentrate contains.

Surface treatment and particle size: the white that shows in the part

Inorganic and organic particle treatment

The surface of titanium dioxide is photoactive: under ultraviolet radiation it can accelerate the degradation of the surrounding polymer, and the part ends up with chalking, loss of gloss or yellowing. To control this, TiO2 manufacturers coat the particle with inorganic layers, such as alumina, silica or zirconia, which reduce that activity and improve outdoor durability. On top of these, an organic treatment is applied that helps the polymer wet the particle and aids dispersion. That is why there are grades for film, for indoor parts and for outdoor use, and a white formulated with the wrong grade can pass on the laboratory plaque and fail in the field months later.

Particle size and undertone

Light scattering is greatest when the particle measures about half the wavelength of visible light, a fraction of a micron. Within that range, size also defines the undertone: finer particles scatter more blue light and give a cool, bluish white; coarser particles give a warm white with a yellowish or cream tendency. Two whites with the same opacity can look different next to a label, a cap or another supplier's part. Fine adjustment of the undertone is made in the formulation, with blue or violet toners in minimal amounts, and is approved against the customer's physical reference.

Dispersion and loading: where white masterbatch succeeds or fails

TiO2 agglomerates and moisture in film

Titanium dioxide arrives as a very fine powder that tends to form agglomerates. If the masterbatch extrusion leaves them unbroken, they appear in the part as specks, streaks or areas with less coverage, and in thin film they can create weak points that break when stretched. A poorly dispersed pigment also covers less per gram, and the plant compensates with a higher percentage, as in the opening case.

Moisture is the other risk. Treated pigment can retain water that, in film extrusion at high temperature, volatilizes and leaves holes or a lacing pattern in the film. It is advisable to store the concentrate in closed bags and, if the supplier indicates it, to dry it before use.

High loading and opacity efficiency

This family works with high pigment loadings. Our PE White Masterbatch reaches up to 70% pigment concentration: with more pigment per kilogram of concentrate, the same amount of TiO2 reaches the part at a lower let-down percentage, and less carrier resin goes in. That loading requires flawless dispersion, because with so much pigment in so little resin any agglomerate is multiplied.

Opacity increases with the TiO2 content in the part up to a point where the particles are so close together that each additional gram provides less coverage. That is why wall thickness matters as much as the percentage: a thin wall needs more pigment per kilogram of resin to cover as well as a thick wall. The correct let-down ratio is defined with trials at the actual thickness of the part, in its thinnest area.

How to compare two white masterbatches on technical criteria

Before changing suppliers or approving a cheaper white, we recommend comparing with the part in hand and with data, at the same cost per finished part:

• Inorganic content: the ash test shows how much inorganic material the concentrate contains; if the white includes fillers such as calcium carbonate, the actual proportion of TiO2 requires additional analysis.

• Opacity at the actual thickness: the part, or a plaque of the same thickness, checked against the light and over a white and black background.

• Undertone: comparison against the approved standard, under the same light source, next to the label or the adjacent component.

• Dispersion: specks and streaks in film or thin plaques, and screen pack pressure in the extruder during the trial.

• Moisture and volatiles: behavior in film extrusion at the processing temperature.

• End use: a TiO2 grade suitable for outdoor exposure, support for food contact and absence of heavy metals according to the technical data sheet.

With these six checks, the comparison is based on the cost per part that meets the opacity and shade requirements, and the price per kilogram becomes one more data point.

The white masterbatch we manufacture at Delta Pigmentos

At Delta Pigmentos we manufacture white masterbatch in our own plant. Our PE White Masterbatch is free of heavy metals, with formulations that comply with NOM standards and FDA CFR regulations. In the Basic Color Line, MB-Blanco DP-4536A is recommended for food contact under FDA 21 CFR 178.3297 and works in HDPE, LDPE and PP, in injection molding, film extrusion, extrusion blow molding and compression molding, with a processing range of 150 °C to 250 °C.

When the part calls for a specific white, such as your customer's brand white, the white of a label or that of a component assembled next to it, we match it in our Quality Control, Design and Development laboratory against your physical reference, your photograph or your Pantone code, and we define the loading and let-down ratio with the thickness of your part. You validate the sample on your machine and, once the shade is approved, we produce it under ISO 9001-2015 certified procedures. A development color takes 10 days from sample approval, with a minimum order of 100 kg.

Frequently asked questions

How much white masterbatch is dosed in a part?

It depends on the TiO2 loading of the concentrate, the wall thickness and the opacity the part requires. A thin wall or a container that must block light calls for more pigment per kilogram of resin. The exact percentage is defined during development, with trials at the actual thickness.

Does white masterbatch cover the shade of a recycled resin?

Yes, within a limit. TiO2 covers the gray or yellowish shades of recycled material well, and the required let-down ratio increases the darker and more variable the base resin is. It is advisable to develop the concentrate on the actual recycled material the plant uses.

Why does a white part turn yellow over time?

The most frequent causes are a TiO2 grade without the appropriate treatment for outdoor use, degradation of the polymer by ultraviolet radiation and a processing temperature above the range of the formulation. For outdoor parts, it is advisable to combine the white with ultraviolet protection in the same concentrate.

At Delta Pigmentos we have been manufacturing white, black, color and functional masterbatch in our own plant for 24 years, with our own laboratory and ISO 9001-2015 certified procedures. If your white part needs more opacity, a different undertone or a lower cost per part, write to us on WhatsApp from https://deltapigmentos.com with your polymer, your process, the wall thickness, your shade reference and the end use; we will respond with a technical proposal. Every request is reviewed within the following 24 business hours.