Titanium Dioxide

Polymers, Light and theScience of TiO2
Product Overview

Ti-Pure™

Contents
Light-Scattering Properties.................................. 4
Refraction.........................................................................4
Refractive Index and Scattering Power............. 5
Diffraction and Particle Size.................................. 5
Particle Size and Scattering Power.........................6
Particle Size and its Effect on Product Color.......6
Optical Properties..................................................... 7
Dispersion In Plastics:.............................................. 8
Dispersion.........................................................................8
Bulk Flow Properties:............................................... 12
Manufacturing Process........................................... 14
Quality Control........................................................... 16
Color....................................................................................16
pH.........................................................................................16
Resistance........................................................................16
Screen-pack Testing......................................................16
Acid Solubility..................................................................16
Nujol Yellowing.................................................................16
Low Shear Dispersion...................................................16
Product Stewardship............................................... 17
FDA Status.......................................................................17
NSF Status.......................................................................17
SDS.....................................................................................17

Titanium Dioxide

Ti-Pure™

Titanium Dioxide

Polymers, Light and the Science

TITANIUM DIOXIDE — TiO2 is a multifaceted material whenused in polymer applications. It has been long established as theleading white pigment, and this is the application that people aremost familiar with. However, titanium dioxide brings more to thepolymer industry than just white, bright opacity. In a more basic
sense, titanium dioxide is a photo-responsive material—its value
is in its interaction with light. For example, this interaction canbe the familiar scattering that results in opacity or it could be theabsorption of UV light energy, thereby protecting the polymer from
UV degradation. Applications continue to develop, all based on theinteraction of the titanium dioxide particle with light.

2

Ti-Pure™

Titanium Dioxideof TiO2

As other applications for titanium dioxide have developed,

Few, if any, commercial grades of titanium dioxide are

its pigmentary properties remain the most important.

pure TiO2. Most have inorganic and, in some cases,

Titanium dioxide is the most important white pigment

organic treatments deposited on the surfaces of theused in the polymer industry. It is widely used, because

TiO2 particles by precipitation, mechanical blending,it efficiently scatters visible light, thereby impartingor via other routes. These surface treatments

whiteness, brightness, and opacity when incorporated

provide improvements in one or more performance

into a plastic product. It is chemically inert, insoluble

properties of the pigment, such as ease of dispersion,in polymers, and heat stable under the harshest of

weatherability, or discoloration resistance. A single

processing conditions. Titanium dioxide is commerciallyprescription for surface treatment does not produce aavailable in two crystal forms—anatase and rutile. The

pigment having maximum value-in-use for all plastics

rutile pigments are preferred over anatase pigments,

applications, and it is a continuing research goal tobecause they scatter light more efficiently, are moredevelop titanium dioxide grades to meet the changing

stable, and are less likely to catalyze photodegradation.

needs of the plastics industry.

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Ti-Pure™

Titanium Dioxide

Light-Scattering Properties

Figure 2a

Titanium Dioxide Provides Opacity by Scattering Light

Path of Light in White Film (both films completely opaque)

Unlike colored pigments that provide opacity by absorbing
visible light, titanium dioxide and other white pigments
provide opacity by scattering light. This scattering ispossible because the white pigment can bend light. If
there is enough pigment in a system, all light striking thesurface, except for the small amount absorbed by thepolymer or pigment, will be scattered outward, and thesystem will appear opaque and white. Light scattering isaccomplished by refraction and diffraction of light as it
passes through or near pigment particles.
Refraction
Refraction is depicted in Figure 1, where the sphere
represents a TiO2 particle suspended in a low refractive
index polymer. As a ray of light falls on the TiO2 particle, it
is bent, because light travels more slowly through the highrefractive index pigment than through the low refractive
index polymer in which it is dispersed.
Figure 1
Refraction of light by particles

High R.I. TiO2

Low R.I. Pigment

Figure 2 schematically depicts a cross-section of two
white-pigmented films and how differences in pigment
refractive index affect opacity. In the film containinga high refractive index pigment Figure 2a, left, light isbent more than in the film containing the low refractive
index Figure 2a, right, with the result that light travels ashorter path in the film and does not penetrate as deeply.
Both upper films appear opaque and white, because noabsorbing particles are present, and practically all incident
light is returned to the surface.
However, in a thinner film Figure 2b, the film containing
the high refractive index pigment still appears opaqueand white, whereas the film with the low refractive index
pigment allows some of the light to pass completely
through the film and be absorbed by the black
background. This film is not completely opaque andappears gray compared with the white film.
Figure 2b
Path of Light in White Film (film on right not opaque)High R.I. TiO2

4

Low R.I. Pigment

Ti-Pure™

Titanium Dioxide

Refractive Index and Scattering Power

Figure 3

To understand why titanium dioxide, especially the rutile
form, offers such great advantages in hiding power, it is
only necessary to compare the refractive index of rutile
TiO2 to the refractive indices of anatase TiO2, othercommercial white pigments, and polymer systems asshown in Table 1. In general, the greater the difference
between the refractive index of the pigment and that ofthe polymer matrix in which it is dispersed, the greater thelight scattering.

Diffraction of Light Around Pigment Particle

Diffraction and Particle Size
Diffraction, the other factor affecting the degree to whicha pigment scatters light, is depicted schematically in
Figure 3. Here, light passing near a pigment particle isbent. This phenomenon accounts for a pigment’s ability
to scatter light in an adjacent area several times larger
than the cross-sectional area of the pigment itself. For
the most effective light scattering, the pigment diametershould be slightly less than one-half the wavelength oflight to be scattered. Because the eye is most sensitive
to yellow-green light (about 0.55 µm wavelength),commercial TiO2 pigments for plastics average
0.2–0.3 µm in diameter.
Light scattering imparted by diffraction is affectedby particle spacing and average pigment particle size.
If particles are too large or too closely spaced, little
diffraction takes place. If the pigment particles are too
small, the light will not “see” the pigment particle.
Table 1
Indices of Refraction for Some White Pigments and Common Polymers
White Pigment

R.I.

Plastic

R.I.

Rutile TiO2

2.73

Polystyrene

1.60

Anatase TiO2

2.55

Polycarbonate

1.59

Antimony Oxide

2.09–2.29

SAN

1.56

Zinc Oxide
Basic Carbonate, White Lead

2.02
1.94–2.09

Lithopone

1.84

Clay

1.65

Magnesium Silicate

1.65

Barytes (BaSO4)

1.64

Calcium Carbonate (CaCO3)

1.63

Polyethylene

1.50–1.54

Acrylic

1.49

Polyvinyl Chloride

1.48

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Titanium Dioxide

Figure 4

Particle Size and its Effect on Product Color

Relative Light Scattering Power versus Rutile Particle Size

In a nonabsorbing, white polymer that is pigmented tocomplete opacity, changing the TiO2 particle size has noeffect on color, because all light striking the surface iscompletely reflected. Figure 5, a cross-sectional view ofsuch a white opaque film, demonstrates this point. The
blue light, having the shortest wavelength and scattering
path, and the red light, having the longest wavelength andpath, are totally reflected; the visual effect is the same as
if all light traveled the same path length.

1.75

Relative Scattering Power

1.50
1.25
1.00
0.75
0.50
0.25
0.00
0.05 0.10 0.15 0.20

0.30

0.50

0.80

Particel Size, mParticle Size and Scattering Power
Curves in Figure 4, derived from theoreticalconsiderations in very dilute systems, show the relative
scattering power of rutile TiO2 for blue, green, and red
light as a function of TiO2 particle size. At about 0.2µm, the sum of the light scattered at all wavelengths ismaximized. When the particle size is increased to 0.25–
0.30 µm, the scattering of blue light decreases rapidly,
but the scattering of green and red light is relatively
unchanged. At 0.15 µm, the diameter corresponding to
the maximum scattering of blue light, light scattering in
the red and green ranges of the spectrum drops markedly.
Therefore, as TiO2 pigment is made bluer, it can actuallylose some of its light scattering capability.

For translucent white film, pigment particle size will affectboth transmitted color and reflected color. Considertransmitted color: as particle size is reduced, a larger
portion of the blue light is reflected and more yellow lightis transmitted. On this basis, if blue transmitted light isdesired, a larger rather than smaller particle size titanium
dioxide pigment is preferred.
If an absorbing pigment such as carbon black or a colored
pigment is added to the titanium dioxide-containing
polymer Figure 6, red light with the longer path length
has a greater chance of being absorbed. Decreasing TiO2
particle size, in this case, reduces red light scattering andenhances blue. Thus, in an opaque polymer containingsome light-absorbing matter such as colored pigment,
decreasing TiO2 particle size will increase blueness asviewed in reflectance. This phenomenon is inherent inlight-scattering pigments and is described as “undertone.”

Figure 5

Figure 6

Scattering of Light by White Plastic

Light Scattering by TiO2 Particles

INCIDENT LIGHT
Equal parts of a shortand long wavelength(blue and red)White pigment particles
WHITE PLASTIC FILM

6REFLECTED LIGHT
SHORT λ (Blue)LONG λ (Red)INCIDENT LIGHT
Equal parts of a shortand long wavelength(blue and red)Black particles in white film

GRAY PLASTIC FILM

REFLECTED LIGHT
SHORT λ (Blue)LONG λ (Red)Ti-Pure™

Titanium Dioxide

Optical Properties

Figure 7

Include Tinting Strength, Undertone, and Color

Optical Properties of Titanium Dioxide shows therelationship between tint strength and undertone for anumber of grades of titanium dioxide.

Tinting strength is easier to measure and most often used
to describe the light scattering efficiency or opacity ofa white pigment. To measure relative tinting strength, asample of TiO2 is dispersed into a black masterbatch ata prescribed ratio of carbon black to TiO2. The resulting
gray polymer is then formed into uniform, opaque sheetsor molded chips. The TiO2 sample with the greatest lightscattering efficiency will provide the lightest gray and thehighest reflectance.
Undertone is the contribution of a TiO2 to the color ofa tint. It is a function of TiO2 particle size and cannot
be determined from the appearance of dry powders or
white polymers. Undertone is usually expressed as theratio of blue (or CIE Z tristimulus value) to red (or CIE X
tristimulus value) reflectances as measured on gray tints
using a three-filter colorimeter or a spectrophotometer(undertone = CIE Z/CIE X). In the gray tint, an undertone
difference of 0.01 is visible only to a trained observer. The
relative undertone can be measured as vinyl undertone
using samples prepared the same way as for relative
tinting strength.
In some applications, the appearance of transmitted
light is important. The trans­mitted appearance of tints
or whites that contain small particle size TiO2 grades
are more yellow than similar products containing alarger particle size TiO2. Thus, in the manufacture ofsuch objects as bottles, light covers, etc., neutral or
yellow undertone TiO2 grades are preferred for their
bluer transmitted light. In color matching, it is important

Tint Strength
115

R-104
110

R-350 R-103

R-101

–0.04

–0.03

105

StrongWhen selecting a commercial grade of TiO2 for coloring
or opacity purposes, the fundamental optical propertiesof opacity/tinting strength, undertone, and color must
be considered. Opacity is the result of scattering of all
wavelengths of incident light. Tinting strength describes
the ability of a white pigment to efficiently scatter lightand provide whiteness and brightness to a coloredpolymer system.

R-105

–0.02

–0.01

Undertone

100
0.01

0.02

0.03

0.04

Blue
95

R-960
90

• 5 g TiO2 per 153 g black PVC• High shear dispersion, two roll millto understand the final appli­cation that the color will
be used for, so that the TiO2 grade with the correctundertone can be selected for an exact match. It isdifficult to compensate for differences in undertone by
the addition of pigment colors.
Color is the appearance of TiO2 pigment alone and isentirely independent of undertone. Most commercial
TiO2 grades do not vary significantly in dry color;
however, poor color can result from contamination. Color
can occur in plastic systems from reactions of TiO2 withthe polymer or additives and heat stability failures.
Color and undertone are sometimes confused. It is
entirely possible for a blue undertone TiO2 to exhibit
a yellow color due to one of the previously mentioned
conditions that can result in poor color. It is notuncommon for different particle size TiO2 grades to beequal in color. The most common method of measuring
the color of TiO2 is the CIE L* a* b*. The L* measures
the brightness of the sample, while the a* measures
the redness-greenness, and the b* measures theyellowness-blueness.

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Ti-Pure™

Titanium Dioxide

Dispersion In Plastics:

Figure 8

Important To Pigment Efficiency

Development of Dispersion Attributes with Time

Dispersion
Titanium dioxide is used most efficiently andeconomically, that is, the value of the pigment is best
realized, when it is well dispersed. Unfortunately, theprimary particles of pigment tend to stick to each otherin the course of manufacture and storage, resulting inaggregates and agglomerates many times the desiredparticle size. Manufacturers can use various techniques,
such as surface coatings and micronization to makedispersion easier and to minimize the aggregates present.
The object of dispersion is to reduce these remaining
aggregates and agglomerates to an acceptable size atreasonable cost.
Agglomerates, consisting of collections of primary
pigment particles, form during manufacture. The degree
that these agglomerates are dispersed can affectimportant appearance and performance traits, such as
those listed in Table 2. Each of these traits depends
on the degree of reduction of agglomerates to an
ideal of the primary particle size. Thus, agglomerates
30 µm or larger are primarily responsible for surface
imperfections, specking, streaking, and such processing
problems as pluggage of screen packs during extrusion.
Particles as small as 5 µm can influence physical orelectrical properties in critical applications. Still, smaller
particles are generally needed to realize the optimumcolor, strength, opacity, or transparency, and weathering
properties inherent in a pigment; it is in this area thatthe question of dispersion cost versus added value mostfrequently arises.

Opacity andTinting Strength

Concentration ofoversize Agglomerates

Dispersion Time

This varying response of dispersion traits to particles ofdifferent size means that some traits will develop more
rapidly than others in the course of dispersion. Focusing
on opacity and tinting strength, Figure 8 illustrates thatthese attributes will increase for a given pigment as theconcentration of agglomerates decreases. It is obvious,
then, that the means selected to measure dispersion
must be meaningful in terms of the more important
properties desired. The concentration of oversize
agglomerates can be measured using a screen-pack test.
The opacity and tinting strength would be a result of thedispersion quality.

Table 2
Effects of Dispersion

8

Appearance

Performance

Surface Texture

Cost

SpecksProcessibility

Streaks

Physical Strength and Porosity

Opacity/Strength

Weatherability

Ti-Pure™

Titanium Dioxide

Having established the dispersion quality needed and an
appropriate basis for measuring it, we can consider themeans of producing it. This requires some understandingof the mechanics by which dispersion takes place. Threeelements are necessary for dispersion, regardless of theprocess, conditions used, or quality desired:Figure 9Size Reduction by Rupture• Initial blending — formation of a suitable pigment/
polymer mix• Size reduction — fracture of pigment aggregates
and agglomerates

Agglomerate

Resin• Intimate wetting — displacement of air from thepigment’s surface
It is not suggested that these necessarily occur
separately, in sequence, or that any or all need be optimal
if the final application does not require it. However, thedispersion process must allow for each to take place.
These three elements will be discussed in further detailin terms of the three basic dispersion processes used in
the plastics industry, i.e., dry blend, melt shear, and liquid
shear dispersions.
Initial wetting, at a minimum, requires that the pigment
and the polymer be sufficiently well mixed and havesufficient affinity for each other to avoid separation
when further work is applied to the system. Better known
and more quantitative measures of initial wetting exist,
however. In fluid systems, for example, the time required
to wet-out pigment in the vehicle, the amount of ballingthat occurs as pigment is added, the amount of tailings
or separations observed in a three-roll grind, and theconsistency changes that take place with mixing, allprovide means by which the progress and quality of initialwetting can be followed. Similarly, in dry-blending, thetendency for pigment to pelletize or cake on equipment
and the amount of loose pigment present following sucha blend are measures of initial wetting. The importanceof initial wetting is often underestimated because of theusually simple means by which it is obtained. Yet, it is not
only essential but also often controls the quality of the
final dispersion or at least the amount of time required
obtaining it. TiO2 producers can influence initial wet-in by

the use of additives matched to the polymers in which thegrade is to be used. Surfactants can aid in increasing theaffinity between pigment and polymer, thereby improving
the quality or reducing the time needed to obtain initialwetting. However, pigments vary substantially in theirchemical compositions and surface characteristics, so
no single surfactant should be expected to serve all
situations equally well.
Size reduction may be achieved by impact, particleto-particle attrition (a rupture mechanism), or by shear
transmitted through an intermediate fluid layer (anerosion mechanism). In any case, sufficient mechanicalenergy must be introduced to overcome forces holding
agglomerates together. Because this is often carried out
in the presence of a polymer, physical characteristics ofthe polymer can be extremely important. For example,
in the case of a dry blend, schematically illustrated
in Figure 9, the size, shape, hardness, and softening
temperature of the polymer can influence the extent andefficiency with which size reduction is accomplished.
Size is of particular importance and will be discussed
later. TiO2 manufacturers use different methods from wet
milling to micronization to surface treatments to break up
and prevent aggregated particles and control particle size
within a consistent narrow range

9Titanium Dioxide

Ti-Pure™

In fluid dispersion processes, it must be first recognizedthat virtually all size reduction occurs either fromshear transmitted through a liquid layer surrounding
the aggregate or by impingement of the aggregate or
agglomerate traveling at a high rate of speed against a
hard surface. Figure 10 is intended to show that effective
size reduction is not accomplished by “crushing” theagglomerates. In this example, the agglomerate is muchlarger than usually desired in a dispersion. When the
agglomerate is exposed to the shearing forces of theflowing polymer, the agglomerate rotates in the polymer
stream and the par­ticle size is reduced through theerosion as shown in Figure 10. The factors which areimportant in the dispersion of pigment by erosion include
the melt viscosity of the polymer and the shear rate.
Small particle-sized polymers, such as powder, are an
important aid to dispersion in processes where dry
mixing of pigment and resin are involved because of thesignificantly more uniform and intimate blends produced.
This may be explained by the much greater polymer
surface the pigment can come in contact with and adhere
to during mixing. Loose pigment present after blending
with the polymer is much more difficult to disperse thanpigment attached to the resin surface.

Figure 10
Size Reduction by Erosion

Pigment
agglomeraterotates inflow field
Velocity vectorsof flowing polymer

Disbursed pigment
being eroded
from theagglomeratesurface

Remainingsmall aggregates

Differences in dispersion will be observed because ofdifferences in the surface treatments of pigment. This
often results in one pigment being superior to another
under one condition of dispersion and inferior underanother. Table 3 provides guidelines for the selection of agrade to be used in a particular dispersion process. These
guidelines only apply to the dispersion process, and otherimportant end-use properties must also be considered
before a final selection is made.

Table 3
Dispersion Performance for Ti-Pure™ Titanium Dioxide Pigments
Ti-Pure™

Melt Compounded

Dry Blended

R-101

R

HR

R-103

R

HR

R-104

HR

HR

R-105

HR

HR

R-350

HR

HR

R-960

R

Liquid Systems

RR
HR = Highly Recommended

10

R

R = Recommended

Titanium Dioxide

Ti-Pure™

The foregoing discussionof dispersion principles canbe summarized by offeringsome guidelines forachieving improved quality
or more rapid dispersion
by the three dispersion
processes used in theplastics industry. These arelisted in:Table 4
Guide to Quality
Dispersion by Dry
Blending
Table 5
Guide to Quality
Dispersion by Melt Shear
Processing
Table 6
Guide to Quality
Dispersion in Liquid
Systems

Table 4 Guide to Quality Dispersion by Dry Blending
Polymer Selection■■■

Small particle size
Hard surface in preference to soft, when option exists. Chemically compatible with pigment underprocessing condition exists
Rheologically compatible with base polymer (especially in concentrate preparation) to minimize letdown difficulties
due to difference in melt flow

Select pigment and additive loadings to provide proper flow under operating conditions
Short, intensive mix cycle (should be adequate for most pigments)
Encourage subsequent melt pressing of these dispersions at high shear

Table 5 Guide to Quality Dispersion by Melt Shear Processing
Polymer Selection■

Good wetting of both pigment and grind surface■

Small viscosity change with temperature.

■

Chemically compatible with pigment under processing conditions■

Rheologically compatible with base polymer (especially in concentrate preparation) to minimize letdown difficulties
due to difference in melt flow

Select pigment loading to develop high shear during operation
Pre-blend dry ingredients (see Table 4—Guide to Quality Dispersion by Dry Blending)
Flux resin by shear rather than by application of external heat where possible (e.g., Banbury mixer)

Table 6 Guide to Quality Dispersion in Liquid Systems
Vehicle Selection■■■

Good wetting of both pigment and grind surfaces
Tack” to suit method, i.e., low tack in processes dependent on impact between particles, high tack in thosedependent on shear through liquid layer
Chemically compatible with pigment under processing conditions

Select pigment and additive loadings to provide proper flow for equipment use
Select let-down procedure to avoid seeding, gelling, or poor mix-in (e.g., viscosity adjustment with thinner,high shear mixing, stepwise reduction)

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Ti-Pure™

Titanium Dioxide

Bulk Flow Properties:

Figure 12

Bulk Handling Systems Can be Designed

Bulk Flow Behavior of Assorted Materials

The flowability of powders and other bulk materials is an
important, but poorly understood property. There are anumber of definitions of both flowability as a measured
parameter and also of what constitutes “good” or “bad”
flowability. An industry accustomed to handling polymer
pellets may consider all pigments to have poor flowability,
while producers and consumers of fine powders may
consider certain powders to have much worse flowability
than others.
Flowability can be defined as the ability of a powder’sinterparticle cohesive strength to resist gravitation forces
trying to cause it to move. For example, free-flowing glass
beads will not form an angle of repose if poured onto alevel surface. They will flow out on the surface, virtually asa liquid. The gravitational forces trying to pull each bead
downward are not significantly impaired by the various
forces that might act between the beads. Conversely, it

Bin Diameter
Rathole Forms

Fill Height

High Wall
Friction

Shallow Cone
Angle

12

TiO2

20
INCREASING DIFFICULTY
Powder Sugar

TiO2

Maximum Fi for
Effective Silo Storage

15

10
DECREASING DIFFICULTY
Portland Cement

5
Flour

Limestone

Granular Sugar

0

Plastic Pellets

Materials Most Suitable For Bulk Storageis usually possible to form a very steep angle of repose
with many powders. In this case, the interparticle forces
generally exceed the gravitation forces, making theformation of stable piles (and flow obstructions in bins)
feasible. TiO2 manufacturers can influence the flowabilityof a grade by the organic and inorganic coatings applied
to the surface (see the Performance Properties section).
Material “piping,” otherwise referred to in the industry as“ratholes,” occurs when powder in a silo (or hopper) flows
from the area directly above the discharge outlet or
hopper section while material located near the walls of
the silo remains stagnant, see Figure 11.

Figure 11 Rathole Formation

D

Materials Highly Dependent on Mechanical Flow Aids
25

Flowability Index (FI)Dry titanium dioxide does not flow freely. It tends tobridge and rathole and cannot be considered to havea well-defined angle of repose. TiO2 handling is also
susceptible to environmental effects such as moistureabsorption, as well as handling history. In the customer’s
process, these effects are often viewed as erratic or
random TiO2 handling performance.

Material hang-up is due to significant resistance fromthe stresses imposed by the silo walls. These stagnant
zones usually remain in place until external forces, suchas vibration or other sources of mechanical intervention,
are applied. The degree to which TiO2 forms “ratholes” will
depend on the specific grade and the silo-bin geometry.
If a poor flowing material with unfamiliar handlingcharacteristics is stored in a bulk system without priorflowability testing, it is not always possible to discharge
the material. However, there are simplified methods todetermine the “flowability” of a material in order to predicthandling characteristics. Figure 12 illustrates the relative
ease of material flowability as a function of a measured
flowability index (FI). The higher the FI, the more difficult
the material will be to discharge from a standard silo orbulk storage unit.

Ti-Pure™

Titanium Dioxide

The FI values for pigmentary TiO2 generally range
between 10 and 20. In addition to the flow characteristics
of a particular material, the ability to discharge a material
will depend in part on the specific storage system design.
Experience has shown that the TiO2 grades located in theregion above the line in Figure 12 generally do not handle
well, unless the system is equipped with well-designed
external mechanical flow aids. In addition, handlingdifficulty increases greatly for TiO2 at the high end of the
FI range.

Figure 14

The FI of titanium dioxide is also sensitive toenvironmental effects such as absorbed moisture.
Therefore, it is not uncommon for the handling difficulty
to increase as ambient conditions fluctuate from dry
to humid. The degree of sensitivity to environmental
moisture will depend on the grade, because each grade
has varying surface treatments. Figure 13 illustrates
how the FI relates to handling behavior as a function of
humidity.

Figure 13
Generalized Response Surface of Powder Handling

External Flow Aids
NeededSilo Storage
Not Recommended

Typical Silo Storage

Maximum

Flowability IndFI For S

ex (FI)

ilo Stora

ge

ca

i
Typ

ure
oist

M

ity

mid

t Hu

ien

b
l Am

ion

orpt

Abs

Handling Difficulty

Environmental
Control
NeededEffect of Humidity on Flowability Index (FI)15

Flowability Index (FI)14

Region of increasing handling difficulty

TiO2

13

12

11

Dried at 120 °C

Exposed to 40% RH

Exposed to 95% RH

Exposure Condition

Figure 14 shows an example of this behavior for a typicalgeneral-purpose grade of titanium dioxide. After drying,
the product has an FI of 12.6, but after exposure for 24
hr to 40% relative humidity, the FI increases to 13.1.
Finally, after exposure for 24 hr to 95% relative humidity,
the FI increased to 13.8. This example shows how a gradethat normally flows from hoppers in dry conditions could
convert into the “difficult to handle” zone upon exposure
to high humidity.
Despite the problems illustrated, robust, reliable
systems for handling dry bulk TiO2 can be designed. It
is recommended that your Ti-Pure representative becontacted for assistance relating to handling problems
with TiO2 and/or design questions relating to TiO2
handling equipment. Often, powder handling equipmentvendors may not have experience with the peculiarities
of TiO2 handling. It is therefore recommended thatwhen considering a particular design for TiO2 handlingequipment that the vendor(s) be requested to supply
the names of contacts who have used the system for atleast one year. The equipment should have been operated
under similar constraints as your process, in terms of size,
conveying distance, etc., as well as operating with similar
grades of TiO2.

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Ti-Pure™

Titanium Dioxide

Manufacturing Process

to obtain titanium tetrachloride and metal chloride
impurities, which are subsequently separated. Highly
purified TiCl4 is then oxidized at a high temperature to
produce intermediate TiO2 of excellent brightness. The
oxidation step in the chloride process permits close
control of particle size distribution and crystal type,making it possible to produce TiO2 with high hiding power
and tinting strength.

Chemours uses the Chloride Process
to Make Titanium Dioxide
Titanium dioxide pigments are made by two commercial
processes: sulfate and chloride. Rutile pigment can bemade by either process, while anatase can only be madeby the sulfate process. Chemours operates only chloride
process plants.
The flow charts in Figure 15 illustrate in simplified
form the two processing routes to intermediate TiO2
products. The lower part of Figure 15 illus­trates finishing
operations, which may be similar for either manufacturingmethod. The sulfate method was commercialized in
1931, producing anatase TiO2 and later (1941) rutile
TiO2. In this process, ore containing titanium is dissolvedin sulfuric acid, yielding a solution of titanium, iron,and other metal sulfates. Then the pigmentary-size
intermediate TiO2 is produced through a series of steps
including chemical reduction, purification, precipitation,
washing, and calcination. The crystal structure, anatase or
rutile, is controlled by nucleation and calcination.

FeTiO3 + 2H2SO4 ➝ TiOSO4 + FeSO4 + 2H2O TiOSO4 +H2O ➝ TiO2 + H2SO4

The chloride method was developed and commercialized
by DuPont in 1948 to produce rutile TiO2. This process
is now owned by Chemours and includes two hightemperature, anhydrous vapor-phase reactions. Titanium
ore is reacted with chlorine gas under reducing conditions

14

2FeTiO3 +7Cl2 + 3C ➝ 2TiCl4 + 2FeCl3 + 3CO2 TiCl4 +O2 ➝TiO2 + 2Cl2

In both sulfate and chloride processes, the intermediate
products are clusters of pigmentary-size TiO2 crystals
that must be separated (ground) for optimum optical
performance. Depending on end-use requirements,
various processing methods are used to modify the
TiO2, including precipitation of hydrous oxides of silicon,
aluminum, or zinc on the pigment particle surface.
Individual hydrous or anhydrous oxide treatments
or various combinations can be used to optimize
performance for specific applications. Organic additives
also can be applied by various methods to enhance
specific performance attributes of the pigment.
Crucial to the manufacture of titanium dioxide pigments isthe supply of titanium ore. Although titanium ranks among
the top 10 elements in abundance, it is widely distributed
in nature at low concentrations. Efficient mining andmineral processing operations are required to develop a
viable ore supply to meet the economic requirements ofTiO2 manufacture.

Titanium Dioxide

Ti-Pure™

Figure 15
TiO2 Manufacturing Process

SulfateTitanium Ore/H2SO4

Solution

Crystallization

Precipitation

Filtration &Washing

Calcination

Intermediate TiO2

FerrousSulfate Crystals

Chloride
Titanium Ore/Chlorine/Carbon

Chlorination

Purification

Oxidation

Chlorides ofmetals otherthan Titanium

OxygenIntermediate TiO2

FinishingIntermediate TiO2

Surface
Modification

Filtration
Washing & Drying

Grinding

Slurry Makeup

PackingFinished
Slurry Storage

Loading &Shipping

Additives

15

Ti-Pure™

Titanium Dioxide

Quality Control
Chemours is committed to maintaining a leadership
position in product quality and uniformity. Ti-Pure™
titanium dioxide pigments are routinely tested forproperties that are appro­priate for the intended
application of the product. The results of the quality
testing are collected and reported using SAP tools. The
testing can include color, tinting strength, undertone,
pH, resistance, screen-pack testing, acid solubility, nujol
yellowing, and low shear dispersion. Brief descriptions ofthese tests are provided in this section.
Color
Three filter reflectance measurements are made oncompressed dry TiO2. These reflectance measurements
are then used to calculate TiO2 L*, a*, b* color.
Tinting Strength and Undertone
Gray medium-hard vinyl exhibits are prepared on a two-rollmill. Three filter reflectance readings on the exhibits froma colorimeter are then used to calculate relative tinting
strength and undertone.
pH
The pH of a 5:1 water:TiO2 slurry is measured as astandard quality control parameter. Product pH is known
to affect performance properties in liquid systems suchas surfactant demand and flocculation.
Resistance
Conductance measurements are used to determine
the resistance of 5:1 water:TiO2 slurries, reflecting thesoluble salt content of the pigment.

16

Screen-pack Testing
50% TiO2 concentrates in low-density polyethylene
are prepared in a Banbury mixer. A given amount of
this concentrate is then extruded through a series ofscreens; performance is rated based on the amountof TiO2 retained on a 500-mesh screen following
extrusion. For R-350, more stringent testing is done
as a 70% concentrate.
Acid Solubility
For grades R-105 and R-960, acid solubility can becorrelated to the degree of surface silica coverage andfurther extrapolated to the durability of the productin an end-use application such as vinyl siding or
window profile. A sample of the pigment is mixed withsulfuric acid and heated for a specified time period. An
indicator is used to determine the amount of TiO2 thatis dissolved by the acid.
Nujol Yellowing
Dry TiO2 is dispersed in an oil containing hinderedamine light stabilizer and phenolic antioxidant. The
mixture is exposed to UV light and measured for rateof yellowing as delta b* color.
Low Shear Dispersion
Dry TiO2 is dispersed in a paint formulation at relatively
low shear. The degree of dispersion is measured using
a draw-down gauge block. (This test is only used on
grades like R-960 which are sold predominantly topaint applications.)

Ti-Pure™

Titanium Dioxide

Product Stewardship
Chemours defines Product Stewardship as: “Anintegrated business process for identifying, managing,
and reducing safety, health, and environmental
risk throughout all stages of a product’s life in thebest interest of our four stakeholders: customers,
employees, shareholders, and society.”
Chemours places high value on Product Stewardshipas a vehicle to differentiate our products and services.
We firmly believe that proactive product management
results in improved product performance and is
responsible business management that positively
affects our stakeholders.
The objectives of our Product Stewardship program
are to use our understanding of our products toprotect our customers, employees, the community,
and the public; to anticipate and respond to societal
expectations and requirements; and to minimize
resource and energy consumption (the environmental“footprint” of our products).
In order to provide assistance to customers inachieving your Product Stewardship objective,
we offer the following information:
FDA Status
Ti-Pure™ grades R-101, R-103, R-104, R-105,
R-108, R-350, and R-960 are acceptable for FDA
indirect food contact uses under 21 CFR 178.3297(Colorants for Polymers). Ti-Pure™ grades R-103,
R-104, R-108 and R-350 are acceptable up to
25 wt% maximum loading of TiO2 to polymer content.
R-101, R-105 and R-960 have no loading limitations.
NSF Status
Ti-Pure™ titanium dioxide grades for polymers R-101,
R-103, and R-105 have been certified as acceptablefor use in potable water piping. NSF certification
allows these grades to be interchanged in approved
pipe compounds at loadings up to 5.0 phr (parts per
hundred resin). For information on other grades,
contact your Ti-Pure™ representative.
SDS
For safety information, please visit the product Safety
Data Sheet (SDS) on our Chemours website or they
can be obtained from your customer service or sales
representative.

17

The information set forth herein is furnishedfree of charge and based on technical datathat Chemours believes to be reliable. It is
intended for use by persons having technicalskill, at their own risk. Because conditionsof use are outside our control, we makeno warranties, express or implied, andassume no liability in connection with any
use of this information. Nothing herein is tobe taken as license to operate under or arecommendation to infringe any patents.
For more information, visit www.titanium.chemours.com© 2023 The Chemours Company FC, LLC. Ti-Pure™ and any associated logos are trademarks or copyrights of The Chemours Company FC, LLC.
Chemours™ and the Chemours Logo are trademarks of The Chemours Company.
Replaces: H-88382-8
C-10434 (1/18)