Polimeros

DuPont™ Ti-Pure

®

TITANIUM DIOXIDE

POLYMERS, LIGHT AND THE SCIENCE OF TiO2

CONTENTS

L ight-Scattering Properties

2

Optical Properties

5

Dispersion in Plastics

6

Bulk Flow Properties

10

Manufacturing Process

12

E-Business Philosophy

14

Quality Control

14

Product Stewardship

15

Safety Precautions

15

TiTanium DioxiDe (TiO2) isa multifaceted material when used in polymer
applications. It has been long established as the leading white pigment, and
this is the application that people are most familiar with. However, titanium
dioxide brings more to the polymer 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. Forexample, this interaction can be
the familiar scattering that results in opacity or it could be the absorption
of UV light energy, thereby protecting the polymer from UV degradation.
Applications continue to develop, all based on the interaction of the
titanium dioxide particle with light.

As other applications for titanium dioxide
have developed, its pigmentary properties
remain themost important. Titanium
dioxide is the most important white
pigment used in the polymer industry.
It is widely used, because it efficiently
scatters visible light, thereby imparting
whiteness, brightness, and opacity when
incorporated into a plastic product. It is
chemically inert, insoluble in polymers,
and heat stable under the harshest of
processing conditions. Titanium dioxide
iscommercially available in two crystal
forms—anatase and rutile. The rutile
pigments are preferred over anatase
pigments, because they scatter light
more efficiently, are more stable, and are
less likely to catalyze photodegradation.

Few, if any, commercial grades of
titanium dioxide are pure TiO2. Most
have inorganic and, in some cases,
organic treatments deposited on
the surfaces of theTiO2 particles by
precipitation, mechanical blending,
or via other routes. These surface
treatments provide improvements in
one or more performance properties of
the pigment, such as ease of dispersion,
weatherability, or discoloration resistance.
A single prescription for surface
treatment does not produce a pigment
having maximum value-in-use for all
plastics applications, and it is acontinuing
research goal to develop titanium dioxide
grades to meet the changing needs of the
plastics industry.



LIGHT-SCATTERING PROPERTIES: TITANIuM DIOxIDE PROvIDES OPACITY BY SCATTERING LIGHT

Unlike colored pigments that provide
opacity by absorbing visible light, titanium
dioxide and other white pigments provide
opacity by scattering light. This scattering
is possible becausethe white pigment
can bend light. If there is enough pigment
in a system, all light striking the surface,
except for the small amount absorbed by
the polymer or pigment, will be scattered
outward, and the system will appear
opaque and white. Light scattering is
accomplished by refraction and diffraction
of light as it passes through or near
pigment particles.

HIGH R.I. TiO2

LOWR.I. PIGMENT

Figure 2a. Path HIGH in White Film (both films completely opaque) R.I.
of Light R.I. TiO
LOW

2

PIGMENT

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 high refractive
indexpigment than through the low
refractive index polymer in which it is
dispersed.

HIGH R.I. TiO2

LOW R.I. PIGMENT
HIGH R.I. TiO2

Figure 2b. Path of Light in White Film (film on right not opaque)

Figure 2 schematically depicts a crosssection of two white-pigmented films
and how differences in pigment refractive
index affect opacity. In the film containing
a high refractive index...