CHAPTER 7Modifying Specific Propert

CHAPTER 7
Modifying Specific Properties: Appearance - Black and White
Pigmentation
Table 7.1 At a glance: white pigments
Function
Properties affected
Materials/characteristics
Disadvantages
New developments
White pigmentation, high reflectance; modification of other
colours, increased brightness
Appearance and surface; may also give higher UV protection to the
plastic, improved weather resistance: some mineral whites will
also improve mechanical properties
Titanium dioxide; zinc sulphide; blanc fixe; white calcites
Possible problems of handling in powder form, needing extra
ventilation: titanium dioxide can act as photocatalyst, unless
suitably treated
Improvement of presentation and dispersability:
high-performance masterbatches with other additives
7.1 Types of White Pigment
7.7.7 Titanium dioxide
Titanium dioxide (Ti02) is the most important white pigment used in the plastics
industry. It has a higher refractive index than any other white pigment and has
good chemical stability. It is also non-hazardous and possesses very good
dispersability and good thermal stability. There are two commercially useful
forms: rutile and anatase. Rutile has higher opacity and is considerably less
photocatalytically active than anatase. It also has a slightly higher refractive
index (2.70 as against 2.55), giving better light-scattering power. Rutile-type
Ti02 also accepts surface treatments more readily, bonding better than anatase.