Blends and Additives - Fundamentals of Industrial Chemistry: Pharmaceuticals, Polymers, and Business - page 159

additives are those that are used in a wet environment such as in the bathroom
or pool liners. Inorganic antimicrobial agents can be used. Silver ions are
effective antimicrobial agents and can be encapsulated to provide controlled
release into the polymer matrix [26]. Organic antibacterial additives can also
be used. Examples include triclosan and salts of the biguanide, chlorhexidine.

Cl OH Cl

NH NH

H
N

H
N

H
N

O

H H H

NH NH

Cl Cl

Cl

triclosan chlorhexidine

A typical plastic formulation might contain two or three polymers and five
or six additives. During processing the formulation is often heated to high
temperatures and thoroughly mixed during extrusion. Chemical reactions can
take place and need to be considered by the formulator. When thinking of
polymers, we often focus on the repeat units, but they have end groups. For
example, a polyester can end in a carboxylic acid end group or in an alcohol
end group. The polyester then might have three functional groups; ester, alco-
hol, and carboxylic acid as well as residual catalyst. Any of these can react
with other functional groups present in other polymers or with additives. It
is common for additives to react with other additives. For example, antimony
oxide, present either as a residual catalyst or as a flame retardant additive, can
react with a phosphite antioxidant additive and cause a black color. When
this is a problem thioesters are used as secondary antioxidants instead of
phosphites. Sometimes the additives can have a deleterious effect on aging
properties. Other additives may bloom to the surface and cause poor adhe-
sion in secondary operations such as painting. Proper selection of additives
requires consideration about the end-use applications and an understanding
of possible interactions with other ingredients in the formulation.

QUESTIONS

1. A miscible blend always
a. has a single Tg
b. has two Tgs
c. has a melting point and a Tg
d. has two melting points
2. This word is used to describe a situation where the combination is
greater than the sum of the parts, for example when the combination of