Page 461 - Handbook of Properties of Textile and Technical Fibres

434 Handbook of Properties of Textile and Technical Fibres

70 KI
Glass transition temperature T g (°C) 50 KS KG KA

60

40

30

0 5 10 15 20
Comonomer content (%)
Figure 13.6 Schematic influence of various comonomers on the T g (KA-adipic acid,
KI-isophthalic acid, KS-sulfoisophthalic acid, KG-glutaric acid).

Marcin cin and Romanov (1975) described an empirical relationship between the T g
of copolymers and the CED. Most of the modification components cause chain irreg-
ularities (reduction of the CED) and introduce flexible groups to the chains. The
mobility of polymer chains is generally increased by the presence of ether links e
CH 2 eOeCH 2 (Mark, 1965).
On the other hand, the mobility of chains is heavily restricted by the presence of
voluminous side groups. Still more distinct is the effect of polar side groups (Militký
et al., 1991).
The glass transition temperature is also influenced by structural fiber parameters and
relative molecular polymer masses. An increase in relative molecular mass is accom-
panied by a hyperbolic increase in T g . The effect of the growth of crystallinity is more
sophisticated. At low proportions of the crystalline phase (below 30%) in PET a great
number of small crystallites are formed and restrict the mobility of chains. This is
accompanied by an increase in T g . As soon as the amount of the crystalline phase ex-
ceeds a certain limit large crystallites begin to be formed. Owing to their relatively low
number the chain mobility is less affected and T g decreases. In statistical copolymers
the relation of T g to the composition is generally not linear but it passes through a
maximum or a minimum.
In copolyesters, the relative number of the rigid benzene rings has a major influence
on T g . A modification replacing TPA will therefore reduce the T g value much more
markedly than modification replacing ethylene glycol. With a growing number of
methylene groups in the polyalkylene terephthalate chains, T g will show a more or
less hyperbolic decrease (Ward and Wilding, 1976). In a block polymer containing
PEG, the decrease in T g due to the increase of the modification component content
is relatively small (Van Krevelen, 1990).
The nonsymmetric modification components are represented by sodium salt of 5-
sulfoisophthalic acid and isophthalic acid. A sodium salt of 5-sulfoisophthalic acid