Page 139 - Engineering Plastics Handbook

112 Engineering Plastics

stabilizer and to use an impact reinforcing agent such as chlorinated
polyethylene (CPE) to compensate for impact strength, because of the
weak thermal stability and impact strength.
1,2-Bis(tribromophenyl) ethane has the advantages of good impact
strength and excellent fluidity and thermal stability in preparing flame-
retardant ABS. In using this flame retardant for a long time, it is diffi-
cult to apply to a resin having black or dark color. The reason is because
this flame retardant migrates to the surface of a finished product.
Use of brominated epoxy oligomer is gradually increasing due to its
excellent weather resistance and heat resistance, and it is suitable for
preparing the heat-resistant flame-retardant ABS resin, since it is possi-
ble to prepare high heat resistance products according to their molecular
weights.
O ) is primarily
As the flame-retardant auxiliary, antimony trioxide (Sb 2 3
used, and it is added at the level of about 30% of the flame retardant to
obtain a synergistic effect. The synergistic effect of the halogen-antimony
flame-retardant system is very effective for improvement of the flame
resistance and therefore has been applied to most of the halogen flame
retardants and has been generalized. See Table 6.2.
Halogen released from combustion is reacted with antimony trioxide
to produce antimony trihalide having a high boiling point, which can be
retained in the state of a noncombustible gas due to its high boiling point
to exhibit a synergistic flame-retarding effect by blocking oxygen and
stabilizing a radical chain reaction.
To compensate for the lowering of impact strength caused by addition
of the flame retardant, auxiliary chlorinated polyethylene, having a
good compatibility with ABS resin and an excellent impact reinforcing
effect, is primarily used as the impact modifier. It is generally added at
the level of 3 to 5%, and one having a chlorine content of about 35% is
most widely used.
Asuitable amount of the amide and metal salt-based internal and exter-
nal lubricants is used to improve the processability of resin, and the antiox-
idant, stabilizer, and ultraviolet stabilizer are used to prevent thermal
degradation of resin in processing and lowering of thermal stability caused
by the flame retardant, and to improve weather resistance.

TABLE 6.2 Synergistic Flame-Retardant Mechanism with Halogen—Antimony
Sb 2 O 3 + 6HX → 2SbX 3 + 3H 2 O (when HX is much produced)
Sb 2 O 3 + 2HX → 2SbOX + H 2 O (when HX is less produced)
SbOX reaction mechanism:
Step 1: 5SbOX → Sb 4 O 5 X 2 (s) + SbX 3 (g)
Step 2: 4Sb 4 O 5 X 2 → 5Sb 3 O 4 X + SbX 3 (g)
Step 3: Sb 3 O 4 X → Sb 2 O 3 + SbX 3 (g)
Step 4: Sb 2 O 3 (s) → Sb 2 O 3 (l) (where X = Br, Cl)