Page 135 - Engineering Plastics Handbook

Acrylonitrile-Butadiene-Styrene (ABS) Resin 109

Preparation of mass polymerization ABS
The greatest difference between the ABS mass process and the HIPS mass
process is the presence or absence of acrylonitrile monomer, but in the two
processes there are many other similar points. See Fig. 6.4. Any other dif-
ferences between the two processes involve the method for removing reac-
tion heat, the radial and vertical mixing extent, the numbers of reactors,
etc. The reaction heat can be removed by means of boiling and reflux
cooling, heat-transfer surface, addition of low-temperature monomer and
solvent, etc.
The radial mixing plays a role in preventing the deviation of tempera-
ture and concentration in the reactors. Such deviation forms the layer on
the surface of the reactor wall, to adversely influence the removal of reac-
tion heat, and eventually influences the quality of products.
The polymerization reaction is initiated by dissolving polybutadiene
rubber in monomer. As mentioned above, rubber is ground and then
added. Together with this, a small amount of the solvent is introduced.
In general, ethyl benzene is used and introduced in the ratio below 5%
for the purpose of lowering the viscosity. This solution is introduced
into the high-temperature reactor to move the reaction forward. The
reaction heat is removed through the reactor jacket. In the phase inver-
sion step, stirring at a high shear rate is essential. At this step, the size
and distribution of rubber particles are determined. When the phase
inversion is completed, the reaction is continued in the matrix phase,
and the monomer present in rubber is reacted in the occlusion state. In

M M
M M M
M M
M
M
M M M M M
M M M M M M M M

TC-701 TC702 TC-703 TC-704

M M M M

M
M
M
M
M
M
Figure 6.4 Mass polymerization process of ABS.