processing

Resin Drying
Sulfone polymers will absorb moisture, and although they
are hydrolytically stable, they should be dried before processing.
Processing wet resin will result in cosmetic
defects, such as surface streaks or splay marks on injection
molded parts and severe bubbling or streaking in
extruded profiles. The moisture does not hydrolyze the
polymer or degrade its properties. Parts formed from
undried resin are only unsatisfactory in appearance, or in
some cases weak due to formation of internal bubbles.
Any parts unsatisfactory due to these cosmetic defects
can be reground, dried, and then remolded without loss of
properties.
Sulfone polymer pellets can be dried in a circulating hot
air oven or in a dehumidifying hopper dryer.
Recommended drying times and temperatures for UDEL
polysulfone are: 2 hours at 163°C (325°F), or 3 hours at
149°C (300°F), or 4 hours at 135°C (275°F).
Figure 1
Drying UDEL Polysulfone
Figure 2
Drying RADEL A Polyethersulfone
Recommended drying times and temperatures for RADEL
resins are: 3 hours at 177°C (350°F), or 4 hours at 150°C
(300°F), or 5 hours at 135°C (275°F).
The desired moisture content for injection molding is
below 500 ppm (0.05%) and for extrusion below 100
ppm (0.01%). Hopper drying requires sufficient insulation
and minimal system leakage. Inlet air temperature must
be high enough to maintain a polymer pellet temperature
of at least 135°C (275°F), and the dew point of the inlet
air should be -40°C (-40°F). These conditions must be
sustained long enough for the polymer moisture content
to drop to below the minimum levels suggested for the
processing technique to be used.
Figure 3
Drying RADEL R Polyphenylsulfone
Drying below 135°C (275°F) is not recommended
because drying times would be excessive. The drying
conditions suggested represent minimums because
sulfone polymers cannot be over-dried In fact, they can
be held at 135°C (275°F) for up to a week without harm.
Drying curves for UDEL and RADEL resins are shown in
Figures 1- 3.
4 Solvay Advanced Polymers