Chemistry Reference
In-Depth Information
Table 7.5 Processing conditions for the injection moulding of SFOC-based
materials.
Operating
Conditions
Synthetic polymers
SFOC-based pellets
d
n
9
r
3
n
g
|
5
Screw L/D
High (28) for heat-resistant
polymers and low (18) for
heat sensitive polymers
Low (20) to decrease residency
time
Compression
ratio (t
c
)
Between 2 and 2.8 for most
materials, high for powders
Between 1.8 and 2 as agropellets
are dense and heat sensitive
(self-heating and degassing)
d
y
y
f
n
n
3
.
Screw speed
Depending on applications
Average to avoid self-heating
Screw
backpressure
Between 3.5 and 21 bar, high
for viscous materials
Between 10 and 20 bar to avoid
water vapour degassing voids
Injection speed
High to improve pace and
decrease material viscosity
Low to control injection pressure
Injection pressure
Low (hundred of bar)
High as materials are more
viscous (1500-2000 bar)
Table 7.6
Injection moulding conditions and mechanical properties in tension
(s
t
: stress at break, E
y
: Young modulus ) and bending (s
f
: stress
at break, E
f
: bending modulus) of SFOC, ESFOC and ESTOC
moulded specimens.
57
SFOC
ESFOC
ESTOC
Moisture Content (%)
30
25
20
T
max
barrel (1C)
50
120
130
T mould (1C)
100
room
room
Average density
1.09
1.20
1.34
Flexural properties
s
max
(MPa)
5
11.1
1.4
37.0
3.2
E
f
(GPa)
0.73
1.8
0.3
3.4
0.3
Tensile properties
s
max
(MPa)
3.4
0.4
9.8
1.2
12.5
2.7
E
y
(GPa)
0.23
0.02
2.0
0.1
2.0
0.1
Teflon
s
mould
cavity
Teflon
s
mould
cavity
Remarks
Without backflow
stop valve
consequently water evaporation. Materials obtained from injection moulding
of the SFOC were fragile and needed to be handled with care (Table 7.6).
Thermomechanical and chemical treatments improve the flow behaviour of
the SFOC (Figure 7.13) and hence, the amount of water necessary for forming
decreases. Moulded materials from the ESTOC are denser and more resistant
than those obtained from SFOC and ESFOC (Table 7.6). In addition, they
could be formed in normal conditions used for the injection of thermoplastic
materials, with the backflow stop valve.
The mechanical characteristics of SFOC-based materials, tensile and flexural
stress at break values, respectively 12.5MPa and 37MPa, are slightly lower than
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