Stereon™ 840A/842A
Plastics Modifier Applications & Processing
Stereon™’s excellent thermal stability and dispersion, along with numerous other characteristics, make it the right styrene butadiene for a variety of plastics modifications, including:
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tips for Stereon™.
Extra Impact Polystyrene
Stereon™ can be added in small amounts to either extrusion or molding grade
HIPS to produce a special alloy exhibiting extra high impact strength with
no serious loss of other physical properties such as tensile strength or
modulus.
Table
I and Table
II present the physical properties resulting from blending
5 and 10 parts of Stereon™ with extrusion and molding grade HIPS.
The productivity of such blends is increased as indicated by the increased
melt flow rate. The significant improvements in gloss should also be noted.
Flame Retardant High Impact Polystyrene
Additives required to produce flame retardancy in HIPS also seriously affect
impact resistance and toughness of the HIPS.
Stereon™ may be added in small amounts to regain these lost properties without
significantly reducing other properties. Table
III and Table
IV show the effects of Stereon™ at various levels in a typical
flame retardant formulation using antimony oxide and decabromodiphenyl oxide
(DBDPO) in extrusion grade and molding grade HIPS.
Comparing the first and the second columns in Table
III shows the effect of the flame retardant formulation on
the physical properties for extrusion grade HIPS. The most significant losses
are seen in yield tensile, ultimate tensile, elongation and impact. The
addition of only 2% Stereon™ regains much of the lost performance. The 7%
formulation shows that the room temperature impact values exceed the uncompounded
impact resin's performance.
Table
IV shows similar physical property improvement for flame retardant
molding grade HIPS.
Modification of General Purpose Polystyrene
Many applications do not require clarity, but they require a moderate improvement
in toughness and flexibility while maintaining high gloss. In addition,
recycled general purpose polystyrene frequently requires a moderate improvement
in toughness to achieve useful properties.
The data in Table
V show that while it is difficult to achieve a balance of properties
characteristic of impact polystyrene, Stereon™ may be added to general
purpose polystyrene to improve toughness and flexibility, while maintaining
adequate gloss.
Improved Stress Crack Resistance
Residual stress in polystyrene products leads to cracking when exposed to
fats and oils in food products. The addition of a small amount of Stereon™
helps to alleviate this problem as shown in Table
VI.
The effectiveness of Stereon™ is demonstrated in Table
VI. For example, the addition of 10% Stereon™ to general purpose
polystyrene resulted in a styrenic product exhibiting stress crack resistance
equivalent to or better than oriented polystyrene (OPS).
While the addition of Stereon™ reduces the visual transmission clarity of
general purpose polystyrene, surface contact clarity remains good. Thus,
Stereon™ blends are ideal for applications such as deli lids.
For those producers using impact grades of polystyrene, the addition of
10% Stereon™ will significantly improve the stress crack resistance.
Processing with Stereon™ 840A/842A
The same extrusion or molding conditions required to process straight polystyrene
are generally suitable for Stereon™ styrene butadiene blends with polystyrene.
However, maximum operating temperatures below 450°F are recommended for
optimum properties and performance. The Stereon™ melt flow rate is in the
range of most commercial grades of polystyrene, and therefore, simple pellet
blends are generally satisfactory for extrusion and for most injection molding
operations.
Stereon™ dispersion can be enhanced by increasing the extruder or molder
back pressure. Some molding operations and the manufacture of flame retardant
polystyrene parts require a precompounding step for adequate Stereon™
dispersion.
Extruders and injection molders should be purged with straight polystyrene
before shutdown and started up on straight polystyrene before beginning
Stereon™ blends.
Our Akron Technical Service Group
can help with your styrene butadiene formulating and development needs
– contact us now for details.
