Enhanced Fire Safety
Additives can improve the flame resistance of many plastics. However, they often also complicate processing. With GENIOPLAST® Pellet S, WACKER has developed a silicone additive that not only reinforces the effect of certain flame-retardant fillers in polyolefin compounds, but also makes extrusion easier. This twofold advantage enhances the production of thermoplastic compounds as used in cable sheathing and in aluminum composite panels for building construction and the automotive sector.
A contradiction that is difficult to solve: although safety is one of our basic needs, we generally want to notice very little or nothing at all of the things that provide a secure environment. Safety should be a given and, ideally, invisible. Take fire safety as an example. Fire extinguishers, smoke detectors and sprinkler systems convey a sense of security when we see them. However, when we are surrounded by a large number of protective devices, we are reminded of potential danger and feel less safe.
Fire safety is not the only requirement that needs to be met in building construction. Energy, design and economical aspects also play a key role and must be harmonized. In modern building construction, aluminum composite panels have become an established component of facade design. Their advantages are obvious: they are easy to transport and work with; with the appropriate outer coatings, they can produce virtually any design; they withstand adverse weather conditions and, with an adequate insulation layer, they contribute to thermal insulation.
However, this is where a particular challenge has presented itself. In order to ensure that the aluminum panels do not act as a cold bridge and contribute to the cooling of the building, a plastic layer is inserted between two aluminum layers, sandwich-like, for insulation. It thermally separates the two outer panels from one another. Polyethylene is typically used here. Unfortunately, it is flammable. To ensure that the panel’s fire-safety characteristics do not suffer as a result, fire-retardant fillers such as aluminum and magnesium hydroxide are incorporated.
“They can account for up to 70 percent of the content,” says Dr. Klaus Pohmer, Director Global Business Development at Wacker Chemie AG’s Performance Silicones business unit. “These kinds of highly filled polymers are more difficult to process,” he explains. The pressures at which the compound – such as a blend of polyethylene and aluminum hydroxide in this case – is mixed in the extruder, and then expelled, increase. Not only the machine’s electricity consumption shoots up as a result. The thermal stress on the compound also rises so much that some of the aluminum hydroxide decomposes. Furthermore, there is die drool at the extruder head – material deposits at the edge of the die unchecked.
Modern Facades that Feature Aluminum Composite Panels
These problems can be solved, however. Compounds find application in almost all areas. They are used wherever well-known, pure plastics do not possess the desired properties. Instead of the elaborate development of new, specialized plastics, it is preferable to alter established materials such as polyethylene and polypropylene with fillers and additives to suit the application. The desired result can generally be obtained more quickly in this way. Plastics that, for example, feature optimized light fastness, surface properties, physical and chemical stability, or flame retardancy are the result.
The additives that are used are simple materials such as chalk and talc, as well as complex organic compounds. Silicones are also gaining in importance – they improve the material’s processing properties, in particular. Furthermore, they reduce friction and thus simplify the processing of thermoplastics, for example. Compared to organic additives with a similar effect, they are thermally stable.
Pelletized silicone additive GENIOPLAST® Pellet S with a silicone content of 70 percent.
With GENIOPLAST® Pellet S, WACKER has developed a silicone additive that can be incorporated into a diverse range of polymer compounds with very little effort. It consists of a pelletized, highly concentrated silicone polymer formulation with a silicone content of 70 percent. A pyrogenic silica, whose properties are tailored to the polydimethylsiloxane used, serves as the carrier.
It is processed by simply adding it to the base polymer in a twin-screw extruder or a co-kneader, followed by extrusion. Pyrogenic silica ensures that the additive is compatible with all thermoplastics and thermoplastic elastomers.
In highly filled, flame-retardant compounds, GENIOPLAST® Pellet S simplifies processing, even at dosages of less than one percent. With the addition of one to three percent, the surface properties and fire-safety effects of respective plastics improve as well. In extensive tests, WACKER was thus able to verify two highly desirable properties.
In polyolefin compounds that contain flame-retardant fillers, GENIOPLAST® Pellet S ensures that less heat is released in the case of a fire, so the fire is not additionally stirred up and harmful smoke formation is reduced.
Compounds containing GENIOPLAST® release less heat on combustion than plastics that do not contain the silicone additive.
Cone calorimetry – an important test method for fire performance – shows that when a compound containing GENIOPLAST® Pellet S combusts, the heat release is spread out over a longer period of time, the peak value of heat development is lowered, the overall heat output is reduced and less smoke is formed. The reason behind this is the more compact and less brittle ash. It deposits on the burning material as a crust.
The combustion residue of compounds containing GENIOPLAST® Pellet S hinders oxygen transport and heat transfer. Both effects counteract the rapid spreading of fire.
Dr. Klaus Pohmer, Director Global Business Development Performance Silicones
GENIOPLAST® Pellet S thus superbly reinforces the effect of flame-retardant fillers such as aluminum hydroxide. This, especially combined with the fact that it simplifies processing, makes it an ideal additive for highly filled polymers that aim to restrict the effects of fires. These are two real advantages – one increases efficiency in production, the other can save lives. Plus, incorporated into aluminum composite panels, GENIOPLAST® Pellet S makes fire safety invisible.