Need of Additives for High Heat Polymers
Need of Additives for High Heat Polymers
Mass production markets, such as aerospace, automotive and electronics need an increasing balance of thermal, mechanical, electrical, optical and tribological properties for high-performance parts. Some specialty polymers used in these markets offer peak or long-time thermal resistance exceeding 250°C. To perform optimally, these polymers often need certain additives. It is these materials that help bring the superior properties of the polymers.
The selection of additives depends on:
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The type of polymers they will be added to, or
- The application for which they will be used
Appropriate selection helps develop value-added plastics with improved durability as well as other advantages. Additive can be particularly useful to improve the performance of high-temperature polymers.
The three of the most common types used with high-temperature polymers are:
Let's discuss the feature provided by each of these additives to high-temperature polymers in detail...
Flame Retardants
Flame Retardants
The most common commercially viable flame retardants for use with high temperature polymers include:
- Brominated and chlorinated types
- Phosphorous-based types, and
- Metallic oxides
While chlorinated and brominated materials are the most common flame retardants for commodity-type polymers, there are health concerns over certain bromine containing compounds. These concerns have lead to investigations of non-halogenated flame retardants for use with high temperature polymers.
There are two classes of non-halogenated flame retardants that can effectively be used with high temperature polymers. They are the phosphorous types or char formers and the metal oxides or endothermic types. Phosphorous-based flame retardants involve both organic and inorganic compounds. They include:
- Organic phosphate esters
- Phosphates
- Halogenated phosphorous compounds &
- Inorganic phosphorous-containing salts
Metal hydroxides are the most commonly used halogen-free flame retardant with high temperature polymers. Aluminum trihydrate is relatively low in cost and is found abundantly in nature. It forms aluminum oxide via an endothermic reaction that absorbs heat from the fire. The potential downside of using metal hydroxides is the high loading level that is required to achieve acceptable flame retardant features of the high temperature polymer. These high loading levels can negatively impact both the mechanical properties and the processability of the the high temperature polymer.
Fire Resistance: Lower FRs loading with Intumescent materials at the surface
A number of other chemistries can provide high temperature polymers with flame retardancy features. These include boron-containing compounds, melamine and ammonium sulfamate. Development work continues on new flame-retardant materials for use with high temperature polymers. These developments include the use of polymer-clay nanocomposites, which can be effective at low addition levels. Also, silica-based materials are being investigated as a way to form protective surface coatings during a fire.
Flame-retardant masterbatches are often custom formulated to match the molecular structure and melt viscosity of the base high temperature polymer. The appropriate flame retardant material is based on what type of flame retardant is allowed and what standard must be met. Also, it is necessary to know what mechanical properties are critical to the product. All of these features are very important in determining which flame retardant material is the optimum one for use with a particular high temperature polymer.
Related read: Get detailed knowledge on selecting the right flame retardants for a specific application
Antioxidants
Processing Aids
Processing Aids
The incompatibility of the processing aid with the high-temperature polymer can negatively impact the mechanical properties of the final part. This has led to recent efforts to improve the compatibility between the two materials. These attempts have focused on the incorporation of chemical functional groups into the fluoropolymer that can interact with the base high-temperature polymer. The type of high-temperature polymer being processed largely decides which chemical group to use.
The fluoropolymer gets coated on the walls of the extruder and the die
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The extruder back pressure gets reduced
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The reduction in pressure allows the high-temperature polymers to be processed at lower temperatures
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This reduces any degradation that occurs during processing of the polymer
Summarizing the activities on high-heat additives, it is clear that as the uses of these high-temperature polymer materials continue to expand, developments in additives will need to continue to address the stringent material requirements. It is only through such work that the performance of high-temperature polymers can be effectively optimized in a particular desired application.