Fire-retardant fillers, development

FIRE RETARDANT FILLERS. The next major fire retardant development resulted from the need for an acceptable fire retardant system for such new thermoplastics as polyethylene, polypropylene and nylon. The plasticizer approach of CP or the use of a reactive monomer were not applicable to these polymers because the crystallinity upon which their desirable properties were dependent were reduced or destroyed in the process of adding the fire retardant. Additionally, most halogen additives, such as CP, were thermally unstable at the high molding temperatures required. The introduction of inert fire retardant fillers in 1965 defined two novel approaches to fire retardant polymers. 

Other systems include the mixture of huntite and hydromagnesite which offers relatively good perfoimance. Also, new grades of clay have been developed to improve the resistance of jacketing where large additions of fire retarding fillers affect the electrical insulating properties. 

Lead bromide is used for developing images in photography as inorganic filler in fire-retardant plastics as a photopolymerization catalyst for acrylamide monomer and as a welding flux for welding aluminum or its alloys to other metals. 

Many variations of these processes exist with the aim of controlling particle surface area, shape, and purity these characteristics define the fire retarding performance of magnesium hydroxide fillers, especially in more demanding applications where processability and good mechanical properties are also important considerations. In more recent developments, nanosize magnesium hydroxide variants have also been produced. 

The sueeess of graphite in this applications shows that filler with plate like struetures should be considered when intumescent materials are being formulated. Reeent developments in intumescent paints show that performanee ean be improved if a layer of organic material is inserted between the layers of the plate like filler. The degradation of this material in the enclosed space increases the expansion rate and the retention of gas inside the degrading material. Based on this prinei-ple any plate like filler has the potential to be useful in an intumescent applieation. The eomposition of filler is also important. When clay was used as a filler in fire retardant applieations, it was found that some of its components interfere with the action of carbonization catalysts and detract from the overall performance of the system in terms of limiting oxygen index. ... 

The major roles of fillers in these applications is to provide reinforcement, fire retarding properties and to lower the cost. Development work on plastic materials is ongoing and the goal is to develop technology which is inexpensive but can perform under adverse conditions. These studies have intensified recently given the increased worldwide demand for new houses. China is an extreme example. It needs 100,000,000 houses to be built in the next five years. 

Manufacturers of various fillers continue studies on altemative systems. Most antimony oxide used as a fire retardant can be replaced by a combination of zinc borate without the loss of other properties (in some cases improvements are reported). Another option is to use the same filler systems which are used in polyethylene insulated cables and wires. These are based on magnesium hydroxide and aluminum hydroxide. These systems pcrfoim as flame retardants but require a high filler concentration which affects jacket resistance and mechanical performance. Recently, new coated grades have been developed which can be used at up to 65 wt% without the loss of properties or productivity (extrusion rates 2,500 m/min of cable are possible). ... 

Polypropylene (PP), for example, burns very easily and dripping is observed during its combustion. The use of virgin PP is thus limited when flammability properties are required. Several approaches have been developed to increase its fire-retardant properties. Hornsby [1] reviewed the approach of using classical fillers in PP to increase its fire-retardancy behaviour. With classical fillers, the main problem is the loading (typically between 40% and 60% of total mass), which directly affects the mechanical properties of the polymer. Another problem is that the filler must be treated to increase its interfacial adhesion with the matrix. 

In order to enhance the property of the HMA, some proper additives are used. Grigat Ernst et al. [91] developed a kind of PEA-based biodegradable HMA. The ester segments of the PEA used consist of oligo-esters with Mn=800- 1300 and 2 COOH end-groups obtained by melt condensation of diols with adipic acid and the amide segments are preferably obtained by reaction of these COOH end-groups with hexamethylene diisocyanate. The ordinary additives such as plasticizers, fire retardants, and/or fillers were mixed into the system. 

As part of a programme to develop improved activity tin-based fire-retardant systems, TTRl has patented a series of processes for producing novel additives, including Ultrafine ZHS/ZS pxjwders and coated fillers. ... 

---