Additives flame retardant trends

J. Murphy, Flame retardants Trends and new developments. Plastics Additives and Compounding, 3 (2001), 16-20. 

Incorporation of modified clays into thermosetting resins, and particularly in epoxy35 or unsaturated polyester resins, in order to improve thermal stability or flame retardancy, has been reported.36 A thermogravimetric study of polyester-clay nanocomposites has shown that addition of nanoclays lowers the decomposition temperature and thermal stability of a standard resin up to 600°C. But, above this temperature, the trend is reversed in a region where a charring residue is formed. Char formation seems not as important as compared with other polymer-clay nanocomposite structures. Nazare et al.37 have studied the combination of APP and ammonium-modified MMT (Cloisite 10A, 15A, 25A, and 30B). The diluent used for polyester resin was methyl methacrylate (MMA). The... 

After PVC, polyolefin copolymers, predominantly polyethylene copolymers, are the next most widely used material for FR applications in wire and cable. Polyethylenes have very good dielectric strength, volume resistivity, mechanical strength, low temperature flexibility, and water resistance. In contrast to PVC, polyolefins are not inherently FR and thus are more highly formulated, requiring the addition of FRs to meet market requirements for flame retardancy. For this reason, and because of the steady global trend toward halogen-free materials for wire and cable applications, more space will be devoted to this section on FR polyolefins compared with the above discussion of PVC. 

As discussed in Chapter 2, BFRs have been used as additive and reactive flame retardants in myriad materials and products for over 30 years because of their effectiveness and low cost (Alcock and Busby, 2006). Similarly to PCBs, some BFRs, notably PBDEs, are widely dispersed in our environment and food supplies (e.g. Lorber, 2008 Pozo et ah, 2006 Ross et al, 2009). Again, we use our concepmal model presented in Figure 8.1 to interpret temporal trends in concentrations and exposure. We also use it to discuss the role and effectiveness of pohcies and legislative controls. We focus our discussion on PBDEs for which most is known, with some information on HBCD and TBBPA and newer BFRs such as bis(2,4,6-tribromophenoxy)ethane, or BTBPE, and (2-ethylhexyl)tetrabromophtha-late, or TBPH (Stapleton et al, 2008 Kolic et al, 2009). We use the quotation marks for newer because at least some of these BFRs have been in the marketplace for decades but have seen revived use as countries have banned penta- and octa-BDE and, most recently, deca-BDE (e.g. Alcock and Busby, 2006 Hoh et al, 2006 Stapleton et al, 2008). 

This chapter overviews the various types of flame retardants that are added to POs. The chapter s content is influenced by recent trends in FR use, and it often focuses more on PP, given the market s needs for better FR solutions for this resin in particular. At the end of the chapter, a few case studies will illustrate recent developments in flame-suppressing additives. 

The same trend is observed for the specific heat capacity. The intensity of the change in specific heat capacity (A is associated with T. Specific heat capacity of control PU is 1392 J/kg-K. Specific heat capacity of the PU composite increased by 5.8 % when 2% FR is added. However, specific heat capacity of FR-filled PU composites decreased by 3.5% and 14% when 4% and 6% FR respectively are added. A significant drop in specific heat capacity (A C ) is observed when more flame retardant is introduced to PU composites, therefore gradual and Unear reduction ocoured according to addition of FR (Sarier Onder 2007). 

EnvirOTimental trends are having an impact on electrical applications. Waste legislation includes WEEE (Waste of Electrical and Electronic Equipment) directive 2002/%/EC which holds producers responsible for collection and recovery of materials at end of Ufe. Additionally, materials that contain bromine-based flame retardants must be removed from the waste and handled separately. In restrictions on use of hazardous substances (ROHS) directive 2002/95/EC, the use of various hazardous materials is restricted. These include lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ether. Since the introduction of Blue Angel in Germany in 1978, several other eco-labels have been implemented. These include TCO (Sweden), Nordic Swan, Milieukeur (Netherlands), and the EU Ecolabel. The general purpose of these labels is to provide cmisumers with information relating to the environmental impact of the products they purchase. 

Additive products have been improved, and several completely new products have been marketed. Individual polymers such as PVC and polypropylene have undergone changes in relative importance and market share. New health and safety eonsiderations and regulatory pressines have had major effects on the sales of eertain additives, espeeially heat stabilisers, brominated flame retardants and plastieisers. The trend towards reoyeling is afleeting additive selection. 

Flame-retardant grades of PBT usually consist of synergistic mixtures of antimony trioxide with various halogenated (brominated) aromatic compounds. A typical recipe for PBT might be 10 wt% decabromodiphenyl oxide and 5 wt% antimony oxide. Recently the trend has been to use polymeric or oligomeric brominated additives. A typical additive is an end-capped polycarbonate derived from tetrabromobisphenol-A [94334-64-2] another is a mixture of epoxy oligomers derived from the diglycidyl ether of tetrabromobisphenol-A [68928-70-1]. The brominated polystyrenes (Zoc. cit.) have only limited usefulness in PBT as they have a low melt compatibility (107). 

The polymer performance and production efficiency can be enhanced as a function of the basic features of the reinforcement fillers. In the attempt to achieve fillers with increased performance, the following features must be monitored density, flame retardancy, mechanical resistance, thermal conductivity, and magnetic properties. Nanoparticles of carbides, nitrides, and carbonitrides can be used to reinforce polymer matrix nanocomposites with desirable thermal conductivity. However, current trends in the design of these materials reveal that is not enough to choose a wellperforming material for each component of the heat dissipation path. In addition, careful attention must be paid to the manner in which these materials interact with each other. A filler that conducts heat well but does not wet the matrix may lead to poor results compared to a lower conductivity filler that does wet the matrix. In other words, a major fact that leads to interfacial resistance is faulty physical contact between filler and matrix, which primarily depends on surface wettability (Han and Fina2011). 

In the modern polymer industry, the various existing types of polymer flame retardants based on halogens (Cl, Br), heavy and transition metals (Zn, V, Pb, Sb) or phosphorus-organic compounds reduce the risk from pol3nner combustion and p5n olysis, but may present ecological issues. The overall use of halogenated flame retardants is still showing an upward trend, but the above concerns have started a search for more environmentally friendly polymer additives. As a result it is quite possible that the future available flame retardants will be more limited than in the past. 

It is concluded, therefore, that the combination of organoclay with oligomeric phosphate or bromine leads to an increase in thermal stability of both the modified clay and the corresponding polymer nanocomposite. The role of the flame retardant element is entirely different. The combination of a phosphate flame retardant with OMT enhances char formation. However, the addition of brominated flame retardant additives appears not to affect char formation. Thus, a general trend may not exist (i.e., in some cases bulk polymerization apparently gives enhanced thermal stability, whereas in others, melt blending may give a better result)." " ... 

Work in our own laboratories has shown, however, that in the presence of conventional flame retardants, nanoclays can promote additive and synergistic effects in PA6, PA6,6 Aims that have been used as models for respective fibers. This work has provided evidence that significant reductions in flame retardant additive concentrations may be achievable, as has been noted for other polymers in Section 11.3.1. Normally, minimal flame retardant additive contents of about 15 to 20% w/w are required, which are too high for inclusion in conventional synthetic fibers. This is because for fusible fiber-forming polymers snch as PA6, PA6,6, PET, and polypropylene, flame retardant property trends versns concentration are not linear but follow an S-shaped curve. " This phenomenon is believed to be a consequence of the need to generate a threshold char level having an extended coherence throughout the polymer. It follows that this will... 

Unique to flame retardant and fire-safe materials research is that fire safety codes and regulations drive the field more than any other phenomena. In addition, there are new trends, codes, and regulations which appear on the surface to have no relation to the flammability performance of materials, but are currently driving the field of flame retardant research. These codes, typically enviromnental in nature, can adversely affect fire safety for polymeric materials and, in turn, limit the existing flame retardant solutions that could yield acceptable fire safety. 

In light of the issues with natural clays, one likely trend is an increase in the use of synthetic clays, such as fiuorinated synthetic mica, magadiite, and layered double hydroxides (LDH). This last clay, since it has the potential to release water under fire conditions [much like Mg(OH)2 or Al(OH)3], may find even more use in flame retardant applications. Cost issues and limited sources for synthetic clays will slow the adaptation of these materials, so most of the work will probably be seen in the patent or open literature. More work will be seen for nanocomposites containing nanofillers, such as carbon nanotubes and nanofibers, and these will probably also be combined with additional fiame retardants. 

A trend that has already begun to arise is the use of multiple types of nanofillers in the same polymer to yield a multicomponent nanocomposite. Some workers have found that some types of nanofillers cannot bring all of the desired properties to the final material, so clays have been combined with multiwall carbon nanotubes to bring enhanced properties.The observation for most polymer additives is that they cannot be used for all applications in all polymers, and the same observation will surely be made about nanocomposites. A clay may be used to enhance the flammability performance, bnt it could also be combined with a conductive nanoflller to impart antistatic aspects or electrical conductivity in the final system. One potential way to look at the use of multiple nanoparticles is that each nanoparticle plays a complementary role in flammability reduction. For example, one could choose a clay for mass loss rate or fuel release reduction, but then use a colloidal particle to flu in the gaps between clay plates as the nanocomposite thermally decomposes. Perhaps even more useful, the colloidal particle could have catalytic or flame retardant properties that encourage... 

Unique materials in themselves, thermotropic LCPs are opening up many non-traditional design and functional possibilities. As will be discussed in more detail, the trend towards miniaturization in electrical/ electronic components places additional demands on the polymer s processability into complex, thin-walled forms, and is opening up a wide variety of applications. Coupled with good electrical properties and flame retardance, tailorable CTEs and excellent dimensional stabilities, thermotropic LCPs are being used in a diversity of final product shapes. 

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