Halogen-free polymer systems

In general, tin compounds do not exhibit flame-retardant properties in halogen-free polymer systems, unless the composition contains a high inorganic filler loading. However, tin additives often act as smoke suppressants in non-halogenated polymers. 

Recent studies have demonstrated that there are major advantages in using a combination of ATH and zinc borate in a variety of halogen-free polymer systems. 

In halogen-free PO systems, the zinc borate is recommended to be used in conjunction with ATH and/or Mg(OH)2 to achieve the most cost effective fire test performances. At a total loading of 80 150 phr, the weight ratio of ZB to ATH is normally in the range of 1 10 to 1 1. This combination can not only provide smoke reduction but can also form a porous ceramic residue, that is important thermal insulator for unburned polymer. The benefit of using the ZB and red phosphorous in halogen free PE insulator is illustrated in Table 4. 

Xie, R.C. and Qu, B.J. 2001. Expandable graphite systems for halogen-free flame-retarding of polyolefins. I. Flammability characterization and synergistic effect. Journal of Applied Polymer Science 80(8) 1181—1189. 

In polymer systems, positron chemistry can occur if the e+ is able to attach itself to a particular atom or group. Halogenated polymers, radicals and certain electron rich unsaturated structures have the capability of forming stable species of the form (e+,R ), with free positrons. These processes can lead to quenching and inhibition of Ps formation. 

Phosphine free catalysts and halogen-free reactions are known for the Heck reaction. Improvements on the palladium catalyst system are constantly being reported, including polymer-supported catalysts." °° The influence of the ligand has been examined." Efforts have been made to produce a homogeneous catalyst for the Heck reaction." The Heck reaction can be done in aq. media," ° in perfluori-nated solvents," in polyethylene glycol," ° in neat tricaprylmethylammonium... 

Less than 10% of the polyamide produced is made in a flame retardant version. The best system is composed of a combination of red phosphorus and zinc borate (see table above). The only drawback of this system is its color which is restricted to brick red or black. If other colors are required, ammonium polyphosphate is used either in combination with organic flame retardants or with antimony trioxide. It is possible to manufacture a very wide range of colors in the halogen free system. Some systems make use of the addition of novolac or melamine resins. For intumescent applications, ammonium polyphosphate, in combination with other components, is the most frequently used additive. Figure 13.6 shows that fillers such as calcium carbonate and talc (at certain range of concentrations) improve the effectiveness of ammonium polyphosphate. This is both unusual and important. It is unusual because, in most polymers, the addition of fillers has an opposite influence on the efficiency of ammonium polyphosphate and it is important because ammonium polyphosphate must be used in large concentrations (minimum 20%, typical 30%) in order to perform as a flame retardant. 

When butadiene and isoprene are polymerised on halogen-free ion-coordination catalytic systems on the basis of compounds of d-elements, polymers are obtained which contain... 

CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Elame retardant, filler in polymer systems, epoxy, EVA, PVA, PVdC, SBR, vinylidene chloride filler pigment in high whiteness papers flame retardant filler, TiOj extender in textile coatings Features Nonsmoking halogen-free 100% reflectance improved print-ability noncorrosive... 

The most important representative of the antimony flame-retardants is antimony trioxide (Sb203 or Sb406). It has very little if any effect on non-halogenic polymers or in halogen-free systems. In the presence of halogens, however, a very strong synergetic effect multiplies the fiame-retardancy. 

With halogen-containing systems, zinc borate can partially or completely replace the antimony synergist in PVC, notably wire and cable, wallcoverings, roof membranes and tarpaulins. It is also effective in polyolefins, elastomers, polyamides and epoxy polymers while, in halogen-free systems, it can be used in conjunction with alumina trihydrate, magnesium hydroxide or red phosphorus. 

Currently, most PHA extraction processes are based on halogenated solvent extraction which is costly and may cause environmental problems and toxicity to humans. Thus, it seems that a practical commercial extraction system with a clean, simple and efficient process for PHA recovery at a reasonable cost focusing on a non-halogenated solvent extraction-based recovery needs to be developed. However, halogen-free methods require further adjustment, depending on both significant process parameters and external factors influencing their performance, to make the process suitable for polymer recovery on an industrial scale. 

In spite of the encouraging results obtained in polymer/LDH flame retardant nanocomposites, the use of LDHs alone is insufficient for ensuring adequate fire resistance to meet the required standards, such as LOI values and UL-94 test ratings, especially at low LDH concentrations. The combination of LDH with conventional flame retardants is an effective way to avoid this limitation. By this means, it is possible to reach the flame retardancy required by the market with a halogen-free, nontoxic flame retardant system and improved mechanical properties. There are also many issues concerning the synergy between LDH and conventional flame retardants. 

In choosing a flame retardant, consideration must be given to the impact on the performance of the resin system and the finished base material. These materials, at the levels required for flame retardancy, can affect the physical properties of the laminate, change rheological properties, and alter cure kinetics of the resin system. Generally, the reactive compounds are preferred since they are bound to the polymer backbone, which prevents release into the environment, and, in comparison to additives or fillers, they seem better suited to obtaining the desired material properties. Table 7.2 summarizes some of the available halogen-free flame retardants. 

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