Flame retardants synergistic systems

Costa, L. Luda, M. P Trossarelli, L. Mechanism of condensed phase action in flame retardants. Synergistic systems based on halogen-metal compounds, Polymer Degradation and Stability, 2000, 68(1), 67-74. 

By means of compounding, tailor-made engineering plastics parts are manufactured to satisfy every conceivable application. The warping problem, which existed in the past for the production of large area parts, e.g. for car body parts and bumpers, can be overcome by selected reinforcement/filler systems. Simultaneously the heat distortion temperature could be raised from about 150 °C for pure PBT homopolymer to approximately 210 °C for reinforced polymer. Self-extinguishing behavior was imparted by incorporation of flame retardant synergistic systems. Further, in the last thirty years, many commercial products have been developed by blending PBT with other polymers in the melt. Moreover, a variety of additives, fillers or reinforcements, which have been mentioned previously in this Chapter, may be added to the PBT blends. 

Of the tin additives studied, the anhydrous and hydrated zinc stannates, ZnSnO and ZnSn(OH), respectively, are considerably more effective flame-retardant synergists with the bromine present in the plastic than 8-stannic acid (Figure 1). In line with this observation, oxidic tin-zinc systems have previously been found to exhibit superior flame-retardant properties to tin oxides alone (19-22). In addition, ZnSnO, gives higher values of 01 than Sb20, incorporation levels studied, and, in fact, the 1% ZnSnO - containing plastics outperform samples containing 2% Sb O,. 

In order to improve the flame retarding action of these Fyarestor additives, antimony trioxide can be enqployed as a flame retarding synergist in these applications which tolerate the use of a powdered additive. The use of this metal oxide will reduce the flame retarding cost. Also, the Fyarestor products can be emulsified for use in water-based systems. Typical Properties ... 

Y. Li, B. Li, J. Dai, H. Jia, and S. Gao, Synergistic effects of lanthanum oxide on a novel intumescent flame retardant polypropylene system. Polymer Degradation and Stability, 93(1) 9-16, January 2008. 

Olefin Polymers. The flame resistance of polyethylene can be increased by the addition of either a halogen synergist system or hydrated fillers. Similar flame-retarder packages are used for polypropylene (see Olefin polymers). Typical formulations of the halogen synergist type are shown in Table 15 the fiUer-type formulations are in Table 16. 

T. Handa, T. Nagashima and N. Ebihara, Synergistic Action of Sb2(>3 with Bromine-Containing Flame Retardants in Polyolefins. II. Structure-Effect Relationships in Flame Retardant Systems," J. of Fire Retardant Chemistry,, 37 (1981). ... 

AS A FLAME RETARDANT. The zinc borate is an efficient synergist of organic halogen sources. In certain halogen-containing systems such as unsaturated polyester, epoxy (3), and rigid PVC, the zinc borate alone can outperform antimony oxide as shown by the Oxygen Index and UL-94 tests (Fig. 3, 4, and 5). 

To improve the fire retardancy of polypropylene, beyond the UL 94 V-2 level, it is necessary to use blends of aromatic bromine fire retardants with antimony trioxide as a synergist. The usual loading is between 35% and 40% fire retardant however, the additional cost may prohibit commercialization. Moreover, the presence of aromatic bromine increases the photooxidation of polypropylene67 69 inactivating hindered amines. To reduce the cost without losing in efficacy the combination of brominated flame-retardant/antimony trioxide system with magnesium hydroxide... 

In this chapter, we have discussed recent developments of intumescent flame-retarded materials in terms of reaction and resistance to fire. Research work in intumescence is very active. New molecules (commercial molecules and new concepts) have appeared. Nanocomposites are a relatively new technology in the held of flame retardancy. This technology gives the best results combined with conventional FRs and leads to synergistic effects with intumescent systems. Very promising developments in the synergy aspects are then expected and efforts should be continued in this way. 

It has been shown that the required loading levels of metal hydroxides to flame retard polyolefins can be reduced by the addition of transition metal oxides as synergistic agents. For example, a combination of 47.6% MH modified with nickel oxide in PP gave a UL94 V-0 flammability rating, which would require -55% of unmodified MH.4 These systems, however, can only be used where the color of the product is not important. 

Recently, some reports have explored the potential of synergistic effect between silica and other flame retardants.53-55 For example, silica showed synergistic effect with alumina in polypropylene (PP)/ammonium polyphosphate (APP)—pentaerythritol (PER) intumescent-based system. The data indicate that the HRR values improved by incorporating silica into the intumescent-based formulation and the improvement was much more pronounced by combining both silica and alumina in the formulation. 

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. 

Since the majority of research carried out on flame retardancy of nanocomposite has dealt with OMLS, the most investigated combinations have concerned the corresponding class of nanocomposites of polymers, particularly EVA copolymer, PP, and polystyrene. The great interest taken in the development of IFR systems has also entailed the development of various and complex compositions in which OMLS have been associated with different intumescent systems containing APP and co-synergists able to promote the formation of a stable and expanded char layer reinforced by aluminophosphate species formed by reaction between APP and OMLS. 

Weil, E.D., Synergists, adjuvants, and antagonists in flame-retardant Systems, mFire Retardancy of Polymeric Materials, Grand, A. and Wilkie, C. (Eds.), Marcel Dekker, New York, 2000, Chapter 4, pp. 115-145. 

Firstly it can be used for obtaining layers with a thickness of several mono-layers to introduce and to distribute uniformly very low amounts of admixtures. This may be important for the surface of sorption and catalytic, polymeric, metal, composition and other materials. Secondly, the production of relatively thick layers, on the order of tens of nm. In this case a thickness of nanolayers is controlled with an accuracy of one monolayer. This can be important in the optimization of layer composition and thickness (for example when kernel pigments and fillers are produced). Thirdly the ML method can be used to influence the matrix surface and nanolayer phase transformation in core-shell systems. It can be used for example for intensification of chemical solid reactions, and in sintering of ceramic powders. Fourthly, the ML method can be used for the formation of multicomponent mono- and nanolayers to create surface nanostructures with uniformly varied thicknesses (for example optical applications), or with synergistic properties (for example flame retardants), or with a combination of various functions (polyfunctional coatings). Nanoelectronics can also utilize multicomponent mono- and nanolayers. 

Flexible PVC (Table 15.6) is made by polymerizing at 40-55°C and then compounding with 20-80 PHR (parts per hundred of resin) of dioctyl phthalate and/or other monomeric liquid plasticizers (e.g., dioctyl adipate for low-temperature flexibility, oligomeric polyesters for permanence, organic phosphates for flame-retardance), plus a synergistic stabilizer system usually composed of barium or calcium soap, zinc soap, epoxidized fatty ester, and organic phosphite. 

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