Zinc borate formulation

Carpentier, F., Bourbigot, S., Le Bras, M., Delobel, R., and Foulon, M., Charring of fire retarded ethylene vinyl acetate copolymer—magnesium hydroxide/zinc borate formulations, Polym. Deg. Stab., 69, 83-92, 2000. 

Table 2 FR-nylon 6,6 using different synergists in combination with zinc borate Formulation (wt %) 1 2 3 4 5...

Alumina trihydtate is also used as a secondary flame retardant and smoke suppressant for flexible poly(vinyl chloride) and polyolefin formulations in which antimony and a halogen ate used. The addition of minor amounts of either zinc borate or phosphoms results in the formation of glasses which insulate the unbumed polymer from the flame (21). 

Low Tinting Strength - The zinc borate has a refractive index similar to most organic polymers, which results in the retention of considerable translucency. This provides for easy visual inspection of the finished products and allows the use of lower pigment loadings in formulations requiring deep shades. 

Fig. 7. Oxygen Index of Flexible PVC Formulations Containing Alumina Trihydrate (30 phr). ZB - Zinc Borate. (Reproduced with permission from Ref. 2. Copyright Plastics Compounding 1985).

Poly (vinyl chloride). PVC is a hard, brittle polymer that is self-extinguishing. In order to make PVC useful and more pliable, plaslict/ers I qv) are added. More often than not the plasticizers are flammable and make Ihe formulation less flame-resistant. The Maine resistance of the polyf vinyl chloride) can he increased by ihe addition of an inorganic llamc-rctardunl synergist, e.g., antimony oxide, mixed metal antimony synergists, zinc borate, molybdenum oxide, zinc stannates. and alumina trihydrale. 

Boron compounds such as borax and boric acid are well-known fire retardants in cellulosic products and coatings.12 However, the use of boron compounds such as zinc borate, ammonium pent-aborate (APB), melamine borate, boric oxide, boron phosphate, and other metal borates in polymers has become prominent only since early 1980s.3 6 This chapter will review the chemical and physical properties, the end-use applications, as well as the mode of actions of major boron compounds as fire retardants in different applications. Since boron-based flame retardants are extensively used and quoted in literature, only those formulations of commercial importance and representative literature examples will be discussed and/or cited in this chapter. 

Crompton reported the use of a combination of vitrifying and devitrifying frits in thermoplastics. The addition of zinc borate in the formulation is claimed to bring down the melt and the flow temperature.62... 

The increasing demand for FR PVC-U applications has prompted work in this area. The use of functional fillers can cause a dramatic deterioration of physical properties at the addition levels necessary to achieve the requirements of flame retardancy and smoke emission. An evaluation has shown zinc hydroxystannate to give the best overall FR and SS characteristics without adversely influencing important physical properties (129). The addition of low levels of zinc borate and/or ATH was noted to improve flame retardancy and reduce smoke density in a PVC-U formulation (265). 

The results are reported of studies on PVC formulations, which show that lead-free, heat stable, flexible PVC compounds can be prepared through the proper selection of calcium/zinc stabilisers combined with selected costabilisers, fillers and other additives. The preparation of PVC insulation and sheathing compounds having oxygen index values greater than 30% using a combination of Firebrake ZB zinc borate and a phosphate ester plasticiser is also demonstrated. 6 refs. 

Introducing zinc borate (in amounts up to 3% w/w) to a WPC formulation does not effect the flexural strength and slightly increases flexural modulus (stiffness) of the materials (Table 13.4), which is understandable, as ZnB is an inorganic material. Besides, zinc borate in this amount does not effect the water absorption, as well as the postmanufactured shrinkage and the coefficient of expansion-contraction (Table 13.5). 

When more fillers, such as fly ash, zinc borate, and a colorant, were added to the formulation and compounded with HDPE and ATH, ATH lost 0.6 water molecule on average, as it was shown by ashing. Repeat with the same formulation but with a gentler mixing resulted in a loss of only 0.3 water molecule per ATH molecule. 

Chem. Descrip. Zinc borate CAS 1332-07-6 EINECS/ELINCS 215-566-6 Uses Flame retardant, smoke suppressant for plastisols, coatings for cellulosics, textiles, and adhesives synergist in PVC and halogenated polyester formulations, and in elastomers, thermoplastic elastomers, polyamides, and polyolefins strong char promoter Properties Wh. free-flowing powd., nonhygroscopic 6 p avg. particle size 99.9% < 30 p sol. 0.5 g/100 ml water sp.gr. 2.50 bulk dens. 18.1 Ib/ff oil absorp. 39 ref. index 1.48 Zb -237 [Great Lakes]... 

Chem. Descrip. Zinc borate CAS 1332-07-6 EINECS/ELINCS 215-566-6 Uses Flame retardant, smoke suppressant for plastisols, coatings for textiles, adhesives synergist in PVC and halogenated polyester formulations, and in elastomers, thermoplastic elastomers, polyamides, and polyolefins strong char promoter... 

Alumina frihydrafe, by itselfor in combination with antimony trioxide, is an effective fire retardant additive (69,70). Antimony trioxide by itself has been shown to effectively reduce the smoke generated in a flexible formulation of PVC (71), as has zinc borate (72) and barium metaborate (73). Phosphate plasticizers, described earlier, are also effective as char formers (71). Smoke suppressants, as a special class of materials, are designed to reduce the... 

Zinc borates have also found uses in PVC formulations. They have been shown to be effective flame/smoke suppressants when used as partial replacements for the antimony oxide that is normally used in a t3 ical flexible PVC cable jacket, for example. For flexible vinyl and PVC plastisol formulations, a half to two-thirds of the antimony trioxide can be replaced by zinc borate without loss of flame retardancy. If a small decrease in flame retardancy can be tolerated, all of the antimony trioxide can be replaced with zinc borate, leading to smoke reductions of up to 65%. The flame retardancy can be increased and smoke formation decreased by adding aitunonium octamolybdate to the borate-containing formulations. 

Polyamide 66 formulations are UL94 V-0 down to 1.6 mm with 16% CFR, 4% zinc borate and 2% of either antimony oxide, zinc sulfide, zinc phosphate or zinc stannate. The most effective package is zinc borate with iron oxide. Here, only 12% CFR with 1.5% zinc borate and 1.5% iron oxide... 

Firebrake ZB and a brominated polystyrene, such as Pyrochek 68PBI or Saytex HP-7010, can provide a highly flame retardant PA66 formulation containing 25% of glass fibre reinforcement, without the presence of any antimony trioxide. 24% loading of the brominated FR plus 7% of the zinc borate produce V-0 at 0.8 mm in the UL94 test, with a CTI of 450 volts. 

Occidental Chemicals supplies Dechlorane and Dechlorane Plus, a Diels-Alder adduct of hexachlorocyclopentadiene. It has a wide range of processing temperatures, offers the advantage of lower smoke than brominated equivalents on burning, and is useful at the 15%-18% level in PBT and the polyamides. A synergist such as zinc borate, oxide or stannate is advisable as well. Chlorinated FRs can be combined with magnesium hydroxide in polyolefin wire and cable formulations. 

Albemarle entered into an agreement in 1999/2000 with Borax, part of Rio Tinto, to collaborate in the development of nonhalogen flame retardants, particularly borates. As a result Albemarle was able to offer zinc borate flame retardants for sale in Asia. More recently Rio Tinto and its subsidiary Borax Europe Ltd. transferred responsibility for the sale of those zinc borate grades intended for polymer formulation purposes to Luzenac. 

This zinc borate has also been used in some PVC wire and cable formulations. Its application has been limited by its low dehydration temperature (starting at around 190°C). 

The major distinction in using the different synergists in these FR-nylon formulations is the CTI (comparative tracking index) values obtained. Formulation 1, with 2% of antimony trioxide and 16% CFR with 4% zinc borate, gives a CTI of 450 volts while tihe use of 2% zinc phosphate, 2% zinc stan-nate or 2% zinc sulfide with 4% zinc borate till give a CTI of 600 volts. 

In halogen-containing PO, a typical formulation for wire and cable application consists of decabromodi-phenyl oxide or Dechlorane Plus, antimony oxide and zinc borate. It is interesting to note that, in presence of Irganox 1010, the zinc borate can significantly improve the physical properties of the wire and cable... 

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