Brominated polyester resin

Earlier studies at the ITRI have demonstrated the effectiveness of tin(IV) oxide, both in its anhydrous and hydrous forms, as a flame- and smoke-retardant additive for laboratory-prepared polyester resin formulations (J5j. In a recent study, carried out in collaboration with a major U.K. company, a number of inorganic tin additives have been incorporated into a commercial brominated polyester resin. Although this resin, which contains 28% by weight bromine, is intrinsically flame-retardant, giving samples with an 01 of ca. 41 and which meet the UL94-VO classification, formulations with improved flame and smoke properties are sought. 

Antimony trioxide, 8-stannic acid (hydrous tin(IV) oxide), zinc hydroxystannate, and zinc stannate were incorporated into the commercial brominated polyester resin at levels of 1,2,5 and 10% by weight. No processing problems were encountered and the samples cured satisfactorily to give rigid, opaque strips. 

Figure 1. Relationship between the flammability and metal compound level of brominated polyester resin samples. (Reproduced with permission from Ref.3 > Copyright 1989 John Wiley Sons Ltd.)...

Figure 2. Effect of incorporation level of tin oxide additives on the flammability of brominated polyester resin.

Figure 3. Effect of inorganic additives on the density of the smoke evolved from brominated polyester resin in the NBS-type Smoke Chamber.

Table III. Effect of Inorganic Additives on the Fire Properties of Brominated Polyester Resin...

Continuous monitoring of the carbon monoxide and carbon dioxide evolved during thermal decomposition of brominated polyester resin samples, has been carried out using a simultaneous thermal analysis-mass spectrometry technique. In order to allow measurement of the carbon monoxide evolved, the atmosphere chosen for these runs was 21% oxygen in argon, since the peak at 28 atomic mass units (amu)... 

Figure 7. Simultaneous TG/DTA traces of brominated polyester resin containing 2% ZnSnO in air and in argon.

Table IV. Thermal Analysis Data for Brominated Polyester Resin Samples ...

Table VI. Residual Char Yields and Extents of Elemental Volatilisation from Brominated Polyester Resin Samples during Combustion in Air... 

ZnSnCOH) and ZnSnO, at levels of 2% or 5%, significantly decreaseooth the total amount and the rate of production, of smoke and carbon monoxide generated from brominated polyester resin, when burnt under limiting or flaming conditions. 

However, the most important performance benefit of the tin additives over antimony trioxide relates to their exceUent smoke-suppressant properties. NBS Smoke Box tests have indicated that, whereas Sb203 increases smoke production for brominated polyester resin and flexible PVC formulations, the same incorporation level of ZHS (or ZS) gives significant reductions in smoke density (Figures 3 and 4). 

Figure 3 Effect of synergists on smoke density for brominated polyester resin.

Further insight into the mode of action of inorganic synergists in halogen-containing polymer formulations has been provided by quantification and analysis of the char residues remaining after combustion of the polymer in air. Data for such experiments on brominated polyester resins are presented in Table 7. 

Table 7 Char yields and elemental volatilization data for brominated polyester resins...

Figure 6 Effect of synergists on the flanunability of brominated polyester resin, highlighting the exceptional performance of Ultrafine ZHS.

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