Char forming polymers

Recent work has shown that magnesium borate provides good surface spread-of-flame performance in PVC, suggesting the possibility of direct antimony replacement. A zinc-free borate has stability advantages in PVC sheeting. Melamine borate is another recent development and is used in phenolic composites to improve fire performance. Zinc borophosphate is also a new development for applications as a smoke and flame retardant in PVC. 

Firebrake 500 is recommended for use in engineering plasties proeessed at above 300 °C, which is the upper limit of Firebrake ZB. It is reported to be an effeetive smoke suppressant in fluoropolymers for certain cable applications. This anhydrous material ean replace antimony oxide completely in high temperature nylon applications. For aircraft applications Firebrake 500 is also reported to be effective in reducing the rate of heat release in polyether ketones and polysulfones. It is also claimed to enhance laser-marking quality of flame-retardant engineering plastics. 

Firebrake 415 has an unusually high onset of dehydration temperature of 415 °C. It is recommended for use in engineering plastics as a synergist of halogen sourees. It ean also be used as a smoke suppressant in flexible PVC. 

Firebrake zinc borates display an interaction with metal oxide partieles resulting from dehydrating metal hydrates in flame retardant polyolefins. The interactions taking place show that surface 

The traditional use of zinc borates as a partial replacement for antimony trioxide and to increase CTI can be extended to polyamide 66 compounds that contain brominated FRs. Their benefits can expand to complete antimony trioxide replacement and improved melt stability during compounding and injection moulding. 

---

In polymers such as polystyrene that do not readily undergo charring, phosphoms-based flame retardants tend to be less effective, and such polymers are often flame retarded by antimony—halogen combinations (see Styrene). However, even in such noncharring polymers, phosphoms additives exhibit some activity that suggests at least one other mode of action. Phosphoms compounds may produce a barrier layer of polyphosphoric acid on the burning polymer (4,5). Phosphoms-based flame retardants are more effective in styrenic polymers blended with a char-forming polymer such as polyphenylene oxide or polycarbonate. 

The same method is applicable to control critical temperature where the reaction between polyphosphates and polyols takes place. For example, melamine polyphosphate-polyol system, which is stable at the degradation temperature of PP, has been activated for application in polyolefins [47], An activating effect is ascribed also to the char-forming polymers in intumescent nanocomposites, according to the blending approach [48],... 

Staggs, J. E. J. Simple mathematical models of char-forming polymers. Polymer International 2000 49 1147. 

As in the case of zeolite, the mechanism of action looks similar. No direct comparison can be made because MMT is a layered silicate compared to the cage structure of zeolite, and also because the carbonization agent is no longer a polyol but a char-forming polymer (PA6). Nevertheless, the main conclusion we can draw is that the action of the synergist (nanoclay or zeolite) is to stabilize in a first step the carbonaceous structure forming aluminophosphates and silicophosphates. With the nanoclay, this effect is only effective up to 310°C, whereas it is still efficient at 560°C with zeolite. To keep its protection efficient at high temperatures, the nanoclay permits the formation of protective ceramiclike material after collapse of the phosphocarbonaceous structure. Note that we did not detect any specific influence of the surfactant of the nanoclays, probably because of its low amount in the formulation. 

In the study above, MMT was only incorporated in the char-forming polymer. The effect of MMT might be different if it is incorporated in the polymeric matrix. We have incorporated MMT both in EVA (EVA containing 19 wt% vinyl... 

---