Intumescent properties

The sueeess of graphite in this applications shows that filler with plate like struetures should be considered when intumescent materials are being formulated. Reeent developments in intumescent paints show that performanee ean be improved if a layer of organic material is inserted between the layers of the plate like filler. The degradation of this material in the enclosed space increases the expansion rate and the retention of gas inside the degrading material. Based on this prinei-ple any plate like filler has the potential to be useful in an intumescent applieation. The eomposition of filler is also important. When clay was used as a filler in fire retardant applieations, it was found that some of its components interfere with the action of carbonization catalysts and detract from the overall performance of the system in terms of limiting oxygen index.  

Thermal conductivity range, W/K-m Filler (thermal conductivity given in parentheses) 

10-29 aluminum oxide (20.5-29.3), pitch-based carbon fiber (25-1000) 

In modem electronic devices there is a need to manufacture materials which have high thermal conductivity and a high electrical resistance. The data in the Table 5.19 show that such a requirement can be easily fulfilled using boron nitride or beryllium oxide. Both fillers have excellent thermal conductivity and they are electrical insulators. 

Some of the insulating fillers found in the first row of Table 5.19 are used in 

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In order to achieve enhanced intumescent properties of stereo-complexed PLA, the in situ REX synthesis of PLA was similarly reported for PLA homopolymers in the presence of nanoclays and carhon nanotubes and for stereo-complexed PDLA-A-PLLA diblock copolymers in the presence of a mixture of ammonium polyphosphate, melamine and nanoclay. ... 

These coatings provide the most effective fire-resistant system available but originally were deficient in paint color properties. Since, historically, the intumescence producing chemicals were quite water-soluble, coatings based thereon did not meet the shipping can stability, ease of application, environmental resistance, or aesthetic appeal required of a good protective coating. 

Intumescent types of aqueous coatings have been produced containing an amine aldehyde, the ammonium salt or salts of polyhydric acid, selected pigment, starch, and thickener. When formulated properly, this type of coating possesses excellent fire- and flame-resistant properties, but would be rated as a relatively poor paint film. 

Intumescent types of nonaqueous coatings have been produced containing an amine aldehyde resin, ammonium salt of polyhydric acid, and pigments, with an appropriate binder. This type of coating possesses excellent fire and flame resistance and good paint properties. There are probably other types of intumescent paints, but their exact composition is not available. 

Perhaps the most important single property for a fire-retardant film is intumescence, the property of swelling or puffing when exposed to the heat of flame. Such swelling providing a thick cellular insulating layer between the fire and the flammable substrate. 

In short, an intumescent formulation has to be optimized in terms of physical (char strength, expansion, viscosity,. ..) and chemical (thermal stability, reactivity) properties in order to form an effective protective char that will be able to protect its host polymer (reaction to fire) or a substrate like steel or wood (resistance to fire).16... 

The use of polyols such as pentaerythritol, mannitol, or sorbitol as classical char formers in intumescent formulations for thermoplastics is associated with migration and water solubility problems. Moreover, these additives are often not compatible with the polymeric matrix and the mechanical properties of the formulations are then very poor. Those problems can be solved (at least partially) by the synthesis of additives that concentrate the three intumescent FR elements in one material, as suggested by the pioneering work of Halpern.29 b-MAP (4) (melamine salt of 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]-undecane-3,9-dioxide) and Melabis (5) (melamine salt of bis(l-oxo-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octan-4-ylmethanol)phosphate) were synthesized from pentaerythritol (2), melamine (3), and phosphoryl trichloride (1) (Figure 6.4). They were found to be more effective to fire retard PP than standard halogen-antimony FR. 

Tang et al.84,85 also examined the incorporation of MMT in intumescent PP with a compatibilizer (hexadecyltrimethylammonium bromide) which is usually used as surfactant for making OMMT. Evidence of making a nanocomposite is shown with and without the intumescent system. Cone calorimetry shows a large improvement in the flammability properties when using OMMT. The results are similar to what we showed above. They postulated a mechanism of action suggesting the formation of an aluminophosphate structure but no evidence was given. 

The flammability properties of an intumescent fire retardant PP formulation with added MH has been investigated.65 The results show that the intumescent flame-retardant ammonium polyphosphate-filled PP has superior flammability properties but gives higher CO and smoke evolution. The addition of MH was found to reduce smoke density and CO emissions, in addition to giving superior fire resistance. PP filled with ammonium polyphosphate, pentaerythritol, and melamine has given improved flammability performance, without reducing its mechanical properties. 

At an optimum addition level of only 1.5 w t %, nano-size magnesium-aluminum LDHs have been shown to enhance char formation and fire-resisting properties in flame-retarding coatings, based on an intumescent formulation of ammonium polyphosphate, pentaerythritol, and melamine.89 The coating material comprised a mixture of acrylate resin, melamine formaldehyde resin, and silicone resin with titanium dioxide and solvent. It was reported that the nano-LDH could catalyze the esterification reaction between ammonium polyphosphate and pentaerythritol greatly increasing carbon content and char cross-link density. 

An extensive study was conducted on the effect of chemical and structural aspects of zeolites on the fire performance of the intumescent system, ammonium polyphosphate-pentaerythritol (APP-PER), where a marked improvement of the fire-retardant properties within different polymeric matrices has been observed.56 58 The synergistic mechanism of zeolite 4A with the intumescent materials was investigated using solid-state NMR. Chemical analysis combined with cross-polarization dipolar-decoupled magic-angle spinning NMR revealed that the materials resulting from the thermal treatment of the APP-PER and APP-PER/4A systems were formed by carbonaceous and phosphocarbonaceous species, and that the zeolite enhances the stability of the phosphocarbonaceous species. 

In an attempt to provide compatibility between the FR and polymer matrix, Wang et al. reported recently on a novel microencapsulated intumescent system containing 4A zeolite as a potential flame retardant for natural rubber (NR).61 The flame-retardant properties of NR composites loaded with different amounts of intumescent flame retardant (IFR), IFR-4A zeolite, and microencapsulated intumescent flame retardant (MIFR)-4A zeolite agents were studied and compared. The LOI data demonstrate that the NR composite filled with 50phr of MIFR-4A zeolite agent and 50phr of IFR-4A zeolite shows better FR properties as compared to NR and 50phr of IFR-filled systems. 

Wang, J. and Chen, Y., Effect of microencapsulation and 4A zeolite on the properties of intumescent flame-retardant natural rubber composites, J. Fire Sci. 2008, 26, 153. 

Similarly, numerous different nanoparticles, including organomodified clays,3 nanoparticles of silica,4 layered double hydroxides (LDH),5 or polyhedral silsesquioxanes (POSS),6 have been combined with intumescent formulations in polymeric materials to create large synergistic effects (see Chapter 12 for more details) the nanoparticles acting as char reinforcer or char expander that result in differences in terms of FR properties. 

The formation of borophosphate partially explains the good performance when APP and boric acid are mixed together in the epoxy resin. Indeed, in that case good mechanical resistance of the intumescent char is observed as borophosphate is a hard material, which also shows a good thermal stability. As a conclusion, the boron containing compounds provide the good structural properties of the char, whereas the phosphorus ensures the adhesion of the char to the steel. 

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