Flame retardancy PMMA

Various additives show considerable extraction resistance, such as impact modifiers (polyacrylates and polyblends PVC/EVA, PVC/ABS, etc.), highpolymeric processing aids (PMMA-based), elastomers as high-MW plasticisers, reactive flame retardants (e.g. tetrabromobisphenol-A, tetrabromophthalic anhydride, tetrabromophthalate diol, dibromostyrene). Direct measurement of additives by UV and IR spectroscopy of moulded films is particularly useful in analysing for additives that are difficult to extract, although in such cases the calibration of standards may present a problem and interferences from other additives are possible. 

A detailed understanding of the course of a reaction between a polymer and an additive will permit one to use that information to design new flame retardants. The reaction between poly(methyl methacrylate), PMMA, and red phosphorus is described and that information used to determine that CIRh(PPh3)3 should be used as a flame retardant. The results of this investigation are then used to choose the next additive. A recurring theme is the efficacy of cross-linking as a means to impart an increased thermal stability. 

PMMA - Red Phosphorus System. The initial reaction that was investigated was that between PMMA and red phosphorus (4-51. Phosphorus was chosen since this material is known to function as a flame retardant for oxygen-containing polymers (1 2). Two previous investigations of the reaction of PMMA with red phosphorus have been carried out and the results are conflicting. Raley has reported that the addition of organic halides and red phosphorus to PMMA caused moderate to severe deterioration in flammability characteristics. Other authors have reported that the addition of chlorine and phosphorus compounds are effective flame retardant additives (12). 

It is unlikely that CIRh(PPh3)3 will ever be useful as a flame retardant due to its red color, expense, and the potential toxicity associated with a heavy metal. An additional disadvantage of the rhodium system is the fact that char formation occurs at a temperature of 250°C, since this is near the processing temperature of PMMA char formation may occur during processing rather than under fire conditions. This discovery is nonetheless... 

Char formation and reduced monomer production are observed for all of these additives upon reaction with PMMA. Char formation increases as a function of temperature, for the hydrido cobalt compound, there is 5% char at 262°, 8.5% at 322°, 15% at 338°, and 19% at 375°C the cobalt(lll) cyanide produces 3% char at 338° and 11% at 375°C the cobalt(ll) cyanide yields 11% char at 375°C. At the highest temperature, 375°C, the amount of monomer formation is 22% for K3Co(CN)5, 11% for K3Co(CN)6, and 10% for HCo[P(OPh)3]4. Ideally one would hope to observe no monomer formation and complete char production. Such is not the case here, these materials probably have no utility as flame retardant additives for PMMA since monomer formation, even at a reduced level, will still permit a propagation of the burning process. While somewhat positive results for these three additives do not prove the validity of the hypothesis, we take this to be a starting point in our search for suitable additives, further work is underway to refine the hypothesis and to identify other potential hydrogenation catalysts and other additives that may prove useful as flame retardants for PMMA... 

In this paper we have presented evidence to show that it is quite feasible to determine the detailed course of reaction between a polymer and an additive. Further, the understanding of this reaction pathway provides insight into new additives and schemes for the identification of efficacious flame retardant additives. Finally, we have elucidated schemes for the cross-linking of PMMA and have shown that the schemes do provide a route for flame retardation. It is imperative to realize that the purpose of this work is not to directly develop new flame retardants, rather the purpose is to expose the chemistry that occurs when a polymer and an additive react. This exposition of chemistry continually provides a new starting point for further investigations. The more that pathways for polymeric reactions are determined the more information is available to design suitable additives to prevent degradation of polymers. 

The reactive approach has been employed recently to prepare various polymeric systems.34 35 Silicon-containing polystyrenes and poly(methyl methacrylate)s (PMMAs) copolymers have been prepared by free radical polymerization. The LOI data indicated that a marginal improvement in flame retardancy has been observed compared to the parent homopolymers. The authors speculated that the nature of the silicon-containing group has an effect on the flame-retardant mechanism.34... 

The CNTs can surpass the clays and other nanoadditives as effective flame-retardant additives, as reflected in the lower loading of the CNTs than the other nanoadditives needed to enhance the thermal and fire resistance.100 For instance, the results for PMMA in the presence of different nanoadditives are seen in Figure 11.29 in which the relationship of mass loss rate (MLR) and loading of... 

A. Laachachi, M. Cochez, E. Leroy, P. Gaudon, M. Ferriol, and J.M. Lopez-Cuesta, Effect of A1203 and Ti02 nano-particles and APP on thermal stability and flame retardance of PMMA, Polym. Adv. Technol. 2006, 17 327-334. 

Whereas UL 94 delivers only a classification based on a pass-and-fail system, LOI can be used to rank and compare the flammability behavior of different materials. In Figure 15.2 the increasing LOI values are presented for different polymers as an example POM = poly(oxymethylene), PEO = poly(ethyl oxide), PMMA = poly(methyl methacrylate), PE = polyethylene), PP, ABS, PS, PET = polyethylene terephthalate), PVA = poly(vinyl alcohol), PBT, PA = poly(amide), PC, PPO = poly(phenylene oxide), PSU, PEEK = poly(ether ether ketone), PAEK = poly(aryl ether ketone), PES, PBI = poly(benzimidazole), PEI = poly(ether imide), PVC = poly(vinyl chloride), PBO = poly(aryl ether benzoxazole), PTFE. The higher the LOI, the better is the intrinsic flame retardancy. Apart from rigid PVC, nearly all commodity and technical polymers are flammable. Only a few high-performance polymers are self-extinguishing. Table 15.1 shows an example of how the LOI is used in the development of flame-retarded materials. The flame retardant red phosphorus (Pred) increases... 

The mechanism of action of flame retardants in thermoplastic materials (polyethylene, polypropylene, polystyrene, cellulosics, PMMA, etc.) is unknown and is certainly quite complex. Broido (7) presented a good example in the difficulties of explaining how fire retardants work. He found that materials which were most effective in preventing flaming combustion of cellulose were also effective in causing sugar cubes to support flame ... 

Bromine is an effective flame retardant and bromine-containing blends poly(di-bromo-propyl acrylate) with PMMA and PMA) have been studied with this in mind [Grassie et al., 1987 Diab, 1986]. Though the degradation products are those expected from the individual components it has recently been found that high temperature pyrolysis of blends (600°C) containing bromine flame retardants can generate detectable (ppm) amounts of para-dioxins [Luijk and Go vers, 1992]. 

Since PVC is known to be quite miscible with PMMA (miscibility with an LCST behavior) [Jager et al., 1983] and is also low in cost, some blends of PVC and PMMA have been used in sheet extrusion and thermoforming applications. However, the acrylic PVC compositions commercially used are invariably contain an acrylic coreshell rubber (PMMA-g-n-BuA or MBS type) to get high toughness), with some PMMA, to reduce the cost/impact performance balance. The role of PVC in these blends is to reduce cost and impart some degree of flame-retardancy. The acrylics definitely help in the processability of PVC. These blends have already been discussed under PVC heading. 

Specifically, PVC blends with polyethylene, polypropylene, or polystyrene could offer significant potential. PVC offers rigidity combined with flammability resistance. In essence, PVC offers the promise to be the lowest cost method to flame retard these polymers. The processing temperatures for the polyolefins and polystyrene are within the critical range for PVC. In fact, addition of the polyolefins to PVC should enhance its ability to be extruded and injected molded. PVC has been utilized in blends with functional styrenics (ABS and styrene-maleic anhydride co-and terpolymers) as well as PMMA offering the key advantage of improved flame resistance. Reactive extrusion concepts applied to PVC blends with polyolefins and polystyrene appear to be a facile method for compatibilization should the proper chemical modifications be found. He et al. [1997] noted the use of solid-state chlorinated polyethylene as a compatibilizer for PVC/LLDPE blends with a significant improvement in mechanical properties. A recent treatise [Datta and Lohse,... 

Improvements in the reduction of flammability of polymers with low clay contents and better processability have been reported, in addition to reductions in the concentration of toxic vapors produced in the combustion stage [116-120]. In connection to their flame-retardant properties, exfoliated nanocomposites based on PP [121, 122, 115, 123], PS [115, 123, 124], poly(ethylene-vinyl acetate) [125, 126], styrene-butadiene rubber [127], PMMA [128], polyesters... 

Poly(methyl methacrylate) PMMA, flame-retarded Polyamide... 

In a study of the flame retardance of styrene-methyl methacrylate copolymer with covalently bound pyrocatechol-vinyl phosphate, diethyl p-vinyl benzyl phosphonate, or di(2-phenyl ethyl phosphonate) groups. Ebdon and co-workers [23] obtained data on their decomposition behaviour. This was achieved by reducing the rate of liberation of flammable methyl methacrylate monomer during combustion. Possible mechanisms for these processes are suggested. Other methacrylate copolymers which have been the subject of thermal degradation studies include PMMA-N-methylmaleimide-styrene [24] and PMMA-ethylene vinyl acetate [25-27]. 

PMMA expandable graphite composites Silane grafted on polymer LOl and TGA used to calculate flame retardance and thermal stability [41]... 

Phosphoms may be incorporated into PMMA to reduce flammability. Work carried out at Salford University has shown that MMA may be reacted with diethyl(methacryloxymethyl) phosphonate (DEMMP) to form a copolymer that provides a better flame retardant performance than a compound to which diethyl ethyl phosphonate (DEEP) has been added. DEEP has a similar stmcture to DEMMP and it might be expected that the two compounds confer a similar degree of flame reatardancy to PMMA at similar loadings. The rise in oxygen index is similar, 17.5 up to 22 at 3.5% of phosphoms in each case. However, the MMA/DEMMP copolymer is more thermally stable and gives better FR properties. It turns out that the DEEP plasticises PMMA whereas the copolymer has similar physical and mechanical properties to unprotected PMMA. 

PVC blends with CPE were patented and commercialized in 1956 as HostaliF. Blends with CSR soon followed. By the mid-1970s, the emphasis shilted toward blends with acrylic elastomers. Ternary alloys were developed, viz., of PVC with CPE and poly(methyl methacrylate-co-butyl acrylate) (MMBA) (Maruyama et al. 1977) or PVC, CPVC, and either MABS or a mixture of PMMA with imidized-PMMA or imidized-SMA (Soby et al. 1994). These blends have been used for outdoor applications, flame-retardant wall coverings, and automobile interiors. Injection molded components include gullies in sewage systems, caps for road reflector posts and bench slats, etc. Evolution of these blends is traced in Table 1.29. 

Vircol (Series), Reactive polyurethane flame retardants, Albright Wilson Americas Virgaloy, PC/PMMA blend, MRC Polymers Inc. Virtual Gibbs, CAM software, Gibbs and Associates... 

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