Flammability PMMA

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). 

PMMA is handicapped by a low impact resistance, limited heat behaviour (except for the acrylic imides), inherent flammability, sensitivity to environmental stress cracking in the presence of certain chemicals, chemical attack by certain current solvents. For some grades, processing can be more difficult than for some other current thermoplastics. 

The normal unzipping process of PMMA decomposition was obstructed in the case of the acrylate copolymers, thus reducing the evolution of the flammable methylmethacrylate (MMA) monomer. 

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 nature and number of the terminal groups, the type of bonds, the presence of aromatic cycles and carbonate groups in the unsaturated ester molecule, as well as other structural features affect polymer flammability. The slope of the straight lines increases from methacrylate to acrylate polymers. Thus, for polymers of alkylene glycol dimethacrylates it is 2,82x 10 kJ/kg, for polymers with carbonate bonds 2.86 X 10 -2.9 X 10 kJ/kg for acrylic polymers it is somewhat higher, 3.27 x 10 kJ per kg. Linear polymers, e.g. PMMA, PE, etc. have a smaller slope corresponding to... 

Silica- and ATH-filled PMMA is an often-nsed material, for example in bathrooms and kitchens. ATH-filled PMMA is less flammable becanse the ATH prodnces water at high temperatures which kills the flame. The question was whether snch highly filled PMMA gives similar amounts of MMA and if there is a catalytic effect of the ATH on the pyrolysis process. 

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... 

The isotherms in a PMMA rod specimen burning in an oxygen index flammability tester under an O2/N2 gas stream containing 21 % of oxygen were measured by Schif-fer and are illustrated in Figure 2.17. 

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]. 

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. 

PMMA/PVC blends provide heat resistance and chemical and flammability resistance into materials for injection moulding and extrusion applications. The major applications of these blends are interior panelling, trim and seat backs in mass transit vehicles. Commercially available PMMA is miscible with PVC [28, 31]. However, its phase behaviour is considered to be only partially miscible [29]. Chlorinated polyethylene blends with PVC have been used as impact modifiers and as secondary plasticisers [32], Chlorine contents of 42% and 30% by weight lead to miscible and immiscible properties, respectively. Impact modification will generally require phase separation, and plasticisation will require miscibility. 

The effect that silica gel/K2C03 has on the flammability of PS is shown in Table 5.5. The results are similar, but reduced in magnitude, to those for PP. Use of silica gel /K2CO3 additives causes the otherwise non-char-forming PS to produce a char yield of 6% (16% residue yield). The additives reduce the rate of heat release by 31%, reduce the total heat release by 11%, and similar to PP, had little effect on the CO yield and soot. The cone calorimeter results for PMMA are also shown in Table 5.5. PMMA is an inherently non-char-forming thermoplastic polymer however, using less than half the usual amount of additives, the reduction in flammability was comparable to PP and PS. Even at this low level... 

Cellulose, like PVA, gives a measurable char yield when combusted (3-4%) and in view of the promising results seen for PVA, and since cellulose is a commercially important polymer, its flammability properties were examined in the presence of silica gel/ K2CO3 additive. Cellulose, in the presence of the additives, like PVA showed a significant increase in the amount of carbonaceous char, 32% (39% residue yield). The peak heat release rate was reduced by 52%, and the total heat release was reduced by 66%. Like PVA, but in contrast to the results for PP, PS, and PMMA, the heat of combustion was reduced (by 53%). The CO yield was increased by -50%, primarily from incomplete oxidation at the end of the combustion, and the soot was ecreased by 26%. 

The evaluation of the flammability properties of PMMA and its composites with AlOOH was done using a cone calorimeter (Fire Testing Technology). A 100 x 100 x 4 mm sheet was exposed to a radiant cone (35 kW.m ). The HRR was calculated from the oxygen consumption as measured with an oxygen analyzer. Table 12.1 gathers the parameters obtained in comparison with the pure PMMA sample. 

FIGURE 5.15 Results of cone calorimetry experiments for various PMMA/carbon allotrope systems. Heavily filled (4 wt%) CNF composites and lightly filled (0.5 wt%) SWCNT composites performed the best due to robust network formation. A quantity of 4 wt% CBP and 0.2 wt% SWCNT samples did not show noticeable improvement in the flammability of the solid due to incomplete network formation. (From T. Kashiwagi et al., Nat Mater., 4, 2005, 928-933.)... 

The flammability properties of nanocomposites consisting of nanoscale titanium oxide (Ti02 with a median diameter of 21 nm) and iron oxide (Fc203 with a median diameter of 23 nm) in PMMA were measured. The nanocomposites were prepared by melt blending. A morphology study of the nanocomposites showed that the particles were well distributed in the sample but had some... 

SWNTs for the flammability study of PMMA-SWNT nanocomposites were synthesized by the high-pressure carbon monoxide method (HiPCO) and the coagulation method was used to produce PMMA-SWNT nanocomposites in... 

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