Filled PMMA

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. 

The parameters of the pyrolysis experiments are shown in Table 24.4. In the experiments, the pyrolysis temperature was 450°C which was found in previous experiment with pure PMMA to be the optimal temperature. Total mass balances are calculated to the organic content even for the filled PMMA to allow a comparison. The losses (1-2%) calculated to 100% were determined on all product fractions proportionately. The following results should be noted. 

The monomer recovery is the highest by feeding pure PMMA pellets (98.4 wt%) in the laboratory plant. But highly filled PMMA yielded monomer concentrations of 83-90 wt%. A short residence time is preferred. The good results of the laboratory-scale experiments were confirmed by the experiments in the technical-scale plant yielding 97% MMA for pure PMMA pellets and 83.5% for silica-filled PMMA. 

In all experiments the gas fraction is small. Only 0.4-4.9 wt% of gas molecules are produced. Other ligand compounds were found in a range of 1-95% filled PMMA affords the higher amounts of oily compounds. In the case of ATH-filled PMMA water is formed as a main product by drying 

Up to 4.3% of water was found on feeding silica-filled PMMA, mostly deriving from hygroscopic PMMA. For unfilled PMMA in the laboratory plant the carbon black formation is very low (0.01%). This value increased to 1.3% for filled PMMA as feedstock. 

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W. Kaminsky and C. Eger, Pyrolysis of filled PMMA for monomer recovery, J. Anal. App. Pyrolysis, 58-59, 781-787 (2001). 

In contrast to this, the residence time of the products in a fluidized bed lies between 1 and 5 s [20]. Buekens [21] studied the influence of the residence times in technical fluidized-bed processes. One of the main advantages in using a fluidized bed reactor for depolymerization is that it involves no contamination of organometallic compounds in the products and less environmental problems [1]. Therefore, companies are looking to use fluidized-bed processes especially for filled PMMA. The filler will contaminate the molten metal bath while in a fluidized bed the often expensive fillers can be recovered. 

Three different filled PMMA were used. One contains 62 wt% of silica (Si02,10-100 p.m), the other 71 wt% of granite (100-1000 p.m) and the third contains 67% of alnminium trihydroxide (A1(0H)3, ATH). For the pyrolysis, the laboratory-scale linidized plant (Figure 25.1) was used and for two runs the pilot plant with a capacity of 10-50 kg/h feeding rate (Ham-bnrg Process)... 

The liquids contain mainly the monomer MMA in the range 92-99% for silica-filled PMMA and 58% for ATH-filled PMMA. Other liqnid compounds in higher concentration are methacrylic acid and dimethylethylcyclohexene. After distillation, the MMA is pure enough for new polymerization. Filled PMMA yielded more by-products such as long-chain methyl esters and Diels-Alder prodncts. The reason for their formation could be the higher residence time and some catalytic effect of the filler. 

The highly filled PMMA (71% Si02) was cross-linked. For the cross-linking trimethyl-(3-propane)trimethacrylate (TRIM) and trimethylol-(3-propane)-isobutyrate-dimethacry-late (TRIM-H2) were nsed. These compounds were detected in small amounts up to 0.2 wt% in the liqnid fraction. 

It was fonnd that the pyrolysis of the ATH-filled PMMA yielded only 58% MMA monomer instead of 97% fonnd with a pure PMMA feed. Hydrolysis products from MMA such as methacrylic acid, methanol and isobutyric acid were found to be the other main by-prodncts from the thermal decomposition of this composite material. Pyrolysis-GC-MS experiments showed that the yield of the monomer MMA can be increased to 65 wt% by lowering the process temperature to 400°C. Water released during pyrolysis of ATH and the chemical starter/stabilizer in the composite material were found to be responsible for the low monomer yield. The high amount of the alnmininm components in this material has almost no catalytic influence on the hydrolysis reaction because the same result was found if steam was used as fluidizing medinm instead of nitrogen. 

Figure 14.7. Resistivity of aluminum powder filled PMMA. [Adapted, by permission from Lei Yang, Schruben D L,Polym. Engng. Sci., 34, No.l4, 1994, 1109-14.]...

Major results. Figure 14.7 shows that the resistivity of aluminum-filled PMMA changes abruptly. Smaller volumes of filler contribute a little to resistivity but, after certain threshold value of filler concentration, further additions have little contribution. A similar relationship was obtained for nickel powder the only difference is in the final value of resistivity, which was lower for nickel due to its higher conductivity. The same conclusions can be obtained from conductivity deteiminations of epoxy resins filled with copper and nickel. Figure 14.8 shows the effect of temperature on the electric conductivity of butyl rubber filled with different grades of carbon black. In both cases, conductivity decreases with temperature, but lamp black is substantially more sensitive to temperature changes. Even more pronounced changes with temperature were detected for the dielectric loss factor and dissipation factor for mineral filled epoxy." ... 

Figure 14.7 shows resistivity of aluminum filled PMMA. The resistance rapidly drops when the concentration of aluminum exceeds 20 vol%. Slightly less (about 18-20 vol%) nickel is needed to obtain the same resistance. ... 

Rucker and Bike (1995) examined the rheological properties of silica-filled PMMA. They showed the existence of a yield stress and a poor fit of viscosity data to existing filler models. 

An insightful analysis was performed by Sinha Ray et al. [114] using day filled PMMA/PC blends. These authors observed that the presence of day in PMMA matrix induced considerably smaller dispersed PC droplets. They also invoked the physical significance of Co and identified that a possible reduction in interfacial tension or possible increase in matrix viscosity in the presence of day particles gave rise to smaller droplets. However, the shear viscosity data did not support the argument of increased matrix viscosity as the origin of reduced droplets size [114]. 

Figure 4.13 Comparison of cristobalite filled PMMA above...

Table 6.4 The effect of ATH particle size on the horizontal burn performance (ASTM D635) [3] of 50% w/w filled PMMA composites ...

Table 9.2 Static properties of silica filled PMMA ...

Other studies have investigated the decomposition of PMMA utilising TG and calorimetry. One study concentrated on polymer layered silicate nanocomposites 825036 and compared the degradation profiles of PMMA-filled nanocomposites to that of pure PMMA by using TG-DSC-FTIR and GC-MS. The results based on TG and DSC indicated enhanced thermal stability and higher glass transition temperature of filled PMMA nanocomposites with respect to that of pure PMMA. Nonetheless, in both cases the decomposition was described as a two-step reaction. 

Figure 45.8 Cross-section of the granular aerogel-based glazing, consisting of two glass panels with a low-emissivity coating on the inside, two gaps, and an aerogel-filled PMMA double-skin sheet [25].

Micro- and nano-scale silica particles filled poly (methyl methacrylate) (PMMA) composites were prepared using high shear compounding and thin-wall micromolding. Mechanical performances of the composites were elucidated through tensile tests and internal structures of fractured surfaces were obtained from microscopic observations. The incorporation of silica particle has raised the tensile modulus of all specimens irrespective of processing conditions. Distribution of micro-fillers in the molded specimens was preferential towards the end side than the gate and center sides. Nano-filler particles were dispersed uniformly in most parts of the specimen while boundary separations between filler and matrix could be observed at the skin layer in micro sihca filled PMMA. This led to an assumption that there was better filler-matrix adhesion in nano-filler composites than in micro-filler composites. 

Figure 3. SEM micrographs (a) PMMA, (b)nano silica filled PMMA, (c) untreated micro silica filled PMMA, (d) treated micro silica filled PMMA.

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