Silica filled PMMA

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. 

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. 

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. 

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. 

Table 9.2 Static properties of silica filled PMMA ...

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

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)... 

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. 

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. 

Today, PMMA is mainly filled by silica, quartz, aluminium hydroxide and other inorganic fillers. For special uses, the polymer is cross-linked. This, together with the high molecular weight, makes regeneration as a raw material in reprocessing impossible. The feedstock recycling by pyrolysis to recover the monomer is therefore a practical way. 

PMMA and other methacrylate and acrylate polymers are widely used in dentistry. PMMA is used for dentures and root canal sealants. Polymers of 2,2-bis[4-(2-hydroxy-3-methacry-loyolxypropoxy)phenyl]propane (BisGMA), triethyleneglycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA) are used in dental composite resins, most commonly with a silica filler. Such composite resins are used for filling cavities, reshaping, and restoring teeth and for full and partial crowns. 

Fig. 10.38 Qualitative comparison between the theory and the experimental phase diagram (cloud points) for the PVA/PMMA polymer blend without fillers (filled diamonds) and with 10 wt% fumed silica (open squares). The two curves correspond to the spinodals calculated using equations. It is assumed that both PVA and PMMA had degrees of polymerization (N) 1,000 and that (pN) a + bT, with (a)-lO.O, (b) 0.026374. Finally, assumed that (F) 0.65. For the filled system, we took nanoparticle loading of 14 vol%, with the dimensionless particle radius (R) 20 (corresponding to the real- particle radius of 10 run) (Ginzburg 2005)...

Catalyst protection is also possible by occlusion in polymer particles. Jackson et al. [30] coated composite polymer particles, consisting of catalyst 1-filled polystyrene and/or PMMA, with a protective layer of silica, which was stable to epoxy curing agents. Figure 10.4a. 

A natural application for DRIFTS is particulate minerals and fillers because the nature of the surfaces can easily be determined. Chalk-filled PP was analysed using the diffuse reflectance probe because this material is not transparent. A calibration model with 18 samples using three relevant spectral regions (5307-6275, 6838-7505, 7987-8894 cm-i) was developed for quantification of the filler content [139]. The interfaces of various organic coatings (PAA, PMMA, oleic or stearic acid) with ceramic or silica glass surfaces were studied by means... 

Fig. 7 Variation of the normalized collective DJDo) (a) and long time self-diffusion (DJDo) ( ) coefficients with the hard-sphere volume fraction ( hs- All filled symbols refer to microemulsion data (taken from ref. [3]) DJDo data shown as open triangles correspond to silica spheres, taken from ref. [21]. DJDq data shown as open circles correspond to the self-diffusion of traces of silica spheres in a dispersion of pmma spheres (data taken from ref. [22]). The broken line is the equation DJDo = 1 + 1.3 4>hs- The solid line shows the relation DJDo = (1 — hs/0.63) ...

The effect of particulate fillers on the stress-strain behavior of polymeric materials is different due to the interaction between the particles and the polymer. The flexural strength measured for different PMMA nanocomposites is shown in Figure 2.20. It can be concluded that as the silica content increases, the flexural strength of PMMA nanocomposites filled either by silica particles or by silicic acid sol increases. The reinforcement mechanism of polymer by silica can be explained as follows as the active surface of silica particles connected with some long polymer chains and... 

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