Pyrolysis of PMMA

Table 24.2 Gas products of the pyrolysis of PMMA in a fluidized bed dependence on temperature (components in wt%)...

Fig 6. Effect of mechanochemical degradation on the yield of methanol from pyrolysis of PMMA.---------------intact polymer degraded polymer. 

Reactions that involve adjacent monomer units have been proposed to account for the appearance of methane, carbon monoxide, methanol and carbon dioxide at high temperatures in the pyrolysis of PMMA polymers.(24,25). Our results suggest a more likely source is mechanochemical degradation products. 

Pyrolysis of PMMA Nanowebs Containing Cydodexlrin-Aniline Indnsion Complexes... 

FIGURE 46.22 Single ion evolution profiles of MMA, C2H4O2 and aniline recorded during the pyrolysis of PMMA nanowebs containing cyclodextiin-aniline inclusion complexes. 

Fig. 9.2. Effect of temperature on monomer yield during pyrolysis of PMMA. [7].

Mukundan and Kishore [28] showed that low temperature pyrolysis of PMMA peroxide gave methylpyruvate and formaldehyde as primary pyrolysis products. Above 350 °C secondary pyrolysis products appear. 

Reaction of HCofPfOPh), with PMMA. A 1.0g sample of PMMA and 1.0g of the cobalt compound were combined as above. After pyrolysis at 375°C for two hours the tube is noted to contain char extending over the length of the tube with a small amount of liquid present. The gases were found to contain CO, C02, hydrocarbon (probably methane), and 0.1 Og methyl methacrylate. Upon addition of acetone, 1.0g of soluble material and 0.19g of insoluble may be recovered. The infrared spectrum of the insoluble fraction is typical of char. 

The acidic nature of the phosphorus compounds (24) alters the course of the pyrolysis of certain polymers. Gruntfest and Young (19) previously postulated that with poly (methyl methacrylate) an acid functions as a chain stopper or causes a primary alteration of the PMMA, such as crosslinking. They noted the formation of high yields of dimethyl... 

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

A special case in terms of application of rotary kiln technology is the pyrolysis of mono fractions such as styrene, PMMA, polycarbonate, or polyethylene terephthalate. Polymethylmethacrylate is an example illustrate the advantages in using fluidized beds or rotary kilns. The feed material does not have a heteroatom problem and the pyrolysis product can easily be handled as a monomer source instead of feedstock. Therefore the... 

Specihcally with regard to the pyrolysis of plastics, new patents have been filed recently containing variable degrees of process description and equipment detail. For example, a process is described for the microwave pyrolysis of polymers to their constituent monomers with particular emphasis on the decomposition of poly (methylmethacrylate) (PMMA). A comprehensive list is presented of possible microwave-absorbents, including carbon black, silicon carbide, ferrites, barium titanate and sodium oxide. Furthermore, detailed descriptions of apparatus to perform the process at different scales are presented [120]. Similarly, Patent US 6,184,427 presents a process for the microwave cracking of plastics with detailed descriptions of equipment. However, as with some earlier patents, this document claims that the process is initiated by the direct action of microwaves initiating free-radical reactions on the surface of catalysts or sensitizers (i.e. microwave-absorbents) [121]. Even though the catalytic pyrolysis of plastics does involve free-radical chain reaction on the surface of catalysts, it is unlikely that the microwaves on their own are responsible for their initiation. 

W. Kaminsky and J. Franck, Monomer recovery by pyrolysis of poly(methylmeth-acrylate) (PMMA), Journal of Analytical and Applied Pyrolysis, 19,311-318 (1991). 

Table 24.4 Process conditions and product fractions for the pyrolysis of filled and pure PMMA in laboratory and mini pilot plants of fluidized beds at 450°C...

Table 24.5 Product gases of the pyrolysis of pure and filled poly(methacrylate) (PMMA) (vol% in relation to the organic input + = traces) a 450°C pyrolysis temperature...

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. 

Polystyrene (PS) is another polymer which can be degradated to the monomer. The required pyrolysis temperature is higher than in the case of PMMA as feedstock. The experiments were carried out in the fluidized-bed reactor (see Figure 24.1) between 515 and 540°C and with different fluidizing gas flows (Table 24.7). The molecular weight of the unfilled PS was 225 000. 

It can be shown that it is possible to recover high amounts of monomers from special polymers by pyrolysis in a tluidized-bed process. Up to 98 wt% of MMA can be recovered from filled or coloured PMMA wastes. In the case of polystyrene the rate of recovered styrene is limited to about 77 wt% the rest is oligomers. The high yields of TFE, HFP and C-C4F8 obtained from PTFE compounds in the experiments described show that tluidized-bed pyrolysis of pure PTFE or PTEE compounds is a feasible and interesting opportunity for the chemical recycling of this polymer. 

Some studies show that pyrolysis of certain polymer blends can be influenced by the migration of a small molecule or a small radical formed from one type of polymer and affecting the other type. For example, poly(methyl methacrylate) (PMMA) in blends with poly(vinyl chloride) (PVC) shows higher resistance to heat. The thermal decomposition of PVC generates HCI, which interacts with the PMMA forming anhydride units in the middle of PMMA chains, as shown below ... 

Fig. 21 Evolution profiles of some characteristic products recorded during the pyrolysis of the coalesced (left) and solution-cast (right) PMMA/PVAc blends...

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]. 

Fig. 8 Left scheme of vertical lifting codeposition of trimodal colloidal particles. Center trimodal colloidal crystal (tCC) consisting of large PS, intermediate PMMA, and small silica particles. Right Top view of binary inverse opal (blO) after PS and PMMA pyrolysis of the tCC in the center [25]...

Poly (methyl methacrylate) is characterized by crystal-clear hght transparency, unexcelled weatherability, and good chemical resistance and electrical and thermal properties. It has a useful combination of stiffness, density, and moderate toughness. PMMA has a moderate Tg of 105°C, a heat deflection temperature in the range of 74 to 100°C, and a service temperature of about 93°C. However, on pyrolysis, it is almost completely depolymerized to its monomer. The outstanding optical properties of PMMA combined with its excellent environmental resistance recommend it for applications requiring light transmission and outdoor exposure. Poly (methyl methacrylate) is used for specialized apphcations such as hard contact lenses. The hydroxyethyl ester of methaciyhc acid is the monomer of choice for the manufacture of soft contact lenses. Typical applications of poly(methyl methacrylate are shown in Table 15.6. 

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