Polymerization heat generated

Reaction calorimetry aims to measure heat released from a polymerization in order to infer monomer conversion and polymerization rate (as reviewed, for example, in Refs. 8, 38, and 39). Careful measurement and balancing of mass and energy flows are necessary for success of this technique. For example, the commercial Metder-Toledo RCl jacketed reactor acts as a calorimeter supplying mass balance, polymerization heat generation, and transport data. 

Although bulk polymerization of acrylonitrile seems adaptable, it is rarely used commercially because the autocatalytic nature of the reaction makes it difficult to control. This, combined with the fact that the rate of heat generated per unit volume is very high, makes large-scale commercial operations difficult to engineer. Lastiy, the viscosity of the medium becomes very high at conversion levels above 40 to 50%. Therefore commercial operation at low conversion requires an extensive monomer recovery operation. 

Early efforts to produce synthetic mbber coupled bulk polymerization with subsequent emulsification (9). Problems controlling the heat generated during bulk polymerization led to the first attempts at emulsion polymerization. In emulsion polymerization hydrophobic monomers are added to water, emulsified by a surfactant into small particles, and polymerized using a water-soluble initiator. The result is a coUoidal suspension of fine particles,... 

Is the product thermosensitive The heat generated by the seal faces may cause polymerization. 

In general, for polymerization reactions, the heat generation rate is not a single-valued function of temperature, g(t), but also a function of monomer and catalyst concentrations, f(c). This is particularly important in high conversion reactions where a certain amount of peaking can be tolerated. 

Concentrations of the monomer, solvent, polymer, and initiator Solution viscosity Number average polymer mol. wt. Weight average polymer mol. wt. Polymerization Rate Reaction time Heat generated Heat losses Solution Temperature Partial pressures of the monomer, solvent, and nitrogen Total pressure... 

C4H6 1,3- butadiene heat generation, violent polymeriza- tion fire, toxic gas generation heat generation, violent polymeriza- tion fla mmable peroxidizes polymerizes decomposes ... 

Interpenetrated Mall Matrix. Ion-exchange hollow libers can be produced by polymerizing an ionic monomer within (he porous wall matrix of a hollow fiber. Requirements of such a fabrication are th the monomers should not dissolve or plastici/c die polymer from which the fibers arc made. f2i the heat generated during the polymerization and contraction prior to the formation of new interpenetrating polymer should be minimized and ( ) the polymerization should not occur within the lumen (and hence cause plugging of the fiber). One drawback of such fibers is brittleness. 

But vitrification may be a problem when the cure is started at room temperature and no external heat source is provided (the only source of heat generation is the polymerization reaction). This is the case of UV (ultraviolet radiation), EB (electron beam), or X-ray curing processes. 

Most thermosetting materials are polymerized in heated molds. Figure 9.4 shows a schematic diagram of the mold L is the part thickness, which is assumed to be much less than the other two dimensions. Therefore, the system may be modeled as a case of unidimensional heat transfer with simultaneous heat generation. 

Equation (9.2) simply states that the rate of heat accumulation in a differential volume (first term) is the difference between the heat flow that enters and leaves the volume element by thermal conduction (second term) plus the rate of heat generation by the polymerization reaction (third term). 

The ratio of the adiabatic heat generation characteristic time to that of heat removal is now a = tAD/(tR + tn) and related to the Nusselt number. For the chain addition polymerization this relation is shown graphically in Fig. 11.7. 

From a process simulation point of view, in addition to impingement mixing, there are two main problems (a) nonisothermal and transient flow with chemical reaction, prevalent during the filling stage of the process, and (b) conductive heat transfer with heat generation due to the polymerization reaction. We discuss these two problems next, using the case of... 

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