Autoclave Buildup

Emulsion Polymers Institute and Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015 

Coagulum is formed in many emulsion polymerizations, from the smallest laboratory size to the largest production reactors. It is observed in many forms, from a single lump of polymer with little or no fluid latex to tiny sand-like grains suspended in an otherwise stable latex. Usually, it is found as lumps in the latex or deposited on the reactor surfaces. The type and amount of coagulum formed depends upon the polymer system and the polymerization recipe and technique. Two mechanisms are proposed for the formation of coagulum (i) a failure of the stability of the latex, giving rise 

All three types of emulsion polymerization can be carried out using seeded emulsion polymerization, i.e., by adding monomer, initiator, and emulsifier to a previously-prepared small-particle-size latex, the particles of which grow in size without initiation of a new crop of particles. The purpose of seeded emulsion polymerization is to avoid the uncertainties of the particle initiation stage, obtain better batch-to-batch reproducibility, and give a stable latex of the desired particle size. 

The usual description of these different polymerization processes suggests that all produce stable latexes, and various hypotheses have been advanced to explain the stability of these latexes to added electrolyte, mechanical shear and freezing and thawing. 

In the literature, there is little mention of the fact that many of these polymerizations produce varying amounts of coagulum, i.e., polymer recovered in a form other than that of a stable latex. This coagulum is produced in all sizes of polymerization reactors, ranging from the smallest laboratory reactor to the largest production reactor. It may be a mere nuisance in small laboratory polymerization reactors, but in large-scale polymerizations it may prevent the scale-up of a commercially-acceptable latex or exact a heavy economic penalty in longer cycle times and reduced yields. 

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The coagulum formed during polymerization may take many forms and is commonly referred to by many names, often colloquial and sometimes profane, e.g., autoclave buildup, reactor fouling, filterable solids, button, sediment, silt, grit, seeds, sand, waste, scrap, or worse. In this discussion, the term coagulum will be used to denote any polymer recovered in a form other than stable latex. The general principles described earlier (1) will be recounted here, and experimental results on the formation of coagulum will be presented. 

Residual concentrations of aminocarb in water as well as in sediment were higher in autoclaved samples because of the absence of microbial activity. The pattern of mobility of the chemical from water to sediment was similar to that observed in non-auto-claved samples, but its overall persistence was higher and because of this, a gradual buildup of the active ingredient in sediment occurred in the closed flask. Most of the aminocarb was likely adsorbed onto particulate matter in suspension and then gradually settled in the sediment. Nearly 97% of the fortified aminocarb remained in the autoclaved sample (closed flask) at the end of experiment out of this 34% was in water and 63% was adsorbed onto sediment. In contrast, 51% of the fortified amount of aminocarb remained in the open flask, of which 26% was in water and the rest in sediment. Sediments, like water, contained detectable levels of demethylated aminocarb moieties as well as the phenol, but among them, the monodemethylated derivative (methylamino Matacil) was predominant compared to the other two metabolites. 

In a second example, CF is promoted by increased impurity-sulfur in ferritic steels subjected to low-frequency loading in pressurized pure water at 288°C (Fig. 15) [22,23], MnS inclusions, which intersect crack flank surfaces, dissolve to enrich the occluded crack solution in sulfide. These anions promote crack advance by increasing the anodic charge that is passed per film rupture event, or perhaps by the HEE mechanism. This effect of steel sulfur content is severe for a stagnant environment within the autoclave, and is eliminated by turbulent solution flow which reduces sulfide buildup within the crack [66],... 

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