Analysis of shear-induced coagulation in an emulsion polymerisation reactor using computational fluid dynamics

Shear-dependent coagulation is a costly problem for the latex manufacturing industry, due to product degradation and reactor downtime. In this study, a method for calculating the shear-dependent coagulation rate in emulsion polymerisation is developed. The method combines simple models for coagulation (only binary collisions being considered) with the effects of rheology on the flow field, using computational fluid dynamics (CFD) to solve the detailed flow field in the reaction vessel. By using the local shear rates (LSR), the method developed provides a more detailed and system-specific assessment compared with using an average shear rate (ASR) for calculating the coagulation rate. The difference in the predictions between the ASR and the proposed LSR method was investigated. It was found that the ASR and LSR methods predict different coagulation rates, especially for more sophisticated coagulation models where the coagulation rate is not linearly dependent on the shear rate. The LSR method was also used to study the effect of the rheology of the latex, of the impeller speed and of the reactor design on the coagulation rate. It was found that the LSR method is useful for providing both visual and numerical means to identify regions with elevated coagulation rates in the modelled reaction vessel. The treatment provides estimates of the amounts of coagulum formed on the vessel walls and on the impeller.     

Operation of semi-batch emulsion polymerisation reactors: Modelling, validation and effect of operating conditions

A detailed dynamic model was developed for a styrene emulsion polymerisation semi-batch reactor to predict the evolution of the product particle size distribution (PSD) and molecular weight distribution (MWD) over the entire range of monomer conversion. A system exhibiting zero-one kinetics was employed, with the model comprising a set of rigorously developed population balance equations to predict monomer conversion, PSD and MWD. The modelling equations included diffusion-controlled kinetics at high monomer conversion where the transition from the zero-one regime to a pseudo-bulk regime occurs. The model predictions were found to be in good agreement with experimental results. Both particle growth and the PSD were found to be strongly affected by the monomer feedrate. Reactor temperature had a major influence on the MWD which was, however, insensitive to changes in the monomer feedrate. These findings were confirmed experimentally. As a result, it seems reasonable to propose that the use of the monomer feedrate to control the PSD and the reactor temperature to control the MWD are appropriate in practical situations. Consequently, an optimal monomer feed trajectory was developed off-line (using the validated reactor simulation) and verified experimentally by producing a polymer with specific PSD characteristics.     

Deformation processing of PMMA into high-strength fibers

Poly(methyl methacrylate) was drawn into fibers by melt extrusion followed immediately by a transient temperature drawing process. By varying five processing variables, fibers ranging from 0.635 mm to 25 μm in diameter were produced. Heat-induced relaxation of the aligned structure was used to determine the draw ratio of the resultant fibers and therefore the degree of polymer chain alignment imposed by the deformation process. The resulting changes in length and diameter were measured and it was found that draw ratios of 5–20 had been achieved under the varying processing conditions. It was also observed that fiber diameter immediately after drawing is a good predictor of the degree of orientation present in the fiber irrespective of the processing conditions. To test the effect molecular orientation has on material properties, fibers with varying degrees of orientation were tested in tension. As expected, increasing alignment resulted in increasing tensile strength. The maximum observed true ultimate tensile strength was 225 ± 53 MPa and was seen in fibers with a draw ratio equal to 18.7 ± 4.5. Fibers with a lower degree of alignment, while not as strong in tension, exhibited significantly increased ductility. True strains of as high as 25% were observed.     

Some properties of an exocellular lipase fromRhizopus arrhizus

Rhizopus arrhizus, a mold of the mucor family, excretes an active lipase when cultured properly. This lipase has a mol wt of 43,000 and a high carbohydrate content, Upon storage at 4C in aqueous solution, lipase I is slowly converted by proteolysis to a more cationic form, lipase II, which has a lower mol wt (32,000) and no carbohydrate.Rhizopus lipase shows the same positional specificity on long chain triglycerides as pancreatic lipase; it has no preferential side chain specificity against oleic vs. palmitic acid. Like pancreatic lipase,Rhizopus lipase acts on micelles of short chain triglycerides and is inhibited by high concentrations of bile acids; however, in the presence of deoxycholate,Rhizopus lipase does not require added Ca⁺⁺ for full activity.     

Ozonization of Aromatic Amines in Water

The oxidation of the following ami no compounds with ozone in aqueous solution (pH 7–2) was investigated: “4–chloroaniline, 2–aminophenol, 4–aminobenzoic acid, 4–amino–2–nitrophenol, 4–amino–5–hydroxynaphthalene–2,7–disulfonic acid, 4–aminobenzene sulfonic acid ( initial conentrations 1 mmole1). Total destruction of the compounds is achieved with 4 to 6 mmole ozone mmole amine. 20–40 % of the amine nitrogen is found as ammonia and a small part as nitrate (4%). In the initial stages of the ozonation the solutions turn colored. In the further course of the reactions the colored intermediates are oxidized and after 6 mmole ozone/mmole amine the solution are colorless. In all cases the colored intermediates are not or only to a small extend biodegradable but the final oxidation products are better biodegradable.     

Dietary fat effects on hepatic lipid peroxidation and enzymes of H2O2 metabolism and NADPH Generation

The purpose of this study was to determine the effects of dietary fat quantity and fatty acid composition on hepatic H₂O₂-metabolizing systems, activities of NADPH-generating enzymes and lipid peroxidation. Onemonth-old male C57BL/6J mice were fed one of six diets: (i) 5% fat, rich in 18∶2n−6 fatty acid (5% N−6); (ii) 20% fat, rich in 18∶3n−3 (N−3); (iii) 20% fat, rich in 18∶2n−6 (N−6); (iv) 20% fat, rich in 18∶1n−9 (N−9); (v) 20% fat, rich in saturated fatty acids (SAT); and (vi) 20% fat, deficient in essential fatty acids (EFAD); for 11 wk. Comparisons between animal groups receiving different fat quantities showed that activities of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and malic enzyme (ME, EC 1.1.1.40) and the levels of conjugated dienes were significantly lower in the N−6 than in 5% N−6 group. Conversely, activities of catalase (CAT, EC 1.11.1.6) and seleniumglutathione peroxidase (SeGSHPx, EC 1.11.1.9) were higher in the N−6 than in 5% N−6 group. Among the five dietary groups receiving 20% fat but differing in fatty acid composition, CAT activity was lower in the N−9 group, SeGSHPx activity was lower in the EFAD group, and glutathione reductase (GSSGR, EC 1.6.4.2) activity was higher in the N−6 than in the N−3, N−9, SAT and EFAD groups. The EFAD group had much higher levels of total lipids and conjugated dienes, as well as activities of NADPH-generating enzymes, including G6PDH, ME and isocitrate dehydrogenase (EC 1.1.1.42), than the other four high-fat groups. The hepatic levels of malondialdehyde were not different among the five groups fed 20% fat. In the EFAD group, higher hepatic lipid content can be attributed to higher activities of NADPH-generating enzymes, and the elevation of conjugated diene levels may be related to increased oxygenation of 20∶−6 (Mead acid)via the lipoxygenase/cyclooxygenase pathway. In short, both dietary fat quantity and fatty acid composition selectively affected hepatic H₂O₂-metabolizing systems, activities of NADPH-generating enzymes and lipid peroxidation status.     

Tensile yield in polyethylene

Uniaxial tension tests to the yield point were performed on polyethylene as a function of temperature from 21 to 117°C at a strain rate of 2 min^?1. At 21, 45, and 69°C, measurements were also made at strain rates from 0.02 to 8 min^?1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (140°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy amorphous polymers. The ratio of yield stress to (initial) Young's modulus is 0.021 at room temperature and increases to 0.059 at 117°C. Also this ratio was found to decrease with log strain rate. For instance, at 21°C for a strain rate of 0.02 min^?1 the value was 0.023, while at 8 min^?1 this value decreased to 0.020.     

Ring contraction and dehydrogenation in polycyclic hydroaromatics at coal liquefaction temperatures

The thermal behaviour of 1,2,3,4,5,6,7,8-octahydroanthracene and 1,2,3,4,5,6,7,8,9,10,11,12-dodecahydrotriphenylene has been observed over the temperature range 400–500 °C in the presence and absence of bituminous coal. It is shown that the ratio of ring contracted product to dehydrogenated product increases with increasing reaction temperature, but the amount of ring dehydrogenated product is increased considerably by the presence of coal. The decomposition reactions are similar to those reported for tetralin, except that the polycyclic hydroaromatics react at much lower temperatures, and also further degrade by ring cracking reactions.     

Structural order in heat treated vinyl chloride polymers

Three vinyl chloride polymers were annealed at temperatures in the range 40–160°C for times varying from 0.5 to 5 h. Structural changes occurring in the polymers were examined by density measurement, differential thermal analysis and X-ray diffraction. It was shown that the three polymers varied in their original crystallinity. Attempts to totally remove this crystallinity, were unsuccessful; further crystallinity could be introduced by annealing above T_g Changes induced by annealing below T_g were not due to crystallization. Methods used to measure crystallinity in poly(vinyl chloride) (PVC) were assessed.     

Ageing of some high surface area solids

The ageing (fall in surface area) of samples of aluminium hydroxide has been studied by observing the changes in surface area and porous texture revealed by nitrogen adsorption. Ageing was carried out over phosphorus pentoxide and at 33% r.h. The effect of this change in r.h. depended on the texture of the aluminium hydroxide. Ageing was faster at 33% r.h. in the amorphous form which contained discrete flocs. Pseudoboehmite behaved as a true xerogel and some samples even increased in surface area by swelling when stored at the higher humidity. Some data for calcium silicate hydrates and samples of a commercial pyrogenic silica are included for comparison. The former were prepared in powder and paste (xerogel) form. The two forms responded differently to the two humidities but in the opposite sense to the corresponding aluminium hydroxide textures: thus the surface area of pastes fell more rapidly at the higher r.h. The surface area of samples of the silica fell when they were stored normally in air tight containers. They eventually reached steady values and a reduction of a similar magnitude could be produced rapidly by agglomerating the spherical particles in hot water. Mechanisms of ageing involving simple adhesion and its reverse depending on r.h., hydroxyl group condensation, and sintering aided by dissolution or surface diffusion are discussed.