Residence time rubber processing

Emulsions Emulsions have particles of 0.05 to 5.0 [Lm diameter. The product is a stable latex, rather than a filterable suspension. Some latexes are usable directly, as in paints, or they may be coagulated by various means to produce massive polymers. Figures 23-23d and 23-23 show bead and emulsion processes for vinyl chloride. Continuous emulsion polymerization of outadiene-styrene rubber is done in a CSTR battery with a residence time of 8 to 12 h. Batch treating of emulsions also is widely used. 

Typical halogenation processes for making halobutyl rubbers involves the injection of chlorine or bromine into a solution of butyl rubber. The reactants are mixed vigorously in the halogenation reactor with a rather short resident time, typically less than 1 min, followed by the neutralization of the HC1 or HBr and removal of the unreacted halogen (13). The procedures of halogenation have been described in detail elsewhere (41,42). 

Chloroprene is of high industrial importance for manufacture of synthetic rubbers. For a long time the synthesis was based on acetylene. More recent processes are based on butadiene as a feedstock, which is substantially cheaper [29]. The initial step is a gas-phase free-radical chlorination at 250 °C and temperature control is ensured by use of excess butadiene (molar ratio of Cl2 to butadiene 1 5 to 1 50) [44]. To limit side reactions, short contact time reactors operating at higher temperatures and residence times below one second are also known [45], Good mix-... 

In GPPS systems, these peroxides mainly supplemented the free radicals generated by thermal initiation, whereas in the HIPS process, it was found that they could enhance the grafting of styrene to unsaturated rubbers, such as polybutadiene. Additional benefits of organic peroxide initiators were increased production per unit reactor volume, reduction of styrene oligomers and lower reactor temperatures. The instantaneous removal of peroxide feed to a runaway reactor also provides a safety mechanism. Peroxide-initiated systems have higher reaction rates owing to shorter reactor residence times, so the ability to remove one source of radical initiation quickly is important. 

This is carried out in the presence of mixed oxides based chiefly on molybdenum, bismuth, tellurium, eta, in the vapor phase, around 350 to 450°C, at low pressure, with residence times of 1 to 5 s to enable once-through isobutene conversion higher than 95 per cent, n-butenes conversion of about 80 to 85 per cent, and methacrolein and butadiene molar yields of 75 to 80 per cent Developed in particular by Japan Synthetic Rubber, Mitsubishi Rayon, Nippon Kayaku, Nippon Zetm, Ube, etc., this type of process comprises the succession of the following sequences ... 

In these cases a dispersed phase of a crosslinkable rubber is vulcanized in the presence of a matrix of a second, immiscible, non-vulcanizable polymer during the residence time of melt processing. Examples have also been reported in which a mixture of two vulcanizable polymers has been employed. Coran [1995] has summarized five key requirements for preparing optimum compositions by dynamic vulcanization ... 

Various processability tests are used to predict how well a rubber compound will process. However the process" can vary greatly. Table 1 shows the diverse categories of rubber processes and some of the quality characteristics and concerns associated with each process. The natures of these processes vary because of differences in applied shear rates, temperatures, residence times, etc. Changing a given compound property can improve performance in one or more of these processes but could hurt the performance in another process. This is why it is important to look at all processes in a manufacturing operation when implementing compound changes. 

Solution processes use autoclave, tubular, or loop reactors. As compared to slurry and gas-phase polymerization, solution processes are commonly operated at a much higher temperature to keep the polymer dissolved in the reaction medium, and at much lower average residence times (5-20 min, as opposed to 1-4 h). Since polymerization conditions are more uniform in solutions reactors - there are no inter- and intraparticle heat- and mass-transfer resistances, for instance - this configuration is commonly used for the production of EPDM rubbers with soluble Ziegler-Natta vanadium-based catalysts. Composition homogeneity is a require-... 

However, it is now a common practice to use the commercial, pre-functionalized rubbers for polyamide blending to achieve a more consistent blending process and product properties. The extruder residence time is utilized for achieving the desired degree of grafting and throughput. 

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