Reproducible mixing

The final quality and reproducibility of rubber compounds mixed from scratch on a two-roll mill, or finalisation of compound batches mixed in an internal mixer, depend to a large degree on the skill of the mill operative. In order to overcome to some extent the reliance on operative skill and to ensure reproducible mix quality many mills are now fitted with stock blender units. These consist of a driven twin roller system, of similar overall length to the mill rolls, fitted above the mill frame. 

In this case, it is generally preferable to use a higher concentration of reagent (if it is soluble enough) and add it at a lower rate than the opposite to ensure more reproducible mixing in the reaction vessel. 

Outline procedures are given for using both mill and internal mixers which provide a very sound basis for obtaining reproducible mixes provided the detailed schedule for any particular mix is properly standardised and adhered to. This is all that can be hoped for considering that, in general, the results from laboratory mills and mixers are not identical with those obtained with full-sized factory equipment. 

If multiple detectors are to be used in FIA, then the gradient must be left intact or complete and reproducible mixing must occur. Ideally all detectors must see a similar dispersed sample plug. The first detector will observe a reproducible concentration gradient. If that detector creates irreproducible turbulence, then subsequent detectors will not observe reproducible sample zones, which results in imprecision. This requirement complicates multiple-cell systems. The simplest approach is to split the stream into enough individual streams to feed all the detectors. This is more costly in terms of components, but avoids significant development time in sensor cell design. 

Primarily because of difficulties in reproducing mixing times. Equation 18.11 is not often applied directly. Some time t (/j 0), when the solution is homogeneously mixed, is used as the initial point from which Equation 18.10 is integrated. Thus, the difference in concentration AA over a time interval A/ (A/ = 2 — ti) is related to [A]o by... 

A versatile and classical method for studying kinetic reactions and other kinetic phenomena on short time scales is the use of a stopped-flow apparatus (SFA) for fast reproducible mixing and then to apply, e.g., spectroscopic methods for detection. In this technique, the reactants are rapidly mixed in a mixing chamber, usually under full turbulent flow that ensures fast homogenization on length scales down to nanometers [99]. Provided that short, synchronized acquisitions can be made. X-ray or neutron scattering can be used to probe kinetic transitions and other processes directly by measuring the temporal evolution of the intensity of the (mixed) sample. 

The need to introduce a reagent solution and reproducibly mix it with the analyte. However, this drawback is not unique to chemiluminescence. For example, fluorescence detection often requires derivatization of the target analyte to create a fluorophore suitable for sensitive detection. 

The SFTR reactor uses two immiscible fluid phases (gas or liquid) to create individual micro volumes of previously well-mixed reactants. A static mixer is placed upstream, which ensures efficient and reproducible mixing of the reactants before they enter the reactor. The reactor is believed to be potentially suitable for the forced precipitation of crystals where the mixing step is of major importance in determining their chemical and physical characteristics. Instead of scaling up by increasing vessel size, the SFTR is to be scaled out by replication of similarly sized configurations, as production demands. 

The speed of the mixer was calibrated using a Mitutoyo digital tachometer before and during the mixing experiments to ensure accurate and reproducible mixing speeds from batch to batch. The prepared blends were dried and kept in separate sealed plastic bags for further analyses. 

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