Dear experts,
I am investigating how polyurethanes are affected by the degree of mixing. More in general, I am interested to study how the contact between the two reactants (in my case polyol and isocyanate), and as a consequence the reaction rate, can be affected by changing tre speed of the stirrer.
May you suggest me which parameter to investigate?
And, please, if you have some reference about this topic can you share it?
Thanks in advance.
A good starting point would be to compare the rate of your chemical reaction to the rate of mixing (Damkohler numbers). If you can mix the reactants much faster than they can react chemically, then the stirring speed will not make much of a difference. But if your mixing rate is slower than the chemical reaction rate, any increase in the stirring speed will have a large impact on the final result.
Surface area of contact of reactants has great influence on rate of chemical reaction. So, the essence of mixing is to increase the surface area of contact of the reactants. Therefore, increasing the surface area of a solid reactant exposes more of its particles to attack, which often results in an increased chance of collisions between reactant particles, since there will be more collisions in any given time and the rate of reaction increases.
In line with what Leander Boer said earlier, rate of chemical reaction is considered in determining the rate of mixing. So, the two important parameters to investigate is the rate of mixing and duration of the mixing. If you have the time and resources, you can adopt RSM/DoE experimental design to investigate the detailed effects.
If you are working in DMF ( dimethylformamide) is very important the purity of the Solvent ; HCCOH and DMA ( dimetyl amine ) are the product of the DMF Hydrolisys and are acting as chain starter and chai stopper, Therefore thericontent is to be less than 5-10 ppm
all three comments are correct, but Cosime, the first thing will be to learn about mechanisms and kinetics of any chemical reaction, indifferent of being unidirectional or bidirectional! Once you understand these, you will be able to ask clever questions and answer cleverly.
In general the Rate of mixing and the duration of mixing... How ever I suggest you investigate on effects of corrugation parameters on fluid mixing characteristics.
Hi,
When the surface area of reactants is increased, the frequency of collision between the reactant particles is also increased. Greater the surface area, higher will be the rate of reaction.
Best regards
For a good reaction of polyurethanes by MDI and Polyols we was utilising a special strirred reactor composed by an anchor and a turbine( two shaft in indipendent one inside the other ) with a turbine at very high speed when introducing the chain starter and the chain stopper
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