Recommended Procedure for Dissolving Dense Nitrocellulose
With common types of mixers having stirrers with high peripheral speeds ,which give good circulation and high shear. Dense nitrocellulose will dissolve quickly and no special technique is necessary.
Due to its compact form dense nitrocellulose may, however, take a little longer to dissolve than the fibrous forms when using low speed mixing equipment. With such equipment the dense nitrocellulose may often be dissolved more readily by using the following method:
1
Place the active component of the solvent mixture in the mixer and start the stirrer. If there is insufficient active solvent add some of the diluents but use as little diluents as possible because it is important to start with the strongest possible active solvent mixture. If it is not possible to separate the active solvent form the diluents use only as much of the total solvent mixture as is necessary to form a suspension of the grains for the initial mixing and add the remainder as required to complete the solution.
2
Slowly add the nitrocellulose through a hopper in a continuous flow.DO NOT add in lumps or handfuls and make sure that any aggregates are broken down before addition. Continue stirring until the grains begin to gel and the solution thickens.
3
Increase the power as the solution thickens to maintain as high a shear rate as possible.
4
When the stirrer begins to labour add the plasticiser and, if necessary, small increments of the diluents keeping the solution as viscous as possible and maintaining a high shear rate. During the process, stop the stirrer and scrape down from the sides and blades any grains of nitrocellulose which are not being properly incorporated in the mix.
5
When the solution appears to be complete add the remaining diluents slowly and continuously. Finally add the resin (in solution) and any pigment base and continue stirring until uniformly mixed.
6
Specks of dust, hairs or other impurities which may be introduced from the packing or the raw materials should be removed by filtering.
Note
When two grades of Nitrocellulose with different viscosities are used in one formulation, it is preferable to dissolve each separately and then mix the two solutions. This is also a useful method for blending two grades of nitrocellulose to obtain the required viscosity. If it is not possible to make two separate solutions the higher viscosity nitrocellulose should be dissolved first.