Introduction To Chemical Mixing And Dispersion

1. Mixing is the process of reducing the non-uniformity of a mixture; it aims to refine and distribute components throughout the system while ensuring that the fundamental units of the components undergo no essential changes.

2. According to Brodkey's mixing theory, mixing involves three types of diffusive motion: molecular diffusion, eddy diffusion (turbulent motion), and bulk diffusion (convective motion).

3. Molecular diffusion dominates in gases and low-viscosity liquids. However, in polymer processing, the high viscosity of the melt renders the rate of molecular diffusion extremely slow, making it practically insignificant.

4. Eddy diffusion requires high flow velocities-implying that the polymer must withstand high shear rates-which can lead to polymer degradation; therefore, special attention is required in high-shear applications.

5. Bulk diffusion plays a dominant role in polymer processing. Based on the mode of mixing, the process can be categorized into two types: distributive mixing and dispersive mixing.

6. Dispersive mixing reduces material particle size through the application of external forces and achieves a uniform distribution of raw material components. This process involves both a reduction in particle size and a change in particle position.

7. Distributive mixing achieves a uniform distribution of raw material components through external forces without altering the size of the raw material particles. This process primarily promotes the random spatial arrangement of particles rather than reducing the dimensions of their structural units.