After a brief review of the breakthrough inventions, we'll discuss the many “rules of thumb” engineers have been using over the years in product and process development. The question is: How to apply the available fundamentals to modify the simple rules to bring about more effective distributive and dispersive mixing? In fact, strictly speaking, the most accepted rule of thumb being applied for dispersive mixing is valid only in simple shear flow of a single non-interactive Newtonian droplet. For more concentrated practical systems, one must consider the forward dispersing effect as well as the backward coalescence effect. The resultant dispersion of immiscible polymer blends is actually the net result of these two opposing processes. Two major innovations significantly affecting the balance will be discussed: in-situ grafting and in-situ crosslinking.
Selected breakthrough inventions in compounding processes (e.g. those utilizing twin-screw co-rotating extruders) and polymer blends, as well as the related fundamental principles, will be discussed in some detail.
Some features of each of the five steps during extrusion of a polymer compound, viz., solid conveying, solid compaction, melting, melt mixing, and pumping, were revealed by means of flow simulations, visualizations, and on-line monitoring studies. (Ref. 1) Challenges observed in each of the steps, such as feeding of powdery material, lubricated melting, melt mixing of ingredients with mismatched viscosities, melt pumping problems, as well as questions related to extrusion rate limitation, polymer degradation, etc., will be examined in view of existing fundamental principles including the phase inversion principles discovered by the author.
In contrast to polymer characterization, very little is known with respect to the compounding process characterization and the progression of the mixing process. We shall review how can one utilize on-line monitoring techniques of dynamic pulse perturbation, and the Q & N (or the Rate & RPM) mapping in the author's recent publications to evaluate the mixing intensity, mixing time, and energy absorption with respect to extrusion operating conditions and screw design. Applications of these on-line monitoring techniques to the operations of the “Mega” or the “Ultra” Compounders, in-situ chemical grafting or degradation during reactive extrusion, as well as product quality control, will also be discussed.