Mixing is the first step of plastics processing allowing to prepare plastic formulations by compounding one or several polymer(s) and additives. There are different critical criteria to achieve a convenient blend of the different raw materials, mainly the good incorporation of additives, their right distribution and dispersion according to the provided conditions. Mixing is the base of a successful end product. If mixing isn’t properly carried out, the other manufacturing steps can’t compensate for it. The oldest and most common sense of mixing is the accurate incorporation, the regular distribution and dispersion of ingredients in a polymer matrix thanks to mechanical and thermal means to make a homogeneous compound at a micro-scale.
Apart mechanical mixing, some other methods, used in particular cases, lead to the same properties thanks to, for example adsorption of an additive solution into the polymer matrix followed by an efficient drying. Mixing by absorption of dye or curing agent solutions followed by an efficient drying are some examples.
More recently new senses appeared leading to well-ordered and structured distribution of ingredients in the matrix with a limited dispersion at the boundary limit between an ingredient and a polymer phase or between two phases of two different polymers. These processes are well represented by chaotic mixing and layer multipliers. For example, chaotic mixing can be used for conductive compounds and layer multipliers for extrusion of two polymers. These methods lead to unique features for common additives incorporated in common polymers.
Basically classic mixing can be sliced into batch processes in internal mixers or in roller mills and in continuous processes based on or derived from single or twin screw extruders. Numerous devices coexist allowing to treat lab problems up to high-volume productions. Static mixers, ultrasonic or vibration assistance can enlarge the scope of mixing efficiency.
Lastly, innovative processes such as Solid-State Shear Pulverization (SSSP) lead to new solutions for desperate cases unsatisfied through classic mixing.