High-Shear Extruded Products

Many methods for the conversion of acid copolymers to ionomers have been described by Du Pont (27,28). The chemistry involved is simple when cations such as sodium or potassium are involved, but conditions must be controlled to obtain uniform products. Solutions of sodium hydroxide or methoxide can be fed to the acid copolymer melt, using a high shear device such as a two-roll mill to achieve uniformity. All volatile by-products are easily removed during the conversion, which is run at about 150°C. A continuous process has been described, using two extruders, the first designed to plasticate the feed polymer and mix it rapidly with the metal compound, eg, zinc oxide, at 160°C (28). Acetic acid is pumped into the melt to function as an activator. Volatiles are removed in an extraction-extruder which follows the reactor-extmder, and the anhydrous melt emerges through a die-plate as strands which are cut into pellets. 

Surelease. a product of Colorcon. is produced by first melt extruding ethylcellulose with oleic acid and dibutyl sebacate (DBS) (or fractionated coconut oil) to form a molten plasticized polymeric blend. This molten blend of plasticized ethylcellulose is then introduced into an ammoniated water solution under high shear and pressure to disperse small droplets of plasticized ethylcellulose into the water phase (67). Ammonium oleate is produced in situ during this emulsification process to stabilize the colloidal ethylcellulose particles (67). Additional purified water is then added to reduce the final solids content of the pseudolatex dispersion to 25%. The Surelease coating system does not contain an ionic surfactant, and therefore does not exhibit the pH-dependent drug relea.se observed with Aquacoat ECD (66),... 

In non-reactive blending, a two- (or multi-)phase mixture is formed when the immiscible polymers are physically mixed with each other. The minor phase, rich in B, is dispersed as droplets into a major phase rich in A. Apart from low interfadal tension, high shear rates and similar viscosities of both polymers are important for the size of the dipersed phase and therefore for the product quality. The reactive route follows the synthesis of a minor component via polymerization into a major component that acts as a host polymer. An alternative route for reactive blending is in situ formation of block co-polymers during the mixing process to decrease the interfacial tension. An extruder is the most commonly applied apparatus for the continuous production of polymer blends. 

Most processes for recycling of commingled plastics depend on a predominance of polyolefin in the mix to serve as a matrix within which the other components are dispersed. One of the early processes was the Mitsubishi Reverzer, which was developed in Japan. This process used a short-time, high-temperature, high-shear machine which could handle up to 50% filler. The plastics were first softened in a hopper and then mixed in an extruder. Products were formed in a variety of shapes by flow molding, extrusion, or compression molding. However, the equipment was never successfully marketed. The Klobbie process, developed in the Netherlands in the 1970s, consisted of an extruder... 

---