TABLE OF CONTENTS This method has only been used for separating low-molecular weight salts and interfacially active substances from protective colloids and high polymer plastics and for fractionating pure plastics according to their molecular weight.
Some examples of these four separation procedures are shown in Table 2.6.
| Plastic | Operation | Aim or separating procedure |
|---|---|---|
| (a) Fractional precipitation procedures (precipitation by addition of non-solvent for polymer to solvent solution of polymer). | ||
| Polyvinyl chloride | Stirring of a concentrated solution of tetrahydrofuran into methanol | Plasticisers, emulsifiers remain in solution, PVC and its polymers are precipitated |
| Polyacrylate | Stirring the solution in acetone into 20 times the amount of water | Emulsifiers, water soluble resins and salts remain in solution, polymerisate is precipitated |
| (b) Fractional precipitation (titration of solvent solution of polymer with non-solvent for polymer). | ||
| Polyacrylate | Water is added to the solution in acetone until faint turbidity occurs, acetone is then distilled off under vacuum | Emulsifiers, water soluble resins and salts remain in solution, polymerisate is precipitated |
| (c) Fractional precipitation (thermal precipitation of polymer from solution at low temperature). | ||
| Polyethylene | Dissolve in enough benzene to make a clear solution appear when warmed then cooled | Polymerisate is precipitated, additives soluble in cold benzene, paraffin, waxes, resins remain in solution |
| (d) Emulsion breaking methods | ||
| (1) Addition of solvent | ||
| Polymethacrylate-dispersions | Dispersion is stirred into 20 times its amount of methanol or isopropanol | Polymerisate is precipitated, emulsifier and... |
