Method for the production of a polypropylene blend
AssigneeDer Grune Punkt - Duales System Deutschland AG
InventorsGuido Gorski, Andreas Thiele
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Abstract
A method for producing a polypropylene blend from a plastic packaging materials containing high molecular weight polypropylene, other high molecular weight polymers such as polyethylene, low molecular weight polymers and other contaminants. The method includes extraction, solid-liquid separation and liquid-liquid phase separation using various organic solvents. The polypropylene blend has a purity of 95% and has favorable melt flow characteristics, while retaining satisfactory mechanical properties.
Claims20
A method for producing a polypropylene blend from a plastic mixture comprising high molecular weight polypropylene, other high molecular weight polymers and low molecular weight polymers, the method comprising the steps of:
- (a) combining the plastic mixture with a first solvent in which at least one of the high molecular weight polymers is soluble;
- (b) maintaining the solvent at an operating temperature at which essentially no high molecular weight polymer is dissolved, and adjusting the weight ratio of plastic mixture to solvent;
- (c) extracting the low molecular weight polymers from the plastic mixture during a residence period;
- (d) dissolving the plastic mixture resulting from step (c) in a second solvent, which is the same as or different from the first solvent, and separating insoluble components from the solution by solid-liquid separation;
- (e) generating at least two liquid phases having different polymer compositions, and selectively precipitating polypropylene from at least one liquid phase using shearing or flow to form a polypropylene fraction;
- (f) degassing the polypropylene fraction;
- and
- (g) granulating the polypropylene fraction to form a polypropylene blend.
A polypropylene blend which has been recovered from a plastic mixture comprising high molecular weight polypropylene, other high molecular weight polymers and low molecular weight polymers, wherein the recovery method comprises the steps of:
- (a) extracting the low molecular weight polymers from the plastic mixture using a first solvent at a temperature at which essentially none of the high molecular weight polymers is dissolved;
- (b) dissolving the plastic mixture resulting from step (a) in a second solvent, which is the same or different from the first solvent, and separating insoluble components from the resulting solution by solid-liquid separation;
- (c) generating at least two liquid phases having different polymer compositions, and selectively precipitating polypropylene from at least one liquid phase using shearing or flow to form a polypropylene fraction;
- and wherein the polypropylene blend contains at least 95% by weight polypropylene, an average melt flow index measured in accordance with ISO 1133 at 230° C. and 2.16 kg load of 14.7 to 17.9 g/10 min., and has an average yield stress of 29.5 to 36.1 Mpa.
Dependencies are inferred from the claim text.