Process to recycle expandable plastic materials and an expandable or expanded plastic material obtainable thereby
A process is disclosed to recycle and/or formulate expandable plastic materials using a system ( 1 ) comprising: an extruder unit ( 10 ), a mixer-heat exchanger unit ( 20 ), said process comprising the steps of: melting in the extruder unit ( 10 ), cooling in the mixer-heat exchanger unit ( 20 ), and controlling the melt pressure by means of a melt pump unit ( 50 ), followed by granulation, extrusion, or injection molding, wherein a first expansion agent ( 81 ) is not degassed during a melt processing in the system ( 1 ) such that it is substantially contained in the granulated expandable plastic material ( 130 ) or used to form either the extruded, formed and expanded plastic material ( 140 ) or the molded expanded plastic article ( 150 ). The present invention also relates to a granulated expandable plastic material ( 130 ), an extruded, formed and expanded plastic material ( 140 ), and a molded expanded plastic article ( 150 ) obtainable by said process.
1. A process to recycle and/or formulate expandable plastic materials using a system comprising the following process equipment in fluid communication with each other and in the following sequence:
an extruder,
a mixer-heat exchanger,
the system further comprising a melt pump also in fluid communication with the extruder and the mixer-heat exchanger,
wherein the melt pump ( 50 ) is located either (i) upstream of the mixer-heat exchanger and downstream of the extruder ( 10 ) OR (ii) downstream of the mixer-heat exchanger ( 20 ),
said process comprising the steps of:
melting a feedstream comprising an expandable plastic material containing a first expansion agent in the extruder to form a molten expandable plastic material,
cooling the molten expandable plastic material in the mixer-heat exchanger;
controlling the melt pressure of the molten expandable plastic material by means of the melt pump,
and subsequently either:
(i) granulating the molten expandable plastic material using a granulator to form a granulated expandable plastic material,
(ii) extruding the molten expandable plastic material by a die to a controlled reduced pressure, to yield an extruded, formed and expanded plastic material, OR
(iii) injection molding the molten expandable plastic material by of an injection molding to form a molded expanded plastic article,
wherein the expandable plastic material comprises at least 40% by weight of the feed stream, wherein the system does not have a degasification unit and the first expansion agent is not degassed during a melt processing in the system such that the first expansion agent is substantially contained in the granulated expandable plastic material or used to form either the extruded, formed and expanded plastic material or the molded expanded plastic article;
wherein the system further comprises one or more static mixers and a melt filter, wherein the method further comprises the steps of:
mixing the molten expandable plastic material using the one or more static mixers, and filtering the molten expandable plastic material using the melt filter prior to (i) granulation, (ii) extrusion, or (iii) injection molding.
2. The process of claim 1 , wherein the expandable plastic material comprises at least 60% by weight of the feedstream.
3. The process of claim 1 , wherein the expandable plastic material comprises at least 90% by weight of the feedstream.
4. The process of claim 1 , wherein the expandable plastic material comprises essentially all of the feedstream.
5. The process of claim 1 , wherein an expansion agent metering device is absent from the system and no addition of additional expansion agent is made.
6. The process of claim 1 , wherein an expansion agent metering device is present and an addition of additional expansion agent by means of the expansion agent metering device is carried out.
7. The process of claim 6 , wherein the expansion agent metering device is embodied so as to inject the additional expansion agent into the extruder.
8. The process of claim 6 , wherein one or more static mixers is present and additional mixing of the molten expandable plastic material by means of the one or more static mixers is carried out, and wherein the expansion agent metering device is embodied so as to inject the additional expansion agent into and/or before the one or more static mixers.
9. The process of claim 8 , wherein at least two static mixers are present, wherein in a first static mixer a dispersing step is carried out and which subjects the molten expandable plastic material to intensive mixing; and wherein in a second static mixer a retaining step is carried out and which subjects the molten expandable plastic material to less intensive mixing than in the first static mixer.
10. The process of claim 6 , wherein the additional expansion agent is injected and comprises an inert gas, a methylol, methyl formate, a pentane, a butane or their mixtures.
11. The process of claim 1 , wherein a masterbatch is added to the extruder.
12. The process of claim 11 , wherein the extruder is a single screw extruder.
13. The process of claim 1 , wherein an additive is added to the extruder.
14. The process of claim 1 , wherein the granulator is an underwater or strand granulator.
15. A granulated expandable plastic material, obtainable by the process of claim 1 .
16. The granulated expandable plastic material of claim 15 , containing one or more additives and at least one of the group consisting of a melt stabilizer, a synergist, an infrared reflector, an infrared absorber, a pigment, a nucleating agent, and a wax, wherein the expandable plastic material in the feedstream is obtained from a suspension polymerization method.
17. The granulated expandable plastic material of claim 15 , containing at least one flame retardant compound.
18. The granulated expandable plastic material of claim 15 , that is obtained by the process of claim 1 .
19. The granulated expandable plastic material of claim 15 , having molecular weight properties of a Mw of 150-250 kDalton, absolute, and a Mw/Mn of between 2.1 and 2.5.