for enriching at least one polymer from a polymer-containing
waste and polymer recyclate
The subject of the invention is a solvent-based plastic material recycling
method with which polymers can be recovered from a polymercontaining
plastic material waste. The method is based on the use of a
solvent doped with a thermostabiliser, with which polymers in the form
of a solid-liquid extraction are extracted from the plastic material waste
at temperatures above 70°C. By means of the presented method,
polymer recyclates which have improved mechanical properties relative
to conventional recycled polymers can be provided. Furthermore, the
use of at least one thermostabiliser in at least one organic solvent is
proposed for solvent-based isolation of at least one polymer from a
polymer-containing waste.
LLDPE, LDPE, HDPE, PP, ABS, PS, EPS, PA, PC, PC/ABS and PET
belong to the widely used types of polymer. These are used in the most
varied of products and are therefore a component of much "postconsumer"
waste. Thus, when recycling and processing old electrical
appliances, old cars, packaging waste and plastic material fractions, a
high proportion of these polymers inter alia are produced.
------' -1, 2
Separation of polymers from waste fractions is frequently undertaken
via density-based technologies, however the density range of the
individual polymers is very wide because of a large number of additives
which are used and therefore only sufficiently specific with good
knowledge of the input qualities.
In addition, density-based waste processing of waste with films is
comparatively difficult. Alternatively, spectroscopic sorting methods are
applied, however these fail generally in the case of film-rich waste since
the automatic sorting is generally effected via compressed air strips, the
reliability of which decreases in the case of a small particle size and
particle weight and also with increasing planarity.
Therefore in the past century, solvent-based plastic material recycling
technologies have already been developed. US 5,278,282 A describes
very comprehensively inter alia recycling of polymers from polymer
mixtures by means of various solvents. A similar procedure for complex
plastic material waste with partly different solvents is described in US
6,329,436 Bl.
The advantage of solvent-based methods hereby resides in the selective
solution of one or more polymers from a complex waste mixture and in
the possibility of extensively separating this solution from insoluble
components by mechanical means. As a result, the resulting polymer
recyclates, compared with products of the above-mentioned densitybased
and spectroscopic technologies, are purer.
Unfortunately however, recyclate qualities which are similar to v1rgm
materials can be achieved only rarely, since the solvent-based
technologies subject the plastic material waste to a significant
temperature-time burden. This is the case in particular for polyolefins
(LLOPE, LOPE, HOPE, PP) which can be dissolved predominantly above
3
100°C. However also for PS, PC, PA and PET, in part very high solution
temperatures of up to above 220oC are described (US 5,278,282 A).
This leads to thermooxidative reactions in the plastic material waste, as
a result of which polypropylene, PC, PET and PA, for example, are
partially decomposed and have mechanical properties which are
changed by the molar mass loss, such as lower melt viscosities
(increased MFR values).
For polyethylene, it is described that a fairly long thermal exposure
leads to increased gel formation, i.e. partial regions of the PE matrix
form a crosslinking as a result of the thermooxidative primary damage.
The resulting gel regions have different solution- and melt properties
which are reflected in impaired mechanical properties and optical faults
in the recyclate.
In order to suppress the thermooxidative damage during extrusion,
thermostabiliser.s, ... which are used both in the production of v1rgm
materials and in recycling by re-extrusion have been developed. Thus
WO 94/07950 A describes the enhanced recyclate quality when using
thermostabilisers in the re-extrusion of polyolefin-containing plastic
material waste. There may be mentioned here in this respect two very
frequently used proprietary products:
Irganox 1010: a sterically hindered phenolic antioxidant which
prevents thermooxidative decomposition of polymers, waxes and
oils; and
Irgafos 168: a hydrolytically stable phosphite-based secondary
process stabiliser.
Starting herefrom, it was the object of the present invention to provide a
method for isolation of polymers from polymer-containing waste which
'-1 4
causes less thermooxidative damage to the polymers relative to known
methods.
The object is achieved by the method for isolation of at least one
polymer from polymer-containing waste according to claim 1 and the
use of at least one thermostabiliser in at least one organic solvent for
solvent-based isolation of at least one polymer from a polymercontaining
waste according to claim 17. The dependent claims reveal
advantageous embodiments.
According to the invention, a method for isolation of at least one
polymer from polymer-containing waste is provided, which compnses
the following steps:
a) mixing a polymer-containing waste with an organic solvent
comprising at least one thermostabiliser for polymers, at least
one polymer being dissolved in the organic solvent and an
insoluble part of the waste being left behind;
b) at least partial isolation of the solution comprising at least one
polymer and at least one thermostabiliser from the insoluble
part of the waste;
c) at least partial separation of the organic solvent from the at least
one precipitated polymer.
It was found that, by using an organic solvent with a thermostabiliser
as extraction agent, the thermooxidative damage to polymers can be
significantly reduced during extraction thereof from polymer-containing
waste. On the one hand, the reduction in the average molar mass of
the extracted polymers can hence be restricted. On the other hand, the
formation of crosslinkings of the polymer molecules, i.e. gel formation,
can consequently be reduced. Both effects have a positive effect on the
5
mechanical properties of the isolated polymers. The negative influence
of the isolation method on the mechanical properties of the isolated
polyolefins, which is known in the state of the art, is hence as low as
possible.
The solubility time in step a) can be varied and/or adapted to the
particle size of the treated plastic material waste.
Preferably, the at least one polymer is dissolved, in the method
according to the invention, at a temperature of<: 20°C, preferably of 70°
to 200°C.
The organic solvent can comprise one or more hydrocarbons or consist
thereof, preferably hydrocarbons with a boiling point of 60 to 250°C,
particularly preferably 100 to 220°C and very particularly preferably
130 to 200°C.
Preferably, the polymer-containing waste which is used in the method
comprises at least one polymer selected from the group consisting of
LLDPE, LDPE, HDPE, PP, ABS, PS, PA, PC, PET and mixtures hereof or
consists of these. Preferably, the polymer-containing waste comprises
at least one film or consists thereof.
The thermostabiliser can be selected from the group consisting of
sterically hindered phenols and organic phosphites and phosphonites,
preferably sterically hindered phenolic antioxidants and phosphitebased
secondary process stabilisers. In particular, the thermostabiliser
comprises no metal oxides, metal hydroxides and/or metal carbonates.
In step b) of the method according to the invention, the solution can be
isolated from the insoluble waste via at least one mechanical method,
preferably sieving and/ or filtration.
6
Preferably, after isolation of the solution in step b), precipitation of the
at least one polyolefin from the solution is undertaken. The
thermostabiliser is thereby jointly precipitated for the large part, i.e. at
least 30% by weight, preferably at least 50% by weight, respectively
relative to the total quantity of thermostabiliser.
In a preferred embodiment, precipitation of the at least one polymer
from the solution is effected by lowering the temperature of the solution,
preferably by lowering the temperature of the solution to :;; 80°C. The
precipitated polymer can hereby have a solid content of 10% by weight
to 40% by weight, preferably 20% by weight to 30% by weight.
Optionally, the precipitation of the at least one polymer can be effected
by the addition of a nonsolvent which is miscible at solubility
temperature, e.g. aliphatic alcohols.
In step c), the at least one precipitated polymer can be separated
mechanically from the solution, preferably filtered off and/ or pressed
off. Separation at a temperature of 50 to 150°C and/or by applying a
vacuum is particularly preferred. The vacuum can have a pressure of :;;
100 mbar.
Preferably, step c) is implemented in a vacuum kneader, in a degassing
extruder and/ or in the form of powder drying.
In a further preferred embodiment of the method according to the
invention, the solvent is used again in step a) after step c). Preferably,
the solvent is guided in circulation in the method according to the
invention, i.e. is permanently recycled.
Optionally, at least one further thermostabiliser can be added in at least
one of the steps of the method according to the invention.
7
In a further preferred embodiment of the method according to the
invention, the polymer-containing waste compnses a plurality of
different polymers. Preferably, the various polymers are dissolved by
successive dissolving steps with an increasing solubility temperature
and subsequently are separated from the insoluble polymers and
insoluble parts of the waste at the respective solubility temperature.
Optionally, different polymer fractions are extracted selectively, m
succession, with the same solvent-thermostabiliser mixture at
increasing solubility temperatures.
In particular, neither a density-based separation method nor separation
via compressed air strips, nor separation via dispersion of the polymercontaining
waste in water is implemented in the method according to
the invention.
Furthermore, a polymer which can be produced or isolated with the
method according to the invention is provided according to the
invention.
The polymer according to the invention can comprise at least one
thermostabiliser, preferably in a concentration of 0.01 to 2% by weight,
particularly preferably of 0.05 to 0.5% by weight.
According to the invention, the use of at least one thermostabiliser in at
least one organic solvent is proposed for solvent-based isolation of at
least one polymer from a polymer-containing waste.
The subject according to the invention is intended to be explained in
more detail with reference to the subsequent Figure and the subsequent
example, without wishing to restrict said subject to the specific
embodiments shown here.
8
Example
In batch A, 10 g of polypropylene(PP) virgin material granulate (Moplen
HP420M) was dissolved for 30 minutes at 150°C in a glass beaker in 90
g of a paraffinic hydrocarbon mixture (CreaSolv® PO), to which
respectively 0.05% of the thermostabilisers Irganox 1010 and Irgafos
168 were added. In a parallel batch B, respectively 0.25% of the two
thermostabilisers was used, in the parallel batch C, respectively 0.5%.
In parallel batch D, no thermostabilisers were used.
Subsequently, the solutions were cooled to below 80°C with agitation, a
dispersion of precipitated PP particles being produced. The PP particles
are filtered off and subsequently dried for 10 hours at 80°C in the
vacuum drying cabinet at 100 mbar.
According to DIN EN ISO 1133, the melt mass flow rate (MFR) of the
initial granulate and also of the dried products of batches A - D was
determined (see Figure 1).
The MFR values listed in Figure 1 verify the advantageous nature of the
addition of thermostabilisers which avoid thermooxidative
decomposition of the PP and hence suppress the increase in the MFR
which is apparent in batch D and caused by decomposition.

Patent claims
1. Method for enriching at least one polymer from a polymercontaining
waste, which comprises the following steps:
a) mixing the polymer-containing waste with an organic
solvent comprising at least one thermostabiliser for
polymers, at least one polymer being dissolved in the
organic solvent and an insoluble part of the waste being left
behind;
b) at least partial separation of the solution comprising at
least one polymer and at least one thermostabiliser from the.
insoluble part of the waste;
c) at least partial separation of the organic solvent from the at
least one polymer.
2. Method according to claim 1, characterised in that the at least
one polymer is dissolved at a temperature of ;, 20oC, preferably
of 7ooc to 200°C.
3. Method according to one of the preceding claims, characterised
in that the organic solvent comprises one or more hydrocarbons
or consists thereof, preferably hydrocarbons with a boiling point
of 60 to 250°C, preferably 100 to 220oc and particularly
preferably 130 to 200°C.
4. Method according to one of the preceding claims, characterised
in that the polymer-containing waste comprises at least one
··-1
polymer selected from the group consisting of LLDPE, LDPE,
HDPE, PP, PS, ABS, PET, PA, PC, PC/ABS, PPO/PS and
mixtures hereof.
5. Method according to one of the preceding claims, characterised
in that the thermostabiliser is selected from the group consisting
of sterically hindered phenols and organic phosphites and
phosphonites, preferably sterically hindered phenolic
antioxidants and phosphite-based secondary process stabilisers
and mixtures thereof.
6. Method according to one of the preceding claims, characterised
in that, in step b), the solution is isolated from the insoluble
waste via at least one mechanical method, preferably sieving
and/ or filtration.
7. Method. according to one of the preceding claims, characterised
in that, after isolation of the solution in step b), precipitation of
the at least one polymer from the solution is effected, preferably
the at least one thermostabiliser being essentially jointly
precipitated.
8. Method according to one of the preceding claims, characterised
in that precipitation of the at least one polymer from the solution
is effected by lowering the temperature of the solution, preferably
by lowering the temperature of the solution to ,; 80oC, in
particular the precipitated polymer having a solid content of 10%
to 40%, preferably 20% to 30%.
9. Method according to one of the preceding claims, characterised
in that, in step c), the at least one precipitated polymer is
separated mechanically from the solution, preferably filtered off
and/or pressed off, particularly preferably at a temperature of 50
, ~' I
to 150°C andjor by applying a vacuum, in particular a vacuum
with a pressure of,; 100 mbar.
10. Method according to one of the preceding claims, characterised
in that step c) is implemented in a vacuum kneader, in a
degassing extruder and/ or in ·the form of a powder drying.
11. Method according to one of the preceding claims, characterised
in that, after step c), the solvent is used again in step a) and/or
the solvent is preferably guided in circulation.
12. Method according to one of the preceding claims, characterised
in that at least one further thermostabiliser is added in at least
one of the steps.
13. Method according to one of the preceding claims, characterised
in that the polymer-containing waste comprises a plurality of
different polymers or consists thereof, preferably the various
polyolefins being dissolved by successive dissolving steps with
an increasing solubility temperature and subsequently being
separated from the insoluble polymers and insoluble part of the
waste at the respective solubility temperature.
14. Polymer recyclate comprising at least one polymer and traces of
at least one organic solvent.
15. Polymer recyclate according to claim 14, producible with the
method according to one of the claims 1 to 13.
16. Polymer recyclate according to claim 14 or 15, characterised in
that the recyclate comprises from 50 to 10,000 ppm of solvent.
17. Use of at least one thermostabiliser in at least one orgamc
solvent for enriching at least one polymer from a polymercontaining
waste.