Note: Descriptions are shown in the official language in which they were submitted.
' ~ OO50/44308
- 2157604
Gentle recycling of styrene polymers
The present invention relates to a process for the gentle recycl-
5 ing of styrene polymers. The present invention relates in partic-
ular to such a process in which spent styrene polyme~s are melted
in the presence of a maleimide having a plurality of imide
groups.
lO Polystyrene and styrene polymers, in particular foams composed of
these, tend to suffer a decrease in molecular weight during melt-
ing in an extruder. This leads to, inter alia, altered flow be-
havior, so that the granule~ obtained are frequently unsuitable
for many applications and have to be di~posed of. The degradation
15 reactions are particularly pronounced if the thermoplastic poly-
mers contain organic peroxides (cf. EP-A-0 405 935 and
US-A-3,806,558).
In order to reduce the decrease in the molecular weight of
20 styrene polymers, it was therefore proposed to melt the styrene
polymer in the presence of maleic anhydride (cf. Reaction of
maleic anhydride and molten polystyrene in the absence and pres-
ence of peroxides, Angew. Makromol. Chem. 117 (1983), 195-209).
This results in a smaller decrea~e in the molecular weight, par-
25 ticularly in the presence of peroxides.
On the other hand, EP-A-0 405 935 propose~ melting thermoplastic
polymer in the presence of dihydroaromatic cuw~ounds. For exam-
ple, 9,10-dihydrophenanthrene is mentioned as the dihydroaromatic
30 compound. In addition to the dihydroaromatic compound, polyfunc-
tional monomer~, in particular bismaleimides, such as N,N'-m-phe-
nylenebismale; m; de and N,N'-ethylenebismaleimide, are used.
EP-A-0 506 614 discloses the use of antioxidants of the Irganox~
35 type from Ciba-Geigy AG, by means of which the degradation of
styrene polymers under extrusion conditions can also be limited
to a certain extent. When peroxides are present in the styrene
polymer, or the residence times of the styrene polymers in the
extruder are relatively long or where damage to the styrene poly-
40 mers has already occurred, their addition alone is, however, nolonger sufficient.
It is an object of the present invention to provide a process
which permits the recycling of styrene polymers by melting in an
45 extruder and ~ubsequent processing to give granules, without any
decrease in the molecular weight as a result of degradation reac-
tions in the styrene polymer. This process should in particular
0050/44308
_ 2 2 1 ~ ~6 04
permit repeated recycling and shoUld give molding materials which
can be used for the production of foams.
We have found that this object is achieved by a process for the
5 gentle recycling of styrene polymers, which comprises the steps
a) melting of the styrene polymer, which may be in comminuted
form, in an extruder and
10 b) extrusion of the resulting melt, to which blowing agent and/
or conventional additives may be added,
wherein the melting i8 carried out in the presence of from 0.01
to 4% by weight, based on the styrene polymer, of a bismaleimide,
15 a trismaleimide and/or a maleimide having more than three imide
groups .
The melt, which may contain blowing agent, i9 advantageously ex-
truded and processed to give granules.
Styrene polymers which are styrene homopolymers prepared by an
anionic or thermal method or with the use of a free radical ini-
tiator and corresponding copolymers of styrene with other comono-
mers are used in particular according to the invention. Particu-
25 larly suitable comonomers of this type are a-methylstyrene,
p-methylstyrene, styrenes halogenated in the nucleus, styrenes
alkylated in the nucleus, acrylonitrile, esters of (meth)acrylic
acid with alcohols of 1 to 8 carbon atoms, unsubstituted or
N-substituted amides of (meth)acrylic acid, N-vinyl compounds,
30 such as N-vinylcarbazole, and maleic anhydride.
Styrene polymers which have been toughened with the use of a rub-
ber-forming polymer, such as polybutadiene, a styrene/acryloni-
trile copolymer, a styrene/acrylate copolymer or a similar elas-
35 tomer or blend of individual elastomers, may also be used.
In the novel process, styrene polymers treated with flameproofingagents may be used. Flameproofing agents are to be understood as
meAn;ng in particular compounds which contain one or more chlo-
40 rine and/or bromine atoms, these being bonded to an aromatic, al-
iphatic-aromatic, aliphatic or cycloaliphatic C6-C20-radical which
may also carry e~ter, anhydride, amide, imide, ether, urethane or
other functional groups.
45 Furthermore, substances which form free radicals, such as azo,
peroxy or other compounds (for example compounds carrying steri-
cally bulky substituents, such as dicumyl - 2,3-dimethyl-2,3-di-
0050/44308 ~ 1 5 7 ~ ~ 4
_ 3
phenylbutane), which decompose at relatively high temperatures(generally > 120 C) with free radical formation and promote the
free radical decomposition of the flameproofing agent, may be
present in the styrene polymer~ as synergistic agents for such
5 flameproofing agents.
The styrene polymers may also contain further conventional assis-
tants, for example dye~, pigments, fillers, glass fibers, stabi-
lizers, nucleating agents and lubricants.
The novel process is particularly suitable for the recycling of
styrene polymers which contain a high proportion of polystyrene
foams. The styrene polymers used in the novel process therefore
preferably contain at least 50, particularly preferably at least
15 90, % by weight of polystyrene foams in comminuted form.
In an advantageous embodiment of the novel process, a blowing
agent, in an amount of from 3 to 17~ by weight, based on the
styrene polymer, is added to the melt in the extruder.
In a particularly preferred embodiment, the melt contA;n;ng blow-
ing agent is extruded to give expanded sheets.
In an alternative ~mhoA;ment of the novel process, a melt which
25 does not contain blowing agent is extruded, the extrudate is pro-
cessed to give granules and the granules are then impregnated
with the blowing agent in a conventional manner in aqueous sus-
pension in the presence of a blowing agent.
30 The conventional and known blowing agents may be used.
For the preparation of particulate, expandable styrene polymers,
C3-c6-hydrocarbons, such as propane, n-butane, isobutane, n-pen-
tane, isopentane, neopentane and/or hexane, are generally used. A
35 commercial pentane isomer mixture is preferably used. For the
production of extruded foams, blowing agents which have very low
contents of chlorofluorocarbons are generally used. Relatively
environment-friendly chlorofluorocarbons and/or fluorocarbons
mixed with halogen-free blowing agent cnmro~ents, such as etha-
40 nol, carbon dioxide or dimethyl ether, are preferably used for
thig purpose.
In the novel process, bismalei_ides of the general formula I
0050!44308 2 15 7 6 0 ~
O O
~N - X-N ~ I,
O O
where X is Rl, R1-R2 or Rl-Y-R2~
10 Rl and R2 may be identical or different and are each a divalent
aromatic, aliphatic, cycloaliphatic or heteroaromatic radical
which may carry further con~tituents and
Y is (CH2)n (where n is from 1 to 5), 0, S02 or NR3 (where R3
15 is Cl--Cs--alkyl),
are preferably used.
The bismaleimides, trismaleimides or maleimides having more than
20 three maleimide functions are used in the novel process in an
amount of from 0.01 to 4% by weight, based on the styrene poly-
mer. Bismaleim;des in an amount of from 0.05 to 3S by weight,
based on the styrene polymer, are preferably used here.
25 According to the invention, bismaleimides of the general formula
I, where Rl and R2 are identical or different and are each meta-
phenylene or para-phenylene, are preferably used.
Particularly suitable bismaleimides are sold under the name Pali-
30 mides0 by BASF Aktiengesellschaft. ~YAmrles of these are Palimid0
M 160 (where X is Rl-Y-Rl, Rl is para-phenylene and Y is CH2),
Palimid0 M 200 (where X is Rl and Rl is meta-phenylene), Pali-
mid0 205 (where X is Rl-Y-R2, Y is S02 and R1 and R2 are each
meta-phenylene).
Bismaleimides are most simply prepared according to
US-A 2,444,536, by reaction of amines with maleic anhydride and
subsequent eliminAtion of water by means of acetic anhydride/so-
dium acetate (cf. also J. Gonzales Ramos, J.M. Barrales-Rienda
40 and M. Sanches Chaves: Anales de Quimica (Madrid) 73 (1977),
139-145).
The maleimides used according to the invention may be employed
alone, as a mixture or together with further stabilizers (for ex-
45 ample sterically hindered phenolic stabilizers).
OO50/44308
-- 2157 604
_ 5
The novel process has seVeral advantages. For example, the re-
cycling of polystyrene or styrene copolymers by melting in an ex-
truder and subsequent processing to give granules is possible
without a decrease in the molecular weight, and it is even pos-
5 sible to use material damaged by degradation.
In the Examples which follow, percentages are by weight.
~yA~rl es 1 to 19
Polystyrene of the type VPT from BASF Aktiengesellschaft (weight
average molecular weight about 200,000), which had a melt flow
index MFI (210 C/10 kp) of 70.4 ml/10 min, was used in Examples 1
to 19.
The polystyrene granules were coated in a paddle mixer (Lodige
type) with the amounts of various coating materials shown in
Table 1. The granules were then melted in a twin-screw extruder
(from Werner & Pfleiderer, Stuttgart) having a screw diameter of
20 30 mm (ZSR 30), the melt was extruded and the extrudate was
passed through a water bath and then granulated. The throughput
was 10 kg/h, which corresponded to a residence time in the ex-
truder of 90 seconds. The melt flow indices MFI (210 C/10 kp)
shown in the Table were measured on the granules. In addition,
25 the viscosity number VN (0.5% strength in toluene at 25 C) was de-
termined according to DIN 53726 using degassed samples of the
granules of ~YA~rles 9 to 19. Dicumyl peroxide, which is fre-
quently used as a flameproofing synergistic agent in flame-
proofed, expandable styrene polymers and accelerates their degra-
30 dation reactions in the extrusion of said polymers, was employedas a coating material component in Examples 9 to 19.
~YAmrle9 20 and 21
35 Example 20
20 kg of polystyrene granules which had been obtained from EPS
moldings by means of a recycling plant (Erema~ plant 60 A from
EREMA, Linz, Austria) by comminution, p~ecG.u~action and subse-
40 quent extrusion (lst extru~ion) with subsequent hot face cutting,were coated with 0.2 kg of Palimid~M 160 (bismaleimide of
4~4~-diaminodiphenylmethane) in a tumbler mixer. The coated gran-
ules were extruded in a twin-screw extruder (screw diameter
53 mm; ZSK 53 from Werner & Pfleiderer, stuttgart) at 180 C,
45 200 rpm and a throughput of 30 kg/h (2nd extrusion). The melt
outlet t~mr~rature was from 222 to 229 C. The emerging extrudates
were cooled in a water bath and processed to granules
0050/44308
2~ 576~4
(1 x 1.5 mm) by means of rotating knives. The VN and MFI
(190 C/10 kp) values were determined thereafter and after a fur-
ther extrusion step (3rd extrusion) under the same conditions.
The results are shown in Table 3.
In each case 6 kg of the granules used in Example 20 before and
after the 3rd extrusion, were introduced into a 40 1 reactor
which had been charged beforehand with 21 kg of water, 76 g of
sodium pyrophosphate, lSS g of magnesium sulfate heptahydrate and
10 50 g of Mersolat~ K 30 in a concentration of 40% in water (alkyl-
benzenesulfonate from Bayer AG). The reactor was closed, flushed
with nitrogen and heated to 90 C under an initial nitrogen pres-
sure of 1 atu gauge pressure. 720 g of a mixture of isopentane
and n-pentane (25/75) were then forced in over 15 minutes, and
15 the suspension was stirred for a further 10 hours at 90 C. The
mixture was then cooled and the reactor was let down. The suspen-
sion was discharged via a wire screen, which trapped the blowing
agent-contA i n i ng beads. Immediately thereafter, the pentane con-
tent of the beads was determined (cf. Table 3). The beads were
20 placed on an open metal sheet in a layer thickness of 4 cm at 23 C
and 50% atmospheric humidity (conditioned), in order to achieve a
uniform foam structure.
After 1 day and after 24 and 45 days, a portion of the beads was
25 expanded in a commercial laboratory expander (Rauscher type) and
the m; ni mllm bulk density BD~n was determined after an expansion
time of 3 minutes. After the beads had been conditioned for 24
days, the pentane content was also determined. The measured data
are likewise listed in Table 3.
0050/44308 ~ 7 6 ~ 4
C
`, o ~ ~ ~o , ~ r~
o E~
_~ 3
~ IIIIIIIo
a
., ._ 3 u~
a r I l l l l I ~ I
_ ~ ~ O
dO
~ 3 ul o
o ~ I I o _~
d~
H o 3 "~
o ~ I I I o
dll
o ~ u~
~ ~ O
P~ o ~
o
.IIIIII
.a
-
o
0050/44308 2 ~ S 7 6 0 ~
-
_.
n o d' O ~ O a~
Z ~
a
~ C .Ir
O ~ O O U~ I` ~ O~
o o ~o ~o ~ o ~
o ~, s~
._
J~ _
q~ ~
a ~ ,~ ~
~ r ~ I I I ¦ ¦ I I I I I _ ~ C
-- ~ ~ O ~ ~ O
C dP ~ )
~ '1 ~
~ ~ I
' 3 u~ o ~ ,1 _I :>.
~ ~ o _. ~ U ~ ~
dP m 1 .
X ~ ~
o ~ ~
~ J~ r
O I
~ Ei L~ ul
~ a~
~~ 1 1 ,
,~ I~d~' r
0~ U~ O ~ a)
t~ ~
~ o -~ n
J ~
~ ~i U
a~
3 ~ O ~ a~
~,Q O O
~ O t
~ ~ -- .
a ~ c ~
c ~ o
o o o ~o
Ui~ ~
a .
~ x ~
~ -- -- .,~ o
o o o ~ ~
a~ ~ u u _ ~ C~ C) ~ H H H
~ X O _I ~ t`~ ~ Ul ~ ~` CO ~
0050/44308 2 1 ~ 7 6 0 4
.
U ~
~ ,., ~. --
to ~ ~ , ,
h ~ a~ --
J~
~ 3 ~ ~, o
~ d~
, ~ a ~,
r
J
~ J ~
J
r~l ~ dP
t~ ~O O d'
z ~ .
e 'D u~
.Y
H ~ e _1 ,~ _, _, ,~ _,
~ ~ O ~
o e
-
~ ~ O ~ ~ O ~ ~ eO '~ Oe ~ ~ O ~ ,~ e
~n c ~ vl e
~ a~ ~
a, ~o --' ~
~ ~ _
0050/44308
21576D4
-- 10
~Y~mrl e 21 (Comparative ~Y~rl e)
The procedure was as in Example 20, but without the use of Pali-
5 mid~ M 160.
The results shown in Tables 1 to 3 demonstrate the particularly
gentle melting of styrene polymers in the novel process. The in-
crease in the MFI and the decrease in the VN which usually occur
10 as a result of melting and extrusion in the case of styrene poly-
mers are very small in the novel process. The effect is pro-
nounced in particular on repeated extrusion of the styrene poly-
- mers.
15 The results also show that the u~e of bismaleimide~ in the extru-
sion of styrene polymers results in improved expandability after
impregnation with blowing agents, which furthermore is maintained
for a longer time than in the case of styrene polymers extruded
without the addition of bismaleimides.
Example 22
Production of an extruded foam
25 Polystyrene having a weight average molecular weight of 220,000
and a polydisper~ity of 3.6 was melted, at a rate of 840 kg/h,
with the addition of 7 kg/h of hexabromocyclododecane, 1.5 kg/h
of dicumyl and 3.8 kg/h of talc and 8.4 kg/h of Palimid~ M 160,
in an extruder a~ described, for example, in DE-A-38 43 537, hav-
30 ing-an internal screw diameter of 120 mm.
The melt was gassed under pressure with the following blowing
agent mixture: HCFC 142 b (CH3-CClF2) 111 kg/h, ethanol 11 kg/h
and C2 11 kg/h.
After an average residence time of 45 minutes, the homogeneous
melt was forced through a die into the open so that the blowing
agent was able to expand and to convert the melt into a foam.
40 The resulting expanded extrudate was cooled and then cut into in-
dividual sheets, and the density thereof was determined by immer-
sion in water (displacement measurement).
. 0050/44308
6 0 ~
11
The compressive strength according to DIN 53421 and the heat dis-
tortion resistance as compregsion according to DIN 18164 were de-
termined using test specimens cut from thi~ foam. The results are
shown in Table 4.
Example 23
The procedure was as in Example 22, except that a recycled EPS,
as obtained in a recycling plant (cf. ~YAmrle 20) and having a
10 weight average molecular weight of 165,000 and a polydispersity
of 3.4, was added in the same amount to the polystyrene (cf.
Table 4).
Example 24 (ComrArison)
The procedure was aq in Example 22, but without the addition of
the bismaleimide (cf. Table 4).
Example 25 (ComrArison)
The procedure wa~ as in ~YAmrle 23, but without the addition of
the bismaleimide (cf. Table 4).
Table 4
Example Foam density Compressive stress at Heat distortion
[kg/m3] 10% compressive ~train resistance as
[N/mm2] compression [%]
22 33.0 0.374 1.8
23 32.5 0.348 2.1
24 (Comp.)33.8 0.350 2.1
25 (Comp.)34.4 0.334 2.5
35 As shown by the results in Table 4, the addition of bismaleimides
gives better expandability of the blowing agent-contA;n;ng melt
and higher compressive strength and heat distortion re~istance of
the foam. It is also possible to use larger amounts of recycled
EPS while retA;n;ng the good properties.
