Expandable styrene polymers containing recycled material

The present invention relates to expandable styrene polymers containing recycled polystyrene, having a recycled material content of from 10 to 50% by weight, based on the total weight of the polystyrene, to which alkyldi(2-hydroxyethyl)amines have been added during the polymerization.

The present invention relates to expandable styrene polymers containing 
recycled material which can be converted into foams having an improved 
foam structure. 
Plastics based on styrene and styrene-containing copolymers are produced in 
large amounts and are used in many areas of industry. Considerable 
importance is also attached to foamed products. 
The production and use of these products have been known for some time and 
have been described in a variety of publications. 
A problem which has become particularly important in recent times is the 
recycling of used plastics. 
In the case of polystyrene foams, various recycling methods are known. 
One possibility comprises using polystyrene foam or unfoamed polystyrene 
waste for the extrusion of polystyrene foams. 
This recycled material can be used either alone or as a mixture with fresh 
polystyrene. 
The production of foams from the recycled materials can be carried out 
directly here, as usual, by steam-treatment of the polymer in the extruder 
with subsequent foaming to give boards or by extrusion to give 
minigranules, which can be impregnated with blowing agent and foamed. 
It is also possible to dissolve the used polystyrene in monomeric styrene 
and to re-polymerize this solution by known methods, for example as 
described in U.S. Pat. No. 5,269,948 and JP-A-5,660,096. 
A particular disadvantage in the polymerization of solutions of recycled 
polystyrene in monomeric styrene is that the foam structure of the foams 
produced using these styrene polymers is unsatisfactory. In particular 
when recycled polystyrene grades containing flameproofing agents are used, 
the resultant polystyrene foams have small cells, which is undesired. 
It is an object of the present invention to provide polystyrene containing 
recycled material which has a uniform foam structure without the undesired 
fine-cell content and has good mechanical properties and is simple to 
prepare. 
We have found that, surprisingly, this object is achieved by adding 
alkyldi(2-hydroxyethyl)amines to the solution of recycled polystyrene in 
vinylaromatic monomers, in particular styrene, during the polymerization. 
The present invention accordingly provides expandable styrene polymers 
containing recycled polystyrene to which alkyldi(2-hydroxyethyl)amines 
have been added during the polymerization. 
The content of recycled polystyrene in the novel products is from 10 to 50% 
by weight, based on the total weight of the polystyrene. 
The alkyldi(2-hydroxyethyl)amines are added to the polystyrene containing 
recycled material in an amount of from 50 to 1000 ppm, preferably from 50 
to 500 ppm, based on the total mixture of recycled material and monomer. 
The alkyldi(2-hydroxyethyl)amines are preferably not added until after 
stabilization of the bead size, i.e. after addition of the suspension 
stabilizer. 
The fact that it was possible to achieve the object of the invention by 
adding alkyldi(2-hydroxyethyl)amines was unforeseeable to the person 
skilled in the art. 
Although the use of amines in the production of polystyrene foams has been 
disclosed, for example in DE-A-25 20 635, these products are usually used 
in the production of flameproofed polystyrene particle foams or as coating 
agents for improving the antistatic properties. 
The prior art did not reveal that the use of such compounds in polystyrene 
foams containing recycled material would result in a uniform foam 
structure. 
The alkyldi(2-hydroxyethyl)amine used is, in particular, a C.sub.12 
-C.sub.14 -alkyldi(2-hydroxyethyl)amine. This product is commercially 
available, for example, as Armostat.RTM. 400 from Akzo. 
In a particularly advantageous embodiment, the 
alkyldi(2-hydroxyethyl)amines are used together with a polyethylene wax. 
The latter is preferably employed in an amount of from 500 to 1000 ppm. 
The polyethylene waxes used here generally have a mean molecular weight 
(number average) of from 2000 to 6000, preferably from 2000 to 4000, 
particularly preferably from 2500 to 3500. A particularly suitable 
polyethylene wax is BASF Luwax.RTM. having a mean molecular weight (number 
average) of 3000. The polyethylene waxes preferably have a mean particle 
size of from 5 to 50 .mu.m. Overlarge particles cause problems with 
distribution in the polymer, while excessively fine products can cause 
problems with dust. 
The vinyl group-containing monomer employed is, in particular, styrene. 
However, it is also possible to employ mixtures of styrene with other 
monomers containing vinyl groups. 
These mixtures advantageously have a styrene content of at least 50% by 
weight. The other monomers containing vinyl groups can be, for example, 
acrylonitrile, methylstyrene, ring-halogenated or ring-alkylated styrenes, 
esters of acrylic acid or methacrylic acid with alcohols having up to 8 
carbon atoms, N-vinyl compounds, such as vinylcarbazole, or alternatively 
small amounts of compounds containing two polymerizable double bonds, such 
as butadiene, divinylbenzene and butadiene diacrylate. 
The styrene polymers can also contain conventional amounts of other 
substances which give the expandable products certain properties. Examples 
which may be mentioned are flameproofing agents based on organic bromine 
or chlorine compounds, such as trisdibromopropyl phosphate, 
hexabromocyclododecane, chlorinated paraffin, and synergists for 
flameproofing agents, such as dicumyl peroxide and highly unstable organic 
peroxides; furthermore antistatics, stabilizers, dyes, lubricants, fillers 
and substances which have a non-stick action during foaming, such as zinc 
stearate, melamine-formaldehyde condensates or silicic acid, and agents 
for shortening the demolding time during expansion, such as glycerol 
esters or hydroxycarboxylic esters. Depending on the intended action, the 
additives can be homogeneously distributed in the particles or in the form 
of a surface coating. 
In order to prepare the novel expandable styrene polymers containing 
recycled material, the dry and, if necessary, precompacted recycled 
polystyrene is first dissolved in the monomers containing vinyl groups, 
preferably at room temperature. 
In order to remove mechanical impurities which are insoluble in the 
monomers containing vinyl groups, the solution is advantageously filtered 
before the polymerization. 
The polymerization is carried out by the suspension method. To this end, 
the solution of the recycled polystyrene in the monomers is transferred 
into the reactor containing the aqueous phase, where the polymerization is 
carried out. 
The suspension polymerization is generally carried out in the presence of 
suspension stabilizers and conventional styrene-soluble polymerization 
catalysts. 
The blowing agent is generally added during the polymerization, but it is 
also possible to introduce the blowing agent into the styrene polymer in a 
subsequent step. 
For the production of foams, the expandable styrene polymer beads are 
expanded in a known manner by heating to above their softening point, for 
example by means of hot air or preferably by means of steam. The foam 
beads obtained can, after cooling and, if desired, after interim storage, 
be re-expanded by further heating. Finally, they can be welded in a known 
manner in non-gas-tight molds to give moldings. 
Further details on conventional impregnation, extrusion and foaming 
processes are given, for example, in Kunststoffhandbuch, Volume 5, 
Polystyrene, edited by R. Vieweg and G. Daumiller, Carl-Hanser-Verlag, 
Munich, 1969. 
The novel polystyrene foams are distinguished from other polystyrene foams 
containing recycled material by a uniform foam structure. Even a small 
amount of contamination by other polymers and additives in the recycled 
material, which cannot be removed from the latter by conventional 
purification methods, do not have any disadvantageous effects on the foam 
structure of novel products. 
This allows even foamed and unfoamed polystyrene waste produced outside the 
actual production process, which have different material characteristics 
and in some cases also different additives, to be re-converted into 
high-quality foams by a very simple process. In particular, it is also 
possible to convert flameproofed polystyrene waste back into polystyrene 
particle foams. 
The invention is described in greater detail with reference to the examples 
below.

EXAMPLES 1-9 
A mixture of 19.5 kg of demineralized water, 19.5 g of Na.sub.4 P.sub.2 
O.sub.7 and 52.7 g of MgSO.sub.4 was introduced into a pressure-tight 50 l 
stirred reactor made of stainless steel. 17 kg of a styrene solution of 
the amount of recycled polystyrene given in the table, 17 g of dibenzoyl 
peroxide and 51 g of dicumyl peroxide were added. The mixture was heated 
from 25.degree. to 100.degree. C. over the course of 2 hours and then from 
100.degree. to 130.degree. C. over the course of 5 hours. The mixture was 
kept at 130.degree. C. for a further 3 hours. 
478 g of a 10% strength aqueous polyvinylpyrrolidone solution (K value 90) 
were added to the mixture 55 minutes after it had reached 80.degree. C., 
the amounts given in the table of C.sub.12 -C.sub.14 
-alkyldi(2-hydroxyethyl)amine (Armostat.RTM. 400 from Akzo) and 
polyethylene wax (Luwax.RTM. from BASF) were added after a further 30 
minutes, and 1.3 kg, corresponding to 7.7% by weight, based on the styrene 
polymer, of n-pentane were added after a further 95 minutes. 
The resultant beads were centrifuged off, dried with cold air in 
countercurrent and coated with 0.1% by weight, based on the weight of the 
uncoated beads, of ethylenebisstearamide. 
The bead size fraction from 0.70 to 1.0 mm was then screened out and coated 
with 0.5% by weight, based on the styrene polymers containing blowing 
agent, of a mixture of 40% by weight of trisstearyl citrate, 50% by weight 
of glycerol monostearate and 10% by weight of silicic acid FK 320 
(Goldschmidt). 
The mixture was prefoamed for 6 minutes in an unpressurized foaming box 
(Rauscher), and the foam structure of the resultant beads was determined. 
The precise mixing ratios of the starting materials and the properties of 
the foams are shown in Table 1. The recycled polystyrene had a viscosity 
number of 60 g/ml, a toluene-insoluble residue of 0.2% by weight and an 
ashing residue of 0.05% by weight, in each case based on the weight of the 
recycled material. 
TABLE 
__________________________________________________________________________ 
Amount of Amine* 
Polyethylene 
Cell 
recycled material 
Suspension 
content 
wax content 
count 
Example 
(% by wt.).sup.(1) 
stabilizer 
(ppm) 
(ppm) (Cells/mm) 
Foam structure 
__________________________________________________________________________ 
1 (Comparison) 
-- MPP -- -- 5 gross, inhomogeneous 
2 (Comparison) 
-- MPP -- 1000 8 medium, inhomogeneous 
3 (Comparison) 
20 MPP -- -- 20 fine, very inhomogeneous 
4 (Comparison) 
20 MPP -- 1000 18 fine, very inhomogeneous 
5 20 MPP 200 -- 10 medium, inhomogeneous 
6 (Comparison) 
20 MPP 200 1000 10 medium, uniform 
7 (Comparison) 
-- KSO -- -- 4 gross, very 
inhomogeneous 
8 20 KSO -- 1000 17 fine, inhomogeneous 
9 20 KSO 200 -- 9 medium, uniform 
__________________________________________________________________________ 
MPP -- Magnesium pyrophosphate 
KSO -- Polyvinylpyrrolidone solution (K value 90) 
Amine* C.sub.12 -C.sub.14 -Alklydi(2hydroxyethyl)amine (Armostat .RTM. 
400, AKZO) 
Polyethylene wax Luwax .RTM. AF31 (BASF) 
.sup.(1) based on the total amount of monomers and recycled material 
The cell count and the cell structure were determined visually.