Expandable vinyl aromatic polymers
The present invention is related to expandable vinyl aromatic polymers comprising comminuted coke, said comminuted coke having an average stack height (Lc) of carbon crystallites at least 4 nm, a volume median particle diameter (D50) comprised between 1 and less than 5 μm and being characterized by a span (D90−D10)/D50 below 2.5 Molded parts produced from the expandable vinyl aromatic polymers prove low thermal conductivities for a low foam density.
1. Expandable vinyl aromatic polymers comprising at least one blowing agent and a plurality of dispersed coke particles, said dispersed coke particles being characterized by:
(i) an average stack height (Lc) of carbon crystallites of at least 4 nm, wherein Lc is given by the formula
L
c
(
nm
)
=
0.89
*
0.154
β
*
cos
(
θ
)
and is estimated from the full width at half maximum of diffraction peak [002];
(ii) a volume median particle diameter (D50) comprised between 1 and 5 μm, as obtained from laser light scattering measurements according to ISO 13320; and
(iii) a span (D90−D10)/D50 below 2.5 as obtained from laser light scattering measurements according to ISO 13320;
wherein the expandable vinyl aromatic polymers comprise between 4 and 6% by weight of the dispersed coke particles; and
wherein polymer foams obtained from the molding of expanded polymer pellets of the expandable vinyl aromatic polymers comprise a thermal conductivity, (λ), measured according to ISO 8301, of 31.0 mW/mK or less at a foam density of 12.5 kg/m 3 or higher.
2. The expandable vinyl aromatic polymers according to claim 1 characterized in that a volume percentage of the dispersed coke particles with a diameter of less than 1 μm is lower than (36−13 ln D50) (36 minus 13 times the natural logarithm of D50).
3. The expandable vinyl aromatic polymers according to claim 1 characterized in that a volume percentage of the dispersed coke particles with a diameter of less than 1 μm is lower than (32−12 ln D50) (32 minus 12 times the natural logarithm of D50).
4. The expandable vinyl aromatic polymers according to claim 1 comprising between 2 and 10% by weight of a C3-C6 alkane.
5. The expandable vinyl aromatic polymers according to claim 1 additionally comprising:
(i) between 0.1 to 5% by weight of a halogenated polymer;
(ii) between 0.05 and 5% by weight of a flame retardant synergist; and
(iii) between 0.01 and 1.0% by weight of polyethylene wax, as cell regulator, characterized by a weight average molecular weight comprised between 1500 and 5000 Da.
6. A process for the preparation of pellets of expandable vinyl aromatic polymers, said process comprising the steps of:
a. producing a polymer melt stream of expandable vinyl aromatic polymers
b. deriving a part of said polymer melt stream and creating a main polymer melt stream (1) and a side loop with an additional polymer melt stream (2);
c. dispersing a plurality of coke particles and a foam cell regulator into said additional polymer melt stream (2), said plurality of coke particles being characterized by:
(i) an average stack height (Lc) of carbon crystallites of at least 4 nm, wherein Lc is given by the formula
L
c
(
nm
)
=
0.89
*
0.154
β
*
cos
(
θ
)
and is estimated from the full width at half maximum of diffraction peak [002];
(ii) a volume median particle diameter (D50) comprised between 1 and 7 μm, as obtained from laser light scattering measurements according to ISO 13320; and
(iii) a span (D90−D10)/D50 below 3.0 as obtained from laser light scattering measurements according to ISO 13320;
d. joining the additional polymer melt stream (2) and the main polymer melt stream (1) to form a new polymer melt stream;
e. introducing a blowing agent into the new polymer melt stream;
f. cooling the new polymer melt stream comprising all ingredients down to a temperature of 200° C. or less;
g. discharging the new polymer melt stream through a die plate with holes; and
h. pelletizing the new polymer melt stream under water with a pressure above 3 bar;
wherein the dispersing is such that the pellets of expandable vinyl aromatic polymers comprise between 4 and 6% by weight of coke;
wherein the dispersed coke particles are characterized by:
(i) an average stack height (Lc) of carbon crystallites of at least 4 nm,
(ii) a volume median particle diameter (D50) comprised between 1 and 5 μm as obtained from laser light scattering measurements according to ISO 13320; and
(iii) a span (D90−D10)/D50 below 2.5 as obtained from laser light scattering measurements according to ISO 13320; and
wherein polymer foams obtained from the molding of expanded vinyl aromatic polymer pellets of the expandable vinyl aromatic polymers comprise a thermal conductivity (λ), measured according to ISO 8301, of 31.0 mW/mK or less at a foam density of 12.5 kg/m 3 or higher.
7. The process according to claim 6 comprising the additional step of introducing a flame retardant agent and a synergist into the new polymer melt stream between step f) and step g).
8. The process according to claim 6 , wherein between 5 and 30% of the polymer melt stream is derived in step b) to form the additional polymer melt stream (2).
9. The process according to claim 6 , wherein in step c), the plurality of coke particles and the foam cell regulator are dispersed into the additional polymer melt stream (2) by means of an extruder.
10. The process according to claim 6 , wherein the dispersing in step c) is performed in the additional polymer melt stream at a temperature comprised between 180 and 250° C.
11. The process according to claim 6 , wherein in step g) one or more thermal stabilizer(s) and anti-acid(s) are added.
12. Polymer foams obtained from the molding of expanded polymer pellets of expandable vinyl aromatic polymers comprising at least one blowing agent and a plurality of dispersed coke particles, said dispersed coke particles being characterized by:
an average stack height (Lc) of carbon crystallites of at least 4 nm; wherein Lc is given by the formula
L
c
(
nm
)
=
0.89
*
0.154
β
*
cos
(
θ
)
and is estimated from the full width at half maximum of diffraction peak [002];
a volume median particle diameter (D50) comprised between 1 and 5 μm, as obtained from laser light scattering measurements according to ISO 13320; and
a span (D90−D10)/D50 below 2.5 as obtained from laser light scattering measurements according to ISO 13320;
where the expandable vinyl aromatic polymers comprise between 4 and 6% by weight of the dispersed coke particles; and
wherein said polymer foams are characterized by a thermal conductivity (λ), measured according to ISO 8301, of 31.0 mW/mK or less at a foam density of 12.5 kg/m 3 or higher.