Expandable vinyl aromatic polymers

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/m3 or higher.

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/m3 or higher.