Improved Expandable Vinyl Aromatic Polymers

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 less than 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.

A process for the preparation of beads or granules of expandable vinyl aromatic polymers comprising the steps of:

• a. producing a polymer melt stream 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 less than 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;
• b. deriving a part of said polymer stream and creating main polymer melt stream (1) and a side loop with an additional polymer melt stream (2);
• c. dispersing the coke particles and the foam cell regulator into said additional polymer melt stream (2);
• d. joining the additional polymer stream (2) and the main stream (1) and forming a new polymer melt stream;
• e. introducing a blowing agent into the new polymer melt stream;
• f. cooling the polymer melt comprising all ingredients down to a temperature of 200° C. or less;
• g. discharging the melt stream through a die plate with holes and pelletizing the melt under water with a pressure above 3 bar, preferably above 5 bar.

Polymer foams obtained from the molding of expanded 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 less than 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;
• said foams being characterized by a thermal conductivity (k), measured according to ISO 8301, of:
• 32.5 mW/m·K or less at a foam density of 12.5 kg/m3 or lower;
• or
• 31 mW/m·K or less at a foam density of 15 kg/m3 or lower;
• or
• 31 mW/m·K or less at a foam density of 18 kg/m3 or lower.