Method for preparing extruded polyamide foams

1. A polyamide foam composition, comprising:

a polyamide resin; and

a composite chain extender including an epoxy chain extender and a maleic anhydride grafted polypropylene (MAPP) wax, wherein the polyamide resin is present in an amount of between 92 wt.% and 98 wt.%, based on the total weight of the polyamide foam composition.

2. The polyamide foam composition of claim 1 , wherein the epoxy chain extender is present in an amount of between 1 wt. % and 3 wt. %, based on the total weight of the polyamide foam composition.

3. The polyamide foam composition of claim 1 , wherein the MAPP wax is present in an amount between 1 wt. % and 5 wt. %, based on the total weight of the polyamide foam composition.

4. The polyamide foam composition of claim 1 , wherein the polyamide foam composition has an average cell size between 50 μm and 700 μm.

5. The polyamide foam composition of claim 1 , wherein the polyamide foam composition has a shear viscosity between 10,000 Pa·s to 150,000 Pa·s.

6. The polyamide foam composition of claim 1 , wherein the density of the polyamide foam composition is between 0.1 g/cm 3 and 1.0 g/cm 3 .

7. The polyamide foam composition of claim 1 , further comprising at least one additive selected from antioxidants, nucleating additives, pigments, fire retardants, antistatic additives, and ultraviolet (UV) stabilizers.

8. A method of producing a polyamide foam composition, comprising the steps of:

a compounding step, comprising:

feeding a polyamide resin and a maleic anhydride grafted polypropylene (MAPP) wax into an extruder at a first location; and

feeding an epoxy chain extender into the extruder at a second location downstream from the first location to form a compounded polyamide; and

an extrusion foaming step, comprising:

extruding the compounded polyamide with a blowing agent in an extruder to form a polyamide foam.

9. The method of claim 8 , wherein said compounding step further comprises, after said feeding step, the additional steps of:

cooling the compounded polyamide;

drying the compounded polyamide; and

pelletizing the compounded polyamide.

10. The method of claim 8 , wherein said compounding step is carried out using one of a co-rotating twin screw extruder, a counter-rotating intermeshing twin screw extruder and a single screw extruder.

11. The method of claim 8 , wherein said extruding step further comprises the additional steps of:

feeding the compounded polyamide into the extruder at a first location;

adding a physical blowing agent to the compounded polyamide in the extruder at a second location downstream of the first location;

mixing the compounded polyamide and the blowing agent in a static mixer; and

conveying the compounded polyamide and the blowing agent through a die to form the polyamide foam composition.

12. The method of claim 11 , wherein the blowing agent is supercritical carbon dioxide.

13. The method of claim 8 , wherein the polyamide foam composition comprises:

polyamide resin in an amount between 92 wt. % and 98 wt. %;

epoxy chain extender in an amount between 1 wt. % and 3 wt. %; and

MAPP wax in an amount between 1 wt. % and 5 wt. %, based on the total weight of the polyamide foam composition.

14. The method of claim 8 , wherein the polyamide foam composition has at least one of the following properties:

an average cell size between 50 μm and 700 μm;

a shear viscosity between 10,000 Pa·s to 150,000 Pa·s; and

a density between 0.1 g/cm 3 and 1.0 g/cm 3 .