Materials and methods

A method of forming a shaped foamed polymer article in an injection moulding tool from a polymer composition, wherein the injection moulding tool comprises:

• an extruder barrel for receiving the polymer composition;
• and
• a cavity in which said article is formed;
• wherein the polymer composition comprises a polymer of high-density polyethylene and a foaming agent comprising a polymer shell encapsulating a gas or liquid;
• wherein the foaming agent is present in the polymer composition in an amount of 4-10% by total weight of the polymer composition;
• wherein the method comprises:
• (a) heating the extruder barrel to a temperature of 160-200° C. to aid melting of the polymer composition to form a melted polymer composition prior to its injection into the cavity;
• (b) reducing the pressure in the cavity;
• and
• (c) injecting the melted polymer composition into the cavity, and wherein the volume of the injected polymer composition is less than the volume of the shaped foamed polymer article in its final form,
• wherein the temperature of the cavity is above a critical onset temperature of the polymer shell, at which the polymer shell softens and expands, and below a maximum expansion temperature of the polymer shell, at which the polymer shell bursts, and
• wherein a shot of the melted polymer composition is injected into the cavity at a reduced injection speed, such that the whole shot is delivered over 2-11 seconds.