Extrusion foaming of protein based thermoplastic and polyethylene blends
Currently the extrusion foamability of Novatein(r) Thermoplastic Protein (NTP) is being investigated at the University of Waikato in collaboration with the Biopolymer Network Ltd (NZ) NTP has been developed from bloodmeal >86 wt% protein) a co product of the meat industry, by adding denaturants and plasticisers (tri ethylene glycol and water) allowing it to be extruded and injection moulded. NTP alone does not readily foam when sodium bicarbonate is used as a chemical blowing agent as its extensional viscosity is too high.The thermoplastic properties of NTP were modified by blending it with different weight fractions of linear low density polyethylene (LLDPE) and polyethylene grafted maleic anhydride (PE g MAH) compatibiliser. Extrusion foaming was conducted in two ways, firstly using the existing water content in the material as the blowing agent and secondly by adding sodium bicarbonate. When processed in a twin screw extruder (L/D 25 and 10 mm die) the material readily expanded due to the internal moi.