Foaming behavior of novatein and blends with polyethylene compatibilised by maleic anhydride

Abstract

Novatein® thermoplastic protein (NTP), a bloodmeal based thermoplastic, was successfully foamed without blowing agent or blending with other polymers using a BOY-35A injection moulder in free expansion mode. Previously, only soy protein has been successfully continuously foamed and zein and gluten batch foamed without blending or rheological modification. The greatest expansion ratio for NTP was 4.4 at 165°C. Blending NTP with compatibilised LLDPE and LDPE and adding blowing agent reduced expansion ratios. The foams exhibited a fibrous nature, with cell structures similar to those reported in literature for extrusion foamed thermoplastic soy protein isolate. SEM pictures suggested a possible role of either sodium sulphite, sodium dodecyl sulphate or sodium sulphate as a nucleating agent as particulates were found on the cell surfaces. Triethylene glycol and urea were thought to contribute to NTP foaming, along with water present in NTP, with two or more acting as the blowing agent.