Hydrolysed protein as a renewable plasticiser for renewable materials

Abstract

Novatein Thermoplastic (NTP) is a bloodmeal based plastic developed by the University of Waikato by mixing bloodmeal (by-product of slaughterhouses) with water, sodium dodecyl sulfate, sodium sulfite and urea, and plasticiser so it can be extruded and injection moulded. The aim of this research was to produce a low molecular weight bloodmeal with low salt content to replace tri-ethylene glycol as a plasticiser for NTP.

Bloodmeal was hydrolysed using alcalase, enzyme mixture of chymotrypsin and trypsin, and papain which was later ultrafiltered to obtain low molecular weight peptides of 5 -12 kDa. All the three enzymes provided low degree of hydrolysis while chymotrypsin/trypsin provided high yield of 65% followed by alcalase with 45% yield and papain with 23% yield. The amount of enzyme, bloodmeal concentration and pH governed the rate of hydrolysis. By ultrafiltering the hydrolysate, a low salt content was achieved.

Large scale hydrolysis was carried out to produce hydrolysate for addition in NTP as a substitute for triethylene glycol. The hydrolysate was ultrafiltered to produce peptides of low molecular weight (less than 10 kDa) in permeate and retentate. Extrusion of mixtures with hydrolysate produced extrudates with lower specific mechanical energy than standard NTP, and the extrudate had a good appearance visually. Tensile strength, impact strength, secant modulus, energy at break, and glass transition temperature, and thermal stability generally decreased with increasing the amount of hydrolysate added. A similar trend was observed for its impact strength but overall, the impact strength improved.