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Materials Based on Protein Nanofibrils

Time: Fri 2021-10-08 10.00

Location: F3, Lindstedsvägen 26,, Stockholm (English)

Doctoral student: Xinchen Ye , Polymera material

Opponent: Doctor Jonny Blaker, University of Manchester

Supervisor: Professor Mikael S. Hedenqvist, Polymera material; Universitetslektor Christofer Lendel, Bioteknologi, Tillämpad fysikalisk kemi; Universitetslektor Richard T. Olsson, Polymera material

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Protein nanofibrils (PNFs) prepared from whey protein isolate (WPI) at low pH and elevated temperature were processed into materials, i.e. hydrogels, films, foams, and fibres, for different applications where they could potentially be sustainable alternatives to petroleum-based polymers. WPI was chosen as the starting material due to the high accessibility of whey as an industrial side-stream product from cheese manufacturing, and its ability to easily grow PNFs.

PNFs grown in the presence of different metal ions were generally curved and short, and they formed hydrogels, in contrast to the straight ones fibrillated without metal ions. The effect of metal ions with different acidity was systematically studied with respect to fibrillation kinetics and gelation behaviour. The protein fibrillation was accelerated by the addition of metal ions. The strength of the hydrogel increased with increasing acidity of the metal ion at the same ion concentration, as long as the ion did not precipitate as hydroxide/oxide. 

Protein nanocomposite films were prepared by adding separately grown PNFs into a non-fibrillar protein matrix from the same WPI starting material. The glycerol-plasticized composite films obtained an increased elastic modulus and decreased strain at break with increasing content of PNFs. 

The produced PNF foams showed high-temperature resistance during aging at 150 °C for as long as one month (maximum testing time), far exceeding the properties of many petroleum-based thermoplastics. The aged foams were also able to retain their properties in different solutions that normally degrade/dissolve protein materials.

PNFs were also organized into microfibres using a flow-focusing method. Genipin was added as a natural crosslinker to improve the mechanical properties of the obtained fibre. The crosslinked fibre (using only 2% genipin) obtained a significantly higher stiffness and strength at break as compared to the fibre assembled without genipin.