Issue 01/2016

Materials
The gluten solution
New TPVs derived from wheat gluten
By Karen Laird
While gluten has got a lot of bad press over the past
few years, there is still good news to report. Gluten,
it turns out, can actually serve as the basis for a new
type of biobased plastic material, say scientists at the KU
Leuven in Belgium. These researchers are working on the development
of a new type of thermoplastic vulcanisate – based
on gluten.
But what is gluten? Very simply put, is the seed storage
protein in mature cereal seeds. More specifically, it is a protein
composite, meaning it is a substance made up of several
different proteins, in this case gliadin and a glutenin. The
cross-linking of gliadin molecules and glutenin molecules
creates the primary properties associated with gluten.
According to Lien Telen, a postdoctoral researcher at KU
Leuven who has spent the past five years exploring the the
use of wheat gluten to produce thermoplastic elastomers,
there are a number of aspects that make gluten an attractive
starting point for novel biobased materials. In the first place,
there is a lot of it: as a co-product of industrial gluten-starch
separation or bioethanol production, gluten is available in
Europe in quantities of up to 1 million tonnes on an annual
basis. Only part of this gluten is used as a high-value bakery
ingredient, while the excess is mostly used in animal feed.
Secondly, unlike most other proteinaceous resources,
gluten contains high molar mass constituents and unique
network forming properties, which means it can readily be
converted into a variety of biobased materials.
The development that has received the most attention of the
gluten team at KU Leuven, said Telen, has been the glutenbased
TPVs (TPV stands for thermoplastic vulcanizates).
These new materials are colorable and can be processed on
conventional processing equipment. Unlike the olefin-based
rubbers in conventional TPVs, wheat gluten intrinsically
crosslinks under the influence of heat, eliminating the need
for an additional chemical crosslinker. Gluten-based TPVs
combine the typical properties and functional performance
of rubbers with the melt processability of thermoplastic
polymers, resulting in recyclable materials. Telen explains:
“The gluten TPV consists of (non-recyclable) crosslinked
gluten particles within a thermoplastic matrix. The main
advantage of these TPVs is that they have elastomeric
characteristics at room temperature combined with the
melt processability of thermoplastic materials. The rubber
particles are very small (a few µm) and will flow in the melt
of the thermoplastic matrix making the entire material
recyclable using standard thermoplastic polymer processing
equipment such as extrusion and injection molding.”
The gluten team is also working on improving the
properties of the new TPVs, which, said Telen, “fall short on
water-resistance, oil and chemical resistance and operational
temperature range”. Yet what also sets gluten-based TPVs
apart is the possibility of combining elastomeric behavior and
biodegradability in a single material, a combination not seen in
conventional oil-based TPVs. Depending on the thermoplastic
component, the gluten TPV’s can be designed to be fully
biodegradable. TPVs with a polyethylene or polyamide matrix
are not completely biodegradable, as the matrix remains
intact, making them unsuitable for composting.
“However, completely biodegradable and (home)
compostable TPVs have also been developed using a
biodegradable and (home) compostable matrix,” said Telen.
Applications for these materials could include indoor soft
touch materials, or functional biodegradation applications in
the agricultural and horticultural sectors.
Next to gluten-based TPVs, the researchers at KU Leuven
are looking at other materials as well. “In the absence of
a plasticizer, the heat induced crosslinking results in a
glassy, rigid material with material properties comparable
to Polystyrene (PS)”, said Telen. “Gluten composites: rigid
gluten bioplastic reinforced with flax fibers are another focus.
Research on these materials is ongoing and very promising.”
http://chem.kuleuven.be
60 – 80 % biobased non biodegradable 100 % biobased biodegradable
anaerobic
TPV 1 2 3 4
Tensile modulus (MPa) 333 197 265 494
Tensile elongation (%) 247 240 120 18
Tensile strength (MPa) 16 12 9 12
Shore D hardness 42 48 43 51
Melting temperature (°C) 129 118 125 140
Crystallization temperature (°C) 113 60 50 85
18 bioplastics MAGAZINE [01/16] Vol. 11