Effect of aldehydes on thermomechanical properties of gluten-based bioplastics

• Glyoxal is the only aldehyde that seems to promote shear-induced cross-linking.
• Aldehydes may favour bending viscoelasticity of bioplastics due to cross-linking.
• Addition of aldehydes always leads to a lower water uptake capacity of bioplastics.
• Aldehydes seem to interfere with some covalent bonding along thermomoulding.

Protein–protein crosslinks play an important role in the design of biodegradable polymeric materials requiring suitable rheological and mechanical properties. The addition of aldehydes to the bioplastic formulation may result in their involvement in some form of protein cross-linking. The objective of this contribution is to evaluate the effect of adding some aldehydes (formaldehyde, glutaraldehyde and glyoxal) on the thermomechanical properties of gluten-based biodegradable polymeric materials processed by a mixing stage followed by compression moulding at 9 MPa and 130 °C. Different bioplastic probes were evaluated by means of DMA measurements, recording the elastic and loss moduli as a function of temperature and uniaxial tensile strength tests. Water absorption capacity and solubility under different extraction media of bioplastic specimens, were also evaluated. Solubility measurements were carried out in order to analyse the effect of the aldehyde on the nature of the interactions taking place in the system, being compared to those performed on blends previous to the moulding process. Glyoxal is the aldehyde that seems to produce bioplastics with best thermal and mechanical properties. This study would contribute to evaluate the potentials of adding aldehyde to gluten/plasticiser systems to control the microstructure and properties of the final bioplastics.