Design of Hygroscopic Bioplastic Products Stable in Varying Humidities. Issue 2 (15th January 2023)

• Record Type: Journal Article
• Authors: Liu, Sirui; Bettelli, Mercedes A.; Wei, Xinfeng; Capezza, Antonio J.; Sochor, Benedikt; Nilsson, Fritjof; Olsson, Richard T.; Johansson, Eva; Roth, Stephan V.; Hedenqvist, Mikael S.
• Is Part Of: Macromolecular materials and engineering. Volume 308:Issue 2(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-01-15
• Subjects: biopolymers -- diffusion -- moisture -- relative humidity -- wheat gluten; Plastics -- Periodicals; Polymers -- Periodicals; Polymerization -- Periodicals; 547.705
• DOI: 10.1002/mame.202200630
• Languages: English
• ISSNs: 1438-7492

Abstract

Abstract: Hygroscopic biopolymers like proteins and polysaccharides suffer from humidity‐dependent mechanical properties. Because humidity can vary significantly over the year, or even within a day, these polymers will not generally have stable properties during their lifetimes. On wheat gluten, a model highly hygroscopic biopolymer material, it is observed that larger/thicker samples can be significantly more mechanically stable than thinner samples. It is shown here that this is due to slow water diffusion, which, in turn, is due to the rigid polymer structure caused by the double‐bond character of the peptide bond, the many bulky peptide side groups, and the hydrogen bond network. More than a year is required to reach complete moisture saturation (≈10 wt.%) in a 1 cm thick plate of glycerol‐plasticized wheat gluten, whereas this process takes only one day for a 0.5 mm thick plate. The overall moisture uptake is also retarded by swelling‐induced mechanical effects. Hence, hygroscopic biopolymers are better suited for larger/thicker products, where the moisture‐induced changes in mechanical properties are smeared out over time, to the extent that the product remains sufficiently tough over climate changes, for example, throughout the course of a year. Abstract : Moisture diffusion is slow in a highly polar protein material (wheat gluten). The reason for the low diffusivity is the rigid polymer system. For small samples the mechanical properties are highly moisture‐history dependent. Designing products with thicker goods limit the effects of climate variations.