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Bentonite extends shelf life of bio-based starch coatings
Researchers have shown that incorporating bentonite nanoclay into corn starch coatings significantly improves their mechanical strength, water resistance and shelf stability. The bio-based formulation offers a sustainable alternative for flexible packaging applications requiring extended storage.
Bio-based corn starch (CS)/bentonite nanoclay coatings have been formulated as sustainable alternatives for packaging applications. Corn starch was plasticised with glycerol and bentonite was added in situ at concentrations of up to 5 wt%. Small-strain tensile oscillation and creep testing revealed that the resulting plasticised coatings were elastomeric and mechanically reinforced by the addition of bentonite. The molecular networks were crosslinked and predominantly elastic, with the tensile modulus |E*| increasing as bentonite content rose.
Creep deformation followed the Kelvin-Voigt model, and the coatings recovered elastically to nearly their original length upon stress release, indicating minimal defects in the crosslinked network. This was further confirmed by the scaling behaviour |η*| = ω⁻ⁿ, where n approached 1.
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Improved humidity resistance and extended shelf life
Under controlled humidity conditions up to 70 %, a plasticising effect caused the elastic modulus of the neat coatings to decay rapidly. At 5 wt% bentonite content, however, humidity had no significant effect on the modulus, indicating an effective barrier function. During storage at room temperature for up to 30 months, the modulus of the neat coating increased sixty-fold due to plasticiser leaching, while the influence of ageing on mechanical performance and stretchability decreased with rising bentonite content.
According to the authors, the nanoclay acts as both a water barrier and a barrier against plasticiser diffusion, thereby extending the shelf life of the coatings. The findings support the use of starch/bentonite systems as sustainable alternatives for flexible packaging applications requiring extended storage stability.
Source: Romo-Uribe, A. et al., Bio-based corn starch/bentonite coatings. Probing the structure and the influence of humidity and shelf storage with rheology and mechanical properties. Progress in Organic Coatings, 110127 (2026).
