A novel polysaccharide/zein conjugate as an alternative green plastic

Abstract

The flax seed cake is a waste product from flax oil extraction. Adding value to this wasted material aligns with the concept of circularity. In this study, we explored zein protein conjugation with flax mucilage for packaging material development. Although both flax mucilage and zein have excellent film-forming properties, they lack the required mechanical properties for industrial processing and are sensitive to high humidity. We present a simple and non-toxic one-pot method for developing the novel flax mucilage/zein conjugate. Where the flax mucilage undergoes oxidation to form aldehyde groups, which then react with zein's amino groups in a glycation process. The conjugates were analyzed using different techniques. The flax mucilage conjugate had a water-holding capacity of 87-62%. Increasing the zein content improved the surface smoothness of the films. On the other hand, higher levels of zein led to a significant decrease in film solubility (p < 0.05). The flax mucilage conjugate exhibited thermoplastic and elastic properties; revealing Young's modulus of 1-3 GPa, glass transition temperature between 49 °C and 103 °C and excellent processability with various industrial techniques. Showing its potential as a sustainable alternative to traditional plastics.

Figure 1

(a) Schematic for the flax mucilage composition. (b) Flax mucilage extraction yield at different extraction conditions. (c) Chemical schematic of the proposed reaction for the conjugation of zein and flax mucilage.

Figure 2

Photographs and SEM micrographs (×500) of the solvent cast (a) neat flax mucilage, (b) zein, and the different flax mucilage/zein conjugates (c) 5%-5D, (d) 5%-3 h, (e) 30%-3 h, and (f) 30%-3 h-DMSO respectively.

Figure 3

FTIR spectra. (a) In the range 4000–500 cm⁻¹ of the flax mucilage, zein, 30%-3 h-DMSO, 30%-3 h and 5%-5D indicating the amide I absorptions and the absence of the pyranose at 1047 cm⁻¹, (b) Deconvoluted region (2000–500 cm⁻¹) of 30%-3 h-DMSO spectrum, showing the formation of imine from an amine and a carbonyl-containing structure.

Figure 4

NMR spectra (a) 1D ¹H NMR, (b) 1D ¹³C NMR, (c) 2D ¹H, ¹³C-HSQC and (d) 2D ¹H, ¹⁵N-HSQC spectra (red: 30%-3 h and Blue: 5%-5D).

Figure 5

(a) A qualitative solubility study showing the percentage weight loss of the different samples, bars with different letters indicate significant difference in percentage water loss (P < 0.05). (b) 30%-3 h sample through different processing techniques. The solubility study were conducted in triplicate, with each set of measurements performed three times (data are expressed as an average ± standard error, N = 9).

Figure 6

(a) Stress–strain cure for 30%-3 h and 30%-3 h-DMSO. (b) Strength, (c) E-modulus, (d) Max. Force (e) Max. Strain, bars with different letters are significantly different (P < 0.05). The the mechanical tests were conducted in triplicate, with each set of measurements performed three times (data are expressed as an average ± standard error, N = 9).