ARS | Publication request: Microstructure of Milk-Protein-Coated Flax Fibers

Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 13, 2007
Publication Date: December 1, 2007
Citation: Onwulata, C.I., Cooke, P.H., Harden, J., Liu, Z., Erhan, S.Z., Akin, D.E., Barton Ii, F.E. 2007. Microstructure of milk-protein-coated flax fibers. Journal of Biobased Materials and Bioenergy. 1(3):372-379.

Interpretive Summary: Agriculture-based natural products such as flax fibers can be used to replace materials such as glass fibers in industrial products. The problem with using natural fibers is that they absorb moisture or oils from the surrounding materials, causing the entire product to become brittle and break. Coating or encapsulating the fibers with a water repelling gel would prevent them from absorbing moisture or oils. In this study, flax fibers were encapsulated using cheese whey isolate, a highly concentrated form of the watery by-product of the cheese making process, rich in protein (90%), as the coating. Whey protein isolate combined with casein forms a very strong coating with the consistency of honey. To create the coating, milk protein gel was made by combining casein and whey (50/50) at very high speed, and boiling under vacuum. The resulting gel was applied evenly to the fiber surface using a spray drying process. Under the microscope, it could be seen that the gel stuck to the fibers, forming a protective barrier around the flax fibers, reducing the amount of moisture and oil that they can absorb. The milk protein coated flax fiber performed better than the uncoated flax by absorbing less moisture and remaining stronger.

Technical Abstract: Unlike synthetic fibers, natural fibers like flax (Linum usitatissimum L,) need to be modified when used in composites to enhance their properties and reduce some adverse physical effects. Creating a structured protective, electro-statically active surface enhances bonding and improves structural properties of composites containing flax. A new coating process developed to protect natural fiber deterioration in high moisture environments was used to coat flax fiber for industrial applications. A cross-linked matrix of milk proteins, which was used as a spray or tray dried with the flax, and afterward a high-melt vegetable wax was applied on flax fibers by hot-melt, making fibers statically active. The milk proteins formed a first layer, and the vegetable wax formed the second. Microstructure of the coated flax show new physical forms characteristic of spray and tray drying, and physical analyses indicate reduction in water holding capacity from 7 g H2O/100 g flax to <1 g H2O / 100 g flax, water absorption from about 5 g H2O/100 g flax to <2 g H2O / 100 g flax, and oil absorption 5 g H2O/100 g flax to <3 g H2O / 100 g flax. This novel technique used to alter the surface properties of flax fiber may provide an environmentally friendly method of enhancing its properties.