Poplar Fibers

Poplar trees, European black poplar, and Populus nigra (See Fig1.), are very fast-growing trees and are grown on 76 million decares of land in the world. Poplar trees are used as raw materials for industrial products such as paper, cellulose pulp, and plywood. Although poplar trees are widely used in the industrial field, the fibers of these trees have never been used for industrial purposes before.

Figure 1. Populus nigra leaves and seeds

Poplar trees have many species due to biological processes and anthropogenic effects etc. The properties of poplar fibers vary depending on the tree species they are growing on. Poplar fibers grow on Populus tree seeds also known as cottonwood fiber. These seeds, which are usually separated from the trees in the last spring months, are carried by the wind thanks to the poplar fibers growing in the seed coat. According to the literature, the length of these fibers surrounding poplar seeds are between 3 and 16 mm, and fiber diameters are 5-30 µm. Poplar fibers, whose fiber lengths are too short to spin, are creamy white, shiny, and soft besides they resemble silk with its shiny appearance.

Figure 2. Poplar seed fibers folling on the ground

Poplar fibers have a finer fiber structure compared to cotton and wool and they are extremely light as hollow tubules. This huge holow lumen inside the fiber constitutes 80-90% of the total fiber diameter. In addition, although poplar fibers are cellulosic, they have hydrophobic properties. In studies conducted to observe its water-repellent properties, the contact angle between water and poplar fiber was reported to be 140°. Its water-repellent properties and huge hollow lumen make poplar fibers an ideal candidate for oil absorption studies.

Figure 3. Scanning Electron Microscope image of cross-section of poplar fiber. Scale bar 5 μm.

A more environmentally friendly approach would be to use poplar fiber as an oil absorbent instead of petroleum-derived non-biodegradable materials. The fact that poplar fibers are recyclable and biodegradable makes them attractive for use as oil-absorbent materials. In addition, oil absorption capacities can be increased by chemical modifications. For example, when natural fibers are subjected to alkali treatment, it improves the effective surface area as well as the adhesion of the interface between the fiber and the matrix. Thanks to the acetylation process, not only increases the hydrophobicity of the fibers but also improves the fiber surface morphology and silane treatment by ensuring the fibers adhere to the polymer that stabilizes the composite material. Acetylation and hydrothermal treatments increase the hydrophobicity of poplar fibers. Thus, poplar fibers exhibit a better oil absorption performance and have 4.60 times the oil absorption capacity than raw poplar fibers. Although we have mentioned the many advantages of poplar fibers, unfortunately, poplar fibers are considered waste today. In this context, the use of poplar fibers will be a more environmentally friendly approach and will allow the development of high value-added products using Europe's natural resources.

“This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 101023459”