**Philippe Evon**

Dr. EVON is Research Engineer at the Laboratoire de Chimie Agro-industrielle (LCA). He specializes in the valorization of wastes from biomass to produce extracts and to design agromaterials. He is mainly developing studies for using biomass as raw material for:


He is the Manager of the LCA's Industrial Technological Hall "AGROMAT" dedicated to agromaterial's (https://www6.toulouse.inra.fr/lca/AGROMAT), which is located in Tarbes (South-West of France).

## *Editorial* **Special Issue "Natural Fiber Based Composites"**

**Philippe Evon**

> Laboratoire de Chimie Agro-Industrielle, Université de Toulouse, INP, ENSIACET, 4 Allée Emile Monso, 31030 Toulouse, France; Philippe.Evon@toulouse-inp.fr

In the last twenty years, the use of cellulosic and lignocellulosic agricultural byproducts for composite applications has been of grea<sup>t</sup> interest, especially for reinforcing matrices. Fibers of renewable origin have many advantages. They are abundant and cheap, they have a reduced impact on the environment, and they are also independent from fossil resources. Their ability to mechanically reinforce thermoplastic matrices is well known, as is their natural heat insulation ability. The matrices can themselves be of renewable origin (e.g., proteins, starch, polylactic acid, polyhydroxyalkanoates, polyamides, etc.), thus contributing to the development of 100% bio-based composites with a controlled end of life.

This Special Issue's objective is to give an inventory of the latest research in this area of composites reinforced with natural fibers, focusing in particular on the preparation and molding processes of such materials (e.g., extrusion, injection-molding, hot pressing, etc.) and their characterization. It contains one review and nineteen research reports authored by researchers from four continents and sixteen countries, namely, Brazil, China, France, Italy, Japan, Malaysia, Mexico, Pakistan, Poland, Qatar, Serbia, Slovenia, Spain, Sweden, Tunisia, and Vietnam.

An overview of the chemical treatments, manufacturing techniques, and potential lightweight engineering applications of natural fiber based biodegradable composites is provided in a comprehensive review paper [1]. Many natural fibers are presented, including jute and sisal. These have been utilized for ages in several applications, such as ropes, building materials, particle boards, automotive industry, etc., and the chemical treatments and surface modifications are presented as solutions to improve the quality of the natural fibers.

Some of the research articles in this Special Issue sugges<sup>t</sup> the use of very different raw materials to obtain biobased materials that may find future applications in many fields, e.g., agriculture, ecological engineering, construction, load-bearing composites, and packaging.

	- After their mechanical mixing, flax and polylactide fibers can be transformed into green sound-absorbing composite materials through hot pressing, and various structure and profiling can be obtained by using different multilayer structures of nonwovens and adjusting the pressing conditions [5].

**Citation:** Evon, P. Special Issue "Natural Fiber Based Composites".*Coatings* **2021**, *11*, 1031. https:// doi.org/10.3390/coatings11091031

Received: 25 August 2021 Accepted: 26 August 2021 Published: 27 August 2021

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**Copyright:** © 2021 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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• reinforcement, respectively, their sound-absorption performance depending on their volume density, the mass fraction of kapok fibers inside the materials, and their thickness [6].


Some other research articles propose various pre-treatments on natural fibers with the objectives to favor both the manufacturing and use properties of the resulting natural fiber-based composites or cellulosic textiles. Pre-treatments for plant fibers are very popular for increasing the fineness of bundles, promoting individualization of fibers, modifying the fiber-matrix interface inside composites, or even reducing their water uptake. For subsequent textile applications, the pre-treatments can also be proposed to make the cellulosic fibers more resistant to fungi, bacteria, fire, etc.


Additionally, last but not least, olive pomace (OP) is presented as a potential fibrous reinforcement in polypropylene (PP) and polyethylene (PE) biocomposite materials [15]. More specifically, this contribution proposes a life cycle assessment (LCA) of these new construction materials (e.g., decking), and the latter confirmed their environmental friendliness. This constitutes a new perspective for the valorization of OP, an agricultural by-product widely present in southern Europe.

The plant world is also the source of natural substances other than fibers, which can also find applications in the field of composite materials, e.g., in the building industry. By way of example, one research article in this Special Issue evidences the interest to add mucilages extracted from five specific plants to improve the quality of lime-based mortars, making these natural extracts promising additives for restoring and protecting historical buildings [16]. Vegetable raw materials can also be the source of natural dyes, possibly useful in the construction sector (case of the exterior wall paints [17]), but also for textiles, paper, etc. In particular, using natural dyes on textiles has many advantages, as they are healthier and more environmentally friendly than the synthetic ones. A natural dye extracted from the purple petals of an invasive plant has thus been successfully used for the screen printing of both cotton and polyester woven fabrics just as various papers [18].

Plants can also be the source of natural adsorbents. Another research report in this Special Issue thus presents the obtaining of efficient biobased carbon adsorbents [19]. Prepared from spruce bark residues, these will find application for efficient removal of reactive dyes and colors from synthetic effluents, and may be used for treating contaminated wastewater to remove pollutants.

In addition to the vegetable fibers and other chemicals from natural resources, the animal world is also the source of promising renewable biopolymers for material applications. In particular, chitin is one of the most abundant polysaccharides, known to possibly act as a structural material in biological systems. In [20], nanochitin/polystyrene composite particles are prepared by Pickering emulsion polymerization using scaled-down chitin nanofibers. Owing to both their biocompatibility and hydrophobicity, these are promising candidates for future medical uses, e.g., by being used as carriers to control the release of hydrophobic drugs over time.

This Special Issue thus presents a very wide range of topics. It provides an update on current research in the field of natural fiber based composite materials. I am convinced that all these contributions will be a source of inspiration for the development of new composites. Generally speaking, these new materials are environmentally friendly and will undoubtedly find numerous applications in the years to come in many sectors.

**Acknowledgments:** I would like to thank all the authors for their valuable contributions to this Special Issue, the reviewers for their reviews and useful comments allowing the improvement of the submitted papers, and the journal editors for their kind support throughout the production of this Special Issue.

**Conflicts of Interest:** The authors declare no conflict of interest.
