**1. Introduction**

Recently, in the construction industry, great attention has been paid to various ecological aspects. As a result, materials that are easily biodegradable and durable are in demand [1,2]. In some applications such as terraces and façades, wood has been replaced by composites. Composite materials are made of polymers (PP, PVC or HDPE) acting as matrices and lignocellulosic particles as fillers. Natural fillers in the form of flour, fibers or shavings, as well as fibers from crop husks, for example, rice or oat [3–5], are used in composite materials. Natural fibers have a low density, are biodegradable, widely available and inexpensive. Therefore, they are viewed as more attractive materials than commonly used synthetic fibers. However, they also have various disadvantages, such as low thermal stability and susceptibility to moisture absorption or microorganisms [6–8]. It was thought that a thermoplastic material completely encapsulates the natural fiber component of the composite, protecting it from moisture and fungal decay. However, some publications show that fully encapsulating natural fibers with a polymer matrix is not possible [9,10].

Some publications prove that biodeterioration has a negative impact on the mechanical and physical properties of natural fiber composites [7,9,11–13]. This is determined by weight loss and changes in material strength [1,3,12,14]. Composite materials used in outdoor conditions are exposed to many factors, such as UV radiation, freezing, leaching, temperature changes and biological agents, so it is difficult to determine which factor has a decisive effect on degradation, since they all act simultaneously [3,15].

One of the most important steps in preparing composite specimens for testing after exposure to fungi is mycelium removal. Following exposure to fungi, specimens usually show significant mycelium overgrowth, which can interfere with the testing equipment and impair measurements. In addition, mycelium can cause damage to human health, so it should be removed before further tests. Often, this step is skipped in method descriptions in composite-related publications [6,13,16,17]. Some authors shortly describe the cleaning process. Composites can be cleaned with a soft sponge [8] or by sanding [18].

As composite materials are now widely used, this study aims to explore the resistance to fungal decay of the *Agaricomycotina* subdivision [19] and the effect of the method of

**Citation:** Goron, M.; Sudoł, E. Effect of Fungi Removal Method on the Mechanical Properties of Polymer Composites Reinforced with Oat and Millet Husks. *Mater. Proc.* **2023**, *13*, 33. https://doi.org/10.3390/ materproc2023013033

Academic Editors: Katarzyna Mróz, Tomasz Tracz, Tomasz Zdeb and Izabela Hager

Published: 16 February 2023

**Copyright:** © 2023 by the authors. 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/).

mycelium removal after microbiological exposure on their mechanical properties. The subject of the study is composites reinforced with natural fibers, including oat and millet husks.
