1. Introduction
Because of greenhouse gas emissions, especially carbon dioxide, which have resulted in extreme weather events, rising sea levels, global warming, and other environmental problems, the globe is today facing grave difficulties [
1,
2,
3,
4]. About one-third of all anthropogenic emissions come from the food system alone, with different sources of emissions in industrialized and poor nations [
2]. Proposals for national licenses with emission fees and internationally transferable emission permits are among the measures to lower these emissions to promote affordable emission reductions [
4]. However, scientists are also attempting to lessen the issue by developing new ecologically friendly technology and concepts, which is why they are making great efforts to cut greenhouse gas emissions.
Growing energy consumption and greenhouse gas emissions are driving developments in renewable energy sources and energy efficiency. This poses a significant barrier to global development as well [
5,
6], as energy is essential to the expansion of the automobile industry as well as societal advancement. Concern over the rising energy use and its negative effects on the environment, human health, and climate change is developing on a global scale. Currently, 40% of the world’s energy is consumed by the building industry; by 2050, this percentage is predicted to climb to 50% [
7]. The primary uses of energy are cooking, lighting, entertainment, different types of sanitation and cleaning, and space heating and cooling. Buildings employ a variety of energy sources, such as pipeline gas, electricity, gasoline, coal, natural gas, liquefied petroleum gas (LPG), solar energy, biogas, and biomass [
8,
9]. Buildings throughout the world now require lower energy usage. A significant portion of energy use may be cut by switching to clean and renewable energy systems for lighting, cooling, and heating. It is not always feasible to rely entirely on renewable energy sources, such as wind and solar energy. For instance, the wind doesn’t constantly blow, and the night sky is dark. [
10] Thus, compared to conventional heating systems, radiant floor heating systems are more sanitary [
11]. Radiant heat is produced by hot water or steam travelling via an underground conduit, which supplies energy to the radiant floor heating system. Without compromising thermal comfort, radiant floor heating and heat storage may greatly boost a building’s energy efficiency [
12].
The need for more reasonably priced, high-capacity thermal energy storage systems has arisen as a result. PCM, or phase change material, is one of numerous energy storage and control technologies [
13]. It is acknowledged that employing phase change materials can enhance a building’s energy management. PCMs have the ability to store and release thermal energy in the form of latent heat due to their high energy storage density and isothermal phase transition [
14,
15]. This explains why they are often used in thermal energy storage systems such as air conditioning in modern buildings [
16], thermal management in electronic equipment [
17], and smart textiles [
18]. However, the leaking of liquid during melting is a major problem that hinders the practical application of both organic solid and liquid PCMs [
19,
20]. A material is said to be latent because its thermal energy is held between its molecules until it transitions from one phase to another. Matter is made up of molecules joined by chemical bonds. These chemical connections allow heat to be both emitted and retained. Heat must be stored (absorbed) for the PCM to function. This dissolves the bonds holding the material together and turns it into a liquid [
21]. Latent heat is the amount of energy needed to change a material’s physical condition at a given temperature [
22]. This can boost a building’s thermal mass and raise its energy efficiency. Stable PCM composites may be created by directly integrating, dipping, encapsulating, shape-stabilizing, and combining PCM with other materials and structural components [
23,
24,
25,
26,
27].
The use of phase change materials (PCMs) significantly enhances the thermal characteristics of wood-based panels. According to studies, PCM-impregnated wood panels offer better qualities including resistance to biological assaults, thermal stability, and effective heat storage and release during phase shift processes [
28,
29]. Using foamed concrete and cement plaster with microencapsulated PCM for exterior wall treatments. During PCM melting, it was discovered to lower air temperature, heat flow, and interior surface temperature, indicating PCM’s excellent efficacy in exterior applications [
30]. Furthermore, the creation of particleboard with modified cassava starch as a binder and Ironwood red chips as a raw material has shown enhanced mechanical qualities appropriate for interior panels and ceilings, underscoring the adaptability and promise of PCM in the production of wood-based panels [
31].
One commonly used method of applying PCM in combination with wood is impregnation. Using this method, researchers have prepared a flooring panel that not only exhibits improved thermal properties but also shows increased scratch resistance, especially in the solid phase of the PCM. In the liquid phase, the hardness is not lower than that of wood, which is a positive aspect. The flammability of the impregnated elements was also investigated, and it was unequivocally stated that using such structural elements without additional protection can be dangerous, as PCM increases the flammability of wood elements after impregnation [
32].
Numerous studies have previously been conducted in this field, and new methods are always being created. For instance, Kumar et al. tested combining solar energy and the HS22 PCM to heat space in frigid climates, keeping a room temperature of 10 to 20
oC even while the outside temperature was -10 to 0
oC [
33]. Furthermore, according to a study by Guimarães et al., adding PCMs to building materials improves energy efficiency by lowering room temperature swings [
34]. Wieland emphasized using finned heat exchangers to accelerate heat transfer rates and PCMs like paraffin wax in storing thermal energy [
35]. To reduce energy costs and boost hot water output when combined with electric heaters, Djeffal et al. created a PCM blend of animal fat and paraffin wax for hot water systems [
36]. According to Mohseni et al., PCM has even been used in phase-change memory technology [
37], and its potential for data storage applications is demonstrated by the study. Moreover, PCM can lessen mechanical stresses in concrete components by absorbing heat during the curing process, as demonstrated by Fabiani et al. [
38].
On the other hand, Yang and colleagues were able to develop a novel phase transition material with strong reversible thermochromic capacity by including a thermochromic chemical onto delignified wood (DW) slides [
39]. Comparably, Ma et al. [
40] used the caprylic-palmitic acid treatment on DW slides to create a stable phase transition composite (PCC) with a resting phase transition temperature of 23.4 °C. According to both investigations, the removal of lignin enhanced PCM adsorption by opening up the catheter chambers and DW slides and increasing their permeability.
In this study, delignification and impregnation with myristyl alcohol (MA) were used to create stable phase change composites (PCCs) based on wood powder (WF), a by-product of the wood industry [
41]. Phase-change composites, urea-formaldehyde (UF) resin, and delignified wood flour (dWF) / myristyl alcohol impregnation have been used to generate composite panels. This approach provides a practical route to widespread use in energy-related domains. This straightforward and flexible method offers significant potential for the large-scale manufacturing of shape-stable phase-change composites and may be expanded to further temperature control applications. In research, Jeong et al. [
42] looked at the use of microencapsulated phase change material (MPCM) in wood-based flooring as a way to introduce MPCM into construction materials. As a consequence of this investigation, scanning electron microscopy (SEM) examination verified that MPCM was evenly distributed throughout the adhesive. The features of a thermal energy storage material were established for this composite by the use of differential scanning calorimetry (DSC) investigation.
The incorporation of hemp for interior wall panels with melamine and formaldehyde as the outside coating and a microencapsulated phase change material (PCM) as the core material was also assessed [
43]. The test employed organic PCM-S28, which has a melting point between 25 and 29
oC. To create the test panels, 10% Kleiberit urea-based formaldehyde resin (UF) was employed as a binder during the cold pressing procedure. The test panels were 25 mm thick and had a density of 310 ± 20 kg m
−3, which satisfied the specifications for low-density panels. When 5% nanocapsules were inserted during the panel production process, the heat capacity improved by 28%.
Another example of PCM application in wood is multifunctional wood-based phase change composite materials with magnetic additions created by impregnating purified balsa wood with a combination of 1-tetradecanol and Fe
3O
4 nanoparticles. The results revealed that these composites had a large energy storage capacity, outstanding thermal reliability even after 100 heating and cooling cycles, and good thermal stability up to 112°C while remaining shape stable. Furthermore, the incorporation of Fe
3O
4 nanoparticles enhances the composites’ magnetic characteristics and increases the efficiency of solar-to-thermal energy conversion. The materials also display a magnetothermal effect, which is the increase in temperature caused by a changing magnetic field [
44].
When taken as a whole, these studies show how versatile and successful PCM is in a range of applications, including building energy systems, thermal energy storage, and space heating. Therefore, this research aims to create a thermally active medium-density fibreboard (MDF) with PCM powder. MDF can be useful for interior design and furniture manufacturing.
2. Materials and Methods
2.1. Materials
In the present study, medium density fiberboards (MDF) were produced under laboratory conditions from pine (Pinus sylvestris L.) and spruce (Picea abies (L.) H.Karst) industrial fibers (IKEA Industry Poland Sp. z o. o. brand Orla, Szczecin, Poland). The fibers were dried to a moisture content (MC) of about 4%. The MDF boards were bonded with urea-formaldehyde resin (UF; Silekol S123, Silekol Sp. z o.o., Kędzierzyn Koźle, Poland), with a formaldehyde to urea (F:U) molar ratio of 0.89, pH of 9.6, viscosity of 470 mPa s, resination of 12%, the latter of which is commonly used in industry. The PLUSICE A22 powder PCM used in the study was provided by Phase Change Material Products Ltd. (Unit 32, Mere View Industrial Estate, Yaxley, Cambridgeshire, PE7 3HS, UK). The PCM was in powder format, phase change temperature of 22 °C, density of 785 kg m−3, latent heat capacity of 160 kJ kg−1, volumetric heat capacity of 126 MJ m−3, specific heat capacity of 2.2 kJ kgK−1, thermal conductivity of 0.18 W mK−1, maximum operating temperature 200 °C.
2.2. Preparation of Panels
The test material consisted of laboratory-produced dry-formed fiberboards, each with a target density of 750 kg m−3, dimensions of 320 mm × 320 mm, and a nominal thickness of 16 mm. Each panel type was produced in triplicate. The panels were made in several variants: reference panels and panels containing various proportions of PCM particles (5%, 10%, 30% and 50% by weight relative to the board weight), added during the resination process. Reference panels were manufactured without any PCM particles. The wood fibers were separated into three layers before resination: one inner layer (68% by weight) and two outer layers (each 16%). The PCM particles were incorporated only into the inner layer fibers during the resination process. The mats were manually formed. The boards were pressed using a hydraulic press (AKE, Mariannelund, Sweden) under the following conditions: a temperature of 180 °C, a pressing factor of 20 s/mm of nominal thickness, and a maximum unit pressing pressure of 2.5 MPa. After production, the boards were stored at 20 °C and 65% humidity until they reached a constant weight.
2.3. Characterization of the MDF Panels
The properties of the panels were determined in accordance with European Standards: density [
45], modulus of rupture (MOR) and modulus of elasticity (MOE) [
46], internal bond (IB) [
47], screw withdrawal resistance (SWR) [
48], water absorption (WA) and thickness swelling (TS) after 2 and 24h of immersion [
49]. No less than 12 samples per every panel type were used to complete the mentioned tests. To evaluate the density profiles, the samples were cut into 50 mm × 50 mm test specimens (3 samples per every panel type; after initial evaluation of results, one representative profile was used for final evaluation). The density profile was measured on a Grecon DA-X measuring instrument (Alfeld, Germany) with direct scanning X-ray densitometry across the panel thickness with an incremental step of 0.02 mm. All the mechanical tests were performed on a computer-controlled universal testing machine (Research and Development Centre for Wood-Based Panels Sp. z o.o. Czarna Woda, Poland). The thermal properties of the tested panel have been investigated on 2 samples per every variant, of dimensions of 300 mm × 300 mm, on the measurement unit designed for this research, consisted on heating plate of the constant temperature of 40 °C. On the plate, the sample of temperature of 20 °C has been placed and the thermocouple connected to the computer has been fitted to the sample surface. The sample surface temperature has been registered every 60 s to reach the temperature of 40 °C ± 1 °C. The all achieved results, whenever possible, have been referred to the requirements of the proper European standards [
50].
2.4. Statistical Analysis
Using the RStudio software, statistical analysis was performed based on ANOVA tests, one-way for MOR, MOE, SWR, and IB, and two-way for thermal properties, TS and WA. After showing statistically significant differences by the ANOVA test, Tukey’s post-hoc test was performed, resulting in homogeneous groups, which translated into an analysis of the significance of differences between variants.
Author Contributions
Conceptualization, G.K.; methodology, G.K.; validation, G.K., A.J., J.D., and A.W.; formal analysis, A.J., J.D., and A.W.; investigation, G.K., A.J., J.D., and A.W.; resources, G.K., A.J.; writing—original draft preparation, G.K., A.J., J.D., and A.W.; writing—review and editing, G.K.; visualization, G.K.; supervision, G.K.; project administration, G.K.; statistical analysis, A.J. All authors have read and agreed to the published version of the manuscript.