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Article

Acoustic Absorption Behavior of Boards Made from Multilayer Packaging Waste

by
Miron Rancea
1,
Ovidiu Nemeș
1,2,*,
Ancuța-Elena Tiuc
1,* and
Ovidiu Vasile
3
1
Faculty of Materials and Environmental Engineering, Technical University of Cluj-Napoca, 103-105 Muncii Ave, 400114 Cluj-Napoca, Romania
2
National Institute for Research and Development in Environmental Protection, 294 Splaiul Independenței Blv., District 6, 060031 Bucharest, Romania
3
Department of Mechanics, Faculty of Biotechnical Systems Engineering, National University of Science and Technology Politehnica Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2026, 16(3), 1206; https://doi.org/10.3390/app16031206 (registering DOI)
Submission received: 2 December 2025 / Revised: 14 January 2026 / Accepted: 22 January 2026 / Published: 24 January 2026
(This article belongs to the Section Ecology Science and Engineering)
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In this study, multilayer waste-based composite materials were produced, and their acoustic properties were evaluated. The results provide a reference for the development of sustainable sound insulation panels and noise control materials, offering an eco-friendly alternative to conventional construction and industrial acoustic solutions.

Abstract

The increasing amount of multilayer packaging waste poses significant environmental challenges and calls for sustainable valorization solutions. This study aimed to investigate the acoustic properties of composite materials produced by hot-pressing multilayer waste without the addition of binders or other substances. The waste was carefully cleaned and shredded into square or strip-like geometries, and the composite material plates were compressed at different temperatures (120 °C, 125 °C, 130 °C, 135 °C, and 140 °C) under a constant pressure of 5 MPa. The sound absorption coefficients were evaluated for representative samples, with results analyzed as a function of constituent geometry and processing temperature. Experimental results indicate that the pressing temperature critically affects the internal structure of the material, while waste shape exhibits a frequency-dependent influence on the absorption coefficient. The resulting composite materials display low porosity, which limits internal sound absorption and promotes sound wave reflection, indicating that these materials are more suitable for sound insulation rather than acoustic absorption. These results highlight the potential of multilayer packaging waste-based composites as a sustainable solution for noise control applications and highlight the importance of processing parameters in tailoring their acoustic performance.

1. Introduction

In the long term, sustainability requires not only reducing environmental impact but also eliminating waste through its reintegration into productive cycles, in line with the principles of the circular economy promoted by the European Union. In this context, widely used packaging materials represent a major challenge, both due to the high volume they generate and the complexity of the recycling processes they require [1,2]. A relevant example is multilayer packaging, one of the most extensively used food packaging materials worldwide. Owing to its composite structure, which combines cardboard, polyethylene, and aluminum, the recycling of this type of packaging poses considerable technical and logistical difficulties [3]. Nevertheless, the efficient integration of such waste streams into circular value chains is essential for achieving the European sustainability targets and advancing the transition toward a green economy.
On average, Tetra Pak multilayer packaging is composed of approximately 75% high-quality paperboard, 20% low-density polyethylene (LDPE), and 5% aluminum (Al), in addition to small amounts of additives [3,4]. These combined layers—primarily, cellulose, polyethylene, and aluminum foil—result in a composite material with desirable barrier and mechanical properties but also significant end-of-life challenges [5,6]. Due to its complex structure, Tetra Pak cannot be processed in conventional paper recycling facilities, and it exhibits limited biodegradability when disposed of in landfills.
In 2021, Tetra Pak® distributed roughly 190 billion packaging units worldwide, generating a net revenue of EUR 11.5 billion and representing close to 79% of the global food packaging sector. Despite this extensive market share, only about 26% of the produced packages entered recycling streams. Consequently, large volumes of post-consumer Tetra Pak® waste persist within municipal solid waste systems, where they are predominantly managed through landfilling or incineration [1].
Conventional recycling strategies for multilayer packaging waste are predominantly based on thermal processing methods, including gasification, incineration, and pyrolysis [7,8,9,10]. These approaches are generally effective in reducing waste volume and facilitating partial energy recovery by converting the organic fraction into heat, syngas, or other energy carriers. However, such treatments are essentially destructive processes, as they degrade the original composite structure and do not allow the recovery or reintegration of valuable raw materials such as cellulose, polyethylene, or aluminum into new production cycles [11]. Consequently, while thermal methods contribute to waste-to-energy strategies, they fall short of addressing the broader goals of circular economy, which emphasize material valorization, resource efficiency, and the creation of closed-loop recycling pathways. Mechanical and chemical routes have also been developed with the aim of separating the individual components—paperboard, aluminum, and polyethylene—or at least isolating them into two main fractions: cellulose and an aluminum/polyethylene composite [12,13].
Among the available recycling strategies, hydro pulping has been identified as one of the most efficient techniques for separating the individual layers of multilayer packaging waste. In this process, the polyethylene and aluminum layers are detached from the cellulose fraction through mechanical agitation in a pulper, allowing partial recovery of the constituent materials. The cellulose fibers obtained through hydro pulping are of particular interest, as they can potentially be reused as renewable raw materials or as structural components in the development of novel composite materials. Despite these advantages, the method is associated with significant drawbacks, primarily related to its high energy demand. This is mainly due to the additional processing steps required to remove residual lignin and to enhance the purity of the recovered cellulose, both of which are essential for ensuring its suitability in advanced material applications [6].
Alternative approaches involve solvent-based extraction methods (organic, supercritical, or acid solvents) [14] or solvent dissolution processes [12]. Despite their potential, these methods face limitations, including the reliance on organic solvents and the low purity of recovered fractions [15]. Consequently, only limited research has addressed the reuse of Tetra Pak derived components as fillers in thermoplastic composite materials [16,17]. For instance, cellulose recovered from multilayer packaging waste has been investigated as a reinforcing filler in polybutylene succinate (PBS) composites, commonly applied in furniture, construction, and packaging. Filler loadings between 10 and 50 wt% demonstrated improvements in elastic moduli, storage moduli, and material bio-content, reaching up to 75% [17]. Similarly, multilayer packaging waste derived from cellulose has been applied as a reinforcement in cement-based composite materials after gamma irradiation treatments aimed at enhancing compatibility with ceramic matrices [16].
Further studies explored the direct recycling of whole multilayer packaging waste without prior component separation. For example, Martínez-López et al. [18] utilized untreated multilayer packaging waste to reinforce polymer mortars composed of polyether resins and silica sand, with investigations into the effects of filler concentration and gamma irradiation on composite material properties. More recently, a novel recycling pathway was proposed in which post-consumer multilayer packaging waste was directly incorporated as a reinforcing filler into sustainable polyurethane (PU) foam, avoiding preliminary separation steps [1]. PU foams represent a versatile class of thermosetting polymers obtained via the polyaddition reaction between hydroxyl groups of polyols and isocyanate groups of diisocyanates, forming urethane bonds, coupled with expansion reactions involving isocyanates and water [19,20,21]. This approach highlights the potential for multilayer packaging residues to be valorized as functional fillers in advanced polymeric systems.
One of the most promising applications of recycled multilayer packaging waste is the production of thermoplastic composite materials, as demonstrated by methods developed in our research group [22]. This study investigates composite materials fabricated from shredded or scissor-cut multilayer packaging waste (Al, paper, and PE), compressed at elevated temperatures without the addition of binders. Variations in material composition and processing conditions were applied to assess their influence on the final properties. Thermal analysis of the resulting composite materials revealed a two-step degradation process following moisture evaporation. The findings indicate that these low-cost thermoplastic composites have potential for diverse applications, provided that their use is limited to temperatures below approximately 200 °C, as exceeding this threshold results in material degradation [23].
Over the past decade, rapid urbanization and changes in lifestyle have contributed to the widespread presence of noise in daily life, establishing noise pollution as a major environmental concern. Noise pollution is defined as the prolonged propagation of unwanted sounds in the environment, which can adversely affect both humans and animals [24]. As a result, sound absorption has emerged as a key strategy for mitigating noise and improving human comfort. The high sound pressures generated by traffic, industrial activities, and machinery have driven the need for cost-effective and efficient production of sound-absorbing materials, commonly referred to as sound absorbers [25].
The aim of this article is to conduct experimental investigations on the production and evaluation of the acoustic properties of composite materials derived from multilayer packaging waste, processed by hot pressing. The novelty of this research lies in the analysis of the acoustic behavior of the materials as a function of processing parameters, such as temperature, and the type and shape of the used multilayer packaging. The innovative aspects of this study include: (a) the identification of a new method for valorizing multilayer packaging waste; (b) the use of this waste as a raw material for producing materials with acoustic properties, representing a significant step toward reducing both waste volume and noise pollution; and (c) the elimination of binders, resins, or polyurethane foams that are commonly used in conventional acoustic panel manufacturing.

2. Materials and Methods

2.1. Materials

Multilayer packaging waste, a widely available post-consumer material, offers both challenges and opportunities for sustainable composite development.
To obtain materials with enhanced acoustic properties, several factors must be considered. First, the size, geometry, and distribution of the raw material particles, in this case multilayer packaging waste, play a crucial role in determining how sound waves are absorbed, reflected, or transmitted through the composite structure. Second, the choice of manufacturing technology, including the method of compaction and hot pressing, directly influences internal morphology and bonding quality between the layers. Finally, specific processing parameters such as temperature and pressure are critical in optimizing material density, porosity, and structural integrity, which ultimately govern the acoustic performance of the resulting composite materials.
The raw material used to produce composite materials consisted of multilayer packaging waste, composed of aluminum, paper, and polyethylene. These multilayer wastes were collected from commonly used beverage containers, such as juice and milk cartons (Figure 1a). The raw material used in this study consisted of waste from multilayer Tetra Pak packages for 250 mL, with an average weight of 13 g. Their composition was approximately 9.10 g paperboard (70%), 3.38 g polyethylene (26%), and 0.52 g aluminum (4%), with each component contributing to rigidity, moisture protection, and an oxygen barrier. This complex structure makes recycling challenging, which is why their valorization as composite material represents a sustainable solution. Prior to processing, the packages were thoroughly cleaned using a commercial detergent (Fairy, Procter & Gamble, Cincinnati, OH, United States) to remove food residues, and then manually cut into small pieces in the form of squares, Figure 1b. The strip-shaped samples were further prepared using a paper shredder (HP OneShred 24CC, Hewlett-Packard (HP), Hattingen, Germany) to obtain a controlled fragmentation, as shown in Figure 1c. This preliminary preparation step was essential to ensure a proper thermoplastic process and to obtain composite materials with reproducible physico-mechanical and acoustic properties.
The density of multilayer packaging waste used in this study was determined for two different forms: 128 kg/m3 for the granulometrically reduced waste in square pieces, and 68 kg/m3 for the waste shredded into strips with a paper shredder.

2.2. Materials Processing Methodology

In this section, the methodology adopted for the preparation of composite materials from multilayer packaging waste is described, using the procedure previously described in literature by our group [22]. The procedure involved several key stages, including the collection and cleaning of raw materials, manual cutting into small pieces, and subsequent hot-pressing under controlled temperature and pressure conditions. Attention was given to the influence of processing parameters, as these play a decisive role in determining the acoustic properties of the resulting composites.
The hot-forming process of composite materials obtained from multilayer packaging waste was carried out using a specially designed mold consisting of two heated, movable plates positioned at the upper and lower sides, as illustrated in Figure 2a. The thermal energy required to plasticize the thermoplastic components within the multilayer waste structure was provided by an electrically heated system integrated into the mold, ensuring the attainment of the required forming temperature. To achieve precise thermal control, the mold was equipped with temperature sensors strategically placed to enable continuous monitoring and maintenance of a uniform temperature across the entire forming surface. The molding assembly was mounted in a fixed mechanical press (Hydraulic press Unicfraft WPP 50 E, Unicraft, Hallstadt, Germany), shown in Figure 2b, which applies a controlled compressive load to the upper movable plate.
Under the combined action of temperature and applied pressure, the thermoplastic constituents within the multilayer structure soften and act as a binding phase, promoting interlayer consolidation and the formation of composite panels without the use of additional binding agents.
The prepared multilayer waste, cut into squares and strips, was subsequently compressed at a pressure of 5 MPa and at various temperatures (120 °C, 125 °C, 130 °C, 135 °C, and 140 °C) without the addition of any binding agents, resulting in composite panels, as illustrated in Figure 3a,b. The pressure value of 5 MPa was established based on experience gained from previous research on the thermoforming of panels derived from various waste materials containing thermoplastic components, with the aim of keeping this process parameter constant throughout the experiments [22,23].
The samples had a diameter of 142 mm and thickness of 5.5 mm with the following mechanical characteristics: tensile strength 9.83 MPa, compressive strength 9.92 MPa, and flexural strength 39.96 MPa for square-shaped used waste and tensile strength 15.40 MPa, compressive strength 13.24 MPa, and flexural strength 50.81 MPa for strip-shaped used waste. Mechanical tests were carried out using a universal testing machine, Instron model 4466 (Instron, Norwood, MA, USA), in accordance with European standards: EN ISO 527-1 [26] for tensile properties, EN ISO 604 [27] for compressive properties, and EN ISO 178 [28] for flexural properties of plastics.
The apparent density of the materials obtained by hot pressing of multilayer waste, determined according to EN 1602 [29], was 1148 kg/m3, highlighting the efficient compaction of paper fibers, polyethylene, and aluminum within the final composite structure.
To analyze the influence of the shape of multilayer packaging waste and the pressing temperature on the acoustic properties, the sound absorption coefficient was measured on ten samples. The sample coding and their individual characteristics are presented in Table 1. For easier correlation with the sample characteristics, the coding system used in this study is as follows: MPW stands for multilayer packaging waste, with sq indicating square-shaped waste and st indicating strip-shaped waste. The last three digits correspond to the pressing temperature (°C) at which the sample was prepared.
The selection of processing temperature and pressure is critical, as these parameters directly affect the consolidation, density, and internal structure of the composite. Adequate temperature ensures sufficient softening of the thermoplastic component (LDPE) to promote adhesion between layers, while excessive temperature may lead to material degradation [23].

2.3. Morphological Analysis

For a morphological analysis of the internal structure of the composites obtained from hot-pressed multilayer waste, a digital microscope (Andonstar AD249S-M Microscope, Shenzhen, China) was employed. The microscope features a magnification of up to 2000× and is equipped with LED lights for illumination, allowing detailed observation of the surface and internal microstructures of the samples.

2.4. Acoustic Properties

The sound absorption coefficients of the composite samples were measured using the impedance tube method according to ISO 10534-2 [30]. Circular samples with a diameter of 63.5 mm were tested over a frequency range of 50 Hz to 3150 Hz. The experimental setup included a Brüel & Kjær Type 4206-A medium impedance tube (Bruel & Kjar, Copenhaga, Denmark), microphones, signal generator, analyzer, and PC for data acquisition and processing. Environmental conditions such as air pressure, temperature, and humidity were monitored to ensure consistent and reliable measurements.

3. Results and Discussion

3.1. Morphological Characterization

The microstructural surface details of the obtained plates are presented in Figure 4a, MPW-sq-140 and Figure 4b, MPW-st-140. The square and strip-shaped multilayer packaging waste samples exhibit a compact, glossy surface. This glossiness is attributed to the polyethylene reaching its softening point during processing, acting as a binder that coats and adheres to the other components of the multilayer waste. As a result, the polyethylene ensures cohesion among the different layers and particles, which directly affects the mechanical integrity and acoustic behavior of the composites. The presence of a pore-free surface with low roughness causes the incident sound wave to be largely reflected, with very little absorption.
The images in Figure 4c,d show that the material is composed of layers that are very well bonded to each other, thanks to polyethylene reaching its softening point and acting as a binder. A compact structure with nearly no open porosity is observed. Consequently, even if a sound wave manages to penetrate the contact surface, it cannot propagate through the interior of the material and is instead reflected.

3.2. Sound Absorption Coefficients

In porous materials, sound waves generally induce vibrations in both the cell walls and the air within the cavities, allowing sound energy to be dissipated through the damping of these vibrations [31,32,33]. The efficiency of sound absorption can be enhanced by increasing the stiffness of the cell walls [34,35], as well as by optimizing the interconnectivity, number, size, and type of pores. These factors are crucial in the mechanism of sound wave attenuation within a porous structure, as the propagation of sound through the pore network enables energy dissipation via visco thermal interactions [36]. Reducing the size of pores in an open-cell structure typically increases airflow resistance, thereby improving sound absorption [37]. Moreover, greater interconnectivity within the porous network, which generates irregular propagation paths for sound waves, is particularly effective for enhancing absorption at lower frequencies [38].
The sound absorption coefficient was measured for ten samples produced during the research activities. The obtained values were processed and graphically represented as a function of the technological parameters and material characteristics mentioned earlier (pressing temperature and shape of the waste).
The experimental results indicate that the produced materials exhibit relatively low sound absorption coefficients, with values below 0.25 across the studied frequency range. This suggests that the materials have a limited capacity to absorb incident sound energy, while reflecting a significant portion of the sound and restricting noise transmission.
Such behavior is expected, considering the hot-pressing and compression manufacturing method, which results in a dense structure with low porosity. The higher density limits of sound absorption within the material contribute to blocking and reflecting sound waves, characteristics typical of materials used for sound insulation.

3.2.1. Influence of the Shape of Multilayer Packaging Waste on Sound Absorption Coefficient

To evaluate the influence of the shape of multilayer packaging waste on the sound absorption coefficient, six representative samples were selected for analysis. The comparison was carried out between specimens pressed at the same temperatures: samples MPW-sq-120 and MPW-st-120, both hot-pressed at 120 °C; samples MPW-sq-125 and MPW-st-125, pressed at 125 °C; and samples MPW-sq-140 and MPW-st-140, pressed at 140 °C. Among them, samples MPW-sq-120, MPW-sq-125, and MPW-sq-140 were fabricated from waste cut into square-shaped pieces, whereas samples MPW-st-120, MPW-st-125, and MPW-st-140 were produced from waste cut into strips. The graphical representation of the sound absorption coefficient as a function of frequency for these six samples is shown in Figure 5, providing a comparative basis for assessing the impact of waste shape on the acoustic performance of the obtained composite materials.
A detailed analysis of the graph presented in Figure 5 reveals that the shape of the multilayer packaging waste does not have a significant impact on the sound absorption coefficient. This behavior can be primarily explained by the manufacturing process. During hot-pressing, the polyethylene contained in the waste reaches its softening point and acts as a binder, coating and fixing the other structural components. As a result, the material obtained exhibits a dense structure and a compact surface (Figure 4c,d), characterized by the absence of open porosity that would allow sound waves to penetrate the bulk of the material. Under these conditions, acoustic absorption is largely limited to the surface, while the predominant acoustic phenomenon is the reflection of sound waves, which substantially reduces the overall sound absorption capacity of the material [39,40].
For the materials MPW-sq-120 and MPW-st-120, hot-pressed at 120 °C, the analysis of the graph in Figure 5 shows that MPW-sq-120, obtained from square-shaped multilayer waste, exhibits the highest sound absorption coefficients across the entire frequency range studied. This suggests that the square shape of the waste may enhance interaction with sound waves at this pressing temperature, promoting more efficient energy dissipation.
For the samples pressed at 125 °C (MPW-sq-125 and MPW-st-125), it can be observed that MPW-sq-125, made from square-shaped waste, demonstrates superior sound-absorbing properties at frequencies below 1500 Hz and above 2850 Hz. In the frequency range of 1500–2850 Hz, the material produced from strip-shaped waste (MPW-st-125) exhibits higher absorption. The MPW-st-125 material exhibits superior acoustic properties, because the waste strips at the surface are not fully covered during pressing, and their larger specific surface requires more binder, which may influence the internal structure and sound absorption. The maximum value of the acoustic absorption coefficient, 0.23, was reached at a frequency of 2500 Hz for the MPW-st-125 material.
The sound absorption coefficient depends on frequency because the interaction between sound waves and the material varies with wavelength. At low frequencies, the waves have long wavelengths and are mostly reflected, resulting in low absorption. As the frequency increases, the waves penetrate more easily into the porous structure of the material, where the sound energy is converted into heat, increasing the absorption coefficient. In general, α increases with frequency, reaching its highest values at high frequencies.
In the case of pressing at 140 °C (MPW-sq-140 and MPW-st-140), it is noted that at frequencies below 1000 Hz, MPW-st-140, obtained from strip-shaped waste, performs better, while at frequencies above 1000 Hz, MPW-sq-140, produced from square-shaped waste, shows superior acoustic properties.
These observations highlight that pressing temperature is a critical parameter in determining the internal structure of the material, which in turn governs its final acoustic characteristics. At the same time, the shape of the waste can influence sound absorption performance in a frequency-dependent manner, interacting with material density and compactness to modulate the absorption coefficient.

3.2.2. Influence of the Temperature on Sound Absorption Coefficient

Sound absorption in porous materials is primarily determined by the number, size, and connectivity of pores, which allow sound waves to penetrate and dissipate energy through interactions with the solid structure and interstitial air [41]. Dense and rigid materials exhibit lower absorption capacity due to limited porosity, which restricts sound wave penetration [42]. In the composites studied here, pressing temperature directly affects the internal structure, influencing both density and porosity. Figure 6 and Figure 7 illustrate how variations in pressing temperature impact the sound absorption coefficient, highlighting the critical role of processing parameters in defining the acoustic performance of the resulting materials.
Figure 6 illustrates the variation of the sound absorption coefficient as a function of the pressing temperature for multilayer waste cut into square shapes. No simple general rule directly correlates pressing temperature with the absorption coefficient, as the frequency range is the determining factor. Therefore, depending on the frequency of the dominant noise, the appropriate processing conditions can be selected.
Materials pressed at lower temperatures, 120 °C and 125 °C (MPW-sq-120 and MPW-sq-125), exhibit acceptable sound absorption values, generally increasing as temperature decreases. In contrast, materials pressed at intermediate temperatures, 130 °C and 135 °C (MPW-sq-130 and MPW-sq-135), show the best acoustic performance in the 1500 ÷ 2200 Hz range. At frequencies below 1500 Hz, MPW-sq-130 demonstrates the highest absorption, while the maximum coefficient value, 0.19, is reached by MPW-sq-135 at 2000 Hz.
Comparing the materials at the minimum and maximum pressing temperatures, MPW-sq-120 and MPW-sq-140 (120 °C and 140 °C), it is observed that for frequencies above 1100 Hz, MPW-sq-140, pressed at 140 °C, provides superior acoustic properties.
If the goal is to achieve a material with high performance over a wide frequency range, the optimal choice is MPW-sq-130, produced at 130 °C. In further studies, acoustic properties will be correlated with mechanical characteristics to determine the optimal processing parameters for producing hot-pressed composites from square-shaped multilayer waste. The maximum peak is reached for the MPW-sq-135 material at a frequency of 2000 Hz, reaching a value of 0.19.
For the composites produced by hot pressing multilayer waste cut into strips, the effect of pressing temperature on the sound absorption coefficient is illustrated in Figure 7, highlighting how processing parameters influence the material’s acoustic performance.
The composites produced at 120 °C and 130 °C (MPW-st-120 and MPW-st-130) exhibit the lowest sound absorption performance across the studied frequency range. In contrast, the material pressed at 125 °C (MPW-st-125) shows the highest sound absorption coefficient at frequencies above 1450 Hz, while for lower frequencies, MPW-st-135 and MPW-st-140 demonstrate superior acoustic performance. These results reflect the direct influence of pressing temperature on the internal structure of the composites, affecting material density, compactness, and porosity. According to the literature, denser and more rigid materials tend to perform better at low frequencies, as their mass restricts the propagation of sound waves [43]. Consequently, selecting the optimal pressing temperature is a critical parameter for enhancing acoustic properties, and correlating these findings with mechanical characteristics can guide the development of multilayer composite materials with tailored performance for specific noise control applications.

3.2.3. Comparison of the Absorption Coefficient with Other Materials

To obtain an overall understanding of the positioning of composite materials produced from multi-layer packaging waste compared to other materials in terms of their acoustic properties, a comparative analysis was carried out with four additional types of composite materials.
One of these materials is particleboard (PB), a commercially available product obtained by hot pressing wood particles (sawdust, chips, and short fibers) mixed with synthetic resins, typically melamine-formaldehyde, urea-formaldehyde, or phenol-formaldehyde resins. Particleboard is among the most used materials in the furniture industry (for cabinet carcasses, shelves, countertops, doors, and decorative panels) as well as in interior construction (partition walls, ceilings, and claddings).
The other three materials used for comparison were taken from scientific literature [44] and were produced under similar technological conditions, using the same hot-pressing method, but derived from a different type of industrial waste—specifically, waste generated during the deburring process of bathtub manufacturing. These composites consist of ABS–PMMA–glass fiber (denoted as T130, T135, and T140).
For a relevant comparison, the present study selected composite samples pressed at identical temperatures (130 °C, 135 °C, and 140 °C), namely MPW-sq-130, MPW-sq-135, MPW-sq-140, MPW-st-130, MPW-st-135, and MPW-st-140, corresponding to those described in the referenced study. This approach enables a coherent evaluation of the influence of pressing temperature on the acoustic properties of composites made from multilayer packaging waste, compared to those based on other polymeric waste types.
Figure 8 presents the variation of the sound absorption coefficient for the ten analyzed materials: six samples produced from multilayer packaging waste (MPW-sq-130, MPW-sq-135, MPW-sq-140, MPW-st-130, MPW-st-135, and MPW-st-140) and four reference materials selected from the scientific literature (PB, T130, T135, and T140).
From the graphical representation, it can be observed that at frequencies below approximately 1450 Hz, the PB (Particleboard) sample exhibits the highest sound absorption performance, showing superior values of the acoustic absorption coefficient. This behavior can be attributed to the porous and heterogeneous internal structure of particleboard, which enhances the dissipation of acoustic energy through internal friction and the conversion of sound energy into heat at the interfaces between the wood particles and the synthetic binder.
At frequencies higher than 1450 Hz, there is a notable increase in the acoustic performance of the ABS–PMMA–glass fiber composites (T130, T135, and T140). These materials possess a denser and more rigid structure, which promotes local resonance and vibration damping, leading to improved sound absorption efficiency in the medium and high-frequency range.
When comparing only the multilayer packaging waste composites with those based on ABS–PMMA–glass fiber, it can be observed that at frequencies below 1300 Hz, all analyzed samples display relatively similar absorption coefficients. However, the MPW-sq-130 sample stands out with the highest sound absorption coefficient within this frequency domain, suggesting a more favorable internal structure for dissipating low-frequency sound waves.
At frequencies above 1300 Hz, the ABS–PMMA–glass fiber composites exhibit better sound absorption properties compared to the multilayer waste-based samples. This behavior can be explained by the presence of aluminum layers within the multilayer waste composites, as aluminum is known to have poor acoustic absorption capability due to its high reflectivity of sound waves. Consequently, the inclusion of aluminum leads to a reduction in the sound-absorbing performance of the multilayer composites, although they may still provide better sound insulation due to their reflective properties.
The analysis reveals a strong correlation between acoustic behavior, material composition, and sound frequency. Porous and heterogeneous materials, such as particleboard, tend to perform more effectively at low frequencies, whereas rigid composites based on ABS–PMMA–glass fiber demonstrate improved sound absorption at medium and high frequencies, highlighting the critical role of internal structure and constituent materials in determining the mechanisms of sound absorption and reflection.

4. Conclusions

The analysis of the acoustic properties of composites produced by hot pressing multilayer waste indicates that, among the variables tested in this study, pressing temperature and waste shape affect sound absorption performance. Based on the results, temperature appears to have a stronger influence and is therefore highlighted. Composites pressed at intermediate temperatures, particularly around 125–130 °C, showed higher sound absorption performance, while density and porosity remained constant across all samples. Materials pressed at very low or very high temperatures exhibited lower sound absorption, indicating that temperature and waste shape influence acoustic behavior. The shape of the waste (squares or strips) affects the absorption coefficient in a frequency-dependent manner, although its impact is secondary compared to pressing temperature. The results indicate that these composites are more suitable for sound insulation rather than direct acoustic absorption, while offering a sustainable solution for the valorization of multilayer waste. Future studies correlating acoustic and mechanical properties will enable the optimization of processing parameters for the development of composite materials with enhanced performance for industrial noise control applications.
The internal structure of the composites, characterized by well-adhered layers and a compact, low-porosity matrix, plays a key role in their functional properties. The polyethylene acts as a binder, ensuring cohesion between components, while the dense structure limits sound wave penetration, resulting in low acoustic absorption and high reflectivity.
The comparison showed a clear influence of composition and internal structure on the acoustic behavior of the materials. Porous materials, such as particleboard, exhibited better absorption at low frequencies, while rigid ABS–PMMA–glass fiber composites performed better at medium and high frequencies. Multilayer waste composites showed intermediate properties, limited by the presence of aluminum, but can be further optimized to develop sustainable composites with improved acoustic performance.

Author Contributions

Conceptualization, A.-E.T. and O.N.; methodology, A.-E.T., M.R., O.N. and O.V.; investigation, M.R. and O.V.; data curation, A.-E.T.; writing—original draft preparation, all authors; writing—review and editing, all authors; visualization, A.-E.T.; supervision, A.-E.T. and O.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 16 01206 g001
Figure 1. Multilayer packaging waste: (a) beverage containers; (b) squares; and (c) strips.
Figure 1. Multilayer packaging waste: (a) beverage containers; (b) squares; and (c) strips.
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Figure 2. Images of the mold (a) and hydraulic press (b).
Figure 2. Images of the mold (a) and hydraulic press (b).
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Figure 3. Images of the obtained plates: (a) square multilayer packaging waste (MPW-sq-140) and (b) strips multilayer packaging waste (MPW-st-140).
Figure 3. Images of the obtained plates: (a) square multilayer packaging waste (MPW-sq-140) and (b) strips multilayer packaging waste (MPW-st-140).
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Figure 4. Microstructural surface details: (a) square multilayer packaging waste and (b) strips multilayer packaging waste. Microstructural section details: (c) square multilayer packaging waste (MPW-sq-140) and (d) strips multilayer packaging waste (MPW-st-140).
Figure 4. Microstructural surface details: (a) square multilayer packaging waste and (b) strips multilayer packaging waste. Microstructural section details: (c) square multilayer packaging waste (MPW-sq-140) and (d) strips multilayer packaging waste (MPW-st-140).
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Figure 5. Variation of the sound absorption coefficient with the shape of multilayer packaging waste.
Figure 5. Variation of the sound absorption coefficient with the shape of multilayer packaging waste.
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Figure 6. Variation of the sound absorption coefficient with pressing temperature for composite materials produced from square-shaped multilayer packaging waste.
Figure 6. Variation of the sound absorption coefficient with pressing temperature for composite materials produced from square-shaped multilayer packaging waste.
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Figure 7. Variation of the sound absorption coefficient with pressing temperature for composite materials produced from stripe-shaped multilayer packaging waste.
Figure 7. Variation of the sound absorption coefficient with pressing temperature for composite materials produced from stripe-shaped multilayer packaging waste.
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Figure 8. Variation of the sound absorption coefficient with other materials.
Figure 8. Variation of the sound absorption coefficient with other materials.
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Table 1. Sample coding based on processing temperature and waste geometry.
Table 1. Sample coding based on processing temperature and waste geometry.
CodeTemperature
(°C)		Multilayer Packaging Waste Shape
MPW-sq-120120square
MPW-sq-125125
MPW-sq-130130
MPW-sq-135135
MPW-sq-140140
MPW-st-120120strips
MPW-st-125125
MPW-st-130130
MPW-st-135135
MPW-st-140140
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Rancea, M.; Nemeș, O.; Tiuc, A.-E.; Vasile, O. Acoustic Absorption Behavior of Boards Made from Multilayer Packaging Waste. Appl. Sci. 2026, 16, 1206. https://doi.org/10.3390/app16031206

AMA Style

Rancea M, Nemeș O, Tiuc A-E, Vasile O. Acoustic Absorption Behavior of Boards Made from Multilayer Packaging Waste. Applied Sciences. 2026; 16(3):1206. https://doi.org/10.3390/app16031206

Chicago/Turabian Style

Rancea, Miron, Ovidiu Nemeș, Ancuța-Elena Tiuc, and Ovidiu Vasile. 2026. "Acoustic Absorption Behavior of Boards Made from Multilayer Packaging Waste" Applied Sciences 16, no. 3: 1206. https://doi.org/10.3390/app16031206

APA Style

Rancea, M., Nemeș, O., Tiuc, A.-E., & Vasile, O. (2026). Acoustic Absorption Behavior of Boards Made from Multilayer Packaging Waste. Applied Sciences, 16(3), 1206. https://doi.org/10.3390/app16031206

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