Sustainable construction materials from leveraging water hyacinth and wastepaper for superior sound absorption and thermal insulation

Environmental challenges, including heat and noise pollution, increasingly impact urban living and architectural comfort [1]. Consequently, there is a growing demand for sustainable construction materials that address these issues. Researchers have actively explored innovative materials for diverse applications, particularly in sound-absorbing and thermal insulation products, by repurposing agricultural waste [[2], [3], [4]]. In studying the acoustic properties of porous materials, Allard [5] emphasized the significance of non-acoustic parameters, such as density and porosity, in influencing sound propagation. Density, which measures mass per unit volume, often inversely correlates with porosity; a reduction in density generally corresponds to increased porosity. These interrelated parameters play a critical role in determining a material’s performance across various applications, including sound absorption and thermal insulation. This foundational relationship underpins the evaluation of innovative materials in the present study.

Thermal-acoustic materials derived from agricultural by-products have gained considerable attention for their ability to reduce environmental impact while promoting the efficient use of local resources. These materials serve as viable alternatives to conventional construction products, mitigating heat and noise pollution, improving energy efficiency, and enhancing indoor comfort [[6], [7], [8]]. Moreover, bio-based materials align with circular economic principles, advancing sustainable development by transforming agricultural waste into valuable construction resources [9].

Thailand has identified water hyacinth (WH), a fast-growing aquatic species, as an invasive plant due to its rapid propagation and detrimental effects on waterways. Recent reports indicate that over 650,000 tons of WH have clogged waterways across 33 of Thailand’s 77 provinces, posing a significant flood risk during the rainy season. To address this issue, the Department of Public Works, Town & Country Planning, and other agencies removed approximately 7.2 million tons of WH between October 2022 and June 2023 [10]. Despite its environmental challenges, WH presents excellent potential as a sound-absorbing material due to its fibrous and porous structure [11,12]. Repurposing WH for construction materials not only mitigates its environmental impact but also leverages its natural microstructural properties to improve acoustic and thermal performance.

Thailand’s vibrant handicraft sector also generates substantial wastepaper (WP) from the production of decorative items, particularly those made from mulberry tree bark [13,14]. Diverting this abundant WP from landfills reduces waste accumulation and creates new opportunities for sustainable construction. WP’s fibrous and porous properties are especially beneficial for enhancing the acoustic performance of panels [[15], [16], [17]]. Studies have shown that plant-based fillers, including WP, can reduce thermal conductivity, minimize shrinkage, and improve mechanical strength [18]. These renewable materials exemplify circular economy principles, transforming waste into valuable construction resources [19].

Lignocellulosic materials, such as WH and other plant-based fibers, have been shown to perform well in composite building materials. These materials are cost-effective, lightweight, and provide robust thermal and acoustic performance [20,21]. Recent studies on WH demonstrate that particleboards and composites made from water hyacinth stems exhibit favorable thermal and acoustic performance [22,23]. However, certain formulations have incorporated chemical binders to enhance mechanical properties, potentially compromising their environmental benefits.

This study builds on the author’s previous work [24], which developed thermal-acoustic panels from rice straw, paper pulp, and Persea Kurzii without the use of chemical binders. The current research extends this concept by analyzing whether WH and WP can serve as effective core materials for thermal-acoustic panels. Key innovations include the integration of advanced microstructural analyses, such as pore volume diameter and characteristic length, derived through Mercury Intrusion Porosimetry (MIP). These metrics provide critical insights into the relationship between pore structure and functional performance, including thermal conductivity and noise reduction. By eliminating chemical binders, this approach aligns with sustainable development principles, minimizing the environmental impact associated with synthetic additives [25,26].

The study systematically evaluates the impact of material thickness and fiber composition on thermal, acoustic, and mechanical properties. Advanced techniques, including Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and acoustic impedance tube testing, ensure a comprehensive performance evaluation. Additionally, fire testing (FTT) was conducted to assess flammability behavior, further supporting the material’s suitability for sustainable construction applications. This holistic evaluation framework ensures that the proposed WH and WP panels meet both performance and sustainability standards.

Ultimately, the study seeks to advance the development of green construction materials by leveraging agricultural by-products, promoting circular economy principles, and reducing reliance on synthetic binders. By systematically linking microstructural parameters to material performance, this research addresses key gaps in the current literature and supports the transition toward environmentally responsible construction practices.