A systematic study was conducted to optimize chemical pretreatments of rice husk (RH) and rice straw (RS) fibers for reinforcing polylactic acid (PLA) biocomposites. Using a Central Composite Design (CCD), the effects of NaOH, HCl, and H\u2082SO\u2084 treatments were evaluated over a range of concentration (0.35 to 0.75%w<\/em>\/v<\/em>), temperatures (9\u00b0C to 120\u00b0C), and time durations (60 to 90\u202fmin). NaOH-treated biocomposites exhibited a 15% higher thermal decomposition (TGA) and achieved the highest ultimate tensile strength of 35.6\u202fMPa with an 8.2% improvement over HCl (32.9\u202fMPa) at optimized conditions (0.55\u202f% NaOH, 105\u00b0C, 75\u202fmin). Comprehensive characterization (FTIR, XRD, EDS, FESEM) confirmed that NaOH selectively removed lignin and amorphous silica while preserving cellulose crystallinity, leading to improved interfacial adhesion and controlled porosity. Water absorption tests showed a 4.2% uptake after 24\u202fh for NaOH biocomposites, balancing moisture resistance with biodegradability. Repurposing rice husk ash as a 3\u202fwt% filler enhanced thermal stability and diverted agricultural waste from combustion. These findings highlight NaOH pretreatment as the most effective strategy for developing sustainable, high-performance PLA\/rice-residue biocomposites.<\/p>\n\n\n\n
Graphical abstract<\/h3>\n\n\n
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Introduction<\/h3>\n\n\n\n
The raising demand for sustainable and eco-friendly construction materials has led to a surge in research on the sustainability by mitigating carbon-emissions [1]. The management of rice residue (RR) plays a crucial role in addressing greenhouse gas (GHG) emissions especially methane (CH4<\/sub>) and Carbon dioxide (CO2<\/sub>) [2]. Open burning 9.3 tons of RR can result in the release of 10.91 tons of CO2<\/sub>\u00a0equivalent, along with 668.68\u202fkg of gaseous air pollutants and 33.05\u202fkg of particulate matter [3,4]. Particulate matter, such as crystalline silica (e.g., tridymite, cristobalite), can cause serious diseases like silicosis and lung cancer [5]. Amorphous silica, however, typically causes only mild, reversible inflammation [6]. Although our primary aim is optimizing biocomposite performance, reducing residual crystalline silica also offers an incidental health benefit by mitigating workplace exposure during material processing [7]. The utilization of RR in biocomposite production offers a promising solution to address Sustainable Development Goal 12: responsible consumption and production [8]. <\/p>\n\n\n\n
These challenges while creating value-added products for the construction industry. Using RR in lightweight ceiling boards or tiles offers several notable benefits [9]. Natural fibers such as rice husk (RH) and rice straw (RS) exhibit poor compatibility with hydrophobic polymers like polylactic acid (PLA) due to their hydrophilic OH groups and non-cellulosic components (lignin, hemicellulose), resulting in inadequate interfacial adhesion, inconsistent mechanical properties, and moisture-induced degradation [10]. Prior studies on fiber\u2013polymer composites report water absorption exceeding 10\u202fwt% after extended immersion, yet few have systematically addressed moisture control in rice fiber\/PLA systems. Rice husk ash (RHA), a by-product of rice milling often burned as charcoal pellets further contributes to GHG emissions when combusted. Rather than direct combustion, this study repurposes RHA as a low-cost filler in PLA biocomposites, diverting its climate impact toward passive mitigation. At 3\u202fwt%, RHA’s predominantly crystalline SiO\u2082 structure enhances thermal stability, while introducing micro-porosity in the PLA matrix, which promotes microbial and water ingress to accelerate biodegradation [11]. <\/p>\n\n\n\n
The extent of this porosity is influenced by factors such as the amount of RHA added, its particle size, and the nature of the matrix material used [12]. Alkali treatment is more effective in removing silica and enhancing fiber-matrix compatibility compared to HCl treatment. NaOH revealed that alkali-treated fibers achieved a tensile strength of 7.833\u202fMPa at 10% filler loading, which is approximately 16% higher than that of HCl-treated fibers in the same composite system [13]. HCl treatment’s impact on the tensile strength of RH and RS\u00a0v<\/em>aries depending on the application context. A study revealed that untreated composites achieved a tensile strength of 12.9\u202fMPa at 10% filler loading and 9.5\u202fMPa at 30\u202f% filler loading [14]. However, HCl-treated composites exhibited significantly lower tensile strengths of 6.7\u202fMPa and 6.5\u202fMPa for the same respective filler loadings, demonstrating approximately a 48% reduction in tensile strength compared to untreated fibers at 10% fiber filler loading [15].<\/p>\n\n\n\n
Although alkaline and acid pretreatments have been applied to various lignocellulosic fibers, no study has systematically optimized treatment concentration (0.35\u20130.75\u202f%\u202fw<\/em>\/v<\/em>), temperature (90\u2013120\u202f\u00b0C), and time (60\u201390\u202fmin) for RH\/RHA\/RS (20\/3\/10\u202fwt%) biocomposites in PLA, balancing amorphous silica removal, mechanical performance, thermal stability, and moisture uptake. Furthermore, occupational health implications of residual crystalline silica in construction-grade biocomposites have been underdressed.<\/p>\n\n\n\n
The novelty of this work lies in the systematic comparison of three different chemical treatments (HCl, NaOH, and H2<\/sub>SO4<\/sub>) on RH and RS to optimize their compatibility with PLA. This study uniquely focuses on optimizing the treatment conditions to enhance the mechanical, thermal, and water absorption properties of RR\/PLA biocomposites. The primary objective of this work is to improve the interfacial adhesion between RR fibers and the PLA matrix by removing non-cellulosic components and modifying the fiber surface properties. This study aims to evaluate the synergistic effects of chemical treatments on the crystallinity, thermal stability, and water absorptivity of the biocomposites, which are critical for their application in sustainable construction materials such as ceiling boards and tiles. Here, synergistic refers to the simultaneous enhancement of both mechanical strength and thermal stability beyond the sum of individual treatment effects. Specifically, alkali pretreatment not only removes non-cellulosic components to increase tensile strength but also selectively dissolves amorphous silica to raise decomposition temperatures [16]. This dual improvement mechanical and thermal under identical pretreatment conditions exemplifies the synergistic effect targeted in this work. By clarifying the roles of amorphous silica removal and RHA addition, we aim to establish a targeted, mechanistic pretreatment protocol that maximizes biocomposite performance and safety for sustainable ceiling-board applications.<\/p>\n\n\n\n
Hence, in this work, the authors have systematically optimized the chemical pretreatments (NaOH, HCl, H\u2082SO\u2084) of RH, RS and RHA using Central Composite Design (CCD) approach to enhance the mechanical strength, thermal stability, and water resistance characteristics of PLA-based biocomposites. By selectively removing lignin, amorphous silica, and non-cellulosic components through this Chemical Pretreatments on PLA\/rice residue biocomposites, this synergistic approach thus enhances the fiber\u2013matrix adhesion, compatibility, and delivers dual gains in performance functionality, strength, thermostability, and durability for engineering applications including, ceiling boards\/panels, where reduced weight and high strength are essential. This targeted methodology lays the foundation for the experimental procedures detailed in the following sections.<\/p>\n\n\n\n
Section snippets<\/h3>\n\n\n\n
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Experimentation: Materials and methods<\/h3>\n\n\n\n
The procedures followed in this experiment are essential to achieving the research goals and include systematic steps for material selection, fiber preparation, chemical treatment, biocomposite fabrication, mechanical and surface characterization, and data optimization and interpretation shown in Fig.1.<\/p>\n\n\n\n
Results and discussions<\/h3>\n\n\n\n
This section presents the experimental findings in the order of characterization techniques outlined above. We begin with spectroscopic and thermal analyses (FTIR, TGA) to reveal molecular, and stability changes due to pretreatment, followed by microstructural (FESEM\/EDS) observations and mechanical testing (tensile strength, CCD optimization). Each subsection links back to how NaOH, HCl, and H\u2082SO\u2084 treatments alter fiber\u2013matrix interactions and performance.<\/p>\n\n\n\n
Overall mechanistic summary of the experimental work<\/h3>\n\n\n\n
This section summarizes the key mechanistic insights derived from the experimental study, highlighting how chemical pretreatments influenced the structural, thermal, mechanical, and moisture absorption behaviours of the PLA-RR biocomposites. The relationships between pretreatment processes, material structure, and functional performance are synthesized to provide a holistic understanding of the observed results.<\/p>\n\n\n\n
Limitations of the present work<\/h3>\n\n\n\n
This study focused on optimizing PLA-based biocomposites using rice residue (RR) reinforced with RH, RS, and RHA through chemical pretreatments (NaOH, HCl, and H\u2082SO\u2084). However, several limitations should be noted. First, only these three pretreatment agents were explored; other promising methods such as silane coupling agents, organic acids (e.g., citric or acetic acid), and hybrid techniques (e.g., sequential alkali\u2013acid treatments) were not ev<\/em>aluated, although they may enhance interfacial<\/p>\n\n\n\n
Future prospects<\/h3>\n\n\n\n
This study provides foundational insights into the pretreatment and characterization of RR-derived biocomposites. This study opens avenues for advancing sustainable biocomposites exploring nanocellulose extraction from treated residues. This will evaluating long-term climate resilience could further bridge lab-scale innovations with industrial adoption, aligning with global sustainability targets for eco-friendly construction materials (ceiling boards and tiles). Future studies should<\/p>\n\n\n\n
Conclusions<\/h3>\n\n\n\n
This study systematically optimized the pretreatment conditions of RH and RS fibers using three chemical treatments (NaOH, HCl, and H\u2082SO\u2084) to develop high-performance PLA-based biocomposites. A comprehensive characterization through FTIR, XRD, EDS, FESEM, TGA, and tensile testing elucidated the mechanisms behind structural and performance improvements. At the optimized NaOH conditions (0.55\u202f%\u202fw<\/em>\/v<\/em>, 105\u202f\u00b0C, 75\u202fmin), NaOH pretreatment proved the most effective in enhancing interfacial adhesion and <\/p>\n\n\n\n
Bhupinder Singh:<\/strong>\u00a0Writing \u2013 original draft, Conceptualization.\u00a0Ravinder Kumar:<\/strong>\u00a0Writing \u2013 original draft, Conceptualization.\u00a0Shubham Sharma:<\/strong>\u00a0Writing \u2013 review & editing.\u00a0Ashutosh Pattanaik:<\/strong>\u00a0Writing \u2013 original draft, Formal analysis.\u00a0Parveen Kumar:<\/strong>\u00a0Writing \u2013 original draft, Formal analysis.\u00a0Ankit Kedia:<\/strong>\u00a0Writing \u2013 original draft, Formal analysis.\u00a0Abinash Mahapatro:<\/strong>\u00a0Writing \u2013 original draft, Formal analysis.\u00a0V.K. Bupesh Raja:<\/strong>\u00a0Writing \u2013 original draft, Formal analysis.\u00a0Deepak Gupta:<\/strong>\u00a0Writing \u2013 original\u00a0<\/p>\n\n\n\n
Declaration of competing interest<\/h3>\n\n\n\n
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.<\/p>\n\n\n\n
Acknowledgments<\/h3>\n\n\n\n
This research work was funded by Umm-Alqura University, Saudi Arabia under grant number: 25UQU4240002GSSR10. In addition, I am deeply grateful to my research advisor, Ms. Amandeep Kaur (UID 30694), for their invaluable guidance and support in material testing. I would like to express my sincere appreciation to the Dr. V<\/em>ijay Kumar, HOD, Division of Research and Development, Central Instrument Facility (CIF) at Lovely Professional University (LPU), Chaheru, Phagwara, Punjab 144411, India, for<\/p>\n\n\n\n
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