Current World Environment

Introduction

Advancements in science and technology have made it essential to develop engineering materials that are both strong and light weight, tailored to specific requirements and cost effective with minimal energy usage. The need for such high performance engineering materials has prompted a lot of research in developing composite materials. Recently, the composite sector has been expanding swiftly and has made a substantial impact on the materials industry. Composite materials result from the blending of two or more materials which may differ physically and chemically from each other but on combining create a product with optimal properties suitable for particular tasks. Specifically, polymer composites consist of a base polymer resin combined with various additives to achieve particular functions or objectives.¹

Conventionally synthetic fibers like glass or carbon fibers are utilized for reinforcing composites and for providing desired properties. However, in this era of global environmental awareness, the main disadvantage of these composites is their slow biodegradability. The need for sustainable development has fostered an inclination towards the utilization of natural alternatives instead of synthetic fibers such as glass in polymer composites. Researchers are recently focussing on natural fibers because they are biodegradable, readily available, economical, and lightweight.²

Natural fibers are grouped into two primary classes based on their source i.e. animal fibers and plant fibers. Plant fibers have gained more attention in research. Previous studies have reported a variety of plant fibers, including bast, wood, seed, leaf, fruit and grass or stalk fibers, etc.^3,4

Employing natural fibers in composites offers several important benefits such as affordability, sustainability, lightweight nature, non-hazardous characteristics, non-abrasiveness, biodegradability, and recyclability.^2,5,6 Despite this, the integration of natural fibers presents certain disadvantages including susceptibility to deterioration within the processing temperature range of the polymer matrix.

This early thermal breakdown of agro-fibers imposes constraints on the permissible processing temperature, restricting it to below 200°C, thereby limits the range of polymers compatible with agro-fibers.^1,7 Additionally, when designing composites with agro-fibers for specific applications, it is crucial to account for other factors, like their inadequate moisture resistance. The hygroscopic nature of cellulose, the chief component in plant fibers, leads to changes in dimensions and subsequent degradation in mechanical performance of the composite.^5,8–10 Integrating the fibers into the polymer with a strong bond is essential to reduce these detrimental effects. The introduction of compatibilizer can prove to be an effective strategy for attaining such strong adhesive forces. Among various compatibilizers e.g. maleic anhydride grafted polymers, silane coupling agents, epoxy resins, organosilanes, isocynates etc.^11–15, the maleic anhydride-grafted polypropylene (MAPP) has frequently been employed to enhance the adhesion at the interface of polymer matrices and agro-fibers. However, the continuous research is going on in exploring new alternatives.^1,16,17

In this comprehensive review, the main focus is on the employment of rice husk (RH) in polymer composites. Paddy (unmilled rice) is among the most extensively harvested crops in the world leading to significant agricultural waste in the form of rice stalks and husks. Rice husk, a significant agricultural byproduct in major rice-producing nations, is generated as a secondary product during the rice milling process.¹⁸ In the milling of raw paddy, the rice kernel is physically separated from other components like edible parts such as the germ and bran, as well as the inedible part, namely the rice husk.^8,19

Despite their abundance, rice husk (RH) is usually discarded as waste and burnt in the fields, which causes environmental concern due to the release of toxic emissions, ashes, and vapours contributing to atmospheric contamination.²⁰ Recognizing the environmental impact, it becomes necessary to explore the use of RH in polymer composites. Figure 1 illustrates the various applications of RH in polymer composites. The inclusion of RH in polymer matrices leads to superior attributes, including toughness, decreased weight, eco-friendliness, flame retardancy, and resistance to atmospheric conditions. Moreover, this integration makes the final products cost-effective.^2,21–23 The use of extracted silica from rice husk has demonstrated success in enhancing the mechanical characteristics of composites.²⁴ The present study primarily centres on reviewing the literature related to the mechanical attributes of polymer composites strengthened with rice husk with a particular emphasis on assessing the effectiveness of various treatment methods in enhancing the compatibility of the base polymer and the RH filler.

Figure 1: Applications of RH in polymer composites. Click here to view Figure

Rice Husk Composition

Rice husk is mainly composed of cellulose that features a broad spectrum of dimensions²⁵.  It comprises of hemicellulose, cellulose, silica, lignin, solubles and moisture. The percentage composition and physical characteristics of RH are detailed in Table 1.^18,19,26

Table 1: Percentage Composition and Physical Characteristics of Rice Husk ^18,19,26

Components	Percentage Composition (%)
Cellulose	25-48
Hemicellulose	18-25
Lignin	12-31
Silica (SiO2)	15-17
Solubles	2-5
Moisture Content	5-10
Physical Characteristics of Rice Husk
Particle size	20-50 (µm)
Surface Area	1 -50 (m2/g)
Density	0.09-3 (g/cm3)

Rice husk primarily comprises elemental substances like Carbon 37.05%, Hydrogen 4 to 5%, Oxygen 31to 37%, Nitrogen 0.23 to 0.32%, Sulphur 0.04 to 0.08%, Silicon 9.01% and Silica 17 to 25%, ash 22.29%, bulk density 0.09 to 3 (g/cm³) and hardness 5 to 6 (Mohr’s scale).^27–29 Different researchers have reported different compositions of the Rice Husk. It relies on several factors such as the rice variety, climatic conditions, fertilizer type, soil properties, testing methods, and the production area's geography.^18,19,30,31

Research has demonstrated rice husk to be composed predominantly of organic matter, comprising about 75 to 90% lignin and cellulose, with the remaining portion consisting of mineral elements like silica, alkalis, and minor constituents.^{1,18,19,26,32,33}

Several methods have been reported by the researchers for the analysis of lignocellulosic biomass composition.^32–34 Krasznai et. al³⁴ presented a historical perspective on various compositional analysis techniques and their detailed progress over time, including the Weende Method (1859), the Klason Method (1923), the Saeman sulfuric acid method (1944), the Saeman gravimetric method (1954), and the Laboratory Analytical Procedures (LAPs) designed by the National Renewable Energy Laboratory (NREL) (2000). Cai et. al³³ classified the methods of compositional analysis into three categories: analysis by sulfuric acid (H₂SO₄) hydrolysis; analysis by Near Infrared Spectroscopy (NIRS); and analysis by kinetics on thermogravimetry (TG). Sluiter et. al³⁵ determined the structural carbohydrate and lignin content in biomass using NREL Laboratory Analytical Procedures based on sulfuric acid hydrolysis. Jin et. al³⁶ reported the compositional analysis of rice straw using NIRS. Cai et. al³⁷ also reported various methods of analysis using kinetics based on the distributed activation energy model. In a recent study, Malik et. al³² reported the analysis of rice husk biomass composition (cellulose – 38%, hemicellulose – 21%, lignin – 17%, ash – 15%, extractives – 8%, moisture content – 9.8%) using NREL standard methods.

Since, rice husk contains a similar quantity of cellulose but lower lignin and hemicellulose levels compared to wood, it can be subjected to higher processing temperature than wood^1,18.

Chemical examination of the non-organic part of rice husks has indicated that silica is the predominant component in its non-crystalline form, with small amounts of alkali and alkaline earth metal oxides, iron and aluminium oxides.^30,31 Rice husk exhibits exceptionally high ash content (10 to 20 %) in contrast to other biofuels. The ash consists predominantly of silica, ranging from 87% to 97%, is highly permeable and has low density along with an extensively large external surface area.^1,27 Its considerable silica content makes it a key material for industrial use¹.

The rice husk serves as the tough outer layer enveloping the rice kernel, mainly covered in silica and marked by a thick outer layer and surface bristles. Additionally, a small portion of silica can be found in the central layer and the inner surface layer. The significant silica concentration in rice husk contributes to its enhanced rigidity and effective flame resistance. ^18,21,31 Differences in the hemicellulose, cellulose, and lignin composition within rice husks from various rice varieties lead to variations in the mechanical characteristics of reinforced  polymer.¹¹

Surface Treatment Methods

A significant challenge has been observed in the preparation of RH composites which is attributed to their limited compatibility with hydrophobic matrices, primarily because rice husk has a hydrophilic nature and contains natural fats and waxes. Efficient integrations at the junction of rice husk and the base polymer are essential for ensuring effective stress distribution from the polymer structure to the strengthening material. This consequently leads to enhancements in the mechanical attributes of polymer blends containing rice husk.

According to research conducted by Yang and Kim³⁸, RH-filled polypropylene-based composites have shown increased brittleness and reduced tensile strength, highlighting the adverse effects of low compatibility between RH and the matrix material. To resolve this issue, researchers have explored and suggested different pre-treatment methods. Depending upon the mode of action, the existing pre-treatment methods can be broadly categorized as follows:

Physical Pre-treatment Methods

These approaches seek to alter the physical properties of the fiber, like its surface morphology, roughness, and porosity, without modifying its chemical composition. These methods include different processes such as the treatment of fibre surface with hot water, with high pressure steam followed by a rapid depressurization process, repeated freezing-thawing process, and exposure to ionized gas (Plasma treatment) etc. These processes modify the structural characteristics of the fiber and increase the accessibility of reactive areas of the fiber and the base polymer. Better interaction between the reactive sites of the additive and the base polymer results in enhanced adhesion and wetting which results in improved physical attributes of the blend. The appropriate pre-treatment method is determined by the distinctive features of fibers and the essential attributes of the resulting polymer blend. Hot water treatment helps to remove the surface impurities like oils, waxes, dust, and can partially remove the hemicellulose, which makes the fiber surface more accessible for bonding with hydrophobic polymer.^39,40 Steam treatment subjects natural fibers to high-pressure steam, followed by rapid depressurization. This process causes the rupture of the lignocellulosic structure, removes a portion of the lignin and hemicellulose, which makes the fiber more porous with increased surface area and enhances its bonding potential with the polymer.^11,19,41,42 Steam treatment has been successfully employed by the researchers on rice husk to enhance the compatibility of the filler in particle board production and composite panels with enhanced mechanical properties.¹⁹ Panels made of rice husk treated with steam and phenol formaldehyde possess enhanced interfacial bonding and hence show superior modulus of rupture and elasticity compared to those treated with alkali.^11,43 The freeze-thaw process subjects natural fibers to repeated cycles of freezing (usually at temperatures below -20°C) and thawing (at or slightly above room temperature). The freezing process causes the moisture inside the fibers to swell, which forms the tiny fractures and amplifies surface roughness. Subsequent thawing releases the water, resulting in a more porous, rough-textured fiber surface, which leads to enhanced mechanical interlocking with the polymer.⁴⁴ In the past few years, the plasma treatment has proven to be a powerful tool for enhancing the binding properties between natural fibers and polymers. Plasma treatment^15,45 subjects the natural fibers to a plasma environment, which is created by applying energy commonly via an electric field to a gas such as nitrogen, oxygen, argon, helium etc. leading to the ionization of gas and the generation of reactive entities (free radicals, ions, electrons, and neutral atoms or molecules etc.). The type of reactive entities produced and their concentration depends upon the selection of gas and the operating conditions. Plasma treatment abrades the fiber's outer layer, which results in enhanced surface texture. It may introduce new functional groups (carbonyl, carboxyl, hydroxyl, amine etc.) onto the surface of the fiber, which may react with the base polymer, considerably improving adhesion at the interface. Additionally, plasma may induce cross-linking within the polymer networks on the surface of the fiber, leading to more stable linkages at the interface of the fiber and the polymer. Several studies^{13–15,31,41,45–47} have highlighted the beneficial impact of plasma treatment on the binding strength between natural fibers and base polymers. This process is both safe for health and the environment, and it effectively enhances the surface properties of fibers. However, due to the requirement of expensive and specialized equipment, it has not been explored for large scale production of composites.^15,45

Chemical Pre-treatment Methods

Different chemical pre-treatment methods have been reported by researchers to strengthen the linkage between the fiber surface and the polymer base such as alkaline treatment known as mercerization, acetylation, the addition of compatibilizers  e.g. maleic anhydride, benzoylation, silane treatment, peroxide treatment and permanganate treatment etc.^1,48,49 Of the various chemical treatments available, the alkaline treatment, known as mercerization, is especially notable for its efficacy and affordability.  ^18,19 When subjected to alkaline treatment using a NaOH solution, the fiber undergoes a process where its inherent fats and coatings are eliminated from the outer layer. This action exposes the reactive sites of the fiber, enhancing its ability to interact with the matrix material.^{18,19,43,50–56} A significant decrease in hemicellulose and lignin content on treating with (2 to 8% weight to volume) NaOH solution has been reported.^18,19,51 The process of mercerization enhances the surface texture of the fiber which connects more efficiently to the polymer structure and enhances the physical performance of the blended material. The physical characteristics of the hybrid material depends on variables like alkali concentration, treatment temperature, and treatment duration.^11,57

Benzoyl chloride is another chemical frequently used in fiber treatment, in addition to alkaline processes. Benzoylation involves the introduction of a benzoyl functional group at the fiber’s surface, which reduces the moisture affinity of the fiber and enhances its interaction with the non-polar base polymer.⁵⁸ Alkaline and benzoylation treatments have been studied on rice husk by various researchers.^18,59 Chemical treatment of rice husk with acetic anhydride i.e. acetylation has also been reported for increasing hydrophobicity of fibers obtained by cross-linking of acetic anhydride with hydroxyl groups of rice husk.^11,60,61 The procedure of acetylation induces plasticization in cellulose fibers. It also enhances the size stability and water resistance of the polymer blend. It has been observed that the application of benzene diazonium salt to RH diminishes its hydrophilic properties and improves its integration with the polymer material.^11,18,19

Maziad et al.⁶² explored how including a silane bonding agent influenced the properties of a polymer base strengthened with rice husk. They revealed that the treatment of rice husk with silane led to superior mechanical performance compared to non-treated samples. In an another study⁶³, the incorporation of silane-treated rice husk into a polymer matrix of natural rubber exhibited a small enhancement in both flexural and tensile strength in comparison to those treated with the alkaline medium. In the bifunctional configuration of silanes, the alkoxysilane part engages with the hydroxyl groups, while the other terminal group participates in copolymerization with the polymer base. These chemical interactions promote the efficient distribution of loads across the filler and the polymer resin, thereby yielding a material characterized by enhanced mechanical properties.¹⁹

It has been reported that rice husk and rice straw composites exhibit improved performance when compatibilizers such as maleic anhydride are incorporated.^{11,49,59,62,64–67} Rosa and co-authors⁶⁷ prepared maleated polypropylene (MAPP) composites with a maximum of 40 weight% loading of rice husk. As per the study, the integration of MAPP enhanced both the loss modulus and storage modulus of the product. Compatibilizers possess both hydrophobic and hydrophilic functional groups that interact with the reinforcement and the polymer to enhance their compatibility, resulting in better bonding and superior mechanical traits of the blended materials¹⁹. Research studies^68–71 have reported the method of permanganation where mercerized cellulose fibers were soaked in acetone solutions containing varying amount of potassium permanganate (KMnO₄). Permanganate treatment establishes radical centers within the cellulose present in natural fibers, which enhances its interaction with the base polymer. In addition to these methods, other compatibilizers and treatments including stearic acid, isocyanates, sodium chlorite and triazine derivatives, etc. can be used for treating cellulose depending upon the specific requirement in the corresponding composites.¹¹

Though chemical methods are effective, they lead to issues like environmental effects, workplace safety, and managing toxic waste. The use of toxic chemicals also prompts regulatory and health concerns. Despite these drawbacks, chemical methods are still commonly used due to their confirmed efficiency and consistency in commercial production. To lower their ecological impact, it is essential to seek greener chemical alternatives and optimize waste management strategies, balancing their benefits with a reduction in environmental damage.¹⁵Top of Form

Bottom of Form

General Applications of Rice Husk

Rice husk (RH) possesses a high calorific value of 15217.20 KJ/Kg, and boiler efficiency comparable to that of coal. Therefore, Rice Husk proves to be a more cost-effective fuel than coal.⁷² The heat energy generated through the ignition and gasification of RH may be applied in multiple applications e.g. in steam generation and electricity generation.^73,74 Rice Husk exhibits good potential for electricity generation, as 1 ton of RH can produce 1 MWH of electricity. Additionally, it can also function as a substitute energy source for domestic power requirements. Due to the high silica (silicon dioxide) amount found in RH, it has emerged as a valuable resource for various silicon compounds. RH is also utilized in the preparation of advanced materials such as SiN, silanes, SiC, Mg₂Si, Si₂N₂O, elemental Si etc.^75,76 Rice husk can be employed as an organic fertilizer to enhance the crop yield as well as water utilization efficiency in agricultural fields. Because of the high content of dietary fibre (more than 30%), rice husk proves to be an abundant provider of proteins and minerals, rendering it a viable ingredient in the creation of functional foods. Utilization of rice husk in brick production increases porosity, which results in to superior thermal insulation.⁷⁷ Studies have shown that rice husk can be processed to generate activated carbon with a microporous structure via physical or chemical activation methods.^78–81 Rice husk possesses insolubility in water, good structural strength and excellent chemical stability because of the high content of silica. This characteristic qualifies it for an important role in the purification of water and wastewater treatment. Sorbents derived from rice husk have been found effective in removing six heavy metals, including Cu, Fe, Cd, Mn, Pb and Zn⁸². Additionally, rice husk acted as an excellent adsorbent for eliminating various contaminants like pesticides, colorants, phenolic compounds, organic substances etc.^83,84 Rice husk has also been recognized as a successful source for bioethanol production.^1,76,85

Mechanical Characteristics of Polymer Composites Reinforced with Rice Husk

Reported studies showing the influence of increasing Rice Husk (RH) loading on mechanical characteristics of reinforced polymer composite have been tabulated in Table 2. The mechanical characteristics examined include tensile modulus, flexural modulus, tensile strength, impact strength, and elongation at break. These properties are very important indicators of a material’s performance in various applications. Existing literature spanning the last 20 years has been extensively explored to analyse the contribution of utilizing RH to the mechanical characteristics of RH-integrated polymer composites.

Table 2: Effect of Increasing Rice Husk Loading on Polymer Mechanical Characteristics: Reported Studies Click here to view Table

Table 2 reveals that higher loading of untreated rice husk in composites leads to increased tensile modulus and flexural modulus, accompanied by a decline in tensile strength, impact strength, and elongation at break. The variation of tensile strength with higher loading of RH content has been shown graphically (Figure 2) by Yang et al.⁸⁹. It was proposed that the decline in tensile strength with higher rice husk flour content is because of the weak interaction at the interface of the non-polar base polymer and the hydrophilic filler. The addition of compatibilizers significantly improved the tensile strength as shown (Figure 3) by Yang et al.⁸⁹ for tensile strength of RHF (30 wt%) reinforced PP composites at different contents of compatibilizers. Similar results for tensile and flexural strength (Figures 4 a & b) have also been reported by Raghu and co-authors¹⁰⁵ for PP/RH composites.         

Figure 2: Tensile strength of PP composites at various loading of RH89 Click here to view Figure

Figure 3: Tensile strength of PP/RHF (30 wt%) with weight percent of compatibilizing agents89 Click here to view Figure

Figure 4: (a) Tensile strength and (b) Flexural strength of PP/RH composites with untreated PP; Polypropylene grafted with MAPP; and Polypropylene grafted with m-TMI-g-PP compatibilizers105 Click here to view Figure

It was found that the inclusion of compatibilizers enhanced the flexural and tensile properties of composites effectively. The action mechanism of compatibilizer (Figure 5) has been proposed by Yang et al.⁸⁹ It has been suggested that the compatibilizers form chemical bonds with the hydrophilic filler and are integrated into the polymer matrix by wetting.

Figure 5: The action mechanism of compatibilizer in enhancing affinity at the interface of hydrophobic base polymer and hydrophilic filler89 Click here to view Figure

From various reported results (Table 2), it can be interpreted that incorporation of pre-treated or modified rice husk or compatibilizers leads to enhanced mechanical performance of the polymer blend. Pre-treatment or modification of rice husk and inclusion of compatibilizers is very crucial in enhancing the mechanical characteristics of RH-reinforced composites. It facilitates better adhesion of RH-filler with the base polymer thereby improves the interfacial bonding and overall composite performance. Toro and co-authors⁸⁷ analysed the influence of adding the compatibilizer PP-g-MMI to RH/PP-Co-PE (rice husk-reinforced poly(propylene-co-ethylene)). The inclusion of 5 wt% of PP-g-MMI to RH/PP-Co-PE resulted in a significant increase in tensile modulus, from 715 MPa to 1181 MPa, and tensile strength, from 16 MPa to 28 MPa. The Scanning electron microscopy (SEM) analysis indicated enhanced adhesion and greater phase consistency at the interface of RH and PP-Co-PE components within the composite, which was attributed to the inclusion of PP-g-MMI. Similarly, Razavi-Nouri and co-authors⁸⁸ investigated the mechanical performance of chopped RH (CRH) in PP. The formulation containing 3 php (part per hundred parts of polymer) of MAPP and 40 php of RH exhibited a notable increase of approximately 33% in tensile modulus, 16% in flexural strength, and 100% in flexural modulus, while the decrease in the impact strength was negligible. Further, Premalal and his team²⁶ evaluated the mechanical performance of PP strengthened with rice husk powder and talc. They found that increasing the loading of both fillers improved Young’s modulus and flexural modulus but reduced yield strength and elongation at break. At similar loading levels, talc enhanced the moduli and yield strength more effectively than the rice husk powder. This difference was attributed to talc's finer particle metrics and greater surface profile, which enhanced the bonding at the interface of the reinforcing material and the polymer substrate. In addition, Rosa et al.⁶⁷ explored the impact of maleated polypropylene (MAPP) on polypropylene composites strengthened with rice husk flour. The inclusion of the compatibilizer MAPP resulted in improved tensile strength for all filler loadings. This improvement was due to the reaction involving the –OH functionalities of the rice husk and the acidic anhydride moieties of MAPP. The formulation containing 1.2 wt% of MAPP and 40 wt% of rice husk, with a MAPP/RH ratio of 0.03, demonstrated the most significant enhancement in mechanical performance. Therefore, the proportion of coupling agent to filler is essential in determining the final attributes of the composite. Moreover, Raghu and others¹⁰⁵ examined the effects of compatibilizers—MAPP and m-TMI-g-PP on rice husk (RH)-filled polypropylene composites. The inclusion of 5 wt% of either compatibilizer, combined with 40-50% of RH filler, showed a 40% rise in tensile strength for MAPP and a 52% rise for m-TMI-g-PP in comparison to the composites with no compatibilizer. Interestingly, m-TMI-g-PP exhibited enhanced performance compared to MAPP, which resulted from the reaction involving the –OH functionalities of RH and the isocyanate moieties of m-TMI-g-PP. They mentioned that the carbamate ester bond formed between the m-TMI-g-PP and the –OH functionalities of RH is stronger than the anhydride ester linkage formed between the MAPP and the –OH group of RH. In a report by Tong and co-authors¹⁰², the mechanical characteristics of recycled HDPE (rHDPE) were evaluated by integrating RH along with MAPE as a compatibilizer. The composite containing 40 wt% RH filler exhibited the maximum tensile modulus of 429.143 MPa and the maximum flexural modulus of 1717.508 MPa. However, the pure HDPE composite demonstrated the highest impact strength (6.171 kJ/m²) compared to the RH-reinforced composites. The decline in impact strength was related to the restriction of base polymer flow in the presence of the filler, leading to increased brittleness in the resultant composite. Additionally, Bisht and others¹⁰⁴ examined the impact of alkali (NaOH) treatment on the RH flour-filled epoxy resin. The mechanical performance of the material was improved with increasing NaOH concentration, reaching an optimal level at 8% NaOH. The composite containing 20 wt% RH modified using 8% NaOH exhibited a remarkable increase in tensile modulus and tensile strength, by 68.07% and 36.63%, respectively, in comparison to the pure epoxy. Furthermore, flexural properties, impact strength, and elongation at break were significantly enhanced with higher loading of RH treated with 8% NaOH. The observed increase in tensile strength, impact strength and elongation at break with RH loading contradicted previously reported results and was attributed to the alkali treatment, which increased the roughness and hydrophobicity of the filler, enhancing its compatibility with the epoxy resin. However, at concentrations above 8% NaOH, the mechanical properties declined due to the degradation of rice husk properties from excessive alkali exposure. In a recent study by Shah and co-authors¹¹⁰, rice husk and wood flour were incorporated in recycled high-density polyethylene (rec-HDPE) to assess their influence on the mechanical, thermal, and flammability characteristics of the composites. The findings indicated an improvement in mechanical characteristics with increasing filler content. The composite (rec-HDPE/RH/MAPE) with a composition of 87/10/3 wt% displayed the best mechanical characteristics, showing enhancements of 15.8% in tensile modulus, 51.9% in flexural modulus, 11.9% in tensile strength, and 32.65% in impact strength compared to unfilled rec-HDPE. The SEM analysis further confirmed a homogeneous distribution of rice husk within the base polymer, with no evidence of agglomeration. The application of MAPE as a compatibilizer enhanced the interactions at the interface of RH and rec-HDPE, resulting in superior mechanical attributes for the composite. Various studies reveal that the careful formulation optimization while considering various parameters like filler-to-polymer ratio, compatibilizer concentration, and processing conditions, is very essential for achieving desired mechanical characteristics of polymer composite. Incorporation of other additives, such as montmorillonite nanoclay can further enhance mechanical properties through synergistic effects. When utilized with recycled polymers like rec-HDPE, the combination of rice husk (RH) and compatibilizers showed marked improvements in the mechanical features of the base polymer. Such combinations can result in high-performance, innovative, and environmentally benign materials suitable for a range of industrial applications.

Conclusion

Rice husk is an abundantly available field residue which is obtained as a byproduct of rice milling. Its integration into polymer composites offers an excellent opportunity to convert this waste into a valuable resource which contributes to sustainability and environmental conservation. Various studies have shown that the inclusion of rice husk in polymer composites improves different mechanical characteristics, such as tensile modulus, flexural modulus, tensile strength, and impact strength. Most of the research findings suggest that the higher loading of untreated rice husk in composites leads to increased tensile modulus and flexural modulus, accompanied by reduction in impact strength, tensile strength, and elongation at break. However, the incorporation of treated or modified rice husk or compatibilizer improves all the mechanical characteristics of polymer composite. The compatibilizers like maleic anhydride polyethylene (MAPE), and m-TMI-g-PP improve mechanical properties of the polymer composites by enhancing filler dispersion and interfacial adhesion. Further, the pre-treatment of RH with the alkali can boost tensile and flexural properties by increasing surface roughness and hydrophobicity, although excessive treatment may degrade the filler. The comparison between RH and other fillers, such as talc, highlights the importance of filler characteristics in determining the composite performance. In recycled polymers like rec-HDPE, the use of RH with a compatibilizer leads to marked improvements in tensile and flexural strength, emphasizing the importance of compatibilizer/filler ratios in optimizing the mechanical performance of the material. These formulations may result in innovative, high-efficiency materials that are both sustainable and suitable for numerous industrial applications. Careful optimization of formulation along with consideration of diverse parameters like the ratio between filler and base polymer, the concentration of compatibilizer, and the conditions of processing, is crucial for attaining the preferred mechanical characteristics of polymer composites. Moreover, the appropriate pre-treatment approach must be selected according to the specific requirements, along with the fiber and polymer characteristics, and the necessity to balance performance, cost, and ecological impact.

Future prospects

The future prospects for utilizing rice husk in polymer composites is bright driven by its sustainability, improved mechanical properties, cost efficiency, biodegradability, eco-friendly nature, and versatile applications. These factors suggest the rice husk-integrated polymers as valuable materials for sustainable and advanced engineering in the future. Rice husk is a cost-effective raw material, particularly in regions where rice cultivation is predominant. Its utilization in polymer composites results in lower production costs compared to conventional fillers or reinforcement agents, which makes these materials more economically viable. Polymer composites that include rice husk offer a greener alternative to conventional materials, especially in applications where biodegradability is desired, such as packaging or disposable items. Moreover, the use of rice husk in recycled polymers, yielding exceptional mechanical properties, presents an effective approach for developing high-performance materials while simultaneously promoting environmental conservation by reducing waste and the demand for new materials. The integration of rice husk into a variety of polymer matrices presents vast potential for diverse applications across industries, such as automotive components, building materials, agricultural equipment, and consumer goods. To fully exploit its potential, further research and optimization of the formulation are necessary. Factors such as the ratio between filler and polymer, the concentration of compatibilizers, and the processing conditions must be carefully adjusted to achieve the desired mechanical performance. Additionally, it will be important to select the appropriate pre-treatment methods for fibers and polymers to effectively balance performance, cost, and ecological considerations. Greener chemical alternatives and optimized waste management strategies will be essential for minimizing ecological damage while maximizing the benefits of rice husk-reinforced polymer composites. As research and innovation continue to progress, the focus on refining these composites will enhance their suitability for a broader spectrum of applications.

Acknowledgement

We sincerely thank to Dr. Sushma, Assistant Professor of Chemistry, Government College, Hisar, Haryana, India for her valuable insights, feedback and suggestions, which have greatly enhanced the quality of this review.

Funding Sources

The author(s) received no financial support for the research, authorship, and/or publication of this article.”

Conflict of Interest

The author(s) do not have any conflict of interest.

Data Availability Statement

The manuscript includes all the datasets generated or analyzed during this research study.

Ethics Statement

This research did not involve human participants, animal subjects, or any material that requires ethical approval

Informed Consent Statement

This study did not involve human participants, and therefore, informed consent was not required.

Clinical Trial Registration

This research does not involve any clinical trials.

Authors' Contributions

Dr. Sweety Monga- Conceptualization, Data Collection, Writing - Original draft; Dr. Meera- Visualization, Methodology; Dr. Malvika Kadian- Writing, review & editing; Dr. Savita Nagoria - Writing, review & editing; Dr. Satyender Kumar - Writing, review & editing.

References

1. Nwosu-obieogu K, Chiemenem L, Adekunle K. Utilization of Rice Husk as Reinforcement in Plastic Composites Fabrication-A Review. Am J Synth Mater Process. 2016;1:32-36. doi:10.11648/j.ajmsp.20160103.12
2. Arjmandi R, Hassan A, Majeed K, Zakaria Z. Rice Husk Filled Polymer Composites. Int J Polym Sci. 2015;2015. doi:10.1155/2015/501471
   CrossRef
3. Chand N, Fahim M. Natural Fibers and Their Composites, In: Tribology of Natural Fiber Polymer Composites. Woodhead Publishing; 2008.
   CrossRef
4. M. Tahir P, Juliana AH, Ashaari Z, H.P.S AK. Nonwood-Based Composites. Curr For Rep. 2015;1:221-238. doi:10.1007/s40725-015-0023-7
   CrossRef
5. Kumar R, Tejeet Singh. Rice Husk-Reinforced Composites: A Review. In: ; 2014. doi:10.1007/978-81-322-1859-3_37
   CrossRef
6. Egute NS, Forster PL, Parra DF, Fermino DM, Lugão AB. MECHANICAL AND THERMAL PROPERTIES OF POLYPROPYLENE COMPOSITES WITH CURAUA FIBRE IRRADIATED WITH GAMMA RADIATION. In: ; 2009.
7. Silva RV, Aquino EMF. Curaua fiber: a new alternative to polymeric composites. J Reinf Plast Compos. 2008;27(1):103-112.
   CrossRef
8. Akil HM, Omar MF, Mazuki AAM, Safiee S, Ishak ZAM, Abu Bakar A. Kenaf fiber reinforced composites: A review. Mater Des. 2011;32(8):4107-4121. doi:10.1016/j.matdes.2011.04.008
   CrossRef
9. Alvarez VA, Fraga AN, Vázquez A. Effects of the moisture and fiber content on the mechanical properties of biodegradable polymer–sisal fiber biocomposites. J Appl Polym Sci. 2004;91(6):4007-4016. doi:10.1002/app.13561
   CrossRef
10. Baiardo M, Zini E, Scandola M. Flax fibre–polyester composites. Compos Part Appl Sci Manuf. 2004;35(6):703-710. doi:10.1016/j.compositesa.2004.02.004
    CrossRef
11. Bassyouni M, Waheed ul hasan S. 13 - The use of rice straw and husk fibers as reinforcements in composites. In: Biofiber Reinforcements in Composite Materials. ; 2015:385-422. doi:10.1533/9781782421276.4.385
    CrossRef
12. Lu JZ, Wu Q, McNabb HS. Chemical coupling in wood fiber and polymer composites: A review of coupling agents and treatments. Wood Fiber Sci. Published online 2000:88-104. Accessed September 3, 2024. http://wfs.swst.org/index.php/wfs/article/view/1311
13. George J, Sreekala MS, Thomas S. A review on interface modification and characterization of natural fiber reinforced plastic composites. Polym Eng Sci. 2001;41(9):1471-1485. doi:10.1002/pen.10846
    CrossRef
14. Väisänen T, Haapala A, Lappalainen R, Tomppo L. Utilization of agricultural and forest industry waste and residues in natural fiber-polymer composites: A review. Waste Manag. 2016;54:62-73. doi:10.1016/j.wasman.2016.04.037
    CrossRef
15. Ezenkwa OE, Hassan A, Samsudin SA. Influence of different surface treatment techniques on properties of rice husk incorporated polymer composites. Rev Chem Eng. 2021;37(8):907-930. doi:10.1515/revce-2019-0027
    CrossRef
16. Kim HS, Lee BH, Choi SW, Kim S, Kim HJ. The effect of types of maleic anhydride-grafted polypropylene (MAPP) on the interfacial adhesion properties of bio-flour-filled polypropylene composites. Compos Part Appl Sci Manuf. 2007;38(6):1473-1482. doi:10.1016/j.compositesa.2007.01.004
    CrossRef
17. Nachtigall S, Cerveira G, Rosa S. New polymeric-coupling agent for polypropylene/wood-flour composites. Polym Test - POLYM TEST. 2007;26(5):619-628. doi:10.1016/j.polymertesting.2007.03.007
    CrossRef
18. Juliana AH, Lee SH, M. Tahir P, Te Chuan L, Selimin MA, Harmaen A. A Review: Chemical Treatments of Rice Husk for Polymer Composites. Biointerface Res Appl Chem. 2021;11:12425-12433. doi:10.33263/BRIAC114.1242512433
    CrossRef
19. Majeed K, Arjmandi R, Al-Maadeed MA, et al. 22 - Structural properties of rice husk and its polymer matrix composites: An overview. In: Jawaid M, Md Tahir P, Saba N, eds. Lignocellulosic Fibre and Biomass-Based Composite Materials. Woodhead Publishing Series in Composites Science and Engineering. Woodhead Publishing; 2017:473-490. doi:10.1016/B978-0-08-100959-8.00022-6
    CrossRef
20. Suhot MA, Hassan MZ, Aziz SA, Md Daud MY. Recent Progress of Rice Husk Reinforced Polymer Composites: A Review. Polymers. 2021;13(15):2391. doi:10.3390/polym13152391
    CrossRef
21. Zhao Q, Zhang B, Quan H, Yam RCM, Yuen RKK, Li RKY. Flame retardancy of rice husk-filled high-density polyethylene ecocomposites. Compos Sci Technol. 2009;69(15):2675-2681. doi:10.1016/j.compscitech.2009.08.009
    CrossRef
22. Kwon JH, Ayrilmis N, Han TH. Enhancement of flexural properties and dimensional stability of rice husk particleboard using wood strands in face layers. Compos Part B Eng. 2013;44(1):728-732. doi:10.1016/j.compositesb.2012.01.045
    CrossRef
23. Mishra S, Dhada I, Haldar P. Rice Husk: From Agro-Industrial to Modern Applications. In: Neelancherry R, Gao B, Wisniewski Jr A, eds. Agricultural Waste to Value-Added Products: Technical, Economic and Sustainable Aspects. Springer Nature; 2023:295-320. doi:10.1007/978-981-99-4472-9_14
    CrossRef
24. Zhang G, Wang G, Jiang Y, Wang S, Zhang Y. Preparation and properties of rice husk ash silica filled natural rubber. Polym Compos. 2024;45(1):438-447. doi:10.1002/pc.27789
    CrossRef
25. Chand N, Sharma P, Fahim M. Tribology of maleic anhydride modified rice-husk filled polyvinylchloride. Wear. 2010;269(11):847-853. doi:10.1016/j.wear.2010.08.014
    CrossRef
26. Premalal HGB, Ismail H, Baharin A. Comparison of the mechanical properties of rice husk powder filled polypropylene composites with talc filled polypropylene composites. Polym Test. 2002;21(7):833-839. doi:https://doi.org/10.1016/S0142-9418(02)00018-1
    CrossRef
27. Sarangi M, Bhattacharyya S, Behera R. Effect of temperature on morphology and phase transformations of nano-crystalline silica obtained from rice husk. Phase Transit. 2009;82(5):377-386. doi:10.1080/01411590902978502
    CrossRef
28. Muthadhi A, Anitha R, Kothandaraman S. Rice husk ash - Properties and its uses: A review. J Inst Eng India Civ Eng Div. 2007;88:50-56.
29. Babaso PN, Sharanagouda H. Rice Husk and Its Applications: Review. Int J Curr Microbiol Appl Sci. 2017;6(10):1144-1156. doi:10.20546/ijcmas.2017.610.138
    CrossRef
30. Turmanova S, Genieva S, Vlaev L. Obtaining Some Polymer Composites Filled with Rice Husks Ash-A Review. Int J Chem. 2012;4(4):p62. doi:10.5539/ijc.v4n4p62
    CrossRef
31. Bisht N, Gope PC, Rani N. Rice husk as a fibre in composites: A review. J Mech Behav Mater. 2020;29(1):147-162. doi:10.1515/jmbm-2020-0015
    CrossRef
32. Malik S, Omre PK, Sivadas S. Compositional Analysis of the Lignocellulosic Biomass from Agricultural Waste (Rice Husk). Arch Curr Res Int. 2024;24(6):78-84. Accessed September 2, 2024. http://archive.jibiology.com/id/eprint/2478/
    CrossRef
33. Cai J, He Y, Yu X, et al. Review of physicochemical properties and analytical characterization of lignocellulosic biomass. Renew Sustain Energy Rev. 2017;76:309-322. Accessed September 2, 2024. https://www.sciencedirect.com/science/article/pii/S1364032117304033
    CrossRef
34. Krasznai DJ, Hartley RC, Roy HM, Champagne P, Cunningham MF. Compositional analysis of lignocellulosic biomass: conventional methodologies and future outlook. Crit Rev Biotechnol. Published online February 17, 2018. Accessed September 2, 2024. https://www.tandfonline.com/doi/abs/ 10.1080/07388551. 2017.1331336
    CrossRef
35. Sluiter A, Hames B, Ruiz R, et al. Determination of structural carbohydrates and lignin in biomass. Lab Anal Proced. 2008;1617(1):1-16. Accessed September 3, 2024. https://www.academia.edu/download/34289991/Determination%E2%80%90Structural%E2%80%90Carbohydrates%E2%80%90L....pdf
36. Jin S, Chen H. Near-infrared analysis of the chemical composition of rice straw. Ind Crops Prod. 2007;26(2):207-211. Accessed September 3, 2024. https://www.sciencedirect.com/science/article/pii/S0926669007000416
    CrossRef
37. Cai J, Wu W, Liu R, Huber GW. A distributed activation energy model for the pyrolysis of lignocellulosic biomass. Green Chem. 2013;15(5):1331-1340. Accessed September 3, 2024. https://pubs.rsc.org/en/content/articlehtml/2013/gc/c3gc36958g
    CrossRef
38. Yang HS, Kim HJ, Son J, Park H, Lee BJ, Hwang TS. Rice-husk flour filled polypropylene composites; mechanical and morphological study. Compos Struct. 2004;63:305-312. doi:10.1016/S0263-8223(03)00179-X
    CrossRef
39. Moura A, De Bolba C, Demori R, Lima L, Santana R. Effect of Rice Husk Treatment with Hot Water on Mechanical Performance in Poly(hydroxybutyrate)/Rice Husk Biocomposite. J Polym Environ. 2018;26:2632-2639. doi:10.1007/s10924-017-1156-5
    CrossRef
40. Santos EBC, Moreno CG, Barros JJP, et al. Effect of Alkaline and Hot Water Treatments on the Structure and Morphology of Piassava Fibers. Mater Res. 2018;21:e20170365. doi:10.1590/1980-5373-MR-2017-0365
    CrossRef
41. Mukhopadhyay S, Fangueiro R. Physical Modification of Natural Fibers and Thermoplastic Films for Composites — A Review. J Thermoplast Compos Mater. 2009;22(2):135-162. doi:10.1177/0892705708091860
    CrossRef
42. Kalia S, Kaith BS, Kaur I. Pretreatments of natural fibers and their application as reinforcing material in polymer composites—A review. Polym Eng Sci. 2009;49(7):1253-1272. doi:10.1002/pen.21328
    CrossRef
43. Ndazi BS, Karlsson S, Tesha JV, Nyahumwa CW. Chemical and physical modifications of rice husks for use as composite panels. Compos Part Appl Sci Manuf. 2007;38(3):925-935. doi:10.1016/j.compositesa.2006.07.004
    CrossRef
44. Tan BK, Ching YC, Poh SC, Abdullah LC, Gan SN. A review of natural fiber reinforced poly (vinyl alcohol) based composites: Application and opportunity. Polymers. 2015;7(11):2205-2222. Accessed September 6, 2024. https://www.mdpi.com/2073-4360/7/11/2205
    CrossRef
45. Nguyen MH, Kim BS, Ha JR, Song JI. Effect of Plasma and NaOH Treatment for Rice Husk/PP Composites. Adv Compos Mater. 2011;20(5):435-442. doi:10.1163/092430411X570112
    CrossRef
46. Molla A, Al Moyeen A, Mahmud RM, Haque MJ. Plant fiber-reinforced green composite: A review on surface modification, properties, fabrications and applications. Mater Open Res. 2024;3(6):6. Accessed September 6, 2024. https://materialsopenresearch.org/articles/3-6?_ga=undefined
    CrossRef
47. Chanda AK, Neogi S, Neogi S. Optimization of Plasma Treatment for Enhanced Filler Matrix Adhesion in Manufacturing Green Composites with Rice Husk. Indian Chem Eng. 2013;55(3):177-188. doi:10.1080/00194506.2013.832026
    CrossRef
48. La Mantia FP, Morreale M. Green composites: A brief review. Compos Part Appl Sci Manuf. 2011;42(6):579-588. doi:10.1016/j.compositesa.2011.01.017
    CrossRef
49. Li X, Tabil L, Panigrahi S. Chemical Treatments of Natural Fiber for Use in Natural Fiber-Reinforced Composites: A Review. J Polym Environ. 2007;15:25-33. doi:10.1007/s10924-006-0042-3
    CrossRef
50. Syafri R, Ahmad I, Abdullah I. Effect of Rice Husk Surface Modification by LENR the on Mechanical Properties of NR/HDPE Reinforced Rice Husk Composite. Sains Malays. 2011;40(7):749-756.
51. Ndazi B, Nyahumwa C, Tesha J. Chemical and thermal stability of rice husks against alkali treatment. BioResources. 2008;3(4):1267-1277. doi:10.15376/biores.3.4.1267-1277
    CrossRef
52. Vijay R, Singaravelu DL, Vinod A, Sanjay MR, Siengchin S. Characterization of Alkali-Treated and Untreated Natural Fibers from the Stem of Parthenium Hysterophorus. J Nat Fibers. 2021;18(1):80-90. doi:10.1080/15440478.2019.1612308
    CrossRef
53. Boonsuk P, Sukolrat A, Bourkaew S, et al. Structure-properties relationships in alkaline treated rice husk reinforced thermoplastic cassava starch biocomposites. Int J Biol Macromol. 2021;167:130-140. doi:10.1016/j.ijbiomac.2020.11.157
    CrossRef
54. Rahman M, Islam M, Huque M, Hamdan S, Ahmed A. Effect of chemical treatment on rice husk (RH) reinforced polyethylene (PE) composites. BioResources. 2010;5(2):854-869. doi:10.15376/biores.5.2.854-869
    CrossRef
55. Emdadi Z, Asim N, Yarmo MA, Sopian K. Effect of Chemical Treatments on Rice Husk (RH) Water Absorption Property. Int J Chem Eng Appl. 2015;6(4):273-276. doi:10.7763/IJCEA.2015.V6.495
    CrossRef
56. Ghani MHA, Royan NRR, Kang SW, Sulong AB, Ahmad S. Effect of Alkaline Treated Rice Husk on the Mechanical and Morphological Properties of Recycled HDPE/RH Composite. J Appl Sci & Agric. 2015;10(5):138-144.
57. Liao Z, Song G, Shi F, et al. Preparation and Characterization of PLA /Rice Straw Fiber Composite. Appl Mech Mater. 2011;71-78:1154-1157. doi:10.4028/www.scientific.net/AMM.71-78.1154
    CrossRef
58. Cholachagudda VV, A UP, Ramalingaiah. MECHANICAL CHARACTERISATION OF COIR AND RICE HUSK REINFORCED HYBRID POLYMER COMPOSITE. Rev Int Pesqui Inovadora Em Ciênc Eng E Tecnol. 2013;2(8):3779-3786. Accessed May 3, 2024. https://portuguese.rroij.com/abstract/mechanical-characterisation-of-coir-and-rice-husk-reinforced-hybrid-polymer-composite-46671.html
59. Wang L, He C, Yang X. Effects of pretreatment on the soil aging behavior of rice husk fibers/polyvinyl chloride composites. BioResources. 2019;14(1):59-69. doi:10.15376/biores.14.1.59-69
    CrossRef
60. Cholachagudda V. V, Ramalingaiah, P.U. Ecocompatible, Biodegradable Polymers. Plastic Items. Preparation & Characterization. Accessed May 3, 2024. https://core.ac.uk/reader/14698480
61. Hill CAS, Khalil HPSA, Hale MD. A study of the potential of acetylation to improve the properties of plant fibres. Ind Crops Prod. 1998;8(1):53-63. doi:10.1016/S0926-6690(97)10012-7
    CrossRef
62. Maziad N, El-Nashar D, Sadek E. The effect of a silane coupling agent on properties of rice husk-filled maleic acid anhydride compatibilized natural rubber/low-density polyethylene blend. J Mater Sci. 2009;44:2665-2673. doi:10.1007/s10853-009-3349-3
    CrossRef
63. Srisuwan Y, Baimark Y, Suttiruengwong S. Toughening of Poly(L-lactide) with Blends of Poly(-caprolactone-co-L-lactide) in the Presence of Chain Extender. Galli C, ed. Int J Biomater. 2018;2018:1294397. doi:10.1155/2018/1294397
    CrossRef
64. Ming-Zhu P, Chang-Tong M, Xu-Bing Z, Yun-Lei P. Effects of Rice Straw Fiber Morphology and Content on the Mechanical and Thermal Properties of Rice Straw Fiber-High Density Polyethylene Composites. J Appl Polym Sci. 2011;121:2900-2907. doi:10.1002/app.33913
    CrossRef
65. Petchwattana N, Covavisaruch S, Chanakul S. Mechanical properties, thermal degradation and natural weathering of high density polyethylene/rice hull composites compatibilized with maleic anhydride grafted polyethylene. J Polym Res. 2012;19:9921. doi:10.1007/s10965-012-9921-6
    CrossRef
66. Park BD, Wi SG, Lee KH, Singh AP, Yoon TH, Kim YS. X-ray photoelectron spectroscopy of rice husk surface modified with maleated polypropylene and silane. Biomass Bioenergy. 2004;27(4):353-363. doi:10.1016/j.biombioe.2004.03.006
    CrossRef
67. Rosa S, Santos E, Ferreira CA, Nachtigall S. Studies on the Properties of Rice-Husk-Filled-PP Composites - Effect of Maleated PP. Mater Res-Ibero-Am J Mater - MATER RES-IBERO-AM J MATER. 2009;12(3):333-338. doi:10.1590/S1516-14392009000300014
    CrossRef
68. Joseph K, Thomas S, Pavithran C. Effect of chemical treatment on the tensile properties of short sisal fibre-reinforced polyethylene composites. Polymer. 1996;37(23):5139-5149. doi:10.1016/0032-3861(96)00144-9
    CrossRef
69. Paul A, Joseph K, Thomas S. Effect of surface treatments on the electrical properties of low-density polyethylene composites reinforced with short sisal fibers. Compos Sci Technol. 1997;57(1):67-79. doi:10.1016/S0266-3538(96)00109-1
    CrossRef
70. Sreekala MS, Kumaran MG, Joseph S, Jacob M, Thomas S. Oil palm fibre reinforced phenol formaldehyde composites: influence of fibre surface modifications on the mechanical performance. Appl Compos Mater. 2000;7:295-329. doi:https://doi.org/10.1023/A:1026534006291
    CrossRef
71. Elfaleh I, Abbassi F, Habibi M, et al. A comprehensive review of natural fibers and their composites: An eco-friendly alternative to conventional materials. Results Eng. 2023;19:101271. doi:10.1016/j.rineng.2023.101271
    CrossRef
72. Yadav J, Singh PBR. Study on Comparison of Boiler Efficiency Using Husk and Coal as Fuel in Rice Mill. SAMRIDDHI J Phys Sci Eng Technol. 2015;2(2):1-15. doi:10.18090/samriddhi.v2i2.1600
    CrossRef
73. Shwetha MK, Geethanjali HM, Kuldeep Chowdary KC. A great opportunity in prospective management of rice husk. INTERNATIONAL JOURNAL OF COMMERCE AND BUSINESS MANAGEMENT. 2014;7(1):176-180.
74. Prasara-A J, Grant T. Comparative life cycle assessment of uses of rice husk for energy purposes. Int J Life Cycle Assess. 2011;16:493-502. doi:10.1007/s11367-011-0293-7
    CrossRef
75. Soltani N, Bahrami A, Pech-Canul MI, González LA. Review on the physicochemical treatments of rice husk for production of advanced materials. Chem Eng J. 2015;264:899-935. doi:10.1016/j.cej.2014.11.056
    CrossRef
76. Patil R, Dongre R, Meshram J. Preparation of Silica Powder from Rice Husk. IOSR J Appl Chem.:26-29.
77. Ugheoke B, Onche E, NAMESSAN O, Asikpo A. Property Optimization of Kaolin - Rice Husk Insulating Fire - Bricks. Leonardo Electron J Pract Technol. 2006;9:167-178.
78. Tongpoothorn W, Sriuttha M, Homchan P, Chanthai S, Ruangviriyachai C. Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties. Chem Eng Res Des. 2011;89(3):335-340. doi:10.1016/j.cherd.2010.06.012
    CrossRef
79. Le Van K, Luong T. Activated carbon derived from rice husk by NaOH activation and its application in supercapacitor. Prog Nat Sci Mater Int. 2014;24:191-198. doi:10.1016/j.pnsc.2014.05.012
    CrossRef
80. Alvarez J, Lopez G, Amutio M, Bilbao J, Olazar M. Physical Activation of Rice Husk Pyrolysis Char for the Production of High Surface Area Activated Carbons. Ind Eng Chem Res. 2015;54(29):7241-7250. doi:10.1021/acs.iecr.5b01589
    CrossRef
81. Mehta A, Ugwekar DRP. Extraction of Silica and other related products from Rice Husk. Int J Eng Res App. 2015;5(8):43-48.
82. Munaf E, Zein R. The Use of Rice Husk for Removal of Toxic Metals from Waste Water. Environ Technol. 1997;18(3):359-362. doi:10.1080/09593331808616549
    CrossRef
83. Lata S, Samadder SR. Removal of Heavy Metals Using Rice Husk: A Review. Int J Environ Res Dev. 2014;4(2):165-170.
84. Chuah TG, Jumasiah A, Azni I, Katayon S, Thomas Choong SY. Rice husk as a potentially low-cost biosorbent for heavy metal and dye removal: an overview. Desalination. 2005;175(3):305-316. doi:10.1016/j.desal.2004.10.014
    CrossRef
85. Srivastava A, Agrawal P, Rahiman A. Delignification of rice husk and production of bioethanol. Int J Innov Res Sci Eng Technol. 2014;3(3):10187-10194.
86. Rozman HD, Lee MH, Kumar RN, Abusamah A, Ishak ZAM. The Effect of Chemical Modification of Rice Husk with Glycidyl Methacrylate on the Mechanical and Physical Properties of Rice Husk-Polystyrene Composites. J Wood Chem Technol. 2000;20(1):93-109. doi:10.1080/02773810009349626
    CrossRef
87. Toro P, Abarca R, Murillo O, Yazdani-Pedram M. Study of the morphology and mechanical properties of polypropylene composites with silica or rice-husk. Polym Int. 2005;54:730-734. doi:10.1002/pi.1740
    CrossRef
88. Razavi?Nouri M, Jafarzadeh Dogouri F, Oromiehie A, Ershad-Langroudi A. Mechanical Properties and Water Absorption Behaviour of Chopped Rice Husk Filled Polypropylene Composites. Iran Polym J Engl Ed. 2006;15(9):757-766.
89. Yang HS, Kim HJ, Park HJ, Lee BJ, Hwang TS. Effect of compatibilizing agents on rice-husk flour reinforced polypropylene composites. Compos Struct. 2007;77(1):45-55. doi:10.1016/j.compstruct.2005.06.005
    CrossRef
90. Crespo JE, Sánchez L, García D, López J. Study of the Mechanical and Morphological Properties of Plasticized PVC Composites Containing Rice Husk Fillers. J Reinf Plast Compos. 2008;27(3):229-243. doi:10.1177/0731684407079479
    CrossRef
91. Ashori A, Nourbakhsh A. Mechanical behavior of agro?residue?reinforced polypropylene composites. J Appl Polym Sci. 2009;111:2616-2620. doi:10.1002/app.29345
    CrossRef
92. Yussuf A, Massoumi I, Hassan A. Comparison of Polylactic Acid/Kenaf and Polylactic Acid/Rise Husk Composites: The Influence of the Natural Fibers on the Mechanical, Thermal and Biodegradability Properties. J Polym Environ. 2010;18:422-429. doi:10.1007/s10924-010-0185-0
    CrossRef
93. Khalf AI, Ward AA. Use of rice husks as potential filler in styrene butadiene rubber/linear low density polyethylene blends in the presence of maleic anhydride. Mater Des 1980-2015. 2010;31(5):2414-2421. doi:10.1016/j.matdes.2009.11.056
    CrossRef
94. Ahmad M, Rahmat A, Hassan A. Mechanical Properties of Unplasticised PVC (PVC-U) Containing Rice Husk and an Impact Modifier. Polym Polym Compos. 2010;18(9):527-536. doi:10.1177/096739111001800908
    CrossRef
95. Rout AK, Satapathy A. PHYSICAL AND THERMAL CHARACTERIZATION OF RICE HUSK FILLED EPOXY MATRIX COMPOSITES. In: ; 2011.
96. Hardinnawirda K, Aisha IS. Effect of Rice Husks as Filler in Polymer Matrix Composites. J Mech Eng Sci. 2012;2:181-186. doi:10.15282/jmes.2.2012.5.0016
    CrossRef
97. Ofem M, Umar M, Friday, Ovat F. Mechanical Properties of Rice Husk Fiiled Cashew Nut Shell Liquid Resin Composites. J Mater Sci Res. 2012;1(4):89-97. doi:10.5539/jmsr.v1n4p89
    CrossRef
98. Santiagoo R, Ismail H, Kamarudin H. Effects of Acetic Anhydride on the Properties of Polypropylene(PP)/Recycled Acrylonitrile Butadiene(NBRr)/Rice Husk Powder(RHP) Composites. Polym-Plast Technol Eng. 2012;51(12):1-8. doi:10.1080/03602559.2012.698685
    CrossRef
99. U. A, A O, Azeez T, C. A, Onukwuli O, C. M. EFFECT OF RICE HUSK FILLER ON MECHANICAL PROPERTIES OF POLYETHYLENE MATRIX COMPOSITE. Int J Curr Res Rev. 2013;5(15):111-118.
100. Duy Tran T, Dang Nguyen M, Thuc CNH, Thuc HH, Dang Tan T. Study of Mechanical Properties of Composite Material Based on Polypropylene and Vietnamese Rice Husk Filler. J Chem. 2013;2013:e752924. doi:10.1155/2013/752924
     CrossRef
101. Majeed K, Hassan A, Bakar A. Influence of maleic anhydride grafted polyethylene compatibilizer on the tensile, oxygen barrier, and thermal properties of rice husk and nanoclay filled low density polyethylene composite films. J Plast Film Sheeting. 2014;30:120-140. doi:10.1177/8756087913494083
     CrossRef
102. Tong J, Rajendran Royan NR, Ng C, Ab Ghani M, Ahmad S. Study of the Mechanical and Morphology Properties of Recycled HDPE Composite Using Rice Husk Filler. Adv Mater Sci Eng. 2014;Volume 2014:1-6. doi:10.1155/2014/938961
     CrossRef
103. Chen RS, Ab Ghani M, Salleh M, Ahmad S, Tarawneh M. Mechanical, Water Absorption, and Morphology of Recycled Polymer Blend Rice Husk Flour Biocomposites. J Appl Polym Sci. 2015;132:41494. doi:10.1002/app.41494
     CrossRef
104. Bisht N, Gope PC. Effect of Alkali Treatment on Mechanical Properties of Rice Husk Flour Reinforced Epoxy Bio-Composite. Mater Today Proc. 2018;5(11, Part 3):24330-24338. doi:10.1016/j.matpr.2018.10.228
     CrossRef
105. Raghu N, Kale A, Chauhan S, Aggarwal PK. Rice husk reinforced polypropylene composites: mechanical, morphological and thermal properties. J Indian Acad Wood Sci. 2018;15(1):96-104. doi:10.1007/s13196-018-0212-7
     CrossRef
106. Jain N, Somvanshi KS, Gope PC, Singh VK. Mechanical characterization and machining performance evaluation of rice husk/epoxy an agricultural waste based composite material. J Mech Behav Mater. 2019;28(1):29-38. doi:10.1515/jmbm-2019-0005
     CrossRef
107. Yap S, Sreekantan S, Hassan M, Sudesh K, Ong MT. Characterization and Biodegradability of Rice Husk-Filled Polymer Composites. Polymers. 2020;13:104. doi:10.3390/polym13010104
     CrossRef
108. Abdul Azam F ’Atiqah, Rajendran Royan NR, Yuhana NY, Mohd Radzuan N, Ahmad S, Bakar A. Fabrication of Porous Recycled HDPE Biocomposites Foam: Effect of Rice Husk Filler Contents and Surface Treatments on the Mechanical Properties. Polymers. 2020;12:475. doi:10.3390/polym12020475
     CrossRef
109. Flach MV, Krauspenhar E, Jahno VD. Recycling of waste from the rice chain: incorporation of rice husk and rice husk ash in polymeric composites. Ciênc E Nat. 2022;44:e8. doi:10.5902/2179460X68817
     CrossRef
110. Shah AUR, Jalil A, Sadiq A, et al. Effect of Rice Husk and Wood Flour on the Structural, Mechanical, and Fire-Retardant Characteristics of Recycled High-Density Polyethylene. Polymers. 2023;15(19):4031. doi:10.3390/polym15194031
     CrossRef
111. Mai Nguyen Tran T, M.N. P, Lee D, Song J. Effect of hybrid eco?friendly reinforcement and their size on mechanical and flame retardant properties of polypropylene composites for technical applications. Polym Compos. 2023;45(3):2427-2443. doi:10.1002/pc.27930
     CrossRef
112. Development of lignocellulosic-plastic composite from rice husk and polyethylene. Clean Circ Bioeconomy. 2023;6:100054-100054. doi:10.1016/j.clcb.2023.100054
     CrossRef
113. Velmurugan G, Karunakaran P, Sampath PS, Varahamoorthi R. Experimental Study of Sugarcane Bagasse Fiber with Rice Husk and Wood Powder Polymer Matrix Composite. J Nat Fibers. 2023;20(2):2224977. doi:10.1080/15440478.2023.2224977
     CrossRef
114. Choo HH, Sreekantan S, Appaturi JN. Preparation, characterization and biodegradability of acrylate graft rice husk/ lignin reinforced PBAT. J Polym Res. 2023;30(10):377. doi:10.1007/s10965-023-03760-0
     CrossRef