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Abstract

The research explores the development and performance evaluation of polyvinyl alcohol (PVA) based composites reinforced with basalt fiber and silane treated biocarbon filler. The composites were fabricated using a hand lay-up technique and characterized for mechanical, dielectric, magnetic and electromagnetic interference (EMI) shielding properties. A progressive increase in reinforcement was employed across five composite formulations (P, PF, PFB1, PFB2 and PFB3) with varying biocarbon content. Among the fabricated specimens, PFB2 comprising 50 vol. % basalt fiber and 2 vol. % silane treated biocarbon demonstrated the best overall performance, with a tensile strength of 147 MPa, flexural strength of 163 MPa, impact energy of 5.0 J, shore-D hardness of 90, dielectric permittivity of 4.4, magnetic permeability of 4.30 and EMI shielding effectiveness of 65.92 dB. These enhancements are attributed to improved filler dispersion, optimized interfacial bonding and synergistic reinforcement effects from silane treatment. The results suggest that such hybrid composites are promising candidates for structural applications requiring superior mechanical integrity, dielectric behaviour and EMI shielding efficiency.

Keywords

Basalt fiber SEM silane PVA EMI shielding

Introduction

The rapid advancement of modern electronics, telecommunication systems, and wearable technologies has resulted in growing concerns over electromagnetic interference (EMI), which can degrade the performance of nearby devices, compromise data integrity, and even pose risks to human health. As a result, the development of lightweight, efficient, and environmentally sustainable EMI shielding materials has become a research priority.¹ Traditional shielding materials such as metals are effective but suffer from limitations like high density, corrosion susceptibility, and poor flexibility, prompting researchers to explore polymer-based composites as promising alternatives. Polyvinyl alcohol (PVA), a water-soluble synthetic polymer, has gained attention as a viable matrix for advanced composites owing to its excellent film-forming ability, biodegradability, good dielectric properties, and compatibility with both natural and synthetic fillers.² However, neat PVA lacks sufficient mechanical robustness and functional conductivity required for structural and shielding applications. To address these limitations, reinforcing PVA with high-performance fibers and conductive fillers has emerged as an effective strategy.

Basalt fiber, derived from the molten lava of volcanic rocks through controlled extrusion processes, has recently emerged as an alternative to traditional reinforcements such as glass or carbon fiber. It possesses remarkable tensile strength, high thermal stability, good chemical resistance, and is considered environmentally friendly due to its natural origin and energy-efficient production.³ Its inorganic, non-toxic nature also makes it an excellent candidate for structural applications where fire retardancy and environmental safety are crucial. Incorporating basalt fiber into polymer matrices can significantly enhance the load-bearing capacity and durability of the resulting composites, making them suitable for demanding engineering applications. For example, Zhao et al.⁴ reported enhanced mechanical and thermal performance in basalt fiber composites using CNT–graphene bridging. Finite element analysis showed a von Mises stress reduction from 375 MPa to 347 MPa, indicating improved structural integrity and heat transfer due to effective nanoscale interfacial reinforcement. Similarly, Lin et al.⁵ demonstrated that incorporating laser-induced graphene (LIG) into basalt fiber reinforced composites significantly improved EMI shielding effectiveness. With one LIG layer, shielding increased to ∼20 dB, and with three layers, it reached ∼50 dB within the X-band frequency range, also enabling ballistic impact damage detection. Likewise, Blackman et al.⁶ investigated the influence of fiber length and content on basalt fiber reinforced polyamide 6, 6 composites. They found that 12 mm fibers at 23 wt.% and 30 wt.% yielded higher tensile strength and modulus, whereas 3 mm fibers at 30 wt.% led to a 25% increase in flexural strength, highlighting the role of fiber morphology in mechanical performance.

In parallel, the inclusion of carbonaceous fillers in polymer matrices has shown potential in enhancing electrical conductivity and electromagnetic shielding. In this study, biocarbon was selected as the functional filler owing to its sustainable origin, tunable surface chemistry, and favorable electrical conductivity when properly treated.⁷ The biocarbon used here was synthesized from dried eucalyptus leaves, a biomass resource abundant in many regions and known for its fast growth and high carbon content. The leaves were carbonized at controlled temperatures and subsequently surface-functionalized using chemical activation techniques to improve dispersion and interfacial bonding within the PVA matrix.⁸ Functionalization not only enhances compatibility with hydrophilic polymers like PVA but also introduces polar groups that contribute to dipolar polarization, aiding in EMI shielding through absorption mechanisms. For instance, Saleheen et al.⁹ developed pine cone–derived biocarbon-based nanocomposite films with high thermal stability and electrical conductivity, achieving a DC conductivity of 73.5 × 10⁻² S/cm, independent of dye concentration. Likewise, Dahal et al.¹⁰ reported that hemp biocarbon-filled, hemp fiber-reinforced biopolymer composites showed a 50% increase in tensile strength at a filler particle size of 75 µm, while larger particles led to strength reduction. Similarly, Balajikrishnabharathi et al.¹¹ found that composite VB3, reinforced with 2 vol% abaca bract biocarbon and 40 vol% pineapple mat fiber in a vinyl ester matrix, exhibited superior mechanical performance with a tensile strength of 143 MPa, flexural strength of 184 MPa, compression strength of 161 MPa, and impact energy of 4.31 J.

Combining basalt fibers with surface-functionalized eucalyptus leaf-derived biocarbon within a PVA matrix is anticipated to yield a hybrid composite with enhanced multifunctional properties. While basalt fibers contribute to mechanical reinforcement, the biocarbon serves as a key element for dielectric and EMI shielding performance. The synergy between the high aspect ratio of the fiber and the electrically active filler is expected to address both structural and functional requirements in a single material platform. This study aims to fabricate and characterize such a hybrid composite and investigate the influence of basalt fiber and functionalized biocarbon on the mechanical, dielectric, magnetic, and EMI shielding behavior of the PVA-based system. Through a detailed analysis of material morphology, interfacial interactions, and electromagnetic response, the work contributes to the ongoing effort to develop lightweight, sustainable, and high-performance shielding materials suitable for next-generation electronic and structural applications.

Experimental procedure

Materials and methods

The composite system was fabricated using polyvinyl alcohol (PVA) resin (Model: PVA-1799, Sigma scientific solutions, Coimbatore, India) as the primary matrix due to its notable mechanical strength, film forming capability and resistance to chemical degradation. All analytical grade chemicals utilized in the synthesis were obtained from Sigma scientific solutions. Eucalyptus leaves, used for biocarbon synthesis were sourced from GreenEarthAgro Tech Pvt. Ltd., India. These leaves were first cleaned, dried and then subjected to controlled pyrolysis in a nitrogen atmosphere at 450 ± 5°C to yield high-purity biocarbon powder which was subsequently ball-milled to an average particle size of 20 µm. Basalt fiber, selected as the main reinforcement material due to its high tensile strength and superior thermal stability was procured from Fiber Rock composites, Bengaluru, India (Grade: BFR-600GSM filament diameter: 13 µm weave: plain). All fabrication and test processes were carried out under controlled laboratory conditions, maintaining a constant temperature of 25 ± 2°C and relative humidity of 50 ± 5%. Further procedural details, including material preparation and composite stacking sequences are elaborated in the upcoming sections.

Synthesis of biocarbon

Eucalyptus leaves were initially collected and thoroughly washed with distilled water to eliminate surface contaminants and adhered impurities. The cleaned leaves were then oven-dried to eliminate residual moisture. Once fully dried, the leaves were ground into smaller fragments using mechanical grinder to facilitate uniform pyrolysis process. The pyrolysis process was conducted in three controlled phases under continuous nitrogen (N₂) atmosphere to prevent oxidation. In the first phase, the ground eucalyptus leaf material was heated to 180°C, effectively removing volatile organic compounds and unstable constituents. In the second phase, the temperature was raised to 430°C, which promoted the decomposition of cellulose and hemicellulose components.¹² Finally, in the third phase, the temperature was gradually increased at a controlled rate of 6°C per minute until it reached 680°C ensuring complete carbonization of the biomass. Following the pyrolysis process, the obtained biocarbon was allowed to cool naturally to room temperature. To enhance particle size uniformity and surface area, the carbonized product was subjected to high-energy ball milling, which reduced agglomerates and yielded finely powdered biocarbon suitable for composite reinforcement. The entire process for extracting biocarbon from eucalyptus leaves is illustrated in Figure 1. Figure 2 presents the FESEM image of the biocarbon particles revealing irregular and rough structure.

Figure 1.

Synthesis of biocarbon from eucalyptus leaves.

Figure 2.

FESEM of biocarbon particles.

Surface modification of biocarbon

For the silane surface modification of biocarbon, 3 wt. % of silane coupling agent (3-APTMS) was dissolved in ethanol to form the silane solution. The solution’s pH was adjusted to between 4 and 5 using few drops of 4 N acetic acid. The biocarbon particles were then immersed in the solution for 15 minutes to facilitate silane bonding onto their surface.¹³ After treatment, the biocarbon was filtered and rinsed thoroughly with distilled water to remove excess silane residues. Finally, the silane treated biocarbon was dried in a hot air oven at 130°C to remove retained moisture. Figure 3 illustrates the surface modification of biocarbon.

Figure 3.

Surface modification of biocarbon.

Fabrication of PVA composites

The basalt fiber and biocarbon reinforced PVA composite was fabricated using the hand lay-up technique. A release agent was first applied to a 200 × 200 × 3 mm rubber mold to facilitate easy demolding. Initially, PVA was dissolved in distilled water and continuously stirrer at 55°C. Eucalyptus derived biocarbon was then added to the solution and uniformly dispersed using magnetic stirrer at 400 rpm to ensure homogeneous mixture.¹⁴ This mixture was poured into the mold and evenly spread to minimize void formation. Subsequently, a basalt fiber mat was place over the resin surface. This layering process was repeated until the composite reached a final thickness of 3 mm. The composite was then cured at room temperature, followed by post curing in a hot air oven at 120°C for 20 min. Table 1 outlines the composite designations used in the fabrication. Table 1 presents the labelling of specimens.

Table 1.

Labelling of specimens.

Composite designation	Reinforcements
P	100 vol. % PVA
PF	50 vol. % PVA, 50 vol. % basalt fiber
PFB1	49 vol. % PVA, 50 vol. % basalt fiber, 1 vol. % biocarbon
PFB2	48 vol. % PVA, 50 vol. % basalt fiber, 2 vol. % biocarbon
PFB3	47 vol. % PVA, 50 vol. % basalt fiber, 3 vol. % biocarbon

Characterizations

The fabricated composites were trimmed to the required dimensions using a CNC Aquajet model G3020 cutting machine, following the appropriate ASTM standards. The prepared specimens were subjected to mechanical, dielectric, magnetic and EMI shielding tests. Five samples were analysed for each test. Figure 4 presents the test specimens of the PVA composites.

Figure 4.

Test specimens prepared.

Mechanical characteristics

Tensile and flexural tests were performed on the composites in compliance with ASTM D638 and D790 standards to assess their mechanical behavior. Tensile test specimens measuring 250 × 25 mm were made in a rectangular shape. The flexural specimens were 125 × 12.5 mm in size. A universal testing machine (INSTRON, UK) was used for these tests, and the cross head speed was set at 1.5 mm/min. The QC-639 series impact tester was used to measure impact strength in accordance with ASTM D256, and the Shore-D durometer (Blue Steel, India) was used to measure hardness in accordance with ASTM D2240.

Dielectric properties

Dielectric behaviour was analysed using an LCR HI-Tester (HIOKI-3532-50, Japan). Five specimens from each composite were tested according to ASTM D150 and average values were reported to evaluate dielectric performance.

Magnetic properties

A vibrating sample magnetometer (VSM, Lakeshore, USA) was used to test the magnetic characteristics of the flexible PVA composites by subjecting them to magnetic fields ranging from 4000 to 12000 G. The electrical permittivity and magnetic permeability were calculated using the scattering parameters (S11, S12, S21, and S22).

EMI shielding effectiveness

EMI shielding effectiveness was evaluated using ME 7868 A distributed modular 2-Port Vector Network Analyzer (VNA), along with a shielding effectiveness test fixture. Measurements were conducted in accordance with ASTM D4935. For each composite, five readings were taken and standard deviation was indicated by error bars on the corresponding graphs.

Results and discussions

Mechanical characteristics

Figures 5 and 6 shows the mechanical properties with their significant analysis. The mechanical performance of the PVA-based composites demonstrated significant improvements with the incorporation of basalt fibers and silane treated biocarbon filler. The control specimen P, composed entirely of PVA, exhibited tensile strength of 54 MPa. With the addition of 50 vol. % basalt fiber (Specimen PF), the tensile strength increased to 110 MPa, 124% improvement due to the high stiffness and effective stress transfer capability of basalt fibers.¹⁵ Introducing 1 vol. % silane treated biocarbon filler in specimen PFB1, further elevated the tensile strength to 132 MPa (144.4% increase). This enhancement is attributed to the improved dispersion of the biocarbon particles and strong chemical bonding between the silane treated filler and the PVA matrix, which minimizes interfacial defects and promotes efficient load transfer. Furthermore, specimen PFB2 containing 2 vol. % biocarbon filler, achieved maximum tensile strength of 147 MPa (172% increase), as the optimized filler content provided a better reinforcing effect through synergistic interactions between the silane modified filler and basalt fibers.¹⁶ However, in specimen PFB3 with 4 vol. % biocarbon filler, the tensile strength slightly declined to 140 MPa (159.2% increase). This reduction is likely due to the agglomeration of excess filler, which causes localized stress concentrations and limits further reinforcement effectiveness despite silane treatment. Additionally, nonlinear responses are observed in the composites, particularly with increasing biocarbon content which is essential to evaluate the yield stress, which indicates the onset of plastic deformation. The neat PVA specimen (P) exhibited a yield stress of 41 MPa, consistent with its viscoelastic nature and low resistance to plastic flow. With the incorporation of basalt fiber (PF), the yield stress increased to 89 MPa, due to the fiber’s high stiffness and load bearing ability.¹⁷ In specimens containing silane treated biocarbon filler, the yield stress improved further. PFB1 and PFB2 recorded yield stresses of 107 MPa and 121 MPa respectively, reflecting enhanced interfacial bonding and stress transfer between matrix and fillers. However, in PFB3, the yield stress slightly decreased to 116 MPa likely due to the biocarbon agglomeration which led to premature localized yielding. These trends demonstrate that while the addition of reinforcing agents elevates the composite’s strength, the optimal filler concentration not only enhances tensile strength but also maximizes the composite’s ability to resists yielding, a critical property for load bearing and impact resistant applications.

Figure 5.

Mechanical properties of the samples.

Figure 6.

Student’s t test distribution.

A similar pattern was observed in flexural strength. The neat PVA specimen P showed a flexural strength of 69 MPa. Incorporation of basalt fiber in PF increased it to 130 MPa (% improvement), owing to enhanced bending resistance from the rigid fiber network. The addition of 1 vol. % silane treated biocarbon in PFB1 improved the flexural strength to 146 MPa (% increase), while specimen PFB2 reached the highest value of 163 MPa (%). This increase is due to the combined effect of the silane treated filler enhancing matrix rigidity and improving fiber-matrix interaction.¹⁸ In PFB3, the flexural strength slightly dropped to 157 MPa (%), which again attributed to filler agglomeration disrupting stress distribution.

The Izod impact energy of the composites showed a dramatic rise with the addition of reinforcing agents. The base specimen P absorbed only 0.58 J, whereas PF showed 2.81 J (% increase), highlighting the role of fibers in absorbing and distributing impact energy. Specimen PFB1 recorded an impact energy of 3.9 J (% increase), while PFB2 peaked at 5.0 J (% increase), indicating that silane treated biocarbon introduced effective crack-bridging and deflection mechanisms.¹⁹ In PFB3, the energy dropped slightly to 4.6 J (%) due to filler clustering which reduced energy dissipation efficiency despite surface functionalization.

Hardness values showed modest yet consistent enhancement. The shore-D hardness of specimen P was 79. Further, PF showed a small increase to 82 (%) due to the inherent stiffness of basalt fibers. With 1 vol. % silane treated biocarbon, specimen PFB1 recorded 87 (%), and PFB2 reached a peak value of 90 (%). The increase is credited to improved matrix densification and interfacial bonding from the silane treatment.²⁰ Furthermore, in PFB3, the hardness slightly increased to 95 (%). Although filler agglomeration is present, surface hardness improved resistance to indentation. Figure 5 presents the overview of mechanical properties across all composite configurations.

‘T’ Test analysis between the groups

Tensile strength PPB1 vs. PPB2

There is a rejection of H0 since the p-value is less than α. There is a discrepancy between the two groups’ average populations, according to this analysis. Statistical significance is achieved when there is a large enough difference between the sample means of Group 1 and Group 2. Because p(x ≤ T) = 1.405e-14, the p-value is 2.81e-14. Type I error, defined as rejecting a true H0, is very unlikely to occur, with a probability of 2.81e-14 (2.8e-12%). The strength of support for H1 increases as the p-value decreases. The 95% confidence interval ([-2.1009:2.1009]) does not contain the test statistic T, which is −21.475. Not within the 95% acceptability interval of [-1.3696:1.3696] is the value x1-x2 = −14. S’ = 0.652, the standard deviation of the difference, is utilised to compute the statistic. Not only is that, but the 9.6-point effect size d rather large. This shows that there is a substantial disparity between the average and its counterpart.

Tensile strength PPB2 vs. PPB3

Not inside the 95% acceptability range of [-1.3696:1.3696] is the value of x1-x2 = 15. S’ = 0.652, the standard deviation of the difference, is utilised to compute the statistic. With a value of 10.29, the effect size d is quite large. This shows that there is a substantial disparity between the average and its counterpart.

Flexural strength PPB1 vs. PPB2

There is a rejection of H0 since the p-value is less than α. There is a discrepancy between the two groups’ average populations, according to this analysis. Statistical significance is achieved when there is a large enough difference between the sample means of Group 1 and Group 2. A p-value of 9.986e-18 is obtained using the formula p(x ≤ T) = 4.993e-18. Type I error, defined as rejecting a true H0, is very unlikely to occur, with a probability of 9.986e-18 (1e-15%). The strength of support for H1 increases as the p-value decreases. Without being inside the 95% confidence interval of [-2.1009:2.1009], the test statistic T = −33.7465 cannot be accepted. In the 95% confidence interval [-1.3696:1.3696], x1-x2 = −22 does not belong. S’ = 0.652, the standard deviation of the difference, is utilised to compute the statistic. With a value of 15.09, the effect size d is really large. This shows that there is a substantial disparity between the average and its counterpart.

Flexural strength PPB2 vs. PPB3

There is a rejection of H0 since the p-value is less than α. There is a discrepancy between the two groups’ average populations, according to this analysis. Statistical significance is achieved when there is a large enough difference between the sample means of Group 1 and Group 2. Assuming that p(x ≤ T) = 1, the p-value is 1.589e-12. With a probability of 1.589e-12 (1.6e-10%), the likelihood of a type I error (the rejection of a correct H0) is low. The strength of support for H1 increases as the p-value decreases. The 95% confidence interval ([-2.1009:2.1009]) does not contain the test statistic T, which is 16.9822. The value of x1-x2 = 13 does not fall within the 95% confidence interval of [-1.6083:1.6083]. The statistic is computed using the standard deviation of the difference, S’, which is 0.766. With a value of 7.59, the effect size d is quite large. This shows that there is a substantial disparity between the average and its counterpart.

Izod impact PPB1 vs. PPB2

There is a rejection of H0 since the p-value is less than α. There is a discrepancy between the two groups’ average populations, according to this analysis. Statistical significance is achieved when there is a large enough difference between the sample means of Group 1 and Group 2. Because p(x ≤ T) = 1.128e-7, the p-value is 2.257e-7. The probability of making a type I error (rejecting a valid null hypothesis) is negligible, with a value of 2.257e-7, or 0.000023%. The strength of support for H1 increases as the p-value decreases. The 95% confidence interval (CI) for the test statistic T is not filled with values between −2.0244 and 2.0244 (−6.2932). The equation x1-x2 = −2 does not fall inside the 95% confidence interval of [-0.6434:0.6434]. Consider the statistic to be S’ = 0.318, the standard deviation of the difference. With a value of 1.99, the effect size d is quite large. This shows that there is a substantial disparity between the average and its counterpart.

Izod impact PPB2 vs. PPB3

Consider the statistic to be S’ = 0.318, the standard deviation of the difference. With a value of 1.09, the effect size d is really large. This shows that there is a substantial disparity between the average and its counterpart.

Hardness PPB1 vs. PPB2

There is a rejection of H0 since the p-value is less than α. There is a discrepancy between the two groups’ average populations, according to this analysis. Statistical significance is achieved when there is a large enough difference between the sample means of Group 1 and Group 2. Given that p(x ≤ T) = 0.000001392, the p-value is 0.000002784. With a probability of 0.000002784 (0.00028%), the likelihood of a type I error (the rejection of a correct H0) is minimal. The strength of support for H1 increases as the p-value decreases. With a value of −4.9752, the test statistic T does not fall inside the 95% confidence interval of [-1.9845:1.9845]. The equation x1-x2 = −1 does not fall inside the 95% confidence interval of [-0.3989:0.3989]. The statistic is calculated using the standard deviation of the difference, which is S’ equals 0.201. There is a big impact size d, 1. This shows that there is a substantial disparity between the average and its counterpart.

Hardness PPB2 vs. PPB3

There is a rejection of H0 since the p-value is less than α. There is a discrepancy between the two groups’ average populations, according to this analysis. Statistical significance is achieved when there is a large enough difference between the sample means of Group 1 and Group 2. The p-value is 1.551e-16, with a significance level of p(x ≤ T) = 7.755e-17. With a probability of 1.551e-16 (1.6e-14%), the likelihood of a type I error (the rejection of a correct H0) is low. The strength of support for H1 increases as the p-value decreases. With a value of −9.9504, the test statistic T does not fall inside the 95% confidence interval of [-1.9845:1.9845]. The equation x1-x2 = −2 does not fall inside the 95% confidence interval of [-0.3989:0.3989]. The statistic is calculated using the standard deviation of the difference, which is S’ equals 0.201. With a value of 1.99, the effect size d is quite large. This shows that there is a substantial disparity between the average and its counterpart.

Figure 7 (a), corresponding to specimen P reveals a relatively smooth matrix surface with the presence of multiple voids, indicating poor compaction and weak structural cohesion. These voids act as stress concentration sites, which likely contribute to the lower mechanical strength observed. Fiber pull-out is evident in specimen PF (Figure 7(b)), indicating weak interfacial adhesion between the PVA matrix and the basalt fibers. This inadequate adhesion impairs stress transfer across the interface, leading to suboptimal tensile and flexural properties. Figure 7(c) representing PFB1 shows reduced voids but still reveals partial delamination indicating that while the silane treatment begins to improve filler matrix interaction, some microstructural discontinuities remain.²¹ Figure 7(d)), corresponding to PFB2 exhibits a well-integrated morphology with significantly improved adhesion between the filler and matrix. The silane treatment enhances chemical bonding at the interface leading to uniform dispersion of biocarbon, fewer voids and improved stress transfer. These features collectively contribute to better mechanical performance. Overall, the SEM confirms that incorporating basalt fibers along with silane treated biocarbon filler enhances the composite’s microstructure by reducing defects, improving filler matrix bonding and minimizing delamination. Among the samples, PFB2 demonstrates the most optimized morphology, aligning with its superior mechanical and functional characteristics.

Figure 7.

SEM micrographs of the specimens.

Dielectric properties

The dielectric properties of the composite materials show a progressive enhancement with the incorporation of basalt fibers and silane treated biocarbon filler as illustrated in Figure 8. The control specimen P, exhibits a dielectric permittivity of 2.65 and dielectric loss of 0.48 indicating limited dipolar polarization within the pure polymer matrix. In specimen PF, the dielectric permittivity increases to 3.4 and dielectric loss to 0.59 due to the higher intrinsic dielectric constant of basalt and increased interfacial polarization.²² The addition of 1 vol. % biocarbon in specimen PFB1 further improves the dielectric permittivity to 3.62 and dielectric loss of 0.64. This enhancement is attributed to better interfacial adhesion and charge trapping efficiency resulting from silane functionalization, which promotes more effective interfacial polarization. With 2 vol. % silane treated biocarbon in specimen PFB2, the dielectric permittivity rises significantly to 4.4 and dielectric loss increases to 0.70, highlighting the role of well dispersed filler in intensifying the Maxwell-Wagner-Sillars (MWS) polarization. The highest values are observed in specimen PFB3, containing 4 vol. % silane treated biocarbon, where the dielectric permittivity reaches 4.9 and dielectric loss is 0.75. These improvements are primarily due to the synergistic effect of basalt fibers and chemically modified biocarbon, which enhance interfacial compatibility increase localized charge storage, and facilitate dipolar and interfacial polarization mechanisms.²³ On overall, the results confirm that silane treated biocarbon not only boosts dielectric performance but also aids in achieving a better balance between charge storage and energy dissipation, making these composites suitable candidates for advanced dielectric.

Figure 8.

Dielectric characteristics of various specimens.

Magnetic permeability

Specimens PFB1, PFB2 and PFB3 containing increasing amounts of silane-functionalized biocarbon, exhibit progressively enhanced magnetic responses as shown in Figure 9. For the real part of magnetic permeability, PFB1 records values of 2.12 at 8 Hz, 2.70 at 12 Hz, 3.20 at 16 Hz and 3.75 at 20 Hz. This increase is due to silane treatment promoting better interfacial bonding and dispersion thereby facilitating smoother magnetic flux pathways.²⁴ In PFB2, the real permeability further improves to 2.50, 3.0, 3.63 and 4.30 across the same frequency range. The increased filler loading, combined with enhanced compatibility due to silane treatment, strengthens inter particle magnetic interactions and domain connectivity, resulting in more efficient flux alignment. PFB3, containing 4 vol. % filler, shows the highest permeability values upto 2.81, 3.25, 3.81 and 4.65. While this indicates strong magnetic flux conduction, excessive filler lead to partial agglomeration, introducing microstructural irregularities that limit uniform domain growth despite the improved surface chemistry.

Figure 9.

Magnetic permeability of the specimens.

In PFB1, it ranges from 0.48 to 1.27 over 8 to 20 Hz. Additionally, PFB2 shows values between 0.58 and 1.37, while PFB3 reaches the highest losses of 0.73 to 1.63. The silane treated biocarbon aids in effective dispersion and interface bonding, contributing to stronger magnetic behaviour but also slightly higher intrinsic losses.²⁵ Overall, these results highlight the potential of silane treated biocarbon in tuning the magnetic properties of polymer composites for electromagnetic and shielding applications.

Electromagnetic interference (EMI) effect

As shown in Figure 10, the absorption, reflection, and overall shielding effectiveness of the composites were measured over frequencies of 8, 12, 16, and 18 GHz in order to evaluate their EMI shielding performance. The base specimen P, composed entirely of 100 vol. % PVA, exhibited low shielding performance, with absorption values of 8, 14, 17 and reflection values ranging from 2.5 to 5.55 across the frequency range. The resulting total shielding effectiveness ranged from 15.03 to 30.14 dB, primarily due to the non-conductive nature of PVA which lacks the ability to attenuate or reflect electromagnetic radiation effectively.²⁶ In specimen PF, the EMI shielding improved with absorption values of 11, 16, 21 and 25 and increased reflection values of 3.32, 9.2, 7.67 and 7.5 leading to total shielding effectiveness between 18.18 and 40.32 dB. This enhancement is attributed to the intrinsic dielectric nature of basalt fibers which promotes interfacial polarization and contributes to better scattering and reflection of incident EM waves. Further enhancement is observed in specimen PFB1 with 1 vol. % silane treated biocarbon records absorption values of 13, 17, 25 and 28 and reflection values of 4.8, 11.8, 10.56 and 12.76 resulting in total shielding effectiveness ranging from 20.21 to 50.76 dB. The silane functionalization improves the dispersion and interfacial adhesion of biocarbon within the matrix, facilitating a more effective conductive network and enhancing interfacial polarization.²⁷ In specimen PFB2, shielding performance reaches its peak: absorption increases to 18, 25, 37 and 40, while reflection improves to 5.43, 18.90, 14.87 and 16.89, yielding the highest total shielding values of 30.08, 45.17, 60.32 and 65.92 dB across the respective frequencies. This optimum performance results from the synergistic effect of basalt fibers and uniformly dispersed, chemically bonded biocarbon filler which maximizes energy dissipation and reflection through enhanced interfacial interactions. However, in specimen PFB3, a decline in shielding performance is observed. Absorption values drop to 14, 19, 28 and 31 while reflection values reduce to 4.8, 14.8, 11.7 and 14.34 leading to comparatively lower total shielding effectiveness. These findings highlight the importance of optimizing silane treated biocarbon content to achieve balanced EMI shielding performance through controlled dispersion and strong interfacial bonding.

Figure 10.

EMI shielding efficacy of the specimens.

Comparative analysis

Table 2 presents the comparative analysis of the prior works which are taken as a reference.

Table 2.

Comparative analysis of prior research.

Author	Research	Results	Reference
Du et al.	Structural health monitoring of CFRP composites using MXene& CNT modified silk fabric.	Mode II fracture toughness increased upto 54% enhancing crack detection and interlaminar properties	²⁸
Song et al.	Surface modified CFF and SNWF hybrid composites for improved mechanical and EMI shielding properties.	Tensile strength increased to 626.7 MPa, EMI shielding effectiveness of 50 dB at 2 mm	²⁹
Huang et al.	CF/SF/CIP epoxy composites with interlayer hybrid structure for EMI shielding and mechanical performance.	EMI shielding of 34.9 dB, tensile strength of 339.9 MPa, impact strength of 98.2 kJ/m²	³⁰
He et al.	Multiscale surface-modified CF/GF hybrid fibers in PU matrix using PVA-GO-OCNT for mechanical enhancement.	Tensile hybrid effect changed from −5.4% to + 4.3%, strain effect from −2.1% to + 2.1%.	³¹
Zhang et al.	Flexible, porous silk fabric-based conductive composites for multimodal sensing and EMI shielding	Detected strain as low as 0.05%; responsive to humidity (0-85% RH), temperature; EMI shielding + Joule heating features for smart electronics.	³²

Conclusion

The integration of basalt fiber and silane treated biocarbon into the PVA matrix significantly enhanced the composite’s multifunctional performance, with notable improvements in mechanical strength, dielectric properties, magnetic behaviour and EMI shielding effectiveness. Among all formulations, the composite labelled PFB2 comprising 2 vol. % silane treated biocarbon exhibited the most balanced and superior properties including a tensile strength of 147 MPa, flexural strength of 163 MPa, impact energy of 5.0 J, hardness of 90 shore-D, dielectric permittivity of 4.4, magnetic permeability of 4.30 and EMI shielding effectiveness of 65.92 dB. These enhancements are primarily attributed to the synergistic reinforcement and improved interfacial bonding facilitated by silane treatment which ensured uniform filler dispersion and efficient stress transfer. While higher filler loading in PFB3 improved surface hardness, it led to particle agglomeration and a slight decline in other properties, confirming that PFB2 is the optimal configuration for multifunctional applications such as EMI shielding enclosures, electronic substrates and structural components demanding a combination of mechanical and electromagnetic performance.

Footnotes

Author contributions

S. Mohanasundaram and Dhandapany Sendil Kumar – Research and manuscript preparation

Manoj Kumar S and Indira Priyadarsini – Experimental testing

B. Sachuthananthan and N. Nagabhooshanam – Material procurement and preparation

VaraprasadBhemuni and Yaswanth K.K. – Writing and editing.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

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

ORCID iD

KK Yaswanth

Data Availability Statement

All data are included within the manuscript*.

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Hybrid PVA composites with basalt fiber and functionalized biocarbon: Mechanical strengthening and EMI shielding efficiency

Abstract

Keywords

Introduction

Experimental procedure

Materials and methods

Synthesis of biocarbon

Surface modification of biocarbon

Fabrication of PVA composites

Characterizations

Mechanical characteristics

Dielectric properties

Magnetic properties

EMI shielding effectiveness

Results and discussions

Mechanical characteristics

‘T’ Test analysis between the groups

Tensile strength PPB1 vs. PPB2

Tensile strength PPB2 vs. PPB3

Flexural strength PPB1 vs. PPB2

Flexural strength PPB2 vs. PPB3

Izod impact PPB1 vs. PPB2

Izod impact PPB2 vs. PPB3

Hardness PPB1 vs. PPB2

Hardness PPB2 vs. PPB3

Dielectric properties

Magnetic permeability

Electromagnetic interference (EMI) effect

Comparative analysis

Conclusion

Footnotes

Author contributions

Declaration of conflicting interests

Funding

ORCID iD

Data Availability Statement

References