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Abstract

The present study investigates the role of silicon carbide (SiC) extracted from macadamia nut shells and natural short fibers in reinforcing polyvinyl alcohol (PVA) composites. The composite materials were prepared by integrating SiC, derived through pyrolysis and chemical processing, with PVA and natural fibers to evaluate their mechanical, thermal, dielectric, and electromagnetic interference (EMI) shielding properties. The prepared composites performance is evaluated as per ASTM standard. The result demonstrated that the ideal ratio of matrix, fibers f 40 vol%, and 3 vol% silicon carbide, PCS2 had the maximum tensile strength (142 MPa), tear strength (33 MPa), Izod impact strength (4.7 Joules (J)), and Shore-D hardness (82). Additionally, PCS2 had the highest EMI shielding performance, peaking at 64.84 dB at 18 GHz, as a result of the fibers and fillers working in concert to increase wave absorption and reflection through improved interfacial bonding and polarization. While, the composite PCS3 with reinforcement of 40 vol% of fiber and 5 vol% of SiC shows improved thermal conductivity of 0.23 W/mK, and maximum dielectric permittivity of 4.8 and dielectric loss of 0.73. This work emphasizes the potential of natural fibers and SiC obtained from macadamia shells as high-performance, sustainable fillers in innovative composite materials and it could be applied in areas such as communication, military, signal processing and navigation performance.

Keywords

Composite SiC fiber mechanical dielectric shielding effectiveness SEM

Introduction

New technological development towards the faster communication networks, educate the importance of protection of human from radio wave frequency, otherwise it will harm to environmental conditions. Generally, the electric and electronic device are working under the electrical and magnetic wave signal frequency. when there is any leakages, are interruption occurs between waves, the operational working efficiency of the devices gets affects, this interference is called electromagnetic interference (EMI).¹ Thus, the Electromagnetic interference (EMI) shielding is mainly applied in electric and electronic based equipment to reduce such electromagnetic interference and improves working efficiency of the material. Traditionally, metal-based EMI shielding is utilized, which are high dense and costlier. In order to produce an cost effective and less dense based EMI shielding the fiber and filler reinforced polymer composite material utilized.^2,3 There were various studies has been carried out using polymer composite because of their significance. Mainly the electromagnetic shielding aredepends upon the wave absorption and reflection characters of the composite material. Thus, the incorporation of conductive fillers and fibers into the polymer matrix influences the wave absorption and reflection effectiveness of the composite.⁴ Because of producing light weight, easy degradable, and circular economy-based compounds, as well as better strengthen composite, the natural fiber is utilized into the EMI shielding polymer composite. Generally, the natural fibers extracted from the stem, leaf, fruit, and root part of the plants. Celosia cristata is an ornamental plant which is native to India, flower is used as decorating and stem part is used to extracting the fiber.⁵ For example, Permata et al.⁶ conducted a study on coconut fiber reinforced polymer composite for EMI shielding application. The study reported coir fiber of 15 wt.% shows maximum shielding effectiveness of −7.69 dB, and tensile strength of 26.7 MPa for adding 5 wt.% of coir fiber. Similarly, the kenaf fiber of 16 (v/v) and carbon nano tubes of 15 wt.% reinforced composite resulted maximum EMI shielding effectiveness of 30 dB, according to Singh et al.⁷ study investigation. Furthermore, Nagaraju et al.⁸ has reported that increase in content of silicon carbide along with carbon fiber reinforced epoxy composite shows better EMI shielding effectiveness of −49.6 dB. Likewise, the composite material developed using silicon carbide infused natural loofah sponge and their shielding effectiveness, thermal conductivity properties are examined by Li et al.⁹ This ceramic particle and natural loofah sponge reinforcement provides better flexural strength of 8.4 MPa, electromagnetic shielding effectiveness of 68.4 dB respectively.

Moreover, the reinforcement of fossil fuel based conventional fillers such as graphite, carbon, other silicon-based particle, etc, shows certain defects. That is, these advantageousandstrength improving properties of filler particle has created pollution in the environment when comes to degradation. To mitigate such issues, the natural biomass extracted filler particle such as biocarbon, biosilica, other silicon-based compounds, etc., are studied.¹⁰ Thebio extracted filler particles are not only eco-friendly but also enhance strength features of the composite. For instance, silicon carbide is a ceramic material having high hardness strength and wear resistant property. Furthermore, the mechanical characteristics of polymer composites, such as their hardness and tensile strength, and thermal stability propertiesare enhanced by this silicon carbide SiC,by ensuring that the material doesn’t deteriorate under stress.¹¹ Therefore, the present study explored bio extracted SiC particle as conductive filler for EMI shielding applications from Macadamia shell nut. Macadamia nut is a flowering plant family, Proteaceae and indigenous to Australia. Macadamia nut has thick grounded shell contains silicious compound when comes to the decomposition process.¹² Due to their improved features in silicon carbide, the present study extracted from it. However, there was no such study done on bio extracted SiC filler particle reinforced composite for EMI shielding applications. Table 1 presents the comparison analysis of previous literatures.

Table 1.

Comparative analysis of previous literatures.

Author	Reinforcing material	Results	Reference
Karthick et al.	Moringa pod microfiber + dragon-fruit biocarbon	Tensile strength ≈74 MPa; dielectric constant: 5.4 → 2.1 (8–20 GHz); EMI SE: 16.7 dB @8 GHz, 54.5 dB @20 GHz — ∼113% and ∼75% improvement over neat PVA	[13]
Naqvi et al.	Ti₃C₂T_x (MXene)–PVA composites	EMI SE: hydrogel 70 dB @10 GHz; film 40 dB; aerogel 21 dB; tensile strength (film): 56 MPa	[14]
Shubhadaet al.	PVA/PEG/PANI @ WO₃ nanocomposite film	Conductivity: 5.55 × 10^-5 S/m → improved by 77.8%; EMI SE: 1.00 → 1.32 dB	[15]

Thus, the present study fills the research gaps by extracting the filler and fiber through natural means, fiber from Celosia cristata stem part and fillers from Macadamia shell nut. In addition to this, the study aims is to explores the mechanical, wear, and shielding effectiveness performance of the composite, and it will help further more research study on EMI shielding composite using natural fiber and filler particle. This study could be applied in areas where electric and electronic equipment are majorly employed for communication, military, signal processing and navigation performance.

Experimental procedure

From this section, the raw material used and their details are highlighted, and the process involved in extraction of fiber, filler and fabrication of composite, and their testing procedures are also highlighted in the subsequent section.

Source material

The EMI shielding composite material is prepared by using Polyvinyl alcohol (PVA) has matrix which was in pellets form by adding distilled water the PVA solution is prepared. The PVA has density of 1.91–1.31 g/cm³, melting point of 200°C and it was purchased from Atulya chemicals, Chennai, India. The Celosia cristata flowering plant used to extract the fiber and it was purchased from Green orchids nursery and garden centre, Chennai, India. The filler particle silicon carbide was prepared from Macadamia nut shell which is procured from Rudra agro nursery, Pune, India. The other chemical additives using throughout the extraction process is procured from Herenba chemical instruments, Chennai, India.

Preparation of fiber

The fiber is extracted from the stem part of the Celosia cristata flowering plant. The stem part is first dissected from the Celosia cristata plant, and defoliated the unwanted leaves flowers from it, a wash it under clean water. Now the cleaned stem part of plant is submerged into the distilled water for 8 days at a room temperature condition and this process is called retting. Thus, retting process utilized for breaking down the non-fibrous tissues around the fiber for easier extraction. After retting, manually scrape or peel off the softer outer bark. Additionally, delicately hand-separate the fibers from the woody core. Finally, the separated fiber is dried under hot air oven for removing the moisture content, then the dried fiber is combed and cut into short form of size 10 mm.¹⁶ The process involved in the extraction procedure was represented under Figures1 and 2 represents Optical microscope of Celosia cristata fibre prepared.

Figure 1.

Extraction of fiber from Celosia cristata.

Figure 2.

Optical microscope of Celosia cristata fibre prepared.

Preparation of filler particles

The filler particle silicon carbide is extracted from Macadamia nut shell and the process involved during preparation is represented in Figure 3. There were three process involved in silicon carbide extraction such as carbonization, silicon impregnation, and carbo thermal reduction. In order to promote the breakdown of the organic components into carbon and volatile gas, the dried husk was burned at temperatures ranging from 250 to 800°C in a low in oxygen atmosphere. This process is called as carbonization. This carbonized substance forms silicon carbide (silicon impregnation process) by absorbing silicon sources such as silicon dioxide. The silicon-impregnated material is then heated to a temperature exceeding 1400°C in an inert atmosphere as part of a carbo-thermal reduction process.¹⁷ This technique creates silicon carbide and CO gas when silicon-impregnated materials react with a reducing agent that contains carbon. Figure 4 shows the FESEM image of SiC particles prepared. The particles are in finer spherical shape has size ranges between 100–200 nm.

Figure 3.

Process flowchart of silicon carbide preparation.

Figure 4.

FESEM image of SiC particles.

Composite Development

After the preparation of fiber and filler, the composite material is fabricated by under hand layup method. The extracted silicon carbide filler particle is mixed into PVA matrix by using magnetic stirrer for 1 h at 65°C. Then, the extracted fiber is mixed into filler reinforced PVA matrix for 20 min at 60°C. The fiber and filler particle reinforced PVA matrix is poured into the wax coated mold for easy removal. Now the composite is allowed to cured at room temperature for a whole day. Similar procedure is followed for various concentration of fiber and filler reinforced PVA matrix composite. Table 2 represents fiber and filler reinforced PVA matrix at various volume percentage.¹⁸

Table 2.

Fiber and filler reinforced PVA matrix composite.

Composite designation	PVA (vol%)	Celosia cristatashort fiber (vol%)	Silicon carbide (vol%)
P	100	–	–
PCS0	60	40	–
PCS1	59	40	1
PCS2	57	40	3
PCS3	55	40	5

Testing of material and its procedure

The prepared composite material performance is analysed by using ASTM standard, and testing involved such as tensile, tear, hardness, dielectric, thermal conductivity, and EMI shielding effectiveness. The tensile test is conducted under universal testing machine (UTM), FIE, UNITEK, United Kingdom. The testing are carried out as per ASTM standard D638, the average of five testing are carried out for each composite specimen to better evaluating their performance. Further, the tear strength of the composite is analysed as per ASTM D1922 by using Electronic Elmendorf tearing strength tester Gester-C11A, UK. Ten samples are cut from the composite film in both the transverse and machine directions. The tester clamps down on a sample that has been placed inside. The sample has a slit made in it that extends 43 mm from the far edge using a cutting knife in the tester. For the slit to spread across the remaining 43 mm, the pendulum is released. The average tearing force is determined by the pendulum’s energy loss. Further, hardness strength of the composite is evaluated as per ASTM standard D2240, under Shore-durometer scale. By an average ten sample is tested for each specimen to identified the accuracy. The thermal conductivity of the composite is assessed based on Lee disc method. On average of five sample is evaluated for each testing specimen. The dielectric test are conducted using Nicholson-Rose-Weir (Agilent/HP E8362B, 3–18 GHz Measuring range). And each specimen is evaluated by taking average of eight sample by cutting a specimen to 14 mm diameter. A high-frequency Vector Network Analyzer (VNA), namely the ME 7868A distributed modular 2-port VNA, purchased from Anristu, India, was used to evaluate the scattering characteristics and EMI shielding effectiveness of each PVA matrix composite testing specimen. Figure 5 represents the testing specimen of composite PCS2.

Figure 5.

Testing specimen of composite PCS2.

Result analysis

Mechanical properties

The mechanical properties of the composites demonstrated significant enhancements with the incorporation of celosia cristata short fibers and silicon carbide (SiC), with variations depending on the volume fraction of fillers in each specimen. For the neat PVA matrix, composite P (100% PVA), the tensile strength was 57 MPa, tear strength was 21 MPa, izod impact strength was 0.37 J, and Shore-D hardness was 76. These values represent the baseline properties of unreinforced PVA, which lacks reinforcements to improve strength, impact resistance, or hardness.¹⁹ With the addition of 40 vol% celosia cristata short fibers in composite PCS0, the tensile strength nearly doubled to 113 MPa, a 98% increase compared to composite P. This improvement is attributed to the efficient stress transfer from the matrix to the fibers. Tear strength also increased from 21 MPa to 26 MPa, a 24% improvement, as the fibers helped resist crack propagation.²⁰ The most dramatic improvement was observed in izod impact strength, which rose from 0.37 J to 2.81 J, representing a remarkable 659% increase. This highlights the ability of the fibers to absorb and dissipate impact energy effectively. Additionally, the Shore-D hardness increased slightly to 78, demonstrating the enhanced resistance to surface deformation due to the fibers.

Further improvements were observed in composite PCS1, which contained 1 vol% SiC in addition to the 40 vol% fibers. The tensile strength increased to 125 MPa, showing a 120% improvement over composite P. The presence of SiC improved interfacial adhesion, further enhancing the load transfer efficiency. Tear strength also rose to 29 MPa, a 38% improvement compared to the neat PVA matrix. Izod impact strength increased to 3.6 J, an 873% increase, as the SiC particles complemented the fibers in dissipating impact forces.²¹ The Shore-D hardness improved further to 80, reflecting the combined stiffening effect of the fibers and SiC.

Composite PCS2 with 3 vol% SiC showed the best overall performance across all tests. The tensile strength peaked at 142 MPa, a 149% increase compared to composite P, due to the optimal balance between the matrix, fibers, and SiC particles.²² Tear strength also reached its highest value of 33 MPa, a 57% improvement over the neat PVA. The izod impact strength reached an exceptional 4.7 J, representing a 1169% increase, as the interaction between fibers and SiC particles effectively dissipated impact energy. Shore-D hardness increased to 82, indicating the highest deformation resistance at this composition. Figure 6 shows the mechanical properties of various composite specimens.

Figure 6.

Mechanical properties of various composite specimens.

However, with composite PCS3 with 5 vol% SiC, a slight decline in some properties was observed. The tensile strength dropped to 136 MPa, which, although still a 138% improvement compared to composite P, was lower than PCS2 due to possible agglomeration of SiC particles that created stress concentration points. Tear strength decreased slightly to 31 MPa, a 48% increase compared to composite P, while izod impact strength reduced to 4.3 J, reflecting a 1062% improvement. Despite the decline in other properties, the Shore-D hardness increased to 85, the highest among all specimens, as the higher SiC content contributed to the composite’s surface stiffness.

Figure 7 presents the SEM micrographs of the PVA composites, highlighting differences in microstructure and filler distribution across various formulations. Figure 7(a) shows the neat PVA matrix (Composite P), which exhibits a smooth and homogeneous surface, indicating the absence of reinforcing agents and a lack of interfacial complexity. In contrast, Figure 7(b) depicts Composite PCS0, incorporating 40 vol% Celosia cristata short fibers, where significant fiber pull-out and tearing are observed. This fiber debonding suggests a key energy-dissipation mechanism during impact loading, where the fiber pull-out length (approximately 50 μm) facilitates greater impact energy absorption by increasing frictional sliding and enlarging the matrix deformation zone.

Figure 7.

(a–d) SEM fracture analysis of mechanical properties of composites.

Figure 7(c) illustrates the microstructure of Composite PCS2, which integrates both 40 vol% fibers and 3 vol% silicon carbide (SiC) particles. Here, a synergistic reinforcement mechanism is evident: SiC particles are well-dispersed and exhibit strong adhesion to the surrounding PVA matrix. These particles enhance interfacial shear strength through physical anchoring, forming mechanical interlocks that bridge microgaps between the fiber and matrix.²³ This improves load transfer efficiency, particularly at the optimal 3% content, where the inter-particle spacing minimizes agglomeration and allows uniform stress distribution. The combined effect of fiber reinforcement and rigid SiC particles results in a tensile strength of 142 MPa, marking a 149% improvement over pure PVA.

Moreover, the impact strength of PCS2 (4.7 J), representing an 1169% increase compared to the neat matrix, can be attributed to the synergistic energy-dissipation mechanisms involving both fiber pull-out and the crack-deflection capability of SiC particles. These hard particulates act as crack-arresting or deflection points, altering the crack propagation path and increasing the energy required for complete failure. Finally, Figure 7(d) presents PCS3 with 5 vol% SiC, where agglomeration of filler particles is clearly visible. This disrupts filler-matrix uniformity, creates local stress concentration zones, and consequently reduces mechanical performance relative to PCS2. These microstructural observations correlate strongly with the mechanical and thermal performance, highlighting the importance of filler dispersion and matrix-fiber-particle interaction in enhancing composite behavior.

The SEM micrographs in Figure 8(a) and (b) offer critical insights into the interfacial behavior between the Celosia cristata fibers, silicon carbide (SiC) fillers, and the PVA matrix. In Figure 8(a), the SEM image of the extracted fibers reveals a relatively clean, fibrillated surface morphology, which enhances mechanical interlocking and promotes effective adhesion with the polymer matrix.²⁴ These surface features are essential for efficient stress transfer and interfacial polarization during electromagnetic interaction. Figure 8(b), showing the fractured surface of the fiber- and filler-reinforced composite, highlights the distribution and bonding quality of the reinforcement phases. The uniform embedding of fibers and presence of a highly reacted particle phase of SiC indicate strong interfacial adhesion, with minimal fiber pull-out or interfacial voids. This well-integrated morphology suggests excellent phase cohesion and matrix continuity, which are crucial for achieving superior tensile strength, impact resistance, and EMI shielding effectiveness. The compact microstructure and reduced crack propagation paths further support the role of robust interfacial bonding in maintaining mechanical integrity and enhancing dielectric and thermal properties. In contrast, any occurrence of microvoids, fiber debonding, or filler agglomeration could compromise load transfer and diminish both polarization efficiency and shielding performance.²⁵ Overall, the SEM observations confirm that optimized interfacial interactions and the presence of a reactive filler phase are key contributors to the composite’s multifunctional behavior.

Figure 8.

FESEM images of fibre, particle interface with polymer matri.

Thermal conductivity

The thermal conductivity of the composites decreased significantly with the addition of Celosia cristata short fibers and silicon carbide, demonstrating the effectiveness of these reinforcements in reducing the heat transfer capacity of the PVA matrix. For the neat PVA matrix, composite P with 100% PVA, the thermal conductivity was measured at 0.45 W/mK. This value reflects the inherent thermal conductivity of PVA, which, as a polymer, already has relatively low thermal conductivity compared to metallic or ceramic materials.²⁶ But with the inclusion of 40% by volume of celosia cristata short fibers in composite PCS0, the thermal conductivity reduced slightly to 0.42 W/mK, showing a reduction of about 7%. This decrease is attributed to the lower thermal conductivity of the fibers compared to the matrix, which interrupted the continuity of heat conduction pathways within the composite. The addition of 1 vol% of silicon carbide in composite PCS1, alongside 40 vol% fibers, further reduced the thermal conductivity to 0.37 W/mK, corresponding to an 18% reduction compared to the neat PVA. This decline is a result of the silicon carbide particles acting as additional barriers to heat flow by disrupting the matrix structure and scattering phonons, which are the primary carriers of heat in polymers.²⁷

Composite PCS2, with 40 vol% fibers, and 3 vol% silicon carbide, showed a marked decrease in thermal conductivity to 0.27 W/mK, representing a 40% reduction compared to composite P. At this composition, the synergistic effect of the fibers and a higher concentration of silicon carbide particles significantly hindered the heat transfer by creating more interfaces and scattering sites within the composite. In composite PCS3, with 5 vol% silicon carbide, the thermal conductivity decreased further to 0.23 W/mK, the lowest among all the specimens, corresponding to a 49% reduction compared to the neat PVA. The increased concentration of silicon carbide particles further disrupted the heat conduction pathways within the matrix. Figure 9 shows the thermal conductivity values of various composite specimens.

Figure 9.

Thermal conductivity values of various composite specimens.

Dielectric properties

The dielectric properties of the composites, including dielectric permittivity and dielectric loss, show a consistent increase with the addition of Celosia cristata short fibers and silicon carbide, indicating enhanced polarization within the material due to the inclusion of these reinforcements. For composite P, the neat PVA matrix with 100% PVA, the dielectric permittivity was measured at 2.63, and the dielectric loss was 0.45. These values reflect the baseline properties of PVA, which inherently possesses moderate dielectric properties due to its molecular structure and limited ability to support polarization under an applied electric field.²⁸ The introduction of 40% by volume of celosia cristata short fibers in composite PCS0 increased the dielectric permittivity to 3.1, representing an 18% rise compared to the neat PVA. This enhancement is attributed to the fibers’ ability to increase the polarization of the composite material by introducing additional interfaces between the fibers and the matrix, which facilitate dipole alignment under the electric field. The dielectric loss also increased to 0.56, reflecting a 24% rise, which is explained by the increased energy dissipation due to interfacial polarization at the fiber-matrix interfaces.

Composite PCS1 with 1 vol% silicon carbide further increased the dielectric permittivity to 3.51, an improvement of 34% compared to composite P. This enhancement is due to the inherent dielectric properties of silicon carbide, which contribute to higher charge storage capacity and polarization within the material. The dielectric loss also rose to 0.62, showing a 38% increase compared to the neat PVA. This increase is linked to the enhanced interfacial polarization caused by the introduction of silicon carbide particles, which act as additional sites for charge accumulation and dissipation.²⁹ In composite PCS2, with 3 vol% silicon carbide, the dielectric permittivity reached 4.1, reflecting a 56% increase compared to the neat PVA. This significant improvement results from the combined effect of increased fiber and silicon carbide content, which amplify the number of interfaces and improve the overall charge storage ability of the composite. The dielectric loss also increased to 0.67, marking a 49% rise, due to the further increase in interfacial polarization and charge relaxation processes at higher filler content. Composite PCS3, containing 5 vol% silicon carbide, showed the highest dielectric permittivity at 4.8, representing an 83% improvement over composite P. This increase is a result of the higher concentration of silicon carbide particles, which intensify the polarization effects within the composite. Similarly, the dielectric loss reached 0.73, indicating a 62% increase compared to the neat PVA. The rise in dielectric loss at this composition is attributed to the increased energy dissipation at higher filler content due to the intensified polarization and charge relaxation mechanisms. Figure 10 represents the Dielectric properties of various composite specimens.

Figure 10.

Dielectric properties of various composite specimens.

EMI shielding

The electromagnetic interference (EMI) shielding performance of the composites was analyzed in terms of absorption, reflection, and total shielding effectiveness across a frequency range of 8 GHz to 18 GHz. The results highlight the improvements achieved through the addition of Celosia cristata short fibers and silicon carbide fillers, with notable differences among the composites. The EMI absorption values increased consistently with the incorporation of fibers and silicon carbide. For composite P, the neat PVA matrix, the absorption ranged from 7 dB at 8 GHz to 17 dB at 18 GHz. This baseline indicates the limited ability of the pure matrix to absorb electromagnetic waves. In composite PCS0, with 40 vol % fibers, the absorption improved to 9 dB at 8 GHz and 20 dB at 18 GHz, showing enhanced wave attenuation due to the addition of the fibers, which introduce dielectric interfaces and scattering centers.³⁰

With the addition of 1 vol % silicon carbide in composite PCS1, the absorption further increased, reaching 10 dB at 8 GHz and 23 dB at 18 GHz. This improvement is attributed to the synergistic effect of silicon carbide, which enhances dielectric losses and improves the material’s ability to dissipate electromagnetic energy. Composite PCS2, with 3 vol % silicon carbide, exhibited the highest absorption values, peaking at 15 dB at 8 GHz and 33 dB at 18 GHz. This significant improvement is due to the optimal combination of fibers and fillers, which creates more interfaces for polarization and energy dissipation.³¹ At 18 GHz in composite PCS2, the reflection value was measured at 15.75 dB, resulting in a total shielding effectiveness (SE_t) of 64.84 dB. Based on this, the separated contributions are as follows:

A b s o r p t i o n l o s s (A) = 33 d B,

R e f l e c t i o n l o s s (R) = 15.75 d B

T for approximately 50.9% of the total EMI shielding, while reflection contributes about 24.3%, with the remainder attributed to minor multiple reflection effects. The enhanced performance in PCS2 can be linked to the optimized conductive network established by the 3 vol % SiC content, achieving an electrical conductivity of approximately 10⁻³ S/m. This semi-percolated structure is sufficient to create effective pathways for charge transport and dielectric loss without causing excessive reflection or filler agglomeration. The silicon carbide particles support both ohmic loss and interfacial polarization, while the fibrous structure introduces dielectric discontinuities that promote multiple scattering. Together, these mechanisms result in enhanced absorption and controlled reflection, indicating a well-balanced EMI shielding profile. However, in composite PCS3, with 5 vol % silicon carbide, the absorption dropped slightly to 11 dB at 8 GHz and 28 dB at 18 GHz, and reflection also declined due to agglomeration of the filler, which disrupts the uniformity of the conductive network and reduces its effectiveness. Figure 11 represents the EMI performance of various composite specimens.

Figure 11.

EMI of various composite specimens.

The reflection values also improved with the addition of fibers and silicon carbide. Composite P exhibited low reflection values, ranging from 2.1 dB at 8 GHz to 5.25 dB at 12 GHz, due to the low conductivity of the neat PVA matrix. For composite PCS0, reflection increased to 3.15 dB at 8 GHz and 8.4 dB at 12 GHz, as the fibers enhanced the conductivity slightly. Composite PCS1 showed further improvement, with reflection values of 4.2 dB at 8 GHz and 11.55 dB at 18 GHz, due to the combined effect of fibers and 1 vol% silicon carbide, which contributed to improved conductivity and electromagnetic wave scattering. Composite PCS2 exhibited the highest reflection, with values ranging from 5.25 dB at 8 GHz to 15.75 dB at 18 GHz, reflecting the enhanced conductivity provided by 3 vol% silicon carbide. In composite PCS3, the reflection values decreased slightly, due to filler agglomeration reducing the material’s conductive network.

The total shielding effectiveness, the sum of absorption and reflection, showed the highest improvement in composite PCS2 due to the optimal combination of 40 vol% fibers and 3 vol% silicon carbide. Composite P exhibited limited shielding, ranging from 14.96 dB at 8 GHz to 29.92 dB at 18 GHz, due to the lack of reinforcements. PCS0 improved to 17.96 dB at 8 GHz and 39.90 dB at 18 GHz as the fibers introduced dielectric polarization and scattering interfaces. PCS1, with 1 vol% silicon carbide, reached 19.95 dB at 8 GHz and 49.88 dB at 18 GHz, benefiting from enhanced conductivity and interfacial polarization. PCS2 peaked at 29.92 dB at 8 GHz and 64.84 dB at 18 GHz, as its balanced composition maximized wave absorption and reflection. PCS3, with 5 vol% silicon carbide, slightly decreased to 24.94 dB at 8 GHz and 54.86 dB at 18 GHz due to filler agglomeration reducing efficiency.

Conclusions

The incorporation of Celosia cristata short fibers and silicon carbide into the PVA matrix led to notable enhancements in mechanical, thermal, dielectric, and EMI shielding properties, with performance varying across composite formulations. Among them, specimen PCS2 exhibited the most balanced performance, achieving the highest tensile strength (142 MPa), tear strength (33 MPa), impact resistance (4.7 J), Shore-D hardness (82), and EMI shielding effectiveness (64.84 dB at 18 GHz). This was attributed to the optimal dispersion and interfacial bonding between the matrix, fibers, and 3 vol % silicon carbide, which promoted efficient stress transfer, polarization, and electromagnetic wave attenuation. In contrast, PCS3, containing 5 vol% silicon carbide, showed superior dielectric behavior and thermal insulation, with the highest dielectric permittivity (4.8), dielectric loss (0.73), and the lowest thermal conductivity (0.23 W/mK). These enhancements resulted from intensified interfacial polarization and disrupted heat conduction pathways due to increased filler content. SEM analysis supported these findings by revealing differences in microstructural uniformity and filler distribution across the composites. Overall, the study confirms that tailoring the fiber–filler ratio and processing conditions can strategically optimize multifunctional properties for applications requiring mechanical durability, thermal insulation, and effective EMI shielding.

Footnotes

Authors’ contributions

Seeniappan Kaliappan, Naveen Kilari: Research. L. Natrayan, M. Muthukannan: Writing and testing. M. Ramya, Sathish Kannan: Material arrangement. Vinayagam Mohanavel, Manzoore Elahi M. Soudagar: Writing

Declaration of conflicting interests

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

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Naveen Kilari

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