Potential of recycled polypropylene: Effect of Gigantochloa scortechinii fiber on the morphology and properties of eco-composite

2.1 Preparation of eco-composites

As shown in Fig. 1, a co-rotating twin-screw extruder (30 mm diameter) was used to compound GSF fiber with the rPP matrix at varying fiber loadings (0-6 wt.%) using a two-step process. The compounding was conducted at a screw speed of 35 rpm, which was selected to ensure effective fiber dispersion while minimizing shear-induced degradation. The temperature profile was set as follows: 150°C (zone 1), 170°C (zone 2), 180°C (zones 3-5), 185°C (zones 6-9), and 190°C (zone 10). The relatively low screw speed facilitated the uniform distribution of bamboo fiber, nanoclay, and PP-g-MA within the matrix, reducing fiber breakage and enhancing interfacial bonding. To ensure process consistency, the initial 5 min of extrudate from each run were discarded before collecting and pelletizing the strands. This controlled processing condition maintained the structural integrity of the composite, resulting in improved mechanical properties.

2.2 Injection moulding processing: Fabrication sample

The experimental trials were conducted using a 50-ton injection molding machine (NP7-1T) with an injection velocity of 250 mm/s and a maximum injection pressure of 1120 bars. The injection molding parameters were systematically optimized based on a Definitive Screening Design (DSD), as detailed in Tables 1 and 2. The fabrication of eco-composites was performed at varying GSF loadings (0-6 wt.%), as outlined in Table 3. Table 1 presents the selected process parameters and their levels, while Table 2 provides the DSD for evaluating the effects of melt temperature, packing pressure, screw speed, filling time, and cooling time on the mechanical performance of rPP-GSF composites. Notably, the packing pressure was adjusted in increments of 1% (equivalent to 1.6 MPa), while the screw speed varied in steps of 1% (corresponding to 2.4 rpm).

2.3 Characterization

The Melt Flow Index (MFI) is a widely used analytical technique in the plastics industry to evaluate the viscosity and flow characteristics of thermoplastic materials, providing insights into their processability. In this study, MFI measurements were conducted at 200°C under a 2.16 kg load, following the ISO 1133 standard. The MFI of rPP was assessed to compare its flow behavior with commercial polypropylene and to evaluate the impact of fiber (GSF) and nanoclay on the composite’s processability. These results were crucial for optimizing the injection molding parameters and understanding how fiber and nanoclay incorporation influence the rheological behavior of rPP-based eco-composites.

XRD analysis was performed to investigate the crystalline structure of the GSF using a Panalytical Xpert3 Powder diffractometer. The instrument features a rotary anode generator with a copper target and a broad-angle powder goniometer. XRD measurements were conducted within the 2θ range of 5–90° at 40 kV and 40 mA, using Cu Kα radiation (λ = 1.5406 Å). This analysis was crucial for determining the degree of crystallinity of GSF, which directly influences its mechanical properties, interfacial bonding with the rPP matrix, and overall composite performance. The crystalline structure assessment also aids in understanding the fiber’s compatibility with polymer matrices and its impact on the thermal and mechanical stability of the developed eco-composites.

Thermal analysis was conducted using a Nitrogen Environment Sample Analysis apparatus, specifically the Perkin Elmer model STA6000, equipped with a nitrogen purge gas system. For each analytical measurement, a specimen mass ranging from 10 to 15 mg was employed. The specimens were subjected to a thermal ramping procedure, increasing from ambient temperature (25°C) to a maximum of 800°C at a controlled rate of 10°C/min. An uninterrupted flow of nitrogen gas, maintained at a rate of 90 mL/min, was sustained throughout the experimental procedure.

FTIR analysis was performed using a Perkin Elmer Frontier 01 spectrometer (Germany) to identify the functional groups present in the composite materials. Spectral data were recorded within the range of 4500-600 cm⁻¹, with a resolution of 4 cm⁻¹ and an average of 32 scans per measurement. This analysis was crucial for detecting chemical interactions between the rPP matrix, GSF, nanoclay, and PP-g-MA. Key observations included the spectra exhibited characteristic peaks corresponding to hydroxyl (-OH), carbonyl (C=O), and C-H stretching, indicating the presence of functional groups from both the polymer matrix and the natural fiber. Shifts in peak positions and changes in intensity suggest hydrogen bonding and possible esterification between the hydroxyl groups of GSF and the polymer matrix, which enhances interfacial adhesion. Additionally, the presence of Si-O stretching peaks confirms the successful incorporation of nanoclay, contributing to improved structural stability. Additionally, shifts in characteristic peaks provided insights into fiber-matrix interactions, confirming the effectiveness of compatibilization and potential improvements in composite bonding.

Flexural three-point bending experiments were conducted using a universal testing apparatus with a capacity of 10 kN (Instron ElectroPuls E10000, Norwood, MA), in accordance with the ASTM D790 standard. The flexural specimen, characterized by a bar shape, exhibited a gauge length of 80 mm, with gauge width and thickness measuring 10 mm and 5 mm, respectively. These experiments were performed at ambient temperature, maintaining an average rate of 2.0417 mm/min across all samples. Calculations for flexural strength, modulus, and elongation at break were derived from the experimental data. A series of flexural tests was conducted on five samples for each distinct composition.

An impact test was performed according to ISO 179 Charpy impact test. Specimens were rectangular bars (80 mm × 10 mm × 5 mm) with a standardized V-shaped notch (2 mm depth, 45° angle) at the midpoint. The impact strength values were reported in kJ/m², following the ISO 179 standard.

3.1 Effect of GSF on crystalline structure

Before the establishment of crystallinity, the rPP samples were evaluated for their MFI to ascertain their quality relative to commercially available polypropylene. The mean MFI of the rPP was determined to be 7.3 g/min, aligning with the prevailing literature and was marginally higher than standard commercial polypropylene. Medium MFI for standard PP typically ranges from 5 to 25 g/10 min, depending on grade and application (Palutkiewicz et al., 2024). Moreover, the amalgamation of various polypropylene grades within the recycling stream may result in variable properties and elevated MFI, representing a common obstacle in the recycling process (Geier et al., 2024). The inclusion of pigments, as observed in studies on injection-molded isotactic PP, can also impact the rheological characteristics of PP melts, potentially affecting the MFI (Janostik et al., 2023). Additionally, the crystallization dynamics (rPP) are influenced by contaminants, which modify the crystallization flow and prolong induction times, as demonstrated in research simulating disposal and recycling scenarios (Veroneze et al., 2022). The integration of additives and degradation byproducts in post-consumer recycled PP, particularly in sectors like food packaging, may also cause fluctuations in MFI and crystallization behaviour (Ignacio et al., 2023). Reactive blending of rPP with other polymers, including poly (ethylene terephthalate) (PET), can further modify the crystallization kinetics and phase morphology, thereby affecting the MFI and overall material attributes (Dehghanpour Baruj et al., 2020)., The presence of foreign particulates and impurities not only influences the MFI but also affects the thermal stability and crystallization behavior of rPP. Some contaminants, such as inorganic fillers or thermally stable residues, may enhance thermal stability by acting as heat-resistant barriers. Others, like low-molecular-weight organic residues, could degrade and reduce stability. These impurities can also alter crystallization mechanisms by serving as nucleating agents or disrupting polymer chain packing. (Veroneze et al., 2022). XRD techniques were employed to investigate the modifications in the physical structure of the fibers, particularly regarding the crystallinity index (CI). Segal et al., 1959 proposed an empirical approach to quantify the crystalline content, as shown in equation (1). Here, I_crystalline represents the maximum intensity of the crystalline peak at diffraction peak 2θ = 16.8°, while I_amorphous represents the intensity of X-ray scattering from the amorphous regions of the specimen, corresponding to the disordered polymer phase without a well-defined crystalline structure. The lowest intensity occurs at peak 2θ = 14°. The crystallite size (D) of the rPP composite with 6 wt.% GSF was determined to be 120.52 nm, and the corresponding CI was calculated as 71.05%. This CI value is comparable to previously reported values for natural fiber-reinforced polypropylene composites, which typically range from 66.3% to 82.10% (Albedah et al., 2024; da Silveira et al., 2023), indicating a moderate level of crystallinity influenced by fiber incorporation.

The XRD analysis of rPP/GSF eco-composites, Fig. 3 illustrates a notable peak shifting phenomenon. This phenomenon is observed in the divergence of the principal diffraction peak locations within the XRD patterns of the eco-composites when compared to those of pristine rPP. Such peak shifting is attributed to variations in the degrees of crystallinity. Specifically, an increase in crystallite size is typically associated with a reduction in degrees of crystallinity, and vice versa. In the context of XRD analysis, microstrain and crystallite size are interrelated through the Williamson-Hall equation (Albedah et al., 2024). This equation is utilized to assess the broadening of diffraction peaks in the XRD pattern, which occurs due to the presence of microstrain and finite crystallite dimensions.

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Fig. 3a.

XRD patterns of rPP and GSF/composites. Figure Caption: XRD patterns of rPP and rPP-based composites with varying GSF content.

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Fig. 3b.

Major peak shifting of XRD patterns for rPP and GSF/composites. Figure caption: Major peak shifting in XRD patterns of rPP and rPP-based composites with varying GSF content.

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The Williamson-Hall equation is articulated as follows:

In equation (2), β denotes the complete width of the diffraction peak at its half-maximum intensity (FWHM), θ represents the Bragg angle, and κ is identified as the shape factor, which is frequently assumed to have a standard value of 0.9. Additionally, λ is the wavelength of the X-ray radiation, and ε indicates the microstrain. The term κλ signifies the broadening of the diffraction peak attributable to the finite dimensions of the crystallites. As the size of the crystallites decreases, the peak broadens, resulting in an elevated β value. Similarly, the term 4ε sinθ reflects the broadening of the diffraction peak arising from the presence of microstrain. Microstrain refers to localized distortions or imperfections within the crystallites, which disrupt the ideal atomic positions and contribute to peak broadening. An increase in microstrain further broadens the peak, leading to a higher β value. Fig. 4 and Table 4 present the crystalline size alongside the microstrain values for various composite samples, providing an assessment of the degree of crystalline phase. It is evident from Fig. 4 that the level of crystallinity increases with the increasing content of GSF in the synthesized eco-composites.

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Fig. 4.

Microstrain and crystallite size of rPP and GSF/composites. Figure caption: Microstrain and crystallite size of rPP and rPP-based composites with varying GSF content.

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The increase in the crystallinity index of the synthesized eco-composites with a higher GSF content suggests improved hydrogen bonding within cellulose chains, thereby enhancing fiber-matrix interactions. Previous studies have documented this phenomenon, where the incorporation of natural fibers into polymer matrices led to an increase in crystallinity due to the formation of stronger interfacial bonding and the alignment of cellulose chains (Albedah et al., 2024). The improved crystallinity is also associated with enhanced mechanical properties and thermal stability, as observed in similar natural fiber-reinforced composites.

3.2 Thermal properties

The characteristics of degradation related to the materials that were synthesized and fabricated have been thoroughly evaluated in connection with the morphological, thermal, and mechanical variations exhibited by the eco-composites produced during this insightful investigation. As shown in Fig. 5, the TGA graph highlights the thermal degradation behavior of rPP along with its corresponding eco-composites, which incorporate varying weight percentages of GSF. Specifically, 0wt.% GSF, 3wt.% GSF, and 6wt.% GSF. These resilient materials were subjected to a comprehensive temperature range, extending from room temperature up to an elevated threshold of 600°C. The decomposition process of these materials is characterized by three distinct and identifiable stages. In Stage I, observed below 265°C, all samples exhibit only a minimal degree of weight loss, resulting from the loss of moisture inside the specimens. Stage II, occurring between approximately 265°C and 450°C, exhibits substantial weight loss corresponding to the primary decomposition of the materials. This transformation is dynamic, with the degradation temperature being lower than that of pure PP (300°C-475°C) (Esmizadeh et al., 2020) but comparable to rPP reinforced with date palm fibers, which decomposes within the range of 280°C-420°C, as reported by (Albedah et al., 2024). Notably, the onset temperature at which substantial weight loss begins shifts to higher values as the content of GSF increases, reflecting an impressive adaptability. Specifically, the materials comprising rPP and 0 wt.% GSF begin decomposition at approximately 300°C, while the eco-composites containing 3 wt.% GSF and 6 wt.% GSF shows the initiation of decomposition at progressively higher temperatures, demonstrating a commendable enhancement in thermal stability afforded by the inclusion of GSF. Stage III, occurring at approximately 450°C, represents the final phase of decomposition, leaving minimal residual weight. The residual weight at 450°C was recorded as 1.04% for sample 1, 2.16% for sample 2, 3.68% for sample 3, and 4.26% for sample 4, indicating the thermal stability and char formation behavior of the composites. The increased content of GSF and the reduction in thermal degradation temperature can be attributed to structural and chemical modifications within the fibers. Higher fiber content typically signifies a rougher fiber surface and greater interaction with the polymer matrix, which may influence thermal stability. These changes have been reported in previous studies (M. Liu et al., 2023; Sethu et al., 2023). Fig. 6(a) presents the microstructural analysis of the eco-composite with 6 wt.% GSF, which reveals visible agglomerates characterized by uneven clustering and localized fiber concentrations. These agglomerates are attributed to the higher volume fraction of GSF, increasing the propensity for clustering within the matrix. In contrast, Fig. 6(b) illustrates the 3 wt.% GSF composites, which exhibit a more homogeneous fiber distribution with minimal evidence of clustering, indicative of superior dispersion. The disparities in microstructure correspond to the observed degradation behavior, whereby the 6 wt.% GSF composite degraded earlier than the 3 wt.% GSF composites but later than the 0 wt.% GSF composite. The earlier degradation of the 6 wt.% composite is likely caused by the detrimental effects of agglomerates on its thermal and mechanical properties, supporting the hypothesized impact of fiber clustering on material performance.

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Fig. 5.

TGA curve of rPP and GSF/composites. Figure caption: TGA curve of rPP and rPP-based composites with varying GSF content.

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Fig. 6a.

FESEM of 6 wt.% GSF composite showing fiber agglomerates. Figure caption: SEM micrograph of the eco-composite with 6 wt.% GSF, showing visible fiber agglomerates characterized by uneven clustering and localized concentrations. These formations indicate reduced dispersion due to the higher volume fraction of GSF.

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Fig. 6b.

FESEM image of 3 wt.% GSF composite showing uniform fiber dispersion. Figure caption: FESEM micrograph of the eco-composite with 3 wt.% GSF, demonstrating a more homogeneous fiber distribution with minimal clustering. The improved dispersion suggests enhanced interaction between fibers and the matrix, contributing to greater stability.

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Table 5 presents a detailed overview of the thermal characteristics of both pure rPP and the fabricated eco-composites made from GSF and rPP. These materials were meticulously analyzed using the differential scanning calorimetry (DSC) technique to determine their thermal properties. The melting temperature (Tm) of pure rPP was found to be 161.07°C. Conversely, the eco-composites incorporate GSF, exhibiting a range of melting temperatures, from 162.06°C to 163.75°C, which aligns well with the typical melting temperatures observed for raw polypropylene materials. The minimal variation in T_m values when GSF and nanoclay were included indicates that these eco-composites possess an adequate level of thermal stability, making them suitable for various processing techniques, including the highly efficient injection molding process. The DSC results further revealed a noticeable decrease in the enthalpy of fusion (ΔH_m) as the content of GSF increases. Pure rPP exhibited a ΔH_m of 108.16 J/g, while the composite containing 6wt.% of GSF showed a significantly reduced ΔH_m of 86.57 J/g. This suggests that the incorporation of GSF fibers disrupts the crystalline structure inherent to rPP. This phenomenon aligns with trends observed in natural fiber eco-composites, where increased fiber content tends to impede crystallinity (Islam & A Gafur, 2023; Venkatesh et al., 2024). However, such a reduction in crystallinity remains acceptable for various industrial applications. The degree of crystallinity (Xc) measured for these eco-composites ranged from 52.25% to 57.74%, indicating a level of crystallinity comparable to raw polypropylene, which typically ranges from 30% to 70%, as highlighted in the findings by Li et al., 2021 & Yao et al., 2021. The obtained Xc values confirm that these eco-composites retain adequate rigidity and structural integrity necessary for successful injection molding, as they remain above the critical threshold of 50%, all while preserving essential mechanical properties such as stiffness and durability. This suggests that these materials can be processed efficiently using standard injection molding techniques, without encountering common issues such as warpage or shrinkage that could compromise the final product quality.

The crystallization temperature (Tc) remains remarkably stable across all samples tested. Pure rPP exhibiting a Tc of 133.33°C, whereas the 0wt.%GSF sample shows a slightly elevated Tc of 133.90°C. The presence of nanoclay appears to enhance the crystallization process slightly, as evidenced by the higher Tc values observed in the nanoclay composites. Conversely, the inclusion of GSF has minimal impact on the crystallization temperature, even with an increase in fiber content.

In conclusion, the comprehensive analysis using DSC demonstrates that rPP eco-composites, which incorporate both nanoclay and GSF cellulose fibers, maintain a high level of thermal stability and crystallinity suitable for the injection moulding process. Although increased fiber content results in reduced crystallinity, the achieved levels remain within acceptable limits for polypropylene materials, ensuring favorable mechanical properties and processability. These findings confirm that the eco-composites can be efficiently injected and processed while achieving an optimal balance between rigidity and flexibility, crucial for various industrial applications.

Fig. 7 presents a detailed FTIR spectral analysis based on meticulously baseline-corrected data for recycled polypropylene (rPP), a material of significant interest in various applications. Characteristic peaks that include asymmetric C-H stretching within the range of 2950 to 2970 cm⁻¹, the symmetric C-H stretching between 2860 and 2870 cm⁻¹, and bending vibrations observed at 1450 cm⁻¹ and 1375 cm⁻¹. These peaks serve as essential references for future research into rPP eco-composites enriched with nanoclay and bamboo fiber additives, highlighting progress in this field. The incorporation of nanoclay into the composite matrix prompted an examination of the Si-O stretching peaks around 1000 to 1100 cm⁻¹, which intriguing potential interactions within the composite’s structure. Conversely, bamboo fiber based eco-composites exhibited distinct features, included broad O-H stretching peaks (3200 to 3500 cm⁻¹), associated with the cellulose and lignin components, along with C-O stretching peaks indicative of chemical bonding changes (1030 and 1050 cm⁻¹). A detailed analysis of the C-H stretching region (2800 to 3000 cm⁻¹) provided evidence of shifts in peak intensity and broadening, reflecting modifications due to fiber content variations, specifically at 3wt% and 6wt% GSF. Additionally, signals within the C=O stretching region (1730 and 1750 cm⁻¹) underscored the presence of carbonyl groups that lignin in bamboo fiber composites. Finally, spectral scrutiny of Si-O and Al-O stretching regions (1000 to 1100 cm⁻¹ and 520 to 620 cm⁻¹) elucidated the critical role of nanoclay in enhancing composite characteristics, further advancing understanding within this remarkable field.

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Fig. 7.

FTIR spectra of rPP and GSF/composites. Figure caption: FTIR spectra of rPP and rPP-based composites with varying GSF content.

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3.3 Mechanical properties

The mechanical characterization of polymer eco-composites is essential for their structural applications. In this study, flexural strength was evaluated to assess the material’s resistance to bending deformation. As shown in Fig. 8(a), the flexural strength of rPP was initially recorded at 31.39 MPa. The inclusion of 0wt.% GSF significantly improved the flexural strength to 47.84 MPa, demonstrating a 52.38% increase due to enhanced interfacial adhesion between the polymer matrix and the filler. This value is notably higher than the 30.01 MPa observed in pure polypropylene containing 0 wt.% bamboo fiber, as reported by Khamis et al. (2017). The rPP’s more polar nature and irregular molecular structure enhance compatibility with nanoclay, promoting stronger interfacial bonding. When 3wt.% GSF was introduced, the flexural strength decreased slightly to 47.23 MPa, a reduction of 1.27% compared to the 0 wt.% GSF composite. This decrease is due to challenges in achieving uniform fiber dispersion and optimal interfacial interaction between the fibers and the polymer matrix. However, the 47.23 MPa flexural strength still exceeds the 32.25 MPa reported for PP with 3wt.% GSF, again underscoring the enhanced compatibility of rPP with fibers. Increasing the fiber content to 6wt.% GSF caused a further decline in flexural strength, reaching 45.54 MPa, representing reductions of 3.58% and 4.8% compared to the 3 wt.% GSF composite and 0 wt.% GSF composite, respectively. The reduction can be attributed to the increased fiber content, potentially leading to agglomeration and weaker stress transfer within the composite. Despite this, the 6wt.% GSF composite exhibited higher flexural strength than the 36.91 MPa reported by (Khamis et al., 2017), for PP with 6wt.% GSF, reinforcing the superior interfacial bonding and dispersion characteristics in the rPP-based composites. These results highlight the need for improved dispersion techniques and interfacial optimization when incorporating higher fiber contents into polymer composites. Moreover, excessive fiber content may disrupt polymer chain continuity, limiting stress transfer and negatively affecting mechanical integrity, as noted by (J. Zhang & Shu, 2023). Therefore, while GSF fibers contribute to reinforcement, their optimal dispersion and interfacial adhesion are essential for maintaining flexural strength (Ladhari et al., 2021).

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Fig. 8a.

Flexural Strength of rPP and GSF/composites. Figure Caption: Box plot of flexural strength for rPP and rPP-based composites with varying GSF content.

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As illustrated in Fig. 8(b), the examination of flexural modulus clarifies a considerable increase in stiffness with the introduction of nanoclay, resulting in a modulus that is more than double that of pure rPP, thereby indicating a significant improvement in the material properties. Moreover, the modulus further increases with the addition of 3 wt.% GSF, demonstrating an effective load transfer mechanism that enhances the material’s rigidity. However, like the findings regarding flexural strength, it becomes evident that the modulus plateaus when the fiber content is increased to 6 wt.% GSF, which can be attributed to the same challenges of fiber agglomeration and insufficient dispersion that hinder the performance. The combined analyses of both flexural strength and modulus suggest that the most effective reinforcement combination occurs at approximately 1 wt.% of nanoclay and 3 wt.% of fibers, as this combination provides an optimal balance between strength and stiffness while avoiding the potential disadvantages associated with higher fiber loadings. The flexural strength and modulus results demonstrate that incorporating nanoclay and an optimal fiber content enhances the mechanical performance of rPP.

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Fig. 8b.

Flexural modulus of rPP and GSF/composites. Figure caption: Flexural modulus of rPP and rPP-based composites with varying GSF content.

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In Fig. 9, the bar chart illustrates how the strength of rPP and its eco-composites varies with different amounts of GSF, highlighting the positive influence of fiber content. The baseline rPP serves as a reliable reference point, with an impact strength of approximately 5500 J/m². Pure rPP exhibits moderate resistance, with reported impact strength of 4.8 kJ/m² for rPP and 7.5 kJ/m² for PP (Ladhari et al., 2021). However, rPP can become brittle under high impacts. The introduction of 0wt.% GSF (with nanoclay) results in a modest increase in impact strength, highlighting the advantages of nanoclay in enhancing energy absorption without significantly altering the structure. The strength peaks at approximately 7500 J/m² with 3wt.% GSF, demonstrating that these fibers markedly improve toughness and energy absorption by effectively managing crack growth and stress distribution. Although the strength slightly decreases at 6wt.% GSF compared to the 3wt.% sample, it still surpasses rPP, reaching around 6500 J/m², a result attributable to fiber clumping and reduced adhesion. This emphasizes the importance of balancing fiber content, as excessive amounts may reduce toughness due to poor dispersion or increased brittleness. The larger error bars show variability in impact strength, caused by differences in fiber distribution and processing, which is reasonable. Overall, the inclusion of GSF positively affects strength up to a limit, with 3wt.% GSF emerging as the optimal point. Incorporating GSF significantly enhances the impact strength of rPP, particularly at 3 wt.%, confirming the value of fiber reinforcement for applications requiring appropriate impact resistance. This underscores the need for careful optimization of fiber content and processing methods.

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Fig. 9.

Effect of fiber fraction on the impact strength of the rPP and GSF/composites. Figure caption: Effect of GSF content on the impact strength of rPP and rPP-based composites.

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3.4 Fracture behavior and strengthening mechanism.

To execute a comprehensive and detailed analysis of the fiber distribution within the complex polymer matrix, we employed FESEM, which was conducted on the fractured surface of the material. The characteristic fractured surface of the rPP composite containing 6 wt.% of GSF, which had been subjected to rigorous flexural loading, has been thoughtfully presented in Fig. 9. The fractured surface exhibits an irregular and jagged texture, indicating a combination of brittle and ductile fracture modes. The brittle regions suggest weak fiber-matrix adhesion or localized stress concentrations, while the ductile areas indicate polymer deformation, demonstrating the composite’s complex failure behavior under mechanical stress. This characteristic is primarily attributed to the random orientation of GSF within the eco-composite matrix, which significantly influences the overall mechanical performance. The detailed distribution of the fiber can be vividly observed in Fig. 10(a), where a few individual strands of GSF are clearly visible, alongside several agglomerated clusters, presenting a rich tapestry of fiber arrangements that contribute to the composite’s performance. It is essential to emphasize that the fractured images provided are specifically representative of the rPP composite with 6wt.%GS, which has been established as the predominant proportion of GSF employed in the present investigation, highlighting its importance in our research findings.

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Fig. 10a.

Fracture behavior and dispersion in 6 wt.% GSF Eco-composites subjected to flexural loading. Figure caption: Fracture behavior and dispersion of GSF in 6 wt.% GSF-based eco-composites subjected to flexural loading.

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Fig. 10b.

Fracture behavior and fiber pull-out in 6 wt.% GSF Eco-composites subjected to flexural loading. Figure caption: Fracture behavior and fiber pull-out of GSF in 6 wt.% GSF-based eco-composites subjected to flexural loading.

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Fig. 10c.

Fracture behaviour and fiber pull-out in 6 wt.% GSF Eco-composites subjected to flexural loading. Figure caption: Fracture behaviour and fiber pull-out of GSF in 6 wt.% GSF-based eco-composites subjected to flexural loading.

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A significant characteristic of the stress-bridging strengthening mechanism is evident in Figs. 10 (b and c), where the intriguing fiber pull-out mechanism is proficiently illustrated, as highlighted by the yellow arrows. These arrows draw attention to this critical process. The random presence of GSF, combined with the straightforward evidence of the pull-out mechanism, significantly contributed to the remarkably high flexural strength of the composite compared to the rPP alone, which exhibits a strength of 90 MPa. This illustrates the effectiveness of incorporating GSF. Furthermore, it is imperative to note that an enhanced distribution of the fibers within the matrix can be achieved by judiciously increasing the viscosity of the rPP. This, in combination with the application of advanced dispersion methodologies such as ultrasonication or vortex mixing during the processing phase, will undoubtedly improve the overall efficacy of the composite.