Construction of polypropylene composite multifilaments filled with sodium perborate trihydrate-treated jute microparticles

2.1 Materials

Jute yarns supplied from Atlantik Halı A.Ş (Turkey) were used as additive materials. The contents of the basic constituents of jute yarns, such as cellulose, hemicellulose, lignin, and the others, were determined as 79.0%, 12.6%, 8.0%, and 0.4%, respectively [13]. SP (NaBO₂·H₂O₂·3H₂O) was supplied by Merck Corp (Germany). Isotactic polypropylene, used as matrix polymer in powder form with a melt flow index value of 35 g/10 min, was supplied from Senkroma Global Colors (Turkey).

2.2 Preparation of the jute microparticles

Jute yarns were ground in Retsch Cutting Mill SM 100 (Haan, Germany) grinder using a sieve having holes of 250 μm. Jute yarns in powder form were ground in Fritsch Pulverisette 7 (Oberstein, Germany) grinder at the speed of 850 rpm for 20 min to decrease the size of the jute particles.

2.3 Surface treatment of the jute microparticles

Jute particles were immersed in distilled water for 1.5 h to remove the impurities and dried in an oven at 90°C. Following the pretreatment process, jute microparticles were treated with 5%, 10%, 15%, and 20% (w/v) SP aqueous solutions for 30 min at 75°C. The jute microparticles were rinsed out with distilled water several times to remove the chemical residues and then oven dried at 105°C and kept in a desiccator. The optimum SP concentration was selected for manufacturing polypropylene composite filaments considering the XPS analysis results of surface-treated jute particles.

2.4 Manufacturing of the composite multifilaments

Initially, both treated jute microparticles and polypropylene in powder form were premixed mechanically in which the contents of jute particles are 0, 0.3, 0.8, and 1.4 wt%, dried at 105°C for 4 h, and then melt blended in the extruder (Lab Tech, Thailand) at the speed of 170 rpm. The compounded material passed through six extrusion zones at the temperature of 190°C and finally extruded through the spinneret holes. After the extrusion process, the material was cooled down with cold water and pelletized as granules with the aforementioned concentrations (Figure 1).

Figure 1:

Polypropylene granules containing (A) 0 wt%, (B) 0.3 wt%, (C) 0.8 wt%, and (D) 1.4 wt% treated jute microparticles.

Then, the polypropylene composite granules were fed into a laboratory-scale melt spinning machine (Plantex Lab Line, Italy) having a single-screw extruder with two spinning nozzles in trilobal cross-sections. The composite granules passed through six zones with different temperatures in the range of 180°C–215°C from the feeder to the spinneret, respectively. The extrusion speed and the extrusion pressure were kept at 14 dpf and 80 bar, respectively. The spun filaments were drawn with a draw ratio of 3.25. Finally, 100% polypropylene (P0) and polypropylene composite multifilaments containing 0.3 wt% (P03), 0.8 wt% (P08), and 1.4 wt% (P14) treated jute microparticles were fabricated. It should be noted that P0 multifilaments as a control sample were also subjected to the same manufacturing processes.

2.5 XPS analysis of the jute microparticles

XPS analysis was carried out to examine the effects of the treatments on the surface chemistry of the jute microparticles. XPS spectra were obtained using a Thermo Scientific Kα XPS (USA).

2.6 Characterization of the polypropylene multifilaments

3.1 XPS analysis of the jute microparticles

Table 1 gives the surface chemical composition by means of atomic concentration (%) and carbon/oxygen (C/O) ratios of the untreated jute (J) and treated jute microparticles with different concentrations of SP aqueous solutions (5%, 10%, 15%, and 20% SPJ). After all SP treatments, the C and O contents of the jute particles remain almost similar. It is clearly seen that the C/O ratio of J increased after all chemical treatments. The maximum increment at C/O ratio of J was achieved after 10% (w/v) SP treatment. The C/O ratio can give information about the hydrophobicity of the fiber surface in general. A high C/O ratio modified the surface of the jute from hydrophilic to more hydrophobic [14], [20]. Accordingly, it is determined that 10% (w/v) SP treatment changed the surface of J from hydrophilic to more hydrophobic. It is probable that 10% (w/v) SP treatment creates a hydrophobic environment on the surface of the jute particles. This may be due to the oxidative modification with SP treatment, which reduced the proportion of O-H groups and increased that of O=C groups of the jute particles [14].

The optimum SP concentration was selected for manufacturing polypropylene composite filaments considering the XPS analysis results of surface-treated jute particles.

3.2 DSC analysis of the polypropylene filaments

Table 2 gives the melting and crystallization temperatures, the melting and crystallization enthalpies, the extent of supercooling, and the crystallinity (%) of the polypropylene filaments obtained by DSC analysis. The DSC curves of the polypropylene filaments are shown in Figure 2. It can be mentioned from DSC results that the difference between the melting point and the crystallization temperature of P0 filaments is calculated to be 39.5°C, and this difference is evaluated as the extent of supercooling of the polymer [21], [22]. The addition of 0.3, 0.8, and 1.4 wt% treated jute microparticles reduced the extent of supercooling of P0 filaments by 33%, 26%, and 12%, respectively. To decrease the extent of supercooling, some substances acting as nucleating agents are added to the polymers. The nucleating agents change the crystallization behavior of polypropylene chains and agglomerate in the molten phase. These agents reduce the extent of supercooling of polypropylene by increasing the onset crystallization temperature [23]. Therefore, it can be stated that the treated jute microparticles acted as nucleating agents in the polypropylene, and the best improvement was achieved by the incorporation of 0.3 wt% jute particles. It is also pointed out that the polypropylene filaments exhibited similar crystallinity values. Similarly, Srisawat et al. reported that silica particulate loading acted as nucleating agent by increasing the crystallization temperature of polypropylene fibers [24].

Figure 2:

(A) Exothermic (crystallization) and (B) endothermic (melting) peaks of the polypropylene filaments.

As presented in Figure 2, the composite filaments have multiple peaks in the melting zone apart from P0 filaments. This may be explained by the difference between melting behaviors of chain folded crystals and the crystals in more extended chain conformation [25], [26]. The formation of the multiple melting peaks is also elucidated by the melting of different sized crystals or disordered crystals [25], [27]. Soitong and Pumchusak revealed that multiwalled carbon nanotube-filled polypropylene composite fibers also presented multiple peaks in the melting zone due to the difference in crystal forms or degree of perfection [28].

3.3 Tensile properties of the polypropylene filaments

To examine the effects of the surface-treated jute microparticles on the tensile properties of the polypropylene filaments at different gauge lengths, single fiber tensile tests were carried out. The tenacity results of P0, P03, P08, and P14 filaments are listed in Table 3. It is obvious that the tenacity results of P0 filament increase with the addition of the treated jute particles. It is also determined that the standard deviation values are noticed to be high for all polypropylene filaments. This may be due to the nonhomogeneous distribution of the treated jute microparticles, which can be seen in the fluorescence images of the polypropylene filaments (Figure 9) or the crystalline regions along the filament.

3.4 TGA analysis of the polypropylene filaments

TGA was conducted to investigate the effect of the surface-treated jute microparticles on the thermal decomposition of the polypropylene filaments. Figures 3 and 4 illustrate the TGA curves of the jute and the polypropylene filaments, respectively. In general, the extrusion in the manufacturing processes of polypropylene granules and polypropylene filaments performs generally at approximately 200°C. On this basis, Figure 3 presents that there is no thermal degradation of jute that existed until 200°C.

Figure 3:

TGA curve of the jute microparticles.

Figure 4:

TGA curves of the polypropylene filaments.

As seen from Table 4 and Figure 4, there is no mass loss that existed until 120°C in the TGA curves of P0, P03, and P08 filaments. However, the mass loss is recorded to be 0.7% at this temperature for P14 filament. This can be due to the dehydration of the jute particles in the polypropylene. T₀₅ and T₅₀ are the temperatures at which a sample loses 5% and 50% of its mass, respectively. T₀₅ and T₅₀ for all polypropylene filaments are determined to be approximately 365°C–381°C and 437°C–449°C, respectively. It is noticed from Table 4 that the addition of treated jute microparticles increased the initial thermal degradation temperature of P0 filament. This enhanced thermal stability may be related to the nucleating agent effect of treated jute microparticles in the polypropylene. The thermal degradation of P0, P03, P08, and P14 was completed at 482°C, 480°C, 486°C, and 490°C, respectively. The improved crystallization and the enhanced molecular order with the addition of fillers may hinder the thermal decomposition of polypropylene [29].

3.5 Moisture content of the polypropylene filaments

Figure 5 presents the effect of the surface-treated jute microparticles on the moisture content of the polypropylene filaments. It is pointed out from the representative results that there are slight differences between the moisture content of P0 and P03 filaments. This can be due to the addition of jute particles in low content. However, the addition of 0.8 and 1.4 wt% jute particles increased the moisture content of the polypropylene filament from 0.04% to 0.34% and 0.70%, respectively. According to statistical analysis, the effect of the addition of 0.8 and 1.4 wt% jute particles is statistically significant on the moisture content of the polypropylene filaments. Wang et al. reported that the polypropylene composite fiber-filled microcrystalline cellulose achieved water uptake performance, which will be beneficial in some applications in the textile industry [30].

Figure 5:

Moisture content of the polypropylene filaments.

3.6 Vertical wicking of the polypropylene knitted fabrics

The experimental results presented in Figure 6 describe that the incorporation of the surface-treated jute microparticles reduces the vertical wicking of P0 filament. Additionally, the increments in the content of the jute particles negatively influence the vertical wicking of the polypropylene. Das et al. [19] explained this behavior by the absorption and wicking phenomena. Due to high absorbency of jute, the water molecules of the solution form bonds with the absorbing group of jute particles, which results in very less water movement along the fabric. However, higher wicking heights were observed in the case of the polypropylene due to its hydrophobic character, which does not form bond with water molecules and the liquid surface dragged very smoothly. Polypropylene acts as a channel to water and enhances the vertical wicking [19], [31]. Therefore, the wicking results indicate that the polypropylene filaments can achieve hydrophilic character with the incorporation of 1.4 wt% treated jute particles, which is more pronounced.

Figure 6:

Vertical wicking of the polypropylene filaments.

3.7 Thermal conductivity of the polypropylene knitted fabrics

Figure 7 summarizes the k-values, the thermal conductivity of the polypropylene filaments. Representative results in Figure 7 reveal that the thermal conductivity of P0 filament decreased by 5%, 32%, and 17% with the addition of 0.3, 0.8, and 1.4 wt% SP-treated jute particles, respectively. This finding is in line with the research by Mounika et al. [32], which focused on the thermal conductivity of bamboo fiber-reinforced polyester composite. It is determined that the thermal insulating of the polypropylene can be improved with incorporating treated jute particles. To examine the details, the interfacial thermal resistance tended to decrease the thermal conductivity of the composite filament at lower content (0.3 and 0.8 wt%) of the jute particles. The enhancement of the heat conduction paths with increasing the particle content counteracted the decreasing effect of the interfacial thermal resistance on the thermal conductivity of the polypropylene composite filament [33].

Figure 7:

Thermal conductivity of the polypropylene filaments.

3.8 FTIR analysis of the polypropylene filaments

Figure 8 represents the FTIR spectra of the polypropylene filaments. The absorption bands at 2950, 2918, and 2838 cm^-1 are related to asymmetric CH₃ and asymmetric and symmetric CH₂ stretching vibrations, respectively [34]. The absorption bands at 1456 and 1376 cm^-1 are assigned to asymmetric and symmetric CH₃ bending vibrations [35]. The band at 1167 cm^-1 is attributed to the presence of isotactic bands of polypropylene [36]. It can be noted that the intensity of this peak increased with incorporating 1.4 wt% treated jute microparticles into the polypropylene filament. However, the intensity of the peak observed at 1102 cm^-1, which is related to C-C and C-H deformations, decreased in the spectrum of P14 filament. The absorption band at 998 cm^-1 is assigned to the characteristic crystalline band of polypropylene [37]. It can be said that the incorporation of the jute microparticles did not modify the functional groups of the polypropylene filament but changed the intensity of isotactic bands, C-C and C-H deformations.

Figure 8:

FTIR spectra of the polypropylene filaments.

3.9 Fluorescence microscopy observation of the polypropylene filaments

The longitudinal views of the jute fiber and the polypropylene filaments were investigated using fluorescence microscopy for tracking the jute particles. The micrographs of the jute and the polypropylene filaments are presented in Figure 9. The jute fiber and the jute particles in the polypropylene are seen in different colors due to their autofluorescence characteristics as displayed in Figure 9. It is determined that the sizes of the jute particles increase with increasing particle content in the polypropylene filament. The jute microparticles in higher loading in the polypropylene filament show a tendency to agglomerate due to the interactions between the particles.

Figure 9:

Fluorescence micrographs of the jute fiber (×20) and the polypropylene filaments (×5).