Melt-spun talc-filled polypropylene fibers and yarns with higher thermal shock resistance

Abstract

An increase in the application areas of textiles has resulted in the need for improved and additional properties and functions, which should be provided by polymers with different functionalities or the addition of particles to the fibers. In the framework of this study, microsized talc particle-filled polypropylene (PP) fibers and yarns were produced and the mechanical, physical and thermal properties of the fibers and yarns were analyzed with respect to production parameters. The main motivation of the selection of talc as the filler material is to improve the thermal shock resistance and decrease the shrinkage of PP fibers and yarns. As a result of experimentation, it was observed that an increase of talc ratio decreases the tensile strength of fibers and yarns. However, this reduction does not seem to be an obstacle to produce fabrics. Furthermore, the addition of microsized talc particles in PP yarns dramatically improved thermal shock resistance and helped to decrease the shrinkage of these yarns.

Keywords

polypropylene fiber yarn talc strength shrinkage thermal shock resistance

Polypropylene (PP), a thermoplastic polymer, is the world’s second most common raw material and is widely used in the textile and plastics industries. Thermoplastics are preferred over thermosets in the plastics industry due to their low production cycle, low production cost and their higher ability to be repaired.¹ Fibers, fibrous and other PP-based textile materials are mainly used in the application areas of carpets, underlays, rugs, hygiene textile products, tapes, ropes, clothing, geotextiles, technical textiles (e.g. filter and separation materials for the automobile industry) and textiles for medicine.² In recent years, clothing and upholstery fabrics, carpets and technical textiles made of PP have been widely used in the textile industry. PP fibers are preferred in the textile industry due to their low cost and easy process ability, low density, high strength and excellent chemical resistance.³

An increase in the application areas of textiles has resulted in need for improved and additional properties and functions. This need can be provided by polymers, either with different functions or the addition of particles to the fibers. Therefore, in recent times, research on the properties of textile fibers has been increased progressively. The provision of the necessary operating functions in textile applications is carried out by modification of existing textile materials or the development of new textile materials. In this respect, production of PP composite textile materials has become popular and important.^1,4

Composite materials are commonly used in most engineering applications because of their adaptability to different situations and relative ease of combination with other materials to serve specific purposes and exhibit desirable properties.⁵ The main remarkable feature of composites is that material properties can be tailored for a specific application or use. In the literature, there are many studies that deal with reinforcing the PP matrix with different filler materials in order to improve a variety of material properties. Most research has focused on the preparation and characterization of polymer composites in the form of plaques, sheets and films.^6–17

However, the number of studies that deal with reinforcing the PP fibers for textile applications is limited. Erdem et al.¹⁸ presented the preparation of PP filaments incorporating various nano-particles and investigated the effects of nano-particles on filaments. Broda et al.¹⁹ produced polypropylene/stearic acid (PP/SA) composite fibers and reported the textile-mechanical properties, surface composition, morphology and supermolecular structure of as-spun fibers. Jeong et al.²⁰ reinforced PP with nano-sized silver particles in order to provide the PP fibers with antibacterial property. They reported that the PP fibers with silver particles exhibited superior antibacterial activity. Naebe et al.²¹ added polyethylene glycol (PEG) and PP-graft-maleic anhydride in order to improve the processability and mechanical properties of aluminum particle-reinforced PP fiber. Surface-modified and unmodified fumed silica particles have also been used as filler material for the reinforcement of PP fibers.^22–25 Rottstegge et al.²⁴ reported that the unmodified fumed silica was found to have a strong influence on the mechanical fiber properties, while the surface-modified silica has only a small one. Caldas et al.²⁵ observed that addition of an ultrafine-particle surface-modified silica pre-dispersed in an alkyl silicone to isotactic PP results in dramatic improvements in the tensile properties of fibers and spunbonded fabrics. Schwartz et al.²⁶ investigated the effect of strain rate and gauge length on the strength of ultra-high strength polyethylene fibers and observed that unlike most polymeric fibers, ultra-high strength polyethylene exhibited no gauge length effects over the range from 10 to 200 mm, holding the strain rate constant.

In the framework of this study, microsized talc particle-filled PP fibers and yarns are produced and mechanical, physical and thermal properties of the fibers and yarns are analyzed with respect to production parameters. Pure talc, the softest of all minerals, is an organophilic, water repellent and chemically inert mineral. It can resist temperatures up to 900℃, is unaffected by chemicals and will not harm living tissue. The main reason for incorporating talc in plastics is to increase the stiffness. Moreover, because of talc’s significantly high thermal conductivity, the heat introduced and generated during processing is transmitted through the mixture more quickly. The heat is also transported out of the compound faster during cooling. Since incorporating talc in a compound increases the thermal conductivity, resulting in faster heating and cooling rates, the thermal shock resistance of the compound can be improved. As a result, talc is one of the most used filler material in thermoset as well as thermoplastic matrix materials, where improvements in electrical insulation, moisture resistance, chemical inertness, heat conductivity and good machinability are required.²⁷ The automotive and domestic appliance markets are still the dominating users of talc-filled compounds, but new markets are being developed. Talc-filled PP is also finding new markets in food packaging applications. In the literature, many studies can be found on talc-reinforced PP composite in the form of plaques and sheets.^15,27–31 To the best of our knowledge, no articles can be found in the current literature that deal with production and characterization of talc-filled PP fibers and yarns. Therefore, talc-filled PP fibers and yarns are produced and investigated for the first time in this research. The change in tensile properties when talc is added to the PP fibers and yarns is analyzed and the findings are reported. The main motivation of adding talc into PP is to produce higher thermal resistant PP fibers and yarns with lower shrinkage and with a mechanical strength that allows the production of yarns and fabrics. The thermal shock resistance property is very important for textile fabric, especially in protective clothing and applications that need high-temperature resistance. Some of the applications where thermal shock resistant fabric is needed are fire fighting clothing, protective clothing for heavy metal industries, clothing for outerspace applications, paratrooper clothing and composites used at high temperatures.^32–35 As a result, the relationship between the change of thermal and mechanical properties of talc-filled fiber and yarns are investigated in this study.

Materials and methods

Materials

PP (density at 23℃ = 0.9 g/cm³) in the form of chips that contain different percentages of microsized talc (i.e. 10%, 18% and 32%) particles were supplied from GEMA Polymer Company, Turkey. The average size of the talc particles was 1–3 µm.

Sample preparation

Firstly, 50% of talc added PP mixtures and 50% of 25mfi 100% Capilene PP chips are mixed at different amounts to achieve different talc percentages and to obtain similar viscosities of the mixtures, since the viscosity during the melt spinning is a very important parameter. The mixed chips are then put into the feeder of the spinning unit. These different percentages of talc added PP chips are then used to produce fibers and yarns by using the typical pilot melt spinning unit located at the Zirve University Fiber Production Center (see Figure 1(a)). All fiber and yarn samples are produced at the same room conditions (i.e. at 20–23℃ and at 50% humidity). At the melt spinning unit, a spinneret with 16 holes, each with a 500 micron diameter is used. The temperature profile of the extruder is T₁ = 165℃, T₂ = 190℃, T₃ = 210℃, T₄ = 220℃; manifold temperature is chosen as T₅ = 240℃; spinneret temperature is chosen as T₆ = 240℃ to have a suitable viscosity for fiber production. The extruder screw rotation is 2.8 rpm with 18 mm screw diameter. The spinning pump speed is 2.5 rpm and the capacity of the spinning pump is 0.6 cc/rev.

Figure 1.

(a) Pilot melt-spinning unit. (b) INSTRON^@ 5944 tensile testing machine at the Zirve University Fiber Production Center.

The spun fibers are fast cooled with cool air and drawn with different drawing ratios (i.e. 5, 6.67, 8.33 and 10 at the first drafting region; 1.33, 1.67, 1.8 and 2 at the second drafting region) to investigate the effect of drawing ratio on the mechanical, physical and thermal properties of fibers and yarns. The effect of the drawing ratios at the first drafting region (between the melt pump and the feeder roller) and the second drafting region (between the feeder roller and the drafting roller) are also studied with different amounts of talc-filled PP. According to the obtained chips, the maximum talc percentage that could be produced as fiber was 32%. However, some problems occurred during the production of talc-filled fibers with a talc ratio of 20% and higher. As a result, a maximum of 17% talc ratio could be reached to produce talc-filled PP fibers in this study.

Eight levels of talc-filled PP fiber and yarn samples were produced that contain between 0% and 17% of talc particles (i.e. 2%, 5%, 7%, 10%, 12%, 15% and 17% in the batch) and the total of eight levels of fiber and yarn fineness were obtained. A total of 50 different talc-filled PP fiber samples and 50 yarn samples were produced for this research. In Figure 2, the bobbins of the produced PP yarns with different talc addition are shown. The addition of talc particles into PP yarns changed the appearance of the bobbins to more opaque and less shiny.

Figure 2.

Bobbins of talc-filled polypropylene (PP) yarns: (a) 17% talk filled PP; (b) 10% talc-filled PP; (c) 100% PP.

Experimental setup

Quasi-static tensile mechanical properties of talc-filled fibers and yarns are measured according to American Society for Testing and Materials (ASTM) D3822 and ASTM D2256 standards, respectively, with an INSTRON^@ 5944 tensile tester equipped with a load cells of 5 N for fiber tests and 2 kN for yarn tests (see Figure 1(b)). From each type of fiber and yarn, 20 samples are tested to provide reliable mean and standard deviation values. The images of the microstructure of the samples are taken using an Olympus CX25 microscope with a 5MP camera.

The thermal properties (thermal shock ratio and shrinkage ratio) of yarns are experimentally measured according to the ASTM D5591–04 standard using a TST2 shrinkage testing device from Lenzing Instruments. For the tests, a specific amount of weight (depending on the fiber linear density) is applied to yarn as provided in the ASTM D5591–04 standard in order to apply the required tension during the testing. The test temperature is taken as 140℃ and the specimen length is taken as 50 cm. According to the standard, the testing time can be chosen as 1–60 minutes. The first experiments with the investigated yarns showed that after 1 minute, no change in the length of the yarns was observed. Therefore, the total shrinkage testing time is chosen as 1 minute. Thermal shrinkage test results are affected by the environmental laboratory conditions. Tests are performed at 20 ± 2℃ and 65% humidity. Therefore, the sudden temperature change is 120℃ and this sudden change is very significant for PP fibers.

Results and discussion

Microstructure characterization

Microstructures of fibers are investigated using an Olympus C31 microscope with a 5MP camera attached. As shown in Figure 3(a), higher percentages of talc in PP fibers result in a lumpier surface of the fibers. Fifteen percent of talc-filled PP fibers have higher fiber diameters. The talc particles become more visible as the talc ratio increases. Distribution of talc particles throughout the fiber is shown in close-captioned microscope pictures (Figure 3(b)). These pictures show that the particles are distributed to the fiber length evenly and few agglomerated particles are seen. Actually, in order to reach PP fiber with different amounts of talc particles, 2% dispersant has already been added in the talc-filled PP chips, which is provided from the industrial company.

Figure 3.

Optical photographs of talc filler polypropylene (PP) fibers with (a) talc ratios of (i); 100% PP; (ii) 5% talc-filled PP; (iii) 10% talc-filled PP; (iv) 15% talc-filled PP. (b) Magnification of 15% talc-filled PP.

Furthermore, in Figure 3(b), it is seen that talc particles are not only distributed on the surface of the fiber, but mostly inside of the fibers. Normally, the talc particles on the surface of fibers can leave the fiber in the long term. However, in our samples, even the particles on the surfaces are coated with PP and this coating will prevent them leaving the fiber easily. Therefore, the talc-filled PP fibers will most likely maintain their long-term thermal and mechanical properties.

Physical and mechanical properties

The linear densities, applied force at break, tensile strength and elongation at break values are measured and the results are shown in Figures 4 –9. The main motivation of this research is to see how the thermal properties of the talc-filled PP fibers change and whether the fibers and yarns are strong enough for the possible production of fabrics. Therefore, strengths of the talc-filled PP fibers and yarns are very important.

Figure 4.

Measured linear densities as a function of total drawing ratio for samples containing talc ratio of (a) 17%, (b) 15%, (c) 12% (d) 10%, (e) 7%, (f) 5%, (g) 2%, (h) 0%.

Figure 5.

Measured tensile strength values as a function of total drawing ratio for samples containing talc ratio of (a) 17%, (b) 15%, (c) 12% (d) 10%, (e) 7%, (f) 5%, (g) 2%, (h) 0%.

Figure 6.

Measured elongation values as a function of total drawing ratio for samples containing talc ratio of (a) 17%, (b) 15%, (c) 12% (d) 10%, (e) 7%, (f) 5%, (g) 2%, (h) 0%.

Figure 7.

Measured linear density values as a function of talc ratio for samples containing drawn by ratios of (a) 6.7, (b) 8.9, (c) 11, (d) 15, (e) 16.7, (f) 20.

Figure 8.

Measured tensile strength values as a function of talc ratio for samples containing drawn by ratios of (a) 6.7, (b) 8.9, (c) 11, (d) 15, (e) 16.7, (f) 20.

Figure 9.

Measured elongation values as a function of talc ratio for samples containing drawn by ratios of (a) 6.7, (b) 8.9, (c) 11, (d) 15, (e) 16.7, (f) 20.

Figure 4 shows the effect of drawing ratio on fiber and yarn linear densities (tex values) for different amounts of talc added to PP fibers and yarns. All the samples have the same type of tendencies with drawing ratio and all the results show that fiber linear densities decrease with increasing drawing ratios. As known in the literature, fiber linear density decreases with increasing drawing ratio because polymer molecules in the fiber become more parallel to each other so the thickness of the fiber decreases and the length of the fiber increases.

According to Figure 4, as the talc ratio increases from 0% to 17%, the linear density tends to decrease more (the slope of the trend lines increases) as the drawing ratio increases. This shows that the addition of talc increases the effect of drawing ratio on linear density. Moreover, it is shown in Figure 4 that the decrease in the linear density of yarns is higher than the decrease in the linear density of fibers as the drawing ratio increases.

The addition of particles to the PP polymer makes produced fibers and yarns more brittle. Therefore, finding the maximum amount of particle addition with the certain drawing ratio is important. When the talc ratio is 17%, yarn could not be drawn more than 11 times because the amount of talc in the yarn is very high and the produced fibers and yarns are very brittle. Therefore, 17% talc in the PP yarn is the highest amount that could be added to the yarn so yarn could be drawn as much as 11 times. Particularly at the second drafting region (between the feeder roll and drawing roll), yarn could be drawn a maximum 1.33 times. In industry, PP yarns are drawn around 2.8 times to produce usable fiber and yarn for the different applications. So 1.33 times is not enough.

Figure 5 shows the effect of drawing ratio on fiber and yarn tensile strengths when different amounts of talc are added. According to the results, tensile strength increases with increasing drawing ratios. As detailed in the literature, tensile strengths of fiber and yarn increase with increasing drawing ratio because polymer molecules in the fiber becomes more parallel to each other so fibers and yarns break when the larger force is applied, and because more polymer molecules in the fiber resist the force during testing. In addition, more molecules in the tensile direction also result in more molecular interactions among PP molecules and degmore friction. Higher friction results in higher tensile strength. The drawing ratio affects the yarn linear densities similarly with all samples. Talc percentage in the yarn did not affect the slopes of the trend lines.

For all type of fibers and yarns (including different amounts of talc), the slope of the best line representing the relationship between total drawing ratio and tensile strength is almost the same. This result shows that independent of talc percentage, the drawing ratio affects the tensile strength in a similar manner. Moreover, for all samples fiber tensile strength is greater than yarn tensile strength. The main reason for this difference is that the talc powders are not distributed throughout the fiber evenly, so that at some parts of the fibers, powders agglomerate and form weak points in the fiber. These weak points are placed randomly. Since these weak points are differently distributed throughout the fiber length and break at the different applied forces, all of the fibers cannot resist the applied force all together at the same time during the testing. Therefore, fibers start breaking during the tensile test at different times so the tensile strength of yarn is lower than the tensile strength of fiber for all the samples.

Figure 6 shows the effect of drawing ratio on fiber and yarn elongation at break for different amounts of talc added PP fibers and yarns. As expected, when fiber is drawn more during the production, the elongation at break of that fiber decreases because some of the molecules have already become more parallel so less elongation happens during the tensile testing. The slope of the decrease for higher talc added PP fibers is less, so the decrease on elongation is less because more talc powder in the cross-section of the fiber makes the fiber more brittle and a smaller number of molecules in the fiber resist the force applied during testing so the elongation decreases. Even at very small drawing ratios applied during spinning, higher talc amounts in the fibers shows less elongation so at the higher drawing ratios, elongation does not decrease more. The sample that has 17% talc in PP fiber shows higher elongation with increasing drawing ratios. Actually, 17% talc added PP fibers could not be produced continuously so the fiber characteristics change dramatically.

Figure 7 shows the effect of talc ratio on fiber and yarn linear densities (tex values) for different amounts of talc added PP fibers and yarns. As seen in Figure 7, higher talc ratio increases the fiber and yarn linear densities a little amount. These fiber and yarn samples are produced at the same conditions. When the talc ratio increases in PP, fiber and yarn will be heavier because the density of talc is around 2.6 g/cm³ and the density of PP is around 0.9 g/cm³. So the results show that the same length of fibers and yarns with higher talc ratios result in higher linear densities (tex and dtex values for the yarn and fiber, respectively).

Figure 8 shows the effect of talc ratio on fiber and yarn tensile strengths for different amounts of talc added PP fibers and yarns. At the lower drawing ratios (Figures 8(a) and (b)) the fiber strength is maintained as much as 5% talc addition to PP fiber and yarn. This effect happens because a very small amount of talc powder addition makes better mixtures and particles are placed between fibers separately. Therefore, the strength of the fiber does not decrease significantly.

It is seen in Figure 8 that higher talc ratios in the PP fiber and yarn result in less tensile strength, because talc is powder and talc powder cannot contribute to the tensile strength of fiber and yarn. Therefore, a smaller amount of PP in fiber and yarn results in less tensile strength. When the drawing ratio increases, the tensile strength difference between pure PP fiber and the higher amount of talc added PP fiber increase because higher drawing makes the PP molecules more parallel to each other and, for the higher talc-filled PP fiber, talc powders prevent the PP molecules from relocating.

In Figure 9, elongation at break values are given as a function of talc ratio for different amounts of talc added PP fibers and yarns. The higher talc ratio in the fiber makes the fiber more brittle; therefore, elongation decreases. Furthermore, talc powders in the fiber stick to the PP molecules and prevent these molecules relocating and moving. At higher drawing ratios, the effect of talc on the elongation decreases.

Reduction in tensile strength (see Figure 8) and elongation at break value (see Figure 9) show that the addition of talc particles into the pure PP results in reduction of ductility of the material. In Figure 10, tensile stress of 17% talc-filled and pure PP fibers are given as a function of elongation.

Figure 10.

Tensile strength versus elongations curves of (a) 17% talc-filled polypropylene (PP) fibers and (b) pure PP fibers.

The reduction in tensile strength and elongation at break can also be seen in the tensile stress–elongation curves shown in Figure 10. It is clearly observed that the plastic hardening regions and the fracture toughness values (area under the curves) of 17% talc-filled PP fibers are much smaller than those for pure PP fibers. These results show that the addition of talc particles in pure PP makes the produced fibers more brittle.

Thermal properties

Shrinkage and thermal shock resistance properties of talc-filled PP fibers and yarns are investigated as the thermal properties. The thermal shock ratio is defined as the percent of deformation of the material when the sudden temperature changes occur. PP polymer has the tendency to shrink very fast when the temperature changes dramatically. This is a big problem for the polymer, because having a dimensional change in the material is not a desired property for most of the applications, such as the sack industry. Cement, especially, is packaged at high temperatures and when PP sacks are used for cement packaging, packages shrink when the hot cement is put into the sacks.

Thermal shock ratio can be measured using the shrinkage test method in which a very high temperature is introduced to the material and the first reaction of the fiber can be called the thermal shock ratio. In Figure 11, the thermal shock ratio is read at point A. As shown in Figure 11, PP shrinks (dimensionally change) dramatically during the first 2–3 seconds of the test.

Figure 11.

Shrinkage test results of some selected samples.

Shrinkage value is another parameter that is measured using the same test method. It is the percent of shrinkage when the yarn is treated with a high temperature for at least 1 minute. Shrinkage is a permanent physical deformation of the material. The shrinkage values of the samples are shown in Figure 11 at point B.

The parameter that shows thermal shock resistance is the thermal shock ratio of the yarns and it is found using shrinkage testing. The thermal shock ratio is the percent of the sudden change in length of the yarn just after the temperature is applied. An increase in thermal shock ratio defines a decrease in thermal shock resistance. Therefore, thermal shock resistance is the opposite of the thermal shock ratio value. Increased thermal shock resistance should show lower thermal shock ratios of the yarn.

As shown in Figure 12, both thermal shock and shrinkage ratios decrease with increasing talc ratio in the yarn. This behavior can also be seen in Figure 11 for selected samples, including different amounts of talc filler. The main purpose of this research is actually to increase the thermal shock resistance of pure PP yarns so the results show that the talc makes the yarns more resistant to the temperature. The thermal shock ratio (tested values of talc-filled PP fibers and yarns) increase, meaning that thermal resistance of the material is not good. So they have an opposite relationship. Thermal shock ratio is around 12% for the 100% PP yarn and around 4.5% for the 15% talc added PP yarn. The reason for the decrease in thermal shock ratio is that talc has a very high thermal conductivity value so when the temperature is introduced, talc heats up more quickly than PP and the sudden physical shrinkage does not happen in the mixed yarn as much as it happens in 100% PP yarn. After some time of the shrinkage test, talc particles in the PP yarn already heat up quickly and PP polymer starts to heat up too, so talc-filled PP yarn shrinks since the testing time is 60 seconds.

Figure 12.

Thermal shock ratio (a) and shrinkage ratio (b) of polypropylene yarns produced by a drawing ratio of 15 with different amounts of talc particles.

The shrinkage ratio of the yarn also decreases when talc powder is added. The reason for this change is that yarn becomes more resistant to heat because heat is kept by the talc material more because of its high thermal conductivity. Even when the heat is applied for a while, the yarn produced with both PP and talc behaves as the new type of material because its thermal properties have changed.

Table 1 shows the thermal shock and shrinkage ratios of yarns produced from 100% PP and 10% talc added PP with different drawing ratios. As shown in the table, the shrinkage ratios of all yarns are negative. This is expected because yarn is produced with a small drawing ratio so that molecules in the fibers still have some space to be drawn more and become parallel to each other. As a result, yarn elongates rather than shrinks. The results shown in Table 1 are important, since both thermal shock and shrinkage ratios decrease dramatically with only 10% talc powder added to PP yarn.

Table 1.

Thermal properties of pure polypropylene and 10% talc-filled fibers with different drawing ratios

Sample	Talc ratio [%]	Drawing ratio	Thermal shock ratio [%]	Shrinkage ratio [%]
1	10	6.7	0.02	–16.09
2	0	6.7	1.24	–36.53
3	10	9	0.03	–11.05
4	0	9	1.76	–30.2
5	10	11	0.04	–9.48
6	0	11	2.26	–22.29

Conclusions

In the framework of this study, talc-filled fibers and yarns have been produced and characterized. The main purpose of this research is actually to increase the thermal shock resistance of pure PP fibers and yarns. According to the results, the following conclusions are made.

As the total drawing ratio increases, the linear density of talc-filled fibers and yarns decrease. As the amount of talc particles in PP fibers and yarns increase, linear density also increases since the density of talc particles is higher than pure PP.

Tensile strength of all samples increases with increasing drawing ratio because polymer molecules in the fiber become more parallel to each other so fibers and yarns break at higher forces, and more polymer molecules in the fiber resist the force during testing. It was observed that higher talc ratios in the PP fiber and yarn resulted in less tensile strength.

When fiber is drawn more during the production, the elongation at break of that fiber decreases. Higher talc ratio in the fiber makes the fiber more brittle; therefore, elongation decreases.

Both thermal shock ratio and shrinkage ratio decreased with increasing talc ratio in the yarn. Thermal shock ratio was measured to be around 12% for the 100% PP yarn and around 4.5% for the 15% talc added PP yarn. The reason for the decrease in thermal shock ratio is that talc has very high thermal conductivity value so when the temperature is introduced, talc heats up more quickly than PP and the sudden physical shrinkage does not happen in the mixed yarn. A decrease in thermal shock ratio means higher thermal shock resistance.

In conclusion, it has been shown that the addition of talc particles into PP fibers and yarns improves the thermal resistance of the pure PP and provides new application possibilities in the future.

As a future work it is planned to produce fabrics from the talc-filled PP fibers/yarns and measure the mechanical and thermal properties of the fabric.

Footnotes

Acknowledgements

The authors would like to thank ANSA Tekstil Ürünleri San. ve Tic. Ltd. Sti., Gaziantep, Turkey for their support in thermal measurements and Zirve University Industry Cooperation Center (ZUSIM), Gaziantep, Turkey for providing PP chips.

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.

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