Preparation and characterization of composite-modi ﬁ ed PA6 ﬁ ber for spectral heating and heat storage applications

: Composite coating technology was used to prepare a modi ﬁ ed polyamide 6 (PA6) polymer material mas-terbatch with low mutual interference and good spinnability using molybdenum oxide, tungsten trioxide, graphene oxide, etc., as modi ﬁ ers. Experiment shows that using nanoscale composite-coated modi ﬁ ed masterbatches capable of spectral heating and heat storage in the preparation of nylon 6 ﬁ ber, adding modi ﬁ ed masterbatches with a mass ratio of 6% online, and controlling various process parameters can result in good functionality and usability as well as enable consistent production. Optimal production conditions are achieved by utilizing pre-dried PA6 chips with a moisture content of 420 ppm. The master batch is subjected to drying at a temperature of 95°C for 12 h. During this process, the master batch is introduced at an addition ratio of 6%. Subsequent spinning is conducted at a speed of 4,300 m·min − 1 and a temperature of 255°C. Cooling is facilitated by air set at a temperature of 17°C, ﬂ owing at a speed of 0.45 m·min − 1 . In the production line, one roller operates without heating, while the second roller is maintained at a temperature range of 160°C. The stretching process is performed at a ratio of 1.3. To ensure proper lubrication, an oil rate of 1.3% is applied. These meticulously controlled process parameters collectively contribute to the most favorable production status.


Introduction
Multi-functional comprehensive thermal fabrics that can generate and store heat constitute an important trend in the fashion industry, with spectral heating fiber fabrics and thermal storage fabrics being at the forefront of research [1].The spectral heating fiber studied by Shengjun et al. [2] recorded a temperature rise of 20°C after exposure to sunlight for more than 5 min.However, the fiber fabric does not have a heat storage function, and the temperature quickly returns to normal when removed from sunlight.Xuehai et al. [3] designed thermal storage and temperature-regulating fibers through microcapsule melt spinning technology research.The prepared fabric has excellent thermal storage performance, but no spectral heating function.Existing materials, hence, have single functions, making it difficult for them to fully realize the comprehensive thermal insulation effect of the multiple function fabrics.Endowing the fabric with multiple functions of heating and heat storage can make garments thinner and lighter, promote ease of wearing and mobility, and better suit extreme climates [4,5].
The spectral heating and thermal storage-modified nylon 6 fiber uses molybdenum oxide, tungsten trioxide, and graphene oxide as the main modifiers for spectral heating and thermal storage.Molybdenum oxide and tungsten trioxide are mineral components with good spectral heating function and good thermal storage performance, while graphene oxide can store heat effectively.The three modifiers were used to prepare a masterbatch by layered coating of the matrix.In the process of fiber preparation, the modified components do not mix and agglomerate on contact.The interaction of the functionalities and their influence on the spinnability of fiber preparation is small, Yaoding Tao, Mei Xu, Yuyan Qin, Shang Gao: High Fashion (China) Co., Ltd., Hangzhou 311231, Zhejiang, China  * Corresponding author: Shouyun Zhang, Hangzhou Vocational & Technical College, Hangzhou 310018, Zhejiang, China; Zhejiang Jinzili New Material Technology Co., Ltd., Jinhua 32100, Zhejiang, China, e-mail: syzhang2008741208@163.comresulting in good fiber formation performance.If the appropriate process parameters and control conditions are selected, the production operation is stable and the quality and functionality of the finished products are good [4,5].We used polyamide 6 (PA6) chips as raw material and added an appropriate amount of the modified masterbatch through melt addition during spinning.Taking the preparation of 44dtex/24f spectral heating and thermal storage composite-modified nylon 6 fiber fully drawn yarn (FDY) as an example, the preparation and characterization of the fiber was examined.

Raw material
Semi-matte, fiber-grade PA6 chips were produced by Hangding Nylon Technology Co., Ltd.
Composite-modified masterbatches were produced by Zhejiang Jincai New Materials Co., Ltd., with an effective ingredient mass ratio of 30% at the nanoscale.
The main indicators of slicing and masterbatch are shown in Tables 1 and 2.

Equipment
The equipment used for the experimental setup included a W-300 electric heating double cone vacuum drum dryer produced by Nanjing Feixiang Drying and Refrigeration Equipment Factory, 300L; a JBe-FLD weightless master batch injection machine produced by Jiangsu Jiangben Automatic Control Equipment Co., Ltd., equipped with a drying system and an injection rate of 13 kg•h −1 ; an 80 × 200 screw extruder produced by German Leonard Co.; and a spin and pull joint testing machine from Beijing Sanlian Hongpu New Synthetic Fiber Technology Service Co., Ltd.

Fiber preparation
Spinning tests were conducted under different process conditions on the Beijing Sanlian Spinning Hongpu Spinning Shallow Joint Testing Machine, and different proportions of spectral heating and thermal storage composite modified masterbatches were added and modified using a masterbatch injection machine from Jiangsu Jiangben Automation Equipment Co., Ltd.

Spinning process
The modified masterbatches and PA6 chips were mixed together in a predetermined proportion and placed in a screw extruder where it was melted and transferred into a filter and metering pump.The measured melt flowed into the module and through spinneret holes in a uniform manner and was cooled to form fiber.The primary fiber was coated with oil by passing through an oil nozzle to form a filament bundle and was then subjected to tensile deformation and heat setting by the hot rollers.The filament bundle underwent a process of enhanced bunching through the application of compressed air crossflow.Subsequently, the bundled filaments were directed into the winding system, where they were meticulously wound onto a spool to yield a roll of phase-change-profiled, luminous polyester FDY.Refer to Figure 1 for a depiction of the principal spinning procedure and the main process flow.
The starting process parameters of the spinning experiment are shown in Table 3.

Testing and characterization
The thermal performance testing of fiber fabrics is conducted in accordance with the Japanese standard "BQE A036-2015 Temperature Performance Light Absorption Insulation Performance Test Method".The thermal resistance, heat transfer coefficient, and Cro value of fiber fabrics are tested for thermal storage performance indicators.The test temperature was room temperature and the test time was 20 min.According to the national standard "GB/T 1735762-2017 Test Method for Thermal Transmission Performance of Textiles -Flat Plate Method."According to the national standard "GB-T16603-2017 Nylon Drawing Silk," the mechanical properties of the fibers were tested using a tensile tester.The stretching speed was 100 mm•min −1 , the spacing was 500 mm, and the pre-tension was 0.5 cN•dtex −1 .Based on "GB T 14346-1993 Test Method for Electronic Yarn Unevenness of Chemical Fiber Filaments", an evenness tester was used to determine how even the fiber was.The test speed was 300 m•min −1 and the test length was 1,000 m.
3 Discussion and analysis

Preparation and application of composite modified masterbatch
The surface of molybdenum dioxide was modified using a dodecyl benzenesulfonic acid cationic surfactant using ball milling and mechanical stirring, while the surface of the tungsten trioxide was modified with platinum and gold bimetallic materials to give it a certain polarity.At the same time, the functional groups formed by the oxygen atoms on the surface of graphene oxide are also polar.The modifiers on the surface and graphene oxide interact easily with the C]O and N-H polar groups of the amide bonds, improving the uniformity of distribution in the melt.At the same time, during the preparation of the master batch, three modifiers are added separately and sequentially to the matrix.Once a stable coating is formed by mixing a modified component with nodular graphite using mechanical stirring, another modifier is added.This second modifier is introduced to create an additional coating through layer milling and mechanical stirring.This step keeps the different modifiers apart within the matrix, preventing them from directly touching.This separation helps avoid clumping and interference in functionality.Produce 44dtex/24f FDY fibers by spinning masterbatches with varying modifier ratios  at a dosage of 6%.Evaluate the spun fibers' performance through a 24-h testing period.From Table 4, when the mass of the three modifiers accounts for less than 30% of the total mass of the master batch, their performance is better.When the amount of modifier added is greater than 30%, the filtration performance decreases and fiber production breaks increase.This may be because during the preparation of the master batch, as the amount of modifier added increases, the matrix ratio decreases, and the dispersibility of the modified powder deteriorates.At the same time, the coating state of the matrix on the modified powder particles deteriorates, making it prone to agglomeration and reducing its performance [6][7][8].Table 5 shows the experimental data of the effects of different proportions of three modifiers on fiber functionality.The ratio of modifiers in the masterbatch was adjusted while maintaining other process conditions and the addition of 6% masterbatch.When the mass ratio of molybdenum oxide in the masterbatch is 15%, tungsten trioxide is 9%, and graphene oxide is 6%, the fibers prepared using the initial process of fiber preparation experiment in Section 2.3 have the best functionality.

Drying of PA6 chips and masterbatch
Usually, PA6 chips are dried by the chip manufacturer and then vacuum packaged and sold to downstream chemical fiber enterprises for use.The moisture content of the chips is usually between 500 and 600 ppm, which can meet the needs of conventional fiber preparation.The preparation of the fibers involves the addition of three types of inorganic modifiers, and the macromolecules are prone to thermal degradation.Therefore, the moisture content of the chips should be low to reduce the degradation of macromolecules caused by hydrolysis, avoiding fiber flotation, and increasing the number of broken ends, resulting in a decrease in production efficiency.Therefore, the secondary drying of PA6 chips can reduce the moisture content of the chips and improve their spinnability.A nitrogen-protected drying tower is used for slow, continuous, low-temperature drying of the chips.The drying temperature is generally 80-120°C and the drying time is about 8 h.For drying the masterbatch, a vacuum drum or vacuum oven is used for high temperature and short time drying at a vacuum of −0.1 MPa, drying temperature 150°C, and drying time 3 h.The moisture content of the masterbatch after drying is approximately 50 ppm.From Table 6, under the conditions of nitrogen protection and drying temperature of 85°C for 6 h, when the moisture content of the dried chips is 350 ppm, the uniform relative viscosity of the chips is good and the spinning condition is good.When the drying temperature exceeds 100°C and the drying time exceeds 7 h, although the operation is normal, the relative viscosity increases significantly, which may be due to the high drying temperature and long drying time.However, an increase in solid-state viscosity occurred locally, resulting in a non-uniform distribution of viscosity [9][10][11].

Fiber preparation process
During the preparation of the fiber FDY, the types and proportions of modifiers added are relatively high, and the control requirements for various process conditions are relatively strict.The spinning temperature has a significant impact on the preparation of the FDY.The high thermal conductivity of the introduced inorganic modifier can lead to undesired effects if the spinning temperature is excessively elevated.This can cause localized increases in liquid phase viscosity or intensified thermal degradation within the melt.These outcomes result in uneven viscosity, notable production fluctuations, and abnormal occurrences such as drifting and substantial fiber breakage [12][13][14].If the temperature is too low, the rheological properties of the melt will deteriorate, and the swelling effect will increase at the exit of the spinneret holes, which can easily cause the melt to rupture, resulting in poor uniformity of the linear density of the injection head or fiber, increased evenness CV value, uneven dyeing of the fabric, and the appearance of stripes or patches on the fabric surface [15].Table 7 shows the study and analysis of the influence of spinning temperature on the preparation and performance of the modified PA6 fiber FDY.The experiment shows that when the spinning temperature is controlled between 250°C and 255°C, the melt has a good fiber forming condition, stable production operation, fewer broken ends, uniform fiber strands, and high fracture strength, as shown in Table 7.
Compared with the preparation of PA6 fibers of the same specification, the modified PA6 fibers show an increased solidification point when the melt is cooled into fibers.This may be because the addition of inorganic modifiers in the melt facilitates heat exchange between the melt and the surrounding cooling medium and promotes nucleation during the crystallization process of large molecules in the melt, resulting in relatively fast cooling of the melt into fibers [16].Therefore, the cooling conditions have a significant impact on the performance and operational status of the spectral heating and thermal storage composite-modified PA6 fibers.When the cooling air speed is too low or the temperature is excessively high, the melt's cooling rate diminishes.This leads to sufficient crystallization, resulting in elevated fiber crystallinity and well-formed lattices.However, the influence of macromolecular reorientation becomes more pronounced, and it becomes highly sensitive to the surrounding conditions.This ultimately leads to reduced fiber strength and uniformity.
On the other hand, when the cooling air speed is too high or the air temperature is too low, the cooling process accelerates.This causes a decline in both the crystallinity and the lattice perfection of macromolecules in the fibers.As a consequence, the fibers become more prone to becoming brittle, experiencing a decrease in toughness.Individual fibers are more susceptible to breaking and drifting away, giving rise to the formation of floating filaments [16].During post-processing or use, the monofilament is prone to breakage, resulting in the formation of filaments, broken ends, etc., which can lead to a decrease in product quality and usability.Tables 8  and 9 show the effects of cooling air speed and temperature on fiber performance and production, respectively.Using the side blowing cooling method, with a cooling air speed of 0.45-0.50m•s −1 and a cooling air temperature of 17-18°C, the fiber production and operation status is stable, with few abnormal situations such as breakage and floating wire, low C-value of the strip, good uniformity, and high strength of the finished product.
The initial fiber of PA6 fiber modified by spectral heating and thermal storage composite has a relatively high crystallinity, while the uniformity of supramolecular structures such as macromolecular crystallization and orientation is low.This is not conducive to improving the crystallinity and orientation of the final product during tensile deformation, resulting in lower strength.In the process of fiber preparation, spinning methods such as increasing spinning speed, high stretching ratio, and stretching deformation temperature are usually used to improve fiber strength.Due to the relatively high crystallinity and poor uniformity of the primary fibers, if the spinning speed is too high, it is easy for the single fibers to break, forming filaments and clumps, which can affect their performance and make the breakage prone.Therefore, a low speed, high temperature, and high magnification stretching process is adopted to rearrange the macromolecular chain segments under high temperature and high tensile conditions, improving crystallinity, orientation, and uniformity [17].Tables 10-12, respectively, show the effects of stretching ratio, secondary heat roller temperature, and spinning speed on fiber properties and operating conditions, which were analyzed under the optimal process conditions obtained from previous experiments.The stretching ratio is 1.5-1.6, the stretching temperature of the second hot roller is 170-180°C, and the first hot roller is a wire guide roller.When not heated, the production state is stable, and the fiber finished product has high strength.
The spinning speed has an important impact on the operational stability, mechanical properties, and production efficiency of the fiber sliver.If the spinning speed is too high, the fiber sliver will not operate stably, and the uniformity will be reduced, which may result in the formation of filaments or even breakage.If the speed is too low, the strength of the fiber product and the production efficiency will decrease, resulting in an increase in costs.Table 12 presents experimental data on the impact of different production speeds on fiber preparation and performance.The results show that at 4,200-4,300 m•min −1 , the production is relatively stable, with fewer broken ends.The fibers have good mechanical properties and uniform dyeing, and the finished product has a good appearance, as shown in Table 12.

Oiling process
By adding mineral inorganic powders to the fiber preparation process, friction between fibers and contact parts like the wire guide increases.This can damage the wire surface and even break single filaments, leading to clumping.This negatively affects fiber performance [15].Because of this, there are strict requirements for the wetting and coating abilities, as well as the strength of the oil film in spinning oil agents.The better these properties are, the more they protect the fiber.They can expand the options for processing the fiber and improve its mechanical properties.At the same time, the oil flow rate has a great impact on the Preparation and characterization of composite-modified PA6 fiber  7 preparation of fiber and the performance of the finished product.Insufficient oil flow leads to a thin film on the fiber surface, causing poor uniformity and making the fiber strip more prone to damage and breakage.This leads to issues like filaments, hairballs, and broken heads during operation, reducing production efficiency and the strength of the final product.On the other hand, excessive oil causes slipping of the silk strip during tension, uneven drying, and poor strength and dyeing uniformity.The production of the modified PA6 fiber FDY utilizes a high-temperature and intensive drawing process route, and the oiling rate should be relatively high.However, if the oiling rate is too high, the fiber is prone to slipping when stretched, producing stiff points or filaments, and causing coking on the surface of the heat roller, uneven heating of the fiber, increased unevenness, and decreased strength.If the oiling rate is too low, it is easy to cause single fiber breakage, resulting in finished filaments and clumps, which affects its utility for weaving.Table 13 shows the impact analysis of different oiling rates on fiber preparation and performance.When the oiling rate is between 1.3% and 1.5%, the fiber sliver runs stably and has high strength, good appearance, and uniform dyeing.

Characterization of fiber functionality
Utilizing the optimal process parameters derived from the preceding experimental phase, we will investigate the impacts of various increments of modified masterbatches on both fiber preparation and mechanical properties during production.This endeavor involves a comprehensive analysis and characterization of samples prepared using the ideal additive proportions.Table 14 shows the experimental analysis of the impact of different addition ratios of masterbatches on fiber preparation and performance.The mass ratio of masterbatch addition is between 6.0% and 8.0%, and the fiber strength, elongation at break, appearance quality, dyeing uniformity, and appearance quality are all good.When the additional amount of masterbatch is 10%, the CV values of breaking strength and elongation at break significantly increase, the uniformity of fiber quality decreases, and the appearance, dyeing uniformity, and operating condition deteriorate.
Functional testing analysis was conducted on the fiber sample with a 6% addition of the prepared masterbatch, and the results are shown in Table 15.It can be seen that when the fiber fabric reaches equilibrium under exposure to sunlight, the temperature is 21°C, which is higher than that of conventional product fabrics, and during the  heating process, the heating rate is as high as 1.9°C•min −1 , resulting in better spectral heating effect.The heat transfer coefficient is as low as 12 W•m −2 •K −1 , the Cro value is as high as 0.5, and the far infrared emissivity is as high as 98%, which indicates a good thermal storage and warmth preservation effect.

Conclusion
In this study, molybdenum oxide, tungsten trioxide, and graphene oxide have been harnessed as spectral heating and thermal storage modifiers for PA6 fibers.Each of these materials undergoes specific surface modifications.Subsequently, we employ a matrix layered coating technique to craft modified masterbatches.Through meticulous adjustment of addition ratios and precise control of spinning process parameters, we can achieve the fabrication of high-quality FDY composite fibers with exceptional mechanical strength and functional spectral heating and thermal storage properties.The basis of ensuring the seamless formation of melt fibers lies in the judicious management of water content within the PA6 chips.Furthermore, the optimal drying conditions for the masterbatch are carefully chosen to provide a solid basis and assurance for the subsequent fiber formation process.
The crux of maintaining consistent production operations and achieving superior product performance is in the careful selection and regulation of spinning speed, spinning temperature, stretching ratio, hot roller temperature, and oiling rate.These factors collectively contribute to the stability of the production process and the attainment of desired product attributes.
speed 4,300 m•min −1 , spinning temperature 255°C, cooling air speed 0.45 m•s −1 , cooling air temperature 18°C.The stretching ratio is 1.6, and the temperature of the secondary heating roller is 180°C.

Table 1 :
Main indicators of PA6 chips (after drying)

Table 2 :
Main indicators of PA6 composite modified masterbatch

Table 3 :
Main spinning process parameters of spectral heating and thermal storage composite modified PA6 fiber FDY

Table 4 :
Effect of modifier content in master batch on its performance

Table 5 :
Effect of different proportions of modifiers on fiber functionality

Table 6 :
Effect of drying conditions on production and operation efficiency

Table 7 :
Effect of spinning temperature on the preparation and performance of spectral heating and thermal storage composite modified PA6 fiber FDY

Table 8 :
Effect of cooling air speed on fiber preparation and performance (side blowing)

Table 9 :
Effect of cooling air temperature on fiber production status and physical properties (side blowing)

Table 10 :
Effect of stretching ratio on fiber properties and production status Note: The spinning temperature is 255°C, the cooling air speed is 0.45 m•s −1 , and the cooling air temperature is 18°C.

Table 11 :
Effect of second heat roll temperature on fiber properties and production status

Table 12 :
Effect of production speed on fiber preparation and performance

Table 13 :
Effect of oil rate on fiber preparation and performance Spinning speed 4,300 m•min −1 , spinning temperature 255°C, cooling air speed 0.45 m•s −1 , cooling air temperature 18°C.The stretching ratio is 1.6, and the temperature of the secondary heating roller is 180°C.

Table 14 :
Effect of masterbatch addition on

Table 15 :
Functional indicators of spectral heating and thermal storage composite modified PA6 fiber FDY