Preparation and characterization of biodegradable polyester fibers enhanced with antibacterial and antiviral organic composites

2.1 Raw materials

PET chips (semi-extinction, fiber grade) were purchased from Zhejiang Hengyi High-tech Material Co., Ltd. The average molecular weight of the PET chip was about 2.4 × 10⁴, and this was the main raw material for fiber preparation. The PET chips were pre-crystallized and dried before use. PHBV antibacterial and antiviral masterbatch was purchased from a prime masterbatch manufacturer Zhejiang Jincai New Materials Co., Ltd, One of the leading masterbatch suppliers in the industry. PHBV is an active ingredient, with an average molecular weight of approximately 5.3 × 10⁵ and an active ingredient mass ratio of 50%. It was used as a natural antibacterial and antiviral modifier, and drying was required before use. Anaerobic infective agents were purchased from a major domestic biodegradable agent business enterprise Shanghai Tiansu Trading Co., Ltd., with epoxide [poly(ethylene oxide)], glycine (α-glucosidase), and bisphenol A as the main components. It was used as an organic biodegradable modifier, requiring no treatment before use. The indexes of PET chips and PHBV masterbatch are summarized in Tables 1 and 2, respectively.

2.2 Main equipment

An FBM320-type pre-crystallization in-line drying equipment was procured from Zhengzhou Zhongyuan Drying Technology Co., Ltd. An SZG-type double-cone vacuum drum dryer was procured from Changzhou Yongjin Drying Equipment Co., Ltd. An FDY two-component chemical fiber spinning test machine was purchased from Beijing Zhongli Machine Engineering Technology Co., Ltd. A weightless masterbatch-adding device with a three-component mixing feeding system was purchased from Jiangsu Jiangben Automatic Control Equipment Co., Ltd. A YG023B-II-type automatic single-yarn strength machine was procured from Changzhou Textile Instrument Co., Ltd. A USTER Ⅴ-type evenness tester was procured from Uster Technology Co., Ltd. (Switzerland). An SU8010-type scanning electron microscope (SEM) (Hitachi Ltd.) and an ARL™ EQUINOX6000-type X-ray diffractometer (XRD) (Thermo Fisher Scientific Co., Ltd.) were used. A 209F1 Irish-type thermogratings tester (Netzsch, Germany) was used and operated under nitrogen atmosphere conditions with a temperature rise rate of 10°C·min⁻¹ from room temperature to 700°C.

2.3 Testing and characterization

According to the national standard “GB/T 8960-2015 Polyester FDY,” the mechanical performance of profiled bright and colorful polyester fiber was tested using a polyester strength and elongation tester manufactured by Changzhou Textile Instrument Co., Ltd., with a tensile speed of 150 mm·min⁻¹, a spacing of 300 mm, and a preloaded tension of 0.5 cN·dtex⁻¹. Each sample was randomly sampled three times, and the average was taken. According to the national standard “GB/T 14346-1993 Test method for electronic unevenness of chemical fiber filaments,” the evenness of the profiled bright and colorful polyester fiber was tested using an evenness tester manufactured by Uster Technology Co., Ltd. (Switzerland). The test length was 1,000 m, and the test speed was 200 m·min⁻¹. Each sample was randomly sampled three times, and the average was taken. The cross-sectional morphology of the profiled fiber was observed using an SEM. The biodegradable performance of the fiber was tested over a 45-day cycle according to the American standard “ASTM D5511 (American standard for anaerobic microbial degradation D5511) anaerobic biodegradation test method.” The antibacterial and bacteriostatic properties of fiber fabrics were tested according to the national standard “GB/T 31713-2015 Safety and health requirements for antibacterial textiles.” The antiviral properties of fiber fabrics were tested according to the international standard “ISO 18184 2019 (E) (International Organization for Standardization 18184 2019 (E)) textiles-Determination of antiviral activity of textile products.” Different proportions of PET, PHBV, and biodegradable agents were mixed, and the resulting mixture was prepared according to the fiber preparation process conditions before being passed through the production line screw extruder manufactured by Beijing Zhongli Machine Engineering Technology Co., Ltd. The TG, DSC, XRD, and fiber cross-sectional structures were observed and analyzed.

2.4 Spinning procedure

The main spinning process of the biodegradable, antibacterial, and antiviral organic composite-modified polyester fiber is shown in Figure 1. After drying, the PHBV antibacterial and antiviral masterbatch, PET chips, and biodegradable agent were mixed in a certain proportion. The mixture was then squeezed with a screw and heated at a high temperature until it melted. After screw metering, pre-filter filtration, and metering pump, the melt was accurate metering and filtering and then entered into the spinner hole. Under a certain melt pressure, the melt was sprayed from the spinneret hole, forming a stream of melt, which was cooled and dried by air and solidified into a fiber. After passing through the oil nozzle and undergoing pre-network bunching, the fiber was fed into the first and second hot rolls, where it was heated, stretched, and deformed. Subsequently, the fiber entered the main network nozzle for additional bunching treatment to further strengthen the bunching and adhesion between single fibers. Finally, the fiber was directed into the winding system to be winded into the finished fiber FDY.

Figure 1

Main spinning process of the biodegradable, antibacterial, and antiviral organic composite–modified polyester fiber.

The PET chips were the main raw material for fiber preparation, usually accounting for 93–98.5% of the mass ratio of the finished fiber. PHBV is a biological antibacterial and antiviral modifier. Its addition ratio was 1.0–5.0%, which guaranteed the biological antibacterial and antiviral properties of the prepared polyester fiber. The biodegradable agent was a modifier that ensured the biodegradable properties of the prepared polyester fiber, and it was added at a ratio of 0.5–2.0%. The screw extruder melted the slices to form a melt, and the melt was measured. The pre-filter coarse filtered impurities of large particle sizes in the melt to extend the service cycle of the component, with a filtration accuracy of 15 μm. If the filtration accuracy was too high, the service cycle of the filter element was too short. If the filtration accuracy was too low, a large number of impurities entered the melt after filtering into the component, the service cycle of the component was shortened, and the quality of the fiber product worsened. The component performed fine filtration of the melt to further reduce impurities and improve the quality of the finished fiber. At the same time, a fine flow of melt was formed through the spinneret hole on the spinneret plate in the component. The diameter of the spinneret hole was 0.15 mm, the length of the microhole was 0.30 mm, and the length–diameter ratio was 2:1. The melt trickle was heat exchanged with the side-blowing air flow with a certain temperature, humidity, and blowing speed, and the temperature gradually decreased. When the temperature was lower than the melting point, the melt trickle solidified into a fiber. The wind temperature was maintained at 18°C, with a relative humidity of 95% and a wind speed of 0.40 m·s⁻¹. The oil nozzle mainly oases the fiber, forming a uniform oil film on its surface, reducing the wear of the fiber strip during postprocessing and use, and increasing the bunching between individual fibers. The pre-network was used to cluster the fiber bundles, facilitating fiber stretching, deformation, and heat setting. The fiber was stretched and deformed by the speed difference between the first hot roll and the second hot roll. The temperature of the first and second hot rolls provided heat for fiber deformation and fiber shaping, respectively. The winding system shaped the finished fiber according to the predetermined specifications, forming the finished yarn roll. The important spinning process parameters are listed in Table 3.

3.1 Drying of raw materials and additives

The formation of a biodegradable, antibacterial, and antiviral organic composite–modified polyester fiber requires the addition of appropriate amounts of biodegradation agents and PHBV within the PET melt. Polyester biodegradable agents mainly comprise organic materials, such as polymers and monosaccharides, formed by the polymerization of polylactic acid molecules, which are mostly short-chain hydrophilic polyhydroxy mixtures. If the raw materials and additives are not dried well and the water content is too high, enhancing the hydrolysis of PET melt is easy in the high-temperature melting state, resulting in a rapid decline in the viscosity of the PET melt, making it easy to rupture and challenging to form fibers (4,5). The polyester PET chips were dried using an in-line drying device and the masterbatch was dried using the vacuum drum dryer at high temperature. Table 4 shows the effects of different drying conditions on the spinnability of fibers and the physical properties of products. As observed, the drying temperature of PET chips and PHBV antibacterial and antiviral masterbatch was 175°C, the drying time was 20 h, and the water content of chips and masterbatch was about 15 ppm after drying. The melt had good fiber-forming performance, and the mechanical performance of the product was good. When the water content was higher than 30 ppm, the strength and elongation at the break of the finished fiber obviously reduced, the spinnability became worse, and the breakage was severe, indicating that the hydrolysis of macromolecules was serious and the strength and toughness of the finished fiber were worse. When the drying temperature was 182°C, the water content of the chips after drying did not change significantly. However, the mechanical performance and operational status of the fibers exhibited a tendency to deteriorate, which might be due to the high drying temperature, long drying time, and thermal decomposition of PET. The biodegradation agents did not have an obvious melting point, and the softening temperature was extremely low, so they were not dried.

3.2 Effects of modifiers

The amount of PHBV organic antibacterial antiviral modifier and biodegradable modifier added had certain effects on the structure and thermal stability of the blend system, significantly influencing the fiber-forming and physical properties of the finished product. PHBV masterbatches and slices were dried at 175°C for 20 h and then prepared in different proportions of PHBV masterbatches, biodegraders, and PET blends according to the same process for thermogravimetric and XRD analyses. The cross-sectional structure of the blends was observed using SEM. The fiber-forming and physical properties of finished products were tested and analyzed with varying amounts of modifiers. Additionally, the biodegradability of fiber fabric under anaerobic conditions was tested according to the American standard ASTM D 5511 anaerobic biodegradation test method.

Figure 2 shows the effects of additives on thermal stability. It shows the influence of different proportions of the modifier on thermal stability. The increase in additives decreased the start and end temperatures of the mixture during thermal decomposition. Also, the thermal stability decreased. This might be due to the addition of the modifier, which reduced the regularity of the arrangement of PET macromolecules and decreased its thermal stability. However, the temperature was higher than 300°, meeting the requirements of high-temperature melt spinning.

Figure 2

Effects of additives on thermal stability for (a) pure PET, (b) biodegradant 1.0%, PHBV masterbatch 0.5%, and (c) biodegradant 2.0%, PHBV masterbatch 5.0%.

Figure 3 shows the influence of modifier on crystallization properties and Table 5 shows the XRD analysis data and peak analysis of mixture samples. It illustrates the XRD analysis of blends. It shows that crystallinity and crystal particle size decreased somewhat with the increase in modifier addition, but the change was not significant.

Figure 3

Influence of modifier on crystallization properties for (a) XRD test of pure PET and (b) XRD test of blends with different proportions of modifier.

Figure 4 shows the SEM images of different proportions of blends. The SEM images of the cross-sections of blends of different proportions showed that the blends had no stratification, agglomeration, and catalysis, and continuous dispersion was better than that of the blends.

Figure 4

SEM images of different proportions of blends for (a) pure PET, (b) biodegradable agent 1.0% and PHBV masterbatch 2.0%, and (c) biodegradable agent 2.0%, PHBV masterbatch 5.0%.

Table 6 shows the effects of modifier content on the fiber-forming performance and physical properties of products. It shows the effects of different modifiers on the fiber-forming performance and physical properties of products. As indicated, when the content of biodegradation agents was 1.5% and the PHBV masterbatch content was 4.0%, the fiber spinnability, biodegradation performance, and fiber mechanical strength were all good. When the content of two modifiers was too high, the fibers were difficult to form and the mechanical strength of the finished product and the elongation at break were poor. When the content was too low, the biodegradation performance deteriorated (3,5).

3.3 Fiber preparation process

During the preparation of a biodegradable, antibacterial, and antiviral organic composite-modified polyester fiber, biodegradation agents and PHBV, which were easily hydrolyzed, were added. The optimization of the spinning process parameters was explored to improve the fiber-forming performance and the usability of the finished products. Table 7 shows the effects of spinning temperature on the fiber-forming performance and physical properties of the products of FDY. As indicated, when the spinning temperature was 285°C, the spinning condition was the best, the fiber strength was the highest, the coefficient of variance (CV) value was the smallest, and the uniformity was the best. At this time, the rheological properties of the melt and the dispersion uniformity of each component were also the best. When the temperature was higher than 290°C, the breakage increased, the fiber strength decreased obviously, the CV value increased, and the uniformity decreased. This could be ascribed to the enhanced hydrolysis and thermal degradation of macromolecules at high temperatures. When the temperature was reduced to 282°C, the enhancement was negligible and the operation was good. However, the CV value of the fiber evenness increased and the uniformity decreased significantly. This was because the viscosity of the PET melt increased and the rheological properties deteriorated with the decrease in temperature (6,7).

During the preparation of a biodegradable, antibacterial, and antiviral organic composite-modified polyester fiber, the cooling rate during the PET melt cooling process significantly impacted the fiber formation and properties of the finished products. If the cooling was too slow, the macromolecules took longer to arrange in an orderly manner, easily leading to insufficient crystallization, lower fiber crystallinity and orientation, and lower strength. If the cooling was too fast, the fiber monofilament skin-core effect was serious and the uniformity of fabric dyeing decreased (8,9). Table 8 shows the effects of cooling wind speed on the stability of fiber preparation operation and the performance of finished products. Table 9 shows the effects of cooling wind temperature on fiber preparation operation and fiber properties. As indicated, when the cooling wind speed was 0.35 m·s⁻¹ and the cooling wind temperature was 20°C, the fiber production was more stable, with less breakage and fluttering, good uniformity, and higher strength of finished products.

The stretching process between the primary and secondary hot rolls directly affected the crystallinity, orientation, and homogeneity of polymer molecules. The selection of the tensile deformation temperature of the primary hot roll, the setting temperature of the secondary hot roll, and the draw ratio obtained from the speed difference between the primary and secondary hot rolls is essential. Generally, the fiber strength is increased by choosing a high draw ratio, tensile deformation temperature, and setting temperature. Usually, the higher the temperature of the two hot rollers, the greater the speed difference, the higher the tensile multiple, the regular the arrangement of fiber macromolecules, the higher the degree of crystallinity, orientation, and uniformity, the higher the strength of the fiber product, and the better the quality uniformity, and vice versa. However, if the deformation, setting temperature, and draw ratio are too high, monofilament breakage, formation of hairy filaments and clusters, and reduction in strength and usability occur (10,11). If the draw ratio, deformation, and setting temperatures are too low, insufficient tensile deformation and poor stability easily occur, the fibers are prone to stiffness and tightness, and the fabric dyeing presents stripe abnormalities. The experimental results in this study showed that the production operation was stable and the strength and dyeing uniformity of the finished fiber were good under the condition of a draw ratio of 2.8, primary hot roll temperature of 74°C, and secondary hot roll temperature of 153°C. The product indicators under different process conditions are shown in Tables 10–12.

In the fiber FDY production process, the speed of the second hot roll is usually used as an indicator to evaluate the production speed and is called the production speed. The production speed influences the stability of fiber preparation and the mechanical strength of the finished product. Generally, a low winding speed improves the stability of production, makes the aggregation state of fiber macromolecules more homogeneous, and increases the strength (12). As shown in Table 13, when the production speed was 4,100–4,200 m·min⁻¹, the production was more stable, the breakage was less, the fiber had good mechanical strength and dyeing uniformity, and the finished product had a good appearance.

3.4 Mechanical and biodegradation performances of the fiber products

The optimum process parameters obtained from the aforementioned test process were the process conditions. The fiber samples were prepared with the content of PHBV antibacterial and antiviral masterbatch being 4.0% and the content of biodegradable agents being 1.5%. Also, their mechanical performance and biodegradability indexes were tested. Table 14 Sample indexes of biodegradable antibacterial and antiviral organic composite modified polyester FDY fiber. It shows that the linear density of the fiber was 71.5 dtex. The failure strength was 3.5 cN·dtex⁻¹, and the elongation at break was 23%. The CV of each index was small, and the quality was uniform. The 65D/72f FDY fiber samples were woven using a high-speed three-thread fleece weft knitting machine (Fujian Longwei Precision Machinery Co., Ltd.) according to the conventional weft knitted fabric structure. The biodegradable performance of the fabric was tested according to the American standard “ASTM D5511 Anaerobic biodegradation test method.” The degradation rate of the fabric was 13.17% within 45 days.

Figure 5 shows the stress–strain curves of the fiber tensile process. It shows the tensile stress-strain curve of the fiber. It can be seen that the strength of the fiber decreases with the increase of the addition of biodegradable agents and PHBV masterbatch, which is because the addition of modifiers intensifies the thermal degradation of PET macromolecules in the spinning process. However, the curve shape did not change significantly, indicating that the intrinsic quality of the fiber was uniform and stable.

Figure 5

Stress–strain curves of fiber tensile process.

Figure 6 shows the fiber biodegradability test diagram It shows the fiber biodegradability test data and process analysis diagram. It can be seen that the fiber has good biodegradability, and methane (CH₄) and carbon dioxide (CO₂) are generated after degradation, without residue.

Figure 6

Fiber biodegradability test diagram for (a) test data diagram, (b) test process diagram, (c) before test fiber diagram, and (d) after test fiber diagram.

Figure 7 shows the data of antibacterial and antiviral tests of fiber. It shows the test data of antibacterial and antiviral performances of the fiber. It can be seen that the antibacterial rate of Staphylococcus aureus, Escherichia coli, and Candida albicans of fiber is 99% and 96% and the antiviral activity value Mv reaches 2.92. It indicated good comprehensive antibacterial and antiviral performances.

Figure 7

Data of antibacterial and antiviral test of fiber: for (a) antibacterial performance and (b) antiviral performance.