High-strength polylactic acid melt-spun fiber prepared by low-temperature cold drawing

Abstract

The application discloses a kind of high-strength polylactic acid melt-spun fibers prepared by low-temperature cold drawing.The preparation method comprises the following steps: (1) drying, polylactic acid chip is placed in oven for drying; (2) melt extrusion, polylactic acid chip after drying is put into screw extruder for heating and extrusion; (3) drawing, extruded polylactic acid melt is introduced to drawing roller, and the fiber is thinned by rotating speed; (4) collection, polylactic acid fiber is introduced to collection roller for winding.The application dries polylactic acid chip before use to remove moisture, avoiding hydrolysis in melt processing; spinning is carried out at a lower spinning temperature, ensuring the flowability of polylactic acid while avoiding the probability of high-temperature thermal degradation; drawing is carried out at room temperature, and polylactic acid fiber is oriented and induced to crystallize.The polylactic acid fiber obtained by the method has good mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of textile material processing technology, specifically relating to a high-strength polylactic acid melt-spun fiber prepared by low-temperature cold stretching. Background Technology

[0002] Plastics possess characteristics such as durability, lightweight, stability, and low cost, enabling high-level production and a wide range of applications. Furthermore, the chemical structure of most plastics allows for natural degradation, albeit extremely slowly. These two factors combined contribute to the highly prominent problem of plastic pollution. Currently, plastic pollution has become the second most significant global environmental issue after climate change, even forming new plastic strata, which has negatively impacted the environment and human health, posing a significant challenge to global sustainable development.

[0003] Driven by the concepts of sustainability and biodegradability, biopolymers synthesized from natural (plant / animal or microbial) sources are considered alternatives to synthetic polymers in various aspects. Compared with other biodegradable plastics, polylactic acid (PLA) has advantages in research foundation, market applications, key properties, and processing technology. It possesses characteristics such as transparency comparable to traditional resins and excellent mechanical properties, and has found some applications in food packaging, textiles and apparel, and biomedicine.

[0004] However, polylactic acid (PLA) suffers from poor mechanical properties, poor hydrophilicity, slow degradation rate, and poor thermal properties due to its numerous ester bonds, relatively low toughness, low melt strength, and slow crystallization rate, limiting its application and promotion. Many researchers have modified PLA for various applications, but research on pure PLA melt-spun fibers is limited. Extensive research and analysis have revealed that the molecular characteristics of PLA chips and processing conditions have a crucial impact on the performance of PLA melt-spun fibers. Due to different molecular characteristics and processing conditions, the tensile properties of PLA fibers vary greatly. Based on this, this invention provides a method for preparing PLA fibers with excellent mechanical properties, offering more research options for PLA fiber preparation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing high-strength polylactic acid melt-spun fibers by low-temperature cold stretching. Temperature and stretching are the most important factors in fiber processing, as polylactic acid crystallization can be caused by molecular rearrangement or by stress stretching of the material. Based on this, polylactic acid fibers with excellent mechanical properties are obtained by subjecting dried polylactic acid chips to low-temperature and cold stretching conditions.

[0006] This invention is achieved using the following technical solution:

[0007] A method for preparing high-strength polylactic acid melt-spun fibers by low-temperature cold stretching includes the following steps:

[0008] (1) Drying: Place the polylactic acid slices in an oven to dry;

[0009] (2) Melt extrusion: The dried polylactic acid chips are placed in a screw extruder and heated and extruded in an air atmosphere;

[0010] (3) Stretching: The extruded polylactic acid melt is guided onto the stretching roller, and the fiber is made thinner by rotating the roller.

[0011] (4) Collection: The polylactic acid fiber is guided onto the collection roller for winding.

[0012] In the above technical solution, the drying temperature of step (1) is 80-100℃ and the drying time is 12-24h.

[0013] Furthermore, the optical purity of the polylactic acid slices from step (1) meets the requirement of OP ≥ 90%.

[0014] Furthermore, the molecular weight of the polylactic acid chips in step (1) satisfies 0.8 × 10⁻⁶. 5 ≤WM≤1.5×10 5 .

[0015] Furthermore, the polylactic acid chips from step (1) have a narrow molecular weight distribution, satisfying WMD≤1.8.

[0016] Furthermore, the melt spinning temperature in step (2) is 170-190°C, and it can be carried out at a lower temperature (e.g., below 180°C), with a screw speed of 8-15 m / min. The stretching process is performed after melt spinning extrusion without sufficient cooling to utilize the remaining heat within the fiber to facilitate molecular chain segment movement.

[0017] Furthermore, the stretching temperature in step (3) is room temperature.

[0018] Furthermore, in step (3), there are two stretching rollers, with stretching roller 1 rotating at a speed of 100-150 m / min and stretching roller 2 rotating at a speed of 200-250 m / min.

[0019] Furthermore, the collecting roller speed in step (4) is 300 m / min.

[0020] The above technical solution has the following beneficial effects:

[0021] This invention involves drying polylactic acid (PLA) chips before use to remove moisture and prevent hydrolysis during melt processing; spinning is performed at a lower spinning temperature to ensure PLA flowability while minimizing the chance of high-temperature thermal degradation; and stretching is carried out at room temperature, causing the PLA fibers to orient and crystallize. PLA fibers obtained using this method exhibit good mechanical properties. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings:

[0023] Figure 1 The appearance morphology of the polylactic acid fibers obtained in Example 1;

[0024] Figure 2 The stress-strain curve of the polylactic acid fiber obtained in Example 1 is shown.

[0025] Figure 3 The image shows the XRD pattern of the polylactic acid fiber obtained in Example 1. Specific implementation methods

[0026] The present invention will be further described below with reference to embodiments:

[0027] Unless otherwise specified, the reagents, materials and equipment used in the following examples are commercially available or prepared by conventional methods.

[0028] Example 1

[0029] (1) Dry the polylactic acid slices in an oven at 80°C for 24 hours;

[0030] (2) The dried polylactic acid chips were placed in a screw extruder and heated and extruded. The melt spinning temperature was 170℃ and the screw speed was 10m / min.

[0031] (3) Stretching: The extruded polylactic acid melt is guided onto the stretching rollers. The speed of stretching roller 1 is 150 m / min and the speed of stretching roller 2 is 225 m / min.

[0032] (4) The polylactic acid fiber is guided onto the collecting roller for winding. The collecting roller speed is 300m / min.

[0033] Tests showed that polylactic acid fiber has a high refractive index, a relatively smooth surface, a fiber strength greater than 2.5 cN / dtex, and an elongation greater than 100%.

[0034] In addition, the polylactic acid chips in Example 1 were not dried, and the final polylactic acid fiber strength was less than 2.5 cN / dtex.

[0035] In addition, the melt spinning temperature of the polylactic acid chips in Example 1 was 200°C, and the polylactic acid melt underwent significant shear thinning, resulting in a polylactic acid fiber strength of less than 2.5 cN / dtex.

[0036] In addition, when the screw speed of the polylactic acid chips in Example 1 was greater than 15 m / min, the resulting polylactic acid fibers became brittle and had a strength of less than 2.5 cN / dtex.

[0037] In addition, when the stretch ratio of the polylactic acid fiber in Example 1 is greater than 3, the resulting polylactic acid fiber turns white, has a reduced elongation, and a strength greater than 2.5 cN / dtex.

[0038] As can be seen from the XRD pattern of the polylactic acid fiber obtained in Example 1, the polylactic acid fiber prepared by the method of the present invention has strong diffraction peaks and high crystallinity without the addition of any additives, and also has excellent mechanical properties.

[0039] Example 2

[0040] (1) Place the polylactic acid slices in an oven at 100°C and dry for 18 hours;

[0041] (2) The dried polylactic acid chips were placed in a screw extruder and heated and extruded. The melt spinning temperature was 175℃ and the screw speed was 10m / min.

[0042] (3) Stretching: The extruded polylactic acid melt is guided onto the stretching rollers. The speed of stretching roller 1 is 150 m / min and the speed of stretching roller 2 is 225 m / min.

[0043] (4) The polylactic acid fiber is guided onto the collecting roller for winding. The collecting roller speed is 300m / min.

[0044] Tests showed that polylactic acid fiber has a high refractive index, a relatively smooth surface, a fiber strength greater than 2.5 cN / dtex, and an elongation greater than 100%.

[0045] Example 3

[0046] (1) Dry the polylactic acid slices in an oven at 80°C for 24 hours;

[0047] (2) The dried polylactic acid chips were placed in a screw extruder and heated and extruded. The melt spinning temperature was 180℃ and the screw speed was 9m / min.

[0048] (3) Stretching: The extruded polylactic acid melt is guided onto the stretching rollers. The speed of stretching roller 1 is 150 m / min and the speed of stretching roller 2 is 225 m / min.

[0049] (4) The polylactic acid fiber is guided onto the collecting roller for winding. The collecting roller speed is 300m / min.

[0050] Tests showed that polylactic acid fiber has a high refractive index, a relatively smooth surface, a fiber strength greater than 2.5 cN / dtex, and an elongation greater than 100%.

[0051] Example 4

[0052] (1) Dry the polylactic acid slices in an oven at 80°C for 24 hours;

[0053] (2) The dried polylactic acid chips were placed in a screw extruder and heated and extruded. The melt spinning temperature was 175℃ and the screw speed was 10m / min.

[0054] (3) Stretching: The extruded polylactic acid melt is guided onto the stretching rollers. The speed of stretching roller 1 is 130 m / min and the speed of stretching roller 2 is 210 m / min.

[0055] (4) The polylactic acid fiber is guided onto the collecting roller for winding. The collecting roller speed is 300m / min.

[0056] Tests showed that polylactic acid fiber has a high refractive index, a relatively smooth surface, a fiber strength greater than 2.5 cN / dtex, and an elongation greater than 100%.

[0057] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A high-strength polylactic acid melt-spun fiber prepared by low-temperature cold stretching, characterized in that: Includes the following steps: (1) Drying: Place the polylactic acid slices in an oven for drying; the drying temperature is 80-100℃ and the drying time is 12-24h. (2) Melt extrusion: The dried polylactic acid chips are placed in a screw extruder and heated for extrusion; the melt spinning temperature is 170-190℃ and the screw speed is 8-15 m / min; (3) Stretching: The extruded polylactic acid melt is guided onto the stretching roller, and the fiber is made thinner by rotating the roller. The stretching temperature is room temperature. There are two stretching rollers. The rotation speed of stretching roller 1 is 100-150 m / min, and the rotation speed of stretching roller 2 is 200-250 m / min. (4) Collection: The polylactic acid fiber is guided onto the collection roller for winding.

2. The high-strength polylactic acid melt-spun fiber prepared by low-temperature cold stretching according to claim 1, characterized in that: The optical purity of the polylactic acid slices obtained in step (1) meets the requirement of OP≥90%.

3. The high-strength polylactic acid melt-spun fiber prepared by low-temperature cold stretching according to claim 1, characterized in that: The polylactic acid chips obtained in step (1) have a molecular weight of 0.8 × 10⁻⁶. 5 ≤WM≤1.5×10 5 .

4. The high-strength polylactic acid melt-spun fiber prepared by low-temperature cold stretching according to claim 1, characterized in that: The molecular weight distribution of the polylactic acid chips in step (1) satisfies WMD≤1.

8.

5. The high-strength polylactic acid melt-spun fiber prepared by low-temperature cold stretching according to claim 1, characterized in that: The collecting roller speed in step (4) is 300 m / min.

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