CN116288808A

CN116288808A - Preparation method of all-stereo composite melt electrostatic spinning polylactic acid fiber

Info

Publication number: CN116288808A
Application number: CN202310463771.3A
Authority: CN
Inventors: 汪滨; 金旭; 张秀芹; 马佳瑜; 赵晰蒙; 杨梦娟; 武文琦
Original assignee: Beijing Institute Fashion Technology
Current assignee: Beijing Institute Fashion Technology
Priority date: 2023-04-26
Filing date: 2023-04-26
Publication date: 2023-06-23

Abstract

The invention provides a preparation method of an all-stereo composite melt electrostatic spinning polylactic acid fiber, belonging to the technical field of high polymer materials and preparation thereof. Comprising the following steps: melt blending poly-L-lactic acid and poly-D-lactic acid to obtain a composite polylactic acid material; carrying out melt electrostatic spinning on the composite polylactic acid material to obtain a full-stereo composite melt electrostatic spinning polylactic acid fiber; the conditions of the melt electrospinning include: the air flow pushing speed is 0.2-5 psi, the spinning voltage is 11-17 kV, and the rotating speed of the roller is 500-2000 rpm. The full-stereo composite PLA superfine fiber is prepared by regulating and controlling spinning parameters. The molecular chains are arranged in a highly oriented way under the action of a high-voltage electric field during the melt electrostatic spinning, the subsequent heat treatment is more easy to generate stereocrystals, and the stereocrystal content is improved. The obtained polylactic acid fiber material has the characteristics of high stereocrystal content and good heat resistance.

Description

Preparation method of all-stereo composite melt electrostatic spinning polylactic acid fiber

Technical Field

The invention relates to the technical field of high polymer materials and preparation thereof, in particular to a preparation method of a full-stereo composite melt-spun polylactic acid fiber.

Background

Polylactic acid (PLA) is a biodegradable aliphatic polyester, which is manufactured by processing renewable crops such as corn starch, and can be degraded into CO in natural environment after being used ₂ And H ₂ O has the advantages of no toxicity, no stimulation, green environmental protection and the like, is an environment-friendly type green polymer material with great development potential, and becomes the focus of research in recent years. In addition, polylactic acid has good biocompatibility and better thermoplastic processability, and has been widely applied to the fields of plastics, clothing, medical treatment and the like. The fiber can be obtained by spinning polylactic acid, the surface of the polylactic acid fiber is slightly acidic, and the polylactic acid fiber has good affinity with skin and natural antibacterial property; the polylactic acid fiber also has better slip, softness, comfort, dryness, ventilation and ultraviolet resistance, and has good luster, elasticity and bulkiness, is a sustainable textile material with development prospect, but has poor heat resistance and is easy to hydrolyze in hot and humid environment, thus limiting the large-scale application.

The polylactic acid monomer lactic acid is a chiral molecule, and the formed polylactic acid has two enantiomers of poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA), and researches show that the poly-L-lactic acid and the poly-D-lactic acid can be mixed under certain conditions to form the stereocomplex polylactic acid (Sc-PLA) with a special spiral structure, the Sc-PLA has stereocrystal crystal with a melting point which is about 50 ℃ higher than that of the polylactic acid homopolymer crystal alpha crystal, the heat resistance of the polylactic acid can be improved, the excellent mechanical property and hydrolysis resistance can be shown, and the application range of the polylactic acid can be greatly widened. The report that PLLA and PDLA can be blended to form a stereocomplex crystal is published for the first time in 1987 by IKADY et al, which indicates that Sc-PLA has obvious difference in structure and performance from PLLA and PDLA. The discovery of the stereocrystal provides a new idea for the modification of heat-resistant PLA.

The current methods for preparing Sc-PLA fibers mainly comprise a solution spinning method, a solution electrostatic spinning method and a melt spinning method. The solution spinning method is divided into wet spinning and dry spinning, the wet spinning is to extrude the spinning solution prepared by the solution method from the fine holes of the spinneret to form thin flow, then solidify the thin flow into filaments in the coagulating liquid, and the dry spinning is to extrude the spinning solution prepared by the solution spinning from the spinneret holes to form thin flow, and then solidify the thin flow into filaments in hot air due to sonic volatilization of the solvent. The PLA solution spinning method mostly uses toluene, methylene dichloride or chloroform and the like as solvents, and has the advantages that PLLA and PDLA molecules in the solution are easy to disperse uniformly, a structural composite structure is easy to form, and the spinning process is stable. However, the commercialization process for preparing Sc-PLA fibers by solution spinning is restricted by a plurality of factors such as high cost, large environmental damage, toxic solvent, difficult recovery and the like.

The solution electrostatic spinning method is a polymer jet electrostatic drawing spinning method capable of preparing superfine fibers, and the charged polymer solution is solidified in an electrostatic field to form nano-scale or submicron-scale fibers. However, the commercialization process of PLA electrostatic spinning is restricted by a plurality of factors such as toxic solvents and difficult recovery.

The melt spinning method is a spinning method in which a polymer is heated and melted and extruded through a spinneret orifice, and cooled and solidified in air to form a fiber. In contrast, the melt spinning method has no solvent, directly melt-spins the polymer, and avoids the problems of toxicity and difficult recovery of the solvent used in the electrostatic spinning method, but the solvent is difficult to uniformly disperse molecular chains so as to achieve the precondition of forming the stereocomplex crystal. Therefore, it remains a difficulty how to spin polylactic acid and obtain polylactic acid fibers having as high a stereochemical content as possible without using a solvent.

As a novel electrostatic spinning technology, the melt electrostatic spinning technology does not need solvents, does not have complex processes such as solution preparation, residual solvent removal and the like, and can be used for preparing ultrafine fibers such as PP, PE, PPS which cannot be prepared at normal temperature by the solution electrostatic spinning technology. And the solvent is not volatilized, and the conversion rate of the raw materials is 100%. The spinning efficiency is at least one order of magnitude higher than that of solution electrostatic spinning, and the obtained fiber has no pores caused by solvent volatilization and high fiber strength. Therefore, the PLA superfine fiber with high stereocrystal content can be obtained by adopting a melt electrostatic spinning method.

Therefore, developing a novel all-stereo composite melt electrostatic spinning polylactic acid fiber and a preparation method thereof has very important significance for promoting the application of the polylactic acid fiber.

Disclosure of Invention

In order to solve the problems, the present invention provides a method for preparing a fully-stereo composite melt-spun polylactic acid fiber, and the inventor of the present invention has conducted intensive studies and found that: and the melt electrostatic spinning technology is adopted, and the spinning parameters (voltage, air flow, roller rotating speed and the like) are regulated and controlled to prepare the full-stereo composite PLA superfine fiber. And the molecular chains are highly oriented and arranged under the action of a high-voltage electric field during melt electrostatic spinning, so that the stereocrystal is easier to generate after subsequent heat treatment, and the stereocrystal content is improved. The polylactic acid fiber material has the characteristics of high content of stereocrystal and good heat resistance, and the method for preparing the full-stereocomplex polylactic acid material by adopting the melt electrostatic spinning technology is simple, has no toxic solvent, low cost and no pollution, and can be used for further preparing surgical sutures, medical filter materials, high-grade clothing fabrics and the like, thereby having wide application prospect.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a preparation method of an all-stereo composite melt-spun polylactic acid fiber, which comprises the following steps:

1) Melt blending poly-L-lactic acid and poly-D-lactic acid to obtain a composite polylactic acid material;

2) Carrying out melt electrostatic spinning on the composite polylactic acid material obtained in the step 1) to obtain a full-stereo composite melt electrostatic spinning polylactic acid fiber;

the conditions of the melt electrospinning include:

the air flow pushing speed is 0.2-5 psi, the spinning voltage is 11-17 kV, and the rotating speed of the roller is 500-2000 rpm.

Preferably, the conditions of the step 2) of melt electrospinning include: the air flow pushing speed is 0.5-2 psi, the spinning voltage is 13-15 kV, and the rotating speed of the roller is 1000-1500 rpm.

Preferably, the conditions of the step 2) of melt electrospinning further include: the temperature of the material pipe is 180-250 ℃, and the temperature of the needle head is 185-255 ℃.

Preferably, the mass ratio of the poly-L-lactic acid to the poly-D-lactic acid in the step 1) is 2-8:2-8.

Preferably, the conditions of the melt blending in the step 1) include: the temperature is 180-250 ℃, the time is 1-20 min, and the rotating speed is 10-100 rpm.

Preferably, the conditions of melt blending include: the temperature is 190-230 ℃, the time is 3-15 min, and the rotating speed is 30-80 rpm.

Preferably, the obtained composite polylactic acid material is subjected to melt electrostatic spinning and then further comprises annealing treatment, so that the all-dimensional composite melt electrostatic spinning polylactic acid fiber is obtained.

Preferably, the annealing temperature is 130-190 ℃.

Preferably, the annealing temperature is 160 ℃.

Preferably, the annealing time is 60s.

The temperature of the melting peak of the polylactic acid fiber material measured by a differential scanning calorimeter is more than 210 ℃; the XRD pattern of the polylactic acid material has crystal face diffraction peaks of stereocrystals at 12 degrees, 21 degrees and 24 degrees of 2 theta.

The beneficial effects of the invention are as follows:

1. the invention provides an all-stereo composite polylactic acid fiber material.

2. The melting point of the full-stereo composite polylactic acid fiber material provided by the invention can reach more than 210 ℃, the heat resistance is good, the defect of inherent low heat resistance of polylactic acid is overcome, and the application range of the polylactic acid is widened.

3. The invention adopts a melt-based electrostatic spinning method to prepare the full-stereo composite polylactic acid fiber. Firstly, PLLA and PDLA are blended to prepare the stereocomplex polylactic acid, and then the stereocomplex polylactic acid is prepared into filaments by a melt electrostatic spinning method. The preparation method of the melt electrostatic spinning is novel and simple to operate, avoids the problems of toxicity and difficult recovery of the traditional electrostatic spinning solvent, and does not generate harmful substances to pollute the environment. And the molecular chains are highly oriented and arranged under the action of a high-voltage electric field during melt electrostatic spinning, so that the stereocrystal is easier to generate after subsequent heat treatment, and the content of the stereocrystal is improved.

4. The preparation method of the all-stereo composite polylactic acid fiber provided by the invention is simple, easy to operate and controllable, low in cost, environment-friendly, energy-saving and suitable for industrial mass production.

5. The method provided by the invention is beneficial to preparing the molded products of the polylactic acid fiber material with full-stereocrystal content, such as surgical suture lines, medical filter materials, high-grade fabrics for administration and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments will be briefly described below.

FIG. 1 is an electron microscope image obtained in examples 1-4, and it can be seen from FIG. 1 that under certain conditions, the greater the air flow pushing speed, the faster the fiber melt tends to be extruded, the less the voltage is than when the molecular chain is stretched, and the fiber is in a distorted shape;

FIG. 2 is an electron microscope image obtained in examples 5-8, and it can be seen from FIG. 2 that under certain conditions, the spinning voltage is too low, the melt is not well stretched, and the spun fibers are mostly bent and uneven in thickness; under the condition of proper spinning voltage, the obtained fiber has uniform thickness, smooth surface and good appearance; the spinning voltage is too high, the drawing is too fast, the fiber is easy to break, and the fiber thickness is uneven;

FIG. 3 is an electron microscope image obtained in examples 9-12, and it can be seen from FIG. 3 that under certain conditions, the rotation speed of the roller is too low, the melt is not well stretched, the fibers are not fully oriented, and the spun fibers are bent in a plurality of numbers; under the condition of proper rotating speed of the roller, the obtained fiber has uniform thickness, smooth surface and good appearance. And as the rotational speed of the roller increases, the diameter of the fiber becomes smaller gradually, for example, the average diameter of the fiber at 2000rpm is 8.3 μm;

FIG. 4 is a plot of DSC curves of the fibers prepared in examples 13-15 at one temperature rise, where the melting point of the Sc-PLA fibers is above 210℃and the melting peak of the polymer alpha crystals does not appear, which is a good indication of successful preparation of the fully stereocomplex polylactic acid fibers. And the heat treatment accompanied with annealing causes the cold crystallization peak to disappear completely, the area of the melting peak of the stereocrystal is basically unchanged, the peak becomes sharp gradually, the crystal is perfected gradually, and the heat resistance is improved;

fig. 5 is an XRD pattern of the fibers prepared in examples 13 to 15, from which it can be seen that the XRD pattern of the polylactic acid fiber material has crystal plane diffraction peaks at 2θ of 12 °, 21 ° and 24 °, which are crystal plane diffraction peaks of stereocrystal, and crystal plane diffraction peaks of alpha-crystal do not occur, which fully illustrates successful preparation of the all-stereocomplex polylactic acid fiber.

Detailed Description

the conditions of the melt electrospinning include:

And step 1, blending the poly-L-lactic acid and the poly-D-lactic acid.

According to the invention, the PDLA and the PLLA can be blended to form the stereocomplex polylactic acid (Sc-PLA), the melting point of the stereocomplex crystal (Sc) is higher than that of the pure PLLA or the pure PDLA by about 50 ℃, and the Sc-PLA has excellent mechanical property and heat resistance, has good practical application value, and widens the application range of the polylactic acid. The PLLA and PDLA crystals are alpha crystals, the molecular chains of the PLLA and PDLA crystals form a pseudo-orthorhombic system through spiral stacking, and the crystal of the stereocomplex crystal (Sc) is converted into a triclinic system or a trigonal system, and in the stacking formed by the spirals, the chain stacking is more compact, so that the melting point of the material is improved, and the heat resistance is improved.

In the invention, the poly-L-lactic acid and the poly-D-lactic acid are commercial products. Poly-l-lactic acid was purchased from zhejiang ocean biotechnology limited under the designation revole 190; poly-d-lactic acid was purchased from Nature Works, usa.

In the invention, in the step 1, poly-L-lactic acid and poly-D-lactic acid are subjected to blending modification to prepare the full-stereo composite polylactic acid. According to the invention, in step 1, the mass ratio of total poly-L-lactic acid PLLA to total poly-D-lactic acid PDLA is from 2:8 to 8:2, preferably from 3:7 to 7:3, more preferably from 4:6 to 6:4, for example 5:5. According to the invention, in the process of preparing Sc-PLA by blending PLLA and PDLA, sc-PLA with high stereocrystal content is easier to form when the blending weight ratio of total PLLA to total PDLA is 1:1.

The blending method for preparing the stereocomplex polylactic acid comprises melt blending and solution blending. When Sc-PLA is prepared by solution blending, a large amount of toxic solvents such as dichloromethane, chloroform and the like are required, and the preparation process is complex, long in time consumption and low in efficiency, so that environmental pollution is caused. And Sc-PLA is prepared by melt blending without adding an organic solvent, and the preparation process is simple and has high efficiency.

According to the invention, in step 1, the blending mode is melt blending. According to the invention, in step 1, the blending apparatus is one of those commonly used in the art, a single screw extruder, a twin screw extruder or an internal mixer is selected, preferably an internal mixer.

In the invention, in the step 1, the blending melting temperature has an important influence on the formation of the stereocomplex crystals, and when the blending melting temperature is lower, the obtained product is powdery solid and cannot be molded, namely, a one-step molded product cannot be obtained; when the temperature is high, polylactic acid is extremely easy to degrade, and a stereocomplex polylactic acid material cannot be obtained. According to the invention, in step 1, the temperature of the blending is 180 to 250 ℃, preferably 190 to 230 ℃, more preferably 200 to 230 ℃, for example 230 ℃.

In the invention, the length of the blending time also has an influence on the formation of the stereoscopic composite crystal, the blending time is too long, the copolymerization and crosslinking structure of PLLA and PDLA is destroyed, the content of the formed stereoscopic crystal is raised, and the blending efficiency is influenced; the blending time is too short, and PLLA and PDLA cannot be sufficiently mixed, and polylactic acid having high stereocrystal content cannot be formed. According to the invention, in step 1, the blending time is from 1 to 20 minutes, preferably from 3 to 15 minutes, more preferably from 5 to 10 minutes, for example 5 minutes.

In the invention, in the step 1, the blending speed is too high, and the molecular structures of PLLA and PDLA are easily damaged; the blending speed is too slow, PLLA and PDLA cannot be fully mixed, and the blending speed is too fast or too slow, so that Sc-PLA with high stereocrystal content is difficult to form. According to the invention, in step 1, the blending rotation speed is 10 to 100rpm, preferably 30 to 80rpm, more preferably 40 to 70rpm, for example 50rpm.

And cooling to room temperature under natural conditions after blending is finished, so as to obtain the high-stereotactic composite polylactic acid granules. According to the preparation method, the granules of the high-stereotactic composite polylactic acid material can be prepared, the preparation method is simple, and the content of the stereocrystal is high and is more than 29%.

And 2, carrying out melt electrostatic spinning on the Sc-PLA obtained by blending.

In the invention, in the step 2, sc-PLA subjected to blending treatment is crushed into granules by using a crusher to be subjected to melt electrostatic spinning, so as to prepare the full-stereo composite polylactic acid fiber. According to the invention, the spinning device is a melt electrostatic spinning machine, purchased from Shenzhen City Tongli micro-nano technology Co.

According to the invention, in the step 2, the melting temperature has an important influence on the formation of polylactic acid fibers, when the melting temperature is low, sc-PLA granules are not completely melted, and a melt electrostatic spinning machine cannot normally discharge filaments and cannot form; when the temperature is high, polylactic acid is extremely easy to degrade, and the full-stereo composite polylactic acid fiber material cannot be obtained. According to the invention, in step 2, the tube temperature is 180 to 250 ℃, preferably 190 to 230 ℃, more preferably 200 to 230 ℃, for example 215 ℃. The needle temperature is 185 to 255 ℃, preferably 195 to 235 ℃, more preferably 205 to 235 ℃, for example 220 ℃.

In the invention, the high and low spinning voltage also has influence on the formation of polylactic acid fibers, the spinning voltage is too low, the melt is not well stretched, and the spun fibers are mostly bent and have uneven thickness; the spinning voltage is too high, the drawing is too fast, the melt is broken, and the spun fiber is broken and discontinuous at multiple positions. According to the invention, in step 2, the spinning voltage is 0 to 20kV, preferably 5 to 17kV, more preferably 10 to 17kV, for example 15kV.

In the invention, the gas pushing speed also has influence on the formation of polylactic acid fibers, the gas pushing speed is too high, the melt is often extruded too fast, the voltage is not as high as that of stretching a molecular chain, and the condition of molten drops is easily caused in the spinning process; the gas pushing speed is too high, the molecular chain is sufficiently stretched by the voltage, but the subsequent supply is not up, and the condition of current interruption is easy to occur. In step 2, the gas push rate is in the range of 0.1 to 50psi, preferably 0.2 to 20psi, more preferably 0.2 to 5psi, for example 0.2psi, according to the present invention.

In the invention, the far and near spinning distance can also influence the formation of polylactic acid fibers, the spinning distance is too high, the melt is not stretched by an electrostatic field, and the melt is easy to cool in air, and the spinning is discontinuous; the spinning distance is too low and the fibers are not sufficiently drawn, and the resulting fiber diameter tends to be relatively large. According to the invention, in step 2, the spinning distance is 0.5 to 10cm, preferably 0.5 to 5rpm, more preferably 0.5 to 1rpm, for example 0.5rpm.

In the invention, the high and low rotation speeds of the rollers can also influence the formation of polylactic acid fibers, and the fibers are easy to break and discontinuous in spinning due to the excessively high rotation speeds of the rollers; the rotation speed of the roller is too low, the fibers cannot be sufficiently oriented, and the performance strength of the obtained fibers is not high. According to the invention, in step 2, the roller speed is 500 to 3000rpm, preferably 500 to 2500rpm, more preferably 1500 to 2500rpm, for example 2500rpm.

And cooling to room temperature under natural conditions after spinning is finished to obtain the full-stereo composite polylactic acid fiber.

According to the preparation method, the full-stereo composite polylactic acid fiber material can be prepared, the preparation method is simple, and the obtained product has a certain stereo crystal, so that the heat resistance is effectively improved.

Step 3, carrying out annealing heat treatment on the Sc-PLA fiber;

the inventors found that annealing was the primary method of increasing the content of PLLA/PDLA blend fiber stereocomplex crystals. The heat treatment is beneficial to the formation of the stereocomplex crystal and the orientation of the crystal region.

According to the invention, in step 3, the annealing temperature is 100 ℃ to 250 ℃, preferably 130 ℃ to 220 ℃, more preferably 140 ℃ to 190 ℃, for example 160 ℃. The annealing time is 10s to 300s, preferably 30 to 200 ℃, more preferably 30 to 100 ℃, for example 60 ℃.

According to the preparation method, the full-stereo composite polylactic acid fiber material can be prepared, the preparation method is simple, the obtained product can be observed to disappear cold crystals through DSC, only the peaks of the stereo crystals are left, and the product has excellent heat resistance.

The full-stereo composite polylactic acid fiber material provided by the invention has higher melting point and good heat resistance, for example, XRD test is carried out on the full-stereo composite polylactic acid material to obtain the XRD spectrum of the polylactic acid material, wherein crystal plane diffraction peaks of the stereo crystals exist at the positions of 12 DEG, 21 DEG and 24 DEG of 2 theta; DSC test is carried out on the materials, and the melting points are all above 210 ℃.

The present invention will be described in detail with reference to examples for further illustration of the invention, but they should not be construed as limiting the scope of the invention.

Crystallization behavior test:

melt crystallization process testing was performed using a Differential Scanning Calorimeter (DSC) model Q2000 from the company TA, U.S. and the instrument was indium corrected prior to testing and the test was performed under nitrogen. The sample was warmed to 250℃at 10℃per minute and the temperature profile of the sample was recorded. The flow rate of nitrogen is 50mL/min, and the sample dosage is 5-10 mg.

Wide angle X-ray diffraction (XRD) test:

two-dimensional wide angle X-ray diffraction test was performed using BRUKER company D8DISCOVER, germany, light source wavelength 1.54A, exposure time 300s, and sample-to-detector distance 85.6mm.

Example 1

A preparation method of a full-stereo composite melt electrostatic spinning polylactic acid fiber comprises the following steps:

weighing 25g of poly-L-lactic acid and 25g of poly-D-lactic acid, adding into an internal mixer for melt blending, setting the temperature of the internal mixer to be 230 ℃, the rotating speed to be 50r/min, and the internal mixing time to be 5min, and naturally cooling to room temperature after the internal mixing is finished to obtain the three-dimensional composite polylactic acid. Crushing the mixture into granules by a crusher, and drying the granules for later use.

5g of Sc-PLA granules are weighed and added into a material pipe, the material pipe temperature of a melting electrostatic spinning machine is set to 215 ℃, the needle temperature is set to 220 ℃, the spinning voltage is set to 15kV, the rotating speed of a roller is set to 500rpm, the air flow pushing speed is set to 0.2psi, and after spinning is finished, the material pipe is naturally cooled to room temperature, so that the full-stereo composite polylactic acid fiber is obtained.

The morphology of the obtained all-stereocomplex polylactic acid fiber is shown in figure 1 by a scanning electron microscope, and the average diameter of the obtained fiber is 12.9+/-1.4 mu m as can be obtained from figure 1.

Example 2

The air flow push rate was 0.5psi, and the results are shown in FIG. 1, with the result that the average diameter of the resulting fibers was 15.1.+ -. 2.5. Mu.m, as can be seen from FIG. 1.

Example 3

The air flow push rate was 2psi, and the results are shown in FIG. 1, as can be seen in FIG. 1, to give fibers having an average diameter of 44.1.+ -. 16.8. Mu.m.

Example 4

The air flow push rate was 5psi, and the results are shown in FIG. 1, and as can be seen in FIG. 1, the average fiber diameter obtained was 58.9.+ -. 10.8. Mu.m.

Example 5

5g of Sc-PLA granules are weighed and added into a material pipe, the temperature of the material pipe of a melting electrostatic spinning machine is set to 215 ℃, the temperature of a needle head is set to 220 ℃, the air flow pushing speed is 0.2psi, the rotating speed of a roller is 500rpm, the spinning voltage is 11kV, and after spinning is finished, the material pipe is naturally cooled to room temperature, so that the full-stereo composite polylactic acid fiber is obtained.

The morphology of the obtained all-stereocomplex polylactic acid fiber is shown in FIG. 2 by a scanning electron microscope, and the average diameter of the obtained fiber is 24.3+ -3.5 μm as can be obtained from FIG. 2.

Example 6

The filament voltage was 13kV, and the results are shown in FIG. 2, which shows that the average diameter of the obtained fiber was 21.2.+ -. 2.8. Mu.m.

Example 7

The filament voltage was 15kV, and the results are shown in FIG. 2, which shows that the average diameter of the obtained fiber was 17.2.+ -. 2.9. Mu.m.

Example 8

The filament voltage was 17kV, and the results are shown in FIG. 2, and as can be seen from FIG. 2, the average diameter of the obtained fiber was 16.9.+ -. 6.0. Mu.m.

Example 9

5g of Sc-PLA granules are weighed and added into a material pipe, the temperature of the material pipe of a melting electrostatic spinning machine is set to 215 ℃, the temperature of a needle head is set to 220 ℃, the air flow pushing speed is 0.2psi, the spinning voltage is 15kV, the rotating speed of a roller is 500rpm, and after spinning is finished, the material pipe is naturally cooled to room temperature, so that the full-stereo composite polylactic acid fiber is obtained.

The morphology of the obtained all-stereocomplex polylactic acid fiber is shown in FIG. 3 by a scanning electron microscope, and the average diameter of the obtained fiber is 14.0+ -1.0 μm as can be obtained from FIG. 3.

Example 10

The drum rotation speed was 1000rpm, and the results are shown in FIG. 3, and it can be seen from FIG. 3 that the average diameter of the obtained fibers was 12.5.+ -. 2.1. Mu.m.

Example 11

The drum rotation speed was 1500rpm, and the results are shown in FIG. 3, as can be seen from FIG. 3, to obtain a fiber having an average diameter of 11.4.+ -. 1.7. Mu.m.

Example 12

The drum rotation speed was 2000rpm, and the results are shown in FIG. 3, and it can be seen from FIG. 3 that the average diameter of the obtained fibers was 9.6.+ -. 1.8. Mu.m.

Example 13

And cutting part of Sc-PLA fiber prepared in the example 12, carrying out annealing heat treatment in a forced air oven in a pre-tensioning mode for 60s at 130 ℃,160 ℃ and 190 ℃ respectively, and naturally cooling to room temperature to obtain the full-stereo composite polylactic acid fiber with cold crystallization removed.

DSC test is carried out on the fully-stereo composite polylactic acid fiber obtained by annealing, the DSC curve of the obtained first temperature rise is shown in figure 4, and as can be seen from figure 4, the temperature of the melting peak of the fiber which is not annealed is more than 210 ℃, and the temperature of the melting peak of the fiber which is annealed at 130 ℃ is further raised to more than 214 ℃. The content of the unannealed full-stereo composite polylactic acid fiber is 29%, and the content of the stereo crystal is further improved to more than 49% after annealing at 130 ℃. XRD test was performed on the annealed fully-stereocomplex polylactic acid fiber, and the test results are shown in FIG. 5. As can be seen from FIG. 5, the fiber annealed at 130℃has crystal plane diffraction peaks of stereocrystals at 2θ of 12 °, 21℃and 24 °.

Example 14

The annealing temperature was 160℃and the rest was the same as in example 13, and DSC test was conducted on the annealed all-stereocomplex polylactic acid fiber, and the DSC curve of the first temperature rise obtained was shown in FIG. 4, and it can be seen from FIG. 4 that the temperature of the melting peak of the unannealed fiber was 210℃or higher, and the temperature of the melting peak of the fiber after 160℃annealing was further raised to 215℃or higher. The content of the unannealed full-stereo composite polylactic acid fiber is 29%, and the content of the stereo crystal is further improved to more than 55% after annealing at 130 ℃. XRD test was performed on the annealed fully-stereocomplex polylactic acid fiber, and the test results are shown in FIG. 5. As can be seen from FIG. 5, the fiber annealed at 160℃has crystal plane diffraction peaks of stereocrystals at 12 DEG, 21 DEG and 24 DEG of 2 theta.

Example 15

The annealing temperature was 190℃and the rest was the same as in example 13, and DSC test was conducted on the annealed fully stereocomplex polylactic acid fiber, and the DSC curve of the first temperature rise obtained was shown in FIG. 4, and it can be seen from FIG. 4 that the temperature of the melting peak of the unannealed fiber was 210℃or higher, and the temperature of the melting peak of the fiber after 190℃annealing was further raised to 216℃or higher. The content of the unannealed full-stereo composite polylactic acid fiber is 29%, and the content of the stereo crystal is further improved to more than 52% after annealing at 130 ℃. XRD test was performed on the annealed fully-stereocomplex polylactic acid fiber, and the test results are shown in FIG. 5. As can be seen from FIG. 5, the fiber annealed at 190℃has crystal plane diffraction peaks of stereocrystals at 2θ of 12 °, 21℃and 24 °.

Although the foregoing embodiments have been described in some, but not all, embodiments of the invention, it should be understood that other embodiments may be devised in accordance with the present embodiments without departing from the spirit and scope of the invention.

Claims

1. The preparation method of the all-stereo composite melt-spun polylactic acid fiber is characterized by comprising the following steps of:

the conditions of the melt electrospinning include:

2. The method according to claim 1, wherein the conditions of the step 2) of melt electrospinning include: the air flow pushing speed is 0.5-2 psi, the spinning voltage is 13-15 kV, and the rotating speed of the roller is 1000-1500 rpm.

3. The method according to claim 1, wherein the conditions of the step 2) of melt electrospinning further comprise: the temperature of the material pipe is 180-250 ℃, and the temperature of the needle head is 185-255 ℃.

4. The preparation method according to claim 1, wherein the mass ratio of the poly-L-lactic acid to the poly-D-lactic acid in the step 1) is 2-8:2-8.

5. The method of claim 1, wherein the conditions of the melt blending of step 1) include: the temperature is 180-250 ℃, the time is 1-20 min, and the rotating speed is 10-100 rpm.

6. The method of claim 5, wherein the melt blending conditions comprise: the temperature is 190-230 ℃, the time is 3-15 min, and the rotating speed is 30-80 rpm.

7. The method according to claim 1, wherein the obtained composite polylactic acid material is subjected to melt electrospinning and further comprises annealing treatment to obtain the fully-stereo composite melt electrospun polylactic acid fiber.

8. The method according to claim 7, wherein the annealing temperature is 130 to 190 ℃.

9. The method of claim 8, wherein the annealing is performed at a temperature of 160 ℃.

10. The method of claim 7, wherein the annealing time is 60s.