CN107366039B - Preparation method and product of cross-linked L-polylactic acid/low-molecular-weight L-lactic acid blend fiber - Google Patents

Abstract

The invention relates to a preparation method of cross-linked L-lactic acid/low-molecular-weight L-lactic acid blended fiber, which comprises the following steps: 1) Carrying out electron beam irradiation and cross-linking of high-molecular-weight L-lactic acid to prepare cross-linked L-lactic acid ; 2) Melting and mixing the cross-linked L-lactic acid and the low-molecular-weight L-polylactic acid, extruding and granulating to obtain a blend; the mass fraction of the cross-linked L-lactic acid in the blend is 5-50%. The mass fraction of the low-molecular-weight L-polylactic acid is 50-95%; 3) The blend is melt-spun to obtain a cross-linked L-polylactic acid/low-molecular-weight L-polylactic acid blended fiber. The present invention also relates to the product prepared by the above preparation method. The preparation method has simple process and controllable production process. The prepared polylactic acid blended fiber has abundant shish-kebab superlattice structure, its crystallinity is 40-60%, the dry hot air shrinkage rate is 3.2-6.0%, and the boiling water shrinkage rate is 0.4-2.0%.

Description

Preparation method of cross-linked L-polylactic acid/low molecular weight L-polylactic acid blend fiber and products

technical field

The invention relates to the field of preparation of polylactic acid fibers, in particular to a preparation method and product of crosslinked L-lactic acid/low molecular weight L-polylactic acid blended fibers.

Background technique

Polylactic acid (Poly Lactic Acid, PLA) is a new type of polyester material obtained by hydrolysis and fermentation of various renewable natural resources such as starch, cellulose, polysaccharides, and polymerization. It is a completely degradable environmental friendly resin.

Polylactic acid has excellent biocompatibility, good mechanical properties and physical properties, making it widely used in packaging, biomedical, automotive electronics and other fields, and also has potential application value in chemical fiber and nonwoven fields.

But at this stage, due to the slow crystallization of polylactic acid, it is still difficult to obtain PLA fibers with high crystallinity (55-60%) even under the force of a strong tensile flow field during spinning. The poor thermal stability caused by low crystallinity (20-30%) seriously affects its performance.

The key problem to solve the limitation of the use of polylactic acid fiber is to improve its thermal stability. Usually the way to solve its thermal stability can be by improving its crystallinity, as Chinese invention patent (CN 106366594 A) discloses a kind of preparation method of the high-toughness polylactic acid blend containing polylactic acid stereocomplex, this method has high optical The pure D-polylactic acid is used as a nucleating agent and the L-polylactic acid is mixed at room temperature to obtain a high-toughness polylactic acid blend containing a polylactic acid stereocomplex. This method is to improve the heat resistance by increasing the crystallinity. Compared with improving the heat resistance by crystallinity, the change of the crystal form is more effective in improving the heat resistance.

Contents of the invention

The object of the present invention is to aim at the deficiencies in the prior art, provide a kind of preparation method and product of cross-linked poly-L-lactic acid/low-molecular-weight poly-lactic acid blended fiber, this method can improve the shish-kebab superlattice structure in the blended fiber content, and can greatly reduce the dry hot air shrinkage and boiling water shrinkage of the blended fiber, and obtain a high heat-resistant blended fiber that can be widely used.

The technical scheme provided by the present invention is:

A preparation method of cross-linked L-polylactic acid/low-molecular-weight L-polylactic acid blended fiber, comprising the steps of:

1) Carrying out cross-linking of high molecular weight L-polylactic acid by electron beam irradiation to obtain cross-linked L-polylactic acid;

2) melt-mixing cross-linked L-lactic acid and low-molecular-weight L-polylactic acid, extruding and granulating to obtain a blend; the mass fraction of cross-linked L-lactic acid in the blend is 5-50%, and the The mass fraction of low molecular weight L-polylactic acid is 50-95%;

3) The blend is melt-spun to obtain a cross-linked L-polylactic acid/low-molecular-weight L-polylactic acid blended fiber.

In the above technical solution, the blended fiber is obtained by blending crosslinked L-polylactic acid (hereinafter referred to as CPLLA) and low molecular weight L-polylactic acid (hereinafter referred to as LPLLA) and melt spinning. The CPLLA in the blend forms a chemical cross-linked network structure after cross-linking, which is different from the characteristics of the physical entangled network that is easy to slip and disentangle under the action of an external field, and the chemical cross-linked network structure is permanent and stable. As shown in Figure 1, during the spinning process, under the action of an external field, the chemical cross-linked network of CPLLA entrains the deformation and orientation of LPLLA molecular chains to generate shish, which is conducive to promoting the stable existence of shish that has been generated, and the stable shish further causes the surrounding environment to be undisturbed The short chain crystallization of LPLLA in the state produces kebab, and finally forms a shish-kebab superlattice structure, thereby obtaining a polylactic acid blend fiber with significantly improved thermal stability.

Preferably, the electron beam irradiation crosslinking in the step 1) refers to: pressing the high molecular weight L-polylactic acid into a thin plate with a thickness of 0.3-0.8 mm, and placing it in an electron accelerator for electron beam irradiation crosslinking, irradiating The dose is 5-10KGy to prepare cross-linked L-lactic acid. The gel content of the cross-linked L-lactic acid is controlled at 5-30%.

Further preferably, the high molecular weight L-polylactic acid is pressed into a 0.5 mm thick sheet at 200° C. and 5 MPa, and cross-linked by electron beam irradiation in a 1.7 MeV electron accelerator.

Preferably, the mass fraction of the cross-linked L-lactic acid in the blend in step 2) is 5-15%, and the mass fraction of the low-molecular-weight L-lactic acid is 85-95%.

Preferably, masterbatch and low molecular weight L-polylactic acid are used as raw materials for melt mixing in step 2).

Preferably, the masterbatch is prepared by dissolving cross-linked L-polylactic acid and low molecular weight L-polylactic acid in dichloromethane and pouring them into ethanol to obtain a precipitate, which is then dried to obtain the masterbatch.

Preferably, the mass ratio of cross-linked L-lactic acid and low molecular weight L-polylactic acid in the masterbatch is 1:0.9-1.1. More preferably 1:1.

Preferably, the melting and mixing temperature in the step 2) is 180-220°C. More preferably, it is 200°C.

Preferably, the melt spinning conditions in the step 3) are: spinning temperature 190-250°C, winding speed 100-500m/min, hot drawing temperature 100-150°C, draw ratio 1-5.

Preferably, the weight-average molecular weight of the high-molecular-weight L-polylactic acid is 5-19×10 ⁵ g/mol, and the weight-average molecular weight of the low-molecular-weight L-polylactic acid is 1.5-3×10 ⁵ g/mol.

The present invention also provides a cross-linked L-polylactic acid/low-molecular-weight L-polylactic acid blend fiber prepared by the above-mentioned preparation method. The blended fiber has a rich shish-kebab superlattice structure, its crystallinity is 40-60%, the dry hot air shrinkage rate is 3.2-6.0%, and the boiling water shrinkage rate is 0.4-2.0%.

Compared with the prior art, the beneficial effects of the present invention are reflected in:

(1) The preparation method provided by the present invention has simple process and controllable production process.

(2) The polylactic acid blend fiber provided by the present invention can be completely biodegradable, so the fiber can be used not only in the engineering field, but also in the medical and health field.

(3) The CPLLA in the polylactic acid blend fiber provided by the present invention is cross-linked to form a chemical cross-linked network structure, which not only facilitates the cross-linked network of CPLLA to coerce the deformation and orientation of LPLLA molecular chains to generate shish, but also helps to promote the already generated The stable existence of shish, the stable shish further triggers the crystallization of short LPLLA chains in the surrounding undisturbed state to form kebab, and finally forms a shish-kebab superlattice structure, and obtains a polylactic acid blend fiber with significantly improved thermal stability, and its crystallinity is 40-60%, dry hot air shrinkage rate 3.2-6.0%, boiling water shrinkage rate 0.4-2.0%.

Description of drawings

Figure 1 is a schematic flow diagram of the formation of a shish-kebab superlattice structure in the spinning process of blended fibers.

Detailed ways

The present invention will be further described below in conjunction with specific examples.

Example 1

Taking HPLLA with a weight average molecular weight of 5×10 ⁵ g/mol and LPLLA with a weight average molecular weight of 1.5×10 ⁵ g/mol as raw materials, the steps are as follows:

1) Press high molecular weight L-polylactic acid (HPLLA) into a 0.5mm thick sheet at 200°C and 5MPa, and place the sheet in a 1.7MeV electron accelerator for cross-linking by electron beam irradiation with a radiation dose of 5KGy , the cross-linked L-lactic acid (CPLLA) with a gel content of 5% was obtained;

2) Dissolve 10g CPLLA and 10g LPLLA in 150ml dichloromethane, stir magnetically for 3h at room temperature, pour the mixed solution into 50ml absolute ethanol while stirring, to obtain a precipitate with a mass ratio of CPLLA/LPLLA of 1:1, Drying in a vacuum oven to obtain the masterbatch;

3) 10g of the above-mentioned masterbatch and 40g of LPLLA were melt-extruded and granulated in a micro extruder at 200°C to obtain a CPLLA/LPLLA blend;

4) The blend was melt-spun at a spinning temperature of 190°C, a winding speed of 100m/min, a hot drawing temperature of 100°C, and a draw ratio of 2 times to obtain PLA blended fibers.

Specific test methods: 1) Use a single fiber heat shrinkage tester to test the hot air shrinkage rate of PLA blended fibers. The test temperature is set at 140°C and the test time is 30 minutes. 2) Test the boiling water shrinkage of PLA blended fibers under standard atmospheric conditions, and the test time is 30 minutes.

Heat shrinkage is calculated by the following formula:

In the formula, L ₀ is the initial length of the fiber, and L is the final length of the fiber after heat shrinkage.

The hot air shrinkage rate of the PLA blended fiber measured by a single fiber heat shrinkage tester is 5.7%; its boiling water shrinkage rate is 1.8% measured under standard atmospheric conditions, its crystallinity is 42%, and the Herman orientation index is 0.18.

Example 2

Taking HPLLA with a weight average molecular weight of 10×10 ⁵ g/mol and LPLLA with a weight average molecular weight of 1.5×10 ⁵ g/mol as raw materials, the steps are as follows:

1) Press high-molecular-weight L-polylactic acid (HPLLA) into a 0.5mm thick sheet at 200°C and 5MPa, and place the sheet in a 1.7MeV electron accelerator for cross-linking by electron beam irradiation with a radiation dose of 7KGy , making cross-linked L-lactic acid (CPLLA) with a gel content of 10%;

2) Dissolve 10g CPLLA and 10g LPLLA in 150ml dichloromethane, stir magnetically for 3h at room temperature, pour the mixed solution into 50ml absolute ethanol while stirring, to obtain a precipitate with a mass ratio of CPLLA/LPLLA of 1:1, Drying in a vacuum oven to obtain the masterbatch;

3) 10g of the above-mentioned masterbatch and 40g of LPLLA were melt-extruded and granulated in a micro extruder at 200°C to obtain a CPLLA/LPLLA blend;

4) The blend was melt-spun at a spinning temperature of 210°C, a winding speed of 120m/min, a hot drawing temperature of 120°C, and a draw ratio of 2.5 times to obtain PLA blended fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA blended fiber measured by a single fiber heat shrinkage tester is 4.7%; its boiling water shrinkage rate is 1.2% measured under standard atmospheric conditions, its crystallinity is 45%, and the Herman orientation index is 0.19.

Example 3

Taking HPLLA with a weight average molecular weight of 10×10 ⁵ g/mol and LPLLA with a weight average molecular weight of 1.5×10 ⁵ g/mol as raw materials, the steps are as follows:

1) High molecular weight L-polylactic acid (HPLLA) was pressed into a 0.5mm thick sheet at 200°C and 5MPa, and the sheet was placed in a 1.7MeV electron accelerator for cross-linking by electron beam irradiation with a radiation dose of 8KGy , the cross-linked L-lactic acid (CPLLA) with a gel content of 15% was obtained;

2) Dissolve 10g CPLLA and 10g LPLLA in 150ml dichloromethane, stir magnetically for 3h at room temperature, pour the mixed solution into 50ml absolute ethanol while stirring, to obtain a precipitate with a mass ratio of CPLLA/LPLLA of 1:1, Drying in a vacuum oven to obtain the masterbatch;

3) 10g of the above-mentioned masterbatch and 40g of LPLLA were melt-extruded and granulated in a micro-extruder at 240°C to obtain a CPLLA/LPLLA blend;

4) The blend was melt-spun at a spinning temperature of 230°C, a winding speed of 200m/min, a hot drawing temperature of 120°C, and a draw ratio of 3.5 times to obtain PLA blended fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA blended fiber measured by a single fiber heat shrinkage tester is 3.8%; its boiling water shrinkage rate is 0.9% measured under standard atmospheric conditions, its crystallinity is 49%, and the Herman orientation index is 0.23.

Example 4

Taking HPLLA with a weight average molecular weight of 17×10 ⁵ g/mol and LPLLA with a weight average molecular weight of 2.5×10 ⁵ g/mol as raw materials, the steps are as follows:

1) High molecular weight L-polylactic acid (HPLLA) was pressed into a 0.5mm thick sheet at 200°C and 5MPa, and the sheet was placed in a 1.7MeV electron accelerator for cross-linking by electron beam irradiation with a radiation dose of 8KGy , the cross-linked L-lactic acid (CPLLA) with a gel content of 15% was obtained;

2) Dissolve 10g CPLLA and 10g LPLLA in 150ml dichloromethane, stir magnetically for 3h at room temperature, pour the mixed solution into 50ml absolute ethanol while stirring, to obtain a precipitate with a mass ratio of CPLLA/LPLLA of 1:1, Drying in a vacuum oven to obtain the masterbatch;

3) 10g of the above-mentioned masterbatch and 40g of LPLLA were melt-extruded and granulated in a micro extruder at 200°C to obtain a CPLLA/LPLLA blend;

4) The blend was melt spun at a spinning temperature of 230°C, a winding speed of 300m/min, a hot drawing temperature of 130°C, and a draw ratio of 3.5 times to obtain PLA blended fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA blended fiber measured by a single fiber heat shrinkage tester is 3.4%; its boiling water shrinkage rate is 0.7% measured under standard atmospheric conditions, its crystallinity is 52%, and the Herman orientation index is 0.24.

Example 5

Taking HPLLA with a weight average molecular weight of 19×10 ⁵ g/mol and LPLLA with a weight average molecular weight of 3×10 ⁵ g/mol as raw materials, the steps are as follows:

1) High molecular weight L-polylactic acid (HPLLA) was pressed into a 0.5mm thick sheet at 200°C and 5MPa, and the sheet was placed in a 1.7MeV electron accelerator for cross-linking by electron beam irradiation with a radiation dose of 8KGy , the cross-linked L-lactic acid (CPLLA) with a gel content of 15% was obtained;

2) Dissolve 10g CPLLA and 10g LPLLA in 150ml dichloromethane, stir magnetically for 3h at room temperature, pour the mixed solution into 50ml absolute ethanol while stirring, to obtain a precipitate with a mass ratio of CPLLA/LPLLA of 1:1, Drying in a vacuum oven to obtain the masterbatch;

3) 15g of the above-mentioned masterbatch and 35g of LPLLA were melt-extruded and granulated in a micro extruder at 200°C to obtain a CPLLA/LPLLA blend;

4) The blend was melt-spun at a spinning temperature of 250°C, a winding speed of 500m/min, a hot drawing temperature of 150°C, and a draw ratio of 5 times to obtain PLA blended fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA blended fiber measured by a single fiber heat shrinkage tester is 3.2%; its boiling water shrinkage rate is 0.4% measured under standard atmospheric conditions, its crystallinity is 57%, and the Herman orientation index is 0.29.

Example 6

Taking HPLLA with a weight average molecular weight of 19×10 ⁵ g/mol and LPLLA with a weight average molecular weight of 3×10 ⁵ g/mol as raw materials, the steps are as follows:

1) Press the high molecular weight L-polylactic acid (HPLLA) into a 0.5mm thick sheet at 200°C and 5MPa, and place the sheet in a 1.7MeV electron accelerator for cross-linking by electron beam irradiation with a radiation dose of 10KGy , the cross-linked L-lactic acid (CPLLA) with a gel content of 25% was obtained;

2) Dissolve 10g CPLLA and 10g LPLLA in 150ml dichloromethane, stir magnetically for 3h at room temperature, pour the mixed solution into 50ml absolute ethanol while stirring, to obtain a precipitate with a mass ratio of CPLLA/LPLLA of 1:1, Drying in a vacuum oven to obtain the masterbatch;

3) 15g of the above-mentioned masterbatch and 35g of LPLLA were melt-extruded and granulated in a micro extruder at 200°C to obtain a CPLLA/LPLLA blend;

4) The blend was melt-spun at a spinning temperature of 230°C, a winding speed of 500m/min, a hot drawing temperature of 150°C, and a draw ratio of 5 times to obtain PLA blended fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA blended fiber measured by a single fiber heat shrinkage tester is 3.4%; its boiling water shrinkage rate is 0.6% measured under standard atmospheric conditions, its crystallinity is 52%, and the Herman orientation index is 0.26.

Comparative example 1

1) 50 g of LPLLA raw material with a weight average molecular weight of 2×10 ⁵ g/mol is passed through a micro extruder, melt-extruded and granulated at 240° C. to obtain LPLLA pellets;

2) The pellets were melt spun at a spinning temperature of 240° C., a winding speed of 100 m/min, a hot drawing temperature of 100° C., and a draw ratio of 2.5 times to obtain PLA fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA fiber measured by a single fiber heat shrinkage tester is 20%; its boiling water shrinkage rate is 7.8% measured under standard atmospheric conditions, its crystallinity is 27%, and the Herman orientation index is 0.12 .

Comparative example 2

1) 50 g of LPLLA raw material with a weight average molecular weight of 2×10 ⁵ g/mol is passed through a micro extruder, melt-extruded and granulated at 240° C. to obtain LPLLA pellets;

2) The pellets were melt-spun at a spinning temperature of 250° C., a winding speed of 300 m/min, a hot drawing temperature of 120° C., and a draw ratio of 4.5 times to obtain PLA fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA fiber measured by a single fiber heat shrinkage tester is 12%; its boiling water shrinkage rate is 4.5% measured under standard atmospheric conditions, its crystallinity is 30%, and the Herman orientation index is 0.14 .

Comparative example 3

1) passing 50 g of LPLLA raw materials with a weight average molecular weight of 15×10 ⁵ g/mol through a micro extruder, melt extrusion and granulation at 200° C. to obtain LPLLA pellets;

2) The pellets were melt spun at a spinning temperature of 260° C., a winding speed of 300 m/min, a hot drawing temperature of 130° C., and a draw ratio of 4.5 times to obtain PLA fibers.

The test method of shrinkage in hot air and shrinkage in boiling water is the same as in Example 1.

The hot air shrinkage rate of the PLA fiber measured by a single fiber heat shrinkage tester is 23%; its boiling water shrinkage rate is 8.5% measured under standard atmospheric conditions, its crystallinity is 34%, and the Herman orientation index is 0.15 .

Claims (7)

1. a kind of crosslinking l-lactic acid/low molecular weight l-lactic acid blended fiber preparation method, which is characterized in that including Following steps:

1) high molecular weight l-lactic acid is subjected to electron beam irradiation crosslinking, crosslinking l-lactic acid is made；

2) l-lactic acid will be crosslinked and low molecular weight l-lactic acid passes through melting mixing, extruding pelletization obtains blend；Institute Stating and being crosslinked the mass fraction of l-lactic acid in blend is 5~50%, the mass fraction of the low molecular weight l-lactic acid It is 50~95%；

Melting mixing is using masterbatch and low molecular weight l-lactic acid as raw material in the step 2)；The preparation of the masterbatch: Crosslinking l-lactic acid and low molecular weight l-lactic acid are dissolved in methylene chloride, and poured into ethyl alcohol, sediment is obtained, Masterbatch is obtained after drying；

3) described by blend progress melt spinning to get crosslinking l-lactic acid/low molecular weight l-lactic acid blended fiber Being crosslinked l-lactic acid/low molecular weight l-lactic acid blended fiber includes shish-kebab superlattice structure.

2. crosslinking l-lactic acid/low molecular weight l-lactic acid blended fiber preparation method according to claim 1, It is characterized in that, electron beam irradiation crosslinking refers in the step 1): high molecular weight l-lactic acid is compressed to 0.3~ The thin plate of 0.8mm thickness is placed in progress electron beam irradiation crosslinking in electron accelerator, and irradiation dose is 5~10KGy, is made and hands over Join l-lactic acid.

3. crosslinking l-lactic acid/low molecular weight l-lactic acid blended fiber preparation method according to claim 1, It is characterized in that, the mass ratio for being crosslinked l-lactic acid and low molecular weight l-lactic acid in the masterbatch is 1:0.9~1.1.

4. crosslinking l-lactic acid/low molecular weight l-lactic acid blended fiber preparation method according to claim 1, It is characterized in that, the temperature of melting mixing is 180~220 DEG C in the step 2).

5. crosslinking l-lactic acid/low molecular weight l-lactic acid blended fiber preparation method according to claim 1, It is characterized in that, in the step 3) melt spinning condition are as follows: 190~250 DEG C of spinning temperature, wind 100~500m/ of rate Min, 100~150 DEG C of hot gas spring temperature, draw ratio 1~5.

6. crosslinking l-lactic acid/low molecular weight l-lactic acid blended fiber preparation method according to claim 1, It is characterized in that, the weight average molecular weight of the high molecular weight l-lactic acid is 5~19 × 10⁵G/mol, low molecular weight are left-handed poly- The weight average molecular weight of lactic acid is 1.5~3 × 10⁵g/mol。

7. a kind of crosslinking l-lactic acid that the preparation method as described in claim 1~6 is any is prepared/low molecular weight is left Revolve polylactic acid blend fiber.