CN100543060C - Preparation Technology of Polylactic Acid for Spinning - Google Patents

Abstract

The invention belongs to the technical field of polymer materials, and specifically relates to a preparation process for polylactic acid used in spinning. The specific steps are as follows: (1). Lactic acid concentration: control temperature, vacuum degree, dehydration and concentration, and obtain dehydration and concentrated lactic acid liquid ; (2). Pre-condensation: add compound catalyst, control temperature, vacuum range, reaction time, get pre-condensation powder; (3). Solid phase polymerization: add heat stabilizer, antioxidant, control temperature, vacuum range, constant temperature, to obtain polylactic acid particles; (4). Thermal shrinkage modification: add thermal modifier and inorganic acid, control temperature and reaction time, to obtain polylactic acid. It is a direct bulk polymerization of lactic acid monomers, without adding solvents, and does not require an inert gas environment. The process is easy to control, the polycondensation process is short, the yield is high, and the environmental pollution is small. It is modified by solid-state polycondensation and thermal shrinkage. , The molecular weight of polylactic acid has been greatly increased, and the heat shrinkage rate has been greatly reduced.

Description

Preparation Technology of Polylactic Acid for Spinning

technical field

The invention belongs to the technical field of polymer materials, and in particular relates to a preparation process of polylactic acid used for spinning.

Background technique

Polylactic acid (English abbreviation: PLA) is a new type of fully biodegradable material, which can be used for spinning, injection molding, manufacturing packaging materials, medical materials and other purposes. In recent years, the demand for non-woven fabrics has increased greatly, making polylactic acid materials more widely used in textiles, clothing, industry, and agriculture and forestry. The synthesis methods of polylactic acid include two-step ring-opening polymerization method and direct polycondensation method, wherein the direct polycondensation method is divided into solution polycondensation method and melt-solid phase polycondensation method.

Polylactic acid products with higher molecular weight can be obtained by ring-opening polymerization. U.S. Patent No. 5,357,035 discloses a method for preparing high-molecular polylactic acid by ring-opening: prepare oligomerized polylactic acid from lactic acid, and then use oligomerized polylactic acid After distillation and purification, the acrylic ester is obtained, and then the acrylic ester is used to polymerize polylactic acid. However, this method has a long process route, complex procedures, consumption and recovery of a large amount of organic solvents, difficulty in storing the intermediate product lactide, large loss of raw materials in the reaction process, low yield and high product price. The preparation cost of this method is too high, which restricts the wide use of polylactic acid.

The process of direct polycondensation method is simple, the amount of chemical raw materials and reagents used is less, and the product yield is higher, but the solvent used in the polymerization is more polluting to the environment, and it is difficult to clean the residue in the product.

The use of melt polycondensation is to directly carry out bulk polymerization of lactic acid monomers without adding solvents, the process is easy to control, and the molecular weight is greatly improved through solid-state polycondensation. The operation is mainly divided into two steps: melt polycondensation and solid-state polycondensation. Compared with the ring method, the reaction time is greatly shortened, and the process is simple. It only needs to pulverize the crude product from the melt polycondensation stage to the solid-phase polycondensation stage, and the second-stage solid-phase polycondensation is easy to operate, without consuming a large amount of solvent and repeated recrystallization. Purification operation.

The research on the process of preparing polylactic acid by the direct method started late. The molecular weight of the prepared polylactic acid is not high, the requirements for the atmosphere environment are high, the crystallization rate is low, and the heat shrinkage rate is high, which cannot meet the requirements of spinning nonwovens. Therefore, the development of polylactic acid preparation technology with high molecular weight and low heat shrinkage rate is of great significance to make full use of my country's natural resources to increase the added value of agricultural products and promote the development of the domestic lactic acid industry.

Contents of the invention

The purpose of the present invention is to provide a kind of preparation technology method of polylactic acid for spinning, it is to carry out bulk polymerization directly by lactic acid monomer, does not add solvent, does not need inert gas environment atmosphere, and technology is easy to control, polycondensation process flow is short, obtains High efficiency, low environmental pollution, through solid-state polycondensation and thermal shrinkage modification, the molecular weight of polylactic acid is greatly improved, and the thermal shrinkage rate is greatly reduced.

The technical scheme of the present invention is, a kind of preparation technology of polylactic acid for spinning, and its specific steps are as follows:

(1). Lactic acid concentration:

Put the lactic acid into the evaporator, control the temperature at 45°C-95°C, and the vacuum at 9,000Pa-80,000Pa, dehydrate and concentrate for 1-3 hours to obtain dehydrated and concentrated lactic acid liquid, which is ready for use;

(2). Precondensation:

Using dehydrated and concentrated lactic acid as raw material, add compound catalyst, control the temperature at 170-190°C, vacuum range 0-1,600Pa, react for 8-12 hours, break the white prepolymer, separate the catalyst, and crush it into 0.1 -0.3mm pre-condensation powder, spare;

(3). Solid state polymerization:

Add thermal stabilizers and antioxidants to the precondensation powder, raise the temperature from room temperature to 140-165°C in the air, vacuum range 0-100Pa, and keep it warm for 10-33 hours to obtain polycondensate with a weight average molecular weight of 120,000-210,000. Lactic acid granules;

(4).Heat shrinkage modification:

Add thermal modifier and inorganic acid to solid-phase polymerized polylactic acid particles, vacuum range 3,000-8,000Pa, raise temperature to 170-230°C, and react for 10-60 minutes under atmospheric pressure in air atmosphere to obtain Polylactic acid with a weight average molecular weight of 120,000-210,000 and a heat shrinkage rate of 1-5% in saturated steam.

The control temperature is programmed temperature control, and the vacuum degree is programmed controlled vacuum degree. The process of temperature programming and vacuum degree programming is as follows:

(1) Lactic acid concentration: The specific process starts at 45°C-55°C, then increases the temperature by 6-12°C every half hour, starts at 50,000Pa-80,000Pa, and then every half hour Reduce the vacuum degree by 10,000-15,000Pa, and after 1-2.5 hours, the evaporation temperature reaches 85-95°C and the vacuum degree reaches 9,000-12,000Pa, and the constant temperature concentration process is completed for half an hour;

(2) Precondensation: Use dehydrated and concentrated lactic acid as raw material, add compound catalyst, raise the temperature to 170-190°C at a rate of 1°C-3°C per minute, adjust the vacuum to 600-1,600Pa, and react for 6-9 hours Finally, the temperature is lowered to 100-120°C, the vacuum degree is adjusted to 0-100Pa, and after constant temperature for 2-3 hours, a white polylactic acid prepolymer is obtained;

(3) Solid-state polymerization: add thermal stabilizers and antioxidants to the precondensed powder in the air, heat up from room temperature to 140-165°C, vacuum degree ranges from 0-100Pa, and keep warm for 33 hours to control the temperature in two stages. The temperature in the first 10-11h is 140-155°C, the vacuum range is 90-100Pa, and the temperature in the next 10-22h is 145-165°C, and the vacuum range is 0-90Pa;

(4) Thermal shrinkage modification: add thermal modifier and inorganic acid to the solid-phase polymerized polylactic acid particles, the vacuum range is 3,000-8,000Pa, and the temperature is raised to 170-230°C at 1-3°C per minute, 3 - After 5 minutes, react for 10-60 minutes under normal atmospheric pressure conditions in an air atmosphere.

The solid phase polymerization: another 20-33h is three-stage temperature control, wherein 0-10h is 140-150°C, the vacuum range is 90-100Pa, 10-20h is 145-155°C, the vacuum range is 80-90Pa , 12-30h is 150-165°C, and the vacuum range is 0-80Pa.

The composite catalyst is a composite catalyst prepared by compounding 0.04-0.06 of commercially available 37% analytically pure HCl, 0-0.95 nanoscale tin powder and 0-0.95 of 200-mesh tin powder.

The heat stabilizer is any one of methyl tin, barium stearate, zinc stearate, magnesium stearate and calcium stearate, and the consumption is 0-0.3%.

The antioxidants are tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, β(3,5-di-tert-butyl-4-hydroxyphenyl)propane Octadecyl ester, dilauryl thiodipropionate, triphenyl phosphite, tris(nonylated phenyl) phosphite, 2,5-di-tert-butylhydroquinone, 4,4' -Any one of butyl-bis(3-methyl-6-tert-butyl)phenol, the dosage is 0-0.3%.

The modifier is triglycidyl isocyanurate, trihydroxyethyl isocyanurate, phthalic anhydride, 2-methylimidazole, bisphenol A phosphite, vinyl triethoxy Any one of cinnamon, diethylenetriaminopropyltriethoxycinnamate, 3,3'-diaminodiphenyl sulfone, isopropyl tris(dioctyl pyrophosphate) titanate, the dosage is 0-15%.

The preparation method of the nanoscale tin powder is to dissolve SnCl ₄ with commercially available 37% analytically pure HCl, dilute it into 5-20% SnCl ₄ hydrochloric acid solution, add 1-5% NaBH ₄ NaOH solution to the solution, Until the pH=11, stand still for 1-3 hours, separate the nano-tin, and obtain the nano-tin powder after drying.

Described mineral acid is any in sulfuric acid, phosphoric acid, hydrochloric acid.

The features of the present invention are:

1. In all reactions, programmed temperature control and programmed control reaction vacuum degree are adopted. Avoid bumping of lactic acid caused by too high temperature and too low vacuum, and increase the yield of concentrated lactic acid.

2. In the pre-condensation process, the catalyst is used as a composite component of inorganic acid and ultra-fine and nano-metal powder, so that the solid-phase catalyst can be separated after the pre-condensation process is completed, and the impurities of the final polylactic acid can be reduced.

3. In the solid state polymerization, which is commonly referred to as the chain extension process, no chain extender is used, but antioxidants and heat stabilizers are added, and an inert gas atmosphere is not provided at the same time. The production equipment is reduced, and the production energy consumption is reduced.

4. The heat-resistant modification is carried out, so that the thermal shrinkage rate of the polylactic acid for spinning is 1-5%, which meets the technical requirements of the existing non-woven fabric. There are no reports and patents in China.

Detailed ways

The present invention will be further described below in conjunction with the embodiment process flow.

The technological process of melt-solid phase polymerization is as follows:

1. Lactic acid concentration process: the temperature and vacuum degree are controlled by a program. When the lactic acid starts to concentrate, the lactic acid contains a lot of water and the viscosity is low. If the temperature is too high and the vacuum is too low, it will cause lactic acid bumping and reduce the yield of lactic acid , as the concentration proceeds, some lactic acid will polymerize into small molecular polylactic acid, and the generated water will also be pumped out of the concentration system by the vacuum pump. The viscosity of lactic acid will gradually increase, and the temperature can be gradually increased to reduce the vacuum degree. The specific process starts at 45°C-55°C, then increases the temperature by 6-12°C every half hour, starts with a vacuum of 50,000-80,000Pa, and then reduces the vacuum by 10,000- 15,000Pa, after 1-2.5 hours, the evaporation temperature reaches 85-95°C, the vacuum degree reaches 9,000-12,000Pa, the constant temperature concentration is completed for half an hour, and the concentrated dehydrated lactic acid is obtained. After the dehydration of lactic acid is completed, the yield of concentrated lactic acid reaches 83-92%.

2. Pre-condensation process: After adding the dehydrated and concentrated lactic acid to the compound catalyst, when the temperature is raised to 170-190°C at a rate of 1°C-3°C per minute, adjust the vacuum to 600-1,600Pa, and react for 6-9 hours , the temperature is lowered to 100-120°C, the vacuum degree is adjusted to 0-100Pa, and after 2-3 hours of constant temperature, the white prepolymer obtained by the reaction is crushed, the catalyst is separated, and it is crushed into a precondensed powder of 0.1-0.3mm.

3. Solid phase polymerization process: add heat stabilizer and antioxidant in the air and precondensation powder, heat up from room temperature 20°C to 140-165°C, vacuum degree range 0-100Pa, heat preservation 20-33h is two-stage control Temperature, wherein the first 10-11h temperature is 140-155°C, the vacuum range is 90-100Pa, the next 10-22h temperature is 145-165°C, the vacuum range is 0-90Pa, and the polylactic acid with a weight average molecular weight of 120,000-210,000 is obtained particles;

In addition, the heat preservation for 20-33 hours can also be three-stage temperature control, of which 0-10h is 140-150°C, the vacuum range is 90-100Pa, 10-20h is 145-155°C, the vacuum range is 80-90Pa, and 20-30h is 150-165°C, vacuum range 0-80Pa, to obtain polylactic acid particles with a weight average molecular weight of 120,000-210,000.

4. Thermal shrinkage modification process: adding thermal modifier and inorganic acid to the solid-phase polymerized polylactic acid particles, the vacuum range is 3,000-8,000Pa, and the temperature is raised to 170-230°C at 1-3°C per minute, 3 After -5 minutes, react for 10-60 minutes in the air atmosphere under normal atmospheric pressure conditions to obtain polylactic acid with a weight-average molecular weight of 120,000-210,000 and a saturated steam heat shrinkage rate of 1-5%.

In the above-mentioned preparation process, wherein:

Catalyst: The catalyst used is a combined catalyst prepared by compounding 0.04-0.06 commercially available (37%, analytically pure) HCl and 0-0.95 nanometer tin powder and 0-0.95 tin powder (less than 200 mesh), wherein the nanometer tin powder is self-made .

Nano-scale tin powder self-made method: dissolve SnCl ₄ with commercially available (37%, analytically pure) HCl, dilute to 5-20% SnCl ₄ hydrochloric acid solution, add 1-5% NaBH ₄ NaOH solution to the solution until the pH =11, stand still for 1-3 hours, separate the nano-tin, and obtain the nano-tin powder after drying.

Antioxidant: tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, β(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid deca Octyl alcohol ester, dilauryl thiodipropionate, triphenyl phosphite, tris(nonylated phenyl) phosphite, 2,5-di-tert-butylhydroquinone, 4,4'-butyl Any one of base-bis(3-methyl-6-tert-butyl)phenol, the dosage is 0-0.3%.

Heat stabilizer: any one of methyl tin, barium stearate, zinc stearate, magnesium stearate, calcium stearate, consumption is 0-0.3%.

Heat shrinkable modifier: triglycidyl isocyanurate, trihydroxyethyl isocyanurate, phthalic anhydride, 2-methylimidazole, bisphenol A phosphite, vinyl triethoxy Any one of cinnamon, diethylenetriaminopropyltriethoxycinane, 3,3'-diaminodiphenyl sulfone, isopropyl tris(dioctyl pyrophosphate) titanate, dosage 1%-15%.

Inorganic acid: any of sulfuric acid, phosphoric acid, and hydrochloric acid.

The present invention will be further elaborated below by specific examples.

Example 1:

1. Lactic acid concentration

Put 300mL of lactic acid into a 1000mL round-bottomed flask, and fix it on a rotary evaporator so that the round-bottomed flask is submerged in a water bath. °C, the vacuum degree is reduced by 10,000Pa, and the evaporation temperature reaches 90°C after 1 hour. When the vacuum degree is reduced by 9,000Pa, the constant temperature concentration is completed after half an hour, and dehydrated concentrated lactic acid is obtained. The yield of concentrated lactic acid reaches 85-91%.

2. Precondensation

Put 220g of concentrated lactic acid into the rotary bottle of rotary film evaporator, add composite catalyst 0.015% HCl, 0.1% tin powder, 0.2% self-made nano-tin powder, and heat up to 180°C at a rate of 1°C per minute in the oil bath , start the vacuum pump, slowly adjust the vacuum degree to 750Pa, polymerize under this condition for 8 hours, cool down to 110°C, and keep the vacuum degree at 80Pa for 2.5 hours to obtain milky white lactic acid prepolymer. After breaking it and separating the catalyst aggregates (in the rotary bottle of the rotary film evaporator, through the pre-condensation process, the catalyst has been aggregated into agglomerates due to different densities, wrapped by pre-condensed lactic acid, when the milky white lactic acid prepolymer is broken , natural separation of the catalyst), crushed into 0.2mm precondensed powder.

The catalyst ratio can be divided into the following three types:

(1) Catalyst ratio: 0.3% tin powder (200 mesh), 0.015% (37% analytically pure) HCl such as 2 precondensation can obtain a lactic acid prepolymer with a weight average molecular weight of 29,000;

(2) Catalyst ratio: 0.3% nano-tin powder (self-made), 0.015% (37% analytically pure) HCl such as 2 precondensation can obtain a lactic acid prepolymer with a weight average molecular weight of 30,000;

(3) Catalyst ratio: 0.1% nano-tin powder (self-made), 0.2% tin powder (200 mesh), 0.015% (37% analytically pure) HCl such as 2 precondensation can obtain a lactic acid prepolymer with a weight average molecular weight of 40,000.

3. Solid state polymerization:

Add 0.3% tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester, raise the temperature from room temperature to 140°C, and keep the temperature for 20h as two-stage temperature control, in which the temperature for the first 10h is 140°C °C, the vacuum degree is 100Pa, and the temperature in the next 10h is 145 °C, the vacuum degree is 90Pa, and polylactic acid particles with a weight average molecular weight of 135,000 are obtained.

4. Thermal shrinkage modification:

Add 10% thermal modifier triglycidyl isocyanurate and 0.02% (37% analytically pure) HCl to the solid-phase polymerized polylactic acid particles, the vacuum is 8,000Pa, and the temperature is raised to the temperature at a rate of 3°C per minute. After 3 minutes at 190°C, react for 20 minutes under normal atmospheric pressure in air atmosphere to obtain polylactic acid with a weight average molecular weight of 145,000 and a saturated steam heat shrinkage rate of 1-4%.

Example 2

Its concrete preparation method is the same as embodiment 1, and difference is:

1. Lactic acid concentration

Put 300mL of lactic acid into a 1000mL round-bottomed flask, fix it on a rotary evaporator so that the round-bottomed flask is submerged in a water bath, control the temperature at 45°C and the pressure at 70,000Pa, and then increase the temperature by 12°C every half hour. ℃, the vacuum degree is reduced by 15,000Pa, after 2 hours, the evaporation temperature reaches 85℃, and the vacuum degree is reduced by 10,000Pa, the concentration is completed after constant temperature for half an hour, and dehydrated concentrated lactic acid is obtained. The yield of concentrated lactic acid reaches 83-90%.

2. Precondensation

Put 220g of concentrated lactic acid into a rotary bottle, add composite catalyst 0.015% HCl, 0.2% tin powder, 0.1% self-made nano-tin powder, heat up to 170°C at a rate of 2°C per minute in the oil bath, start the vacuum pump, and slowly Slowly adjust the vacuum degree to 600Pa, polymerize under this condition for 6 hours, lower the temperature to 100°C, keep the vacuum degree at 100Pa, and keep the temperature constant for 2 hours to obtain milky white lactic acid prepolymer. This was crushed to separate the catalyst aggregate, and then crushed into a precondensed powder of 0.1 mm.

Catalyst proportioning is with embodiment 1.

3. Solid state polymerization:

Add 0.3% barium stearate, raise the temperature from room temperature to 140°C, and keep warm for 30 hours for three-stage temperature control, of which 0-10h is 140°C, and the vacuum degree is 90Pa; 10-20h is 145°C, and the vacuum degree is 80Pa; 20- 30h is 150°C, the vacuum degree is 70Pa, and polylactic acid particles with a weight average molecular weight of 145,000 are obtained.

4. Thermal shrinkage modification:

Add 10% thermal modifier trishydroxyethyl isocyanurate and 0.02% (37% analytically pure) HCl to the solid-phase polymerized polylactic acid particles, the vacuum degree is 6,000Pa, and the temperature is raised at a rate of 1°C per minute. After 5 minutes at a temperature of 230° C., react for 10 minutes under normal atmospheric pressure in an air atmosphere to obtain polylactic acid with a weight-average molecular weight of 150,000 and a saturated steam heat shrinkage rate of 1-4%.

Example 3

Its concrete preparation method is the same as embodiment 1, and difference is:

1. Lactic acid concentration

Put 300mL of lactic acid into a 1000mL round-bottomed flask, fix it on a rotary evaporator so that the round-bottomed flask is submerged in a water bath, control the temperature at 55°C and the pressure at 80,000Pa, and increase the temperature by 6 every half hour thereafter. ℃, the vacuum degree is reduced by 14,000Pa. After 2.5 hours, the evaporation temperature reaches 95℃ and the vacuum degree decreases to 12,000Pa. After half an hour of constant temperature, the concentration is complete, and dehydrated concentrated lactic acid is obtained. The yield of concentrated lactic acid reaches 83-92%.

2. Precondensation

Put 220g of concentrated lactic acid into a rotary bottle, add composite catalyst 0.015% HCl, 0.1% tin powder, 0.2% self-made nano-tin powder, heat up to 190°C at a rate of 3°C per minute in the oil bath, start the vacuum pump, and slowly Slowly adjust the vacuum degree to 1,600 Pa, polymerize under this condition for 9 hours, lower the temperature to 120°C, and keep the vacuum degree at 70 Pa for 3 hours to obtain a milky white lactic acid prepolymer. This was crushed to separate the catalyst aggregate, and then crushed into a precondensed powder of 0.3 mm.

Catalyst proportioning is with embodiment 1.

3. Solid state polymerization:

Add 0.3% heat stabilizer barium stearate, keep warm for 33 hours as two-stage temperature control, in which the temperature for the first 11 hours is 155 ° C, the vacuum degree is 95 Pa; the temperature for the next 22 hours is 165 ° C, the vacuum degree is 75 Pa, and the weight average molecular weight is 167 , 000 polylactic acid particles.

4. Thermal shrinkage modification:

Add 0.3% of 3,3'-diaminodiphenylsulfone, the vacuum degree is 3,000Pa, the temperature is raised to 170°C at a heating rate of 2°C per minute, and after 4 minutes, the temperature is kept at normal atmospheric pressure for 60 minutes to obtain a weight average molecular weight of Polylactic acid with 170,000 saturated steam heat shrinkage rate of 1-3%.

It should be noted that the present invention is not limited to the above examples, and the catalyst used in the specific implementation process of the present invention can also be inorganic acid (H ₂ SO ₄ , H ₃ PO ₄ , HCl) and other metal powders of nanoscale (magnesium, zinc , any one or more of different graded mixtures of aluminum) compound components, so that after the precondensation process is completed, the solid-phase catalyst can be separated to reduce the impurities of the final polylactic acid.

In the solid phase polymerization, that is to say, chain extenders are not used in the chain extension process, but antioxidants and thermostabilizers are added. Adding antioxidants and thermostabilizers is not limited to the items listed in the above examples, but also Can be: octadecyl beta (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, dilauryl thiodipropionate, triphenyl phosphite, tris(nonylated phenyl) Phosphite 2,5-di-tert-butylhydroquinone, 4,4'-butyl-bis(3-methyl-6-tert-butyl)phenol, methyl tin, zinc stearate, stearin Any one of magnesium stearate and calcium stearate. At the same time no inert gas atmosphere is provided. The production equipment is reduced, and the production energy consumption is reduced.

The heat-resistant modification is carried out, and the modifiers added are not limited to the number of items listed in the above examples, but can also be: phthalic anhydride, bisphenol A phosphite, vinyl triethoxy cinnamon, di Any one of ethylene triaminopropyl triethoxy cinnamon, 3,3'-diaminodiphenyl sulfone, and isopropyl tris(dioctyl pyrophosphate), heat the saturated steam of polylactic acid for spinning The shrinkage rate is 1-5%, which meets the technical requirements of the existing non-woven fabrics.

Claims (5)

1, the preparation technology of poly lactic acid in use for spinning is directly to carry out mass polymerization by lactic acid monomer, and its concrete steps are as follows:

1), lactic acid concentrates: lactic acid is packed into when beginning to concentrate on the evaporimeter, with 45 ℃～55 ℃ is that starting temperature, 50000～80000Pa are initial vacuum tightness, every 0.5h 6～12 ℃ of temperature risings, vacuum tightness are reduced 10000-15000Pa, behind 1～2.5h, temperature reaches 85～95 ℃, vacuum tightness and reaches 9000～12000Pa, constant temperature 0.5h can obtain the lactic acid that dewaters again, and the acid by dehydrating lactic enrichment factor reaches 83～92%;

2), system precondensation powder: commercially available 37% of will dewater spissated lactic acid and 0.04-0.06, the catalyst compounded mixing of analytical pure HCl and the compound preparation of 200 order glass puttys of 0-0.95 nano level glass putty and 0-0.95, when being warmed up to 170～190 ℃ with 1 ℃～3 ℃ temperature rise rates of per minute, vacuum tightness is transferred to 600～1600Pa, behind reaction 6～9h, temperature drops to 100～120 ℃, vacuum tightness transfers to 0～100Pa, constant temperature 2～3h again, obtain the preshrunk aggressiveness of white, separating liquiding catalyst, must pulverize is the precondensation powder of 0.1～0.3mm;

3), solid state polymerization: in air, the precondensation powder is mixed with 0-0.3% thermo-stabilizer, 0-0.3% antioxidant, rise to 140～165 ℃ for 20 ℃ by vacuum tightness 0～100Pa, temperature, insulation 33h obtains weight-average molecular weight and is 120000～210000 poly(lactic acid) particle; Insulation 33h is two sections temperature controls, and wherein preceding 11h temperature is 140-155 ℃, vacuum ranges 90-100Pa, and back 22h temperature is 145-165 ℃, vacuum ranges 0-90Pa;

4), red shortness's modification: the poly(lactic acid) particle of solid state polymerization is mixed with heat modification agent and the mineral acid of 0-15% again, vacuum tightness 3000-8000Pa, reach 170～230 ℃ with 1～3 ℃ of intensification of per minute, after 3～5 minutes, under the air atmosphere atmospheric pressure, reacted 10～60 minutes, and obtained the poly(lactic acid) of weight-average molecular weight 120000～210000 saturation steam percent thermal shrinkages 1～5%.

2, the preparation technology of poly lactic acid in use for spinning according to claim 1 is characterized in that: described thermo-stabilizer is wherein a kind of in methyl tin, barium stearate, Zinic stearas, Magnesium Stearate, the calcium stearate.

3, the preparation technology of poly lactic acid in use for spinning according to claim 1, it is characterized in that: described antioxidant is four [β-(3, the 5-di-tert-butyl-hydroxy phenyl) propionic acid] pentaerythritol ester, β (3,5-di-t-butyl-4-hydroxybenzene) propionic acid octadecanol ester, Tyox B, triphenyl phosphite, three (nonylated phenyl) phosphorous acid ester, 2,5-di-tert-butyl hydroquinone, 4, wherein a kind of in 4 '-butyl-two (3-methyl-6-tertiary butyl) phenol.

4, the preparation technology of poly lactic acid in use for spinning according to claim 1, it is characterized in that: described heat modification agent is isocyanuric acid three-glycidyl ester, trihydroxyethyl isocyanuric ester, Tetra hydro Phthalic anhydride, glyoxal ethyline, phosphorous acid dihydroxyphenyl propane ester, vinyltriethoxysilane, divinyl triamino propyl-triethoxysilicane, 3, wherein a kind of in 3 '-diaminodiphenylsulfone(DDS), sec.-propyl three (dioctylphyrophosphoric acid ester) titanic acid ester.

5, the preparation technology of poly lactic acid in use for spinning according to claim 1 is characterized in that: described mineral acid is wherein a kind of in sulfuric acid, phosphoric acid, the hydrochloric acid.