CN1247653C - Process for direct preparation of poly-lactic acid from lactic acid by melt/solid phase polycondensation - Google Patents

Abstract

The invention discloses a method for directly preparing polylactic acid from lactic acid ester through a melting/solid-state polycondensation method, which relates to a preparation method of polylactic acid. The object of the present invention is to provide a kind of method that directly prepares polylactic acid by lactic acid ester by melt/solid-state polycondensation method, and it is prepared according to the following steps: a. take lactic acid ester as raw material or with lactic acid and lactic acid ester The mixture is used as a raw material, and an inert gas is passed through, and the reaction temperature is controlled at 100-160°C and the pressure is 30-760mmHg to prepolymerize to obtain a lactic acid oligomer; b. Add a catalyst to the above-mentioned lactic acid oligomer, and control the reaction temperature at Melt polymerization at 120-190°C and pressure of 1-20mmHg, then lower the reaction temperature, control the reaction temperature to cool at 100-110°C to obtain polylactic acid; c. Finally, control the reaction temperature at 100-175°C, The solid phase polymerization is carried out under the condition of pressure of 0.5-10 mmHg to obtain high molecular weight polylactic acid solid. The invention has the advantages of simple process, low cost and low corrosion.

Description

Direct preparation of polylactic acid from lactate by melt/solid-state polycondensation

technical field

The invention relates to a preparation method of polylactic acid, in particular to a synthesis process for preparing polylactic acid through a melting/solid-state polycondensation method.

Background technique

Polylactic acid is a synthetic aliphatic polyester polymer material that can be completely degraded. It is a polymer obtained by polymerizing lactic acid as the main monomer. The polymer includes not only homopolymers of lactic acid, but also lactic acid and Copolymers of other monomers. Generally, there are three methods for preparing polylactic acid, namely the direct polycondensation method of lactic acid, the dealcoholization condensation method of lactide and the ring-opening polymerization method of lactide. But, because the preparation of lactic acid and the preparation of polylactic acid are carried out respectively in different manufacturers, there are many useless procedures in the synthetic process from the preparation of lactic acid to polylactic acid, have increased process cost; And, when using lactic acid as raw material In the process of synthesizing polylactic acid, there is also the problem of corrosion of equipment by lactic acid. Chinese patent CN1298892A discloses a method of directly condensing lactic acid into polylactic acid. This method needs to consume a large amount of azeotropic solvent, and there is also the problem of removing the azeotropic solvent remaining in the lactic acid polymer. Chinese patent CN1326997A also discloses a method for preparing high-molecular-weight polylactic acid by direct polycondensation of lactic acid. This method needs to consume a large amount of dehydrating agent during the preparation process, which increases the process cost. Chinese patent CN1068011C discloses a method for preparing polylactic acid by lactide melting/solid-state polycondensation method. This method adopts the ring-opening polymerization method of lactide, but the raw material lactide needs to be recrystallized several times. Re-polymerization, otherwise high molecular weight polylactic acid cannot be obtained, and the cost is high.

Contents of the invention

In order to solve the deficiencies in the prior art, the present invention provides a method for directly preparing polylactic acid from lactic acid ester through a melt/solid-state polycondensation method. The method has the characteristics of low cost and simple process. The present invention is prepared according to the following steps: a, using lactic acid ester as raw material or the mixture of lactic acid and lactic acid ester as raw material, feeding inert gas, controlling the reaction temperature at 100-160°C and the pressure at 30-760mmHg Prepolymerize at low temperature for 8-12 hours to obtain lactic acid oligomers with a weight-average molecular weight of 700-1100; b. Add a catalyst to the above-mentioned lactic acid oligomers, and control the reaction temperature at 120-190°C and the pressure at 1-20mmHg Melt polymerization under low temperature for 4-8 hours, then reduce the reaction temperature, control the reaction temperature to cool down for 1-2 hours under the condition of 100-110°C, and obtain polylactic acid with a weight-average molecular weight of 12000-15000; c, finally, control the reaction temperature at Solid phase polymerization under the conditions of 100-175°C and pressure of 0.5-10mmHg for 10-25 hours to obtain a high molecular weight polylactic acid solid with a weight-average molecular weight of 100,000-600,000 and a melting point of 175-180°C. The present invention omits the hydrolysis process of lactic acid ester and the process of synthesizing lactide, simplifies the technological process; does not need to consume a large amount of dehydrating agent, azeotropic solvent and recrystallization agent, saves cost; alleviates the need to use lactic acid as raw material to synthesize The problem of equipment corrosion in the polylactic acid process has the advantages of simple process, low cost and low corrosion.

Specific Embodiment 1: This embodiment is prepared according to the following steps: a. Use lactic acid ester as raw material or a mixture of lactic acid and lactic acid ester as raw material, feed inert gas, control the reaction temperature at 100-160°C, and the pressure Pre-polymerize under the condition of 30-760mmHg for 8-12 hours to obtain a lactic acid oligomer with a weight-average molecular weight of 700-1100; b. Add a catalyst to the above-mentioned lactic acid oligomer, control the reaction temperature at 120-190°C and pressure Melt polymerization under the condition of 1～20mmHg for 4～8 hours, then reduce the reaction temperature, control the reaction temperature to cool down for 1～2 hours under the condition of 100～110°C, to obtain polylactic acid with a weight average molecular weight of 12000～15000; c, Finally, control the reaction temperature at 100-175°C and the pressure at 0.5-10mmHg for solid-state polymerization for 10-25 hours to obtain a high-molecular-weight polylactic acid solid with a weight-average molecular weight of 100,000-600,000 and a melting point of 175-180°C. The lactic acid ester is a compound formed by condensation reaction between lactic acid and C ₁ -C ₈ alcohol or a compound formed by esterification reaction between ammonium lactate obtained from food waste fermentation and alcohol, preferably lactic acid and C ₁ -C ₄ A compound formed by alcohol condensation reaction; in the mixture of lactic acid and lactic acid ester, the weight ratio of lactic acid and lactic acid ester is (1-99): (99-1); the content of the catalyst is 0.01-6.0% of the total weight of the monomers, preferably the catalyst content is 0.1-2.0% of the total weight of the polymer monomers; the catalyst is a tin-based catalyst, or a zinc-based catalyst, or a tin-based compound and a protonic acid binary composite catalyst; the tin catalyst is tin octoate or tin dichloride dihydrate; the zinc catalyst is zinc powder or zinc oxide; the tin compound and protonic acid dihydrate The element compound catalyst is a binary compound catalyst of SnCl ₂ ·2H ₂ O and p-toluenesulfonic acid; the protonic acid is boric acid, phosphoric acid or p-toluene sulfonic acid; the weight ratio of the tin compound to the protonic acid (1-2):1, preferably the weight ratio of the tin compound to the protonic acid is 1:1.

Specific embodiment 2: This embodiment is prepared according to the following steps: a. Use lactic acid ester as raw material or a mixture of lactic acid and lactic acid ester as raw material to feed inert gas, control the reaction temperature at 140-160°C, and the pressure at Under the condition of 30-760mmHg, pre-polymerize for 8-12 hours to obtain lactic acid oligomers with a weight average molecular weight of 700-1100; b. Add catalyst to the above-mentioned lactic acid oligomers, control the reaction temperature at 180°C and the pressure at 1- Melt polymerization under the condition of 20mmHg for 4 to 8 hours, then reduce the reaction temperature, control the reaction temperature and cool it under the condition of 105°C for 1 to 2 hours to obtain polylactic acid with a weight average molecular weight of 12000 to 15000; c. Finally, control the reaction temperature Solid phase polymerization under the conditions of 150°C and pressure of 5mmHg to obtain high molecular weight polylactic acid solids with a weight average molecular weight of 100,000-300,000 and a melting point of 175-180°C.

Specific embodiment three: this embodiment is prepared according to the following steps: a, 145.0g butyl lactate is put into the 500ml four-necked bottle that has stirring device and nitrogen inlet tube, feeds nitrogen after 1 hour, puts into 160 ℃ in an oil bath, and under nitrogen flow, reduce the pressure from 760mmHg to 200mmHg in stages over 10 hours to obtain a lactic acid oligomer with a weight average molecular weight of 1000; In the flask, add a binary composite catalyst of SnCl ₂ 2H ₂ O and p-toluenesulfonic acid with 1% of the total weight of polymer monomers, wherein the weight ratio of SnCl ₂ 2H ₂ O to p-toluenesulfonic acid is 1:1 , seal the beaker and connect it to a decompression system, then immerse it in an oil bath at 180°C, polymerize for 6 hours under stirring and a pressure of 15mmHg, then put it in an oil bath at 105°C for cooling and crystallization for 1.5 hours, and then shape it into a granular shape , to obtain polylactic acid with a weight average molecular weight of 15,000; c, move the molded granular polylactic acid to a vacuum drying incubator, and perform solid phase polymerization for 15 hours at a temperature of 140°C and a pressure of 5mmHg to obtain a weight average molecular weight 150,000 polylactic acid.

Embodiment 4: The difference between this embodiment and Embodiment 1 is that a, 73.0 g of butyl lactate and 50.0 g of DL-lactic acid aqueous solution with a weight concentration of 85-90% are put into a pipe with a stirring device and nitrogen gas In a 500ml four-necked flask, nitrogen was introduced for 1 hour, then heated in an oil bath at 160°C, and the pressure was continuously adjusted from 760mmHg to 200mmHg under nitrogen flow for 8 hours to obtain a lactic acid prepolymer with a weight average molecular weight of 1000 , other preparation steps and process conditions are the same as those in Embodiment 3, and polylactic acid with a weight average molecular weight of 200,000 is finally obtained.

Claims (7)

1, the method for directly preparing polylactic acid by melt/solid-state polycondensation method is characterized in that it is prepared according to the following steps: a, take lactic acid ester as raw material or take the mixture of lactic acid and lactic acid ester as raw material , feed an inert gas, control the reaction temperature at 100-160°C, and pre-polymerize under the conditions of 30-760mmHg for 8-12 hours to obtain lactic acid oligomers with a weight-average molecular weight of 700-1100; b. Add a catalyst to the polymer, control the reaction temperature at 120-190°C, and melt the polymerization under the conditions of 1-20mmHg for 4-8 hours, then lower the reaction temperature, control the reaction temperature at 100-110°C and cool for 1-2 hours Hours, obtain the polylactic acid that weight average molecular weight is 12000～15000; c, finally, control reaction temperature at 100～175 ℃, solid state polymerization 10～25 hours under the condition of 0.5～10mmHg, obtain weight average molecular weight is 100000～ 600000, high molecular weight polylactic acid solid with a melting point of 175-180°C. 2. The method for directly preparing polylactic acid from lactic acid ester by melt/solid-state polycondensation method according to claim 1, characterized in that lactic acid ester is a compound formed by condensation reaction of lactic acid and C ₁ -C ₈ alcohol or The compound formed by esterification reaction of ammonium lactate obtained from food waste fermentation and alcohol; in the mixture of lactic acid and lactic acid ester, the weight ratio of lactic acid and lactic acid ester is 1-99:99-1. 3. The method for directly preparing polylactic acid from lactic acid ester by melt/solid-state polycondensation method according to claim 2, characterized in that lactic acid ester is a compound formed by condensation reaction of lactic acid and C ₁ -C ₄ alcohol. 4. The method for directly preparing polylactic acid from lactate by melt/solid-state polycondensation according to claim 1, characterized in that the catalyst is a tin catalyst, or a zinc catalyst, or a tin compound and a protonic acid binary compound catalyst. 5. The method for directly preparing polylactic acid from lactate by melt/solid-state polycondensation according to claim 4, characterized in that the tin catalyst is tin octoate or the dihydrate of tin dichloride; the zinc catalyst is Zinc powder or zinc oxide; the binary compound catalyst of tin compound and protonic acid is the binary compound catalyst of SnCl ₂ ·2H ₂ O and p-toluenesulfonic acid. 6. The method for directly preparing polylactic acid from lactic acid ester by melt/solid-state polycondensation according to claim 4 or 5, characterized in that the weight ratio of tin compound to protonic acid is 1-2:1. 7. The method for directly preparing polylactic acid from lactic acid ester by melt/solid-state polycondensation method according to claim 4 or 5, characterized in that the weight ratio of tin compound to protonic acid is 1:1.