CN110938181A - Polylactic acid injection molding method - Google Patents
Polylactic acid injection molding method Download PDFInfo
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- CN110938181A CN110938181A CN201911057074.8A CN201911057074A CN110938181A CN 110938181 A CN110938181 A CN 110938181A CN 201911057074 A CN201911057074 A CN 201911057074A CN 110938181 A CN110938181 A CN 110938181A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F293/00—Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains bound exclusively at one or both ends of the starting macromolecule
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/0001—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor characterised by the choice of material
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
- C08G63/08—Lactones or lactides
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/78—Preparation processes
- C08G63/82—Preparation processes characterised by the catalyst used
- C08G63/87—Non-metals or inter-compounds thereof
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
- B29K2067/04—Polyesters derived from hydroxycarboxylic acids
- B29K2067/046—PLA, i.e. polylactic acid or polylactide
Abstract
The invention relates to the field of polylactic acid, in particular to a polylactic acid injection molding method. The invention discloses a polylactic acid injection molding method, which comprises the following steps: step 1, firstly, carrying out polycondensation reaction on lactic acid to obtain a polylactic acid intermediate; opening the ring of the polylactic acid intermediate to obtain a polylactic acid primary product; step 2, polymerizing the polylactic acid primary product with 2-methyl-1, 3-butadiene to obtain triblock polylactic acid; step 3, grafting glycine to the triblock polylactic acid through a third initiator to obtain modified triblock polylactic acid; step 4, drying the modified triblock polylactic acid in a drying oven; and 5, extruding, granulating and performing injection molding by using an injection molding machine. The invention solves the problems of high brittleness and insufficient toughness of the polylactic acid prepared by the existing injection molding method of the polylactic acid, and is beneficial to the development of the polylactic acid industry and the wide application of polylactic acid resin.
Description
Technical Field
The invention relates to the field of polylactic acid, in particular to a polylactic acid injection molding method.
Background
The polylactic acid is a polymer polymerized by using lactic acid as a main raw material, can be synthesized by renewable plant resources, such as corn starch, cassava starch, plant fiber, biosaccharides and the like, has low synthesis energy consumption and no pollution, and is beneficial to ecological cycle; the polylactic acid has good biodegradability, does not release toxic gases such as nitrides, sulfides and the like after incineration, can be completely degraded by microorganisms in the nature after being buried, finally generates carbon dioxide and water, and does not pollute the environment; and the polylactic acid has good processing performance and mechanical property, is equivalent to the performance of general plastics of polystyrene and polyethylene glycol terephthalate, and is expected to become a substitute product of petroleum-based general plastics. However, although polylactic acid prepared by the conventional injection molding method of polylactic acid has high hardness, it has high brittleness and insufficient toughness, which hinders the development of the polylactic acid industry and the wide application of polylactic acid resin.
Disclosure of Invention
In order to solve the above problems, the present invention provides a polylactic acid injection molding method, comprising the steps of:
step 1, firstly, carrying out polycondensation reaction on lactic acid, and depolymerizing the lactic acid into a polylactic acid intermediate under the conditions of high temperature and low pressure; then, carrying out ring opening on the polylactic acid intermediate under the action of a first initiator and a ring opening catalyst to obtain a polylactic acid primary product;
wherein the ring-opening catalyst is N, N-dimethylethanolamine;
the first initiator is obtained by reacting disodium hydrogen phosphate dihydrate, 2-mercaptoethanol and p-dibromide.
Step 2, polymerizing the polylactic acid primary product with 2-methyl-1, 3-butadiene through a second initiator to obtain triblock polylactic acid; the second initiator is ditert-butane peroxide;
step 3, grafting glycine to the triblock polylactic acid through a third initiator to obtain modified triblock polylactic acid; the third initiator is azobisisobutyronitrile;
step 4, drying the modified triblock polylactic acid in a drying oven; wherein the temperature of the oven is 80 ℃ and the time is 6 h;
step 5, adding the modified triblock polylactic acid dried in the step 4 into a co-rotating twin-screw extruder for extrusion, granulating and then performing injection molding by using an injection molding machine; wherein the injection pressure of the injection molding machine is set to 95.61MPa, and the injection speed is set to 67cm3S, barrel temperature 200 DEG CAnd the temperature of the die is 50 ℃.
Preferably, the preparation method of the polylactic acid intermediate in the step 1 specifically comprises the following steps:
weighing 30g of lactic acid and 0.15g of trimethyl orthoformate, placing the lactic acid and the trimethyl orthoformate into a reaction flask, and stirring the mixture at room temperature for reaction for 3 hours to obtain a product M; wherein the stirring speed is 300 rpm;
and adding 1.4g of antimony chloride into the product M, uniformly stirring, carrying out reduced pressure distillation for 2 hours at 40-50 ℃ and 0.1Mpa, depolymerizing, drying, and recrystallizing to obtain a polylactic acid intermediate.
Preferably, the preparation method of the first initiator in the step 1 is as follows:
s1, uniformly mixing disodium hydrogen phosphate dihydrate and n-butanol, adding 2-mercaptoethanol, uniformly stirring, adding chloroform, and stirring at room temperature for 30min to obtain a solution A; wherein the solid-to-liquid ratio of the disodium hydrogen phosphate dihydrate to the n-butanol is 1: 10-15; the molar ratio of the 2-mercaptoethanol to the disodium hydrogen phosphate dihydrate is 1: 1; the molar ratio of trichloromethane to 2-mercaptoethanol is 1: 3.
S2, adding p-dibromide benzyl into n-butyl alcohol, and stirring and dissolving to obtain a solution B; wherein the solid-to-liquid ratio of the p-dibromide to the n-butyl alcohol is 1: 10-15;
s3, adding the solution B into the solution A, stirring for 10 hours at room temperature, filtering, removing filter residues, and performing rotary evaporation until the filter residues are dried to obtain a solid C;
s4, passing the solid C through a silica gel column, eluting and purifying, recrystallizing in dichloromethane, and drying under reduced pressure at room temperature to obtain a first initiator;
preferably, the step 1 specifically comprises:
and (2) uniformly mixing 0.5g of the first initiator, 10g of the polylactic acid intermediate and 60mL of dichloromethane, adding 0.08g N, N-dimethylethanolamine, hermetically stirring for 3h at 30 ℃, adding 0.1g of benzoic acid, stirring for dissolving, precipitating in ethylene diamine tetraacetic acid, recrystallizing twice, and drying in vacuum to obtain a polylactic acid primary product.
Preferably, the step 2 specifically comprises:
weighing 1.2g of polylactic acid primary product and 0.0022g of ditert-butane peroxide into a thick-wall pressure-resistant bottle, adding 35mL of 2-methyl-1, 3-butadiene, then adding 20mL of ethylene glycol diether, stirring until the solid is completely dissolved, sealing with a polytetrafluoroethylene plug, vacuumizing, heating to 100-150 ℃ and reacting for 18-30 h; and after the reaction is finished, rapidly cooling to room temperature, recrystallizing twice, and drying in vacuum to obtain the product, namely the triblock polylactic acid.
Preferably, the step 3 specifically comprises:
weighing 1.6g of triblock polylactic acid into a thick-wall pressure-resistant bottle, adding 30mL of tetrahydrofuran and 0.012g of azodiisobutyronitrile, sealing and stirring for 1h, adding 0.05g of thioglycolic acid, vacuumizing, reacting at 60-120 ℃ for 10-12 h, and vacuum drying to obtain a product X; dissolving the product X and 1.7g of glycine in 50mL of dimethyl sulfoxide, adding 0.13g of 4-dimethylaminopyridine, stirring at 50 ℃ for reaction for 12-18 h, recrystallizing, and drying to obtain the modified triblock polylactic acid.
Preferably, a closed nozzle is arranged on the injection molding machine in the step 5; the closed nozzle comprises one of a double-lock type nozzle, a material pressure lock type nozzle and a controllable lock type nozzle.
Preferably, the lactic acid is one or more of L-lactic acid, D-lactic acid and DL-lactic acid.
The invention has the following beneficial effects:
1. compared with the metal oxide used in the prior art, the material has the advantages of stronger dehydration property and capability of saving the step of needing higher temperature after dehydration. The specific reason is that trimethyl orthoformate can be decomposed to obtain methyl formate and methanol by reaction with water after promoting lactic acid dehydration, the methyl formate is volatilized at room temperature and can be easily removed, and the methanol can be used as a donor and an acceptor of a hydrogen bond and can simultaneously activate antimony chloride and a low molecular weight polymer, so that the reaction activity of a low molecular weight polymer chain can be improved, the catalytic polycondensation and depolymerization effects of the antimony chloride can be promoted, and the generation of a polylactic acid intermediate product can be effectively increased.
2. The invention firstly prepares and uses a compound which has-OH at both ends and has a centrosymmetric structure as a first initiator to initiate ring-opening polymerization of a polylactic acid intermediate product. The initiator is obtained by reacting disodium hydrogen phosphate dihydrate with 2-mercaptoethanol, purifying and recrystallizing. In the prior art, ring-opening polymerization reaction (such as stannous octoate) usually needs higher temperature to occur, so that the effects of a ring-opening catalyst and an initiator cannot be completely matched, and the first initiator used by the invention can perform the ring-opening polymerization reaction at room temperature and has higher reaction speed by matching with the ring-opening catalyst N, N-dimethylethanolamine because both ends of the first initiator have symmetrical hydroxyl structures. Therefore, the first initiator prepared by the invention can provide wider application prospects for the initiated polymerization of other block materials.
3. The invention greatly improves the toughness of the polylactic acid by modifying the polylactic acid. Because polylactic acid is a semi-crystalline polyester, the glass transition temperature is higher, and although the polylactic acid has certain hardness, the toughness is poorer; while the synthesized polymer of 2-methyl-1, 3-butadiene has lower glass transition temperature. Therefore, the multi-block polylactic acid prepared by carrying out block polymerization on the polylactic acid and the poly-2-methyl-1, 3-butadiene not only has higher hardness, but also has certain flexibility, so that the flexibility of the polylactic acid is greatly improved to a certain extent, and the prepared modified tri-block polylactic acid can be applied at higher temperature.
4. According to the invention, the glycine is used for grafting the triblock polylactic acid, so that the hydrophilicity of the triblock polylactic acid is increased, and the biocompatibility and biodegradability of the triblock polylactic acid are increased, for example, the tail end of the glycine can be connected with some medicines, and the like, and the glycine has the structural characteristics of amino and carboxyl, so that the functionality of the triblock polylactic acid can be enhanced, and the application prospect is wider.
Detailed Description
Example 1
A polylactic acid injection molding method is characterized by comprising the following steps:
step 1, 0.5g of first initiator, 10g of polylactic acid intermediate and 60mL of dichloromethane are taken and uniformly mixed, 0.08g N of N-dimethylethanolamine is added, the mixture is hermetically stirred for 3 hours at the temperature of 30 ℃, 0.1g of benzoic acid is added, the mixture is stirred and dissolved, the mixture is precipitated in ethylene diamine tetraacetic acid, the recrystallization is carried out twice, and the vacuum drying is carried out, so as to obtain a polylactic acid primary product.
The preparation method of the polylactic acid intermediate comprises the following steps:
weighing 30g of lactic acid and 0.15g of trimethyl orthoformate, placing the lactic acid and the trimethyl orthoformate into a reaction flask, and stirring the mixture at room temperature for reaction for 3 hours to obtain a product M; wherein the stirring speed is 300 rpm;
and adding 1.4g of antimony chloride into the product M, uniformly stirring, carrying out reduced pressure distillation for 2h at 40 ℃ and 0.1Mpa, depolymerizing, drying, and recrystallizing to obtain a polylactic acid intermediate.
The preparation method of the first initiator comprises the following steps:
s1, uniformly mixing disodium hydrogen phosphate dihydrate and n-butanol, adding 2-mercaptoethanol, uniformly stirring, adding chloroform, and stirring at room temperature for 30min to obtain a solution A; wherein the solid-to-liquid ratio of the disodium hydrogen phosphate dihydrate to the n-butanol is 1: 10; the molar ratio of the 2-mercaptoethanol to the disodium hydrogen phosphate dihydrate is 1: 1; the molar ratio of trichloromethane to 2-mercaptoethanol is 1: 3.
S2, adding p-dibromide benzyl into n-butyl alcohol, and stirring and dissolving to obtain a solution B; wherein the solid-to-liquid ratio of the p-dibromide benzyl to the n-butyl alcohol is 1: 10;
s3, adding the solution B into the solution A, stirring for 10 hours at room temperature, filtering, removing filter residues, and performing rotary evaporation until the filter residues are dried to obtain a solid C;
and S4, passing the solid C through a silica gel column, eluting and purifying, recrystallizing in dichloromethane, and drying under reduced pressure at room temperature to obtain a first initiator.
Step 2, weighing 1.2g of polylactic acid primary product and 0.0022g of ditert-butane peroxide into a thick-wall pressure-resistant bottle, adding 35mL of 2-methyl-1, 3-butadiene, then adding 20mL of ethylene glycol diether, stirring until the solid is completely dissolved, sealing with a polytetrafluoroethylene plug, vacuumizing, heating to 100 ℃ and reacting for 18; and after the reaction is finished, rapidly cooling to room temperature, recrystallizing twice, and drying in vacuum to obtain the product, namely the triblock polylactic acid.
Step 3, weighing 1.6g of triblock polylactic acid into a thick-wall pressure-resistant bottle, adding 30mL of tetrahydrofuran and 0.012g of azobisisobutyronitrile, sealing and stirring for 1h, adding 0.05g of thioglycolic acid, vacuumizing, reacting for 10h at the temperature of 60 ℃, and vacuum-drying to obtain a product X; dissolving the product X and 1.7g of glycine in 50mL of dimethyl sulfoxide, adding 0.13g of 4-dimethylaminopyridine, stirring at 50 ℃ for reaction for 12 hours, recrystallizing, and drying in vacuum to obtain the modified triblock polylactic acid.
Step 4, drying the modified triblock polylactic acid in a drying oven; wherein the temperature of the oven is 80 ℃ and the time is 6 h;
and 5, adding the modified triblock polylactic acid dried in the step 4 into a co-rotating twin-screw extruder for extrusion, granulating, and performing injection molding by using an injection molding machine, wherein the injection pressure of the injection molding machine is set to be 95.61MPa, and the injection speed is set to be 67cm3The cylinder temperature was 200 ℃ and the die temperature was 50 ℃.
Example 2
A polylactic acid injection molding method is characterized by comprising the following steps:
step 1, 0.5g of first initiator, 10g of polylactic acid intermediate and 60mL of dichloromethane are taken and uniformly mixed, 0.08g N of N-dimethylethanolamine is added, the mixture is hermetically stirred for 3 hours at the temperature of 30 ℃, 0.1g of benzoic acid is added, the mixture is stirred and dissolved, the mixture is precipitated in ethylene diamine tetraacetic acid, the recrystallization is carried out twice, and the vacuum drying is carried out, so as to obtain a polylactic acid primary product.
The preparation method of the polylactic acid intermediate comprises the following steps:
weighing 30g of lactic acid and 0.15g of trimethyl orthoformate, placing the lactic acid and the trimethyl orthoformate into a reaction flask, and stirring the mixture at room temperature for reaction for 3 hours to obtain a product M; wherein the stirring speed is 300 rpm;
and adding 1.4g of antimony chloride into the product M, uniformly stirring, carrying out reduced pressure distillation for 2h at 50 ℃ and 0.1Mpa, depolymerizing, drying, and recrystallizing to obtain a polylactic acid intermediate.
The preparation method of the first initiator comprises the following steps:
s1, uniformly mixing disodium hydrogen phosphate dihydrate and n-butanol, adding 2-mercaptoethanol, uniformly stirring, adding chloroform, and stirring at room temperature for 30min to obtain a solution A; wherein the solid-to-liquid ratio of the disodium hydrogen phosphate dihydrate to the n-butanol is 1: 15; the molar ratio of the 2-mercaptoethanol to the disodium hydrogen phosphate dihydrate is 1: 1; the molar ratio of trichloromethane to 2-mercaptoethanol is 1: 3.
S2, adding p-dibromide benzyl into n-butyl alcohol, and stirring and dissolving to obtain a solution B; wherein the solid-to-liquid ratio of the p-dibromide benzyl to the n-butyl alcohol is 1: 15;
s3, adding the solution B into the solution A, stirring for 10 hours at room temperature, filtering, removing filter residues, and performing rotary evaporation until the filter residues are dried to obtain a solid C;
and S4, passing the solid C through a silica gel column, eluting and purifying, recrystallizing in dichloromethane, and drying under reduced pressure at room temperature to obtain a first initiator.
Step 2, weighing 1.2g of polylactic acid primary product and 0.0022g of ditert-butane peroxide into a thick-wall pressure-resistant bottle, adding 35mL of 2-methyl-1, 3-butadiene, then adding 20mL of ethylene glycol diether, stirring until the solid is completely dissolved, sealing with a polytetrafluoroethylene plug, vacuumizing, heating to 150 ℃ and reacting for 30 h; and after the reaction is finished, rapidly cooling to room temperature, recrystallizing twice, and drying in vacuum to obtain the product, namely the triblock polylactic acid.
Step 3, weighing 1.6g of triblock polylactic acid into a thick-wall pressure-resistant bottle, adding 30mL of tetrahydrofuran and 0.012g of azobisisobutyronitrile, sealing and stirring for 1h, adding 0.05g of thioglycolic acid, vacuumizing, reacting at 120 ℃ for 12h, and vacuum-drying to obtain a product X; dissolving the product X and 1.7g of glycine in 50mL of dimethyl sulfoxide, adding 0.13g of 4-dimethylaminopyridine, stirring at 50 ℃ for reacting for 18h, recrystallizing, and drying in vacuum to obtain the modified triblock polylactic acid.
Step 4, drying the modified triblock polylactic acid in a drying oven; wherein the temperature of the oven is 80 ℃ and the time is 6 h;
and 5, adding the modified triblock polylactic acid dried in the step 4 into a homodromous double-screw extruder for extrusion, granulating, and then using an injection molding machine for injection moldingMolding, wherein the injection pressure of the injection molding machine is 95.61MPa, and the injection speed is 67cm3The cylinder temperature was 200 ℃ and the die temperature was 50 ℃.
Example 3
A polylactic acid injection molding method is characterized by comprising the following steps:
step 1, 0.5g of first initiator, 10g of polylactic acid intermediate and 60mL of dichloromethane are taken and uniformly mixed, 0.08g N of N-dimethylethanolamine is added, the mixture is hermetically stirred for 3 hours at the temperature of 30 ℃, 0.1g of benzoic acid is added, the mixture is stirred and dissolved, the mixture is precipitated in ethylene diamine tetraacetic acid, the recrystallization is carried out twice, and the vacuum drying is carried out, so as to obtain a polylactic acid primary product.
The preparation method of the polylactic acid intermediate comprises the following steps:
weighing 30g of lactic acid and 0.15g of trimethyl orthoformate, placing the lactic acid and the trimethyl orthoformate into a reaction flask, and stirring the mixture at room temperature for reaction for 3 hours to obtain a product M; wherein the stirring speed is 300 rpm;
and adding 1.4g of antimony chloride into the product M, uniformly stirring, carrying out reduced pressure distillation for 2h at 45 ℃ and 0.1Mpa, depolymerizing, drying, and recrystallizing to obtain a polylactic acid intermediate.
The preparation method of the first initiator comprises the following steps:
s1, uniformly mixing disodium hydrogen phosphate dihydrate and n-butanol, adding 2-mercaptoethanol, uniformly stirring, adding chloroform, and stirring at room temperature for 30min to obtain a solution A; wherein the solid-to-liquid ratio of the disodium hydrogen phosphate dihydrate to the n-butanol is 1: 12; the molar ratio of the 2-mercaptoethanol to the disodium hydrogen phosphate dihydrate is 1: 1; the molar ratio of trichloromethane to 2-mercaptoethanol is 1: 3.
S2, adding p-dibromide benzyl into n-butyl alcohol, and stirring and dissolving to obtain a solution B; wherein the solid-to-liquid ratio of the p-dibromide benzyl to the n-butyl alcohol is 1: 12;
s3, adding the solution B into the solution A, stirring for 10 hours at room temperature, filtering, removing filter residues, and performing rotary evaporation until the filter residues are dried to obtain a solid C;
and S4, passing the solid C through a silica gel column, eluting and purifying, recrystallizing in dichloromethane, and drying under reduced pressure at room temperature to obtain a first initiator.
Step 2, weighing 1.2g of polylactic acid primary product and 0.0022g of ditert-butane peroxide into a thick-wall pressure-resistant bottle, adding 35mL of 2-methyl-1, 3-butadiene, then adding 20mL of ethylene glycol diether, stirring until the solid is completely dissolved, sealing with a polytetrafluoroethylene plug, vacuumizing, heating to 125 ℃ and reacting for 24 hours; and after the reaction is finished, rapidly cooling to room temperature, recrystallizing twice, and drying in vacuum to obtain the product, namely the triblock polylactic acid.
Step 3, weighing 1.6g of triblock polylactic acid into a thick-wall pressure-resistant bottle, adding 30mL of tetrahydrofuran and 0.012g of azobisisobutyronitrile, sealing and stirring for 1h, adding 0.05g of thioglycolic acid, vacuumizing, reacting for 11h at the temperature of 80 ℃, and vacuum-drying to obtain a product X; dissolving the product X and 1.7g of glycine in 50mL of dimethyl sulfoxide, adding 0.13g of 4-dimethylaminopyridine, stirring at 50 ℃ for reaction for 15 hours, recrystallizing, and drying in vacuum to obtain the modified triblock polylactic acid.
Step 4, drying the modified triblock polylactic acid in a drying oven; wherein the temperature of the oven is 80 ℃ and the time is 6 h;
and 5, adding the modified triblock polylactic acid dried in the step 4 into a co-rotating twin-screw extruder for extrusion, granulating, and performing injection molding by using an injection molding machine, wherein the injection pressure of the injection molding machine is set to be 95.61MPa, and the injection speed is set to be 67cm3The cylinder temperature was 200 ℃ and the die temperature was 50 ℃.
Comparative example 1
Step 1, 0.5g of zinc oxide, 10g of lactide purchased from the market and 60mL of dichloromethane are uniformly mixed, and after stirring for 1h at 120 ℃, precipitation, recrystallization twice and vacuum drying are carried out to obtain a polylactic acid primary product.
Step 2, weighing 1.2g of polylactic acid primary product and 0.08g of stannous octoate, heating to 180 ℃ and reacting for 24 h; and after the reaction is finished, rapidly cooling to room temperature, recrystallizing twice, and drying in vacuum to obtain the product polylactic acid.
Step 3, adding polylactic acid into a homodromous twin-screw extruder for extrusion, granulating, and then using an injection molding machine for injection molding, wherein the injection pressure of the injection molding machine is set to be 95.61MPa, and the injection speed is set to be 95.61MPa67cm3The cylinder temperature was 200 ℃ and the die temperature was 50 ℃.
In order to more clearly illustrate the content of the invention, the invention carries out mechanical property detection, and specifically comprises the following steps:
the tensile strength and elongation at break of the polylactic acid materials prepared in example 1, example 2, example 3 and comparative example 1 of the present invention were measured under the conditions of GB/T3923.1-1997, as shown in Table 1.
TABLE 1 mechanical Properties measurements
| Example 1 | Example 2 | Example 3 | Comparative example 1 | |
| Tensile strength/MPa | 48.3 | 42.3 | 45.2 | 46.1 |
| Elongation at break/% | 207.5 | 221.7 | 236.8 | 8.9 |
As can be seen from Table 1, the modified triblock polylactic acid material prepared by the injection molding method of the present invention has a greatly improved elongation at break. Among them, the elongation at break of example 3 of the present invention is more than 26 times that of the conventional polylactic acid in comparative example 1. Therefore, the injection molding method of polylactic acid used in embodiment 3 of the present invention has a great improvement in toughness of polylactic acid.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the protection scope of the present invention, although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.
Claims (8)
1. A polylactic acid injection molding method is characterized by comprising the following steps:
step 1, firstly, carrying out polycondensation reaction on lactic acid, and depolymerizing the lactic acid into a polylactic acid intermediate under the conditions of high temperature and low pressure; then, carrying out ring opening on the polylactic acid intermediate under the action of a first initiator and a ring opening catalyst to obtain a polylactic acid primary product;
wherein the ring-opening catalyst is N, N-dimethylethanolamine;
the first initiator is obtained by reacting disodium hydrogen phosphate dihydrate, 2-mercaptoethanol and p-dibromide.
Step 2, polymerizing the polylactic acid primary product with 2-methyl-1, 3-butadiene through a second initiator to obtain triblock polylactic acid; the second initiator is ditert-butane peroxide;
step 3, grafting glycine to the triblock polylactic acid through a third initiator to obtain modified triblock polylactic acid; the third initiator is azobisisobutyronitrile;
step 4, drying the modified triblock polylactic acid in a drying oven; wherein the temperature of the oven is 80 ℃ and the time is 6 h;
step 5, adding the modified triblock polylactic acid dried in the step 4 into a homodromous twin-screw extruder for extrusion and granulation, and thenThen injection molding is carried out by using an injection molding machine; wherein the injection pressure of the injection molding machine is set to 95.61MPa, and the injection speed is set to 67cm3The cylinder temperature was 200 ℃ and the die temperature was 50 ℃.
2. The polylactic acid injection molding method according to claim 1, wherein the preparation method of the polylactic acid intermediate in the step 1 specifically comprises:
weighing 30g of lactic acid and 0.15g of trimethyl orthoformate, placing the lactic acid and the trimethyl orthoformate into a reaction flask, and stirring the mixture at room temperature for reaction for 3 hours to obtain a product M; wherein the stirring speed is 300 rpm;
and adding 1.4g of antimony chloride into the product M, uniformly stirring, carrying out reduced pressure distillation for 2 hours at 40-50 ℃ and 0.1Mpa, depolymerizing, drying, and recrystallizing to obtain a polylactic acid intermediate.
3. The injection molding method of polylactic acid according to claim 1, wherein the first initiator of step 1 is prepared by:
s1, uniformly mixing disodium hydrogen phosphate dihydrate and n-butanol, adding 2-mercaptoethanol, uniformly stirring, adding chloroform, and stirring at room temperature for 30min to obtain a solution A; wherein the solid-to-liquid ratio of the disodium hydrogen phosphate dihydrate to the n-butanol is 1: 10-15; the molar ratio of the 2-mercaptoethanol to the disodium hydrogen phosphate dihydrate is 1: 1; the molar ratio of trichloromethane to 2-mercaptoethanol is 1: 3.
S2, adding p-dibromide benzyl into n-butyl alcohol, and stirring and dissolving to obtain a solution B; wherein the solid-to-liquid ratio of the p-dibromide to the n-butyl alcohol is 1: 10-15;
s3, adding the solution B into the solution A, stirring for 10 hours at room temperature, filtering, removing filter residues, and performing rotary evaporation until the filter residues are dried to obtain a solid C;
and S4, passing the solid C through a silica gel column, eluting and purifying, recrystallizing in dichloromethane, and drying under reduced pressure at room temperature to obtain a first initiator.
4. The polylactic acid injection molding method according to any one of claims 1 to 3, wherein the step 1 specifically comprises:
and (2) uniformly mixing 0.5g of the first initiator, 10g of the polylactic acid intermediate and 60mL of dichloromethane, adding 0.08g N, N-dimethylethanolamine, hermetically stirring for 3h at 30 ℃, adding 0.1g of benzoic acid, stirring for dissolving, precipitating in ethylene diamine tetraacetic acid, recrystallizing twice, and drying in vacuum to obtain a polylactic acid primary product.
5. The polylactic acid injection molding method according to claim 1, wherein the step 2 specifically comprises:
weighing 1.2g of polylactic acid primary product and 0.0022g of ditert-butane peroxide into a thick-wall pressure-resistant bottle, adding 35mL of 2-methyl-1, 3-butadiene, then adding 20mL of ethylene glycol diether, stirring until the solid is completely dissolved, sealing with a polytetrafluoroethylene plug, vacuumizing, heating to 100-150 ℃ and reacting for 18-30 h; and after the reaction is finished, rapidly cooling to room temperature, recrystallizing twice, and drying in vacuum to obtain the product, namely the triblock polylactic acid.
6. The polylactic acid injection molding method according to claim 1, wherein the step 3 specifically comprises:
weighing 1.6g of triblock polylactic acid into a thick-wall pressure-resistant bottle, adding 30mL of tetrahydrofuran and 0.012g of azodiisobutyronitrile, sealing and stirring for 1h, adding 0.05g of thioglycolic acid, vacuumizing, reacting at 60-120 ℃ for 10-12 h, and vacuum drying to obtain a product X; dissolving the product X and 1.7g of glycine in 50mL of dimethyl sulfoxide, adding 0.13g of 4-dimethylaminopyridine, stirring at 50 ℃ for reaction for 12-18 h, recrystallizing, and drying in vacuum to obtain the modified triblock polylactic acid.
7. The polylactic acid injection molding method according to claim 1, wherein the lactic acid is one or more of L-lactic acid, D-lactic acid, and DL-lactic acid.
8. An injection molding method of polylactic acid according to claim 1, wherein the injection molding machine of step 5 is provided with a closed nozzle; the closed nozzle comprises one of a double-lock type nozzle, a material pressure lock type nozzle and a controllable lock type nozzle.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112315605A (en) * | 2020-11-03 | 2021-02-05 | 吉林大学 | Implantable bone cyst windowing drainage system |
| CN113461880A (en) * | 2021-07-21 | 2021-10-01 | 无锡御束生物材料科技有限公司 | Polylactic acid injection molding method |
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2019
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112315605A (en) * | 2020-11-03 | 2021-02-05 | 吉林大学 | Implantable bone cyst windowing drainage system |
| CN113461880A (en) * | 2021-07-21 | 2021-10-01 | 无锡御束生物材料科技有限公司 | Polylactic acid injection molding method |
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