Additive composition for inhibiting yellowing of polyglycolic acid and polymerization process

Abstract

The invention discloses an additive composition for inhibiting yellowing of polyglycolic acid and a polymerization process. The additive composition comprises an antioxidant, a heat stabilizer and a carbon free radical scavenger, wherein the antioxidant accounts for 90-120 parts by weight, the heat stabilizer accounts for 80-110 parts by weight, and the carbon free radical capturing agent accounts for 120-150 parts by weight. The additive composition inhibits degradation and yellowing of long-chain polyglycolic acid under high-temperature and high-vacuum conditions, so that glycolic acid is directly polycondensed to synthesize a polyglycolic acid product, and good color and luster can be kept under high molecular weight.

Description

Technical Field

[0001] The present invention relates to the field of polyglycolic acid (PGA) preparation, and in particular to an auxiliary agent composition and a polymerization process for inhibiting yellowing of polyglycolic acid, and in particular to an auxiliary agent composition and a polymerization process for PGA for inhibiting yellowing of polyglycolic acid (PGA) and improving product quality in a method for synthesizing PGA by direct polycondensation of glycolic acid. Background Art

[0002] At present, the main biodegradable plastic products are polylactic acid (PLA), PBAT, PHA, PBS and modified starch. Among them, PLA has the largest industry consumption, with a global output of more than 450,000 tons, and is widely used in packaging, film materials, construction and other fields. Develop engineering biodegradable polymer materials with better comprehensive performance than PLA and gradually replace PLA. The global market capacity of biodegradable polymer materials has reached one million tons, and the market demand is strong, which will bring significant economic benefits in the future. PGA has better service heat resistance, gas barrier performance, mechanical strength, and seawater degradability than PLA. It has great development potential in packaging, biomedicine, oil extraction, engineering plastics and other fields in the future. It is a rare biodegradable engineering polymer material, and its biodegradability is similar to that of natural cellulose. At the same time, it meets the requirements of industrial composting, household composting and seawater degradation. It has obtained safe biodegradable plastic material certification in the United States, the European Union, Japan and other countries, and is widely used in high-end biomedicine, food packaging, shale and oil extraction and agricultural production. The market space is broad, and it is expected that the global PGA market will reach 10 billion yuan in 2030.

[0003] At present, the synthesis methods of polyglycolic acid with industrial value include direct polycondensation and glycolide ring-opening polymerization. At present, the synthesis of PGA at home and abroad is mainly based on glycolide ring-opening polymerization. This route has high requirements for the purity of glycolide and the product cost is very high. It is only suitable for high-end materials in specific fields such as biomedicine and oil extraction, and is mainly mass-produced in Japan and the United States.

[0004] In recent years, with the development of coal chemical technology and the breakthrough of key technology for preparing glycolic acid (methyl ester) from dimethyl oxalate at low cost, my country's PGA industry has brought important turning points and hope. The rapid growth of domestic glycolic acid monomer production scale and the reduction of costs make direct polymerization more likely to become the preferred solution for large-scale production of PGA in the future.

[0005] The method of synthesizing PGA by direct polycondensation of glycolic acid is shorter and cheaper than the ring-opening polymerization of glycolide, and is more suitable for the production of bulk products. However, it is generally reported that this method is difficult to synthesize products with higher molecular weight and lighter color, and there is a problem of mutual exclusion between molecular weight and color. Because in the later stage of the polycondensation reaction, the required temperature increases and the pressure decreases, the thermal stability of polyglycolic acid deteriorates, and the long-chain molecules will degrade into short-chain molecules. At the same time, color changes will occur due to complex mechanisms, which brings challenges and opportunities to the development of the entire industry.

[0006] Therefore, it is necessary to develop a process for synthesizing PGA based on direct polycondensation of glycolic acid to inhibit the yellowing of polyglycolic acid (PGA) so that the product synthesized from direct polycondensation of glycolic acid can maintain good color at a high molecular weight. Summary of the invention

[0007] The purpose of the present invention is to provide an auxiliary agent composition and a polymerization process for inhibiting the yellowing of polyglycolic acid (PGA), so as to inhibit the yellowing of polyglycolic acid (PGA) and improve product quality.

[0008] To achieve one aspect of the above-mentioned invention object, the auxiliary agent composition provided by the present invention adopts the following technical scheme:

[0009] An auxiliary agent composition for inhibiting yellowing of polyglycolic acid comprises an antioxidant, a heat stabilizer and a carbon free radical scavenger; wherein, by weight, the antioxidant is 90-120 parts, the heat stabilizer is 80-110 parts and the carbon free radical scavenger is 120-150 parts.

[0010] The antioxidant, heat stabilizer and carbon free radical scavenger described in the present invention are all commercially available conventional products, and their purity can be as high as 98% or more to reduce interference. The weight parts described in the present invention can be μg, mg, g, kg and other weight units known in the chemical and pharmaceutical fields.

[0011] According to the auxiliary agent composition of the present invention, preferably, the antioxidant is one or more of pentaerythritol tetrakis (di-tert-butyl hydroxyhydrocinnamate) (Antioxidant 1010), α-tocopherol, and 5-tert-butyl-4-hydroxy-2-methylphenyl sulfide (Antioxidant 300).

[0012] According to the auxiliary agent composition of the present invention, preferably, the heat stabilizer is one or more of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite (THP-24), diphenyl phosphite, triphenyl phosphite (TPP), and triethyl phosphate (TEP).

[0013] According to the auxiliary agent composition of the present invention, preferably, the carbon radical scavenger is one or more of 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylphenyl)methyl-4-methylphenyl acrylate (TH-330), N,N-bis(n-octadecyl)hydroxylamine (Revonox 420), and 2-(2-hydroxy-3-tert-butyl-5-methylbenzyl)-4-methyl-6-tert-butylphenyl acrylate (IRGANOX 3052).

[0014] In the present invention, the finished preparation of the auxiliary agent composition can be a powdered mixture or a suspension, such as an alcohol suspension, a suspension diluted with glycolic acid, or a suspension diluted with ethylene glycol.

[0015] In the present invention, various dosage forms of the auxiliary agent composition can be prepared according to conventional production methods in the field of auxiliary agent production, such as using powder mixing equipment or solid-liquid mixing equipment to make it into the desired dosage form.

[0016] In a preferred embodiment, the auxiliary agent composition is a suspension further comprising a diluent to facilitate subsequent mixing of the auxiliary agent with the reactants; the diluent is glycolic acid and / or ethylene glycol.

[0017] Preferably, the diluent is ethylene glycol; the suspension is prepared by adding ethylene glycol to a preparation tank, heating to 50°C-70°C, such as 55, 60 or 65°C, adding antioxidants, heat stabilizers and carbon free radical scavengers according to the proportion under stirring conditions, and stirring thoroughly to fully disperse. It is understood in the art that the prepared auxiliary composition can be kept warm, nitrogen-filled and sealed until use.

[0018] Preferably, the diluent is used in an amount of 97.5wt%-98.5wt% of the suspension, such as 98wt%.

[0019] In the auxiliary composition of the present invention, the antioxidant is 90-120 parts, such as 100 or 110 parts, preferably 95-110 parts, the heat stabilizer is 80-110 parts, such as 90 or 100 parts, preferably 85-100 parts, and the carbon radical scavenger is 120-150 parts, such as 130 or 140 parts, preferably 130-145 parts.

[0020] In order to achieve another aspect of the above-mentioned invention object, the polymerization process provided by the present invention adopts the following technical scheme:

[0021] A polymerization process for preparing polyglycolic acid comprises the following steps:

[0022] (1) adding glycolic acid and a catalyst into a reaction kettle to carry out a polymerization reaction until the reactant is solidified;

[0023] (2) adding the auxiliary agent composition according to any one of claims 1 to 6 to the reaction kettle;

[0024] (3) heating the reactor until the reactants are melted and uniformly mixed with the auxiliary agent composition, and reacting under high vacuum to obtain a PGA crystalline polymer;

[0025] (4) Cutting the PGA crystalline polymer prepared in step (3) into pellets, drying and removing water, and controlling the temperature to 195-210° C. to perform solid phase polymerization to further increase the molecular weight of PGA.

[0026] In step (1) of the present invention, glycolic acid and a catalyst are subjected to catalytic polymerization in a reactor. The reaction is well known in the art, and the catalyst used is also well known in the art, such as stannous octoate, which will not be described in detail here.

[0027] In a preferred embodiment, when the polymerization is carried out in step (1), the reactor is first heated to 185-195°C, such as 190°C, and reacted until the theoretical water output rate of the system reaches more than 98% (such as reaction under normal pressure) to obtain PGA oligomers; then the temperature is lowered to 165-175°C, such as 170°C, and the pressure is controlled to react under rough vacuum (preferably 2000-3000 Pa) until the reactants are solidified. The study found that lowering the temperature of the reaction system to 165-175°C can reduce the melting point of PGA in the subsequent vacuum polycondensation process, so that the PGA polycondensation temperature is controlled within a relatively low range that is not prone to yellowing (while directly raising the temperature from 190°C to the polycondensation temperature is likely to increase the melting point of PGA), thereby inhibiting the yellowing of the product; in addition, reacting to solidify the product can maximize the degree of polymerization of PGA oligomers (for example, the degree of polymerization of polyglycolic acid after reaction to solidification can be about 10, such as 8-12, such as 9-11), reducing the subsequent high vacuum polycondensation time, and too long high vacuum polycondensation time can easily cause PGA yellowing.

[0028] In step (2) of the present invention, the auxiliary composition is further added to the reaction kettle to inhibit yellowing; in a preferred embodiment, in step (2), based on the mass of glycolic acid, the auxiliary composition is used in a ratio of 1 / 10,000 to 1 / 1,000, preferably 4 / 10,000 to 6 / 10,000.

[0029] In step (3) of the present invention, the reactor is heated until the reactants are melted so as to be fully and evenly mixed with the auxiliary agent composition, and then reacted under high vacuum to obtain a PGA crystalline polymer to ensure the reaction effect.

[0030] In a preferred embodiment, in step (3), the reactor is heated to 215-220° C. to fully melt the reactants.

[0031] In a preferred embodiment, in step (3), the PGA crystalline polymer is obtained by reaction at a pressure of 10-100 Pa, such as 40, 60, 70 or 80 Pa; the reaction time is preferably 120-180 min, such as 150 min.

[0032] In step (4) of the present invention, after the PGA crystalline polymer prepared by melting is cut into pellets, it can be dried to remove water under vacuum or blowing conditions at 100-120°C, and then solid-phase polymerization can be carried out under vacuum or dry nitrogen flow at 195-210°C to further increase the molecular weight of PGA.

[0033] In the present invention, unless otherwise specified, all ratios or percentages involved are mass ratios or mass percentages.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] The PGA prepared by the present invention has high quality and high profit margin, and has significant economic benefits;

[0036] The auxiliary agent composition and process of the present invention can effectively inhibit the yellowing of polyglycolic acid (PGA), improve product quality, inhibit the degradation of long-chain polyglycolic acid and inhibit yellowing under high temperature and high vacuum conditions, directly condense glycolic acid to synthesize polyglycolic acid products, and maintain good color at high molecular weight. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only embodiments of a part of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0038] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values, such as values ​​of ±10% of the endpoint values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0039] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatus.

[0040] In the following examples / comparative examples, unless otherwise specified, all reagents used were of analytical grade.

[0041] The preparation processes of Examples 1-12 and Comparative Examples 1-24 are as follows:

[0042] 1. Take 2000g glycolic acid, put it into a reactor, add a catalyst (0.5g stannous octoate), heat it to 190°C and react until the theoretical water output rate of the system reaches more than 98%;

[0043] 2. Cool down to 170°C, control the pressure to react under rough vacuum (2000Pa) until the reactant solidifies;

[0044] 3. Add the auxiliary agent composition (the dosage is 0.5 ten thousandths of glycolic acid);

[0045] 4. Raise the temperature to 220° C. until the reactants are completely melted and evenly mixed with the auxiliary composition, and react under high vacuum (70 Pa) for 125 min to obtain a PGA crystalline polymer.

[0046] 5. The PGA crystalline polymer prepared by melting was cut into pellets, dried and dehydrated under vacuum conditions at 100°C, and then the PGA pellets were put into a vacuum drum reactor for solid phase polycondensation at a polycondensation temperature of 198°C for 20 hours to obtain a PGA solid material.

[0047] Embodiment 13

[0048] The difference between Example 13 and Example 1 is that after the temperature is raised to 190° C., the reaction is directly carried out until the reactants are solidified.

[0049] The auxiliary agent compositions used in the above examples / comparative examples (wherein the auxiliary agent compositions used in Examples 4, 7 and 10 are suspensions diluted with ethylene glycol), polymerization conditions and test results are shown in Tables 1 and 2 below:

[0050] Table 1

[0051]

[0052]

[0053]

[0054] Table 2

[0055]

[0056] Comparative Example 25 (cited from CN107177032B)

[0057] Weigh 3kg of glycolic acid, add 3g of titanium dioxide and 15g of stannous octoate, add to a 5L polymerization reactor, mix evenly, control the absolute pressure in the reactor to 500KPa, heat to 150℃ to start the reaction, and heat to 200℃ at a rate of 0.2℃ / min. The by-product water is discharged and collected from the top of the distillation tower. Then, the pressure is reduced to 20Pa at a rate of 6KPa / min, and the temperature is raised to 240℃ at 0.35℃ / min. At 20Pa and 240℃, continue the reaction for 0.5h to obtain glycolic acid oligomers. The obtained oligomer was crushed and sieved to 200-300 mesh, 500g was weighed, and sent to a boiling dryer for solid phase polycondensation reaction. The solid phase polycondensation temperature was set to 110°C and the carbon dioxide flow rate was 500L / min. Under the action of the airflow, the glycolic acid prepolymer powder was in a "boiling" state. After 100h of reaction, the PGA product was obtained with a weight average molecular weight of about 110,000, a B value of 12.6, and a brown-yellow color.

[0058] Example 1-12 is a PGA product obtained by adding the antioxidant composition of the present invention and within the ratio range of the antioxidant composition of the present invention. After testing, the weight average molecular weight is about 110,000, the B value is less than 2, the color is white, and the hue is good;

[0059] Compared with Example 1, Example 13 directly reacts until the reactants solidify after the temperature is raised to 190° C., resulting in severe yellowing of the final product.

[0060] Comparative Example 1 is a PGA product obtained without adding the antioxidant composition of the present invention or other antioxidants. Compared with Examples 1-12, the B value is larger, the color is brown-yellow, and the hue is poor; this shows that the antioxidant composition of the present invention can effectively improve the yellowing problem in the PGA preparation process and obtain a PGA product with high molecular weight and high hue.

[0061] Comparative Example 2-11 is a PGA product obtained by adding a single component antioxidant alone, with a higher molecular weight but a larger B value, a dark yellow to brownish yellow color, and a poor hue;

[0062] Comparative Examples 12-19 are PGA products obtained by adding the antioxidant composition of the present invention but in an amount outside the ratio range of the auxiliary composition of the present invention:

[0063] Compared with Example 1, the amount of the three components or a single component added in the antioxidant composition in Comparative Examples 12-15 is less, the obtained PGA product has a better molecular weight, a larger B value, and a slightly lighter color than Comparative Examples 2-11, but a worse color than Example 1;

[0064] Compared with Example 1, the addition amount of the three components or a single component in the antioxidant composition in Comparative Examples 16-19 is larger, the molecular weight of the obtained PGA product is poor, the B value is larger, the color is slightly lighter than that of Comparative Examples 2-11, but the color is worse than that of Example 1;

[0065] From the above comparison, it can be seen that the three components of the antioxidant composition of the present invention have excellent synergistic effects, which can effectively improve the yellowing problem in the preparation process of PGA and obtain a PGA product with high molecular weight and high hue.

[0066] Comparative Examples 20-24 are PGA products obtained by adding other antioxidant combinations other than the antioxidant composition of the present invention:

[0067] Compared with Example 1, the PGA product obtained by adding other antioxidant combinations other than the antioxidant composition of the present invention has a larger B value and a darker color, which further illustrates that the synergistic effect of the three components of the antioxidant composition of the present invention can effectively improve the yellowing problem in the preparation process of PGA and obtain a PGA product with high molecular weight and high hue.

[0068] Compared with Examples 1-13, Comparative Example 25 has a larger B value and a darker color than the PGA product obtained by the conventional method, which further illustrates that the synergistic effect of the three components of the antioxidant composition of the present invention can effectively improve the yellowing problem in the PGA preparation process and obtain a PGA product with high molecular weight and high hue.

[0069] Obviously, the present invention is not limited to the above embodiments, and many variations are possible. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should be considered as falling within the protection scope of the present invention.

Claims

1. An auxiliary composition for inhibiting yellowing of polyglycolic acid, comprising an antioxidant, a heat stabilizer and a carbon free radical scavenger; wherein: In parts by weight, the antioxidant is 90-120 parts, the heat stabilizer is 80-110 parts and the carbon free radical scavenger is 120-150 parts.

2. The auxiliary agent composition according to claim 1, characterized in that The antioxidant is one or more of pentaerythritol tetrakis (di-tert-butyl hydroxyhydrocinnamate), α-tocopherol, and 5-tert-butyl-4-hydroxy-2-methylphenyl sulfide; and / or The heat stabilizer is one or more of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, diphenyl phosphite, triphenyl phosphite, and triethyl phosphate; and / or The carbon radical scavenger is one or more of 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylphenyl)methyl-4-methylphenyl acrylate, N,N-bis(n-octadecyl)hydroxylamine, and 2-(2-hydroxy-3-tert-butyl-5-methylbenzyl)-4-methyl-6-tert-butylphenyl acrylate.

3. The auxiliary agent composition according to claim 1 or 2, characterized in that The composition is a suspension further comprising a diluent; the diluent is glycolic acid and / or ethylene glycol.

4. The auxiliary agent composition according to claim 3, characterized in that The diluent is ethylene glycol; The suspension is prepared by adding ethylene glycol into a preparation tank, heating the tank to 50° C.-70° C., adding an antioxidant, a heat stabilizer and a carbon free radical scavenger according to a proportion under stirring conditions, and then stirring and dispersing the mixture evenly.

5. The auxiliary agent composition according to claim 4, characterized in that The diluent is used in an amount of 97.5wt%-98.5wt% of the suspension.

6. The auxiliary agent composition according to any one of claims 1 to 5, characterized in that The antioxidant is 85-110 parts, the heat stabilizer is 95-110 parts and the carbon free radical scavenger is 130-145 parts.

7. A polymerization process for preparing polyglycolic acid, comprising the following steps: (1) adding glycolic acid and a catalyst into a reaction kettle to carry out a polymerization reaction until the reactant is solidified; (2) adding the auxiliary agent composition according to any one of claims 1 to 6 to the reaction kettle; (3) heating the reactor until the reactants are melted and uniformly mixed with the auxiliary agent composition, and reacting under high vacuum to obtain a PGA crystalline polymer; (4) Cutting the PGA crystalline polymer prepared in step (3) into pellets, drying and removing water, and controlling the temperature to 195-210° C. to perform solid phase polymerization to further increase the molecular weight of PGA.

8. The polymerization process according to claim 7, characterized in that When the polymerization is carried out in step (1), the reactor is first heated to 185-195° C. and reacted until the theoretical water yield of the system reaches more than 98% to obtain PGA oligomers; then the temperature is lowered to 165-175° C. and the pressure is controlled to react under rough vacuum until the reactants are solidified; Preferably, the pressure is controlled to be between 2000 and 3000 Pa and the reaction is carried out until the reactants are solidified.

9. The polymerization process according to claim 8, characterized in that In step (2), based on the mass of glycolic acid, the auxiliary agent composition is used in a ratio of 1 / 10,000 to 1 / 1,000, preferably 4 / 10,000 to 6 / 10,000.

10. The polymerization process according to claim 9, characterized in that In step (3), the reactor is heated to 215-220° C. to melt the reactants, and the reaction is carried out at a pressure of 10-100 Pa for 120-180 min to obtain a PGA crystalline polymer.

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