A process for the preparation of a yellowing resistant polybutylene succinate for food contact materials

Abstract

This invention provides a method for preparing yellowing-resistant polybutylene succinate (PBS) for food contact materials. In this method, raw materials undergo an esterification-condensation reaction in the presence of a catalyst to generate the yellowing-resistant PBS for food contact materials. The raw materials are succinic acid and 1,4-butanediol, and the fumaric acid content and / or maleic acid content in the succinic acid raw material are controlled to be ≤300 ppm and ≤300 ppm, respectively. The preparation method of this invention can significantly improve the yellowing resistance of PBS and reduce the total migration.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable polymer materials, specifically relating to a method for preparing yellowing-resistant polybutylene succinate for food contact materials. Background Technology

[0002] Polybutylene succinate (PBS) and its copolyesters are a class of aliphatic polyesters with good biodegradability and comprehensive properties. They are typically prepared by direct esterification and polycondensation of succinic acid and 1,4-butanediol, and are among the most promising materials to replace traditional polyolefin plastics. Due to their excellent biodegradability and mechanical properties, PBS has strong application potential in food contact materials such as disposable lunch boxes and straws. However, its use in food contact materials is subject to strict legal and regulatory requirements. The material must not only possess excellent resistance to yellowing but also control the total migration amount in food contact materials and products; however, related research is limited.

[0003] Patent CN1424339 discloses a method for preparing PBS, which uses succinic acid and butanediol as raw materials to prepare PBS degradable plastic with a weight average molecular weight of 100,000 and good physical and mechanical properties by melt polycondensation, but does not involve the color of PBS products.

[0004] CN1424339 discloses a method for preparing PBS using a composite catalyst such as tin oxide, antimony trioxide, chromium acetate and titanium alkoxide. However, this type of catalyst has low activity and requires a high amount to be added, which leads to many side reactions and increases the melt flow rate, decreases the mechanical properties, and causes severe yellowing of the product.

[0005] CN1861660A discloses a method for preparing PBS using tetrabutyl titanate, isopropyl titanate, antimony trioxide and n-butyl titanate. However, although titanate catalysts have high activity, they are unstable and easily hydrolyzed.

[0006] In summary, there is an urgent need for an efficient and easily industrialized method to prepare polybutylene succinate with yellowing resistance, which can be used in food contact materials. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing yellowing-resistant polybutylene succinate (PBS) for food contact materials. This method allows for the efficient and engineered preparation of PBS with yellowing resistance for use in food contact materials.

[0008] The inventors have surprisingly discovered that by controlling the content of fumaric acid and / or maleic acid in the raw material succinic acid, the yellowing resistance of PBS can be significantly improved and the total migration of the product can be reduced, thus completing this invention.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing yellowing-resistant polybutylene succinate for food contact materials, wherein succinic acid and 1,4-butanediol undergo an esterification polycondensation reaction in the presence of a catalyst to generate polybutylene succinate, wherein the succinic acid in the raw material contains ≤300ppm fumaric acid and / or ≤300ppm maleic acid.

[0011] This invention has found that the migration products of PBS obtained using the national standard testing method are small molecule oligomers, mainly oligomers containing unsaturated double bonds, which are derived from the reaction of fumaric acid and / or maleic acid contained in succinic acid. By controlling the fumaric acid and / or maleic acid in succinic acid, the raw material for preparing PBS, the generation of conjugated chromophores in PBS during use can be effectively inhibited, thus effectively preventing the yellowing of the PBS product.

[0012] In this invention, the method includes the following steps:

[0013] S1: Esterification reaction. The catalyst, succinic acid and 1,4-butanediol are added to the reactor to carry out the esterification reaction, and the by-product water is removed to complete the esterification reaction.

[0014] S2: Polycondensation reaction. The reactor is evacuated and then evacuated again. After the polycondensation reaction is completed, the reactor is restored to normal pressure to obtain polymer melt. After water cooling and pelletizing, polybutylene succinate polymer is obtained.

[0015] In this invention, the catalyst in S1 is a titanate ester and a phosphorus compound; preferably, the titanate ester is Ti(OR)4, wherein R is an alkyl group with 1 to 10 carbon atoms, preferably one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, and tetramethyl titanate; preferably, the titanate ester has a content of 50 to 300 ppm based on elemental Ti, based on the total mass of polyester; preferably, the phosphorus compound is an organophosphorus compound and / or an inorganic phosphorus compound, preferably one or more of trimethyl phosphate, triethyl phosphate, and triphenyl phosphate; the phosphorus compound has a content of 10 to 100 ppm based on elemental P, based on the total mass of polyester.

[0016] In this invention, the molar ratio of succinic acid and 1,4-butanediol in S1 is 1:1.1 to 1:1.5, preferably 1:1.1 to 1:1.3.

[0017] In this invention, the esterification reaction temperature in S1 is 180–250°C.

[0018] In this invention, the reaction S1 ends when the total esterification rate reaches 95%.

[0019] In this invention, S2 first evacuates to 1000-30000 PaA and continues for 10-60 minutes, then evacuates to a high vacuum below 100 PaA.

[0020] In this invention, the S2 polycondensation reaction temperature is 220–260°C, and the high-vacuum polycondensation time is 60–200 min.

[0021] In this invention, the method for controlling fumaric acid and / or maleic acid in the raw material succinic acid is adsorption; preferably, the adsorbent for the adsorption method is selected from one or more of activated carbon, molecular sieves, and resins, preferably activated carbon, and more preferably acid-modified activated carbon. The acid is one or more of nitric acid, phosphoric acid, and hydrochloric acid.

[0022] In one embodiment, the method for preparing acid-modified activated carbon is as follows: Activated carbon and acid solution are placed in a beaker, stirred at room temperature, then washed with deionized water until neutral, and dried to obtain acid-modified activated carbon.

[0023] In another embodiment, the pretreatment process of the raw material succinic acid is as follows: succinic acid and activated carbon are mixed evenly, then deionized water is added, the mixture is stirred at room temperature, the activated carbon is removed by filtration, and the filtrate is dried for later use.

[0024] Another object of the present invention is to provide a yellowing-resistant polybutylene succinate for use in food contact materials.

[0025] A yellowing-resistant polybutylene succinate for use in food contact materials is prepared by the above-mentioned esterification polycondensation reaction method, wherein the fumaric acid content in the succinic acid raw material of the esterification polycondensation reaction is ≤300ppm and / or the maleic acid content is ≤300ppm.

[0026] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0027] (1) By controlling the fumaric acid and / or maleic acid in the raw material succinic acid, the generation of conjugated chromophores in PBS during use can be effectively inhibited, and the yellowing of the product PBS can be simply and effectively inhibited (yellowing resistance Δb value <3), and the total migration amount can be reduced (<80mg / 50g).

[0028] (2) The preprocessing method used in this invention is relatively simple and easy to implement, and can be used in practical engineering applications. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments. It should be noted that the embodiments do not constitute a limitation on the scope of protection of the present invention.

[0030] Raw material information:

[0031] Succinic acid, superior grade, Shandong Feiyang Chemical Co., Ltd.;

[0032] 1,4-Butanediol (BDO), industrial grade, Xinjiang Meike Chemical Co., Ltd.;

[0033] Tetrabutyl titanate 98%, reagent grade, Aladdin Reagent Co., Ltd.

[0034] Trimethyl phosphate 98%, reagent grade, Aladdin Reagent Co., Ltd.

[0035] Activated carbon, 100 mesh, Aladdin Reagent Co., Ltd.

[0036] Fuming nitric acid, Aladdin Reagent Co., Ltd.

[0037] 85% aqueous solution of phosphoric acid, Aladdin Reagent Co., Ltd.

[0038] Unless otherwise specified, the equipment and methods used in this invention are all common in the art.

[0039] The color of polybutylene succinate (PBS) was evaluated using the L, a, b color system, where L is the brightness factor, and a and b are the color measurements. b represents the yellow-blue balance, which is crucial for polyester color; a lower b value indicates better color. Yellowing resistance was determined by testing the change in b value after PBS was placed in an 80°C environment for one month. Hue (b value) was automatically measured using a BYK Gardner Color35 automatic colorimeter. Fumaric acid and maleic acid in the raw material succinic acid were detected by high-performance liquid chromatography (HPLC) using a Shimadzu LC-6A HPLC system. The total migration of PBS was tested according to the national standard "Plastic Materials and Products for Food Contact," where 50g of PBS particles were immersed in 200mL of 50% (volume fraction) ethanol aqueous solution and placed at 70°C for 2 hours. Non-volatile matter was measured using a Labthink C830 migration and non-volatile matter analyzer.

[0040] Preparation method of acid-modified activated carbon:

[0041] Add activated carbon and acid solution (acid concentration of 10%-20%) to a beaker at a mass:volume ratio of 1:100-150, stir at room temperature for 5-8 hours, then wash with deionized water until neutral, and dry at 100℃ for 10-20 hours to obtain acid-modified activated carbon.

[0042] Raw material pretreatment process:

[0043] Mix succinic acid and activated carbon at a mass ratio of 10-20:1 until homogeneous. Then add deionized water and stir at room temperature for 5-8 hours. Filter to remove the activated carbon and dry the filtrate at 100-120℃ for 15-20 hours for later use.

[0044] Raw material processing:

[0045] Example 1

[0046] 300g of activated carbon and nitric acid solution (10% nitric acid concentration) were placed in a beaker at a mass:volume ratio of 1:100. After stirring at room temperature for 5 hours, the mixture was washed with deionized water until neutral and dried at 100℃ for 10 hours to obtain nitric acid-modified activated carbon.

[0047] Succinic acid (500 ppm fumaric acid and 600 ppm maleic acid) was mixed with the above-mentioned nitric acid-modified activated carbon at a mass ratio of 10:1. Then, deionized water was added to the beaker, with the amount of deionized water being 10 times the amount of succinic acid. The mixture was stirred at room temperature for 5 hours and then filtered to remove the activated carbon. The filtrate was then dried at 100°C for 15 hours to obtain the pretreated raw material succinic acid A. The fumaric acid content was 200 ppm and the maleic acid content was 200 ppm.

[0048] Example 2

[0049] 300g of activated carbon and a 20% phosphoric acid solution were placed in a beaker at a mass:volume ratio of 1:120. After stirring at room temperature for 6 hours, the mixture was washed with deionized water until neutral and dried at 100°C for 20 hours to obtain phosphoric acid modified activated carbon.

[0050] Succinic acid (500 ppm fumaric acid and 600 ppm maleic acid) was mixed with the above-mentioned phosphoric acid modified activated carbon at a mass ratio of 15:1. Then, deionized water was added to the beaker, with the amount of deionized water being 10 times the amount of succinic acid. The mixture was stirred at room temperature for 8 hours and then filtered to remove the activated carbon. The filtrate was then dried at 120°C for 20 hours to obtain the pretreated raw material succinic acid B. The fumaric acid content was 100 ppm and the maleic acid content was 100 ppm.

[0051] Example 3

[0052] 300g of activated carbon and a phosphoric acid solution (15% phosphoric acid concentration) were placed in a beaker at a mass:volume ratio of 1:150. After stirring at room temperature for 8 hours, the mixture was washed with deionized water until neutral and dried at 100℃ for 15 hours to obtain nitric acid-modified activated carbon.

[0053] Succinic acid (500 ppm fumaric acid and 600 ppm maleic acid) was mixed with the above-mentioned nitric acid-modified activated carbon at a mass ratio of 20:1. Then, deionized water was added to the beaker, with the amount of deionized water being 10 times the amount of succinic acid. The mixture was stirred at room temperature for 7 hours and then filtered to remove the activated carbon. The filtrate was then dried at 110°C for 18 hours to obtain the pretreated raw material succinic acid C. The fumaric acid content was 200 ppm and the maleic acid content was 100 ppm.

[0054] Example 4

[0055] 300g of activated carbon and nitric acid solution (20% nitric acid concentration) were placed in a beaker at a mass:volume ratio of 1:120. After stirring at room temperature for 5 hours, the mixture was washed with deionized water until neutral and dried at 100℃ for 10 hours to obtain nitric acid-modified activated carbon.

[0056] Succinic acid (500 ppm fumaric acid and 600 ppm maleic acid) was mixed with the above-mentioned nitric acid-modified activated carbon at a mass ratio of 17:1. Then, deionized water was added to the beaker, with the amount of deionized water being 10 times the amount of succinic acid. The mixture was stirred at room temperature for 5 hours and then filtered to remove the activated carbon. The filtrate was then dried at 100°C for 15 hours to obtain the pretreated raw material succinic acid D. The fumaric acid content was 100 ppm and the maleic acid content was 200 ppm.

[0057] Preparation of polyester:

[0058] Example 5

[0059] In a 5L polyester reactor, 10 mol of succinic acid A (200 ppm of fumaric acid and 200 ppm of maleic acid), 15 mol of butanediol, 3.67 g of tetrabutyl titanate, and 0.78 g of trimethyl phosphate were added. The reactor was kept at atmospheric pressure, and the mixture was stirred at a constant speed of 100 rpm. The temperature was raised to 150°C to initiate the reaction. The temperature was gradually increased to 250°C over 1 hour. Esterification was completed when the amount of water distilled from the reactor reached 95% of the theoretical yield. The reactor was then gradually evacuated to 20000 PaA for 30 minutes, then gradually evacuated to 90 PaA. The temperature was raised to 220°C and maintained for 200 minutes to induce polycondensation, yielding a polymer melt. This melt was then water-cooled and pelletized to obtain the final product.

[0060] Example 6

[0061] In a 5L polyester reactor, 10 mol of succinic acid B (100 ppm of fumaric acid and 100 ppm of maleic acid), 12 mol of butanediol, 1.83 g of tetrabutyl titanate, and 0.39 g of trimethyl phosphate were added. The reactor was kept at atmospheric pressure and stirred at a constant speed. The temperature was raised to 150°C to initiate the reaction. The temperature was gradually increased to 220°C over 1 hour. Esterification was completed when the amount of water distilled from the reactor reached 95% of the theoretical yield. The reactor was then gradually evacuated to 2000 PaA for 50 minutes, then gradually evacuated to 90 PaA. The temperature was raised to 240°C and maintained for 150 minutes to induce polycondensation, yielding a polymer melt. This melt was then water-cooled and pelletized to obtain the final product.

[0062] Example 7

[0063] In a 5L polyester reactor, 10 mol of succinic acid (200 ppm of fumaric acid and 100 ppm of maleic acid), 11 mol of butanediol, 0.61 g of tetrabutyl titanate, and 0.08 g of trimethyl phosphate were added. The reactor was kept at atmospheric pressure and stirred at a constant speed. The temperature was raised to 150°C to initiate the reaction. The temperature was gradually increased to 180°C over 1 hour. Esterification was completed when the amount of water distilled from the reactor reached 95% of the theoretical yield. The reactor was then gradually evacuated to 1000 PaA for 20 minutes, then gradually evacuated to 90 PaA. The temperature was raised to 260°C and maintained for 100 minutes to induce polycondensation, yielding a polymer melt. This melt was then water-cooled and pelletized to obtain the final product.

[0064] Example 8

[0065] In a 5L polyester reactor, 10 mol of succinic acid D (100 ppm of fumaric acid and 200 ppm of maleic acid), 13 mol of butanediol, 1.22 g of tetrabutyl titanate, and 0.23 g of trimethyl phosphate were added. The reactor was kept at atmospheric pressure and stirred at a constant speed. The temperature was raised to 150°C to initiate the reaction. The temperature was gradually increased to 200°C over 1 hour. Esterification was completed when the amount of water distilled from the reactor reached 95% of the theoretical yield. The reactor was then gradually evacuated to 5000 PaA for 30 minutes, then gradually evacuated to 90 PaA. The temperature was raised to 250°C and maintained for 120 minutes to induce polycondensation, yielding a polymer melt. This melt was then water-cooled and pelletized to obtain the final product.

[0066] Comparative Example 1

[0067] In a 5L polyester reactor, 10 mol of succinic acid (500 ppm of fumaric acid and 600 ppm of maleic acid), 12 mol of butanediol, 1.83 g of tetrabutyl titanate, and 0.39 g of trimethyl phosphate were added. The reactor was kept at atmospheric pressure and stirred at a constant speed. The temperature was raised to 150°C to initiate the reaction. The temperature was gradually increased to 220°C over 1 hour. Esterification was completed when the amount of water distilled from the reactor reached 95% of the theoretical yield. The reactor was then gradually evacuated to 2000 PaA for 30 minutes, then gradually evacuated to 90 PaA. The temperature was raised to 240°C and maintained for 150 minutes to induce polycondensation, yielding a polymer melt. This melt was then water-cooled and pelletized to obtain the final product.

[0068] Table 1 Performance of products synthesized from different raw materials

[0069] Group Yellowing resistance △b Total migration (mg / 50g) Example 5 2.4 35 Example 6 0.5 17 Example 7 1.1 24 Example 8 1.6 26 Comparative Example 1 5.3 139

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing yellowing-resistant polybutylene succinate for food contact materials, wherein succinic acid and 1,4-butanediol undergo an esterification polycondensation reaction in the presence of a catalyst to generate polybutylene succinate, characterized in that, The content of fumaric acid and maleic acid in the succinic acid raw material is ≤300ppm.

2. The preparation method according to claim 1, characterized in that, The method includes the following steps: S1: Esterification reaction. The catalyst, succinic acid and 1,4-butanediol are added to the reactor to carry out the esterification reaction, and the by-product water is removed to complete the esterification reaction. S2: Polycondensation reaction. The reactor is evacuated and then evacuated again. After the polycondensation reaction is completed, the reactor is restored to normal pressure to obtain polymer melt. After water cooling and pelletizing, polybutylene succinate polymer is obtained.

3. The preparation method according to claim 2, characterized in that, The catalyst described in S1 is a titanate ester and a phosphorus compound; And / or, the molar ratio of succinic acid and 1,4-butanediol in S1 is 1:1.1 to 1:1.5; And / or, the esterification reaction temperature described in S1 is 180–250°C; And / or, the reaction in S1 ends when the total esterification rate reaches 95%.

4. The preparation method according to claim 3, characterized in that, In S1, the titanate is Ti(OR)4, wherein R is an alkyl group with 1 to 10 carbon atoms; The titanate content, calculated as elemental Ti, is 50-300 ppm, based on the total mass of polyester. The phosphorus compound is an organic phosphorus compound and / or an inorganic phosphorus compound; The phosphorus compound content, calculated as elemental phosphorus (P), is 10–100 ppm, based on the total mass of polyester. And / or, the molar ratio of succinic acid and 1,4-butanediol in S1 is 1:1.1 to 1:1.

3.

5. The preparation method according to claim 4, characterized in that, In S1, the titanate ester is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, and tetramethyl titanate; The phosphorus compound is one or more of trimethyl phosphate, triethyl phosphate, and triphenyl phosphate.

6. The preparation method according to claim 2, characterized in that, S2 first evacuates to 1000-30000 PaA and holds for 10-60 minutes, then evacuates to a high vacuum below 100 PaA. And / or, the S2 polycondensation reaction temperature is 220–260°C, and the high-vacuum polycondensation time is 60–200 min.

7. The preparation method according to claim 2, characterized in that, The method for controlling fumaric acid and / or maleic acid in the raw material succinic acid is adsorption.

8. The preparation method according to claim 7, characterized in that, The adsorbent used in the adsorption method is selected from one or more of activated carbon, molecular sieves, and resins.

9. The preparation method according to claim 8, characterized in that, The adsorbent used in the adsorption method is activated carbon.

10. The preparation method according to claim 8, characterized in that, The adsorbent used in the adsorption method is acid-modified activated carbon.

11. A yellowing-resistant polybutylene succinate for use in food contact materials, prepared by the esterification polycondensation reaction method according to any one of claims 1-10, characterized in that, The succinic acid used in the esterification polycondensation reaction contains ≤300ppm fumaric acid and ≤300ppm maleic acid.