Aging-resistant polylactic acid material, preparation method thereof and tableware

Abstract

The present invention relates to the technical field of polymer materials, and in particular to an aging-resistant polylactic acid material, a preparation method thereof, and tableware. The aging-resistant polylactic acid material comprises a polylactic acid resin magnesium element; the mass proportion of the magnesium element in the aging-resistant polylactic acid material is 5ppm to 700ppm. After an accelerated aging test, the aging-resistant polylactic acid material of the present invention has a good viscosity retention rate and has good aging resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular to an aging-resistant polylactic acid material and a preparation method thereof and tableware. Background Art

[0002] Lactic acid is a colorless, transparent liquid produced from starchy corn using modern biotechnology. Lactic acid can then undergo a special polymerization process to generate a granular polymer material, namely polylactic acid (PLA) material.

[0003] PLA material has the best tensile strength, but at this stage, the large-scale promotion and application of PLA material as a general plastic is still subject to certain restrictions. This is mainly due to the poor aging resistance of PLA material. For example, in simulated accelerated aging tests, the viscosity drops too quickly, affecting its use. Summary of the invention

[0004] Based on this, the present invention provides an aging-resistant polylactic acid material and a preparation method thereof and tableware, which solve the problem that the aging resistance of PLA material is poor.

[0005] The first aspect of the present invention provides an aging-resistant polylactic acid material. The technical solution is as follows:

[0006] An aging-resistant polylactic acid material, comprising polylactic acid resin and magnesium element;

[0007] The mass proportion of the magnesium element in the aging-resistant polylactic acid material is 5ppm to 700ppm.

[0008] In some of the embodiments, the mass proportion of magnesium element in the aging-resistant polylactic acid material is 5ppm to 300ppm.

[0009] In some of the embodiments, the mass proportion of magnesium element in the aging-resistant polylactic acid material is 10ppm to 100ppm.

[0010] In some embodiments, the magnesium element is derived from one or more of magnesium salts, magnesium oxide, magnesium nitride and magnesium hydroxide.

[0011] In some embodiments, the magnesium salt is selected from one or more of magnesium sulfate, magnesium nitrate and magnesium halide.

[0012] In some embodiments, the weight average molecular weight of the polylactic acid resin is 100,000 to 250,000.

[0013] In some embodiments, the method for preparing the polylactic acid resin comprises the following steps:

[0014] mixing L-lactic acid and a first catalyst to carry out a polycondensation reaction to generate a lactide intermediate;

[0015] The lactide intermediate, an initiator and a second catalyst are mixed to carry out a ring-opening polymerization reaction to generate the polylactic acid resin.

[0016] In some embodiments, the first catalyst is stannous octoate.

[0017] In some embodiments, the second catalyst is stannous octoate.

[0018] In some embodiments, the initiator is ethylene glycol.

[0019] In some of the embodiments, the conditions of the polycondensation reaction include: reaction temperature of 80-140° C., reaction pressure of 3 KPa-8 KPa, and reaction time of 6 h-12 h.

[0020] In some embodiments, the ring-opening polymerization reaction includes at least two stages. The conditions of the first stage include: reaction temperature of 140-160°C, reaction pressure of 105000Pa-115000Pa, and reaction time of 3h-5h; the conditions of the second stage include: reaction temperature of 170-190°C, reaction pressure of 105000Pa-115000Pa, and reaction time of 2h-3h.

[0021] In some of the embodiments, the viscosity retention rate of the aging-resistant polylactic acid material is not less than 50% after being placed at a temperature of 60° C. and a humidity of 60% for 9 days.

[0022] The second aspect of the present invention provides a method for preparing an aging-resistant polylactic acid material. The technical scheme is as follows:

[0023] A method for preparing an aging-resistant polylactic acid material comprises the following steps:

[0024] Mixing polylactic acid resin and a magnesium-containing compound, and processing the obtained mixture into a shape to prepare an aging-resistant polylactic acid material;

[0025] The added amounts of the polylactic acid resin and the magnesium-containing compound satisfy the requirement that the mass proportion of the magnesium element in the aging-resistant polylactic acid material is 5ppm to 700ppm.

[0026] In some embodiments, the processing and molding method includes extrusion molding, injection molding, blown film molding, foaming molding or vacuum molding.

[0027] In some embodiments, the extrusion molding temperature is 140°C to 240°C.

[0028] A third aspect of the present invention provides tableware, which comprises the above-mentioned aging-resistant polylactic acid material or the aging-resistant polylactic acid material prepared by the above-mentioned preparation method.

[0029] Compared with the traditional solution, the present invention has the following beneficial effects:

[0030] The inventor of the present invention unexpectedly discovered in the research that adding magnesium to polylactic acid material is conducive to alleviating the viscosity drop of polylactic acid material in aging test, and the amount of magnesium is crucial to the presentation of the above effect. The reason may be that the addition of magnesium reduces the activity of the terminal carboxyl or terminal hydroxyl groups of polylactic acid resin, controls the polylactic acid resin to be difficult to hydrolyze, and then delays the viscosity drop of polylactic acid material. The aging-resistant polylactic acid material of the present invention has a higher viscosity retention rate (reaching more than 50%) after the simulated accelerated aging test, showing good aging resistance. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with specific embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0033] the term

[0034] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0035] In the present invention, "plurality", "multiple", "multiple times", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0036] In the present invention, “preferred”, “better”, “more preferred” and “suitable” are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute limitations on the scope of protection of the present invention.

[0037] In the present invention, the words “further”, “furthermore”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present invention.

[0038] In the present invention, "optionally", "optional" and "optional" refer to optional, that is, to any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0039] In the present invention, in the "first aspect", "second aspect", "third aspect", "fourth aspect", etc., the terms "first", "second", "third", "fourth", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0040] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0041] In the present invention, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all sub-ranges included therein.

[0042] The temperature parameters in the present invention, if not specifically limited, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the precision range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0043] In the present invention, when it comes to percentage content, unless otherwise specified, for solid-liquid mixing and solid-solid mixing, it refers to mass percentage, and for liquid-liquid mixing, it refers to volume percentage.

[0044] In the present invention, when it comes to percentage concentration, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of the component.

[0045] The inventors of the present invention unexpectedly discovered during research that adding magnesium-containing compounds to polylactic acid materials is beneficial to alleviating the viscosity drop of polylactic acid materials in aging tests, and the content of magnesium is crucial to the presentation of the above-mentioned effect.

[0046] In one embodiment of the present invention, an aging-resistant polylactic acid material is provided, comprising polylactic acid resin and magnesium element;

[0047] The mass proportion of the magnesium element in the aging-resistant polylactic acid material is 5ppm to 700ppm.

[0048] It can be understood that the mass proportion of the magnesium element in the aging-resistant polylactic acid material includes but is not limited to 5ppm, 10ppm, 40ppm, 25ppm, 50ppm, 60ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, and 700ppm.

[0049] In some preferred embodiments, the mass proportion of magnesium element in the aging-resistant polylactic acid material is 5ppm-300ppm.

[0050] In some further preferred embodiments, the mass proportion of magnesium element in the aging-resistant polylactic acid material is 10ppm-100ppm.

[0051] Adding magnesium to aging-resistant polylactic acid materials can alleviate the viscosity decrease of polylactic acid materials in aging tests. The reason for improving its aging resistance may be: the addition of magnesium reduces the activity of the terminal carboxyl or terminal hydroxyl groups of the polylactic acid resin, controls the polylactic acid resin from being easily hydrolyzed, and thus delays the viscosity decrease of the polylactic acid material.

[0052] Optionally, the magnesium element comes from one or more of magnesium salt, magnesium oxide, magnesium nitride and magnesium hydroxide.

[0053] The magnesium salt is selected from one or more of magnesium sulfate, magnesium nitrate and magnesium halide, such as magnesium sulfate, magnesium nitrate, magnesium chloride, magnesium bromide and the like.

[0054] The addition of magnesium element can not only improve the aging resistance of polylactic acid material, but also help to improve the tensile strength of polylactic acid material.

[0055] In this embodiment, the weight average molecular weight of the polylactic acid resin is 100,000-200,000.

[0056] Optionally, the preparation method of polylactic acid resin comprises the following steps:

[0057] mixing L-lactic acid and a first catalyst to carry out a polycondensation reaction to generate a lactide intermediate;

[0058] The lactide intermediate, an initiator and a second catalyst are mixed to carry out a ring-opening polymerization reaction to generate the polylactic acid resin.

[0059] Optionally, the first catalyst is stannous octoate.

[0060] Optionally, the second catalyst is stannous octoate.

[0061] Optionally, the initiator is ethylene glycol.

[0062] Optionally, the conditions of the polycondensation reaction include: reaction temperature of 80 to 140° C., reaction pressure of 3 KPa to 8 KPa, and reaction time of 6 h to 12 h.

[0063] It can be understood that after the polycondensation reaction, the oligomers generated by the polycondensation reaction are distilled under reduced pressure to obtain a lactide intermediate.

[0064] Optionally, the conditions for the reduced pressure distillation include: a temperature of 170 to 210° C. and a pressure of 102 Pa to 103 Pa. The reduced pressure distillation is performed until no product is distilled out, and the time may be 7 h to 15 h.

[0065] Optionally, the ring-opening polymerization reaction includes at least two stages, and the conditions of the first stage include: reaction temperature of 140-160°C, reaction pressure of 105000Pa-115000Pa, and reaction time of 3h-5h; the conditions of the second stage include: reaction temperature of 170-190°C, reaction pressure of 105000Pa-115000Pa, and reaction time of 2h-3h.

[0066] It can be understood that the ring-opening polymerization reaction is performed, and the polymer generated by the ring-opening polymerization reaction is dissolved in a chloroform aqueous solution and then precipitated with ethanol to obtain a polylactic acid resin.

[0067] In this embodiment, after the aging-resistant polylactic acid material is placed at a temperature of 60° C. and a humidity of 60% for 9 days, the viscosity retention rate is not less than 50%.

[0068] The present invention also provides a method for preparing an aging-resistant polylactic acid material. In one embodiment, the method for preparing an aging-resistant polylactic acid material comprises the following steps:

[0069] Mixing polylactic acid resin and a magnesium-containing compound, and processing the obtained mixture into a shape to prepare an aging-resistant polylactic acid material;

[0070] The added amounts of the polylactic acid resin and the magnesium-containing compound satisfy the requirement that the mass proportion of the magnesium element in the aging-resistant polylactic acid material is 5ppm to 700ppm.

[0071] It can be understood that the polylactic acid resin in the preparation method of the above-mentioned aging-resistant polylactic acid material is the same as the polylactic acid resin in the aging-resistant polylactic acid material, and will not be described in detail here.

[0072] Those skilled in the art know that when a small amount of magnesium-containing compound is added to a large amount of polylactic acid resin, the two can be mixed evenly by pre-mixing for multiple times.

[0073] It is understandable that the magnesium-containing compound is selected from one or more of magnesium salt, magnesium oxide, magnesium nitride and magnesium hydroxide. The magnesium salt is as described above and will not be described in detail here.

[0074] Optionally, the processing and molding methods include extrusion molding, injection molding, film blowing molding, foaming molding or vacuum molding.

[0075] In this embodiment, the processing and molding method is extrusion molding, and the extrusion molding temperature is 140°C to 240°C.

[0076] In one embodiment of the present invention, tableware is provided, which comprises the above-mentioned aging-resistant polylactic acid material or the aging-resistant polylactic acid material prepared by the above-mentioned preparation method. The tableware includes but is not limited to disposable bowls, disposable cups, disposable plates, etc.

[0077] The following is further described in conjunction with specific examples and comparative examples. The raw materials involved in the following specific examples, unless otherwise specified, can all be sourced from commercial sources. The instruments used, unless otherwise specified, can all be sourced from commercial sources. The processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0078] Example 1

[0079] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0080] Step 1: Preparation of polylactic acid resin

[0081] (1) Add L-lactic acid and a first catalyst (stannous octoate) accounting for 0.04 wt% of the L-lactic acid into a reaction vessel, stir evenly, and carry out polycondensation reaction at a temperature of 100° C. and a pressure of 5 KPa. After 9 hours, distill off water to obtain an oligomer. The obtained oligomer is distilled under reduced pressure at a temperature of 190° C. and a pressure of 102 Pa until no product is distilled out. The time is 11 hours to obtain a lactide intermediate.

[0082] (2) The lactide intermediate obtained in the above step is dissolved in an initiator (hexanediol) accounting for 0.24 wt% of the lactide intermediate, and a second catalyst (stannous octoate) accounting for 0.04 wt% of the lactide intermediate is added to carry out a ring-opening polymerization reaction, specifically: first react at a temperature of 150° C. and a relative pressure of 110,000 Pa for 4 hours, and then react at a temperature of 180° C. and a relative pressure of 110,000 Pa for 2.5 hours to obtain a polymer, and the obtained polymer solid is refluxed and dissolved with a 5% (W / W) chloroform aqueous solution, and after filtering the solution, ethanol 5 times the volume of chloroform is used for precipitation to obtain a white flocculent precipitate to obtain a polylactic acid resin. The weight average molecular weight of the obtained polylactic acid resin is 200,000.

[0083] Step 2: Preparation of aging-resistant polylactic acid material

[0084] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 was uniformly mixed with 0.34 g of magnesium oxide, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0085] The aging resistance performance of the aging-resistant polylactic acid material prepared in step 2 was evaluated. The evaluation method is as follows. The evaluation results are shown in Table 1.

[0086] Before and after the simulated accelerated aging test, the intrinsic viscosity of the aging-resistant polylactic acid material was measured. According to the public: viscosity retention rate = (η 前 -η 后 ) / η 前 × 100%, calculate the viscosity retention rate.

[0087] Among them, the test method for the characteristic viscosity η of the aging-resistant polylactic acid material is as follows: at 23°C, accurately weigh 0.1250±0.0005g of the sample and dissolve it in 25mL (o-dichlorobenzene: phenol = 2:3 mass ratio) solution, heat and stir at 110°C until the aging-resistant polylactic acid material is completely dissolved, measure with a viscometer at room temperature of 23°C, and retain two decimal places for the viscosity value.

[0088] The conditions of the simulated accelerated aging test are as follows: temperature of 60°C, humidity of 60%, and placement for 9 days.

[0089] Example 2

[0090] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0091] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 5.8 g of magnesium bromide, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0092] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0093] Example 3

[0094] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 8.5 g of magnesium hydroxide, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0095] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0096] Example 4

[0097] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 10 g of magnesium sulfate, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0098] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0099] Example 5

[0100] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0101] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 21.8 g of magnesium chloride, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0102] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0103] Example 6

[0104] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0105] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 30 g of magnesium nitrate, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0106] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0107] Example 7

[0108] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0109] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 36.3 g of magnesium chloride, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0110] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0111] Example 8

[0112] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0113] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 108.9 g of magnesium chloride, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0114] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0115] Example 9

[0116] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0117] Referring to Table 1, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 254.1 g of magnesium chloride, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0118] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0119] Example 10

[0120] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0121] Step 1: Preparation of polylactic acid resin

[0122] (1) Add L-lactic acid and a first catalyst (stannous octoate) accounting for 0.04 wt% of the L-lactic acid into a reaction vessel, stir evenly, and carry out polycondensation reaction at a temperature of 100° C. and a pressure of 5 KPa. After 9 hours, distill off water to obtain an oligomer. The obtained oligomer is distilled under reduced pressure at a temperature of 190° C. and a pressure of 102 Pa until no product is distilled out. The time is 11 hours to obtain a lactide intermediate.

[0123] (2) The lactide intermediate obtained in the above step is dissolved in an initiator (hexanediol) accounting for 0.3 wt% of the lactide intermediate, and a second catalyst (stannous octoate) accounting for 0.04 wt% of the lactide intermediate is added to carry out a ring-opening polymerization reaction, specifically: first react at a temperature of 150° C. and a relative pressure of 110,000 Pa for 4 hours, and then react at a temperature of 180° C. and a relative pressure of 110,000 Pa for 2.5 hours to obtain a polymer, and the obtained polymer solid is refluxed and dissolved with a 5% (W / W) chloroform aqueous solution, and after filtering the solution, ethanol 5 times the volume of chloroform is used for precipitation to obtain a white flocculent precipitate to obtain a polylactic acid resin. The weight average molecular weight of the obtained polylactic acid resin is 100,000.

[0124] Step 2: Preparation of aging-resistant polylactic acid material

[0125] Referring to Table 2, 100 kg of the polylactic acid resin prepared in step 1 was uniformly mixed with 0.34 g of magnesium oxide, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0126] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0127] Embodiment 11

[0128] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0129] Step 1: Preparation of polylactic acid resin

[0130] (1) Add L-lactic acid and a first catalyst (stannous octoate) accounting for 0.04 wt% of the L-lactic acid into a reaction vessel, stir evenly, and carry out polycondensation reaction at a temperature of 100° C. and a pressure of 5 KPa. After 9 hours, distill off water to obtain an oligomer. The obtained oligomer is distilled under reduced pressure at a temperature of 190° C. and a pressure of 102 Pa until no product is distilled out. The time is 11 hours to obtain a lactide intermediate.

[0131] (2) The lactide intermediate obtained in the above step is dissolved in an initiator (hexanediol) accounting for 0.4 wt% of the lactide intermediate, and a second catalyst (stannous octoate) accounting for 0.04 wt% of the lactide intermediate is added to carry out a ring-opening polymerization reaction, specifically: first react at a temperature of 150° C. and a relative pressure of 110,000 Pa for 4 hours, and then react at a temperature of 180° C. and a relative pressure of 110,000 Pa for 2.5 hours to obtain a polymer, and the obtained polymer solid is refluxed and dissolved with a 5% (W / W) chloroform aqueous solution, and after the solution is filtered, ethanol 5 times the volume of chloroform is used for precipitation to obtain a white flocculent precipitate to obtain a polylactic acid resin. The weight average molecular weight of the obtained polylactic acid resin is 80,000.

[0132] Step 2: Preparation of aging-resistant polylactic acid material

[0133] Referring to Table 2, 100 kg of the polylactic acid resin prepared in step 1 was uniformly mixed with 0.34 g of magnesium oxide, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0134] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0135] Example 12

[0136] This embodiment provides an aging-resistant polylactic acid material and a preparation method thereof, and the steps are as follows:

[0137] Step 1: Preparation of polylactic acid resin

[0138] (1) Add L-lactic acid and a first catalyst (stannous octoate) accounting for 0.04 wt% of the L-lactic acid into a reaction vessel, stir evenly, and carry out polycondensation reaction at a temperature of 100° C. and a pressure of 5 KPa. After 9 hours, distill off water to obtain an oligomer. The obtained oligomer is distilled under reduced pressure at a temperature of 190° C. and a pressure of 102 Pa until no product is distilled out. The time is 11 hours to obtain a lactide intermediate.

[0139] (2) The lactide intermediate obtained in the above step is dissolved in an initiator (hexanediol) accounting for 0.2 wt% of the lactide intermediate, and a second catalyst (stannous octoate) accounting for 0.04 wt% of the lactide intermediate is added to carry out a ring-opening polymerization reaction, specifically: first react at a temperature of 150° C. and a relative pressure of 110,000 Pa for 4 hours, and then react at a temperature of 180° C. and a relative pressure of 110,000 Pa for 2.5 hours to obtain a polymer, and the obtained polymer solid is refluxed and dissolved with a 5% (W / W) chloroform aqueous solution, and after filtering the solution, ethanol 5 times the volume of chloroform is used for precipitation to obtain a white flocculent precipitate to obtain a polylactic acid resin. The weight average molecular weight of the obtained polylactic acid resin is 300,000.

[0140] Step 2: Preparation of aging-resistant polylactic acid material

[0141] Referring to Table 2, 100 kg of the polylactic acid resin prepared in step 1 was uniformly mixed with 0.34 g of magnesium oxide, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain an aging-resistant polylactic acid material.

[0142] The aging resistance performance of the prepared aging-resistant polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0143] Table 1

[0144]

[0145] Table 2

[0146]

[0147] Among them, the test of the mass proportion of Mg element is tested by microwave digestion-ICP-OES method, and the unit of measurement result is ppm, where 1ppm=0.001‰. Specifically: weigh 0.1g of crushed aging-resistant polylactic acid material as a sample, put it into a microwave digestion tank, add 5mL of nitric acid to completely immerse the sample, and then slowly drip 1.0mL of hydrogen peroxide. After reacting for 2 minutes, cover the lid, seal the digestion tank, put it into a microwave digestion furnace for digestion, cool to room temperature, filter the solution in the digestion tank with a 0.45μm filter membrane, transfer it to a volumetric flask, dilute it to 50mL with distilled water, and use ICP-OES test.

[0148] As can be seen from Table 1 and Table 2, in Example 1-Example 12, magnesium is added to the aging-resistant polylactic acid material by adding magnesium-containing compounds. After testing, when the amount of Mg added is 5ppm to 700ppm, the aging-resistant polylactic acid material has a higher viscosity retention rate (all reaching more than 50%) after the simulated accelerated aging test, showing good aging resistance. And with the change of the mass of the magnesium element, the viscosity retention rate of the aging-resistant polylactic acid material also changes. With the change of the weight-average molecular weight of the polylactic acid resin, the viscosity retention rate of the aging-resistant polylactic acid material also changes. Among them, after testing, when the amount of Mg added is 10ppm to 100ppm, the aging-resistant polylactic acid material has a viscosity retention rate of more than 65% after the simulated accelerated aging test, and the effect is good. The weight-average molecular weight of the polylactic acid resin is 100000 to 200000, and the aging-resistant polylactic acid material has a viscosity retention rate of more than 60% after the simulated accelerated aging test, and the effect is good.

[0149] Comparative Example 1

[0150] This comparative example provides a polylactic acid material and a preparation method thereof, the steps are as follows:

[0151] Referring to Table 3, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was put into a single screw extruder, extruded and granulated at 190° C. to obtain a polylactic acid material.

[0152] The aging resistance of the prepared polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0153] Comparative Example 2

[0154] This comparative example provides a polylactic acid material and a preparation method thereof, the steps are as follows:

[0155] Referring to Table 3, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 658 g of magnesium bromide, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain a polylactic acid material.

[0156] The aging resistance of the prepared polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0157] Comparative Example 3

[0158] This comparative example provides a polylactic acid material and a preparation method thereof, the steps are as follows:

[0159] Referring to Table 3, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 1.56 g of zinc sulfate, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain a polylactic acid material.

[0160] The aging resistance of the prepared polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0161] Comparative Example 4

[0162] This comparative example provides a polylactic acid material and a preparation method thereof, the steps are as follows:

[0163] Referring to Table 3, 100 kg of the polylactic acid resin prepared in step 1 of Example 1 was uniformly mixed with 8.5 g of cupric chloride, and the resulting mixture was put into a single-screw extruder, extruded and granulated at 190° C. to obtain a polylactic acid material.

[0164] The aging resistance of the prepared polylactic acid material was evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0165] Table 3

[0166]

[0167] Among them, the test of the mass proportion of metal elements is tested by microwave digestion-ICP-OES method, and the unit of measurement result is ppm, where 1ppm=0.001‰. Specifically: weigh 0.1g of crushed polylactic acid material or aging-resistant polylactic acid material as a sample, put it into a microwave digestion tank, add 5mL of nitric acid to completely immerse the sample, and then slowly drip 1.0mL of hydrogen peroxide. After reacting for 2 minutes, cover the lid, seal the digestion tank, and put it into a microwave digestion furnace for digestion. After cooling to room temperature, filter the solution in the digestion tank with a 0.45μm filter membrane and transfer it to a volumetric flask, dilute it to 50mL with distilled water, and use ICP-OES for testing.

[0168] As shown in Table 3, in Comparative Example 1, no magnesium-containing compound was added, and the polylactic acid material directly prepared from polylactic acid resin as raw material had a low viscosity retention rate (47%) after the simulated accelerated aging test, and had poor aging resistance.

[0169] In Comparative Example 2, although a magnesium-containing compound is added, when the amount of the magnesium-containing compound added is large (800 ppm), the viscosity retention rate decreases (the viscosity retention rate is 45%). Combined with Examples 1 to 12, the mass proportion of the magnesium element is controlled within a certain range (5 ppm to 700 ppm), and the viscosity retention rate of the polylactic acid material can be maintained at 50% to 70%, which can have an unexpected effect on improving the aging resistance of the aging-resistant polylactic acid material.

[0170] In Comparative Example 3, the aging resistance of the aging-resistant polylactic acid material prepared by adding the zinc-containing compound was not significantly improved, and even the viscosity retention rate decreased (the viscosity retention rate was 48%).

[0171] In Comparative Example 4, the aging-resistant polylactic acid material prepared by adding a copper-containing compound showed a significant decrease in viscosity retention, and the aging resistance performance decreased instead of increased (viscosity retention was 35%).

[0172] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0173] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An aging-resistant polylactic acid material, characterized in that: including polylactic acid resin and magnesium element; The mass proportion of magnesium in the aging-resistant polylactic acid material is 5ppm to 700ppm, and the test method for the mass proportion of Mg is as follows: weigh 0.1g of the crushed aging-resistant polylactic acid material as a sample, put it into a microwave digestion tank, add 5mL of nitric acid to completely immerse the sample, and then slowly drip 1.0mL of hydrogen peroxide. After reacting for 2 minutes, cover the lid, seal the digestion tank, put it into a microwave digestion furnace for digestion, cool to room temperature, filter the solution in the digestion tank with a 0.45μm filter membrane, transfer it to a volumetric flask, dilute it to 50mL with distilled water, and use ICP-OES for testing; The magnesium element is derived from one or more of magnesium salt, magnesium oxide, magnesium nitride and magnesium hydroxide, and the magnesium salt is selected from one or more of magnesium sulfate, magnesium nitrate and magnesium halide.

2. The aging-resistant polylactic acid material according to claim 1, characterized in that: The mass proportion of the magnesium element in the aging-resistant polylactic acid material is 5ppm to 300ppm.

3. The aging-resistant polylactic acid material according to claim 2, characterized in that: The mass proportion of the magnesium element in the aging-resistant polylactic acid material is 10ppm to 100ppm.

4. The aging-resistant polylactic acid material according to claim 3, characterized in that: The mass proportion of magnesium element in the aging-resistant polylactic acid material is 25ppm to 50ppm.

5. The aging-resistant polylactic acid material according to claim 4, characterized in that: The mass proportion of magnesium element in the aging-resistant polylactic acid material is 40 ppm.

6. The aging-resistant polylactic acid material according to any one of claims 1 to 5, characterized in that: The weight average molecular weight of the polylactic acid resin is 100,000 to 200,000.

7. The aging-resistant polylactic acid material according to claim 6, characterized in that: The preparation method of the polylactic acid resin comprises the following steps: mixing L-lactic acid and a first catalyst to carry out a polycondensation reaction to generate a lactide intermediate; The lactide intermediate, an initiator and a second catalyst are mixed to carry out a ring-opening polymerization reaction to generate the polylactic acid resin.

8. The aging-resistant polylactic acid material according to claim 7, characterized in that: The preparation method of the polylactic acid resin includes one or more of the following conditions: a) the first catalyst is stannous octoate; b) the second catalyst is stannous octoate; c) the initiator is ethylene glycol; d) The conditions of the polycondensation reaction include: reaction temperature of 80 to 140° C., reaction pressure of 3 KPa to 8 KPa, and reaction time of 6 h to 12 h; e) The ring-opening polymerization reaction includes at least two stages. The conditions of the first stage include: reaction temperature of 140-160° C., reaction pressure of 105000Pa-115000Pa, and reaction time of 3h-5h; the conditions of the second stage include: reaction temperature of 170-190° C., reaction pressure of 105000Pa-115000Pa, and reaction time of 2h-3h.

9. The aging-resistant polylactic acid material according to any one of claims 1-5, 7-8, characterized in that: The aging-resistant polylactic acid material meets the following characteristics: After being placed at a temperature of 60°C and a humidity of 60% for 9 days, the viscosity retention rate is not less than 50%.

10. A method for preparing the aging-resistant polylactic acid material according to any one of claims 1 to 9, characterized in that: The following steps are involved: Mixing polylactic acid resin and a magnesium-containing compound, and processing the obtained mixture into a shape to prepare an aging-resistant polylactic acid material; The added amounts of the polylactic acid resin and the magnesium-containing compound satisfy the requirement that the mass proportion of the magnesium element in the aging-resistant polylactic acid material is 5ppm to 700ppm.

11. A tableware, characterized in that: The invention comprises the aging-resistant polylactic acid material according to any one of claims 1 to 9 or the aging-resistant polylactic acid material prepared by the preparation method according to claim 10.

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