A composition of lactide, a hydrolysis-resistant polylactic acid prepared therefrom and a method of preparing the hydrolysis-resistant polylactic acid

Abstract

This invention relates to a lactide composition comprising: lactide and an anti-hydrolysis aid, wherein the anti-hydrolysis aid comprises a molecular sieve and / or an inorganic filler, the molecular sieve having a pore size of 0.1 to 1 nm and the inorganic filler having a particle size of 800 to 3000 mesh; wherein, based on the weight of lactide: the amount of the molecular sieve is 0.01 to 5% by weight; and / or the amount of the inorganic filler is 0.01 to 5% by weight.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a lactide composition, polylactic acid prepared therefrom, and a method for preparing the polylactic acid. Background Technology

[0002] Among numerous biodegradable materials, polylactic acid (PLA) is currently the most widely used and has the highest degree of industrialization. PLA's raw materials come from renewable green plants, and whether composted or landfilled, it can degrade into environmentally harmless CO2 and H2O in a short period, thus not causing negative environmental impacts. However, PLA is prone to hydrolysis in humid environments. Its molecular structure contains a large number of ester bonds (-COO-), and polar water molecules can form hydrogen bonds with the carbonyl oxygen and alkyl oxygen in the ester bonds, thereby attacking the ester bonds and breaking the molecular chain. Furthermore, the terminal carboxyl groups produced by the hydrolysis reaction can further catalyze the degradation of the polymer, forming an autocatalytic reaction that accelerates the hydrolysis of PLA. This leads to a decline in the mechanical properties and insufficient dimensional stability of PLA products, severely affecting their performance and service life.

[0003] Polylactic acid (PLA) is highly sensitive to water. Once hydrolysis begins, the degradation reaction proceeds rapidly, leading to a sharp decline in polymer properties. Macroscopically, this manifests as a significant reduction in the smoothness, strength, elasticity, and hardness of the finished product. Currently, the degradation rate of PLA is controlled primarily through end-capping during synthesis, adding anti-hydrolysis agents, and blending with hydrophobic materials. Among these methods, adding anti-hydrolysis agents is relatively convenient and widely used. Anti-hydrolysis agents can react with the terminal carboxyl groups of PLA, thereby interrupting the autocatalytic hydrolysis chain reaction. For example, Chinese patent application CN118792754A discloses a high-temperature hydrolysis-resistant PLA fiber prepared by adding the anti-hydrolysis agent polycarbodiimide.

[0004] Industrially, polylactic acid (PLA) is typically prepared from lactide via ring-opening polymerization. Compared to directly polymerizing PLA monomers, this method facilitates the polymerization of high molecular weight PLA. However, conventional hydrolysis resistant agents, such as polycarbodiimide and isocyanates, may react uncontrollably with impurities or polymer end groups in the ring-opening polymerization process, leading to fluctuations in product molecular weight. They may also compete with the catalyst for coordination, inhibiting its activation ability of cyclic esters and reducing the ring-opening rate. Furthermore, conventional hydrolysis resistant agents improve hydrolysis resistance by reacting with the terminal carboxyl groups of PLA, and are thus consumable additives. The effectiveness of these consumable additives in improving the hydrolysis resistance of PLA diminishes with prolonged aging.

[0005] Therefore, there is a need for an additive that is more compatible with ring-opening polymerization reactions and has a more lasting and stable effect in improving hydrolysis resistance. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, the present invention provides a lactide composition, polylactic acid prepared therefrom, and a method for preparing polylactic acid. This polylactic acid exhibits good and stable hydrolysis resistance.

[0007] On one hand, the present invention provides a lactide composition comprising: lactide and an anti-hydrolysis aid, wherein the anti-hydrolysis aid comprises a molecular sieve and / or an inorganic filler, the molecular sieve having a pore size of 0.1 to 1 nm and the inorganic filler having a particle size of 800 to 3000 mesh; wherein, based on the weight of lactide: the content of the molecular sieve is 0.01 to 5% by weight; and the content of the inorganic filler is 0.01 to 5% by weight.

[0008] On the one hand, the lactide composition of the present invention comprises lactide, molecular sieve and inorganic filler.

[0009] On the other hand, the present invention provides a polylactic acid prepared from the lactide composition of the present invention.

[0010] In another aspect, the present invention provides a method for preparing polylactic acid, comprising: providing the lactide composition of the present invention; heating; and stirring. Attached Figure Description

[0011] Figure 1 The experimental process of the polymerization reaction in Example 1 of this application is shown.

[0012] Figure 2 This is an isothermal crystallography of Example 1 of this application, where the black line represents the comparative example and the red line represents the example.

[0013] Figure 3 This is an isothermal crystallography of Example 2 of this application, where the black line represents the comparative example and the red line represents the example.

[0014] Figure 4 This is an isothermal crystallography of Example 3 of this application, where the black line represents the comparative example and the red line represents the example. Detailed Implementation

[0015] General definitions and terms

[0016] Unless otherwise stated, all publications, patent applications, patents and other references mentioned herein are incorporated herein in their entirety by way of citation.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of any conflict, the definitions provided herein shall prevail.

[0018] Unless otherwise stated, all percentages, parts, proportions, etc. are by weight.

[0019] When a quantity, concentration, or other value or parameter is given as a range, preferred range, or preferred upper and lower limits, or a specific value, it should be understood as specifically disclosing all ranges formed by pairs of values ​​from any upper or preferred range and any lower or preferred range, regardless of whether the range is disclosed individually. Unless otherwise stated, when a numerical range is referred to herein, the range means including its endpoints and all integers and fractions within that range. The scope of this invention is not limited to the specific numerical value referenced when defining a range. For example, "2-8" or "2 to 8" encompasses 2, 3, 4, 5, 6, 7, 8, and any subrange consisting of any two of these values, such as 2-6, 3-5.

[0020] When used with a numerical variable, the terms "about" or "approximately" usually mean that the value of the variable and all values ​​of the variable are within the experimental error (e.g., within a 95% confidence interval for the mean) or within ±10% of the specified value, or a wider range.

[0021] The terms “comprising,” “including,” “having,” “containing,” or “involving,” and their other variations herein, are inclusive or open-ended and do not exclude other unlisted elements or method steps. Those skilled in the art will understand that the foregoing terms such as “comprising” encompass the meaning of “consisting of.” The expression “consisting of” excludes any unspecified elements, steps, or ingredients. The expression “substantially constitutes” limits the scope to the specified elements, steps, or ingredients, plus optional elements, steps, or ingredients that do not materially affect the essential and novel features of the claimed subject matter. It should be understood that the expression “comprising” encompasses both the expressions “substantially constitutes” and “consisting of.”

[0022] The term “selected from…” means one or more elements from the groups listed below, selected independently, and may include combinations of two or more elements.

[0023] When describing numerical or range endpoints in this document, it should be understood that the disclosure includes the specific values ​​or endpoints referenced.

[0024] As used herein, the terms “one or more” or “at least one” refer to one, two, three, four, five, six, seven, eight, nine or more.

[0025] Furthermore, if the number of components or parts of the present invention is not previously specified, it indicates that there is no limitation on the number of times a component or part may appear (or be present). Therefore, it should be interpreted as including one or at least one, and the singular form of a component or part also includes the plural, unless the value clearly indicates a singular number.

[0026] As used herein, the terms “optional” or “optionally” mean that the event or situation subsequently described may or may not occur, including both the occurrence and non-occurrence of the event or situation.

[0027] When methods, components, or steps are described, the use of letters or numbers for identification purposes is for distinguishing purposes only and does not imply that these methods, components, or steps must be performed in the order or sequence indicated. Those skilled in the art can make reasonable adjustments.

[0028] When the lower and upper limits of a numerical range are disclosed, any numerical value falling within that range and any included range are specifically disclosed. In particular, each range of values ​​disclosed herein (in the form of “about a to b”, or equivalently, “approximately a to b”, or equivalently, “about ab”) should be understood to represent each numerical value and range encompassed within a wider range.

[0029] lactide composition

[0030] Lactide, with the chemical formula C6H8O4, exhibits a six-membered ring diester structure. Under specific conditions, the two ester bonds in its molecule can undergo a ring-opening reaction. Lactide is commonly used as a raw material for the industrial synthesis of polylactic acid (PLA). Compared to directly synthesizing PLA from lactic acid monomers, using lactide to synthesize PLA achieves a higher degree of polymerization. Direct polymerization of lactic acid to prepare PLA is a reversible reaction. However, as the molecular chain grows, the viscosity of the reaction system increases dramatically, and water, as a byproduct, is difficult to remove. Therefore, the reaction often remains at a low molecular weight stage, such as tens of thousands of Daltons. PLA materials obtained in this way are brittle and difficult to use as engineering plastics. Under appropriate conditions, however, the ring-opening polymerization of lactide is an irreversible process. By opening the highly reactive ring structure, PLA with a weight-average molecular weight exceeding 100,000 Daltons can be easily synthesized. PLA materials obtained in this way possess excellent mechanical strength and processing properties, meeting the requirements of various industrial applications.

[0031] However, the structure of polylactic acid (PLA) makes it prone to hydrolysis. Even when high molecular weight PLA is prepared, hydrolysis in a humid environment leads to a rapid decrease in molecular weight, ultimately resulting in the loss of its original mechanical properties. Adding a certain amount of anti-hydrolysis additives to the raw materials used in PLA preparation can improve the hydrolysis resistance of the finished product.

[0032] Therefore, in one aspect, the present invention relates to a lactide composition comprising lactide and an anti-hydrolysis agent.

[0033] Different anti-hydrolysis additives improve the hydrolysis resistance of finished polylactic acid (PLA) through different mechanisms. One type of anti-hydrolysis additive or two or more can be added. A synergistic effect can be achieved between multiple appropriately selected anti-hydrolysis additives, further enhancing the hydrolysis resistance of the resulting PLA.

[0034] In one embodiment, the anti-hydrolysis aid of the present invention comprises a molecular sieve.

[0035] In one embodiment, the anti-hydrolysis additive of the present invention comprises an inorganic filler.

[0036] In one embodiment, the anti-hydrolysis additive of the present invention comprises a molecular sieve and an inorganic filler.

[0037] The dosage of anti-hydrolysis additives is crucial for improving the hydrolysis resistance of polylactic acid (PLA). Insufficient dosage may not achieve the desired improvement in PLA's hydrolysis resistance. Excessive dosage may negatively impact the physical and mechanical properties of the finished PLA, adversely affecting its subsequent processing into finished products and its applications.

[0038] In one embodiment, based on the weight of lactide, the content of the molecular sieve of the present invention is 0.01 to 5% by weight, preferably 0.02 to 3% by weight, for example, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2 3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, 3, 3.05, 3.1, 3.15, 3.2, 3.25, 3.3, 3.35, 3.4, 3.45, 3.5, 3.55, 3.6, 3.65, 3.7, 3.7 5, 3.8, 3.85, 3.9, 3.95, 4, 4.05, 4.1, 4.15, 4.2, 4.25, 4.3, 4.35, 4.4, 4.45, 4.5, 4.55, 4.6, 4.65, 4.7, 4.75, 4.8, 4.85, 4.9, 4.95, 5% by weight, and a range consisting of any two of these values.

[0039] In one embodiment, based on the weight of lactide, the content of the inorganic filler of the present invention is 0.01 to 5% by weight, preferably 0.02 to 3% by weight, for example, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2 3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, 3, 3.05, 3.1, 3.15, 3.2, 3.25, 3.3, 3.35, 3.4, 3.45, 3.5, 3.55, 3.6, 3.65, 3.7, 3.7 5, 3.8, 3.85, 3.9, 3.95, 4, 4.05, 4.1, 4.15, 4.2, 4.25, 4.3, 4.35, 4.4, 4.45, 4.5, 4.55, 4.6, 4.65, 4.7, 4.75, 4.8, 4.85, 4.9, 4.95, 5% by weight, and a range consisting of any two of these values.

[0040] In one embodiment, the weight ratio of the molecular sieve to the inorganic filler of the present invention is from 1:0.1 to 1:10, preferably from 1:0.2 to 1:8, for example, 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5, 1:9, 1:9.5, 1:10, and a range consisting of any two of these values.

[0041] Molecular sieve

[0042] Molecular sieves are inorganic non-metallic materials with a regular, uniform microporous structure. Because the pore size of a molecular sieve is fixed, only molecules with diameters smaller than the pore size can enter and be adsorbed, while larger molecules are blocked, thus enabling precise separation of different molecules. Furthermore, the microporous structure of molecular sieves results in a very large specific surface area, providing ample space for adsorption. They can neutralize some acidic groups, such as the terminal carboxyl groups in polylactic acid (PLA) molecules, through physical adsorption, ion exchange, or coordination, thereby interrupting the autocatalytic cycle and delaying the hydrolysis of PLA molecules.

[0043] A common type of molecular sieve is the aluminosilicate molecular sieve, whose framework consists of silicon-oxygen tetrahedra (SiO4) and aluminum-oxygen tetrahedra (AlO4) linked by shared oxygen atoms. The negative charge carried by the aluminum-oxygen tetrahedra is transmitted through metal cations, such as Na+. + K + When the molecular sieve reaches equilibrium, it forms strongly polar adsorption sites, which can adsorb polar groups, such as ester bonds in polylactic acid, through electrostatic interactions or hydrogen bonding. After the molecular sieve adsorbs ester bonds, it hinders the attack of water molecules, thereby improving the hydrolysis resistance of polylactic acid.

[0044] Therefore, in one embodiment, the molecular sieve of the present invention is an aluminosilicate molecular sieve.

[0045] The connection method of the three-dimensional structure inside a molecular sieve is a crucial factor determining its pore size. The basic structural units of aluminosilicate molecular sieves are silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. These tetrahedra are connected by oxygen atoms sharing vertices, forming a three-dimensional network framework. The pore size of aluminosilicate molecular sieves primarily depends on how the basic structural units are connected in rings. If the basic structural units are connected in eight-membered rings, a pore size of approximately 0.4 to 0.5 nm will be formed, such as in type A molecular sieves; if the basic structural units are connected in ten-membered rings, a pore size of approximately 0.5 to 0.6 nm will be formed, such as in ZSM-5 molecular sieves; and if the basic structural units are connected in twelve-membered rings, a pore size of approximately 0.7 to 0.9 nm will be formed, such as in type Y molecular sieves.

[0046] Furthermore, since different metal cations have different radii, the types of metal cations outside the three-dimensional framework of the molecular sieve also affect the pore size of the molecular sieve. For example, Na... + Na in 4A molecular sieve + Change to K + This allows for the acquisition of K with a smaller aperture. + 3A molecular sieve.

[0047] The pore size of molecular sieves has a certain impact on their effect on improving the hydrolysis resistance of polylactic acid. Molecular sieves with appropriate pore sizes need to be used to ensure that they improve the hydrolysis resistance of the finished polylactic acid.

[0048] In one embodiment, the molecular sieve of the present invention has a pore size of 0.1 to 1 nm, preferably 0.3 to 0.7 nm, for example 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 nm, and a range consisting of any two of these values.

[0049] In one embodiment, the molecular sieve of the present invention comprises one or more elements selected from Na, Ca, and K.

[0050] Based on the requirement for different pore sizes, the molecular sieve of the present invention can be a commercially available molecular sieve.

[0051] In one embodiment, the molecular sieve of the present invention comprises: Na-based 4A molecular sieve, Ca-based 5A molecular sieve, K-based 3A molecular sieve, 13X molecular sieve, Y-type molecular sieve, or a combination thereof.

[0052] Na-based 4A molecular sieves belong to the cubic crystal system, consisting of a three-dimensional framework of silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra linked by shared oxygen atoms. The metal cation outside this framework is sodium ion. The chemical formula of Na-based 4A molecular sieves is usually represented as 2Na₂O·2Al₂O₃·4SiO₂·9H₂O. 4A indicates that its standard pore size is 4 angstroms (Å), or 0.4 nm.

[0053] Ca-based 5A molecular sieves belong to the cubic crystal system, consisting of a three-dimensional framework formed by silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra linked by shared oxygen atoms. They are prepared by exchanging some sodium ions in Na-based 4A molecular sieves with calcium ions. Therefore, the metal cations outside the framework are calcium and sodium ions, and its chemical formula is usually represented as 3CaO·Na₂O·4Al₂O₃·8SiO₂·18H₂O. 5A indicates that its standard pore size is 5 angstroms (Å), or 0.5 nm.

[0054] K-based 3A molecular sieves belong to the cubic crystal system, consisting of a three-dimensional framework formed by silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra linked by shared oxygen atoms. They are prepared by exchanging some sodium ions in Na-based 4A molecular sieves with potassium ions. Therefore, the metal cations outside the framework are potassium and sodium ions, and its chemical formula is usually represented as 4K₂O·2Na₂O·6Al₂O₃·12SiO₂·27H₂O. 3A indicates that its standard pore size is 3 angstroms (Å), or 0.3 nm.

[0055] 13X molecular sieves belong to the cubic crystal system, and the cations outside the framework are mainly sodium ions. The chemical formula is usually represented as 20Na2O·20Al2O3·49SiO2·120H2O. Its standard pore size is 10 angstroms (Å), or 1 nm.

[0056] Y-type molecular sieves belong to the cubic crystal system, where the cations outside the framework are mainly sodium ions, usually represented by the chemical formula Na. 56 [(AlO2) 56 (SiO2) 136 ]·xH2O. Its standard pore size is 7.4 Å, or 0.74 nm.

[0057] Furthermore, molecular sieves, by dispersing into fine particles, provide heterogeneous nucleation sites for polylactic acid (PLA) crystallization, which helps lower the nucleation energy barrier and facilitates rapid crystal nucleation within PLA, thereby increasing the crystallization rate and crystallinity. Since water molecules have difficulty penetrating tightly packed crystalline regions, increased crystallinity directly reduces the number of amorphous target sites that water molecules can attack, thus improving the overall hydrolysis resistance of PLA.

[0058] In one embodiment, the molecular sieve of the present invention has a particle size of 1 to 6 μm, preferably 1.5 to 5 μm, for example 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6 μm, and a range consisting of any two of these values.

[0059] In one embodiment, the molecular sieve of the present invention has a bulk density of 0.3 g / ml or more, preferably 0.4 g / ml or more, for example 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8 g / ml or more, and a range consisting of any two of these values.

[0060] Inorganic packing

[0061] The inorganic filler used in this invention can provide heterogeneous nucleation sites for polylactic acid (PLA) crystallization by dispersing into fine particles. This helps to lower the nucleation energy barrier and facilitate the rapid formation of crystal nuclei within PLA, thereby increasing the crystallization rate and crystallinity of PLA. Since water molecules have difficulty penetrating tightly packed crystalline regions, the increased crystallinity directly reduces the number of amorphous target sites that water molecules can attack, thus improving the overall hydrolysis resistance of PLA.

[0062] In one embodiment, the inorganic filler of the present invention has a particle size of 800 to 3000 mesh, preferably 900 to 2500 mesh, for example, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750. 1800, 1850, 1900, 1950, 2000, 2050, 2100, 2150, 2200, 2250, 2300, 2350, 2400, 2450, 2500, 2550, 2600, 2650, 2700, 2750, 2800, 2850, 2900, 2950, ​​3000, and a range consisting of any two of these values.

[0063] The surface ionic bonds or silanol groups of silicate-based and silica-based inorganic fillers can interact polarly with polylactic acid (PLA) segments. This polar interaction facilitates the directional induction of PLA molecular chains to stack orderly around the crystal nucleus, resulting in a more regular molecular chain arrangement and the formation of a dense crystalline structure. Simultaneously, it enhances the material's cohesion and reduces its susceptibility to hydrolysis.

[0064] Therefore, in one embodiment, the inorganic filler of the present invention comprises silicate inorganic fillers, silica inorganic fillers, or combinations thereof.

[0065] In one embodiment, the inorganic filler of the present invention comprises one or more of Mg, Al, and Ca.

[0066] In one embodiment, based on the total weight of the inorganic filler, the SiO2 content in the inorganic filler of the present invention is 40 to 80% by weight, preferably 50 to 70% by weight, for example 40, 45, 50, 55, 60, 65, 70, 75, 80% by weight, and a range consisting of any two of these values.

[0067] The refractive index of inorganic fillers is a physical parameter that measures their ability to alter the direction of light propagation. When inorganic fillers are dispersed in a polymer matrix, the final optical properties they exhibit depend on the difference between the refractive indices of the inorganic fillers and the matrix.

[0068] In one embodiment, the refractive index of the inorganic filler of the present invention is from 1.3 to 2.5, preferably from 1.4 to 2, for example 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2.0, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, and a range consisting of any two of these values.

[0069] catalyst

[0070] A catalyst is a substance that can alter the rate of a chemical reaction without changing its own mass or chemical properties before and after the reaction. A chemical reaction requires overcoming an energy barrier; this minimum energy threshold is called the activation energy. The working principle of a catalyst is to provide reactant molecules with a new reaction pathway that requires a lower activation energy.

[0071] Therefore, in one embodiment, the lactide composition of the present invention further comprises a catalyst.

[0072] Catalysts come in a wide variety of types. Classified by the chemical reaction they catalyze, catalysts can include oxidation catalysts that promote the combination of substances with oxygen, such as vanadium catalysts commonly used in sulfuric acid production and silver catalysts commonly used in the oxidation of ethylene to ethylene oxide; hydrogenation catalysts that promote the combination of hydrogen with other substances, such as nickel, palladium, and platinum catalysts commonly used in oil hardening, petroleum refining, and pharmaceutical synthesis; polymerization catalysts that catalyze the linking of small monomer molecules into long-chain polymers, such as Ziegler-Natta catalysts commonly used in the production of plastics like polyethylene and polypropylene; and cracking catalysts that break down large hydrocarbon molecules into smaller molecules. Based on their chemical composition, catalysts can be classified into several categories: metal catalysts, which are mainly composed of transition metals or their alloys and are commonly used in hydrogenation, dehydrogenation, and oxidation reactions. Examples include iron catalysts for ammonia synthesis and noble metal catalysts such as platinum, palladium, and rhodium for automobile exhaust treatment; metal oxide catalysts, which include single metal oxide (e.g., titanium dioxide, alumina) catalysts and composite metal oxide (e.g., vanadium-titanium oxide) catalysts; acid-base catalysts, which catalyze reactions by donating or accepting protons and can be liquid acids or bases (e.g., sulfuric acid, sodium hydroxide) or solid acids or bases (e.g., solid phosphoric acid, modified alumina); organometallic complex catalysts, which consist of a central metal ion and organic ligands and are mainly used for homogeneous catalysis; and organic catalysts.

[0073] The catalyst used in this invention is mainly used to catalyze the ring-opening polymerization of lactide to produce polylactic acid.

[0074] In one embodiment, the catalyst of the present invention comprises: a tin-based catalyst, a zinc-based catalyst, or a combination thereof. A tin-based catalyst refers to a catalyst containing tin, which may be an organotin compound or an inorganic tin compound. A zinc-based catalyst refers to a catalyst containing zinc, which may be an organozinc compound or an inorganic zinc compound.

[0075] In one embodiment, the catalyst of the present invention comprises stannous chloride, stannous octoate, zinc oxide, zinc lactate, or a combination thereof.

[0076] The amount of catalyst used affects the reaction rate of the catalyzed reaction, and also the cost. Therefore, it is necessary to control the amount of catalyst within an appropriate range.

[0077] In one embodiment, the catalyst content of the present invention is 0.01 to 2% by weight, preferably 0.02 to 1% by weight, based on the weight of lactide, for example, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2% by weight, and a range consisting of any two of these values.

[0078] antioxidants

[0079] The oxidation process of organic compounds is a series of free radical chain reactions. Under the influence of light, heat, or oxygen, the chemical bonds of organic molecules break, generating reactive free radicals and hydroperoxides. Hydroperoxides undergo decomposition reactions, also generating hydrocarbon oxygen free radicals and hydroxyl free radicals. These free radicals can initiate a series of free radical chain reactions, leading to fundamental changes in the structure and properties of polymers, thereby affecting their performance.

[0080] Antioxidants effectively prevent free radical chain reactions, but different antioxidants exert their antioxidant effects through different mechanisms. Primary antioxidants, such as hindered phenols and aromatic amines, preferentially react with highly reactive free radicals generated during oxidation, such as hydrocarbon radicals and peroxide radicals. By providing an active hydrogen atom, they neutralize these free radicals into stable molecules, thereby directly interrupting the propagation of the free radical chain reaction and preventing further damage to the polymer chain. On the other hand, secondary antioxidants, such as phosphites and thioesters, decompose the hydroperoxides generated in the early stages of oxidation into harmless, stable non-free radical products, preventing their decomposition and the generation of new free radicals, thus indirectly preventing free radical chain reactions.

[0081] Therefore, in one embodiment, the lactide composition of the present invention further comprises an antioxidant.

[0082] Appropriate single primary antioxidants, single secondary antioxidants, two or more primary antioxidants, two or more secondary antioxidants, or combinations of primary and secondary antioxidants can be used to prevent free radical chain reactions in organic compounds.

[0083] In one embodiment, the antioxidant of the present invention comprises hindered phenolic compounds, phosphorus-containing organic compounds, sulfur-containing organic compounds, or combinations thereof.

[0084] The antioxidant of the present invention can be a commercially available antioxidant.

[0085] Antioxidant 1010 belongs to the hindered phenolic antioxidant class. Its main component is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; CAS number is 6683-19-8; it is a white powder, odorless; melting point is 115 to 118 ℃; boiling point is 779.1 ℃; it is soluble in benzene, acetone, and chloroform, slightly soluble in ethanol, and insoluble in water.

[0086] Antioxidant 1076 belongs to the hindered phenolic antioxidant class. Its main component is octadecyl ester of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; CAS number is 2082-79-3; it is a white crystalline powder, odorless and tasteless; melting point is 50 to 52 ℃; it is soluble in solvents such as benzene, acetone, and esters, but insoluble in water.

[0087] Antioxidant 1035 belongs to the hindered phenolic antioxidant class. Its main component is thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; CAS number is 41484-35-9; it is a white crystalline powder, odorless; melting point is 78 ℃; it is insoluble in water, but readily soluble in organic solvents such as methanol, ethanol, toluene, and acetone.

[0088] Antioxidant 168 belongs to the phosphite antioxidant class, and its main component is tris(2,4-di-tert-butyl)phosphite; CAS number is 31570-04-4; it is a white crystalline powder; melting point is 180 to 186 ℃; it is insoluble in water and alcohols, but soluble in benzene, toluene, and gasoline.

[0089] Antioxidant 3010 belongs to the phosphite ester antioxidant class, and its main component is pentaerythritol diisodecyl diphosphite; CAS number is 26544-27-4.

[0090] Antioxidant 2010 belongs to the phosphite ester antioxidant class. Its main component is triisodecyl phosphite; CAS number is 25448-25-3; it is a colorless to almost colorless transparent liquid; boiling point is 166℃; density at 25℃ is 0.884 g / mL; it is readily soluble in ethanol and toluene.

[0091] In one embodiment, the antioxidant of the present invention comprises antioxidant 1010, antioxidant 1076, antioxidant 1035, antioxidant 168, antioxidant 3010, antioxidant 2010, or a combination thereof.

[0092] The amount of antioxidant used will affect the final antioxidant effect, so it is necessary to control the amount of antioxidant in the composition within an appropriate range.

[0093] In one embodiment, the antioxidant content of the present invention is 0.01 to 2% by weight, preferably 0.02 to 1% by weight, based on the weight of lactide, for example, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2% by weight, and a range consisting of any two of these values.

[0094] Hydrolysis-resistant polylactic acid

[0095] This invention also relates to a hydrolysis-resistant polylactic acid (PLA) prepared from the lactide composition of this invention. Under water bath aging conditions, the hydrolysis-resistant PLA of this invention can effectively control the increase in the melt flow rate of PLA, and the products prepared therefrom exhibit good stability. The hydrolysis-resistant PLA of this invention broadens the application of PLA in scenarios requiring long-term stability.

[0096] Isothermal crystallization pattern

[0097] The ring-opening polymerization of lactide to produce polylactic acid can include a crystallization process. Crystallization is a physical process that transforms a disordered melt or amorphous state into an ordered crystal structure, which mainly includes two core steps: nucleation and crystal growth.

[0098] Nucleation mainly occurs in two ways. One is homogeneous nucleation. For example, in a pure polylactic acid melt, due to the thermal motion of molecular chains, localized areas spontaneously aggregate and arrange themselves in an orderly manner to form crystal nuclei. However, this method has a high energy barrier and a slow growth rate. The second is heterogeneous nucleation. By adding foreign substances, such as the molecular sieves and / or inorganic fillers of this invention, ready-made attachment sites are provided for the polylactic acid molecular chains. Heterogeneous nucleation can significantly reduce the energy barrier of nucleation, thereby significantly accelerating the crystallization rate. Once a stable crystal nucleus is formed, the surrounding polylactic acid molecular chains will continuously diffuse, fold, and stack neatly onto the surface of the nucleus, causing the crystal size to continuously increase. Under static conditions, crystals typically grow radially outward from the crystal nucleus.

[0099] Crystallization is a process in which molecules change from disorder to order, releasing heat in the process. Therefore, by monitoring the change in heat release over time during the crystallization process at a constant temperature, crystallization kinetic parameters such as the crystallization initiation time, enthalpy of crystallization, and crystallization rate can be obtained. The graph of the heat release over time can be obtained using conventional experimental equipment in this field, such as differential scanning calorimetry (DSC). An exemplary procedure is illustrated in the following embodiments.

[0100] The isothermal crystallization pattern obtained by DSC represents time on the x-axis and specific heat flux on the y-axis. Rapid crystallization is characterized by rapid exothermic reaction over a short period. The isothermal crystallization patterns of the embodiments and comparative examples of this invention are as follows: Figure 2 , 3 As shown in Figure 4.

[0101] Melt flow rate (MFR)

[0102] Melt flow rate, also known as melt index, refers to the amount of thermoplastic material that flows through a standard die within a specified time under certain temperature and pressure conditions. It is usually expressed in grams per 10 minutes (g / 10min). This index reflects the melt flow properties of the material, that is, how easily the material becomes a fluid in the molten state.

[0103] When polylactic acid (PLA) is attacked by water molecules, the ester bonds within it hydrolyze, the polymer molecular chains break, and the molecular weight decreases. The shorter the molecular chains, the less intermolecular entanglement, and the lower the internal frictional resistance during flow. Therefore, one manifestation of PLA hydrolysis is an increase in molecular friction ratio (MFR). If the increase in MFR of PLA materials under humid aging conditions, such as water bath aging, is not significant, it indicates that internal hydrolysis has been effectively controlled.

[0104] In one embodiment, the increase in melt flow rate of the hydrolytically resistant polylactic acid of the present invention after water bath aging is 10% to 60%, preferably 10% to 60%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 19.3%, 20%, 21%, 22%, 23%, 24%, 24.5%, 25%, 26%, 27%, 28%, 29%, 29.2%, 30%, 30.4%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 38.5%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, and a range consisting of any two of these values.

[0105] acid value

[0106] The acid value, also known as acid strength or acidity, is an important indicator for measuring the content of free acidic components in a substance. It is defined as the number of milligrams of potassium hydroxide (KOH) required to neutralize the acidic substances in 1 gram of sample. Therefore, according to its definition, the unit of acid value is mg KOH / g. Another commonly used unit for acid value is mol / t, and the conversion relationship between the two is mol / t = (mg KOH / g) / 56.1. The free acidic component in polylactic acid (PLA) is mainly the carboxyl groups at the ends of its molecular chains.

[0107] The acid value of the sample can be tested using conventional experimental methods and equipment in the art, such as a Metrohm 905 potentiometric titrator. Exemplary operating procedures are described in the following examples.

[0108] The acid value reflects the amount of free acid in a sample. On one hand, polylactic acid (PLA) hydrolysis produces free carboxylic acids, leading to an increase in the sample's acid value. Therefore, the acid value directly reflects the degree of PLA hydrolysis in the sample. On the other hand, free carboxylic acids act as catalysts for ester bond hydrolysis, accelerating the hydrolysis reaction. A high acid value usually means that subsequent hydrolysis reactions will occur more quickly.

[0109] In one embodiment, the polylactic acid of the present invention has an acid value of 13 to 22 mol / t, preferably 15 to 20. mol / t, for example, 13.0, 13.1, 13.2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 14.0, 14.1, 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.8, 14.9, 15.0, 15.1, 15.2, 15.3, 15.4, 15.5, 15.6, 15.7, 15.8, 15.9, 16.0, 16.1, 16.2, 16.3, 16.4, 16.5, 16.6, 16.7, 16.8, 16.9, 17.0, 17.1, 17.2, 17.3, 17 4, 17.5, 17.6, 17.7, 17.8, 17.9, 18.0, 18.1, 18.2, 18.3, 18.4, 18.5, 18.6, 18.7, 18.8, 18.9, 19.0, 19.1, 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8, 19.9, 20.0, 20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8, 20.9, 21.0, 21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7, 21.8, 21.9, 22.0 mol / t, and the range consisting of any two of these values.

[0110] Water bath aging test

[0111] Water bath aging test is an experimental method that simulates and accelerates the evaluation of a material's durability under humid and hot conditions by immersing the sample in hot water at a controlled temperature. The water bath aging test can be performed using conventional equipment in the art, such as a constant temperature water bath and a vacuum oven, with exemplary operating steps shown in the following embodiments.

[0112] Controlling the duration of water bath aging tests helps assess the performance changes of materials exposed to humid environments for short or long periods.

[0113] In one embodiment, the duration of the water bath aging test of the present invention is 3 to 9 hours, preferably 4 to 8 hours, for example 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9 hours, and a range consisting of any two of these values.

[0114] The hydrolysis-resistant polylactic acid of the present invention exhibits good hydrolysis resistance under water bath aging conditions, specifically reflected in the fact that its MFR only shows a small increase after water bath aging.

[0115] Preparation method of hydrolysis-resistant polylactic acid

[0116] The present invention also relates to a method for preparing hydrolysis-resistant polylactic acid.

[0117] A method for preparing hydrolysis-resistant polylactic acid includes the following steps: providing a lactide composition, particularly the lactide composition of the present invention, comprising: lactide and an anti-hydrolysis aid, wherein the anti-hydrolysis aid comprises a molecular sieve and / or an inorganic filler, the molecular sieve having a pore size of 0.1 to 1 nm and the inorganic filler having a particle size of 800 to 3000 mesh; wherein, based on the weight of lactide: the amount of the molecular sieve is 0.01 to 5 wt%; and / or the amount of the inorganic filler is 0.01 to 5 wt%; heating; and stirring.

[0118] Optionally, the method for preparing hydrolysis-resistant polylactic acid of the present invention further includes the step of adding a catalyst and / or an antioxidant.

[0119] Accordingly, the present invention also relates to the use of the lactide composition of the present invention in the preparation of polylactic acid.

[0120] heating

[0121] In the preparation of the hydrolysis-resistant polylactic acid of the present invention, heating can be carried out in stages. Heating is performed after the lactide composition of the present invention is provided, the purpose of which is to melt the lactide and mix it thoroughly with the anti-hydrolysis agent.

[0122] In one embodiment, the heating melting temperature of lactide is 100 to 200°C, preferably 120 to 180°C, for example 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200°C, and a range consisting of any two of these values.

[0123] After the lactide and anti-hydrolysis agent are thoroughly mixed, a suitable catalyst and / or antioxidant can be optionally added, and then the system is further heated to a suitable temperature for polymerization. Too low a reaction temperature is detrimental to the reaction, leading to a reduced reaction rate and consequently a lower yield of the target product; too high a reaction temperature increases energy consumption during the reaction and can also cause decomposition of the reactants, similarly resulting in a lower yield of the target product. Therefore, it is necessary to control the polymerization temperature within a suitable range.

[0124] In one embodiment, the polymerization reaction temperature is 100 to 250°C, preferably 120 to 230°C, for example, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250°C, and a range consisting of any two of these values.

[0125] Different heating methods can be used during the heating process, such as instantaneous heating, slope heating, isothermal heating, and gradient heating. Among them, gradient heating sets different rates or holding times at different stages of the reaction, which can achieve precise temperature control at different stages of the reaction and meet the needs of different stages of the reaction.

[0126] Therefore, in one embodiment, a gradient heating method is used in the process of heating the system to the appropriate temperature for the polymerization reaction.

[0127] In one embodiment, the heating rate during the gradient heating process is 10°C every 20 to 120 minutes, preferably 10°C every 30 to 110 minutes, for example, 10°C every 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120 minutes, and a range consisting of any two of these values.

[0128] Stir

[0129] Stirring during a reaction is essential for better mixing of the components in the reaction system. Different stirring methods can be used, such as mechanical stirring, hydraulic stirring, gas stirring, ultrasonic stirring, and electromagnetic stirring. Among these, mechanical stirring is a mature technology that offers fast mixing speed and good results.

[0130] Therefore, in one embodiment, the hydrolysis-resistant polylactic acid of the present invention is prepared by mechanical stirring.

[0131] Maintaining the stirring rate within a suitable range is crucial for the thorough mixing of the reaction components. Too low a stirring rate will not provide sufficient energy to drive effective mixing. Too high a stirring rate may damage the component structure, accelerate equipment wear, and waste energy.

[0132] In one embodiment, during the preparation of the hydrolysis-resistant polylactic acid of the present invention, the stirring rate is 5 to 200 r / min, preferably 20 to 180 r / min, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200 r / min, and a range consisting of any two of these values.

[0133] Controlling the stirring time within a suitable range during the stirring process is also beneficial for the thorough mixing of the system.

[0134] In one embodiment, during the preparation of the hydrolysis-resistant polylactic acid of the present invention, the stirring time is 0.01 to 6 hours, preferably 0.05 to 5.5 hours, for example, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2 .95, 3, 3.05, 3.1, 3.15, 3.2, 3.25, 3.3, 3.35, 3.4, 3.45, 3.5, 3.55, 3.6, 3.65, 3.7, 3.75, 3.8, 3.85, 3.9, 3.95, 4, 4.05, 4.1, 4.15, 4.2, 4.25, 4.3, 4.35, 4.4, 4.45 4.5, 4.55, 4.6, 4.65, 4.7, 4.75, 4.8, 4.85, 4.9, 4.95, 5, 5.05, 5.1, 5.15, 5.2, 5.25, 5.3, 5.35, 5.4, 5.45, 5.5, 5.55, 5.6, 5.65, 5.7, 5.75, 5.8, 5.85, 5.9, 5.95, 6 h, and the range formed by any two of these values.

[0135] Reaction Atmosphere

[0136] Oxygen and water vapor in the air can adversely affect the reaction. For example, oxygen may oxidize reactants or catalysts, leading to their inactivation and affecting the reaction rate and final yield. Water vapor may cause hydrolysis of products, thus affecting the final yield. Furthermore, components in the system may undergo side reactions with components in the air, hindering the smooth progress of the reaction. Therefore, isolating the reaction from air is beneficial for its efficient execution.

[0137] Isolation from air can be achieved using vacuum conditions or an inert gas atmosphere. However, in the preparation of the hydrolysis-resistant polylactic acid of this invention, using vacuum conditions may cause lactide, a reactant, to be carried out, resulting in a reduction in the yield of the target product. Therefore, in one embodiment, the preparation of the hydrolysis-resistant polylactic acid of this invention is carried out under an inert atmosphere.

[0138] Nitrogen, argon, helium, etc., can be selected as the inert atmosphere for the reaction. In one embodiment, the inert atmosphere includes nitrogen, argon, helium, or a combination thereof.

[0139] Nitrogen gas is characterized by its ease of preparation and low cost. Therefore, in one embodiment, the hydrolysis-resistant polylactic acid of the present invention is prepared under a nitrogen atmosphere.

[0140] Maintaining the gas pressure within a suitable range during the reaction process also helps the reaction proceed smoothly.

[0141] In one embodiment, the reaction pressure for preparing the hydrolytically resistant polylactic acid of the present invention is 0.05 to 0.4 MPa, preferably 0.1 to 0.35 MPa, for example 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 MPa, and a range consisting of any two of these values.

[0142] reaction time

[0143] Controlling the reaction time is crucial for obtaining the desired product and achieving a high yield. Too short a reaction time may result in incomplete polymerization, leading to a low molecular weight of the target product, which is detrimental to obtaining high molecular weight polylactic acid (PLA). Too long a reaction time can easily cause thermal degradation and increase energy consumption during the reaction process.

[0144] In one embodiment, during the preparation of the hydrolysis-resistant polylactic acid of the present invention, the polymerization reaction is carried out for 0.5 to 10 h, preferably 3 to 8 h, for example 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 h, and a range consisting of any two of these values.

[0145] Beneficial effects

[0146] This invention relates to a lactide composition comprising: lactide and an anti-hydrolysis aid, wherein the anti-hydrolysis aid comprises a molecular sieve and / or an inorganic filler, the molecular sieve having a pore size of 0.1 to 1 nm and the inorganic filler having a particle size of 800 to 3000 mesh; wherein, based on the weight of lactide: the amount of the molecular sieve is 0.01 to 5% by weight; and / or the amount of the inorganic filler is 0.01 to 5% by weight. The lactide composition of this invention is suitable for the preparation of polylactic acid, and particularly suitable for the preparation of polylactic acid with excellent hydrolysis resistance.

[0147] Polylactic acid (PLA) molecules contain numerous ester bonds, making them susceptible to hydrolysis in humid environments. This hydrolysis leads to a decrease in the degree of polymerization, affecting material properties and product lifespan. Industrially, anti-hydrolysis agents are typically added to inhibit PLA hydrolysis. However, commonly used anti-hydrolysis agents in ring-opening polymerization reactions may react uncontrollably with impurities or polymer end groups, causing fluctuations in product molecular weight. They may also compete with catalysts for coordination, inhibiting their activation of cyclic esters and reducing the ring-opening rate. Furthermore, conventional anti-hydrolysis agents improve hydrolysis resistance by reacting with the terminal carboxyl groups of PLA, making them consumable additives. As aging time increases, the effectiveness of consumable additives in improving PLA hydrolysis resistance diminishes.

[0148] The anti-hydrolysis additive used in this invention has good compatibility with ring-opening polymerization and has almost no adverse effect on the reaction rate. Furthermore, it is not a consumable additive; therefore, its effect on improving the hydrolysis resistance of polylactic acid will not decrease even in prolonged humid aging environments.

[0149] Example

[0150] The present invention will now be described in further detail with reference to specific embodiments.

[0151] It should be noted that the following embodiments are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Those skilled in the art can make other variations or modifications based on the above description; it is neither necessary nor possible to exhaustively list all possible implementations here, and obvious variations or modifications derived therefrom are still within the protection scope of this invention. Unless otherwise specified, the instruments, equipment, and reagents used herein are commercially available.

[0152] Material

[0153] L-lactide: Zhejiang Hisun Biomaterials Co., Ltd., purity 98.8%.

[0154] K-based 3A molecular sieve: Shanghai Jiading Zhengda Molecular Sieve Co., Ltd., standard pore size 0.3 nm, particle size 2-4 μm, bulk density ≥ 0.45 g / ml.

[0155] Na-based 4A molecular sieve: Jiangxi Xintao Technology Co., Ltd., standard pore size 0.4 nm, particle size 2-4 μm, bulk density ≥0.45 g / ml.

[0156] Ca-based 5A molecular sieve: Jiangxi Xintao Technology Co., Ltd., standard pore size 0.5 nm, particle size 2-4 μm, bulk density ≥0.45 g / ml.

[0157] Inorganic filler: Guangzhou Chaoshun Chemical Co., Ltd., composed of composite silicate containing Mg, Al and Ca, with SiO2 content of 55 to 60% by weight, particle size of 1250 mesh, and refractive index of 1.5-1.6.

[0158] Stannous octoate: Shandong Qiangsen Chemical Co., Ltd.

[0159] Stannous chloride: Shanghai Aladdin Biochemical Technology Co., Ltd.

[0160] Antioxidant 1010: Shanghai Maclean Biochemical Technology Co., Ltd.

[0161] Antioxidant 1035: Shanghai Maclean Biochemical Technology Co., Ltd.

[0162] Antioxidant 1076: Tianjin Lianlong New Materials Co., Ltd.

[0163] Antioxidant 2010: Nanxiong Zhiyi Fine Chemical Co., Ltd.

[0164] Antioxidant 3010: Nanxiong Zhiyi Fine Chemical Co., Ltd.

[0165] Sample preparation

[0166] Under a nitrogen atmosphere, 1000 g of L-lactide was placed in a reactor and brought into contact with a suitable proportion of molecular sieves and / or inorganic fillers. The mixture was heated to 140°C or 150°C and mechanically stirred at a speed of 80 r / min or 100 r / min. After the lactide was completely melted, appropriate amounts of catalyst and antioxidant were added to the system. Stirring was continued until the viscosity of the mixture increased, at which point stirring was stopped. The temperature was gradually increased to 180 to 200°C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0167] Example 1

[0168] 1000g of L-lactide, 0.5g of inorganic filler, and 0.5g of Na-based 4A molecular sieve were placed in a reactor. Nitrogen gas was purged to 0.15 MPa, and the temperature was raised to 150 °C. The mechanical stirring speed was set to 100 r / min. After 20 min, 1.5g of a compound antioxidant of 2010 and 1010 (the weight ratio of antioxidant 2010 and antioxidant 1010 was 1:1) and 1g of stannous chloride were added to initiate the reaction. Nitrogen gas was purged to 0.15 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually increased to 200 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0169] Example 2

[0170] 1000g of L-lactide, 0.3g of inorganic filler, and 0.2g of Ca-based 5A molecular sieve were placed in a reactor. Nitrogen gas was purged to 0.2 MPa, and the temperature was raised to 150 °C. The mechanical stirring speed was set to 80 r / min. After 20 min, 2g of a compound antioxidant of 168 and 1035 (the weight ratio of antioxidant 168 and antioxidant 1035 was 1:1) and 1g of stannous octoate were added to initiate the reaction. Nitrogen gas was purged to 0.2 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually increased to 190 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0171] Example 3

[0172] 1000 g of L-lactide, 0.5 g of inorganic filler, and 1.0 g of K-based 3A molecular sieve were placed in a reactor. Nitrogen gas was purged to 0.15 MPa, and the temperature was raised to 140 °C. The mechanical stirring speed was set to 100 r / min. After 20 min, 1 g of a compound antioxidant of 1076 and 3010 (the weight ratio of antioxidant 1076 and antioxidant 3010 was 1:1) and 1.5 g of stannous octoate were added to initiate the reaction. Nitrogen gas was purged to 0.15 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually increased to 200 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0173] Example 4

[0174] 1000 g of L-lactide and 1.0 g of Na-based 4A molecular sieve were placed in a reactor, and nitrogen gas was purged to 0.15 MPa. The temperature was raised to 150 °C, and the mechanical stirring speed was set to 100 r / min. After 20 min, 1.5 g of a compound antioxidant of 2010 and 1010 (the weight ratio of antioxidant 2010 and antioxidant 1010 was 1:1) and 1 g of stannous chloride were added to the reactor. Nitrogen gas was purged to 0.15 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually raised to 200 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0175] Example 5

[0176] 1000 g of L-lactide and 1.0 g of inorganic filler were placed in a reactor, and nitrogen gas was purged to 0.15 MPa. The temperature was raised to 150 °C, and the mechanical stirring speed was set to 100 r / min. After 20 min, 1.5 g of a compound antioxidant of 2010 and 1010 (the weight ratio of antioxidant 2010 and antioxidant 1010 was 1:1) and 1 g of stannous chloride were added to carry out the reaction. Nitrogen gas was purged to 0.15 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually raised to 200 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0177] Comparative Example 1

[0178] 1000 g of L-lactide was placed in a reaction vessel, and nitrogen gas was purged to 0.15 MPa. The temperature was raised to 150 °C, and the mechanical stirring speed was set to 100 r / min. After 20 min, 1.5 g of a compound antioxidant of 2010 and 1010 (the weight ratio of antioxidant 2010 and antioxidant 1010 was 1:1) and 1 g of stannous chloride were added to carry out the reaction. Nitrogen gas was purged to 0.15 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually raised to 200 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0179] Comparative Example 2

[0180] 1000 g of L-lactide was placed in a reaction vessel, and nitrogen gas was purged to 0.2 MPa. The temperature was raised to 150 °C, and the mechanical stirring speed was set to 80 r / min. After 20 min, 2 g of a compound antioxidant of 168 and 1035 (the weight ratio of antioxidant 168 and antioxidant 1035 was 1:1) and 1 g of stannous octoate were added to initiate the reaction. Nitrogen gas was purged to 0.2 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually raised to 190 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0181] Comparative Example 3

[0182] 1000 g of L-lactide was placed in a reaction vessel, and nitrogen gas was purged to 0.15 MPa. The temperature was raised to 140 °C, and the mechanical stirring speed was set to 100 r / min. After 20 min, 1 g of a compound antioxidant of 1076 and 3010 (the weight ratio of antioxidant 1076 and antioxidant 3010 was 1:1) and 1.5 g of stannous octoate were added to initiate the reaction. Nitrogen gas was purged to 0.15 MPa, and stirring was stopped after the viscosity increased. The temperature was then gradually raised to 200 °C to continue the reaction, yielding a high molecular weight polylactic acid sample.

[0183] Table 1 below shows the formulations for each embodiment and comparative example.

[0184] Table 1

[0185] Acquisition of sample isothermal crystallization patterns

[0186] Using a Netzsch differential scanning calorimeter (DSC 3500 Siruis) from Germany, the samples of the examples and comparative examples were measured according to the following procedure: the gas flow rate was set to 50 ml / min, the temperature was increased from 0 ℃ to 200 ℃ at a heating rate of 10 ℃ / min, held at 200 ℃ for 5 min, and then the temperature was decreased from 200 ℃ to 110 ℃ at a cooling rate of 100 ℃ / min, and held at 110 ℃ for 1 h.

[0187] Measurement of sample melt flow rate

[0188] The samples of the examples and comparative examples were tested using a melt flow index tester (MFI-1211) at 190 °C and a load of 2.16 kg.

[0189] Acid value measurement

[0190] The test was conducted using a Metrohm 905 potentiometric titrator. The sample was first dissolved in a mixture of dichloromethane and methanol. The sample solution was then titrated with a standard concentration titrant. The potential jump point was monitored using electrodes. The acid value was calculated based on the volume and concentration of the titrant consumed and the sample mass.

[0191] Water bath aging test

[0192] Water bath aging tests were conducted on the materials using a constant temperature water bath and a vacuum oven. The constant temperature water bath was set to 70℃. After the water bath temperature stabilized, a beaker containing distilled water was placed inside. After 20 minutes, the sample was added to the beaker, the mouth of the beaker was covered with plastic wrap, and the beaker was placed in the constant temperature water bath. After 6 hours in the 70℃ constant temperature water bath, the sample was removed, drained, and dried in a 90℃ vacuum oven for 16 hours. The melt flow index (MFR) of the sample after water bath aging was then measured using a melt flow index (MFI-1211). The changes were evaluated by comparing the MFR of the sample before and after water bath aging.

[0193] result

[0194] The results of MFR and acid value measurements for each embodiment and comparative example are shown in Table 2 below.

[0195] Table 2

[0196] As shown in Table 2, the MFR increase of polylactic acid prepared from the lactide composition of this application after water bath aging is significantly lower than that of the comparative example. Adding molecular sieves or inorganic fillers alone can effectively reduce the MFR increase of polylactic acid after water bath aging (Examples 4, 5, and Comparative Example 1). Adding molecular sieves alone can also effectively reduce the acid value of polylactic acid (Example 4 and Comparative Example 1).

[0197] Furthermore, with a fixed total amount of anti-hydrolysis additives, the increase in MFR after water bath aging was further reduced compared to adding molecular sieves or inorganic fillers alone (Examples 1, 4, and 5). This demonstrates that the molecular sieves and inorganic fillers of the present invention have a synergistic effect in improving the hydrolysis resistance of polylactic acid.

[0198] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A lactide composition comprising: lactide and an anti-hydrolysis agent, wherein The anti-hydrolysis additive comprises molecular sieves and / or inorganic fillers. The molecular sieve has a pore size of 0.1 to 1 nm, and the inorganic filler has a particle size of 800 to 3000 mesh. Wherein, based on the weight of lactide: The content of the molecular sieve is 0.01% to 5% by weight. The content of the inorganic filler is 0.01 to 5% by weight.

2. The composition of claim 1, wherein, The molecular sieve contains one or more elements selected from Na, Ca, and K; and / or The inorganic filler includes silicate inorganic fillers, silica inorganic fillers, or combinations thereof.

3. The composition of claim 1, wherein, The lactide composition comprises lactide, a molecular sieve, and an inorganic filler, optionally in a weight ratio of 1:0.1 to 1:10 for the molecular sieve and the inorganic filler.

4. The lactide composition according to claim 1, further comprising a catalyst and / or antioxidant, optionally, based on the weight of lactide: The catalyst content is from 0.01 to 2% by weight; and / or The antioxidant content is 0.01 to 2% by weight.

5. The lactide composition according to claim 4, wherein: The catalyst comprises a tin-based catalyst, a zinc-based catalyst, or a combination thereof; and / or The antioxidant comprises hindered phenolic compounds, phosphorus-containing organic compounds, sulfur-containing organic compounds, or combinations thereof, optionally: The catalyst comprises stannous chloride, stannous octoate, zinc oxide, zinc lactate, or a combination thereof; and / or The antioxidant comprises one or more of the following: pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], tris(2,4-di-tert-butyl)phosphite, pentaerythritol diisodecyl diphosphite, and triisodecyl phosphite.

6. A polylactic acid prepared from the lactide composition according to any one of claims 1-5.

7. The polylactic acid according to claim 6, wherein it has one or more of the following properties: (a) The melt flow rate (MFR) after water bath aging was 6 to 19 g / 10 min; (b) The increase in melt flow rate after water bath aging is 10% to 60%.

8. Use of the lactide composition according to claim 1 in the preparation of polylactic acid.

9. A method for preparing polylactic acid, comprising: Provide a lactide composition according to any one of claims 1-5; heating; Stir.

10. The method of claim 9, wherein: The heating temperature is 100 to 250 °C; and / or The stirring rate is 5 to 200 r / min.

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