Polylactic acid composition and preparation method of polylactic acid composition product

Abstract

The invention designs a polylactic acid composition and a preparation method of a polylactic acid composition product. The polylactic acid composition comprises 60-100 parts by weight of polylactic acid; 0-40 parts by weight of an inorganic filler; 0.3 to 2.0 parts by weight of a nucleating agent; 0.3 to 2.0 parts by weight of a lubricant; 0.5 to 3.0 parts by weight of a plasticizer; wherein the polylactic acid comprises levorotatory polylactic acid and dextrorotatory polylactic acid, and the weight of the dextrorotatory polylactic acid accounts for 5-50% of the total weight of the polylactic acid. The polylactic acid product prepared by the preparation method under specific conditions contains a proper stereocomplex crystal proportion, the adhesion effect of polylactic acid melt and the surface of a mold is reduced, the processing time is greatly shortened, and the demolding efficiency is improved, so that the production efficiency is improved, the mold loss is reduced, and the product quality is improved. And the production cost is saved, the labor intensity of operators is reduced, and the operation safety and comfort are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable materials, and particularly relates to a preparation method of a polylactic acid composition and its products. Background Art

[0002] Plastic products can be seen everywhere in daily life. However, due to their difficult-to-degrade characteristics and huge usage amount, they have brought increasingly serious problems to the environment. With the promotion of relevant government policies and the continuous improvement of the public's environmental protection awareness, degradable plastics have shown broad market prospects.

[0003] Polylactic acid (PLA) is a bio-based thermoplastic polymer material with good biocompatibility and biodegradability. Although this material has environmental protection advantages and meets the requirements of reducing carbon emissions, due to its weak crystallization ability, it is difficult to crystallize during the processing and molding of polylactic acid products. The heat resistance of uncrystallized polylactic acid is poor, and it is easily deformed when heated. During the processing, polylactic acid will not be sufficiently cooled or crystallized, resulting in sticking to the mold during the demolding process and causing the product to deform. These characteristics limit its application range in injection molded products.

[0004] The stereocomplex crystal (SC) formed by blending poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) has a faster crystallization rate than the homocrystal (HC) formed by PLLA (or PDLA), and it can crystallize at high temperatures (for example, 200 - 220 °C).

[0005] CN 111534064A discloses a polylactic acid with a high stereocomplex content and its preparation method. By mixing the prepared stereocomplex polylactic acid premix with A (L-lactic acid and D-lactic acid; or L-lactic acid / mineral system and D-lactic acid; or L-lactic acid and D-lactic acid / mineral system), and injecting and molding the mixture to obtain a polylactic acid with a high stereocomplex content. This polylactic acid with a high stereocomplex content can form perfect crystals with a high crystallinity of X sc > 50%. Summary of the Invention

[0006] To solve the problems existing in the prior art, on the one hand, the present invention provides a polylactic acid composition, which includes: 60 - 100 parts by weight of polylactic acid; 0 - 40 parts by weight of an inorganic filler; 0.3 - 2.0 parts by weight of a nucleating agent; 0.3 - 2.0 parts by weight of a lubricant; 0.5 - 3.0 parts by weight of a plasticizer; wherein, the polylactic acid includes L-lactic acid and D-lactic acid, and the weight of the D-lactic acid accounts for 5 - 50% of the total weight of the polylactic acid.

[0007] In one embodiment, the weight of the right-handed polylactic acid accounts for 10-50% of the total weight of the polylactic acid. In one embodiment, the number-average molecular weight of the left-handed polylactic acid is 100,000-160,000. In another embodiment, the number-average molecular weight of the right-handed polylactic acid is 40,000-160,000.

[0008] In one embodiment, the inorganic filler material is selected from one or more of calcium carbonate, talcum powder, mica, wollastonite, silica, glass beads, montmorillonite, potassium titanate. In another embodiment, the nucleating agent is selected from one or more of norbornene dicarboxylate nucleating agents, amide nucleating agents, organic phosphate nucleating agents, hydrazide nucleating agents, polyvinyl alcohol, sodium polyacrylate, polystyrene. In one embodiment, the lubricant is selected from one or more of rice bran wax, candelilla wax, palm wax, polyethylene wax, oxidized polyethylene wax, paraffin wax, ethylene bisstearamide, stearamide, oleamide. In yet another embodiment, the plasticizer is selected from one or more of tributyl acetylcitrate, tributyl citrate, triethyl citrate, citric acid fatty acid glyceride, heptyl nonyl adipate, epoxy soybean oil, polyethylene glycol, dioctyl phthalate, dioctyl sebacate, dioctyl adipate.

[0009] On the other hand, the present invention also provides a polylactic acid product comprising the polylactic acid composition of the present invention. In one embodiment, the proportion of the stereocomplex crystal in the total crystallinity of the polylactic acid product is not less than 20%. In a preferred embodiment, the proportion of the stereocomplex crystal in the total crystallinity of the polylactic acid product is not less than 30%. In a more preferred embodiment, the proportion of the stereocomplex crystal in the total crystallinity of the polylactic acid product is not less than 40%. In another embodiment, the processing time of the polylactic acid product is not more than 20 s.

[0010] In yet another aspect, the present invention also provides a method for preparing a polylactic acid product, which includes: providing each component of the polylactic acid composition of the present invention, including: polylactic acid; inorganic filler material; nucleating agent; lubricant; plasticizer; slicing and drying the polylactic acid to obtain polylactic acid slices; melt-blending the polylactic acid slices with the remaining components and then granulating; and subjecting the obtained granules after granulation to shaping processing to obtain the polylactic acid product.

[0011] In one embodiment, the shaping processing includes injection molding process, composite material molding process and stamping process. In a preferred embodiment, the shaping processing is selected from ordinary injection molding, thin-wall injection molding, compression molding and rotational molding.

[0012] In one embodiment, the shaping process is an injection molding process, which includes: drying the particles obtained after granulation and then performing injection molding, wherein the drying temperature for drying the particles obtained after granulation is 40 - 80°C; and / or the drying time for drying the particles obtained after granulation is 2 - 15 h.

[0013] In one embodiment, the injection temperature is 180 - 250°C. In another embodiment, the injection pressure is 50 - 150 Bar.

[0014] In yet another aspect, the present invention also relates to the use of the polylactic acid composition of the present invention for preparing polylactic acid products. The polylactic acid products of the present invention are polylactic acid products that are easy to demold, and their processing time is not more than 20 s.

[0015] The method of the polylactic acid composition and its products of the present invention is applicable to a preparation method including a demolding processing and forming process. The present invention controls the content of stereocomplex crystals in the melt by controlling the ratio of D - polylactic acid and L - polylactic acid to obtain a melt containing stereocomplex crystals with processing fluidity at a certain temperature (for example, 190 - 230°C). By controlling the appropriate ratio of stereocomplex crystals in the polylactic acid melt during the preparation process, the products can at least have the following characteristics: 1. Have better heat resistance and will not deform due to high temperature during demolding; 2. The proportion of the amorphous region is reduced; 3. If completely crystallized, the time is shortened; 4. The surface of the product is partially crystallized, and its adhesion strength to the inner wall of the mold cavity becomes weaker. These characteristics make the product easier to demold, thereby improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Shows the appearance of the products of Comparative Example 1 and Example 3 at the same processing time with a mold temperature of 110°C.

[0017] Figure 2 Shows the appearance of the product of Comparative Example 2 and the appearance of the products of Example 6 at different processing times with a mold temperature of 30°C. DETAILED DESCRIPTION OF THE INVENTION

[0018] General Definitions and Terms

[0019] All publications, patent applications, patents, and other references mentioned herein are incorporated herein by reference in their entirety if not otherwise indicated.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0021] Unless otherwise specified, all percentages, parts, ratios, etc. are by weight.

[0022] When a quantity, concentration, or other value or parameter is given as a range, a preferred range, or a preferred upper and lower value, or as a specific value, it is to be understood as specifically disclosing all ranges formed from any pair of upper range or preferred values and any lower range or preferred values, whether or not the ranges are separately disclosed. Unless otherwise stated, when the present invention refers to a numerical range, the range is meant to include its endpoints, as well as all integers and fractions within that range. The scope of the present invention is not limited to the specific numerical values recited when defining the range. For example, "0.3 - 2.0" encompasses 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, etc., and any sub-ranges formed by any two of these values, such as 0.4 - 1.8, 0.6 - 1.5, 0.8 - 1.3, 1.0 - 1.2, etc.

[0023] The terms "about" or "approximately" when used in conjunction with a numerical variable generally 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 within a wider range.

[0024] When describing a numerical value or range endpoint in the present invention, it is to be understood that the disclosure includes the specific value or endpoint recited.

[0025] The expression "comprising" or similar expressions synonymous therewith, such as "including", "containing", and "having", etc., are open-ended and do not exclude additional unrecited elements, steps, or components. The expression "consisting of" excludes any element, step, or component not specified. The expression "consisting essentially of" means that the scope is limited to the specified elements, steps, or components, plus optionally present elements, steps, or components that do not substantially affect the basic and novel features of the claimed subject matter. It should be understood that the expression "comprising" encompasses the expressions "consisting essentially of" and "consisting of".

[0026] Where the number of components or constituents of the present invention is not specified beforehand, it means that there is no limitation on the number of occurrences (or existence) of the components or constituents. Therefore, it should be construed as including one or at least one, and the singular form of the component or constituent also includes the plural, unless the value clearly indicates the singular.

[0027] The term "optional" or "optionally" used in the present invention means that the subsequent described event or situation may or may not occur, and the description includes the occurrence and non-occurrence of the said event or situation.

[0028] The term "one or more" or "at least one" used in the present invention refers to one, two, three, four, five, six, seven, eight, nine or more.

[0029] The term "weight-average molecular weight" used in the present invention may also be referred to as weight-average molar mass, and can be measured by methods such as light scattering method, ultracentrifugation sedimentation velocity method, gel chromatography method, etc. The weight-average molecular weight and its distribution of the present invention can be measured, for example, using a gel permeation chromatograph (GPC).

[0030] In the present invention, the stereocomplex crystal (SC crystal) of polylactic acid refers to a racemic crystal formed by L-polylactic acid (also referred to as PLLA) and an equal amount of D-polylactic acid (also referred to as PDLA).

[0031] In the present invention, the homogenous crystal of polylactic acid, or also referred to as the isotropic crystal, refers to a crystal formed only by L-polylactic acid or only by D-polylactic acid.

[0032] The term "number-average molecular weight" used in the present invention is also referred to as "number-average molar mass". If the molar fraction of molecules with molecular weight M j in the polymer is x j , and the number of molecules is N j , then the number-average molecular weight is

[0033]

[0034] where can be measured by methods such as end group determination method, gel chromatography method, membrane osmometry method, vapor phase osmometry method, boiling point elevation method, mass spectrometry method, etc. Unless otherwise specified, the molecular weight described in this article is the number-average molecular weight. The number-average molecular weight and its distribution of the present invention can be measured, for example, using a gel permeation chromatograph (GPC) and a mass spectrometer.

[0035] In the present invention, the term "demolding" refers to the operation of removing the molded polylactic acid product from the mold during the manufacturing process.

[0036] In the present invention, the term "easy demolding" indicates that the difficulty of demolding the polylactic acid product is relatively low, and is usually characterized by the processing time. For example, easy demolding can refer to a processing time not greater than 20 s.

[0037] In the present invention, the term "total crystallinity" represents the proportion of the mass of the crystalline part in the polylactic acid product relative to the total mass of the polylactic acid product, and refers to the proportion of the mass of the L-polylactic acid crystal and / or D-polylactic acid crystal and the stereocomplex crystal part in the total polylactic acid mass of the polylactic acid product.

[0038] In the present invention, the term "processing time" refers to the time from when the melt to be processed is injected into the mold to when the product starts to separate from the mold.

[0039] In one aspect, the present invention relates to a polylactic acid composition comprising:

[0040] 60 - 100 parts by weight of polylactic acid;

[0041] 0 - 40 parts by weight of an inorganic filler;

[0042] 0.3 - 2.0 parts by weight of a nucleating agent;

[0043] 0.3 - 2.0 parts by weight of a lubricant;

[0044] 0.5 - 3.0 parts by weight of a plasticizer;

[0045] wherein,

[0046] the polylactic acid comprises L - polylactic acid and D - polylactic acid, and the weight of the D - polylactic acid accounts for 5 - 50% of the total weight of the polylactic acid.

[0047] Polylactic Acid (PLA)

[0048] Polylactic acid (PLA), also known as poly(lactic acid), is a polyester polymer formed by the polymerization of lactic acid monomers and is a biodegradable material made from renewable plant resources. Polylactic acid has good mechanical and physical properties, including tensile strength, elongation at break, and elastic modulus. Therefore, polylactic acid is widely used in fields such as food packaging, agriculture, and medicine. In the food packaging field, polylactic acid can be used to make transparent and highly glossy food containers and films; in the agricultural field, it can be used to manufacture agricultural fabrics and health fabrics; in the medical field, due to its good biocompatibility and bioabsorbability, polylactic acid is used to produce disposable infusion devices and dissolvable surgical sutures, etc. Polylactic acid includes any one or a mixture of more of L - polylactic acid (PLLA), D - polylactic acid (PDLA), and meso - polylactic acid (PDLLA). In one embodiment, the polylactic acid composition of the present invention comprises L - polylactic acid and D - polylactic acid. In another embodiment, the polylactic acid in the polylactic acid composition of the present invention consists of L - polylactic acid and D - polylactic acid. In one embodiment, in the polylactic acid composition of the present invention, the D - polylactic acid accounts for about 5 - 50% of the total weight of the polylactic acid, preferably about 10 - 50%, such as about 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, etc.

[0049] In one embodiment, the number-average molecular weight of the poly(L-lactic acid) is about 100,000 - 160,000, preferably about 120,000 - 140,000, such as about 100,000, 105,000, 110,000, 115,000, 120,000, 125,000, 130,000, 135,000, 140,000, 145,000, 150,000, 155,000, 160,000, etc. In another embodiment, the number-average molecular weight of the poly(D-lactic acid) is about 40,000 - 160,000, preferably about 50,000 - 70,000, such as about 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 160,000, etc. The processing time of the composition of the present invention is related to the number-average molecular weight of the polylactic acid (including poly(L-lactic acid) and poly(D-lactic acid)) therein. Within a suitable range (e.g., the number-average molecular weight is 20,000 - 200,000), generally, polylactic acid with a smaller number-average molecular weight can obtain a shorter processing time.

[0050] In one embodiment, the polylactic acid composition contains about 60 - 100 parts by weight of polylactic acid, preferably about 60 - 80 parts by weight of polylactic acid, such as about 60 parts by weight, 65 parts by weight, 70 parts by weight, 75 parts by weight, 80 parts by weight, 85 parts by weight, 90 parts by weight, 95 parts by weight, 100 parts by weight, etc.

[0051] Inorganic Filler

[0052] In the present invention, the inorganic filler refers to solid particles that do not chemically react with polylactic acid and are physically dispersed in the polylactic acid matrix. Generally, the inorganic filler does not chemically react with polylactic acid, has a relatively high melting point and thermal stability, can remain stable during the processing, and can also improve properties such as the rigidity, strength, heat resistance, impact toughness, and elongation at break of polylactic acid. The particle size of the inorganic filler can have an important impact on the performance of the polylactic acid product. For example, a smaller particle size may help improve the uniformity and performance of the product. Therefore, the inorganic filler can reduce costs, improve the processing performance of the polylactic acid composition, enhance the mechanical properties, increase toughness, improve the thermal stability, and adjust the density of the polylactic acid composition.

[0053] In one embodiment, the inorganic filler includes but is not limited to calcium carbonate, talc, mica, wollastonite, silica, glass beads, montmorillonite, potassium titanate. In another embodiment, the inorganic filler is selected from one or more of calcium carbonate, talc, mica, wollastonite, silica, glass beads, montmorillonite, potassium titanate. In a preferred embodiment, the inorganic filler is selected from one or more of calcium carbonate, talc, mica, wollastonite, silica, glass beads. In a more preferred embodiment, the inorganic filler is talc.

[0054] Different inorganic filler materials may involve different functions. For example, the functions of calcium carbonate include, but are not limited to, improving the mechanical properties of polylactic acid products, increasing their hardness and / or rigidity; the functions of talc include, but are not limited to, increasing the crystallinity of polylactic acid products, improving their thermal stability and mechanical strength; the functions of mica include, but are not limited to, improving the high-temperature resistance and dimensional stability of polylactic acid products; the functions of wollastonite include, but are not limited to, enhancing the heat resistance and wear resistance of polylactic acid products; the functions of silica include, but are not limited to, improving the mechanical properties and heat resistance of polylactic acid products while maintaining good biocompatibility; the functions of glass microspheres include, but are not limited to, reducing the density of polylactic acid products, improving their impact resistance and wear resistance, etc.

[0055] In one embodiment, the polylactic acid composition contains about 0 - 40 parts by weight of inorganic filler material, preferably about 20 - 40 parts by weight of inorganic filler material, such as about 0, 5 parts by weight, 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, etc.

[0056] In one embodiment, the polylactic acid composition contains about 0 - 40 parts by weight of talc, preferably about 20 - 40 parts by weight of talc, such as about 0, 5 parts by weight, 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, etc.

[0057] Nucleating Agent

[0058] In the present invention, the nucleating agent is an additive used to improve the crystallization process of polymers. By providing additional crystal nuclei, it accelerates the ordered arrangement of polymer molecular chains to form a finer and more uniform crystal structure.

[0059] Those skilled in the art can select a suitable nucleating agent according to needs. In one embodiment, the nucleating agent includes, but is not limited to, norbornene dicarboxylate nucleating agents, amide nucleating agents, organic phosphate nucleating agents, hydrazide nucleating agents, polyvinyl alcohol, sodium polyacrylate, polystyrene. In another embodiment, the nucleating agent is selected from one or more of norbornene dicarboxylate nucleating agents, amide nucleating agents, organic phosphate nucleating agents, hydrazide nucleating agents, polyvinyl alcohol, sodium polyacrylate, polystyrene.

[0060] The norbornene dicarboxylate nucleating agents include, but are not limited to, sodium norbornene dicarboxylate, potassium norbornene dicarboxylate, calcium norbornene dicarboxylate, magnesium norbornene dicarboxylate, zinc norbornene dicarboxylate, aluminum norbornene dicarboxylate, barium norbornene dicarboxylate, strontium norbornene dicarboxylate, lithium norbornene dicarboxylate, ammonium norbornene dicarboxylate, etc. The amide nucleating agents include, but are not limited to, aliphatic amides, aromatic amides, heterocyclic amides, composite amide nucleating agents, etc. The organic phosphate nucleating agents include, but are not limited to, NA-10, NA-11, NA-21, etc. The hydrazide nucleating agents include, but are not limited to, aromatic dihydrazide compounds (e.g., diphenyl terephthalate dihydrazide, dicyclohexyl terephthalate dihydrazide, etc.), organic hydrazide nucleating agents (e.g., 1,4-dibenzoyl terephthalate dihydrazide, 1,4-bis(4-methylbenzoyl) terephthalate dihydrazide, 1,4-bis(4-tert-butylbenzoyl) terephthalate dihydrazide, sebacic acid diphenyl dihydrazide, etc.), hydrazide compounds with specific substituents (e.g., hydrazide compounds derived from benzoic acid, 2-hydroxybenzoic acid, 3-tert-butylbenzoic acid, and 2-aminobenzoic acid), etc.

[0061] In a preferred embodiment, the nucleating agent is selected from one or more of norbornene dicarboxylate nucleating agents, amide nucleating agents, organic phosphate nucleating agents, and hydrazide nucleating agents. In a more preferred embodiment, the nucleating agent is a hydrazide nucleating agent, such as BTD-8008 (sebacic acid diphenyl dihydrazide).

[0062] In one embodiment, the polylactic acid composition contains about 0.3 - 2.0 parts by weight of the nucleating agent, preferably about 0.5 - 1.5 parts by weight of the nucleating agent, such as about 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1.0 parts by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, 1.9 parts by weight, 2.0 parts by weight, etc.

[0063] In one embodiment, the polylactic acid composition contains about 0.3 - 2.0 parts by weight of BTD-8008, preferably about 0.5 - 1.5 parts by weight of BTD-8008, such as about 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1.0 parts by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, 1.9 parts by weight, 2.0 parts by weight, etc.

[0064] Selecting an appropriate amount of the nucleating agent of the present invention can increase the crystallinity and hardness of polylactic acid products, and improve the melting point and thermal stability of polylactic acid products by promoting the formation of hydrogen bonds between polylactic acid molecules or reacting with hydroxyl groups in polylactic acid molecules and other means.

[0065] Lubricant

[0066] In the present invention, the lubricant is an auxiliary agent used to improve the fluidity and processing performance of polymer melts. It can reduce the friction between the polymer melt and the surface of the processing machinery, thereby reducing the viscosity of the melt and improving its fluidity. Good fluidity helps the uniform distribution and molding of materials, avoiding the accumulation of heat generated by friction, which in turn affects the performance and appearance of the materials.

[0067] Those skilled in the art can select appropriate lubricants according to needs. In one embodiment, the lubricant includes but is not limited to rice bran wax, candelilla wax, palm wax, polyethylene wax, oxidized polyethylene wax, paraffin wax, ethylene bisstearamide, stearamide, and oleic acid amide. In another embodiment, the lubricant is selected from one or more of rice bran wax, candelilla wax, palm wax, polyethylene wax, oxidized polyethylene wax, paraffin wax, ethylene bisstearamide, stearamide, and oleic acid amide.

[0068] Rice bran wax is obtained by separating and refining rice bran oil and has natural ingredients, environmental protection and sustainability, versatility, and excellent physical properties, such as heat resistance, low melting point, antioxidant properties, etc.; candelilla wax has good chemical stability and thermal stability and is suitable for various environments; palm wax has a relatively high melting point and heat of fusion, can remain stable under high-temperature conditions, and is not easy to volatilize and lose; polyethylene wax has excellent cold resistance, heat resistance, chemical resistance, and wear resistance. It can increase the gloss and processing performance of products, has good compatibility with various resins, and can improve fluidity and demoulding properties; oxidized polyethylene wax has good chemical stability, is acid and alkali resistant, and can improve the wear resistance, scratch resistance, and smoothness of materials; paraffin wax has the characteristics of low viscosity and high dropping point, and also has good hydrophobicity and electrical insulation properties; ethylene bisstearamide can improve the fluidity and processing efficiency of materials; stearamide can improve the processing performance of materials, improve the wear resistance and anti-aging properties of materials; oleic acid amide can improve the lubricity and wear resistance of materials, reduce the friction coefficient and energy consumption of materials, and can also form complexes with certain metal ions to play an anti-rust and anti-corrosion role.

[0069] In a preferred embodiment, the lubricant is selected from one or more of rice bran wax, candelilla wax, palm wax, polyethylene wax, oxidized polyethylene wax, and paraffin wax. In a more preferred embodiment, the lubricant is rice bran wax.

[0070] In one embodiment, the polylactic acid composition contains about 0.3 - 2.0 parts by weight of a lubricant, preferably about 0.5 - 1.5 parts by weight of a lubricant, such as about 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1.0 parts by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, 1.9 parts by weight, 2.0 parts by weight, etc.

[0071] In one embodiment, the polylactic acid composition contains about 0.3 - 2.0 parts by weight of rice bran wax, preferably about 0.5 - 1.5 parts by weight of rice bran wax, such as about 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1.0 parts by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, 1.9 parts by weight, 2.0 parts by weight, etc.

[0072] In the present invention, the lubricant has an important influence on both the molding and demolding of polylactic acid products. A suitable lubricant can ensure the processing performance of polylactic acid products and can reduce the processing time of polylactic acid products. If there is no lubricant in the polylactic acid composition of the present invention, it may even cause the polylactic acid products to be unable to complete molding.

[0073] Plasticizer

[0074] In the present invention, a plasticizer is a chemical substance that can increase the flexibility and ductility of a polymer. The plasticizer plays an important role in the polymer composition of the present invention, such as reducing the glass transition temperature of the polymer, making it have better flexibility at room temperature, increasing the plasticity of the polymer, increasing the processability, and improving the heat resistance, etc.

[0075] Those skilled in the art can select a suitable plasticizer according to needs. In one embodiment, the plasticizer includes but is not limited to tributyl acetylcitrate, tributyl citrate, triethyl citrate, citric acid fatty acid glyceride, heptyl nonyl adipate, epoxy soybean oil, polyethylene glycol, dioctyl phthalate, dioctyl sebacate, dioctyl adipate. In another embodiment, the plasticizer is selected from one or more of tributyl acetylcitrate, tributyl citrate, triethyl citrate, citric acid fatty acid glyceride, heptyl nonyl adipate, epoxy soybean oil, polyethylene glycol, dioctyl phthalate, dioctyl sebacate, dioctyl adipate.

[0076] Tributyl acetylcitrate has good compatibility and high plasticizing effect; tributyl citrate has the characteristics of good compatibility and high plasticizing efficiency; triethyl citrate has excellent thermal stability and low volatility and can be used in combination with other plasticizers to improve the processability and flexibility of resins; citric acid fatty acid glycerides can be used to improve the flexibility and processability of polymers; heptyl nonyl adipate has good plasticizing effect and stability; epoxidized soybean oil contains epoxy functional groups and has good thermal and light stability; polyethylene glycol has excellent thermal stability and low volatility; phthalate plasticizers have good plasticizing effect and durability; dioctyl sebacate has good compatibility and cold resistance; dioctyl adipate has good heat resistance and light resistance.

[0077] In a preferred embodiment, the plasticizer is selected from one or more of tributyl acetylcitrate, tributyl citrate, triethyl citrate, citric acid fatty acid glycerides, heptyl nonyl adipate, epoxidized soybean oil, and polyethylene glycol. In a more preferred embodiment, the plasticizer is tributyl acetylcitrate.

[0078] In one embodiment, the polylactic acid composition contains about 0.5 - 3.0 parts by weight of the plasticizer, preferably about 1.5 - 2.5 parts by weight of the plasticizer, such as about 0.5 parts by weight, 0.7 parts by weight, 0.9 parts by weight, 1.0 parts by weight, 1.2 parts by weight, 1.4 parts by weight, 1.6 parts by weight, 1.8 parts by weight, 2.0 parts by weight, 2.2 parts by weight, 2.4 parts by weight, 2.6 parts by weight, 2.8 parts by weight, 3.0 parts by weight, etc.

[0079] In one embodiment, the polylactic acid composition contains about 0.5 - 3.0 parts by weight of tributyl acetylcitrate, preferably about 1.5 - 2.5 parts by weight of tributyl acetylcitrate, such as about 0.5 parts by weight, 0.7 parts by weight, 0.9 parts by weight, 1.0 parts by weight, 1.2 parts by weight, 1.4 parts by weight, 1.6 parts by weight, 1.8 parts by weight, 2.0 parts by weight, 2.2 parts by weight, 2.4 parts by weight, 2.6 parts by weight, 2.8 parts by weight, 3.0 parts by weight, etc.

[0080] Through the combination of polylactic acid, inorganic filler, nucleating agent, lubricant, and plasticizer and their specific contents, the polylactic acid composition of the present invention can significantly reduce the processing time while maintaining good biodegradability, heat resistance, and toughness of the polylactic acid products containing or prepared therefrom, thereby improving production efficiency and facilitating industrial production.

[0081] Polylactic Acid Products and Their Preparation Methods

[0082] On the other hand, the present invention also provides a polylactic acid product and a preparation method thereof. The polylactic acid product of the present invention has the property of easy demolding, and its processing time is not more than 20 s.

[0083] In one embodiment, the polylactic acid product of the present invention comprises the polylactic acid composition described herein. In a preferred embodiment, the proportion of the stereocomplex crystals in the total crystallinity of the polylactic acid product is not less than 20%, preferably not less than 30%, more preferably not less than 40%; and / or the processing time of the polylactic acid product is not more than 20 s.

[0084] In one embodiment, the preparation method of the polylactic acid product of the present invention comprises:

[0085] Providing each component of the polylactic acid composition of the present invention, wherein the components are as described above. For example, it may include: polylactic acid; inorganic filler; nucleating agent; lubricant; plasticizer;

[0086] Slicing and drying the polylactic acid to obtain polylactic acid slices;

[0087] Melting and blending the polylactic acid slices with the remaining components and then pelletizing;

[0088] Performing molding processing on the pellets obtained after pelletizing to obtain a polylactic acid product.

[0089] Each component and its dosage in the preparation method of the polylactic acid product of the present invention are as defined herein.

[0090] Drying of Polylactic Acid Chips

[0091] The present invention can use polylactic acid slices as the raw material of the method of the present invention.

[0092] Before heating the polylactic acid, the polylactic acid can be mixed to make the L-polylactic acid and D-polylactic acid therein evenly distributed, which is beneficial to the formation of stereocomplex crystals. In one embodiment, the polylactic acid chips are obtained by melt-blending L-polylactic acid and D-polylactic acid and then extrusion granulation. In the present invention, the polylactic acid chips can be prepared by melt-blending and extrusion granulation in a twin-screw extruder. In one embodiment, the weight ratio of L-polylactic acid to D-polylactic acid is about 19:1 - 1:1, preferably about 9:1 - 1:1, for example, about 95:5 (19:1), 90:10 (9:1), 85:15 (17:3), 80:20 (4:1), 75:25 (3:1), 70:30 (7:3), 65:35 (13:7), 60:40 (3:2), 55:45 (11:9), 50:50 (1:1), etc. In one embodiment, the polylactic acid chips include: L-polylactic acid and D-polylactic acid are melt-blended by a twin-screw and then extrusion granulated to obtain the polylactic acid chips, wherein the screw temperature is about 180 - 220 °C and the blending time is about 0.5 - 5 min. In a specific embodiment, the polylactic acid chips include: L-polylactic acid and D-polylactic acid are melt-blended by a twin-screw and then extrusion granulated to obtain the polylactic acid chips, wherein the screw temperature is about 200 °C and the blending time is about 1 min.

[0093] In the present invention, dry polylactic acid can be used, or the polylactic acid can be dried before mixing to avoid the possible adverse effects caused by moisture. In one embodiment, the chip drying includes drying the polylactic acid chips. The drying of the polylactic acid chips can include placing the polylactic acid chips at a temperature of about 40 - 80 °C, preferably about 50 - 70 °C, and passing dry air for drying. Those skilled in the art can adjust the drying temperature and time of the polylactic acid chips according to needs. In the present invention, the temperature for drying the chips can be about 40 - 80 °C, preferably about 50 - 70 °C, for example, about 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, etc. The time for drying the chips can be about 5 - 15 h, preferably about 8 - 12 h, for example, about 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, etc. In a specific embodiment, the drying includes placing the polylactic acid chips in an oven at about 60 °C and passing air dried at about 160 °C for drying for about 10 h.

[0094] Melting Blending and Pelletizing

[0095] Those skilled in the art can select a suitable method to melt-blend and granulate the polylactic acid chips as needed. In the present invention, the polylactic acid chips are melt-blended with the remaining components in the composition of the present invention (for example, inorganic filler, nucleating agent, lubricant, and plasticizer) in a twin-screw extruder and then granulated. In one embodiment, the granulation temperature is about 160 - 230 °C, preferably about 170 - 210 °C, such as about 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C, 225 °C, 230 °C, etc. In another embodiment, the screw speed is about 200 - 450 rpm, preferably about 250 - 400 rpm, such as about 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm, 400 rpm, 410 rpm, 420 rpm, 430 rpm, 440 rpm, 450 rpm, etc.

[0096] The suitable granulation temperature and screw speed for the composition of the present invention not only maintain the uniformity of the particles and the good particle size distribution, provide excellent processing raw materials for molding processing, and improve production efficiency.

[0097] Molding Process

[0098] Those skilled in the art can select a suitable method to perform shaping processing on the obtained particles after granulation according to needs. The shaping processing includes, but is not limited to, injection molding process, composite material molding process, and stamping process. In one embodiment, the shaping processing includes general injection molding, thin-wall injection molding, compression molding, and rotational molding. In a preferred embodiment, the shaping processing is an injection molding process. The injection molding process may include: drying the obtained particles after granulation and then performing injection molding. The drying may include placing the polylactic acid chips at a temperature of about 40 - 80°C, preferably about 50 - 70°C, and passing dry air for drying. In one embodiment, the drying temperature for drying the obtained particles after granulation is about 40 - 80°C, preferably about 50 - 70°C, such as about 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc. In another embodiment, the drying time for drying the obtained particles after granulation is about 2 - 15 h, preferably about 3 - 12 h, such as about 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, etc. In a more preferred embodiment, the shaping processing is general injection molding.

[0099] In the present invention, hot mold injection molding or cold mold injection molding can be used in the injection molding process. In the present invention, the mold temperature of hot mold injection molding is not lower than 80°C. In one embodiment, the mold temperature of hot mold injection molding is about 80 - 130°C, preferably about 90 - 120°C, such as about 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, etc. In the present invention, the mold temperature of cold mold injection molding is not higher than 60°C. In another embodiment, the mold temperature of cold mold injection molding is about 10 - 60°C, preferably about 20 - 50°C, such as about 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, etc.

[0100] In one embodiment, the injection temperature of the injection molding process is about 180 - 250°C, preferably about 190 - 230°C, more preferably 200 - 220°C, such as about 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, etc. In another embodiment, the injection pressure is about 50 - 150 Bar, preferably about 80 - 120 Bar, such as about 50 Bar, 60 Bar, 70 Bar, 80 Bar, 90 Bar, 100 Bar, 110 Bar, 120 Bar, 130 Bar, 140 Bar, 150 Bar, etc.

[0101] In yet another aspect, the present invention provides a polylactic acid article prepared by the method of the present invention. In one embodiment, the proportion of stereocomplex crystals in the polylactic acid article prepared by the method of the present invention in the total crystallinity is not less than about 20%, preferably not less than about 30%, more preferably not less than about 40%, such as about 20%, 25%, 30%, 32%, 35%, 40%, 42%, 45%, 50%, 55%, 60%, 61%, 65%, 67%, 70%, etc. The polylactic acid article prepared by the method of the present invention has the characteristic of easy demolding. Those skilled in the art can select a suitable method to determine the processing time of the polylactic acid article according to needs. For example, the processing time of the polylactic acid article can be measured by directly observing and recording the time required for the melt to be processed from being injected into the mold to the article starting to separate from the mold, or precisely measured using a timing tool such as an electronic timer or stopwatch. In one embodiment, the processing time of the polylactic acid article of the present invention is not greater than about 20 s, such as about 1 s, 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, 9 s, 10 s, 11 s, 12 s, 13 s, 14 s, 15 s, 16 s, 17 s, 18 s, 19 s, 20 s, etc. Therefore, the present invention also relates to the use of the polylactic acid composition of the present invention for preparing a polylactic acid article.

[0102] The method for preparing a polylactic acid article of the present invention can significantly reduce the processing time of the polylactic acid article by selecting a suitable polylactic acid composition as the raw material, adjusting the weight ratio of L-polylactic acid and D-polylactic acid, and selecting a combination of suitable injection molding temperature and other conditions, thereby improving the production efficiency, expanding the use scenarios of polylactic acid, and being beneficial to the application of industrial production.

[0103] Beneficial Effects

[0104] The present invention provides a preparation method of a polylactic acid composition and its products. By reasonably matching the components in the composition, especially configuring the weight ratio of L-polylactic acid and D-polylactic acid, selecting appropriate dosages of the components in the composition, and cooperating with the control of conditions such as injection temperature in the preparation method, etc., a polylactic acid product with significantly reduced processing time is obtained. Its processing time is not more than 20 s, and even the processing time can be reduced to within 10 s. The polylactic acid products of the present invention can at least have the following characteristics: 1. Have better heat resistance and will not deform due to high temperature during demolding; 2. The proportion of the amorphous region is reduced; 3. If completely crystallized, the time is shortened; 4. The surface of the product is partially crystallized, and its adhesion strength to the inner wall of the mold cavity becomes weak. While maintaining the excellent biodegradable environmental protection characteristics of the polylactic acid product, the heat resistance of the polylactic acid product is improved, the problems such as the difficulty of crystallization and easy deformation under heat of polylactic acid are solved, and the demolding efficiency of the polylactic acid product is further significantly improved, thereby improving the production efficiency, reducing the mold loss, saving the production cost, reducing the labor intensity of the operator, enhancing the operation safety and comfort, and being beneficial to industrial application.

[0105] Examples

[0106] The following further describes the solution of the present invention in detail with specific examples.

[0107] It should be noted that the following examples are only examples for clearly illustrating the technical solutions of the present invention and are not limitations on the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here, and the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

[0108] Materials

[0109] L-polylactic acid and D-polylactic acid: Both are purchased from Hisun Biomaterials Co., Ltd.; among them, the number-average molecular weight of L-polylactic acid is 120,000 - 140,000, and the number-average molecular weight of D-polylactic acid is 50,000 - 70,000.

[0110] Talcum powder: Shanghai Chuangyu Chemical New Materials Co., Ltd.

[0111] BTD-8008: Nanjing Baitong New Materials Co., Ltd.

[0112] Tributyl acetylcitrate: Guangzhou Suixin Chemical Co., Ltd.

[0113] Rice bran wax: Chongqing Hecai Chemical Technology Co., Ltd.

[0114] Prepare the samples of the examples and comparative examples according to the following operations

[0115] Polylactic acid chips: L-lactic acid and D-lactic acid are melt-blended by a twin-screw extruder and then pelletized to obtain polylactic acid chips. Among them, the screw temperature is about 200 °C, the blending time is about 1 min, the number-average molecular weight of L-lactic acid is about 120,000 - 140,000, and the number-average molecular weight of D-lactic acid is about 50,000 - 70,000.

[0116] Chip drying: The polylactic acid chips are placed in an oven at about 60 °C, and air dried at about 160 °C for about 10 h.

[0117] Melt blending and pelletizing: The polylactic acid chips, inorganic filler, nucleating agent, plasticizer, and lubricant are cold-blended in a certain proportion and then added to a twin-screw extruder for pelletizing. The pelletizing temperature is about 160 - 210 °C, and the screw speed is about 250 - 400 rpm.

[0118] Molding process: The pellets obtained after pelletizing are dried under the above drying conditions for about 3 h; the polylactic acid products are prepared by ordinary injection molding. Among them, the injection molding temperature is about 190 - 230 °C; the injection molding pressure is about 80 - 120 bar; the mold temperature of the cold mold is about 30 °C, and the mold temperature of the hot mold is about 110 °C.

[0119] Example 1

[0120] 70 parts by weight of polylactic acid, in which the proportion of D-lactic acid is about 10%, 30 parts by weight of talc, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operations to prepare a cup with a wall thickness of 2 mm. Among them, the pelletizing temperature is about 200 °C, hot mold injection molding is used, the injection molding temperature is about 200 °C, and the injection molding pressure is about 100 Bar. Crystallinity Measured by Differential Scanning Calorimeter Testing. The shortest processing time required is 17 - 19 s, and it is completely crystallized, with a total crystallinity of 36.3%, and the proportion of SC crystals is 42%. The specific results are shown in Table 1 and Table 2.

[0121] Example 2

[0122] 70 parts by weight of polylactic acid, in which the proportion of D-lactic acid is about 20%, 30 parts by weight of talc, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operations to prepare a cup with a wall thickness of 2 mm. Among them, the pelletizing temperature is about 200 °C, hot mold injection molding is used, the injection molding temperature is about 210 °C, and the injection molding pressure is about 100 Bar. The crystallinity is tested by differential scanning calorimetry. The shortest processing time required is 11 - 13 s, and it is completely crystallized, with a total crystallinity of 30.7%, and the proportion of SC crystals is 55%. The specific results are shown in Table 1 and Table 2.

[0123] Example 3

[0124] 70 parts by weight of polylactic acid, in which the proportion of dextrorotatory polylactic acid is about 30%, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operation to prepare a cup with a wall thickness of 2 mm. Among them, the granulation temperature is about 200 °C, hot mold injection molding is adopted, the injection molding temperature is about 210 °C, and the injection molding pressure is about 100 Bar. The crystallinity is tested by a differential scanning calorimeter. The shortest required processing time is 8 - 10 s, and it is completely crystallized, with a total crystallinity of 38.8%, among which the proportion of SC crystals is 67%. The specific results are shown in Table 1 and Table 2.

[0125] Example 4

[0126] 70 parts by weight of polylactic acid, in which the proportion of dextrorotatory polylactic acid is about 20%, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operation to prepare cutlery. Among them, the granulation temperature is about 200 °C, cold mold injection molding is adopted, the injection molding temperature is about 210 °C, and the injection molding pressure is about 100 Bar. The crystallinity is tested by a differential scanning calorimeter. The shortest required processing time is 13 - 15 s, and it is not completely crystallized, with a total crystallinity of 18.2%, among which the proportion of SC crystals is 61%. The specific results are shown in Table 1 and Table 2.

[0127] Example 5

[0128] 70 parts by weight of polylactic acid, in which the proportion of dextrorotatory polylactic acid is about 40%, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operation to prepare cutlery. Among them, the granulation temperature is about 200 °C, hot mold injection molding is adopted, the injection molding temperature is about 220 °C, and the injection molding pressure is about 100 Bar. The crystallinity is tested by a differential scanning calorimeter. The shortest required processing time is 8 - 10 s, and it is completely crystallized, with a total crystallinity of 50.86%, among which the proportion of SC crystals is 86%. The specific results are shown in Table 1 and Table 2.

[0129] Example 6

[0130] 70 parts by weight of polylactic acid, in which the proportion of dextrorotatory polylactic acid is about 50%, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operation to prepare cutlery. Among them, the granulation temperature is about 200 °C, hot mold injection molding is adopted, the injection molding temperature is about 220 °C, and the injection molding pressure is about 100 Bar. The crystallinity is tested by a differential scanning calorimeter. The shortest required processing time is 7 - 9 s, and it is completely crystallized, with a total crystallinity of 49.93%, among which the proportion of SC crystals is 91%. The specific results are shown in Table 1 and Table 2.

[0131] Comparative Example 1

[0132] 70 parts by weight of levorotatory polylactic acid, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operation to prepare a cup with a wall thickness of 2 mm. Among them, the granulation temperature is about 180 °C, hot mold injection molding is adopted, the injection molding temperature is about 210 °C, and the injection molding pressure is about 100 Bar. The crystallinity is tested by a differential scanning calorimeter. The shortest required processing time is 26 - 28 s, and it is completely crystallized, with a total crystallinity of 35.3%. The specific results are shown in Table 1 and Table 2.

[0133] Comparative Example 2

[0134] 70 parts by weight of levorotatory polylactic acid, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operation to prepare cutlery. Among them, the granulation temperature is about 180 °C, cold mold injection molding is adopted, the injection molding temperature is about 210 °C, and the injection molding pressure is about 100 Bar. The shortest required processing time is 24 - 26 s. When the processing time is less than 25 s, the product is softer, prone to deformation, not completely crystallized, and the total crystallinity is 19.3%. The specific results are shown in Table 1 and Table 2.

[0135] Comparative Example 3

[0136] 70 parts by weight of polylactic acid, in which the proportion of dextrorotatory polylactic acid is about 10%, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, 2 parts by weight of plasticizer tributyl acetylcitrate, and 1 part by weight of lubricant rice bran wax are used for the above operation to prepare a cup with a wall thickness of 2 mm. Among them, the granulation temperature is about 200 °C, hot mold injection molding is adopted, the injection molding temperature is about 230 °C, and the injection molding pressure is about 100 Bar. It is tested by a differential scanning calorimeter. The shortest required processing time is 26 - 28 s, and it is completely crystallized, with a total crystallinity of 37.6%, among which the proportion of SC crystals is 12%. The specific results are shown in Table 1 and Table 2.

[0137] Comparative Example 4

[0138] 70 parts by weight of polylactic acid, in which the proportion of dextrorotatory polylactic acid is about 30%, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, and 2 parts by weight of plasticizer tributyl acetylcitrate were used for the above operation to prepare a cup with a wall thickness of 2 mm. Among them, the granulation temperature was about 200 °C, hot mold injection molding was used, the injection molding temperature was about 210 °C, and the injection molding pressure was about 100 Bar. During the preparation process, due to poor melt fluidity, the cup could not be completely formed, and the screw plugging occurred from time to time.

[0139] Comparative Example 5

[0140] 70 parts by weight of polylactic acid, in which the proportion of dextrorotatory polylactic acid is about 30%, 30 parts by weight of talcum powder, 1 part by weight of nucleating agent BTD-8008, and 1 part by weight of lubricant rice bran wax were used for the above operation to prepare a cup with a wall thickness of 2 mm. Among them, the granulation temperature was about 200 °C, hot mold injection molding was used, the injection molding temperature was about 210 °C, and the injection molding pressure was about 100 Bar. During the preparation process, due to poor melt fluidity, the cup could not be completely formed, and the screw plugging occurred from time to time.

[0141] Preparation conditions and properties of the specimens in Table 1

[0142]

[0143]

[0144] "-" indicates non-existence or not measured.

[0145] Crystallinity of the examples and comparative examples of the present invention in Table 2

[0146]

[0147] "-" indicates non-existence or not measured.

[0148] As shown in Table 1 and Table 2, compared with the comparative examples, the examples of the present invention have a shorter processing time, indicating that the polylactic acid products prepared by the method of the present invention have the advantage of easy demolding.

[0149] According to the results of Example 1 and Comparative Example 3, the polylactic acid products prepared by both are completely crystalline, with a comparable total crystallinity, but have significantly different proportions of SC crystals. The proportion of SC crystals in Comparative Example 3 accounts for 12% of the total crystallinity, while that in Example 1 is 42%. Within a certain temperature range (for example, 190 - 230 °C), the processing time of the polylactic acid products of the present invention is positively correlated with the injection molding temperature. This indicates that within a certain temperature range (for example, 190 - 230 °C), the smaller the injection molding temperature, the shorter the processing time of the product. Therefore, it is necessary to select an appropriate injection molding temperature to achieve the technical effect of reducing the processing time of polylactic acid products.

[0150] According to the results of Examples 2 - 3, Examples 5 - 6, and Comparative Example 1, compared with the case where only L-polylactic acid exists, the inclusion of both L-polylactic acid and D-polylactic acid in the polylactic acid composition can reduce the processing time of the polylactic acid product. In addition, the processing time of the polylactic acid products of the present invention is inversely correlated with the proportion of D-polylactic acid in the polylactic acid. As the proportion of D-polylactic acid in the polylactic acid increases, the processing time of the polylactic acid product decreases. However, when the proportion of D-polylactic acid is too high (for example, the proportion of D-polylactic acid in the polylactic acid composition ≥ 40%), it is necessary to increase the injection molding temperature, otherwise, the situation of screw plugging is likely to occur, and at this time, the processing time does not decrease significantly.

[0151] According to the results of Example 2 and Example 4, the processing time of the polylactic acid products of the present invention is related to the temperature of the mold used. Compared with injection molding using a cold mold, injection molding using a hot mold can achieve less processing time. Compared with Example 2, the total crystallinity of Example 4 is smaller, and the proportion of its SC crystals in the total crystallinity is comparable to that of Example 2. This indicates that the total crystallinity of the polylactic acid products of the present invention is related to the mold temperature, but the proportion of SC crystals in the total crystallinity has no direct relationship with the mold temperature and is related to the components and their contents of the polylactic acid products of the present invention.

[0152] According to the results of Example 3 and Comparative Example 4 / Comparative Example 5, rice bran wax and tributyl acetylcitrate have an important influence on the processing time of the polylactic acid products of the present invention. When rice bran wax or tributyl acetylcitrate is absent, the melt fluidity during the preparation process is poor, the situation of screw plugging occurs, and even the polylactic acid product cannot be completed.

[0153] According to the results of Examples 1 - 6 in Table 2, the processing time of the polylactic acid products of the present invention has no direct relationship with whether they are completely crystalline, and is related to their total crystallinity and the proportion of SC crystals in the total crystallinity. The processing time is inversely correlated with the total crystallinity and the proportion of SC crystals relative to the total crystallinity. The higher the total crystallinity and the higher the proportion of SC crystals, the shorter the required processing time.

[0154] In summary, the polylactic acid product of the present invention is prepared by controlling the ratio of dextrorotatory polylactic acid and levorotatory polylactic acid to control the content of stereocomplex crystals in the melt, making a suitable proportion combination of polylactic acid with inorganic filler, nucleating agent, lubricant and plasticizer, and through appropriate preparation conditions. It has the property of being easier to demold, reduces the processing time of the polylactic acid product, improves the demolding efficiency, thereby improving the production efficiency, reducing the mold loss, saving the production cost and reducing the labor intensity of the operator, and enhancing the operation safety and comfort.

[0155] The above are only specific embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent transformation using the present invention, directly or indirectly applied in other related technical fields, is similarly included in the patent protection scope of the present invention.

Claims

1. A polylactic acid composition comprising: 60-100 parts by weight of polylactic acid; 0-40 parts by weight of inorganic filler; 0.3-2.0 parts by weight of a nucleating agent; 0.3-2.0 parts by weight of a lubricant; 0.5-3.0 parts by weight of a plasticizer; in, The polylactic acid comprises L-polylactic acid and D-polylactic acid, and the weight of the D-polylactic acid accounts for 5-50% of the total weight of the polylactic acid.

2. The polylactic acid composition according to claim 1, comprising: 60-80 parts by weight of polylactic acid; and / or 20-40 parts by weight of inorganic filler; and / or 0.5-1.5 parts by weight of a nucleating agent; and / or 0.5-1.5 parts by weight of a lubricant; and / or 1.5-2.5 parts by weight of plasticizer.

3. The polylactic acid composition according to claim 1 or 2, wherein The weight of the dextrorotatory polylactic acid accounts for 10-50% of the total weight of the polylactic acid; and / or The number average molecular weight of the L-polylactic acid is 100,000-160,000, preferably 120,000-140,000; and / or The number average molecular weight of the dextrorotatory polylactic acid is 40,000-160,000, preferably 50,000-70,000.

4. The polylactic acid composition according to claim 1, wherein The inorganic filler material is selected from one or more of calcium carbonate, talc, mica, wollastonite, silicon dioxide, glass microspheres, montmorillonite, and potassium titanate; and / or The nucleating agent is selected from one or more of norbornene dicarboxylate nucleating agents, amide nucleating agents, organic phosphate nucleating agents, hydrazide nucleating agents, polyvinyl alcohol, sodium polyacrylate, and polystyrene; and / or The lubricant is selected from one or more of rice bran wax, candelilla wax, palm wax, polyethylene wax, oxidized polyethylene wax, paraffin, ethylene bis stearamide, stearamide, and oleamide; and / or The plasticizer is selected from one or more of acetyl tributyl citrate, tributyl citrate, triethyl citrate, citric acid fatty acid glyceride, heptyl nonyl adipate, epoxy soybean oil, polyethylene glycol, dioctyl phthalate, dioctyl sebacate, and dioctyl adipate.

5. The polylactic acid composition according to claim 4, wherein The inorganic filler is talcum powder; and / or The nucleating agent is a hydrazide nucleating agent, preferably BTD-8008; and / or The lubricant is rice bran wax; and / or The plasticizer is acetyl tributyl citrate.

6. A polylactic acid product comprising the polylactic acid composition according to any one of claims 1 to 5.

7. The polylactic acid product according to claim 6, wherein The proportion of stereocomplex crystals in the total crystallinity of the polylactic acid product is not less than 20%, preferably not less than 30%; more preferably not less than 40%.

8. A method for preparing the polylactic acid product according to claim 6 or 7, comprising: The components of the polylactic acid composition are provided, including: Polylactic acid; Inorganic filling materials; Nucleating agent; Lubricants; Plasticizers; Slicing and drying the polylactic acid to obtain polylactic acid slices; The polylactic acid slices are melt-blended with other components and then pelletized; The particles obtained after granulation are molded to obtain polylactic acid products.

9. The method of claim 8, wherein: The slice drying comprises: melt blending L-polylactic acid and D-polylactic acid, extruding and granulating to obtain polylactic acid slices; The polylactic acid slices are dried.

10. The method of claim 9, wherein: The weight ratio of the L-polylactic acid to the D-polylactic acid is 19:1-1:1, preferably 9:1-1:1; The drying temperature is 40-80°C, preferably 50-70°C; and / or The drying time is 5-15 hours, preferably 8-12 hours.

11. The method of claim 8, wherein: The granulation after the melt mixing is carried out in a twin-screw extruder; The granulation temperature is 160-230°C, preferably 170-210°C; and / or The screw speed is 200-450 rpm, preferably 250-400 rpm.

12. The method of claim 8, wherein: The molding process includes injection molding, composite material molding and stamping, preferably ordinary injection molding, thin-wall injection molding, compression molding and rotational molding.

13. The method of claim 8, wherein: The molding process is an injection molding process, which includes: The granules obtained after the granulation are dried and then injection molded; Wherein, the drying temperature of the granules obtained after granulation is 40-80°C, preferably 50-70°C; and / or The drying time of the granules obtained after granulation is 2-15 hours, preferably 3-12 hours.

14. The method of claim 13, wherein: The injection molding process includes hot mold injection molding or cold mold injection molding; in, The mold temperature of the hot mold injection is 80-130°C, preferably 90-120°C; and / or The mold temperature of the cold mold injection is 10-60°C, preferably 20-50°C.

15. The method of claim 13, wherein: The injection molding process has an injection molding temperature of 180-250° C., preferably 190-230° C.; and / or The injection molding pressure is 50-150 Bar, preferably 80-120 Bar.

16. The method of any one of claims 8 to 15, wherein The processing time of the forming process is no more than 20s.

17. Use of the polylactic acid composition according to any one of claims 1 to 5 for preparing polylactic acid products.

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