Polylactic acid material composition and preparation method of polylactic acid product

Abstract

The invention relates to the technical field of high polymer materials, in particular to a polylactic acid composition and a product containing the same. The polylactic acid composition provided by the invention has proper components, and related products with excellent heat resistance and mechanical properties can be directly obtained through injection molding without an additional treatment process, so that the processing efficiency can be remarkably improved. The invention also relates to a method for preparing a polylactic acid article and a corresponding article.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular materials, and in particular to a high-heat-resistant polylactic acid (PLA) composition and a preparation method of a corresponding product. BACKGROUND

[0002] The invention and application of plastics have significantly changed people's production and life style, but the abandoned plastic products and microplastic particles formed by their disintegration have caused serious harm to the natural environment. Since 2020, the National Development and Reform Commission, the Ministry of Ecology and Environment and many provinces have successively issued "plastic bans", actively responding to plastic pollution, orderly prohibiting or restricting the production, sale and use of some plastic products, and actively promoting plastic products that are easy to recycle, recyclable and degradable.

[0003] Compared with traditional non-degradable polymers, the development and application of biodegradable polymers is an effective way to cope with "white pollution" of plastic garbage, therefore, promoting biodegradable polymers to replace some non-degradable polymers has important social significance.

[0004] Polylactic acid (PLA) is one of the typical biodegradable polymers that have been commercialized at present. Although PLA has good degradability and biocompatibility, compared with traditional polyester materials, the current PLA material still has the shortcomings of low heat resistance temperature and poor mechanical properties. The Vicat softening temperature of ordinary poly-L-lactic acid (PLLA) is about 55℃, which is difficult to be used in occasions with high requirements on heat resistance temperature and mechanical properties, such as microwave-resistant or high-temperature-resistant packaging materials, etc. Therefore, heat resistance modification is one of the key directions to expand the application market of PLA.

[0005] Currently, the injection molding process of PLA stereocomplex (i.e. PLLA / PDLA blend) generally includes the following process: first, the PLA stereocomplex is completely melted at a temperature higher than the melting point of the stereocomplex crystal, and then the obtained amorphous melt is solidified in a mold cavity and then demolded. Since the crystallization rate of high molecular weight PLA material (such as number average molecular weight of 40,000 or more) is slow (J. Phys. Chem. B 2015, 119, 6462), the PLA material after solidification basically does not contain PLA crystals. In order to obtain a PLA product with high stereocomplex crystal content, annealing treatment needs to be carried out in the temperature range between the melting point of the PLA homocrystal and the melting point of the stereocomplex crystal (about 170-220°C), so as to increase the content of the stereocomplex crystal in the material (Polymer 2015, 63, 144). However, since the heat distortion temperature of the PLA product is relatively low, generally in the range of 50-85°C, in order to avoid deformation or collapse of the material during high-temperature annealing, the annealing must be completed in the mold, which significantly reduces the processing efficiency compared with the traditional injection molding process. Chinese patent CN111534064A discloses that a mixture of PLLA and PDLA is first mixed in a twin-screw extruder or an internal mixer to prepare a premix with high stereocomplex crystal content, and then injection molded to prepare a high-heat-resistant PLA product. However, the processing process is relatively complex and still needs to be annealed in the mold.

[0006] Therefore, it is of great significance and application value to develop a polylactic acid composition that can be used for direct injection molding and a method for preparing a PLA product by direct injection molding. SUMMARY

[0007] In order to overcome the shortcomings of the prior art polylactic acid material (such as: the need to improve the heat resistance and mechanical properties, the low processing efficiency, etc.), in one aspect, the present application provides a polylactic acid composition, which comprises, based on the total weight of the polylactic acid composition: 1-15 wt% of a first polylactic acid (PLLA); 1-15 wt% of a first polylactic acid (PDLA); 35-49 wt% of a second polylactic acid (PLLA); and 35-49 wt% of a second polylactic acid (PDLA); wherein the number average molecular weight of the first PLLA and the first PDLA is independently 0.2-20,000; the number average molecular weight of the second PLLA and the second PDLA is independently 8-250,000; and the structure of the first PLLA, the first PDLA, the second PLLA and the second PDLA independently comprises a structural fragment selected from formula (I):

[0008]

[0009] In formula (I), L is selected from an aliphatic fragment of 1-20 carbon atoms.

[0010] In another aspect, the present application relates to a polylactic acid article comprising the polylactic acid composition of the present application.

[0011] In yet another aspect, the present application relates to a method of preparing a polylactic acid article, comprising: performing ring-opening polymerization of L-lactide with a compound of formula (II) as an initiator to obtain a first poly-L-lactic acid (PLLA); performing ring-opening polymerization of D-lactide with a compound of formula (II) as an initiator to obtain a first poly-D-lactic acid (PDLA); performing ring-opening polymerization of L-lactide with a compound of formula (II) as an initiator to obtain a second poly-L-lactic acid (PLLA); performing ring-opening polymerization of D-lactide with a compound of formula (II) as an initiator to obtain a second poly-D-lactic acid (PDLA); injection molding the first PLLA, the first PDLA, the second PLLA and the second PDLA; and demolding to obtain the polylactic acid article;

[0012]

[0013] wherein in formula (II), L' is selected from an aliphatic fragment of 1-20 carbon atoms.

[0014] In another aspect, the present application relates to a polylactic acid (PLA) article prepared by the method of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A schematic diagram of the hydrazide fragment in the polylactic acid composition of the present application enabling intermolecular hydrogen bonding interactions. DETAILED DESCRIPTION

[0016] General definitions and terms

[0017] All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety unless otherwise indicated.

[0018] 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. In case of conflict, the present specification, including definitions, controls.

[0019] All percentages, parts, ratios, etc. are based on weight unless otherwise indicated.

[0020] When a number, concentration or other value or parameter is given as a range, preferred range or a range of preferred values, it is intended to include all ranges of values thereof and individual values thereof, whether or not within the recited range of values and whether or not the range of values is expressly delineated. Unless otherwise stated, the description herein of a range of values is intended to include the recited endpoint, and all integers and fractions within that range. The scope of the application is not limited to the specific values recited when defining a range.

[0021] The terms "about," "approximately" when used in connection with a numerical variable, generally mean that the variate is within an experimental error (e.g., within a 95% confidence interval for a mean) or within ±10% of the indicated value, or within a wider range.

[0022] When describing numerical values or ranges of values herein, it is understood that the disclosure includes the recited specific values or endpoints.

[0023] The expressions "comprising" or "comprise," and "including," "include," and "contain" or "contains," and any variations thereof, are open-ended, and do not exclude additional, unrecited elements, steps, or ingredients. The expression "consisting of" excludes any element, step, or ingredient not specified. The expression "consisting essentially of" indicates a range of equivalents limited to elements, steps, or ingredients that do not materially affect the basic and novel characteristics of the claimed subject matter. It is understood that the expression "comprising" encompasses the expressions "consisting of" and "consisting essentially of."

[0024] The term "combination thereof, unless otherwise indicated, denotes a multi-component mixture of the recited elements, e.g., two, three, four, and up to the maximum possible multi-component mixture.

[0025] Further, unless otherwise indicated, the use of the singular herein, such as "a" or "an," is not intended to limit the description to a single element unless the description specifically recites otherwise. Thus, "a" or "an" means "one or more." Use of the term "another" is intended to cover "at least a second" or "more than one," unless otherwise indicated.

[0026] The terms "optional" or "optionally," as used herein, mean that the subsequently described event or circumstance can or can not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0027] The terms "one or more" or "at least one," as used herein, mean one, two, three, four, five, six, seven, eight, nine, or more.

[0028] The term "number average molecular weight" used herein can also be referred to as number average molar mass, and can be determined by light scattering method, ultracentrifugation sedimentation velocity method, gel chromatography method, and the like. The number average molecular weight and its distribution of the present application can be determined, for example, using a gel permeation chromatograph (GPC).

[0029] In the present context, stereocomplex crystals (SC crystals) of polylactic acid refer to racemic crystals formed from equal amounts of poly-L-lactic acid (PLLA, which can also be referred to as "poly-L-lactic acid") and poly-D-lactic acid (PDLA, which can also be referred to as "poly-D-lactic acid").

[0030] In the present context, homogenous crystals of polylactic acid, which can also be referred to as homocrystals, refer to crystals formed from poly-L-lactic acid alone or poly-D-lactic acid alone.

[0031] In the present context, the term "aliphatic moiety" can refer to a carbon-hydrogen building block which does not contain aromatic structures, which can be in the form of a chain, a ring, or a combination of chain and ring.

[0032] In the present context, the term "hydrocarbon chain" can refer to a chain consisting of carbon and hydrogen only, which can be saturated or unsaturated. Unsaturated hydrocarbon chains contain at least one carbon-carbon double bond and / or carbon-carbon triple bond.

[0033] Polylactic acid composition

[0034] In one aspect, the present application provides a polylactic acid composition comprising a first poly-L-lactic acid (PLLA), a first poly-D-lactic acid (PDLA), a second poly-L-lactic acid (PLLA), and a second poly-D-lactic acid (PDLA). The polylactic acid composition of the present application has a suitable composition, and can directly obtain relevant articles with excellent heat resistance and mechanical properties by injection molding without additional processing (e.g., annealing treatment), which can improve the processing efficiency.

[0035] Without being bound by theory, the performance improvement of the PLA articles of the present application benefits from the stereocomplex crystals in the PLA articles. The increased content of the stereocomplex crystals in the PLA articles of the present application, the hydrogen bonding between the enantiomeric PLLA and PDLA molecular chains in the stereocomplex crystals can form, which allows for close packing between the chains. This unique crystalline structure helps to improve the performance of the PLA articles, such as heat resistance and mechanical properties (e.g., modulus). The melting point of the stereocomplex crystals of PLLA and PDLA is significantly increased compared to the homocrystals of each, which is beneficial to increase the heat distortion temperature of the PLA articles, thereby achieving the improvement of heat resistance. In addition, the PLA articles of the present application comprise a network of stereocomplex crystals. The stereocomplex crystals can be regarded as physical crosslinking points distributed in the matrix of the articles, and the network of stereocomplex crystals can be correspondingly deformed by the tensile deformation of the articles. The crystal regions of the stereocomplex crystals can effectively dissipate energy by slipping or breaking, and the amorphous regions can act as a soft phase in the network, effectively dispersing stress to prevent stress concentration, thereby improving the modulus of the articles while also improving the fracture toughness of the articles. The presence of the network of stereocomplex crystals in the articles of the present application overcomes the difficulty of simultaneously improving the modulus and toughness of the articles.

[0036] In this context, the melting point (M) of the stereocomplex crystals of polylactic acid refers to the melting point of the stereocomplex crystals formed by the left-handed polylactic acid and the right-handed polylactic acid contained in the polylactic acid material. The melting point of the stereocomplex crystals of polylactic acid is affected by the specific properties and structures of the left-handed and right-handed polylactic acid. The above-mentioned melting point can be determined by differential scanning calorimetry (DSC). The peak temperature of the melting peak of the left-handed polylactic acid or the right-handed polylactic acid determined by DSC can be taken as the melting point of the homocrystal, and the melting range of the homocrystal is the temperature range from the starting temperature to the ending temperature of the melting peak. The peak temperature of the melting peak of the stereocomplex crystal can be taken as the melting point of the stereocomplex crystal, and the melting range of the stereocomplex crystal is the temperature range from the starting temperature to the ending temperature of the melting peak.

[0037] Molecular weight

[0038] In the polylactic acid composition of the present application, relatively low molecular weight PLLA and PDLA and relatively high molecular weight PLLA and PDLA are combined, which helps to achieve the performance improvement and processing efficiency improvement of the PLA articles.

[0039] In the present application, the first PLLA and the first PDLA have lower molecular weight compared to the second PLLA and the second PDLA. The first PLLA and the first PDLA having suitable molecular weight in the present application help to improve the processing efficiency of preparing the polylactic acid article and the performance of the article. In one embodiment, the number average molecular weight of the first PLLA can be about 0.2-20,000, preferably about 0.5-10,000, for example, can be about 0.2, 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. In one embodiment, the number average molecular weight of the first PDLA can be about 0.2-20,000, preferably about 0.5-10,000, for example, can be about 0.2, 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.

[0040] The second PLLA and the second PDLA can have relatively high molecular weight, which helps to improve the performance of the PLA article. In one embodiment, the number average molecular weight of the second PLLA can be about 8-250,000, preferably about 10-220,000, for example, can be about 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, etc. In one embodiment, the number average molecular weight of the second PDLA can be about 8-250,000, preferably about 10-220,000, for example, can be about 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, etc.

[0041] The present application creatively introduces lower molecular weight PLLA and PDLA into higher molecular weight PLLA and PDLA, and the combination of lower and higher molecular weight PLLA and PDLA helps to promote the increase of stereocomplex crystal content and the formation of stereocomplex crystal network, which in turn helps to improve the performance of the PLA article and improve the processing efficiency, which is significantly different from the conventional way of improving the performance by increasing the molecular weight of PLA in the art.

[0042] Without being bound by theory, when the polylactic acid composition is melted to form an amorphous melt, the first PLLA and the first PDLA can preferentially assemble to form stereocomplex crystals due to the high melt index and good flowability of the first PLLA and the first PDLA with suitable molecular weight. The stereocomplex crystals can act as nucleating agents to increase the interaction between the PLLA and PDLA molecular chains, and promote the assembly and folding of the segments in the second PLLA and the second PDLA with high molecular weight. This process helps to increase the crystallization rate of the stereocomplex crystals in the PLA melt, and the increase in the crystallization rate can promote the amount of stereocomplex crystals generated in the melt stage of the PLA, thereby significantly increasing the content of the stereocomplex crystals in the PLA product after the PLA melt is directly cooled and formed. In addition, this process also helps to promote the formation of a stereocomplex crystal network.

[0043] In the present application, the number average molecular weight of the first PLLA and the first PDLA can have a close ratio, which is beneficial to promote the assembly of the first PLLA and the first PDLA to form stereocomplex crystals, thereby helping to improve the performance and processing efficiency of the product. In an embodiment, the ratio of the number average molecular weight of the first PLLA and the first PDLA can be about 0.8-1.2, for example, 0.8, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. Preferably, the ratio of the number average molecular weight of the first PLLA and the first PDLA can be about 0.9-1.1, more preferably, about 0.95-1.05, and further preferably, 1.

[0044] The number average molecular weight of the second PLLA and the second PDLA can have a close ratio, which is also beneficial to promote the assembly of the second PLLA and the second PDLA to form stereocomplex crystals, thereby helping to improve the performance and processing efficiency of the product. In an embodiment, the ratio of the number average molecular weight of the second PLLA and the second PDLA can be about 0.8-1.2, for example, 0.8, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. Preferably, the ratio of the number average molecular weight of the second PLLA and the second PDLA can be about 0.9-1.1, more preferably, about 0.95-1.05, and further preferably, 1.

[0045] Structure

[0046] In the present application, the first PLLA, the first PDLA, the second PLLA, and the second PDLA can each independently comprise a structural fragment selected from Formula (I):

[0047]

[0048] In formula (I), L is selected from an aliphatic segment of 1-20 carbon atoms.

[0049] The structural segment of formula (I) can be flanked by PLA chains. For the first PLLA, the structural segment of formula (I) is flanked by PLLA chains. For the first PDLA, the structural segment of formula (I) is flanked by PDLA chains. For the second PLLA, the structural segment of formula (I) is flanked by PLLA chains. For the second PDLA, the structural segment of formula (I) is flanked by PDLA chains.

[0050] The presence of the structural segment of formula (I) in the first PLLA, the first PDLA, the second PLLA and the second PDLA helps to improve the performance and processing efficiency of the article.

[0051] Without being bound by theory, the presence of the hydrazide segment in the structural segment of formula (I) can form hydrogen bonding interactions (e.g. Figure 1 as shown) between molecules, which helps to increase the interaction between the PLLA and PDLA molecular chains, promote the assembly and folding of the segments in the second PLLA and the second PDLA with high molecular weight, which helps to increase the crystallization rate of the stereocomplex crystals in the PLA melt, thereby increasing the content of the stereocomplex crystals in the PLA melt, and also helps to form the stereocomplex crystal network.

[0052] L can be an aliphatic segment of 1-20 carbon atoms, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 carbon atoms. The structure of such L also helps to increase the content of the stereocomplex crystals and optimize the stereocomplex crystal network. The interaction between the PLLA and PDLA molecular chains is free of aromatic structure and can be in the form of a chain, a ring or a combination of chain and ring. Such L structure is beneficial to increasing the content of the stereocomplex crystals in the PLA melt formed by the polylactic acid composition. Without being bound by theory, such L has the property of relative flexibility, which is beneficial to the flexible spatial orientation of the hydrazide groups on both sides of L and the PLLA and PDLA molecular chains, which is beneficial to the formation of the stereocomplex crystals and the optimization of the stereocomplex crystal network.

[0053] In one embodiment, in formula (I), L is selected from a linear or branched hydrocarbon chain of 1-20 carbon atoms, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 carbon atoms. The good flexibility of the hydrocarbon chain is beneficial to further increasing the content of the stereocomplex crystals and optimizing the stereocomplex crystal network.

[0054] In a preferred embodiment, in formula (I), L is selected from a linear or branched hydrocarbon chain of 1-10 carbon atoms, for example, a linear or branched hydrocarbon chain of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 carbon atoms. Such shortened chain length can further enhance the content of stereocomplex crystals. Without being bound by theory, the shortened chain length helps to promote the hydrazide groups on both sides thereof and the PLLA and PDLA molecular chains to be close to each other in space, which is beneficial to the formation of stereocomplex crystals and optimization of the stereocomplex crystal network.

[0055] In an embodiment, in formula (I), L is selected from the following structures: -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -, -(CH2) 11 -, -(CH2) 12 -, -(CH2) 13 -, -(CH2) 14 -, -(CH2) 15 -, -CH(CH3)-, -CH2CH(CH3)CH2-, -CH(CH3)CH2-, -CH(CH3)(CH2)2-, -CH(CH3)(CH2)3-, -(CH2)2CH(CH3)(CH2)2-, -(CH2)3CH(CH3)CH2-, -CH=CH-, -CH2-C(CH2)=CH-, -C(CH3)=CH-. The above L structures are beneficial to the formation of stereocomplex crystals, can enhance the content of stereocomplex crystals and optimize the stereocomplex crystal network, thereby achieving the improvement of the performance and processing efficiency of the product.

[0056] In a preferred embodiment, in formula (I), L is selected from the following structures: -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -. Such L structure not only has a significant effect on the improvement of the performance and processing efficiency of the product, but also can reduce the preparation difficulty and cost of obtaining the first PLLA, the first PDLA, the second PLLA and the second PDLA.

[0057] It should be understood that the structural fragment of formula (I) in the first PLLA and the first PDLA structure can be the same or different. In one embodiment, the structural fragment of formula (I) in the first PLLA and the first PDLA structure is the same, and the first PLLA and the first PDLA with more similar structure and properties are beneficial to the formation of stereocomplex crystals of both and the optimization of the stereocomplex crystal network, which can further improve the performance of the product.

[0058] Similarly, the structural fragment of formula (I) in the second PLLA and the second PDLA structure can be the same or different. In one embodiment, the structural fragment of formula (I) in the second PLLA and the second PDLA structure is the same, and the second PLLA and the second PDLA with more similar structure and properties are beneficial to the formation of stereocomplex crystals of both and the optimization of the stereocomplex crystal network, which can further improve the performance of the product.

[0059] In a further embodiment, the structural fragment of formula (I) in the first PLLA, the first PDLA, the second PDLA, and the second PDLA structure is the same. This is beneficial to further improve the performance of the polylactic acid product.

[0060] Content

[0061] The polylactic acid composition of the present application comprises the first PLLA, the first PDLA, the second PLLA, and the second PDLA each having a suitable content, which is beneficial to the formation of a good combination of components and can improve the improvement effect of the performance of the PLA product by the introduction of the first PLLA and the first PDLA with low molecular weight.

[0062] In one embodiment, the polylactic acid composition comprises about 1-15 wt% of the first poly-L-lactic acid (PLLA), for example, about 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, etc., based on the total weight of the polylactic acid composition. In a preferred embodiment, the polylactic acid composition comprises 3-10 wt% of the first PLLA, based on the total weight of the polylactic acid composition. The preferred content of the first PLLA can further improve the performance of the product.

[0063] In one embodiment, the poly-lactic acid composition comprises about 1-15 wt% of a first poly-D-lactic acid (PDLA), such as about 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, etc., based on the total weight of the poly-lactic acid composition. In a preferred embodiment, the poly-lactic acid composition comprises about 3-10 wt% of a first PDLA, based on the total weight of the poly-lactic acid composition. Preferred amounts of the first PDLA can further improve the performance of the article.

[0064] In one embodiment, the poly-lactic acid composition comprises about 35-49 wt% of a second poly-L-lactic acid (PLLA), such as about 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, etc., based on the total weight of the poly-lactic acid composition. In a preferred embodiment, the poly-lactic acid composition comprises about 40-47 wt% of a second PLLA, based on the total weight of the poly-lactic acid composition. Preferred amounts of the second PLLA can further improve the performance of the article.

[0065] In one embodiment, the poly-lactic acid composition comprises about 35-49 wt% of a second poly-D-lactic acid (PDLA), such as about 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, etc., based on the total weight of the poly-lactic acid composition. In a preferred embodiment, the poly-lactic acid composition comprises about 40-47 wt% of a second PDLA, based on the total weight of the poly-lactic acid composition. Preferred amounts of the second PDLA can further improve the performance of the article.

[0066] In the polylactic acid composition of the present application, the first PLLA and the first PDLA can have a weight ratio close to 1, which is beneficial to promote the assembly of the first PLLA and the first PDLA to form stereocomplex crystals, thereby helping to improve the performance and processing efficiency of the product. In an embodiment, the weight ratio of the first PLLA and the first PDLA can be about 0.8-1.2, for example, 0.8, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. Preferably, the weight ratio of the first PLLA and the first PDLA can be about 0.9-1.1, more preferably, about 0.95-1.05, and further preferably, 1.

[0067] The number average molecular weight of the second PLLA and the second PDLA can have a ratio close to 1, which is also beneficial to promote the assembly of the second PLLA and the second PDLA to form stereocomplex crystals, thereby helping to improve the performance and processing efficiency of the product. In an embodiment, the weight ratio of the second PLLA and the second PDLA can be about 0.8-1.2, for example, 0.8, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. Preferably, the weight ratio of the second PLLA and the second PDLA can be about 0.9-1.1, more preferably, about 0.95-1.05, and further preferably, 1.

[0068] Other components

[0069] According to the need, various auxiliary components and additives in the art, such as heat stabilizers, antioxidants, anti-hydrolysis agents, plasticizers, etc., can be added to the polylactic acid composition of the present application.

[0070] Related products

[0071] The present application also provides a polylactic acid product comprising the polylactic acid composition of the present application.

[0072] Process for preparing a polylactic acid (PLA) material

[0073] In one aspect, the present application relates to a method for preparing a polylactic acid product, comprising:

[0074] ring-opening polymerization of L-lactide by using a compound of formula (II) as an initiator to obtain a first poly-L-lactic acid (PLLA);

[0075] ring-opening polymerization of D-lactide by using a compound of formula (II) as an initiator to obtain a first poly-D-lactic acid (PDLA);

[0076] ring-opening polymerization of L-lactide by using a compound of formula (II) as an initiator to obtain a second poly-L-lactic acid (PLLA);

[0077] ring-opening polymerization of D-lactide by using a compound of formula (II) as an initiator to obtain a second poly-D-lactic acid (PDLA);

[0078] injection molding of the first PLLA, the first PDLA, the second PLLA and the second PDLA; and

[0079] demolding to obtain the poly-lactic acid article;

[0080]

[0081] wherein in formula (II), L’ is selected from an aliphatic fragment of 1 to 20 carbon atoms.

[0082] the compound of formula (II)

[0083] In the process of the present application, a compound of formula (II) is used as an initiator to initiate the ring-opening polymerization of L-lactide and the ring-opening polymerization of D-lactide, respectively, to obtain the respective poly-lactic acids. The role of the initiator is to start the polymerization reaction of the lactide units. The compound of formula (II) can be an aliphatic dihydrazic acid as shown below.

[0084]

[0085] In one embodiment, in formula (II), L’ is selected from a linear or branched hydrocarbon chain of 1 to 20 carbon atoms. In a preferred embodiment, in formula (II), L’ is selected from a linear or branched hydrocarbon chain of 1 to 10 carbon atoms.

[0086] In one embodiment, in formula (II), L’ is selected from the following structures: -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -(CH2) 11 -(CH2) 12 -(CH2) 13 -(CH2) 14 -(CH2) 15-CH(CH3)-, -CH2CH(CH3)CH2-, -CH(CH3)CH2-, -CH(CH3)(CH2)2-, -CH(CH3)(CH2)3-, -(CH2)2CH(CH3)(CH2)2-, -(CH2)3CH(CH3)CH2-, -CH=CH-, -CH2-C(CH2)=CH-, -C(CH3)=CH-. In a preferred embodiment, in formula (II), L' is selected from the group consisting of -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -.

[0087] The compound of formula (II) initiates the polymerization reaction of lactide units, and in the obtained PLA, the compound of formula (II) corresponds to the formation of the structural fragment of formula (I) described above. The compound of formula (II) improves the performance of the PLA product and the processing efficiency lies in that it can introduce the structural fragment of formula (I) into the structure, which in turn helps to achieve the advantages brought by the structural fragment of formula (I) as described above, which will not be repeated here. In addition, the present application, especially the preferred compound of formula (II), has good activity and can effectively act as an initiator to initiate the polymerization reaction of lactide units

[0088] It should be understood that the ring-opening polymerization of L-lactide and the ring-opening polymerization reaction of D-lactide are aimed to provide the first PLLA, the first PDLA, the second PLLA and the second PDLA, which can be independently carried out respectively, or can be independently carried out simultaneously, and there is no specific order requirement.

[0089] In the method of the present application, the molecular weight of the first PLLA, the first PDLA, the second PLLA and the second PDLA can be as described above, which will not be repeated here.

[0090] It should be understood that in the method of the present application, the compound of formula (II) as the initiator of the ring-opening polymerization of L-lactide in the process of obtaining the first PLLA can be the same as or different from the compound of formula (II) as the initiator of the ring-opening polymerization of D-lactide in the process of obtaining the first PDLA. In an embodiment, the compound of formula (II) as the initiator of the ring-opening polymerization of L-lactide in the process of obtaining the first PLLA is the same as the compound of formula (II) as the initiator of the ring-opening polymerization of D-lactide in the process of obtaining the first PDLA, which helps to obtain the first PLLA and the first PDLA with more similar structures and properties, so that the product of the polylactic acid material is further improved.

[0091] Similarly, in the process of the present application, the compound of formula (II) obtained as initiator of the ring-opening polymerization reaction of L-lactide in the second PLLA process can be the same as, or different from, the compound of formula (II) obtained as initiator of the ring-opening polymerization reaction of D-lactide in the second PDLA process. In one embodiment, the compound of formula (II) obtained as initiator of the ring-opening polymerization reaction of L-lactide in the second PLLA process is the same as the compound of formula (II) obtained as initiator of the ring-opening polymerization reaction of D-lactide in the second PDLA process, which helps to obtain second PLLA and second PDLA with more similar structure and properties, thus further improving the performance of the polylactic acid product.

[0092] In one embodiment, the compound of formula (II) obtained as initiator in the process of the first PLLA, the first PDLA, the second PDLA, and the second PDLA is the same. This is conducive to further improving the performance of the polylactic acid product.

[0093] In the present application, the compound of formula (II) as initiator can have a suitable amount, which can effectively initiate ring-opening polymerization and is beneficial to improve the performance of the final product. In one embodiment, in the ring-opening polymerization reaction for obtaining the first or second PLLA, the amount of the compound of formula (II) is about 0.02% to 2% by weight of the weight of L-lactide, for example, about 0.02%, 0.05%, 0.08%, 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.35%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% and the like. In one embodiment, in the ring-opening polymerization reaction for obtaining the first or second PDLA, the amount of the compound of formula (II) is about 0.02% to 2% by weight of the weight of D-lactide, for example, about 0.02%, 0.05%, 0.08%, 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.35%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0% and the like.

[0094] In the method of the present application, a catalyst can be used to accelerate the reaction in the ring-opening polymerization reaction for preparing PLLA and PDLA. The catalyst of the present application can be selected from any conventional catalyst in the art, but the catalyst should not affect the initiation effect of the initiator (aliphatic diacid hydrazide) of the present application.

[0095] Injection molding and demolding

[0096] After obtaining the first PLLA, the first PDLA, the second PLLA and the second PDLA, the melt can be directly injected into a mold through an injection molding process, and after cooling, the PLA product with excellent performance can be directly obtained by demolding. In the method of the present application, no premix with high stereocomplex content is needed before injection molding, and the obtained product also does not need subsequent heat treatment (such as annealing).

[0097] The polylactic acid components can be dried prior to injection molding, or the polylactic acid components can be dried to avoid the adverse effects of moisture.

[0098] The polylactic acid components can be ground, which facilitates the uniform mixing of the components and the formation of stereocomplex crystals during injection molding.

[0099] The amounts of the first PLLA and the first PDLA in proximity to each other facilitate the formation of stereocomplex crystals, which in turn improves the properties of the articles. In one embodiment, the weight ratio of the first PLLA to the first PDLA in the process of the present application can be about 0.8-1.2, such as 0.8, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. Preferably, the weight ratio of the first PLLA to the first PDLA can be about 0.9-1.1, more preferably, about 0.95-1.05, and even more preferably, 1.

[0100] The amounts of the second PLLA and the second PDLA in proximity to each other also facilitate the formation of stereocomplex crystals, which in turn improves the properties of the articles. In one embodiment, the weight ratio of the second PLLA to the second PDLA in the process of the present application can be about 0.8-1.2, such as 0.8, 0.82, 0.85, 0.88, 0.90, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, etc. Preferably, the weight ratio of the second PLLA to the second PDLA can be about 0.9-1.1, more preferably, about 0.95-1.05, and even more preferably, 1.

[0101] The process of the present application can have a suitable injection molding temperature, which facilitates the formation of PLA melt and avoids the destruction of the stereocomplex crystals formed in the melt, and in turn, facilitates the high stereocomplex crystal content and stereocomplex crystal network of the PLA article formed by injection molding, which ensures the high heat resistance and excellent mechanical properties of the article. In one embodiment, the injection molding can be performed at a temperature of 190°C-230°C, such as about 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, etc. The injection molding process can be performed using conventional equipment and methods in the art, such as using an injection molding machine, feeding the PLA raw material into the feeding port, melting the PLA raw material at the injection molding temperature, and then injecting the PLA into a mold.

[0102] The temperature of the injection mold can be adjusted according to actual conditions, for example, it can be about 10-80°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc. In a preferred embodiment, the temperature of the injection mold can be about 10-40°C. The temperature of the injection mold can be room temperature. The present application can use a room temperature mold for injection molding, which is beneficial to improve production efficiency and reduce cost.

[0103] The method of the present application can also optionally include the step of adding one or more auxiliary ingredients and / or additives during the injection molding process.

[0104] In another aspect, the present application also relates to a polylactic acid (PLA) article prepared by the method of the present application.

[0105] Advantages

[0106] Compared with the prior art, the present application has at least the following advantages: the polylactic acid composition of the present application can be used for direct injection molding of polylactic acid composition, has high processing efficiency, and the corresponding article obtained has improved performance (heat resistance, mechanical properties, etc.). The method for preparing a PLA article of the present application can obtain a PLA article with improved performance (for example, excellent heat resistance and mechanical properties), and has high processing efficiency, without the need to prepare a premix with high stereocomplex content, and the article also does not need subsequent heat treatment (for example, annealing), avoiding the problems of time cost and easy deformation of the article in the pretreatment and post-treatment processes in the prior art. In addition, the method for preparing a PLA article of the present application is simple and feasible, and can be completed on a conventional injection molding equipment, and can realize industrialized continuous production.

[0107] Examples

[0108] The schemes of the present application will be further described in detail below in combination with specific examples.

[0109] It should be noted that the following examples are merely examples for clearly illustrating the technical schemes of the present application, and are not intended to limit the present application. Based on the above description, those skilled in the art can make other different forms of changes or modifications, which are not required to be exhaustively enumerated here, and the changes or modifications thus extended are still within the protection scope of the present application. Unless otherwise specified, the instruments and reagent materials used herein are commercially available.

[0110] Unless otherwise specified or clearly contradicted by context, the proportions (including percentages) used herein are by weight.

[0111] Materials

[0112] L-lactide: purchased from Genencor.

[0113] D-lactide: purchased from Genencor.

[0114] aliphatic diacid hydrazide: purchased from Aladdin Biochem Technology Co., Ltd.

[0115] Equipment

[0116] injection molding machine: Guangzhou Pudong Experimental Analysis Instrument Co., Ltd.

[0117] Example 1-5

[0118] The ring-opening polymerization of L-lactide and D-lactide was initiated respectively using initiator, to obtain first PLLA, first PDLA, second PLLA and second PDLA, and the type of initiator and the respective molecular weight are shown in Table 1 below.

[0119] The first PLLA, the first PDLA, the second PLLA and the second PDLA were taken in the amounts shown in Table 1 below, mixed uniformly, and then directly added to the feeding port of the injection molding machine for injection molding, wherein the injection molding temperature and the mold temperature are shown in Table 1 below.

[0120] The PLA product was directly obtained after demolding, without annealing treatment.

[0121] Table 1

[0122]

[0123] Comparative Example 1

[0124] The ring-opening polymerization of L-lactide and D-lactide was initiated respectively using adipic acid dihydrazide as initiator, to obtain high molecular weight PLLA (number average molecular weight: 120,000) and high molecular weight PDLA (number average molecular weight: 120,000);

[0125] 50 parts by weight of high molecular weight PLLA and 50 parts by weight of high molecular weight PDLA were mixed uniformly, and then directly added to the feeding port of the injection molding machine for injection molding, wherein the injection molding temperature was 220°C and the mold temperature was 25°C.

[0126] The PLA product was directly obtained after demolding, without annealing treatment.

[0127] Comparative Example 2

[0128] The ring-opening polymerization of L-lactide and D-lactide was initiated respectively using hexanediol as an initiator to obtain low molecular weight PLLA (number average molecular weight 8000), low molecular weight PDLA (number average molecular weight 8000), high molecular weight PLLA (number average molecular weight: 120,000), and PDLA (number average molecular weight: 120,000).

[0129] After 5 parts by weight of low molecular weight PLLA, 5 parts by weight of low molecular weight PDLA, 50 parts by weight of high molecular weight PLLA, and 50 parts by weight of high molecular weight PDLA were mixed uniformly, they were directly added to the feeding port of an injection molding machine for injection molding, wherein the injection molding temperature was 220°C, and the mold temperature was 25°C.

[0130] After demolding, the PLA product was directly obtained without annealing treatment.

[0131] Comparative Example 3

[0132] The ring-opening polymerization of L-lactide was initiated using adipic acid dihydrazide as an initiator to obtain high molecular weight PLLA (number average molecular weight: 120,000).

[0133] After 100 parts by weight of high molecular weight PLLA were directly added to the feeding port of an injection molding machine for injection molding, wherein the injection molding temperature was 220°C, and the mold temperature was 25°C.

[0134] After demolding, the PLA product was directly obtained without annealing treatment.

[0135] Test Example

[0136] The corresponding PLA products obtained in the above examples and comparative examples were randomly selected and subjected to performance tests according to the following test methods, and the specific test results are shown in Table 1.

[0137] Tactic crystallinity: The melting enthalpy of the sample was analyzed by DSC when the temperature was increased from -20°C to 260°C at a rate of 10°C / min. The melting enthalpy at 200-250°C was taken to calculate the tactic crystallinity (X c,SC ) of the sample: X c,SC = ΔH m / ΔH 0 m , wherein ΔH m is the melting enthalpy of the tactic crystal, and ΔH 0 m is the standard melting enthalpy (ΔH 0 m = 142 J / g) of the tactic crystal.

[0138] Vicat softening temperature: take the standard injection molding sample of PLA material, and measure the Vicat softening point of the injection molding product by the Vicat softening temperature tester under the condition of 5 N additional load and 50 ℃ / / h heating rate.

[0139] Elongation at break: test by GB / T 1040.3-2006 using a universal testing machine.

[0140] Tensile modulus: test by GB / T 1040.2-2006 using a universal testing machine.

[0141] Table 2: PLA product performance test results

[0142]

[0143] The results are shown in Table 2.

[0144] Compared with the comparative example, the content of stereocomplex crystals in the PLA product (samples of examples 1-5) of the application is increased, the Vicat softening temperature is higher, and the heat resistance is better.

[0145] In addition, the mechanical properties of the samples of examples 1-5 are better than those of the comparative example. Among them, the stereocomplex crystals can be distributed as physical crosslinking points in the product matrix, so that when the sample is stretched and deformed, the stereocomplex crystal network also corresponds to be pulled and deformed, so that the crystal region of the stereocomplex crystal slips or breaks, which can effectively dissipate energy, and the amorphous region corresponds to the soft phase in the network, which can effectively disperse stress and prevent stress concentration, thereby improving the modulus of the product while also improving the fracture toughness of the product.

[0146] As can be seen from comparative example 1 and example 2, the low molecular weight first PLLA and first PDLA in example 2 can increase the content of PLA stereocomplex crystals in the product and form a stereocomplex crystal network in the product, thereby improving the performance of the product.

[0147] As can be seen from comparative example 2 and example 2, compared with the hexanediol structure in comparative example 2, the adipic acid dihydrazide structure existing between the PLA molecular chains in example 2 can form hydrogen bond interaction, which improves the interaction between the PLLA and PDLA molecular chains, promotes the assembly and folding of high molecular weight PLLA and PDLA, thereby increasing the content of stereocomplex crystals in the PLA melt and forming a stereocomplex crystal network, so that the heat resistance and mechanical properties of the PLA product are improved.

[0148] In comparative example 3, only high molecular weight PLLA is used for injection molding processing, and the obtained injection molding part is amorphous, and no stereocomplex crystal is generated, so the Vicat softening temperature is low (54 ℃), and the mechanical properties are poor.

[0149] Although the specific embodiments of the present application have been described above, it is understood by those skilled in the art that the present application is only illustrated by way of example, and the scope of protection of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to the embodiments without departing from the principles and essence of the present application, and such changes and modifications fall within the scope of protection of the present application.

Claims

1. A polylactic acid composition, comprising, by total weight of the polylactic acid composition: 1-15 wt% of a first L-polylactic acid (PLLA); 1-15 wt% of a first dextrorotatory polylactic acid (PDLA); 35-49 wt% of a second poly (L-lactic acid) (PLLA); and 35-49 wt% of a second dextrorotatory polylactic acid (PDLA); in, The number average molecular weights of the first PLLA and the first PDLA are each independently 0.2-20,000; The number average molecular weight of the second PLLA and the second PDLA are each independently 80,000-250,000; The structures of the first PLLA, the first PDLA, the second PLLA and the second PDLA each independently comprise a structural fragment selected from formula (I): In formula (I), L is selected from aliphatic moieties having 1 to 20 carbon atoms.

2. The polylactic acid composition according to claim 1, wherein In formula (I), L is selected from a straight or branched hydrocarbon chain of 1 to 20 carbon atoms; Preferably, In formula (I), L is selected from a straight or branched hydrocarbon chain of 1 to 10 carbon atoms.

3. The polylactic acid composition according to claim 1, wherein In formula (I), L is selected from the following structures: -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -、-(CH2) 11 -、-(CH2) 12 -、-(CH2) 13 -、-(CH2) 14 -、-(CH2) 15 -, -CH(CH3)-, -CH2CH(CH3)CH2-, -CH(CH3)CH2-, -CH(CH3)(CH2)2-, -CH(CH3)(CH2)3-, -( CH2)2CH(CH3)(CH2)2-, -(CH2)3CH(CH3)CH2-, -CH=CH-, -CH2-C(CH2)=CH-, -C(CH3)=CH-; Preferably, In formula (I), L is selected from the following structures: -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -.

4. The polylactic acid composition according to claim 1, wherein The number average molecular weights of the first PLLA and the first PDLA are each independently 0.5-10,000; and / or The number average molecular weights of the second PLLA and the second PDLA are independently 100,000-220,000.

5. The polylactic acid composition according to claim 1, wherein The ratio of the number average molecular weights of the first PLLA to the first PDLA is 0.8-1.2, preferably 0.9-1.1, more preferably 0.95-1.05, and further preferably 1; and / or The ratio of the number average molecular weight of the second PLLA to the second PDLA is 0.8-1.2, preferably 0.9-1.1, more preferably 0.95-1.05, and further preferably 1.

6. The polylactic acid composition according to claim 1, wherein The weight ratio of the first PLLA to the first PDLA is 0.8-1.2, preferably 0.9-1.1, more preferably 0.95-1.05, and further preferably 1; and / or The weight ratio of the second PLLA to the second PDLA is 0.8-1.2, preferably 0.9-1.1, more preferably 0.95-1.05, and further preferably 1.

7. The polylactic acid composition according to claim 1, wherein Based on the total weight of the polylactic acid composition, The polylactic acid composition comprises 3-10 wt% of a first PLLA; and / or The polylactic acid composition comprises 3-10 wt% of a first PDLA; and / or The polylactic acid composition comprises 40-47 wt% of a second PLLA; and / or The polylactic acid composition comprises 40-47 wt % of the second PDLA.

8. A polylactic acid product comprising the polylactic acid composition according to any one of claims 1 to 7.

9. A method for preparing a polylactic acid product, comprising: A ring-opening polymerization reaction of L-lactide is carried out by using a compound of formula (II) as an initiator to obtain a first L-polylactic acid (PLLA); Performing a ring-opening polymerization of D-lactide using a compound of formula (II) as an initiator to obtain a first dextrorotatory polylactic acid (PDLA); Using the compound of formula (II) as an initiator, a ring-opening polymerization reaction of L-lactide is carried out to obtain a second L-polylactic acid (PLLA); Using the compound of formula (II) as an initiator, a ring-opening polymerization reaction of D-lactide is carried out to obtain a second dextrorotatory polylactic acid (PDLA); injection molding a first PLLA, a first PDLA, a second PLLA, and a second PDLA; and Demolding to obtain the polylactic acid product; Wherein, in formula (II), L' is selected from aliphatic segments of 1 to 20 carbon atoms.

10. The method according to claim 9, wherein In formula (II), L' is selected from a straight or branched hydrocarbon chain of 1 to 20 carbon atoms; Preferably, In formula (II), L' is selected from a linear or branched hydrocarbon chain of 1 to 10 carbon atoms. More preferably, In formula (II), L' is selected from the following structures: -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -、-(CH2) 11 -、-(CH2) 12 -、-(CH2) 13 -、-(CH2) 14 -、-(CH2) 15 -, -CH(CH3)-, -CH2CH(CH3)CH2-, -CH(CH3)CH2-, -CH(CH3)(CH2)2-, -CH(CH3)(CH2)3-, -( CH2)2CH(CH3)(CH2)2-, -(CH2)3CH(CH3)CH2-, -CH=CH-, -CH2-C(CH2)=CH-, -C(CH3)=CH-; More preferably, In formula (II), L' is selected from the following structures: -CH2-, -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -.

11. The method of claim 9, wherein The injection molding is carried out at a temperature of 190-230°C; and / or The temperature of the injection mold is 10-40°C.

12. A polylactic acid product prepared by the method according to any one of claims 9 to 11.

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