Modified polylactic acid and preparation method therefor, polylactic acid fiber, plastic substrate and plastic product

Abstract

A modified polylactic acid and a preparation method therefor, a polylactic acid fiber, a plastic substrate and a plastic product. The tensile strength of the modified polylactic acid is not lower than 45 MPa, and the melt flow rate of the modified polylactic acid at 180-200°C and a load of 2-3 kg is not lower than 2 g / 10 min. In addition, the modified polylactic acid has excellent mechanical properties and processing performance.

Description

Modified polylactic acid, preparation method thereof, polylactic acid fiber, plastic substrate and plastic product

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 2023109725852 filed on August 3, 2023, entitled “A modified polylactic acid, its preparation method and its plastic product” and Chinese Patent Application No. 2023116823421 filed on December 8, 2023, entitled “A polylactic acid fiber, fiber substrate and fiber product”, both of which are incorporated herein by reference in their entirety. Technical Field

[0003] The invention belongs to the technical field of resin modification, and particularly relates to a modified polylactic acid and a preparation method thereof. Background Art

[0004] Polylactic acid (PLA) is a new type of biodegradable material made from starch raw materials extracted from renewable plant resources (such as corn). It has good biocompatibility and degradability, as well as high strength and good transparency. Therefore, it has great application potential in the fields of packaging and medicine.

[0005] However, polylactic acid has poor mechanical properties, which greatly limits its application.

[0006] To improve the mechanical properties of polylactic acid fibers, polylactic acid is often blended with other resins, such as polyamide and polyester, before spinning. These resins, such as polyamide and polyester, are difficult to fully degrade or degrade very slowly in the natural environment, placing a significant burden on the environment and hindering the full bio-friendliness of polylactic acid.

[0007] In order to expand the application range of polylactic acid, it is often modified to improve its mechanical properties. However, the modification of the mechanical properties of polylactic acid often significantly reduces the processing performance or degradability of polylactic acid, which cannot meet the processing requirements.

[0008] Summary of the Invention

[0009] The present application is made in view of the above-mentioned problems, and its object is to provide a modified polylactic acid having both excellent mechanical properties and processability.

[0010] To achieve the above objectives, the first aspect of the present application provides a modified polylactic acid, wherein the modified polylactic acid has a tensile strength of not less than 45 MPa and a melt flow rate of not less than 2 g / 10 min at 180°C-200°C and a load of 2 kg-3 kg. In any embodiment, the tensile strength of the modified polylactic acid is 45 MPa-100 MPa, optionally 50 MPa-60 MPa.

[0011] The second aspect of the present application further provides a method for preparing modified polylactic acid, which comprises: blending polylactic acid and a chain extender, and using an extrusion process to prepare the modified polylactic acid of the first aspect of the present application.

[0012] The third aspect of the present application provides a polylactic acid fiber, which comprises polylactic acid and the modified polylactic acid provided in the first aspect of the present application or the modified polylactic acid prepared by the preparation method provided in the second aspect of the present application.

[0013] The fourth aspect of the present application also provides a plastic substrate, which is prepared by processing the modified polylactic acid of the first aspect of the present application or the modified polylactic acid prepared by the preparation method of the second aspect, or the polylactic acid fiber provided by the third aspect of the present application.

[0014] A fifth aspect of the present application further provides a plastic product, wherein the plastic product is prepared from the plastic substrate of any embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is an infrared spectrum of the chain extender used in the examples and comparative examples of the present application.

[0016] Figure 2 is a two-dimensional X-ray diffraction pattern of the polylactic acid fiber of Example 13 and Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0017] The following detailed description specifically discloses the embodiments of the modified polylactic acid, its preparation method, polylactic acid fiber, plastic substrate, and plastic product of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0018] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0019] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0020] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0021] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0022] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0023] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0024] The first aspect of the present application provides a modified polylactic acid, wherein the tensile strength of the modified polylactic acid is not less than 45 MPa, and the melt flow rate of the modified polylactic acid is not less than 2 g / 10 min at 180°C-200°C and a load of 2kg-3kg.

[0025] Modified polylactic acid refers to a product obtained by modifying polylactic acid. It can be understood that the modification method of modified polylactic acid can include both physical modification and chemical modification.

[0026] The tensile strength of the modified polylactic acid can be measured by any known method. For example, the test can be performed with reference to the national standard GB 13022-91 "Test method for tensile properties of plastics and films".

[0027] In some embodiments, the tensile strength of the modified polylactic acid may be 43 MPa, 44 MPa, 45 MPa, 48 MPa, 50 MPa, 51 MPa, 52 MPa, 53 MPa, 54 MPa, 55 MPa, 56 MPa, 57 MPa, 58 MPa, 59 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa or any value therebetween.

[0028] Melt flow rate, also known as melt index, is the amount of molten resin that flows through a standard capillary tube in a standardized melt indexer under specific temperature and pressure over a specified time period (generally 10 minutes). The unit is g / 10min. Melt flow rate is an important indicator for evaluating the processing performance of plastics. Modified polylactic acid has a low melt flow rate, which meets processing requirements, reduces processing costs, and improves quality stability.

[0029] Resins with a melt flow rate below 2g / 10min at 180-200°C and a load of 2kg-3kg are usually difficult to process and mold. They require extremely high reaction temperatures or pressures to be processed and molded. This greatly increases processing costs and reduces quality stability.

[0030] The melt flow rate of modified polylactic acid can be measured by any known method. For example, the test is performed in accordance with ISO 1133-1:2022, "Plastics. Thermoplastics - Determination of melt mass flow rate (MFR) and melt volume flow rate (MVR). Part 1: Standard method."

[0031] The modified polylactic acid provided in this application has both excellent mechanical properties and processing properties, and can simultaneously meet the use and processing requirements of the product.

[0032] In some embodiments, the tensile strength of the modified polylactic acid is 45 MPa-100 MPa, optionally 50 MPa-60 MPa.

[0033] In some embodiments, the melt flow rate of the modified polylactic acid is 2 g / 10 min-10 g / 10 min, and can be optionally 2 g / 10 min-6 g / 10 min.

[0034] In some embodiments, the melt flow rate of the modified polylactic acid is 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, or any value therebetween.

[0035] In some embodiments, the weight average molecular weight of the modified polylactic acid is 100,000-200,000, and can be optionally 100,000-150,000.

[0036] In some embodiments, the weight average molecular weight of the modified polylactic acid is 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 160,000, 170,000, 180,000, 190,000, 200,000, or any value therebetween.

[0037] The weight average molecular weight is the statistical average molecular weight by mass, which is the molecular weight averaged over a unit weight. The weight average molecular weight can be measured by any known method, and can be obtained, for example, by gel permeation chromatography.

[0038] The weight-average molecular weight of the modified polylactic acid is within an appropriate range, which can effectively extend the chain of polylactic acid without having an excessively negative impact on its processing performance, thereby enabling it to have both excellent mechanical properties and processing properties.

[0039] In some embodiments, the polydispersity coefficient of the modified polylactic acid is 1.7-2.2.

[0040] In some embodiments, the polydispersity coefficient of the modified polylactic acid is 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, or any value therebetween.

[0041] The polydispersity index, also known as the molecular weight distribution coefficient, is defined as the ratio of the weight-average molecular weight to the number-average molecular weight. The polydispersity index measures the breadth of the molecular weight distribution.

[0042] In some embodiments, the weight loss rate of the modified polylactic acid after heat aging in an air environment at 200° C.-230° C. for 4 hours is not higher than 0.8%, and can be optionally 0.1%-0.5%.

[0043] The weight loss rate of the modified polylactic acid after heat aging in an air environment at 200°C-230°C for 4 hours can be obtained by testing using a known method. As an example, it can be obtained by testing using the following method: measuring the mass M1 of the modified polylactic acid sample, heat aging the modified polylactic acid sample in an air environment at 200°C-230°C for 4 hours in a thermogravimetric analyzer to measure the mass M2 of the modified polylactic acid sample, and taking (M1-M2) / M1 as the weight loss rate of the modified polylactic acid after heat aging in an air environment at 200°C-230°C for 4 hours.

[0044] In some embodiments, the weight loss rate of the modified polylactic acid after heat aging in an air environment at 200°C-230°C for 4 hours can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or any numerical range therebetween.

[0045] The modified polylactic acid provided in the embodiments of the present application has low weight loss rate and high thermal stability under high temperature environment.

[0046] In some embodiments, the elongation at break of the modified polylactic acid is not less than 2%, and can be optionally 2.5%-4%.

[0047] In some embodiments, the elongation at break of the modified polylactic acid can be selected as 2%, 2.2%, 2.5%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0% or any value therebetween.

[0048] The modified polylactic acid provided in the examples of this application not only has high mechanical strength and thermodynamic properties, but also maintains a high elongation at break and excellent toughness. The modified polylactic acid provided in this application has a low polydispersity coefficient, indicating that it is uniformly modified and has a high reactivity, thus being able to simultaneously possess excellent mechanical properties and processing properties. In some embodiments, the elongation at break of the modified polylactic acid is 3%-4%.

[0049] The elongation at break of the modified polylactic acid can be selected as 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0% or any value therebetween.

[0050] The modified polylactic acid has high elongation at break and its toughness is further improved.

[0051] In some embodiments, the modified polylactic acid comprises a structure shown in Formula I

[0052] Wherein, A1 and A2 each independently include carboxyl, hydroxyl, At least one of; R includes The chain segments, R1, R2, R3, R4, R5, and R6 each independently include an organic group, x:y:z is (1-5):(3-7):(5-10), and the structural units are randomly copolymerized.

[0053] In some embodiments, the organic group includes at least one of a hydrocarbon group, an ester group, a carboxyl group, an alkoxy group, an aryl group, an amino group, and an amide group.

[0054] In some embodiments, x:y:z is (1-2):(3-4):(5-6).

[0055] In some embodiments, the contact angle of the modified polylactic acid is not less than 63°, and can be optionally 63°-80°.

[0056] In some embodiments, the contact angle of the modified polylactic acid can be 63°, 65°, 67°, 69°, 71°, 73°, 75°, 77°, 78°, 80° or any value therebetween.

[0057] Polylactic acid contains reactive groups such as carboxyl and hydroxyl groups. Modifiers often modify polylactic acid by reacting with these reactive groups. The high contact angle of the modified polylactic acid indicates a low content of reactive groups such as carboxyl and hydroxyl groups in the modified polylactic acid, demonstrating that the modified polylactic acid provided in this application has a high yield and a high degree of modification.

[0058] In some embodiments, the modified polylactic acid comprises polylactic acid and a chain extender, wherein the chain extender is an epoxy chain extender, and the infrared spectrum of the chain extender is located at 860 cm -1 -870cm -1 The characteristic peak of epoxy group at 3000cm -1 -3300cm -1 The ratio of the carbon-hydrogen bond stretching vibration peak at is not less than 2.1.

[0059] Chain extenders are used to modify the polylactic acid chain. Chain extenders introduce additional segments and reactive functional groups into the polylactic acid molecular chain to increase its molecular weight, alter its structure, and optimize its mechanical properties. Epoxy chain extenders contain epoxy groups, which react with reactive functional groups (such as carboxyl and hydroxyl) on the polylactic acid to modify the polylactic acid.

[0060] In some embodiments, the chain extender comprises styrene-co-glycidyl methacrylate.

[0061] In some embodiments, the chain extender structure is as shown in Formula II,

[0062] R1, R2, R3, R4, R5, and R6 each independently include an organic group, x:y:z is (1-5):(3-7):(5-10), and the structural units are randomly copolymerized.

[0063] In some embodiments, x:y:z is (1-2):(3-4):(5-6).

[0064] In the infrared spectrum of the chain extender, the -1 -870cm -1 The characteristic peak of epoxy group at 3000cm -1 -3300cm -1 The ratio of the carbon-hydrogen bond stretching vibration peak at is not less than 2.1, indicating that the chain extender has a high epoxy degree. The chain extender with high epoxy degree has many active sites and can greatly improve the mechanical properties of polylactic acid at a low addition amount without bringing too much negative impact on the processing performance of polylactic acid.

[0065] In some embodiments, based on the total mass of the modified polylactic acid, the mass percentage of the chain extender is 0.1%-2.0%, optionally 0.4%-1.0%.

[0066] In some embodiments, based on the total mass of the modified polylactic acid, the mass percentage of the chain extender is 0.1%, 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% or any value therebetween.

[0067] The chain extender used in the modified polylactic acid provided in the present application has high reactivity and can effectively improve the mechanical properties of polylactic acid at a low addition amount without bringing too much negative impact on the processing performance of polylactic acid.

[0068] In some embodiments, the modified polylactic acid consists of polylactic acid and a chain extender.

[0069] In the prior art, improvements in the mechanical properties of modified polylactic acid often come at the expense of significant processing performance. Therefore, plasticizers are often added during the modification process to aid in the modification process. However, the addition of plasticizers can reduce production efficiency, increase production costs, and degrade biodegradability. The modified polylactic acid provided in the embodiments of the present disclosure, comprising only polylactic acid and a chain extender, achieves a balance between mechanical and processing performance, effectively reducing production costs and improving production efficiency.

[0070] In some embodiments, the modified polylactic acid comprises polylactic acid, a chain extender, and an antioxidant.

[0071] Antioxidants are compounds that can inhibit or delay the thermal oxidation of polymers and other organic compounds in the air. In layman's terms, they are substances that can prevent polymer materials from deteriorating due to oxidation.

[0072] The thermal oxidation process of polylactic acid (PLA) involves the breaking of chemical bonds in PLA under the influence of heat, light, or oxygen, generating active free radicals and hydroperoxides. Hydroperoxides decompose to produce hydrocarbon oxygen radicals and hydroxyl radicals. These free radicals can trigger a series of free radical chain reactions, leading to fundamental changes in the structure and properties of organic compounds. Antioxidants can promptly eliminate newly generated free radicals or promote the decomposition of hydroperoxides, thereby preventing the chain reaction.

[0073] Antioxidants are a common method for improving the thermal stability of polylactic acid (PLA), but they often require large amounts of antioxidants to effectively improve the thermal stability of PLA. Such large amounts of antioxidants can negatively impact the mechanical and processing properties of PLA. The present invention unexpectedly discovered that the combination of antioxidants and chain extenders effectively improves the thermal stability of PLA with only a small amount of antioxidant added, improving the thermal stability of PLA while also maintaining its mechanical properties and processing efficiency.

[0074] In some embodiments, the antioxidant includes a primary antioxidant and a secondary antioxidant.

[0075] Primary antioxidants refer to antioxidants that can eliminate free radicals. For example, primary antioxidants include but are not limited to aromatic amine compounds and hindered phenol compounds and their derivatives.

[0076] Auxiliary antioxidants are antioxidants that can decompose hydroperoxides. In some embodiments, the auxiliary antioxidants include phosphorus- and sulfur-containing organic compounds. As examples, auxiliary antioxidants include but are not limited to thiodipropionic acid diesters and phosphite compounds.

[0077] The main antioxidant and the auxiliary antioxidant can further significantly improve the thermal stability of the modified polylactic acid through the synergistic effect of the two.

[0078] In some embodiments, the primary antioxidant includes at least one of a hindered phenol antioxidant and an aromatic amine antioxidant, the hindered phenol antioxidant includes at least one of 2,6-tert-butyl-4-methylphenol, bis(3,5-tert-butyl-4-hydroxyphenyl) sulfide, and pentaerythritol tetrakis[β-(3,5-tert-butyl-4-hydroxyphenyl) propionate], and the auxiliary antioxidant includes at least one of thiodipropionic acid diester and tris[2,4-di-tert-butylphenyl] phosphite.

[0079] In some embodiments, the primary antioxidant comprises pentaerythritol tetrakis[β-(3,5-tert-butyl-4-hydroxyphenyl)propionate] (1010), and the secondary antioxidant comprises tris[2,4-di-tert-butylphenyl]phosphite (168). In some embodiments, the modified polylactic acid is completely degradable.

[0080] In existing technologies, improving the mechanical properties of modified polylactic acid often requires blending it with other poorly degradable engineering plastics. While this improves the mechanical properties of the modified polylactic acid, the modified polylactic acid cannot be fully degraded, failing to meet environmental protection requirements and limiting its application. The modified polylactic acid provided in the undisclosed examples achieves improved mechanical properties while maintaining full degradability.

[0081] The second aspect of the present application provides a method for preparing modified polylactic acid, which comprises: blending polylactic acid and a chain extender, and preparing the modified polylactic acid of the first aspect of the present application by an extrusion process.

[0082] In some embodiments, the preparation method includes: drying the polylactic acid before the extrusion process at a drying temperature of 60°C to 80°C.

[0083] In some embodiments, the extrusion process includes reacting at a temperature of not less than 200° C. for not less than 2 minutes.

[0084] In some embodiments, the extrusion process includes reacting at 200° C. for 2 minutes.

[0085] In some embodiments, the extrusion process includes reacting at 210° C. for 3 minutes.

[0086] Reacting at a temperature of not less than 200°C for not less than 2 minutes is beneficial for the epoxy groups of the chain extender to fully undergo a ring-opening reaction, thereby effectively modifying the polylactic acid. In some embodiments, the extrusion process includes a screw speed of 150 to 170 rpm.

[0087] In some embodiments, the extrusion screw speed is 150 rpm, 155 rpm, 160 rpm, 165 rpm, 170 rpm, or any value therebetween.

[0088] Controlling the screw speed can control the reaction time in a temperature range of not less than 200°C, thereby ensuring that the ring-opening reaction of the epoxy group proceeds fully.

[0089] In some embodiments, the extrusion temperature is 160°C-180°C in zone 1, 170°C-190°C in zone 2, 170°C-190°C in zone 3, 200°C-210°C in zone 4, 190°C-200°C in zone 5, 170°C-190°C in zone 6, the die head temperature is 170°C-190°C, and the screw speed is 150r / min~170r / min, so that the time for the material to pass through the four zones is at least two minutes.

[0090] In some embodiments, the modified polylactic acid further comprises an antioxidant.

[0091] It is generally believed in the prior art that high processing temperatures can easily lead to thermal degradation of polylactic acid, hindering its thermal stability. Although the mechanism is unclear, the present examples unexpectedly discovered that an extrusion process including a reaction temperature of not less than 200°C for not less than 2 minutes further improves the thermal stability and thermodynamic properties of the modified polylactic acid. This is presumably due to the synergistic effect of the primary antioxidant, secondary antioxidant, and chain extender at this temperature.

[0092] The third aspect of the present application provides a polylactic acid fiber, which comprises polylactic acid and the modified polylactic acid provided in the first aspect of the present application or the modified polylactic acid prepared by the preparation method provided in the second aspect of the present application.

[0093] This polylactic acid fiber has both good mechanical properties and excellent degradability. The polylactic acid is chain-extended and modified using a chain extender. The chain extender introduces other chain segments and active functional groups into the polylactic acid molecular chain to increase the molecular weight of the polylactic acid and change its structure, thereby improving the mechanical properties of the chain-extended polylactic acid, which in turn helps improve the mechanical properties of the polylactic acid fiber. The content of the chain extender as an auxiliary agent in the modified polylactic acid is low, and will not have too much negative impact on the degradability of the polylactic acid fiber. The blending of polylactic acid and modified polylactic acid further reduces the content of the chain extender in the polylactic acid fiber, allowing the polylactic acid fiber to fully utilize its degradable advantages.

[0094] In some embodiments, based on the total mass of the polylactic acid fiber, the mass proportion of the modified polylactic acid is less than 33%, and can be optionally 1%-20%.

[0095] In some embodiments, based on the total mass of the polylactic acid fiber, the mass content of the modified polylactic acid can be selected as 1%, 4.76%, 5%, 9.09%, 10%, 15%, 16.67%, 20%, 25%, 30%, 32% or any numerical range therebetween.

[0096] The molecular weight of the modified PLA after chain extender modification increases, resulting in a high shear viscosity, making melt spinning difficult. Modified PLA within the aforementioned mass ratio can improve spinnability by blending with PLA, effectively reducing the cost of PLA fiber while improving its mechanical properties.

[0097] In some embodiments, the polylactic acid fibers are capable of substantially complete degradation.

[0098] In existing technologies, improving the mechanical properties of polylactic acid fibers often requires blending polylactic acid with other poorly degradable resins before spinning. While this improves the mechanical properties of polylactic acid fibers, polylactic acid fibers are difficult to fully and effectively decompose in natural environments, failing to meet environmental protection requirements and limiting their application. The modified polylactic acid provided in the embodiments of the present disclosure improves mechanical properties while maintaining a high degree of degradability.

[0099] In some embodiments, the tensile strength at break of the polylactic acid fiber is greater than 1.05 cN / dtex, and may be in the range of 1.5 cN / dtex to 2 cN / dtex.

[0100] The breaking strength of polylactic acid fibers can be measured according to ASTM D2256-2002, "Standard Test Method for Tensile Properties of Yarn Using the Single-Strand Method." The tensile strength of the polylactic acid fibers provided in the examples of this application is measured in centinewon / dtex (cN / dtex), where dtex refers to the weight in grams per 10,000-meter-long fiber bundle and centinewon refers to 0.01 Newton.

[0101] In some embodiments, the tensile strength at break of the polylactic acid fiber can be selected as 1.05 cN / dtex, 1.1 cN / dtex, 1.2 cN / dtex, 1.3 cN / dtex, 1.4 cN / dtex, 1.5 cN / dtex, 1.6 cN / dtex, 1.7 cN / dtex, 1.8 cN / dtex, 1.9 cN / dtex, 2 cN / dtex or any range of values ​​therebetween.

[0102] The polylactic acid fiber has high tensile strength and can improve the tensile resistance of fiber products.

[0103] In some embodiments, the elongation at break of the polylactic acid fiber is greater than or equal to 35%, and can be optionally 35%-90%.

[0104] The elongation at break of polylactic acid fibers can be measured with reference to ASTM D2256-2002, “Standard Test Method for Tensile Properties of Yarn by Single-Twist Method”.

[0105] The elongation at break of the polylactic acid fiber can be selected to be 35%, 40%, 45%, 50%, 60%, 70%, 80%, 90% or any numerical range therebetween.

[0106] The polylactic acid fiber with an elongation at break within the above range has both good processability (such as spinnability) and a certain stiffness, and will not be easily deformed due to an excessively high elongation at break.

[0107] In some embodiments, the linear density of the polylactic acid fiber is 130 decitex (dtex) to 150 dtex.

[0108] In some embodiments, the linear density of the polylactic acid fiber can be selected as 130 dtex, 135 dtex, 140 dtex, 145 dtex, 150 dtex, or any range therebetween.

[0109] In some embodiments, the tensile strength at break of the polylactic acid fiber is greater than 1.5 cN / dtex, and the elongation at break of the polylactic acid fiber is greater than 40%.

[0110] The improvement of the strength of polylactic acid fiber often comes at the expense of its elongation at break. This polylactic acid fiber has both high elongation at break and high elongation at break, which can improve both mechanical properties and processability.

[0111] In some embodiments, the crystallinity of the polylactic acid fiber is greater than or equal to 10%, and can be optionally 10%-30%.

[0112] The crystallinity was measured by a two-dimensional wide-angle X-ray diffractometer (2D-WAXD, Bruker, Germany). The detector (2048x2048 pixels) was equipped with Cu Kα as the light source, with a wavelength of 0.154 nm, a voltage of 40 kV, and a current of 40 mA. The crystallinity was calculated by calculating the ratio of the crystallization peak of the polylactic acid fiber to the total peak area in the X-ray spectrum.

[0113] In some embodiments, the crystallinity of the polylactic acid fiber can be selected to be 10%, 15%, 20%, 25%, 30% or any range therebetween.

[0114] Increasing the crystallinity is beneficial to improving the mechanical strength of polylactic acid fibers, but too high a crystallinity can lead to brittle fracture. Polylactic acid fibers with a crystallinity within the above range have both good mechanical strength and processability.

[0115] In some embodiments, the orientation factor of the polylactic acid fiber is greater than or equal to 0.90, and can be optionally 0.90-0.97.

[0116] The orientation factor was measured by a two-dimensional wide-angle X-ray diffractometer (2D-WAXD, Bruker, Germany). Detector (2048x2048 pixels), Cu Kα light source, light source wavelength 0.154nm, voltage 40kV, current 40mA. The orientation factor can be calculated by the following formula,

[0117] Where f is the orientation factor of the crystal phase, and FWHM is the half-peak width of the phase orientation curve of the (110) crystal plane and (200) crystal plane obtained by fitting a single peak with the Lorentz function. When the crystal plane is completely parallel to the fiber axis, the f value is 1. When the crystal plane is arranged in a random direction, the f value is 0. Since the (110) crystal plane and the (200) crystal plane are the main crystal planes in the polylactic acid fiber, and their peak positions are close, the two crystal plane peaks overlap with each other, making it difficult to completely distinguish the two. Therefore, the orientation factor of the polylactic acid fiber is evaluated based on the (110) crystal plane and the (200) crystal plane directions.

[0118] The increase in orientation factor is beneficial to improving the molecular orientation of polylactic acid fibers and improving the mechanical strength of polylactic acid fibers. Polylactic acid fibers with an orientation factor within the above range have good mechanical properties.

[0119] In some embodiments, the preparation method of the polylactic acid fiber includes: mixing polylactic acid resin and modified polylactic acid resin to obtain a mixture; melt-spinning the mixture to obtain spun fibers, and hot-drawing the spun fibers to obtain the polylactic acid fiber.

[0120] Melt spinning is a forming method that uses polymer melt as raw material and adopts melt spinning machine to spin.

[0121] Hot stretching utilizes the thermoplasticity of fibers. During the heating and stretching process, the molecular structure of the primary fibers changes, making them more slender, softer and stronger.

[0122] In some embodiments, the temperature of the heat drawing is less than 100°C.

[0123] In some embodiments, the temperature of the heat drawing can be selected from room temperature, 60°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or any range therebetween.

[0124] It is understood that room temperature refers to 25±5° C. The temperature of the heat drawing may include a plurality of different temperature intervals.

[0125] The heat drawing temperature is less than 100° C., which is beneficial to improving the flexibility of the polylactic acid fiber and its structural stability.

[0126] In some embodiments, the spinning speed of the melt spinning is less than 3 km / min.

[0127] The winding speed of the spun fiber was used as the spinning speed of the melt spinning.

[0128] In some embodiments, the spinning speed of melt spinning can be selected to be 0.5 km / min, 1 km / min, 1.5 km / min, 2 km / min, 2.5 km / min, or any range therebetween.

[0129] Excessively high spinning speeds increase the tensile strength of PLA fibers, but reduce their elongation at break. PLA fibers with too low an elongation at break cannot be bundled and wound, making them difficult to reel and subsequently process into fiber substrates and fiber products. Melt spinning at speeds below 3 km / min ensures PLA fibers have good spinnability and are suitable for subsequent processing.

[0130] The fourth aspect of the present application provides a plastic substrate, which includes the modified polylactic acid provided by the first aspect of the present application, or the modified polylactic acid prepared by the preparation method provided by the second aspect of the present application, or the polylactic acid fiber provided by the third aspect of the present application.

[0131] In some embodiments, the plastic substrate is a nonwoven fabric.

[0132] Non-woven fabrics, also known as non-woven fabrics, are made of directional or random fibers. They are breathable, thin, flexible, non-flammable, non-toxic, non-irritating, and inexpensive.

[0133] The non-woven fabric formed from the modified polylactic acid provided in this application has the characteristics of high mechanical strength, good processing performance, and is completely degradable.

[0134] A fifth aspect of the present application provides a plastic product, wherein the plastic product is prepared from the plastic substrate according to any embodiment of the present application.

[0135] In some embodiments, the plastic product is a desiccant package.

[0136] It can be understood that the desiccant packaging product includes any form of desiccant packaging product, such as a desiccant bag.

[0137] Desiccant refers to a reagent with a drying effect. In some embodiments, the desiccant includes silica gel, alumina gel, molecular sieves, activated carbon, bone charcoal, charcoal, mineral desiccant, phosphorus pentoxide, anhydrous copper sulfate, lime, soda lime, anhydrous calcium chloride, and anhydrous magnesium sulfate.

[0138] In some embodiments, the desiccant comprises a clay-based desiccant. In some embodiments, the clay-based desiccant comprises bentonite. This desiccant has a fast adsorption rate, a strong adsorption capacity, and is fully biodegradable.

[0139] The modified polylactic acid provided herein possesses sufficient mechanical strength and processing properties, allowing it to be directly used in the preparation of desiccant packaging products. There is no need to mix it with non-biodegradable engineering plastics such as polyethylene and polypropylene to improve the mechanical properties of the desiccant packaging, nor is there a need to mix it with non-biodegradable additives to improve processing performance. As a result, the prepared desiccant packaging products possess both excellent mechanical properties and biodegradability.

[0140] Example

[0141] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0142] 1. Preparation method:

[0143] Example 1

[0144] Polylactic acid L130, styrene-glycidyl methacrylate copolymer chain extender (BASF ADR-4468), and antioxidant 1010 (RIANOX 1010 from Rianlon, with a chemical composition of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) were added into a twin-screw extruder at a mass ratio of 99.1:0.6:0.3, and the mixture was melt-blended, extruded, and granulated to obtain modified polylactic acid.

[0145] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0146] The chain extender is a styrene-glycidyl methacrylate copolymer, and the structural formula of the chain extender is shown in Formula II.

[0147] R1, R2, R3, R4, R5, and R6 each independently include an organic group, x:y:z is (1-5):(3-7):(5-10), and the structural units are randomly copolymerized.

[0148] The chain extender is a polyvalent epoxy chain extender. The infrared spectrum of the chain extender is shown in FIG1 , and the infrared spectrum of the chain extender is located at 860 cm -1 -870cm -1 The characteristic peak of epoxy group at 3000cm -1 -3300cm -1 The ratio of the carbon-hydrogen bond stretching vibration peak at is 3.3.

[0149] Example 2

[0150] Polylactic acid L130, styrene-glycidyl methacrylate copolymer chain extender (the same as in Example 1), and antioxidant 168 (RIANOX 168 from Rianlon, with a chemical composition of tris[2,4-di-tert-butylphenyl]phosphite) were added to a twin-screw extruder in a mass ratio of 99.1:0.6:0.3 and a mass ratio of 99.4:0.6, and melt-blended and extruded into granules through a twin-screw extruder to obtain modified polylactic acid.

[0151] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0152] Example 3

[0153] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 1), antioxidant 1010 (the same as in Example 1), and antioxidant 168 (the same as in Example 2) were melt-blended and extruded into granules in a mass ratio of 99.1:0.6:0.2:0.1 through a twin-screw extruder to obtain modified polylactic acid.

[0154] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0155] Example 4

[0156] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 1), antioxidant 1010 (the same as in Example 1), and antioxidant 168 (the same as in Example 2) were melt-blended and extruded into granules in a mass ratio of 99.1:0.6:0.1:0.2 through a twin-screw extruder to obtain modified polylactic acid.

[0157] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0158] Example 5

[0159] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 1), antioxidant 1010 (the same as in Example 1), and antioxidant 168 (the same as in Example 2) were added to a twin-screw extruder in a mass ratio of 99.1:0.6:0.1:0.2, and melt-blended and extruded into granules through a twin-screw extruder to obtain modified polylactic acid.

[0160] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 180r / min, so that the time for the material to pass through the four zones is 1 minute.

[0161] Example 6

[0162] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 1), antioxidant 1010 (the same as in Example 1), and antioxidant 168 (the same as in Example 2) were added to a twin-screw extruder in a mass ratio of 99.1:0.6:0.1:0.2, and melt-blended and extruded into granules through a twin-screw extruder to obtain modified polylactic acid.

[0163] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 195°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is 2 minutes.

[0164] Example 7

[0165] Polylactic acid L130, styrene-glycidyl methacrylate copolymer chain extender (BASF ADR-4468), and antioxidant 1010 (RIANOX 1010 from Rianlon, with a chemical composition of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) were added into a twin-screw extruder at a mass ratio of 99.1:0.6:0.3, and the mixture was melt-blended, extruded, and granulated to obtain modified polylactic acid.

[0166] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0167] Example 8

[0168] Polylactic acid L130, styrene-glycidyl methacrylate copolymer chain extender (the same as in Example 7), and antioxidant 168 (RIANOX 168 from Rianlon, with a chemical composition of tris[2,4-di-tert-butylphenyl]phosphite) were added to a twin-screw extruder in a mass ratio of 99.1:0.6:0.3, and the mixture was melt-blended, extruded, and granulated to obtain modified polylactic acid.

[0169] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0170] Example 9

[0171] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 7), antioxidant 1010 (the same as in Example 7), and antioxidant 168 (the same as in Example 8) were melt-blended and extruded into granules in a mass ratio of 99.1:0.6:0.2:0.1 through a twin-screw extruder to obtain modified polylactic acid.

[0172] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0173] Example 10

[0174] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 7), antioxidant 1010 (the same as in Example 7), and antioxidant 168 (the same as in Example 8) were melt-blended and extruded into granules in a mass ratio of 99.1:0.6:0.1:0.2 through a twin-screw extruder to obtain modified polylactic acid.

[0175] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0176] Example 11

[0177] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 7), antioxidant 1010 (the same as in Example 7), and antioxidant 168 (the same as in Example 8) were added to a twin-screw extruder in a mass ratio of 99.1:0.6:0.1:0.2, and melt-blended and extruded into granules through a twin-screw extruder to obtain modified polylactic acid.

[0178] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 180r / min, so that the time for the material to pass through the four zones is 1 minute.

[0179] Example 12

[0180] Polylactic acid L130, styrene-methylglycidyl methacrylate copolymer chain extender (the same as in Example 7), antioxidant 1010 (the same as in Example 7), and antioxidant 168 (the same as in Example 8) were added to a twin-screw extruder in a mass ratio of 99.1:0.6:0.1:0.2, and melt-blended and extruded into granules through a twin-screw extruder to obtain modified polylactic acid.

[0181] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 195°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is 2 minutes.

[0182] Example 13

[0183] (1) Preparation of modified polylactic acid

[0184] Polylactic acid L130 and styrene-glycidyl methacrylate copolymer chain extender (BASF ADR-4468) were added into a twin-screw extruder at a mass ratio of 99.4:0.6, and melt-blended and extruded into granules through the twin-screw extruder to obtain a modified polylactic acid resin.

[0185] The temperature of the twin-screw extruder is 175°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is two minutes.

[0186] (2) Preparation of polylactic acid fiber

[0187] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 20:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The resulting spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roller for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25±5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 1 km / min.

[0188] The preparation methods of the modified polylactic acid in Examples 14-21 are the same as those in Example 13, except that the preparation method of the polylactic acid fiber is adjusted.

[0189] Example 14

[0190] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 10:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roller for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25 ± 5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 1 km / min.

[0191] Example 15

[0192] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 5:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roll for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25 ± 5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 1 km / min.

[0193] Example 16

[0194] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 20:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The resulting spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roll for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25±5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 1.5 km / min.

[0195] Example 17

[0196] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 10:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roll for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25±5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 1.5 km / min.

[0197] Example 18

[0198] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 5:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roll for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25 ± 5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 1.5 km / min.

[0199] Example 19

[0200] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 20:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The resulting spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roller for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25±5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 2 km / min.

[0201] Example 20

[0202] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 10:1. The mixture was melt-spun and hot-stretched to produce PLA fibers. The spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roller for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25 ± 5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 2 km / min.

[0203] Example 21

[0204] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 5:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roll for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25 ± 5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 2 km / min.

[0205] The sample in Comparative Example 1 was prepared from pure polylactic acid, and the preparation process was the same as in Example 1.

[0206] Comparative Example 2

[0207] Polylactic acid L130 and styrene (St)-methyl methacrylate (MMA)-glycidyl methacrylate chain extender (BASF ADR-4370) were added into a twin-screw extruder at a mass ratio of 99.4:0.6, and melt-blended and extruded into granules through the twin-screw extruder to obtain modified polylactic acid.

[0208] The temperature of the twin-screw extruder is 180°C in zone 1, 185°C in zone 2, 185°C in zone 3, 200°C in zone 4, 195°C in zone 5, and 180°C in zone 6. The die head temperature is 185°C, the material temperature is 185°C, and the screw speed is 160r / min, so that the time for the material to pass through the four zones is 2 minutes.

[0209] In the infrared spectrum of the chain extender, the -1 -870cm -1 The characteristic peak of epoxy group at 3000cm -1 -3300cm -1 The ratio of the carbon-hydrogen bond stretching vibration peak at is 1.7.

[0210] Comparative Example 3

[0211] Polylactic acid L130, styrene (St)-methyl methacrylate (MMA)-glycidyl methacrylate chain extender (BASF ADR-4370), antioxidant 1010 (the same as in Example 8), and antioxidant 168 (the same as in Example 9) were added to a twin-screw extruder in a mass ratio of 99.1:0.6:0.1:0.2, and melt-blended and extruded into granules through the twin-screw extruder to obtain modified polylactic acid.

[0212] Comparative Example 4

[0213] Pure polylactic acid (PLA) L130 is melt-spun and heat-stretched to produce PLA fibers. The resulting spun fibers are passed through five heated rollers, namely the first, second, third, fourth, and fifth rollers, before being collected on a winding roller. The rotational speeds of the five heated rollers are 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers are room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, where room temperature is 25±5°C. The draft ratio is fixed at 1.4. A first heating plate is placed along the path from the third to the fourth roller, and a second heating plate is placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates are 95°C and 85°C, respectively. The spinning speed of the spun fibers is 1 km / min.

[0214] Comparative Example 5

[0215] PLA L130 and the prepared modified PLA resin PLA-SM were mixed in a mass ratio of 2:1. The resulting mixture was melt-spun and heat-stretched to produce PLA fibers. The spun fibers were passed through five heated rollers, the first, second, third, fourth, and fifth, in sequence, before reaching a take-up roller for collection. The speeds of the five heated rollers were 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers were room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, with room temperature being 25±5°C. The draft ratio was fixed at 1.4. A first heating plate was placed along the path from the third to the fourth roller, and a second heating plate was placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates were 95°C and 85°C, respectively. The spinning speed of the spun fibers was 1 km / min.

[0216] Comparative Example 6

[0217] Pure polylactic acid (PLA) L130 is melt-spun and heat-stretched to produce PLA fibers. The resulting spun fibers are passed through five heated rollers, namely the first, second, third, fourth, and fifth rollers, in sequence, before reaching a take-up roller for collection. The rotational speeds of the five heated rollers are 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers are room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, where room temperature is 25±5°C. The draft ratio is fixed at 1.4. A first heating plate is placed along the path from the third to the fourth roller, and a second heating plate is placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates are 95°C and 85°C, respectively. The spinning speed of the spun fibers is 1.5 km / min.

[0218] Comparative Example 7

[0219] Pure polylactic acid (PLA) L130 is melt-spun and heat-stretched to produce PLA fibers. The resulting spun fibers are passed through five heated rollers, namely the first, second, third, fourth, and fifth rollers, in sequence, before reaching a winding roller for collection. The rotational speeds of the five heated rollers are 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers are respectively room temperature, 75°C, 90°C, 95°C, and room temperature, where room temperature is 25±5°C. The draft ratio is fixed at 1.4. A first heating plate is placed along the path from the third to the fourth roller, and a second heating plate is placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates are 95°C and 85°C, respectively. The spinning speed of the spun fibers is 2 km / min.

[0220] Comparative Example 8

[0221] Pure polylactic acid (PLA) L130 is melt-spun and heat-stretched to produce PLA fibers. The resulting spun fibers are passed through five heated rollers, namely the first, second, third, fourth, and fifth rollers, before being collected on a winding roller. The speeds of the five heated rollers are 125 m / min, 125 m / min, 170 m / min, 175 m / min, and 175 m / min, respectively. The temperatures of the five heated rollers are room temperature, 75°C, 90°C, 95°C, and room temperature, respectively, where room temperature is 25±5°C. The draft ratio is fixed at 1.4. A first heating plate is placed along the path from the third to the fourth roller, and a second heating plate is placed along the path from the fourth to the fifth roller to heat the fibers. The temperatures of the first and second heating plates are 95°C and 85°C, respectively. The spinning speed of the spun fibers is 2.5 km / min.

[0222] 2. Test methods

[0223] (1) Tensile strength and elongation at break test methods

[0224] The tensile strength and elongation at break are tested in accordance with the national standard GB 13022-91 “Test method for tensile properties of plastics and films”.

[0225] (2) Melt index test method

[0226] The melt index is tested in accordance with the national standard ISO 1133-1:2022 "Plastics. Determination of melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics. Part 1: Standard method". The test temperature is 190°C and the test load is 2.16 kg.

[0227] (3) Weight loss rate test method

[0228] The isothermal weight loss rate was tested using a DHG-9075A electric constant temperature blast drying oven. The sample was placed in an electric oven in an air environment to accelerate aging under the action of heat and oxygen. The weight loss rate after 4 hours of thermal oxygen aging at 220°C was calculated using the following formula:

[0229] W%=[(Wo-W) / Wo]×100%

[0230] Where W% is the isothermal weight loss rate, Wo is the initial mass of the sample, and W is the residual mass of the sample after thermal oxidative aging at 220°C for 4 h.

[0231] (4) Weight average molecular weight test method

[0232] The weight average molecular weight of the modified polylactic acid was determined by gel permeation chromatography. The test method was as follows: the sample was dissolved in chloroform at room temperature and the molecular weight was calibrated by gel permeation chromatography.

[0233] (5) Contact angle test method

[0234] The static contact angle method was used to measure the contact angle of the modified polylactic acid. The testing instrument was a contact angle meter and the testing standard was ISO 8296.

[0235] (6) Infrared spectrum testing method

[0236] Infrared spectra are used to characterize the functional groups of organic matter. The testing instrument is a Fourier transform infrared spectrometer and the testing method is a tablet pressing method.

[0237] (7) Linear density test

[0238] The test was carried out according to ASTM D2256-2002, a standard test method for determining the tensile properties of yarns by the single twist method.

[0239] (8) Breaking strength and breaking elongation test

[0240] The test was carried out according to ASTM D2256-2002, a standard test method for determining the tensile properties of yarns using a single twisted wire method. Specifically, the breaking strength was calculated according to the following formula:

[0241] B=F / T

[0242] F is the force corresponding to the fiber breaking, unit is cN; T is the linear density, unit is dtex; B is the breaking strength, unit is cN / dtex.

[0243] 3. Performance data

[0244] The test results of the embodiments and comparative examples are shown in Table 1.

[0245] Table 1

[0246] From the comparison of the embodiments and comparative examples, it can be seen that the tensile strength of the modified polylactic acid provided in the present application is not less than 45 MPa, and the melt flow rate of the modified polylactic acid is not less than 2 g / 10 min at 180°C-200°C and a load of 2kg-3kg.

[0247] From the comparison between Example 2 and Examples 5 and 6, it can be seen that including a reaction at a temperature of not less than 200° C. for not less than 2 minutes in the extrusion process can further improve the mechanical strength of the modified polylactic acid.

[0248] Table 2

[0249] Table 3

[0250] From the comparison of the examples and comparative examples in Table 3, it can be seen that the modified polylactic acid provided in the examples of the present application can take into account both mechanical properties and thermal stability.

[0251] From the comparison of Examples 7-10, it can be seen that the inclusion of both the primary antioxidant and the auxiliary antioxidant in the modified polylactic acid can further reduce the thermal weight loss rate of the polylactic acid.

[0252] From the comparison of Examples 10-12, it can be seen that the thermal weight loss rate of polylactic acid can be further reduced by including a reaction at not less than 200° C. for not less than 2 minutes during the extrusion process of the modified polylactic acid.

[0253] From the comparison between Example 10 and Comparative Example 3, it can be seen that the infrared spectrum of the chain extender in the modified polylactic acid is located at 860 cm -1 -870cm -1 The characteristic peak of epoxy group at 3000cm -1 -3300cm -1 The ratio of the carbon-hydrogen bond stretching vibration peak at is not less than 2.1, which helps to further reduce the thermal weight loss rate of polylactic acid and achieve simultaneous improvement of thermal stability and mechanical properties.

[0254] Table 4

[0255] Table 5

[0256] Table 6

[0257] Comparison of the examples and comparative examples shows that the mechanical strength of the PLA fibers, including both PLA and modified PLA, is significantly improved compared to PLA. In Comparative Example 5, due to the excessively high content of modified PLA, the nascent fibers were difficult to wind during the melt spinning process, resulting in the inability to spin the PLA fibers.

[0258] Figure 2 shows two-dimensional X-ray diffraction patterns of the polylactic acid fibers of Example 13 and Comparative Example 4 of the present application. As can be seen from the figure, the polylactic acid fibers of Example 13, to which a small amount of modified polylactic acid is added, exhibit bright and sharp diffraction spots, while the two-dimensional X-ray diffraction pattern of the polylactic acid fibers of Comparative Example 4 only shows diffuse signals. These results demonstrate that the addition of a small amount of modified polylactic acid can effectively increase the crystallinity and orientation of polylactic acid fibers, thereby effectively improving the mechanical properties of the polylactic acid fibers.

[0259] As can be seen from Tables 4 to 6, by adjusting the added content of modified polylactic acid and the spinning rate, the polylactic acid fiber can have both good strength and elongation at break.

[0260] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A modified polylactic acid, wherein: The tensile strength of the modified polylactic acid is not less than 45 MPa, and the melt flow rate of the modified polylactic acid is not less than 2 g / 10 min at 180° C.-200° C. and a load of 2 kg-3 kg.

2. The modified polylactic acid according to claim 1, wherein The tensile strength of the modified polylactic acid is 45MPa-100MPa, and can be optionally 50MPa-60MPa.

3. The modified polylactic acid according to claim 1 or 2, wherein The melt flow rate of the modified polylactic acid is 2g / 10min-10g / 10min, and can be optionally 2g / 10min-6g / 10min.

4. The modified polylactic acid according to any one of claims 1 to 3, wherein The weight average molecular weight of the modified polylactic acid is 100,000-200,000, and can be 100,000-150,000; and / or The polydispersity coefficient of the modified polylactic acid is 1.7-2.

2.

5. The modified polylactic acid according to any one of claims 1 to 4, wherein The weight loss rate of the modified polylactic acid after heat aging for 4 hours in an air environment at 200° C.-230° C. is not higher than 0.8%, and can be optionally 0.1%-0.5%.

6. The modified polylactic acid according to any one of claims 1 to 5, wherein The elongation at break of the modified polylactic acid is not less than 2%, and can be selected to be 2.5%-4%.

7. The modified polylactic acid according to any one of claims 1 to 6, wherein The modified polylactic acid comprises a structure shown in formula I Wherein, A1 and A2 each independently include carboxyl, hydroxyl, At least one of; R includes R1, R2, R3, R4, R5, and R6 each independently include an organic group, x:y:z is (1-5):(3-7):(5-10), and the structural units are randomly copolymerized.

8. The modified polylactic acid according to any one of claims 1 to 7, wherein The contact angle of the modified polylactic acid is not less than 63°, and can be selected to be 63°-80°.

9. The modified polylactic acid according to any one of claims 1 to 8, wherein The modified polylactic acid comprises polylactic acid and a chain extender, wherein the chain extender is an epoxy chain extender, and the infrared spectrum of the chain extender is located at 860cm -1 -870cm - 1 The characteristic peak of epoxy group at 3000cm -1 -3300cm -1 The ratio of the carbon-hydrogen bond stretching vibration peak at is not less than 2.

1.

10. The modified polylactic acid according to claim 9, wherein Based on the total mass of the modified polylactic acid, the mass percentage of the chain extender is 0.1%-2.0%, and can be optionally 0.4%-1.0%.

11. The modified polylactic acid according to any one of claims 1 to 10, wherein The modified polylactic acid also includes an antioxidant.

12. The modified polylactic acid according to claim 11, wherein The antioxidant includes a primary antioxidant and an auxiliary antioxidant. Optionally, the primary antioxidant includes at least one of a hindered phenol antioxidant and an aromatic amine antioxidant. The hindered phenol antioxidant includes at least one of 2,6-tert-butyl-4-methylphenol, bis(3,5-tert-butyl-4-hydroxyphenyl) sulfide, and pentaerythritol tetrakis[β-(3,5-tert-butyl-4-hydroxyphenyl) propionate. Optionally, the auxiliary antioxidant includes at least one of thiodipropionic acid diester and tris[2.4-di-tert-butylphenyl] phosphite.

13. The modified polylactic acid according to claim 11 or 12, wherein Based on the total mass of the modified polylactic acid, the mass percentage of the antioxidant is 0.1%-1%, and can be optionally 0.1%-0.5%.

14. A method for preparing modified polylactic acid, wherein: The preparation method comprises: The polylactic acid is blended with a chain extender and an extrusion process is adopted to prepare the modified polylactic acid according to any one of claims 1 to 13.

15. The preparation method according to claim 14, wherein: The extrusion process includes reacting at a temperature not lower than 200° C. for not less than 2 minutes.

16. The preparation method according to claim 14 or 15, wherein: The extrusion process includes an extrusion screw speed of 150 to 170 rpm.

17. The preparation method according to any one of claims 14 to 16, wherein The modified polylactic acid also includes an antioxidant.

18. A polylactic acid fiber, wherein: The polylactic acid fiber comprises polylactic acid and the modified polylactic acid described in any one of claims 1 to 13 or the modified polylactic acid prepared by the preparation method described in any one of claims 14 to 17.

19. The polylactic acid fiber according to claim 18, wherein Based on the total mass of the polylactic acid fiber, the mass proportion of the modified polylactic acid is less than 33%, and can be optionally 1%-20%.

20. The polylactic acid fiber according to claim 18 or 19, wherein The tensile breaking strength of the polylactic acid fiber is greater than 1.05 cN / dtex, and can be selected to be 1.5 cN / dtex-2 cN / dtex.

21. The polylactic acid fiber according to any one of claims 18 to 20, wherein The elongation at break of the polylactic acid fiber is greater than or equal to 35%, and can be selected from 35% to 90%.

22. The polylactic acid fiber according to any one of claims 18 to 21, wherein The linear density of the polylactic acid fiber is 130dtex-150dtex.

23. The polylactic acid fiber according to any one of claims 18 to 22, wherein The crystallinity of the polylactic acid fiber is greater than or equal to 10%, and can be optionally 10%-30%.

24. The polylactic acid fiber according to any one of claims 18 to 23, wherein The orientation factor of the polylactic acid fiber is greater than or equal to 0.90, and can be selected to be 0.90-0.

97.

25. The polylactic acid fiber according to any one of claims 18 to 24, wherein The preparation method of the polylactic acid fiber comprises: Mixing polylactic acid resin and modified polylactic acid resin to obtain a mixture; Melt spinning the mixed material to obtain nascent fibers; The polylactic acid fiber is obtained by heat drawing the spun fiber.

26. The polylactic acid fiber according to claim 25, wherein The temperature of the heat drawing is room temperature-100°C.

27. The polylactic acid fiber according to claim 25, wherein The spinning speed of the melt spinning is less than 3 km / min.

28. A plastic substrate, wherein The plastic substrate comprises the modified polylactic acid according to any one of claims 1 to 13, or the modified polylactic acid prepared by the preparation method according to any one of claims 14 to 17, or the polylactic acid fiber according to any one of claims 18 to 27.

29. The plastic substrate according to claim 28, wherein The plastic substrate is non-woven fabric.

30. A plastic product, wherein the plastic product is prepared from the plastic substrate according to claim 28 or 29.

31. The plastic article according to claim 30, wherein: The plastic product is a desiccant packaging product.

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