Foaming bead and preparation method thereof

Abstract

The invention provides a foamed bead and a preparation method thereof. The foamed bead comprises poly-L-lactic acid and poly-D-lactic acid, wherein the mass percentage content of an L-lactic acid monomer of the poly-L-lactic acid is greater than or equal to 98%; the mass percentage content of a dextrolactic acid monomer of the poly-dextrolactic acid is greater than or equal to 98%. The foamed bead provided by the embodiment of the invention comprises poly-L-lactic acid with high optical purity and poly-D-lactic acid with high optical purity, and the poly-L-lactic acid and the poly-D-lactic acid form a stereocomplex crystal in the processing process, so that the thermally induced deformation temperature of the foamed bead is increased.

Description

Technical Field

[0001] The present application relates to the field of foam beads, and in particular to foam beads and a preparation method thereof. Background Art

[0002] Foam plastics have become a popular material in the packaging industry due to their lightweight, cushioning, and thermal insulation properties. Among bio-based biodegradable foam plastics, foam beads offer a unique combination of high expansion ratios (>20x) and the ability to create complex geometries.

[0003] In recent years, biodegradable foam beads are prepared by extrusion foaming using polylactic acid (PLA) as the main material, including crystalline PLA, amorphous PLA and PLA blends.

[0004] However, when PLA is used in packaging materials, it may be exposed to high temperature environments in specific usage scenarios or during transportation, causing the packaging materials to deform and resulting in damage to the product during transportation. Summary of the Invention

[0005] The embodiments of the present application provide a foamed bead and a preparation method thereof, aiming to improve the technical problem of deformation of packaging materials caused by poor temperature resistance of PLA.

[0006] In order to achieve the above objectives, in a first aspect, embodiments of the present application provide a foamed bead, wherein the foamed bead comprises the following components in parts by mass:

[0007] 3-55 parts of poly (L-lactic acid);

[0008] 3-20 parts of poly (dextrose) lactic acid;

[0009] 40-90 parts of forming regulator;

[0010] 1 to 5 parts of chain extender masterbatch;

[0011] 3-12 parts of foaming agent;

[0012] Wherein, the mass percentage of L-lactic acid monomer of the poly-L-lactic acid is greater than or equal to 98%;

[0013] The mass percentage of the dextrorotatory lactic acid monomer in the poly (dextrorotatory lactic acid) is greater than or equal to 98%.

[0014] Optionally, in some embodiments of the present application, the mass percentage of L-lactic acid monomer in the poly-L-lactic acid is greater than or equal to 99%; and / or

[0015] The mass percentage of the dextrorotatory lactic acid monomer in the poly (dextrose) lactic acid is greater than or equal to 99%.

[0016] Optionally, in some embodiments of the present application, the mass ratio of the poly-L-lactic acid to the poly-D-lactic acid ranges from 1 to 5.

[0017] Optionally, in some embodiments of the present application, the melt index of the poly-L-lactic acid ranges from 2 g / 10 min to 20 g / 10 min; and / or

[0018] The melt index of the poly (D-lactic acid) ranges from 2 g / 10 min to 50 g / 10 min.

[0019] Optionally, in some embodiments of the present application, the foamed beads meet at least one of the following conditions:

[0020] The thermal deformation temperature of the foamed beads is greater than or equal to 100°C;

[0021] The maximum melting temperature of the foamed beads ranges from 200°C to 240°C.

[0022] Optionally, in some embodiments of the present application, the molding regulator includes a second poly-L-lactic acid or poly (butylene terephthalate-adipate), and the mass percentage of D-lactic acid in the second poly-L-lactic acid is greater than or equal to 4% and less than or equal to 8%.

[0023] Optionally, in some embodiments of the present application, the chain extender masterbatch includes a first polymer carrier and an epoxy chain extender.

[0024] Optionally, in some embodiments of the present application, the epoxy chain extender includes styrene acrylate-glycidyl methacrylate copolymer.

[0025] Optionally, in some embodiments of the present application, the foamed beads further include 1 to 6 parts by mass of a nucleating agent masterbatch;

[0026] Wherein, the nucleating agent masterbatch includes a second polymer carrier and a heterogeneous nucleating agent.

[0027] In a second aspect, the present invention provides a method for preparing foam beads, which is used to prepare the aforementioned foam beads. The method comprises:

[0028] Poly (L-lactic acid), poly (D-lactic acid), a molding regulator, a chain extender masterbatch and a foaming agent are melt-blended, and the foamed beads are obtained by extrusion foaming and air-cooling pelletizing.

[0029] The foamed beads of the embodiments of the present application include poly (L-lactic acid) and poly (D-lactic acid) of high optical purity, which are conducive to the formation of stereocomplex crystals, thereby increasing the thermal deformation temperature of the foamed beads. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0031] Figure 1 is a schematic diagram of the cell morphology after foaming in some embodiments of the present application;

[0032] Figure 2 is a DSC curve diagram of the expanded beads in some embodiments of the present application;

[0033] Figure 3 is a DSC curve diagram of the expanded beads in some embodiments of the present application;

[0034] Figure 4 It is the DSC curve of the foamed beads of the comparative example of this application. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0036] In related art, poly (L-lactic acid) (PLLA) is primarily polymerized from L-lactic acid monomers. The optical purity and crystallinity of PLLA are adjusted by adjusting the content of the optically isomeric monomer (D-lactic acid) in the molecular chain. For example, when the D-lactic acid content is greater than 8%, PLA becomes an amorphous polymer and loses its crystallinity. When the D-lactic acid content is less than 7%, PLA forms homogeneous crystals with a heat deflection temperature (HDT) of approximately 60°C.

[0037] However, when polylactic acid is used as packaging material, during the sea transportation of the packaging material for export, the ambient temperature inside the container may be higher than the deformation temperature of PLA for a long time, causing the packaging material to deform, affecting its cushioning performance and the coating effect on the packaged product, causing damage to the product during subsequent transportation.

[0038] In view of this, the embodiments of the present application provide a foamed bead, a preparation method thereof, and a packaging material, aiming to improve the problem of poor temperature resistance of polylactic acid when used as a packaging material.

[0039] According to a first aspect of the embodiments of the present application, there is provided a foamed bead comprising the following components in parts by mass:

[0040] 3-55 parts of poly (L-lactic acid);

[0041] 3-20 parts of poly (dextrose) lactic acid;

[0042] 40-90 parts of forming regulator;

[0043] 1 to 5 parts of chain extender masterbatch;

[0044] 3-12 parts of foaming agent;

[0045] Wherein, the mass percentage of L-lactic acid monomer in the poly-L-lactic acid is greater than or equal to 98%;

[0046] The mass percentage of the D-lactic acid monomer in the poly D-lactic acid is greater than or equal to 98%.

[0047] By adopting the above scheme, the foamed beads of the embodiment of the present application include poly (L-lactic acid) and poly (D-lactic acid) of high optical purity, which helps to form stereocomplex crystals, thereby increasing the thermal deformation temperature of the foamed beads.

[0048] In some embodiments of the present application, the mass percentage of L-lactic acid monomer in poly-L-lactic acid is greater than or equal to 99%.

[0049] By adopting the above solution, the higher the mass percentage of the L-lactic acid monomer in the poly-L-lactic acid, the more conducive it is to ensuring that the poly-L-lactic acid has higher optical purity and more excellent crystallization properties.

[0050] In some embodiments of the present application, the mass percentage of D-lactic acid monomer in poly (D-lactic acid) is greater than or equal to 99%.

[0051] By adopting the above scheme, the higher the mass percentage of the D-lactic acid monomer in the poly (D-lactic acid), the more conducive it is to ensure that the poly (D-lactic acid) has higher optical purity and better crystallization properties.

[0052] In some embodiments of the present application, the mass ratio of poly-L-lactic acid to poly-D-lactic acid may range from 1 to 5. Further, the mass ratio of poly-L-lactic acid to poly-D-lactic acid may range from 3 to 5. Exemplarily, the mass ratio of poly-L-lactic acid to poly-D-lactic acid may be 3, 3.2, 3.5, 3.7, 4, 4.2, 4.5, 4.7, 5, and any value between two adjacent values ​​mentioned above.

[0053] By adopting the above scheme, poly-L-lactic acid and poly-D-lactic acid are configured in an appropriate mass ratio, which helps the molecular chain segments of L-lactic acid monomers and D-lactic acid monomers to be arranged alternately in parallel and co-crystallized, thereby promoting the formation of stereocomplex crystals, which helps to improve the temperature resistance of the foamed beads.

[0054] In some embodiments of the present application, the melt index of the poly (L-lactic acid) may range from 2 g / 10 min to 20 g / 10 min. Further, the melt index of the poly (L-lactic acid) may range from 4 g / 10 min to 10 g / 10 min. Exemplarily, the melt index of the poly (L-lactic acid) may be 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, and any value between two adjacent values.

[0055] In some embodiments of the present application, the melt index of poly (D-lactic acid) can range from 2 g / 10 min to 50 g / 10 min. Further, the melt index of poly (D-lactic acid) can range from 4 g / 10 min to 25 g / 10 min. Further, the melt index of poly (D-lactic acid) can range from 4 g / 10 min to 10 g / 10 min. Exemplarily, the melt index of poly (D-lactic acid) can be 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, and any value between two adjacent values.

[0056] It is understandable that the lower the melt index of polylactic acid, the better the foaming effect, and the less amount of chain extender required; the higher the melt index of polylactic acid, the lower the foaming effect, and the more amount of chain extender required.

[0057] In some embodiments of the present application, the thermal deformation temperature of the expanded beads may be in a range of greater than or equal to 100° C. Further, the thermal deformation temperature of the expanded beads may be in a range of 105° C. to 115° C. For example, the thermal deformation temperature of the expanded beads may be 105° C., 106° C., 107° C., 108° C., 109° C., 110° C., 111° C., 112° C., 113° C., 114° C., 115° C., and any value between two adjacent values ​​mentioned above.

[0058] By adopting the above scheme, the foamed beads form stereocomposite crystals through the alternating arrangement and stacking of optical isomers of lactic acid. Compared with the homogeneous crystals of polylactic acid, the molecular chains in the stereocomposite crystals are more densely stacked and the interactions between the molecular chains are stronger, thereby forming a larger number of crystallization nucleation points. These high-density crystal nuclei act as physical cross-linking points by connecting the molecular chains between crystals, which is beneficial to improving the temperature resistance of the foamed beads and making their thermal deformation temperature greater than 100°C.

[0059] In some embodiments of the present application, the maximum melting temperature of the expanded beads may range from 200° C. to 240° C. For example, the maximum melting temperature of the expanded beads may be 200° C., 202° C., 205° C., 208° C., 210° C., 212° C., 215° C., 218° C., 220° C., 222° C., 225° C., 228° C., 230° C., 232° C., 235° C., 237° C., 240° C., and any value between two adjacent values ​​mentioned above.

[0060] By adopting the above scheme, the maximum melting temperature of the expanded beads is increased to 200° C. to 240° C. This is due to the formation of stereocomplex crystals, which are beneficial to improving the heat resistance of the expanded beads.

[0061] In some embodiments of the present application, the molding regulator includes a second poly-L-lactic acid or poly(butylene terephthalate-adipate), and the mass percentage of the D-lactic acid monomer in the second poly-L-lactic acid is greater than or equal to 4% and less than or equal to 8%.

[0062] By adopting the above scheme, the nucleating regulator can be deformed and softened preferentially during the processing, which helps to improve the mutual contact between adjacent foaming beads and improve product quality.

[0063] In some embodiments of the present application, the molding regulator may include a second poly (L-lactic acid) or poly (butylene adipate-co-terephthalate), abbreviated as PBAT; wherein the weight percentage of the D-lactic acid monomer in the second poly (L-lactic acid) is greater than or equal to 4%. Furthermore, the weight percentage of the D-lactic acid monomer in the second poly (L-lactic acid) is greater than or equal to 4% and less than or equal to 8%. Exemplarily, the weight percentage of the D-lactic acid monomer in the second poly (L-lactic acid) is 4%, 5%, 6%, 7%, 8%, or any value between the above two adjacent values.

[0064] By adopting this solution, the optical purity of the second poly-L-lactic acid is low due to the low mass percentage of D-lactic acid monomer in the second poly-L-lactic acid. The thermal deformation temperature of this low-optical-purity poly-lactic acid is lower than the steam forming temperature of the foam beads. During the steam forming process, the molding agent on the surface of the foam beads deforms and softens, improving the contact between adjacent foam beads. Furthermore, the glass transition temperature (Tg) of the molding agent is also lower than the steam forming temperature, allowing its chain segments to freely pass through the interface between adjacent foam beads, thereby regulating the bonding quality between adjacent foam beads.

[0065] Raw materials such as PLLA, PDLA, and PBAT are typically low-molecular-weight linear polymers with low melt viscosity and strength. During the molten-state extrusion foaming process, they are unable to withstand the intense tensile stress imposed on the cell walls by cell growth, leading to cell rupture. Chain extender masterbatches can simultaneously increase the molecular weight of poly-L-lactic acid, poly-D-lactic acid, and molding modifiers during the extrusion foaming process, introducing long-branched structures into their molecular backbones, thereby increasing their melt strength and elasticity, improving the polymer's melt-foamability and the stability of the extrusion foaming process.

[0066] In some embodiments of the present application, the chain extender masterbatch may include a first polymer carrier and an epoxy chain extender; wherein the melting point of the first polymer carrier is greater than the melting point of the molding regulator.

[0067] By adopting the above scheme, the epoxy groups in the epoxy chain extender can react with the end groups of PLLA, PDLA and PBAT in the extruder to introduce a long-chain branched structure into the polymer; the epoxy groups in the epoxy chain extender can also react with PLA and PBAT at the same time to perform reactive compatibilization.

[0068] It should be noted that the melting temperature of epoxy chain extenders is approximately 60°C. In the reaction system, the melting temperature of epoxy chain extenders is lower than the processing temperatures of poly-L-lactic acid, poly-D-lactic acid, and the molding modifier. This makes the epoxy chain extender more likely to undergo chain extension reactions with the low-melting-point components, failing to fully extend the chain and act as a compatibilizer.

[0069] The first polymer carrier uses poly (L-lactic acid), wherein the mass percentage of L-lactic acid monomer in the poly (L-lactic acid) is greater than or equal to 98%, and the melting point of the poly (L-lactic acid) is about 175°C, which is higher than the melting point of the molding regulator, to ensure that the polymer carrier can be delayed in melting during the extrusion foaming process to fully undergo chain extension reaction with the remaining components.

[0070] The present application obtains a chain extender masterbatch by melt-blending an epoxy chain extender with a first polymer carrier having a relatively high melting point, thereby improving the stability of the extrusion foaming process and product performance.

[0071] The preparation method of chain extender masterbatch is exemplified as follows:

[0072] The polymer carrier and the epoxy chain extender are melt-blended in a twin-screw extruder having an L / D ratio of 30 to 48, preferably 36 to 40. The screw speed during the blending process is 150 to 300 rpm, preferably 150 to 250 rpm, and the blending temperature is 155 to 220° C., preferably 175 to 200° C. The concentration of the epoxy chain extender in the chain extender masterbatch is 10 to 50 wt%, preferably 20 to 30 wt%. The prepared chain extender masterbatch is dehumidified and dried at 75 to 100° C. to a moisture content of ≤400 ppm, preferably ≤200 ppm, and more preferably ≤100 ppm, and then packaged in aluminum foil bags for later use.

[0073] In some embodiments of the present application, the epoxy chain extender includes styrene-acrylate-glycidyl acrylate copolymer.

[0074] By adopting the above scheme, the styrene-acrylate-glycidyl acrylate copolymer contains epoxy groups, which can react with the end groups of PLLA, PDLA and PBAT in the extruder to introduce long-chain branched structures into polylactic acid; the epoxy groups can also react with PLA and PBAT at the same time to perform reactive compatibilization.

[0075] It should be noted that styrene-acrylate-glycidyl acrylate copolymer may refer to styrene-(meth)acrylate-glycidyl methacrylate copolymer, or styrene-glycidyl methacrylate copolymer and other copolymers containing glycidyl methacrylate copolymer segments, with an average functionality of 4 to 20, preferably 5 to 12, and more preferably 8 to 10.

[0076] In some embodiments of the present application, the expanded beads may further include nucleating agent masterbatch.

[0077] By adopting the above scheme and adding nucleating agent masterbatch, it is helpful to increase the nucleation rate of the foam cells, increase the foam cell density and reduce the foam cell size.

[0078] In some embodiments of the present application, the nucleating agent masterbatch may include a second polymer carrier and a heterogeneous nucleating agent.

[0079] By adopting this approach, the heterogeneous nucleating agent is blended with a second polymer carrier to produce a nucleating agent masterbatch in order to better disperse it within the foaming bead system and avoid the impact of direct addition of the heterogeneous nucleating agent on the feeding stability of other components. The heterogeneous nucleating agent can significantly improve cell morphology and reduce cell size.

[0080] Specifically, the heterogeneous nucleating agent may include at least one of talc, calcium carbonate, silicon dioxide, and nanoclay.

[0081] The following is an example of the preparation method of nucleating agent masterbatch:

[0082] The twin-screw extruder used in the chain extender masterbatch preparation process has an L / D ratio of 30 to 48, preferably 36 to 40. The screw speed during the blending process is 150 to 350 rpm, preferably 200 to 300 rpm, and the blending temperature is 110 to 175°C, preferably 135 to 165°C. The concentration of the nucleating agent in the nucleating agent masterbatch is 10 to 50 wt%, preferably 15 to 25 wt%. The prepared nucleating agent masterbatch is dried at 50 to 80°C to a moisture content of ≤400 ppm, preferably ≤200 ppm, and more preferably ≤100 ppm, and then packaged in aluminum foil bags for later use.

[0083] In some embodiments of the present application, supercritical carbon dioxide is used as the foaming agent.

[0084] The following is an example of the formula of foam beads:

[0085] The mass fraction of poly-L-lactic acid is preferably 10 to 50 parts; more preferably 10 to 30 parts;

[0086] The mass parts of poly (dextrose) lactic acid are preferably 5 to 10 parts;

[0087] The mass parts of the molding regulator are preferably 40 to 60 parts;

[0088] The mass parts of chain extender masterbatch are preferably 1 to 3 parts;

[0089] The mass fraction of the nucleating agent masterbatch is 0 to 6 parts; preferably 1 to 4 parts; more preferably 2 to 3 parts;

[0090] The foaming agent is preferably present in an amount of 6 to 9 parts.

[0091] In addition, in order to improve the quality and functionality of the product, one or more of the following additives may be added to the above-mentioned masterbatch: crystallization nucleating agents for stereocomplex crystals (such as polyhydroxy organics), antioxidants, heat stabilizers, antistatic agents, UV absorbers, pigments or other plastic processing aids.

[0092] According to a second aspect of the present application, a method for preparing foamed beads is provided, for preparing the aforementioned foamed beads, the preparation method comprising:

[0093] Poly (L-lactic acid), poly (D-lactic acid), a molding regulator, a chain extender masterbatch and a foaming agent are melt-blended, and foamed beads are obtained through extrusion foaming and air-cooling pelletizing.

[0094] This application uses a series extrusion foaming unit to prepare high-temperature resistant biodegradable foam beads. The foaming unit mainly includes: a raw material drying system, a loss-in-weight feeder, an upper-stage twin-screw extruder, a lower-stage single-screw extruder, a foaming agent injection system, a start-up valve, and an air-cooled pelletizing system. After unpacking, the poly (L-lactic acid), poly (D-lactic acid), and molding regulator raw materials are vacuum-sucked into the corresponding raw material storage tanks. The low-dew point air (dew point ≤ -45°C) generated by the raw material drying system is pressurized and heated by a fan and then sent into the storage tank. All polymer raw materials are maintained in a low-dew point dry environment to avoid absorbing moisture in the air, which causes hydrolysis during the extrusion process and a decrease in molecular weight and melt-foamability. The temperature in the storage tanks for high-optical-purity poly-L-lactic acid and poly-D-lactic acid raw materials is 75-100°C, the temperature in the storage tanks for low-optical-purity poly-L-lactic acid (forming modifier) ​​raw materials is 50-80°C, and the temperature in the storage tanks for PBAT raw materials (forming modifier) ​​is 70-85°C. The raw materials in the storage tanks are fed into a loss-in-weight feeder through a buffer hopper. The different components are fed into the extruder at a constant mass flow rate according to the set formula ratio.

[0095] The twin-screw extruder, single-screw extruder, foaming agent injection system, and air-cooled pelletizing system used in this application are the same as those in the invention patent CN 116284954B. Each polymer component completes melt plasticization, mixing, and chain extension reaction in the upper twin-screw extruder. The twin-screw barrel temperature is 100-250°C, preferably 160-240°C, and more preferably 180-220°C. The foaming agent supercritical CO2 is injected into the barrel of the twin-screw extruder at a constant flow rate through the injection system, dispersed and mixed in the polymer melt, and formed a homogeneous solution with it before entering the lower single-screw extruder. The melt pressure at the twin-screw extruder outlet is 10-20 MPa, preferably 15-18 MPa. The polymer melt / CO2 solution is homogenized and cooled in the single-screw extruder to further improve the melt strength of the system. After the foaming agent is injected, the barrel temperature of the single-screw extruder is 110-180°C, preferably 120-160°C, and more preferably 120-145°C. At the die head, the pressure of the foaming system is 10-16 MPa, preferably 12-15 MPa. The foaming system is depressurized and foamed at the porous die plate in the single-screw extruder die. After exiting the die plate, the foamed material is cut into foamed beads with a particle size of approximately 1-6 mm by a high-speed rotary cutter in an air-cooled pelletizing system, preferably 2-5 mm, and more preferably 2-3 mm.

[0096] In some embodiments of the present application, the density of the expanded beads can be 18 to 60 g / L, preferably 20 to 35 g / L. The density of the expanded beads is relatively low, and the expanded beads of the embodiments of the present application can achieve both light weight and excellent foaming effect.

[0097] In some embodiments of the present application, the average cell diameter of the expanded beads after foaming ranges from 15 to 100 μm, preferably from 50 to 80 μm. The expanded beads of the embodiments of the present application have a moderate average cell diameter after foaming, which ensures that the foamed product has good mechanical properties while also ensuring good processability.

[0098] According to a third aspect of the present application, a cushioning material is provided, which comprises the steam-molded product of the aforementioned foamed beads.

[0099] By adopting the above scheme, when the steam-molded product of the aforementioned foamed beads is used as a cushioning material, it helps to improve the temperature resistance of the packaging material and helps to expand the application scenarios of the cushioning material.

[0100] In some embodiments of the present application, the cushioning material may be a filling material or a packaging material.

[0101] It should be explained that the foamed beads can be used as filling materials, and the steam-molded products of the foamed beads can be used as packaging materials.

[0102] The present invention is described in detail below by means of specific examples, which are only some examples of the present invention and are not intended to limit the present invention. The raw materials used in the following examples, unless otherwise specified, are all commercially available products.

[0103] Example 1

[0104] A foamed bead is prepared by the following steps:

[0105] 20 parts by weight of poly (L-lactic acid), 5 parts by weight of poly (D-lactic acid), 62.5 parts by weight of a molding regulator, 2 parts by weight of a chain extender masterbatch, 2 parts by weight of a nucleating agent masterbatch, and 8.5 parts by weight of a foaming agent were successively added to a tandem extruder unit for extrusion foaming. The screw diameter of the upper twin-screw extruder was D = 52 mm, and the aspect ratio L / D = 48. The diameter of the lower single-screw extruder was D = 90 mm, and the aspect ratio L / D = 30. A three-way valve and a porous foaming template with a pore diameter of 0.9 mm were sequentially installed at the end of the lower single-screw extruder. The melt pressure at the end of the upper twin-screw extruder was 17-18 MPa, and the melt pressure at the template position was 13-14 MPa. The temperatures at each stage of the tandem extruder unit are shown in Table 1.

[0106] The mass percentage of L-lactic acid in poly-L-lactic acid is ≥99%, and the melt index is 4 g / 10 min; the mass percentage of D-lactic acid in poly-D-lactic acid is ≥99%, and the melt index is 10 g / 10 min. The above components are mixed to obtain foam beads;

[0107] In this embodiment, the molding regulator is a second poly-L-lactic acid, the mass percentage of D-lactic acid in the second poly-L-lactic acid is 4%, and the melt index is 4g / 10min;

[0108] In this embodiment, the chain extender masterbatch is prepared by the following steps:

[0109] BASF Joncryl ADR-4368, a styrene-methacrylate-glycidyl methacrylate copolymer, was used as a chain extender at a concentration of 30 wt% in the chain extender masterbatch. Poly(L-lactic acid) was used as a carrier resin with a melting point of 175°C, a D-lactic acid monomer content of ≤1%, and a melt index of 3 g / 10 min. The concentration in the chain extender masterbatch was 70 wt%. The chain extender masterbatch was prepared using a twin-screw extruder with an aspect ratio of L / D = 36, a screw speed of 200 rpm, and a blending temperature of 150-200°C. The prepared chain extender masterbatch was then dehumidified and dried at 75°C to a moisture content of ≤200 ppm.

[0110] In this embodiment, the nucleating agent masterbatch is prepared by the following steps:

[0111] Talc was selected as the nucleating agent, with a concentration of 25wt% in the nucleating agent masterbatch and a mesh size of 2500. Polybutylene adipate / terephthalate (PBAT) was used as the carrier resin, with a concentration of 75wt% in the nucleating agent masterbatch. The PBAT had a melt index of 5g / 10min and an acid value of 30mol / ton. The nucleating agent masterbatch was prepared using a twin-screw extruder with an aspect ratio of L / D = 48, a screw speed of 300rpm, and a blending temperature of 110-135°C. The nucleating agent masterbatch was extruded and granulated to obtain the nucleating agent masterbatch. The prepared nucleating agent masterbatch was dehumidified and dried at 80°C to a moisture content of ≤100ppm.

[0112] In this embodiment, supercritical carbon dioxide is used as the foaming agent.

[0113] Table 1

[0114]

[0115] Example 2

[0116] A foamed bead is prepared by the following steps:

[0117] 35 parts by weight of poly (L-lactic acid), 8 parts by weight of poly (D-lactic acid), 46 parts by weight of a molding regulator, 1.5 parts by weight of a chain extender masterbatch, 1.5 parts by weight of a nucleating agent masterbatch, and 8 parts by weight of a foaming agent were successively added to a tandem extruder unit for extrusion foaming. The screw diameter of the upper twin-screw extruder was 52 mm, and the aspect ratio (L / D) was 48. The diameter of the lower single-screw extruder was 90 mm, and the aspect ratio (L / D) was 30. A three-way valve and a porous foaming template with a pore diameter of 1.2 mm were sequentially installed at the end of the lower single-screw extruder. The melt pressure at the end of the upper twin-screw extruder was 16-17 MPa, and the melt pressure at the template position was 12-13 MPa. The temperatures at each stage of the tandem extruder unit are shown in Table 2.

[0118] The mass percentage of L-lactic acid in poly-L-lactic acid is greater than 98%, and the melt index is 6 g / 10 min; the mass percentage of D-lactic acid in poly-D-lactic acid is greater than 98%, and the melt index is 15 g / 10 min. The above components are mixed to obtain foam beads;

[0119] In this embodiment, the molding regulator is polybutylene terephthalate-adipate, with a melt index of 2 g / 10 min and an acid value of 35 mol / ton;

[0120] In this embodiment, the chain extender masterbatch is prepared by the following steps:

[0121] BASF Joncryl ADR-4368, a styrene-methacrylate-glycidyl methacrylate copolymer, was used as a chain extender at a concentration of 30 wt% in the chain extender masterbatch. Poly(L-lactic acid) was used as a carrier resin with a melting point of 175°C, a D-lactic acid monomer content of ≤1%, and a melt index of 3 g / 10 min. The concentration in the chain extender masterbatch was 70 wt%. The chain extender masterbatch was prepared using a twin-screw extruder with an aspect ratio of L / D = 36, a screw speed of 200 rpm, and a blending temperature of 150-200°C. The prepared chain extender masterbatch was then dehumidified and dried at 75°C to a moisture content of ≤200 ppm.

[0122] In this embodiment, the nucleating agent masterbatch is prepared by the following steps:

[0123] Talc was selected as the nucleating agent, with a concentration of 25wt% in the nucleating agent masterbatch and a mesh size of 2500. Polybutylene adipate / terephthalate (PBAT) was used as the carrier resin, with a concentration of 75wt% in the nucleating agent masterbatch. The PBAT had a melt index of 5g / 10min and an acid value of 30mol / ton. The nucleating agent masterbatch was prepared using a twin-screw extruder with an aspect ratio of L / D = 48, a screw speed of 300rpm, and a blending temperature of 110-135°C. The nucleating agent masterbatch was extruded and granulated to obtain the nucleating agent masterbatch. The prepared nucleating agent masterbatch was dehumidified and dried at 80°C to a moisture content of ≤100ppm.

[0124] In this embodiment, supercritical carbon dioxide is used as the foaming agent.

[0125] Table 2

[0126]

[0127] Comparative Example 1

[0128] A comparative example of expanded beads, differing from Example 1 in the formulation of the expanded beads. This comparative example comprises 25 parts by weight of poly (L-lactic acid), 62.5 parts by weight of a molding regulator, 2 parts by weight of a chain extender masterbatch, 2 parts by weight of a nucleating agent masterbatch, and 8.5 parts by weight of a foaming agent; wherein the mass percentage of L-lactic acid in the poly (L-lactic acid) is ≥ 99%.

[0129] Comparative Example 2

[0130] A comparative example of expanded beads, differing from Example 1 in the formulation of the expanded beads. This comparative example comprises 25 parts by weight of poly (D-lactic acid), 62.5 parts by weight of a molding regulator, 2 parts by weight of a chain extender masterbatch, 2 parts by weight of a nucleating agent masterbatch, and 8.5 parts by weight of a foaming agent; wherein the weight percentage of D-lactic acid in the poly (D-lactic acid) is ≥ 99%.

[0131] Detection methods:

[0132] (1) Particle size: Select 10-20 foam beads of moderate size and place them end to end. Measure the total length and take the average value as the particle size of the foam beads.

[0133] (2) Density: The density of the expanded beads of the embodiment and the comparative example was tested using the drainage method;

[0134] (3) Pore diameter: The foamed beads of the embodiment and the comparative example were tested using a SEM electron scanning microscope with a magnification of 300 times.

[0135] (4) DSC test: Differential scanning calorimetry (DSC) was used to characterize the melting behavior and crystallinity changes of Example 1 and Comparative Example 1. After about 5-10 mg of sample was placed in the DSC chamber, the DSC gas system was purged several times with normal pressure N2 to displace the air and avoid possible oxygen decomposition of the sample during the test. The temperature was then raised to 240°C at a rate of 10°C / min, and the change in the heat capacity of the sample was recorded.

[0136] The test results are shown in Table 1:

[0137] Table 1

[0138] Sample Particle size (mm) Density (g / L) Cell diameter (μm) Example 1 2 35 58 Example 2 1 25 85 Comparative Example 1 2 40 52 Comparative Example 2 2 32 65

[0139] Figure 1 This is the morphology of the expanded beads after expansion in Example 1. Figure 1 It can be seen that the cell morphology is good, the pore size distribution is uniform, and the closed cells are the main ones, which is conducive to ensuring the mechanical properties of the foamed product. This is because if the cell diameter is too small, the possibility of open cells is greater. On the other hand, if the closed cell ratio is too low, it is not conducive to subsequent molding processing.

[0140] Figure 2 DSC graph of foamed beads using PBAT as molding regulator. Figure 2 It can be seen that T m1 is the melting peak of polylactic acid stereocomplex crystal, T m2 It is the melting peak of homogeneous crystals of high optical purity PLLA, while PBAT has no obvious melting peak.

[0141] Figure 3 DSC graph of foamed beads using a second poly-L-lactic acid as a molding regulator. Figure 3 It can be seen that T m3 is the melting peak of homogeneous crystals of low optical purity PLLA, T m1 is the melting peak of polylactic acid stereocomplex crystal, T m2 It is the melting peak of homogeneous crystals of high optical purity PLLA.

[0142] Figure 4 The DSC diagram of the foamed beads of Comparative Example 1, the molding regulator is PBAT, reference Figure 4 , no melting peak of stereocomplex crystals appeared.

[0143] The above is a detailed introduction to the foamed beads and their preparation method provided in the examples of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, based on the ideas of the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A foamed bead, characterized in that: The foam beads include the following components in parts by mass: Wherein, the mass percentage of L-lactic acid monomer of the poly-L-lactic acid is greater than or equal to 98%; The mass percentage of the dextrorotatory lactic acid monomer in the poly (dextrorotatory lactic acid) is greater than or equal to 98%.

2. The expanded beads according to claim 1, characterized in that The mass percentage of L-lactic acid monomer in the poly-L-lactic acid is greater than or equal to 99%; and / or The mass percentage of the dextrorotatory lactic acid monomer in the poly (dextrose) lactic acid is greater than or equal to 99%.

3. The expanded beads according to claim 1 or 2, characterized in that The mass ratio of the poly (L-lactic acid) to the poly (D-lactic acid) is in the range of 1 to 5.

4. The expanded beads according to claim 1 or 2, characterized in that The melt index of the poly-L-lactic acid is in the range of 2 g / 10 min to 20 g / 10 min; and / or The melt index of the poly (D-lactic acid) ranges from 2 g / 10 min to 50 g / 10 min.

5. The expanded beads according to any one of claims 1 to 4, characterized in that The foamed beads meet at least one of the following conditions: The thermal deformation temperature of the foamed beads is greater than or equal to 100°C; The maximum melting temperature of the foamed beads ranges from 200°C to 240°C.

6. The expanded beads according to claim 1, characterized in that The molding regulator includes a second poly (L-lactic acid) or poly (butylene terephthalate-adipate), and the mass percentage of D-lactic acid in the second poly (L-lactic acid) is greater than or equal to 4% and less than or equal to 8%.

7. The expanded beads according to claim 1, characterized in that The chain extender masterbatch comprises a first polymer carrier and an epoxy chain extender.

8. The expanded beads according to claim 7, characterized in that The epoxy chain extender includes styrene-acrylate-glycidyl methacrylate copolymer.

9. The expanded beads according to claim 1, characterized in that The foam beads further include 1 to 6 parts by mass of a nucleating agent masterbatch; Wherein, the nucleating agent masterbatch includes a second polymer carrier and a heterogeneous nucleating agent.

10. A method for preparing foamed beads, characterized in that: For preparing the foamed beads according to any one of claims 1 to 9, the preparation method comprises: Poly (L-lactic acid), poly (D-lactic acid), a molding regulator, a chain extender masterbatch and a foaming agent are melt-blended, and the foamed beads are obtained by extrusion foaming and air-cooling pelletizing.

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