A phase change temperature regulating PLA / PPC multi-layer hose and a preparation method thereof

Abstract

The present application relates to the field of high polymer material modification and hose extrusion molding, and discloses a phase change temperature regulating PLA / PPC multilayer hose and a preparation method thereof. The hose comprises, in sequence along the radial direction, an inner isolation layer, a phase change functional layer and an outer protective layer. The phase change functional layer comprises polylactic acid, polypropylene carbonate, a multifunctional epoxy chain extender and phase change microcapsules composed of a phase change core material, a heat-resistant inner shell and a flexible reaction interface layer with active functional groups. During preparation, the PLA / PPC is first reacted with part of the chain extender to increase compatibility, then the microcapsules and the remaining chain extender are fed downstream of the double screw, and low shear mixing and three-layer co-extrusion molding are performed. The present application can reduce the damage of the microcapsules under heat and shear and the migration of the phase change material, improve the melt strength, dimensional stability, thermal cycle stability and bending durability, and is suitable for temperature regulating delivery, wearing, packaging and medical auxiliary hoses.

Description

Technical Field

[0001] This invention relates to the fields of polymer material modification, phase change energy storage materials and extrusion molding technology, and more specifically, to a phase change temperature-regulating polylactic acid / polypropylene carbonate multilayer hose with a reactive interface layer and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is widely available and possesses good bio-based properties and biodegradability. However, it is relatively brittle and has low melt strength, making it prone to melt sag, billet collapse, and wall thickness fluctuations during the extrusion of thin-walled hollow products. Polypropylene carbonate (PPC) has good flexibility and can be used to improve the toughness of PLA. However, the compatibility between PLA and PPC is limited, and PPC has a narrow heat processing window, which can easily lead to surface roughness, dimensional instability, and fluctuations in mechanical properties in blended materials.

[0003] To enable the hose to absorb or release heat and regulate temperature in response to changes in external temperature, phase change materials such as n-octadecane and paraffin can be added to the polymer matrix. However, uncoated phase change materials are in a molten state at extrusion temperatures and are prone to volatilization, migration, and precipitation on the surface of the product. This results in the loss of latent heat of phase change and may also contaminate the medium transported inside the hose or the external contact surface of the hose.

[0004] Microencapsulation of phase change core materials can reduce migration risk to some extent, but the capsule walls of common amino resin or urea-formaldehyde resin microcapsules are relatively brittle. If the microcapsules are added together with the resin from the main feed port of a twin-screw extruder, they will undergo prolonged high-temperature shearing in the resin melting zone, kneading zone, and metering zone, which can easily lead to capsule wall rupture, core material loss, and localized carbonization. Simply reducing the temperature or screw speed may result in insufficient plasticization of PLA / PPC, inadequate compatibilization reaction, and unstable pipe forming.

[0005] In existing technologies, epoxy chain extenders can be used to improve the melt strength of PLA / PPC blends, downstream side feeding of microcapsules can shorten the time particles can withstand shear and high temperatures, and multilayer co-extrusion structures can form inner and outer isolation layers. However, the above measures are usually used separately and have not fully solved the interconnected problems such as the inability of chain extenders to participate in microcapsule interface bonding after being consumed upstream, the debonding and rupture of microcapsules during repeated bending of the tubing, and the migration of phase change materials to the inner and outer surfaces of the tubing.

[0006] Therefore, there is a need for a technical solution that can simultaneously achieve PLA / PPC reaction compatibilization, phase change microcapsule processing protection, microcapsule / matrix interface bonding, and tubing inner and outer surface isolation. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a phase change temperature-controlled PLA / PPC multilayer hose and its preparation method. By combining reactive phase change microcapsules, segmented addition of chain extenders, downstream side feeding low-shear mixing, and a three-layer radial isolation structure, the breakage and migration of phase change microcapsules during extrusion and use are reduced, thereby improving the melt forming stability, phase change cycle stability, and bending durability of the hose.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A phase change temperature-regulating PLA / PPC multilayer flexible hose includes an inner isolation layer, a phase change functional layer, and an outer protective layer arranged sequentially from the inside to the outside along the radial direction of the hose. The inner isolation layer and the outer protective layer do not contain phase change microcapsules, or the content of phase change microcapsules does not exceed 1% of the mass of the polymer matrix of the corresponding layer, so that the phase change microcapsules are concentrated within the phase change functional layer, and continuous polyester isolation layers are formed between the phase change functional layer and the inner cavity of the hose, as well as between the phase change functional layer and the external environment.

[0009] The thickness of the inner isolation layer accounts for 10% to 25% of the total wall thickness of the hose, the thickness of the phase change functional layer accounts for 50% to 75% of the total wall thickness of the hose, and the thickness of the outer protective layer accounts for 15% to 30% of the total wall thickness of the hose. Preferably, the thickness ratio of the three layers is 20:60:20.

[0010] The phase change functional layer, based on the total amount of PLA and PPC, includes 65-80 parts of PLA, 20-35 parts of PPC, 8-18 parts of reactive phase change microcapsules, 0.4-1.0 parts of multifunctional epoxy chain extender, 0.2-0.8 parts of lubricating dispersant, and 0.1-0.4 parts of antioxidant.

[0011] The inner isolation layer and outer protective layer, based on the total weight of PLA and PPC, respectively, include 70-85 parts PLA, 15-30 parts PPC, 0.3-0.8 parts multifunctional epoxy chain extender, 0.1-0.4 parts antioxidant, and 0.2-0.8 parts lubricant. All three layers use PLA / PPC as the main resin, which can improve interlayer melt compatibility and reduce additional adhesive layers.

[0012] The reactive phase change microcapsule comprises a phase change core material, a heat-resistant inner shell covering the phase change core material, and a flexible reactive interface layer covering the heat-resistant inner shell. The phase change core material is n-octadecane, n-hexadecane, paraffin, or a mixture of two or more alkanes, with a phase change temperature of 15–45°C, preferably 24–34°C for use in human contact or wearable temperature regulation scenarios; the phase change core material accounts for 60%–80% of the total mass of the microcapsule.

[0013] The heat-resistant inner shell is made of cross-linked amino resin, polyurea resin, or polyurethane-polyurea resin, with an average thickness of 0.3–2.0 μm. The flexible reactive interface layer is an elastic polyurethane layer containing hydroxyl, amino, and / or carboxyl end groups, with an average thickness of 0.1–1.0 μm and a surface-active functional group content of 0.05–0.80 mmol / g. The flexible reactive interface layer is used to absorb the local stress generated by extrusion pressure and hose bending, and allows its surface functional groups to react with the multifunctional epoxy chain extender, forming an interfacial connection between the microcapsule and the PLA / PPC matrix.

[0014] The median particle size (D50) of reactive phase change microcapsules is 5–25 μm, the D90 is no greater than 50 μm, and the temperature corresponding to 5% thermal weight loss is no less than 220℃. Smaller and controlled particle size helps reduce stress concentration during tubing bending and lowers the probability of large particles forming defects in the tubing wall.

[0015] A method for preparing a phase change temperature-controlled PLA / PPC multilayer flexible tube, comprising the following steps: (1) Raw material pretreatment: PLA was vacuum dried at 55-70℃ for 4-8 hours; PPC was vacuum dried at 30-45℃ for 4-8 hours to prevent PPC from softening and sticking at high temperatures; reactive phase change microcapsules were vacuum dried at 25-40℃ for 2-6 hours to prevent leakage of the core material under high temperature and vacuum conditions. After drying, the microcapsules were premixed with the lubricating dispersant using a low-speed drum mixer or a plow-type low-shear mixer, without high-speed impact mixing.

[0016] (2) Matrix reaction compatibilization: 70% to 90% of the total amount of PLA, PPC and chain extender are added from the main feed port of the twin-screw extruder. The temperature from the main feed zone to the reaction compatibilization zone is 145 to 175°C, so that PLA and PPC can be fully melted, and the multifunctional epoxy chain extender reacts with the end groups of the two polyesters to improve the molecular weight, branching degree and melt strength of the blend.

[0017] (3) Upstream vacuum exhaust: A vacuum exhaust port is set upstream of the microcapsule side feed port to remove residual moisture from resin drying, low molecular weight volatiles generated or introduced by the compatibilization reaction, and to prevent microcapsule powder from being carried out by the vacuum.

[0018] (4) Downstream side feeding of microcapsules: 10% to 30% of the total amount of reactive phase change microcapsules and chain extenders are added through the side feed port located at 65% to 80% of the effective length of the twin-screw. The retained epoxy groups of the chain extender can react with the active functional groups and matrix end groups on the flexible reactive interface layer of the microcapsules, reducing the insufficient interfacial connection caused by the complete consumption of the chain extender upstream.

[0019] (5) Low-shear distribution mixing: The melt temperature between the microcapsule side feed port and the die is controlled at 155-168℃, the screw speed is 80-180rpm, and the residence time after the microcapsules are added is 20-60s. Downstream of the side feed port, a forward large-lead conveying element and a distribution mixing element with a stagger angle of no more than 30° are used. No reverse threaded elements and strong kneading blocks with a stagger angle of more than 45° are set.

[0020] (6) Three-layer co-extrusion molding: The inner isolation layer material, the phase change functional layer material and the outer protective layer material are respectively fed into the three-layer annular co-extrusion die head to form a tubular melt with a layer thickness ratio of (10~25):(50~75):(15~30); the tubular melt is cooled and shaped in a vacuum sizing box with a vacuum degree of -0.02~-0.06MPa and a water temperature of 15~25℃, and then pulled and cut.

[0021] By adopting the above technical solution, the beneficial effects of the present invention are as follows: 1. By placing microcapsules in the phase change functional layer in the middle of the tubing and isolating them from both radial sides by an inner isolation layer and an outer protective layer, the risk of phase change core material or microcapsule fragments migrating to the inner cavity and outer surface of the tubing can be reduced.

[0022] 2. The heat-resistant inner shell ensures the thermal stability of the microcapsules at PLA / PPC extrusion temperatures, while the flexible reaction interface layer buffers shear, compression, and bending stresses, thereby reducing capsule wall damage.

[0023] 3. The chain extender is added in stages, with the upstream part used for compatibilization of the PLA / PPC reaction and the downstream part used for microcapsule interface connection, so as to improve melt strength and form a stable microcapsule interface in synergy.

[0024] 4. The microcapsules are added from downstream after the resin has been melted and compatibilized, and they no longer pass through the strong kneading zone after addition, which can shorten the time that the microcapsules have to withstand high temperature and shear.

[0025] 5. Using the same or similar PLA / PPC base resin for all three layers can improve the interlayer melt bonding force and reduce delamination caused by thermal cycling and repeated bending.

[0026] 6. By quantitatively limiting the layer thickness ratio, microcapsule particle size, functional group content, side feeding position, residence time, and screw element, the temperature regulation performance, dimensional stability, and durability of the hose can be stably reproduced. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the radial structure of the three-layer flexible tube of the present invention.

[0028] Figure 2 This is a schematic cross-sectional view of the reactive phase change microcapsules of the present invention.

[0029] Figure 3 This is a schematic flowchart of the multilayer flexible tube preparation method of the present invention.

[0030] Figure 4 This is a schematic diagram of the functional zones and feeding positions of the twin-screw extruder of the present invention.

[0031] Figure reference numerals: 1-Inner isolation layer; 2-Phase change functional layer; 3-Outer protective layer; 4-Cavity; 5-Reactive phase change microcapsule; 51-Phase change core material; 52-Heat-resistant inner shell; 53-Flexible reaction interface layer; 6-Twin-screw extruder; 61-Main feeding zone; 62-Resin melting zone; 63-Reaction compatibilization zone; 64-Vacuum exhaust zone; 65-Microcapsule side feeding zone; 66-Low shear distribution mixing zone; 67-Metering extrusion zone; 7-Three-layer annular co-extrusion die head; 8-Vacuum sizing box; 9-Traction device. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] PLA can be polylactic acid suitable for extrusion molding, with a melt flow rate preferably of 3-10 g / 10 min; the number average molecular weight of PPC is preferably 50,000-200,000. Multifunctional epoxy chain extenders can be styrene-acrylate copolymers containing multiple epoxy functional groups; lubricating dispersants can be ethylene bis-stearamide, oxidized polyethylene wax, or silicone masterbatch; antioxidants can be a combination of hindered phenolic antioxidants and phosphite antioxidants.

[0035] Ordinary microcapsules M1 are single-layer cross-linked amino resin wall phase change microcapsules; reactive microcapsules M2 are bilayer microcapsules with a heat-resistant inner shell and a flexible reactive interface layer. M2 can be formed by interfacial polymerization to form a polyurea or polyurethane-polyurea inner shell, and then secondary encapsulated with an aqueous polyurethane prepolymer containing hydroxyl, amino or carboxyl groups. After curing, a flexible reactive interface layer with an outer active functional group is obtained.

[0036] The latent heat retention rate after extrusion is calculated as "the measured latent heat of the sample after extrusion ÷ the theoretical latent heat calculated based on the amount of microcapsules added × 100%"; the latent heat retention rate after thermal cycling is calculated as "latent heat after cycling ÷ latent heat before cycling × 100%".

[0037] II. Microcapsule Basic Performance Validation Scheme The above-mentioned items were tested using differential scanning calorimetry, thermogravimetric analysis, laser particle size analyzer, scanning electron microscopy or transmission electron microscopy, chemical titration combined with infrared spectroscopy, and microcompression testing. At least three independent batches of each microcapsule were prepared.

[0038] III. Basic Formula The phase change functional layer, based on the total weight of PLA and PPC, comprises 72 parts PLA, 28 parts PPC, 15 parts phase change microcapsules, 0.70 parts multifunctional epoxy chain extender, 0.50 parts lubricating dispersant, and 0.20 parts antioxidant. Calculated based on an initial latent heat of M2 of 171.2 J / g, the theoretical latent heat of the phase change functional layer is approximately 22.06 J / g.

[0039] The inner isolation layer and outer protective layer are composed of 78 parts PLA, 22 parts PPC, 0.50 parts multifunctional epoxy chain extender, 0.40 parts lubricant, and 0.20 parts antioxidant, respectively. Examples 2 and 3 use an inner isolation layer:phase change functional layer:outer protective layer thickness ratio of 20:60:20, and the theoretical latent heat of the complete flexible tube is approximately 13.24 J / g.

[0040] IV. Experimental Group and Comparative Group V. Example 1 PLA was vacuum dried at 65℃ for 6 hours, PPC was vacuum dried at 40℃ for 6 hours, and reactive microcapsules M2 were vacuum dried at 35℃ for 4 hours. 80% of the total chain extender required for the phase change functional layer was added to the twin-screw extruder along with PLA, PPC, and antioxidant through the main feed port. The remaining 20% ​​of the chain extender was premixed with M2 and lubricant / dispersant at low speed and then added through the side feed port located at 70% of the effective screw length.

[0041] The main feeding zone temperature is 50℃, and the melting and reaction compatibilization zone temperatures are 158℃, 165℃, 170℃, and 172℃ respectively; the temperatures in each zone after microcapsule side feeding are 166℃, 164℃, and 162℃; the screw speed is 140 rpm, and the average residence time after microcapsule addition is controlled at 46 s. Only a forward conveying element and a 30° distribution mixing element are installed downstream of the side feed inlet. The resulting phase change functional layer material is extruded into a flexible tube through a single-layer annular die head.

[0042] VI. Example 2 The raw material pretreatment and twin-screw reactive extrusion conditions for the phase change functional layer material were the same as in Example 1. The formulations for the inner isolation layer and outer protective layer were separately melt-plasticized, and the three melt streams were fed into a three-layer annular co-extrusion die head at a flow ratio of 20:60:20 to form the inner isolation layer, phase change functional layer, and outer protective layer.

[0043] The three-layer tube blank is cooled and shaped in a vacuum sizing box with a vacuum degree of -0.04MPa and a water temperature of 20℃. It is then pulled and cut at a stable traction speed to produce a three-layer phase change temperature regulating hose with an outer diameter of 10mm and a total wall thickness of 1.2mm.

[0044] VII. Example 3 Example 3 is basically the same as Example 2, except that: the microcapsule side feeding position is adjusted to 75% of the effective screw length, 75% of the total chain extender is added from the main feed port and 25% is fed with the microcapsules; the screw speed is reduced to 110 rpm, the melt temperature after the microcapsules are added is 158-164℃, and the average residence time is 34s.

[0045] Example 3 was used to verify the effect of shortening the thermal shear time of microcapsules in the extruder on latent heat retention, breakage rate and migration stability.

[0046] VIII. Comparative Example C1 replaces M2 with an equal amount of uncoated paraffin wax, and the rest of the basic formula is similar to that of Example 1. The paraffin wax is added through the main feed port.

[0047] C2 uses ordinary microcapsules M1, which are added together with the resin through the main feed port; the screw speed is 300 rpm, and the microcapsules pass through the 45° and 60° kneading blocks and the reverse thread element along with the material.

[0048] C3 uses ordinary microcapsules M1, which are side-fed from the 70%L position with a screw speed of 140 rpm. After side feeding, a low-shear element is used, but all chain extenders are added from the main feed port.

[0049] C4 uses reactive microcapsules M2, which are side-fed from the 70%L position at a screw speed of 140 rpm. After side feeding, a low-shear element is used, but all chain extenders are added from the main feed port.

[0050] IX. Testing of Microcapsule Integrity and Thermal Properties After Extrusion C2 and C3 were used to verify the role of downstream side feeding and low-shear elements; C3 and C4 were used to verify the buffering effect of the flexible reaction interface layer; C4 and E1 were used to verify the effect of segmented addition of chain extender on the stability of the microcapsule / matrix interface.

[0051] 10. Phase change cycle performance testing of the complete flexible tube Because the phase change functional layer of E2 and E3 accounts for about 60% of the total wall thickness, the latent heat per unit mass of the complete tube is lower than that of the single-layer E1, but its latent heat retention rate after thermal cycling is higher, reflecting the mechanical protection and migration barrier effect of the inner and outer isolation layers on the microcapsules.

[0052] XI. High-Temperature Deposition and Migration Detection Place the tubing samples in a 45℃ environment for 168 hours, with no fewer than 5 samples per group; weigh the samples before and after treatment and observe the surface oil spots; determine the content of free phase change material by solvent extraction; and simultaneously measure the migration amount on the inner and outer surfaces of the tubing. Suggested target data are as follows.

[0053] E1 and E2 use similar phase change functional materials, but E2 shows a significant reduction in the migration of the inner and outer surfaces, which is used to prove that the three-layer radial isolation structure directly blocks the migration of the phase change material to the contact surface.

[0054] 12. Mechanical Properties and Processing Stability Testing The reciprocating bending conditions can be set as follows: bending radius of 5 times the outer diameter of the hose, bending angle of ±90°, and frequency of 30–60 times / min. The hose is considered to have failed when it develops continuous cracks, phase change material leakage, interlayer separation, or a decrease in latent heat exceeding 15%.

[0055] XIII. Characterization of Interfacial Reactions The proportion of porosity at the pull-out interface can be statistically analyzed using scanning electron microscopy images after low-temperature brittle fracture. Each group should include at least five fields of view, and the number of microcapsules should be at least 300. The number of microcapsules with the highest breakage rate should preferably be at least 500.

[0056] XIV. Recommended Testing Items and Statistical Requirements Microcapsule raw material testing includes particle size D10, D50, D90, DSC phase transition temperature and latent heat, TGA thermal decomposition temperature, core material mass fraction, free paraffin content, capsule wall morphology and thickness, surface functional group content, and single particle compression performance.

[0057] The extrusion process testing includes the latent heat retention rate before and after extrusion, microcapsule morphology and breakage rate, free phase change material, extruder torque, die head pressure fluctuation, actual melt temperature, and residence time after microcapsule addition.

[0058] Finished product testing includes initial latent heat, 200 and 500 phase change cycles, heating and cooling curves, duration of isothermal plateau, infrared thermal imaging, mass loss after 168 hours at 45°C, migration of inner and outer surfaces, tensile strength, elongation at break, tear strength, ellipticity, wall thickness deviation, reciprocating bending, radial compression recovery, burst pressure, and interlaminar peel strength.

[0059] At least three independent batches should be prepared for each experimental group. DSC, TGA, and extraction assays should be performed at least three times per batch; tensile, bending, migration, and dimensional stability assays should be performed on at least five samples per group. Data are expressed as mean ± standard deviation, and one-way ANOVA was performed for C2, C3, C4, E1, and E2, with a significance level set at P < 0.05.

[0060] 15. Recommended Core Acceptance Indicators

[0061] XVI. Correspondence between Technical Effects By comparing C2 and C3, the effects of downstream side feeding and low-shear mixing on reducing microcapsule breakage rate and improving latent heat retention rate can be verified.

[0062] By comparing C3 and C4, the effect of the flexible reactive interface layer on improving the extrusion resistance, thermal cycling stability and flexural life of microcapsules can be verified.

[0063] By comparing C4 and E1, the effect of segmented addition of chain extender on reducing free phase change material, narrowing interfacial gaps, and improving melt strength can be verified.

[0064] By comparing E1 and E2, the effects of the inner isolation layer and the outer protective layer on reducing the migration of the inner and outer surfaces, improving bending life and thermal cycling stability can be verified.

[0065] When E2 or E3 simultaneously achieves a microcapsule breakage rate of no more than 5%, a latent heat retention rate of no less than 85% after 500 thermal cycles, an inner and outer surface migration of no more than 0.05 mg / dm², and a reciprocating bending life of no less than 2000 cycles, a chain of evidence for the synergistic technical effects between "microcapsule structure - segmented feeding - low shear extrusion - three-layer isolation" can be formed.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A phase change temperature-regulating PLA / PPC multilayer flexible hose, comprising an inner insulating layer, a phase change functional layer, and an outer protective layer arranged sequentially from the inside to the outside along the radial direction of the hose, characterized in that: The phase change functional layer, based on the total amount of polylactic acid and polypropylene carbonate, comprises 65-80 parts of polylactic acid, 20-35 parts of polypropylene carbonate, 8-18 parts of reactive phase change microcapsules, 0.4-1.0 parts of multifunctional epoxy chain extender, 0.2-0.8 parts of lubricating dispersant, and 0.1-0.4 parts of antioxidant. The reactive phase change microcapsule includes a phase change core material, a heat-resistant inner shell covering the phase change core material, and a flexible reactive interface layer covering the heat-resistant inner shell. The surface of the flexible reactive interface layer has at least one active functional group selected from hydroxyl, amino, and carboxyl groups, and forms an interfacial connection structure with the polylactic acid / polypropylene carbonate matrix through the multifunctional epoxy chain extender. The inner isolation layer and the outer protective layer do not contain phase change microcapsules, or the content of phase change microcapsules does not exceed 1% of the mass of the corresponding polymer matrix.

2. The phase change temperature-regulating PLA / PPC multilayer flexible hose according to claim 1, characterized in that: The thickness of the inner isolation layer accounts for 10% to 25% of the total wall thickness of the hose, the thickness of the phase change functional layer accounts for 50% to 75% of the total wall thickness of the hose, and the thickness of the outer protective layer accounts for 15% to 30% of the total wall thickness of the hose.

3. The phase change temperature-regulating PLA / PPC multilayer flexible hose according to claim 1, characterized in that: The phase change core material is n-octadecane, n-hexadecane, paraffin, or a mixture of two or more alkanes. The phase change core material accounts for 60% to 80% of the total mass of the reactive phase change microcapsules, and the phase change temperature is 15 to 45°C.

4. The phase change temperature-regulating PLA / PPC multilayer flexible hose according to claim 1, characterized in that: The heat-resistant inner shell is made of cross-linked amino resin, polyurea resin, or polyurethane-polyurea resin, and the flexible reactive interface layer is an elastic polyurethane layer containing hydroxyl, amino, and / or carboxyl end groups; the average thickness of the heat-resistant inner shell is 0.3–2.0 μm, and the average thickness of the flexible reactive interface layer is 0.1–1.0 μm.

5. The phase change temperature-regulating PLA / PPC multilayer flexible hose according to claim 1, characterized in that: The median particle size D50 of the reactive phase change microcapsules is 5–25 μm, the D90 is not greater than 50 μm, the temperature corresponding to 5% thermal weight loss is not lower than 220℃, and the content of active functional groups on the surface of the flexible reactive interface layer is 0.05–0.80 mmol / g.

6. The phase change temperature-regulating PLA / PPC multilayer flexible hose according to claim 1, characterized in that: The inner isolation layer and outer protective layer, respectively, are based on the total weight of polylactic acid and polypropylene carbonate, comprising 70-85 parts of polylactic acid, 15-30 parts of polypropylene carbonate, 0.3-0.8 parts of multifunctional epoxy chain extender, 0.1-0.4 parts of antioxidant, and 0.2-0.8 parts of lubricant; the total wall thickness of the hose is 0.5-3.0 mm, and the outer diameter is 3-50 mm.

7. A method for preparing a phase change temperature-regulating PLA / PPC multilayer flexible tube according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1, respectively, is dried to treat polylactic acid, polypropylene carbonate and reactive phase change microcapsules; S2, 70% to 90% of the total amount of polylactic acid, polypropylene carbonate and chain extender are added through the main feed port of the twin-screw extruder. After melting and reaction compatibilization, vacuum degassing is performed upstream of the location where the reactive phase change microcapsules are added. S3, 10% to 30% of the total amount of reactive phase change microcapsules and chain extenders are added through the side feed port located at 65% to 80% of the effective length of the twin screw, so that the reactive phase change microcapsules are mixed with low shear distribution to form a phase change functional layer material. S4, the inner isolation layer material, phase change functional layer material and outer protective layer material are fed into the three-layer annular co-extrusion die head to form a three-layer tubular melt, and then vacuum sizing, cooling, traction and cutting are performed to obtain the phase change temperature-regulating PLA / PPC multilayer hose.

8. The preparation method according to claim 7, characterized in that: The polylactic acid was vacuum dried at 55–70°C for 4–8 hours, the polypropylene carbonate was vacuum dried at 30–45°C for 4–8 hours, and the reactive phase change microcapsules were vacuum dried at 25–40°C for 2–6 hours. The dried reactive phase change microcapsules were premixed with a lubricating dispersant using a low-speed drum mixer or a plow-type low-shear mixer.

9. The preparation method according to claim 7, characterized in that: The twin-screw extruder has a temperature of 145–175°C from the main feed port to the reaction expansion zone, a melt temperature of 155–168°C between the reactive phase change microcapsule side feed port and the die, a screw speed of 80–180 rpm, and a residence time of 20–60 s after the reactive phase change microcapsules are added. A forward conveying thread element and a distribution mixing element with a stagger angle of no more than 30° are provided downstream of the side feed port, and no reverse thread element or strong kneading block with a stagger angle of more than 45° is provided.

10. The preparation method according to claim 7, characterized in that: The flow rate ratio of the inner isolation layer material, the phase change functional layer material, and the outer protective layer material in the three-layer annular co-extrusion die head is (10~25):(50~75):(15~30). The tubular melt is cooled and shaped in a vacuum sizing box with a vacuum degree of -0.02~-0.06MPa and a water temperature of 15~25℃.

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