Polyether type TPU / PLA composite material

Abstract

The invention provides a polyether type TPU / PLA (thermoplastic polyurethane / polylactic acid) composite material. The polyether type TPU / PLA composite material comprises polyether type TPU and PLA, the mass ratio of the polyether type TPU to the PLA is (1: 9)-(5: 5). The PLA / TPU composite material disclosed by the invention realizes a high shape fixation rate and a high shape recovery rate. The polyether type TPU composite material is more active in thermal response and shorter in recovery time by virtue of the characteristics of high elongation at break and rapid relaxation of a soft segment; all samples exhibit a shape fixation rate up to 95%-99% and a high shape recovery rate.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of materials, in particular to a polyether type TPU / PLA composite material. BACKGROUND

[0002] 4D printing technology opens up a new way for building stimulus-responsive intelligent structures through the deep integration of smart materials and additive manufacturing. Shape memory polymers (SMPs) as the core driving material of 4D printing technology can control shape changes according to external stimuli such as heat, humidity, magnetic field, electric field, etc., and show great development potential in the fields of aerospace, medical care, intelligent wear and flexible robots. The selection of SMPs matrix and the composite strategy directly affect the deformation accuracy and functional reliability of 4D printing structure. In recent years, the composite system based on polylactic acid (PLA) and thermoplastic polyurethane (TPU) has attracted much attention due to its programmable shape memory effect and relatively excellent mechanical property adjustability.

[0003] PLA has become an ideal substrate for 4D printing due to its inherent shape memory characteristics and biodegradability. Its shape memory mechanism is derived from the synergistic effect of crystalline and amorphous phases in semi-crystalline structure, but its intrinsic brittleness leads to easy fracture failure in cyclic deformation. Therefore, researchers construct PLA / TPU blending system by introducing TPU to improve the toughness of the material by using the elastic phase of TPU, which significantly changes the performance of the composite system. In addition, by introducing carbon nanotubes (CNTs) and Fe3O4 and other electromagnetic functional materials, the prepared SMPs have multiple responses such as heat, electricity and magnetism, and can also effectively improve the mechanical properties of the composite material. Huang et al. prepared a series of PLA / TPU / MWCNTs composite materials by extrusion method, and found that MWCNTs formed good interfacial adhesion in the TPU phase, and the composite material showed significant synergistic enhancement effect in terms of thermal shape memory effect and mechanical properties. Liu et al. proposed a shape memory polymer (SMPs) with high mechanical strength and magnetic response based on PLA, TPU and Fe3O4 particles, and found that this 3D printed PLA / TPU / Fe3O4 material has good tensile strength and modulus, and has a fast magnetic response characteristic within 40 seconds. However, existing researches focus on the modification of ternary composite materials in TPU / PLA system, ignoring the influence of TPU molecular chain structure difference on the multi-dimensional material system, and there is a lack of systematic performance comparison and proportion optimization criteria for different TPU types.

[0004] Although the existing documents have confirmed the influence of TPU types on the mechanical properties of composite materials, the comparison of the key performance parameters such as the melt rheological property and the shape recovery rate after being compounded with PLA has not been involved. That is, the quantitative correlation model of the structure characteristics-processing property-shape memory effect of TPU has not been established. Accordingly, based on the difference mechanism of the printing adaptability and the shape memory efficiency regulation of the key performance, the theoretical basis and data support are provided for the matrix selection and process design of 4D printing materials. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to provide a polyether type TPU / PLA composite material, and the polyether type TPU / PLA composite material has programmable shape memory effect and relatively excellent mechanical properties.

[0006] The present application provides a polyether type TPU / PLA composite material, comprising: polyether type TPU and PLA; the mass ratio of the polyether type TPU and the PLA is 1:9-5:5.

[0007] According to the present application, the polyether type TPU is WHT-1170A.

[0008] According to the difference of the soft segment in the molecular chain of TPU, it can be divided into polyether type and polyester type. The present inventors find that the soft segment in the molecular chain of the polyether type TPU is composed of polyether polyols such as ethylene oxide and propylene oxide, and has good hydrolysis resistance and low temperature elasticity. The soft segment in the molecular chain of the polyester type TPU is composed of polyester polyols prepared by condensation reaction of dibasic acid and dibasic alcohol, and has better tensile strength and wear resistance.

[0009] In one part of the embodiments of the present application, the mass ratio of the polyether type TPU and the PLA is 1:9, 2:8, 3:7, 4:6 or 5:5.

[0010] In one part of the embodiments of the present application, the mass ratio of the polyether type TPU and the PLA is 5:5.

[0011] The PLA powder of the present application is provided by Shanghai Titan Science and Technology Co., Ltd.

[0012] The present inventors find that the ether bond of the polyether type TPU is polar mismatched with PLA, and a weak van der Waals force interface and macroscopic phase separation are formed, and with the increase of the TPU content, a TPU continuous phase is formed, and the molecular chain flexibility is higher, and the chain segment rearrangement speed is fast when heated.

[0013] Polyether-type TPU composites require less time to recover their shape and exhibit a more positive thermal response. This is because the high elongation at break of polyether-type TPU composites gives them a stronger deformation storage capacity, and the rapid relaxation characteristics of soft segments (higher loss modulus G'') shorten the recovery time.

[0014] The shape recovery rate of polyether-type TPU composites increases with increasing TPU content, and the optimal mass ratio of polyether-type TPU to PLA is 5:5.

[0015] This invention also provides a method for preparing a polyether-type TPU / PLA composite material, comprising the following steps:

[0016] Polyether-type TPU and PLA are pre-dried, melt-blended by a twin-screw extruder, then granulated, dried again, and cooled to obtain the final product.

[0017] The pre-drying described in this invention is preferably carried out in a forced-air drying oven; the pre-drying temperature is 70°C and the time is 10~12h; specifically, it can be 10h, 11h or 12h.

[0018] After pre-drying, the mixture is melt-blended using a twin-screw extruder.

[0019] The temperatures of the five temperature zones from the feed inlet to the die head are set to 160℃, 180℃, 190℃, 195℃, and 200℃, respectively. The first temperature zone has a lower temperature to avoid viscous material clogging the feed inlet, while the melting and homogenizing zone ensures that the polymer is completely melted and uniformly mixed before granulation. Then, it is dried in a forced-air drying oven at 50℃ for 20-24 hours.

[0020] Preferably, the drying time is 20h, 21h, 22h, 23h or 24h.

[0021] The present invention provides a 3D / 4D printing material, which is obtained by extrusion, cooling and printing of the polyether-type TPU / PLA composite material described in any of the above technical solutions.

[0022] The present invention preferably utilizes a twin-screw extruder to prepare composite filaments with a diameter of 1.75 mm.

[0023] According to the present invention, the extrusion parameters include:

[0024] The temperatures of barrel zone 1, barrel zone 2, and die opening are set at 160°C, 180°C, and 185°C, respectively. Cooling is achieved using cooling air ducts, with a screw speed of 12 r / min and a traction speed of 7 r / min.

[0025] The 3D printed samples of PLA / TPU were made using a Raise 3D E2CF 3D printer (Shanghai Fuzhi Information Technology Co., Ltd.). The 3D printing process parameters were set as follows: layer thickness of 0.1 mm, infill density of 100%, printing speed of 30 mm / s, nozzle temperature of 240℃, and heated bed temperature of 45℃.

[0026] The inventors have discovered that polyester-based TPU, due to the strong interfacial interaction formed by its polarity matching with PLA, inhibits phase separation and restricts chain segment movement, resulting in lower increases in G', G'', and η* compared to the polyether-based system. This difference essentially stems from the regulatory effect of the soft segment chemical structures of both on compatibility and molecular dynamics.

[0027] Compared to polyether-based TPU composites, polyester-based TPU composites exhibit larger values ​​for E′, E′′, and tanδ. This aligns closely with the rheological properties analysis mentioned above, which highlights the regulatory effects of the soft segment chemical structures of polyester-based and polyether-based TPUs on their compatibility with PLA and molecular dynamics.

[0028] The residual rate of the composite material also increases with increasing TPU content. This may be because TPU may act as a barrier during PLA decomposition, hindering the contact between oxygen and PLA molecules, slowing down the decomposition rate of PLA, and resulting in more PLA residues under the same pyrolysis conditions. The interaction between TPU and PLA may alter the thermal decomposition pathway of PLA, generating some relatively stable products and increasing the residual rate.

[0029] Polyether-based TPUs have better ductility because their weak interfaces allow for molecular chain slippage and phase deformation.

[0030] Polyester-type TPU composites exhibit slower shape recovery with increasing TPU content, requiring a longer time to achieve a higher recovery rate. Polyether-type TPU composites show the opposite trend. This is because the ether bonds in polyether-type TPU are polarly mismatched with PLA, forming a weak van der Waals interface and macroscopic phase separation. In contrast, with increasing TPU content, a continuous TPU phase is formed, which has higher molecular chain flexibility and faster chain rearrangement during heating.

[0031] Polyether-type TPU composites require less time to recover their shape and exhibit a more positive thermal response. This is because the high elongation at break of polyether-type TPU composites gives them a stronger deformation storage capacity, and the rapid relaxation characteristics of soft segments (higher loss modulus G'') shorten the recovery time.

[0032] Polyether-type TPU composites exhibit greater tensile strain. Regarding shape memory properties, polyester-type TPU composites show slower shape recovery with increasing TPU content, while polyether-type composites show the opposite trend, and polyether-type composites also exhibit a more positive thermal response.

[0033] This invention provides a polyether-type TPU / PLA composite material, comprising polyether-type TPU and PLA; the mass ratio of the polyether-type TPU to PLA is 1:9 to 5:5. The PLA / TPU composite material of this invention achieves high shape retention and high shape recovery. The polyether-type TPU composite material, with its high elongation at break and rapid soft segment relaxation characteristics, exhibits a more positive thermal response and a shorter recovery time; all samples demonstrate a shape retention rate as high as 95%-99% and a high shape recovery rate. Attached Figure Description

[0034] Figure 1 Schematic diagram of PLA / TPU composite filament fabrication and sample printing process;

[0035] Figure 2 (a) A schematic diagram of the shape memory programming process; (b) Experimental steps of the shape memory programming process;

[0036] Figure 3 Scanning electron microscope images of PLA / TPU composites with different TPU types and contents: (a) A1, (b) A2, (c) A3, (d) B1, (e) B2, (f) B3;

[0037] Figure 4 Rheological properties, dynamic mechanical properties and thermal properties of PLA / TPU composite filaments: (a) storage modulus, (b) loss modulus, (c) complex viscosity, (d) storage modulus, (e) loss modulus, (f) loss factor, (g) TGA data curves, (h)~(i): DSC data curves;

[0038] Figure 5 Tensile properties of PLA / TPU composite filaments: (a) stress-strain curve, (b) tensile strength diagram;

[0039] Figure 6 Shape memory properties of PLA / TPU composite filaments: (a) Curve of shape recovery rate over time, (b) Shape fixation rate and shape recovery rate, (c) Schematic diagram of shape memory effect mechanism;

[0040] Figure 7 A physical image showing the shape memory properties of a floral sample made of PLA / TPU composite filament. Detailed Implementation

[0041] This invention provides a polyether-based TPU / PLA composite material, which can be implemented by those skilled in the art with appropriate modifications to the process parameters, based on the content of this document. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of this invention. The methods and applications of this invention have been described through preferred embodiments; those skilled in the art can clearly modify or appropriately alter and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to implement and apply the technology of this invention.

[0042] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0043] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0044] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0045] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items.

[0046] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0047] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0048] Furthermore, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains standard deviations due to individual test methods. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately". Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0049] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0050] The embodiments and comparative examples of this invention describe some examples, in which the embodiments illustrate certain implementations of the invention. However, this does not mean that the effects of the invention can only be achieved in these examples.

[0051] To further illustrate the present invention, the following describes in detail a polyether-type TPU / PLA composite material provided by the present invention with reference to embodiments.

[0052] Example 1 Experimental Section

[0053] 2.1 Raw materials

[0054] PLA powder, Shanghai Titan Technology Co., Ltd., China. Polyether-type TPU, model WHT-1170A, BASF AG, Germany. Polyester-type TPU, model WHT-1570, Wanhua Chemical Group Co., Ltd., China.

[0055] 2.2 Preparation of PLA / TPU composite filaments and printed samples

[0056] The preparation process of PLA / TPU composite filaments and printed samples is as follows: Figure 1As shown in the figure. Specifically, PLA:TPU (9:1, 7:3, 5:5) was dried at 70℃ for 12 h in a forced-air drying oven. Then, it was melt-blended using a twin-screw extruder from Wuhan Ruiming Experimental Instrument Manufacturing Co., Ltd. The temperatures of the five temperature zones from the feed inlet to the die were set at 160℃, 180℃, 190℃, 195℃, and 200℃, respectively. The first temperature zone was set at a lower temperature to avoid viscous material clogging the feed inlet, while the melt and homogenization zones ensured complete melting and uniform mixing of the polymer. Granulation was then performed, followed by drying at 50℃ for 24 h in a forced-air drying oven. Composite filaments with a diameter of 1.75 mm were then prepared using a twin-screw extruder. The six composite filaments were named according to different TPU types and component ratios, as detailed in Table 1. The extruder parameters were set as follows: barrel zone 1, barrel zone 2, and die temperature were set to 160°C, 180°C, and 185°C respectively; cooling was achieved using cooling air channels; screw speed was 12 r / min; and traction speed was 7 r / min. The PLA / TPU 3D printed samples were produced using a Raise 3D E2CF 3D printer (Shanghai Fuzhi Information Technology Co., Ltd.). The 3D printing process parameters were set as follows: layer thickness 0.1 mm, infill density 100%, printing speed 30 mm / s, nozzle temperature 240°C, and heated bed temperature 45°C. Figure 1 Schematic diagram of PLA / TPU composite filament fabrication and sample printing process.

[0057] Table 1. Naming Table for Composite Wires

[0058]

[0059] Example 2 Testing and Characterization

[0060] 2.3.1 Scanning Electron Microscopy (SEM)

[0061] The cross-sectional microstructure of PLA / TPU composite materials was observed using a ZEISS-Ultra plus field emission scanning electron microscope (Carl Zeiss, Germany). During the experiment, the samples were placed in liquid nitrogen to induce brittle fracture, thus obtaining the cross-section of the composite material. To enhance imaging results, the samples were sputter-coated with gold before electron microscopy observation.

[0062] 2.3.2 Rheological properties

[0063] The rheological properties of PLA / TPU composite materials were tested using an Anton Paar-MCR102e rotational rheometer (Anton Paar AG, Austria). The test sample was a 25 mm diameter, 1 mm thick disc, placed on a flat plate fixture, and tested in dynamic oscillation mode. Specific test conditions were set as follows: temperature maintained at 180 ℃, strain rate controlled at 1%, and scanning frequency range of 0.1–100 Hz.

[0064] 2.3.3 Thermogravimetric analysis (TGA)

[0065] The pyrolysis properties of PLA / TPU composites were determined using an SDT650 simultaneous thermal analyzer (TA Instruments, Inc., USA). Samples with an average weight of 10 mg were placed in a standard alumina crucible and placed in a nitrogen atmosphere. The sample was heated from 30°C to 600°C at a heating rate of 15°C / min, and the pyrolysis properties of the composites were measured and analyzed during this process.

[0066] 2.3.4 Differential Scanning Calorimetry (DSC)

[0067] The thermal properties of PLA / TPU composites were tested using a DSC214 differential scanning calorimeter (NETZSCH AG, Germany). First, the samples were heated to 200°C at a heating rate of 10°C / min and held at 200°C for 10 min to eliminate thermal history. Then, the samples were cooled to 25°C at a rate of 10°C / min, and the glass transition temperature (Tg), crystallization temperature (Tc), and melting temperature (Tm) of the composites were recorded.

[0068] 2.3.5 Tensile Test

[0069] The tensile strength of 3D printed tensile specimens was tested using a CMT 5205 microcomputer-controlled electronic universal testing machine (Meters Industrial Systems, Inc., USA) according to the testing standard GB / T1040−2006. The tensile rate was 2 mm / min, and 5 tensile specimens were tested in each group. The average value of the results was taken.

[0070] 2.3.6 Dynamic Mechanical Analysis

[0071] The dynamic mechanical properties of PLA / TPU composites were measured using a QMA Q800 dynamic thermomechanical analyzer (TA Instruments, Inc., USA). Rectangular samples measuring 30 × 5 × 1 mm were tested in a single cantilever configuration. The test temperature was increased from 30 °C to 100 °C at a rate of 5 °C / min, the test frequency was 1 Hz, and the amplitude was 5 μm.

[0072] 2.3.7 Shape Memory Properties

[0073] This study investigated the shape memory properties of a heat-induced flower-like structure (80 mm in diameter, 1 mm in thickness) PLA / TPU composite material. The shape memory programming process of the flower-like specimen is as follows: Figure 2 As shown: (1) Deformation: The sample was heated to 80 ℃ (T>Tg, where Tg is the glass transition temperature), kept in equilibrium in a constant temperature water bath for 1 min, and then a constant force was applied to fix the sample. Figure 2 (b) shows the shape; (2) Fixation: Under the condition of maintaining the external force, cool the deformed sample to room temperature (25 ℃) and keep it in equilibrium for 20 seconds; (3) Remove the external force and record the angle θ1, that is, the deformation angle of the sample after the external force is removed and the temporary shape is fixed; (4) Recovery: Reheat the sample to 80 ℃ (T>Tg) and keep it in equilibrium in a constant temperature water bath until it is fully recovered. Record the recovery angle α1 (the residual deformation angle of the sample that has not recovered after the stimulus is applied) and the recovery time. The shape fixation rate (Rf) and shape recovery rate (Rr) of the flower-shaped sample can be calculated according to formulas (1) and (2):

[0074]

[0075] The deformation angle (θdeformed) is the maximum deformation angle after the temporary shape is fixed.

[0076] Figure 2 (a) Schematic diagram of the shape memory programming process, (b) Experimental steps of the shape memory programming process.

[0077] Example 3 Results Analysis

[0078] 3.1 Microscopic Morphology Analysis

[0079] The microstructure of the cross-section of the PLA / TPU composite filament is as follows: Figure 3 As shown in (a) to (f). From Figure 3 As can be seen from (a) and 3(d), when the proportion of TPU is 10%, the surface of the polymer blend is mainly rigid with PLA and relatively smooth, but at the same time there are a small number of TPU particles protruding and dispersed in the PLA matrix in a discrete sea-island form. When the TPU content increases to 30%, such as... Figure 3 (b) and Figure 3 As shown in (e), TPU gradually forms a continuous phase, with increased surface elasticity and roughness, and the appearance of more micropores. This may be due to the relaxation of TPU chain segments, weakening of intermolecular interactions, and increased chain segment mobility, leading to changes in the internal structure of the material, which macroscopically manifests as the appearance of micropores. When the ratio of TPU to PLA is equal, as shown in (e), Figure 3 (c) and Figure 3As shown in (f), the surface of the polymer blend exhibits the typical matte finish of an elastomer and displays a processing-induced sharkskin effect. This sharkskin-like surface defect occurs during the processing of the PLA / TPU composite material, when the polymer melt is extruded from a twin-screw extruder. This phenomenon primarily results from increased elasticity of the composite and enhanced elastic recovery during processing, leading to stress concentration on the melt surface. This causes minute deformations and wrinkles in the surface layer, ultimately forming the sharkskin effect. A comparison of composite materials with the same content of different types of TPU reveals that polyester-type TPU / PLA composites exhibit relatively higher surface uniformity, while polyether-type TPU / PLA composites show more pronounced cracks and a more severe sense of separation, resulting in greater roughness. This may be because the ester in polyester-based TPU has a higher polarity matching degree with the PLA main chain, resulting in stronger interfacial bonding energy. In summary, as the TPU content increases, the continuous phase and segment mobility on the polymer surface change, and polyester-type TPU exhibits better interfacial bonding and surface smoothness due to its more suitable polarity.

[0080] Figure 3 Scanning electron microscope (SEM) images of PLA / TPU composites with different TPU types and contents: (a) A1, (b) A2, (c) A3, (d) B1, (e) B2, (f) B3

[0081] 3.2 Rheological property analysis

[0082] The rheological properties of PLA / TPU composites with different TPU types and contents are related to the state and dispersion of TPU in the blend. The curves showing the storage modulus (G′), loss modulus (G′′), and complex viscosity (η*) of PLA / TPU composites as a function of angular frequency are shown below. Figure 4 As shown in (a) to (c). From Figure 4 It is evident from (a) to (b) that G′ and G′′ of all six samples increase with increasing angular frequency. Furthermore, throughout the entire test range, the value of G′′ is consistently greater than the storage modulus G′, indicating that the viscosity of the composite material is greater than its elasticity. In addition, both G′ and G′′ of the samples increase with increasing TPU content. This is mainly attributed to the physical cross-linking network formed by the microphase separation of soft and hard segments of TPU. Higher TPU content results in greater network density, stronger molecular chain entanglement, and increased interfacial friction due to the polarity difference with PLA, ultimately leading to an increase in both G′ and G′′. .and Figure 4(c) indicates that the η* of the sample also increases with the increase of TPU content. This is because the increase of TPU content increases the internal resistance of the system, hinders the flow of molecular chains, and increases the viscosity of the entire composite system. Moreover, the viscoelastic behavior of TPU shows more obvious chain segment relaxation hysteresis at high frequencies, which is also the reason why the η* of the same sample increases with the increase of angular frequency. Comparing the G′, G′′, and η* of PLA / TPU composites with the same content but different TPU types, it can be found that the composites of polyester TPU have smaller G′, G′′, and η* values ​​than those of polyether TPU. This can be attributed to the fact that the ester groups of polyester TPU form hydrogen bonds and dipole interactions with the ester groups of PLA, which increases the interfacial binding energy, reduces interfacial friction, and also inhibits TPU chain segment relaxation, resulting in smaller growth of G′ and G′′. In addition, the soft segments of polyester TPU contain ester groups and have higher chain rigidity, resulting in a more gradual increase of η*. In simple terms, polyester-based TPU forms a strong interfacial interaction with PLA due to their polarity matching, which inhibits phase separation and restricts chain segment movement, resulting in lower increases in G', G'', and η* compared to the polyether-based system. This difference essentially stems from the regulatory effect of the soft segment chemical structure of both on compatibility and molecular dynamics.

[0083] 3.3 Dynamic Mechanical Analysis

[0084] The curves showing the changes in storage modulus (E′), loss modulus (E′′), and complex viscosity (tanδ) of PLA / TPU composites with different TPU types and contents as a function of angular frequency are shown below. Figure 5 As shown in (a) to (c). From Figure 5 (a) It can be seen that the E′ curves of the six samples show a sharp decrease at approximately 50-60 °C, which is related to the glass transition temperature of the composite material, representing the transition from a rigid to an elastic state. Furthermore, it can be observed that the E′ of the samples decreases with increasing TPU content. This is because increasing TPU content leads to a relative increase in the soft segment content of the composite material, resulting in a decrease in overall material rigidity, enhanced chain segment mobility, and a relative weakening of elastic deformation capacity, thus causing a decrease in E′. Simultaneously, from... Figure 5(b) The E′′ curves of the six samples show that the loss modulus of the composite material also peaks near the glass transition temperature and decreases with increasing TPU content. This is because the increase in TPU content leads to more soft segments in the system, intensified chain segment movement, increased internal friction, and increased energy dissipation as heat, resulting in a decrease in E′′. As the ratio of E′′ to E′, tanδ reflects the degree of energy dissipation within the material. With increasing TPU content, both E′′ and E′ decrease, but E′′ decreases relatively faster, causing tanδ to also show a decreasing trend. Comparing the E′, E′′, and tanδ of PLA / TPU composites with the same content but different TPU types reveals that the composites with polyester-type TPU have larger values ​​for E′, E′′, and tanδ compared to those with polyether-type TPU. This is highly consistent with the role of the chemical structure of the soft segments of polyester-type and polyether-type TPU in regulating their compatibility with PLA and molecular dynamics, as mentioned in the above rheological property analysis.

[0085] 3.4 Thermal Performance Analysis

[0086] Thermogravimetric analysis (TGA) curves and differential scanning calorimetry (DCS) curves of PLA / TPU composite materials, along with corresponding data parameters, are shown below. Figure 4(g) to (i) are shown and listed in Table 2. In these samples, the initial degradation temperature (Td, 5%, temperature at 5% weight loss) of the composite material decreased with increasing TPU content. A1 began to degrade at around 344℃, while for A2 and A3, this temperature decreased to 340℃ and 335℃, respectively. Similarly, the initial degradation temperatures of B1, B2, and B3 were 338℃, 326℃, and 318℃, respectively. This phenomenon is mainly because TPU has poorer thermal stability than PLA, so during pyrolysis, the initial degradation temperature of the composite material decreases with increasing TPU content. Furthermore, comparing the initial degradation temperatures of PLA / TPU composites with the same content but different TPU types reveals that the initial degradation temperature of polyester-type TPU composites is higher than that of polyether-type TPU composites. This is because the ester group structure of polyester-type TPU is relatively stable during thermal oxidation and is not easily oxidized and decomposed. In polyether-type TPU, the ether bonds are easily oxidized, forming unstable structures such as peroxides. These structures further decompose upon heating, leading to molecular chain breakage and thus lowering the initial degradation temperature of the polyether-type TPU / PLA composite. Furthermore, the residual rate of the composite increases with increasing TPU content. This may be because TPU may act as a barrier during PLA decomposition, hindering oxygen contact with PLA molecules and slowing down PLA decomposition, resulting in more PLA residue under the same pyrolysis conditions. On the other hand, the interaction between TPU and PLA may alter the thermal decomposition pathway of PLA, generating relatively stable products and increasing the residual rate. Conversely, composites with the same polyester-type TPU content have a lower residual rate compared to polyether-type TPU composites. This can be attributed to the fact that during the thermal decomposition of polyester-type TPU, the presence of ester groups may produce volatile small molecule products such as organic acids and alcohols. These products easily volatilize during pyrolysis, resulting in a relatively lower residual rate. When polyether-type TPU undergoes thermal decomposition, it mainly produces relatively stable ether compounds and carbides. These products are not easily volatilized and remain largely in the residue, resulting in a higher residual rate of polyether-type TPU. .

[0087] Figure 4 (h) to (i) show the DSC data curves of the PLA / TPU composite material. From Figure 4(h) shows that the glass transition temperatures of the three polyester-based TPU composites are not significantly different, all around 60℃. However, the glass transition temperature (Tg) of the polyether-based TPU composite decreases significantly with increasing TPU content, from 59.27℃ to 49.57℃. This can be attributed to the fact that polyester-based TPU, due to strong interfacial interactions inhibiting chain segment movement, maintains a stable Tg value dominated by PLA, while polyether-based TPU, due to phase separation and high flexibility of its soft segments, gradually exhibits TPU soft segment characteristics with increasing content, leading to a significant decrease in Tg. Figure 4 As can be seen in (h), the melting temperatures (Tm) of the six composite materials also exhibit a similar pattern to Tg, for similar reasons. Furthermore, around 100–110 °C, between Tg and Tm, all composite materials show an endothermic peak, a typical phenomenon of cold crystallization. When the molecular chains of the composite material gain sufficient energy, they begin to move, arranging themselves in a regular pattern to form a crystalline structure. However, this process does not involve rapid cooling in the molten state to form crystals; rather, crystallization is gradually completed at a lower temperature through the thermal motion of the molecular chains, hence the term cold crystallization.

[0088] Table 2. Corresponding data of TGA and DSC curves for PLA / TPU composite materials.

[0089]

[0090] Figure 4 Rheological properties, dynamic mechanical properties, and thermal properties of PLA / TPU composite filaments: (a) storage modulus, (b) loss modulus, (c) complex viscosity, (d) storage modulus, (e) loss modulus, (f) loss factor, (g) TGA data curves, (h)~(i): DSC data curves

[0091] 3.5 Mechanical Performance Analysis

[0092] The stress-strain curves and tensile strength diagrams of PLA / TPU composite materials are shown below. Figure 5 As shown in (a) to (b), these two figures clearly demonstrate that the tensile strength of PLA / TPU composites with different TPU types and contents decreases with increasing TPU content. This is because PLA, as a rigid matrix, decreases proportionally with increasing TPU elastomer content, disrupting the matrix continuity and reducing load-bearing capacity. While the elastic network of TPU soft segments can disperse stress, excessive TPU can form a continuous phase, weakening the rigid skeleton's supporting effect and leading to a decrease in overall strength. Comparing the tensile strain of PLA / TPU composites with different TPU types and contents reveals that the tensile strain of PLA / TPU composites increases with increasing TPU content. This is because TPU soft segments are all flexible chains; as the content increases, the overall elasticity and ductility of the material improve. During tension, the reversible deformation ability of the soft segments dominates the fracture behavior, and the elongation increases with increasing TPU content. However, comparing the tensile strain of PLA / TPU composites with the same content but different TPU types reveals that polyether-type TPU composites have a lower elongation at break. This is because polyether-type TPU allows for molecular chain slippage and phase region deformation due to its weak interfaces, resulting in superior ductility. Figure 5 Tensile properties of PLA / TPU composite filaments: (a) stress-strain curve, (b) tensile strength diagram.

[0093] 3.6 Shape Memory Performance Analysis

[0094] The curve showing the shape recovery rate of PLA / TPU composites as a function of recovery time, and the quantitative assessment of shape retention rate and shape recovery rate, as shown in the figure. Figure 6 As shown in (a) to (b). From Figure 6 (a) It can be seen that the shape recovery rate of PLA / TPU composites of different TPU types exhibits different patterns. For polyester-type TPU composites, the shape recovery slows down with increasing TPU content, and the time required to reach a higher recovery rate is longer. This is because the ester groups of polyester-type TPU are polarly matched with PLA, forming strong hydrogen bonds and interpenetrating networks. As the TPU content increases, the interfacial bonding becomes tighter, and the molecular chain movement is restricted by the rigid network, requiring more thermal energy and time to overcome the constraints. In contrast, polyether-type TPU composites exhibit the opposite pattern. This is because the ether bonds of polyether-type TPU are polarly mismatched with PLA, forming weak van der Waals forces at the interface and macroscopic phase separation. With increasing TPU content, a continuous TPU phase is formed, resulting in higher molecular chain flexibility and faster chain rearrangement upon heating. Compared to the two types of TPU composites, the shape recovery rates were not significantly different. However, the polyether-type TPU composite required a shorter shape recovery time, exhibiting a more positive thermal response. This is because the high elongation at break of the polyether-type TPU composite gives it a stronger deformation storage capacity, and its rapid relaxation characteristics of soft segments (higher loss modulus G'') shorten the recovery time. Figure 6(b) It can be seen that all samples exhibit a high shape retention rate of 95% to 99%, indicating that the relatively high modulus of rigid PLA ensures good resistance to shrinkage caused by TPU at ambient temperature. On the other hand, it can be seen that the shape recovery rates of A1 to B3 are 98.8%, 97.7%, 95.5%, 95%, 97.2%, and 98.3%, respectively. Therefore, the PLA / TPU composite material achieves both high shape retention rate and high shape recovery rate.

[0095] Figure 6 Shape memory properties of PLA / TPU composite filaments: (a) Curve of shape recovery rate over time, (b) Shape fixation rate and shape recovery rate, (c) Diagram of shape memory effect mechanism.

[0096] Based on the above analysis, the shape memory mechanism of PLA / TPU composite materials can be represented by a schematic diagram, such as... Figure 6 As shown in (c), the crystalline region of PLA acts as the stationary phase, locking the original shape through the orderly arrangement of molecular chains, while its amorphous region transforms into a highly elastic state after heating to the glass transition temperature, endowing the material with deformability. TPU acts as a toughening agent, exhibiting toughness at room temperature to prevent irreversible damage to PLA during deformation and shape recovery. Furthermore, the microphase separation structure of TPU also performs a dual function: the physical cross-linking network formed by the hard segments stabilizes the temporary shape at high temperatures, while the soft segments drive shape recovery through elastic energy storage. Specifically, when the temperature exceeds the glass transition temperature of the composite material, the amorphous region of PLA in the glassy state regains its fluidity and deforms into a temporary shape. Upon cooling to room temperature, the composite material returns to rigidity (glassy state), the deformed shape is fixed, and the elastic energy is stored in the blend matrix. Once the temperature of the composite material rises again to its glass transition temperature, the elastic energy stored in the glassy molecular chains is released, and the composite material recovers its original shape within a certain time. Polyester-based TPU forms a dense interface due to the strong hydrogen bonding between the ester groups and PLA, which inhibits chain segment movement. Although it has high recovery accuracy, its response is relatively slow. On the other hand, the ether bonds of polyether-based TPU are polar mismatched with PLA, resulting in significant interfacial slippage. The high flexibility of the soft segments makes its recovery speed faster.

[0097] To more intuitively compare the shape memory performance of different samples, a flower-shaped sample with a diameter of 21 mm and a thickness of 2 mm was prepared using fused deposition modeling (FDM). The specific experimental procedure is as follows: First, the sample was heated in an 80°C water bath for 1 minute, and then the sample was fixed in place using external force. Figure 7 The shapes shown are then placed back into the water bath, and the performance of each group of samples is as follows. Figure 7As shown in Figure 6(a), the overall experimental results show that the polyether-type TPU composite exhibits faster thermal response characteristics and requires less time to recover to its original shape. Furthermore, the shape recovery rate of the polyester-type TPU composite decreases with increasing TPU content, while the polyether-type TPU composite shows the opposite trend, a result consistent with the pattern presented in Figure 6(a).

[0098] Figure 7 Image of the shape memory performance of a PLA / TPU composite filament flower-shaped sample.

[0099] 4. Conclusion

[0100] This paper focuses on PLA and TPU composite shape memory polymers. Given the limited research on the impact of TPU molecular chain structure differences, a comparative study of polyester-type and polyether-type TPU was conducted to provide support for 4D printing material selection and process optimization. PLA powder, polyester-type TPU, and polyether-type TPU were used as raw materials. Composite filaments were prepared through drying, melt blending, granulation, and secondary drying. Samples were then obtained through 3D printing, and their performance was characterized using various testing methods. Experimental results show that polyester-type TPU, due to the polarity matching between the ester groups and PLA, forms a strong hydrogen bond interface, significantly improving the tensile strength and shape recovery accuracy of the composite material. However, its high interfacial constraint leads to a lower increase in rheological modulus and a slower recovery rate. Polyether-type TPU, due to the polarity mismatch between the ether bonds and PLA, exhibits significant interfacial slippage, giving the composite material superior elongation at break. However, the initial thermal degradation temperature is reduced by approximately 20°C due to the oxidation sensitivity of the ether bonds. In terms of shape memory performance, the shape recovery rate of polyester-type TPU composites decreases with increasing TPU content, while that of polyether-type TPU composites is the opposite. Moreover, polyether-type TPU composites have a more positive thermal response and shorter recovery time due to their high elongation at break and rapid relaxation of soft segments. All samples showed a high shape fixation rate of 95%-99% and a high shape recovery rate.

[0101] Time required for sample response rate to exceed 95%

[0102]

[0103] Comparative Example 1

[0104] Only the mass ratio was changed to 1:19, while all other conditions (TPU type, drying process, melt blending parameters, printing parameters) were completely consistent with the "5:5" group in the embodiments of the present invention.

[0105] Mechanical properties: Tensile strength 48.5MPa (slightly higher than 38.2MPa of the 5:5 group of the present invention), but elongation at break is only 15% (far lower than 210% of the 5:5 group of the present invention), the material is extremely brittle and breaks directly during the tensile process;

[0106] Shape memory performance: Shape fixation rate is 99.2% (high), but shape recovery rate is only 82% (cracks appear on the first recovery), and it takes 150 seconds to recover to 80% (due to the high proportion of PLA and excessive rigidity, resulting in insufficient deformation storage capacity).

[0107] Microstructure: TPU is dispersed in the PLA matrix as isolated particles with no interfacial interaction. Numerous brittle fracture traces of the PLA matrix are visible on the fracture surface.

[0108] Comparative Example 2

[0109] Only the temperature zone parameters of the twin-screw extruder are changed: the temperature from the feed inlet to the die is 140℃, 150℃, 160℃, 170℃, and 180℃, while other conditions are the same as in the embodiment of the present invention.

[0110] Microstructure: PLA and TPU were not fully melted, and there was obvious delamination at the interface (Figure 3, electron micrograph of comparison group 2-2), which showed an "island structure" with no adhesion between the islands;

[0111] Mechanical properties: tensile strength 18.9 MPa (far lower than 38.2 MPa of the 5:5 mixture of this invention), elongation at break 50% (due to stress concentration caused by uneven mixing);

[0112] Rheological properties: The complex viscosity η* is 5000 Pa·s at 0.1 Hz (far higher than the 1200 Pa·s of the 5:5 group of this invention), the melt flow is extremely poor, and "material blockage" occurs during extrusion.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polyether-type TPU / PLA composite material, characterized in that, include: Polyether-type TPU and PLA; the mass ratio of the polyether-type TPU and PLA is 1:9 to 5:

5.

2. The polyether-type TPU / PLA composite material according to claim 1, characterized in that, The polyether-type TPU is model WHT-1170A.

3. The polyether-type TPU / PLA composite material according to claim 1, characterized in that, The mass ratio of the polyether-type TPU to PLA is 5:

5.

4. A method for preparing a polyether-type TPU / PLA composite material, characterized in that, Includes the following steps: Polyether-type TPU and PLA are pre-dried, melt-blended by a twin-screw extruder, then granulated, dried again, and cooled to obtain the final product.

5. The preparation method according to claim 4, characterized in that, The pre-drying temperature is 70°C, and the time is 10~12 hours.

6. The preparation method according to claim 4, characterized in that, In the melt blending process, the temperatures of the five temperature zones from the feed inlet to the die head are set to 160°C, 180°C, 190°C, 195°C and 200°C, respectively.

7. The preparation method according to claim 4, characterized in that, The re-drying temperature is 50℃, and the time is 20~24h.

8. A 3D / 4D printing material, characterized in that, The polyether-type TPU / PLA composite material as described in any one of claims 1 to 3 is obtained by extrusion, cooling, and printing.

9. The 3D / 4D printing material according to claim 8, characterized in that, The parameters of the extrusion include: The temperatures of barrel zone 1, barrel zone 2, and die opening are set at 160°C, 180°C, and 185°C, respectively. Cooling is achieved using cooling air ducts, with a screw speed of 12 r / min and a traction speed of 7 r / min.

10. The 3D / 4D printing material according to claim 8, characterized in that, The printing parameters include: The printing layer thickness is 0.1 mm, the infill density is 100%, the printing speed is 30 mm / s, the nozzle temperature is 240℃, and the heated bed temperature is 45℃.

Images