External-stress-free bidirectional shape memory polyurethane / nano composite material and preparation method thereof

Abstract

The invention discloses an external-stress-free bidirectional shape memory polyurethane / nano composite material and a preparation method thereof.The preparation method comprises the steps that firstly, polytetrahydrofuran ether glycol and hexamethylene diisocyanate serve as raw materials and are subjected to a prepolymerization reaction under the catalytic action of dibutyltin dilaurate, then 1, 4-butanediol is added into a polyurethane prepolymer system, the reaction continues, and the external-stress-free bidirectional shape memory polyurethane / nano composite material is obtained; the polytetrahydrofuran ether glycol-based shape memory polyurethane is obtained; then, the polytetrahydrofuran ether glycol-based shape memory polyurethane is used as a polymer matrix, and is subjected to melt blending with a carboxylated multi-walled carbon nanotube and an aminated multi-walled carbon nanotube respectively, so that the external stress-free bidirectional shape memory polyurethane / nano composite material is successfully prepared. The external stress-free bidirectional shape memory polyurethane / nano composite material not only has excellent thermal stability and mechanical properties, but also has good shape memory cycle performance. In addition, the preparation method is simple in process, easy to operate and suitable for large-scale popularization and application.

Description

Technical Field

[0001] This invention relates to the field of functional material preparation, and specifically to a stress-free bidirectional shape memory polyurethane / nanocomposite material and its preparation method. Background Technology

[0002] Shape memory polyurethane (SMPU) is a multifunctional material that has attracted much research attention and is widely used in fields such as smart clothing, flexible displays, electronic textiles, durable wheels, and high-performance adhesives. It possesses excellent properties such as good flexibility, transparency, abrasion resistance, and mechanical strength. Despite the many applications and potential of SMPU, certain limitations remain, such as poor electrical and thermal conductivity, which restrict its full utilization. Traditional SMPU suffers from low stress recovery and low reversible strain due to its low stiffness. Using reinforcing materials at the nanoscale and microscale can further expand the application range of SMPU. Nanofillers, such as nanoclay, carbon nanotubes, nanosheet graphene, and other inorganic fillers, are used to improve the shape memory properties of miscible blends. These nanoparticles not only improve the stiffness and mechanical properties of SMPU but also effectively enhance its shape memory behavior as a fixed structure. However, during the preparation of polymer nanocomposites, some nanoparticles, due to their high surface area and interfacial effects with the polymer matrix, are prone to agglomeration within the polymer matrix. Therefore, achieving sufficient and uniform dispersion of nanomaterials in the polymer matrix is ​​a significant challenge.

[0003] On the other hand, nanoparticles play a crucial role in driving shape changes in SMPs. The earliest reported method for stimulating SMP shape changes was direct heating activation. While this method is simple and straightforward, it requires operation in an environment similar to an oven or water bath, limiting its application. Therefore, adding nanoparticles to the SMP matrix to achieve indirect heating becomes necessary and important. For example, indirect heating methods such as electric fields, magnetic fields, light, and microwaves can activate SMPNC materials, thus better meeting practical application requirements. Summary of the Invention

[0004] In view of the technical problems existing in the background art, the purpose of the present invention is to provide a stress-free bidirectional shape memory polyurethane / nanocomposite material and its preparation method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The first aspect of this invention provides a method for preparing stress-free bidirectional shape memory polyurethane / nanocomposite materials, comprising the following steps: S1. Using polytetrahydrofuran ether glycol (PTMEG) and hexamethylene diisocyanate (HDI) as raw materials, a prepolymerization reaction is carried out under the catalysis of dibutyltin dilaurate (DBTDL) to obtain a polyurethane prepolymer; then 1,4-butanediol (BDO) is added to the polyurethane prepolymer system, and the reaction is continued to obtain polytetrahydrofuran ether glycol-based shape memory polyurethane, denoted as PTMEG-based SMPU, as the polymer matrix; S2. Carbon-based nanomaterials are blended with PTMEG-based SMPU by melt blending to obtain stress-free bidirectional shape memory polyurethane / nanocomposite material, denoted as stress-free bidirectional; wherein, the carbon-based nanomaterials are carboxylated multi-walled carbon nanotubes (MWNTs-COOH) or aminated multi-walled carbon nanotubes (MWNTs-NH2).

[0007] Preferably, the prepolymerization reaction temperature is 70-90℃ and the reaction time is 90-120 min.

[0008] Preferably, the continued reaction temperature is 70-90℃ and the reaction time is 30-60 min.

[0009] Preferably, the molecular weight of the polytetrahydrofuran ether diol is 650-2000.

[0010] Preferably, the molar ratio of polytetrahydrofuran ether diol (PTMEG), hexamethylene diisocyanate (HDI), and dibutyltin dilaurate (DBTDL) is 0.01-0.1:0.22-0.3:0.012-0.20.

[0011] Preferably, the mass ratio of the carbon-based nanomaterial to the polytetrahydrofuran ether diol-based shape memory polyurethane is 0.1-8:100.

[0012] Preferably, the melt blending temperature is 65-85℃ and the blending time is 36-54h.

[0013] The present invention has the following beneficial effects: (1) In this invention, polytetrahydrofuran ether diol-based shape memory polyurethane is used as the polymer matrix. Different carbon-based nanomaterials (MWNTs-COOH and MWNTs-NH2) are melt-blended with it to successfully prepare shape memory polyurethane composites containing different carbon-based nanomaterials and SMPU composites with different contents of MWCNTs-NH2. After programming, stress-free bidirectional shape memory polyurethane / nano composites are obtained.

[0014] (2) By analyzing the shape memory trigger temperature of the SMPU / nanocomposite material using DSC, it was found that the crystallization and melting properties of SMPU / MWCNTs-COOH changed significantly.T c and T m All were significantly improved; TG test results showed that the SMPU composite material with added nanomaterials could improve the thermal stability of pure shape memory polyurethane (SMPU) to varying degrees; mechanical property results showed that the composite material with different contents of MWNTs-NH2 had a reduced elongation at break to varying degrees, while the tensile strength was significantly improved, reaching a maximum of 31.2 MPa when the MWNTs-NH2 content was 0.5 wt.%.

[0015] (3) By testing the bidirectional shape memory performance of the SMPU / MWNTs-COOH composite material, good shape memory cycle performance was obtained. In addition, the preparation method of the present invention is simple and easy to operate, and is suitable for large-scale promotion and application. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 Infrared characterization results for pure SMPU and SMPU / nanocomposite materials; Figure 2 DSC curves of SMPU with different nanomaterials: (a) melting curve; (b) crystallization curve; DSC curves of SMPU / MWNTs-NH2(Y) with different mass fractions: (c) melting curve; (d) crystallization curve; Figure 3 For example: (a) XRD curves of different SMPU / nanocomposites; (b) XRD curves of SMPU with different contents of MWNTs-NH2; Figure 4 For: (a) thermogravimetric curves of SMPU with different contents of MWNTs-NH2; (b) DTG of SMPU with different contents of MWNTs-NH2; Figure 5 Stress-strain curves of SMPU composites with different contents of MWNTs-NH2; Figure 6 The following are: (a) Strain reversibility effect diagram of SMPU / MWNTs-COOH spline at -36 ℃ to 25 ℃; (b) Strain reversibility effect diagram of SMPU / MWNTs-COOH spline at -36 ℃ to 50 ℃. Detailed Implementation

[0018] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention may be implemented in other embodiments without these specific details.

[0019] Example 1 (1) Weigh 0.01 mol of PTMEG with a molecular weight of 1800 g / mol and 30 ml of DMF into a three-necked flask connected to nitrogen gas, stir at 70 °C for 30 min, then add 0.22 mol of HDI and two drops of DBTDL into the three-necked flask, stir at a constant temperature for 1.5 h to obtain polyurethane prepolymer; then add 0.012 mol of BDO to the prepolymer system, and continue to react in an oil bath at 70 °C for 30 min to obtain shape memory polyurethane (SMPU). (2) A dispersion of aminated multi-walled carbon nanotubes (MWCNTs-NH2) nanoparticles, comprising 0.5 wt% of shape memory polyurethane (SMPU), was slowly added to the reaction system and stirred thoroughly for 2 h to ensure uniform dispersion of the nanomaterials in the polymer matrix. The mixture was then transferred to a polytetrafluoroethylene (PTFE) mold and placed in a vacuum oven at 70 ℃ for 48 h. The vacuum was used to remove tiny air bubbles, further polymerize, and remove the solvent, resulting in a cured SMPU / nanocomposite material, denoted as SMPU / MWCNTs-NH2. 2（0.5） .

[0020] Example 2 The steps are basically the same as in Example 1, except that a dispersion of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) nanoparticles with a mass of 0.5 wt% polyurethane (SMPU) is slowly added to the reaction system to finally obtain a cured SMPU / nanocomposite material, denoted as SMPU / MWCNTs-COOH.

[0021] Example 3 The steps are basically the same as in Example 1, except that an aminated multi-walled carbon nanotube (MWCNTs-NH2) nanoparticle dispersion with a mass of 0.2 wt% polyurethane (SMPU) is slowly added to the reaction system to finally obtain a cured SMPU / nanocomposite material, denoted as SMPU / MWCNTs-NH2. 2（0.2） .

[0022] Example 4 The steps are basically the same as in Example 1, except that an aminated multi-walled carbon nanotube (MWCNTs-NH2) nanoparticle dispersion with a mass of 0.8 wt% polyurethane (SMPU) is slowly added to the reaction system to finally obtain a cured SMPU / nanocomposite material, denoted as SMPU / MWCNTs-NH2. 2（0.8） .

[0023] Example 5 The steps are basically the same as in Example 1, except that an aminated multi-walled carbon nanotube (MWCNTs-NH2) nanoparticle dispersion with a mass of 1.0 wt% polyurethane (SMPU) is slowly added to the reaction system to finally obtain a cured SMPU / nanocomposite material, denoted as SMPU / MWCNTs-NH2. 2（1） .

[0024] Comparative Example 1 The steps are basically the same as in Example 1, except that a dispersion of multi-walled carbon nanotubes (MWCNTs) with a mass of 0.5 wt% polyurethane (SMPU) is slowly added to the reaction system to finally obtain a cured SMPU / nanocomposite material, denoted as SMPU / MWCNTs.

[0025] Performance testing and characterization (1) FT-IR analysis The structures of pure SMPU and SMPU nanocomposites composited with MWNTs-COOH and MWNTs-NH2, respectively, were characterized by infrared spectroscopy. The results are as follows: Figure 1 As shown.

[0026] Depend on Figure 1 The results show that at 2940 cm -1 2869 cm -1 1720 cm -1 1531 cm -1 1373 cm -1 and 1112cm -1 A strong absorption peak appeared nearby, at 3345 cm⁻¹. -1 A small absorption peak appeared at 3358 cm⁻¹. The figure shows a peak at 3358 cm⁻¹. -1 The absorption peak at 2940 cm⁻¹ is the deformation vibration peak of the NH bond in the urethane group of SMPU and various SMPU / nanocomposite materials. -1 and 2850 cm -1 The absorption peak at 1720 cm⁻¹ is due to the symmetrical and asymmetric stretching vibrations of the methyl and methylene groups. -1 The absorption peak at this position corresponds to the C=O stretching vibration peak, 1531 cm⁻¹. -1The absorption peak at 1373 cm⁻¹ is due to the bending vibration of the NH group in the amide group. -1 The peak at 1130 cm⁻¹ is the deformation vibration peak of the hydroxyl group. -1 The absorption peaks in the ether bond region are mainly due to the irregular stretching vibrations of COC, while the vibrational absorption peaks are significantly weakened, possibly due to the chemical reaction between the filler and the polyurethane material. These characteristics indicate the successful preparation of SMPU / nanocomposite materials. Furthermore, it can be observed that the addition of a small amount of aminated multi-walled carbon nanotubes did not affect the peaks of the main functional groups in the polyurethane material.

[0027] (2) DSC analysis The thermal properties of SMPU / nanocomposites with MWNTs-COOH and MWNTs-NH2 of different mass fractions were analyzed. The DSC curves and data results are shown below. Figure 2 As shown in Table 1.

[0028] Table 1. DSC results of various SMPU composites

[0029] Depend on Figure 1 The results show that the SMPU after being combined with MWNTs-COOH has... T m It increased by 18.1 ℃. T c The temperature increased by 6.2 °C, and the enthalpy of crystallization also increased. This is likely because the addition of carboxylated multi-walled carbon nanotubes disrupted the hydrogen bonding between the amino (NH) and carbonyl (C=O) groups originally present in the polyurethane. Through hydrogen bonding between the -COOH groups on their surface and the carbonyl (C=O) groups in the hard segment phase and the ether (COC) groups in the soft segment phase, the soft and hard segments of the polyurethane are induced to arrange themselves systematically around the carbon nanotubes, which is beneficial for polyurethane crystallization and acts as a nucleating agent.

[0030] For SMPU composites containing MWNTs-NH2, the temperatures corresponding to both the highest melting peak and the highest crystallization peak initially increase and then decrease with increasing MWNTs-NH2 content. This is likely because an appropriate amount of MWNTs-NH2 can be well dispersed in the PU matrix, interacting effectively with it and promoting polyurethane crystallization, thus acting as a nucleating agent. Conversely, excessive MWNTs-NH2 hinders uniform dispersion within the SMPU matrix.

[0031] (3) XRD characterization XRD characterization was performed on pure SMPU, SMPU with composite MMWNTs-COOH, and SMPU with different contents of MWNTs-NH2. The results are shown in the figure. Figure 3 .

[0032] Depend on Figure 3 The results show that the diffraction peak intensity of the composite material increases with the addition of MWNTs-NH2, indicating that the orderliness of the internal structure of the composite system is improved after the addition of MWNTs-NH2. It is clearly shown in the figure that the SMPU / MWNT-NH2 prepared with 0.5 wt.% aminated multi-walled carbon nanotubes exhibits the highest diffraction peak intensity. However, with the addition of more MWNTs-NH2, the diffraction peak intensity of the composite material begins to decrease slightly. This phenomenon is because with the increase of MWNTs-NH2 content, the dispersion of CNTs within the composite material becomes more difficult, and a certain degree of agglomeration occurs, leading to a decrease in diffraction peak intensity. Adding an appropriate amount of MWNTs-NH2 can promote the orderly formation of the internal structure of the MWNTs-NH2 / SMP composite material, but with further increases in the MWNTs-NH2 content, the dispersion of MWNTs-NH2 in the composite matrix is ​​affected, thus weakening the effect of MWNTs-NH2 on the internal system of the composite material.

[0033] (4) TGA analysis Thermal stability tests were conducted on pure SMPU, SMPU / MWNTs, composite MMWNTs-COOH, and SMPU with different contents of MWNTs-NH2. The results are shown in Table 2 and 3. Figure 4 .

[0034] Table 2. Thermogravimetric Results

[0035] Table 2 shows that all samples exhibited three stages of thermal degradation. The first stage, at 265–300 °C, corresponds to the degradation of the end-capping agent. The second stage, at 320–380 °C, corresponds to the thermal decomposition range of the hard segments of the urethane chain. The third stage, at 380–500 °C, corresponds to the decomposition of the soft segments and a small amount of carbonaceous residue in SMPU. The maximum thermogravimetric peak was observed in the third stage, and the temperature at which the maximum mass loss occurred is the decomposition temperature of the SMPU / nanocomposite material. Compared to the pure SMPU matrix, the composite SMPU with added nanomaterials showed a shift in the initial decomposition temperature to a higher temperature range, indicating that the addition of nanoparticles improved the thermal stability of the SMPU matrix.

[0036] from Figure 4 (a) and Figure 4(b) The results show that, with a mass loss of 5%, the thermal decomposition temperature of the SMPU composite material exhibits a trend of first increasing and then decreasing after adding different contents of MWNTs-NH2. However, the thermal decomposition temperature of all SMPU composites with added MWNTs-NH2 is increased to varying degrees in the range of 283 ℃ to 290 ℃ compared to pure SMPU at a mass loss of 5%. Among them, the thermal decomposition temperature corresponding to 0.5 wt% MWNTs-NH2 is the highest, and the corresponding composite SMPU has the best thermal stability, which is 7 ℃ higher than that of pure SMPU. The thermal stability decreases when the MWNTs-NH2 nanomaterial addition is 0.8 wt.% and 1 wt.%, which may be due to the relatively poor dispersion of the nanomaterial in the SMPU matrix due to excessive content, resulting in uneven and discontinuous distribution. Heat accumulates along the tube wall, easily leading to a decrease in decomposition temperature. It may also be due to the increased nanomaterial content affecting the hydrogen bonding force between hard segments, resulting in reduced heat resistance.

[0037] (5) Mechanical property testing The influence of nanomaterials dispersed in the polymer matrix on the mechanical properties of the polymer is twofold. Firstly, they act as nucleating agents, promoting the crystallization of the soft segment structure of PU, thereby enhancing tensile mechanical properties. Secondly, the nanomaterials themselves form complex hydrogen-bonded cross-linked structures with the SMPU matrix. This cross-linking effect possesses strong tensile strength. The reinforcing effect of nanomaterials on the polymer is influenced by the type, size, and content of the nanomaterials. Stress-strain curves of SMPUs with composite MWNTs-COOH and different contents of MWNTs-NH2 are shown in [Figure / image / reference needed]. Figure 5 And Table 3.

[0038] Table 3 Mechanical properties of various composite materials

[0039] From Table 3 and Figure 5The results showed that the tensile strength of pure SMPU was 25.9 MPa, and the elongation at break was 1601.1%. The tensile strength of the SMPU composites improved significantly with the addition of different nanomaterials, while the elongation at break of the composites with different nanomaterials exhibited different patterns. The SMPU composite film with added MWNTs-COOH showed a significant increase in elongation at break, likely due to the lack of interfacial interaction between MWNTs-COOH and the SMPU matrix, which improved the toughness of the SMPU composite and thus increased the elongation at break. The composite SMPU film with added MWNTs-NH2 showed a decrease in elongation at break, likely due to the weak adhesion between the carbon-based nanomaterials and SMPU, with the nanomaterials acting as structural defects, leading to stress concentration.

[0040] With increasing MWNTs-NH2 content, the tensile strength of the SMPU composite material initially increases and then decreases, reaching a maximum of 31.2 MPa at a MWNTs-NH2 content of 0.5 wt.%. Compared to pure SMPU, the tensile strength is increased by approximately 20.4%. This is likely due to the formation of good hydrogen bonds between the -NH2 groups in the nanomaterials and the remaining -NCO groups after the reaction, allowing for good and uniform dispersion within the SMPU matrix. However, when the MWNTs-NH2 mass percentage is high, the movement of neighboring MWNTs may be constrained, reducing their alignment and leading to localized agglomeration in the composite material. This creates defects, resulting in stress concentration zones under external forces, reducing the adhesion of MWNTs-NH2 within the composite material, and ultimately decreasing its tensile strength.

[0041] (5) Shape memory performance analysis The shape memory effect of the SMPU spline with 0.5% MWNTs-COOH added in Example 5 was tested under a heating-cooling cycle at -36 ~ 25℃ and -36℃ ~ 50℃. The results are shown in [Figure 5]. Figure 6 .

[0042] Depend on Figure 6 (a) The results show that the reversible strain of the SMPU / MWNTs-COOH spline is approximately 15%, which is about 3% higher than that of pure SMPU, enabling a bidirectional shape memory effect without external stress. When the sample temperature is above 5℃ (T0 of the SMPU soft segment phase), the reversible strain is approximately 15%, which is about 3% higher than that of pure SMPU, enabling a bidirectional shape memory effect. mWhen the sample is cooled to -36°C, the oriented crystalline regions will melt, and the corresponding macroscopic shrinkage will be noticeable. When the sample cools to -36°C, guided by the internal stress provider, oriented crystalline regions will regenerate, thereby increasing the sample length. This depends on the crystal orientation of the soft segments in the sample and the internal stress storage and coordination during the programming process, ensuring that the SMPU can repeatedly deform without external force. Therefore, SMPU / MWNTs-COOH can lead to molecular-scale ordering of the polymer chains, resulting in a good shape memory effect.

[0043] Depend on Figure 6 (b) The results show that the reversible strain is approximately 19.6%. With increasing and decreasing temperature, the shape memory behavior of SMPU / MWNTs-COOH is mainly achieved through the melting and crystallization of the soft segments. The anisotropy of the polymer network and internal stress cause changes in the length of the sample, indicating that the sample exhibits good bidirectional shape memory behavior. Due to the shape memory effect, when the SMPU sample with both ends fixed is uniformly heated and cooled in cycles, the longitudinal shrinkage during heating is almost invisible, and crystallization is easily induced at low temperatures to form an arch shape. The macroscopic shape memory behavior of melt shrinkage and cooling elongation is achieved. During the testing process, it was found that the shape change was greater at the beginning of the different environments, regardless of whether it was the cooling or melting stage.

[0044] Furthermore, the elongation and shrinkage rates of SMPU / MWNTs-COOH samples were tested within the temperature range of -36 to 50°C. The results showed that compared to pure SMPU samples, the crystallization-induced elongation time of the SMPU composite sample with added MWNTs-COOH was shortened from 200 s to 150 s, and the melt-induced recovery rate was significantly improved, decreasing from 50 s to 33 s. This result demonstrates that the addition of MWNTs-COOH nanomaterials can improve the shape change rate of the material.

[0045] This invention is not limited to the specific embodiments described above. Any modifications made by those skilled in the art based on the above concept without creative effort are within the scope of protection of this invention.

Claims

1. A method for preparing a stress-free bidirectional shape memory polyurethane / nanocomposite material, characterized in that, Includes the following steps: S1. Using polytetrahydrofuran ether diol and hexamethylene diisocyanate as raw materials, a prepolymerization reaction is carried out under the catalysis of dibutyltin dilaurate to obtain a polyurethane prepolymer; then 1,4-butanediol is added to the polyurethane prepolymer system and the reaction is continued to obtain polytetrahydrofuran ether diol-based shape memory polyurethane as the polymer matrix. S2. Carbon-based nanomaterials are blended with polytetrahydrofuran ether diol-based shape memory polyurethane by melt blending to obtain stress-free bidirectional shape memory polyurethane / nanocomposite material; wherein, the carbon-based nanomaterials are carboxylated multi-walled carbon nanotubes or aminated multi-walled carbon nanotubes.

2. The method for preparing stress-free bidirectional shape memory polyurethane / nanocomposite material according to claim 1, characterized in that, The prepolymerization reaction temperature is 70-90℃, and the reaction time is 90-120 min.

3. The method for preparing stress-free bidirectional shape memory polyurethane / nanocomposite material according to claim 1, characterized in that, The continued reaction temperature is 70-90℃, and the reaction time is 30-60 min.

4. The method for preparing stress-free bidirectional shape memory polyurethane / nanocomposite material according to claim 1, characterized in that, The molecular weight of the polytetrahydrofuran ether diol is 650-2000.

5. The method for preparing stress-free bidirectional shape memory polyurethane / nanocomposite material according to claim 1, characterized in that, The molar ratio of polytetrahydrofuran ether diol, hexamethylene diisocyanate, and dibutyltin dilaurate is 0.01-0.1:0.22-0.3:0.012-0.

20.

6. The method for preparing stress-free bidirectional shape memory polyurethane / nanocomposite material according to claim 1, characterized in that, The mass ratio of the carbon-based nanomaterial to the polytetrahydrofuran ether diol-based shape memory polyurethane is 0.1-8:

100.

7. The method for preparing stress-free bidirectional shape memory polyurethane / nanocomposite material according to claim 1, characterized in that, The melting and blending temperature is 65-85℃, and the blending time is 36-54h.

8. A stress-free bidirectional shape memory polyurethane / nanocomposite material prepared by the preparation method according to any one of claims 1-7.

Images