CN113683900B - Modified lignin-polyamide-based thermosetting composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a modified lignin-polyamide-based thermosetting composite material and a preparation method thereof; the modified lignin-polyamide-based thermosetting composite material is prepared from raw materials containing modified lignin, polyamide and bismaleimide; the modified lignin is obtained by modifying lignin by an anhydride compound. The composite material of the invention forms a semi-interpenetrating network structure, has a lignin cross-linked network phase and a polyamide crystal phase, maintains excellent mechanical properties, gives a high-temperature shape memory effect, and can realize rapid high-temperature shape recovery at 180 ℃.

Description

A kind of modified lignin-polyamide-based thermosetting composite material and preparation method thereof

technical field

The invention relates to the technical field of bio-based functional materials, in particular to a modified lignin-polyamide-based thermosetting composite material and a preparation method thereof.

Background technique

Thermosetting resins represented by epoxy resins and phenolic resins are an important part of high-performance composite materials and play an important role in daily life and industrial production. However, most thermosetting materials are derived from fossil fuels, and the growing environmental The problem and the inherent requirement of "carbon neutrality" have provided the impetus for the development of bio-based thermosets.

Lignin is a natural biomass macromolecule second only to cellulose in reserves. As a by-product of the papermaking and biorefinery industries, lignin has a huge output and has not yet fully utilized its value. It is in urgent need of high-value utilization. The main structural units of lignin are p-coumarol, coniferyl alcohol and sinapyl alcohol, which are linked together by carbon-carbon bonds and ether bonds to form an amorphous hyperbranched structure. Lignin has a variety of functional groups, and phenolic and aliphatic hydroxyl groups are the reactive sites of lignin, which allows lignin to act as a natural cross-linking agent. It has been reported that lignin is used as a copolymerization component to prepare thermosetting materials such as phenolic resins and polyurethane resins. Such thermosetting materials are mostly amorphous or low-melting-point materials, while the use of lignin for preparing high-melting-point thermosetting composite materials has not yet been seen. report. Therefore, the present invention provides a modified lignin-polyamide-based thermosetting composite material and a preparation method thereof.

SUMMARY OF THE INVENTION

Purpose of the invention: The technical problem to be solved by the present invention is to provide a modified lignin-polyamide-based thermosetting composite material in view of the deficiencies of the prior art.

The technical problem to be solved by the present invention is to provide a preparation method of the above-mentioned modified lignin-polyamide-based thermosetting composite material.

Invention idea: The present invention proposes a new idea of lignin-based semi-interpenetrating network composite material. It intends to use the structural characteristics of lignin to introduce thermal cross-linking groups through modified lignin, which is compounded with polyamide with a higher melting point. The resulting composite material has a special structure in which the cross-linked network of lignin and the crystalline phase of polyamide coexist, which not only maintains excellent mechanical properties, but also reflects the high-temperature shape memory effect, providing technology for the development of bio-based smart materials. Learn from.

In order to solve the above-mentioned first technical problem, the present invention discloses a modified lignin-polyamide-based thermosetting composite material. The modified lignin and the polyamide form a semi-interpenetrating network structure, which has semi-crystalline properties. , with shape memory properties.

Wherein, the thermosetting composite material is prepared from raw materials containing modified lignin, polyamide and bismaleimide.

Wherein, the modified lignin is obtained by modifying lignin with acid anhydride compounds and imidazole compounds.

Wherein, the lignin includes but is not limited to sulfate lignin, organic lignin, alkali lignin, enzymatic lignin and lignin sulfate.

Wherein, the acid anhydride compounds include but are not limited to maleic anhydride.

Wherein, the imidazole compounds include but are not limited to 1-methyl-imidazole.

Wherein, the weight ratio of the lignin, the acid anhydride compound and the imidazole compound is 10:(1.5-2.5):(0.25-0.75).

Wherein, the modified solvent includes but is not limited to tetrahydrofuran; wherein, the amount of the solvent depends on the amount of lignin, and only needs to be dissolved; preferably, the mass concentration of the lignin in the reaction solution is 12 %-15%.

Wherein, the temperature of the modification is 20-100°C, preferably 40-80°C, more preferably 50-70°C, and even more preferably 60°C.

Wherein, the modification time is 0.5-5.5h, preferably 1-5h, more preferably 2-4h, still more preferably 3h.

Wherein, in the modification, after the reaction is completed, the solvent is removed, washed, filtered and dried to obtain the modified lignin; preferably, after the reaction is completed, the solvent is removed by rotary evaporation, washed with water, filtered and dried to obtain the modified lignin lignin.

Wherein, the weight fraction ratio of the modified lignin, polyamide and bismaleimide is (40-60):(40-60):(20-30).

In order to solve the above-mentioned second technical problem, the present invention discloses a preparation method of the above-mentioned thermosetting composite material. The mixed solution containing lignin, polyamide and bismaleimide is poured into a flat mold, and in the mold, the mixed solution is Casting to form a film, volatilizing at room temperature to remove the solvent, and curing.

Wherein, the mixed solution containing lignin, polyamide and bismaleimide can be mixed and dissolved according to common methods, that is, modified lignin, polyamide and bismaleimide can also be mixed and dissolved. The imides are respectively dissolved in the solvent and then mixed, preferably, the modified lignin, polyamide and bismaleimide are respectively dissolved in the solvent, and the three obtained solutions are ultrasonically centrifuged and then mixed.

Wherein, the solvent of the mixed solution is hexafluoroisopropanol and/or tetrahydrofuran.

Wherein, in the mixed solution, the ratio of the total weight of lignin, polyamide and bismaleimide to the weight of the solvent is (12-13):(85-110).

Wherein, the curing temperature is 150-250°C, preferably 170-220°C, more preferably 190-210°C, and even more preferably 200°C.

Wherein, the curing time is 5-45min, preferably 15-35min, more preferably 20-30min.

Beneficial effect: Compared with the prior art, the present invention has the following advantages:

(1) The content of lignin in the modified lignin-polyamide-based thermosetting composite material prepared by the present invention is as high as 40 wt%, which has high utilization efficiency of biomass resources and is beneficial to reduce the use of other materials.

(2) The present invention adopts the solution coating method to prepare the composite material, the preparation method is simple, and the matching degree with the existing production process is high.

(3) The present invention makes full use of the rich structural characteristics of lignin functional groups, obtains thermally cross-linkable modified lignin through derivatization modification, and the cross-linking temperature matches the material processing temperature window.

(4) A semi-interpenetrating network structure is formed in the composite material of the present invention, which has both a lignin cross-linked network phase and a polyamide crystal phase, which maintains excellent mechanical properties and gives it a high-temperature shape memory effect. Rapid high temperature shape recovery at °C.

Description of drawings

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the above-mentioned and/or other aspects of the present invention will become clearer.

Figure 1 shows the rheological analysis of thermosetting composite materials; (a) Example 1, (b) Comparative Example 1, (c) Example 2, (d) Comparative Example 2, (e) Example 3, (f) Comparative Example 2 Scale 3.

Figure 2 is a DSC analysis of thermoset composites.

Figure 3 shows the shape memory behavior of the thermosetting material in Example 3; (a) is the original shape, (b) is the temporary shape, (c-f) is the shape recovery process, and (g) is the final recovered shape.

Figure 4) Shape memory behavior of thermosets in Comparative Example 3.

Figure 5 shows the phosphorus spectrum analysis of modified lignin.

Detailed ways

The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

Example 1

(1) Dissolve 10 g of sulfate lignin, 2 g of maleic anhydride, and 0.5 ml of 1-methyl-imidazole in 80 ml of tetrahydrofuran, and stir under reflux at 60° C. for 3 hours. Upon completion, the solvent was removed by rotary evaporation. Washed with ultrapure water, filtered, and then vacuum-dried at 75 °C for 24 h to obtain modified lignin.

(2) Dissolve 5g of modified lignin, 5g of polyamide 12, and 2g of bismaleimide in 40ml, 40ml, and 16ml of hexafluoroisopropanol respectively; after ultrasonic centrifugation of the obtained three solutions, mix to ensure that the three are evenly mixed ; The mixed solution is poured into the mold, and the solution is cast to form a film.

(3) After the formed film is kept at a high temperature of 200° C. for 20 minutes, the curing is completed, and a thermosetting composite material with shape memory potential is obtained.

Comparative Example 1

(1) Get 5g sulfate lignin, 5g polyamide 12, 2g bismaleimide and dissolve in 40ml, 40ml, 16ml hexafluoroisopropanol respectively; Mix after the ultrasonic centrifugation of the three solutions to ensure that the three are evenly mixed ; The mixed solution is poured into the mold, and the solution is cast to form a film.

(2) After the formed film is kept at a high temperature of 200° C. for 20 minutes, the curing is completed, and a thermosetting composite material is obtained.

Example 2

(1) Dissolve 10 g of sulfate lignin, 2 g of maleic anhydride, and 0.5 ml of 1-methyl-imidazole in 80 ml of tetrahydrofuran, and stir under reflux at 60° C. for 3 hours. Upon completion, the solvent was removed by rotary evaporation. Washed with ultrapure water, filtered, and then vacuum-dried at 75 °C for 24 h to obtain modified lignin.

(2) Dissolve 5g of modified lignin, 5g of polyamide 12, and 2.5g of bismaleimide in 40ml, 40ml, and 20ml of hexafluoroisopropanol, respectively; the obtained three solutions are mixed after ultrasonic centrifugation to ensure that the three are mixed Homogeneous; the mixed solution is poured into the mold, and the solution is cast to form a film.

(3) After the formed film is kept at a high temperature of 200° C. for 20 minutes, the curing is completed, and a thermosetting composite material with shape memory potential is obtained.

Comparative Example 2

(1) get 5g sulfate lignin, 5g polyamide 12, 2.5g bismaleimide and dissolve in 40ml, 40ml, 20ml hexafluoroisopropanol respectively; After the obtained three solutions are ultrasonically centrifuged, mixing ensures that the three are mixed Homogeneous; the mixed solution is poured into the mold, and the solution is cast to form a film.

(2) After the formed film is kept at a high temperature of 200° C. for 20 minutes, the curing is completed, and a thermosetting composite material is obtained.

Example 3

(1) Dissolve 10 g of sulfate lignin, 2 g of maleic anhydride, and 0.5 ml of 1-methyl-imidazole in 80 ml of tetrahydrofuran, and stir under reflux at 60° C. for 3 hours. Upon completion, the solvent was removed by rotary evaporation. Washed with ultrapure water, filtered, and then vacuum-dried at 75 °C for 24 h to obtain modified lignin.

(2) Dissolve 5g of modified lignin, 5g of polyamide 12, and 3g of bismaleimide in 40ml, 40ml, and 25ml of hexafluoroisopropanol respectively; Mix the above solutions uniformly; pour the mixed solution into a mold , the solution was cast to form a film.

(3) After the formed film is kept at a high temperature of 200° C. for 20 minutes, the curing is completed, and a thermosetting composite material with shape memory potential is obtained.

Comparative Example 3

(1) get 5g sulfate lignin, 5g polyamide 12, 3g bismaleimide and dissolve in 40ml, 40ml, 25ml hexafluoroisopropanol respectively; The above solution is mixed uniformly; The mixed solution is poured into the mold , the solution was cast to form a film.

(2) After the formed film is kept at a high temperature of 200° C. for 20 minutes, the curing is completed, and a thermosetting composite material is obtained.

Example 4: Detection

(1) Rotational rheometer

In an air atmosphere, the composite films obtained in the step (2) in Examples 1, 2, and 3 and the composite films obtained in the step (3) in Comparative Examples 1, 2, and 3 were tested with a German MARS II rotational rheometer. The rheological properties were characterized. The storage modulus (G′) and loss modulus (G″) of the samples as a function of temperature program and time are shown in Figure 1. The composite films G obtained in step (2) in Examples 1, 2, and 3 The intersection point of ' and G" is at about 15-17 min, and at 25 min, the values of G' and G" tend to be stable. The composite films G' obtained in step (1) in Comparative Examples 1, 2, and 3 are similar to The intersection point of G" is at about 25min, and up to 45min, the values of G' and G" have not stabilized. Therefore, it is shown that the composite membrane obtained in step (2) in Examples 1, 2, and 3 can rapidly grow at 200 °C form a cross-linked network.

(2) DSC

Differential scanning calorimetry (DSC) was performed using a TA DSC25 to characterize the change in polymer thermal properties at a heating rate of 10°C/min. From Figure 2 and Table 1, it can be known that the cured thermosetting sample is semi-crystalline. In Examples 1-3, Tm is 175-176 ° C, ΔHm is 15-16 J/g, which is lower than the Tm of polyamide 12 (180.6 ℃) and ΔHm (35.4J/g), which indicated that the thermosetting polymer chain still had crystallinity, but the crystallinity decreased, which verifies the formation of the network structure. In Comparative Examples 1-3, the Tm is much lower than that of polyamide 12. This fully shows that the samples obtained in Comparative Examples 1-3 have a lower degree of perfection of the crystal region.

Table 1 Thermal properties of cured thermoset samples

sample T_m(℃) ΔH_m(J/g) nylon 180.6 35.4 Example 1 176.1 17.6 Example 2 176.0 17.6 Example 3 175.5 16.2 Comparative Example 1 170.6 14.4 Comparative Example 2 172.3 15.2 Comparative Example 3 174.2 17.0

(3) Shape memory performance

To qualitatively characterize the shape memory behavior, the rectangular strip samples were placed in an oven with a temperature of 190 °C, placed for 5 minutes and deformed by external force, and then taken out to be completely cooled and crystallized at room temperature, and then the force was removed. In the absence of external force, the deformed sample was placed in an oven at a temperature of 190 °C for 5 min to recover its shape.

Taking the sample of Example 3 (Fig. 3a) as an example, when heated to above Tm (190°C), the melting of the crystalline phase leads to an increase in the mobility of the molecular chains, while the cross-linked network still binds the movement of the molecular chains, so that the material does not become viscous. fluid state. At this time, an external force is applied to the sample to deform it. After cooling under the external force, the material re-formed the crystalline phase, and after the external force was released, a stable new shape, i.e., a temporary shape, was obtained (Fig. 3b). The shape at this time is maintained by the reversible phase, and its molecular chains are oriented and frozen along the direction of the external force, while the stationary phase is in a state of high stress deformation. When the temporary shape is heated to the shape recovery temperature of 190 °C, the crystalline phase melts to restore the mobility of molecular chains, and the orientation is released under the recovery stress of the stationary phase, and gradually reaches a thermodynamic equilibrium state (Fig. 3cdef). So far, the material recovered its original shape macroscopically (Fig. 3g), and it only took 9 s to recover.

Taking the sample of Comparative Example 3 (Fig. 4a) as an example, when heated to above Tm (190°C), an external force is applied to the sample to deform it, but the material part is transformed into a viscous flow state, and its original shape is destroyed due to the external force. (Fig. 4b).

(4) Phosphorus spectrum

Phosphorus spectra were measured on a Varian Mercury 400MHz NMR instrument. Acquisition parameters: 25°C, 11 spectral windows of 990 Hz, 256 sweeps, 20 s delay between pulses. The calculation of hydroxyl groups was based on the integration of the following spectral regions: as shown in Figure 5, alcoholic hydroxyl (149.6–145.6 ppm), 5-substituted units (144.2–141.2 ppm), guaiacyl-hydroxy (141.0–138.7 ppm), para Hydroxyphenylhydroxyl (138.7-137.2ppm) and carboxylic acid (135.9-133.ppm). Cholesterol as an internal standard. It can be found that the hydroxyl groups in the modified lignin are significantly reduced, indicating that the hydroxyl groups of lignin react with maleic anhydride. At the same time, it is verified that the alcoholic hydroxyl groups of lignin are easier to react with maleic anhydride than the phenolic hydroxyl groups.

Table 2 Quantitative analysis results of lignin ³¹ P-NMR

Unmodified lignin (mmol/g) Modified lignin (mmol/g) Alcohol hydroxyl 0.63 0.22 Condensed phenolic hydroxyl 0.23 0.21 eugenol hydroxyl 0.20 0.19 guaiacol hydroxyl 0.43 0.39 p-hydroxyphenyl phenolic hydroxyl 0.29 0.28 hydroxyl in carboxyl 0.58 0.63

The present invention provides an idea and method for a modified lignin-polyamide-based thermosetting composite material and a preparation method thereof. There are many specific methods and approaches for realizing the technical solution. The above are only the preferred embodiments of the present invention. It is pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims (5)

1. a modified lignin-polyamide-based thermosetting composite material is characterized in that, obtained by the raw material containing modified lignin, polyamide and bismaleimide; Wherein, the modified lignin is obtained by modifying lignin with maleic anhydride and 1-methyl-imidazole; the parts by weight of the lignin, maleic anhydride and 1-methyl-imidazole The ratio is 10:(1.5-2.5):(0.25-0.75); the modification temperature is 50-70℃, and the modification time is 2-4h; Wherein, the preparation method of the modified lignin-polyamide-based thermosetting composite material is to put a mixed solution containing modified lignin, polyamide and bismaleimide in a mold, cast to form a film, remove the solvent, curing; the curing temperature is 150-250°C; the weight fraction ratio of the modified lignin, polyamide and bismaleimide is (40-60): (40-60): (20- 30). 2 . The thermosetting composite material according to claim 1 , wherein the thermosetting composite material has shape memory properties. 3 . 3 . The thermosetting composite material according to claim 1 , wherein the solvent of the mixed solution is hexafluoroisopropanol and/or tetrahydrofuran. 4 . 4. The thermosetting composite material according to claim 1, wherein in the mixed solution, the ratio of the total weight of the modified lignin, polyamide and bismaleimide to the weight of the solvent is (12-13) : (85-110). 5 . The thermosetting composite material according to claim 1 , wherein the curing time is 5-45 min. 6 .

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