An inlaid biodegradable polyurethane / lignin composite material, a preparation method and application thereof

Abstract

The application discloses an inlaid biodegradable polyurethane / lignin composite material and a preparation method and application thereof. The preparation method of the inlaid biodegradable polyurethane / lignin composite material comprises the following steps: (1) obtaining NCO-terminated polyurethane prepolymer by taking polycaprolactone, polycarbonate diol and polyisocyanate as raw materials; (2) mixing and stirring lignin with the NCO-terminated polyurethane prepolymer under a solvent-free condition; (3) adding glycerol or 1,4-butanediol into the system to perform a chain extension reaction, so as to obtain a chain-extended product; and (4) vulcanizing the chain-extended product to obtain the inlaid biodegradable polyurethane / lignin composite material. The application provides application of the composite material in preparation of an armored track shock-absorbing block. The polyurethane / lignin composite material prepared by the application has high strength, low compression permanent deformation and biodegradability and the like, and can improve the bearing capacity and durability of the armored track as a whole.

Description

Technical Field

[0001] This invention relates to an embedded biodegradable polyurethane / lignin composite material, its preparation method, and its application in the preparation of armored track damping blocks. Background Technology

[0002] Armored vehicle track systems are subjected to complex impact and vibration loads during operation. Track shock absorbers, as key buffer components, need to have excellent wear resistance, impact resistance, and resistance to compressive permanent deformation.

[0003] Currently, most armored track shock absorbers are made of traditional petroleum-based rubber or polyurethane materials. Although they can meet certain mechanical performance requirements, the following problems still exist: the raw materials rely on petroleum resources, which is not conducive to sustainable development; the wear resistance and compression set resistance of the materials still have room for improvement; and although traditional fillers can improve material performance, they need to be improved in terms of material biodegradability.

[0004] In recent years, using natural biomass materials to reinforce polyurethane elastomers has become an important research direction. Among them, lignin is an abundant natural polymer with a large number of phenolic hydroxyl groups, which can form hydrogen bonds in polyurethane systems, thereby improving the strength of the material.

[0005] However, due to the poor compatibility between biomass fillers and polyurethane matrix, direct addition to the system often leads to uneven dispersion of the fillers, thus affecting the material properties.

[0006] The published patent CN120463895A relates to lignin-modified polyurethane, but it requires complex amination pretreatment of lignin. Furthermore, this patent uses polyether polyols and diisocyanates to prepare polyether-based polyurethane prepolymers. The chemical structure of the polyether segments is dominated by stable COC ether bonds, making them extremely difficult to hydrolyze or biodegrade in the natural environment. In addition, this patent uses polyether segments as soft segments and BDO as a chain extender, resulting in a linear or slightly branched structure lacking chemical crosslinking points. The molecular chains are prone to slippage under pressure, and the compression set is typically high. Therefore, the polyurethane material prepared by this patent cannot meet the requirements of high strength, low compression set, and biodegradability required for polyurethane materials used in armored track shock absorbers.

[0007] Therefore, it is of great significance to develop a method for preparing polyurethane materials that can achieve uniform dispersion of biomass fillers and improve the strength, compression set, and biodegradability of polyurethane materials. Summary of the Invention

[0008] The first objective of this invention is to provide a method for preparing an embedded polyurethane / lignin composite material, the prepared polyurethane / lignin composite material, and the application of this material in the preparation of shock-absorbing blocks for armored tracks. The preparation method is simple, environmentally friendly, and low-cost; the prepared polyurethane / lignin composite material possesses high strength, low compression set, and biodegradability, thereby improving the overall load-bearing capacity and durability of armored tracks.

[0009] In a first aspect, the present invention provides a method for preparing an embedded biodegradable polyurethane / lignin composite material, comprising the following steps:

[0010] (1) Obtaining NCO-terminated polyurethane prepolymer: Polycaprolactone (PCL) and polycarbonate diol (PCDL) are mixed evenly in a reactor at 70~130℃, and then polyisocyanate is added. The mixture is stirred at 70~130℃ for 1~3 h to obtain NCO-terminated polyurethane prepolymer.

[0011] (2) The dried lignin was mixed with the NCO-terminated polyurethane prepolymer obtained in step (1) under solvent-free conditions and mechanically stirred at 70~90℃ for 5~10 min. During the stirring process, the viscosity of the system showed a trend of "first gradually increasing and then stabilizing". This is because in the initial stage of stirring, lignin and prepolymer underwent partial interfacial reaction, resulting in an increase in molecular weight and viscosity. When the reaction sites reached saturation due to steric hindrance or local reaction equilibrium, the viscosity tended to stabilize. At this time, the system was still in a flowable liquid or paste state, indicating that the overall cross-linking and curing did not occur at this stage. Only the uniform dispersion and interfacial anchoring of lignin in the polyurethane matrix were completed. In addition, the hydroxyl groups in the lignin molecules that did not participate in the reaction constructed a dynamic physical cross-linking network through hydrogen bonding.

[0012] (3) After completing the interfacial reaction regulation in step (2), add glycerol or 1,4-butanediol to the system to carry out the chain extension reaction. The chain extension temperature is 70~90℃, so that the system is transformed into a solid state and the chain-extended product is obtained. During the chain extension reaction, it can be observed that the system gradually changes from a flowable state to a solid state, indicating that the chain extender triggers the rapid cross-linking reaction of residual -NCO.

[0013] (4) The chain-extended product is vulcanized to obtain a biodegradable polyurethane / lignin composite material;

[0014] The amount of lignin added is 10 to 40 wt% of the total mass of polycaprolactone, polycarbonate diol, polyisocyanate and glycerol or 1,4-butanediol.

[0015] The present invention does not add any organic solvents or aqueous dispersion media during the preparation process. The system completes the polymerization reaction by forming a reaction system by each reactant itself, which avoids the environmental pollution problems caused by the volatilization of organic solvents in traditional solvent methods or emulsion methods. Compared with the method of dissolving lignin with solvents or emulsion system, the present invention has the advantages of simple process, environmental friendliness and easy industrial scale-up.

[0016] In this invention, the moisture content of the polycaprolactone (PCL), polycarbonate diol (PCDL), and polyisocyanate should all be less than 0.05%. Preferably, the number average molecular weights of the polycaprolactone (PCL) and polycarbonate diol (PCDL) are 800-1200.

[0017] Preferably, in step (1), the feed ratio of polycaprolactone (PCL) and polycarbonate diol (PCDL) is 2:1-3:1 based on the molar ratio of their respective -OH groups; the polyisocyanate is added according to a molar ratio of -NCO groups in the polyisocyanate to the total -OH groups in the polycaprolactone (PCL) and polycarbonate diol (PCDL) of 1.5:1-3:1. More preferably, the feed ratio of polycaprolactone (PCL) and polycarbonate diol (PCDL) is 7:3 based on the molar ratio of their respective -OH groups.

[0018] Preferably, the polyisocyanate is selected from one or a combination of several of diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI). More preferably, the polyisocyanate is diphenylmethane diisocyanate (MDI).

[0019] Preferably, the lignin has a particle size between 1 and 5 μm.

[0020] Preferably, the amount of lignin added is 20% of the total mass of polycaprolactone (PCL), polycarbonate diol (PCDL), polyisocyanate, and glycerol or 1,4-butanediol.

[0021] Preferably, in step (2), the reaction temperature is 80°C.

[0022] In step (3) of the present invention, the amount of glycerol or BDO added is preferably such that all the residual -NCO in the system undergoes cross-linking reaction. In some embodiments, the mass percentage of BDO or glycerol is 4-5% based on the total mass of polycaprolactone, polycarbonate diol, polyisocyanate and glycerol or 1,4-butanediol as 100%.

[0023] Preferably, in step (4), the vulcanization is carried out on a flat vulcanizer. The pressing conditions of the flat vulcanizer are: temperature of 100-130 ℃, preheating time of 2-5 min, pre-pressing time of 3-6 min, full-pressing time of 5-10 min, cooling time of 1-5 min, and pressure of 50-80 bar.

[0024] In a second aspect, the present invention provides an embedded biodegradable polyurethane / lignin composite material prepared by the preparation method described in the first aspect.

[0025] The polyurethane / lignin composite material prepared by this invention includes a polyurethane matrix and lignin embedded or dispersed therein; wherein, the lignin portion reacts with isocyanate in the polyurethane matrix to form a chemically bonded interface layer, and the remaining unreacted portion forms a physical cross-linked network through hydrogen bonding, thereby constructing a multi-scale structural system in which chemical bonds and hydrogen bonds work synergistically; an interface transition layer structure is formed inside the composite material, and it exhibits heterogeneous distribution characteristics.

[0026] Thirdly, the present invention provides the application of the embedded biodegradable polyurethane / lignin composite material described in the second aspect in the preparation of armored track shock absorbers.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) In this invention, lignin is introduced into the polyurethane system, and the interface reaction and hydrogen bond synergistic effect between lignin and polyurethane prepolymer are achieved through the process of "dispersion followed by chain extension". This significantly improves the tensile strength of the material and reduces the permanent compression deformation, thereby enhancing the load-bearing capacity and durability of the shock absorber under complex impact load conditions. This enhancement effect comes from the synergistic effect of interface chemical bonds and hydrogen bonds, which is different from the traditional physical filler enhancement mechanism.

[0029] (2) The present invention adopts a solvent-free preparation process, which does not require the use of organic solvents or emulsion systems, thus avoiding the emission of volatile organic compounds (VOCs). It has significant environmental friendliness and industrial application advantages, which is different from polyurethane preparation methods that rely on solvent systems.

[0030] (3) This invention utilizes polycaprolactone diol (PCL) and polycarbonate diol (PCDL) as soft segment raw materials, and combines them with the biomass characteristics of natural lignin, so that the resulting material has good biodegradability and can gradually degrade in the natural environment, thereby reducing the environmental burden after the material is discarded.

[0031] (4) The biodegradability of the material of the present invention mainly comes from the ester bond structure contained in the soft segments of polycaprolactone (PCL) and polycarbonate diol (PCDL). This type of structure can be gradually broken under hydrolysis and microbial action. At the same time, lignin, as a natural polymer, has good environmental compatibility. In the present invention, due to the uniform dispersion of lignin in the polyurethane system and the optimization of the interface structure, it is beneficial for the degradation medium to penetrate into the interior of the material, thereby further promoting the overall degradation process of the material.

[0032] (5) In this invention, glycerol is further preferred as a chain extender. The trifunctional structure of glycerol can form chemical crosslinking points in the polyurethane system, constructing a three-dimensional network structure. Compared with traditional diol chain extenders (such as 1,4-butanediol), the glycerol chain extender system has a higher crosslinking density, which can significantly improve the tensile strength of the material, reduce compression set, and improve wear resistance. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] The lignin used in this embodiment of the invention is a product of Hangzhou Chemical Technology Co., Ltd., model D50, with a particle size of approximately 2 μm; the PCL model is Wanhua PCL1000, with a number-average molecular weight of 800~1200, a hydroxyl value of 112.58 mg KOH / g, and an acid value of 0.04 mg KOH / g; the MDI model is Wanhua MDI100, with a purity of 99.9%; the BDO model is G14172B, with a purity ≥99.0%; the glycerol model is G66258C, with a purity ≥99.0%; and the PCDL model is Ube UH1000, with a number-average molecular weight of 800~1200, a hydroxyl value of 111.9 KOH / g, and an acid value of 0.03 mg KOH / g.

[0035] In this embodiment of the invention, the moisture content of polycaprolactone (PCL), polycarbonate diol (PCDL), polyisocyanate, BDO, and glycerin used must be less than 0.05%. If the moisture content exceeds the standard, pretreatment is required to bring the moisture content to the standard. The pretreatment method includes: treating PCL, PCDL, polyisocyanate, BDO, and glycerin under vacuum at 120 °C for a certain period of time to bring the moisture content to the required level, and drying the lignin in an oven at 80 °C for 12 h.

[0036] In this invention, the content of -NCO groups is quantified by di-n-butylamine titration, and the content of lignin hydroxyl groups is determined by phenolic hydroxyl titration.

[0037] Example 1

[0038] By weight, the polyurethane matrix comprises 100 parts, including 44 parts PCL, 19 parts PCDL, 32 parts MDI, and 5 parts BDO, wherein the molar ratio of hydroxyl groups in PCL to PCDL is 7:3. The lignin content is 10 wt% of the polyurethane matrix.

[0039] (1) Preparation of component A polyurethane prepolymer

[0040] PCL and PCDL were placed in an 80 °C reactor and mixed at a constant 250 rpm for 15 min. MDI was weighed according to the formula, crushed into powder or small pieces and added to the reactor. The mixture was stirred at a constant 250 rpm for 2 h to obtain NCO-terminated polyurethane prepolymer.

[0041] (2) Preparation of biodegradable polyurethane

[0042] Lignin was added to the NCO-terminated polyurethane prepolymer, and the mechanical stirrer was set to 300 rpm and stirred at 80°C for 10 min. During stirring, the viscosity of the system showed a trend of "gradually increasing first and then stabilizing". This is because in the initial stage of stirring, some interfacial reactions occurred between lignin and the prepolymer, resulting in an increase in molecular weight and viscosity. When the reaction sites reached saturation due to steric hindrance or local reaction equilibrium, the viscosity tended to stabilize, and the system was still in a flowable state.

[0043] (3) Add BDO to the mixture from step (2) and react at 80°C for 10 min to extend the chain. During the chain extension reaction, the system can be observed to gradually change from a flowable state to a solid state. Then, press the mixture into polyurethane / lignin composite test strips in a flat vulcanizing machine.

[0044] The vulcanization temperature of the specimens used for tensile strength testing in a flat vulcanizer was 120 ℃, with a preheating time of 3 min, a pre-compression time of 4 min, a full compression time of 5 min, a cooling time of 2 min, and a pressure of 70 bar. The vulcanization temperature of the specimens used for compression set and Din abrasion testing in a flat vulcanizer was 120 ℃, with a preheating time of 5 min, a pre-compression time of 5 min, a full compression time of 10 min, a cooling time of 3 min, and a pressure of 70 bar. The prepared specimens were tested for tensile strength according to GB / T 528-2009, compression set according to GB / T 7759-2015, and abrasion resistance according to GB / T 9867. The results are shown in Table 1.

[0045] Example 2

[0046] Same as Example 1, except that the lignin content is 20 wt%.

[0047] Example 3

[0048] Same as Example 1, except that the lignin content is 30 wt%.

[0049] Example 4

[0050] Same as Example 1, except that the lignin content is 20wt%, and the chain extender is glycerol instead of 1,4-butanediol. The amount added is 100 parts by mass of polyurethane matrix, of which PCL is 46 parts, PCDL is 19 parts, MDI is 32 parts, and glycerol is 4 parts.

[0051] Compare with Example 1

[0052] The preparation of component A polyurethane prepolymer was the same as in Example 1. However, lignin was not added during the preparation of biodegradable polyurethane; instead, BDO was directly added according to the specified ratio for chain extension to obtain polyurethane resin. The polyurethane resin was then chopped into small pieces and premixed at 120°C for 5 minutes at 60 rpm in a torque rheometer. The mixing speed was then increased to 80 rpm, and lignin (equivalent to 10 wt% of the polyurethane resin) was added and mixed for 5 minutes to obtain lignin-reinforced polyurethane.

[0053] The testing procedure for the samples was the same as in Example 1. The results are shown in Table 1.

[0054] Compare with Example 2

[0055] Same as Control Example 1, except that the lignin content is 20 wt%.

[0056] Compare with Example 3

[0057] Same as Control Example 1, except that the lignin content is 30 wt%.

[0058] Compare with Example 4

[0059] Similar to Control Example 1, the difference is that no lignin was added, but the test sample was made directly.

[0060] Compare with Example 5

[0061] The difference between this comparative example and Example 1 is that lignin is not added during the preparation of the biodegradable polyurethane, and glycerol is used instead of 1,4-butanediol as the chain extender. The amount added, by mass, is 100 parts of polyurethane matrix, including 46 parts of PCL, 19 parts of PCDL, 32 parts of MDI, and 4 parts of glycerol. Sample preparation is the same as in Example 1.

[0062] Table 1 Tensile strength, compressive set, and Din abrasion of each sample

[0063]

[0064] Regarding interfacial and mechanical properties, this invention incorporates lignin into the polyurethane prepolymer before the chain extension reaction. This allows the active groups on the lignin surface to undergo a partial interfacial reaction with the isocyanate groups, forming a chemically bonded structure and simultaneously constructing a hydrogen bond network. Compared to simple physical filler systems, this structure significantly improves interfacial compatibility and stress transfer efficiency, thereby enhancing the overall mechanical properties of the material. Compared to the "post-addition" method of the comparative example, the "dispersion followed by chain extension" process of this invention significantly improves the dispersion uniformity of lignin and the interfacial compatibility between the two phases. As shown in Examples 1-3, the interfacial bonding is most ideal when the lignin addition is 20 wt%, with a tensile strength of 34.21 MPa and a compression set reduced to 38.50%. When the lignin addition increases to 30 wt%, excess lignin agglomerates, disrupting the interfacial structure and causing the tensile strength to decrease to 17.90 MPa, indicating the existence of an optimal addition range. In terms of mechanical properties, the composite material of the present invention is superior to the pure polyurethane system as a whole. The tensile strength of Example 2 is increased by about 35.8% compared with the control example 4, and the compression set is reduced from 52.40% to 38.50%. At the same addition amount, the tensile strength and compression set of the process of the present invention are both better than those of the control example, which verifies the advantages of the "dispersion first and then chain extension" process.

[0065] Regarding abrasion resistance, lignin, as a rigid biomass filler, can enhance tensile strength and reduce compression set by increasing the crosslinking density and hard segment content of the material through hydrogen bonding and physical crosslinking effects. However, this enhancement also restricts the mobility of molecular chain segments, reducing ductility and toughness. This leads to a shift in the wear mechanism from elastic deformation to brittle peeling and abrasive wear, exhibiting a trade-off between "rigidity enhancement, toughness loss, and decreased abrasion resistance." The Din abrasion losses in Examples 1-3 increased to 36.84, 43.93, and 49.37 mm³ with increasing lignin addition, respectively, all higher than the 15.30 mm³ of Control Example 4. However, at the same addition amount, the abrasion loss of the process of this invention (43.93 mm³) was better than that of the control example (47.65 mm³), indicating that improving dispersibility and interfacial bonding helps to mitigate the negative impact on abrasion resistance.

[0066] The effects of triol chain extender (glycerol) on material properties were further explored in Comparative Example 5 and Example 4. Compared with diol chain extender (BDO), the trifunctional structure of glycerol forms chemical crosslinking points in the system, constructing a three-dimensional network structure and significantly improving the crosslinking density of the material. As shown in Table 1, without the addition of lignin, the tensile strength of the glycerol chain extender system (Example 4) was 28.34 MPa, slightly higher than that of the BDO system (Comparative Example 4, 25.19 MPa); the compression set decreased from 52.40% to 37.42%, a reduction of 28.6%; and the abrasion resistance was particularly significantly improved, with Din abrasion decreasing from 15.30 mm³ to 12.12 mm³, a reduction of 20.8%. At a lignin content of 20%, the glycerol chain extender system (Example 4) achieved the best overall performance: tensile strength of 36.87 MPa (7.8% higher than 34.21 MPa in Example 2 of the BDO system), compression set of 32.65% (15.2% lower than 38.50% in Example 2), and Din abrasion of 35.24 mm³ (19.8% lower than 43.93 mm³ in Example 2). These results indicate a synergistic reinforcing effect between the glycerol chain extender and lignin. Lignin provides rigidity reinforcement through interfacial chemical bonding and hydrogen bonding, while glycerol increases the matrix crosslinking density by constructing a three-dimensional crosslinked network. The combined effect of these two factors achieves a comprehensive improvement in the material's mechanical properties, compression set resistance, and abrasion resistance. This technical feature further distinguishes it from polyurethane systems using diol chain extenders.

Claims

1. A method for preparing an embedded biodegradable polyurethane / lignin composite material, characterized in that: The preparation method includes the following steps: (1) Obtain NCO-terminated polyurethane prepolymer: Polycaprolactone and polycarbonate diol are mixed evenly in a reactor at 70~130℃ and then polyisocyanate is added. The mixture is stirred at 70~130℃ for 1~3 h to obtain NCO-terminated polyurethane prepolymer. (2) The dried lignin is mixed with the NCO-terminated polyurethane prepolymer obtained in step (1) under solvent-free conditions and mechanically stirred at 70~90℃ for 5~10 min. (3) Add glycerol or 1,4-butanediol to the system obtained in step (2) to carry out chain extension reaction. The chain extension temperature is 70~90℃ and the chain extension time is 10~15min, so that the system is converted into solid and the chain-extended product is obtained. (4) The extended product was vulcanized to obtain an embedded biodegradable polyurethane / lignin composite material. The amount of lignin added is 10 to 40 wt% of the total mass of polycaprolactone, polycarbonate diol, polyisocyanate and glycerol or 1,4-butanediol.

2. The preparation method according to claim 1, characterized in that: The number average molecular weights of the polycaprolactone and polycarbonate diol are 800-1200, respectively.

3. The preparation method according to claim 1, characterized in that: In step (1), the feeding ratio of polycaprolactone and polycarbonate diol is 2:1-3:1 based on the molar ratio of -OH groups contained in each; the polyisocyanate is added according to a molar ratio of -NCO groups contained in the polyisocyanate to the total -OH groups contained in the polycaprolactone and polycarbonate diol of 1.5:1-3:

1.

4. The preparation method according to claim 1, characterized in that: The polyisocyanate is selected from one or a combination of several of diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and isophorone diisocyanate.

5. The preparation method according to claim 1, characterized in that: The lignin has a particle size between 1 and 5 μm.

6. The preparation method according to claim 1, characterized in that: The amount of lignin added is 20% of the total mass of polycaprolactone, polycarbonate diol, polyisocyanate and glycerol or 1,4-butanediol.

7. The preparation method according to claim 1, characterized in that: The vulcanization is carried out on a flat vulcanizer. The pressing conditions of the flat vulcanizer are as follows: temperature 100-130 ℃, preheating time 2-5 min, pre-pressing time 3-6 min, full-pressing time 5-10 min, cooling time 1-5 min, and pressure 50-80 bar.

8. An embedded biodegradable polyurethane / lignin composite material prepared by the preparation method according to any one of claims 1-7.

9. The application of the inlaid biodegradable polyurethane / lignin composite material as described in claim 8 in the preparation of armored track damping blocks.

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