A thermoplastic-to-thermoset switchable artificial wood and method of making the same

Abstract

The present application belongs to the technical field of artificial wood, and particularly relates to a switchable artificial wood from thermoplastic to thermosetting and a preparation method thereof. The switchable artificial wood from thermoplastic to thermosetting comprises the following steps: melt blending degradable polyester, lignin containing C=C double bond, wood powder and group protective agent at 120-220 DEG C, the group protective agent inhibits the crosslinking reaction of C=C double bond, and thermoplastic artificial wood is obtained; the thermoplastic artificial wood is reacted at 240-290 DEG C, the group protective agent volatilizes, the crosslinking reaction of C=C double bond in the lignin occurs, and thermosetting artificial wood is obtained. The present application utilizes the plasticity at low temperature and the network structure curing at high temperature to prepare artificial wood material, thereby improving the processing performance, mechanical property, stability and water resistance of the artificial wood, realizing the consideration of the processing convenience and high performance of the artificial wood, and adapting to efficient production and complex application scenarios.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of artificial wood, and particularly relates to a switchable artificial wood from thermoplastic to thermosetting and a preparation method thereof. BACKGROUND

[0002] In order to adapt to the needs of social and economic development, artificial wood as an important substitute for natural wood has been widely used. Traditional artificial wood usually adopts polyethylene / polypropylene and other thermoplastic plastics mixed with lignin / wood powder to prepare artificial wood materials, such as the artificial wood provided in Patent Nos. JP2016138214A, CN201416251Y and CN104059371A, etc. In order to expand the wide application of wood-plastic composite materials in other aspects, such as the need for materials to have heat resistance, chemical resistance and moisture resistance, etc., wood-plastic composite materials obtained by using thermosetting resin are obviously a better choice. For example, in Patent No. CN105058692A, a continuous wood fiber reinforced thermosetting plastic composite material is disclosed, which is formed by one-shot injection molding of BMC plastic and wood fiber preform.

[0003] However, in the preparation process of artificial wood, there is a technical bottleneck that it is difficult to balance the processing efficiency and product performance. When using thermoplastic materials, although the processing flow can be simplified and the preparation period can be shortened, the prepared board has insufficient performance in terms of heat resistance, water resistance and dimensional stability, etc. When using thermosetting materials, although the high performance requirements of the board can be met, the preparation process is complex, time-consuming and energy-consuming, and cannot simultaneously adapt to the requirements of high efficiency production and complex application scenarios for product performance. SUMMARY

[0004] In order to solve the technical problem that the existing artificial wood is difficult to balance the processing efficiency and product performance in the preparation process, the present application provides a switchable artificial wood from thermoplastic to thermosetting and a preparation method thereof.

[0005] The present application uses a compound containing a phenol structure as a group protecting agent to protect the C=C double bond structure in lignin at a temperature of 120℃ to 220℃, so that the designed degradable artificial wood has the plasticity of traditional thermoplastic wood-plastic products at low temperature. After high-temperature strengthening deprotection at 240℃ to 290℃, the material becomes crosslinked, and the obtained wood-plastic product shows higher thermal stability and strength, is more suitable for extreme environments and is environmentally friendly. The present application provides a simple and easy-to-implement preparation method of artificial wood, and the prepared artificial wood has simple and reasonable raw material composition, scientific and environmentally friendly ingredients, high deformation resistance, high compressive strength, and can effectively replace natural wood.

[0006] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0007] A method for preparing a thermoplastic-to-thermoset switchable artificial wood, comprising the following steps:

[0008] A compound containing a phenol structure is used as a group protecting agent, and the degradable polyester, the lignin containing C=C double bond, the wood powder and the group protecting agent are melt-blended at 120-220 DEG C, the group protecting agent inhibits the cross-linking reaction of the C=C double bond, and the thermoplastic artificial wood is obtained; the thermoplastic artificial wood is reacted at 240-290 DEG C, the group protecting agent volatilizes, and the cross-linking reaction of the C=C double bond in the lignin occurs, and the thermoset artificial wood is obtained.

[0009] It should be noted that in the process of preparing the thermoplastic artificial wood, a suitable temperature needs to be selected, and a temperature that is too high will cause the components of the wood powder and the lignin to be oxidized and carbonized, affecting the quality of the final artificial wood material; a temperature that is too low will cause the lignin and the polyester to not be in a molten state, and the adhesion is poor, causing the production process to be unable to proceed. At a temperature of 240-290 DEG C, the group protecting agent sublimates, and the temperature is maintained for a period of time to ensure that the cross-linking reaction can be fully carried out. The essence of cross-linking is that the carbon-carbon double bond between the lignins undergoes a cross-linking reaction, and the linear structure material is combined into a three-dimensional network structure material, thereby realizing the conversion of the material from thermoplasticity to thermoset.

[0010] The requirement for temperature in the present application mainly depends on two aspects, one is the glass transition temperature of the degradable polyester used, and the other is the glass transition temperature of the lignin. The lignin used in the present application is all ordinary commercially available lignin, and the glass transition temperature thereof is between 160 DEG C and 190 DEG C. The second is the glass transition temperature of the degradable polyester, and the commonly used one is polybutylene adipate terephthalate, and the glass transition temperature thereof is between 100 DEG C and 140 DEG C. In summary, the temperature range selected in the present application when preparing the thermoplastic artificial wood is between 120 DEG C and 220 DEG C. Then, the cross-linking reaction is carried out at a temperature of 240 DEG C to 290 DEG C in the present application, so that the thermoplastic artificial wood is converted from thermoplasticity to thermoset, and due to the addition of the wood powder as the aggregate component in the formula component, necessary skeleton support is provided for further improving the strength before and after cross-linking.

[0011] Further, the group protecting agent is p-tert-butyl catechol or 4-methoxy phenol. The group protecting agent has a protective effect on the C=C double bond structure at a specific temperature.

[0012] Further, the thermoplastic artificial wood is prepared from the following raw materials in parts by weight: 10-30 parts of degradable polyester, 30-60 parts of lignin containing C=C double bond, 30-60 parts of wood powder and 1-2 parts of group protecting agent.

[0013] Further, the lignin containing C=C double bond is lignin formed by polymerization of phenylpropane units or C-type lignin formed by polymerization of caffeol units, wherein the phenylpropane units are coniferyl alcohol or sinapyl alcohol, both of which contain allyl structure at the gamma position of the side chain, and the caffeol units contain propenyl structure in the side chain.

[0014] Further, the degradable polyester is at least one of polybutylene adipate terephthalate, polybutylene terephthalate, polylactic acid, polyhydroxyalkanoate, polybutylene succinate, polycaprolactone and polypropylene carbonate. The degradable polyester ensures the biodegradability of the artificial wood.

[0015] Further, the wood powder is pine powder with a particle size of 150-200 mesh. The pine powder is mainly derived from needle tree species such as radiata pine and spruce, and has long fibers and can be used as a skeleton structure material for artificial wood.

[0016] Further, in the preparation process of the thermosetting artificial wood, the reaction time is 2-5 min.

[0017] Further, before melt blending, the degradable polyester, the lignin containing C=C double bond and the wood powder need to be dried in advance.

[0018] The thermosetting artificial wood is prepared by the above method.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] In the present application, a compound containing a phenol structure is used as a group protecting agent. The degradable polyester, the lignin containing C=C double bond, the wood powder and the group protecting agent are melt blended at 120-220 DEG C. At this temperature, the group protecting agent protects the C=C double bond structure in the lignin and inhibits the crosslinking reaction of the C=C double bond in the lignin, thereby obtaining a thermoplastic artificial wood. Then, the thermoplastic artificial wood is reacted at 240-290 DEG C. At this temperature, the group protecting agent volatilizes and the C=C double bond in the lignin undergoes crosslinking reaction, thereby obtaining a thermosetting artificial wood. Through step-by-step temperature control and dynamic crosslinking regulation and design, the present application precisely solves the technical problem that the processing efficiency and product performance are difficult to be considered in the preparation process of traditional artificial wood.

[0021] The present application is in the process of preparing thermoplastic artificial wood, melt blending at 120℃-220℃, which is compatible with the traditional thermoplastic wood processing temperature, can adapt to the existing blending equipment, without modifying the production line. At the same time, at this temperature, the group protecting agent inhibits the crosslinking of C=C double bond in lignin, so that the system remains thermoplastic, can be freely shaped with the mold, retains the advantages of traditional thermoplastic board processing convenient, flexible forming, solves the problem of complex operation of thermosetting board. Then the thermoplastic artificial wood is reacted at 240℃-290℃, at this temperature, the group protecting agent volatilizes, the C=C double bond in lignin crosslinks to form a three-dimensional network structure, combined with the skeleton support of wood powder, significantly improves the heat resistance, water resistance, dimensional stability and mechanical strength of the material, makes up for the performance short board of traditional thermoplastic board. And the thermosetting conversion only needs 2-5 minutes, without the curing period of several hours of traditional thermosetting board, the energy consumption is lower, solves the problem of long time and large energy consumption. The preparation method of the artificial wood provided by the present application realizes the combination of convenient processing and high performance of artificial wood, and adapts to efficient production and complex application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the physical photo of the thermosetting artificial wood in example 1.

[0023] Figure 2 It is the strength test result of the thermosetting artificial wood in example 1.

[0024] Figure 3 It is the wetting test result of the artificial wood prepared in comparative example 3 and the thermosetting artificial wood prepared in example 1. Among them, a is the contact angle data graph of the artificial wood prepared in comparative example 3, b is the contact angle data graph of the thermosetting artificial wood prepared in example 1.

[0025] Figure 4 It is the heat resistance test result of the thermosetting artificial wood prepared in example 1.

[0026] Figure 5 It is the degradation data of the thermosetting artificial wood prepared in example 1.

[0027] Figure 6 It is the mechanical property test of the artificial wood prepared in example 6 and comparative example 1.

[0028] Figure 7 It is the mechanical property test of the artificial wood prepared in comparative example 2.

[0029] Figure 8 It is the water absorption data graph of the thermosetting artificial wood prepared in example 1.

[0030] Figure 9 It is the impact strength data graph of the thermosetting artificial wood prepared in example 1-4.

[0031] Figure 10 A shrinkage data chart of the thermosetting artificial wood prepared for Examples 1-4. DETAILED DESCRIPTION

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0033] The specific embodiments of the present application will be described in detail below, but it should be understood that the protection scope of the present application is not limited by the specific embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application. The experimental methods described in the embodiments of the present application are all conventional methods, and the materials, reagents, etc. used in the following embodiments are commercially available unless otherwise specified.

[0034] The lignin formed by polymerization of the phenylpropanoid unit of coniferyl alcohol, the lignin formed by polymerization of the phenylpropanoid unit of sinapyl alcohol and the C-type lignin containing caffeic alcohol unit used in the present application are purchased from Anhui Fengyuan Group, and the weight average molecular weight of the three lignins is 2000-6000; the wood powder is pine powder, which is purchased from Guangdong Mujiang Weihua Spice Factory, and the particle size is 150-200 mesh; the weight average molecular weight of polybutylene adipate terephthalate is 50000-150000; the weight average molecular weight of polybutylene terephthalate is 100000; the weight average molecular weight of polylactic acid is 100000-120000; the weight average molecular weight of polyhydroxy aliphatic acid is 100000-150000; the weight average molecular weight of polybutylene succinate is 100000-150000; the weight average molecular weight of polycaprolactone is 80000; and the weight average molecular weight of polypropylene carbonate is 100000.

[0035] The English name of polybutylene adipate-co-terephthalate is Poly(butylene adipate-co-terephthalate), and the English abbreviation is PBAT; the English name of polylactic acid is Polylactic Acid, and the English abbreviation is PLA; the English name of polyhydroxyalkanoate is Polyhydroxyalkanoate, and the English abbreviation is PHA; the English name of polybutylene succinate is Poly(butylene succinate), and the English abbreviation is PBS; the English name of polycaprolactone is Polycaprolactone, and the English abbreviation is PCL; the English name of polypropylene carbonate is Poly propylenecarbonate, and the English abbreviation is PPC.

[0036] A method for preparing a thermoplastic-to-thermofix switchable artificial wood, comprising the following steps:

[0037] The raw materials are as follows in parts by weight: 10-30 parts of degradable polyester, 30-60 parts of lignin containing C=C double bond, 30-60 parts of wood powder, and 1-2 parts of group protecting agent. The degradable polyester, lignin containing C=C double bond and wood powder are mixed, and screw blending or open mill mixing can be used. The temperature is set to 120-220 DEG C. At this temperature, the group protecting agent has a protective effect on the C=C double bond structure, avoiding crosslinking reaction of the C=C double bond. After reaching the preset temperature, the components are mixed. During the mixing process, the degradable polyester retains the basic thermoplasticity of the artificial wood composite, and its shape can be changed at will according to the mold, retaining the advantages of the existing wood-plastic products on the market, and having biodegradable properties. After mixing, the plasticizing is completed, and a thermoplastic artificial wood is obtained.

[0038] The thermoplastic artificial wood is strengthened and cured. The thermoplastic artificial wood is placed in a high-temperature oven for baking, and the temperature is set to 240-290 DEG C, and the baking time is 2-5 min. Because the group protecting agent of p-tert-butyl catechol or 4-methoxy phenol volatilizes at high temperature, the C=C double bond structure in the lignin is deprotected and crosslinked. Based on the rigid skeleton structure of the wood powder fiber, the thermoplastic artificial wood changes from thermoplasticity to thermofixity at this time, obtaining a thermofixity artificial wood, which further improves the water resistance, mechanical strength and dimensional stability of the artificial wood material, so that it can be used in high temperature, humid environment for a long time.

[0039] Example 1

[0040] A method for preparing a thermoplastic-to-thermofix switchable artificial wood, comprising the following steps:

[0041] Step 1, preparation of thermoplastic artificial wood:

[0042] Lignin 40 parts, pine wood powder 40 parts, PBAT 20 parts, put the above raw materials into a 60℃ air oven for drying for 8h, and reserve for use. The lignin containing polymerized benzene propane unit of sinapyl alcohol is referred to as lignin hereinafter.

[0043] Weigh 4-methoxyphenol 1 part, check the equipment state of the open mill, ensure that the surface of the double rollers is clean and free of impurities, set the temperature of the open mill to 160℃, start the heating system and preheat for 30min, and after the temperature of the open mill reaches 160℃, first add PBAT and 4-methoxyphenol between the double rollers of the open mill, start the double rollers, set the speed of the front roller to 20r / min and the speed of the rear roller to 25r / min, keep the speed ratio of the front roller to the rear roller at 1:1.25, and after the PBAT is completely melted and uniformly adheres to the double rollers, continue mixing for 5min to make the 4-methoxyphenol melt fully integrated with the PBAT, and during this period, use a triangular spatula to gather the material at the edge of the roller to the middle 2-3 times.

[0044] Then slowly reduce the distance between the double rollers to 0.2mm, and start to add lignin in batches, and the amount of lignin added each time is determined according to the width of the double rollers of the open mill and the width of the melt, for example, for a 30cm wide roller, the amount of lignin added each time is about 5 parts. The specific operation is as follows: first add lignin to cover the part of the PBAT melt on the surface of the double rollers completely, immediately use a triangular spatula to repeatedly cut, fold and turn the material to ensure that the lignin is uniformly dispersed in the melt, and this process lasts for 5min, until the surface of the material presents a uniform light brown color. Then add pine wood powder in equal batches, mix in the same way as the lignin, until the color of the material is uniform and there is no obvious pine wood powder particles exposed. After each mixing is completed, increase the distance between the double rollers by about 0.1mm, and the adjustment process should be slow to avoid the material falling off suddenly.

[0045] Repeat the above lignin and pine wood powder addition and mixing operation until all the lignin and pine wood powder is completely added. After all the materials are added, continue mixing for 15min, and during this period, clean the material at the edge of the roller with a triangular spatula every 3min to ensure uniform mixing of the whole material, and finally obtain a thermoplastic artificial wood with uniform texture, no obvious particles and uniform color.

[0046] In the process of preparing the thermoplastic artificial wood, a suitable temperature needs to be selected, and too high a temperature will cause the pine wood powder and lignin components to oxidize and carbonize, affecting the quality of the final artificial wood material. Too low a temperature will cause the lignin and PBAT not to be in a molten state, resulting in poor adhesion and making the production process impossible.

[0047] Step 2, preparation of thermosetting artificial wood:

[0048] The thermoplastic artificial wood is shaped and then placed in a high-temperature oven for baking at 245°C for 3 minutes. At this time, the thermoplastic artificial wood changes from its original thermoplasticity to thermosetting, thus obtaining thermosetting artificial wood.

[0049] It should be noted that at temperatures above 240°C, the protective agents in the thermoplastic engineered wood sublime, and maintaining this temperature for a period of time ensures that the crosslinking reaction proceeds fully. The essence of crosslinking in this embodiment is the crosslinking reaction of carbon-carbon double bonds between lignin, combining linear materials into a three-dimensional network structure, thereby achieving the transformation of the material from thermoplastic to thermosetting.

[0050] In the processing stage of thermoplastic engineered wood, a group-protecting agent is added. This agent preferentially binds to free groups activated during heating, making it difficult for them to react with carbon-carbon double bonds and thus crosslink. During the blending stage, interfacial separation is observed regardless of whether wood flour or lignin is added. Poor compatibility between materials makes blending difficult, and separation leads to a significant decrease in strength. Adding lignin to wood flour can solve these problems to some extent, as lignin acts as a compatibilizer and crosslinking agent. Microscopically, the hydroxyl and ester groups on lignin interact with the biodegradable polyester chains and pine flour through hydrogen bonds, allowing the pine flour and lignin to be uniformly dispersed between the polyester chains. Furthermore, large wood flour particles attached to the lignin also provide skeletal support, offering certain mechanical properties. During the second heating and curing process, the group-protecting agent is eliminated at high temperatures, causing free radical reactions between the carbon-carbon double bonds in the lignin, which then combine with the biodegradable polyester chains to form a three-dimensional network composite material. In the above preparation process, the specific parameters such as time and temperature are related to the melting temperature and processing temperature of the polymer used. Excessive temperatures may cause the biodegradable polyester to exceed the processing temperature, resulting in poor blending performance. Furthermore, excessively long blending times can also lead to a decline in material properties.

[0051] Figure 1 This is a photograph of the thermosetting artificial wood used in Example 1. Figure 2 The results show the strength test results of the thermosetting engineered wood in Example 1. The thermosetting engineered wood obtained in Example 1 has a breaking strength of 21 MPa, demonstrating excellent mechanical properties.

[0052] Example 2

[0053] A method for preparing artificial wood that can switch between thermoplastic and thermosetting processes, prepared according to the method described in Example 1, with the difference being:

[0054] In step 1, the biodegradable polyester is converted into PLA, and the open mill temperature is set to 180℃.

[0055] The tensile strength of the thermosetting artificial wood obtained in this embodiment is 33.6 MPa.

[0056] Example 3

[0057] A method for preparing a thermoplastic-to-thermoset switchable artificial wood, prepared according to the method described in Example 1, with the difference that:

[0058] In step 1, the lignin is lignin formed by polymerization of cinnamyl alcohol units, the pine powder is 30 parts, and the PBAT is 10 parts; in step 2, the molded thermoplastic artificial wood is placed in a high-temperature oven for baking, and the temperature is set to 290°C.

[0059] The tensile strength of the thermosetting artificial wood obtained in this embodiment is 20.3 MPa.

[0060] Example 4

[0061] A method for preparing a thermoplastic-to-thermoset switchable artificial wood, prepared according to the method described in Example 1, with the difference that:

[0062] In step 1, the lignin is lignin formed by polymerization of cinnamyl alcohol units, and the group protecting agent is p-tert-butyl catechol; in step 2, the molded thermoplastic artificial wood is placed in a high-temperature oven for baking, and the temperature is set to 240°C.

[0063] The tensile strength of the thermosetting artificial wood obtained in this embodiment is 22.1 MPa.

[0064] Example 5

[0065] A method for preparing a thermoplastic-to-thermoset switchable artificial wood, prepared according to the method described in Example 4, with the difference that:

[0066] In step 2, the molded thermoplastic artificial wood is placed in a high-temperature oven for baking, and the temperature is set to 285°C, and the baking time is 5 min.

[0067] The tensile strength of the thermosetting artificial wood obtained in this embodiment is 21.3 MPa.

[0068] Example 6

[0069] A method for preparing a thermoplastic-to-thermoset switchable artificial wood, prepared according to the method described in Example 1, with the difference that:

[0070] In step 1, the lignin is C-type lignin formed by polymerization of coffee alcohol units, and the degradable polyester PBAT and PLA, and the mass ratio of PBAT to PLA is 3:7, and the temperature of the open mill is set to 220°C; in step 2, the molded thermoplastic artificial wood is placed in a high-temperature oven for baking, and the temperature is set to 287°C, and the baking time is 5 min.

[0071] The tensile strength of the thermoset artificial wood obtained in this example was 35 MPa, as shown in Figure 6 .

[0072] Comparative Example 1

[0073] A method for preparing a thermoplastic artificial wood was prepared according to the method described in Example 6, with the difference that step 2 was omitted.

[0074] The tensile strength of the thermoplastic artificial wood obtained in this comparative example was 22 MPa, as shown in Figure 6 .

[0075] Comparative Example 2

[0076] A method for preparing a thermoplastic artificial wood was prepared according to the method described in Example 1, with the difference that step 2 was omitted.

[0077] The tensile strength of the thermoplastic artificial wood obtained in this comparative example was 12.0 MPa, as shown in Figure 7 .

[0078] Example 7

[0079] A method for preparing a thermoplastic-to-thermoset switchable artificial wood was prepared according to the method described in Example 1, with the difference that:

[0080] In step 1, the lignin was C-type lignin formed by polymerization of caffeol units, the degradable polyester was PHA, and the temperature of the open mill was set to 200°C; in step 2, the molded thermoplastic artificial wood was placed in a high-temperature oven for baking, with the temperature set to 250°C and the baking time set to 4 min.

[0081] The tensile strength of the thermoset artificial wood obtained in this example was 39.5 MPa.

[0082] Example 8

[0083] A method for preparing a thermoplastic-to-thermoset switchable artificial wood was prepared according to the method described in Example 1, with the difference that:

[0084] In step 1, the lignin was C-type lignin formed by polymerization of caffeol units, the degradable polyester was PBS, and the temperature of the open mill was set to 150°C; in step 2, the molded thermoplastic artificial wood was placed in a high-temperature oven for baking, with the temperature set to 250°C and the baking time set to 4 min.

[0085] The tensile strength of the thermoset artificial wood obtained in this example was 43.1 MPa.

[0086] Example 9

[0087] A method for preparing a thermoplastic-to-thermofix switchable artificial wood, prepared according to the method described in Example 1, with the difference that:

[0088] In step 1, the degradable polyester is PCL, and the temperature of the open mill is set to 120℃; in step 2, the thermoplastic artificial wood that has been molded is placed in a high-temperature oven for baking, with the temperature set to 247℃ and the baking time set to 4min.

[0089] The tensile strength of the thermofix artificial wood obtained in this example is 26.2MPa.

[0090] Example 10

[0091] A method for preparing a thermoplastic-to-thermofix switchable artificial wood, prepared according to the method described in Example 1, with the difference that:

[0092] In step 1, the lignin is lignin formed by polymerization of coniferyl alcohol benzyl alcohol units, and the degradable polyester is PPC, and the temperature of the open mill is set to 220℃; in step 2, the thermoplastic artificial wood that has been molded is placed in a high-temperature oven for baking, with the temperature set to 247℃ and the baking time set to 4min.

[0093] The tensile strength of the thermofix artificial wood obtained in this example is 18.1MPa

[0094] Comparative Example 3

[0095] A method for preparing a thermofix artificial wood, prepared according to the method described in Example 1, with the difference that: in step 1, no group protecting agent is added; step 2 is omitted.

[0096] The tensile strength of the thermofix artificial wood obtained in this example is 27.8MPa.

[0097] Test method:

[0098] 1. Tensile strength test: The prepared plastic artificial wood is dried at 60℃ for 4 hours, and then 2mm thick dumbbell-shaped samples are prepared on a micro-injection molding machine according to the sample preparation standards specified in national standards GB / T17037.2-2020 and GB / T17037.3-2003, and the stress-strain curve, tensile strength and elongation at break of the sample are obtained on a universal tensile testing machine at a tensile speed of 20mm / min. For thermofix materials after crosslinking, 2mm thick sheets are prepared under a hot press, and then cut into 2cm x 8cm samples for tensile testing.

[0099] 2. Contact angle test: A DSA 100 contact angle tester from KRUSS, Germany, is used. The sample with a smooth surface is placed on the test table, a drop of water is dropped on the surface, and the contact angle of the water drop on the surface is photographed. Generally, the greater the contact angle, the stronger the hydrophobicity.

[0100] 3. Degradation performance test: The sample was crushed into powder by the method of liquid nitrogen freezing and crushing with a crusher. Three parallel controls were set for each group of samples, about 300g for each group of samples, and about 100g for each test sample. In addition, fully degradable cellulose was used as a positive reference, non-degradable polyethylene as a negative reference, and a group of blank controls were set, a total of 6 groups of samples were tested in the compost degradation tank. According to GB / T19277.1 and GB / T19277.2, the degradation temperature was set to 58℃, the temperature change of the compost sample was controlled within ±2℃, the humidity was maintained at about 50%, the pH was maintained at 7-9, the CO2 concentration was monitored regularly, the biodegradation rate was calculated, and the pH was tested every week, the soil color was observed, and the performance change rule of the degradation process was obtained. The degradation performance test is shown in Figure 5 .

[0101] 4. The sample was analyzed by simultaneous thermal analyzer, about 10mg sample was heated from ambient temperature to 800℃ at a heating rate of 10℃ / min under 60mL / min nitrogen environment, and the mass change was recorded. The thermal gravimetric test is shown in Figure 4 .

[0102] 5. Water resistance test: The material was processed into uniform 4mmx20mmx100mm rectangular strip samples, which were placed in deionized water until completely immersed, and the sample was taken out every 24h, the surface moisture was absorbed with absorbent paper, and then the mass was measured, the mass change within one week was recorded, and three groups were measured and the average value was taken.

[0103] 6. Impact test: According to the national standard ISO 179-1, 4mm thick rectangular samples were prepared, and the impact strength of the sample was measured by a simply supported beam impact testing machine. Each sample was tested three times and the average value was taken.

[0104] 7. Shrinkage rate test: 4mmx20mmx100mm rectangular strip samples were prepared, which were placed in a constant temperature and humidity chamber with a temperature of 40℃ and a humidity of 95%, and after 96h, the sample was taken out and the surface moisture was immediately measured using a vernier caliper. Three samples were tested at the same time, and the average value was taken.

[0105] Data analysis:

[0106] From Figure 3 , it can be seen that the thermosetting artificial wood prepared in Example 1 has a larger contact angle than pure wood powder material, i.e. the material has better water resistance.

[0107] Through Figure 2 and Figure 7Comparative Example 2, the tensile strength of the wood-like material prepared in Example 1 is increased to 21 MPa by the cross-linking operation; the tensile strength increase rate is 75.0%. The elongation at break of the wood-like material prepared in Comparative Example 2 is 4.7%; the elongation at break of the wood-like material prepared in Example 1 is increased to 6%; the elongation at break increase rate is 27.7%.

[0108] As shown in Figure 4 , the wood-like material prepared in Example 1 starts to slightly decompose at about 245℃, and reaches the highest decomposition rate at 350℃. The decomposition amount reaches 5wt% at 366℃. Thus, it is shown that the wood-like material prepared in the embodiment of the present application has excellent heat resistance.

[0109] As shown in Figure 5 , the wood-like material prepared in Example 1 has a degradation rate of 88% at the 24th week. Thus, it is shown that the wood-like material prepared in the embodiment of the present application has excellent degradability.

[0110] As shown in Figure 6 , the tensile strength of the wood-like material prepared in Comparative Example 1 is 22 MPa, and the elongation at break is 3.8%; under the same formulation conditions, the tensile strength of the wood-like material prepared in Example 6 is increased to 35 MPa, and the elongation at break is increased to 6.2%.

[0111] As shown in Figure 8 , the wood-like material prepared in Example 1 has a water absorption amount of less than 3% at the seventh day of water soaking; and the water absorption amount is 0.7% at the first day, which is lower than the national standard of 1%.

[0112] As shown in Figure 9 , the impact strength of the wood-like material prepared in Examples 1-4 is ≥12kJ / m 2 .

[0113] As shown in Figure 10 , the shrinkage rate of the wood-like material prepared in Examples 1-4 is stably in the range of 0.3%-0.5%.

[0114] In summary, the tensile strength of the wood-like material prepared in the embodiment of the present application is greater than 20 MPa, the impact strength of the wood-like material obtained after secondary cross-linking strengthening is ≥12kJ / m 2 , the shrinkage rate is stably in the range of 0.3%-0.5%, and the water absorption rate after 24h soaking is <0.7%.

[0115] The traditional artificial wood usually adopts a wood-like material prepared by blending lignin / wood powder with thermoplastic plastic such as polyethylene / polypropylene, which has the following inherent defects: non-degradability, easy structure collapse in high temperature environment, poor dimensional stability caused by high water absorption, low temperature embrittlement, etc., which is difficult to meet the requirements of high strength and heat resistance of artificial wood material. In view of the above defects, the present application is based on a new theory of thermoplastic-thermoset switchable polymer synthesis, and a new type of artificial wood with reversible processing characteristics and permanent setting ability is developed by constructing a dynamic covalent bond network system. Through the change of material properties from thermoplasticity to thermosetting, the process of wood-plastic composite material from thermoplastic forming to thermoset strengthening can be completed in one step, which solves the problem of difficult processing of thermosetting materials and the problem of limited application scene of thermoplastic materials. Specifically as follows: first, a composite system composed of degradable polyester, lignin, wood powder and group protecting agent is used, that is, a thermoplastic artificial wood. The system can realize the filling of lignin and wood powder of more than 70%, and retains the degradability. And due to the presence of lignin and group protecting agent, the system can adapt to the existing polyethylene / polypropylene thermoplastic wood-plastic processing technology under low temperature processing conditions of 120 DEG C to 220 DEG C, has cyclic operability, and the preparation process is simple and the production efficiency is high. Then, after the thermoplastic artificial board is formed, secondary high temperature strengthening at 240 DEG C to 290 DEG C can be carried out according to the use requirements, the group protecting agent in the whole system is volatilized and removed, and the double bond is crosslinked and solidified to prepare a thermosetting artificial wood, which further improves the heat resistance, mechanical strength and water resistance of the artificial wood material. At the same time, the system still retains the degradability, providing a high-performance green alternative solution for infrastructure construction, home manufacturing and other fields. The preparation process provided by the embodiment of the present application not only solves the problem of low processing efficiency of thermosetting wood-plastic composite material, but also changes from thermoplasticity to thermosetting in the subsequent strengthening process, which solves the performance problems of thermoplastic materials.

[0116] Although preferred embodiments of the application have been described, those skilled in the art who have the benefit of the present disclosure will appreciate that additions, deletions and modifications to the described embodiments can be made without departing from the scope of the application.

[0117] Obviously, various modifications and changes can be made to the present application by those skilled in the art without departing from the spirit and scope of the present application. If these modifications and changes belong to the scope of the equivalent technology of the present application, the present application also intends to include these modifications and changes.

Claims

1. A method of making a thermoplastic-to-thermoset switchable artificial wood, characterized by, The method comprises the following steps: The thermoplastic artificial wood is obtained by melt blending the degradable polyester, the lignin containing C=C double bond, the wood powder and the radical protecting agent at 120-220 DEG C, wherein the radical protecting agent inhibits the cross-linking reaction of the C=C double bond, and the radical protecting agent is p-tert-butyl catechol or 4-methoxy phenol. The lignin containing C=C double bond is lignin formed by polymerization of coniferyl alcohol or sinapyl alcohol, or C-type lignin formed by polymerization of caffeol units. The degradable polyester is at least one of polybutylene adipate terephthalate, polybutylene terephthalate, polylactic acid, polyhydroxyaliphatic acid, polybutylene succinate, polycaprolactone and polypropylene carbonate. The thermosetting artificial wood is obtained by reacting the thermoplastic artificial wood at 240-290 DEG C, wherein the radical protecting agent volatilizes, and the C=C double bond in the lignin undergoes cross-linking reaction.

2. The method of claim 1, wherein, The thermoplastic artificial wood is prepared from 10-30 parts of the degradable polyester, 30-60 parts of the lignin containing C=C double bond, 30-60 parts of the wood powder and 1-2 parts of the radical protecting agent.

3. The method of claim 1, wherein, In the preparation of the thermosetting artificial wood, the reaction time is 2-5 min.

4. The method of claim 1, wherein, The wood powder is pine powder with a particle size of 150-200 mesh.

5. A switchable artificial wood from thermoplastic to thermoset, characterized in that, The thermoplastic-to-thermoset switchable artificial wood is prepared by the method of any one of claims 1-4. The thermoplastic-to-thermoset switchable artificial wood is prepared by the method of any one of claims 1-4.

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