A tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material and its preparation method and application

Abstract

The present invention belongs to the field of wood-plastic composite materials, and discloses a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material, its preparation method and application. A tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material comprises the following raw material components in parts by mass: 20-100 parts of polylactic acid, 1.4-12 parts of tung oil, 6-30 parts of plant fiber, 0.07-0.6 part of initiator, and 0.006-0.05 part of accelerator. The high impact-resistant and environment-friendly wood-plastic composite material reinforced by the tung oil / fiber three-dimensional core-shell structure prepared by the present invention not only has excellent impact resistance, with an impact strength of up to 4.6 KJ / m<supgt;2< / supgt; and a flexural modulus of up to 6400 MPa at most, but also all materials are derived from natural biomass resources, have complete degradability, and can be applied to industries such as packaging and transportation, home decoration and furniture, electronic appliances, etc.

Description

Technical Field

[0001] The invention belongs to the field of wood-plastic composite materials, and in particular relates to a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material and a preparation method and application thereof. Background Art

[0002] Wood plastic composites are lightweight, cheap composite materials with excellent mechanical properties. Most commercial wood plastic composites are mainly composed of petroleum-based materials and plant fibers, such as polyethylene, polypropylene, polyvinyl chloride and sawn wood, straw, rice husks, corn stalks and other waste crops. The mechanical properties of this type of wood plastic composites mainly rely on the plastic matrix. The wood material mainly plays the role of filling to reduce costs and improve environmental protection. The mechanical properties are often poor, and some wood plastic composites rely on adhesives and are difficult to be completely degraded in nature. With the increasing use of such materials, the requirements for environmental protection are getting higher and higher. Wood plastic composites face huge challenges in saving resources and protecting the environment.

[0003] There are a lot of organic matter in nature. Human beings have used a lot of natural organic matter to synthesize polymers using knowledge of polymer chemistry, physics, organic chemistry, etc. Polylactic acid, as a polymer material polymerized from lactic acid, has great application value in the field of wood-plastic composite materials due to its excellent mechanical properties and excellent environmental protection. Plant fiber, as a widely existing natural resource, has the advantages of abundant reserves, low price, strong regeneration ability, and green environmental protection. There has been extensive research on the application of plant fiber in polymer-based composite materials. However, it is difficult for existing wood-plastic composite materials to achieve true complete degradation, and the plastic matrix has poor adhesion to the wood material and is extremely dependent on adhesives, especially in the field of home decoration, which will produce harmful gases such as formaldehyde.

[0004] Polylactic acid has poor brittleness, poor toughness, and poor impact resistance. Its products have poor cold processing performance and need to be toughened by other substances to obtain better impact resistance. Chinese patent CN111647256B discloses a polyethylene terephthalate-1,4-cyclohexanedimethanol (PCTG) toughened polylactic acid composite material, and uses polyethylene grafted glycidyl methacrylate as a compatibilizer and a ternary random copolymer of styrene-acrylonitrile-methacrylate dehydrated glyceryl ester as a toughening agent. PCTG, the compatibilizer, and the toughening agent are all non-degradable polymers, and only when the PCTG content reaches 60% can a better toughening effect be achieved, with an impact strength of about 6.26KJ / m 2, which is not only costly, but also greatly reduces the environmental friendliness of the composite material. Plant fiber itself contains a large amount of cellulose, and there are a large number of hydroxyl groups on cellulose, which makes it highly hydrophilic and has poor affinity for polymer matrices. Traditional wood-plastic composite materials need to add adhesives to obtain high-performance composite materials, but the cost is high and it is easy to produce harmful substances such as formaldehyde. Chinese patent CN109651782B discloses a composite plant fiber modified polylactic acid composite material, which uses ramie fiber, coconut shell fiber, polylactic acid, starch and rubber for thermal blending, and then hot pressing to obtain a board. The coconut shell fiber needs to be treated with cellulase and pectinase, and the ramie fiber needs to be treated with low-temperature plasma. The process is complicated and the cost is high. In addition, the prepared composite board has a maximum impact strength of about 1.85KJ / m 2 Therefore, the preparation of an environmentally friendly and high-performance wood-plastic composite material has broad application prospects. Summary of the invention

[0005] In view of the shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned wood-plastic composite material.

[0007] Another object of the present invention is to provide an application of the above-mentioned wood-plastic composite material.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material, comprising the following raw material components in parts by weight:

[0010]

[0011]

[0012] Preferably, the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material comprises the following raw material components in parts by weight:

[0013]

[0014] Preferably, the plant fiber is one or more of coconut petiole fiber, sisal fiber, hemp fiber and ramie fiber.

[0015] Preferably, the initiator and the promoter are 2-methyl ethyl ketone peroxide and cobalt cyclohexaneate, or benzoyl peroxide and tert-butyl hydroperoxide, respectively.

[0016] The preparation method of the above-mentioned tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material comprises the following steps:

[0017] (1) mixing tung oil, an initiator and an accelerator in a certain proportion to obtain prefabricated tung oil;

[0018] (2) treating the plant fiber with alkali and then washing it to neutrality to obtain prefabricated fiber;

[0019] (3) immersing the prefabricated fiber in step (2) in the prefabricated tung oil in step (1), vacuum-adsorbing the prefabricated tung oil in a vacuum box until saturated, and then vulcanizing the prefabricated fiber to obtain a mixed fiber;

[0020] (4) adding polylactic acid, the prefabricated tung oil in step (1), and the mixed fiber in step (3) into an internal mixer for melt blending, and continuing vulcanization, cooling, and granulation to obtain a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

[0021] Preferably, the vulcanization temperature in step (3) is 180-200° C., and the vulcanization time is 90-100 min.

[0022] More preferably, the vulcanization temperature in step (3) is 180° C. and the vulcanization time is 90 min.

[0023] Preferably, the alkali treatment in step (2) is a treatment with an alkaline solution having a concentration of 5 to 20 wt % for 2 to 4 hours, and the alkaline solution is a sodium hydroxide solution and / or a potassium hydroxide solution.

[0024] Preferably, the vacuum adsorption in step (3) is performed at a vacuum degree of ≥85% for 5 to 10 minutes;

[0025] More preferably, the vacuum degree is 95% for 5 minutes.

[0026] In step (4), the melting temperature is 180° C., the rotation speed is 60 to 100 r / min, the time is 8 to 10 min, and the continuous vulcanization time is 20 to 40 min.

[0027] Preferably, the mixing temperature in step (1) is 25 to 30° C., and the mixing time is 20 to 30 min.

[0028] Preferably, the mass ratio of the tung oil to the initiator and the accelerator in step (1) is 200:10:1.

[0029] The above-mentioned tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material is used in furniture, packaging and transportation, and electronic appliances.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] (1) The present invention mixes tung oil with an initiator and a promoter, and then adsorbs it onto plant fibers, and reacts and extrude it with polylactic acid. Under high negative pressure conditions, tung oil can penetrate into the interior of the plant fibers to form a tung oil / fiber three-dimensional core-shell structure. Under high heat fields at different times, the tung oil phase has different physical forms at different positions inside the composite material, thereby playing different roles. Under high shear fields, the tung oil mixed in first enhances the mobility of polylactic acid macromolecules, reduces the shear friction of polylactic acid on the fibers during mixing, and effectively retains the tung oil layer on the surface of the mixed fibers. The wood-plastic composite material prepared by the present invention not only has excellent impact resistance, but also has a high modulus. The impact strength can reach up to 4.6KJ / m 2 , the flexural modulus can reach up to 6400MPa.

[0032] (2) The tung oil in the formula can form a multiphase structure and a three-dimensional structure, which can toughen the matrix and enhance the compatibility of the fiber / PLA two-phase. Tung oil first penetrates into the plant fiber, fills the gaps between the microfiber bundles, and forms a tung oil / fiber three-dimensional core-shell structure with the tung oil on the fiber surface. After being fully vulcanized, it can transfer energy when impacted, and even destroy itself to absorb energy. The tung oil on the fiber can not only form a complex core-shell three-dimensional structure and firmly adhere to the fiber body, but also be miscible with the polylactic acid matrix, which is also an organic substance, to reduce the defects between the fiber and the matrix, and effectively transfer energy between the two phases when impacted.

[0033] (3) Since the short fibers themselves have a certain toughness, and the modulus increases after the tung oil phase is polymerized, the combination of the two can significantly reduce costs while retaining excellent mechanical properties. The application of this composite material can reduce the use of petroleum-based materials; the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material is prepared with polylactic acid, plant fiber, and tung oil as the main materials, has good biodegradability, and the preparation process is simple and efficient. It does not require complex processes and equipment and is more environmentally friendly. The composite material prepared by the present invention has a wide range of applications, such as home decoration, transportation, electronic appliances and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the SEM image of the cross section of the hybrid fiber prepared in Example 3.

[0035] Figure 2 This is the SEM image of the wood-plastic composite material prepared in Example 3.

[0036] Figure 3 This is the SEM image of the wood-plastic composite material prepared in Example 4.

[0037] Figure 4 SEM image of the wood-plastic composite material prepared in Example 2

[0038] Figure 5 This is the SEM image of the wood-plastic composite material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0040] The polylactic acid (brand number: 4032D) in the embodiments and comparative examples was purchased from Nature Works, USA; tung oil (first grade) was purchased from Jiangsu Jinyunxuan Building Materials Co., Ltd., 2-methyl ethyl peroxide was purchased from Shanghai Aladdin Reagent Co., Ltd., cobalt cyclohexane was purchased from Shanghai McLean Biochemical Reagent Co., Ltd., and coconut fiber was produced in Hainan.

[0041] Example 1

[0042] 200 grams of tung oil, 10 grams of 2-butanone peroxide, and 1g of cobalt cyclohexane acid are mixed evenly to obtain prefabricated tung oil. 20 grams of coconut handle fiber are treated in 10wt% sodium hydroxide solution for 2h to obtain alkali-treated coconut handle fiber. 10 grams of alkali-treated coconut handle fiber are immersed in prefabricated tung oil, vacuumed and adsorbed to saturation, fished out and wiped off the excess tung oil on the fiber surface, and vulcanized at 180°C for 90min to obtain a mixed fiber with a three-dimensional tung oil network attached to the inside and a tung oil film layer attached to the surface. 42.5 grams of polylactic acid, 1g of prefabricated tung oil, and 7.5g of mixed fiber are added to an internal mixer in sequence and melt-blended at 180°C for 8min, with a rotor speed of 60r / min, and vulcanized for 20min, and the material can be discharged and cooled to obtain a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

[0043] Example 2

[0044] 200 grams of tung oil, 10 grams of 2-butanone peroxide, and 1g of cobalt cyclohexane are mixed evenly to obtain prefabricated tung oil. 20 grams of coconut handle fiber are treated in 10wt% sodium hydroxide solution for 2h to obtain alkali-treated coconut handle fiber. 10 grams of alkali-treated coconut handle fiber are immersed in prefabricated tung oil, vacuumed and adsorbed to saturation, fished out and wiped off the excess tung oil on the fiber surface, and vulcanized at 180°C for 90min to obtain a mixed fiber with a three-dimensional tung oil network attached to the inside and a tung oil film layer attached to the surface. 40 grams of polylactic acid, 1g of prefabricated tung oil, and 10g of mixed fiber are added to an internal mixer in sequence, melt blended at 180°C for 8min, the rotor speed is 60r / min, and the vulcanization is continued for 20min, and the material can be discharged and cooled to obtain a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

[0045] Example 3

[0046] 200 grams of tung oil, 10 grams of 2-butanone peroxide, and 1g of cobalt cyclohexane are mixed evenly to obtain prefabricated tung oil. 20 grams of coconut handle fiber are treated in 10wt% sodium hydroxide solution for 2h to obtain alkali-treated coconut handle fiber. 10 grams of alkali-treated coconut handle fiber are immersed in prefabricated tung oil, vacuumed and adsorbed to saturation, fished out and wiped off the excess tung oil on the fiber surface, and vulcanized at 180°C for 90min to obtain a mixed fiber with a three-dimensional tung oil network attached to the inside and a tung oil film layer attached to the surface. 37.5 grams of polylactic acid, 0.8g of prefabricated tung oil, and 12.5g of mixed fiber are added to an internal mixer in sequence and melt-blended at 180°C for 8min, with a rotor speed of 60r / min, and vulcanized for 20min, and the material can be discharged and cooled to obtain a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

[0047] Example 4

[0048] 200 grams of tung oil, 10 grams of 2-butanone peroxide, and 1g of cobalt cyclohexane are mixed evenly to obtain prefabricated tung oil. 20 grams of coconut handle fiber are treated in 10wt% sodium hydroxide solution for 2h to obtain alkali-treated coconut handle fiber. 10 grams of alkali-treated coconut handle fiber are immersed in prefabricated tung oil, vacuumed and adsorbed to saturation, fished out and wiped off the excess tung oil on the fiber surface, and vulcanized at 180°C for 90min to obtain a mixed fiber with a three-dimensional tung oil network attached to the inside and a tung oil film layer attached to the surface. 35 grams of polylactic acid, 0.8g of prefabricated tung oil, and 15g of mixed fiber are added to an internal mixer in sequence, melt blended at 180°C for 8min, the rotor speed is 60r / min, and the vulcanization is continued for 20min, and the material can be discharged and cooled to obtain a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

[0049] Comparative Example 1

[0050] 40g of polylactic acid and 10g of alkali-treated coconut handle fiber were sequentially added into an internal mixer and melt-blended at 180°C for 8 minutes with a rotor speed of 60r / min. The material was then discharged and cooled to obtain a polylactic acid-based wood-plastic composite material that had not been blended with tung oil.

[0051] Comparative Example 2

[0052] 35g of polylactic acid and 15g of alkali-treated coconut handle fiber were sequentially added into an internal mixer and melt-blended at 180°C for 8 minutes with a rotor speed of 60r / min. The material was then discharged and cooled to obtain a polylactic acid-based wood-plastic composite material that had not been blended with tung oil.

[0053] The wood-plastic composite materials prepared in the above Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to an impact resistance test (tested according to GB / T 1843.2-2008 standard) and a bending performance test (tested according to GB / T1449-2005 standard). The test results are shown in Tables 1 and 2.

[0054] The impact fracture morphology of the wood-plastic composite materials prepared in the above examples and the composite materials obtained in Comparative Example 1 was observed using SEM. The results are as follows: Figure 1 , Figure 2 , Figure 3 shown.

[0055] Table 1 shows the impact properties of the wood-plastic composite materials prepared in Examples 1-4 and Comparative Examples 1-2.

[0056] Table 2 shows the flexural modulus of the wood-plastic composite materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2.

[0057] Table 1

[0058]

[0059] Table 2

[0060]

[0061] As shown in Table 1, compared with the comparative example, the impact strength of the wood-plastic composite material is significantly improved after being modified with tung oil. Tung oil plays a full toughening role on the polylactic acid matrix in the composite material. At a low content, tung oil can be evenly dispersed in the polylactic acid matrix and form a microphase with a diameter of about 1 micron. The micron-level tung oil phase has a certain toughness after solidification, which can enhance the mobility of polylactic acid macromolecules, so that when impacted, the polylactic acid group can fully deform and absorb energy, and can play a role in absorbing impact energy. At the interface between plant fiber and polylactic acid group, the tung oil phase with a higher degree of solidification can be fully compatible with the polylactic acid matrix on the one hand, and firmly adhere to the fiber surface on the other hand. The three-dimensional structure formed through the fiber interior can provide greater friction when deformed, and can also efficiently transfer energy.

[0062] As shown in Table 2, the bending modulus of Examples 1-4 is generally higher than that of Comparative Examples 1 and 2, and the highest bending modulus of Example 2 can reach 6406MPa. When the composite material is bent and deformed, the part above the neutral plane is subjected to compression, and the part below the neutral plane is subjected to tension. The short-cut fibers have a certain rigidity, and the tung oil phase at the interface can effectively transfer the tension and pressure borne by the polylactic acid matrix to the fibers, thereby achieving the effect of enhancing the modulus of the composite material. Figure 1 , Figure 2 , Figure 3 , Figure 4 It can be seen that tung oil is tightly attached to the fiber surface and penetrates into the fiber in large quantities. These two parts of tung oil are connected to each other to form a tung oil / fiber three-dimensional core-shell structure, which can perfectly bridge the defects of the interface between polylactic acid and plant fiber. The fiber failure form is breakage and tearing. Figure 5In the composite material shown, the interface compatibility between the fiber and the polylactic acid matrix is ​​poor, and there are a lot of gaps. When damaged, the force cannot be effectively transmitted to the fiber, and the fiber failure form is debonding, which is in sharp contrast to the two. Figure 3 It can be seen that the tung oil phase is evenly distributed in the polylactic acid matrix, forming a spherical microphase with a diameter of about 1 micron, which has a good toughening effect on the polylactic acid matrix. The combination of the spherical phase tung oil and the shell tung oil that wraps the fiber can maximize the energy absorption capacity of the polylactic acid matrix and the plant fiber, achieving the purpose of high impact performance.

[0063] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material, It is characterized in that The raw material components include the following parts by weight: Polylactic acid 20-100 parts 1.4-12 parts of tung oil 6-30 parts of plant fiber Initiator 0.07-0.6 parts Accelerator 0.006-0.05 parts; The initiator and the promoter are 2-methyl ethyl peroxide and cobalt cyclohexane acid respectively; The preparation method of the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material comprises the following steps: (1) Mixing tung oil, initiator and accelerator in proportion to obtain prefabricated tung oil; (2) treating the plant fiber with alkali and then washing it to neutrality to obtain prefabricated fiber; (3) immersing the prefabricated fiber in step (2) in the prefabricated tung oil in step (1), vacuum-absorbing the prefabricated tung oil until saturated, and then vulcanizing the prefabricated fiber to obtain a mixed fiber; (4) adding polylactic acid, the prefabricated tung oil in step (1), and the mixed fiber in step (3) into an internal mixer for melt blending, and continuing vulcanization, cooling, and granulation to obtain a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

2. The tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to claim 1, It is characterized in that The tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material comprises the following raw material components in parts by mass: Polylactic acid 35-50 parts 3-6 parts tung oil 7.5-15 parts of plant fiber Initiator 0.07-0.3 parts Accelerator 0.006-0.01 parts.

3. The tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to claim 1, It is characterized in that The plant fiber is one or more of coconut petiole fiber, sisal fiber, hemp fiber and ramie fiber.

4. The method for preparing the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to any one of claims 1 to 3, It is characterized in that The following steps are involved: (1) Mixing tung oil, initiator and accelerator in proportion to obtain prefabricated tung oil; (2) treating the plant fiber with alkali and then washing it to neutrality to obtain prefabricated fiber; (3) immersing the prefabricated fiber in step (2) in the prefabricated tung oil in step (1), vacuum-absorbing the prefabricated tung oil until saturated, and then vulcanizing the prefabricated fiber to obtain a mixed fiber; (4) adding polylactic acid, the prefabricated tung oil in step (1), and the mixed fiber in step (3) into an internal mixer for melt blending, and continuing vulcanization, cooling, and granulation to obtain a tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material.

5. The method for preparing the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to claim 4, It is characterized in that The vulcanization temperature in step (3) is 180-200° C., and the vulcanization time is 90-100 min.

6. The method for preparing the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to claim 4, It is characterized in that The alkali treatment in step (2) is a treatment with an alkaline solution having a concentration of 5 to 20 wt % for 2 to 4 hours, wherein the alkaline solution is a sodium hydroxide solution and / or a potassium hydroxide solution.

7. The method for preparing the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to claim 4, It is characterized in that The vacuum adsorption in step (3) is performed at a vacuum degree of ≥85% for 5 to 10 minutes; In step (4), the melting temperature is 180° C., the rotation speed is 60 to 100 r / min, the time is 8 to 10 min, and the continuous vulcanization time is 20 to 40 min.

8. The method for preparing the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to claim 4, It is characterized in that The mixing temperature in step (1) is 25-30° C. and the mixing time is 20-30 min.

9. Application of the tung oil / fiber three-dimensional core-shell structure reinforced polylactic acid-based wood-plastic composite material according to any one of claims 1 to 3 in furniture, packaging and transportation, and electronic appliances.

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