Torreya grandis shell-based bioplastic and preparation method thereof

Abstract

The application discloses a torreya grandis shell-based biological plastic and a preparation method thereof, and relates to the technical field of biological-based materials.The preparation method comprises the following steps: removing lignin from the torreya grandis shell which is cleaned, dried and crushed, disc mill-fibrillating the remaining part, and finally mixing the obtained torreya grandis shell fiber with polybutylene adipate terephthalate and part of the added torreya lignin to form a film, gradient hot pressing, so as to obtain the biological plastic.The preparation method of the torreya grandis shell-based biological plastic has high utilization rate of waste torreya grandis shell, and the process is convenient because no precise purification is performed; and the obtained biological plastic has unique torreya essential oil fragrance, antibacterial property and high anisotropic mechanical property.

Description

Technical Field

[0001] This invention relates to the field of bio-based materials, and more specifically, to a Torreya grandis shell-based bioplastic and its preparation method. Background Technology

[0002] Torreya grandis not only has landscape and ecological value, but its dried fruit is also rich in various nutrients. The entire Torreya grandis plant contains a large amount of volatile aromatic substances, hence its name. Current research and utilization of Torreya grandis mainly focuses on the chemical composition and physiological activity of its leaves and seeds. Some patented technologies also involve the extraction and utilization of essential oils, flavonoids, and other components from the aril of Torreya grandis. However, the fruit shell of Torreya grandis receives less attention and is often directly discarded as a byproduct of Torreya grandis product production.

[0003] Since Torreya grandis shells are mainly composed of cellulose and lignin, some existing technologies involve carbonizing them to produce activated carbon or even hard carbon anode materials (Chinese invention CN116443852A). However, carbonization results in the loss of volatile components and beneficial substances such as polyphenols and flavonoids, leading to low utilization of Torreya grandis shells. Furthermore, the resulting products lack distinctive features and advantages compared to similar products obtained from other raw materials. Similarly, methods that separate and purify the cellulose within the Torreya grandis shell before application are also wasteful and cannot meet the current development needs of materials science for low-cost, full-component utilization of biomass raw materials.

[0004] Existing technologies, such as Chinese invention patents CN101550378A and CN111820394A, attempt to prepare fragrances using Torreya grandis shells. However, because the volatile oil content in Torreya grandis shells is far lower than that in the aril and leaves, and according to research by Hu Liuyan et al., the volatile oil in pure Torreya grandis shells does not have significant antibacterial activity compared to other Torreya grandis fragrances, the cost-effectiveness of using Torreya grandis shells to prepare fragrances is low, and the products are not competitive. Most of the effective substances in existing Torreya grandis shell essential oils on the market actually still originate from the aril.

[0005] Replacing petroleum-based materials with bio-based materials is a crucial means of achieving sustainable development and environmental protection goals. Compared to traditional technologies that extract bio-based materials from biomass raw materials before manufacturing products, cutting-edge literature discloses a method for directly processing and pressing corn husks into high-strength, high-transmittance biomaterials. However, a similar method for using Torreya grandis shells is still lacking, which involves targeted pretreatment based on the characteristics of the raw material and fully utilizing the beneficial substances in Torreya grandis shells to enhance product added value. Summary of the Invention

[0006] The present invention aims to provide a Torreya grandis shell-based bioplastic and its preparation method, which makes full use of Torreya grandis shell components to obtain an anisotropic high-strength bioplastic of poly(butylene adipate / terephthalate)-delignified Torreya grandis shell fiber-Torreya grandis shell lignin, while retaining the main fragrance substances in Torreya grandis shell.

[0007] This invention discloses a method for preparing Torreya grandis shell-based bioplastics, comprising the following steps:

[0008] (1) After cleaning and drying, the Torreya grandis shells are crushed and then the lignin is removed in a eutectic solvent to obtain Torreya grandis lignin and deligated Torreya grandis shells;

[0009] (2) The lignin-free Torreya grandis shells were milled and defibriled to obtain lignin-free Torreya grandis shell fibers;

[0010] (3) Poly(butylene adipate / terephthalate), delignified Torreya husk fiber and Torreya lignin are mixed and spread into a film. The fibers are arranged in the same direction, and then subjected to gradient hot pressing, cooling and demolding to obtain Torreya husk-based bioplastic.

[0011] Furthermore, the Torreya husk-based bioplastic comprises, by mass parts, 40-60 parts of polybutylene adipate / terephthalate, 30-45 parts of delignified Torreya husk fiber, and 5-15 parts of Torreya lignin.

[0012] Preferably, the Torreya grandis shell-based bioplastic further comprises, by weight, 1-3 parts chitosan and 0.5-2 parts lubricant, wherein the lubricant is selected from oleamide, erucamide, calcium stearate and combinations thereof.

[0013] Preferably, the eutectic solvent comprises choline chloride and lactic acid in a molar ratio of 1:1.5 to 3, and also comprises water in a mass fraction of 3 to 5%.

[0014] More preferably, the temperature for removing lignin is 80-100°C, the time is 4-7 hours, and the material-to-liquid ratio is 1:8-15 g / mL.

[0015] Furthermore, the crushing process involves crushing the Torreya grandis shells to a particle size of 1.5–4 mm.

[0016] More preferably, the disc milling and fiber unwinding is performed by disc milling at a speed of 200-300 rpm for 3-5 minutes.

[0017] Preferably, the fiber arrangement in the same direction is achieved by heating the mixture to 60-80°C, and then repeatedly applying unidirectional shear force with a scraper, wherein the scraper gap is 0.5-1 mm and the traction rate is 1-2 m / min.

[0018] Furthermore, the gradient hot pressing is as follows: first, preheating at 90-100℃ and 5MPa pressure for 2-3 minutes, and then pressing at 130-140℃ and 20MPa pressure for 4-6 minutes.

[0019] The present invention also discloses a Torreya grandis shell-based bioplastic prepared according to the above method.

[0020] The beneficial effects of the technical solution of the present invention are:

[0021] 1. The method for preparing Torreya grandis shell-based bioplastics described in this invention utilizes all components of Torreya grandis shells, resulting in high waste utilization and a green, environmentally friendly, and cost-effective product.

[0022] 2. The preparation method of the present invention is based on the existing low eutectic solvent delignination method and the lignin-free fiber hot pressing molding method. It improves the low eutectic solvent formulation and bioplastic raw material ratio according to the characteristics of Torreya grandis shell production, and adds back the degenerated lignin part, thereby improving the mechanical properties of the product and better preserving the main essential oil substances without extraction and separation.

[0023] 3. The Torreya husk-based bioplastic of the present invention is a fully biodegradable bioplastic with unique Torreya husk essential oil fragrance, antibacterial properties, and anisotropic mechanical properties, which has distinctive advantages compared with existing products. Detailed Implementation

[0024] To make the technical means, creative features, objectives, and effects of this invention easier to understand, the technical solution of this invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the implementation methods of this invention and should be understood as illustrative rather than limiting of the technical solution of this invention.

[0025] The present invention provides a method for preparing a Torreya grandis shell-based bioplastic, comprising the following steps:

[0026] (1) After cleaning and drying, the Torreya grandis shells are crushed and then the lignin is removed in a eutectic solvent to obtain Torreya grandis lignin and deligated Torreya grandis shells;

[0027] (2) The lignin-free Torreya grandis shells were milled and defibriled to obtain lignin-free Torreya grandis shell fibers;

[0028] (3) Polybutylene adipate / terephthalate (PBAT), delignified Torreya husk fiber and Torreya lignin are mixed and spread into a film, the fibers are arranged in the same direction, and then gradient hot pressing, cooling and demolding are performed to obtain Torreya husk-based bioplastic.

[0029] This invention employs the eutectic solvent (DES) method to roughly separate the main components of Torreya grandis shell, cellulose and lignin, under mild conditions. Then, the cellulose is defibriled under conditions that minimize damage to the long fibers. Finally, it is hot-pressed together with PBAT, refilled lignin, and other components to form a bioplastic.

[0030] Existing technologies utilize conventional methods for separating and reusing cellulose from Torreya grandis husks, which are time-consuming, labor-intensive, and result in the loss of other components. Other existing technologies involve directly hot-pressing plant fiber tissue after removing lignin, but the cellulose in Torreya grandis husks lacks a regular two-dimensional structure, making it difficult to press tightly. To address this, this invention uses a portion of recycled lignin as a hydrophobic binder and employs thermoplastic substrate PBAT to penetrate fiber voids and enhance interfacial bonding. Compared to ordinary cellulose / cellulose nanocrystal-filled plastics, the bioplastic of this invention features more intact cellulose fibers, exhibiting unique mechanical properties such as high strength and high orientation, while significantly reducing costs.

[0031] Furthermore, the Torreya husk-based bioplastic comprises, by mass parts, 40-60 parts of polybutylene adipate / terephthalate, 30-45 parts of delignified Torreya husk fiber, and 5-15 parts of Torreya lignin.

[0032] The torreya lignin can be added in the form of solids or DES solution, and only the content of the active ingredient is considered when calculating the mass fraction. The poly(butylene adipate) / terephthalate is added in the form of fine particles.

[0033] Preferably, the Torreya grandis shell-based bioplastic further comprises, by weight, 1-3 parts chitosan and 0.5-2 parts lubricant, wherein the lubricant is selected from oleamide, erucamide, calcium stearate and combinations thereof.

[0034] Chitosan can crosslink fibers through ester bonds during the pressing process, acting as a binder, while the lubricant components of the conventional components can improve the smoothness of the film surface after subsequent coating. Since the delignified Torreya grandis husk fiber and Torreya grandis lignin in the bioplastic formulation of this invention are biomass mixtures mainly composed of cellulose and lignin, containing natural antioxidants and anti-hydrolysis components, and rich in surface-active groups from crude cellulose and lignin, they can be compounded with PBAT without the need for other processing aids or modifications.

[0035] Preferably, the eutectic solvent comprises choline chloride and lactic acid in a molar ratio of 1:1.5 to 3, and also comprises water in a mass fraction of 3 to 5%.

[0036] Acidic eutectic solvents have a stronger ability to dissolve lignin and are more suitable for nut shell raw materials with high lignin content. In addition, when the amount of acid is controlled, their ability to retain cellulose is also stronger than that of basic eutectic solvents. Water can adjust the polarity and permeability of the solvent, enhance its selective affinity for the β-O-4 bonds of lignin, and a small amount of water will not weaken the hydrogen bond network.

[0037] More preferably, the temperature for removing lignin is 80-100°C, the time is 4-7 hours, and the material-to-liquid ratio is 1:8-15 g / mL.

[0038] To reduce the volatilization of essential oil substances, this invention uses a low eutectic solvent to remove lignin at a temperature slightly lower than that of the prior art, and correspondingly extends the removal time slightly. The lignin removal rate is between 90% and 96%, and the cellulose retention rate is between 88% and 93%.

[0039] Furthermore, the crushing process involves crushing the Torreya grandis shells to a particle size of 1.5–4 mm.

[0040] More preferably, the disc milling and fiber unwinding is performed by disc milling at a speed of 200-300 rpm for 3-5 minutes.

[0041] Larger particle size and low-intensity disc milling can retain 80% of the long fibers (≥1mm) in Torreya grandis shells, and dissociate the fiber bundles into single fibers during grinding (average diameter reduced by about 50%), thereby improving the tensile strength of the material in the direction parallel to the fiber extension.

[0042] Preferably, arranging the fibers in the same direction involves heating the mixture to 60–80°C, then repeatedly applying unidirectional shear force with a doctor blade, wherein the doctor blade gap is 0.5–1 mm and the traction speed is 1–2 m / min. Alternatively, a directional roller can be used to apply the unidirectional shear force.

[0043] Furthermore, the gradient hot pressing is as follows: first, preheating at 90-100℃ and 5MPa pressure for 2-3 minutes, and then pressing at 130-140℃ and 20MPa pressure for 4-6 minutes.

[0044] The first stage of preheating softens and plies PBAT, initially fixing the fiber orientation under low pressure. The second stage of hot pressing melts the PBAT and penetrates the fiber gaps, locking the fiber orientation. The hot pressing temperature of 130-140℃ is higher than the melting point of PBAT but lower than the boiling point of the main essential oil components of Torreya grandis shell (limonene, α-pinene), but the pressing time still needs to be controlled to reduce essential oil volatilization.

[0045] Furthermore, preferably, the cooling and demolding is performed by holding the temperature under pressure and cooling to below 60°C before demolding. Holding pressure during the cooling process allows the PBAT crystallization and solidification to better align with the fiber alignment.

[0046] The following detailed description is provided in conjunction with specific examples. Unless otherwise specified, all experimental methods described are conventional methods, and all raw materials described are from undifferentiated, conventional sources.

[0047] Example 1

[0048] (1) Wash 1 kg of Torreya grandis shells (rice Torreya grandis, produced in Yixian County, Anhui Province) and dry them at a low temperature of 45℃, then crush them into Torreya grandis shell particles with an average particle size of 2.5 mm.

[0049] (2) In a closed container, 4 kg of choline chloride, 8 kg of lactic acid and 630 g of water are mixed, stirred and heated to 80 °C to completely dissolve, thus obtaining a eutectic solvent (DES).

[0050] (3) Immerse 1 kg of Torreya grandis shell particles in 10 L of eutectic solvent and stir at 90 °C for 5 h, then filter and separate. The obtained solid is washed with 50% ethanol, 0.5% sodium hydroxide and distilled water respectively to obtain deligated Torreya grandis shells. The obtained liquid is precipitated with hydrochloric acid at pH=2 to separate Torreya grandis lignin (>80%). The remaining DES is regenerated after alkali neutralization and desalting.

[0051] (4) The lignin-free Torreya grandis shells were milled and defibriled in a disc mill at 250 rpm for 4 minutes to obtain lignin-free Torreya grandis shell fibers.

[0052] (5) Mix 510g PBAT masterbatch, 340g delignified Torreya grandis shell fiber, 120g Torreya grandis lignin, 10g oleamide and 20g chitosan, and spread them into a film with a thickness of 0.1mm using a casting machine; then heat the film to 70℃ and coat it three times along the machine direction with a doctor blade with a gap of 1mm and a traction speed of 1.5m / min.

[0053] (6) Heat the above film to 90°C, pre-press it for 2 minutes under 5MPa pressure, then heat it to 135°C, press it for 5 minutes under 20MPa pressure, hold the pressure and cool it to 60°C before demolding to obtain a 0.02mm thick Torreya grandis shell-based bioplastic.

[0054] Example 2

[0055] (1) Wash 1 kg of Torreya grandis shells (rice Torreya grandis, produced in Yixian County, Anhui Province) and dry them at a low temperature of 45℃, then crush them into Torreya grandis shell particles with an average particle size of 1.5 mm.

[0056] (2) In a closed container, 6 kg of choline chloride, 9 kg of lactic acid and 500 g of water are mixed, stirred and heated to 80 °C to completely dissolve, thus obtaining a eutectic solvent (DES).

[0057] (3) Immerse 1 kg of Torreya grandis shell particles in 13 L of eutectic solvent and stir at 100 °C for 4 h, then filter and separate. The obtained solid is washed with 50% ethanol, 0.5% sodium hydroxide and distilled water respectively to obtain deligated Torreya grandis shells. The obtained liquid is precipitated with hydrochloric acid at pH=2 to separate Torreya grandis lignin (>80%). The remaining DES is regenerated after alkali neutralization and desalting.

[0058] (4) The lignin-free Torreya grandis shells were milled and defibrinated in a disc mill at 200 rpm for 5 minutes to obtain lignin-free Torreya grandis shell fibers.

[0059] (5) Mix 600g PBAT masterbatch, 300g delignified Torreya grandis shell fiber, 70g Torreya grandis lignin, 10g calcium stearate and 30g chitosan, and spread them into a film with a thickness of 0.1mm using a casting machine; then heat the film to 80℃ and coat it three times along the machine direction with a scraper with a gap of 0.5mm and a traction speed of 1m / min.

[0060] (6) Heat the above film to 100°C, pre-press it for 2 minutes under 5MPa pressure, then heat it to 140°C, press it for 4 minutes under 20MPa pressure, hold the pressure and cool it to 60°C before demolding to obtain a 0.02mm thick Torreya grandis shell-based bioplastic.

[0061] Example 3

[0062] (1) Wash 1 kg of Torreya grandis shells (rice Torreya grandis, produced in Yixian County, Anhui Province) and dry them at a low temperature of 45℃, then crush them into Torreya grandis shell particles with an average particle size of 4 mm.

[0063] (2) In a closed container, 2.5 kg of choline chloride, 7.5 kg of lactic acid and 500 g of water are mixed, stirred and heated to 80 °C to completely dissolve, thus obtaining a eutectic solvent (DES).

[0064] (3) Immerse 1 kg of Torreya grandis shell particles in 8 L of eutectic solvent and stir at 80 °C for 7 h, then filter and separate. The obtained solid is washed with 50% ethanol, 0.5% sodium hydroxide and distilled water respectively to obtain deligated Torreya grandis shell. The obtained liquid is precipitated with hydrochloric acid at pH=2 to separate Torreya grandis lignin (>80%). The remaining DES is regenerated after alkali neutralization and desalting.

[0065] (4) The lignin-free Torreya grandis shells were milled and defibriled in a disc mill at 300 rpm for 3 minutes to obtain lignin-free Torreya grandis shell fibers.

[0066] (5) Mix 320g PBAT masterbatch, 360g delignified Torreya grandis shell fiber, 100g Torreya grandis lignin, 5g oleamide, 5g calcium stearate and 10g chitosan, and spread them into a film with a thickness of 0.1mm through a casting machine; then heat the film to 60℃ and scrape it three times along the machine direction with a doctor blade with a gap of 1mm and a traction speed of 2m / min.

[0067] (6) Heat the above film to 80°C, pre-press it for 3 minutes under 5MPa pressure, then heat it to 130°C, press it for 6 minutes under 20MPa pressure, hold the pressure and cool it to 60°C before demolding to obtain a 0.02mm thick Torreya grandis shell-based bioplastic.

[0068] Comparative Example 1

[0069] The only difference between this comparative example and Example 1 is that, after the mixed material is spread into a film, it is not coated with a doctor blade to make the fibers distribute in the same direction.

[0070] Comparative Example 2

[0071] The only difference between this comparative example and Example 1 is that the Torreya husk-based bioplastic raw material does not include delignified Torreya husk fiber, and correspondingly, there is no preliminary step for preparing this substance.

[0072] Comparative Example 3

[0073] The only difference between this comparative example and Example 1 is that the Torreya husk-based bioplastic raw material does not include Torreya lignin, and correspondingly, there is no preliminary step for preparing this substance.

[0074] Comparative Example 4

[0075] The only difference between this comparative example and Example 1 is that, in the Torreya husk-based bioplastic raw material, the lignin-derived Torreya husk fibers are replaced with an equal mass of cellulose nanocrystals (<20 nm).

[0076] The mechanical properties of the plastics obtained in each embodiment and comparative example were tested, specifically including tensile strength and elongation at break in two directions (the longitudinal direction being the direction of the coating machine). The test results are shown in Table 1.

[0077] Table 1 Mechanical properties of bioplastics

[0078]

[0079]

[0080] The *Torreya grandis* shell-based bioplastic obtained by this invention exhibits extremely high longitudinal tensile strength and a certain elongation at break. The addition of delignified *Torreya grandis* shell fibers and *Torreya grandis* lignin both significantly enhance the material's mechanical properties, clearly demonstrating a biomimetic synergistic toughening effect in its composite with PBAT. Compared to conventional PBAT-cellulose nanocrystalline composites in the prior art, the bioplastic of this invention exhibits significantly superior mechanical properties in specific directions.

[0081] The surface water contact angle and antibacterial activity of the plastics obtained in each embodiment and comparative example were tested. The antibacterial activity was tested according to the method in the national standard GB / T 31402-2023, but only the reduction in bacterial count before and after the test was calculated, i.e., the inhibition rate. The test results are shown in Table 2.

[0082] Table 2 Hydrophobicity and antibacterial activity of bioplastics

[0083]

[0084] The bioplastic described in this invention has a significantly higher water contact angle than ordinary PBAT materials, with both the delignified fibers and lignin contributing to the improved hydrophobicity. The bioplastic containing oriented fibers exhibits differences in contact angles along the longitudinal and transverse directions, leading to varying droplet movement speeds on the film surface in different directions, which has potential application value. Furthermore, the bioplastic demonstrates antibacterial activity against *Escherichia coli* and *Staphylococcus aureus*, particularly the latter.

[0085] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description, and any obvious variations or modifications derived therefrom should still be considered within the scope of protection of this invention.

Claims

1. A method for preparing a Torreya grandis shell-based bioplastic, characterized in that, Includes the following steps: (1) After cleaning and drying, the Torreya grandis shells are crushed and then the lignin is removed in a eutectic solvent to obtain Torreya grandis lignin and deligated Torreya grandis shells; (2) The lignin-free Torreya grandis shells were milled and defibriled to obtain lignin-free Torreya grandis shell fibers; (3) Poly(butylene adipate / terephthalate), delignified Torreya grandis shell fiber and Torreya grandis lignin are mixed and spread into a film, the fibers are arranged in the same direction, and then gradient hot pressing, cooling and demolding are performed to obtain Torreya grandis shell-based bioplastic, wherein; The Torreya husk-based bioplastic comprises, by mass parts, 40-60 parts of polybutylene adipate / terephthalate, 30-45 parts of delignified Torreya husk fiber, and 5-15 parts of Torreya lignin. The eutectic solvent comprises choline chloride and lactic acid in a molar ratio of 1:1.5 to 3, and also includes water in a mass fraction of 3 to 5%. The lignin removal temperature is 80–100℃, the time is 4–7 h, and the material-to-liquid ratio is 1:8–15 g / mL; The crushing process involves crushing the shells of Torreya grandis to a particle size of 1.5–4 mm. The process of arranging the fibers in the same direction specifically involves heating the mixture to 60-80°C, and then repeatedly applying unidirectional shear force with a scraper, wherein the scraper gap is 0.5-1 mm and the traction rate is 1-2 m / min. The disc milling and fiber debonding process involves disc milling at a speed of 200-300 rpm for 3-5 minutes. The gradient hot pressing process specifically involves preheating at 90–100°C and 5 MPa for 2–3 minutes, followed by pressing at 130–140°C and 20 MPa for 4–6 minutes.

2. The method for preparing Torreya grandis shell-based bioplastics according to claim 1, characterized in that, The Torreya grandis shell-based bioplastic also includes, by mass, 1-3 parts chitosan and 0.5-2 parts lubricant, wherein the lubricant is selected from oleamide, erucamide, calcium stearate and combinations thereof.

3. A Torreya grandis shell-based bioplastic prepared according to the preparation method of claim 1 or 2.

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