Preparation method of degradable high-strength and high-toughness xylan plastic based on photo-initiated polymerization

Abstract

The degradable xylan plastic with excellent mechanical properties is prepared from the viscose fiber industrial byproduct xylan. The method relates to two key technologies: (1) carrying out etherification reaction on hydroxyl and cyclooxyalkyl in allyl glycidyl ether through base catalysis, introducing unsaturated C = C double bonds on a xylan skeleton as free radical polymerization reaction sites, and carrying out photopolymerization under ultraviolet light or sunlight to obtain transparent gel; and (2) preparing the high-strength and high-toughness xylan plastic by combining ethanol gradient dehydration and a hot pressing technology. Aiming at the limitations of the prior art and theory, high-valued utilization of an industrial byproduct xylan is taken as a core, and a cross-linked network structure is constructed through photo-initiation polymerization reaction, so that the mechanical property of xylan plastic is remarkably enhanced, and an innovative solution is provided for developing a degradable xylan material capable of replacing a petroleum-based material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of biomass materials, and specifically relates to a method for preparing high-strength and high-toughness xylan plastic with excellent biodegradability and mechanical properties by photo-initiated polymerization using xylan, a by-product of viscose industry, as raw material. BACKGROUND

[0002] Global plastic consumption is showing an exponential growth trend. Statistics show that more than 50% of the total amount of plastics produced in human history has been concentrated in the past 20 years since 2000. According to the current development trend, the global plastic production will double by 2050. However, about 60% of plastic products are discarded after being used only once, and the global plastic waste recycling rate is less than 10%, resulting in a large amount of non-degradable plastics accumulating in land and aquatic environments, posing a serious threat to the ecosystem. In this context, the development of biodegradable plastics to replace traditional petroleum-based plastics has become the focus of the global scientific community. In particular, biomass-based plastics prepared from agricultural and forestry biomass resources are favored due to their renewability and environmental friendliness. Currently, plastics prepared from major biomass components such as cellulose and lignin have successfully achieved industrial production and commercial application, providing a new solution for sustainable development.

[0003] Xylan, as a kind of monosaccharide with high content in hemicellulose, is used to obtain functional oligosaccharides with 2 to 6 xylose units connected by beta-1, 4-glycosidic bonds through hydrolysis in the past, and is widely used in various fields such as food, nutritional health products, drugs and animal feed. In terms of replacing petroleum-based materials, it is often necessary to change it into lactide, hydroxy fatty acid ester, furan dicarboxylic acid and other monomers through biomass refining technology, and then obtain biodegradable polymers such as polylactic acid (PLA), polyhydroxyalkanoate (PHA) and polyethylene glycol furanate (PEF) through polymerization, so as to prepare degradable plastics. Such a way is accompanied by high energy consumption and high cost, and the bioplastics obtained can only be degraded by composting. In order to avoid the complex biomass refining process, directly using xylan to prepare high-performance petroleum-based materials is a more green way. However, due to the strong hydrogen bonding effect within and between xylan molecules, the processability of xylan is limited. And xylan film material is prone to cracking due to uneven internal stress distribution during drying, and it is difficult to obtain high-quality film material. At present, xylan materials are mainly limited by mechanical properties and cannot achieve the unity of high strength and high toughness. The present application proposes a preparation method of degradable, high-strength and high-toughness xylan plastics based on photo-induced polymerization, which successfully solves the key technical problems of xylan materials in processing performance and mechanical strength. Not only provides an innovative solution for the high-value utilization of xylan materials, but also opens up a new way for the development of biobased components to prepare degradable plastics. Through testing, the mechanical performance indicators of the xylan plastics prepared by the method all reach or exceed those of existing petroleum-based plastics and biobased plastics products. And the xylan plastics can be completely degraded after being buried in nature for 10 days. SUMMARY

[0004] The present application uses xylan extracted from viscose fiber industrial byproducts as raw material, which has significant advantages compared with traditional plant-extracted xylan. Through high-performance liquid chromatography (HPLC) and gel permeation chromatography (GPC) analysis, this industrial xylan has high xylan content (96%) and high molecular weight (38,050 g / mol). Moreover, X-ray diffraction (XRD) analysis shows that it has high crystallinity. The technical solution of the present application uses this high-purity, high-molecular-weight, and high-crystallinity industrial byproduct xylan, not only realizing the high-value utilization of waste resources, but more importantly, the technology has important practical value for improving the economic benefits of the pulp and paper industry and promoting the substitution of petroleum-based products. However, due to the high crystallinity of xylan, there is a strong hydrogen bond interaction between and within the molecules, which limits the processability of xylan and requires chemical modification. In the present application, industrial xylan is used as the starting material, and etherification reaction is carried out between the hydroxyl group and the oxygen ring alkyl group in allyl glycidyl ether (AGE) through alkali catalysis, introducing unsaturated C=C double bonds into the xylan skeleton. With C=C as the free radical copolymerization active site, XAG is copolymerized and crosslinked by photo-initiation to obtain XAG gel. Through ethanol dehydration and hot pressing, the water in the XAG gel is gradually removed to obtain xylan plastic (XAGP) with excellent mechanical properties and degradation performance. Moreover, the unsaturated C=C double bonds in the present patent can be polymerized under the irradiation of sunlight to prepare xylan plastic (Example 4) with the same mechanical properties as the xylan plastic prepared by ultraviolet polymerization (Example 2). In addition, by changing the reaction conditions to control the modification degree of XAG, the physicochemical properties of XAGP are realized.

[0005] To achieve the above, the present application adopts the following technical solutions:

[0006] (1) Dissolving xylan in sodium hydroxide solution to obtain a transparent xylan solution;

[0007] (2) Adding allyl glycidyl ether (AGE) in a corresponding proportion to the xylan solution, and after reaction, dialysis is carried out to obtain a xylan derivative (XAG) aqueous solution with different modification degrees;

[0008] (3) Adding a corresponding proportion of water-soluble photoinitiator (2-hydroxy-4'-(2-hydroxyethoxy)-2-methylbenzophenone, I2958) to the xylan derivative (XAG) aqueous solution. After complete dissolution, XAG gel is obtained by photo-polymerization under 365 nm ultraviolet light;

[0009] (4) Through ethanol dehydration and hot pressing, the water in the XAG gel is gradually removed to obtain xylan plastic (XAGP);

[0010] In order to realize the polymerization under sunlight, the present application adopts the following technical solutions:

[0011] (1) dissolving xylan in sodium hydroxide solution to obtain transparent xylan solution;

[0012] (2) adding allyl glycidyl ether (AGE) in corresponding proportion into the xylan solution, and after reaction and dialysis, obtaining xylan derivative (XAG) aqueous solution with different substitution degree and double bond content;

[0013] (3) adding water-soluble photoinitiator (2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl propiophenone, I2958) in corresponding proportion into the xylan derivative (XAG) aqueous solution. After complete dissolution, transparent XAG gel is obtained after photo-crosslinking under sunlight for 30 min;

[0014] (4) removing water in the XAG gel by ethanol dehydration and hot pressing to obtain xylan plastic (XAGP); BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 for the abstract of the present application

[0016] Figure 2 for the xylan, AGE and XAG in the embodiment of the present application 1 H NMR;

[0017] Figure 3 for the xylan, AGE and XAG in the embodiment of the present application 13 C NMR;

[0018] Figure 4 for the XRD spectrum of xylan and XAG in the embodiment of the present application

[0019] Figure 5 for the mechanical tensile diagram and mechanical statistics diagram of embodiment 1, 2 and 3 of the present application

[0020] Figure 6 for the mechanical tensile and mechanical statistics comparison diagram of embodiment 2 and embodiment 4 of the present application

[0021] Figure 7 for the transparency diagram and haze diagram of embodiment 2 of the present application

[0022] Figure 8 for the degradation process of embodiment 2, which can be completely degraded in 10 days DETAILED DESCRIPTION

[0023] Embodiment 1

[0024] (1) Accurately weigh 2.64 g of xylan and dissolve in 40 mL of 5wt% NaOH aqueous solution, get a transparent solution at 50°C for 30 min;

[0025] (2) Drop 4.04 g of allyl glycidyl ether (molar ratio 1:2) into the transparent xylan solution drop by drop, and react at room temperature for 24 h;

[0026] (3) After the reaction is completed, the mixed solution is adjusted to neutral using hydrochloric acid. After adjusting to neutral, the solution is dialyzed to remove impurities. The solution after dialysis is concentrated until a 5wt% XAG2 solution is obtained;

[0027] (4) Dissolve 0.1wt% of a photoinitiator (2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl benzophenone, I2958) in the XAG2 solution obtained in step 3, and pour it into a mold. Under the irradiation of a UV light source with a light intensity of 30 mW / cm 2 at an excitation wavelength of 365 nm for 5 min, free radical polymerization is carried out to obtain a transparent XAG2 gel;

[0028] (5) Preliminary dehydration is carried out in anhydrous ethanol to a constant weight. Subsequently, hot pressing is carried out at 20 MPa and 80°C for 6 h to obtain a xylan-based plastic (XAGP2);

[0029] Example 2

[0030] (1) Accurately weigh 2.64 g of xylan and dissolve in 40 mL of 5wt% NaOH aqueous solution, get a transparent solution at 50°C for 30 min;

[0031] (2) Drop 6.06 g of allyl glycidyl ether (molar ratio 1:3) into the transparent xylan solution drop by drop, and react at room temperature for 24 h;

[0032] (3) After the reaction is completed, the mixed solution is adjusted to neutral using hydrochloric acid. After adjusting to neutral, the solution is dialyzed to remove impurities. The solution after dialysis is concentrated until a 5wt% XAG3 solution is obtained;

[0033] (4) Dissolve 0.1wt% of a photoinitiator (2-hydroxy-4'-(2-hydroxyethoxy)-2-methyl benzophenone, I2958) in the XAG3 solution obtained in step 3, and pour it into a mold. Under the irradiation of a UV light source with a light intensity of 30 mW / cm 2 at an excitation wavelength of 365 nm for 5 min, free radical polymerization is carried out to obtain a transparent XAG3 gel;

[0034] (5) The preliminary dehydration was carried out in anhydrous ethanol to constant weight. Then hot-pressing was carried out at 20 MPa, 80 °C for 6 h to obtain xylan-based plastic (XAGP3);

[0035] Example 3

[0036] (1) Accurately weigh 2.64 g of xylan and dissolve in 40 mL of 5 wt% NaOH aqueous solution, get a transparent solution at 50 °C for 30 min;

[0037] (2) Drop 8.08 g of allyl glycidyl ether (molar ratio 1:4) into the transparent xylan solution drop by drop, and react at room temperature for 24 h;

[0038] (3) After the reaction is completed, the mixture is adjusted to neutral using hydrochloric acid. After adjusting to neutral, the solution is dialyzed to remove impurities. The solution after dialysis is concentrated until a 5 wt% XAG4 solution is obtained;

[0039] (4) Dissolve 0.1 wt% of a photoinitiator (2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, I2958) in the XAG4 solution obtained in step 3, and pour it into a mold. Under the irradiation of a UV light source with a light intensity of 90 mW / cm 2 , an excitation wavelength of 365 nm, free radical polymerization is carried out for 5 min to obtain a transparent XAG4 gel;

[0040] (5) The preliminary dehydration was carried out in anhydrous ethanol to constant weight. Then hot-pressing was carried out at 20 MPa, 80 °C for 6 h to obtain xylan-based plastic (XAGP4);

[0041] Example 4

[0042] (1) Accurately weigh 2.64 g of xylan and dissolve in 40 mL of 5 wt% NaOH aqueous solution, get a transparent solution at 50 °C for 30 min;

[0043] (2) Drop 6.06 g of allyl glycidyl ether (molar ratio 1:3) into the transparent xylan solution drop by drop, and react at room temperature for 24 h;

[0044] (3) After the reaction is completed, the mixture is adjusted to neutral using hydrochloric acid. After adjusting to neutral, the solution is dialyzed to remove impurities. The solution after dialysis is concentrated until a 5 wt% XAG3 solution is obtained;

[0045] (4) 0.1 wt% of photoinitiator (2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, I2958) was dissolved in the XAG3 solution obtained in step 3, which was poured into a mold. Under sunlight irradiation for 30 min, free radical polymerization was carried out to obtain a transparent XAG3 gel;

[0046] (5) Primary dehydration was carried out in anhydrous ethanol to constant weight. Subsequently, hot-pressing was carried out at 20 MPa and 80 °C for 6 h to obtain a xylan-based plastic (XAGP3-Sunlight).

Claims

1. A method for preparing a degradable high-strength and high-toughness xylan plastic based on photoinitiated polymerization, characterized in that: The following steps are involved: Step 1, dissolving xylan in a sodium hydroxide solution to obtain a transparent xylan solution; Step 2, adding allyl glycidyl ether in a corresponding proportion to the xylan solution, and dialyzing after the reaction to obtain aqueous solutions of xylan derivatives with different degrees of modification; Step 3: Add a corresponding proportion of a water-soluble photoinitiator (2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone) to the aqueous solution of the xylan derivative. After complete dissolution, perform photopolymerization under a light source to obtain a transparent gel. Step 4: gradually remove the water from the gel by ethanol dehydration and hot pressing to obtain xylan plastic.

2. The method for preparing xylan plastic according to claim 1, characterized in that: Step 1: 2.64 g of xylan was weighed and dissolved in 40 mL of a 5 wt% sodium hydroxide aqueous solution at a dissolution temperature of 50° C. for 30 minutes.

3. The method for preparing xylan plastic according to claim 1, characterized in that: In step 2, the molar ratio of xylan to allyl glycidyl ether is 2 to 4, the reaction temperature is room temperature, and the reaction time is 24 hours; the pH of the solution needs to be adjusted to neutral to terminate the reaction; and the dialyzed xylan derivative aqueous solution is concentrated to a concentration of 5 wt%.

4. The method for preparing xylan plastic according to claim 1, characterized in that: Step 3, the amount of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone added is 0.1wt% of the xylan derivative aqueous solution; the light source can be divided into 30mW / cm 2 Light intensity, excitation wavelength 365nm ultraviolet light and sunlight. The illumination time under ultraviolet light is 5 minutes, and the illumination time under sunlight is 30 minutes.

5. The method for preparing xylan plastic according to claim 1, characterized in that: Step 4: After dehydration with ethanol to constant weight, hot pressing is performed at 20 MPa and 80° C. for 6 h.

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