A kind of loofah seed oil microcapsule and loofah seed oil microcapsule-impregnated modified bamboo and its preparation method

Abstract

The present invention discloses a loofah seed oil microcapsule and a loofah seed oil microcapsule-impregnated modified bamboo and a preparation method thereof. The preparation method of the loofah seed oil microcapsule comprises the following steps: (1) dissolving and treating a natural polymer to obtain a natural polymer solution; (2) adding the loofah seed oil into the natural polymer solution for microencapsulation reaction treatment to obtain an emulsion containing the loofah seed oil microcapsule. The preparation method of the loofah seed oil microcapsule-impregnated modified bamboo comprises the following steps: (1) pre-treating the bamboo; (2) impregnating the bamboo. The present invention first applies the microcapsule technology to the anti-mildew modification of bamboo, prepares microcapsules with a particle size less than 1000 nm, ensures deep impregnation, can protect the chemical components of the plant essential oil, realizes the slow release of the active ingredients of the loofah seed oil, regulates the pore structure of the bamboo by means of microwave treatment and freeze-drying, improves the porosity of the bamboo, enables the microcapsules to be effectively combined with the bamboo, and realizes the long-term anti-mildew of the bamboo.

Description

Technical Field

[0001] The present invention relates to the technical field of bamboo materials, and particularly to a loofah seed oil microcapsule, a loofah seed oil microcapsule-impregnated modified bamboo material and a preparation method thereof. Background Art

[0002] Bamboo is a natural polymer material. Due to its high sugar content and high starch content, when the moisture content of the surface material exceeds 19.0%, the surface of bamboo products is extremely prone to mildew. A large amount of research work has been devoted to the modification of bamboo, such as heat treatment, chemical modification, vegetable oil impregnation and other methods. In order to reduce environmental pollution and damage to the mechanical properties of bamboo, the research on vegetable oil-modified bamboo has been developed to a certain extent. For example, litsea cubeba oil, neem oil, lavender, tea tree and eucalyptus essential oils have been applied to the research on the anti-mildew and anti-corrosion modification of bamboo.

[0003] Loofah seed oil contains rich bioactive components, such as (E)-2-decenal and ethyl oleate with insecticidal and acaricidal effects; butylated hydroxytoluene with anti-corrosion effect. Therefore, loofah seed oil also has the potential for anti-mildew modification of bamboo. However, conditions such as light, oxygen and heat have a great influence on unsaturated fatty acids in vegetable oils, making them prone to oxidation, polymerization, transposition rearrangement, etc., which have adverse effects on their processing and storage. Microencapsulation technology is to encapsulate core materials such as particles, droplets or bubbles with a polymer film-forming material (wall material) into microparticles to protect the physical state of the core material and control its slow release, so as to achieve functional applications, and has always received extensive attention. In recent years, microcapsules with anti-corrosion, fragrance release and other functions have been combined with wood through impregnation, surface coating, and adhesive bonding. In theory, microcapsules with plant essential oils such as loofah seed oil as the core material can be designed and prepared, and the functional modification of bamboo with fragrance release and long-term anti-mildew can be realized through microcapsule impregnation treatment of bamboo.

[0004] However, bamboo usually lacks transverse ray tissue in its tissue structure, has a low porosity and small pore diameter, and the current microencapsulation technology has a large particle size, so the microcapsules cannot be deeply impregnated into bamboo. Therefore, how to achieve the tight combination of microcapsules and bamboo, and achieve the effect of long-term anti-mildew of microcapsule-modified bamboo is the primary problem to be solved. Summary of the Invention

[0005] The main purpose of the present invention is to provide a loofah seed oil microcapsule, a loofah seed oil microcapsule-impregnated modified bamboo material and a preparation method thereof, aiming to solve the technical problem that microcapsules in the prior art cannot be deeply impregnated into bamboo.

[0006] To achieve the above object, the present invention provides a preparation method of a loofah seed oil microcapsule, using loofah seed oil as the core material and a natural polymer as the wall material, including the following steps:

[0007] (1) Dissolve the natural polymer to obtain a natural polymer solution;

[0008] (2) Add loofah seed oil to the natural polymer solution for microencapsulation reaction to obtain an emulsion containing loofah seed oil microcapsules.

[0009] Further, the natural polymer is selected as β-cyclodextrin, and the dosage ratio of the wall material to the core material is 0.33 - 5:1. The specific process of step (1) is: add β-cyclodextrin to hot water, stir to dissolve, and cool to no more than 70 °C after the solution becomes clear.

[0010] Further, the specific process of step (2) is: dissolve loofah seed oil in ethanol and then add it to the β-cyclodextrin solution, and then stir and react at 40 - 70 °C for 2 - 4 h.

[0011] Further, it also includes step (3) separating the loofah seed oil microcapsules from the emulsion. The specific process is: place the emulsion in a refrigerator at 4 °C for 12 - 16 h to precipitate, then take out the precipitate, wash it by vacuum filtration with ethanol and distilled water in sequence, and finally freeze-dry the precipitate at -60 °C for 72 - 96 h to obtain loofah seed oil microcapsules.

[0012] Further, the natural polymer is selected as chitosan, and the dosage ratio of the wall material to the core material is 0.5 - 10:1. The specific process of step (1) is: add chitosan to a 1% v / v acetic acid solution, let it stand at room temperature for 12 - 16 h, and then add Tween 80 and stir to form a homogeneous phase at 45 °C.

[0013] Further, the specific process of step (2) is: directly add loofah seed oil to the chitosan solution, then add a 0.3% w / v sodium tripolyphosphate solution with a pH value of 5.6, stir at room temperature for 60 min, and finally adjust the pH value of the emulsion to 3.5 - 5.5 with a 0.5 mol / L hydrochloric acid / sodium hydroxide solution.

[0014] Further, it also includes step (3) separating the loofah seed oil microcapsules from the emulsion. The specific process is: centrifuge the emulsion for 10 - 14 min, take out the precipitate, wash it with distilled water, and finally freeze-dry the precipitate at -60 °C for 72 - 96 h to obtain loofah seed oil microcapsules.

[0015] The present invention also provides a loofah seed oil microcapsule prepared by the above preparation method.

[0016] The present invention also provides a preparation method of loofah seed oil microcapsule-impregnated modified bamboo, including the following steps:

[0017] (1) Bamboo pretreatment

[0018] Immerse the bamboo in distilled water until the moisture content reaches 40 - 60%, then microwave it at a frequency of 2450 MHz for 1 - 30 min. After that, submerge the bamboo in distilled water, freeze it at -20°C for 48 h, and then freeze-dry it at -60°C for 72 - 96 h until the moisture content of the bamboo slices reaches 12%.

[0019] (2) Impregnation treatment of bamboo

[0020] Place the modified bamboo slices in the emulsion of the above-mentioned loofah seed oil microcapsules, impregnate them at a vacuum of -0.08 MPa for 10 min, then impregnate them at a pressure of -1 MPa for 24 h. Then remove the emulsion on the surface of the bamboo, place it in a constant temperature and humidity chamber at a temperature of 20°C and a humidity of 65% for 6 h, and finally dry it in an oven at 60°C.

[0021] The present invention also provides a loofah seed oil microcapsule-impregnated modified bamboo prepared according to the above preparation method.

[0022] The present invention mainly has three aspects of innovation. First, it innovatively uses microcapsules to modify bamboo to achieve mildew prevention. Second, it prepares loofah seed oil microcapsules for the first time. Third, it prepares microcapsules with adjustable particle sizes through different schemes to meet the needs of impregnating bamboo.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The present invention applies the microcapsule technology to the mildew prevention and modification of bamboo for the first time. By selecting a suitable microcapsule wall material and controlling the synthesis process of the microcapsules, microcapsules with a particle size less than 1000 nm are prepared to enable the microcapsules to enter the pores of the bamboo and ensure deep impregnation.

[0025] (2) The present invention uses natural and biodegradable loofah seed oil and microcapsule wall materials to make microcapsules to replace traditional antibacterial agents for the mildew prevention and modification of bamboo, avoiding the environmental pollution problems caused by traditional bamboo mildew preventives.

[0026] (3) The microcapsules prepared by the present invention have a protective and slow-release effect on vegetable oil, overcoming the drawback that traditional plant essential oils are easily affected by the environment and change their chemical properties. Utilizing the slow-release effect of the microcapsules and the anti-corrosion active ingredients of loofah seed oil, it can not only protect the chemical components of the plant essential oil, achieve the slow release of the active ingredients of loofah seed oil, but also achieve the long-term mildew prevention of bamboo.

[0027] (4) The present invention breaks through the application limitations of microcapsules in bamboo. By using microwave treatment and freeze-drying methods to control the pore structure of bamboo, the porosity of bamboo is increased, enabling the microcapsules to effectively combine with bamboo, realizing the retention of microcapsules in the deep pores of bamboo, that is, ensuring the slow-release effect of the microcapsules and achieving the mildew prevention of bamboo.

[0028] (5) The present invention overcomes the drawbacks that the combination of traditional microcapsules and wood materials only remains on the surface or is enclosed. By vacuum impregnating bamboo in the microcapsule emulsion, the deep retention of microcapsules is achieved, which is beneficial for the microcapsules to play a long-term and stable sustained-release role. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is (a) the ultraviolet absorption spectrum of loofah seed oil; (b) the standard curve of loofah seed oil.

[0030] Figure 2 It is the relationship between the encapsulation efficiency of β-CD microcapsules and (a) the wall-core ratio; (b) temperature; (c) time.

[0031] Figure 3 It is (a) the response surface of temperature (A) and wall-core ratio (B) to the encapsulation efficiency; (b, c, d) the contour maps of the influence of temperature (A), wall-core ratio (B), and encapsulation time (C) on the encapsulation efficiency.

[0032] Figure 4 It is the relationship between the encapsulation efficiency of CS microcapsules and (a) pH; (b) the wall-core ratio.

[0033] Figure 5 It is the particle size and Zeta potential distribution of two kinds of microcapsules (a) particle size map; (b) Zeta potential map.

[0034] Figure 6 It is the curve of microcapsule concentration changing with time (a) high temperature condition; (b) normal temperature condition.

[0035] Figure 7 It is (a-b) the microstructure of β-CD microcapsules; (c-d) the microstructure of CS microcapsules.

[0036] Figure 8 It is the transmission electron microscope image of CS microcapsules (a-b) CS microcapsules with high core material content; (c-d) CS microcapsules with low core material content.

[0037] Figure 9 It is the comparison of Fourier transform infrared spectra of the wall material and microcapsules (a) β-CD and β-CD microcapsules; (b) CS and CS microcapsules.

[0038] Figure 10 It is the SEM pictures of bamboo impregnated with different microcapsules (a-c) impregnated with β-CD microcapsules; (d-f) impregnated with CS microcapsules.

[0039] Figure 11 It is the comparison of Fourier transform infrared spectra of bamboo slices impregnated with different microcapsules (a) in the range of 500 - 4000 cm -1 and (b) in the range of 500 - 1800 cm -1 range.

[0040] Figure 12 Comparison of the anti - mildew performance of bamboo treated with different micro - capsules after 30 days.

[0041] Figure 13 Microscopic structure of bamboo decayed after being impregnated with different micro - capsules. Among them, (a - b) Cross - section of β - CD impregnated bamboo slices; (c - d) Radial section of β - CD impregnated bamboo slices; (e - f) Cross - section of CS impregnated bamboo slices; (g - h) Radial section of CS impregnated bamboo slices.

[0042] Figure 14 Three - point bending stress - strain curves of bamboo slices impregnated with different micro - capsules. (a) Loading on the yellow side of bamboo; (b) Loading on the green side of bamboo.

[0043] Figure 15 Moisture absorption rate and moisture desorption rate of bamboo slices impregnated with different micro - capsules varying with time. Detailed implementation manners

[0044] The present invention will be further described below in conjunction with embodiments:

[0045] All kinds of raw materials and equipment used in the following embodiments, unless otherwise specified, are commercially available products well - known in the art.

[0046] Embodiment 1

[0047] Preparation and performance characterization of loofah seed oil micro - capsules

[0048] A. Preparation of β - CD loofah seed oil micro - capsules

[0049] Add 2 g of β - CD (β - cyclodextrin) to 30 ml of deionized water at 70 °C, stir to dissolve it. After the solution becomes clear, cool it to 50 °C to obtain a β - CD solution. Dissolve loofah seed oil in ethanol at a ratio of 1:20, and then slowly add it to the above - mentioned β - CD solution. Stir and react at 40 - 70 °C for 1 - 4 h to obtain an emulsion containing β - CD loofah seed oil micro - capsules. Place the emulsion in a 4 °C refrigerator and refrigerate it overnight for 12 h to precipitate. Then take out the precipitate, vacuum - filter and wash it successively with ethanol and distilled water. Finally, freeze - dry the precipitate at - 60 °C for 72 h to obtain β - CD loofah seed oil micro - capsules. Prepare β - CD loofah seed oil micro - capsules (hereinafter referred to as β - CD micro - capsules) according to different conditions in Table 1.

[0050] Table 1 Single - factor level design table of β - CD micro - capsules

[0051]

[0052] Draw the standard curve of the concentration of loofah seed oil: Add ethanol to 50 μL of loofah seed oil to make up to 25 mL. Add 25 μL, 50 μL, 100 μL, 200 μL, 300 μL, and 400 μL of the above solution into 10 mL centrifuge tubes respectively, and make up to 5 mL with absolute ethanol. Then standard solutions with concentrations of 0.01 μL / mL, 0.02 μL / mL, 0.04 μL / mL, 0.06 μL / mL, 0.08 μL / mL, and 0.10 μL / mL can be obtained. Measure the maximum absorbance of solutions with different concentrations in the ultraviolet wavelength range of 185 - 300 nm, draw the relationship diagram between absorbance and the concentration of loofah seed oil, as Figure 1 shown, and calculate the linear relationship.

[0053] Extract the loofah seed oil from β-CD microcapsules: Weigh 0.05 g of β-CD microcapsules, add 2.5 mL of absolute ethanol, heat in a water bath at 40 °C for 30 min, then perform ultrasonic treatment for 1 h and centrifuge. Take 200 μL, 400 μL, and 600 μL of the supernatant respectively into 10 mL graduated test tubes, and make up with absolute ethanol to obtain samples with unknown concentrations. Measure the absorbance of the samples, substitute it into the above standard curve, and calculate the concentration of loofah seed oil. According to the results of the single-factor experiment as Figure 2 shown, the response surface levels in Table 2 are designed accordingly.

[0054] Table 2 Response surface design and levels

[0055]

[0056] B. Preparation of CS loofah seed oil microcapsules

[0057] Add 0.15 g of CS (chitosan) to 1% v / v acetic acid solution, let it stand at room temperature for 12 h to obtain a solution with a concentration of 0.3% w / v, 50 mL, and a pH value of 4.6. Then add 0.12 g of Tween 80 and stir at 45 °C for 2 h to obtain a homogeneous phase, getting the CS solution; Add loofah seed oil to the CS solution, stir for 30 min, then add 0.3% w / v, 20 mL, and a pH value of 5.6 TPP solution (sodium tripolyphosphate), stir at room temperature for 60 min, and adjust the pH value to 3.5 - 5.5 with 0.5 M (mol / L) hydrochloric acid / sodium hydroxide solution to obtain an emulsion containing CS loofah seed oil microcapsules; Centrifuge the emulsion for 14 min, take out the precipitate, wash it with distilled water, and finally freeze-dry the precipitate at -60 °C for 72 h to obtain CS loofah seed oil microcapsules. Prepare CS loofah seed oil microcapsules (hereinafter referred to as CS microcapsules) according to different conditions in Table 3

[0058] Table 3 Single-factor level design table of CS microcapsules

[0059]

[0060] Extraction of loofah seed oil from CS microcapsules: Take 50 μL of the emulsion, add 2.5 ml of hydrochloric acid with a concentration of 2 mol / L, place it in a water bath at 95 °C for 30 min, and add 1 ml of ethanol after cooling. Centrifuge at 9000 rpm for 2 min at 25 °C, take 200 μL of the supernatant and make up to 5 ml, and compare it with the standard solution curve of 0.06 μL / mL to obtain the concentration of loofah seed oil. Take the embedding rate of loofah seed oil as the main index for optimizing the process conditions. The calculation formula for the embedding rate M is as follows in formula (1):

[0061]

[0062] In the formula: M1 is the mass of loofah seed oil in the microcapsules; M2 is the total amount of loofah seed oil added during the preparation process.

[0063] The calculation formula for the yield W is shown in formula (2):

[0064]

[0065] In the formula: m1 is the mass of the microcapsules; m2 is the mass of the core material; m3 is the mass of the wall material.

[0066] C. Performance characterization of two types of microcapsules

[0067] The present invention designs and regulates the embedding rates of two types of microcapsules, and characterizes the performance such as the microstructure and chemical composition of the microcapsules at the maximum embedding rate.

[0068] Embedding rate regulation:

[0069] Based on the single-factor experiment, variables are set. The response surface experiment design and results of β-CD microcapsules are shown in Table 4, with a total of 17 experimental combinations. The embedding rate range of β-CD microcapsules is between 46.57 - 91.95%. Using the Box-Behnken experiment provided by Design-Expert 10, a multiple regression equation is fitted as shown in formula (3):

[0070] M = 91.79 - 8.80A - 9.40B - 2.28C + 6.71AB - 6.63AC + 1.29BC - 12.27A 2 - 18.81B2 - 3.26C 2 In formula (3), M is the embedding rate, A is the embedding temperature, B is the core-wall ratio, and C is the embedding time.

[0071] Table 4 Response surface design and indexes of the preparation process of β-CD microcapsules

[0072]

[0073] Table 5 lists the results of the analysis of variance of β-CD microcapsules and is used to evaluate the significance of the model. This model has a significant effect (p < 0.0001), indicating that the error of the model fitting test is very small. At the same time, the embedding temperature (A), the core-wall ratio (B) and their squared terms have a highly significant effect on the embedding rate of β-CD microcapsules (p < 0.01). The embedding time (C) and its squared term have a relatively small effect on the embedding rate (p > 0.05), and the interaction terms between A, B, and C also have no significant effect on the embedding rate of β-CD microcapsules (p > 0.05). The larger the F-test, the greater the impact on the response variable. In the optimization experiment of β-CD microcapsules, the order of influence on its embedding rate from large to small is: B, A, C, the interaction between B and A, and the interaction between A and C.

[0074] Analysis of Variance of Experimental Results in Table 5

[0075]

[0076] Figure 3 The response surface and contour plots show the effects of temperature (A), wall-core ratio (B), and embedding time (C) on the embedding rate. As can be seen from Figure 3 (a), with the embedding time unchanged, the embedding rate first increases and then decreases with the increase of the core-wall ratio and embedding temperature. That is, when the core-wall ratio and embedding temperature reach a certain point, the embedding rate of β-CD microcapsules can reach the maximum value. At the same time, as can be found from Figure 3 (b), the contour lines of the core-wall ratio and embedding temperature tend to be circular, indicating that their interaction has no obvious effect on the embedding rate, which is consistent with the results of the regression equation. Figure 3 (c) shows that the interaction between the embedding temperature and time has a similar effect on the embedding rate as the interaction between the core-wall ratio and embedding temperature. In addition, as can be seen from Figure 3 (d), the effect of the embedding time on the embedding rate is different from that of the core-wall ratio or embedding temperature. The contour plot of the core-wall ratio (B) and embedding time (C) is elliptical, indicating that their interaction has an effect on the embedding rate.

[0077] The optimal parameters shown by the regression model: the ratio of loofah seed oil to β-CD is 1.98:1, the embedding time is 3.03 h, the embedding temperature is 53.75 °C, and the predicted embedding rate is 94.38%. Under the conditions of a core-wall ratio of 2:1, an embedding time of 3 h, and an embedding temperature of 54 °C, it was verified 3 times. The average actual embedding rate was 94.72 ± 0.5%, and the yield was 50.34%. This is similar to the data of the regression model, indicating that the established regression model can fit the production process of β-CD microcapsules, and the maximum embedding rate of loofah seed oil can be obtained under the optimized conditions.

[0078] From Figure 4It can be seen that the pH value has a great influence on the embedding rate of CS microcapsules. When the pH value is 3.5, the embedding rate is about 13.5%. This is mainly because a large amount of CS in the reaction system still exists independently. When the pH value increases, the negative charge carried by the carboxyl group on the TPP molecule increases, and an electrostatic reaction occurs with the positive charge carried by the amino group on chitosan, forming more solidified phases on the surface of loofah seed oil, thereby gradually increasing the coating rate of loofah seed oil. Therefore, the pH value should be about 4.5 in the preparation of CS microcapsules. Finally, CS microcapsules were prepared with a wall-core ratio of 1:1 (g / mL) and a pH value of 4.5. The average embedding rate was measured to be 17.65 ± 0.6%, and the yield was 36.2 ± 0.8%.

[0079] Particle size distribution:

[0080] Figure 5 The particle sizes and Zeta potentials of the two types of microcapsules are shown and summarized in Table 6. The bulk density of β-CD microcapsules is 0.51 g / cm 3 , while the density of CS microcapsules is 0.37 g / cm 3 . When the absolute value of the Zeta potential is greater than 30, the microcapsule suspension is relatively stable; when the absolute value of the Zeta potential is less than 10, the attractive potential energy caused by van der Waals forces between microcapsules is greater than the repulsive potential energy caused by electrostatic repulsion, and the microcapsules will quickly coagulate, and it is difficult for the system to maintain its physical stability. CS in an acidic medium has amino groups, which can be protonated and interact with negatively charged TPP to form intermolecular and intramolecular crosslinks, generating ionically crosslinked CS microcapsules. In addition, the loofah seed oil CS microcapsules form a relatively stable dispersion system, probably because Tween 80, as a non-ionic surfactant, produces a steric hindrance effect on the surface of the microcapsules. Therefore, the spontaneously formed positively charged CS microcapsules have a potential value less than 30 but greater than 10, and are still considered stable.

[0081] The particle size of β-CD microcapsules is about 3.3 times that of CS microcapsules, and the particle sizes of both are larger than the sizes observed by scanning electron microscopy and transmission electron microscopy. This is because the particle size determined by the nano-particle size analysis technology is the hydrodynamic diameter, which may be due to the swelling of individual particles around the microcapsules or the aggregation of particles when in water, resulting in a larger measured particle size. Nevertheless, the particle size of CS microcapsules can still meet the requirements of passing through the pits of bamboo fibers, while some of the β-CD microcapsules are less than 1 μm, but can penetrate into large pores such as ducts.

[0082] Under high-temperature slow-release conditions, the initial concentrations of loofah seed oil in β-CD microcapsules and CS microcapsules were 0.083 μL / mL and 0.03 μL / mL, respectively. The content of loofah seed oil in β-CD microcapsules decreased rapidly with time at 80 °C, but the content of loofah seed oil still reached 0.07 μL / mL at the 30th minute. However, CS microcapsules had better protection for loofah seed oil at high temperature. Although the initial concentration of loofah seed oil was low, the concentration of loofah seed oil did not show an obvious downward trend over time. Under normal-temperature slow-release conditions, the initial concentrations of loofah seed oil in β-CD microcapsules and CS microcapsules were 0.088 μL / mL and 0.035 μL / mL, respectively. Observation Figure 6 As can be seen from (b), the concentration of loofah seed oil in β-CD microcapsules gradually decreased over time, while the concentration of loofah seed oil in CS microcapsules decreased more from the 5th to the 10th day, and the concentration of loofah seed oil gradually stabilized after the 10th day. The β-CD microcapsules still maintained a loofah seed oil concentration of 0.07 μL / mL at the 30th day, and chitosan had a good slow-release effect on loofah seed oil. Therefore, both types of microcapsules had good stability and slow-release properties, which was beneficial to the application of microcapsules in modified bamboo.

[0083] Table 6 Density, Zeta potential and particle size of two kinds of microcapsules

[0084]

[0085] Microstructure:

[0086] The scanning electron microscope images of the two kinds of microcapsules are shown in Figure 7 . The β-CD microcapsules presented as irregular parallelograms or rhombuses, with a relatively smooth surface but adhesion between them, which was due to the viscosity and electrostatic interaction of the wall material. It could be observed from the figure that the particle size was about 150 nm - 2 μm. The shape of CS microcapsules was spherical or irregular spherical-like, with a relatively smooth surface and relatively dispersed particles. The structure of CS microcapsules was shown as a spherical object with an outer wall material coating oil droplets, and the wall material was formed by the electrostatic interaction between chitosan and sodium tripolyphosphate. Figure 8 (a - b) and (c - d) showed two morphologies of CS microcapsules. The former directly encapsulated a single core material, and the latter encapsulated multiple small core material units. The particle size of CS microcapsules was less than 100 nm.

[0087] Chemical composition:

[0088] Figure 9 The infrared spectra of the two wall materials and their corresponding microcapsules were shown. The characteristic absorption peaks of β-CD and β-CD microcapsules were basically similar. The infrared spectrum of β-cyclodextrin showed a characteristic peak of symmetric stretching vibration of –OH at 3307 cm -1 −1, while at 2919 cm -1The characteristic peak at [position] is related to the stretching vibration of C–H, and the characteristic peaks at 1152 and 1025 cm -1 are the symmetric and asymmetric stretching vibrations of C–O–C respectively. The peak at 1743 cm -1 corresponds to the stretching of the carbonyl ester functional group of triglycerides in loofah seed oil. Comparing the FTIR spectra of β-CD and β-CD microcapsules, it is found that almost no new absorption peaks appear, but a weaker peak at 1743 cm -1 is shown, indicating that only physical embedding occurs between β-CD and loofah seed oil. This enables the wall material not to react with loofah seed oil and can well protect the core material loofah seed oil.

[0089] The absorption peak at 1646 cm -1 is the stretching vibration absorption peak of C=O in chitosan; the absorption peak at 1589 cm -1 is the bending vibration absorption peak of N–H in chitosan; the absorption peak at 1025 cm -1 is formed by the superposition of the C–O stretching vibration absorption peak in the six-membered mono-oxygen ring and the C–O stretching vibration absorption peak of the primary alcohol hydroxyl group. Compared with CS, CS microcapsules show absorption peaks at 2927 cm -1 , 2857 cm -1 and 1743 cm -1 , which are the characteristic peaks of loofah seed oil, indicating that loofah seed oil is physically combined with CS. The chitosan molecular structure contains amino groups, which can undergo Schiff base reactions with dialdehyde substances, thereby crosslinking loofah seed oil with the microcapsule wall material. An absorption peak appears at 1626 cm -1 in the spectrum corresponding to the -C=N characteristic absorption peak in Schiff base, indicating that a crosslinked structure is formed between loofah seed oil and the chitosan wall material.

[0090] Example 2

[0091] Bamboo pretreatment

[0092] The present invention uses microwave treatment combined with freeze-drying to regulate the pores of bamboo. The specific process is as follows: The de-greened and de-yellowed moso bamboo is cut into bamboo slices with dimensions of 50 mm * 20 mm * 5 mm, immersed in distilled water until the moisture content reaches 40 - 60%, then microwave-treated at a frequency of 2450 MHz for 1 - 30 min. After that, the bamboo slices are immersed in distilled water, frozen at -20 °C for 48 h, and freeze-dried at -60 °C for 72 - 96 h until the moisture content of the bamboo slices reaches 12%;

[0093] The mass change rate, volume change rate, and porosity change rate of bamboo slices under different microwave treatment times are shown in Table 7. From the comparison data, it can be seen that there are significant differences in the volume change rate and porosity change rate among bamboo slices with different microwave treatment durations. As the microwave treatment time prolongs, the mass loss rate of bamboo slices is relatively stable, the volume change rate generally shows an increasing trend, and the porosity change rate first increases and then stabilizes. When the microwave treatment time is 10 min, the porosity change rate tends to be stable. Relevant research shows that prolonging the microwave time will reduce the mechanical properties of fibers. To obtain a larger porosity while ensuring the mechanical properties of bamboo slices, in this invention, it is determined that 10 min of microwave treatment is the optimal experimental condition, and subsequent designs are carried out based on this.

[0094] Table 7 Porosity change of bamboo slices before and after microwave treatment and its variance analysis

[0095]

[0096] Example 3

[0097] Preparation and performance testing of loofah seed oil microcapsule-impregnated modified bamboo

[0098] The pretreated bamboo slices obtained in Example 2 were respectively impregnated in the emulsion containing β-CD loofah seed oil microcapsules and the emulsion containing CS loofah seed oil microcapsules under a vacuum of -0.08 MPa for 10 min, then impregnated under a pressure of -1 MPa for 24 h, then the emulsion on the surface of the bamboo was removed, placed in a constant temperature and humidity box at a temperature of 20 °C and a humidity of 65% for 6 h, and finally dried in an oven at 60 °C to obtain the modified bamboo.

[0099] The emulsion containing β-CD loofah seed oil microcapsules and the emulsion containing CS loofah seed oil microcapsules used here are the emulsion containing β-CD loofah seed oil microcapsules and the emulsion containing CS loofah seed oil microcapsules obtained before precipitation in the preparation process of Example 1.

[0100] In specific practice, it is also possible to redisperse the dried microcapsules in a solvent to prepare an emulsion for use. The β-CD microcapsules use water as the solvent, and the CS microcapsules use a sodium hydroxide solution with a pH of 4.5 as the solvent.

[0101] Test the performance of loofah seed oil microcapsule-impregnated modified bamboo and analyze the anti-mildew effect of the modified bamboo. The performance testing of the specimens mainly includes: microscopic structure observation, chemical composition, anti-mildew performance, mechanical properties, hygroscopicity, and wettability, etc.

[0102] Weight gain rate:

[0103] The weight gain rates of the bamboo after being impregnated with the two kinds of microcapsules are similar, that is, the impregnation degrees in bamboo are similar. The volume change rate of the bamboo slices after impregnation is small, indicating that the influence on the dimensional stability of the bamboo slices is small. The porosity of the bamboo slices after being impregnated with the two kinds of microcapsules both decreases slightly. Among them, the decrease in the porosity of the bamboo slices impregnated with β-CD microcapsules is small, mainly because the particle size of β-CD microcapsules is large and it is difficult to enter the micropores of bamboo fibers. By comparing the significance of the variance analysis, it can be seen that the impregnation of different microcapsules is significantly not correlated with the weight gain rate, volume change rate, and porosity change rate of bamboo slices.

[0104] Table 8 Changes in the mass, volume, and porosity of bamboo slices before and after microcapsule impregnation and variance analysis

[0105]

[0106] Microstructure observation:

[0107] Figure 10 (a - b) It can be seen that some microcapsules with larger particle sizes are mainly deposited in the fiber cell cavities on the surface after impregnation with β-CD microcapsules. In the fiber cell cavities inside the bamboo slices, β-CD microcapsules pass through the pits and enter the cell cavities, and are dispersed on the fiber cell walls. In Figure 10 (c), it can also be found that there are many β-CD microcapsules with larger particle sizes distributed in the large vessels of bamboo. This shows that β-CD microcapsules are successfully mechanically combined or electrostatically adsorbed with bamboo fibers through impregnation. The particle size of CS microcapsules is uniform and much smaller than that of β-CD microcapsules. They are evenly dispersed in the cell cavities and CS microcapsules are found in the pits of the thin-walled cells of bamboo fibers. This shows that CS microcapsules can achieve deep impregnation through pits and can form a relatively stable bond with the cell wall. CS microcapsules are evenly distributed on the walls of bamboo fiber vessels and have good adsorption, adhesion, or fusion. Therefore, both of these loofah seed oil microcapsules are proven to be able to enter bamboo fiber cells and achieve physical connection, and the overall distribution is relatively uniform, which is of great significance for the regulation of bamboo fiber properties.

[0108] Chemical composition:

[0109] Figure 11 The Fourier transform infrared spectra of bamboo slices impregnated with different microcapsules are shown. The infrared spectra of bamboo slices after the two kinds of microcapsule impregnation treatments mainly show the characteristic peaks of bamboo cellulose, hemicellulose, and lignin. 2927 cm -1 , 2857 cm -1 and 1743 cm -1The peaks at [specific positions] respectively correspond to the stretching vibrations of the carbon-carbon double bonds of unsaturated fatty acids, the methylene groups, and the stretching of the carbonyl ester functional groups of triglycerides in loofah seed oil. Peaks are shown at these two positions in the infrared spectra of bamboo slices impregnated with both types of microcapsules, indicating that a combination has formed between the microcapsule emulsion and the bamboo slices. The positions of some peaks of the β-CD microcapsules are basically similar to the absorption peaks of bamboo impregnated with β-CD microcapsules. For example, a characteristic peak of the symmetric stretching vibration of –OH appears at [specific wavenumber], and the characteristic peak at [specific wavenumber] may coincide with the peak at [specific wavenumber]. Comparing the FTIR spectra of β-CD microcapsules and bamboo slices impregnated with β-CD microcapsules, it is found that almost no new absorption peaks appear, indicating that only physical embedding occurs between the β-CD microcapsules and the bamboo slices. This is beneficial for the stable existence of the microcapsules in bamboo fibers. -1 At [specific wavenumber], -1 and the characteristic peak at [specific wavenumber] -1 may coincide with the peak at [specific wavenumber].

[0110] There are no obvious differences in the peaks of bamboo slices impregnated with both types of microcapsules in the range of 1600 - 4000 cm -1 , indicating that the loofah seed oil microcapsules also exist in bamboo fibers. The absorption peak at 1158 cm -1 is attributed to the C–O–C group in bamboo cellulose. There is still a peak at this position for bamboo slices impregnated with loofah seed oil, while the absorption peak at 1158 cm -1 disappears for bamboo slices impregnated with CS microcapsules, indicating a chemical bond between the chitosan microcapsules and the bamboo slices. Chitosan contains hydroxyl and amino groups and can undergo various reactions such as carboxylation, hydroxylation, etherification, esterification, hydrolysis, oxidation, grafting, and crosslinking to form various derivatives. In this study, the chitosan microcapsule emulsion is weakly acidic, so it may promote the chemical reaction between cellulose and chitosan. However, no new absorption peaks are formed in the spectrum, indicating that chemical crosslinking has occurred between the chitosan microcapsules and the bamboo fibers.

[0111] Mildew resistance:

[0112] Figure 12 The mold test conducted in a petri dish for a total of 30 days is shown. It is observed that the mildew resistance of bamboo slices impregnated with microcapsules is better than that of untreated specimens. There are a small number of light green mildew spots on the surface of bamboo slices impregnated with β-CD microcapsules on the 5th day; the change in the mildew spot area is small on the 15th day; by the 30th day, the infection area on the bamboo green side is 20%, and there are only a small number of light gray hyphae on the bamboo yellow side. According to the infection situation on the surface of the bamboo slices, the infection level of bamboo slices impregnated with β-CD microcapsules is comprehensively judged to be level 2. The lighter infection degree may be because the effective anti-mildew components in loofah seed oil and the β-CD microcapsules deposited on the surface block the large-scale spread of hyphae.

[0113] On the 5th day, only a small amount of white hyphae were observed on the surface of the bamboo slices impregnated with CS microcapsules; on the 10th day, the hyphae turned grayish-brown; on the 15th day, the infection area on the bamboo green side reached 5%; until the 30th day, there were still only a small amount of hyphae on the bamboo yellow side, and there were fewer black hyphae on the bamboo green side. Until the 30th day, the comprehensive infection level of the bamboo slices impregnated with CS microcapsules was still grade 1, indicating that CS microcapsules endow the bamboo slices with excellent mildew-proof properties. Chitosan itself has excellent antibacterial properties, which are generally considered to be mainly in three aspects: the positive charge of the CS molecule acts on the negative charge of the cell membrane, affecting the permeability of the cell membrane; the hydroxyl and amino groups of CS can form complexes with trace metal ions, interfering with fungal metabolism and the stability of the cell membrane; low-molecular-weight chitosan can enter microbial cells and act on DNA, affecting its transcription. In addition, Tween 80 is added to the CS microcapsules, and Tween 80 is a surfactant that can strongly stimulate the cell membrane. Therefore, the impregnation of CS microcapsules enhances the mildew-proof property of the bamboo slices.

[0114] Figure 13 The microscopic structure of the two kinds of microcapsule-impregnated bamboo slices after being decayed by mold at the end of the 30-day anti-mildew experiment is shown. The surface of the untreated bamboo was severely infected by mold, and the mold spores were concentrated on the fiber surface, but there were a large number of mold spores and hyphae in the vessels, and the vessel walls were severely eroded. This shows that the erosion of mold is from the surface to the inside of the vessels and then to the parenchyma cells. The structures of the cross-sections of the two kinds of microcapsule-impregnated and modified bamboo slices were intact after decay. Observation Figure 13 (a-d) shows that there are more hyphae and spores in some areas of the cross-section of the bamboo slice, and the main erosion site is the cell wall of bamboo fibers. The presence of β-CD microcapsules can be observed on the radial section, and there are distributions of hyphae and spores inside the parenchyma cells, indicating that the mold does not only erode the surface of the bamboo slice. Figure 13 (e-f) shows that the distribution of hyphae on the cross-section of the bamboo slice is less, and the number of hyphae is small, and the overall structure of the bamboo fiber cell wall is also relatively complete, indicating that the mold causes less damage to the bamboo slice impregnated with CS microcapsules. In addition, no obvious hyphae and spores were seen in the large vessels on the radial section of the bamboo slice, while spores and CS microcapsules deposited on the fiber cell wall can be observed in the parenchyma cells at the end of the bamboo slice. Microscopic structure observation shows that the degree of mold infection of the bamboo slice impregnated with β-CD microcapsules is low, and the bamboo slice impregnated with CS microcapsules is only infected on the surface.

[0115] Table 9 shows the weight loss rates of the bamboo slices after being impregnated with the two kinds of microcapsules in the 30-day anti-mildew test. By comparison, it is found that the weight loss rate of the bamboo slices impregnated with β-CD microcapsules is higher than that of the bamboo slices impregnated with CS microcapsules, and this result is consistent with Figure 15 the erosion results of the surface and inside of the bamboo slice presented. The smaller weight loss rate of the bamboo slice after being impregnated with CS microcapsules also indicates that CS microcapsules have good mildew-proof protection for the bamboo slice.

[0116] Figure 13 Microstructure of bamboo after decay with different microcapsule impregnation treatments. (a - b) Cross-section of β-CD impregnated bamboo slices; (c - d) Radial section of β-CD impregnated bamboo slices; (e - f) Cross-section of CS impregnated bamboo slices; (g - h) Radial section of CS impregnated bamboo slices

[0117] Table 9 Weight loss rate of bamboo after decay with different treatments

[0118]

[0119] Flexural strength:

[0120] Table 10 shows the flexural properties of bamboo slices after impregnation with two kinds of microcapsules. Compared with untreated bamboo, the ultimate load and elastic modulus of bamboo slices treated with two kinds of microcapsules both increase. The mechanical property data of bamboo slices obtained by compression on the bamboo green side and bamboo yellow side of untreated bamboo slices are different. Similarly, there are differences in the ultimate loads obtained by compression on different sides after microcapsule impregnation treatment, but the elastic moduli are relatively close. Since the density and quantity of vascular bundles on the bamboo green side are higher than those on the bamboo yellow side, the untreated bamboo green side usually shows a larger failure load when compressed. However, the ultimate load on the bamboo yellow side after β-CD impregnation is 5.4% higher than that on the bamboo green side, and the deflection corresponding to the ultimate load reaches 8.6 mm. This may be because β-cyclodextrin has a rigid conical cavity structure, which provides less mechanical support for the bamboo yellow side after impregnation treatment. Chitosan is a kind of semi-rigid polymer with strong intermolecular and inter-molecular hydrogen bonds. Since the CS microcapsules have a small particle size and are evenly distributed in bamboo fibers, the densification of bamboo pores is not achieved, so the mechanical properties of the bamboo green side are still better than those of the bamboo yellow side. For the bamboo slices modified with microcapsules, the adjustable range of the ultimate load is 311.3 - 449.6 N, the adjustable range of elasticity is 7879.2 - 7985.9 MPa, and the adjustable range of deformation corresponding to the ultimate load is relatively wide, which is 5.6 - 8.6 mm. This shows that the bamboo slices modified with microcapsules have good adjustable deformability and have the potential to be used as filling materials.

[0121] Figure 14 The stress-strain curves of three-point bending of bamboo slices after impregnation with two kinds of microcapsules are shown. It can be seen from the figure that for the loading on the bamboo yellow side, the individual differences of bamboo materials treated with two kinds of microcapsules are both obvious, indicating that the bamboo itself has a greater influence on mechanical properties. For the loading on the bamboo green side, the differences in elastic modulus among bamboo slices after microcapsule impregnation are smaller, mainly because the vascular bundles on the bamboo green side mainly play a role in mechanical support. After treatment with two kinds of microcapsules, the mechanical strength of bamboo slices does not decrease, which provides favorable conditions for the application of microcapsule-impregnated bamboo slices in furniture materials.

[0122] Table 10 Flexural strength of bamboo slices before and after microcapsule impregnation

[0123]

[0124]

[0125] Hygroscopicity and anti-loss property:

[0126] Table 11 shows the hygroscopicity rate, moisture dissipation rate, water absorption rate, contact angle, etc. of bamboo slices after microcapsule impregnation. The hygroscopicity rate, water absorption rate, and moisture dissipation rate of bamboo slices impregnated with the two kinds of microcapsules are similar to those of bamboo slices treated by microwave for 10 minutes, indicating that microcapsule impregnation has little effect on the hygroscopicity, moisture dissipation, and water absorption of bamboo slices. Among them, the hygroscopicity rate, water absorption rate, and moisture dissipation rate of bamboo slices impregnated with β-CD microcapsules are 12.6%, 16.3%, and 1.5% lower than those of bamboo slices treated by microwave for 10 minutes, respectively. This may be because the β-CD microcapsules partially block the pores of bamboo fibers, hindering the absorption and diffusion of water and moisture. The hygroscopicity rate and moisture dissipation rate curves of bamboo slices impregnated with the two kinds of microcapsules are also relatively similar. After impregnating bamboo slices with the two kinds of microcapsules, the loss rate of β-CD microcapsules is 3.2 times that of CS microcapsules. This is mainly because β-CD microcapsules only form physical connections with bamboo fibers, and most of the microcapsules with larger particle sizes are distributed on the surface of bamboo fibers and in large ducts, so the retention rate is poor. While CS has cell adhesion and can enter the interior of bamboo fiber cell cavities and form chemical connections with cellulose, so it can well achieve functions such as slow release in bamboo fibers.

[0127] Comparing the data in the table, it can be seen that the contact angle of bamboo slices impregnated with β-CD microcapsules is 1.6 times that of bamboo slices treated by microwave for 10 minutes, while the contact angle of bamboo slices impregnated with CS microcapsules is 0.46 times that of bamboo slices treated by microwave for 10 minutes. β-CD is hydrophilic and loofah seed oil is hydrophobic. However, the contact angle of the surface of bamboo slices impregnated with β-CD microcapsules is relatively large, probably because the β-CD microcapsule emulsion contains some unencapsulated loofah seed oil, and these loofah seed oils are deposited on the surface of bamboo slices after impregnating the bamboo slices. Chitosan particles are hydrophilic particles with a water contact angle of 13.9°. Due to the deposition of CS microcapsules on the surface of bamboo slices, the water contact angle is mainly affected by the hydrophilicity of the microcapsule surface.

[0128] Table 11 Hygroscopicity, moisture dissipation and contact angle of bamboo slices after impregnation with different microcapsules

[0129]

[0130] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of loofah seed oil microcapsules, characterized in that, Using loofah seed oil as the core material and natural polymers as the wall material, the natural polymer is selected as β-cyclodextrin, and the dosage ratio of the wall material to the core material is 0.33 - 5 g:1 ml. Or, the natural polymer is selected as chitosan, and the dosage ratio of the wall material to the core material is 0.5 - 10 g:1 ml, including the following steps: (1) Dissolve the natural polymer to obtain a natural polymer solution; (2) Add loofah seed oil to the natural polymer solution for microencapsulation reaction treatment to obtain an emulsion containing loofah seed oil microcapsules; When the natural polymer is selected as β-cyclodextrin, the specific process of step (1) is: add β-cyclodextrin to hot water, stir to dissolve, and cool to no more than 70 °C after the solution becomes clear; the specific process of step (2) is: dissolve loofah seed oil in ethanol and then add it to the β-cyclodextrin solution, and then stir and react at a temperature of 40 - 70 °C for 2 - 4 h; When the natural polymer is selected as chitosan, the specific process of step (1) is: add chitosan to a 1% v / v acetic acid solution, let it stand at room temperature for 12 - 16 h, then add Tween 80 and stir into a homogeneous phase at a temperature of 45 °C; the specific process of step (2) is: directly add loofah seed oil to the chitosan solution, then add a 0.3% w / v sodium tripolyphosphate solution with a pH value of 5.6, stir at room temperature for 60 min, and finally adjust the pH value of the emulsion to 3.5 - 5.5 with a 0.5 mol / L hydrochloric acid / sodium hydroxide solution.

2. The preparation method of the loofah seed oil microcapsule according to claim 1, characterized in that, When the natural polymer is selected as β-cyclodextrin, it also includes step (3) separating the loofah seed oil microcapsules from the emulsion. The specific process is: refrigerate the emulsion at 4 °C for 12 - 16 h to precipitate it, then take out the precipitate, wash it by vacuum filtration with ethanol and distilled water in sequence, and finally freeze-dry the precipitate at a temperature of -60 °C for 72 - 96 h to obtain loofah seed oil microcapsules.

3. The preparation method of the loofah seed oil microcapsule according to claim 1, characterized in that, When the natural polymer is selected as chitosan, it also includes step (3) separating the loofah seed oil microcapsules from the emulsion. The specific process is: centrifuge the emulsion for 10 - 14 min, take out the precipitate, wash it with distilled water, and finally freeze-dry the precipitate at a temperature of -60 °C for 72 - 96 h to obtain loofah seed oil microcapsules.

4. A loofah seed oil microcapsule, characterized in that, Prepared by the preparation method according to any one of claims 1 to 3.

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