A method for preparing bicarboxylated nanocellulose

Abstract

The application discloses a preparation method of double-carboxylated nanocellulose and belongs to the technical field of nanocellulose material preparation. The method comprises the following steps: obtaining double-aldehyde nanocellulose by selectively oxidizing nanocellulose through a high-iodate; adjusting the pH of the double-aldehyde nanocellulose solution obtained through reaction to alkalinity; and then introducing ozone into the alkaline double-aldehyde nanocellulose suspension to perform oxidation treatment, so as to obtain double-carboxylated nanocellulose. The application realizes the regeneration of the high-iodate by controlling the ozone introduction time and the pH value in the blending system. The regenerated high-iodate acts as a catalyst and cooperates with ozone to the double-aldehyde nanocellulose, so as to prepare double-carboxylated nanocellulose with high carboxyl content. The method is efficient and environmentally friendly, realizes the recycling of the catalyst high-iodate, reduces the production cost, avoids the excessive degradation of the double-aldehyde nanocellulose and the carboxylated product thereof, and has the potential for large-scale production of double-carboxylated nanocellulose.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cellulose nanomaterials, and particularly relates to a preparation method of double-carboxylated nanocellulose. BACKGROUND

[0002] With the depletion of fossil energy, finding green and environmentally friendly renewable resources has become the focus of researchers. Cellulose is the most abundant natural polymer compound in the world. Nanocellulose is a new emerging polymer material derived from cellulose, which can be torn, degraded or peeled off into nanofiber products of different sizes, crystallinity and properties through mechanical, biological or chemical methods. As one of the derived products of cellulose, nanocellulose has high surface area, low thermal expansion coefficient, biodegradability, biocompatibility, excellent mechanical strength and chemical stability, and shows great application prospects in food packaging, electronics, pharmaceuticals, cosmetics and other industries.

[0003] Carboxylated nanocellulose is a kind of nanocellulose material with carboxyl groups on the surface. Due to the introduction of functional carboxyl groups, this material has been widely studied in the fields of biomedicine, wastewater treatment, bioelectronics, etc. At present, researchers mainly use TEMPO oxidation method and etherification method to prepare carboxylated nanocellulose. However, TEMPO oxidation method has problems such as expensive oxidation reagent, toxicity and non-recyclable use. Although the etherification method has lower cost, it has problems such as complicated preparation process and uneven product quality. Chinese patent application CN108484782A discloses a carboxyl-modified nanocellulose crystal and a preparation method thereof. The method uses microcrystalline cellulose as raw material, and uses a composite oxidizing agent composed of TEMPO, sodium periodate, sodium hypochlorite and sodium chlorite to oxidize the microcrystalline cellulose by "one-pot method" to obtain carboxyl-modified cellulose. However, the method does not reuse the oxidizing agent periodate, and the use of expensive oxidizing agent increases the preparation cost. Therefore, a simple, fast and low-cost preparation technology of carboxylated nanocellulose will become a new breakthrough in nanocellulose production technology. SUMMARY

[0004] In view of the problems of long production cycle and high cost of oxidation reagent in the production process of carboxylated nanocellulose in the prior art, the application provides a preparation method of low-cost double-carboxylated nanocellulose.

[0005] The purpose of the application is achieved by the following technical solutions.

[0006] A preparation method of double-carboxylated nanocellulose, comprising the following steps:

[0007] (1) mixing nanocellulose suspension and periodate to obtain double-aldehyde nanocellulose suspension;

[0008] (2) adjusting the pH of the dialdehyde nanocellulose suspension obtained in step (1) to alkaline;

[0009] (3) introducing a gas containing ozone into the alkaline dialdehyde nanocellulose suspension obtained in step (2) for oxidation treatment to obtain dicarboxylated nanocellulose.

[0010] Preferably, the nanocellulose suspension in step (1) comprises nanocellulose from broadleaf wood fibers, coniferous wood fibers, cotton fibers or other biomass sources.

[0011] Preferably, the periodate in step (1) is sodium periodate.

[0012] Preferably, the reaction conditions of the nanocellulose suspension in step (1) with the periodate are that the mass ratio of the periodate to the nanocellulose is 0.1-1:0.5-4, the reaction slurry concentration is 0.2wt%-4.0wt%, the reaction temperature is 25-50℃, and the reaction time is 1-5h.

[0013] Preferably, in step (2), the pH of the dialdehyde nanocellulose suspension obtained in step (1) is adjusted to 10-14, and further preferably to 11-13.

[0014] Preferably, the oxidation treatment conditions in step (3) are that the oxidation reaction temperature is 0-45℃, the introduction time is 10-60min, and further preferably 10-40min.

[0015] Preferably, in step (3), the gas containing ozone has a flow rate of 0.5-2.5NL / min, and the ozone gas concentration is 0.5wt%-4.0wt%.

[0016] Preferably, the oxidation treatment in step (3) is carried out in the dark.

[0017] Preferably, in step (3), the ozone is prepared from industrial oxygen (purity 99.2%) through an ozone generator, and the output gas includes ozone and oxygen.

[0018] The present application successfully prepares dicarboxylated nanocellulose by regenerating periodate in an alkaline solid-liquid blending system and combining ozone oxidation, and by adjusting the process parameters, the degradation of the degree of polymerization of the carboxylated nanocellulose is small, the entire process is simple, green and environmentally friendly, and the cost is low.

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

[0020] (1) The present application uses efficient cleaning ozone as an oxidizing agent, realizes the regeneration of high iodate in the blending system, and oxidizes the dialdehyde nanocellulose in the solid-liquid blending system with regenerated high iodate, reduces the use of chemical high iodate while improving the preparation efficiency, and is suitable for large-scale continuous production of double-carboxylated nanocellulose products. The method has low preparation cost, is environmentally friendly in the preparation process, and has high preparation efficiency.

[0021] (2) The method of the present application can realize low-cost double-carboxylated nanocellulose preparation while keeping the degree of polymerization of double-carboxylated nanocellulose to a minimum. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The FT-IR spectra of dialdehyde nanocellulose before and after ozone oxidation in the blending system in Example 1 1 H and 13 C spectra of dialdehyde nanocellulose; (c), (d) are the 1 H and 13 C spectra of carboxylated nanocellulose. 1 H and 13 C spectra of carboxylated nanocellulose. DETAILED DESCRIPTION

[0023] The specific implementation of the present application is further specifically described in combination with the examples, but the implementation of the present application is not limited thereto.

[0024] Example 1

[0025] The absolute dry mass of 1 g of wood fiber-based nanocellulose was mixed with sodium periodate under light-proof conditions, the absolute dry mass ratio of sodium periodate to nanocellulose was 1:1, the reaction slurry concentration was 0.5%, the reaction temperature was 45°C, and the reaction time was 4 h, to obtain a dialdehyde nanocellulose suspension. After the oxidation reaction was completed, the dialdehyde nanocellulose suspension was immediately cooled to room temperature, and the pH of the solution was adjusted to 13 using sodium hydroxide. The obtained alkaline dialdehyde nanocellulose solution was transferred to a three-necked flask wrapped with tin paper and ozone-containing gas was introduced, wherein the gas inlet flow and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas inlet time was 10 min. After the reaction was completed, solid-liquid separation was achieved by centrifugation, the concentrations of periodate ions and iodate ions in the supernatant were detected by high performance liquid chromatography, and the solid part was washed with deionized water by centrifugation until it was neutral, to obtain double-carboxylated nanocellulose. The high performance liquid chromatography calculation results showed that the concentration of periodate ions in the supernatant obtained by centrifugation of the solid-liquid blending system after ozone treatment was 1.46 mmol / L, and the concentration of iodate ions was 18.71 mmol / L.

[0026] In the comparative experiment, the dialdehyde nanocellulose suspension obtained above was subjected to solid-liquid separation, and then ozone-containing gas was introduced into the obtained liquid, wherein the gas inlet flow rate and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas inlet time was 10 min. The concentrations of periodate ions and iodate ions in the obtained solution at the end of the reaction were 18.83 mmol / L and 4.74 mmol / L, respectively. Before the ozone gas was introduced, the concentrations of periodate ions and iodate ions in the solution were 10.77 mmol / L and 12.53 mmol / L, respectively. This indicates that ozone oxidation converts iodate into periodate under alkaline conditions.

[0027] The above results show that, in the solid-liquid blending system, ozone converts iodate ions into periodate ions again. The regenerated periodate, as an oxidizing agent, rapidly oxidizes dialdehyde nanocellulose. Dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone.

[0028] Nuclear magnetic resonance analysis and carboxyl content titration results show that dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone and periodate. The carboxyl content of dicarboxylated nanocellulose is 0.84 mmol / g. The degree of reduction in the degree of polymerization is small when the dialdehyde nanocellulose is prepared by the method of the present application. In the process from dialdehyde nanocellulose to dicarboxylated nanocellulose, the degree of polymerization is reduced from 57 to 55.

[0029] Example 2

[0030] The wood fiber-based nanocellulose with an absolute dry mass of 1 g was mixed with sodium periodate under light-proof conditions, wherein the absolute dry mass ratio of sodium periodate to nanocellulose was 1:1, the reaction slurry concentration was 0.5%, the reaction temperature was 45°C, and the reaction time was 4 h, to obtain a dialdehyde nanocellulose suspension. After the oxidation reaction was completed, the dialdehyde nanocellulose suspension was immediately cooled to room temperature, and sodium hydroxide was used to adjust the pH of the solution to 12. The obtained alkaline dialdehyde nanocellulose solution was transferred to a three-neck flask wrapped with tin paper and ozone-containing gas was introduced, wherein the gas inlet flow rate and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas inlet time was 20 min. After the reaction was completed, solid-liquid separation was achieved by centrifugation, and the concentrations of periodate ions and iodate ions in the supernatant were detected by high-performance liquid chromatography. The solid part was washed with deionized water by centrifugation until it was neutral, to obtain dicarboxylated nanocellulose. The high-performance liquid chromatography calculation results show that, in the supernatant obtained by centrifugation of the ozone-treated solid-liquid blending system, the concentration of periodate ions was 1.76 mmol / L, and the concentration of iodate ions was 18.80 mmol / L.

[0031] In the comparative experiment, the dialdehyde nanocellulose suspension obtained above was subjected to solid-liquid separation, and then ozone-containing gas was introduced into the obtained liquid, wherein the gas inlet flow and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas inlet time was 20 min. The concentrations of periodate ions and iodate ions in the obtained solution at the end of the reaction were 23.43 mmol / L and 0.38 mmol / L, respectively, and the concentrations of periodate ions and iodate ions in the solution before the ozone gas was introduced were 10.77 mmol / L and 12.53 mmol / L, respectively, indicating that the ozone oxidation under alkaline conditions converted iodate into periodate.

[0032] The above results show that under the solid-liquid blending system, ozone reconverts iodate ions into periodate ions, and the regenerated periodate serves as an oxidizing agent to rapidly oxidize dialdehyde nanocellulose. Dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone.

[0033] Nuclear magnetic resonance analysis and carboxyl content titration results show that dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone and periodate, and the carboxyl content of dicarboxylated nanocellulose is 1.12 mmol / g. The degree of reduction of the polymerization degree is smaller when dialdehyde nanocellulose is prepared by the method of the present application, and the degree of reduction of the polymerization degree is smaller from 57 to 49 in the process from dialdehyde nanocellulose to dicarboxylated nanocellulose.

[0034] Example 3

[0035] The wood fiber-based nanocellulose with an absolute dry mass of 1 g was mixed with sodium periodate under light-proof conditions, wherein the absolute dry mass ratio of sodium periodate to nanocellulose was 1:1, the reaction slurry concentration was 0.5%, the reaction temperature was 45°C, and the reaction time was 4 h, to obtain a dialdehyde nanocellulose suspension. After the oxidation reaction was completed, the dialdehyde nanocellulose suspension was immediately cooled to room temperature, and sodium hydroxide was used to adjust the pH of the solution to 11. The obtained alkaline dialdehyde nanocellulose solution was transferred to a tin paper-wrapped three-necked flask and ozone-containing gas was introduced, wherein the gas inlet flow and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas inlet time was 30 min. After the reaction was completed, solid-liquid separation was achieved by centrifugation, and the concentrations of periodate ions and iodate ions in the supernatant were detected by high-performance liquid chromatography. The solid part was washed with deionized water by centrifugation until it was neutral, to obtain dicarboxylated nanocellulose. The high-performance liquid chromatography calculation results show that the concentration of periodate ions in the supernatant obtained by centrifugation of the ozone-treated solid-liquid blending system was 1.90 mmol / L, and the concentration of iodate ions was 19.82 mmol / L.

[0036] In the comparative experiment, the dialdehyde nanocellulose suspension obtained above was subjected to solid-liquid separation, and then ozone-containing gas was introduced into the obtained liquid, wherein the gas inlet flow and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas inlet time was 30 min. The concentrations of periodate ions and iodate ions in the obtained solution at the end of the reaction were 23.74 mmol / L and 0.35 mmol / L, respectively, and the concentrations of periodate ions and iodate ions in the solution before the ozone gas was introduced were 10.77 mmol / L and 12.53 mmol / L, respectively, indicating that the ozone oxidation under alkaline conditions converted iodate into periodate.

[0037] The above results show that under the solid-liquid blending system, ozone converts iodate ions into periodate ions again, and the regenerated periodate serves as an oxidizing agent to rapidly oxidize dialdehyde nanocellulose. Dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone.

[0038] NMR analysis and carboxyl content titration results show that dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone and periodate, and the carboxyl content of dicarboxylated nanocellulose is 1.20 mmol / g. The degree of polymerization reduction is smaller when the dialdehyde nanocellulose is prepared by the method of the present application, and the degree of polymerization reduction is smaller from 57 to 48 in the process from dialdehyde nanocellulose to dicarboxylated nanocellulose.

[0039] Example 4

[0040] The wood fiber-based nanocellulose with an absolute dry mass of 1 g was mixed with sodium periodate under light-proof conditions, wherein the absolute dry mass ratio of sodium periodate to nanocellulose was 1:1, the reaction slurry concentration was 0.5%, the reaction temperature was 45°C, and the reaction time was 4 h, to obtain a dialdehyde nanocellulose suspension. After the oxidation reaction was completed, the dialdehyde nanocellulose suspension was immediately cooled to room temperature, and sodium hydroxide was used to adjust the pH of the solution to 13. The obtained alkaline dialdehyde nanocellulose solution was transferred to a three-neck flask wrapped with tin paper and ozone-containing gas was introduced, wherein the gas inlet flow and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas inlet time was 40 min. After the reaction was completed, solid-liquid separation was achieved by centrifugation, and the concentrations of periodate ions and iodate ions in the supernatant were detected by high performance liquid chromatography. The solid part was washed with deionized water by centrifugation until it was neutral, to obtain dicarboxylated nanocellulose. The high performance liquid chromatography calculation results show that the concentration of periodate ions in the supernatant obtained by centrifugation of the ozone-treated solid-liquid blending system was 2.02 mmol / L, and the concentration of iodate ions was 20.34 mmol / L.

[0041] In the comparative experiment, the dialdehyde nanocellulose suspension obtained above was subjected to solid-liquid separation, and then ozone-containing gas was introduced into the obtained liquid, wherein the gas flow rate and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas introduction time was 40 min. The concentrations of periodate ions and iodate ions in the obtained solution at the end of the reaction were 23.74 mmol / L and 0.35 mmol / L, respectively, and the concentrations of periodate ions and iodate ions in the solution before the ozone gas was introduced were 10.77 mmol / L and 12.53 mmol / L, respectively, indicating that the ozone oxidation under alkaline conditions converted iodate into periodate.

[0042] The above results show that in the solid-liquid blending system, ozone reconverts iodate ions into periodate ions, and the regenerated periodate serves as an oxidizing agent to rapidly oxidize dialdehyde nanocellulose. Dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone.

[0043] NMR analysis and carboxyl content titration results show that dialdehyde nanocellulose is oxidized into dicarboxylated nanocellulose under the action of ozone and periodate, and the carboxyl content of dicarboxylated nanocellulose is 1.46 mmol / g. The degree of reduction in the degree of polymerization is small when dialdehyde nanocellulose is prepared by the method of the present application, and the degree of polymerization is reduced from 57 to 31 during the process of dialdehyde nanocellulose to dicarboxylated nanocellulose.

[0044] Comparative Example 1

[0045] The wood fiber-based nanocellulose with an absolute dry mass of 1 g was mixed with sodium periodate under light-proof conditions, the absolute dry mass ratio of sodium periodate to nanocellulose was 1:1, the reaction slurry concentration was 0.5%, the reaction temperature was 45°C, and the reaction time was 4 h, to obtain a dialdehyde nanocellulose suspension. After the oxidation reaction was completed, the dialdehyde nanocellulose suspension was immediately cooled to room temperature, and sodium hydroxide was used to adjust the pH of the solution to 4. The obtained alkaline dialdehyde nanocellulose solution was transferred to a three-neck flask wrapped with tin paper and ozone-containing gas was introduced, wherein the gas flow rate and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas introduction time was 10 min. After the reaction was completed, solid-liquid separation was achieved by centrifugation, and the concentrations of periodate ions and iodate ions in the supernatant were detected by high performance liquid chromatography. The solid part was washed with deionized water by centrifugation until it was neutral, to obtain dicarboxylated nanocellulose. The high performance liquid chromatography calculation results show that the concentration of periodate ions in the supernatant obtained by centrifugation of the ozone-treated solid-liquid blending system was 0 mmol / L, and the concentration of iodate ions was 21.78 mmol / L.

[0046] In the comparative experiment, the dialdehyde nanocellulose suspension obtained above was subjected to solid-liquid separation, and then ozone-containing gas was introduced into the obtained liquid, wherein the gas flow rate and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, the gas introduction time was 10 min, and the concentrations of periodate ions and iodate ions in the obtained solution at the end of the reaction were almost unchanged compared with those before the ozone gas was introduced, indicating that ozone oxidation under acidic conditions cannot convert iodate into periodate.

[0047] Comparative Example 2

[0048] The wood fiber-based nanocellulose with an absolute dry mass of 1 g was mixed with sodium periodate under light-proof conditions, the absolute dry mass ratio of sodium periodate to nanocellulose was 1:1, the reaction slurry concentration was 0.5%, the reaction temperature was 45°C, and the reaction time was 4 h, to obtain a dialdehyde nanocellulose suspension. After the oxidation reaction, the dialdehyde nanocellulose suspension was immediately cooled to room temperature, and the pH of the solution was adjusted to 8 using sodium hydroxide. The obtained alkaline dialdehyde nanocellulose solution was transferred to a tin paper-wrapped three-necked flask and ozone-containing gas was introduced, wherein the gas flow rate and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, and the gas introduction time was 10 min. After the reaction, solid-liquid separation was achieved by centrifugation, the concentrations of periodate ions and iodate ions in the supernatant were detected by high performance liquid chromatography, and the solid part was washed with deionized water by centrifugation until it was neutral to obtain double-carboxylated nanocellulose. The high performance liquid chromatography calculation results showed that the concentration of periodate ions in the supernatant obtained by centrifugation of the ozone-treated solid-liquid blending system was 0.65 mmol / L, and the concentration of iodate ions was 20.71 mmol / L.

[0049] In the comparative experiment, the dialdehyde nanocellulose suspension obtained above was subjected to solid-liquid separation, and then ozone-containing gas was introduced into the obtained liquid, wherein the gas flow rate and the ozone inlet concentration were 1.5 NL / min and 2.0 wt%, respectively, the gas introduction time was 10 min, and the concentrations of periodate ions and iodate ions in the obtained solution at the end of the reaction were almost unchanged compared with those before the ozone gas was introduced, indicating that ozone oxidation under acidic conditions cannot convert iodate into periodate.

[0050] The above results show that under the neutral solid-liquid blending system, ozone reconverts iodate ions into periodate ions, and the regenerated periodate rapidly oxidizes dialdehyde nanocellulose, and dialdehyde nanocellulose is oxidized into double-carboxylated nanocellulose under the action of ozone.

[0051] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations, simplifications, etc. made without departing from the spirit and principles of the present application shall be equivalent replacement manners and shall be included in the protection scope of the present application.

Claims

1. A method for preparing bicarboxylated nanocellulose, characterized by, The method comprises the following steps: (1) mixing and reacting a nanocellulose suspension with a periodate salt to obtain a dialdehyde nanocellulose suspension; (2) adjusting the pH of the dialdehyde nanocellulose suspension obtained in step (1) to be alkaline; (3) introducing a gas containing ozone into the alkaline dialdehyde nanocellulose suspension obtained in step (2) for oxidation treatment to obtain a double-carboxylated nanocellulose; In step (2), the pH of the dialdehyde nanocellulose suspension obtained in step (1) is adjusted to 11-13; In step (3), the oxidation treatment is performed for 10-40 min at a temperature of 0-45℃.

2. The method for preparing dicarboxylated cellulose nanoparticles according to claim 1, characterized in that, In step (3), the gas containing ozone has an inlet flow rate of 0.5-2.5 NL / min, and the ozone inlet concentration is 0.5 wt%-4.0 wt%.

3. The method for preparing dicarboxylated cellulose nanoparticles according to claim 1, characterized in that, In step (3), the oxidation treatment is performed in the dark.

4. The method for preparing dicarboxylated cellulose nanoparticles according to claim 1, characterized in that, In step (1), the nanocellulose includes broadleaf wood fibers, coniferous wood fibers, cotton fibers, or nanocellulose from other biomass sources; and the periodate salt is sodium periodate.

5. The method for preparing dicarboxylated cellulose nanoparticles according to claim 1, characterized in that, In step (1), the absolute dry mass ratio of the periodate salt to nanocellulose is 0.1-1:0.5-4, and the reaction slurry concentration is 0.2 wt%-4.0 wt%.

6. The method for preparing dicarboxylated cellulose nanoparticles according to claim 1, characterized in that, In step (1), the reaction temperature is 25-50℃, and the reaction time is 1-5 h.

Images