CN111138686A - Green method for continuously dissolving natural polymer material - Google Patents
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- CN111138686A CN111138686A CN202010039537.4A CN202010039537A CN111138686A CN 111138686 A CN111138686 A CN 111138686A CN 202010039537 A CN202010039537 A CN 202010039537A CN 111138686 A CN111138686 A CN 111138686A
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Abstract
The invention relates to a method capable of continuously dissolving a natural polymer material, and belongs to the field of polymer materials. The invention provides a method for continuously dissolving a natural polymer material, which comprises the following steps: firstly, uniformly stirring and mixing a solvent and natural high polymer material powder or natural high polymer pulp at room temperature to obtain a natural high polymer material suspension; then grinding the suspension until the particle size is less than or equal to 5 mm; then shearing the ground suspension at a high speed in a double-screw extruder at a shearing rate of 600-1000 rpm at a temperature of-20 to-12 ℃, and dissolving a natural polymer material within 1-3min to prepare a transparent natural polymer solution; wherein, the natural polymer material powder or the natural polymer material in the natural polymer pulp is a natural polymer material which can be dissolved by low-temperature alkali urea aqueous solution. The invention provides a green and environment-friendly method capable of industrially and continuously dissolving natural macromolecules such as cellulose, which is simple and easy to implement.
Description
Technical Field
The invention relates to a method capable of continuously dissolving a natural polymer material, and belongs to the field of polymer materials.
Background
Cellulose, chitin and other natural polysaccharide polymer materials; because molecules contain a large amount of hydrogen bonds inside, the decomposition temperature is higher than the melting temperature, and only a special solvent can dissolve, wherein the sodium hydroxide/urea/water low-temperature dissolution system has the advantages of low cost, environmental friendliness, safety and no toxicity, and has good industrialization prospect. But it has the following drawbacks: 1) the system is in a metastable state, is easy to gel at low temperature or high temperature, and has a narrow dissolution processing window; 2) the dissolution temperature is harsh, the cellulose and the solvent need to be quickly mixed, and the cellulose cannot be dissolved once the specific temperature is exceeded; 3) the system obtained by mixing the solvent with cellulose and the like is difficult to carry out subsequent defoaming and filtering procedures, so that the industrial production cannot be realized; in addition, the solubility of the cellulose with the molecular weight of 9 ten thousand dissolved by the solvent system is only 4-5%, the solution is easy to be gelatinized, and the gelation time is within 1 hour, so that the subsequent normal spinning can not be realized.
In view of the above drawbacks, in the prior art, LiOH and urea systems are often used to replace NaOH and urea systems, for example, chinese patent 200301115678 discloses a lithium hydroxide and urea composition solvent for dissolving cellulose and its use, which is prepared by a freeze thawing method or a method for directly dissolving cellulose and preparing cellulose or a film. NaOH, urea and thiourea systems are also used to replace NaOH and urea systems, for example, Donghua university proposes a continuous low-temperature alkali-urea method, which is to add a certain amount of thiourea into an alkali/urea dissolving system, directly prepare a cellulose raw material and an alkali/urea/thiourea/aqueous solution into a suspension, and then quickly reduce the temperature to the dissolving temperature; in the system, a spherical complex is formed among sodium hydroxide, urea, thiourea and water, wherein the thiourea is a main part for forming an outer complex, so that the dissolving time of cellulose is greatly shortened, and the production efficiency is improved (the preparation and performance research of cellulose membranes such as Boxian waves and the like; a cellulose composite solvent system such as wood fire and the like and the application thereof); however, the solvent system needs to be added with thiourea, which has toxicity and has a certain pollution problem, so that the industrial production is not environment-friendly.
As can be seen from the above analysis, there is no report in the prior art about "continuous industrial production of natural polysaccharide polymers such as cellulose can be realized without adding non-toxic additives by using NaOH and urea systems as solvents"; if the technical problem can be solved, the method has excellent industrial value because the method is low in cost, environment-friendly and nontoxic.
Disclosure of Invention
Aiming at the defects, the invention provides a green and environment-friendly method capable of continuously dissolving natural polymers such as cellulose, chitin and other materials, which is simple and easy to implement, not only realizes the industrial continuous production of natural polysaccharide polymer materials, but also improves the solubility of the natural polymers such as cellulose (the solubility of 9 ten thousand molecular weight cellulose is improved from 4 percent to 7 percent), and prolongs the gelation time (the gelation time of 9 ten thousand molecular weight cellulose at 15 ℃ is prolonged from 1 hour to more than 48 hours).
The technical scheme of the invention is as follows:
the technical problem to be solved by the invention is to provide a method for continuously dissolving a natural high polymer material, which comprises the following steps: firstly, uniformly stirring and mixing a solvent and natural high polymer material powder or natural high polymer pulp at room temperature to obtain a natural high polymer material suspension; then grinding the suspension until the particle size is less than or equal to 5 mm; then shearing the ground suspension at a high speed in a double-screw extruder at a shearing rate of 600-1000 rpm at a temperature of-20 to-12 ℃, and dissolving a natural polymer material within 1-3min to prepare a transparent natural polymer solution;
wherein, the natural polymer material powder or the natural polymer material in the natural polymer pulp is a natural polymer material which can be dissolved by low-temperature alkali urea aqueous solution;
the solvent comprises the following components in percentage by mass:
5-9 parts of NaOH
10-15 parts of urea
76-85 parts of water.
Preferably, the solvent comprises the following components in percentage by mass:
NaOH 7 parts by weight
12 parts of urea
And 81 parts by weight of water.
Further, the solvent also comprises zinc oxide, and the components and the mass content of the zinc oxide are as follows:
preferably, the solvent comprises the following components in percentage by mass:
further, the viscosity average molecular weight of the natural high molecular material is 4 to 20 ten thousand. When the molecular weight of the cellulose exceeds 20 ten thousand, the solubility of the cellulose is 1 wt% or less, the molecular weight is too small, and the soluble amount can be increased, but the properties of the regenerated product obtained are poor.
Further, the natural polymer material suspension satisfies: stirring to mix solvent and natural polymer material powder or pulp, standing for at least 10min, and comparing the densities of the bottom and top layer dispersions until the density error is within 1%.
Further, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows:
when the molecular weight of the selected natural polymer material is more than or equal to 4 to less than 7 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 6.5-8.3 wt% of solvent: 90.5 wt% -93.5 wt%;
when the molecular weight of the selected natural polymer material is more than or equal to 7 to less than 10 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 5-6.5 wt% of a solvent: 93.5 wt% -95 wt%;
when the molecular weight of the selected natural polymer material is more than or equal to 10 to less than 16 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 2.5-5 wt% of a solvent: 95 to 97.5 weight percent;
when the molecular weight of the selected natural polymer material is 16-20 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 1-2.5 wt% of a solvent: 97.5 wt% -99 wt%.
Further, the natural polymer material is a natural polysaccharide polymer material; preferably: cellulose, chitin, and chitosan; more preferably cellulose.
Furthermore, in the double-screw extruder, the temperature of the first five sections is-20 ℃ to-18 ℃, and the temperature of the last three sections is-15 ℃ to-12 ℃.
Further, when the natural polymer material is cellulose, the method for continuously dissolving the natural polymer material comprises the following steps:
1) adding NaOH into a stirring kettle, adding urea, adding water, and stirring to completely dissolve the urea and the water to obtain a solvent;
2) then adding dried natural polymer material powder or natural polymer pulp, and stirring and mixing the solvent and the natural polymer material powder or the natural polymer pulp uniformly at room temperature to obtain a natural polymer material suspension; the preparation of the suspension of the natural polymer material powder or the natural polymer pulp and the solvent is limited under the room temperature condition, because the natural polymer material powder or the natural polymer pulp (such as cellulose) can be prevented from being partially dissolved after being contacted with the solvent at the room temperature, once the partial dissolution is carried out, on one hand, the partially dissolved glue liquid can wrap the undissolved natural polymer material powder or the natural polymer pulp (such as cellulose microfiber), and further, the dissolution of the subsequent natural polymer material powder or the natural polymer pulp (such as cellulose) is inhibited; on the other hand, the partially dissolved glue solution can be gelled in the following low-temperature step (step 4);
3) grinding the natural polymer material suspension until the particle size is less than or equal to 5 mm; the purpose of the milling is to ensure that the suspension does not clog during the metered delivery in step 4) and that its composition is homogeneous (i.e. the concentration of the suspension is uniform), so that it is capable of instantaneous dissolution (within 1-3 min) after it enters the twin-screw extruder;
4) conveying the milled suspension to a pre-cooled low-temperature double-screw extruder by a screw pump in a metering manner, and dissolving for 1-3min at a shear rate of 600-1000 rpm to obtain a natural high polymer material solution containing a small amount of bubbles; removing bubbles at the head of the discharge to obtain a completely transparent natural polymer material solution; wherein, the temperature of each section of the double-screw extruder is as follows: 1-5 sections: 6-8 sections at-20 ℃ to-18 ℃: -15 ℃ to-12 ℃.
Further, in the step 4), the milled suspension is metered by a screw pump and then is conveyed to a pre-cooled low-temperature double-screw extruder at a constant speed at a flow rate of 10-100 liters per hour.
Further, in the above method, when the natural polymer material is cellulose and the solvent includes zinc oxide, the method in step 1) is: adding NaOH into a stirring kettle, adding part of water, stirring at room temperature, adding zinc oxide, continuously stirring, adding urea after the zinc oxide is completely dissolved, supplementing the rest water, and continuously stirring until the urea is completely dissolved to obtain a solvent; wherein, the adding amount of part of water is needed to ensure that the concentration of the sodium hydroxide is more than 20 weight percent. In the step, the water is added in batches, mainly in order to ensure that the concentration of the sodium hydroxide is more than 20 wt% before the zinc oxide is added, the zinc oxide can be better dissolved only when the requirement is met, otherwise, the zinc oxide cannot be well dissolved, and the zinc oxide particles are in the solvent and cannot play a role in improving the solubility.
The invention has the beneficial effects that:
according to the method, under the condition that no other environmentally-friendly additives such as thiourea and the like are added to a natural high polymer material (capable of being dissolved by a low-temperature alkaline urea aqueous solution), the natural high polymer material and a solvent are stirred and uniformly mixed at room temperature, then are milled to have the particle size of less than or equal to 5mm, and then are completely dissolved within 1-3min under the action of high-speed shearing at 600-1000 rpm at the temperature of-20 to-12 ℃ to obtain a transparent solution of the natural high polymer material; the gelation time of the obtained cellulose solution is greatly prolonged (the gelation time of the 9 ten thousand molecular weight cellulose at 15 ℃ is prolonged from 1 hour to more than 48 hours), the normal spinning can be completely realized, the continuous dissolution of natural high polymer materials such as cellulose and the like is realized, and the industrial production is realized; and the solubility of the obtained cellulose solution is correspondingly improved, such as the solubility of 9 ten thousand molecular weight cellulose is improved from 4 percent to 7 percent.
Description of the drawings:
FIG. 1 is a polarization microscope photograph of a cellulose solution obtained by stirring cellulose at a high speed in example 1, and it is understood from FIG. 1 that any cellulose-like substance is not visible except for the stained black spots on the glass plate, indicating that the cellulose has been completely dissolved to obtain a true solution of cellulose.
Fig. 2 is a polarization microscope photograph of the cellulose solution in comparative example 1 at a speed of less than 300rpm, and it can be seen from fig. 2 that most of the cellulose is dissolved, but a large amount of micron-sized fibrous cellulose is still in the solution and is not completely dissolved, indicating that the cellulose cannot be completely dissolved at a low speed at the same concentration as in example 1.
Detailed Description
In the technical scheme of continuously dissolving cellulose in the prior art, various additives are generally added to increase the dissolving performance and the solution stability, and various toxic substances such as thiourea which can generate pollution are inevitably introduced; the invention breaks through the design concept, still based on the adoption of a solvent with a general dissolving effect (the cost is lowest), the transparent cellulose solution can be obtained by adjusting the process, namely blending at room temperature, grinding to ensure that the particle size is less than or equal to 5mm, and then increasing the shearing rate of a screw to 600-1000 rpm, the gelation time of the obtained cellulose solution is greatly prolonged, and the spinning time can be completely met, so that the continuous industrial production of cellulose is realized, although the energy consumption is slightly improved, the full-green production of the cellulose solution can be realized, the price of the used raw materials is very low, the cost is greatly reduced, and the high energy consumption is offset.
The following examples are given to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.
Example 1
Adding 14 kg of NaOH into a stirring kettle, adding 24 kg of urea, adding 162 liters of water, and continuously stirring until the urea is completely dissolved; obtaining a cellulose solvent with the weight ratio of NaOH being 7 wt% and the weight ratio of urea being 12 wt%; finally, 10 kg of dried 9-ten-thousand-molecular-weight cellulose pulp is added, the mixture is stirred for half an hour at the stirring speed of 50RPM at the temperature of 15-25 ℃ to obtain cellulose pulp porridge, and then a grinding pump is adopted to grind for one hour (the pulp porridge can smoothly pass through a screen with the aperture of 5mm, the pulp porridge can not be blocked in metering and conveying, and the whole pulp porridge component is stable and uniform); then accurately metering by a screw pump, and injecting the paste into a screw extruder at a constant speed with the flow of 50 liters per hour, wherein the temperature of each section of the screw extruder is as follows: 1-5 sections: -18 ℃, 6-8 stages: -12 ℃ and twin screw shear rate at 800 rpm; dissolving for 1-3min by using a double-screw extruder to obtain a cellulose solution containing a small amount of bubbles; removing residual micro bubbles from the final discharge head by a vacuum pump connected with the head to obtain a completely transparent cellulose solution; the cellulose concentration was 5.3 wt% and the gel time was 6h at room temperature 22 ℃.
Example 2
Adding 14 kg of NaOH into a stirring kettle, adding 50L of water, stirring at room temperature, then adding 1.6 kg of zinc oxide, continuing to stir, adding 24 kg of urea after the zinc oxide is completely dissolved, supplementing 110.4L of water, and continuing to stir until the urea is completely dissolved; obtaining a cellulose solvent with 7 wt% of NaOH, 12 wt% of urea and 0.8 wt% of zinc oxide; finally, 10 kg of dried 9-ten-thousand-molecular-weight cellulose pulp is added, the mixture is stirred for half an hour at the stirring speed of 50RPM at the temperature of 15-25 ℃ to obtain cellulose pulp porridge, and then a grinding pump is adopted to grind for one hour (the pulp porridge can smoothly pass through a screen with the aperture of 5mm, the pulp porridge can not be blocked in metering and conveying, and the whole pulp porridge component is stable and uniform); then accurately metering by a screw pump, and injecting the paste into a screw extruder at a constant speed with the flow of 50 liters per hour, wherein the temperature of each section of the screw extruder is as follows: 1-5 sections: -18 ℃, 6-8 stages: -12 ℃ and twin screw shear rate at 800 rpm; dissolving for 1-3min by using a double-screw extruder to obtain a cellulose solution containing a small amount of bubbles; removing residual micro bubbles from the final discharge head by a vacuum pump connected with the head to obtain a completely transparent cellulose solution; the cellulose concentration was 7 wt% and the gel time was 48h at room temperature 22 ℃.
Comparative example 1
The other conditions were the same as in example 2 except that the shearing speed of the twin-screw extruder was 300 rpm; the resulting solution contained a large amount of undissolved filament material (see fig. 2), and the resulting solution was not transparent, i.e., continuous production was not possible in this comparative example.
Comparative example 2
The other conditions are the same as example 2, and the difference is only that the solvent and the cellulose pulp are stirred at the stirring speed of 50RPM for half an hour at the temperature of 15-25 ℃ to obtain cellulose pulp porridge, and the cellulose pulp porridge is directly conveyed into the double screws without grinding by a grinding pump, and in the experimental process, the cellulose pulp porridge is either blocked during the conveying process so that the pulp porridge cannot be normally conveyed, so that the continuous production is not mentioned; or the cellulose pulp gruel can not be instantly dissolved due to the non-uniform components after entering the twin-screw extruder, and the finally obtained solution also contains a large amount of undissolved microfibril substances, so that the obtained solution is not transparent.
Example 3
Adding 14 kg of NaOH into a stirring kettle, adding 24 kg of urea, adding 162 liters of water, and continuously stirring until the urea is completely dissolved; obtaining a cellulose solvent with the weight ratio of NaOH being 7 wt% and the weight ratio of urea being 12 wt%; finally, 13 kg of dried 7-ten-thousand-molecular-weight cellulose pulp is added, and the mixture is stirred for half an hour at the temperature of 15-25 ℃ at the stirring speed of 50RPM, so that cellulose pulp porridge is obtained, and then the cellulose pulp porridge is milled for one hour by a milling pump (the pulp porridge can smoothly pass through a screen with the aperture of 5 mm); then accurately metering by a screw pump, and injecting the paste into a screw extruder at a constant speed with the flow rate of 30 liters per hour, wherein the temperature of each section of the screw extruder is as follows: 1-5 sections: -18 ℃, 6-8 stages: -12 ℃ and twin screw shear rate at 800 rpm; dissolving for 1-3min by using a double-screw extruder to obtain a cellulose solution containing a small amount of bubbles; removing residual micro bubbles from the final discharge head by a vacuum pump connected with the head to obtain a completely transparent cellulose solution; the cellulose concentration was 6.5 wt% and the gel time was 6h at room temperature 22 ℃.
Example 4
Adding 14 kg of NaOH into a stirring kettle, adding 50L of water, stirring at room temperature, then adding 1.6 kg of zinc oxide, continuing to stir, adding 24 kg of urea after the zinc oxide is completely dissolved, supplementing 110.4L of water, and continuing to stir until the urea is completely dissolved; obtaining a cellulose solvent with 7 wt% of NaOH and 12 wt% of urea and 0.8 wt% of zinc oxide; finally, 7 kg of dried 15 ten thousand molecular weight cellulose pulp is added, the mixture is stirred for half an hour at the temperature of 15-25 ℃ at the stirring speed of 50RPM, and then cellulose pulp porridge is obtained, and is milled for one hour by a milling pump (ensuring that the pulp porridge can smoothly pass through a screen with the aperture of 5 mm); then accurately metering by a screw pump, and injecting the paste into a screw extruder at a constant speed with the flow rate of 30 liters per hour, wherein the temperature of each section of the screw extruder is as follows: 1-5 sections: -18 ℃, 6-8 stages: -12 ℃ and twin screw shear rate at 800 rpm; dissolving for 1-3min by using a double-screw extruder to obtain a cellulose solution containing a small amount of bubbles; removing residual micro bubbles from the final discharge head by a vacuum pump connected with the head to obtain a completely transparent cellulose solution; the cellulose concentration in the solution was 3.5 wt% and the gel time was 24h at room temperature 22 ℃.
Example 5
Adding 14 kg of NaOH into a stirring kettle, adding 50L of water, stirring at room temperature, then adding 1.6 kg of zinc oxide, continuing to stir, adding 30 kg of urea after the zinc oxide is completely dissolved, supplementing 104.4L of water, and continuing to stir until the urea is completely dissolved; obtaining a cellulose solvent with 7 wt% of NaOH and 15 wt% of urea and 0.8 wt% of zinc oxide; finally, 10 kg of dried 10-ten-thousand-molecular-weight cellulose pulp is added, the mixture is stirred for half an hour at the temperature of 15-25 ℃ at the stirring speed of 50RPM, and then cellulose pulp porridge is obtained, and a grinding pump is adopted to grind the mixture for one hour (the pulp porridge can smoothly pass through a screen with the aperture of 5 mm); then accurately metering by a screw pump, and injecting the slurry into a screw extruder at a constant speed at a flow rate of 70 liters per hour, wherein the temperature of each section of the screw extruder is as follows: 1-5 sections: -18 ℃, 6-8 stages: -12 ℃ and twin screw shear rate at 700 rpm; dissolving for 1-3min by using a double-screw extruder to obtain a cellulose solution containing a small amount of bubbles; removing residual micro bubbles from the final discharge head by a vacuum pump connected with the head to obtain a completely transparent cellulose solution; the cellulose concentration in the solution was 6.3 wt% and the gel time was 12h at room temperature 22 ℃.
Example 6
Adding 14 kg of NaOH into a stirring kettle, adding 24 kg of urea, adding 162 liters of water, and continuously stirring until the urea is completely dissolved; obtaining a cellulose solvent with the weight ratio of NaOH being 7 wt% and the weight ratio of urea being 12 wt%; finally, 5 kg of dried cellulose pulp with 16 ten thousand molecular weight is added, the cellulose pulp is stirred for half an hour at the temperature of 15-25 ℃ at the stirring speed of 50RPM, and then the cellulose pulp is milled for one hour by a milling pump (ensuring that the pulp can smoothly pass through a screen with the diameter of 5 mm); then accurately metering by a screw pump, and injecting the slurry into a screw extruder at a constant speed at a flow rate of 100 liters per hour, wherein the temperature of each section of the screw extruder is as follows: 1-5 sections: -18 ℃, 6-8 stages: -12 ℃ and twin screw shear rate at 800 rpm; dissolving for 1-3min by using a double-screw extruder to obtain a cellulose solution containing a small amount of bubbles; removing residual micro bubbles from the final discharge head by a vacuum pump connected with the head to obtain a completely transparent cellulose solution; the cellulose concentration in the solution was 3.5 wt% and the gel time was 6h at room temperature 22 ℃.
Cellulose of different molecular weights in this solvent, the maximum soluble content is different, for example 15 ten thousand molecular weight cellulose, adding cellulose exceeding the maximum soluble content of the solvent in the solvent, even if adjusted to a shear rate of up to 1000rpm, still cannot be dissolved completely. In addition, when zinc oxide is added into the alkali-urea system, the zinc oxide must be dissolved in the alkali-urea system when the concentration of sodium hydroxide is more than 20 wt%, otherwise the zinc oxide cannot be dissolved in the solvent, so that zinc oxide particles are in the solvent, and the effect of improving the solubility cannot be achieved.
Claims (10)
1. A method for continuously dissolving natural polymer materials is characterized by comprising the following steps: firstly, uniformly stirring and mixing a solvent and natural high polymer material powder or natural high polymer pulp at room temperature to obtain a natural high polymer material suspension; then grinding the suspension until the particle size is less than or equal to 5 mm; then shearing the ground suspension at a high speed in a double-screw extruder at a shearing rate of 600-1000 rpm at a temperature of-20 to-12 ℃, and dissolving a natural polymer material within 1-3min to prepare a transparent natural polymer solution;
wherein, the natural polymer material powder or the natural polymer material in the natural polymer pulp is a natural polymer material which can be dissolved by low-temperature alkali urea aqueous solution;
the solvent comprises the following components in percentage by mass:
5-9 parts of NaOH
10-15 parts of urea
76-85 parts of water.
2. The method for continuously dissolving natural polymer materials according to claim 1, wherein the solvent comprises the following components by mass:
NaOH 7 parts by weight
12 parts of urea
81 parts by weight of water;
further, the solvent also comprises zinc oxide, and the components and the mass content of the zinc oxide are as follows:
preferably, the solvent comprises the following components in percentage by mass:
3. the method according to claim 1 or 2, wherein the viscosity average molecular weight of the natural polymer material is 4 to 20 ten thousand.
4. The method according to any one of claims 1 to 3, wherein the natural polymer material suspension satisfies the following conditions: stirring to mix solvent and natural polymer material powder or pulp, standing for at least 10min, and comparing the densities of the bottom and top layer dispersions until the density error is within 1%.
5. The method for continuously dissolving natural polymer materials according to any one of claims 1 to 4, wherein the mass ratio of the solvent to the natural polymer material powder or natural polymer pulp is as follows:
when the molecular weight of the selected natural polymer material is more than or equal to 4 to less than 7 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 6.5-8.3 wt% of solvent: 90.5 wt% -93.5 wt%;
when the molecular weight of the selected natural polymer material is more than or equal to 7 to less than 10 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 5-6.5 wt% of a solvent: 93.5 wt% -95 wt%;
when the molecular weight of the selected natural polymer material is more than or equal to 10 to less than 16 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 2.5-5 wt% of a solvent: 95 to 97.5 weight percent;
when the molecular weight of the selected natural polymer material is 16-20 ten thousand, the mass ratio of the solvent to the natural polymer material powder or the natural polymer pulp is as follows: natural polymer material powder or natural polymer pulp: 1-2.5 wt% of a solvent: 97.5 wt% -99 wt%.
6. The method for continuously dissolving natural polymer materials according to any one of claims 1 to 5, wherein the natural polymer materials are natural polysaccharide polymer materials; preferably: cellulose, chitin, and chitosan; more preferably cellulose.
7. The method for continuously dissolving natural polymer materials according to any one of claims 1 to 6, wherein the temperature of the first five sections in the twin-screw extruder is-20 ℃ to-18 ℃, and the temperature of the last three sections in the twin-screw extruder is-15 ℃ to-12 ℃.
8. The method for continuously dissolving natural polymer material according to claim 6 or 7, wherein when the natural polymer material is cellulose, the method for continuously dissolving natural polymer material comprises the following steps:
1) adding NaOH into a stirring kettle, adding urea, adding water, and stirring to completely dissolve the urea and the water to obtain a solvent;
2) then adding dried natural polymer material powder or natural polymer pulp, and stirring and mixing the solvent and the natural polymer material powder or the natural polymer pulp uniformly at room temperature to obtain a natural polymer material suspension;
3) grinding the natural polymer material suspension until the particle size is less than or equal to 5 mm;
4) conveying the milled suspension to a pre-cooled low-temperature double-screw extruder by a screw pump in a metering manner, and dissolving for 1-3min at a shear rate of 600-1000 rpm to obtain a natural high polymer material solution containing a small amount of bubbles; removing air bubbles at the head of the discharge head to obtain completely transparent natural polymer material solution.
9. The method according to claim 8, wherein in the step 4), the milled suspension is metered by a screw pump and then delivered to a pre-cooled low-temperature twin-screw extruder at a constant flow rate of 10-100 l/hr.
10. The method for continuously dissolving natural polymer materials according to claim 8 or 9, wherein when the solvent further comprises zinc oxide, the method in step 1) is: adding NaOH into a stirring kettle, adding part of water, stirring at room temperature, adding zinc oxide, continuously stirring, adding urea after the zinc oxide is completely dissolved, supplementing the rest water, and continuously stirring until the urea is completely dissolved to obtain a solvent; wherein, the adding amount of part of water is needed to ensure that the concentration of the sodium hydroxide is more than 20 weight percent.
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