CN110698624B - Preparation method of thermoplastic cellulose grafted polyurethane - Google Patents
Preparation method of thermoplastic cellulose grafted polyurethane Download PDFInfo
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Abstract
The invention relates to a preparation method of thermoplastic cellulose grafted polyurethane, belonging to the field of high molecular compounds. The invention provides a preparation method of thermoplastic cellulose grafted polyurethane, which comprises the following steps: heating cellulose/polyethylene glycol gel and diisocyanate to 100-140 ℃ in an inert gas environment, fully stirring for 7-12 h to obtain a crude product, and washing the crude product to obtain thermoplastic cellulose grafted polyurethane; wherein the molar ratio of the diisocyanate to the polyethylene glycol in the cellulose/polyethylene glycol gel is 1-1.1: 1; the molar ratio of polyethylene glycol to cellulose repeating units in the cellulose/polyethylene glycol gel is 18-36: 1. the invention adopts a simple method without using organic solvent to graft polyurethane on a cellulose molecular chain to prepare the thermoplastic cellulose grafted polyurethane which can be melt-processed, and has low melting temperature, good flexibility and high transparency.
Description
Technical Field
The invention relates to a preparation method of thermoplastic cellulose grafted polyurethane, belonging to the field of high molecular compounds.
Background
Cellulose (Cellulose) is a high molecular compound with the largest yield in nature, 50-70% of the components of the cell wall of higher plants are Cellulose, and organisms or metabolites such as some animals (such as tunicates), bacteria and the like also contain a large amount of Cellulose. According to statistics, the annual output of cellulose in the world currently exceeds 2000 million tons, and the cellulose is one of natural high polymer materials developed and utilized earlier by human beings, and has a plurality of excellent properties such as renewability, biodegradability, derivatizability, no toxicity and the like. The molecular weight of the natural cellulose is large, the molecular structure contains a large amount of hydroxyl, a large amount of intramolecular hydrogen bonds and intermolecular hydrogen bonds can be formed through self-assembly, and the strong intermolecular action ensures that the cellulose is decomposed before melting, namely the natural cellulose has no melting behavior. The molding of cellulose can not be realized by using the advantages of high production efficiency, strong designability of product shape, mature process and the like of thermoplastic molding processing, so that most of cellulose can not be well developed and utilized. Therefore, the utilization of the cellulose can be effectively improved by developing the thermoplastic cellulose, so that the dilemma that the traditional petroleum-based polymer material is not renewable and degradable is hopefully solved, and the thermoplastic cellulose has high development value.
Research has shown that cellulose can exhibit thermoplasticity under strong physical action. As early as 2005, Schroeter Johannes et al reported a method of melt-flowing cellulose, and according to the authors, under pressure, shear force and laser irradiation, satin-like fibers in cotton linters disappeared, indicating that melt-flowing of cellulose occurred (Schroeter Johannes et al cellulose,12(2005): 159-. Subsequently, Zhang et al have found that thermoplastic flow of previously ball-milled cellulose powders can be achieved by specific shearing actions (back pressure-equal channel angular pressure) at relatively low temperatures (150 ℃) to form continuous thermoplastic materials with significantly reduced crystallinity (Xiaoming Zhang et al carbohydrate Polymers,87(2012): 2470-. The intense physical action can enable the cellulose to generate melt flow to a certain extent, but the reported physical method has some defects, such as stronger physical action, higher requirement on processing equipment and potential safety hazard; strong physical effects require a large amount of energy consumption; in addition, the above mentioned physical actions require severe conditions and the whole process is difficult to control, which makes it reported that the physical measures for achieving melt flow of cellulose are difficult to industrialize.
Furthermore, with the discovery of cellulosic proton inert solvents, reports on the melt processing of cellulose by the preparation of cellulose derivatives have also been generated in response, such as Zhang et al dissolving cellulose in ionic liquids (1-allyl-3-methylimidazole chloride), cellulose grafted L-polylactic acid, cellulose acetate grafted polylactic acid (YIHAo L uranet al. Cellulose,20(2013), 327. Cellulose,21(2014), 2369. 2378. and cellulose esters containing hard/soft side chains (Zhangyan chemical Chemistry. ACS Sustaininavailable & Engineering,6(2018), 6. 1. 4939. through optical microscopy observation, it was found that cellulose derivatives produced can significantly melt flow during elevated temperatures, in addition, cellulose derivatives prepared by the methods of ionic modification have been found to have a higher cost than cellulose derivatives prepared by the conventional methods of ionic modification of cellulose esters, such as DMAC, cellulose derivatives are still available in the melt processing of cellulose, such as cellulose derivatives under the conditions of the melt modification of cellulose, such as DMSO, cellulose derivatives are not disclosed in the industry, but have been effectively popularized in the melt processing of cellulose derivatives under the conditions of cellulose polymers of DMSO, such as DMAc, cellulose derivatives under the temperature-ionic modification of DMSO, cellulose derivatives under the current industrial processes, and the cost report that the ionic modification of DMSO (DMAc) is lower than under the ionic modification of cellulose derivatives produced by the Zhangyan-ionic modification of DMSO industries, the methods of DMSO industries, the cellulose derivatives under the methods of DMSO industries, the cellulose derivatives, the methods, the cellulose derivatives produced by the methods of DMSO industries, the DMAc, the methods of the cellulose derivatives under the methods of the ionic modification of the methods of the cellulose derivatives under the ionic modification of the.
Cellulose derivatives, such as cellulose acetate, cellulose acetate butyrate, cellulose propionate, etc., which have been commercialized at present, can melt flow in a narrow temperature range, so many researches have been made to improve the melt processing behavior of cellulose by using a plasticizing means, such as ethylene glycol, glycerol, etc., as a plasticizer, which can effectively improve the processability of cellulose derivatives. Izabela cielca et al plasticize hydroxymethylcellulose and hydroxyethylcellulose made from bacterial cellulose with glycerol, and studies have shown that the processing behavior of cellulose derivatives can be improved and the flexibility of the resulting cellulose composite material can be improved by the plasticization effect of glycerol (Izabela cielca et al cellulose,26(2019): 5409-. In addition, due to the strong swelling and dissolving capacity of the ionic liquid to cellulose, the ionic liquid is also an ideal plasticizer for cellulose, and Chinese patents CN 104163943A and CN 104194059A report that the ionic liquid is used as the plasticizer to prepare thermoplastic cellulose materials. The Xiaolin Xie research team also prepared thermoplastic cellulose using ionic liquids as plasticizers and prepared cellulose samples by injection molding, and performance test analysis showed that the properties of thermoplastic cellulose materials were related to the ionic liquid content of the materials (Jun Wu et al cellulose,22(2014): 89-99.). Plasticization enables melt-forming of cellulose, but the aggregation state of cellulose in the resulting material remains highly controversial, and the use of large amounts of plasticizer makes stability of the material in use difficult to ensure, e.g., plasticizer migration affects the useful life of the resulting cellulosic material.
In summary, in the currently reported thermoplastic cellulose, a barrier of high energy consumption and high equipment requirement exists in the strong physical action; the stability of the product is difficult to ensure by using the plasticizer; the homogeneous method for preparing the thermoplastic cellulose derivative needs to use a large amount of expensive aprotic solvent, so the cost is higher and the production efficiency is lower. There are still significant challenges to making thermoplastic cellulose.
Disclosure of Invention
Aiming at the defects, the invention provides a preparation method of thermoplastic cellulose grafted polyurethane, which grafts polyurethane on a cellulose molecular chain by a simple method without using an organic solvent to prepare a thermoplastic cellulose grafted polyurethane material capable of being melt-processed, and the cellulose grafted polyurethane material has low melting temperature, good flexibility and high transparency.
The technical scheme of the invention is as follows:
the first technical problem to be solved by the invention is to provide a preparation method of thermoplastic cellulose grafted polyurethane, which comprises the following steps: heating cellulose/polyethylene glycol (PEG) gel and diisocyanate to 100-140 ℃ in an inert gas environment (nitrogen atmosphere), fully stirring for 7-12 h to obtain a crude product, and washing the crude product to obtain thermoplastic cellulose grafted polyurethane; wherein the molar ratio of the diisocyanate to the polyethylene glycol in the cellulose/polyethylene glycol gel is 1-1.1: 1; the molar ratio of polyethylene glycol to cellulose repeat units (AGU) in the cellulose/polyethylene glycol gel is 18-36: 1.
Further, the diisocyanate is Hexamethylene Diisocyanate (HDI), Toluene Diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), or lysine diisocyanate (L DI).
Further, the cellulose in the cellulose/polyethylene glycol gel comprises: microcrystalline cellulose, cotton pulp, bamboo pulp, cellulose filter paper, or absorbent cotton. In the present invention, any cellulose that can be dissolved in an aqueous solution of sodium hydroxide (or lithium hydroxide) can be used.
Further, the cellulose/polyethylene glycol gel is prepared by the following method, and the method comprises the following steps:
1) dissolving cellulose in an aqueous alkali solution, dripping the cellulose/aqueous alkali solution into liquid polyethylene glycol, adding acid with the same molar ratio as alkali to adjust the pH of a system to be neutral, and fully stirring to obtain Regenerated Cellulose (RC);
2) carrying out suction filtration on the regenerated cellulose obtained in the step 1), reserving a suction filtration product, and repeatedly replacing a solvent in the suction filtration product with polyethylene glycol for 3-5 times to prepare cellulose/polyethylene glycol gel;
3) dehydrating the cellulose/polyethylene glycol gel obtained in the step 2), and then adding polyethylene glycol to ensure that the cellulose/polyethylene glycol gel meets the following requirements: the molar ratio of polyethylene glycol to cellulose repeating units in the cellulose/polyethylene glycol gel is 18-36: 1.
further, in the step 1), the alkali is sodium hydroxide or lithium hydroxide.
Further, in the above step 1), the acid is hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid or nitric acid, and the concentration thereof is 1 mol/L.
Further, in the step 3), the water removal method comprises: adding the cellulose/polyethylene glycol gel obtained in the step 2) into a container (such as a three-necked bottle), and immersing the container into an oil bath at 70-90 ℃ (preferably 80 ℃) for vacuum dewatering for 1-2 h (preferably 1 h).
Preferably, the molar ratio of polyethylene glycol to cellulose repeat units (AGU) in the cellulose/polyethylene glycol gel is 24-36: 1.
Further, in the above method, the obtained crude product is washed with acetone, butanone, benzene, toluene or xylene.
Further, in the above method, the polyethylene glycol may be one of PEG200 (average molecular weight 200), PEG300, PEG400, or PEG 600.
Preferably, in the above method, the cellulose/polyethylene glycol gel and diisocyanate (HDI) are heated to 100 ℃ to 140 ℃ (preferably 120 ℃) in an inert gas environment (nitrogen atmosphere) and fully stirred for 7 to 12 hours (preferably 8 hours) to prepare a crude product.
The second technical problem to be solved by the invention is to provide thermoplastic cellulose grafted polyurethane which is prepared by adopting the method.
The invention has the beneficial effects that:
1) the preparation method of the thermoplastic cellulose grafted polyurethane does not use expensive aprotic solvent, has low cost and is green and environment-friendly;
2) the thermoplastic cellulose grafted polyurethane disclosed by the invention is low in melting temperature, good in flexibility and high in transparency.
Drawings
FIG. 1 is an infrared spectrum of microcrystalline cellulose, comparative example 1, comparative example 2, comparative example 3, and example 3; as can be seen from FIG. 1, the modified cellulose showed 1695cm in IR spectrum compared with microcrystalline cellulose-1And 1530cm-1A characteristic absorption peak representing polyurethane appears, which indicates that the polyurethane side chain is successfully grafted to the cellulose; in addition, the characteristic absorption peak intensity of the polyurethane in the infrared spectrum of example 3 is significantly higher than that of the comparative example, indicating that more polyurethane can be grafted onto the cellulose by the chemical modification of the present invention.
FIG. 2 is an optical micrograph of comparative example 1, comparative example 2, comparative example 3 and example 3 during temperature elevation; as can be seen from FIG. 2, in example 3, in the course of temperature rise, softening occurred at 160 ℃, distinct melt flow occurred at 180 ℃, and a transparent melt was formed at 200 ℃, indicating that example 3 is thermoplastic cellulose-grafted polyurethane; while the comparative examples did not melt during the temperature rise, the comparative examples did not exhibit thermoplasticity even at a high temperature of 240 ℃.
FIG. 3 is a digital photograph of films obtained by hot-pressing the products obtained in example 3, example 5, example 6 and example 7, which were placed on the "RCP-g-PU print"; as can be seen from FIG. 3, the word "RCP-g-PU" beneath the film can be clearly seen through the hot-pressed films of examples 3, 5, 6 and 7, indicating that the cellulose-grafted polyurethane film obtained by the thermoplastic processing method has high transparency.
FIG. 4 is a graph showing transmittance curves of the films obtained by hot-pressing the products obtained in example 3, example 5, example 6 and example 7 for light waves of different wavelengths; as can be seen from fig. 4, the film obtained in example has high transparency in the visible light range.
Detailed Description
The preparation method of the thermoplastic cellulose grafted polyurethane comprises the following steps: dissolving cellulose in alkaline aqueous solution such as sodium hydroxide, and preparing regenerated cellulose by using polyethylene glycol (PEG) as an anti-solvent; then, the wet regenerated cellulose/polyethylene glycol (PEG) gel is used as a reactant, and the reactant is heated and stirred under the inert gas environment to be fully reacted with diisocyanate to prepare the thermoplastic cellulose grafted polyurethane.
According to the invention, after the cellulose is activated by a dissolving/regenerating method, under the condition of not using an organic solvent, the cellulose/PEG gel is reacted with diisocyanate to graft polyurethane onto a cellulose molecular chain, so that the movement capability of the cellulose molecular chain in a thermal field is improved, and the thermoplastic cellulose grafted polyurethane material with low melting temperature, good flexibility and high transparency is prepared. The invention prepares regenerated cellulose by taking PEG as an anti-solvent, and then directly uses the regenerated cellulose/PEG gel for graft modification to prepare the thermoplastic cellulose graft polyurethane material; the whole process does not need to dissolve the cellulose in an aprotic organic solvent for chemical reaction.
The thermoplastic cellulose grafted polyurethane of the invention can be prepared by adopting the following embodiments:
1. dripping transparent cellulose/sodium hydroxide aqueous solution into liquid polyethylene glycol (PEG), adding hydrochloric acid with equal molar ratio to sodium hydroxide, and stirring to obtain Regenerated Cellulose (RC);
2. performing suction filtration on the RC obtained in the step 1, reserving a suction filtration product, and repeatedly replacing a solvent in the suction filtration product by PEG for 3-5 times to prepare cellulose/polyethylene glycol (PEG) gel;
3. weighing the cellulose/PEG gel obtained in the step 2, adding the weighed cellulose/PEG gel into a three-necked bottle, immersing the three-necked bottle into an oil bath at the temperature of 80 ℃, and regulating the content of PEG according to a proportion after vacuum dehydration for 1 h;
4. adding Hexamethylene Diisocyanate (HDI) into a three-necked bottle according to a certain proportion, heating to 100-140 ℃ in a nitrogen atmosphere, and fully stirring for 8-12 h to obtain a crude product;
5. and (4) washing the crude product obtained in the step (4) by using acetone to obtain the thermoplastic cellulose grafted polyurethane.
The present invention is further illustrated by the following examples, which are provided only for the purpose of facilitating understanding of the present invention and are not intended to limit the scope of the present invention.
In the examples, the cellulose/sodium hydroxide aqueous solution is prepared by a freeze-thaw method according to the reference literature, i.e. microcrystalline cellulose is added into a 5% sodium hydroxide aqueous solution by mass fraction, the mixture is placed into a refrigerator for freezing overnight after being vigorously stirred, and the clear and transparent cellulose/sodium hydroxide aqueous solution is obtained after thawing the mixture under vigorous stirring, wherein the ratio of the cellulose/sodium hydroxide/water by mass fraction is 2/5/95; then 33g of cellulose/sodium hydroxide aqueous solution is dropped into 50ml of liquid PEG, 40.44mmol of hydrochloric acid is added dropwise after full regeneration, and vacuum filtration is carried out after full reaction to prepare regenerated cellulose; washing the regenerated cellulose with 50ml of liquid polyethylene glycol, and performing suction filtration for five times to obtain regenerated cellulose/PEG gel; adding the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 ℃ in vacuum for 1h, adjusting the content of PEG in proportion, and adding hexamethylene diisocyanate in proportion; the above system is N2Heating to a target temperature in an atmosphere, and stirring for reaction to obtain a crude product; the crude product was fully purified using acetone as solvent to give the thermoplastic cellulose-grafted polyurethane of the examples.
To illustrate the effects of the examples, the structure of the resulting thermoplastic cellulose-grafted polyurethane was analyzed by infrared spectroscopy; after thermoplastic cellulose grafted polyurethane is hot-pressed into a film, the mechanical property and the transparency are tested. Furthermore, the melting temperature of the thermoplastic cellulose-grafted polyurethane was measured by an Optical Microscope (OM) equipped with a temperature-raising hot stage, and the sample was measured at N2Heating to the temperature just at which the flow phenomenon occurs in the atmosphere, and recording as a melting temperature; the tensile strength and elongation at break of the thermoplastic cellulose grafted polyurethane are shown by a film prepared by testing hot press molding by an electronic universal tester, and a sampleSize: 50 x 5 x 0.3mm3The stretching rate: 5 mm/min. A transmittance spectrum of the film prepared by hot press forming is obtained by using an ultraviolet-visible spectrophotometer, and the transmittance at 600nm is recorded to represent the transparency of the sample.
Example 1
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing/filtering the regenerated cellulose with 50ml of polyethylene glycol 300 for five times to prepare regenerated cellulose/PEG gel; transferring the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 ℃ under vacuum for 1h, adding polyethylene glycol 300 to make the content of polyethylene glycol in the system 28.8g (96mmol), adding 17.74g (105.6mmol) hexamethylene diisocyanate, and adding N2Heating to 80 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; the crude product was fully purified using acetone as solvent to give thermoplastic cellulose grafted polyurethane with properties as shown in table 1.
Example 2
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing/filtering the regenerated cellulose with 50ml of polyethylene glycol 300 for five times to prepare regenerated cellulose/PEG gel; transferring the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 ℃ under vacuum for 1h, adding polyethylene glycol 300 to make the content of polyethylene glycol in the system 28.8g (96mmol), adding 17.74g (105.6mmol) hexamethylene diisocyanate, and reacting in N2Heating to 100 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; the crude product was fully purified using acetone as solvent to give thermoplastic cellulose grafted polyurethane with properties as shown in table 1.
Example 3
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; regenerated fiber washed/filtered with 50ml of polyethylene glycol 300Performing cellulose five times to prepare regenerated cellulose/PEG gel; transferring the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 ℃ under vacuum for 1h, adding polyethylene glycol 300 to make the content of polyethylene glycol in the system 28.8g (96mmol), adding 17.74g (105.6mmol) hexamethylene diisocyanate, and reacting in N2Heating to 120 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; and using acetone as a solvent, and fully purifying the crude product to obtain the thermoplastic cellulose grafted polyurethane. The IR spectrum of the resulting thermoplastic cellulose-grafted polyurethane is shown in FIG. 1; the optical micrograph during the temperature increase is shown in FIG. 2; the film digital photo obtained by hot pressing is shown in FIG. 3; the transparency spectrum of the hot-pressed film is shown in FIG. 4, and other specific properties are shown in Table 1.
Example 4
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing/filtering the regenerated cellulose with 50ml of polyethylene glycol 300 for five times to prepare regenerated cellulose/PEG gel; transferring the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 ℃ under vacuum for 1h, adding polyethylene glycol 300 to make the content of polyethylene glycol in the system 28.8g (96mmol), adding 17.74g (105.6mmol) hexamethylene diisocyanate, and reacting in N2Heating to 140 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; the crude product was fully purified using acetone as solvent to give thermoplastic cellulose grafted polyurethane with properties as shown in table 1.
TABLE 1 Effect of polymerization temperature on thermoplastic cellulose graft polyurethane Properties
As can be seen from a comparison of the data in Table 1, the resulting cellulose-grafted polyurethane gradually exhibits thermoplasticity as the polymerization temperature increases, and the flexibility of the resulting thermoplastic polyurethane material also gradually increases. However, when the polymerization temperature reaches 140 ℃, the tensile strength of the resulting cellulose-grafted polyurethane material is lowered due to the introduction of too many flexible side chains. The data in Table 1 are combined to obtain the cellulose grafted polyurethane obtained by polymerization at 120 ℃ with excellent comprehensive performance, and the preparation method of the thermoplastic cellulose grafted polyurethane is further explained by using a fixed polymer process of polymerization at 120 ℃ for 8 hours.
Example 5
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing/filtering the regenerated cellulose with 50ml of polyethylene glycol 300 for five times to prepare regenerated cellulose/PEG gel; transferring the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 deg.C under vacuum for 1h, adding polyethylene glycol 300 to make the content of polyethylene glycol in the system 21.6g (72mmol), adding 13.3g (79.2mmol) hexamethylene diisocyanate, and adding N2Heating to 120 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; and using acetone as a solvent, and fully purifying the crude product to obtain the thermoplastic cellulose grafted polyurethane. The digital photo of the film obtained by hot-pressing the thermoplastic cellulose grafted polyurethane is shown in FIG. 3; the transparency spectrum of the hot-pressed film is shown in FIG. 4, and other specific properties are shown in Table 2.
Example 6
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing/filtering the regenerated cellulose with 50ml of polyethylene glycol 300 for five times to prepare regenerated cellulose/PEG gel; transferring the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 ℃ under vacuum for 1h, adding polyethylene glycol 300 to ensure that the content of polyethylene glycol in the system is 36g (120mmol), adding 22.18g (132mmol) of hexamethylene diisocyanate, and reacting in N2Heating to 120 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; and using acetone as a solvent, and fully purifying the crude product to obtain the thermoplastic cellulose grafted polyurethane. The digital photo of the film obtained by hot-pressing the thermoplastic cellulose grafted polyurethane is shown in FIG. 3; the transparency spectrum of the hot-pressed film is shown in FIG. 4, and other specific properties are shown in Table 2.
Example 7
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing regenerated cellulose with 50ml polyethylene glycol 300, and extracting/filtering the regenerated cellulose five times to prepare regenerated cellulose/PEG gel; transferring the regenerated cellulose/PEG gel into a three-necked bottle, removing water at 80 ℃ under vacuum for 1h, adding polyethylene glycol 300 to make the content of polyethylene glycol in the system 43.2g (144mmol), adding 26.61g (158.4mmol) hexamethylene diisocyanate, and adding N2Heating to 120 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; and using acetone as a solvent, and fully purifying the crude product to obtain the thermoplastic cellulose grafted polyurethane. The digital photo of the film obtained by hot-pressing the thermoplastic cellulose grafted polyurethane is shown in FIG. 3; the transparency spectrum of the hot-pressed film is shown in FIG. 4, and other specific properties are shown in Table 2.
TABLE 2 Effect of monomer ratios on thermoplastic cellulose graft polyurethane Properties
Comparing the data in table 2, it can be found that the content of PEG in the polymerization system has a significant influence on the performance of the thermoplastic cellulose grafted polyurethane, and when the amount of substance AGU/PEG is 1/18, the amount of monomer participating in the reaction is too small, so that the branched chain in the grafted product is shorter, the reaction is more uneven, and the thermoplastic cellulose grafted polyurethane has no significant thermoplastic flow under OM and poor flexibility; as the PEG content increases, the resulting thermoplastic cellulose grafted polyurethane exhibits significant thermoplastic flow at OM and the melting temperature gradually decreases.
Comparative example 1
0.648g of dried microcrystalline cellulose (4 mmol of AGU in substance) are taken in a three-necked flask, 28.8g of polyethylene glycol 300(96mmol) are added, followed by 17.74g (105.6mmol) of hexamethylene diisocyanate in N2Heating to 120 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; with acetoneAnd (3) fully purifying the crude product as a solvent to obtain a microcrystalline cellulose grafted polyurethane comparison sample. The infrared spectrum of the obtained microcrystalline cellulose grafted polyurethane is shown in figure 1; the optical micrograph during the temperature increase is shown in FIG. 2, and other properties are shown in Table 3.
Comparative example 2
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of polyethylene glycol 300, after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing/filtering regenerated cellulose with 50ml of ultrapure water for five times to prepare regenerated cellulose hydrogel; freezing and drying the regenerated cellulose water to obtain regenerated cellulose aerogel; after removing the water from the cellulose aerogel at 80 ℃ under vacuum for 1h, 28.8g of polyethylene glycol 300(96mmol) were added, followed by 17.74g (105.6mmol) of hexamethylene diisocyanate in N2Heating to 120 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; and (3) using acetone as a solvent, and fully purifying the crude product to obtain a regenerated cellulose aerogel grafted polyurethane contrast sample. The infrared spectrum of the obtained regenerated cellulose aerogel grafted polyurethane is shown in figure 1; the optical micrograph during the temperature increase is shown in FIG. 2, and other properties are shown in Table 3.
Comparative example 3
33g of cellulose/sodium hydroxide aqueous solution (AGU content is 4mmol) is dropped into 50ml of Ethylene Glycol (EG), after full regeneration, 40.44mmol of hydrochloric acid is dropped, after full reaction, vacuum filtration is carried out to obtain regenerated cellulose; washing/filtering the regenerated cellulose for five times by using 50ml of ethylene glycol to prepare regenerated cellulose/EG gel; the regenerated cellulose/EG gel was transferred to a three-necked flask, after vacuum dewatering at 80 ℃ for 1h, EG was added to make the EG content in the system 5.76g (96mmol), and 17.74g (105.6mmol) hexamethylene diisocyanate was added thereto under N2Heating to 120 ℃ in the atmosphere, and polymerizing for 8 hours to obtain a crude product; and using acetone as a solvent, and fully purifying the crude product to obtain a regenerated cellulose/EG gel grafted polyurethane comparison sample. The infrared spectrum of the regenerated cellulose/EG gel-grafted polyurethane is shown in FIG. 1; the optical micrograph during the temperature increase is shown in FIG. 2, and other properties are shown in Table 3.
TABLE 3 Effect of precursor species on thermoplastic cellulose graft polyurethane Properties
The comparative example shows that the chemical grafting is difficult to be directly carried out by taking the microcrystalline cellulose as a reaction monomer because the molecular chains of the microcrystalline cellulose are regularly stacked, have higher crystallinity and have stronger capacity of resisting chemical reagents; after the microcrystalline cellulose is prepared into the aerogel, although the cellulose precursor is loose and porous macroscopically, a large number of molecular chains are recrystallized microscopically, so that the chemical grafting is difficult to be carried out efficiently; when micromolecular ethylene glycol is used as a grafting monomer, the molecular weight of the ethylene glycol is too small, so that branched chains grafted on cellulose are short, and the performance of the obtained cellulose grafted polyurethane is not satisfactory; the thermoplastic cellulose grafted polyurethane with good flexibility and high transparency can be prepared only by grafting polyurethane on cellulose by taking the regenerated cellulose/PEG gel containing PEG as a reaction monomer.
As can be seen from the data in tables 1 to 3, after dissolving cellulose in sodium hydroxide solution and regenerating with liquid polyethylene glycol (PEG), PEG can act as a transient spacer structure to prevent the reestablishment of hydrogen bonds between cellulose molecular chains and within the molecules, so that a large amount of-OH in cellulose is exposed to chemical environment to participate in chemical reaction. Then, the PEG is chemically bonded on the cellulose by flexible Hexamethylene Diisocyanate (HDI) to form a Polyurethane (PU) side chain, so that the hydrogen bond reconstruction in the cellulose can be permanently isolated, and the movement of the cellulose chain is not bound by the hydrogen bond any more, namely, thermoplasticity is shown; the PU side chain changes the regular arrangement of the cellulose, so that the cellulose is converted from high crystallization to amorphous, and the obtained cellulose grafted polyurethane material has high transparency; in addition, the high-flexibility straight-chain PU side chain plays a toughening role in a semi-rigid cellulose system, so that the prepared cellulose grafted polyurethane material has high elongation at break and excellent flexibility.
According to the invention, polyurethane is grafted on a cellulose molecular chain under the condition of not using an expensive aprotic solvent, so that the movement capability of the cellulose molecular chain in a thermal field is improved, and the thermoplastic cellulose grafted polyurethane material with low melting temperature, good flexibility and high transparency is prepared. The preparation process has the advantages of simple process, low equipment requirement, low production cost and environmental protection. The upper and lower limits and interval values of the raw materials and the upper and lower limits and interval values of the process parameters can all realize the invention, and examples are not listed here.
Claims (9)
1. A preparation method of thermoplastic cellulose grafted polyurethane is characterized by comprising the following steps: heating cellulose/polyethylene glycol gel and diisocyanate to 100-140 ℃ in an inert gas environment, fully stirring for 7-12 h to obtain a crude product, and washing the crude product to obtain thermoplastic cellulose grafted polyurethane; wherein the molar ratio of the diisocyanate to the polyethylene glycol in the cellulose/polyethylene glycol gel is 1-1.1: 1; the molar ratio of polyethylene glycol to cellulose repeating units in the cellulose/polyethylene glycol gel is 18-36: 1;
and, the cellulose/polyethylene glycol gel is prepared using a method comprising the steps of:
1) dissolving cellulose in an aqueous alkali solution, dripping the cellulose/aqueous alkali solution into liquid polyethylene glycol, adding acid with the same molar ratio as alkali to adjust the pH of a system to be neutral, and fully stirring to prepare regenerated cellulose;
2) carrying out suction filtration on the regenerated cellulose obtained in the step 1), reserving a suction filtration product, and repeatedly replacing a solvent in the suction filtration product with polyethylene glycol for 3-5 times to prepare cellulose/polyethylene glycol gel;
3) dehydrating the cellulose/polyethylene glycol gel obtained in the step 2), and then adding polyethylene glycol to ensure that the cellulose/polyethylene glycol gel meets the following requirements: the molar ratio of polyethylene glycol to cellulose repeating units in the cellulose/polyethylene glycol gel is 18-36: 1.
2. the method of claim 1, wherein the diisocyanate is hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, or lysine diisocyanate.
3. The method of claim 1 or 2, wherein the cellulose in the cellulose/polyethylene glycol gel comprises: microcrystalline cellulose, cotton pulp, bamboo pulp, cellulose filter paper, or absorbent cotton.
4. The method of claim 1, wherein the thermoplastic cellulose-grafted polyurethane is prepared by the method comprising the steps of,
in the step 1), the alkali is sodium hydroxide or lithium hydroxide; or:
in the step 1), the acid is hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid or nitric acid.
5. The method for preparing thermoplastic cellulose-grafted polyurethane according to claim 1, wherein the water is removed in step 3) by: placing the cellulose/polyethylene glycol gel obtained in the step 2) into a container, and immersing the container into an oil bath at the temperature of 70-90 ℃ for vacuum dehydration for 1-2 h.
6. The method for preparing thermoplastic cellulose grafted polyurethane according to claim 1 or 2, wherein the molar ratio of polyethylene glycol to cellulose repeating units in the cellulose/polyethylene glycol gel is 24-36: 1.
7. the process for preparing thermoplastic cellulose-grafted polyurethanes according to claim 1 or 2, wherein the crude product is washed with acetone, butanone, benzene, toluene or xylene.
8. The method of claim 1 or 2, wherein the polyethylene glycol is one of PEG200, PEG300, PEG400, or PEG 600.
9. A thermoplastic cellulose grafted polyurethane, wherein the thermoplastic cellulose grafted polyurethane is prepared by the method of any one of claims 1 to 8.
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