阅读说明：本技术 一种共聚物改性纤维素纳米晶用于聚二甲基硅氧烷增稠的方法 (Method for thickening polydimethylsiloxane by using copolymer modified cellulose nanocrystal ) 是由 朱焱 林宁 于 2021-02-24 设计创作，主要内容包括：本发明公开了一种共聚物改性纤维素纳米晶用于聚二甲基硅氧烷增稠的方法,以天然棉纤维为原料,用硫酸水解法透析3天提取CNCs,甲氧基聚乙二醇(MPEG)的末端羟基和溴丙烯在氢化钠的催化下制备了Allyl-MPEG,用八甲基环四硅氧烷(D4)单体聚合法制备了聚二甲基硅氧烷(PDMS),将已得到的APEG和PDMS经硅氢化反应合成三嵌段共聚物,选择THF作为表面吸附MPFG-PDMS-MPEG三嵌共聚物对CNCs进行物理改性的溶剂,然后剧烈搅拌3小时,促进共聚物在CNCs表面的充分接触和表面吸附,得到改性的CNCs(mCNCs),产品在流变和润滑系统的实际应用中充当可再生和无毒的增稠润滑效果的添加剂,具有环保、化学性能稳定、相容性好、在基础油中分散性好等特点。(The invention discloses a method for thickening polydimethylsiloxane by copolymer modified cellulose nanocrystalline, which takes natural cotton fiber as raw material, extracts CNCs by sulfuric acid hydrolysis method for 3 days, prepares Ally-MPEG by terminal hydroxyl of methoxy polyethylene glycol (MPEG) and bromopropylene under the catalysis of sodium hydride, prepares Polydimethylsiloxane (PDMS) by octamethylcyclotetrasiloxane (D4) monomer polymerization method, synthesizes triblock copolymer by hydrosilylation reaction of obtained APEG and PDMS, selects THF as solvent for physically modifying CNCs by surface adsorption of MPFG-PDMS-MPEG triblock copolymer, then vigorously stirs for 3 hours to promote full contact and surface adsorption of copolymer on the surface of CNCs, obtains modified CNCs (mCNCs), and the product is used as additive with reproducible and nontoxic thickening lubrication effect in the practical application of rheology and lubrication system, has the characteristics of environmental protection, stable chemical property, good compatibility, good dispersibility in base oil and the like.)

1. A method for thickening polydimethylsiloxane by using copolymer modified cellulose nanocrystals is characterized by comprising the following steps:

1) end-finishing of MPEG: MPEG and Allyl bromide are used as raw materials, under the catalytic action of NaH, terminal hydroxyl of the MPEG and the Allyl bromide are subjected to chemical reaction to prepare the Allyl-MPEG,

2) polymerization of PDMS: with D₄The monomer is taken as raw material, Tetramethyldisiloxane (TMDS) and trifluoromethanesulfonic acid (TFMS) catalyst are added for induction, PDMS is prepared by polymerization method,

3) synthesis of MPEG-PDMS-MPEG block copolymer: synthesizing the Allyl-MPEG prepared in the step 1 and the PDMS prepared in the step 2 into a triblock copolymer through hydrosilylation,

4) preparation of CNCs: preparing aqueous suspension of cellulose nanocrystalline with sulfate group on the surface by using natural cotton fiber as a raw material and adopting a sulfuric acid hydrolysis method,

5) physical modification of CNCs surfaces: taking the triblock copolymer prepared in the step 3 and the CNCs prepared in the step 4 as raw materials, selecting THF solvent to promote the surface of the CNCs to adsorb MPEG-PDMS-MPEG triblock copolymer to obtain modified CNCs (mCNCs),

6) and (3) preparing a mixed lubricating oil/grease with mNCC as a thickening agent, namely, taking the mNCs prepared in the step (5) and polydimethylsiloxane as raw materials, and carrying out interaction on the mNCs and the polydimethylsiloxane at different loading levels to prepare the mixed lubricating oil/grease.

2. The method of claim 1, wherein the NaH in step 1 catalyzes a chemical reaction between terminal hydroxyl groups of MPEG and allyl bromide, and comprises the following steps: adding 0.5 g NaH suspension in 5 mL of THF into 30 mL of THF, dissolving MPEG, mixing, stirring for 2 hours, adding bromopropylene, reacting at room temperature for 24 hours, centrifuging the obtained product with ethyl acetate to remove NaH, performing rotary evaporation to remove redundant bromopropylene and solvent, and performing vacuum drying to obtain a solid light yellow allyl polyethylene glycol product.

3. The method of claim 1, wherein the step 2 polymerization method is used to prepare PDMS comprising the following steps:

D₄controlling the molar ratio of TMDS and TMDS to be 5:1, and adding TMFS as a catalyst to induce D₄Polymerization at 70 ℃ for 8 hours, after the reaction, NaHCO₃Addition to 200 ml of diethyl ether reacted to precipitate the product, yielding a colorless viscous PDMS liquid that was rotary evaporated to remove any residual monomer and solvent.

4. The method of claim 1, wherein the step 3 of hydrosilation of the copolymer-modified cellulose nanocrystals into the MPEG-PDMS-MPEG triblock copolymer comprises the steps of:

the Allyl-MPEG is dissolved in toluene, then under the protection of nitrogen at the temperature of 90 ℃, the catalyst of the SbBer is added into the magnetic stirring and stirred for 20 minutes, the synthesized PDMS is dissolved in toluene, the mixture is injected by a syringe, the reaction is started for 24 hours at the temperature of 90 ℃, the mixture of pentane and methanol is washed and purified twice to remove the unreacted PDMS and the Allyl-MPEG, then the mixture is dialyzed for 3 days in distilled water, and finally, at the temperature of 60 ℃, the mixture is baked for one night, and a light yellow copolymer is obtained.

5. The method of claim 1, wherein the step 4 of preparing the CNCs comprises the steps of:

taking natural cotton fiber as raw material, and using 64 wt% H₂SO₄The solution was hydrolyzed at 45 ℃ for 1 hour, washed continuously in distilled water, then centrifuged to remove the free acid, and after dialyzing in water for 3 days, an aqueous suspension of CNCs in which negatively charged sulfate groups were present on the surface was uniformly dispersed was obtained.

6. The method of claim 1, wherein the step 5 of surface modifying the CNCs comprises the steps of:

the aqueous suspension of CNCs was dissolved in THF to achieve uniform dispersion by successive centrifugation and redispersion processes, then added dropwise to the CNCs suspension with vigorous stirring to ensure dispersion of the CNCs, the mixture was stirred vigorously for 3 hours to promote adequate contact and surface adsorption of the copolymer on the CNCs surfaces to obtain mCNCs, and then the mCNCs were purified by three successive centrifugations and washings with THF to remove any free copolymer.

7. The method for thickening polydimethylsiloxane according to claim 1, wherein the method for preparing the mixed lubricating oil/grease with the mCNC as the thickening agent in the step 6 comprises the following steps:

to ensure the dispersibility of mCNC in polydimethylsiloxane, mCNCs suspension was slowly added to polydimethylsiloxane, mechanically stirred for 10 minutes, then the mixture was heated to 70 ℃ and continuously stirred for 5 hours to evaporate THF solvent, the mixed oil/grease was further treated in a vacuum oven at 80 ℃ overnight to completely remove traces of THF and air bubbles, and a mixed oil/grease was prepared by interaction of mCNC with different loading levels and polydimethylsiloxane.

Technical Field

The invention belongs to the technical field of nano science, and relates to a method for thickening polydimethylsiloxane by using copolymer modified cellulose nanocrystals.

Background

The method is characterized in that cotton fibers from cotton are hydrolyzed by hydrochloric acid to obtain rigid Cellulose Nanocrystals (CNCs), the raw materials belong to renewable resources, and the cellulose nanocrystals have the characteristics different from the traditional materials, including special rod-shaped forms, nanometer sizes, high length-diameter ratio, high specific surface area, rheological property, mechanical strength, surface chemical reaction, biocompatibility, biodegradability, low toxicity, low cost, light weight, low density, high modulus and the like. Many of the hydroxyl groups on the surface of CNCs provide an accessible modification to the nanoparticle to improve its compatibility with the matrix or functional applications. Because the cellulose has more excellent properties, the composite material with better performance and stronger function can be prepared on the basis, and the composite material has the potential to play an important role in the development of advanced materials in the 21 st century.

Methoxy polyethylene glycol (MPEG) has good water solubility, wettability, lubricity, physiological inertia, no stimulation to human body, mildness and wide application in cosmetics and pharmaceutical industry. The tail end of the Allyl-modified polyethylene glycol is modified by bromopropylene to obtain Allyl-polyethylene glycol (Allyl-MPEG), and the polymer synthesized by using the raw material has the advantages of high particle dispersibility, high retention capacity, good reinforcing effect, high durability, environmental friendliness and the like.

Low molecular weight oligomers of Polydimethylsiloxane (PDMS) with octamethylcyclotetrasiloxane (D)₄) And carrying out polymerization reaction to obtain PDMS. D₄The product is prepared by hydrolysis and synthesis of dimethyldichlorosilane, and is separated and rectified to obtain the combustible, odorless, transparent or milky liquid compound. The prepared Polydimethylsiloxane (PDMS) has special hydrophobicity, heat resistance, cold resistance, small viscosity change along with temperature, water resistance and small surface tension, can form an amphiphilic nonionic surfactant structure after being modified with hydrophilic MPEG, can be dispersed in water as micelles and vesicles, and has important industrial application.

MPEG-PDMS-MPEG is a copolymer of two components, which is only completely soluble in THF and forms micelles by self-assembly in n-pentane and methanol. During the surface modification process, the hydrophilic MPEG segments in the copolymer are adsorbed onto the CNC surface by the organic THF, while the hydrophobic PDMS segments are exposed, resulting in a switch of the surface hydrophilicity and hydrophobicity.

The mNCs are obtained by CNC through triblock copolymer modification, the viscosity of the oil is obviously improved by introducing the mass fraction (5 wt%) of the mNCs into the mixed oil, the mixed oil is enabled to have gel behavior by introducing the mass fraction (10-15 wt%) of the mNCs into the mixed oil, and the mNCs introduced into the mixed oil with the mass fraction (17.5-20 wt%) of the mNCs are converted into a quasi-solid state of the lubricating grease. The direct interaction between the original CNC and the polydimethylsiloxane can cause the CNC nanoparticles to be incompatible and aggregated in a mixed system, and the surface modification is an effective way to improve the compatibility and stability of the mCNCs nanoparticles in the base oil. The mNCs can be used as rigid cross-linking points, and the compatibility and the dispersibility are expected to form a stable three-dimensional network through entanglement of polymer chains so as to stabilize the microstructure of the mixed oil, thereby obviously increasing the viscosity of the system and having obvious thickening effect of the base oil. The modified CNCs (mNCs) are expected to be used as renewable and nontoxic thickening and lubricating effect additives in the practical application of rheological and lubricating systems, and the effective thickening effect in petroleum provides a new application prospect for the biological nano-additives in the rheological and lubricating fields.

Disclosure of Invention

The invention aims to provide a method for thickening polydimethylsiloxane by using copolymer modified cellulose nanocrystals, the preparation process is simple and convenient, the raw materials are environment-friendly and pollution-free, and the prepared thickening agent has the characteristics of environmental protection, stable chemical performance, good compatibility, good dispersibility in base oil and the like.

In order to achieve the purpose, the technical scheme is as follows:

a method for thickening polydimethylsiloxane by using copolymer modified cellulose nanocrystals comprises the following steps:

1) end-finishing of MPEG: MPEG and Allyl bromide are used as raw materials, under the catalytic action of NaH, terminal hydroxyl of the MPEG and the Allyl bromide are subjected to chemical reaction to prepare the Allyl-MPEG,

2) polymerization of PDMS: with D₄The monomer is taken as raw material, Tetramethyldisiloxane (TMDS) and trifluoromethanesulfonic acid (TFMS) catalyst are added for induction, PDMS is prepared by polymerization method,

3) synthesis of MPEG-PDMS-MPEG block copolymer: synthesizing the Allyl-MPEG prepared in the step 1 and the PDMS prepared in the step 2 into a triblock copolymer through hydrosilylation,

4) preparation of CNCs: preparing aqueous suspension of cellulose nanocrystalline with sulfate group on the surface by using natural cotton fiber as a raw material and adopting a sulfuric acid hydrolysis method,

5) physical modification of CNCs surfaces: taking the triblock copolymer prepared in the step 3 and the CNCs prepared in the step 4 as raw materials, selecting THF solvent to promote the surface of the CNCs to adsorb MPEG-PDMS-MPEG triblock copolymer to obtain modified CNCs (mCNCs),

6) and (3) preparing a mixed lubricating oil/grease with mNCC as a thickening agent, namely, taking the mNCs prepared in the step (5) and polydimethylsiloxane as raw materials, and carrying out interaction on the mNCs and the polydimethylsiloxane at different loading levels to prepare the mixed lubricating oil/grease.

Further, the method for catalyzing the chemical reaction between the terminal hydroxyl of MPEG and bromopropylene by NaH comprises the following steps: a suspension of 0.5 g NaH in 5 mL of THF was added to 30 mL of THF, MPEG (14.70 g, 7.35 mmol) was dissolved, and after mixing, stirring was carried out for 2 hours, and bromopropylene (2.61 g, 21.75 mmol) was added thereto, followed by reaction at room temperature for 24 hours. The resulting product was centrifuged with ethyl acetate (10000 rpm, 5 min) to remove NaH, and then rotary evaporated to remove excess bromopropene and solvent. Vacuum drying to obtain yellowish Allyl polyethylene glycol (Allyl-MPEG) product.

Further, the method for preparing PDMS by the polymerization method comprises the following steps:

D₄and TMDS in a molar ratio of 5:1, with TMFS (0.98 g, 3 wt%) added as catalyst to induce D₄The polymerization was carried out at 70 ℃ for 8 hours. After the reaction, NaHCO₃(2 g) Adding into ether (200 ml) to react and precipitate to obtain the product. A colorless viscous PDMS liquid was obtained and rotary evaporation was performed to remove any residual monomer and solvent.

Further, the method for hydrosilation synthesis of the MPEG-PDMS-MPEG triblock copolymer comprises the following steps:

APEG is dissolved in toluene, and then the catalyst of the SBayer is added to the magnetic stirring and stirred for 20 minutes at the temperature of 90 ℃ under the protection of nitrogen. The synthesized PDMS was dissolved in toluene, injected into the mixture by a syringe, and the reaction was started at 90 ℃ for 24 hours. The mixture of pentane and methanol was washed and purified twice to remove unreacted PDMS and Allyl-MPEG, and then dialyzed against distilled water for 3 days. Finally, a pale yellow copolymer was obtained by baking overnight at a temperature of 60 ℃.

Further, the above method for preparing CNCs comprises the steps of:

taking natural cotton fiber as raw material, and using 64 wt% H₂SO₄The solution was hydrolyzed at 45 ℃ for 1 hour, washed successively in distilled water, and then centrifuged to remove the free acid. After 3 days of dialysis in water, an aqueous CNC suspension with a homogeneous dispersion of negatively charged sulfate groups present on the surface of the acid was obtained.

Further, the above method for surface-modifying CNCs comprises the steps of:

the aqueous CNC suspension was dissolved in THF, uniformly dispersed by successive centrifugation and redispersion processes, and then added dropwise to the CNCs suspension with vigorous stirring to ensure dispersion of the CNCs. The mixture was stirred vigorously for 3 hours to facilitate adequate contact and surface adsorption of the copolymer on the CNCs surfaces to yield mCNC. mCNC was then purified by three successive centrifugations and washings with THF to remove any free copolymer.

Further, the method for preparing the mixed lubricating oil/grease with the mCNC as the thickening agent comprises the following steps:

to ensure the dispersibility of mCNC in polydimethylsiloxane, mCNC suspension (4.8 wt%, THF) was slowly added to polydimethylsiloxane, mechanically stirred for 10 minutes, then the mixture was heated to 70 ℃, stirred continuously for 5 hours, and the THF solvent was allowed to evaporate. The combined lube/grease was further treated in a vacuum oven with a one night 80 c bake to completely remove THF and air bubbles. A mixed lube/grease was prepared by the interaction of mCNC with different mass fractions (0, 5, 10, 12.5, 15 and 20 wt%) of polydimethylsiloxane.

The invention relates to MPEG end modification, and aims to generate Ally-MPEG through chemical reaction between MPEG and bromopropylene, synthesize a copolymer with PDMS product conveniently, and modify the copolymer into a hydrophobic surface.

By means of D₄Polymerization to obtain PDMS with the technical aim of using D₄The monomer controls the molecular weight and chain length of PDMS, so that an organosiloxane mixture with chain structure with different polymerization degrees can be formed, the end group and the side group of the organosiloxane mixture are all hydrocarbon groups (such as methyl, ethyl, phenyl and the like), the condition plays an important role in the subsequent surface modification of CNCs, the organosiloxane mixture is convenient to react with Allyl-MPEG to form a copolymer, and the organosiloxane mixture becomes a widely applied polymer material due to the characteristics of low cost, simple use, good adhesion, good chemical inertness and the like.

The invention relates to synthesis of an MPEG-PDMS-MPEG triblock polymer, and aims to synthesize a triblock copolymer by using MPEG and PDMS to simultaneously realize hydrophilic and hydrophobic properties and other good material properties of the two materials. PDMS has non-toxicity, hydrophobicity, inertia, heat resistance and good biocompatibility, and MPEG has good water solubility, lubricity and physiological inertia and is suitable for being used as a consistency regulator.

The invention relates to preparation of CNCs, which technically aims to use natural cotton fibers to carry out hydrolysis separation dialysis with sulfuric acid with the concentration of 64 wt% to obtain CNCs, so that the surfaces of the CNCs carry negatively charged sulfonate groups, like charges repel each other, and the dispersibility of the CNCs is better.

The invention relates to modification of CNCs, and the technical purpose is to physically modify the surfaces of CNCs by using an MPEG-PDMS-MPEG triblock copolymer so as to adjust the surface properties of CNCs and improve the compatibility and dispersibility of CNCs and base oil.

Compared with the prior art, the invention has the beneficial effects that:

the invention adopts the technical scheme that the synthesized MPEG-PDMS-MPEG triblock copolymer is used for physically modifying the cellulose nanocrystals, and the modified CNCs are added into the base oil, thereby showing obvious antifriction and tackifying effects. The PDMS in the triblock copolymer contains a Si-O-Si structure, so that the compatibility between the modified CNCs and the base oil is promoted, and the CNCs are dispersed in the hydrophobic matrix more stably. Cellulose Nanocrystals (CNCs) are renewable nano materials, have the advantages of good crystallinity, unique rod-shaped appearance, no toxicity, high modulus, rigidity and the like, and are rigid crystal components separated from cellulose fibers. The new generation of lubricating oil/grease thickening agent has the characteristics of environmental protection, stable chemical performance, good compatibility, good dispersibility in base oil and the like.

Detailed Description

In order to better understand the present invention, the following examples are further provided to illustrate the present invention, but the present invention is not limited to the following examples.

Preparation of cellulose nanocrystals used in the examples:

obtaining 25 g of weighed cotton linters and 1000 g of prepared sodium hydroxide solution with the mass fraction of 2%, continuously reacting for 12 hours at room temperature, removing impurities, putting the prepared suspension into a Buchner funnel, washing and filtering for many times to make the suspension neutral, and putting the suspension into an oven to be dried at 50 ℃; dissolving dried 12.5 g of cotton linter into 250 ml of sulfuric acid solution with the mass fraction of 64%, stirring and continuously hydrolyzing for 1 hour at the temperature of 45 ℃ by using a stirring paddle, removing an amorphous area of a cellulose chain to obtain cellulose nanocrystals, pouring 200 ml of ice distilled water to terminate the acid hydrolysis reaction, uniformly pouring the obtained suspension into a centrifuge tube, repeatedly washing the centrifuge tube with distilled water for three times at 8000 rpm of the centrifuge to remove free sulfonic acid groups, mashing the mixture for 1 minute by using a mashing machine, filling the trituration tube into a dialysis bag, sealing the dialysis bag, dialyzing the mixture in a container filled with distilled water for 5 to 7 days, changing the distilled water for 1 to 2 times every day, and finally freeze-drying the mixture to obtain the cellulose nanocrystal powder.

Preparation of the PDMS used in the examples:

get D₄Monomers (30 g, 101 mmol) and TMDS (2.72 g, 20.2 mmol) were polymerized as 5:1, adding TFMS (0.98 g, 3 wt%) as a catalyst, carrying out polymerization reaction at 70 ℃ for 8 hours, and after the reaction is finished, adding NaHCO₃(2 g) The product was precipitated by addition of 200 ml of diethyl ether. A colorless, viscous PDMS liquid (31.33 g) was obtained and subjected to rotary evaporation to remove any residual monomer and solvent.

Preparation of the MPEG-PDMS-MPEG triblock copolymers used in the examples:

Ally-MPEG (6.74g, 330 mmol) was dissolved in toluene (4 ml) and then magnetically stirred for 20 minutes at 90 ℃ under nitrogen at a temperature of 12. mu.L with addition of a Sbyl catalyst. PDMS (5.55 g, 150 mmol) was dissolved in toluene (2 ml) and transferred to the mixture via syringe for reaction at 90 ℃ for 24 h. After the reaction was completed, the reaction mixture was washed twice with n-pentane and methanol to remove unreacted PDMS and Allyl-MPEG, and then dialyzed against distilled water for 3 days. Finally, by baking overnight at a temperature of 60 ℃ a pale yellow copolymer (9.72 g, solid) was obtained.

Example 1

The mCNC suspension (4.8 wt%, THF) was slowly added to the polydimethylsiloxane, mechanically stirred for 10 minutes, then the mixture was heated to 70 ℃ and stirred continuously for 5 hours to evaporate the THF solvent, then a 5 wt% blend oil/grease was formulated and the resulting blend oil/grease was further treated in a vacuum oven at 80 ℃ overnight to completely remove traces of THF and air bubbles.

Example 2

This embodiment is different from example 1 in that 10 wt% of mixed lubricating oil/grease was prepared, and other steps and parameters were kept the same as example 1.

Example 3

This embodiment is different from example 1 in that 15 wt% of mixed lubricating oil/grease was prepared, and other steps and parameters were kept the same as example 1.

Example 4

This embodiment is different from example 1 in that a mixed lubricating oil/grease with a mass fraction of 17.5 wt% was prepared, and other steps and parameters were kept in accordance with example 1.

Example 5

This embodiment is different from example 1 in that 20 wt% of mixed lubricating oil/grease was prepared, and other steps and parameters were kept the same as example 1.

Example 6

The PDMS obtained was taken without adding anything to control.

Comparative example

The CNC suspension (4.8 wt%, THF) was slowly added to the polydimethylsiloxane, mechanically stirred for 10 minutes, then the mixture was heated to 70 ℃, stirred continuously for 5 hours, the THF solvent was allowed to evaporate, then a mass fraction of the mixed lube/grease was obtained, which was further treated in a vacuum oven at 80 ℃ overnight to completely remove traces of THF and gas bubbles.

The MPEG-PDMS-MPEG triblock copolymer, the cellulose nanocrystal suspension, the mixed lubricating oil/grease prepared by adding mCNC in the examples 1, 2, 3, 4, and 5, and the PDMS in the example 6 obtained in the present invention were compared with each other before and after two months, and the mixed lubricating oil had more mCNC, less good flow effect, changed state from uniformly dispersed liquid to gel to quasi-solid, and had higher and higher viscosity, which significantly increased viscosity. And then preparing the compound lubricating oil containing 1 wt% of mCNC, and centrifuging the compound lubricating oil at 10000 rpm for 5 minutes to further obtain better dispersion stability of the mCNC in polydimethylsiloxane than CNC, which indicates that the MPEG-PDMS-MPEG triblock copolymer successfully modifies CNCs.