CN110452333B

CN110452333B - Molecular weight-controllable cellulose graft copolymerization acrylamide synthetic substance and application thereof

Info

Publication number: CN110452333B
Application number: CN201910660354.1A
Authority: CN
Inventors: 万俊杰; 冯新; 赵娜; 林达武; 陈洁花; 周明珠; 梁志鹏; 肖晓明; 区柏豪; 李淑彬
Original assignee: Guangdong Industry Technical College
Current assignee: Guangdong Industry Technical College
Priority date: 2019-07-22
Filing date: 2019-07-22
Publication date: 2021-11-09
Anticipated expiration: 2039-07-22
Also published as: CN110452333A

Abstract

The invention discloses a cellulose graft copolymerization acrylamide synthetic substance with controllable molecular weight and application thereof, wherein the flocculation performance of PAM is regulated and controlled by the combination of carboxyl and hydroxyl functional groups in CMC and an olefin bond of polyacrylamide, the molecular weight of the cellulose graft copolymerization acrylamide synthetic substance can be controlled, so as to meet the product requirements of the cellulose graft copolymerization acrylamide synthetic substance under different conditions, and the flocculation performance can be improved and the actual dosage can be reduced when the cellulose graft copolymerization acrylamide synthetic substance is applied to wastewater treatment.

Description

Molecular weight-controllable cellulose graft copolymerization acrylamide synthetic substance and application thereof

Technical Field

The invention relates to the technical field of water treatment agent preparation, in particular to a cellulose graft copolymerization acrylamide synthetic substance with controllable molecular weight and application thereof.

Background

The inorganic polymer material polyacrylamide is a water treatment agent widely applied to the flocculation and sedimentation of sewage and the dehydration process of sludge. A large number of previous researches show that the action mechanism of the flocculant is attributed to a plurality of action modes such as trapping, bridging and the like, and the flocculant treatment effect of the flocculant is far better than that of other high polymer materials due to the long-chain structure and the amide group which contains charges and has water-soluble hydrophilic characteristics in the structure. Although less in its amount used in water treatment, its widespread and long-term use increases the total amount of emissions into the environment, which causes its long-chain polymeric structure to be decomposed in the natural environment to form acrylamide monomers, remaining and migrating in the environment with the potential for biological neurotoxicity and carcinogenesis. The international health organization in 1985 has provided polyacrylamide standards indicating that: the residual acrylamide content in the polyacrylamide is controlled below 0.05 percent and the dosage is controlled. Therefore, reducing the amount of water used in the water treatment process at the source is of great importance for protecting the environment.

The dosage of the polyacrylamide in water treatment is reduced, and the natural non-toxic high molecular material can be adopted for replacing or improving the structure of the polyacrylamide without reducing the treatment effect, which is an important research direction for the development of the polyacrylamide material to green environmental protection in the future. Some past researches adopt natural organic high molecular materials or inorganic flocculants to replace polyacrylamide flocculation wastewater, but compared with polyacrylamide, the treatment effect is still not ideal, so that the method cannot be widely popularized and applied.

Some studies have been reported on the structural improvement of natural organic high molecular compounds such as cellulose, starch, protein, etc. grafted co-polyacrylamide. Among them, cellulose is a renewable biopolymer material with the lowest price and the most functions, the functions of which are usually used to improve the moisture-swelling property, oxidation resistance and antibacterial ability of the material, construct membrane materials, thicken and improve flocculation ability, and sodium carboxymethyl cellulose (CMC) is a water-soluble anionic linear polysaccharide which is the most widely used and used in the world today, and is prepared by replacing glucose repeating units of cellulose at 2, 3 and 6 positions, and is widely used in operations such as flocculation, cleaning agents, fabric drag reduction, food, paper, medicine and oil well drilling.

Carboxymethyl cellulose grafted copolyacrylamide is a high molecular compound in which a large number of carboxyl groups are introduced into a polyacrylamide chain. Such compounds carry both a large number of amide groups and a large number of carboxyl groups. The amide group is a nonionic group, and easily forms a secondary valence bond to be adsorbed and bonded to an active group of another substance. The pure polyacrylamide can be applied to the general wastewater treatment to flocculate suspended matters in water. The carboxyl grafted in the polyacrylamide is an electronegative group which is a key factor for generating electric neutralization flocculation and is easy to form a bridging effect with cations in a solution, so that the flocculation effect is further improved.

However, when the carboxyl content is too high, i.e. the molecular weight of the carboxymethyl cellulose grafted co-polyacrylamide is too large, the molecules have too strong negative charges, and the mutual repulsion between the molecules is too large, which is not favorable for flocculation. Therefore, it is important to maintain the proper ratio of carboxyl groups in the flocculant molecule. That is, the polyacrylamide flocculant having carboxyl groups is not designed to have a higher flocculation performance as the molecular weight is larger, but a graft copolymer having a certain molecular weight is selected according to actual needs.

Disclosure of Invention

The invention aims to provide a cellulose graft copolymerization acrylamide synthetic substance with controllable molecular weight and application thereof, wherein carboxyl and hydroxyl functional groups in CMC are combined with the olefin bond of polyacrylamide to regulate and control the flocculation performance of PAM, and the prepared cellulose graft copolymerization acrylamide synthetic substance can improve the flocculation performance and reduce the actual dosage when being applied to wastewater treatment.

In order to achieve the purpose, the invention adopts the following technical scheme:

the cellulose graft copolymerization acrylamide synthetic substance with controllable molecular weight is prepared by the following method:

s1, accurately weighing 1g of sodium carboxymethylcellulose, placing the sodium carboxymethylcellulose in a four-necked bottle, adding 100mL of distilled water, and stirring and dissolving in a constant-temperature water bath;

s2, introducing nitrogen into the four-necked bottle, exhausting air in the four-necked bottle, adding 1% of potassium persulfate and 1% of sodium bisulfite serving as a dual initiator, and uniformly stirring; slowly adding acrylamide monomer solution, adjusting the pH value and the reaction temperature, and sealing the four-necked bottle to perform polymerization reaction; continuously introducing nitrogen in the whole process of the step S2 until the polymerization reaction is finished;

s3, after polymerization reaction, pouring the obtained reaction liquid into a beaker, adding absolute ethyl alcohol, and slowly stirring until precipitates are separated out;

s4, placing the precipitated precipitate in a Soxhlet extractor, and carrying out reflux purification by taking acetone as an extracting solution to remove polyacrylamide homopolymer and unreacted acrylamide monomer;

s5, placing the purified product in a vacuum oven at 60 ℃ to dry to constant weight, and obtaining the cellulose graft copolymerization acrylamide compound.

Further, in step S2, the molar ratio of the 1% potassium persulfate to the 1% sodium bisulfite was 1:0.75, and the total volume of the potassium persulfate and the sodium bisulfite was 7.8mL, 11.7mL, 15.6mL, or 19.5 mL.

Further, in step S2, the acrylamide monomer solution was added in a volume of 50mL, and the acrylamide monomer content thereof was 8.0g, 10.0g, 13.0g, or 17.0 g.

Further, in step S2, the pH is adjusted to 5.0, 7.0, 9.0, or 11.0.

Further, in step S2, the reaction temperature is 45 ℃, 50 ℃, 60 ℃ or 70 ℃.

Further, in step S4, the polymerization time is 2.5hr, 3hr, 3.5hr or 4 hr.

Further, in step S4, 300mL of absolute ethanol was added.

Further, in step S5, the reflux purification time was 8 hr.

Further, in step S5, 100mL to 150mL of acetone was used as the extract.

The cellulose graft copolymerization acrylamide compound with controllable molecular weight can be applied to the treatment of wastewater.

The invention has the beneficial effects that:

the invention provides a cellulose graft copolymerization acrylamide synthetic substance with controllable molecular weight and application thereof, which can control the molecular weight of the cellulose graft copolymerization acrylamide synthetic substance by regulating and controlling the flocculation performance of PAM through the combination of carboxyl and hydroxyl functional groups in CMC and an olefin bond of polyacrylamide so as to meet the product requirements of the cellulose graft copolymerization acrylamide synthetic substance under different conditions and realize the aims of improving the flocculation performance and reducing the actual dosage.

Drawings

FIG. 1 is a reaction scheme of a preparation process in example 1 of the present invention;

FIG. 2 is a graph showing the relationship between the relative molecular weight of a cellulose graft copolymerized acrylamide composition and the limiting viscosity, dissolution time, conductivity and degree of hydrolysis in example 2 of the present invention;

FIG. 3 is a graph showing the change in flocculation performance of each sample in example 2 of the present invention in simulated printing and dyeing wastewater of different pH values;

FIG. 4 is a graph showing the experimental results of floc settling ratio in example 2 of the present invention;

FIG. 5 is a schematic diagram showing the flocculation mechanism process of CMC-g-PAM in example 2 of the present invention;

FIG. 6 is a graph showing the result of FTIR analysis in example 2 of the present invention;

FIG. 7 is a diagram showing the results of HMNR analysis in example 2 of the present invention;

FIG. 8 is a schematic view showing the result of DSC analysis in example 2 of the present invention;

Detailed Description

The present invention will be further described with reference to the accompanying drawings, and it should be noted that the present embodiment is based on the technical solution, and the detailed implementation and the specific operation process are provided, but the protection scope of the present invention is not limited to the present embodiment.

Example 1

This embodiment provides a molecular weight-controllable cellulose graft-copolymerized acrylamide composite, as shown in fig. 1, which is prepared by the following method:

s2, introducing nitrogen into the four-necked bottle for 10min, exhausting the air in the four-necked bottle, adding 1% of potassium persulfate and 1% of sodium bisulfite serving as a dual initiator, and uniformly stirring; slowly adding an acrylamide monomer solution, adjusting the pH value, and sealing the four-necked bottle to perform polymerization reaction; continuously introducing nitrogen in the whole step S2 until the polymerization reaction is finished;

s4, after the polymerization reaction is finished, pouring the obtained reaction solution into a beaker, adding 300mL of absolute ethyl alcohol, and slowly stirring by using a glass rod until the precipitate is completely precipitated;

s5, placing the precipitated precipitate in a Soxhlet extractor, taking 100-150 mL of acetone as an extracting solution, refluxing and purifying for 8hr, removing polyacrylamide homopolymer and unreacted acrylamide monomer, and finally placing the product in a vacuum oven at 60 ℃ to dry to constant weight to obtain a cellulose graft copolymerization acrylamide synthetic substance (CMC-g-PAM);

in step S2, the molar ratio of the 1% potassium persulfate to the 1% sodium bisulfite is 1:0.75, and the total volume of the potassium persulfate and the sodium bisulfite added is 7.8mL, 11.7mL, 15.6mL or 19.5 mL; the volume of the added acrylamide monomer solution is 50mL, and the content of the acrylamide monomer is 8.0g, 10.0g, 13.0g or 17.0 g; adjusting the pH to 5.0, 7.0, 9.0 or 11.0; the reaction temperature is 45 ℃, 50 ℃, 60 ℃ or 70 ℃; the polymerization time is 2.5hr, 3hr, 3.5hr or 4 hr.

The specific value is determined according to the desired molecular weight of the cellulose graft-copolymerized acrylamide composition.

Example 2

This example aims to further verify the properties of the cellulose graft-copolymerized acrylamide composite material with controllable molecular weight prepared by the preparation method described in example 1 through experiments.

1. Testing instrument

DK-S22 model electric heating constant temperature water bath (Shanghai sperm macro experimental facilities, Inc.);

electronic analytical balance (mettler-toledo instruments (shanghai) ltd);

model JJ-1 timed electric stirrer (zhengji instruments ltd, jin tan city, Jiangsu province); model DZF-6021 vacuum drying oven (Shanghai sperm macroexperimental facilities, Inc.);

721 spectrophotometer (Beijing Pujingyo general instruments, LLC).

2. Reagents and raw materials

Sodium carboxymethylcellulose; analytical pure, Tianjin Yongda chemical reagent Co Ltd

Acrylamide (AM): analytical pure, Shanghai Mecline Biochemical Co., Ltd

A dual initiator: prepared by mixing 1% of potassium persulfate (analytically pure) and 1% of sodium bisulfite (analytically pure) according to a molar ratio of 1: 0.75.

Simulating printing and dyeing wastewater: 2.5g of the printing powder was dissolved in 1L of water at a concentration of 0.25%. After the sample is diluted by 20 times, the light absorption value scanning is carried out in the wavelength range of 1100-400nm, and the wavelength corresponding to the peak value of the absorption wave is determined to be 644 nm.

Cellulose graft copolymerization acrylamide synthetic solution: 1g of the prepared cellulose graft copolymerization acrylamide synthetic sample is dissolved in 0.5L of water (0.2 percent), and is fully dissolved after being stirred for 1 hour at a slow speed, and the cellulose graft copolymerization acrylamide synthetic sample is prepared for use.

Polyaluminum chloride solution: 50g of polyaluminum chloride were dissolved in 1L of water (5%).

Commercially available PAM, i.e. commercially available polyacrylamide: analytically pure, provided by Dalochi chemical reagent factory of Tianjin, the limiting viscosity number is 11.99dL/g, the dissolution time is 38min, the conductivity is 152.5S/cm, and the hydrolysis degree is 3.42%. The solution was prepared by dissolving 1g of commercially available PAM in 0.5L of water (0.2%) and stirring slowly for 1 hour to dissolve it thoroughly.

3. Preparation of cellulose graft-copolymerized acrylamide Synthesis

Accurately weighing 1g of sodium carboxymethylcellulose, placing the sodium carboxymethylcellulose in a four-necked flask, adding 100mL of distilled water, and stirring and dissolving in a constant-temperature water bath. And then introducing nitrogen into the four-neck flask for 10min, exhausting the air in the four-neck flask, adding 1% of potassium persulfate and 1% of sodium bisulfite as a dual initiator, stirring uniformly, slowly adding an acrylamide monomer solution, adjusting the pH value, sealing the flask, and continuously introducing nitrogen to perform polymerization reaction.

After the polymerization reaction is finished, pouring the reaction solution into a beaker, adding 300mL of absolute ethyl alcohol, slowly stirring by using a glass rod until precipitates are completely precipitated, then placing the precipitates in a Soxhlet extractor, carrying out reflux purification for 8 hours by using 100mL-150mL of acetone as an extracting solution, removing monomers and polyacrylamide homopolymers which do not participate in the reaction, and finally placing the product in a vacuum oven at 60 ℃ to dry to constant weight to obtain the cellulose graft copolymerization acrylamide complex (CMC-g-PAM).

The preparation process is shown in figure 1.

4. Performance testing

4.1 degree of hydrolysis test

The hydrolysis degree test adopts methyl orange-indigo disulfonic acid sodium as an indicator, and hydrochloric acid standard titration is adopted for determination. Accurately weighing about 0.03g +/-0.0002 of the prepared cellulose graft copolymerization acrylamide compound, dissolving the cellulose graft copolymerization acrylamide compound in 100mL of distilled water, adding 1 drop of methyl orange indicating solution and 1 drop of sodium indigo disulfonate indicating solution, titrating by using a hydrochloric acid standard titration solution, and recording the volume of consumed hydrochloric acid, wherein the color is changed from yellow green to light grey as a terminal point. The calculation is shown below:

in the formula, H is the degree of hydrolysis,%; c is the actual concentration of the hydrochloric acid standard titration solution, mol/L; v is the volume of hydrochloric acid standard titration solution consumed in titration, mL; m is the mass of the cellulose graft copolymerization acrylamide compound, g; x is the number of₁Is in terms of solid content (%). The value 0.071 is the mass of the acrylamide linkage expressed in grams equivalent to 1.00mL of hydrochloric acid solution (c ═ 1.000 mol/L); the value 0.023 is the difference between the millimolar masses of sodium acrylate and of enamide.

4.2 determination of molecular weight

0.0300g cellulose graft copolymerization acrylamide synthetic substance of 0.0002 is accurately weighed and dissolved in 85g/L sodium nitrate solution, and the volume is determined to be 100 mL. The ultimate viscosity of the cellulose graft-copolymerized acrylamide compound is measured by using an Ubbelohde viscometer, the molecular weight of the cellulose graft-copolymerized acrylamide compound is calculated by the ultimate viscosity, and the calculation formula is as follows:

where MW represents molecular weight, η represents limiting viscosity measured by Ubbelohde viscometer, and K and α are empirical constants, as shown in Table 1.

TABLE 1

Degree of hydrolysis%	K	α
				0	3.73E-04	0.66
5	3.36E-04	0.68
			10	3.22E-04	0.692
15	3.15E-04	0.70
			20	3.17E-04	0.705
25	3.20E-04	0.707
			30	3.34E-04	0.708

4.3 flocculation test

250mL of simulated printing and dyeing wastewater is placed in a 1L beaker, 10mL of aluminium polychlorid liquid (the concentration of aluminum chloride is 2000mg/L) is added, the mixture is rapidly stirred for 2min, then 2.0mL of cellulose graft copolymerization acrylamide compound solution (the concentration is 15.27mg/L) is added, and the mixture is slowly stirred for 3 min. After the stirring is stopped, the treated printing and dyeing wastewater is poured into a 1cm glass cuvette for standing, and the absorbance A is continuously measured for 90min at 644 nm. In addition, 100mL of the treated printing and dyeing wastewater was poured into a 100mL measuring cylinder, and the sedimentation volume of the precipitate was immediately recorded to calculate the Sedimentation Ratio (SR), and each treatment was repeated 3 times.

4.4 structural feature analysis

(1) Infrared spectroscopy

Sampling CMC, PAM, cellulose graft copolymerization acrylamide compound, mixing with KBr solid at a ratio of 1:100, grinding, tabletting, and measuring its infrared spectrum with a Necolet-670 type Fourier infrared spectrometer with a wavelength detection range of 400-^-1。

(2) Nuclear magnetic resonance analysis

Samples of CMC, PAM and cellulose graft-copolymerized acrylamide complexes were dissolved in heavy water, and 1H NMR spectra were measured on a Bruker AVANCE DRX-500 type 500MHz nuclear magnetic resonance spectrometer for Mest Re Nova software analysis.

(3) DSC thermal analysis

Samples of CMC, PAM and cellulose graft copolymer acrylamide are respectively placed in a covered DSC aluminum dish box and analyzed by a Perkin-Elmer DSC-7 type analyzer, and the setting conditions are as follows: the temperature is increased from 20 ℃ to 300 ℃ at a temperature increase rate of 20 ℃/min.

4.5 results and analysis

4.5.1 Effect of preparation conditions on grafting ratio and relative molecular weight of cellulose graft copolymerized acrylamide Synthesis:

a five-factor four-level orthogonal test is designed by taking the substrate mass ratio, the initiator amount, the grafting temperature, the grafting time and the pH value as synthesis factors, and the influence of different factors on the performance of the cellulose graft copolymerization acrylamide compound is discussed by using the evaluation index of the relative molecular weight (see table 2).

TABLE 2

As shown in Table 2, the results of orthogonal experiments show that when the grafting rate is the highest, i.e., the synthesis efficiency is the highest, the optimal preparation conditions are pH5, initiator amount 19.5mL, temperature 60 ℃, synthesis time 2.5h, and monomer mass 10g, and the order of the influence factors is as follows: grafting temperature > PH > initiator amount > monomer mass > grafting time. When the graft copolymer with the largest relative molecular weight is obtained, the optimal preparation conditions are that the PH is 7, the initiator amount is 7.8mL, the temperature is 45 ℃, the synthesis time is 3.5h, the monomer mass is 17g, and the order of the influencing factors is as follows: the initiator amount > monomer mass > grafting temperature > pH > grafting time.

Therefore, the evaluation method is different, the pursuit target is different, and the required production conditions are also different. From the analysis in table 2, it can be seen that by changing the graft copolymerization conditions, the copolymer with the target molecular weight can be customized and synthesized, which provides convenient design parameters for product customization.

4.5.2 correlation of relative molecular weight of cellulose graft-copolymerized acrylamide Synthesis with product Properties:

FIG. 2 is a graph showing the relationship between the relative molecular weight of a cellulose graft-copolymerized acrylamide complex and the limiting viscosity, dissolution time, conductivity and degree of hydrolysis.

The relative molecular weight is an important index for characterizing the performance of the high molecular polymer, and reflects the sum of the number of each atom in the chemical formula of the copolymer, i.e., the longer the polymer chain or the more branched chains, the larger the relative molecular weight, which is shown in the increase of the limiting viscosity. As can be seen from fig. 2(a), the relative molecular weight of the cellulose graft-copolymerized acrylamide composite obtained by the preparation method described in example 1 has a linearly significant correlation with the limiting viscosity (R ═ 0.9891). That is, as the relative molecular weight of the copolymer increases, the greater the amount of sodium carboxymethylcellulose grafted, the greater the contribution to the increase in limiting viscosity. Studies have also shown that the greater the molecular weight, the greater the limiting viscosity. Research also shows that the flocculant is applied to the water treatment process, the higher the molecular weight is, the higher the limiting viscosity is, and the better the flocculation performance is, but according to the sewage characteristics and experimental verification, the proper flocculant with the relative molecular weight is selected. Therefore, the relative molecular weight is an important performance parameter for determining flocculation performance.

In order to fully express the performance characteristics of the copolymer product, the dissolution time, the conductivity and the hydrolysis degree of the cellulose graft copolymerization acrylamide compound are analyzed, and the correlation between the dissolution time, the conductivity and the hydrolysis degree and the relative molecular weight is discussed. FIG. 2(b) shows that the dissolution time of the cellulose graft copolyacrylamide complex increases with the relative molecular weight, as a result of the time required for more carboxyl groups in the structure to combine with more hydrogen ions in water molecules to form carboxylic acids, as the relative molecular weight increases, and more sodium carboxymethylcellulose is grafted into the chains. The dissolution time of the cellulose graft-copolymerized acrylamide complex shows a good correlation with the relative molecular weight (R ═ 0.7821), and this correlation is reflected by a tendency of change, i.e., more sodium carboxymethylcellulose is grafted, meaning that the dissolution time of the cellulose graft-copolymerized acrylamide complex becomes longer, which is not favorable for practical use. Since sodium carboxymethylcellulose belongs to an anionic cellulose ether structure, the first-class dissolution time of the grafted polyacrylamide copolymer is less than 90min according to the Chinese product standard (GB-17514-. As shown in FIG. 2(b), the relative molecular weight of the sodium carboxymethylcellulose grafted copolyamide is controlled within 350 ten thousand so as to meet the dissolution time standard requirement of the product.

The conductivity is a measure of the concentration of the soluble inorganic salt present in the graft copolymer solution. As can be seen from FIG. 2(c), the conductivity of the cellulose graft copolymer acrylamide complex with relative molecular weight in the two regions of 75-100 ten thousand and 150-200 ten thousand is significantly increased, which indicates that the carboxyl group in the cellulose graft copolymer acrylamide complex in this relative molecular weight range is easy to form carboxylic acid group, so that sodium ions are released to form electrolyte ions, thereby increasing the solution conductivity, which is the same as the change rule of the hydrolysis degree of the cellulose graft copolymer acrylamide complex with relative molecular weight (FIG. 2 (d)). The hydrolysis degree is the ability of carboxyl ions in the sodium carboxymethylcellulose graft copolymerization acrylamide solution to combine with water to form weak acidity. Within the 2 relative molecular weight intervals, the cellulose graft copolymerization acrylamide compound also shows the characteristic of obviously increased hydrolysis degree, which is the result of the combination of a large amount of carboxyl groups in the cellulose graft copolymerization acrylamide compound and water to form carboxylic acid groups, and the increased hydrolysis degree is helpful for promoting the flocculation effect. Meanwhile, the dissolving time of the cellulose graft copolymerization acrylamide compound in the range of the 2 relative molecular weight intervals is below 35min, which creates favorable conditions for the practical application of the cellulose graft copolymerization acrylamide compound. In summary, the cellulose graft-copolymerized acrylamide composite material with the relative molecular weight of 150-.

4.5.3 flocculation property change of copolymer in different pH simulated printing and dyeing wastewater

In this example, 5 cellulose graft-copolymerized acrylamide compositions with different relative molecular weights were selected from orthogonal experiments in order of decreasing relative molecular weights to increase relative molecular weights, and subjected to flocculation test for simulating dyeing wastewater. Table 3 shows data of cellulose graft copolymer acrylamide compositions (ordered from small to large molecular weight) for treating simulated printing and dyeing wastewater.

TABLE 3

Wherein ZJJZR represents the preparation condition of the highest grafting rate obtained by an orthogonal test; ZJFZL represents the preparation condition of the graft copolymer with the maximum molecular weight obtained by an orthogonal test; M-PAM is commercially available PAM.

The flocculation performance of each sample in the simulated printing wastewater at different pH values shown in table 3 varies as shown in fig. 3.

The main factors influencing the flocculation sedimentation effect are the pH value, the water temperature, the impurity content in water, the type of the flocculating agent, the adding amount of the flocculating agent and the like. In this example, the influence of the graft copolymer under different pH conditions on the flocculation settling performance of the simulated printing and dyeing wastewater was discussed on the premise of consistent factors. The results of the study show (FIG. 3) that the flocculation settling rate of the carboxymethyl cellulose graft copolymer on the simulated printing and dyeing wastewater is increased along with the increase of the molecular weight under the same pH condition. The higher the molecular weight of the flocculant, the faster the flocculation settling rate; and vice versa. The higher the molecular weight of the graft copolymer is, the longer the carbon chain is, the more the carboxyl and amido groups are contained, the larger the charge quantity is, the higher the charge density is, the more the chain can be fully extended, the larger the action range of the adsorption bridge is, and the stronger the adsorption bridge and the sweeping capability on the sewage colloid are.

As can be seen from FIGS. 3 and 4, the strong acidity (pH3) causes the graft copolymer to exhibit the strongest flocculating settling ability during the pH change from strongly acidic to strongly alkaline, and the higher the molecular weight, the stronger the flocculating ability. The flocculation settling capacity of the graft copolymers of different molecular weights decreases as the pH rises to neutrality (pH 7). Further increasing the pH to slightly alkaline pH9, the flocculating settling ability of these graft copolymers is increased. When the solution becomes strongly alkaline (pH11), the flocculation settling capacity of the low molecular weight graft copolymer of less than 100 ten thousand is enhanced, while the flocculation settling capacity of the graft copolymer of more than 100 ten thousand molecular weight begins to decrease, and the larger the molecular weight, the more obvious the decrease. It is clear that the synthesized graft copolymer can be well adapted to the strong acid and weak base environmental conditions, resulting in enhanced flocculation settling properties, which can be explained from the synthetic structure of the graft copolymer (FIG. 2).

The results in FIG. 3 also show that, no matter how the pH is changed, a graft copolymer with a relative molecular weight of 356 ten thousand (CMC-g-PAM 5) and 543 ten thousand of simple polyalkenamide (M-PAM) can achieve a comparable flocculation and sedimentation effect, which is a result of a large amount of carboxymethyl fibers grafted to polyacrylamide to increase the number of carboxyl groups rapidly to enhance the electrically neutralizing flocculation capability. From the synthesis condition of CMC-g-PAM 5, 1g of carboxymethyl cellulose and 17g of acrylamide are subjected to graft copolymerization, namely, the carboxymethyl cellulose accounts for 5.55 percent of the total mass of the substrate. It is believed that acrylamide in a PAM structure in a corresponding amount by weight is replaced with carboxymethyl cellulose, resulting in a corresponding reduction in the amount of acrylamide used, which has important application value in increasing flocculation capacity while simultaneously reducing the amount of polyacrylamide used.

Carboxymethyl cellulose grafted copolyacrylamide is a high molecular compound in which a large number of carboxyl groups are introduced into a polyacrylamide chain. Such compounds carry both a large number of amide groups and a large number of carboxyl groups. The amide group is a nonionic group, under a slightly acidic condition, water and protonated amido carbonyl group undergo nucleophilic addition to eliminate amino, the amide structural unit is hydrolyzed into a carboxylic acid structural unit, which is a key factor for generating electric neutralization flocculation, and a secondary valence bond is easily formed to be adsorbed and connected with an active group of other substances (fig. 5). Therefore, when the simple polyacrylamide is applied to general wastewater treatment, suspended matters in water can be flocculated by action modes such as trapping, bridging and the like. Moreover, acidic hydrolysis exhibits a remarkable temporary catalytic effect, i.e., the carboxyl groups formed after hydrolysis have an accelerating effect on the hydrolysis of the temporary acylamino groups, which results in an accelerated rate of acidic hydrolysis with an increase in the degree of hydrolysis. Thus, acidic, particularly strongly acidic conditions are effective in promoting the hydrolysis of amide building blocks to carboxylic acids. When a large amount of carboxymethyl cellulose is grafted into polyacrylamide, the number of carboxyl groups is further increased rapidly, and the carboxyl groups are electronegative groups and are easy to form an electric neutralization effect with cations in a solution, so that the flocculation performance of the polyacrylamide is further enhanced.

The study showed that the hydrolysis of the amido group proceeded very slowly under neutral conditions and did not change appreciably at 40 ℃ for 10 days. Under the alkalescent condition, the hydrolysis carboxylation process of the amido group is still continued, so that the flocculation settling property is enhanced. The strong alkalinity obviously inhibits the hydrolysis and carboxylation of the polyacrylamide, so that the amido group still keeps nonionic, and the carboxylate grafted in the polyacrylamide is not effectively hydrolyzed and is negatively charged. The larger the molecular weight, the more pronounced the inhibitory effect. Therefore, the strong alkaline condition greatly weakens the electric neutralization flocculation capability of the graft copolymer, and the flocculation sedimentation performance of the simulated printing and dyeing wastewater is obviously reduced.

4.5.4 structural characterization of cellulose graft copolymerization acrylamide composition

4.5.4.1 FTIR analysis

Infrared Spectroscopy (FTIR) is an important technique for characterizing the structure of the chemical functional groups of the graft copolymers. FIG. 6 shows infrared spectra of Acrylamide (AM), sodium carboxymethylcellulose (CMC) and CMC-g-PAM 5(w (CMC): w (AM) ═ 1:17) in FIG. 6. As can be seen from FIG. 6, the sharp absorption peak in acrylamide was 3355cm^-1And 3187cm^-1Is caused by the stretching vibration of amide N-H, the vibration peak is not existed in the sodium carboxymethyl cellulose, and 3401cm appears in CMC-g-PAM 5^-1And 3201cm^-1The broad absorption band, which is the stretching vibration peak produced by-NH and-OH, indicates that the amide group in acrylamide has been grafted as a constituent of CMC-g-PAM 5. 3033cm above the unsaturated carbon in acrylamide^-1is-C-H stretching vibration and 2919cm in sodium carboxymethyl cellulose^-1Saturated carbon C-H stretching vibration superposition, migration to 2933cm in CMC-g-PAM 5^-1Of (C-CH)₂. 1673cm in acrylamide^-1、1614cm^-1and-C-with 2165cm in sodium carboxymethylcellulose^-1Are grafted in CMC-g-PAM 5, as represented by 1679cm^-1、1621cm^-1Stretching vibration of carbon double bond and vibration of benzene ring skeleton of (2) and 2171cm^-1、2433cm^-1is-C ═ O. These results indicate that acrylamide and sodium carboxymethylcellulose have been successfully grafted as part of CMC-g-PAM 5.

4.5.4.2 HMNR analysis

The results of the HMNR analysis are shown in FIG. 7.

The 1HNMR is used for recording a signal spectrum of hydrogen atoms under resonance based on the principle that hydrogen atoms absorb electromagnetic wave energy to generate transition through resonance. In a nuclear magnetic resonance hydrogen spectrogram, the number of characteristic peaks reflects the types of chemical environments of hydrogen atoms in organic molecules, and the intensity ratio of different characteristic peaks reflects the number ratio of the hydrogen atoms in different chemical environments. As can be seen from fig. 7, in the Acrylamide Monomer (AM), the absorption peak at δ ═ 5.71 to 5.74ppm is a proton in methine-CH- (amide group-linked), and the absorption peak at δ ═ 6.11 to 6.26ppm is a proton in methylene-CH 2-. In sodium carboxymethylcellulose, the characteristic peak at δ -4.16 ppm corresponds to the proton in methylene-CH 2-on the CMC ring side chain, and the absorption peak at δ -3.12-4.00 ppm is the proton in methine-CH-on the CMC ring. In the graft copolymer CMC-g-PAM 5, the doublet of δ ═ 1.57, 1.70ppm was the proton in methylene-CH 2-of polyacrylamide, and the doublet of δ ═ 2.09, 2.25ppm was the proton in methine-CH-of polyacrylamide, indicating that the acrylamide monomer was polymerized. A peak packet appears at the position of delta-3.74 ppm, which corresponds to the protons in H1-H6 in sodium carboxymethyl cellulose, and the protons have chemical shifts, indicating that the sodium carboxymethyl cellulose is successfully grafted and copolymerized with polyacrylamide. From the peak intensity, the polyacrylamide is significantly higher than the hydrogen spectrum resonance signal of sodium carboxymethylcellulose, and it can be presumed that the main bond of CMC-g-PAM 5 is PAM and the side chain is CMC.

4.5.4.3 DSC analysis

The results of the DSC analysis are shown in FIG. 8.

Differential Scanning Calorimetry (Differential Scanning Calorimetry) is a technical means for reflecting the relationship between the difference of thermal power of a polymer and the temperature T under the condition of constant heating rate, and can be used for judging the thermal stability of a substance, which is represented by the value of the glass transition temperature Tg. The higher the Tg, the better the temperature resistance of the material and the higher the thermal stability. As can be seen from FIG. 8, the vitrification intermediate temperatures of AM, CMC and CMC-g-PAM 5 on the DSC curve are 196.6 ℃, 186.3 ℃ and 243.0 ℃ respectively, which shows that the thermal stability of the copolymer CMC-g-PAM 5 product formed after the AM and the CMC are subjected to graft copolymerization is obviously improved. Studies have shown that the factors affecting Tg are mainly the chemical structure of the material, relative molecular weight, crystallinity, cross-linking cure, sample history effects, etc. Generally, polymers with large pendant groups have a higher Tg. The copolymer CMC-g-PAM 5 has a large amount of side chain structures of sodium carboxymethylcellulose, and simultaneously, the relative molecular weight of the copolymer CMC-g-PAM 5 is further increased, so that the Tg of the copolymer is improved, and the thermal stability of the copolymer is increased.

Various corresponding changes and modifications can be made by those skilled in the art based on the above technical solutions and concepts, and all such changes and modifications should be included in the protection scope of the present invention.

Claims

1. The cellulose graft copolymerization acrylamide synthetic material with controllable molecular weight is characterized by being prepared by the following method:

2. The controllable molecular weight cellulose graft copolymerized acrylamide complex as set forth in claim 1, wherein in step S2, the molar ratio of 1% potassium persulfate to 1% sodium bisulfite is 1:0.75, and the total volume added is 7.8mL, 11.7mL, 15.6mL or 19.5 mL.

3. The cellulose graft copolymerization acrylamide complex with controllable molecular weight as claimed in claim 1, wherein in step S2, the volume of the solution of acrylamide monomer added is 50mL, and the content of acrylamide monomer is 8.0g, 10.0g, 13.0g or 17.0 g.

4. The cellulose graft copolymerization acrylamide complex with controllable molecular weight as claimed in claim 1, wherein in step S2, the pH is adjusted to 5.0, 7.0, 9.0 or 11.0.

5. The cellulose graft copolymerization acrylamide complex with controllable molecular weight as claimed in claim 1, wherein the reaction temperature in step S2 is 45 ℃, 50 ℃, 60 ℃ or 70 ℃.

6. The cellulose graft copolymerization acrylamide complex with controllable molecular weight as claimed in claim 1, wherein in step S3, the polymerization reaction time is 2.5hr, 3hr, 3.5hr or 4 hr.

7. The cellulose graft copolymerization acrylamide complex with controllable molecular weight as claimed in claim 1, wherein in step S3, 300mL of absolute ethanol is added.

8. The cellulose graft copolymerization acrylamide complex with controllable molecular weight as claimed in claim 1, wherein the reflux purification time in step S4 is 8 hr.

9. The cellulose graft copolymer acrylamide complex with controllable molecular weight as defined in claim 1, wherein in step S4, 100mL-150mL of acetone is used as the extraction solution.

10. Use of a controllable molecular weight cellulose graft co-acrylamide composition according to any one of claims 1 to 9 in wastewater treatment.