CN108794702B - A method for improving the rheological properties of crop straw by using irradiation grafted vinyl acetate - Google Patents

Abstract

The invention relates to the technical field of agriculture, in particular to a method for improving the rheological properties of crop straws by using radiation grafted vinyl acetate. The method adopts vinyl acetate as a grafting monomer, and mixes vinyl acetate and methanol to prepare Grafting liquid; then immersed in crop straw, passed into high-purity nitrogen for deoxygenation, and then irradiated and grafted under sealing; finally, firstly wash unreacted monomers with benzene, and then use benzene as a solvent to extract by Soxhlet extraction , remove the remaining monomers and homopolymers, and dry at low temperature to constant weight. In the invention, crop straw is used as raw material, vinyl acetate is used as monomer, and ⁶⁰ Coγ rays are used to induce crop straw to irradiate and graft vinyl acetate to obtain polyvinyl acetate-grafted crop straw, thereby improving the rheological properties of crop straw. It provides a theoretical basis for the development of straw-based materials, and plays an important role in the comprehensive utilization of straw resources, improving and protecting the environment, and promoting the development of modern agriculture.

Description

A method for improving the rheological properties of crop straw by using irradiation grafted vinyl acetate method

technical field

The invention relates to the technical field of agriculture, in particular to a method for improving the rheological properties of crop straws by grafting vinyl acetate with irradiation.

Background technique

my country is a big agricultural country, with an annual output of nearly 800 million tons of crop straw, which is one of the most promising biomass raw materials. Using crop straws as raw materials to prepare agricultural materials (such as mulching films, fruit bagging, wrapping films, bags, seedling containers, etc.) can not only effectively consume straws, but also reduce the dependence on petroleum-based raw materials, which has huge application prospects. However, the material utilization of straw in my country only accounts for about 3% of the total output of straw. One of the important constraints is the poor rheological properties of the straw material itself.

Rheological properties are an important index in the process of straw materialization. Rheological properties can provide basic data for material design, formulation design, and process design of straw materials, and control and achieve the desired processing fluidity and main physical and mechanical properties. Meng Haibo and others studied the processing and utilization characteristics of straw, and the analysis showed that the rheological properties of straw under impact load have practical significance for the processing and molding of straw materials. Feng et al. used a torque rheometer to measure the effect of sisal fiber shape on the rheological properties of composites. The results showed that the specific surface area of the fibers had a great influence on the viscosity index of the composites. Straw is an elastic solid with the properties of viscous fluid and certain rheology. However, cellulose in the straw forms fine fibers through hydrogen bonding, and lignin and hemicellulose are filled between the fine fibers and fiber cells with fillers and binders, forming a three-dimensional spatial network structure, and between molecules and molecules. There are strong hydrogen bonds, van der Waals forces and other forces inside, so that the melting and softening temperature of straw is much higher than its thermal decomposition temperature, which causes the difficulty of straw material utilization. Therefore, it is necessary to modify the straw raw material to improve its rheological properties while retaining the biodegradability.

At present, there are three ways to improve straw rheology at home and abroad, including physical, biological and chemical. Among them, the physical method has little damage to cellulose and high energy consumption, and the improvement of rheological properties is not obvious. The biological treatment method uses microorganisms and enzymes to treat the surface of the straw, but the treatment period is long, the product properties are difficult to control, and the inoculants are difficult to screen. Preliminary work found that composting can improve the rheological properties of straw, but the improvement of rheological properties is limited due to the existence of cellulose crystalline structure. In order to improve the crystal structure of cellulose and weaken the hydrogen bonds between cellulose molecules and molecules, domestic and foreign scholars use its active groups to chemically modify it, that is, etherification and esterification. It softens or even melts at a relatively low temperature, and has a certain fluidity, making it a new material that can be thermoplastically molded. However, the modified product is resistant to fungi, light and refractory, so it is necessary to further explore new modification methods to improve its rheological properties.

Studies have shown that the "three elements" of straw, namely cellulose, lignin, and hemicellulose, can improve their own rheological properties in the grafted molecular segment, such as the second largest component of straw, lignin and vinyl acetate. After grafting, the glass transition temperature decreased by 1 °C when the grafting ratio was 60%; Laurichsse used chemically initiated method to graft and copolymerize polycaprolactone and lignin, and the results showed that the flow of the grafted material was The variable performance is significantly improved; Dong et al. used a chemically initiated method to graft and copolymerize acrylamide and methacryloyloxyethyltrimethylammonium chloride with hemicellulose, which improved thermal stability and tensile strength. In addition to the three elements in the straw can change its own rheological properties through grafting, the undissociated straw can also undergo graft copolymerization. Kellersztein et al. grafted polycaprolactone to straw by the method of ring-opening polymerization, and the biodegradable composite material made by blending with polylactic acid had significantly improved bending properties and elastic modulus. After grafting methyl methacrylate on the surface of plant fibers by Thakur et al., the tensile strength of the composites was significantly improved. This shows that chemically induced grafting can effectively improve the rheological properties of straw, but the initiator is harmful to the growth of crops, and the three-dimensional structure of the straw is less damaged during the grafting process.

The grafting reaction is induced by ⁶⁰ Coγ-ray irradiation, which has the characteristics of green reaction, no pollution, and no harmful substances to crop growth. The reaction progress can also be controlled by changing the irradiation dose, and the grafting rate is easy to control. After high-energy ray irradiation, both the straw and the monomer can generate free radicals, so functional structural units can be grafted on the straw to improve the rheological properties of the straw. At the same time, high-energy rays can weaken the van der Waals forces and hydrogen bonds between the three elements, reduce the molecular weight of the three elements, destroy the crystalline structure of cellulose, make the structure loose, and improve the accessibility of the reaction. Straw cellulosic material can be softened at relatively low temperatures, improving its rheology. The grafting monomer has an important influence on the rheological properties of the straw, so it has specific requirements for the grafting monomer. Among many monomers, vinyl acetate (CH ₃ COOCH=CH ₂ ) has a double bond, and can form monomer free radicals under the excitation of ⁶⁰ Coγ rays. By means of free radical graft copolymerization, polyvinyl acetate with low surface energy can be converted into polyvinyl acetate with low surface energy. The ester is grafted onto the straw to form a strong covalent bond with high surface stability. The grafted monomer further induces chain growth, and polymerizes itself into polyvinyl acetate. The molecular segment is soft, has good toughness, plasticity, non-toxic and harmless, and can form biodegradable polyvinyl alcohol after hydrolysis. On the basis of this theory, the applicant has studied the grafting of vinyl acetate on the surface of the straw to improve the rheological properties of the straw. At present, straw grafting is mainly used to enhance the mechanical properties of the matrix, and there is no report on the mechanism of irradiation grafting vinyl acetate to improve the rheological properties of straw.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for improving the rheological properties of crop straws by using radiation grafting vinyl acetate, so as to solve the problem that the chemically induced grafting in the prior art is harmful to the growth of crops, and the degree of damage to the three-dimensional structure of the straws during the grafting process is solved. Fewer problems.

For achieving the above object, the present invention adopts the following technical scheme:

A method for improving the rheological properties of crop straw by using irradiated grafted vinyl acetate, characterized in that the method adopts vinyl acetate as a grafting monomer, and mixes and stirs vinyl acetate and methanol to prepare a grafting liquid; then Immerse the crop straws, pass high-purity nitrogen to deoxygenate, and then carry out irradiation grafting under sealing; finally, first wash unreacted monomers with benzene, and then use benzene as a solvent to extract by Soxhlet extraction method to remove the remaining monomers. Monomers and homopolymers can be dried at low temperature to constant weight.

The crop straw is wheat straw, rice straw, corn straw, sorghum straw, sugarcane straw or cotton straw.

The mass ratio of the vinyl acetate to the crop straw is 2-5:1.

The volume ratio of the vinyl acetate to methanol is 1:3-9.

The purity of the high-purity nitrogen gas is greater than or equal to 99.99%, and the inflow time of the high-purity nitrogen gas is 20-30 minutes.

The irradiation grafting adopts ⁶⁰ Coγ rays as the radiation source, the total radiation dose is 15-25kGy, and the radiation dose rate is 1-2kGy·h ^-1 .

The extraction time is 24-48h.

The drying temperature is 50-60°C.

The beneficial effects of the present invention are:

The invention uses crop straw as raw material and vinyl acetate as monomer, utilizes ⁶⁰ Coγ rays to induce crop straw to irradiate and graft vinyl acetate to obtain polyvinyl acetate-grafted crop straw, which can not only destroy the crystal of straw cellulose It can also improve the rheological properties of crop straws, provide a theoretical basis for the development of straw-based materials, and play an important role in comprehensively utilizing straw resources, improving and protecting the environment, and promoting the development of modern agriculture, and the method of the invention is green and environmentally friendly. It is non-toxic, harmless, non-polluting and degradable.

Description of drawings

Figure 1 shows the surface morphology of rice straw before and after ⁶⁰ Coγ-ray irradiation. It can be seen from the scanning electron microscope pictures that under the same magnification (500× and 5000×) conditions, the straw after irradiation (100kGy) has many Hole defects appear because the absorption of ionizing radiation by straw is a highly localized phenomenon, indicating that the specific surface area of the straw increases after irradiation, and the exposed active groups on the surface of the straw increase, and the irradiation grafting does not only occur in the straw. The surface of the stalk will also be grafted inside the straw.

Figure 2 shows the infrared spectra of rice straw before and after ⁶⁰ Coγ-ray irradiation, where a and b are the straw before and after irradiation, respectively; the absorption peak at about 3335 cm ^-1 was significantly enhanced after straw irradiation (100kGy), This peak is the stretching vibration peak of hydroxyl group and the absorption peak of intermolecular hydrogen bond association, indicating that the siliceous wax layer on the surface of straw is destroyed by radiation and the hydroxyl functional group is exposed, indicating that the irradiation process can increase the reactive matrix of straw.

Figure 3 shows the X-ray diffraction patterns of straw before and after ⁶⁰ Coγ irradiation, where a and b are the straw before and after irradiation, respectively; after irradiation, the peak intensity of 101 and 002 crystal planes decreased slightly, and the peak shape became wider; This shows that the crystalline structure of cellulose can be destroyed and its crystallinity can be reduced under the irradiation dose of 100kGy.

Figure 4 shows the infrared spectra of rice straw before and after irradiation with vinyl acetate, where a is the ^ungrafted straw, and b is the straw after grafting with vinyl acetate by irradiation; There is an absorption peak at , which belongs to the stretching vibration peak of COC; the absorption peak at 1160 cm ^-1 belongs to the bending vibration peak of CH ; in addition, a new irradiated straw after grafting vinyl acetate appears at 1730 cm ^-1 The absorption peak belongs to the ester group C=O stretching vibration absorption peak of polyvinyl acetate; infrared characterization proves that polyvinyl acetate has been successfully grafted to straw.

Figure 5 shows the X-ray diffraction patterns of rice straw before and after irradiating and grafting vinyl acetate, in which a is the ungrafted straw, and b is the straw after grafting vinyl acetate by irradiation; the straw at 16.7° and 22.8° There are two crystallization peaks, which belong to the characteristic peaks of 101 and 002 crystal planes of cellulose; the intensity of the peak at 16.7° decreases after irradiation grafting, indicating that irradiation grafting affects the crystal structure of cellulose.

The above drawings illustrate that vinyl acetate monomer can be grafted onto rice straw by ⁶⁰ Coγ ray irradiation, and at the same time ⁶⁰ Coγ ray can destroy the crystal structure of straw cellulose.

Detailed ways

Example 1

A method for improving the rheological properties of wheat straw by utilizing irradiation grafted vinyl acetate, comprising the following steps:

(1) Mix 100 mL of vinyl acetate and 300 mL of methanol, and fully stir to obtain a graft solution;

(2) 400g of wheat straw was immersed in the grafting solution, and then irradiated and grafted with ⁶⁰ Coγ rays under sealing under high-purity nitrogen for 20 minutes. The total radiation dose was 15kGy, and the radiation dose rate was 1kGy·h ^-1 ;

(3) After the radiation grafting is completed, the unreacted monomers are washed with benzene, and then extracted with benzene as a solvent by Soxhlet extraction method for 24 hours to remove the remaining monomers and homopolymers, and dried at a low temperature of 50 °C to constant heavy.

Example 2

A method for improving the rheological properties of rice straw by utilizing irradiation grafted vinyl acetate, comprising the following steps:

(1) Mix 150 mL of vinyl acetate and 600 mL of methanol, and fully stir to obtain a graft solution;

(2) 600g of rice straw was immersed in the grafting solution, and then irradiated and grafted with ⁶⁰ Coγ ray under sealing under high-purity nitrogen gas for 20min. The total radiation dose was 20kGy, and the radiation dose rate was 1.5kGy·h ^-1 ;

(3) After the irradiation grafting is completed, first wash off the unreacted monomers with benzene, and then use benzene as a solvent to extract by Soxhlet extraction method for 36 hours, remove the remaining monomers and homopolymers, and dry at a low temperature of 55 °C to constant heavy.

Example 3

A method for improving the rheological properties of corn stover by utilizing irradiation grafted vinyl acetate, comprising the following steps:

(1) mix 200mL vinyl acetate and 1000mL methanol, fully stir to obtain a graft solution;

(2) 1000g of rice straw was immersed in the grafting solution, and then irradiated with ⁶⁰ Coγ rays for grafting under sealing under high-purity nitrogen gas for 25 minutes. The total radiation dose was 22kGy, and the radiation dose rate was 1kGy·h ^-1 ;

(3) After the radiation grafting is completed, the grafted product is placed for 36 hours, and then the unreacted monomer is washed with benzene, and then extracted with benzene as a solvent by Soxhlet extraction method for 36 hours to remove the remaining monomers and homopolymers , 58 ℃ low temperature drying to constant weight can be.

Example 4

A method for improving the rheological properties of sorghum straw by utilizing irradiation grafted vinyl acetate, comprising the following steps:

(1) Mix 120 mL of vinyl acetate and 600 mL of methanol, and fully stir to obtain a graft solution;

(2) 800g of sorghum straw was immersed in the grafting solution, and after 20min of high-purity nitrogen was irradiated and grafted with ⁶⁰ Coγ rays under sealing, the total radiation dose was 18kGy, and the radiation dose rate was 1.5kGy·h ^-1 ;

(3) After the irradiation grafting is completed, first wash off the unreacted monomers with benzene, and then use benzene as a solvent to extract the remaining monomers and homopolymers by Soxhlet extraction method for 48 hours, and then dry at 52 °C to constant temperature. heavy.

Example 5

A method for improving the rheological properties of sugarcane straw by utilizing irradiation grafted vinyl acetate, comprising the following steps:

(1) Mix 240 mL of vinyl acetate and 1200 mL of methanol, and fully stir to obtain a graft solution;

(2) 1800g sugarcane straw was immersed in the grafting solution, and after 30min of high-purity nitrogen gas was irradiated and grafted under sealing with ⁶⁰ Coγ rays, the total radiation dose was 28kGy, and the radiation dose rate was 2kGy·h ^-1 ;

(3) After the irradiation grafting is completed, the unreacted monomers are washed with benzene, and then extracted with benzene as a solvent by Soxhlet extraction method for 48 hours to remove the remaining monomers and homopolymers, and then dried at a low temperature of 54 °C to constant heavy.

Example 6

A method for improving the rheological properties of cotton straw by utilizing irradiation grafted vinyl acetate, comprising the following steps:

(1) Mix 300 mL of vinyl acetate and 1800 mL of methanol, and fully stir to obtain a graft solution;

(2) immersing 2500g of cotton stalks in the grafting solution, irradiating and grafting ⁶⁰ Coγ rays under sealing after 30min of high-purity nitrogen, the total radiation dose is 30kGy, and the radiation dose rate is 2kGy·h ^-1 ;

(3) After the irradiation grafting is completed, first wash off the unreacted monomers with benzene, and then use benzene as the solvent to extract the remaining monomers and homopolymers by Soxhlet extraction method for 48 hours, and then dry at 60℃ to constant temperature. heavy.

The changes of straw rheology before and after the irradiation and grafting of Example 1-6 are shown in Table 1:

Table 1 Changes in rheological properties of straw before and after irradiation grafting

It can be seen from Table 1 that the maximum torque and equilibrium torque of the straws after irradiation grafting increase, and the equilibrium time decreases, which indicates that the force between the straws after irradiation grafting is enhanced, and the rheology of the straws is improved. Improve the processing performance of straw.

Claims (7)

1. a method utilizing radiation grafting vinyl acetate to improve crop straw rheological properties, is characterized in that, the method adopts vinyl acetate as grafting monomer, and vinyl acetate and methanol are mixed and stirred to form grafting liquid Then immersed in crop straw, passed high-purity nitrogen to remove oxygen, and then carried out irradiation grafting under sealing. The irradiation grafting used ⁶⁰ Coγ rays as the radiation source, the total radiation dose was 15-25kGy, and the radiation dose rate was 1-2kGy h ^-1 ; at last, first wash off unreacted monomers with benzene, then take benzene as a solvent and adopt Soxhlet extraction to extract, remove remaining monomers and homopolymers, and dry at low temperature to constant weight. . 2. a kind of method utilizing irradiation grafting vinyl acetate to improve crop straw rheological properties according to claim 1, is characterized in that, described crop straw is wheat straw, rice straw, corn straw, sorghum straw, Sugarcane straw or cotton straw. 3. a kind of method utilizing radiation grafting vinyl acetate to improve crop straw rheological properties according to claim 1, is characterized in that, the mass ratio of described vinyl acetate and crop straw is 2-5: 1 . 4 . The method for improving the rheological properties of crop straws by using radiation grafted vinyl acetate according to claim 1 , wherein the volume ratio of the vinyl acetate to methanol is 1:3-9. 5 . 5. A method for improving the rheological properties of crop straw by using irradiation grafted vinyl acetate according to claim 1, wherein the high-purity nitrogen purity is greater than or equal to 99.99%, and the high-purity nitrogen The entry time is 20-30min. 6 . The method of claim 1 , wherein the extraction time is 24-48h. 7 . 7 . The method of claim 1 , wherein the drying temperature is 50-60° C. 7 .

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