CN108794702B - Method for improving rheological property of crop straw by irradiation grafting of vinyl acetate - Google Patents
Method for improving rheological property of crop straw by irradiation grafting of vinyl acetate Download PDFInfo
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- XTXRWKRVRITETP-UHFFFAOYSA-N Vinyl acetate Chemical compound CC(=O)OC=C XTXRWKRVRITETP-UHFFFAOYSA-N 0.000 title claims abstract description 50
- 238000000034 method Methods 0.000 title claims abstract description 39
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- RRHXZLALVWBDKH-UHFFFAOYSA-M trimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]azanium;chloride Chemical compound [Cl-].CC(=C)C(=O)OCC[N+](C)(C)C RRHXZLALVWBDKH-UHFFFAOYSA-M 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F289/00—Macromolecular compounds obtained by polymerising monomers on to macromolecular compounds not provided for in groups C08F251/00 - C08F287/00
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/46—Polymerisation initiated by wave energy or particle radiation
- C08F2/48—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Graft Or Block Polymers (AREA)
Abstract
The invention relates to the technical field of agriculture, in particular toThe method adopts vinyl acetate as a grafting monomer, and mixes and stirs the vinyl acetate and methanol to prepare a grafting solution; then soaking the crop straws, introducing high-purity nitrogen to remove oxygen, and then carrying out irradiation grafting under sealing; and finally, washing unreacted monomers by using benzene, extracting by using benzene as a solvent by adopting a Soxhlet extraction method, removing the residual monomers and homopolymers, and drying at low temperature to constant weight. The invention takes crop straws as raw materials and vinyl acetate as a monomer, and utilizes60The Co gamma rays trigger the irradiation grafting of the vinyl acetate on the crop straws to obtain the polyvinyl acetate grafted crop straws, thereby improving the rheological property of the crop straws, providing a theoretical basis for the development of straw-based materials, and having important functions of comprehensively utilizing straw resources, improving and protecting the environment and promoting the development of modern agriculture.
Description
Technical Field
The invention relates to the technical field of agriculture, in particular to a method for improving rheological property of crop straws by using irradiation grafted vinyl acetate.
Background
China is a big agricultural country, the annual yield of crop straws is nearly 8 hundred million tons, and the crop straws are one of the most potential biomass raw materials. The agricultural material (such as mulching film, fruit bag, coating film, bag, seedling container, etc.) prepared from the crop straw as the raw material not only can effectively consume the straw, but also can reduce the dependence on petroleum-based raw materials, and has huge application prospect. But the utilization amount of the straw material in China only accounts for about 3 percent of the total straw yield. One of the important limiting factors is the poor rheological properties of the straw material itself.
The rheological property is an important index in the straw material making process. The rheological property can provide basic data for material design, formula design and process design of the straw material, and control and achieve the expected processing fluidity and main physical mechanical properties. The Monghai waves and the like research the processing and utilization characteristics of the straws, and analysis shows that the rheological characteristics of the straws under the impact load have practical significance on processing and forming of the straw materials. Feng et al measured the effect of sisal fiber shape on the rheological properties of the composite material by using a torque rheometer, and the results show that the specific surface area of the fiber has a large effect on the viscosity index of the composite material. The straw belongs to elastic solid, has the property of viscous fluid and has certain rheological property. However, cellulose in the straw is combined through hydrogen bonds to form micro-fibers, lignin and hemicellulose are filled between the micro-fibers and fiber cells through a filler and an adhesive to form a three-dimensional space network structure, and strong acting forces such as hydrogen bonds, van der waals force and the like exist between molecules and in molecules, so that the melting and softening temperature of the straw is far higher than the thermal decomposition temperature of the straw, and the straw material utilization is difficult. Therefore, it is necessary to modify straw raw materials to improve their rheological properties while maintaining biodegradability.
At present, the methods for improving the rheological property of the straws at home and abroad comprise three modes of physics, biology and chemistry. Wherein the damage degree of the physical method to the cellulose is small, the energy consumption is high, and the rheological property is not obviously improved. The biological treatment method is to treat the surfaces of the straws by using microorganisms and enzymes, but has long treatment period, difficult control of product properties and difficult screening of microbial inoculum. Earlier work found that composting improved the rheology of straw, but the improvement was limited due to the presence of crystalline structures of cellulose therein. In order to improve the crystal structure of cellulose and weaken the hydrogen bond effect between cellulose molecules and in the cellulose molecules, scholars at home and abroad use active groups to carry out chemical modification, namely etherification and esterification, so that the plant fiber can be softened at a relatively low temperature and even melted, has certain fluidity and becomes a new material capable of carrying out thermoplastic molding. However, the modified product has the characteristics of fungus resistance, light resistance and difficult degradation, so that a new modification method is required to be further searched for to improve the rheological property of the modified product.
Researches have shown that the rheological property of the grafted molecular chain segment of the 'three elements', namely cellulose, lignin and hemicellulose of the straw can be improved, for example, the glass transition temperature is reduced by 1 ℃ under the condition that the grafting rate is 60 percent after the second major component lignin in the straw is grafted with vinyl acetate; laurichesse adopts a chemical initiation method to graft and copolymerize polycaprolactone and lignin, and the result shows that the rheological property of the grafted material is obviously improved; dong et al use chemical initiation method to graft copolymerize acrylamide, methacryloyloxyethyl trimethyl ammonium chloride and hemicellulose, and improve thermal stability and tensile strength. In addition to the fact that the three elements in the straws can change the rheological property of the straws through grafting, the undissociated straws can also undergo graft copolymerization reaction. Kellersztein and the like graft polycaprolactone onto straws by a ring-opening polymerization method, and the biodegradable composite material prepared by blending the polycaprolactone with polylactic acid is obviously improved in bending property and elastic modulus. After the surface of the plant fiber is grafted with methyl methacrylate by Thakur and the like, the tensile strength of the composite material is obviously improved. This shows that chemical initiation grafting can effectively improve the rheological property of the straw, however, the initiator and the like are harmful to the growth of crops, and the three-dimensional structure of the straw is damaged to a lesser extent in the grafting process.
By using60The Co gamma ray irradiation initiates the grafting reaction, has the characteristics of green reaction, no pollution, no introduction of harmful substances to the growth of crops and the like, can control the reaction progress by changing the irradiation dose, and has easily controlled grafting rate. After the high-energy rays are irradiated, the straws and the monomers can generate free radicals, so that functional structural units can be grafted on the straws to improve the rheological property of the straws. Meanwhile, the high-energy rays can weaken Van der Waals force and hydrogen bond action among cellulose, reduce the molecular weight of the cellulose macromolecules, destroy the crystalline structure of the cellulose, loosen the structure of the cellulose, improve the reaction accessibility, finally enable the straw cellulose material to be softened at a relatively low temperature and improve the rheological property of the straw cellulose material. The grafting monomer has important influence on the rheological property of the straw, so that the grafting monomer has special requirements. Among the monomers, vinyl acetate (CH)3COOCH＝CH2) Having a double bond, a carboxyl group,60the polyvinyl acetate with low surface energy is grafted to the straw by utilizing free radical graft copolymerization reaction to form a firm covalent bond, and the surface stability is high. The grafted monomer further initiates chain growth, which polymerizes itself into a polymer vinegarThe vinyl acetate has soft molecular chain segment, good toughness and plasticity, no toxicity and no harm, and can form biodegradable polyvinyl alcohol after hydrolysis. On the basis of the theory, the applicant researches that vinyl acetate is grafted on the surface of the straw through irradiation, so that the rheological property of the straw is improved. At present, the straw grafting is mainly used for enhancing the mechanical property of a matrix, and a mechanism for improving the rheological property of the straw by irradiation grafting of vinyl acetate is not reported.
Disclosure of Invention
The invention aims to provide a method for improving rheological property of crop straws by irradiation grafting of vinyl acetate, which aims to solve the problems that chemical-induced grafting in the prior art is harmful to crop growth and the damage degree of the grafting process to the three-dimensional structure of the straws is low.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for improving rheological property of crop straws by irradiation grafting of vinyl acetate is characterized in that vinyl acetate is used as a grafting monomer, and the vinyl acetate and methanol are mixed and stirred to prepare a grafting solution; then soaking the crop straws, introducing high-purity nitrogen to remove oxygen, and then carrying out irradiation grafting under sealing; and finally, washing unreacted monomers by using benzene, extracting by using benzene as a solvent by adopting a Soxhlet extraction method, removing the residual monomers and homopolymers, and drying at low temperature to constant weight.
The crop straws are wheat straws, rice straws, corn straws, sorghum straws, sugarcane straws or cotton straws.
The mass ratio of the vinyl acetate to the crop straws is 2-5: 1.
the volume ratio of the vinyl acetate to the methanol is 1: 3-9.
The purity of the high-purity nitrogen is more than or equal to 99.99 percent, and the introducing time of the high-purity nitrogen is 20-30 min.
The irradiation grafting adopts60Co gamma-ray is used as radiation source, the total radiation dose is 15-25kGy, and the radiation dose rate is 1-2 kGy.h-1。
The extraction time is 24-48 h.
The drying temperature is 50-60 ℃.
The invention has the beneficial effects that:
the invention takes crop straws as raw materials and vinyl acetate as a monomer, and utilizes60The Co gamma rays initiate the irradiation grafting of the vinyl acetate on the crop straws to obtain the polyvinyl acetate grafted crop straws, not only can damage the crystal structure of the straw cellulose, but also can improve the rheological property of the 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.
Drawings
FIG. 1 is a drawing of60The surface appearance of the rice straw before and after Co gamma ray irradiation is shown in scanning electron microscope pictures, under the condition of the same magnification (500 × and 5000 ×), the irradiated (100kGy) straw has a plurality of hole defects, because the straw absorbs ionizing radiation and is a highly localized phenomenon, the specific surface area of the irradiated straw is increased, the active groups exposed on the surface of the straw are increased, and the irradiation grafting is not only on the surface of the straw, but also inside the straw.
FIG. 2 is60Infrared spectrograms of the rice straw before and after Co gamma ray irradiation, wherein a and b are the straw before and after irradiation respectively; after the straw is irradiated (100kGy), the length of the irradiated straw is 3335cm-1The absorption peaks on the left and the right are obviously enhanced, and the peaks are the absorption peaks associated with the stretching vibration peak of the hydroxyl and intermolecular hydrogen bonds, which shows that the siliceous wax layer on the surface of the straw is damaged by rays and the hydroxyl functional groups are exposed, and shows that the reactive matrix of the straw can be increased in the irradiation process.
FIG. 3 is a drawing showing60X-ray diffraction patterns of the straws before and after Co gamma irradiation, wherein a and b are the straws before and after irradiation respectively; after irradiation, the peak intensities of the 101 and 002 crystal planes are slightly reduced, and the peak shapes are widened; this indicates that the crystalline structure of cellulose can be destroyed and the crystallinity thereof can be reduced at an irradiation dose of 100 kGy.
FIG. 4 is an infrared spectrum before and after irradiation grafting of vinyl acetate on rice straw, wherein a is ungrafted straw and b is irradiated grafted vinyl acetate straw; the straws before and after grafting are 1038cm-1An absorption peak is formed, and the peak belongs to a stretching vibration peak of C-O-C; at 1160cm-1The absorption peak belongs to the bending vibration peak of C-H; in addition, the straw irradiated and grafted with the vinyl acetate is 1730cm-1A new absorption peak appears, and the peak belongs to the stretching vibration absorption peak of the ester group C ═ O of the polyvinyl acetate; infrared characterization demonstrated that polyvinyl acetate had been successfully grafted onto the straw.
FIG. 5 is an X-ray diffraction pattern before and after irradiation grafting of vinyl acetate on rice straw, wherein a is ungrafted straw and b is irradiated grafted vinyl acetate straw; the straw has two crystallization peaks at 16.7 degrees and 22.8 degrees, and the two crystallization peaks belong to characteristic peaks of cellulose 101 and 002 crystal faces; the peak intensity at 16.7 ℃ after irradiation grafting is reduced, indicating that the irradiation grafting affects the crystal structure of the cellulose.
The above figures illustrate the passage of60The Co gamma ray irradiation method can graft vinyl acetate monomer onto rice straw and stalk and at the same time60The Co gamma rays can damage the crystal structure of the straw cellulose.
Detailed Description
Example 1
A method for improving rheological property of wheat straw by irradiation grafting of vinyl acetate comprises the following steps:
(1) mixing 100mL of vinyl acetate and 300mL of methanol, and fully and uniformly stirring to obtain a grafting solution;
(2) soaking 400g of wheat straw in the grafting liquid, introducing high-purity nitrogen for 20min, and sealing60Co gamma-ray irradiation grafting, the total radiation dose is 15kGy, and the radiation dose rate is 1 kGy.h-1；
(3) After the irradiation grafting is finished, benzene is used for washing unreacted monomers, then the benzene is used as a solvent, and the Soxhlet extraction method is adopted for extracting for 24 hours, so that the residual monomers and homopolymers are removed, and the product is dried at the low temperature of 50 ℃ to constant weight.
Example 2
A method for improving rheological property of rice straws by using irradiation grafted vinyl acetate comprises the following steps:
(1) mixing 150mL of vinyl acetate and 600mL of methanol, and fully and uniformly stirring to obtain a grafting solution;
(2) soaking 600g rice straw in grafting liquid, introducing high-purity nitrogen for 20min, and sealing60Co gamma-ray irradiation grafting, the total radiation dose is 20kGy, and the radiation dose rate is 1.5 kGy.h-1；
(3) After the irradiation grafting is finished, benzene is used for washing off unreacted monomers, then the benzene is used as a solvent, and the Soxhlet extraction method is adopted for extracting for 36 hours, so that the residual monomers and homopolymers are removed, and the mixture is dried at the low temperature of 55 ℃ to constant weight.
Example 3
A method for improving rheological property of corn straw by irradiation grafting of vinyl acetate comprises the following steps:
(1) mixing 200mL of vinyl acetate and 1000mL of methanol, and fully and uniformly stirring to obtain a grafting solution;
(2) soaking 1000g rice straw in the grafting liquid, introducing high-purity nitrogen for 25min, and sealing60Co gamma-ray irradiation grafting, the total radiation dose is 22kGy, and the radiation dose rate is 1 kGy.h-1；
(3) And (3) after the irradiation grafting is finished, placing the grafted product for 36h, washing the unreacted monomer by using benzene, extracting for 36h by using benzene as a solvent through a Soxhlet extraction method, removing the residual monomer and homopolymer, and drying at a low temperature of 58 ℃ to constant weight.
Example 4
A method for improving rheological property of sorghum straws by using irradiation grafted vinyl acetate comprises the following steps:
(1) mixing 120mL of vinyl acetate and 600mL of methanol, and fully and uniformly stirring to obtain a grafting solution;
(2) soaking 800g of sorghum straw in the grafting solution, introducing high-purity nitrogen for 20min, and sealing60Co gamma-ray irradiation grafting, the total radiation dose is 18kGy, and the radiation dose rate is 1.5 kGy.h-1；
(3) After the irradiation grafting is finished, unreacted monomers are washed away by using benzene, then the benzene is used as a solvent to extract for 48 hours by adopting a Soxhlet extraction method, and the residual monomers and homopolymers are removed, and the mixture is dried at the low temperature of 52 ℃ to constant weight.
Example 5
A method for improving rheological property of sugarcane straws by using irradiation grafted vinyl acetate comprises the following steps:
(1) mixing 240mL of vinyl acetate and 1200mL of methanol, and fully and uniformly stirring to obtain a grafting solution;
(2) soaking 1800g of sugarcane straws in a grafting solution, introducing high-purity nitrogen for 30min, and sealing60Co gamma-ray irradiation grafting, the total radiation dose is 28kGy, and the radiation dose rate is 2 kGy.h-1；
(3) After the irradiation grafting is finished, benzene is used for washing off unreacted monomers, then the benzene is used as a solvent, and the Soxhlet extraction method is adopted for extracting for 48 hours, so that the residual monomers and homopolymers are removed, and the mixture is dried at the low temperature of 54 ℃ to constant weight.
Example 6
A method for improving rheological property of cotton straws by using irradiation grafted vinyl acetate comprises the following steps:
(1) mixing 300mL of vinyl acetate and 1800mL of methanol, and fully and uniformly stirring to obtain a grafting solution;
(2) soaking 2500g cotton stalk in grafting liquid, introducing high purity nitrogen for 30min, and sealing60Co gamma-ray irradiation grafting, the total radiation dose is 30kGy, and the radiation dose rate is 2 kGy.h-1；
(3) After the irradiation grafting is finished, benzene is used for washing unreacted monomers, then the benzene is used as a solvent, and the Soxhlet extraction method is adopted for extracting for 48 hours, so that the residual monomers and homopolymers are removed, and the product is dried at the low temperature of 60 ℃ to constant weight.
Examples 1-6 changes in straw rheology before and after irradiation grafting are shown in table 1:
TABLE 1 Change in rheological Properties before and after radiation grafting of straw
As can be seen from Table 1, the maximum torque and the balance torque of the irradiated and grafted straws are increased, and the balance time is reduced, which shows that the acting force between the irradiated and grafted straws is enhanced, the rheological property of the straws is improved, and the processing performance of the straws is improved.
Claims (7)
1. A method for improving rheological property of crop straws by irradiation grafting of vinyl acetate is characterized in that vinyl acetate is used as a grafting monomer, and the vinyl acetate and methanol are mixed and stirred to prepare a grafting solution; then soaking the straws in the culture medium, introducing high-purity nitrogen to remove oxygen, and then carrying out irradiation grafting under sealing condition, wherein the irradiation grafting adopts60Co gamma-ray is used as radiation source, the total radiation dose is 15-25kGy, and the radiation dose rate is 1-2 kGy.h-1(ii) a And finally, washing unreacted monomers by using benzene, extracting by using benzene as a solvent by adopting a Soxhlet extraction method, removing the residual monomers and homopolymers, and drying at low temperature to constant weight.
2. The method for improving rheological properties of crop straws by using irradiation grafted vinyl acetate as claimed in claim 1, wherein the crop straws are wheat straws, rice straws, corn straws, sorghum straws, sugarcane straws or cotton straws.
3. The method for improving rheological properties of crop straws by using irradiation grafted vinyl acetate as claimed in claim 1, wherein the mass ratio of vinyl acetate to crop straws is 2-5: 1.
4. the method for improving rheological properties of crop straws by using irradiation grafted vinyl acetate as claimed in claim 1, wherein the volume ratio of vinyl acetate to methanol is 1: 3-9.
5. The method for improving rheological properties of crop straws by using irradiation grafted vinyl acetate as claimed in claim 1, wherein the purity of the high-purity nitrogen is greater than or equal to 99.99%, and the introduction time of the high-purity nitrogen is 20-30 min.
6. The method for improving rheological properties of crop straws by using irradiation grafted vinyl acetate as claimed in claim 1, wherein the extraction time is 24-48 h.
7. The method for improving rheological properties of crop straws by using irradiation grafted vinyl acetate as claimed in claim 1, wherein the drying temperature is 50-60 ℃.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201710283059.XA CN108794702B (en) | 2017-04-26 | 2017-04-26 | Method for improving rheological property of crop straw by irradiation grafting of vinyl acetate |
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| Application Number | Priority Date | Filing Date | Title |
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| CN201710283059.XA CN108794702B (en) | 2017-04-26 | 2017-04-26 | Method for improving rheological property of crop straw by irradiation grafting of vinyl acetate |
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| Publication Number | Publication Date |
|---|---|
| CN108794702A CN108794702A (en) | 2018-11-13 |
| CN108794702B true CN108794702B (en) | 2020-10-16 |
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