CN110684311B - Modified corn straw flame-retardant degradable foam material and preparation method thereof - Google Patents

Abstract

The invention provides a foaming material prepared from modified corn straws. The foaming material prepared from the modified corn straws can be naturally degraded, the problem that the foaming material produced by the corn straws is flammable at present is solved by carrying out esterification graft modification on the corn straws, and the foaming material has good compression resistance and high resilience rate. The modified corn straw foaming material has good comprehensive application performance, can be popularized and applied in the aspects of buffering, shock-proof, fireproof and heat-insulating packaging materials, and has practical significance for comprehensive utilization of agricultural waste straws.

Description

Modified corn straw flame-retardant degradable foam material and preparation method thereof

Technical Field

The invention belongs to the technical field of foaming materials, and particularly relates to modified corn straws, a foaming material prepared from the modified corn straws and a preparation method of the foaming material.

Background

The synthetic foamed plastic has excellent performances of small density, light weight, easy forming, impact resistance and the like, and is widely used in various industries such as packaging, transportation, construction and the like. However, the synthetic foaming material has stable chemical properties, is very difficult to degrade under natural conditions after being discarded, causes serious white pollution, and also causes the consumption of non-renewable resources such as petroleum, natural gas and the like and energy. The recycling and degradation need to consume a large amount of cost, so that the search for environment-friendly green packaging materials becomes a focus of research in various countries.

The straw is rich in elements such as nitrogen, phosphorus, potassium and the like, and organic substances such as cellulose, hemicellulose, lignin and the like, so that the straw is a multipurpose and renewable biological resource. China is a big agricultural country, the grain yield is greatly improved along with the development of agricultural production in China in recent years, the number of straws is increased, and a large amount of surplus straws are left in rural areas by the popularization of firewood and coal saving technology. The data shows that the amount of various straw wastes generated in China is about 7 hundred million tons each year. In view of the practical application of the current straw materials, most of the crop straws all over the world are directly returned to the field or burnt as living energy, a small part of the crop straws are used as building materials or vegetable production covering materials and the like, and a part of the crop straws are used as feeds for herbivorous livestock and raw materials for handicraft industry, but the resource utilization technology of the straws which really form industrialized mass production is not much. This not only causes a great waste of resources, but also causes serious pollution to the atmospheric environment due to the exhaust gas generated during the combustion process. Therefore, how to accelerate the comprehensive utilization of straw materials, realize the recycling and industrialization of the straw, promote the resource conservation, the environmental protection and the income increase of farmers is one of the important subjects in the agricultural field of China at present.

In recent years, the development and research of plant fiber cushioning packaging materials by utilizing crop straws is another research direction of packaging materials. But causes a series of environmental problems during the production and use processes due to the non-degradability and inflammability. The agricultural waste corn straw is a renewable resource which has large total amount, wide source, easy degradation and environmental protection, so the development of the foam material by using the straw as the raw material is an important development direction.

At present, the corn straws are mainly utilized by simply treating the corn straws or directly using the crushed corn straws to be mixed with adhesives, foaming agents and auxiliary agents such as starch and the like for foaming, and the product has low strength, is inflammable and has unsatisfactory mechanical properties and application properties. Therefore, the deep development of the corn straw foam material and the improvement of various performances of the corn straw foam material are problems to be solved urgently.

Disclosure of Invention

The invention provides a modified corn straw and a foam material prepared from the same. The foaming material is a plant fiber foaming material which is cheap, difficult to burn, non-toxic, harmless and naturally degradable, and has better compression resistance, rebound resilience and flame retardance. Has wide application prospect in the aspects of buffering, shock-proof, fire-proof and heat-insulation packaging materials. Meanwhile, agricultural wastes are used as raw materials, the sources are wide, the comprehensive utilization of the straws is realized, the existing foaming material is replaced, and the method has considerable economic benefits, is environment-friendly and saves energy.

The invention also provides modified corn straws capable of preparing the foaming material with good flame retardant property, which are prepared by corn straw esterification and graft modification. The esterified-grafted modified corn straw has flame retardance, can reduce the use of flame retardants or does not add flame retardants, further improves the properties of the material in the aspects of strength, elasticity, color and the like, and widens the application range of the material. The flame retardant is reduced or not added, so that the properties of the material in the aspects of strength, elasticity, color and the like can be improved, and the application range of the material is widened.

The invention also aims to provide a preparation method of the modified corn straw foaming material, which comprises the following steps:

step one, carrying out esterification and graft modification on corn straws to obtain esterified-graft modified corn straws;

in the invention, the preparation of the esterification-graft modified corn straw comprises the following steps:

step 1, pretreating corn straws;

step 2, esterifying the pretreated corn straws to obtain esterified corn straws;

and 3, carrying out graft modification on the esterified corn straws to obtain the esterified-graft modified corn straws.

Step two, preparing foaming slurry by using esterification-grafting modified corn straws as a raw material;

And step three, pouring the foaming slurry into a mold, and carrying out mold pressing and foaming to obtain the corn straw foaming material.

The modified corn foaming material prepared by the method has excellent compression resistance and rebound resilience, can be naturally degraded, and has good flame retardance compared with the straw foaming material prepared by the prior art. And the raw materials are easy to obtain, the problem of effective utilization of domestic large-batch straws can be solved, and the method has double benefits of environmental protection and economy.

The modified corn straw foam material has the following technical effects:

(1) the natural corn straws have poor reaction activity, and active ingredients in the corn straws can be obtained by pretreating the corn straws, and lignin which is difficult to react in the corn straws can be partially removed.

(2) The esterified-grafted modified corn straw obtained by the method is rich in flame-retardant elements and active groups, is a green and environment-friendly plant fiber monomer with low preparation cost, can replace synthetic resin monomers, and can be directly subjected to cross-linking polymerization reaction to prepare a flame-retardant material.

(3) The foaming material prepared by the modified corn straw keeps the natural degradability of the corn straw foaming material, solves the problem that the foaming material produced by the corn straw at present is inflammable through modified grafting, and expands the application field of the material.

(4) Active groups are introduced in the modification process, so that crosslinking copolymerization is realized, and the compressive strength of the material is improved.

(5) The plasticity, the compression resistance and the resilience rate of the corn straw foaming material are improved by using the plasticizer, so that the buffering performance of the material is improved.

(6) The inorganic foaming agent and the organic foaming agent are mixed for foaming, so that the cost is further reduced.

(7) The obtained modified corn straw foaming material has good comprehensive application performance, can be popularized and applied in the aspects of buffering shockproof, fireproof and heat-insulating packaging materials, and has practical significance for comprehensive utilization of agricultural waste straws.

Drawings

FIG. 1 shows a flow chart of the preparation of a modified corn stalk fire-retardant degradable foam material according to the invention;

FIG. 2 shows an infrared spectrum of a corn stover powder and pretreated corn stover according to the present invention;

FIG. 3 shows an infrared spectrum of an esterified corn stover according to the present invention;

FIG. 4 shows an infrared spectrum of an esterified-grafted corn modified straw of the present invention;

FIG. 5 shows an X-ray diffraction pattern of one of corn stover and pretreated corn stover in the present invention;

FIG. 6 shows an X-ray diffraction pattern of an esterified corn stover according to the present invention;

FIG. 7 shows an X-ray diffraction pattern of an esterified-grafted modified corn stover according to the present invention;

FIG. 8 shows a thermogram of corn stover in example 1, pretreated corn stover in example 1, esterified corn stover prepared in example 2, esterified-grafted modified corn stover prepared in example 2 of the present invention;

FIG. 9a shows an SEM image of corn stover in example 1 of the present invention; FIG. 9b shows an SEM image of pre-treated corn stover obtained in example 1 of the present invention; FIG. 9c shows an SEM image of esterified corn stover made according to example 2 of the present invention; FIG. 9d shows an SEM image of esterified-grafted modified corn stover made according to example 2 of the present invention; FIG. 9e is an SEM image of a modified corn stalk fire retardant degradable foam material prepared in example 3 of the invention;

FIG. 10 is a graph showing the degradation effect of the modified corn stalk fire retardant and degradable foam material prepared in example 3 of the invention;

FIG. 11 is a graph showing the effect of the amount of modified corn stover on the compression resistance and resilience of a modified corn stover flame retardant degradable foam material according to the present invention;

FIG. 12 is a graph showing the effect of the amount of the cross-linking agent acrylamide on the compression resistance and the resilience of the modified corn stalk flame-retardant degradable foam material in the invention;

FIG. 13 is a graph showing the influence of the amount of the organic foaming agent and the initiator azobisisobutyronitrile on the compressive capacity and the resilience of the modified corn stalk flame-retardant degradable foam material;

FIG. 14 is a graph showing the influence of the amount of water as the solvent and inorganic foaming agent on the compression resistance and the resilience of the modified corn stalk flame-retardant degradable foam material.

Detailed Description

The present invention will now be described in detail by way of specific embodiments, and features and advantages of the present invention will become more apparent and apparent from the following description.

In order to improve various performances of the existing corn straw foaming material and break through the limitation of the use of the existing corn straw foaming material, the invention provides a modified corn straw foaming material with good comprehensive performance and a preparation method of the foaming material. The specific preparation process comprises the following steps.

Step one, carrying out esterification and graft modification on corn straws to obtain the esterified-graft modified corn straws.

The invention provides modified corn straws capable of preparing a foaming material with good flame retardant property, which are prepared by corn straw esterification and graft modification, wherein the esterification-graft modification of the corn straws comprises the following steps:

Step 1, pretreating corn straws;

step 2, esterifying the pretreated corn straws to obtain esterified corn straws;

and 3, carrying out graft modification on the esterified corn straws to obtain the esterified-graft modified corn straws.

First, corn stover is pretreated.

The pretreatment process comprises the steps of washing with clean water, drying, crushing and screening, soaking in alkali liquor, treating at high temperature, washing after treatment and drying after treatment.

Firstly, the corn straws are dried and crushed after being washed by clean water, and then the corn straws are screened by a standard sieve to obtain corn straw powder.

Mixing the corn stalk powder with a proper amount of alkaline solution, and carrying out reflux reaction at constant temperature for several hours.

And after the reaction is finished, cooling the reaction solution to room temperature, carrying out suction filtration, washing with deionized water, repeatedly carrying out leaching with absolute ethyl alcohol, and carrying out vacuum drying to obtain the pretreated corn straw.

The mesh number of the standard sieve is 40-150 meshes, preferably 60-120 meshes, and more preferably 80-110 meshes.

Wherein the alkaline solution used for soaking is a sodium hydroxide or potassium hydroxide aqueous solution, or a mixed aqueous solution of sodium hydroxide and anhydrous sodium sulfite, preferably a mixed aqueous solution of sodium hydroxide and anhydrous sodium sulfite, and the molar ratio of sodium hydroxide to anhydrous sodium sulfite is 2: 1-7: 1, preferably 3: 1-6: 1, and more preferably 5: 1. The concentration of the sodium hydroxide solution is 0.1-10 mol/L, preferably 0.5-5 mol/L, and more preferably 1-3 mol/L.

The constant temperature reflux reaction is carried out under the condition of slight boiling of the solution, and the reaction time is 2 to 15 hours, preferably 4 to 12 hours, and more preferably 6 to 10 hours.

After the reaction is finished, washing the reaction product to be neutral by using deionized water, and leaching by using absolute ethyl alcohol for 3-5 times; the vacuum drying temperature is 60-90 ℃, and the vacuum drying time is 2-15 h, preferably 4-10 h, and more preferably 5-8 h.

The main components of the corn straw are cellulose, hemicellulose and lignin. During the modification reaction process, the lignin has low reactivity and needs to be removed as much as possible during the pretreatment reaction process.

In the pretreatment process, an alkaline solution added with sodium sulfite is used, so that lignin in the decomposed corn straws can be better dissolved in the alkaline solution, and then removed along with the solvent in the suction filtration process.

Analyzing the infrared spectrograms of the corn straw and the pretreated corn straw at 3350-3450 cm^-1The characteristic absorption peak is a hydroxyl-OH stretching vibration peak, can be used for representing the corn straws, and in an infrared spectrogram of the pretreated corn straws, the lignin characteristic peak is about 1730cm^-1An ester group stretching vibration peak of 1400-1600 cm^-1About 1300cm at the stretching vibration peak of benzene ring C ═ C skeleton ^-1The C-O stretching vibration peak of syringyl is about 1030cm^-1The bending vibration peak of the C-H plane of the guaiacol is weakened or disappeared. Indicating that the alkali treatment dissolved or removed a portion of the lignin in the corn stover. In addition, the X-ray diffraction analysis of the original corn stalks and the pretreated corn stalks shows that the diffraction peak of the pretreated corn stalks is widened, and a new diffraction peak also appears. From the above characterization, it can be seen that alkali treatment opens ester bonds unstable to alkali in molecules, partial ester bonds disappear, partial intermolecular hydrogen bonds are broken, and the form and structure of cellulose are changed.

Secondly, esterifying the pretreated corn straws to obtain esterified corn straws.

The corn stalks mainly contain natural macromolecules such as cellulose, hemicellulose, lignin and the like. The hydroxyl on the natural macromolecular sugar ring can react with various organic acid derivatives such as carboxylic acid, acid anhydride, acyl chloride and the like, and a denser nitrogen-containing structure is introduced, so that the corn straw has flame retardant property.

In the invention, the corn stalks are preferably esterified and pretreated by imidazole acyl chloride compounds, so that acyl chloride compounds and the pretreated corn stalks are dissolved in a solvent, and then an acid-binding agent and a catalyst are added for heating reaction to prepare the esterified corn stalks.

The imidazole acyl chloride can be imidazole formyl chloride, imidazole acetyl chloride and imidazole propionyl chloride, and is preferably imidazole formyl chloride.

The imidazole formyl chloride and hydroxyl in the corn straws are subjected to esterification reaction, so that the corn straws are provided with imidazole-4-methyl ester groups, and the esterified corn straws are generated. Meanwhile, the imidazole-4-carbomethoxy is a grafting modified active group of the corn straw.

The imidazole formyl chloride is prepared by synthesizing imidazole-4-formic acid and a halogenating agent: dissolving imidazole-4-formic acid in equal amount of halogenating agent, refluxing and reacting for 3-8 h at 50-80 ℃, and performing rotary evaporation to obtain the product imidazole-4-formyl chloride.

The halogenating agent adopts thionyl chloride or phosphorus pentachloride, and preferably thionyl chloride; the molar ratio of the imidazole formic acid to the thionyl chloride is 1 (1-1.8), preferably 1 (1.1-1.5), and more preferably 1 (1.2-1.4).

The esterification reaction is carried out in a solvent, which may be an amide such as N, N-dimethylformamide, N-methylformamide, N-methylacetamide, N-diethylformamide, N-dimethylacetamide; halogenated hydrocarbons such as dichloroethane, dichloromethane; aromatic hydrocarbons such as benzene, toluene; pyridine derivative compounds such as 3-methylpyridine, 4-dimethylaminopyridine and pyridine are preferably amides, and more preferably N, N-dimethylformamide. The pretreated corn stalks are dissolved in a solvent, and particularly can be converted into esterification raw materials which have certain activity and can be chemically modified under the action of N, N-dimethylformamide.

In the preferred experimental scheme of the invention, the acid-binding agent is an organic base, such as triethylamine, tetramethylethylenediamine, 4-dimethylaminopyridine, n-butyllithium, potassium tert-butoxide and the like, or an inorganic base, such as sodium acetate, sodium carbonate, potassium carbonate and sodium hydroxide, preferably an organic base, and more preferably 4-dimethylaminopyridine.

Hydrogen chloride is generated in the esterification reaction process of the pretreated corn straws and acyl chloride, and an acid-binding agent can be used for effectively absorbing acidic substances in a reaction system, so that the reaction is favorably carried out. Pyridine is used as an acid-binding agent and can also be used as a catalyst in the reaction. Meanwhile, due to the existence of the acid binding agent, the pretreated corn straws can be promoted to better enter a reaction solution.

The catalyst is alkaline catalyst, and can be pyridine compound, such as 4-dimethylamino pyridine, pyridine; or basic amine compounds such as triethylamine, dimethylformamide, N-dimethylaniline; or quinolines, such as quinoline and isoquinoline, preferably pyridines and amines, more preferably 4-dimethylaminopyridine.

In the invention, the molar ratio of acyl chloride to acid binding agent is 1 (0.6-1.5), preferably 1 (0.8-1.2), and more preferably 1: 1; the molar ratio of the acyl chloride to the catalyst is (2-50): 1, preferably (5-30): 1, and more preferably (8-15): 1.

The mass concentration of the pretreated corn stalks in the solvent is (0.001-0.05) wt%, preferably (0.008-0.03) wt%, and more preferably (0.01-0.015) wt%.

The mass ratio of the pretreated corn straws to the acyl chloride is 1 (0.1-8.0), preferably 1 (0.5-5.0), and more preferably 1 (1.0-3.5).

The invention is preferably carried out in a magnetically stirred, thermostated oil bath.

The reaction temperature is 15-80 ℃, preferably 25-70 ℃, and more preferably 35-60 ℃.

The reaction time is 1-12 h, preferably 2-10 h, and more preferably 4-8 h.

The stirring speed is 40 to 200r/min, preferably 60 to 150r/min, and more preferably 80 to 100 r/min.

And after the reaction is finished, carrying out suction filtration on the reaction product, washing with deionized water, carrying out suction filtration, washing with absolute ethyl alcohol, carrying out suction filtration, and carrying out vacuum drying to obtain the esterified corn straw.

The water washing and the absolute ethyl alcohol washing are respectively carried out for 3-5 times. The drying temperature of the vacuum drying oven is 60-120 ℃; the drying time is 1 to 10 hours, preferably 2 to 8 hours, and more preferably 3 to 7 hours.

The corn stalks react with acyl chloride to obtain esterified corn stalks, and meanwhile, molecular chains are provided with imidazole groups, and nitrogen atoms in the imidazole groups enable the corn stalks to have grafting modification activity.

The esterified corn stalks were analyzed by infrared analysis to about 3440cm^-1The stretching vibration peak of the hydroxyl is weakened, which is caused by the reduction of the hydroxyl due to the esterification of the hydroxyl in the cellulose of the pretreated corn stalks. 1740cm^-1In the vicinity of which ester groups-CO are presentOR sharp expansion and contraction vibration strong characteristic absorption peak of 1250cm^-1Around the ester group, an antisymmetric stretching vibration peak of 1050cm appears^-1The left and the right are symmetric stretching vibration peaks of the ester group; 1650cm^-1Around the C-C stretching vibration peak at 1550cm^-1And 1450cm^-1Around the imidazole ring C ═ N stretching vibration peak, 1160cm^-1And 1080cm^-1And an imidazole ring C-H bending vibration peak appears nearby.

From X-ray diffraction analysis, a new diffraction peak appears after esterification, which indicates that new groups are introduced on the corn straws after esterification.

And grafting modification is carried out on the esterified corn straws to obtain the esterified-grafted modified corn straws.

The invention adopts active alkene monomers, such as halogenated olefin, to graft and modify the esterified corn straws. Adding the corn stalk esterified substance into halogenated olefin, refluxing at constant temperature in nitrogen atmosphere for grafting reaction, and performing rotary evaporation to remove redundant halogenated olefin after the reaction is finished. The halogenated olefin may be a chlorinated or brominated olefin, preferably vinyl chloride, chloropropene, chlorobutene, bromoethylene, bromopropylene or bromobutene, more preferably chloropropene or bromopropylene.

The mass ratio of the esterified corn straws to the halogenated olefin is (1.0-6.5): 1, preferably (1.5-4.0): 1, and more preferably (2.0-2.8): 1. In the grafting reaction process, excessive chloropropene can ensure that the esterified corn straw is reacted more completely, and the post-treatment process can be simplified.

When the reaction is carried out, the magnetic stirring speed is 30-120 r/min, preferably 40-100 r/min, and more preferably 50-80 r/min.

When the reaction is carried out, the heating temperature is 40-120 ℃, preferably 50-90 ℃, and more preferably 60-75 ℃.

The reaction time is 10-50 h, preferably 15-40 h, and more preferably 20-30 h. And after the reaction is finished, obtaining a reaction solution, removing redundant chloropropene by rotary evaporation to obtain the esterified-grafted modified corn straw rich in nitrogen and chlorine elements and imidazole groups, and grafting chloropropene onto an imidazole ring through losing chlorine atoms so that the esterified-grafted modified corn straw has a C ═ C double bond group.

The esterification-graft modification corn straw has flame retardance, because the esterification-graft modification corn straw is a nitrogenous organic matter, forms nitrogen, water and other incombustibles after being heated and decomposed to block oxygen, absorbs a large amount of heat during decomposition, reduces the surface temperature of the material and further achieves the flame retardant effect.

The grafting reaction is a quaternization reaction, and chloropropene enters the corn straws in a branched chain manner. In the reaction process, chlorine atoms of chloropropene are lost and nitrogen atoms in imidazole groups are attacked, so that the whole molecular positive charge and chloride ions form hydrochloride with polysaccharide ester groups.

Compared with the infrared spectrogram of esterified-grafted modified corn straw obtained by chloropropene graft modification, the infrared spectrogram of esterified-grafted modified corn straw is 2850-2950 cm^-1The stretching vibration peak of the methyl or methylene is obviously enhanced, 1630cm^-1The expansion vibration peak of the C ═ C double bond is obviously enhanced, which indicates that chloropropene is successfully grafted to the imidazole ring.

The crystal forms of the graft and the esterified substance are basically consistent from X-ray diffraction patterns of esterified-graft modified corn straws and esterified corn straws obtained by chloropropene graft modification, which shows that the graft mainly occurs on imidazole rings, and the influence on the crystallinity of the corn straws is small because allyl is introduced on imidazole nitrogen atoms.

And step two, preparing the foaming slurry by using the esterified-grafted modified corn straw as a raw material.

Before preparing the foaming material, the ingredients are required to be firstly mixed, the esterification-graft modification corn straw, the solvent, the cross-linking agent, the foaming agent, the initiator and other components are mixed with each other, and the mixture is processed and formed after being uniformly stirred.

In the material mixing process, firstly, adding the cross-linking agent into a solvent, and magnetically stirring until the cross-linking agent is completely dissolved; further, adding a foaming agent and an initiator, and uniformly stirring; furthermore, adding the esterified-grafted modified corn straw and the plasticizer, and uniformly stirring to be pasty. The feeding sequence in the material mixing process is matched with the physical properties and the chemical reaction sequence of the system of each component, and the feeding sequence in the invention can enable the system to form more uniform paste, thereby being beneficial to the next crosslinking foaming process.

The cross-linking agent used in the foaming process of the present invention may be amides such as acrylamide, N-methylol acrylamide, diacetone acrylamide, dicarboxylic acids such as succinic anhydride, succinyl chloride, dialdehydes such as glyoxal, malondialdehyde, succindialdehyde, preferably amides and dialdehydes, more preferably acrylamide.

The solvent used in the foaming process may be an aqueous solvent, an alcoholic solvent such as ethanol, methanol, propanol, or a phenolic solvent such as phenol, o-cresol, preferably water or ethanol, more preferably water, which is at least three-stage laboratory water, i.e., having a conductivity of 0.5mS/m or less at 25 ℃.

The foaming agent can be one or two of an organic foaming agent and an inorganic foaming agent, and can also be foamed by using inert gas or low-boiling-point liquid. The organic foaming agent may be an azo compound, a sulfonylhydrazide compound or a nitroso compound, and the inorganic foaming agent may be sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium carbonate, etc., preferably an azo compound and sodium bicarbonate, more preferably an azo compound.

The plasticizer can be one or two of phthalate esters, fatty acid esters, phosphate esters, epoxy esters, polyol esters and camphor, preferably phthalate esters and camphor, and more preferably dioctyl phthalate in phthalate esters.

The invention can play the roles of foaming and plasticizing while taking water as a solvent. Under the high-temperature and high-pressure environment, the water vapor in the matrix expands rapidly to drive the matrix to form a loose porous structure to complete the foaming process. In addition, the esterification-grafting modified corn straw contains a certain amount of free water, so that intermolecular force can be weakened, the mobility of polymer molecular chains is increased, and the crystallinity of the polymer molecular chains is reduced, so that the elasticity is increased, and the function of a plasticizer is achieved.

The initiator may be selected from azo initiators such as azobisisobutyronitrile, azobisisoheptonitrile, azobisformamide, organic peroxy initiators such as dialkyl peroxide, dibenzoyl peroxide, inorganic peroxy initiators such as potassium persulfate, ammonium persulfate, preferably azobisisobutyronitrile or persulfate, more preferably azobisisobutyronitrile. The azobisisobutyronitrile simultaneously plays the role of an initiator and an organic foaming agent in the foaming process.

The mass ratio of the esterification-grafting modified corn straw, the acrylamide and the water in the foaming slurry is (1-25): 0.5-50): 1-50), preferably (2-20): 1-40): 2-40), more preferably (5-12.5): 2.5-20): 5-20); the mass ratio of the initiator to the esterified-grafted modified corn straw is (0-1) to (1-15), preferably 1 (1.5-12), and more preferably 1 (2.5-7); the mass ratio of the plasticizer to the modified corn straws is 1 (1-20), preferably 1 (2-18), and more preferably 1 (5-12.5).

The components of the foaming slurry are mixed at the temperature of 20-40 ℃, and the stirring speed is 20-100 r/min, preferably 25-80 r/min, and more preferably 30-60 r/min.

And step three, pouring the foaming slurry into a mold, and carrying out mold pressing foaming to prepare the foaming material.

The invention uses steam mould pressing to foam, fills the foaming slurry into the mould cavity, closes the mould and compresses the mould to prevent the mould from being pushed open in the foaming process. Heating steam enters the cavity through a small hole or a narrow slot on the inner wall surface of the die, a foaming agent in the cavity is evaporated into gas and steam to permeate into the cavity, the cavity is further expanded to increase the volume, the expanded slurry is filled in the cavity and is sintered into a whole due to the limitation of the space of the cavity, and the die is opened and taken out after cooling and shaping.

And carrying out die pressing foaming under a heating condition to obtain the modified corn straw flame-retardant degradable foaming material. The mould pressing temperature is 100-240 ℃, preferably 120-200 ℃, and more preferably 140-180 ℃; the mould pressing time is 1-12 h, preferably 2-8 h, and more preferably 4-6 h.

In the foaming process, if the content of the foaming agent is too low, the gas generation is insufficient, the foaming speed is slow, the foaming is insufficient, the foam holes are rare, the foam holes are uneven, the prepared foaming material is compact and hard, and the compression resistance and the rebound resilience are poor; if the amount of the foaming agent is too much, the foaming speed is high, cells are enlarged and even connected into large cells, and the pressure resistance and the rebound resilience are reduced.

The modified corn straw foaming material can be prepared by the experimental scheme. The invention provides a modified corn straw foaming material with good flame retardance, excellent compression resistance and high resilience, which greatly expands the use environment and application field of the corn straw foaming material, is beneficial to forming an agricultural industrial chain and has great economic benefit.

Examples

Example 1

Preparing pretreated corn straws:

washing and drying the corn straw with clear water, crushing the corn straw, and screening the crushed corn straw through a standard sieve of 100 meshes to obtain corn straw powder. Adding corn stalk powder into a mixed solution of a proper amount of 2.5mol/L sodium hydroxide solution and 0.4mol/L anhydrous sodium sulfite solution, wherein the molar ratio of the sodium hydroxide to the anhydrous sodium sulfite is 5:1, boiling, and refluxing for 7 h.

After the reaction is finished, cooling the reaction solution to room temperature, carrying out suction filtration on the reaction solution, repeatedly carrying out deionized water washing and suction filtration for 5 times, then carrying out drip washing by using absolute ethyl alcohol, and carrying out vacuum drying for 4 hours at the temperature of 80 ℃ to obtain the pretreated corn straw.

Example 2

Preparing esterified-grafted modified corn straws:

adding 1mol of imidazole formic acid into 1.2mol of thionyl chloride while stirring, and carrying out reflux reaction for 5h at the temperature of 60 ℃ to obtain imidazole formyl chloride.

Weighing 3.9g of the pretreated corn straw obtained in example 1, 9.5g of imidazole carbonyl chloride and 8g of triethylamine in a reaction kettle, adding 300mL of N, N-dimethylformamide, heating to 40 ℃, uniformly stirring, adding 0.5g of 4-dimethylaminopyridine, heating to 55 ℃, carrying out esterification reaction for 6 hours, carrying out suction filtration after the reaction is finished, washing with deionized water and absolute ethyl alcohol sequentially for three times, drying in a vacuum drying oven at 80 ℃ for 3 hours to obtain esterified corn straw, and placing in a dryer for later use.

And adding the product into 2.6g of chloropropene, magnetically stirring, heating to 65 ℃ for grafting reaction, performing reaction for 24 hours, performing rotary evaporation to remove excessive chloropropene, and drying in an oven to obtain the esterification-graft modified corn straw with the solvent removed.

Example 3

Preparing foaming slurry and carrying out mould pressing foaming: adding 19.1g of acrylamide into deionized water with equal mass, and magnetically stirring until the acrylamide is completely dissolved; adding 1.25g of azobisisobutyronitrile, and stirring uniformly; adding 9.55g of esterified-grafted modified corn straw and 1g of dioctyl phthalate, and uniformly stirring to be pasty; pouring the paste into a mold, cross-linking and blending, and molding for 4h at the molding temperature of 150 ℃ for foaming to obtain the modified corn straw flame-retardant degradable foam material.

Example 4

Keeping the quality of other materials in example 3 unchanged, and changing the use amounts of the esterification-graft modification corn straws to 5.0g, 7.5g, 10.0g and 12.5g to prepare a foaming material of group 1;

keeping the quality of other materials in example 3 unchanged, and changing the dosage of acrylamide into 2.5g, 5.0g, 10.0g, 15.0g and 20.0g to prepare a group 2 foaming material;

keeping the quality of other materials in example 3 unchanged, and changing the dosage of azobisisobutyronitrile into 0.0g, 0.25g, 0.5g, 1.0g and 2.0g to prepare a group 3 foaming material;

A group 4 foam was prepared by changing the amount of water used to 5.0g, 10.0g, 15.0g, 20.0g, while keeping the quality of the other materials of example 3 unchanged.

Examples of the experiments

Experimental example 1

Infrared spectroscopic analysis was performed on the corn stover powder used in example 1 and the pretreated corn stover prepared, and the esterified corn stover and the esterified-graft modified corn stover prepared in example 2. FIG. 2 is an infrared spectrum of corn stover powder used in example 1 and pretreated corn stover prepared, FIG. 3 is an infrared spectrum of esterified corn stover prepared in example 2, and FIG. 4 is an infrared spectrum of esterified-grafted corn stover prepared in example 2.

In the figures 2, 3 and 4, the length of the groove is 3350-3450 cm^-1The range of (1) shows a characteristic absorption peak of the corn straw, namely a hydroxyl-OH stretching vibration peak, of 2850-2950 cm^-1Where a stretching vibration peak of methyl or methylene appears. As can be seen from FIG. 2, the characteristic peak 1730cm of lignin after pretreatment^-1An ester group stretching vibration peak of 1400-1600 cm^-1About 1300cm at the stretching vibration peak of benzene ring C ═ C skeleton^-1C-O stretching vibration peak of lilac base, 1030cm^-1The C-H plane bending vibration peak of the guaiacol group is weakened or disappeared. The results show that the alkali treatment dissolved or removed a portion of the lignin in the corn stover. This is because part of ester bonds in the molecule are unstable in an alkaline environment, and the ester bonds are broken after the alkali treatment, and part of the intermolecular hydrogen bonds are broken, whereby the form and structure of cellulose are changed.

3400cm in FIGS. 3 and 4^-1The stretching vibration peak of the hydroxyl is weakened, because the hydroxyl on the corn straw fiber is subjected to esterification reaction, so that the hydroxyl is reduced, and the vibration peak of the hydroxyl is weakened; 1740cm^-1A sharp characteristic absorption peak of ester group-COO-stretching vibration intensity, 1250cm appears nearby^-1The left and right are antisymmetric stretching vibration peak of ester group, 1050cm^-1The left and the right are symmetric stretching vibration peaks of the ester group; 1650cm^-1The left and the right are C-telescopic vibration peaks on imidazole rings and grafted chains, 1550cm^-1And 1450cm^-1The left and the right are imidazole ring C ═ N stretching vibration peak, 1080cm^-1And imidazole ring C-H bending vibration peaks appear on the left and right. 1630cm in FIG. 4^-1The stretching vibration peaks of the left and right C ═ C double bonds are obviously enhanced. The esterification and the grafting reaction of the corn straws, the imidazole formyl chloride and the chloropropene are illustrated.

Experimental example 2

X-ray diffraction tests (XRD) were performed on the corn stover in example 1, the pretreated corn stover obtained in example 1, the esterified corn stover obtained in example 2, and the esterified-graft modified corn stover obtained in example 2. Fig. 5 is an XRD spectrum of corn stover and pretreated corn stover, fig. 6 is an XRD spectrum of esterified corn stover, and fig. 7 is an XRD spectrum of esterified-grafted modified corn stover. Fig. 5 shows that the corn stover and the pretreated corn stover both have a strong diffraction characteristic peak at about 2 θ 23 °, but the fibers in the pretreated corn stover after the alkali treatment swell, the cellulose structure is destroyed, and the morphology and crystallinity change, so that the diffraction peak at 2 θ 23 ° widens, the intensity decreases, and a new weak diffraction peak at 2 θ 29 ° appears.

As can be seen from fig. 6, a new diffraction peak appears at a position of 19 ° after esterification, and diffraction peaks at positions of 23 ° and 29 ° after 2 θ is esterified are significantly enhanced, which indicates that new groups are introduced on the corn stalks after esterification, so that the diffraction angles and intensities of the diffraction peaks are changed, and the crystallinity is significantly changed, which is beneficial to subsequent further graft crosslinking reaction.

As can be seen from FIG. 7, the crystal forms of the esterified-grafted modified corn stover and the esterified corn stover are substantially consistent, which indicates that grafting mainly occurs on imidazole rings, and allyl groups are introduced on imidazole nitrogen atoms, so that the influence on the crystallinity of the corn stover is small.

Experimental example 3

Thermogravimetric analysis was performed on the corn stover in example 1, the pretreated corn stover obtained in example 1, the esterified corn stover obtained in example 2, and the esterified-grafted modified corn stover obtained in example 2, and the thermogravimetric characterization results are shown in fig. 8. The corn straw is in stage weight loss, which is divided into four stages, including drying, free water loss, structural water loss, hydroxyl loss and the like, and as can be seen from the TG curve of figure 8, the main weight loss is 255-350 ℃, the mass loss is about 65 percent, and the weight loss is almost complete at 480 ℃; the initial weight loss temperature of the pretreated corn straws is increased to 300 ℃ and is constant when the temperature is 480 ℃; the weight loss of the esterified corn straws and the esterified-grafted modified corn straws is mainly between 250 and 350 ℃, the mass loss is about 60 percent, but the weight loss is complete only at about 570 ℃, and the modification is successful because new groups are introduced into the esterification and the grafting from the side.

Experimental example 4

Scanning Electron Microscope (SEM) tests were performed on corn stover in example 1, pretreated corn stover obtained in example 1, esterified corn stover obtained in example 2, and esterified-grafted modified corn stover obtained in example 2, with SEM images as shown in fig. 9a, 9b, 9c, and 9 d.

As can be seen from FIG. 9a, the untreated corn stover has a compact structure, uniform and regular arrangement of plant tissues, small gaps, and high crystallinity of cellulose molecules.

As shown in FIG. 9b, after the corn stalks are subjected to alkali treatment, the compact surface structure is damaged, the appearance is changed, the original smooth surface shows stripping signs and obvious cracks, part of lignin and hemicellulose are removed to enable the surface to become loose, the coating effect of the lignin is damaged, and the internal active groups are exposed, so that the reaction activity of the corn stalks is improved.

Fig. 9c and 9d show that, after a new group is introduced on the corn stalks by esterification and grafting, the new group is attached to the surfaces of the corn stalk fibers, so that the peeled surfaces and cracks of the pretreatment are restored again, and the fiber crystal monofilaments with regular shapes are formed, so that the structure is looser, and the crosslinking polymerization is further facilitated.

Scanning electron microscope tests are performed on the modified corn stalk flame-retardant degradable foam material prepared in example 3, and the results are shown in fig. 9 e. As can be seen from fig. 9e, the fibers of the modified corn stalks are crossed with each other under the action of the cross-linking agent to form a three-dimensional network structure, and the structure enables the foam material to have certain mechanical strength and resilience; after heating, pressing and foaming, gas escapes to form a plurality of small holes wrapped by fibers, the inner part is fully foamed, the foam holes are uniformly distributed, the foam walls are continuous, and the modification has a greater effect on the mechanical properties of the corn straw material, such as the compressive strength, the rebound rate and the like.

Experimental example 5

The degradation performance of the modified corn stalk flame-retardant degradable foam material prepared in example 3 is tested, and photos of sample blocks before and after degradation are shown in fig. 10. The experiment adopts a field environment test method, the modified corn straw flame-retardant foaming material sample soil is buried in soil with the depth of 30cm, and the degradation effect of the sample is observed after one month. As can be seen from FIG. 10, after the modified corn stalk flame-retardant foam material sample is buried for 30 days, the sample material is degraded to a great extent, only a small part of the sample material remains (the white part in the black frame in the right picture of FIG. 10 is the residual sample), and earthworms inhabit around the soil. The prepared modified corn straw flame-retardant foaming material has good biodegradability, is non-toxic and harmless, and the degraded organic components can provide certain nutrients for microorganisms in soil, so that the degradable characteristic of the plant fiber material is met, and the modified corn straw flame-retardant foaming material belongs to an environment-friendly pollution-free material.

Experimental example 6

The influence of the mechanical properties of the four groups of modified corn straw flame-retardant degradable foam materials prepared in example 4 is tested. FIG. 11 is a graph showing the change of the impact of the modified corn stalk dosage on the compression resistance and the resilience of the modified corn stalk fire-retardant degradable foam material of example 4 in group 1; FIG. 12 is a graph showing the change of the impact of the amount of acrylamide as a crosslinking agent on the compression resistance and the resilience of the modified cornstalk flame retardant and degradable foam material in example 2; FIG. 13 is a graph showing the change of the impact of changing the amount of azobisisobutyronitrile used on the compression resistance and the resilience of the modified cornstalk flame retardant degradable foam material in example 3; FIG. 14 is a graph showing the change of the impact of the 4 groups of foams in example 4, namely the change of the amount of water on the compression resistance and the resilience of the modified corn stalk flame retardant degradable foam.

The apparent density is tested according to the requirement of a static compression test method of the buffer material for GB/T8168-2008 packaging; the compression resistance is tested according to the requirement of the GB/T8168-2008 packaging buffer material static compression test method; rebound performance according to the requirements of the test method of creep property of GB/T14745-.

As can be seen from fig. 11, fig. 12, fig. 13 and fig. 14, the amount of the modified corn stalks, the amount of the cross-linking agent acrylamide, the amount of the organic foaming agent and the initiator azobisisobutyronitrile, and the amount of the solvent and inorganic foaming agent water all have certain effects on the compression resistance and the resilience of the modified corn stalk flame-retardant degradable foaming material, wherein the contribution of the cross-linking agent acrylamide to the compression resistance is larger than that of other components, and the effect of the foaming agent on the resilience is more significant than that of other components.

As can be seen from FIG. 11, the compression resistance is rapidly increased along with the increase of the amount of the modified corn stalks, when the amount of the modified corn stalks is changed from 5g to 7.5g, the active groups on the modified corn stalks are effectively crosslinked and polymerized under the action of the crosslinking agent to form a three-dimensional space network structure with a certain mechanical strength, so that the compression resistance is increased to 17.7MPa, the resilience is also good, and the resilience rate reaches 38%; the use amount of the modified corn straws is continuously increased, the excessive modified corn straws only play a role in filling, the formability is deteriorated, and the pressure resistance and the resilience performance are slowly reduced along with the excessive modified corn straws.

As can be seen from FIG. 12, the effect of the amount of acrylamide as a crosslinking agent on the compressive strength was significant. When the dosage of the acrylamide is increased to 15.0g, the modified corn straws and the cross-linking agent are subjected to full cross-linking reaction, the compressive property is quickly increased to 38MPa, the compressive strength is highest, the foaming ratio is 1.27, and the apparent density is 0.43g/cm³And the good rebound rate is ensured to be 38%.

As can be seen from FIGS. 13 and 14, the amounts of azobisisobutyronitrile and water used as blowing agents were limited, and when the amount of azobisisobutyronitrile was 1.0g and the amount of water was 15.0g, the compression resistance and the rebound resilience were the best. The content of the foaming agent is too low, the gas production is insufficient, the foaming speed is slow, the foaming is insufficient, the foam holes are rare, the foam holes are uneven, the prepared foaming material is compact and hard, and the compression resistance and the rebound resilience are poor; too much foaming agent is used, the foaming speed is high, the cells are enlarged and even connected into large cells, and the compression resistance and the rebound resilience are reduced. The inorganic foaming agent water is simultaneously used as a solvent, the dosage of the inorganic foaming agent water is far larger than that of the organic foaming agent water, but the rebound rate is rapidly reduced due to excessive water.

Experimental example 7

The flame retardant performance of the modified corn stalk flame retardant degradable foam material prepared in example 3 was tested. According to the UL94 material combustion test standard, a comprehensive flame retardant property tester is adopted to test the vertical combustion performance and the horizontal combustion performance. The vertical combustion with flame combustion time is 6s, and the flameless combustion time is 0 s; the horizontal combustion flame combustion time is 2s, the flameless combustion time is 0s, the flame retardant grade is V-0 grade, and the prepared modified corn straw flame retardant degradable foaming material has good flame retardant property.

The invention has been described in detail with reference to specific embodiments and/or illustrative examples and the accompanying drawings, which, however, should not be construed as limiting the invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (10)

1. A corn stalk foaming material is characterized in that the material is prepared by esterification and graft modification of corn stalk, and the preparation comprises the following steps;

step one, carrying out esterification and graft modification on corn straws to obtain esterified-graft modified corn straws; drying and crushing the corn straws washed by clear water, mixing the corn straws with an alkaline solution, carrying out constant-temperature reflux reaction, esterifying the obtained pretreated corn straws with imidazole acyl chloride compounds, and carrying out graft modification on the esterified corn straws by using halogenated olefin;

the imidazole acyl chloride compound is selected from imidazole formyl chloride, imidazole acetyl chloride and imidazole propionyl chloride; the halogenated olefin is chloroethylene, chloropropene, chlorobutene, vinyl bromide, bromopropylene or bromobutene;

Step two, preparing foaming slurry by using esterification-grafting modified corn straws as a raw material;

mixing esterified-grafted modified corn straws, a solvent, a cross-linking agent, a foaming agent, an initiator and a plasticizer; the cross-linking agent is amide or binary aldehyde; the solvent is water; the initiator is an azo initiator, an organic peroxide initiator or an inorganic peroxide initiator; the foaming agent is an azo compound; the plasticizer is phthalate and camphor; the mass ratio of the initiator to the esterified-grafted modified corn straw is (0-1) to (1-15); the mass ratio of the plasticizer to the modified corn straw is 1 (1-20);

pouring the foaming slurry into a mold, and carrying out mold pressing foaming under a heating condition to obtain a corn straw foaming material; the mold pressing temperature is 100-240 ℃.

2. The preparation method of the corn straw foam material as claimed in claim 1, which is characterized by comprising the following steps:

step one, carrying out esterification and graft modification on corn straws to obtain esterified-graft modified corn straws;

step two, preparing foaming slurry by using esterification-grafting modified corn straws as a raw material; mixing esterified-grafted modified corn straws with a solvent, a cross-linking agent, a foaming agent, an initiator and a plasticizer, and uniformly stirring;

And step three, pouring the foaming slurry into a mold, and carrying out mold pressing and foaming to obtain the corn straw foaming material.

3. The method of claim 2, wherein step one comprises the steps of:

step 1, pretreating corn straws;

step 2, esterifying the pretreated corn straws to obtain esterified corn straws;

and 3, carrying out graft modification on the esterified corn straws to obtain the esterified-graft modified corn straws.

4. The method according to claim 2 or 3, wherein in the second step, the cross-linking agent is firstly added into the solvent, and the magnetic stirring is carried out until the cross-linking agent is completely dissolved; adding a foaming agent and an initiator, and uniformly stirring; adding the esterified-grafted modified corn straw and the plasticizer, and uniformly stirring to be pasty.

5. The method according to claim 4, wherein, in step two,

the solvent is water, and the solvent is water,

the cross-linking agent is amide and binary aldehyde,

the foaming agent is an azo compound,

the plasticizer is phthalate and camphor,

the initiator is selected from azo initiators, organic peroxy initiators or inorganic peroxy initiators.

6. The method of claim 5, wherein, in step two,

The cross-linking agent is acrylamide; the plasticizer is dioctyl phthalate; the initiator is azobisisobutyronitrile or persulfate;

the stirring speed is 20-100 r/min;

the mass ratio of the initiator to the modified corn straws is (0-1) to (1-15);

the mass ratio of the plasticizer to the modified corn straw is 1 (1-20).

7. The method of claim 5, wherein, in step two,

the initiator is azobisisobutyronitrile;

the mass ratio of the modified corn straw, the acrylamide and the water in the foaming slurry is (1-25): 0.5-50): 1-50),

the mass ratio of the initiator to the modified corn straws is 1 (1.5-12),

the mass ratio of the plasticizer to the modified corn straw is 1 (2-18).

8. The method of claim 5, wherein, in step two,

the mass ratio of the initiator to the modified corn straws is 1 (2.5-7);

the mass ratio of the plasticizer to the modified corn straw is 1 (5-12.5).

9. The method of claim 2, wherein in step three, the molding foaming is performed by steam molding;

the mould pressing temperature is 120-200 ℃; the mould pressing time is 2-8 h.

10. The method according to claim 9, wherein in the third step, the molding temperature is 140-180 ℃ and the molding time is 4-6 h.

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