阅读说明：本技术 一种改性锯末的方法 (Method for modifying sawdust ) 是由 潘钢华 周飞飞 于 2020-12-22 设计创作，主要内容包括：本发明公开了一种改性锯末的方法,包括如下步骤：(1)将锯末在碱性硅源溶液中浸泡处理,得碱处理锯末；(2)在步骤(1)所得碱处理锯末中,边搅拌边加入钙源,钙源加入完成后,继续搅拌反应,然后洗涤、干燥,得水化硅酸钙改性锯末。本发明的改性方法通过在锯末表面包覆具有早强作用的水化硅酸钙,获得的水化硅酸钙改性锯末能够为水泥水化提供形核位点,加快水泥水化,促进锯末水泥基复合材料的强度发展；而且,包覆锯末的水化硅酸钙能够强化锯末与水泥基体的界面过渡区,从而在提高锯末水泥基复合材料的强度的同时减少水泥基体中碱性孔溶液对锯末的侵蚀,提高锯末水泥基复合材料的耐久性。(The invention discloses a method for modifying sawdust, which comprises the following steps: (1) soaking sawdust in an alkaline silicon source solution to obtain alkaline treated sawdust; (2) and (2) adding a calcium source into the alkali-treated sawdust obtained in the step (1) while stirring, continuing stirring for reaction after the calcium source is added, and then washing and drying to obtain the calcium silicate hydrate modified sawdust. According to the modification method, calcium silicate hydrate with an early strength effect is coated on the surface of the sawdust, so that the obtained calcium silicate hydrate modified sawdust can provide nucleation sites for cement hydration, cement hydration is accelerated, and strength development of the sawdust cement-based composite material is promoted; in addition, the calcium silicate hydrate coating the sawdust can strengthen the interface transition area between the sawdust and the cement matrix, so that the strength of the sawdust-cement-based composite material is improved, meanwhile, the erosion of alkaline pore solution in the cement matrix to the sawdust is reduced, and the durability of the sawdust-cement-based composite material is improved.)

1. A method of modifying sawdust, comprising the steps of:

(1) soaking sawdust in an alkaline silicon source solution to obtain alkaline treated sawdust;

(2) and (2) adding a calcium source into the alkali-treated sawdust obtained in the step (1) while stirring, continuing stirring for reaction after the calcium source is added, and then washing and drying to obtain the calcium silicate hydrate modified sawdust.

2. A method for modifying sawdust according to claim 1, wherein in step (1), the alkaline silicon source solution is an aqueous solution of sodium silicate or sodium metasilicate.

3. The method for modifying sawdust according to claim 1, wherein in step (1), the concentration of the alkaline silicon source solution is 0.5-5% by mass, and the mass ratio of sawdust to alkaline silicon source solution is 1: 5-10.

4. The method for modifying sawdust according to claim 1, wherein the temperature of the alkaline silicon source solution in step (1) is 20-100 ℃ and the soaking time is 2-12 hours.

5. The method for modifying sawdust according to claim 1, wherein in step (2), the molar ratio of calcium ions in the calcium source to silicate ions in the alkaline silicon source solution is 0.5-2: 1.

6. A method of modifying sawdust according to claim 1 or 5, wherein the calcium source is an aqueous solution of calcium chloride, calcium nitrate or calcium acetate.

7. The method for modifying sawdust according to claim 1, wherein in step (2), the reaction is continued for 15-30 min with stirring after the addition of the calcium source is completed, and then the sawdust is washed and vacuum-dried at 40-60 ℃.

Technical Field

The invention relates to a method for modifying sawdust, and belongs to the technical field of building materials.

Background

Sawdust is a common industrial byproduct, is low in price and is easy to obtain. Can be used in the technical field of building material production to improve the performance of building materials and reduce the production cost of the building materials. If the sawdust can be used in the cement-based composite material, the dead weight of the cement-based composite material is reduced, and the heat preservation, sound absorption and sound insulation performance of the cement-based composite material is improved.

However, the main components of the sawdust are cellulose, hemicellulose and lignin, and also comprise a small amount of substances such as fat, wax and the like, the substances are very easily degraded in an alkaline solution, and monosaccharide, sucrose, glucose, tannin and other substances which are degraded and dissolved out can seriously hinder the hydration of cement, so that the strength development of the cement-based composite material is delayed. In addition, the alkaline liquid in the pores of the cement-based composite material continuously erodes and degrades the sawdust, so that the interface bonding between the sawdust and the cement matrix is damaged, the performance of the cement-based composite material is finally deteriorated, the durability of the cement-based composite material is not facilitated, and the service life of the cement-based composite material is shortened.

For this reason, the prior art often modifies sawdust by alkali treatment. By alkali treatment of the sawdust, substances such as hemicellulose and lignin in the sawdust and delaying cement hydration can be degraded in advance, so that the adverse effect of the sawdust on cement hydration is reduced, and the strength development of the cement-based composite material is promoted. However, although the alkali treatment can degrade and dissolve the components in the sawdust which are not favorable for the performance of the cement-based composite material in advance, the excessive degradation and dissolution can significantly reduce the strength of the sawdust, which is also not favorable for the performance of the cement-based composite material. In addition, in the subsequent service process of the saw dust cement-based composite material, due to the lack of an effective protective layer in the alkali treatment of the saw dust, the alkaline environment of the cement matrix can still continuously erode the saw dust, the interface transition area between the saw dust and the cement matrix is degraded, and the service life of the saw dust cement-based composite material is shortened.

Therefore, in order to further reduce the adverse effect of sawdust on cement-based composite materials, it is necessary to further modify sawdust on the basis of alkali treatment of sawdust. In contrast, the chinese patent application No. 201710390408.8 discloses a method for pretreating sawdust with carbon dioxide, which carbonizes a calcium source adsorbed in sawdust with carbon dioxide to generate calcium carbonate. The generated calcium carbonate can fill the pores of the sawdust, reduce the water absorption of the sawdust and strengthen the interface transition area of the sawdust and the cement matrix. However, calcium carbonate does not have the early strength effect, and the effect of pre-treating saw dust by using carbon dioxide on promoting the strength development of saw dust cement-based composite materials is limitedAnd the requirement of high early strength of the cement-based composite material cannot be met. In addition, calcium carbonate can only be filled in the interface transition area of the sawdust and the cement matrix, is difficult to participate in the cement hydration process, and has limited strengthening effect on the interface transition area. And can only block OH in a cement matrix through physical action^-The sawdust is eroded, the process is passive, and the sawdust is protected only with limited effect.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the problem that the existing modified sawdust can not improve the strength and durability of the sawdust cement-based composite material or has limited improvement effect, the invention provides the method for modifying the sawdust.

The technical scheme is as follows: the invention discloses a method for modifying sawdust, which comprises the following steps:

(1) soaking sawdust in an alkaline silicon source solution to obtain alkaline treated sawdust;

(2) and (2) adding a calcium source into the alkali-treated sawdust obtained in the step (1) while stirring, continuing stirring for reaction after the calcium source is added, and then washing and drying to obtain the calcium silicate hydrate modified sawdust.

Preferably, in the step (1), the mass concentration of the alkaline silicon source solution is 0.5-5%, and the mass ratio of the sawdust to the alkaline silicon source solution is 1: 5-10. Optionally, the alkaline silicon source solution is an aqueous solution of sodium silicate or sodium metasilicate; the molar concentration of calcium ions in the calcium source is preferably 0.1-0.5 mol/L. Further preferably, the temperature of the alkaline silicon source solution is 20-100 ℃, and the soaking time is 2-12 h.

Preferably, in the step (2), the molar ratio of calcium ions in the calcium source to silicate ions in the alkaline silicon source solution is 0.5-2: 1. The calcium source may be an aqueous solution of calcium chloride, calcium nitrate or calcium acetate.

Preferably, after the calcium source is added, stirring and reacting for 15-30 min, then washing the sawdust, and drying the sawdust in vacuum at 40-60 ℃.

The invention principle is as follows: firstly, the alkaline silicon source solution such as the aqueous solution of sodium silicate or sodium metasilicate has alkalinity, and the alkaline silicon source solution can be used for carrying out alkaline treatment on the sawdust, and can degrade and dissolve components which are not beneficial to the performance of the sawdust cement-based composite material, such as hemicellulose, lignin, fat and the like in the sawdust through the alkaline treatment. Then, a calcium source is added into the alkali-treated sawdust, calcium ions can perform chemical coprecipitation reaction with silicate ions in the alkaline silicon source solution to generate calcium silicate hydrate, and the generated calcium silicate hydrate can be coated on the surface of the sawdust or filled in pores of the sawdust. The calcium silicate hydrate coated on the surface of the sawdust can provide nucleation sites for cement hydration and promote strength development of the cement-based composite material, particularly early strength; on the other hand, the calcium silicate hydrate coating the sawdust can be used as a substrate for the growth of cement hydration products, the growth of the hydration products in an interface transition area is promoted, the interface transition area of the sawdust and a cement matrix can be compacted, the bonding force between the sawdust and the cement matrix is enhanced, the difficulty of eroding the sawdust by alkaline pore solution in the cement matrix through the area is increased, the strength of the sawdust cement-based composite material is improved, and meanwhile, the durability of the sawdust cement-based composite material is improved. In addition, the hydrated calcium silicate coated on the surface of the sawdust can physically prevent OH < - > from contacting with the sawdust, passively protect the coated sawdust and actively absorb OH < - > so as to further reduce the corrosion of alkaline environment to the sawdust and enable the sawdust cement-based composite material to have better durability.

Has the advantages that: compared with the prior art, the invention has the advantages that: according to the modification method, calcium silicate hydrate with an early strength effect is coated on the surface of the sawdust, so that the obtained calcium silicate hydrate modified sawdust can provide nucleation sites for cement hydration, cement hydration is accelerated, and strength development of the sawdust cement-based composite material is promoted; in addition, the calcium silicate hydrate coating the sawdust can strengthen the interface transition area between the sawdust and the cement matrix, so that the strength of the sawdust-cement-based composite material is improved, meanwhile, the erosion of alkaline pore solution in the cement matrix to the sawdust is reduced, and the durability of the sawdust-cement-based composite material is improved.

Drawings

FIG. 1 is X-ray diffraction patterns of calcium silicate hydrate modified sawdust obtained in example 1, raw sawdust in comparative example 1, and alkali-treated sawdust in comparative example 2;

FIG. 2 is an SEM topography of raw sawdust of comparative example 1 at 1000 times magnification;

FIG. 3 is an SEM topography of the alkali-treated sawdust obtained in comparative example 2 at 1000 times magnification;

FIG. 4 is an SEM topography of calcium silicate hydrate modified sawdust obtained in example 1 at 1000 times magnification;

FIG. 5 is an SEM image of the interface transition zone of the raw sawdust and the cement matrix in comparative example 1, magnified 2000 times;

FIG. 6 is an SEM image of the interface transition zone of the alkali-treated sawdust and the cement matrix obtained in comparative example 2, magnified 1000 times;

FIG. 7 is an SEM image of the transition area of the interface between the calcium silicate hydrate modified sawdust and the cement matrix obtained in example 1, which is magnified 2000 times.

Detailed Description

The technical solution of the present invention is further explained with reference to the drawings and the embodiments.

Example 1

A method of modifying sawdust comprising the steps of:

(1) alkali treatment: soaking 250g of sawdust in 2500g of alkaline silicon source solution for 2 hours to obtain alkali-treated sawdust; wherein the alkaline silicon source solution is an aqueous solution of sodium metasilicate pentahydrate, the mass concentration of the sodium metasilicate pentahydrate in the alkaline silicon source solution is 2%, and the temperature of the alkaline silicon source solution is 100 ℃;

(2) chemical coprecipitation reaction: and (2) adding a calcium acetate water solution with the molar concentration of 0.5mol/L (calculated by calcium ions) while stirring the alkali-treated sawdust obtained in the step (1), controlling the molar ratio of the calcium ions in the calcium source to silicate ions in the alkali solution to be 1:1, then continuing stirring for 15min, washing, and drying in vacuum at 60 ℃ to constant weight to obtain the calcium silicate hydrate modified sawdust.

Example 2

A method of modifying sawdust comprising the steps of:

(1) alkali treatment: soaking 250g of sawdust in 1250g of alkaline silicon source solution for 12 hours to obtain alkali-treated sawdust, wherein the alkaline silicon source solution is an aqueous solution of sodium metasilicate pentahydrate, the mass concentration of the sodium metasilicate pentahydrate in the alkaline silicon source solution is 0.5%, and the temperature of the alkaline silicon source solution is 60 ℃;

(2) chemical coprecipitation reaction: and (2) adding a calcium acetate water solution with the molar concentration of 0.1mol/L (calculated by calcium ions) while stirring the alkali-treated sawdust obtained in the step (1), controlling the molar ratio of the calcium ions in the calcium source to silicate ions in the alkali solution to be 2:1, then continuing stirring for 15min, washing, and drying in vacuum at 60 ℃ to constant weight to obtain the hydrated calcium silicate modified sawdust.

Example 3

A method of modifying sawdust comprising the steps of:

(1) alkali treatment: soaking 250g of sawdust in 1800g of alkaline silicon source solution for 6 hours to obtain alkaline treated sawdust, wherein the alkaline silicon source solution is aqueous solution of sodium metasilicate pentahydrate, the mass concentration of the sodium metasilicate pentahydrate in the alkaline silicon source solution is 3%, and the temperature of the alkaline silicon source solution is 40 ℃;

(2) chemical coprecipitation reaction: and (2) adding a calcium acetate water solution with the molar concentration of 0.25mol/L (calculated by calcium ions) while stirring the alkali-treated sawdust obtained in the step (1), controlling the molar ratio of the calcium ions in the calcium source to silicate ions in the alkali solution to be 1.5:1, continuing stirring for 15min, washing, and drying in vacuum at 60 ℃ to constant weight to obtain the hydrated calcium silicate modified sawdust.

Example 4

A method of modifying sawdust comprising the steps of:

(1) alkali treatment: soaking 250g of sawdust in 2500g of alkaline silicon source solution for 6 hours to obtain alkali-treated sawdust, wherein the alkaline silicon source solution is an aqueous solution of sodium metasilicate pentahydrate, the mass concentration of the sodium metasilicate pentahydrate in the alkaline silicon source solution is 5%, and the temperature of the alkaline silicon source solution is 20 ℃;

(2) chemical coprecipitation reaction: and (2) adding a calcium acetate water solution with the molar concentration of 0.5mol/L (calculated by calcium ions) while stirring the alkali-treated sawdust obtained in the step (1), controlling the molar ratio of the calcium ions in the calcium source to silicate ions in the alkali solution to be 0.5:1, then continuing stirring for 15min, washing, and drying in vacuum at 60 ℃ to constant weight to obtain the hydrated calcium silicate modified sawdust.

Comparative example 1

Undisturbed sawdust which is dried to constant weight at 60 ℃.

Comparative example 2

Alkali treatment of sawdust, the method of alkali treatment is as follows:

soaking 250g of sawdust in 2500g of aqueous alkali for 2 hours, wherein the aqueous alkali is 2% sodium metasilicate pentahydrate aqueous solution, and the temperature of the aqueous alkali is 100 ℃; then washing and drying at 60 ℃ to constant weight to obtain the alkali-treated sawdust.

The calcium silicate hydrate modified sawdust obtained in examples 1 to 4, the original sawdust in comparative example 1 and the alkali-treated sawdust in comparative example 2 were characterized as follows:

(1) x-ray diffraction analysis

FIG. 1 is an X-ray diffraction pattern of calcium silicate hydrate modified sawdust obtained in example 1, alkali-treated sawdust in comparative example 2, and raw sawdust in comparative example 1, and it can be seen from the figure that: the characteristic diffraction peak of the calcium silicate hydrate exists in the calcium silicate hydrate modified sawdust obtained in example 1, which shows that the calcium silicate hydrate is synthesized in the environment where the sawdust exists by the method of the invention. The X-ray diffraction pattern of the calcium silicate hydrate modified sawdust prepared in examples 2 to 4 is similar to that of example 1, and a characteristic diffraction peak of the calcium silicate hydrate exists.

(2) SEM analysis of morphology

FIGS. 2 to 4 are SEM topography images of the original sawdust in comparative example 1, the alkali-treated sawdust in comparative example 2, and the calcium silicate hydrate modified sawdust obtained in example 1, which are magnified 1000 times, respectively, and it can be seen from the images: in the comparative example 1, the undisturbed sawdust has more chips on the surface and a large amount of substances which are easily degraded and dissolved out by alkali liquor; the alkali-treated sawdust in the comparative example 2 has a clean surface and high roughness, and meanwhile, part of substances which are not beneficial to cement hydration are degraded and dissolved out by alkali liquor, so that the performance of the sawdust cement-based composite material is improved; the surface of the calcium silicate hydrate modified sawdust obtained in the embodiment 1 is coated with calcium silicate hydrate, and the calcium silicate hydrate can be filled in pores of the sawdust, which shows that the method provided by the invention can realize the adhesion, growth and coating of the calcium silicate hydrate on the sawdust, so that the sawdust is prevented from being eroded by alkaline pore solution in a cement matrix, and the performance of the sawdust cement-based composite material is finally improved. The SEM appearance of the calcium silicate hydrate modified sawdust prepared in the embodiments 2-4 is similar to that of the sawdust prepared in the embodiment 1, and the calcium silicate hydrate is partially coated on the surface of the sawdust and partially filled in pores of the sawdust.

The influence of the calcium silicate hydrate modified sawdust obtained in examples 1 to 4, the original sawdust in comparative example 1 and the alkali-treated sawdust in comparative example 2 on the performance of the cement-based material is analyzed, and the method specifically comprises the following steps:

(1) influence of calcium silicate hydrate modified sawdust obtained in examples 1 to 4, raw sawdust in comparative example 1, and alkali-treated sawdust in comparative example 2 on performance of sawdust cement-based composite material

The calcium silicate hydrate modified sawdust obtained in examples 1 to 4, the original sawdust in comparative example 1 and the alkali-treated sawdust in comparative example 2 are respectively used for preparing a sawdust cement-based composite material, and the preparation method comprises the following steps: the sawdust cement-based composite material is formed by referring to JGJ/T70-2009 Standard test method for basic Performance of building mortar, and the sawdust cement-based composite material is composed of the following raw materials in parts by weight: P.O 42.5.5 parts of Portland cement 1200; 200 parts of sawdust; 12 parts of a polycarboxylic acid high-efficiency water reducing agent; 576 parts of water.

The following table 1 shows the performance test results of the saw dust cement-based composite material, and the results show that: the calcium silicate hydrate modified sawdust prepared by the method can effectively solve the adverse effect of sawdust on the cement-based composite material, and under the condition of the same water consumption, the calcium silicate hydrate modified sawdust can obviously improve the working performance of the sawdust cement-based composite material, greatly shorten the setting time of the sawdust cement-based composite material and promote the strength development of the sawdust cement-based composite material.

TABLE 1 saw dust Cement-based composite Performance test results

(2) Calcium silicate hydrate modified sawdust obtained in example 1, original sawdust in comparative example 1, and interface transition zone between alkali-treated sawdust and cement matrix in comparative example 2

The calcium silicate hydrate modified sawdust obtained in example 1, the original sawdust in comparative example 1 and the alkali-treated sawdust in comparative example 2 were used for preparing sawdust cement-based composite materials, respectively, and the preparation methods were as follows: the sawdust cement-based composite material is formed by referring to JGJ/T70-2009 Standard test method for basic Performance of building mortar, and the sawdust cement-based composite material is composed of the following raw materials in parts by weight: P.O 42.5.5 parts of Portland cement 1200; 200 parts of sawdust; 12 parts of a polycarboxylic acid high-efficiency water reducing agent; 576 parts of water.

FIGS. 5 to 7 are SEM images of the interface transition zone of the original sawdust in comparative example 1, the alkali-treated sawdust in comparative example 2, and the hydrated calcium silicate modified sawdust obtained in example 1 with the cement matrix, respectively. As can be seen from fig. 5, the bonding between the raw sawdust and the cement matrix is poor, and a large gap exists, which inevitably deteriorates the transition zone, and becomes a weak area in the sawdust-cement-based composite material, and reduces the strength and durability of the sawdust-cement-based composite material. As can be seen from FIG. 6, the alkali-treated sawdust and the cement matrix are bonded well, but large gaps still exist, the interface transition zone is weak, and the improvement on the strength and durability of the sawdust cement-based composite material is limited. And figure 7 shows that the hydrated calcium silicate modified sawdust is tightly bonded with the cement matrix, no gap exists, and the interface transition area is obviously strengthened. Further analysis shows that the calcium silicate hydrate on the calcium silicate hydrate modified sawdust can provide nucleation sites for cement hydration, promote the enrichment and deposition of hydration products on the sawdust, thereby enhancing the bonding of the sawdust and a cement matrix and strengthening the interface transition region of the sawdust and the cement matrix; the process not only can accelerate the hydration of cement and promote the strength development of the sawdust cement-based composite material, but also can obviously improve the durability of the sawdust cement-based composite material. Therefore, the hydration acceleration effect of the hydrated calcium silicate on the hydrated calcium silicate modified sawdust improves the strength development of the sawdust cement-based composite material, strengthens an interface transition area and improves the durability of the sawdust cement-based composite material.