阅读说明：本技术 塑料专用淀粉的制备方法及其应用 (Preparation method and application of starch special for plastics ) 是由 刘一帆 于 2021-07-12 设计创作，主要内容包括：为了解决淀粉基塑料制品的增塑剂析出及淀粉回生变脆的技术问题,本发明披露了塑料专用淀粉的制备方法及塑料专用淀粉的应用。塑料专用淀粉制备的步骤是：将含有一定水分的淀粉先进行膨化,再进行干燥,然后再粉碎至规定细度,得到塑料专用淀粉。塑料专用淀粉可以不经塑化,直接与塑料母粒熔融混合,制备淀粉基塑料产品。本发明还克服了技术偏见,在制备淀粉基塑料制品时,不添加淀粉塑化剂,但获得的产品性能更好、成本更低。(The invention discloses a preparation method of special starch for plastics and application of the special starch for plastics, aiming at solving the technical problems of plasticizer precipitation and starch retrogradation and brittleness of starch-based plastic products. The preparation method of the starch special for the plastic comprises the following steps: the starch containing certain moisture is firstly puffed, then dried and then crushed to specified fineness to obtain the special starch for plastics. The special starch for plastics can be directly melted and mixed with the plastic master batch without plasticizing to prepare a starch-based plastic product. The invention also overcomes the technical prejudice that the starch plasticizer is not added when the starch-based plastic product is prepared, but the obtained product has better performance and lower cost.)

1. A preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) mixing water with starch, wherein the addition amount of the water can meet the condition that the water accounts for 15-30 wt% of the total weight;

(2) puffing the mixture obtained in the step (1) through a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

2. A preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) adding starch and water into a bulking machine simultaneously, wherein the amount of water added is 15-30 wt% of the total weight of the starch and water;

(2) puffing by a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

3. A preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) selecting semi-wet starch with water content of 15-30 wt% from the wet milling starch processing procedure;

(2) puffing semi-wet starch in a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

4. A preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) selecting wet starch obtained from a wet milling method starch production process, and drying the water content of the wet starch to 15-30% by weight to obtain semi-wet starch;

(2) puffing semi-wet starch in a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

5. The method for preparing starch specially used for plastics according to any one of claims 1 to 4, wherein the drying method in the step (3) is hot air drying.

6. The method for preparing starch specially used for plastics according to any one of claims 1 to 4, wherein the particle size of the starch specially used for plastics in the step (4) is larger than 100 meshes.

7. Melting and mixing the special plastic starch prepared by the method of any one of claims 1 to 4 and plastic master batches in a granulator to prepare starch-based plastic master batches, wherein the mass percent of the special plastic starch is between 3% and 70%, and no starch plasticizer is added.

8. Melting and mixing the special plastic starch prepared by the method of any one of claims 1 to 4 and plastic master batches in a forming machine to prepare the starch-based plastic product, wherein the mass percent of the special plastic starch is between 3% and 70%, and no starch plasticizer is added.

9. The method for preparing starch specially used for plastics according to any one of claims 1 to 4, wherein the sequence of the steps (3) and (4) is interchanged, that is, the starch puffed body is firstly crushed into the starch specially used for plastics with fineness not less than 80 meshes, and then the water content of the starch specially used for plastics is dried to be less than 6%.

10. Melting and mixing the special plastic starch prepared by the method in claim 9 and plastic master batches in a forming machine to prepare the starch-based plastic product, wherein the mass percent of the special plastic starch is between 3% and 70%, and no starch plasticizer is added.

Technical Field

The invention relates to the field of plastic raw materials, in particular to a preparation method and application of special starch for plastics.

Background

With the improvement of environmental protection requirements and the implementation of environmental protection policies, in the field of plastics, especially biodegradable plastics, it is required to apply renewable, natural polymer materials to plastic products as much as possible, thereby reducing the cost and saving the use of petroleum-based biodegradable plastic materials. There are many prior arts disclosing the addition of natural high molecular starch to biodegradable materials such as PLA, PBAT, etc., but starch is a relatively rigid material, and its melting point is even higher than its carbonization point, so that starch is difficult to be mixed and melted with materials such as PLA, PBAT, etc. For this reason, the prior art has taken the technical route of plasticizing starch by combining starch with a plasticizer for blending. For example, the technologies of the publication No. CN 111548536A, the name of a thermoplastic starch biodegradable material and a patent for preparing the thermoplastic starch biodegradable material, the name of an authorized publication No. CN103992517B, the name of a continuously producible fully degradable starch-based plastic alloy and a preparation method thereof, the publication No. CN104448402A, the name of a starch-based plastic and a preparation method thereof, the name of a U.S. Pat. No. US7608649B2 and the like all adopt a mode of adding a plasticizer to apply starch to the field of biodegradable plastics. Commonly used plasticizers are, as disclosed in CN103992517B, water, glycerol, formamide, urea, sorbitol, low molecular weight polyethylene glycol, and the like. Although the plasticizer can plasticize starch into thermoplastic starch at higher temperature, the adverse effect is that when the thermoplastic starch is used for making products, the plasticizer can be slowly separated out of the products, which causes poor quality strain and narrow application range, and the technical difficulty which can not be overcome by the prior art at present is solved. In addition, the thermoplastic starch product inevitably has the technical defect of retrogradation and brittleness due to incomplete water treatment in the thermoplastic starch.

Disclosure of Invention

In order to solve the technical problems, the invention overcomes the technical prejudice, provides a method for preparing the starch special for plastics and discloses the application of the starch special for plastics, and can solve the technical defects of plasticizer precipitation and starch retrogradation of starch-based plastic products. The invention is realized by the following technical scheme:

a preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) mixing water with starch, wherein the addition amount of the water can meet the condition that the water accounts for 15-30 wt% of the total weight;

(2) puffing the mixture obtained in the step (1) through a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

A preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) adding starch and water into a bulking machine simultaneously, wherein the amount of water added is 15-30 wt% of the total weight of the starch and water;

(2) puffing by a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

A preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) selecting semi-wet starch with water content of 15-30 wt% from the wet milling starch processing procedure;

(2) puffing semi-wet starch in a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

A preparation method of special starch for plastics applied to the field of plastics is characterized by comprising the following steps:

(1) selecting wet starch obtained from a wet milling method starch production process, and drying the water content of the wet starch to 15-30% by weight to obtain semi-wet starch;

(2) puffing semi-wet starch in a puffing machine to obtain a starch puffed body;

(3) drying the starch puffed body to make the water content of the starch puffed body less than 6%;

(4) and (4) crushing the starch puffed body obtained in the step (3) into powder with the fineness not less than 80 meshes to obtain the special starch for plastics.

Preferably, the drying method in step (3) is hot air drying.

Preferably, the particle size of the starch special for plastics in the step (4) is larger than 100 meshes.

And melting and mixing the special plastic starch prepared by any method and the plastic master batch in a granulator to prepare the starch-based plastic master batch, wherein the mass percent of the special plastic starch is between 3 and 70 percent, and no starch plasticizer is added.

And melting and mixing the special plastic starch prepared by any method and the plastic master batch in a forming machine to prepare the starch-based plastic product, wherein the mass percent of the special plastic starch is between 3 and 70 percent, and no starch plasticizer is added.

Preferably, the sequence of the step (3) and the step (4) is interchanged, namely, the starch puffed body is firstly crushed into the special plastic starch with the fineness of not less than 80 meshes, and then the water content of the special plastic starch is dried to be less than 6%.

And melting and mixing the special plastic starch prepared by the method and the plastic master batch in a forming machine to prepare the starch-based plastic product, wherein the mass percent of the special plastic starch is between 3 and 70 percent, and no starch plasticizer is added.

Compared with the prior art, the theoretical basis and the innovation of the invention are as follows:

firstly, the removal of water adopts the technical idea of proceeding with the retreat.

One of the purposes of the invention is to reduce the moisture content in common starch and obtain the starch special for plastics. However, the first step in the present embodiment is to increase the moisture content of the starch beyond that of commercial starches. The reason for the additional water addition to the starch is:

1. as a processing aid and plasticizer for starch. The water content of commercial starch is about 13%, the starch is powder, and when the starch is added into the bulking machine, if the water content of the starch is low (such as less than 15%), the screw can slip and cannot be pushed forwards; when the water content of the starch is increased, the screw can be driven to move to the next stage due to the bonding effect of the water on starch particles, so that the slipping phenomenon of the screw is prevented, and the starch plays a role of a processing aid at the moment; in addition, although the starch is extruded and heated in the screw cavity of the bulking machine, the working condition of the bulking machine cannot change the rigid and solid state of the starch, and water can plasticize the starch under the condition so as to convert the starch from rigid to flexible and from solid to fluid, and at the moment, the water plays the role of a plasticizer, and the larger the water content is, the better the plasticizing effect is, but the influence on the screw feeding is generated. Therefore, when the commercial starch is plasticized, the water content is required to be not less than 15%. Of course, if the water content added is too high, e.g., above 40%, this can result in stickiness of the starch to the screw, and extruder cavity upon introduction into the extruder, and plasticizing of the starch to a less viscous liquid state at the rear of the extruder, which also does not facilitate processing. Experiments show that when the moisture content in the starch reaches 15%, the starch can be extruded and expanded in an extruder, the processing effect is good when the moisture content is 18-25%, and when the moisture content exceeds 30%, the processing condition of the starch is worse and worse due to higher humidity. Thus, the amount of water added can be controlled from the point of view of the processing technology. On the other hand, when the moisture content of the starch is small, the melting temperature of the starch is high, which is not favorable for sufficiently plasticizing the starch.

2. As a bulking agent for starch. One technical means of the invention is to puff the starch, and the water just plays the role of a puffing agent. Experiments prove that when the moisture content in the starch is 13%, the starch can be expanded in an expander, and the higher the moisture content is, the better the expansion effect is. However, the water content of the starch is generally selected to be about 18% to 22% in consideration of the plasticizing requirements of the starch and cost factors.

Secondly, the starch is dried in a puffing state, so that the defects of the prior art can be overcome, and the moisture content in the starch can be easily removed.

1. The moisture content of the existing commercial starch is about 13 percent. Applicants have found that there are two states for the water to be present in the starch: one is free water, which is loosely bound to the starch molecules. When dried, free water can be dried more easily from within the starch; the other is bound water, which is represented by the fact that water and starch molecules are bound into fixed hydrate in the form of hydrogen bonds. When ordinary starch is dried, bound water is difficult to separate from starch due to the action of hydrogen bonds unless additional large energy is consumed. The reason why the water content of the existing starch is difficult to remove after being reduced to 13% is due to the influence of bound water.

2. The moisture of the starch is easy to remove after the starch is puffed. The reason is that, as mentioned above, the starch exists in the form of fluffy and porous blocks after exiting the bulking machine, which facilitates the volatilization of water in the starch and the deep drying of the starch by the existing drying means compared with the powder starch; applicants have further found that bound water is present predominantly in the crystalline regions of the starch granules, while free water is present predominantly in the amorphous regions. When the starch is extruded and heated in the extruder, the crystalline state of the crystalline part of the starch is transformed into amorphous state, so that the combined water is transformed into free water, and the starch can be easily removed from the starch by the existing drying means. This is also the key mechanism of the inventive solution. In addition, when amorphous starch and contained moisture pass through the die orifice of the bulking machine, the moisture can be instantly converted into gas under the action of high temperature and high pressure, and most of the moisture can be volatilized without being continuously present in the starch; meanwhile, when the moisture is changed from liquid to gas, the starch is expanded, so that the starch is changed into a fluffy solid block form with porous inside and outside. This form, in turn, is very advantageous for the removal of moisture again by the drying device. Thus, although moisture is added to the starch at the beginning of the process, the moisture in the starch is more easily removed by extrusion, puffing, and drying. Moreover, when the starch is dried in a block shape, the operation is simpler and more convenient, and compared with the drying of powdery common starch, the starch is not easy to catch fire and is not easy to generate dust explosion.

And thirdly, after the starch is dried by puffing, the water content is low, the brittleness is high, the starch is easy to refine, and the high-fineness starch is obtained.

As mentioned above, the starch for plastics has low moisture content, the internal structure of the starch is amorphous rather than crystalline, and the expanded starch has expanded pores, and many factors determine that the starch for plastics is very easy to crush. The special starch for the plastic can be thinned to the granularity of more than 150 meshes by using a micro-grinder with less time and electric energy. Under the same conditions, commercial starch cannot be thinned to the same mesh size in a micronizer. According to inspection, no starch with more than 150 meshes is found in the existing starch commodity. In the ultramicro-powder machine, the special starch for plastics can also reach more than 300 meshes, which cannot be achieved by commercial starch. This is also one of the features of the present invention that distinguishes it from the prior art.

Fourthly, the special starch for the plastic is a new material of an application type.

The definition of the starch special for plastics by the applicant is: the starch has a water content of less than 6 percent, is expanded by an expansion process, has a starch granule fineness of not less than 100 meshes, and has an internal organization structure which is mainly amorphous and non-crystalline.

No commodity with the special starch for plastics is found in the market at present for sale, and no expression about the concept of the special starch for plastics and a preparation process of the special starch for plastics are found in the prior art.

Fifthly, when the special starch for plastics is applied to the field of plastics, particularly the field of biodegradable plastics, the technical route and means different from the prior art are adopted.

In the prior art, when starch is applied to plastic products, the technical means adopted is that the starch is plasticized under the action of a plasticizer and then is mixed with other plastic raw materials to obtain the starch-based plastic products. Wherein, in the process, the selection of the plasticizer is an indispensable technical means. Such as CN 111548536A, CN103992517B, CN104448402A and US7608649B2, all use combinations of plasticizers, starch and plastic resins.

For starch, the plasticizer is mainly alcohols with hydroxyl and smaller molecular weight or amines with amino and smaller molecular weight, such as CN103992517B, and the plasticizer is water, glycerol, formamide, sorbitol, low molecular weight polyethylene glycol, etc.; in addition, urea, methylamine, ethylamine, etc. are also disclosed as plasticizers for starch. Both alcohols and amines are strongly polar molecules. Starch can only be melt-plasticized at higher temperatures under the action of the aforementioned strongly polar molecules. However, the plasticizer plasticizes starch and causes performance deterioration of plastic resins such as PBAT, PLA, etc. mixed therewith, and even when mixed with conventional plastics such as PP, PE, etc., the plasticizer causes performance deterioration of PP, PE.

The following table shows the mechanical properties of the materials after melt mixing of starch, glycerol and PBAT. Wherein, the starch is prepared according to the invention, the water content is 3 percent, and the fineness is 150 meshes; the mass ratio of the starch to the PBAT is 20: 80; the percentage of glycerol is determined by the mass of the starch.

Table one:

content of Glycerol	0	5％	10％	20％	30％	40％
							Tensile strength MPa	21.4	20.7	18.3	16.7	14.6	13.8
Elongation percentage%	189	181	167	153	141	127

As can be seen from the table, as the content of glycerin increases, both the tensile strength and the elongation of the material decrease. I.e. glycerol as plasticizer, the effect of which on the material properties is deteriorated. In addition, through experiments, the glycerol can plasticize the starch, and when the content of the glycerol reaches 20% of the starch, the starch can be completely plasticized. Thus, glycerin plasticizes starch and also deteriorates the mechanical properties of the final material. The material has the best mechanical properties at a glycerol content of 0.

Experiments show that except glycerol, plasticizers of starch such as urea and ethylene glycol have basically similar influence on the material.

It has also been found that when starch, glycerol and PP, PE are blended, the properties change in the same way as the aforementioned blends of starch, glycerol and PBAT, i.e. when starch is added to plastics, the starch plasticizer composition will have a degrading effect on the material alloy.

Therefore, the two technical schemes of the two special plastic starch applications abandon the use of starch plasticizer, and the starch is directly combined with plastic resin such as PBAT and the like, so that the alloy material has better mechanical property.

The publication numbers CN 111548536A, CN103992517B, CN104448402A and US7608649B2 all adopt starch plasticizers, so that the technical route of the invention is obviously different from the prior art in the field of starch-based degradation materials. The invention has the advantages that the material alloy has better mechanical property, the cost and the process of the plasticizer are saved, and the cost is reduced. More importantly, the technical scheme of the invention can solve two major problems which are puzzling the prior art, namely plasticizer precipitation and starch retrogradation: no plasticizer exists, and the problem of plasticizer precipitation does not exist naturally; the water content of the starch special for the plastic is far lower than that of the commercial starch (13 percent), and the retrogradation problem of starch-based plastic products can be solved.

The technical schemes are further described and explained as follows:

first, the addition amount of water before starch expansion

Technical solution 1, technical solution 2 technical solution 3 and technical solution 4 are different from each other in the step (1), and the step (1) is different in the mixing manner of water and starch. The same requirement is, however, that the starch, before expansion, should meet a certain moisture content, i.e. a moisture content of 15-30% by weight in the starch.

The wet starch in technical scheme 4 is obtained from the production process of starch. At present, the wet milling process technology is mainly used in starch production in China and the United states, and is published by the China light industry publishing house and the "corn starch engineering technology" written by Baikun. Wherein, the dehydration link of the production process is described, starch is separated by a scraper centrifuge to obtain wet starch and filtrate, wherein the moisture content of the wet starch is about 38%; and (3) the drying link is described, the wet starch enters a drying pipe in an airflow drying system, and the moisture inside and outside the starch granules is removed to obtain the commodity starch, wherein the moisture content of the commodity starch is less than or equal to 14%.

The semi-wet starch in the technical scheme 3 is selected from starch in a drying link in a starch processing technology directly, and is non-commercial starch. The method specifically comprises the following steps: when wet starch enters an airflow drying system for drying, the wet starch is not required to be dried to the degree that the water content is less than or equal to 14 percent, but only dried to the water content of 15-30 percent. This can reduce the drying cost and can be directly applied to the present invention.

The semi-wet starch in the technical scheme 4 is obtained from a starch factory, and then is dried in a drying device outside the starch factory until the water content is 15-30%.

The reason for the water content of 15-30% has been explained above. In a particular process, the manner in which water is added to the starch can be determined according to the actual conditions. The determination of the moisture content in the process is selected in conjunction with the puffing process. At higher speeds of the expander, the moisture content of the wet starch may be lower, e.g. below 18%, but preferably not lower than 15%. When the rotating speed of the bulking machine is low, the water content of the wet starch can be higher, for example, when the rotating speed of the bulking machine is 50r/h and the water content of the wet starch reaches 30%, the wet starch can still be bulked in the single-screw bulking machine.

Second, puffing of starch

Technical solution 1, technical solution 2, technical solution 3 and technical solution 4 in step (2), the starch puffed body is a starch solid obtained by puffing starch with a specified water content (15-30% wt) by a puffing machine. Puffing means that starch is firstly melted and plasticized in a puffing machine under the action of water and a certain temperature, pressure is generated in the rotation of a screw of the puffing machine, then when the starch is discharged from a die orifice of the puffing machine, because of sudden decompression, moisture in the plasticized starch is vaporized, the volume of the plasticized starch is expanded, and a porous solid is formed.

Starch, after being puffed, can produce two effects:

first, the presence state of starch changes: through puffing, the starch is changed into porous and fluffy blocks from powder, and compared with powder, the fluffy and porous shape is very favorable for drying the starch.

Secondly, the structure of the starch is changed: the document discloses that starch granules are composed of two parts, a crystalline region and an amorphous region. The applicant has found that when applying starch in the field of plastics, the two parts have different effects on the properties of the final starch product. The amorphous part, because of the disorder of its arrangement, is advantageous for the plasticizing process of the starch and for the plasticity of the product; the crystalline part is unfavorable for plasticizing process of starch due to the existence of crystals. From a process point of view, reducing the amount of crystalline fraction in starch granules will contribute to the plasticizing process of starch. Based on the above, when the starch is puffed, under the high temperature and high pressure of the puffing machine and the plasticizing effect of water as a plasticizer, the crystalline structure in the starch granules is broken to promote the starch granules to be converted from the crystalline state to the amorphous state, and when the starch in the condition is discharged from the puffing machine through a die opening, the water plays the role of a puffing agent to puff the starch into a porous and loose solid block, and the internal structure of the solid block is still in the amorphous state after analysis. In a word, after the starch is puffed, the internal structure of the starch is changed differently from the original starch, and the performance of a final product during plasticizing and forming of the starch is greatly improved.

Bulking machines are common devices, can be single-screw, twin-screw or triple-screw extruders with heating arrangements, are often used in the food and feed fields. The speed of rotation of the expander is slightly higher, generally in the range of 20-200 revolutions, or higher, relative to other extruders used in the plastics field, the choice of which is related to the expansion pressure and die size required by the process, and other parameters of the expander.

The operating temperature of the bulking machine is set to meet the bulking requirements and is typically greater than 110 ℃. The shape of the starch puffed body can be the original shape extruded by a puffing machine, such as a long strip shape, a granular shape and the like, or the starch puffed body can be appropriately crushed (preferably pre-dried, such as blow-dried by a blower, and dried until the water content is less than 15%), such as crushed into small pieces or blocks, or powdery, but from the drying convenience angle of the step (3), the starch puffed body is preferably not ground into too fine powder, such as more than 100 meshes. Too high a mesh reduces the porosity in the starch puff, which is detrimental to the subsequent drying.

Drying the starch puffed body

As mentioned above, the starch puffed body from the puffing machine is solid in appearance, and is in the form of strips, blocks or granules, so that the starch puffed body can be dried by adopting a more flexible drying mode, such as hot air drying, which cannot be adopted by common starch drying. In a preferred embodiment of the present invention, the solid starch puff is dried directly by hot air drying. Hot air is typically generated by a hot air blower. In view of the reaction of starch molecules to heat, the temperature of hot air can be selected within the range of 80-150 ℃, and the time consumption is long when the temperature is too low; the starch molecules are easily carbonized due to overhigh temperature; more preferably at a temperature of 100 ℃ to 120 ℃. Because the starch puffed body is a porous massive solid, the drying mode can achieve the drying effect and prevent dust pollution in the drying process. Other methods such as drying, vacuum drying, microwave drying and the like are also completely suitable for drying the starch puffed body. And when these drying methods are used, the moisture in the starch is more easily volatilized and removed due to the porous and fluffy shape of the starch-expanded body compared to that of ordinary starch. The forms of hot air drying, drying, vacuum drying and the like are all conventional operation means.

The second table shows the drying data (drying time and water content) of commercial corn starch and the starch puffed body after puffing in the same dryer, wherein the particle size of the starch puffed body is 1-2 mm; the initial mass is 100 g; the drying temperature of the dryer is 120 ℃; the water content of the starch is mass percent (%).

Table two:

time (minutes)	0	15	20	30	40	70
							Commercial starch	13.15	10.67	8.21	6.34	5.27	2.41
Starch puffed body	12.54	5.94	3.69	1.46	0.62	0.12

From experimental data, it is known that the moisture of the starch extrudate is removed to more than 50% in 15 minutes compared to commercial starch, which takes approximately 2 times to achieve similar results. Therefore, after the starch is puffed, the moisture in the starch is very easy to dry and remove, and the drying effect is achieved in a short time, so that the drying cost is greatly reduced.

In another embodiment of the present invention, the starch puff is first pulverized and then dried. Compared with the prior drying, the drying cost after powdering is higher. The reason is that the powdery pellets may block heat transfer and moisture volatilization from each other. Even so, the expanded powder still has the advantages of less time consumption and low energy consumption when being dried compared with commercial starch. The reason is that no matter how fine the granules are, small pores still exist in the granules after the granules are puffed, which is very beneficial to drying; more importantly, the starch in the starch puffed body and the water molecules are not in the form of combined water, and the water molecules are easy to remove from the interior of the starch granules.

The moisture in the starch extrudate or starch specific to plastics is required to be less than 6% because the moisture content affects the performance of the plastic alloy and, when the moisture content is high, the material alloy will revert.

Table three is the properties of material alloys formed from 80% PBAT and 20% starch specific for plastics of different water content:

table three:

water content	0	1％	2％	3％	5％	6％
							Tensile strength MPa	21.4	21.1	20.7	18.4	18.1	16.8
Elongation percentage%	189	189	184	177	171	163
							Retrogradation phenomenon	Is free of	Is free of	Is free of	Fine and minute	Is lighter	Is more obvious

It can be seen from the table that the mechanical properties of the material alloy gradually decrease with the increase of the water content in the starch, and in addition, when the water content in the starch is lower than 3%, the material alloy does not generate the retrogradation phenomenon, and when the water content in the starch reaches 6%, the retrogradation embrittlement phenomenon occurs. Therefore, in each technical scheme of the invention, the water content of the starch special for plastics is required to be less than 6%.

And fourthly, crushing the starch puffed body to a proper mesh number.

Compared with the prior art, one of the technical requirements of the invention is to thin the starch special for the plastic to a certain mesh number. Higher mesh sizes of starch are required because starch is not plasticized when alloyed with other plastic resins. This is different from the prior art. Thus, the size of the starch particle size will affect the performance of the alloy (on the premise that the starch moisture content is low), with smaller fineness giving better performance.

The following table shows the effect of starch fineness on performance (PBAT 80%; special starch 20%; starch moisture 1%):

fineness of starch (mesh)	50	80	100	150	250
						Tensile strength MPa	15.3	18.1	20.6	21.4	24.7
Elongation percentage%	132	154	175	189	213

As can be seen from the table, the mechanical properties of the starch and the plastic resin are better and better with the increase of the mesh number. When the mesh number of the starch special for plastics reaches 80 meshes, the tensile strength of the alloy is equivalent to that of PBAT, and when the mesh number reaches 100 meshes, the strength of the alloy exceeds that of PBAT resin (about 18-20 MPa). In addition, from the appearance of the resulting material alloy, the higher the mesh number, the higher the smoothness. Therefore, the invention has the requirement of reaching 80 meshes, preferably exceeding 100 meshes.

Application of starch special for plastic

When the starch is applied to the field of plastics, in particular degradable plastics, the invention adopts a technical route which is different from the prior art, namely a technical route which is adopted for thinning the starch instead of plasticizing the starch. This route is taken with the proviso that the moisture content of the starch is reduced to the greatest possible extent. The starch specially used for the plastic is prepared for the purpose.

When the special starch for plastics is applied, the processing method is to directly mix the special starch for plastics with the plastic master batch and then enter a plastic forming machine or to simultaneously add the special starch for plastics and the plastic master batch into the plastic forming machine. The processing method is basically the same as the current method for adding calcium carbonate powder into plastics. Sometimes, for processing convenience, a small amount of a processing aid such as paraffin or the like may be added.

The plastic master batch can be biodegradable plastics such as PLA, PBAT, PHA and the like, and can also be traditional petroleum-based plastics such as PP, PE, PVC, PET and the like.

When the special starch for plastics forms an alloy with biodegradable plastics such as PLA, PBAT, PHA and the like, a plastic product obtained by using the alloy is a completely biodegradable plastic product; when the special starch for plastics and petroleum-based plastics such as PP, PE, PVC, PET and the like form an alloy, a plastic product obtained by utilizing the alloy is a partially biodegradable plastic product.

The starch special for the plastic is a recyclable material and has low price, so that the functions of reducing carbon emission and reducing the product cost can be achieved as long as the starch is added into the plastic. Moreover, because no starch plasticizer is added, the mechanical property of the alloy is not affected by the weakening of the starch plasticizer, and the function of enhancing the material property is realized invisibly.

In practical application, the adding amount of the starch special for the plastic can be determined according to requirements of different plastic types, different degradation requirements, product functions and the like. For disposable degradable plastic products, the special addition amount of the plastic is generally between 10 and 30 percent, the addition amount is small, the advantage of the starch cannot be reflected, but when the addition amount of the starch exceeds 30 percent, the plasticity, toughness and the like of the alloy formed by the starch, PBAT, PLA and the like cannot meet the requirements;

when the starch special for plastics is applied to the plate, a large amount of starch can be added. For example, 50% of starch can be combined with PP to prepare a starch plastic plate, and the processing technology and the application thereof are similar to those of a commercial wood-plastic plate. However, when the content of starch exceeds 70%, the existing processing equipment and process cannot process the alloy, so the invention requires that the addition amount of the starch special for plastics in the alloy does not exceed 70% at most.

Even if a small amount of the special starch for plastics is added into the plastic master batch, the special starch for plastics can play a reinforcing role: experiments show that when 3% of special plastic starch with the water content of 1% and the mesh number of 250 is added into PE, the tensile strength of PE can be improved by about 23%.

Has the advantages that:

compared with the prior art, the invention has the advantages that:

1. the invention provides a novel material which does not appear in the market in the field, namely special starch for plastics;

2. the special starch for plastics is applied to plastics, can improve material performance and can reduce carbon emission;

3. the invention overcomes the technical prejudice, and when preparing the starch-based plastic product, the starch plasticizer is not added, so that the product performance is better and the cost is lower;

4. the invention solves the problem of plasticizer precipitation in the prior degradable plastic technology and solves the problem of starch-based product regeneration.

Best mode for carrying out the invention

Example 1

5000g of starch (commercial starch, moisture content 13.4% wt) and 420g of water were mixed in a high-speed mixer for 10 minutes. Continuously adding the mixture into a bulking machine, wherein the bulking machine is a double-screw extruder, the diameter of a screw is 35mm, the rotating speed is 150r/min, the number of heating zones is 3, the temperature is set to be 90 ℃, 120 ℃, and the diameter of a neck mold is 3 mm. Extruding, heating and puffing starch by a puffing machine to obtain a starch puffed body; an air heater is arranged after the procedure of the bulking machine, the air heater is purchased from the market, the temperature of an air port of the air heater is set to be 130 ℃, the starch bulked body coming out of the neck mold is immediately dried by the air heater, and after 10 minutes, the water content of the starch is measured to be 1.54 percent; crushing the dried puffed body into small pieces, then crushing the small pieces in a jet mill, and obtaining the special starch for plastics after 20 minutes, wherein the mesh number of the starch is 150-200 meshes.

Example 2

5000g of starch from a corn starch factory was purchased and measured to have a moisture content of 13.2% wt. A water inlet pipe orifice is additionally arranged at the feed inlet of the bulking machine. Water flows through the orifice into the feed inlet. Starch and water are continuously added into the bulking machine at the same time, wherein the starch and the water are added according to the proportion of 7: 1 (mass ratio). The bulking machine is a double screw, the diameter of the screw is 35mm, the rotating speed is 150r/min, the number of heating zones is 3, the temperature is set to be 90 ℃, 120 ℃, and the diameter of the neck mold is 3 mm. Extruding, heating and puffing starch by a puffing machine to obtain a starch puffed body; the starch puff was pre-dried by a blower and the moisture content of the starch puff was measured to be 7.3%. Then crushing the pre-dried starch puffed body into small pieces by a crusher, and drying in an electric oven, wherein the temperature of the oven is set to be 120 ℃. After 20 minutes, the water content of the starch was measured to be 1.06%. Then crushing in a jet mill for 30 minutes to obtain the starch special for plastics, wherein the mesh number of the starch is 250 meshes.

Example 3

Semi-moist starch with a moisture content of 20% was customized from a certain starch factory. Continuously adding 5kg of semi-wet starch into a bulking machine, wherein the bulking machine is a double screw, the diameter of the screw is 35mm, the rotating speed is 150r/min, the number of heating zones is 3, the temperature is set to be 90 ℃, 130 ℃, 120 ℃, and the diameter of an opening die is 1 mm. Extruding, heating and puffing semi-wet starch by a puffing machine to obtain a starch puffed body; an air heater is arranged after the procedure of the bulking machine, the air heater is purchased from the market, the temperature of an air port of the air heater is set to be 130 ℃, the starch bulked body coming out of the neck mold is immediately dried by the air heater, and after 15 minutes, the water content of the starch is measured to be 0.93 percent; and crushing the dried puffed body into small pieces, and then crushing in a jet mill for 15 minutes to obtain the special starch for plastics, wherein the mesh number of the starch is 180 meshes.

Example 4

From a starch plant, wet starch was purchased with a moisture content of 37.4%. Putting 5kg of wet starch into a dryer for drying, and taking out when the water content of the wet starch reaches 20% to obtain semi-wet starch; then, the semi-wet starch is continuously added into a bulking machine, wherein the bulking machine is a double screw, the diameter of the screw is 35mm, the rotating speed is 150r/min, the number of heating zones is 3, the temperature is set to be 90 ℃, 130 ℃, 120 ℃, and the diameter of an opening die is 1 mm. Extruding, heating and puffing semi-wet starch by a puffing machine to obtain a starch puffed body; an air heater is arranged after the procedure of the bulking machine, the air heater is purchased from the market, the temperature of an air port of the air heater is set to be 130 ℃, the starch bulked body coming out of the neck mold is immediately dried by the air heater, and after 15 minutes, the water content of the starch is measured to be 0.93 percent; and crushing the dried puffed body into small pieces, and then crushing in a jet mill for 30 minutes to obtain the special starch for plastics, wherein the mesh number of the starch is 250 meshes.

Example 5

5000g of starch (commercial starch, moisture content 13.4% wt) and 420g of water were mixed in a high-speed mixer for 10 minutes. Continuously adding the mixture into a bulking machine, wherein the bulking machine is a double-screw extruder, the diameter of a screw is 35mm, the rotating speed is 150r/min, the number of heating zones is 3, the temperature is set to be 90 ℃, 120 ℃, and the diameter of a neck mold is 3 mm. Extruding, heating and puffing starch by a puffing machine to obtain a starch puffed body; the water content of the starch puffed body is 8.2 percent by measurement; crushing the starch puffed body into small pieces, then crushing in a jet mill for 20 minutes to obtain the starch special for plastics, wherein the mesh number of the starch is 90 meshes; and drying the special starch for the plastic in a fluidized bed dryer for 20 minutes to obtain the special starch for the plastic with the moisture content of 3.27 percent.

Example 6

2000 g of the starch special for plastics obtained in example 1, 3000 g of LPE and 200 g of paraffin wax are added into a forming machine, the forming machine is an experimental extruder, the heating temperature is 80 ℃, 130 ℃, 135 ℃, the size of a die opening is 1mm and 30mm, and a starch-based PE sheet is obtained through extrusion, the tensile strength of the sheet is 14.2MPa, and the elongation is 246%.

Example 7

2000 g of the starch obtained in example 1 and 8000 g of PBAT were added to a granulating extruder at the same time, the extruder was heated at80 ℃, 130 ℃, 135 ℃ and the die diameter was 3 mm. And granulating by a granulator after extrusion to obtain the starch-based biodegradable masterbatch.

Cutting the granules, taking a material with the length of 200mm, cooling, and measuring the tensile strength and the elongation of the material in a tensile testing machine, wherein the tensile strength and the elongation are respectively as follows: 23MPa, 217 percent.