CN114058086A

CN114058086A - Starch-based plastic master batch

Info

Publication number: CN114058086A
Application number: CN202111337367.9A
Authority: CN
Inventors: 刘一帆
Original assignee: Shandong Hongming Biotechnology Co ltd
Current assignee: Shandong Hongming Biotechnology Co ltd
Priority date: 2021-11-12
Filing date: 2021-11-12
Publication date: 2022-02-18

Abstract

The invention provides a novel starch-based plastic master batch which is characterized in that a plastic master batch matrix is plasticized dry starch, the plasticized dry starch is formed by melting and plasticizing dry starch and a starch plasticizer (except water), wherein the dry starch is starch with the water content of less than or equal to 5 percent (by weight). The all-starch-based plastic master batch and the product thereof have good mechanical properties, low cost and good economic and social effects compared with petroleum-based plastics.

Description

Starch-based plastic master batch

Technical Field

The invention relates to the field of plastic raw materials, in particular to a starch-based plastic master batch.

Background

Starch, as a natural, renewable polymer material, has been increasingly used in the field of plastics due to its plasticization. However, starch has poor plasticity and high brittleness due to its texture and composition compared with petroleum-based plastics, and the fresh technology discloses plastic materials prepared from all starch. The technical means of the prior starch applied to the field of plastics is mainly to plasticize the starch and then mix the starch with other plastic raw materials so as to prepare the starch-based plastic alloy. For example, many technologies such as CN 111548536 a, a patent named thermoplastic starch biodegradable material and its preparation, CN103992517B, a plastic alloy named fully degradable starch-based plastic alloy and its preparation method, CN104448402A, a plastic named starch-based plastic and its preparation method, and US7608649B2 are applied by synthesizing starch and plastic resin into plastic alloy. And the matrix of the starch-based plastic alloy is plastic or the combination of plastic and plasticized starch. The prior art with the publication number of CN101302321A and the name of thermoplastic starch plastic discloses a plastic material with the raw material mainly comprising starch, and the matrix of the material is plasticized starch, but the technical means of taking water as the material component in the technology inevitably leads to the technical defects of regeneration, brittleness and reduced mechanical property of the final product.

Disclosure of Invention

The invention overcomes the technical prejudice and provides a starch-based plastic master batch aiming at the defects of the prior art, wherein the matrix of the master batch is plasticized starch instead of plastic or the combination of the plastic and the plasticized starch. The invention is realized by the following technical scheme:

a starch-based plastic master batch is characterized in that a plastic master batch matrix is plasticized dry starch, the plasticized dry starch is formed by melting and plasticizing dry starch and a starch plasticizer (except water), and the dry starch is starch with the water content of less than 5 percent (by weight).

Preferably wherein the dry starch has a moisture content of not more than 3% by weight.

Preferably, the starch plasticizer is one or a combination of polar molecular materials rich in hydroxyl and/or amino, such as methanol, ethanol, ethylene glycol, glycerol, sorbitol, polyethylene glycol, urea, formamide, acetamide, and the like.

Preferably, the master batch also contains a filler, and the addition amount is 0-70% (by weight).

Preferably, the filler is one or a combination of wood powder, bamboo powder, straw powder and other organic fillers.

Preferably, the dry starch is prepared by puffing starch with water content of 15-30 wt% and drying.

Preferably, the preparation method of the dry starch is to prepare the starch by drying the starch by microwave.

Preferably, the dry starch is prepared by heating and drying starch while applying a pressing force and a shearing force to the starch.

Preferably, the dry starch is prepared by drying pregelatinized starch.

The theoretical basis of the invention is as follows:

starch, as a biomass for biological energy storage, does not have the mechanical properties and the use properties of plastics due to its structure and composition. Therefore, in the prior art, when the starch is applied to the field of plastics, the starch is usually plasticized to prepare the plasticized starch. Common starch plasticizers are mainly water, alcohols with smaller molecular weight, and amides with smaller molecular weight, as disclosed in CN103992517B, and the plasticizers used are water, glycerol, formamide, sorbitol, low molecular weight polyethylene glycol, etc.; in addition, urea, formamide, acetamide, and the like are also disclosed as plasticizers for starch; relatively high molecular weight materials such as sucrose, maltose, etc. can also plasticize starch at higher temperatures, or in combination with other alcohols (e.g., ethanol, glycerol, etc.). Whether water, alcohols or amides, are strongly polar molecules. Starch can only be melt-plasticized at a given temperature by the action of the aforementioned strongly polar molecules and is melt-mixed with conventional plastics.

The applicant finds that the application performance of the existing plasticized starch products is poor, and is mainly represented by the following characteristics: (1) the mechanical property of the product is not enough to meet the requirement of the existing plastic; (2) the regeneration phenomenon of the product is obvious: when the processing is just finished, the plasticity and toughness of the product are better, and the product has certain usability, but although the time is prolonged, the plasticity and toughness of the product slowly disappear, and the product is higher in brittleness, easy to break and easy to crack, so that the usability is extremely poor. This is also the main reason that the whole starch plastic products are not available in the market at present.

The first inventor filed application No. 202110792308.4 entitled "method for preparing starch specific to plastics and use thereof" on 12.7.2021 and disclosed starch specific to plastics and a method for preparing the same. The applicant finds that the special starch for plastics has unexpected effects after being plasticized by a non-aqueous starch plasticizer, and compared with the existing plasticized starch, the plastic properties of the product are obviously enhanced, which is shown in the following steps: has higher value of plasticity and toughness; strength with a higher value; the product hardly generates retrogradation phenomenon, and the performance is obviously superior to that of the existing plasticized starch. The following tables show the comparison of the mechanical properties and retrogradation of the plastic special starch and the commercial starch (70 parts) after plasticizing with glycerol. Wherein the amount of the special starch for plastics and the amount of the commercial starch are respectively 70 parts, and the amount of the glycerol is 30 parts; the moisture content of the starch special for the plastic is 2.1 percent, and the moisture content of the commercial starch is 13.5 percent; plasticizing the special starch for the plastic to obtain a product A, and plasticizing the commercial starch to obtain a product B; the first table is a tensile strength comparison table; the second table is an elongation rate comparison table; the third table is a retrogradation phenomenon comparison table.

Table one:

tensile Strength sigma (MPa)

Time of formation of the product (day)	1	5	10	20	30
						Product A	8.2	8.2	8.1	8.1	7.9
Product B	7.5	8.7	7.6	5.3	4.7

Table two:

elongation delta (%)

Time of formation of the product (day)	1	5	10	20	30
						Product A	187	184	172	165	131
Product B	193	137	76	41	18

Table three:

retrogradation phenomenon

Time of formation of the product (day)	1	5	10	20	30
						Product A	Is not obvious	Is not obvious	Is not obvious	Is not obvious	Light and slight
Product B	Is not obvious	Is obvious	Is quite obvious	Is quite obvious	Is quite obvious

As can be seen from the above table, the mechanical properties of the product obtained after the commercial starch is plasticized are unstable, and especially the elongation delta (%) of the plasticity index is greatly reduced. After 20 days it becomes very brittle and loses plasticity. The product prepared by plasticizing the starch special for the plastic has very stable mechanical property, higher strength, good plastic toughness and unobvious retrogradation phenomenon. The high plastic performance is still maintained after 30 days, and the retrogradation phenomenon is not shown. Thus, product a is significantly more plastic than product B.

Application No. 202110792308.4 entitled "method for preparing starch specific to plastics and use thereof", the definition of starch specific to plastics being: 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. The applicant has found that when the fineness of the starch is less than 100 mesh, 80 mesh, even when the particle size reaches 1mm, the relevant parameters in the above tables do not change much as long as they can be plasticized by the action of the plasticizer, i.e. the properties of the starch product are not greatly related to the particle size of the starch, and the water content in the starch is the main factor affecting the properties. In addition, due to the existence of crystal water, when the commercial starch is dried by adopting traditional drying means such as a dryer, a fluidized bed and the like, the moisture content can only be dried to about 6%, and the heat consumption needs to be multiplied when the heat consumption is reduced continuously. Therefore, in the present invention: the starch with the water content less than or equal to 5 percent and the organization structure inside the starch granules mainly in an amorphous state and a non-crystalline state is the dry starch of the invention.

The applicant has also found that, in the case of dry starch, the mechanical properties and retrogradation are also related to the moisture content.

Table four shows a comparison of plasticized starch products (after 10 days of molding) formed after plasticizing dry starch (70 parts) and glycerin (30 parts) at different moisture contents:

moisture content (%)	1.34	2.1	4.7	5.0	6.8
						Tensile strength	8.7	8.1	8.0	8.2	8.0
Elongation percentage	189	172	164	132	108
						Retrogradation phenomenon	Is not obvious	Is not obvious	Light and slight	Light and slight	Is lighter

As can be seen from the above table, the lower the moisture content in the dry starch, the better the plasticity of the starch product and the lighter the retrogradation phenomenon. When the water content of the dry starch is not more than 3%, the plasticized dry starch hardly generates a retrogradation phenomenon; when the moisture content of the dry starch reaches 6.8%, a retrogradation phenomenon is exhibited, so that in the present invention, the moisture content of the dry starch is required to be not more than 5%.

In the application number 202110792308.4 entitled "preparation method of starch special for plastics and application thereof", a technical means for removing moisture from commercial starch is used as a distinguishing technology, and the technical means is still one of the technical means which is distinguished from the prior art, namely, the method for obtaining starch with moisture content less than or equal to 5% - -dry starch is creative. The concrete content is as follows:

1. conventional starch drying means have difficulty removing moisture from the starch.

The moisture content of the existing commercial starch is about 13 percent. The applicants believe that water is present in starch in two states: one is free water, which is loosely bound to the starch molecules. When dried, the free water can be dried from the starch relatively easily, using conventional drying means; 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 starch is dried by conventional methods, such as drying ovens, fluid bed drying, etc., bound water is difficult to separate from the starch due to the effect of hydrogen bonding. The water content of the existing commercial starch is 13%, and experiments show that when the water content of the starch is reduced to 6-7% by drying the starch in a dryer, the starch is difficult to reduce again, and the energy consumption is huge. The applicant believes that this is due to the effect of the bound water.

2. The applicant has found through experiments that starch with a water content of 15-30 wt% can be deeply dewatered after being puffed by a puffing machine, so that the water content in the starch is reduced to below 5%.

1) Compared with the existing drying method of starch, the technical method has innovation, and the reason is that the invention adopts the technical idea to be retreated to obtain the dry starch.

The creative first choice of the invention is to reduce the moisture content in the common starch to obtain dry starch, namely to remove the moisture of the commercial starch. However, the water removal means of the present invention is to add water to the starch first to adjust the water content of the commercial starch from about 13% by weight to 15-30% by weight.

The step of adding water to the starch can be selected from the following four methods:

(1) preparing semi-wet starch: adding water directly into commercial starch, wherein the water is added in an amount which enables the water content in the starch to reach 15-30% by weight;

(2) 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;

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

(4) wet starch obtained from a wet milling starch production process is selected and dried to a moisture content of 15-30% wt.

2) The purpose of adjusting the water content of the starch is to expand the starch in the next step, wherein the expansion equipment is an expander.

(1) Water acts as a processing aid and plasticizer for the starch. Commercial starches are powders with moisture contents typically between 13-14%. When starch is added to the bulking machine, if the starch has a low moisture content (e.g., less than 15%), the screw can slip and not be advanced; 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 conditions of the bulking machine cannot change the rigid and solid state of the starch, and water can plasticize the starch under the conditions, so that the starch is converted from rigid to flexible and from solid to fluid, and the water plays the role of a plasticizer, and the larger the water content is, the better the plasticizing effect is. 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) Water acts as a bulking agent for the starch. 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 15%, the starch can be puffed in a puffing machine, and the higher the moisture content is, the better the puffing effect is. However, the water content of the starch is usually selected to be about 18% -22% in consideration of the plasticizing requirement, the subsequent drying requirement, the cost and other factors of the starch.

(3) The bulking machine is a device for bulking starch with a water content of 15-30% by weight.

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. Compared with the extruder used in the plastic field, the rotating speed of the bulking machine is slightly higher, which is approximately in the range of 20-200 revolutions and can also be higher, and the selection is related to the bulking pressure and the size of a die opening required by the process, other parameters of the bulking machine and the like. The speed of rotation of the expander shaft is 30-100 rpm as disclosed in patent CN 1049271A. The operating temperature of the bulking machine is set to meet the bulking requirements and is typically greater than 110 ℃.

The starch extruded from the extruder is solid, and may be formed into a long strip, a pellet or the like depending on the die set and the pelletizer head, or may be appropriately crushed, for example, into a small piece or a block, or a powder, and may be collectively referred to as "starch extrudate" herein. 3) Through puffing, starch puffs are significantly different from commercial starches:

first, the presence state of starch changes: the starch is changed into porous and fluffy blocks from powder through the expansion of the expander, and the fluffy and porous shape (starch expanded body) is very favorable for drying the starch compared with powder.

Secondly, compared with starch, the tissue structure of the puffed body is changed: the document discloses that starch granules are composed of two parts, a crystalline region and an amorphous region. When the starch is expanded, under the high temperature and high pressure of an expander and the plasticizing effect of water as a plasticizer, the crystal structure in the starch granules can be broken to promote the starch granules to be changed from the crystal state to the amorphous state, when the starch in the condition is discharged out of the expander through a die opening, the water plays the role of an expanding agent to expand the starch into a porous and loose starch expanded body, and the internal structure of the starch expanded body 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.

4) The drying of the starch puffed body can overcome the defects of the prior art, and the moisture content in the starch can be easily reduced to be less than 5%, less than 1.5%, less than 1%, even less than 0.5%. The reason why starch puffs are easy to dry is that: firstly, as mentioned above, after the starch exits the bulking machine, the starch exists in the form of fluffy and porous blocks, and compared with the powdery starch, the form of the blocks contributes to the volatilization of water in the starch and the deep drying of the starch by the conventional drying means; secondly, the applicant has found that the water exists in the starch in two states: 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. 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 the amorphous starch and the contained water pass through the die orifice of the bulking machine, under the action of high temperature and high pressure, part of the water is instantly converted into gas to be blown out instead of 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 inner and outer parts, and the moisture in the solid block form is very easy to remove after the solid block form is dried.

In summary, 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.

In the invention, the crushing of the starch puffed body is a conventional technical means, for example, the starch puffed body is crushed in a crusher and a flour mill; if a smaller particle size is desired for the dry starch, it can be milled in an ultra-micro mill.

3. In addition to the foregoing preparation methods, applicants have found that dry starch can also be prepared by several routes:

1) and (5) microwave drying.

The experimental applicant finds that the microwave can easily dry not only the free water in the amorphous area of the starch granule, but also the bound water in the crystalline area inside the starch granule. Because of the directional osmotic energy, the microwave can directly act on water molecules in a crystallization area and excite the water molecules, so that the water molecules are separated from the constraint of hydrogen bonds and released from the interior of the starch, and the aim of drying is fulfilled. The commonly used microwave heating equipment mainly comprises a box type microwave heater and a tunnel type microwave heater, and the commonly used microwave frequency is 915MHz and 2450 MHz. The microwave drying has the characteristics of high speed, good effect and the like, for example, 200g of commercial starch is dried in a household microwave heater, and the water content can be dried to 2.1 percent within 10 minutes.

When the moisture content of the starch after microwave drying is below 5%, the Maltese cross extinction phenomenon disappears under a polarizing microscope, which shows that the crystal structure in the starch is destroyed, and the crystalline state is converted into the amorphous state; the dried starch after microwave drying is also soluble in water, but the degree of dissolution and the rate of dissolution are significantly worse compared to the dried starch after puffing.

2) Deeply drying the commercial pregelatinized starch.

There are two methods of starch pre-gelatinization, the physical method: mixing raw starch with a certain amount of water, heating, and swelling and pasting starch granules;

and then quickly drying and removing the water to obtain the pre-gelatinized starch. The chemical method comprises the following steps: firstly, uniformly stirring the original starch in an alkali liquor with a certain pH value, swelling and pasting starch granules, and then quickly drying and removing moisture to obtain the alkaline pregelatinized starch.

The production process for preparing the pregelatinized starch commonly used in industry specifically comprises the following steps: drum drying, spray drying, extrusion, pulse jet, and the like. The moisture content of commercial pregelatinized starch is about 10-14%.

The pre-gelatinized starch is dried at the temperature of 100-150 ℃ by adopting the conventional drying method, drying by a dryer, fluidized bed drying, vacuum drying and the like, and the dry starch can also be obtained.

For the commercial pregelatinized starch, the Maltese cross extinction phenomenon can be observed under a polarizing microscope, and the applicant believes that a part of moisture also participates in the crystal construction in the starch granules due to the high moisture content of the pregelatinized starch; however, when the pregelatinized starch was dried to 5% or less, the Maltese crossed extinction phenomenon disappeared under a polarizing microscope, indicating that the crystalline state in the starch was changed to an amorphous state. It is also stated that water plays an important role in the formation of starch crystals; both the pregelatinized starch and the dry starch are soluble in water to form a colloid, but the dry starch has a greater affinity for water than the pregelatinized starch.

The water solubility of dry starch is also different from pregelatinized starch. The dry starch has low water content and obviously increased affinity with water. When a certain amount of dry starch is put into water, the outside starch reacts with the water quickly, the starch can form a protective layer in the water, so that the starch floats on the water in a bulk shape, the protective layer is opened, and the starch in the protective layer is still dry and powdery dry starch. This phenomenon is more pronounced the finer the particle size of the dry starch. The dry starch needs strong external mechanical force to break and dissolve the starch cluster; for commercial pregelatinized starch, when the particle size reaches a certain fineness, the agglomeration of starch in water also occurs, but the starch mass settles into water in a shorter time. The agglomerates were opened with no dry powdered starch in between.

3) The commercial starch is heated and dried while bearing extrusion force and shearing force.

As previously mentioned, the applicants believe that bound water in starch is present primarily in the crystalline regions of the starch granules, while free water is present primarily in the amorphous regions. When the crystalline region of the starch is broken and destroyed, the bound water in the original crystalline region can be changed into free water, and the free water is easily removed from the starch granules. Experiments show that the crystalline regions inside the starch granules can be broken up by extruding and shearing the starch. The specific means can be that the two rollers rotate in an unequal contact manner, and can extrude and shear starch between the rollers; the gears are meshed with each other, the racks are meshed with each other or the threads are meshed with each other, and extrusion and shearing can be provided for starch between tooth surfaces; starch between the contact surfaces of the stator and the rotor can be extruded and sheared. The starch is heated while undergoing extrusion and shearing, wherein moisture is easily removed. The conventional apparatuses such as a kneader, a mixer, an internal mixer, and an extruder can provide the above-mentioned extrusion force and shearing force, and thus can be used as an apparatus for drying starch in the present invention.

The following table shows the conditions for drying (a) a commercial starch in a dryer and (b) in an internal mixer (drying temperature 110 ℃ C.):

table five:

time (minutes)	0	15	20	30	40	70
							a water content%	13.15	10.67	8.21	6.34	5.27	3.41
b water content%	13.15	6.21	4.16	3.23	1.97	1.22

As can be seen from the table, the commercial starch is banburied in an internal mixer, and the crystal structure in the starch granules is broken, so that the moisture can be deeply removed and reduced to below 5 percent, and the dry starch is obtained.

The Maltese cross extinction phenomenon disappears when the dry starch is observed under a polarizing microscope, and the dry starch can also be dissolved in water to form a colloid.

4. The dry starch is a new material of an application type.

According to the preceding analysis, the applicant defines dry starch as: the starch with water content below 5% and mainly amorphous internal organization structure is dry starch. The texture inside the commercial starch granules is divided into crystalline and amorphous regions, with semi-crystalline properties. Under a polarizing microscope, the Maltese cross extinction phenomenon can be obviously seen in the commercial starch, namely, crystalline regions exist in commercial starch granules. In addition, the amorphous part of starch is easily compatible with water, forming a colloid with water; however, water hardly invades into the crystallized region portion, so that the starch crystallized region is still present in the original form in water, which results in water insolubility of starch. When commercial starch is placed in water, the starch is usually present in suspension and settles in a relatively short time.

In the case of dry starch, Maltese cross extinction was not observed under a polarizing microscope, indicating that the crystalline state in the internal structure of dry starch disappeared and changed to an amorphous state. Furthermore, when comparing the X-ray diffraction patterns of commercial starch and dry starch, the diffraction peak of the dry starch is significantly weaker than that of the dry starch, and the diffraction peak of the dry starch is wider. In addition, through experiments, the dry starch can be quickly dissolved in water to form a colloidal solution; common starches are largely insoluble in water and form suspensions in water.

No commercial product with dry starch is sold in the market at present, and no expression about the concept of dry starch is found in the prior art.

The starch-based plastic master batch is a starch material with plastic characteristics, wherein the master batch matrix is mainly plasticized dry starch, and is different from starch plastic alloys in the prior art. In the starch plastic alloy, the matrix of the master batch is related plastic rather than starch, the starch is mainly present as a filler, and the material performance related parameters still take the plastic as a main determinant factor. In the starch-based plastic master batch, the performance parameters of the material mainly comprise plasticized dry starch.

The plasticized dry starch is prepared by plasticizing dry starch with a plasticizer. The preparation method comprises the steps of mixing the dry starch with the starch plasticizer, softening and even liquefying the dry starch by the plasticizer at a given temperature and pressure, and cooling to obtain the plasticized dry starch. The plasticized dry starch has the capability of melt molding similar to plastic, can be processed and molded, and the molded product has the characteristics similar to plastic products. Depending on the plasticizing temperature, the plasticized dry starch appears slightly yellow. Taking glycerol as an example for plasticizing dry starch, the cross section color of the plasticized dry starch is clear and colorless, and the dry starch which is slightly not completely plasticized can be observed under an electron microscope.

The preparation and texture characteristics of dry starch are described. Although water is the best plasticizer for starch, the starch plasticizers of the present invention cannot be water. The plasticizer of the dry starch is the same as that of the commercial starch, except for water. CN103992517B discloses that common starch plasticizers are water, glycerol, formamide, urea, sorbitol, low molecular weight polyethylene glycol, etc. Starch plasticizers are mostly small molecular weight, polar molecular materials. As the temperature increases, the starch plasticizer softens the dry starch until both form a molten state.

The moisture content of dry starch is very low and thus a slightly higher amount of plasticizer is required when plasticizing it compared to commercial starch. The proportion of the starch plasticizer in the plasticized dry starch is preferably 15-50 wt%, and when the content is less than 15 wt%, the dry starch is difficult to plasticize; when the content exceeds 50% by weight, the obtained plasticized dry starch is soft and difficult to mold, and the plasticizer precipitation phenomenon is severe. Even between 15% and 50% by weight, there are difficulties in plasticizing the dry starch and the power of the equipment required is high when the plasticizer content is low; however, when the plasticizer content is higher, the plasticized dry starch is softer, and the plasticizer precipitation phenomenon is obvious. Therefore, the plasticizer is preferably contained in an amount of 20 to 30% by weight.

The equipment for plasticizing the dry starch is the existing equipment for processing plastics, wherein an extruder and a refiner are mainly used. The extruder may be a single screw extruder, may be a twin screw extruder, a triple screw extruder, or the like. The extruder is preferably operated to give a material temperature of from 80 ℃ to 180 ℃. The plasticizing effect is influenced when the temperature is low; high temperature, easy decomposition and carbonization of starch. More preferably, the temperature is from 130 ℃ to 150 ℃. The length-diameter ratio of the extruder, the type and the structure of the screw, the rotating speed of the extruder, the working temperature and other processing parameters are combined with each other, and the selection standard of obtaining the melted and homogenized matrix master batch is adopted in the extruder. When preparing sheet products, refiners, like extruders, can be used to determine the relevant parameters as a matter of fact. Similar to plastics, in order to facilitate processing, endow specific properties and the like, a certain amount of processing aids such as a lubricant, a foaming agent and the like can be added in the preparation process of the starch-based plastic master batch; a certain amount of filler such as calcium carbonate, wood powder, bamboo powder, straw powder, etc. can also be added. The lubricant is common lubricant used in plastic processing, white oil, stearic acid, stearate and the like can be adopted, and the adding amount is generally not more than 5 percent (weight). The filler may be an inorganic filler, such as calcium carbonate, typically in an amount of 0 to 50% by weight.

The filler can be organic filler, such as dry starch, wood powder, bamboo powder, straw, etc. The organic fillers can be added in amounts of from 0 to 50% by weight, depending on the toughness required for the desired end product. Because the plasticized dry starch as the matrix, the wood flour, the bamboo powder, the straw and the like are all polyhydroxy high molecules, and the plasticizer is also a polar molecule with hydroxyl or amino, when the plasticized dry starch is mixed and melted with organic fillers such as the wood flour, the bamboo powder, the straw and the like, the compatibility is obviously better than the combination of the organic fillers and plastics, and the product has higher performance. In addition, the filling amount of the organic filler in the plasticized dry starch can be higher than that of the plastic, for example, in the starch-based plastic master batch for preparing the plate, the adding amount of wood powder, bamboo powder or straw powder can account for 70% of the total weight. In order to ensure good mechanical properties of the product, the organic filler is subjected to dewatering and drying before addition, and according to the purpose of the invention, the smaller the water content, the better the water content, and the water content of the filler is preferably not more than 5%.

The starch-based plastic master batch is used as a novel plastic material, and can replace the existing plastic master batch to prepare a plastic product in certain occasions, such as fields of disposable packaging, filling products and the like, thereby achieving the purpose of reducing the cost. More importantly, the product prepared from the starch-based plastic master batch can be completely biodegraded, has small carbon footprint and is more environment-friendly compared with the existing degradable material.

Has the advantages that:

1. the invention provides a novel all-starch plastic material which has better mechanical property;

2. the product prepared from the starch-based plastic master batch can be completely biodegraded, and the carbon footprint is small;

3. compared with petroleum-based plastics, the starch-based plastic master batch and the raw materials of the product thereof are recyclable biomass starch, and compared with PE, PP, PLA and other plastic raw materials, the starch-based plastic master batch has obvious advantages in cost and good economic and social effects.

Best mode for carrying out the invention

Example 1

5000g of starch (commercial starch, the water content of which is 13.4 percent by weight) and 420g of water are mixed in a high-speed mixer for 10 minutes to obtain semi-wet starch, and 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 ℃, 120 ℃, and the diameter of a neck mold is 3 mm. Extruding, heating and puffing semi-wet starch by a puffing machine to obtain a starch puffed body; the starch puffed body is pre-dried by air cooling and drying of an air blower, and the water content of the starch puffed body is measured to be 10.5% -12.5%. Then crushing the pre-dried starch puffed body into granules with the length of 0.1-1mm by using a crusher, taking 250g of the granules, and drying the granules in an electric oven, wherein the temperature of the electric oven is set to be 120 ℃. After 40 minutes the moisture content of the starch was measured to be 0.76%. Obtaining the dry starch.

Mixing 700g of dry starch and 300g of glycerol uniformly in a mixer, and then uniformly adding the mixture into a test extruder, wherein the set parameters of the extruder are as follows: 35mm single screw, rotational speed 7rpm, three heating zones, the heating temperature is in proper order: the diameter of the die orifice is 1mm at 140 ℃, 140 ℃ and 80 ℃. Cooling and dicing the extruded material by a dicing cutter to obtain granular plasticized dry starch.

Example 2

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 puffed starch; the expanded starch was air dried by an air blower and the moisture content of the expanded starch was measured to be 8.6% after drying. Then crushing the pre-dried expanded starch into granules with the diameter of 0.5-2mm by using a crusher, taking 250g of the granules, and drying the granules in an electric oven, wherein the temperature of the oven is set to be 130 ℃. After 30 minutes, the moisture content of the starch was measured to be 0.67%, and the starch was subsequently ground in a mill to give a dry starch with a particle size of 90 mesh.

Mixing 700g of dry starch, 200g of glycerol and 100g of urea in a mixer uniformly, and then adding the mixture into a test extruder uniformly, wherein the set parameters of the extruder are as follows: 35mm single screw, rotational speed 10rpm, three heating zones, the heating temperature is in proper order: the diameter of the die orifice is 3mm at 110 ℃, 110 ℃ and 80 ℃. Cooling and dicing the extruded material by a dicing cutter to obtain granular plasticized dry starch.

Example 3

Taking 700g of dry starch and 450g of glycerol in example 2, uniformly mixing in a mixer, and then adding into an extruder, wherein the parameters set by the extruder are as follows: 35mm single screw, rotational speed 10rpm, three heating zones, the heating temperature is in proper order: the diameter of the die orifice is 1mm at 140 ℃, 140 ℃ and 80 ℃. Cooling the extruded material and pelletizing the extruded material by a pelletizer to prepare granular plasticized dry starch; taking 1000g of 100-mesh bamboo powder (purchased from outsourcing), drying the bamboo powder in a dryer until the water content is 3%, uniformly adding plasticized dry starch and the bamboo powder into an extruder, wherein the parameters of the extruder are as follows: 35mm single screw, rotational speed 10rpm, three heating zones, the heating temperature is in proper order: the size of a die orifice is 0.5 x 20mm at 150 ℃, 150 ℃ and 80 ℃, and the platy starch-based plastic master batch is prepared after extrusion and cooling.

Example 4

2000g of commercial starch (water content 13.2%) were placed in an experimental internal mixer with the following parameters: capacity 1L, temperature range: normal temperature is 300 ℃; heating by an electric heating pipe; the heating power is 2.4KW, and the speed ratio of the rotor is 1: 1.27-1.4; flip angle 110 °, rotor speed: 0-85 rpm. The heating temperature was set at 110 ℃ and the rotational speed was set at 50rpm, and the internal mixer was provided with an exhaust port. Banburying for 20 minutes, discharging to obtain dry starch, and measuring the water content of the dry starch to be 2.2%.

Uniformly mixing 800g of dry starch with 200g of ethylene glycol, 200g of acetamide and 300g of calcium carbonate (800 meshes), and uniformly adding the mixture into a test extruder, wherein the parameters set by the extruder are as follows: 35mm single screw, rotational speed 10rpm, three heating zones, the heating temperature is in proper order: the diameter of the die orifice is 3mm at 140 ℃, 130 ℃ and 80 ℃. And cooling the extruded material and pelletizing by using a pelletizer to obtain the starch-based plastic master batch.

Example 5

700g of commercial pregelatinized starch (water content 11.7%, 50 mesh sieve passage rate 23.6%) was placed in a test dryer and dried at 120 ℃. After 30 minutes, the starch moisture content was measured to be 3.6% to give a dry starch. The dry starch was ground in a ball mill for 0.5 hours with a throughput of 91% in a 180 mesh screen. Uniformly mixing the ground dry starch and 300g of glycerol in a mixer, and uniformly adding the mixture into an extruder for testing, wherein the set parameters of the extruder are as follows: 35mm single screw, rotational speed 10rpm, three heating zones, the heating temperature is in proper order: die size was 0.3 x 10mm at 130 ℃, 120 ℃, 70 ℃. Cooling the extruded material to obtain the flaky starch-based plastic master batch.

Example 6

Mixing 700g of commercial starch (with the water content of 13.2%) and 1400g of water in a stirring kettle, heating to 70 ℃ while stirring, gelatinizing the starch, pouring out, placing into an open container, dehydrating and drying at the drying temperature of 80 ℃ to obtain blocky pre-gelatinized starch. The water content of the pregelatinized starch was 15.6%. And (3) primarily crushing the pregelatinized starch, and then putting the crushed pregelatinized starch into a drying oven for drying at the drying temperature of 120 ℃ for 30 minutes to obtain dry starch with the water content of 5.7%. The dry starch was pulverized in a jet mill and taken out after 20 minutes, and the passing rate in a 270-mesh sieve was 84%. The dry starch, 200g of glycerol and 100g of polyethylene glycol 600 are uniformly mixed in a mixer, and then the mixture is uniformly added into a test extruder, wherein the set parameters of the extruder are as follows: 35mm single screw, rotational speed 10rpm, three heating zones, the heating temperature is in proper order: the diameter of the die orifice is 1mm at 140 ℃, 130 ℃ and 80 ℃. Cooling and dicing the extruded material by a dicing cutter to obtain granular starch-based plastic master batch.

Example 7

700g of commercial starch (water content 13.2%, passing rate of 100 mesh sieve 68%) was dried in a microwave oven at 2450 MHz. After drying for 4 minutes, the starch was found to have a water content of 1.37% to give a dry starch. Mixing dry starch, 100g of glycerol and 200g of urea in a mixer uniformly, and then adding the mixture into an extruder for testing uniformly, wherein the parameters set by the extruder are as follows: 35mm single screw, rotational speed 10rpm, three heating zones, the heating temperature is in proper order: the diameter of the die orifice is 1mm at 110 ℃, 110 ℃ and 80 ℃. Cooling and dicing the extruded material by a dicing cutter to obtain granular starch-based plastic master batch.

Claims

1. A starch-based plastic master batch is characterized in that a plastic master batch matrix is plasticized dry starch, the plasticized dry starch is formed by melting and plasticizing dry starch and a starch plasticizer (except water), wherein the dry starch is starch with the water content of less than or equal to 5 percent (by weight).

2. The starch-based plastic masterbatch of claim 1 wherein said dry starch has a moisture content of no more than 3% by weight.

3. The starch-based plastic masterbatch of claim 1 wherein the starch plasticizer is one or a combination of polar molecular materials containing hydroxyl and/or amino groups, such as methanol, ethanol, ethylene glycol, glycerol, sorbitol, polyethylene glycol, urea, formamide, acetamide.

4. The starch-based plastic masterbatch of claim 1, wherein the masterbatch further comprises a filler in an amount of 0 to 70% by weight.

5. The starch-based plastic masterbatch of claim 4, wherein the filler is one or a combination of wood powder, bamboo powder, straw powder and other organic fillers.

6. The starch-based plastic masterbatch of claim 1 wherein the dry starch is prepared by expanding starch having a moisture content of 15 to 30% by weight and drying the expanded starch.

7. The starch-based plastic masterbatch of claim 1 wherein the dry starch is prepared by microwave drying of starch.

8. The starch-based plastic masterbatch of claim 1 wherein the dry starch is prepared by applying compressive and shear forces to the starch while the starch is dried by heating.

9. The starch-based plastic masterbatch of claim 1 wherein the dry starch is prepared by drying pregelatinized starch.