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Degradable plastic and preparation method thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a degradable plastic and a preparation method thereof, wherein the degradable plastic comprises the following components in parts by weight: 45-70 parts of partially pregelatinized hydroxypropyl starch, 1-30 parts of bio-based resin, 0-5 parts of plasticizer, 1-5 parts of compatilizer, 1-5 parts of lubricant and 1-4 parts of alkali lignin. According to the invention, the degradable bioplastic is prepared by using partial pregelatinized starch with specific cold water solubility to replace natural starch as a raw material, and the degradable bioplastic is found to have more excellent mechanical property and processing property, and contains less plasticizer or even no plasticizer compared with the traditional formula, so that the problem of plasticizer migration is solved; secondly, the water resistance of the pregelatinized starch/PLA composite material is improved by adding the alkali-added lignin, the water absorption rate is lower than 2% after the pregelatinized starch/PLA composite material is placed for 24 hours under the condition that the humidity is 80%, and the pregelatinized starch/PLA composite material can be applied to preparation of safe food packaging materials.

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CN111423627B

China

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Chinese
Inventor
蔡保洪
Current Assignee
SHENZHEN FUHENG NEW MATERIAL Co.,Ltd.

Worldwide applications
2020 CN

Application CN202010481309.2A events
2021-10-08
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Active
Anticipated expiration

Description

Degradable plastic and preparation method thereof
Technical Field
The invention belongs to the technical field of high polymer materials. More particularly, it relates to a degradable plastic and its preparation method.
Background
Starch-based biodegradable plastic is one of the most promising degradable plastics at present, and is generally prepared by blending Starch (TPS), plasticizer and degradable resin, such as polylactic acid, polycaprolactone, polybutylene succinate and the like, and has better processing performance and cost advantage compared with pure degradable resin. The natural starch contains a large amount of hydroxyl groups, has strong polarity and hydrophilicity, contains 13-20% of moisture, and the moisture and the hydroxyl groups in the starch can form strong hydrogen bonds, so that the natural starch presents a granular structure. In conclusion, the natural starch is a natural macromolecule with high rigidity and a plurality of medium chains, the macromolecule comprises crystalline and amorphous heterogeneous substances, and a plurality of groups which can form hydrogen bonds such as hydroxyl groups are learned in the molecule, so that the crystallinity is high, and the properties result in that the melting point of the starch is higher than the degradation temperature of the starch, and the starch cannot be directly processed in practice. In order to improve the fluidity of starch, a plasticizer is required to be added, so that the plasticity of the starch is improved, the hydrogen bonding action of the plasticized starch molecules is weakened, the diffusion capacity of molecular chains is improved, the glass transition temperature of the material is reduced, and the melting of microcrystals can be realized before the starch is decomposed. Meanwhile, the film prepared from the original starch has poor mechanical property and larger brittleness, and the plasticizer is added to increase the distance between starch molecules and improve the flexibility of a molecular chain, so that the toughness of the starch film is improved.
However, like the traditional polymer materials, the starch-based plastics are easy to migrate from the interior of the materials to the packaging interface, and the health hazard caused by the migration of the plasticizer has attracted attention of the masses. At present, in order to inhibit the migration of the plasticizer, related researchers have studied to modify the high molecular polymer by different means, for example, modifying the surface of the material by using a radiation technology; adding nano particles which have stronger interaction with the plasticizer and the material, and the like. However, the above-mentioned technical means are all to suppress the migration of the plasticizer by modifying the material or the like.
Pregelatinized starch refers to modified starch prepared by partially or totally breaking down starch granules by chemical or mechanical means, which is insoluble in organic solvents, slightly soluble to be soluble in cold water, and has better fluidity and mechanical strength than native starch. At present, pregelatinized starch is mainly used as a pharmaceutical adjuvant such as an adhesive, a diluent, a disintegrant and the like, and no report of preparing degradable plastics by using the pregelatinized starch as a plastic main body instead of starch is found.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects and shortcomings of the existing starch-based plastic, and provides the starch-based plastic with low plasticizer content.
The invention aims to provide degradable plastic which comprises the following components in parts by weight: 45-70 parts of partially pregelatinized hydroxypropyl starch, 1-30 parts of bio-based resin, 0-5 parts of plasticizer, 1-5 parts of compatilizer, 1-5 parts of lubricant and 1-4 parts of alkali lignin.
The pregelatinized hydroxypropyl starch can be prepared by adopting any one of corn starch, pea starch, rice starch, wheat starch and sweet potato starch as a raw material, and preferably adopts the corn starch as the raw starch. The pregelatinized hydroxypropyl starch can be prepared by chemical method and mechanical activation method, preferably mechanical activation method. In the mechanical force activation process of the natural starch, due to the action of mechanical forces such as friction, impact, collision, shearing and the like, the appearance, granularity and surface properties of starch particles can be changed, the crystalline structure of the starch is damaged, the crystallinity is reduced, the polycrystalline state is changed into an amorphous state, and meanwhile, the arrangement, molecular weight distribution and the proportion of direct connection and branched chain content of a starch molecular chain can be changed. Therefore, the pregelatinized hydroxypropyl starch obtained by mechanical activation has higher mechanical strength and fluidity and better processability than the original starch.
Further, the partially pregelatinized hydroxypropyl starch has a cold water solubility of 10-45%. Still further, the partially pregelatinized hydroxypropyl starch consists of two partially pregelatinized hydroxypropyl starches having different cold water solubilities.
Further, the different cold water solubilities preferably comprise pregelatinized hydroxypropyl starch with the cold water solubility of 10-25% and pregelatinized hydroxypropyl starch with the cold water solubility of 30-42% in a weight ratio of 3: 1-2. Further, the partially pregelatinized hydroxypropyl starch consists of pregelatinized hydroxypropyl starch with a cold water solubility of 20.2% and pregelatinized hydroxypropyl starch with a cold water solubility of 35.7% in a weight ratio of 3: 1-2. Further, the partially pregelatinized hydroxypropyl starch consists of pregelatinized hydroxypropyl starch having a cold water solubility of 20.2% and pregelatinized hydroxypropyl starch having a cold water solubility of 35.7% in a weight ratio of 3: 1.
As used herein, "cold water solubility" refers to any amount of solubility in water at room temperature (25. + -. 1-2 ℃ C.). The method for measuring the cold water solubility comprises the following steps: a pregelatinized starch sample 2.0g (W) was added to 100 mL of deionized water at a constant temperature (25. + -. 1-2 ℃), continuously stirred, stirred at a high speed for 2min, placed in a centrifuge tube, centrifuged at 3000rpm for 20min, 25mL of the supernatant was removed by a pipette, dried at 110 ℃ to constant weight to obtain the weight (T, g) of the dissolved starch, and the cold water solubility (Sc,%) was calculated according to the following formula.
Sc(%)=
Figure 981991DEST_PATH_IMAGE001
The cold water solubility of the pregelatinized hydroxypropyl starch is continuously increased along with the increase of the activation time, and the pregelatinized hydroxypropyl starch with different cold water solubilities can be accurately prepared by controlling the time and the temperature of mechanical force activation. The mechanical force activation time is controlled to be 10-40 min, and the temperature is controlled to be 50 ℃, so that the pregelatinized hydroxypropyl starch with the cold water solubility of 10-45% can be prepared.
The inventors have surprisingly found that pregelatinized hydroxypropyl starch comprising a particular cold water solubility and particle size can bring significant benefits to the material, such as: firstly, the mechanical property of the material is obviously improved; compared with hydroxypropyl starch, the mechanical strength and the fluidity of the hydroxypropyl starch are obviously improved after the hydroxypropyl starch is pregelatinized, and pregelatinized hydroxypropyl starch molecules and the bio-based resin can be better combined, so that the mechanical property of a material system is better enhanced; ③ systems containing two pregelatinized hydroxypropyl starches with different cold water solubilities can contain smaller amounts of plasticizer, even without plasticizer, still show good processability and mechanical properties. Whereas if pregelatinized starch with a cold water solubility of < 10% or > 45% is added, the same benefits are not imparted to the material.
Further, the plasticizer is selected from one of glycerin, urea, and formamide. In the material system according to the invention, preference is given to using glycerol as plasticizer, which may be present in the form of 2 parts by weight or in smaller amounts.
Further, the bio-based resin is selected from one of polyvinyl alcohol, polylactic acid, polycaprolactone, polybutylene succinate and polyhydroxyalkanoate. Still further, the bio-based resin is polylactic acid.
Further, the compatibilizer is selected from white oil or mineral oil; the lubricant is at least one selected from liquid paraffin, stearic acid amide and n-butyl stearate.
One embodiment of the invention provides degradable plastic which comprises the following components in parts by weight: 45-70 parts of partially pregelatinized hydroxypropyl starch, 1-30 parts of polylactic acid, 0-5 parts of glycerol, 1-5 parts of compatilizer, 1-5 parts of stearic acid and 1-4 parts of alkali lignin; wherein the partial pregelatinized hydroxypropyl starch consists of pregelatinized hydroxypropyl starch with cold water solubility of 10-25% and pregelatinized hydroxypropyl starch with cold water solubility of 30-42% in a weight ratio of 3: 1-2.
Further, the partially pregelatinized hydroxypropyl starch consists of pregelatinized hydroxypropyl starch with a cold water solubility of 20.2% and pregelatinized hydroxypropyl starch with a cold water solubility of 35.7% in a weight ratio of 3: 1-2.
The pregelatinized starch is prepared by mechanical activation of natural starch, and although the material prepared by replacing the natural starch with the pregelatinized starch has good mechanical property and processing property, the mechanical activation destroys the crystalline structure of the pregelatinized starch, increases the free hydroxyl in the pregelatinized starch molecules, improves the water absorption rate, and is unfavorable for the water resistance of the degradable plastic. And proper alkali lignin is added into the material system, so that the water absorption rate of the material system can be obviously reduced, and the water resistance of the material system is improved.
Reference herein to "alkali lignin" is to lignin extracted from plant tissue, preferably said plant is spruce, using alkali.
Further, the invention also provides a method for preparing the degradable plastic, which comprises the following steps:
drying the raw materials at 60-80 ℃ for 6-10 h, adding part of pregelatinized hydroxypropyl starch, plasticizer, bio-based resin and inorganic filler into a high-speed mixer, uniformly mixing, and extruding and granulating by a double-screw extruder.
The invention has the following beneficial effects:
1) the starch-based plastic prepared by replacing natural starch with partial pregelatinized hydroxypropyl starch with specific cold water solubility has higher tensile strength and toughness, contains less plasticizer or even no plasticizer compared with the traditional formula, avoids the problem of plasticizer migration, and can be applied to preparation of safe food packaging materials.
2) The water resistance of the pregelatinized hydroxypropyl starch/PLA composite material is improved by adding the alkali lignin, the water absorption of the material is lower than 2% after the material is placed for 24 hours under the condition that the humidity is 80%, and the method has obvious improvement compared with the prior art.
Detailed Description
The present invention is further illustrated by the following specific examples, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.
Unless otherwise indicated, reagents and materials used in the following examples are commercially available.
Example 1 preparation of partially pregelatinized hydroxypropyl starches of different cold water solubility
The method comprises the following specific steps: adopting a ball mill, wherein the grinding balls are bearing steel balls, cooling by circulating water during ball milling at the rotating speed of 300r/min and the ball-material mass ratio of 20:3, and performing ball milling with other process parameters shown in the following table 1, taking out materials after ball milling, and sieving to obtain part # 1- # 9 of pregelatinized hydroxypropyl starch.
TABLE 1 mechanical force activation parameters
Figure 430290DEST_PATH_IMAGE002
Table 2 examples 2-8 degradable plastic formulations and parts by weight thereof
Figure 364354DEST_PATH_IMAGE003
The preparation method comprises the following steps:
drying the raw materials at 80 ℃ for 8h, adding part of pregelatinized hydroxypropyl starch and glycerol into a high-speed mixer, and uniformly mixing; adding polylactic acid, mineral oil, stearic acid and alkali lignin, uniformly mixing, and extruding and granulating by a double-screw extruder; the length-diameter ratio of the double-screw extruder is 45: 1. The temperatures of the four sections of the twin screw are as follows: the temperature of the first section is 85-90 ℃, the temperature of the second section is 107-110 ℃, the temperature of the third section is 115-118 ℃, and the temperature of the fourth section is 125-130 ℃.
Comparative example 6 differs from example 5 in that instead of pregelatinized hydroxypropyl starch, hydroxypropyl starch was used, and the remaining parameters were the same as in example 6.
Test example I, mechanical Property test
The materials prepared in examples 2-8 and comparative examples 1-6 were injection molded into standard sample bars at injection temperature of 175-185 ℃, injection pressure of 70-90 MPa, and holding pressure of 45MPa, and tensile strength and elongation at break were measured according to GB9341-2000 standard, and the measurement results are shown in Table 3 below.
TABLE 3 test results
Figure 290722DEST_PATH_IMAGE004
From the above table, it can be seen that the inclusion of pregelatinized hydroxypropyl starch having two different cold water solubilities, combined in a specific weight ratio, provides a material system with a significant increase in tensile strength and toughness as compared to the addition of unmodified hydroxypropyl starch (comparative example 6). Wherein, the comprehensive performance of the material is best in the embodiment 5, and the tensile strength and the toughness of the material are respectively improved by 95.2 percent and 89.6 percent compared with the tensile strength and the toughness of the material added with the unmodified hydroxypropyl starch composite material. Whereas the same benefits are not obtained if only one cold water soluble pregelatinized hydroxypropyl starch is added (comparative examples 3 and 4). While comparative example 5 contained no plasticizer, the tensile strength and toughness of the material were improved by 82.8% and 62.7%, respectively, as compared to comparative example 6, indicating that a material system incorporating pregelatinized hydroxypropyl starch with two different cold water solubilities still achieved better performance without the addition of plasticizer.
Test example two, Water resistance test
Putting the samples of the examples 2-8 in a 50 ℃ oven for drying for 24h, and recording the mass as m0The sample was then left to stand at 25 ℃ and 60% and 80% humidity for 24h, recording the mass m1Calculating the sample according to the following formulaWater absorption w, the test results are shown in table 4 below:
w%=
Figure 511619DEST_PATH_IMAGE005
TABLE 4 Water resistance test results
Figure 255453DEST_PATH_IMAGE006
Note: the control group was compared to example 6 with the difference that no alkali lignin was present.
As can be seen from the above table 4, the composite material of the present invention has low water absorption and good water resistance, and the water absorption is lower than 2% after being placed under the condition of humidity 80% for 24 hours, and the water absorption shows an increasing trend along with the increase of the cold water solubility of the composite pregelatinized hydroxypropyl starch; and the control group without the alkali lignin is placed for 24 hours under the same condition, and the water absorption rate reaches 5.06 percent.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (6)
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1. The degradable plastic is characterized by comprising the following components in parts by weight: 45-70 parts of partially pregelatinized hydroxypropyl starch, 1-30 parts of polylactic acid, 0-5 parts of glycerol, 1-5 parts of compatilizer, 1-5 parts of stearic acid and 1-4 parts of alkali lignin; wherein the partial pregelatinized hydroxypropyl starch consists of pregelatinized hydroxypropyl starch with cold water solubility of 10-25% and pregelatinized hydroxypropyl starch with cold water solubility of 30-42% in a weight ratio of 3: 1-2.
2. The degradable plastic of claim 1, wherein the native starch of the partially pregelatinized hydroxypropyl starch is selected from the group consisting of corn starch, pea starch, rice starch, wheat starch, and sweet potato starch.
3. The degradable plastic of claim 1, wherein the compatibilizer is selected from white oil and mineral oil.
4. The degradable plastic of claim 1, wherein the partially pregelatinized hydroxypropyl starch consists of pregelatinized hydroxypropyl starch having a cold water solubility of 20.2% and pregelatinized hydroxypropyl starch having a cold water solubility of 35.7% in a weight ratio of 3:1 to 2.
5. The degradable plastic of claim 1, wherein the plastic comprises the following components in parts by weight: 65 parts of partially pregelatinized hydroxypropyl starch, 20 parts of polylactic acid, 2 parts of glycerol, 5 parts of mineral oil, 3 parts of stearic acid and 3 parts of alkali lignin; the partially pregelatinized hydroxypropyl starch consists of pregelatinized hydroxypropyl starch having a cold water solubility of 20.2% and pregelatinized hydroxypropyl starch having a cold water solubility of 35.7% in a weight ratio of 3: 1.
6. A method for preparing the degradable plastic of claim 5, comprising the steps of:
drying the raw materials at 80 ℃ for 8h, adding part of pregelatinized hydroxypropyl starch and glycerol into a high-speed mixer, and uniformly mixing; adding polylactic acid, mineral oil, stearic acid and alkali lignin, mixing uniformly, and extruding and granulating by a double-screw extruder.