CN109206668B

CN109206668B - Method for preparing thermoplastic starch biodegradable material by supercritical fluid and product

Info

Publication number: CN109206668B
Application number: CN201810791587.0A
Authority: CN
Inventors: 陈勋森; 叶正涛
Original assignee: Shanghai Nytex Composites Products Co ltd
Current assignee: Shanghai Nytex Composites Products Co ltd
Priority date: 2018-05-18
Filing date: 2018-07-18
Publication date: 2021-12-31
Anticipated expiration: 2038-07-18
Also published as: CN109206668A

Abstract

The invention discloses a method for preparing thermoplastic starch biodegradable material by supercritical fluid and a product. Which comprises the following steps: firstly, mixing starch, plasticizer and preplasticizing dispersant in a mass ratio of 1: 0.2-0.4: 0.2-1.2, and obtaining starch mixed liquor I; uniformly mixing the hydrophobic reactant and the starch mixed solution I to obtain a starch mixed solution II; mixing and reacting the starch mixed solution II in a supercritical fluid treatment system to obtain a starch gel; the feeding amount of the starch mixed solution II is 0.16-0.24 kg/L; and fourthly, removing the preplasticizing dispersant from the starch gelatinized product. The invention can add the modifier to carry out one-step modification reaction in the starch gelatinization process, the preparation method is simple, the prepared starch-based biodegradable material has good melt processing fluidity and high tensile strength retention rate, and has better hydrophobicity in the long-time standing process.

Description

Method for preparing thermoplastic starch biodegradable material by supercritical fluid and product

The present application claims priority from chinese patent application CN2018104827967 filed on 2018, 5, month 18. The present application refers to the above-mentioned chinese patent application in its entirety.

Technical Field

The invention relates to a method for preparing thermoplastic starch biodegradable material by supercritical fluid and a product.

Background

Supercritical fluids (SCFs) are fluids of a particular state formed by a substance at or above its critical temperature and pressure. The fluid has the properties of gas and liquid, such as diffusion coefficient, large density, low viscosity, good heat transfer and mass transfer characteristics, and the physical parameters of density, dielectric constant, solubility and the like near a critical point are particularly sensitive to temperature and pressure. Suitable temperatures or pressures may be preferred depending on the particular requirements of the reaction and selectivity. Compared with common liquid solvents, the SCF has obvious advantages in the Transport (Transport) property, the diffusion coefficient of the SCF is nearly 100 times larger than that of the common liquid, and the SCF has high dissolution and fluidity. A material commonly used as SCF is CO₂、H₂O、CH₄、CH₃OH、C₂H₅OH and NH₃Etc., with the most common SCF being a Supercritical carbon dioxide fluid (scCO)₂F) Due to its CO₂Wide source, low critical temperature and pressure, difficult explosion, low price and convenient recovery. The dissolving capacity of the scCO2F can be adjusted, so that the high polymer has strong dissolving, swelling and diffusing capacities, has the advantages of good plasticizing effect, easy purification of products and the like, and is widely applied to extraction, production of reaction media and foaming materials and the like.

Petroleum, as a raw material for plastic production, has the advantages of low price, light weight, easy processing, durability and the like, and is widely applied to various aspects of daily life of people. However, plastic waste is difficult to degrade and recycle, and it takes about 700 years on average to completely decompose plastic bottles. Therefore, the development of renewable materials has been the focus of international research. Polysaccharide renewable materials such as cellulose, chitin and starch widely exist in the nature, wherein the starch has the widest source and is the renewable material with the greatest development prospect. The glass transition temperature and the decomposition temperature of the starch are very close, so that the starch does not have the thermoplastic forming processing characteristic; thermoplastic starches (TPS) are prepared by high temperature, high pressure, plasticizer addition and mechanical shear processing. TPS, however, suffers from a number of disadvantages such as poor mechanical strength and water resistance, which greatly limit its range of applications. Therefore, a great deal of research is carried out by scholars at home and abroad for improving the use property of the thermoplastic starch.

In order to solve the problem that starch-based biodegradable plastic products lose their usability due to water absorption, researchers have used various methods to improve the water resistance of thermoplastic starch. Chinese patent CN101418081B describes a method for esterifying the surface of a thermoplastic starch product, which comprises placing a thermoplastic starch product with an esterifying agent (alkenyl succinic anhydride) on the surface at a certain temperature and for a certain time, so that the esterifying agent reacts with hydroxyl groups on the molecular chain of the starch to form esterified layers with different thicknesses and different degrees of substitution on the surface of the product. Chinese patents CN1273522C and CN1038422C both use modified starches such as oxidized starch, crosslinked starch, ethoxylated starch and acetate starch to produce shaped articles and films having excellent physicomechanical properties (e.g. modulus higher than 4.9X 10)⁸Pascal, yield strength up to 3.9X 10⁷Pascal) and insoluble in water. Chinese patent CN1036659C describes the improvement of hydrophobic properties of thermoplastic starch via the addition of cross-linking agents and other chemical modifiers, such as di-or polyvalent carboxylic acids and/or anhydrides thereof, acyl halides and/or amides of di-or polyvalent carboxylic acids, and the like. Chinese patent CNl190448C and Chinese patent CN1192040C describe the addition of a hydrophobic reactive agent having a hydroxyl group of 4 to 24 carbon atoms to improve the hydrophobic properties of thermoplastic starch. Chinese patent CN103980684A describes a toughened water-resistant starch plastic and a preparation method thereof, wherein thermoplastic starch, polylactic acid, thermoplastic polyurethane and an antioxidant are mixed according to a proportion to obtain the starch plastic with good toughness and water resistance. Chinese patent CN1336936A describes a process for preparing hydrophobic starches by etherification, esterification or acetylation of root or tuber starches or their derivatives with substituents of alkenyl chains of 4-24 carbon atoms. Chinese patent CN101225117A describes the preparation of hydrophobic thermoplastic starch using alkenyl succinic anhydride, which has long aliphatic hydrocarbon chain (C)_12-18) And a five-membered anhydride ring which can react with hydroxyl in starch to generate an ester bond, and the introduced long aliphatic hydrocarbon chain not only has excellent hydrophobicity, but also has good internal plasticization. Chinese patent CNA101328285A describes a process for preparing a hydrophobized thermoplastic starch by mixing starch with an Alkyl Ketene Dimer (AKD) into a high-speed mixer and extruding the mixture through a screw, the AKD having a long aliphatic hydrocarbon chain (C)_14-16) And a quaternary lactone ring which reacts with hydroxyl in the starch to generate a strong hydrophobic beta-carbonyl ester bond. Chinese patent CN1303870A describes a process for hydrophobically modified, degraded hydrated granular starch made by cross-linking starch and epichlorohydrin. Chinese patent CN1850892A describes that starch and aliphatic polyester are mixed, surface graft polylactic acid starch with a proportioning ratio is added for banburying to obtain a completely degradable starch-based compound, the surface graft polylactic acid is a compatibilizer in a blending system, the compatibility between hydrophilic starch and hydrophobic aliphatic polyester materials is improved, and the fully degradable starch-based compound has excellent processing performance, water resistance and acid and alkali resistance. Chinese patent CN103044719A describes that oxidized starch and elastic particles are mixed, then the mixture is washed and dried after centrifugal separation, the elastic particles-oxidized starch coating material with the mesh number larger than 50 is obtained after crushing, the oxidized starch coating material is mechanically mixed with a plasticizer and a lubricant, and finally an extruder is used for extrusion granulation, the prepared thermoplastic starch plastic has good hydrophobic property, the surface contact angle of the thermoplastic starch plastic is increased from 37.5 degrees of pure starch to 108 degrees, the surface contact angle is increased by nearly 3 times, and the surface contact angle is larger than 90 degrees, so that the purpose of hydrophobicity of the thermoplastic starch plastic is realized. Chinese patent CN101302321A describes that the heat resistance, water resistance and physical properties of the obtained thermoplastic starch are obviously improved by mixing and stirring starch, plasticizer, maleic anhydride, tert-butyl peroxide and dioctyl maleate, then carrying out extrusion reaction on the mixture together with water, cooling to obtain master batches, and then carrying out stirring extrusion and granulation on the master batches, secondary plasticizer and glutaraldehyde through a high-speed mixing mill. Chinese patent CN104974381A describes that starch, plasticizer, pre-plasticizer and strengthening agent after microwave treatment are mixed, heated and stirred, and then are blended and extruded for granulation after drying and dewatering, and the obtained starch-based biodegradable composite material has high mechanical strength and good water resistance. Chinese patent CN105218868B describes Glutaraldehyde (GA) -modified thermoplastic starch-based biodegradableThe hydrophobicity and the Strength retention rate (Strength retention) of the material are researched, and the result shows that the hydrophobicity and the tensile Strength retention rate of the thermoplastic starch can be better improved by adding GA.

Summarizing the above patents, the surface of starch is modified for hydrophobicity, mostly after surface modification the hydrophobic properties are general, and there is little practical attempt to affect its mechanical strength after long aging (water absorption) tests. In addition, the research on the preparation of hydrophobic thermoplastic starch biodegradable materials with high mechanical strength by using supercritical carbon dioxide assisted processing technology is rarely reported.

Disclosure of Invention

The invention aims to overcome the defects of poor melt processing fluidity, difficult processing, poor moisture resistance and low strength retention rate of thermoplastic starch prepared in the prior art, and provides a method for preparing a biodegradable thermoplastic starch material by using supercritical fluid and a product. The invention can add the modifier to carry out one-step modification reaction in the starch gelatinization process, the preparation method is simple, the prepared starch-based biodegradable material has good melt processing fluidity and high tensile strength retention rate, and has better hydrophobicity in the long-time standing process.

The invention solves the technical problems through the following technical scheme.

The invention provides a preparation method of a hydrophobic thermoplastic starch-based biodegradable material, which comprises the following steps:

(1) starch, a plasticizer and a pre-plasticizing dispersant are mixed according to a mass ratio of 1: (0.2-0.4): (0.2-1.2) uniformly mixing to obtain a starch mixed solution I;

(2) uniformly mixing a hydrophobic reactant with the starch mixed solution I to obtain a starch mixed solution II;

(3) in a supercritical fluid treatment system, mixing and reacting the starch mixed solution II in the step (2) to prepare a starch gel; wherein the temperature of the mixing reaction is 75-120 ℃, and the time of the mixing reaction is 10-40 min; the feeding amount of the starch mixed solution II is (0.16-0.24) kg/L, and the feeding amount is the ratio of the mass of the starch mixed solution II to the volume of a reaction kettle in the supercritical fluid treatment system;

(4) and (3) removing the preplasticizing dispersant in the step (1) from the starch gel in the step (3).

In step (1), the starch is conventional in the art and is preferably selected from native starch and/or starch modified with a starch modifier. The natural starch is conventional in the art, and is preferably selected from one or more of corn starch, wheat starch, sweet potato starch, potato starch and tapioca starch, and more preferably tapioca starch. The starch modifier is conventional in the art and is preferably selected from one or more of carboxylic acid, anhydride, acid halide and amide. Wherein, the carboxylic acid is preferably one or more of citric acid, acetic acid, malic acid and sebacic acid; the acid anhydride is preferably acetic anhydride and/or maleic anhydride; the acid halide is preferably an acid chloride; the amide is preferably one or more of formamide, N-methylformamide and dimethylacetamide.

In step (1), the mixing is preferably performed by cutting and dispersing in a mechanical mixer, more preferably by cutting and dispersing for 0.5-1h, and most preferably by cutting and dispersing for 1 h.

In step (1), the plasticizer is generally a plasticizer conventionally used in the field of preparing thermoplastic starch-based biodegradable materials, and is preferably one or more of water, ethylene glycol, glycerol, dimethyl sulfoxide and urea, and is more preferably glycerol.

In the actual development process, the selection and addition of the plasticizer have great influence on the physical properties (such as melt index, tensile strength and the like) of the prepared thermoplastic starch under proper pressure and temperature. For example, when the plasticizer is water, an excessive amount of water is added to increase CO in the subsequent modification reaction₂The starch is blended into the starch mixed solution II, so that the acidity of the starch mixed solution II is enhanced, and starch molecules can be severely acidolyzed under the conditions of high temperature and high pressure, so that the tensile strength is remarkably reduced; for another example, when the plasticizer is glycerol, the amount of glycerol added is too small, and the thermoplastic starch obtained under supercritical conditions is dried to a moisture contentAfter less than 0.5 wt%, the melt index of the thermoplastic starch material is significantly reduced.

In step (1), the preplasticizing dispersant is generally a liquid agent which can uniformly mix and disperse starch and plasticizer under certain conditions, preferably one or more of ethanol, water and methanol, and more preferably water.

In the step (1), in the starch mixed solution I, the mass ratio of the starch, the plasticizer and the preplasticizing dispersant is preferably 1: (0.2-0.4): (0.6-0.8), more preferably 1: 0.2: 0.6.

in the step (2), the hydrophobic modifier is a chemical reaction reagent which can chemically react with the starch under certain conditions to reduce hydrophilic groups on the surface of starch molecules and increase the hydrophobic property of the starch, and is preferably selected from one or more of polyaldehydes, phosphates, amides, polyvinyl alcohol and organic acids and anhydrides thereof.

Wherein, when the hydrophobic modifier is polyaldehyde, the mass ratio of the hydrophobic modifier to the starch is preferably (0-0.8): 100, more preferably (0.1-0.4: 100), most preferably 0.2: 100. when the hydrophobic modifier is a phosphate, the mass ratio of the hydrophobic modifier to the starch is preferably (0-32): 100. when the hydrophobic modifier is an amide, the mass ratio of the hydrophobic modifier to the starch is preferably (0-5): 100, more preferably (1.25-5: 100). When the hydrophobic modifier is polyvinyl alcohol, the mass ratio of the hydrophobic modifier to the starch is preferably (0-10): 100, more preferably 2.5: 100. when the hydrophobic modifier is an "organic acid and an acid anhydride thereof", the mass ratio of the hydrophobic modifier to the starch is preferably (0 to 3): 100.

wherein, the polyaldehyde can be water-soluble polyaldehyde hydrophobic modifier which is conventional in the field, and preferably one or more of glyoxal, succinaldehyde and glutaraldehyde. The phosphate may be a phosphate hydrophobing agent modifier conventional in the art, preferably sodium trimetaphosphate and/or sodium hexametaphosphate. The amide may be a hydrophobic modifier of amides conventional in the art, preferably formamide and/or acetamide. The "organic acid and the anhydride thereof" may be a hydrophobic modifier of organic acid and the anhydride thereof, which is conventional in the art, and preferably one or more of citric acid, succinic acid, maleic anhydride and phthalic anhydride.

In the step (2), the hydrophobic modifier is preferably present in the form of an aqueous solution, and the mass percentage of the hydrophobic modifier in the aqueous solution of the hydrophobic modifier is preferably 20 to 40%, more preferably 25%.

In step (3), the supercritical fluid refers to a special state fluid formed by a substance at a temperature above its critical temperature and pressure. The fluid has the properties of both gas and liquid, such as viscosity, density, diffusion coefficient, solvating power and the like, and is sensitive to temperature and pressure changes. The viscosity and diffusion coefficient approach that of a gas, while the density and solvating power approach that of a liquid. The substance used as the supercritical fluid may be a substance conventionally used in the chemical field as a supercritical fluid, preferably CO₂、H₂O、CH₄、CH₃OH、C₂H₅OH or NH₃More preferably CO₂。

In the step (3), the mixing reaction is generally carried out in a high-pressure reaction vessel. The temperature of the mixing reaction is preferably 80 to 100 c, more preferably 90 c. The mixing reaction time is preferably 15-25min, more preferably 20 min.

In step (3), the operation of placing the starch mixed liquor II in the supercritical fluid treatment system in step (2) can be conventional in the art, and is preferably performed according to the following steps: and (3) placing the starch mixed solution II in the step (2) into a high-pressure reaction kettle, and pressurizing the supercritical fluid to 7.5-12MPa by using a booster pump at 15-25 ℃. If the temperature of the pressure rise is too high, the sample part is gelatinized too early, the experimental result is influenced, and if the temperature is too low, the reaction time is increased, the resources are wasted, and the processing cost is increased. The pressure range ensures the pressure range which can be borne by the experimental device, ensures the experimental safety, and simultaneously has the processability and better strength retention rate of the sample prepared in the pressure range.

When the supercritical carbon dioxide is used for assisting in preparing the thermoplastic starch biodegradable material, the addition amount of the starch mixed solution II in the reaction kettle needs to be controlled well, and if the addition amount is too small, the prepared product is starch aerogel or starch foam; if the amount is too large, the starch gelatinization effect is reduced. The feeding amount of the starch mixed solution II is preferably (0.18-0.22) kg/L, and more preferably 0.2 kg/L.

In the step (3), the stirring rate during the mixing reaction can be conventional in the art, preferably 100 rpm/min and 300 rpm/min, and more preferably 190 rpm/min.

In the step (4), the operations of removing the pre-plasticizer in the steps (1) and (2) are conventional in the chemical field, and preferably, the starch gel is dried. When the hydrophobic modifier is present as an aqueous solution, the aqueous solution of the hydrophobic reactant can also be subjected to water removal while drying. Preferably, the water content of the dried product is controlled within 0.5 wt%.

Wherein the drying temperature is preferably 0 to 100 ℃, more preferably 60 to 100 ℃. The drying time is preferably 0.5 to 50 hours, more preferably 2 to 50 hours. The drying operation is preferably carried out as follows: and (3) drying the starch gel in an air-blast drying oven or an infrared direct-heating drying oven, and then drying in a vacuum drying oven or a dew-point drying oven.

Wherein, the temperature for drying in the air-blast drying oven or the infrared direct-heating drying oven is preferably 75-85 ℃, and more preferably 80 ℃. The drying time of the air-blast drying oven or the infrared direct-heating drying oven is preferably 5-10h, and more preferably 8 h. The temperature for drying in the vacuum drying oven or the dew point drying oven is preferably 0 to 100 deg.C, more preferably 60 to 100 deg.C, and most preferably 80 deg.C. The drying time of the vacuum drying oven or the dew point drying oven is preferably 4 to 30 hours, more preferably 10 to 30 hours, and most preferably 8 hours.

Preferably, the product obtained in step (4) is granulated. The granulation is preferably carried out in an internal mixer or a screw extruder, more preferably in a screw extruder.

In the granulation, a compatibilizer is preferably further added. The compatibilizer is preferably one or more of maleic anhydride, succinic anhydride, acetic anhydride, propionic anhydride, and phthalic anhydride, and more preferably maleic anhydride. The mass ratio of the solubilizer to the starch gel without the preplasticizer is preferably (0.5-5): (5-10).

In the granulation, it is preferable to further add a biodegradable material. The biodegradable material is preferably biodegradable aliphatic polyester material and/or biodegradable aliphatic and aromatic copolyester material, more preferably one or more of polylactic acid, polybutylene succinate/terephthalate, polybutylene succinate/adipate, polybutylene adipate/terephthalate and polycaprolactone, and most preferably polylactic acid. The biodegradable material and the starch gel without the pre-plasticizer preferably have a mass ratio of (0.5-5): (5-10).

In the present invention, it is preferable to add a coloring agent to the starch mixture II. The colorant may be conventional in the art, and is preferably a metal oxide, more preferably titanium dioxide. The mass ratio of the coloring agent to the starch is preferably (0.1-20): 100, more preferably (0.5-5): 100, optimally 2: 100.

the invention also provides the hydrophobic thermoplastic starch-based biodegradable material prepared by the preparation method.

In a preferred embodiment of the invention, the glutaraldehyde and/or polyvinyl alcohol modified thermoplastic starch biodegradable material with high mechanical strength is prepared by using a supercritical carbon dioxide auxiliary processing technology, wherein when the content of the glutaraldehyde is 0.1PHR, the tensile strength of an injection molded sample strip can be kept at 17.5MPa after the sample strip is placed for 56 days at the temperature of 20 ℃/50% relative humidity, the elongation at break can reach 15.6%, and the water absorption rate is 4.7% after 56 days. When the content of polyvinyl alcohol is 2.5PHR, the tensile strength of the injection-molded sample strip can be kept at 19MPa after the sample strip is placed for 84 days under the conditions of 20 ℃/50 percent relative humidity, the elongation at break can reach 14.7 percent, and the water absorption rate after 84 days is 3.3 percent.

On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.

The reagents and starting materials used in the present invention are commercially available.

The positive progress effects of the invention are as follows:

1. the invention can add the modifier to carry out one-step modification reaction in the starch gelatinization process under the condition of supercritical carbon dioxide, can prepare the hydrophobic starch-based biodegradable material by the traditional thermoplastic processing equipment, and has simple preparation method.

2. The starch-based biodegradable material prepared by the invention has good melt processing fluidity, and has higher retention rate of tensile strength and better hydrophobicity in the long-time storage process.

Drawings

FIG. 1 is a graph showing the melting index of the thermoplastic starch biodegradable composites of examples 1 to 5 and comparative examples 1 to 7 as a function of the amount of glutaraldehyde aqueous solution added at 20 ℃/50% relative humidity. Wherein, Delta is a comparative example 1,

in the case of comparative example 2,

in the case of comparative example 3,

comparative example 4, □ comparative example 5, O comparative example 6, ● comparative example 7, A in example 1,

for the purposes of example 2, there was a description of the preferred embodiment,

in the case of the example 3, the following example was carried out,

for example 4, ■ is example 5.

FIG. 2 shows the thermoplastics of examples 1 to 5 and comparative examples 1 to 7The water content of the biodegradable starch composite material changes with the standing time under the condition of 20 ℃/50 percent relative humidity. Wherein, Delta is a comparative example 1,

in the case of comparative example 2,

in the case of comparative example 3,

in the case of the example 3, the following example was carried out,

for example 4, ■ is example 5.

FIG. 3 is a graph showing tensile strength and elongation at break of the thermoplastic starch biodegradable composites of examples 1 to 5 and comparative examples 1 to 7 at 20 ℃/50% relative humidity as a function of the standing time. Wherein, Delta is a comparative example 1,

in the case of comparative example 2,

in the case of comparative example 3,

comparative example 4, □ comparative example 5, O comparative example 6, ● comparative example 7,

in order to carry out the method of example 1,

in the case of the example 3, the following example was carried out,

for example 4, ■ is example 5.

FIG. 4 is a graph showing the melting index of the thermoplastic starch biodegradable composite materials of examples 6 to 10 and comparative examples 6 to 12 at 20 ℃/50% relative humidity as a function of the amount of PVA added. Wherein O is comparative example 6, ● is comparative example 7, Delta is comparative example 8,

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12,

in the case of the example 6, the following example was carried out,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10.

FIG. 5 is a graph showing the change of water content with respect to the standing time of the thermoplastic starch biodegradable composite materials of examples 6 to 10 and comparative examples 6 to 12 under the condition of 20 ℃/50% relative humidity. Wherein O is comparative example 6, ● is comparative example 7, Delta is comparative example 8,

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12, a-treatment of example 6,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10.

FIG. 6 is a graph showing the tensile strength of the thermoplastic starch biodegradable composites of examples 6 to 10 and comparative examples 6 to 12 at 20 ℃/50% relative humidity as a function of the standing time. Wherein O is comparative example 6, ● is comparative example 7, Delta is comparative example 8,

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12,

in the case of the example 6, the following example was carried out,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10.

FIG. 7 is a graph showing the elongation at break resistance of the thermoplastic starch biodegradable composites of examples 6 to 10 and comparative examples 6 to 12 at 20 ℃/50% relative humidity as a function of the standing time. Wherein O is comparative example 6, ● is comparative example 7, Delta is comparative example 8,

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12, a-treatment of example 6,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.

The percentages, parts, etc. used in the following examples refer to mass percentages and parts of the materials, unless otherwise specified. In the following examples and comparative examples, the volume of the autoclave is 1L in the supercritical carbon dioxide assisted process for preparing the thermoplastic starch biodegradable material.

Example 1

Thermoplastic starch biodegradable composites were prepared in the formulation ratios described in table 2 below.

(1) Mixing starch (cassava starch), a plasticizer (glycerol) and a pre-plasticizing dispersant (water) according to a mass ratio of 5:2:3 cutting, dispersing and mixing for 1h in a mechanical stirrer, and adding 0.05phr (relative to 100 parts of starch, the amount of the glutaraldehyde aqueous solution is 0.05 part) of glutaraldehyde aqueous solution (the mass percent of the glutaraldehyde is 25 wt%) to prepare a starch mixed solution;

(2) adding titanium dioxide into the starch mixed solution obtained by mixing the above (1), placing into a high-pressure reaction kettle, and pressurizing carbon dioxide to 9.0MPa by using a booster pump at 25 ℃; the volume ratio of the starch mixed solution to the high-pressure reaction kettle is about 0.2 kg/L;

(3) heating to 100 deg.C in a high-pressure reaction kettle, gelatinizing with a magnetic stirrer at 190 rpm for 20min to obtain starch gel;

(4) and (3) drying the modified thermoplastic starch prepared in the step (3) in an infrared direct-heating drying oven at 80 ℃ for 8 hours, then drying in a vacuum drying oven at 80 ℃ for 8 hours, controlling the water content of the dried starch resin to be less than or equal to 0.5 wt%, and performing injection molding to obtain the product.

Example 2

The conditions were the same as in example 1 except that the amount of the aqueous glutaraldehyde solution was changed.

Example 3

Example 4

Example 5

Comparative example 1

Thermoplastic starch biodegradable composites were prepared in the formulation ratios described in table 1 below.

(2) adding titanium dioxide into the starch mixed solution obtained in the step (1), putting the starch mixed solution into a reaction kettle, heating to 100 ℃ under normal pressure, and gelatinizing for 20min under stirring of a magnetic stirrer at 190 revolutions per minute to obtain a starch gel; the volume ratio of the starch mixed solution to the reaction kettle is about 0.2 kg/L;

(3) and (3) drying the thermoplastic starch prepared in the step (2) in an infrared direct-heating drying oven at 80 ℃ for 8 hours, then drying in a vacuum drying oven at 80 ℃ for 8 hours, controlling the water content of the dried starch resin to be less than or equal to 0.5 wt%, and performing injection molding to obtain the product.

Comparative example 2

The conditions were the same as in comparative example 1 except that the amount of glutaraldehyde aqueous solution added was varied.

Comparative example 3

Comparative example 4

Comparative example 5

Comparative example 6

Thermoplastic starch biodegradable composites (prepared under atmospheric conditions) were prepared according to the formulation ratios set forth in table 1 below.

The conditions were the same as in comparative example 1 except that no aqueous glutaraldehyde solution was added.

Comparative example 7

Thermoplastic starch biodegradable composites (prepared under supercritical pressure) were prepared according to the formulation ratios described in table 2 below.

The conditions were the same as in example 1 except that no aqueous glutaraldehyde solution was added.

TABLE 1 formulation proportions (parts by mass) of comparative examples 1 to 6

TABLE 2 formulation proportions (parts by mass) of comparative example 7 and examples 1 to 5

The performance parameters of the composites prepared in comparative examples 2, 6-7 and example 2 are shown in Table 3 and FIGS. 1-3.

TABLE 3 Performance parameters of the composites of comparative examples 2, 6-7 and example 2

As can be seen from Table 3, the melt index (high melt index indicates good flowability and good processability) and the tensile strength after being placed for 56 days of the test piece injection molded by the invention in example 2 are obviously higher than those of comparative examples 2 and 6 under the condition of 20 ℃/50% relative humidity, and the water content and the elongation at break after being placed for 56 days of the test piece injection molded by the invention in example 2 are obviously lower than those of comparative examples 2 and 6-7 under the condition of 20 ℃/50% relative humidity. Further, the densities measured by comparative examples 6 to 7, comparative example 2 and example 2 according to the present invention were 1.31, 1.30, 1.30 and 1.31g/cm, respectively³The density remains substantially the same within experimental error tolerances.

in the case of comparative example 2,

in the case of comparative example 3,

in the case of the example 3, the following example was carried out,

for example 4, ■ is example 5. As can be seen from FIG. 1, comparative examples 1 to 5, which were not subjected to the supercritical carbon dioxide-assisted processing, had a significantly reduced melt index as the amount of glutaraldehyde added was gradually increased, and then were subjected toThe melt index of the examples 1 to 5 which passed through the supercritical carbon dioxide-assisted processing decreased more slowly as the addition amount of glutaraldehyde increased, while the melt index of comparative example 7 was higher than that of comparative example 2.

FIG. 2 is a graph showing the water content of the thermoplastic starch biodegradable composite materials of examples 1 to 5 and comparative examples 1 to 7 at 20 ℃/50% relative humidity as a function of the standing time. Wherein, Delta is a comparative example 1,

in the case of comparative example 2,

in the case of comparative example 3,

in order to carry out the method of example 1,

in the case of the example 3, the following example was carried out,

for example 4, ■ is example 5. As can be seen from FIG. 2, the retention values of the water content for a long time of comparative example 6 modified without addition of glutaraldehyde are respectively significantly higher than those of comparative examples 1 to 5, the retention values of the water content for a long time of comparative example 7 are respectively significantly higher than those of examples 1 to 5, and the retention values of the water content for a long time of comparative example 6 and comparative examples 1 to 5 which are not subjected to supercritical carbon dioxide-assisted processing are significantly higher than those of comparative example 7 and examples 1 to 5. After standing for 56 days, the water content value of example 2 is significantly lower than that of comparative examples 6 and 3.

FIG. 3 shows the biodegradable thermoplastic starch composites of examples 1 to 5 and comparative examples 1 to 7 at 20 ℃/50% relative humidityTensile strength and elongation at break under the conditions as a function of time of standing. Wherein, Delta is a comparative example 1,

in the case of comparative example 2,

in the case of comparative example 3,

in the case of the example 3, the following example was carried out,

for example 4, ■ is example 5.

As can be seen from FIG. 3, the tensile strength of comparative example 6, which was not modified with glutaraldehyde, was significantly lower than that of comparative examples 1 to 5, and that of comparative example 7 was significantly lower than that of examples 1 to 5. Comparative example 6 and comparative examples 1-5, which were not processed with supercritical carbon dioxide assistance, had significantly lower long term tensile strength than comparative example 7 and examples 1-5. After 56 days of standing, the tensile strength of example 2 is significantly higher than that of comparative examples 6 and 3.

As can be seen from FIG. 3, the elongation at break for a long time of comparative example 6 modified without addition of glutaraldehyde is significantly higher than that of comparative examples 1 to 5, and that of comparative example 7 is significantly higher than that of examples 1 to 5. Comparative example 6 and comparative examples 1-5, which were not processed with the aid of supercritical carbon dioxide, had significantly higher long-term elongation at break than comparative example 7 and examples 1-5. After 56 days of standing, the elongation at break of example 2 is significantly lower than that of comparative examples 6 and 3.

Comparative example 8

Thermoplastic starch biodegradable composites were prepared in the formulation ratios described in table 4 below.

(1) Mixing and stirring starch (cassava starch), plasticizer (glycerol) and pre-plasticizing dispersant (water) according to a mass ratio of 5:2:3, and adding PVA (polyvinyl alcohol) (the amount of PVA is 0.5 part relative to 100 parts of starch) with the amount of 2.5g to prepare starch mixed solution;

(2) adding titanium dioxide into the starch mixed solution obtained by mixing the above (1), placing into a reaction kettle, heating to 100 ℃ under normal pressure, and gelatinizing for 20min under stirring of a magnetic stirrer at 190 rpm to obtain a starch gel; the volume ratio of the starch mixed solution to the reaction kettle is about 0.2 kg/L;

Comparative example 9

The conditions were the same as in comparative example 8 except that the amount of PVA added was different.

Comparative example 10

Comparative example 11

Comparative example 12

Example 6

Thermoplastic starch biodegradable composites were prepared in the formulation ratios described in table 5 below.

(4) and (4) putting the supercritical carbon dioxide auxiliary processing thermoplastic starch and the glutaraldehyde modified thermoplastic starch prepared in the step (3) into an infrared direct-heating drying oven at 80 ℃ for drying for 8h, then putting into a vacuum drying oven at 80 ℃ for drying for 8h, controlling the water content of the dried starch resin to be less than or equal to 0.5 wt%, and performing injection molding to obtain the product.

Example 7

The conditions were the same as in example 6 except that the amount of PVA added was changed.

Example 8

Example 9

Example 10

TABLE 4 formulation proportions (parts by mass) of comparative example 6 and comparative examples 8 to 12

TABLE 5 formulation proportions (parts by mass) of comparative example 7 and examples 6 to 10

The performance parameters of the composites prepared in comparative examples 6-7, comparative example 10 and example 8 are shown in Table 6 and FIGS. 4-7.

TABLE 6 Performance parameters of the composites of comparative examples 6-7, 10 and example 8

As can be seen from Table 6, the melt index and the tensile strength after 84 days of storage at 20 ℃/50% RH of the bars obtained by injection molding according to example 8 of the present invention are significantly higher than those of comparative examples 6 and 10, while the water content and the elongation at break after 84 days of storage at 20 ℃/50% RH of the bars obtained by injection molding according to example 8 are significantly lower than those of comparative examples 6 and 10.

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12, a-treatment of example 6,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10. As can be seen from FIG. 4, the melt index of comparative examples 8 to 12 which were not subjected to the supercritical carbon dioxide-assisted processing first rapidly increased to achieve the optimization with the gradually increasing amount of PVA, and then slowly decreased, whereas the melt index of examples 6 to 10 which were subjected to the supercritical carbon dioxide-assisted processing significantly increased to achieve the optimization with the gradually increasing amount of PVA, and at the same time, the melt index of comparative example 7 was higher than that of comparative example 6, and the melt index of examples 6 to 10 which were subjected to the supercritical carbon dioxide-assisted processing was significantly higher than that of comparative examples 8 to 12.

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12, a-treatment of example 6,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10. As can be seen from FIG. 5, the retention values of moisture content for a long period of time of comparative example 6 and comparative example 7 modified without adding PVA are significantly higher than those of examples 6 to 10 and comparative examples 8 to 12, respectively, and the retention values of moisture content for a long period of time of comparative example 6 and comparative examples 8 to 12 without supercritical carbon dioxide-assisted processing are significantly higher than those of comparative example 7 and examples 6 to 10, respectively. After 84 days of standing, the value of the water content of example 8 is significantly lower than that of comparative examples 6 to 12.

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12, a-treatment of example 6,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10. As can be seen from FIG. 6, comparative examples 6 and 7, which were not modified with PVA, had significantly lower retention values of tensile strength for a long period of time than examples 6 to 10 and comparative examples 8 to 12, respectively, and did not contain supercritical dioxygenComparative example 6, which was carbon dioxide-assisted processed, had a significantly lower long-term tensile strength retention value than comparative example 7, and comparative examples 8-12, which were not supercritical carbon dioxide-assisted processed, had significantly lower long-term tensile strength retention values than examples 6-10. After 84 days of standing, the tensile strength values for example 8 are significantly higher than for comparative examples 6-12.

in the case of comparative example 9,

in the case of comparative example 10,

comparative example 11, □ comparative example 12, a-treatment of example 6,

in the case of the embodiment 7, the following example was carried out,

in the case of the embodiment 8, the following example was carried out,

for example 9, ■ is example 10. As can be seen from FIG. 7, comparative example 6 and comparative example 7, which were not modified with PVA, had higher values of retention of elongation at break for a long period of time than comparative examples 8 to 12 and examples 6 to 10, respectively. The retention of elongation at break for long periods of time of comparative example 6 without supercritical carbon dioxide assisted processing was significantly higher than that of comparative example 7, and the retention of elongation at break for long periods of time of comparative examples 8-12 without supercritical carbon dioxide assisted processing was significantly higher than that of examples 6-10. After 84 days of standing, example 8 had lower elongation at break values than comparative examples 6-12.

Comparative example 13

Starch-based biodegradable materials were prepared in the formulation ratios described in table 7 below.

(1) Mixing cassava starch, glycerol and water according to a mass ratio of 5:1:4 to form a starch suspension, and then placing the starch suspension in a mechanical stirrer to disperse for 1h to obtain a starch mixed solution I;

(2) putting a blend of natural bacterial cellulose fibers, glycerol and water in a mass ratio of 0.001:1:1 in a dispersion machine for 2 hours, standing for 6 hours, and then mixing with the starch mixed solution I obtained in the step (1) to obtain a starch mixed solution II; wherein the mass ratio of the natural bacterial cellulose fiber to the cassava starch is 0.02: 100; the length of the natural bacterial cellulose fiber is 0.1-1 μm; the diameter is 20-100nm.

(3) Adjusting the pH value of the starch mixed solution II obtained in the step (2) to 3 by using citric acid, adding 0.5phr of glutaraldehyde aqueous solution, then placing the mixture in a mechanical stirrer, and stirring for 2min at the temperature of 90 ℃ to obtain a starch gel;

(4) and (4) placing the starch gel obtained in the step (3) into an air-blowing drying oven to dehydrate for 48 hours at the temperature of 8 ℃, dehydrating for 24 hours at the temperature of 80 ℃ in a vacuum drying oven, adding titanium dioxide, extruding and granulating in a screw extruder, and performing injection molding to obtain a finished product.

Comparative example 14

Starch-based biodegradable composites (microwave treatment) were prepared according to the formulation ratios described in table 7 below. Firstly, cassava starch is treated by high-power microwave of 900W for 30 seconds, then the corn starch modified by the microwave, glycerol and water are mixed to form starch suspension, and then the starch suspension is placed in a mechanical stirrer for dispersing for 1 hour. Adding the water-dispersed modified bacterial cellulose fiber into the starch suspension, then placing the starch suspension into a mechanical stirrer, stirring the starch suspension for 30min at the temperature of 80 ℃, taking out the starch suspension, placing the starch suspension into a forced air drying oven, dehydrating the starch suspension for 24h at the temperature of 80 ℃, adding titanium dioxide, extruding, granulating and injection-molding to obtain a finished product. The test shows that the tensile strength of the injection molding sample strip can reach 10.6 MPa.

TABLE 7 formulation ratios (parts by mass) of comparative examples 13 to 14 and examples 3 and 8

The performance parameters of the composites prepared in comparative examples 13 and 14 and examples 3 and 8 are shown in Table 8.

TABLE 8 Performance parameters of the composites of comparative examples 13-14 and examples 3, 8

Claims

1. A preparation method of a hydrophobic thermoplastic starch-based biodegradable material comprises the following steps:

(1) starch, a plasticizer and a pre-plasticizing dispersant are mixed according to a mass ratio of 1: (0.2-0.4): (0.6-0.8) uniformly mixing to obtain a starch mixed solution I;

(2) uniformly mixing a hydrophobic modifier with the starch mixed solution I to obtain a starch mixed solution II;

(4) removing the pre-plasticizing dispersant from the starch gel in the step (3);

the hydrophobic modifier is polyaldehyde and/or polyvinyl alcohol;

in the step (1), the plasticizer is one or more of water, ethylene glycol, glycerol, dimethyl sulfoxide and urea;

in the step (1), the preplasticizing dispersant is one or more of ethanol, water and methanol.

2. The method according to claim 1, wherein in the step (1), the starch is selected from a native starch and/or a starch modified with a starch modifier;

in the step (1), the mixing is cutting, dispersing and mixing in a mechanical stirrer.

3. The method of claim 2, wherein the native starch is selected from one or more of corn starch, wheat starch, sweet potato starch, and tapioca starch.

4. The method of claim 3, wherein the native starch is tapioca starch.

5. The method of claim 2, wherein the starch modifier is selected from one or more of carboxylic acid, anhydride, acid halide and amide.

6. The method of claim 5, wherein the carboxylic acid is one or more of citric acid, acetic acid, malic acid and sebacic acid.

7. The process according to claim 5, wherein the acid anhydride is acetic anhydride and/or maleic anhydride.

8. The method according to claim 5, wherein the acid halide is an acid chloride.

9. The method of claim 5, wherein the amide is one or more of formamide, N-methylformamide, and dimethylacetamide.

10. The method according to claim 2, wherein in the step (1), the mixing is performed by cutting and dispersing in a mechanical mixer for 0.5 to 1 hour.

11. The method according to claim 10, wherein in the step (1), the mixing is performed by cutting and dispersing in a mechanical mixer for 1 hour.

12. The method according to claim 1, wherein in the step (2), the hydrophobic modifier is present in the form of an aqueous solution;

and adding a coloring agent into the starch mixed solution II.

13. The method according to claim 12, wherein the hydrophobic modifier is present in an aqueous solution of the hydrophobic modifier in an amount of 20 to 40% by mass.

14. The method according to claim 13, wherein the hydrophobic modifier is present in an aqueous solution of the hydrophobic modifier in an amount of 25% by mass.

15. The method of claim 12, wherein the colorant is a metal oxide.

16. The method of claim 15, wherein the colorant is titanium dioxide.

17. The method according to claim 12, wherein the mass ratio of the coloring agent to the starch is (0.1 to 20): 100.

18. the method according to claim 17, wherein the mass ratio of the coloring agent to the starch is (0.5 to 5): 100.

19. the method of claim 18, wherein the mass ratio of the coloring agent to the starch is 2: 100.

20. the method according to any one of claims 12 to 19, wherein when the hydrophobic modifier is a polyaldehyde, the mass ratio of the hydrophobic modifier to the starch is (0 to 0.8): 100, respectively;

when the hydrophobic modifier is polyvinyl alcohol, the mass ratio of the hydrophobic modifier to the starch is (0-10): 100.

21. the method according to claim 20, wherein when the hydrophobic modifier is a polyaldehyde, the mass ratio of the hydrophobic modifier to the starch is (0.1 to 0.4): 100.

22. the method of claim 21, wherein when the hydrophobic modifier is a polyaldehyde, the mass ratio of the hydrophobic modifier to the starch is 0.2: 100.

23. the method of claim 20, wherein when the hydrophobic modifier is a polyaldehyde, the polyaldehyde is one or more of glyoxal, succinaldehyde, and glutaraldehyde.

24. The method according to claim 20, wherein when the hydrophobic modifier is polyvinyl alcohol, the mass ratio of the hydrophobic modifier to the starch is 2.5: 100.

25. the production method according to claim 1, wherein, in the step (3), the substance used as the supercritical fluid is CO₂、H₂O、CH₄、CH₃OH、C₂H₅OH or NH₃；

In the step (3), the mixing reaction is carried out in a high-pressure reaction kettle;

in the step (3), the starch mixed liquor II in the step (2) is placed in the supercritical fluid treatment system according to the following steps: and (3) placing the starch mixed solution II in the step (2) into a high-pressure reaction kettle, and pressurizing the supercritical fluid to 7.5-12MPa by using a booster pump at 15-25 ℃.

26. The method according to claim 1, wherein in the step (3), the temperature of the mixing reaction is 80 to 100 ℃;

in the step (3), the mixing reaction time is 15-25 min;

in the step (3), the feeding amount of the starch mixed solution II is (0.18-0.22) kg/L;

in the step (3), the stirring rate is 100-.

27. The method of claim 26, wherein in step (3), the temperature of the mixing reaction is 90 ℃.

28. The method according to claim 26, wherein the mixing reaction time in the step (3) is 20 min.

29. The method of claim 26, wherein in step (3), the amount of starch mixture II fed is 0.2 kg/L.

30. The method of claim 26, wherein in the step (3), the mixing is performed at a stirring rate of 190 rpm.

31. The method of claim 1, wherein the step (4) of removing the pre-plasticizer in steps (1) and (2) is performed by drying the starch gel.

32. The method of claim 31, wherein the water content of the dried product is controlled to be within 0.5 wt%.

33. The method of claim 31, wherein the drying temperature is 0-100 ℃.

34. The method of claim 33, wherein the drying temperature is 60-100 ℃.

35. The method of claim 31, wherein the drying time is from 0.5 to 50 hours.

36. The method of claim 35, wherein the drying time is from 2 to 50 hours.

37. The method of claim 31, wherein the drying is performed by: and (3) drying the starch gel in an air-blast drying oven or an infrared direct-heating drying oven, and then drying in a vacuum drying oven or a dew-point drying oven.

38. The method of claim 37, wherein the temperature of the forced air drying oven or the infrared direct heating drying oven is 75-85 ℃;

the drying time of the air-blast drying oven or the infrared direct-heating drying oven is 5-10 h;

the drying temperature of the vacuum drying box or the dew point drying box is 0-100 ℃;

the drying time of the vacuum drying oven or the dew point drying oven is 4-30 h.

39. The method of claim 38, wherein the temperature of the forced air drying oven or the infrared direct heat drying oven is 80 ℃.

40. The method of claim 38, wherein the drying time of the forced air drying oven or the infrared direct heating drying oven is 8 hours.

41. The method of claim 38, wherein the vacuum oven or dew point oven dries at a temperature of 60-100 ℃.

42. The method of claim 41, wherein the vacuum oven or dew point oven dries at a temperature of 80 ℃.

43. The method of claim 38, wherein the vacuum oven or dew point oven is dried for a period of time of 10 to 30 hours.

44. The method of claim 43, wherein the vacuum oven or dew point oven is dried for 8 hours.

45. The method of claim 1, wherein the product obtained in step (4) is granulated.

46. The method of claim 45, wherein the granulating is performed in an internal mixer or a screw extruder.

47. The method of claim 46, wherein the granulating is performed in a screw extruder.

48. The process according to claim 45, wherein a compatibilizer is added during the granulation.

49. The method of claim 48, wherein the compatibilizer is one or more of maleic anhydride, succinic anhydride, acetic anhydride, propionic anhydride, and phthalic anhydride.

50. The method of claim 49, wherein the compatibilizer is maleic anhydride.

51. The method of claim 48, wherein the mass ratio of the compatibilizer to the starch gel without the preplasticizer is (0.5-5): (5-10).

52. The method of claim 45, wherein a biodegradable material is added during said granulating.

53. The method of claim 52, wherein the biodegradable material is biodegradable aliphatic polyester material and/or biodegradable aliphatic and aromatic copolyester material.

54. The method of claim 53, wherein the biodegradable material is one or more of polylactic acid, polybutylene succinate/terephthalate, polybutylene succinate/adipate, polybutylene adipate/terephthalate, and polycaprolactone.

55. The method of claim 52, wherein the mass ratio of biodegradable material to starch gel without pre-plasticizer is (0.5-5): (5-10).

56. A hydrophobic thermoplastic starch-based biodegradable material obtained by the process according to any one of claims 1 to 55.