CN110628087A

CN110628087A - Polyion liquid plasticized thermoplastic starch and preparation method thereof

Info

Publication number: CN110628087A
Application number: CN201910858369.9A
Authority: CN
Inventors: 夏于旻; 汪菁晶; 梁源; 刘洁; 张雯雯; 赵忠政; 梁娇娇; 丁丹宁; 吕晓洁
Original assignee: Donghua University
Current assignee: Donghua University; National Dong Hwa University
Priority date: 2019-09-11
Filing date: 2019-09-11
Publication date: 2019-12-31
Anticipated expiration: 2039-09-11
Also published as: CN110628087B

Abstract

The invention discloses polyion liquid plasticized thermoplastic starch and a preparation method thereof. The thermoplastic starch comprises corn starch and polyion liquid. The preparation method comprises the following steps: respectively dissolving corn starch and polyion liquid in water, mixing, heating and stirring; drying the mixed solution to remove water to obtain a solid product; and heating and melting the solid product, and pressing to form a film to obtain the thermoplastic starch film. The corn starch and Poly [ ECH-MIM ] -Cl form a new hydrogen bond effect, so that the effect of effectively avoiding the recombination of the hydrogen bonds of starch molecules is achieved, the starch is in an amorphous state, and the aim of thermoplasticity is fulfilled. The thermoplastic starch material prepared by the invention has good thermoplasticity and can be repeatedly processed, and the migration of the plasticizer can be effectively reduced by using macromolecules as the plasticizer, so that the application of the starch in the field of thermoplastic materials is expanded.

Description

Polyion liquid plasticized thermoplastic starch and preparation method thereof

Technical Field

The invention belongs to the field of deep processing of starch, and particularly relates to a thermoplastic starch material prepared by using polyion liquid as a macromolecular plasticizer and a preparation method thereof.

Background

Starch is the most common storage form of carbohydrate in plant cells and is present in higher amounts in plant seeds and tubers such as corn, wheat, potato, and the like. Starch can return to the nature in the form of carbon dioxide and water after being degraded, is considered to be a natural renewable material which does not cause any pollution to the environment, has the advantages of wide source, low price, easy transportation and storage and the like, and is widely applied to the industrial fields of textile, medicine, paper making and the like besides the related research and application in the field of food at present. The deep processing of the starch makes the starch become a thermoplastic material and is applied to the industrial field, the application of the starch is further widened, and the starch has important research significance.

Starch is a natural high molecular compound containing a polyhydroxy structure, the molecular arrangement of the starch is compact, a common solvent is difficult to permeate, and the starch can only be dissolved in a few solvents such as ionic liquid, dimethyl sulfoxide and the like. Furthermore, native starch has a high degree of crystallinity, about 19%, while some corn starches may have a degree of crystallinity as high as 39%. The higher crystallinity makes the melting point of the starch too high, the cohesive energy is larger, so the decomposition temperature of the starch is far lower than the melting temperature, the starch is not melted in the plasticizing process and is decomposed firstly, so the starch cannot be processed and molded at the higher temperature, and the natural starch does not have thermoplasticity, so the starch is difficult to process in the actual production.

Therefore, there are many researches for solving the problem that starch is difficult to be processed by thermoplastic processing, and a plasticizer is generally introduced to destroy the hydrogen bond action in and among the original starch molecules, so as to weaken the hydrogen bond in the original starch molecules, so that the starch molecular chains slide under the action of the plasticizer under the conditions of heating and external force action, thereby realizing macroscopic starch melting. The melt processing is a simpler material forming means, and the starch which cannot be melt processed originally is modified into engineering plastics which can be processed by heat plastic, so that the application of the starch is undoubtedly expanded, and even if the starch is used for preparing degradable packaging materials, the increasingly serious problem of environmental pollution can be solved.

Water is a plasticizer commonly used in the starch processing process, and under the action of water, starch granules generate irreversible transformation phenomena such as amorphization, birefringence disappearance, gelatinization and the like, so that the starch is endowed with certain thermoplasticity. However, when the small molecular water is removed, the starch is recrystallized, the thermoplastic property disappears, and the obtained TPS is brittle and has poor mechanical property. Therefore, pure water as a plasticizer cannot be used for plasticizing to produce thermoplastic starch. Subsequent studies have used polyols to replace water for plasticizing starch, mainly glycerol, ethylene glycol, propylene glycol, sorbitol, etc. In page 10 to page 13 of the book of university of Tianjin, 1999, Jiuzao et al published a "study on properties of starch and polyol blends", which prepared polyol-plasticized thermoplastic starch using a single-screw extruder and found that high-molecular-weight and polyhydric-alcohol have poor plasticizing ability because they are less likely to move and do not effectively penetrate into molecular chains of starch as compared with low-molecular-weight ethylene glycol and glycerin. Subsequent researches show that thermoplastic starch with proper mechanical property can be obtained by mixing a hydroxyl-containing high-molecular-weight polyol plasticizer and a low-molecular-weight plasticizer. And Chinese patent application No. 201811008689.7 discloses a plastic modified starch material, which consists of corn starch and a plasticizer, wherein the plasticizer adopts alcohol micromolecules such as glycerol, glycol, sorbitol, xylitol, mannitol and the like and amine micromolecules such as formamide, trimethylolpropane, ethanolamine and the like.

The small molecular plasticizer has small molecular volume and can act as a lubricant among starch molecular chains, so that the starch can be effectively plasticized to obtain thermoplastic starch, but the small molecular plasticizer is prone to migration and aggregation, the phenomenon of starch retrogradation of the thermoplastic starch in the storage process can be caused, and the TPS can even lose the original thermoplasticity. Yang et al published "Preparation of a novel small molecule plasticizer (bisvinylformamide) as a plasticizer for Starch" from Starch-Starke, 58, vol.58, pp.7, 330 to 337 "by Yang et al, and found that there was significant plasticizer overrun in the resulting thermoplastic Starch after storage for 150 days under specific conditions by SEM images. Furthermore, the overflow of small-molecule plasticizers may lead to dimensional shrinkage and changes in the mechanical properties of the thermoplastic starch, which can seriously affect the use properties of the thermoplastic starch. Therefore, the problem of plasticizer migration is to be solved, and the preparation of the thermoplastic starch with excellent comprehensive performance by using the proper macromolecular plasticizer has important practical significance.

Ionic liquids, which are low temperature molten salts composed of positive and negative ions, have been found to interact with polysaccharides such as cellulose, and thus there are reports on the use of ionic liquids to plasticize starch. Sankri et al published "Thermoplastic stage plasticized by synthetic granular" on pages 256 to 263, Vol.82, 2010, book 82, which states that [ Bmim ] Cl was found to be more effective than glycerol in plasticizing by comparing Thermoplastic starch plasticized with ionic liquid ([ Bmim ] Cl) and Thermoplastic starch plasticized with glycerol. The ionic liquid as a small molecule also has the defect of easy migration.

The polyionic liquid is a polymer taking an ionic liquid unit as a repeating unit, has the chemical property of the ionic liquid and the property of macromolecules. The ionic liquid polar groups can interact with starch molecular chains through the ionic liquid polar groups and simultaneously can form molecular chain entanglement with the starch molecular chains, so that the interaction with the starch molecular chains is increased.

Based on the designability of the chemical structure of the polyionic liquid, the polyionic liquid with a flexible chain as a framework and an ionic liquid unit as a polar unit can be designed, and the polyionic liquid has melt processing characteristics while keeping strong polarity and capability of dissociating hydrogen bonds, and can also be used for plasticizing starch. However, no relevant report is found at present.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: provides a polyion liquid plasticized thermoplastic starch and a preparation method thereof.

In order to solve the problems, the invention provides polyion liquid plasticized thermoplastic starch which is characterized by comprising corn starch and polyion liquid, wherein the mass ratio of the corn starch to the polyion liquid is (9.0-1.0): 1, wherein the polyion liquid is Poly [ ECH-MIM ] -Cl.

Preferably, the chemical structural formula of the polyion liquid is as follows:wherein n is 50-5000.

The invention also provides a preparation method of the polyion liquid plasticized thermoplastic starch, which is characterized by comprising the following steps:

step 1): respectively dissolving corn starch and polyion liquid in water, mixing, heating and stirring;

step 2): drying the mixed solution obtained in the step 1) to remove moisture to obtain a solid product;

step 3): heating and melting the solid product obtained in the step 2), and pressing the solid product into a film to obtain the thermoplastic starch film.

Preferably, the concentration of the corn starch dissolved in water in the step 1) is 0.08-0.2 g/mL; the concentration of the polyionic liquid is 0-0.12g/mL after the polyionic liquid is dissolved in water.

Preferably, the heating temperature in the step 1) is 70-120 ℃, the mechanical stirring speed is 150-.

Preferably, the drying temperature in the step 2) is 70-90 ℃, and the drying time is 48-72 h.

Preferably, in the step 3), a flat vulcanizing machine is adopted to heat and melt the solid product and pressurize the solid product to form a film, the heating temperature is 160-²The pressurizing time is 15-45 s.

The principle of the invention is that firstly imidazole and epichlorohydrin are used as monomers to synthesize hydroxyl-containing polyion liquid Poly [ ECH-MIM ] -Cl; the starch is used as a plasticizer to be mixed with starch, the gelatinization of the starch is utilized to destroy the hydrogen bond action in the original starch molecule and among the molecules, and the hydroxyl and the anions and the cations of the polyionic liquid are utilized to generate new hydrogen bond action with the hydroxyl on the starch molecular chain, so that the starch molecular chain has no redundant hydroxyl and then automatically forms the hydrogen bond action, and compared with the original starch, the hydrogen bond action among the molecular chains is greatly weakened, the starch molecular chain can slide at a relatively low temperature, and the melting phenomenon is macroscopically expressed, thus the thermoplastic starch is obtained. The thermoplastic starch material plasticized by the polyionic liquid can be pressed into a sheet by a flat vulcanizing machine, which fully represents the thermoplasticity of the material. And the infrared spectrum, the environmental scanning electron microscope image, the powder X-ray diffraction image, the differential scanning calorimetry image, the thermal weight loss image and the mechanical property test can be used as effective means for analyzing the interaction of the corn starch and the polyion liquid.

The invention selects Poly [ ECH-MIM ] -Cl as a macromolecular plasticizer for preparing thermoplastic starch by selecting and designing the chemical structure of the polyionic liquid, the polyionic liquid contains an ionic liquid unit on the main chain and a hydroxyl structure, can form strong interaction with hydroxyl of a starch molecular chain, destroys the original hydrogen bond network of the starch, obtains thermoplastic processing performance, weakens the hydrogen bond of the starch, endows the starch with thermoplasticity, overcomes the problem of easy migration of the original micromolecular plasticizer, and has simple manufacture and high mechanical property. The preparation method is simple and convenient, does not use micromolecular plasticizers, and the obtained thermoplastic starch has good mechanical property, thereby expanding the application field of the starch and developing the application value of the starch more greatly.

Drawings

FIG. 1 is an infrared spectrum of polyion liquid Poly [ ECH-MIM ] -Cl in the invention;

FIG. 2 is a nuclear magnetic hydrogen spectrum of Poly [ ECH-MIM ] -Cl in the present invention;

FIG. 3 is an infrared spectrum of thermoplastic starch prepared in examples 1 to 3 and a comparative example;

FIG. 4 is a differential scanning calorimetry trace of the thermoplastic starches obtained in examples 1 to 3 and comparative example;

FIG. 5 is an XRD diffractogram of corn starch and the powders obtained in examples 1-3 and comparative example;

FIG. 6 is a photograph of a sheet made of corn starch, the thermoplastic starch obtained in example 1, and a press vulcanizer.

Detailed Description

In order to make the invention more comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.

The macromolecular plasticizer polyionic liquid Poly [ ECH-MIM ] used in examples 1-3]The chemical structural formulae of-Cl are all:wherein n is 1000.

The preparation process of the polyion liquid Poly [ ECH-MIM ] -Cl comprises the following steps: preparing imidazole into 1mol/L aqueous solution, placing the aqueous solution in a reactor, cooling to-5 ℃, and slowly dropwise adding epichlorohydrin with the same molar quantity as the imidazole under stirring; after the dropwise addition is finished, stirring is continued for 12 hours; then heating to 95 ℃, and stirring for reaction for 7 days; and then stopping the reaction, after the reaction liquid is cooled to room temperature, pouring the reaction liquid into acetone with the volume of 20 times, collecting the obtained precipitate, putting the precipitate into a vacuum oven, and drying the precipitate for 24 hours at 80 ℃ to obtain a light yellow solid, namely the target product polyion liquid Poly [ ECH-MIM ] -Cl.

The thermoplastic starches obtained in the examples and comparative examples were tested for their plasticizer mobility with reference to the standard ISO 177. The test principle is as follows: the test specimen is placed between and in intimate contact with two plasticizer-absorbing sheets, heated under specified conditions, and the mass loss of the specimen is measured to characterize plasticizer migration as follows: the plasticizer-absorbing material is polyvinyl alcohol without plasticizer, a sample to be tested with thickness of 1mm and 5cm × 5cm is placed between two absorption sheets during measurement, the axes are aligned to form a sandwich structure, the sample is placed in an environment with constant temperature of 70 ℃ under the pressure of 5kg, and after 24h, the sample is taken out and treated to measure the mass loss of the sample.

And (3) determination of melt index: using a melt index apparatus, the capillary diameter was 2.095mm and the tube length was 8 mm. After heating to 190 ℃, the upper end was pressed downward with a 2.16kg weight applied by a piston, and the weight of the sample extruded in 10 minutes was measured as the melt index of the sample.

Example 1

A polyion liquid plasticized thermoplastic starch has a hot working temperature of 180 ℃, a tensile strength of 10.37MPa, an elongation at break of 2.25%, a plasticizer mobility of 0.59%, and a melt index of 6.2g/10 min.

The preparation method of the polyion liquid plasticized thermoplastic starch comprises the following steps:

step a: weighing corn starch and polyion liquid Poly [ ECH-MIM ] -Cl, wherein the weight is 9g and 1g respectively for later use;

step b: dissolving 9g of corn starch in 50mL of deionized water, dissolving 1g of polyion liquid in 50mL of deionized water, and uniformly mixing the two solutions for later use;

step c: b, uniformly stirring the mixed solution in the step b at the rotating speed of 200r/min at the temperature of 100 ℃, and timing for 60 min;

step d: c, drying the mixture obtained in the step c at 80 ℃ for 48 hours to remove water, and obtaining a solid product;

step e: the heating temperature of the plate vulcanizing machine is set to be 180 ℃ and the pressure is set to be 50kg/cm²And d, heating and melting the solid product obtained in the step d for 5min, pressurizing for 30s, and cooling to obtain the thermoplastic starch sheet.

Example 2

A polyion liquid plasticized thermoplastic starch has a hot working temperature of 170 ℃, a tensile strength of 4.91MPa, an elongation at break of 6.81%, a plasticizer mobility of 0.33%, and a melt index of 6.2g/10 min.

step a: weighing corn starch and polyion liquid Poly [ ECH-MIM ] -Cl, wherein the weight is 4g and 6g respectively for later use;

step b: dissolving 4g of corn starch in 50mL of deionized water, dissolving 6g of polyion liquid in 50mL of deionized water, and uniformly mixing the two solutions for later use;

step c: b, uniformly stirring the mixed solution in the step b at the rotating speed of 250r/min at the temperature of 95 ℃, and timing for 60 min;

step d: c, drying the mixture obtained in the step c at 80 ℃ for 72h to remove water, and obtaining a solid product;

step e: the heating temperature of the vulcanizing press is set to 170 ℃ and the pressure is set to 50kg/cm²And d, heating and melting the solid product obtained in the step d for 3min, pressurizing for 30s, and cooling to obtain the thermoplastic starch sheet.

Example 3

A polyion liquid plasticized thermoplastic starch has a hot working temperature of 180 ℃, a tensile strength of 7.83MPa, an elongation at break of 4.33%, a plasticizer mobility of 0.84%, and a melt index of 6.2g/10 min.

step a: weighing corn starch and polyion liquid Poly [ ECH-MIM ] -Cl which are 7g and 3g respectively for later use;

step b: dissolving 7g of corn starch in 50mL of deionized water, dissolving 3g of polyion liquid in 50mL of deionized water, and uniformly mixing the two solutions for later use;

step c: uniformly stirring the mixed solution in the step b at the rotation speed of 150r/min at the temperature of 100 ℃, and timing for 90 min;

step d: c, drying the mixture obtained in the step c at 90 ℃ for 48 hours to remove water, and obtaining a solid product;

step e: the heating temperature of the plate vulcanizing machine is set to be 180 ℃ and the pressure is set to be 50kg/cm²And d, heating and melting the solid product obtained in the step d for 3min, pressurizing for 45s, and cooling to obtain the thermoplastic starch sheet.

Comparative example

A glycerol plasticized thermoplastic starch material having a hot working temperature of 165 ℃, a tensile strength of 5.53MPa, an elongation at break of 6.23%, a plasticizer mobility of 33.34% and a melt index of 7.1g/10 min.

The preparation method of the glycerin plasticized thermoplastic starch material comprises the following steps:

step a: weighing corn starch and glycerol respectively in an amount of 7g and 3g for later use;

step b: dissolving 7g of corn starch in 100mL of deionized water, adding 3g of glycerol, and uniformly mixing for later use;

step c: uniformly stirring the mixed solution in the step b at the rotation speed of 150r/min at the temperature of 90 ℃, and timing for 90 min;

step e: the heating temperature of the press vulcanizer was set at 165 ℃ and the pressure at 30kg/cm²And d, heating and melting the solid product obtained in the step d for 3min, pressurizing for 15s, and cooling to obtain the thermoplastic starch sheet.

FIG. 5 is a wide angle X-ray diffraction pattern of corn starch and the thermoplastic starches obtained in comparative example, examples 1-3. Among them, corn starch and the thermoplastic starch of the comparative example showed distinct diffraction peaks indicating the presence of crystalline structures. On the other hand, no diffraction peak corresponding to the crystalline structure of the starch appears on the XRD curves of the examples 1, 2 and 3 obtained by plasticizing the polyionic liquid, which shows that the thermoplastic starch obtained by plasticizing the polyionic liquid is still in an amorphous state in a solid state, and the polyionic liquid can effectively inhibit the crystallization of the starch.

FIG. 6 shows that the sheet obtained by hot-pressing the thermoplastic starch obtained in example 1 has better transparency compared with the sheet obtained by hot-pressing corn starch, which indicates that the polyion liquid modified starch obtained in each example has better thermoplasticity and can obtain a uniform and integrated sheet material in the hot-pressing process.

Claims

1. The polyion liquid plasticized thermoplastic starch is characterized by comprising corn starch and polyion liquid, wherein the mass ratio of the corn starch to the polyion liquid is (9.0-1.0): 1, wherein the polyion liquid is Poly [ ECH-MIM ] -Cl.

2. A polyionic liquid plasticized thermoplastic starch according to claim 1 wherein the polyionic liquid has the chemical formula:wherein n is 50-5000.

3. A process for the preparation of polyionic liquid plasticized thermoplastic starch according to claim 1 or 2 comprising the steps of:

4. The method of preparing polyion liquid plasticized thermoplastic starch according to claim 3, wherein the corn starch in step 1) is dissolved in water to a concentration of 0.08 to 0.2 g/mL; the concentration of the polyionic liquid is 0-0.12g/mL after the polyionic liquid is dissolved in water.

5. The method for preparing polyion liquid plasticized thermoplastic starch according to claim 3, wherein the heating temperature in step 1) is 70-120 ℃, the speed of mechanical stirring is 150-300r/min, and the heating and stirring time is 50-90 min.

6. The method for preparing polyion liquid plasticized thermoplastic starch according to claim 3, wherein the drying temperature in the step 2) is 70-90 ℃ and the drying time is 48-72 h.

7. The method for preparing polyion liquid plasticized thermoplastic starch according to claim 3, wherein the solid product is heated and melted by a plate vulcanizer in the step 3) and pressed into a film, the heating temperature is 160 ℃ and 200 ℃, the heating and melting time is 3-8min, and the applied pressure is 30-70kg/cm²The pressurizing time is 15-45 s.