CN112552693B

CN112552693B - Zein/titanium dioxide composite membrane and preparation method and application thereof

Info

Publication number: CN112552693B
Application number: CN202011508584.5A
Authority: CN
Inventors: 王佃刚; 肖飞虹; 王菁; 陈传忠
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2020-12-18
Filing date: 2020-12-18
Publication date: 2022-03-15
Anticipated expiration: 2040-12-18
Also published as: CN112552693A

Abstract

The invention discloses a zein/titanium dioxide composite film and a preparation method and application thereof, wherein the preparation method comprises the following steps: adding zein into an ethanol aqueous solution to prepare a dispersion solution, adding glycerol and eugenol into the dispersion solution, mixing, heating for reaction, adding nano titanium dioxide particles and an emulsifier, mixing to prepare a film forming solution, and drying the film forming solution to obtain the zein/titanium dioxide composite film. The composite membrane prepared by the invention not only solves the problem of high brittleness, but also solves the problem of poor barrier property caused by adding eugenol, and simultaneously, the thermal stability of the composite membrane prepared by the invention is greatly improved.

Description

Zein/titanium dioxide composite membrane and preparation method and application thereof

Technical Field

The invention relates to the technical field of edible nano composite membrane preparation, and relates to a zein/titanium dioxide composite membrane, a preparation method and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The traditional plastic product has the advantages of light weight, low price, convenient storage and transportation, excellent barrier property and the like, thereby becoming one of the important components of the convenient life of people. The problem of environmental pollution of non-degradable plastic articles is not negligible and is of increasing concern. Data-related data report that the degradation rate of conventional plastics is slow, taking approximately 100 years to achieve complete degradation, which virtually exacerbates environmental degradation. In order to solve the problem of environmental pollution, green degradable materials are gradually the object of research of many researchers, and how to prepare green degradable materials into substitutes with excellent properties of traditional plastics becomes the research focus of the researchers.

Among the high molecular materials that can replace plastic products, proteins have emerged as one of the raw materials of intensive research in degradable plastics due to their wide source, reproducibility, degradability, and excellent barrier properties. In addition to the advantages, the protein can be combined with polysaccharide, synthetic polymer materials, inorganic nanoparticles and the like through chemical reaction, enzyme reaction, physical connection and the like to obviously optimize the mechanical property, barrier property and the like of the composite material which is weaker than the traditional plastic material. Zein, a rare hydrophobic protein, is not only a good property, but also a hydrophobic amino acid, so that zein is insoluble in water and can only be dissolved in 60-90% ethanol water. Due to the existence of hydrophobic amino acid residues of glutamine, proline, leucine and alanine, the zein has excellent film-forming performance, a film with a stable network structure is formed by utilizing hydrophobic interaction, and meanwhile, the strong hydrophobic interaction film is very fragile, so that the application of the zein is limited at present.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a zein/titanium dioxide composite film, a preparation method and application thereof, which can improve the film forming property of zein.

In order to achieve the purpose, the technical scheme of the invention is as follows:

on the one hand, the preparation method of the zein/titanium dioxide composite membrane comprises the steps of adding zein into an ethanol water solution to prepare a dispersion solution, adding glycerol and eugenol into the dispersion solution, mixing, heating for reaction, adding nano titanium dioxide particles and an emulsifier, mixing to prepare a membrane forming solution, and drying the membrane forming solution to obtain the zein/titanium dioxide composite membrane.

The invention selects eugenol in phenols to improve the brittleness problem of the film. The mechanism of action is that the zein forms a ring structure with an inward hydrophobic end and an outward hydrophilic end in an ethanol aqueous solution (within 90 percent) to wrap hydrophobic eugenol in molecules, the eugenol breaks the strong hydrophobic action between protein molecules and the compact spiral and folding structure of the zein and replaces the weak hydrogen bond action between the eugenol and the zein, so that the brittleness is improved, and the flexibility is improved. However, the plasticized film, due to its failure of the spiral-folded structure, forms a porous structure of the film, and such pores have a negative effect on the barrier properties of the film. Therefore, the invention improves the barrier property by adding the nano titanium dioxide of the nano particles, and simultaneously can enhance the strength, and the titanium dioxide nano particles also have the advantages of unique photocatalytic property, low price, no toxicity and the like.

On the other hand, the zein/titanium dioxide composite film is obtained by the preparation method.

In a third aspect, a use of the zein/titanium dioxide composite film in packaging and/or replacing traditional plastic products.

The invention has the beneficial effects that:

(1) according to the invention, the nanometer titanium dioxide particles are added into the composite film taking zein as a matrix, so that the film structure with higher porosity caused by the addition of eugenol is effectively improved, and the mechanical property and the barrier property of the film are enhanced.

(2) The zein/nano titanium dioxide composite film is prepared by taking zein as a raw material, so that the commercial value of the zein is increased, a new thought is provided for the field of degradable composite films, and the development of the degradable plastic industry in the future is facilitated.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a graph of the morphology of films of different eugenol addition amounts prepared in example 5, wherein (a), (c), (e), (g), (i) represent the cross-sectional appearances of e1, e2, e3, e4, e5 zein/eugenol composite films, respectively, (b), (d), (f), (h), (j) represent the cross-sectional appearances of e1, e2, e3, e4, e5 film samples, respectively, magnified 3000 times;

FIG. 2 is a graph of the tensile properties of films prepared in example 5 with different eugenol additions;

FIG. 3 is a graph of the oxygen transmission rate of films prepared in example 5 with different amounts of eugenol added;

FIG. 4 is the water absorption of films prepared in example 5 with different eugenol addition;

FIG. 5 is a graph of the water vapor transmission rate of films of different eugenol addition levels prepared in example 5;

FIG. 6 is the contact angles of films prepared in example 5 with different amounts of eugenol added, wherein (a), (b), (c), (d) and (e) represent the contact angles of e1, e2, e3, e4 and e5 zein/eugenol composite films, respectively;

FIG. 7 is a graph of the films prepared in example 6 with different amounts of nano-titania added, where A1 represents the surface topography of T0 with 1000 times magnification, A2 represents the surface topography of T0 with 5000 times magnification, A3 represents the surface topography of T0 with 1000 times magnification, B1 represents the surface topography of T1 with 1000 times magnification, B2 represents the surface topography of T1 with 5000 times magnification, B1 represents the surface topography of T1 with 5000 times magnification, C1 represents the surface topography of T1 with 1000 times magnification, C1 represents the surface topography of T1 with 5000 times magnification, D1 represents the surface topography of T1 with 1000 times magnification, E1 represents the surface topography of T1 with 5000 times magnification, and E1 represents the surface topography of T1 with 5000 times magnification.

FIG. 8 is a graph of the tensile properties of films prepared in example 6 with different amounts of nano-titania added;

FIG. 9 is a stress-strain curve for films prepared in example 6 with different amounts of nano-titania added;

FIG. 10 is a graph of the oxygen transmission rate of films prepared in example 6 with different amounts of nano-titania added;

FIG. 11 is the contact angles of films prepared in example 6 with different amounts of nano-titania added;

FIG. 12 is a graph of the water vapor transmission rate for films prepared in example 6 at various nano-titania additions;

FIG. 13 shows the water absorption of films prepared in example 6 with different amounts of nano-titania added;

FIG. 14 is a thermogravimetric plot of films prepared in example 6 with different amounts of nano-titania added;

FIG. 15 shows the microperimetric thermogravimetry curves of films with different amounts of nano-titania added;

FIG. 16 shows FTIR curves for films of varying amounts of nano-titania added.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The invention discloses a zein/titanium dioxide composite film, a preparation method and application thereof, and solves the problem that barrier property is reduced due to the fact that eugenol is adopted to plasticize a zein film and then a spiral folding structure is damaged to form a porous structure.

The invention provides a typical embodiment of a preparation method of a zein/titanium dioxide composite film, which comprises the steps of adding zein into an ethanol water solution to prepare a dispersion solution, adding glycerol and eugenol into the dispersion solution, mixing, heating for reaction, adding nano titanium dioxide particles and an emulsifier, mixing to prepare a film forming solution, and drying the film forming solution to obtain the zein/titanium dioxide composite film.

In some embodiments of this embodiment, the volume fraction of ethanol in the aqueous ethanol solution is from 60 to 90% v/v. Experiments show that the volume fraction of ethanol influences the strength of the membrane, and the membrane strength is better at the moment. When the volume fraction of ethanol in the ethanol aqueous solution is 79-81% v/v, the membrane strength is higher.

In some examples of this embodiment, the solid to liquid ratio of zein to aqueous ethanol is 1: 10-70 g/ml. Experiments show that the solid-liquid ratio of the zein and the ethanol aqueous solution has influence on the strength of the membrane, and at the moment, the membrane strength is better. When the solid-liquid ratio of the zein to the ethanol aqueous solution is 1: 10-10.1, and g/ml, the membrane strength is higher.

In some examples of this embodiment, the glycerol is 10-40 wt.% of the zein mass. Experiments show that the strength of the membrane is also influenced by the addition amount of the glycerol, and the membrane strength is better at the moment. The film strength is higher when the glycerol accounts for 19.6-20.4 wt.% of the mass of the zein.

In some examples of this embodiment, the eugenol is zein in a volume fraction of 5 to 25% v/v. Experiments show that the addition amount of eugenol influences various properties of the film, such as strength, brittleness, oxygen permeability, water absorption, water vapor permeability, hydrophobicity and the like. When the volume fraction of the eugenol which is zein is 9.6-10.4% v/v, the membrane has better performances such as strength, brittleness, oxygen permeability, water absorption rate, hydrophobicity and the like. And when the volume fraction of the eugenol which is zein is 24.6-25% v/v, the water absorption rate and the water vapor transmission rate of the film are better.

In some examples of this embodiment, the mass fraction of nano-titanium dioxide particles to zein is 0.5 to 3 wt.%. Experiments show that the barrier property of the film can be improved by adding the nano titanium dioxide particles, and meanwhile, the tensile strength of the film is increased, the hydrophobicity is reduced, and the thermal stability is improved. When the mass fraction of the nano titanium dioxide particles which are zein is 0.9-1 wt.%, the film has better performances, and has better water vapor permeation and oxygen resistance.

In some examples of this embodiment, the drying temperature is 50 to 80 ℃. Experiments show that the drying temperature also influences the strength of the membrane, and the membrane strength is better at the moment. When the drying temperature is 79-81 ℃, the film strength is higher. The drying time is 1.6-2.4 h.

In some examples of this embodiment, the temperature of the heating reaction is 76 to 84 ℃.

In some examples of this embodiment, the heating reaction time is 20 to 40 min.

In some embodiments of this embodiment, the emulsifier is tween 20.

In some examples of this embodiment, the film is equilibrated after drying in an environment having a relative humidity of 42% to 44%. The balance time is 22-26 h. The environment with the relative humidity of 42-44% is a dryer with the relative humidity of 42-44%, and the dryer contains saturated potassium carbonate water solution.

In another embodiment of the invention, a zein/titanium dioxide composite film is provided, which is obtained by the preparation method.

In a third embodiment of the present invention, there is provided a use of the zein/titanium dioxide composite film described above in packaging and/or replacing conventional plastic products.

In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.

Materials:

zein (99%, molecular weight 164.2KDa), eugenol and nano titanium dioxide (99.8%, 25nm, anatase) were purchased from Shanghai Mielin Biochemical technology, Inc., and ethanol, glycerol and Tween 20 were purchased from national drug group chemical reagent, Inc.

The performance test method comprises the following steps:

(1) tensile Property test

The tensile properties were evaluated using an electric tensile compression tester model ZQ-990LA (ZQ, Dongguan) according to ASTM Standard method D882. Tensile property samples were made rectangular (10 mm. times.7 mm) and the drawing speed was set at 500 mm/min.

(2) Contact Angle testing

Contact angle is an important test method for analyzing the wettability of a thin film, which reflects the hydrophilicity and hydrophobicity of the thin film. The contact angle of water was analyzed using a visual optical contact angle measuring instrument (DSA100S, KR US S, Shanghai). A drop of ultrapure water (2. mu.L) was dropped onto the film surface, and the image was preserved for 5 seconds. Three different points of each sample (2 cm. times.2 cm) were tested, and the results were averaged.

(3) Measurement of oxygen Transmission Rate

The oxygen transmission rate was measured by using a differential pressure permeability tester VAC-V1. The sampler handle was rotated 90 ° clockwise to make a film sample. Before the test, a start button is pressed to start the test, and the test standard is set in advance (the proportion mode is 5%, the upper and lower degassing time is 4h, and GTR is more than 1). The whole process was tested in a standard environment (23 ℃ C., 50% relative humidity) according to GB/t 2918-1998. The oxygen transmission rate of the sample was recorded after the test.

(4) Testing of Water vapor Transmission Rate

The water vapor transmission rate was measured by the paper cup method under the GB1037-1988 standard using a W3/062 type water vapor permeability test system (Labthink, Jinan). The desiccant is placed in a clean moisture permeable cup in an amount of about 3mm from the surface of the sample. Molten sealing wax is poured into the recess of the cup to ensure sealing. And weighing the sealed moisture permeable cup, and putting the cup into a constant temperature and humidity box with the relative humidity of 90 percent at 38 ℃. After 16 hours, it was removed from the box and placed in a desiccator at a temperature of 23. + -. 2 ℃. After 30 minutes of equilibration, the cups were weighed. This procedure should be repeated before each weighing, and after each weighing, the desiccant in the cup should be gently shaken to mix it up and down. After weighing, putting the moisture permeable cup into the constant temperature and humidity box again, wherein the time intervals of the two times of weighing are respectively 24 hours, 48 hours and 96 hours, and when the difference of the two times of mass increment is not more than 5%, carrying out a test. After each weighing, the desiccant in the cup should be gently shaken and allowed to mix above and below. Three replicates were performed for each sample. The water vapor transmission rate of the composite membrane is calculated according to the following formula:

wherein Δ m (g) is the mass increment, A (m)²) The water vapor area of the sample, and t (h) the time interval between two times after the mass gain stabilized.

(5) Measurement of Water absorption

The film was cut into 2cm by 2cm squares and the initial mass of each sample was recorded as W₁. And then soaking the weighed sample in deionized water for 24 hours at room temperature, taking out the film sample after soaking for 24 hours, wiping off excessive moisture on the surface of the sample by using filter paper, and weighing the sample again and recording the weight as W2. The water absorption of the composite membrane is calculated by the following formula:

in the formula, W₁(g) Is the initial mass of the film sample, W₂(g) To the mass of the film sample after 24 hours of absorption of deionized water.

(6) Analysis of surface and cross-sectional morphology and internal structure of thin films

Scanning Electron Microscopy (SEM) is a tool for characterizing the morphology of thin films, used to observe the surface and cross-sectional internal structure of thin films. The morphology of the film was characterized by a thermal field scanning electron microscope (Hitachi, SU-70). In the surface appearance characterization process, a sample is adhered to a sample table by using a conductive adhesive; in characterizing the cross-sectional morphology, the sample was first treated in liquid nitrogen for 20s, then the sample was peeled off from the middle with tweezers, and the treated sample was similarly bonded to the sample stage with conductive glue. The sample was sprayed with gold at a low current of 20A for 3 minutes, and then a topographical image of the sample was obtained with SEM at a voltage of 5 kV.

(7) Infrared analysis

In order to study the functional groups and structural conformation of the composite film, the infrared spectrum of the composite film was studied by infrared spectroscopy.

(8) Thermogravimetric analysis

The temperature dependence of the weight and thermal stability of the composite membranes was determined by thermogravimetric analysis (relaxation resistance, F3)

Germany) was obtained. The weight of each sample was controlled between 3mg and 5mg prior to testing. The composite membrane was heated from 40 ℃ to 500 ℃ at a ramp rate of 10 ℃/min and 20 mL/min.

Examples

Example 1: optimization of ethanol volume fraction

(1) Preparing ethanol aqueous solution with volume fractions of 70%, 80% and 90% v/v by taking deionized water as a solvent, respectively adding zein powder into the ethanol aqueous solution until the solid-to-liquid ratio is 1:10g/ml, and magnetically stirring at normal temperature until the zein powder is completely dissolved.

(2) Taking out the beaker, adding glycerol accounting for 30 wt.% of the mass fraction of the zein, and continuing to stir by magnetic force until the zein is fully mixed.

(3) The well-mixed dispersion was reacted in a magnetic stirrer at 80 ℃ for 30 minutes while stirring.

(4) And (3) taking out the beaker after the reaction is finished, cooling to room temperature, and pouring the film forming liquid into a square culture dish. The drying oven was preheated to 50 ℃ and the petri dish was placed in the drying oven for 3 hours.

(5) The dried film was cooled to room temperature, gently peeled off with a tweezers, and allowed to equilibrate in a desiccator (containing a saturated aqueous solution of potassium carbonate) at a relative humidity of 43% for 24 hours.

The ethanol volume fraction for preparing the zein/nano titanium dioxide composite film is optimized by taking the tensile strength and the elongation at break as indexes, and the results are shown in table 1, when the ethanol volume fraction is 80% v/v, the tensile strength of the film reaches the maximum value of 14.24 +/-2.93 MPa, the strength of the prepared film is particularly obviously higher than that of the film with the concentrations of 70% v/v and 90% v/v, and the tensile strength of the prepared film with the concentrations of 90% v/v is almost not different from that of the film with the elongation at break. It can be considered that the film is optimal in tensile properties when the ethanol concentration is 80% v/v for the above reasons, and therefore the ethanol concentration of 80% v/v is selected as the optimal concentration for the optimization of the subsequent production process.

TABLE 1 Effect of different concentrations of aqueous ethanol solutions on tensile Properties of films

Example 2: optimization of zein dispersion liquid-solid ratio

(1) Preparing an ethanol water solution with the volume fraction of 80% by taking deionized water as a solvent, adding zein powder into the ethanol water solution respectively until the solid-to-liquid ratio is 1:10, 1:20, 1:40 and 1:70g/ml, and magnetically stirring at normal temperature until the zein powder is completely dissolved.

(2) Taking out the beaker, respectively adding glycerol accounting for 30% of the mass fraction of the zein, and continuing to stir by magnetic force until the zein is fully mixed.

The solid-liquid ratio of the zein dispersion prepared by the zein/nano titanium dioxide composite film is optimized by taking the tensile strength and the elongation at break as indexes, and the results are shown in table 2, on the whole, different solid-liquid ratios still have no obvious influence on the elongation at break of the film, but the tensile strength is gradually reduced along with the reduction of the solid-liquid ratio, and the influence effect is obvious from 12.44 +/-2.13 MPa when the solid-liquid ratio is 1:10g/ml to 2.41 +/-0.06 MPa when the solid-liquid ratio is 1:70 g/ml. And selecting the most optimal solid-liquid ratio of 1:10g/ml by taking the numerical value of the tensile strength as an index for optimizing the next preparation process.

TABLE 2 Effect of solid-liquid ratio on tensile Properties of films

Example 3: optimization of glycerol mass fraction

(1) Preparing an ethanol water solution with the volume fraction of 80% by taking deionized water as a solvent, putting the ethanol water solution into a beaker, respectively adding zein powder into the ethanol water solution until the solid-to-liquid ratio is 1:10g/ml, and magnetically stirring at normal temperature until the zein powder is completely dissolved.

(2) Taking out the beaker, adding glycerol accounting for 20 wt.%, 30 wt.% and 40 wt.% of the mass fraction of the zein respectively, and continuing to stir by magnetic force until the zein is fully mixed.

The mass fraction of glycerol added in the preparation of the zein/nano titanium dioxide composite film is optimized by taking the tensile strength and the elongation at break as indexes, and the result is shown in table 3, wherein the tensile strength and the growth rate at break of the composite film are gradually reduced along with the increase of the mass fraction of the glycerol in the zein, namely the tensile property is gradually weakened. When the mass fraction of glycerol in zein is 20 wt.%, the tensile strength of the film is significantly higher than that of the films with the mass fractions of 30 wt.% and 40 wt.%, and the elongation at break is also optimal, so that the mass fraction of glycerol of 20 wt.% is selected as the optimal mass fraction with tensile properties as an index for the optimization of the subsequent composite film preparation process.

TABLE 3 Effect of different mass fractions of Glycerol on tensile Properties of films

Example 4: optimization of drying temperature

(1) Preparing an ethanol aqueous solution with volume fraction of 80% v/v by taking deionized water as a solvent, putting the ethanol aqueous solution into a beaker, respectively adding zein powder into the ethanol aqueous solution until the solid-to-liquid ratio is 1:10g/ml, and magnetically stirring at normal temperature until the zein powder is completely dissolved.

(2) Taking out the beaker, adding glycerol accounting for 20 wt.% of the mass fraction of the zein respectively, and continuing to stir by magnetic force until the zein is fully mixed.

(4) And (3) taking out the beaker after the reaction is finished, cooling to room temperature, and pouring the film forming liquid into a square culture dish. Drying at 50 deg.C, 60 deg.C, 70 deg.C and 80 deg.C for 3 hr.

The drying temperature for preparing the zein/nano titanium dioxide composite film is optimized by taking the tensile strength and the elongation at break as indexes, and the result is shown in table 4, along with the increase of the drying temperature, the tensile strength of the film tends to increase firstly and then decrease, when the drying temperature is 70 ℃, the tensile property of the composite film reaches the optimum, the tensile strength is 20.51 +/-0.95 MPa, and the elongation at break is 4.88 +/-1.10%, so that the next composite film is dried at the temperature of 70 ℃ by taking the tensile property as an index.

TABLE 4 Effect of different drying temperatures on film tensile Properties

Example 5: optimization of eugenol volume fraction

(2) Taking out the beaker, respectively adding glycerol accounting for 20 wt.% of the mass fraction of the zein and eugenol accounting for 5%, 10%, 15%, 20% and 25% v/v of the volume fraction of the zein, and continuing to stir by magnetic force until the zein and the eugenol are fully mixed.

(4) And (3) taking out the beaker after the reaction is finished, cooling to room temperature, and pouring the film forming liquid into a square culture dish. Drying at 70 deg.C for 3 hr.

A film prepared with eugenol as zein with a volume fraction of 5% v/v is designated as e1, a film prepared with eugenol as zein with a volume fraction of 10% v/v is designated as e2, a film prepared with eugenol as zein with a volume fraction of 15% v/v is designated as e3, a film prepared with eugenol as zein with a volume fraction of 20% v/v is designated as e4, and a film prepared with eugenol as zein with a volume fraction of 25% v/v is designated as e 5.

Performance analysis:

in the sectional scanning electron microscope image of example 5, as shown in FIG. 1, it can be seen that the film as a whole is a porous structure, and the pores of the film tend to increase with the increase of the addition amount of eugenol, but the difference between the pores of the film samples with the addition amounts of 10% v/v and 15% v/v is smaller, which indicates that the network structure looseness of the film increases with the increase of the addition amount of eugenol. The plasticizing effect of eugenol on zein films is to break the strong interaction between zeins by replacing weaker hydrogen bonds. It can also be seen from the figure that the film has good uniformity and no phase separation, indicating that eugenol has good compatibility with zein base material.

In terms of tensile properties, as shown in FIG. 2, it is apparent that eugenol, which is an additive excellent in plasticizing effect, greatly improves the brittleness of the film (except for the addition amount of 5% v/v), the elongation at break is significantly increased, the minimum elongation at break reaches 98.01. + -. 11.02%, but at the same time, the tensile strength is decreased from 20.51. + -. 0.95MPa to 6.43. + -. 0.82 MPa. And with the increase of the addition amount of the eugenol, the tensile strength shows a gradual decline trend, and the elongation at break gradually increases on the whole.

As shown in fig. 3, as the amount of eugenol added increased, the oxygen permeability of the film decreased first and then increased. When the addition amount is 10% v/v, the oxygen permeability of the film reaches the minimum value of 13.77 +/-2.49 cm³/cm²·d·Pa·10^-4Immediately thereafter, the oxygen permeability at an addition level of 15% was 14.55. + -. 4.72cm³/cm²·d·Pa·10^-4The difference between the two is small. The change trend of the oxygen permeability is basically in positive correlation with the change of the porosity of the film, and the non-negligible relation between the oxygen permeability and the film structure is reflected.

From fig. 4, it can be seen that the water absorption of the film increased from 71.59 ± 11.72% to 243.87 ± 10.00% with increasing amount of eugenol, which is a hydrophobic phenol, but was found from numerical analysis of the water absorption that the increase of eugenol did not decrease the water absorption of the film, which is related to the structure of zein in an aqueous ethanol solution with a volume fraction below 90% v/v. Zein forms a hydrophobic end inwards in an ethanol water solution within 90% v/v, a hydrophobic eugenol is wrapped in molecules by an annular structure with an outward hydrophilic end, the strong hydrophobic effect between protein molecules and the compact spiral and folding structure of the zein are destroyed by the eugenol, and a weaker hydrogen bond effect between the eugenol and the zein is replaced, so that the brittleness is improved, and the flexibility is improved, therefore, the hydrophobic effect of the eugenol is greatly weakened, and water molecules are more easily absorbed by a film along with the increase of film pores, and the result of water absorption increase is obtained. It can also be seen that e5 (25% v/v) has a somewhat reduced water absorption compared to e4 (20% v/v), probably due to the small amount of eugenol that is free outside the structure.

The water vapor transmission rate is closely related to the degree of closeness of the network structure of the film and the water absorption rate. The water absorption rate affects the water vapor transmission rate to a certain extent, and when the water absorption rate of the film increases, the amount of water vapor that relatively speaking permeates the film decreases, thereby affecting the value of the water vapor transmission rate. As can be seen from fig. 5, the water vapor transmission rate decreases first and then increases, possibly as a result of the interaction of the two influencing factors. From the results of scanning electron microscopy, it can be seen that the porosity increases as a whole with increasing addition of eugenol, but the e1 (5% v/v) water vapor transmission rate is second only to the maximum 513.03. + -. 19.87g/m of e5 (25% v/v)²24h, while the water absorption is the lowest, it is seen that the water absorption also influences the water vapor transmission of the film to a certain extent. For e5 (25% v/v), both the water absorption and the water vapor transmission rate were at very high levels, and it was seen that the highest porosity had a greater effect on the water vapor transmission rate.

In FIG. 6, (a), (b), (c), (d), (e) represent contact angle images of e1, e2, e3, e4, e5, respectively, whose values are 37.2 + -5.68 °, 37.1 + -3.12 °, 27.2 + -1.03 °, 27.3 + -5.36 °, 36.4 + -4.75 °, respectively. From the values, it can be seen that when the addition amount of eugenol is less than or equal to 10%, the contact angle of the composite film is larger, that is, the surface hydrophobicity is better than that of the rest samples, the contact angle values of e3 (15% v/v) and e4 (20% v/v) are not much different, and the contact angle value is increased again when the addition amount is 25% v/v. The surface hydrophobicity of the film is closely related to the properties of the materials constituting the film and the roughness of the film surface. The five types of films all possess smooth surfaces and therefore have negligible effect on roughness. As mentioned above, the zein in the ethanol water solution within 90% v/v forms a structure with a hydrophobic end inward and a hydrophilic end toward the solution due to the hydrophobic effect of the zein, and the structure wraps hydrophobic substances in the zein, and the structure can be used for explaining the experimental result that the contact angle of all films is less than 90 degrees, namely the surface hydrophilicity is shown. It can also be seen that when eugenol is added in an amount of 20% v/v or less, the value of the contact angle is substantially inversely proportional to the value of the water absorption, and it can be presumed that the water absorption is somewhat correlated with the value of the degree of surface wetting. Finally, an increase in the value of the e5 (25% v/v) contact angle can be associated with a small amount of eugenol escaping out of the structure.

By combining the analysis of the test results, the eugenol addition amount is 10% v/v for the optimization of the subsequent preparation process according to the principle that the tensile property of the film is not too low, the elongation at break is obviously improved, the oxygen transmission rate is low, the film structure is uniform, the porosity is low, and the surface hydrophobicity is strong.

Example 6: optimization of titanium dioxide mass fraction for preparing zein/nano titanium dioxide composite film

(2) Taking out the beaker, respectively adding glycerol accounting for 20 wt.% of the mass fraction of the zein and eugenol accounting for 10% v/v of the volume fraction of the zein, and continuing to stir by magnetic force until the zein and the glycerol are fully mixed.

(4) And after the reaction is finished, taking out the beaker, cooling to room temperature, respectively adding nano titanium dioxide particles accounting for 0.5 wt.%, 1wt.%, 2 wt.% and 3wt.% of the mass fraction of the zein into the dispersion liquid, and magnetically stirring for 10 minutes at normal temperature.

(5) The deposition solution was poured into a square petri dish of 13 mm. times.13 mm. Drying at 70 deg.C for 3 hr.

(6) The dried film was cooled to room temperature, gently peeled off with a tweezers, and allowed to equilibrate in a desiccator (containing a saturated aqueous solution of potassium carbonate) at a relative humidity of 43% for 24 hours.

The film prepared by omitting the step (4) is denoted as T0, the film prepared by using nano titanium dioxide particles with the mass fraction of zein of 0.5 wt.% is denoted as T1, the film prepared by using nano titanium dioxide particles with the mass fraction of zein of 1wt.% is denoted as T2, the film prepared by using nano titanium dioxide particles with the mass fraction of zein of 2 wt.% is denoted as T3, and the film prepared by using nano titanium dioxide particles with the mass fraction of zein of 3wt.% is denoted as T4.

Performance analysis:

(1) analysis of tensile Properties

The histogram of the tensile strength and the elongation at break of the zein/nano titanium dioxide composite film is shown in fig. 8, and the stress-strain curve is shown in fig. 9. With the increase of the loading amount, when the addition amount of the titanium dioxide is 1wt.%, the tensile strength of the composite membrane reaches the maximum value of 15.11 +/-1.57 MPa, and the elongation at break reaches the minimum value of 24.94 +/-7.43 percent. The tensile strength of T2 increased 64.04% and elongation at break decreased 71.64% compared to the control (T0). It is clear from the data that the improvement in film tensile strength is not always proportional to the addition of titanium dioxide nanoparticles. When the content of the nano titanium dioxide is more than 1wt.% zein, the tensile strength of the composite film is gradually reduced, and the elongation at break is increased. However, the tensile strength of the experimental group (T1-T4) was superior to that of the control group (T0). The results of the stress-strain curves show that the entire sample has a well-defined yield peak, showing good toughness, while the elastic modulus values gradually decrease with increasing titanium dioxide nanoparticles. The yield strength value can also be obtained from fig. 9: t2> T0> T1> T3> T4.

The causes of the above phenomenon can be summarized as follows. The titanium dioxide nanofiller enhanced intermolecular cohesion after the introduction of titanium dioxide, which was responsible for the increase in tensile strength in the experimental group (T1-T4). Secondly, the zein film strength improvement effect was best with a 1wt.% loading of titanium dioxide. At this point, the titanium dioxide nanoparticles embedded in the zein matrix have reached a saturated state, resulting in the best physical connection between the titanium dioxide nanoparticles and the polymer matrix. Conversely, when the added amount of the titanium dioxide nanoparticles is greater than 1wt.%, an excessive amount of titanium dioxide nanoparticles are accumulated in the zearalanol/eugenol matrix, resulting in local agglomeration behavior, which increases the interfacial area and surface energy of the composite membrane. In this case, the reinforcing effect of the titanium dioxide nanoparticles in the composite film is relatively weakened. On the other hand, the agglomeration of titanium dioxide deteriorates the compactness of the composite membrane, and therefore the discontinuity in the structure of the membrane weakens the interaction force between the polymer chains, which is the cause of the decrease in the TS values of T3 and T4.

(2) Surface hydrophobicity analysis

The mechanism of surface wettability can be inspired by recent explanations in some studies. First, it is related to the surface roughness of the film. The rougher the surface, the smaller the water contact angle of the composite membrane, and the higher the hydrophilicity of the membrane surface. The film in example 6 hardly had any difference in the roughness of the composite material, and therefore it can be inferred that the influence of the roughness on the water contact angle of the composite material was negligible in this example. In addition, the change in water contact angle is also closely related to the microstructure of the film. The eugenol composite membrane is hydrophilic whether titanium dioxide nano particles are loaded or not. As shown in fig. 11, the reason why the water contact angle gradually decreased from 29.05 ± 2.76 ° (T0) to 26.25 ± 2.90 ° (T2) can be attributed to the addition of the hydrophilic titanium dioxide particles. The imbalance of Ti-O causes the surface of the titanium dioxide nano particles to have strong polarity, and a small amount of water is adsorbed on the surface of the titanium dioxide nano particles. Thus, water adsorbed on the surface is dissociated by polarization to form hydroxyl groups. As the number of titanium dioxide nanoparticles increases, the specific surface area increases due to the generated clusters especially in T3 and T4 groups, resulting in more water adsorbed on the polarity-enhanced surface. Furthermore, porosity may also be responsible for increasing the wettability of the surface.

(3) Analysis of Water vapor Permeability

Fig. 12 shows the results of the study of water vapor transmission rate. The water vapor transmission rate is one of the important indexes for evaluating the barrier performance of the composite film. When the titanium dioxide is added in an amount of 1wt.%, the water vapor transmission rate of the film is improved to the maximum extent, which is consistent with the result of tensile properties. Relevant literature analysis suggests that the addition of titanium dioxide prolongs the permeation path of water vapor in the film, resulting in a reduction in water vapor transmission rate. In addition, the relationship between the internal structure and the water vapor transmission rate is not negligible. The water vapor transmission rates of T1 and T2 were lower than that of the control sample (T0) because the addition of titanium dioxide extended the permeation path of water vapor. The water vapor in the film is more saturated because the titanium dioxide in the film is more easily absorbed by the water vapor. Secondly, there may be a certain correlation between the water absorption and the water vapor transmission rate. Some water vapor may be absorbed by the film and therefore the amount of water vapor absorbed by the desiccant through the film is relatively reduced, which may be one of the reasons for the lower water vapor transmission rate of T2. The increase in water vapor transmission rate of T3 and T4 may be due to the aggregation of the titanium dioxide nanoparticles in the film. Some studies have shown that nanoparticle clusters may push polymer chains apart, leading to disruption of the network structure and hydrogen bonding regularity of the film, thereby increasing the free volume of water vapor and allowing water vapor to pass through the film more easily.

(4) Analysis of oxygen permeability

The oxygen permeability of titanium dioxide nanoparticles of different loadings were measured using a differential pressure gas permeameter VAC-V1, and the results are shown in FIG. 10. The oxygen transmission rate is also a key index for evaluating the barrier property of the composite film. From the analysis of the whole oxygen transmission rate result, the oxygen transmission rate is obviously reduced after the titanium dioxide nano particles are added, which indicates thatThe addition of titanium oxide has a positive effect on improving the oxygen resistance of the film. When the loading of the titanium dioxide nano particles is 1wt.%, the oxygen transmission rate of the composite membrane is 5.87 +/-1.61 cm³/m²·d·Pa·10^-4The oxygen transmission rate of the other samples was also improved to a different extent by 67.39% as compared with the control sample (T0). With T2 as the critical point, the oxygen transmission rate decreased first and then increased. Eugenol is contained in the helical and folded structures, and aromatic hydrogen bonds weaker than hydrophobic interactions are formed between zein molecules and protein molecules through electrostatic interactions, so that the microstructure of the composite membrane is further destroyed. Thus, the role of eugenol as an antioxidant is also impaired during film preparation, resulting in an increase in the oxygen transmission rate of the zein/eugenol composite. After the titanium dioxide nano-filler is added, the water vapor transmission rate and the oxygen transmission rate both show that the barrier property is improved. It can also be seen from the trend of oxygen transmission rate that composites with higher order and dense internal structure have better oxygen resistance.

(5) Water absorption analysis

Fig. 13 shows the water absorption of the composite after soaking in deionized water for 24 hours. The water absorption values are 124.97 + -20.72%, 133.42 + -39.59%, 205.35 + -10.21%, 159.48 + -54.86% and 234.80 + -49.21%, respectively. The composite film was observed to swell rapidly and become opaque to the naked eye in deionized water. Generally, the titania-loaded films absorbed a greater amount of water than the control samples without added titania. The trend of water absorption is very similar to that of the water contact angle, except that the water absorption of T3 is lower than that of T2, contrary to the common sense that the water absorption of a hydrophilic material is higher than that of a hydrophobic material. The opposite result may be due to the non-uniform structure of the T3 film, or the aggregation of protein and titanium dioxide nanoparticles in concentrated locations, resulting in the selection of the higher water absorption fraction during the test. For T4, the excess amount of titanium dioxide nanoparticles destroyed regularity and compactness, resulting in smaller intermolecular interactions, many pores and clusters were seen in D1, as well as aggregates derived from surface hydrophilic titanium dioxide nanoparticles, so the absorbed moisture was significantly higher than the other two.

(6) Surface and cross-sectional topography analysis

Fig. 7 shows scanning electron micrographs of the surface and cross-section of a zein/titanium dioxide composite film. Compared with the control sample (T0), except for T4 (fig. 7E 1), the experimental sample was dense, smooth, and uniform in surface, consisted of a small number of clusters, and no significant grain separation was found, indicating that titanium dioxide has some compatibility with the polymer matrix. The T0 sample (0 wt.% of the sample) had many small pores on the surface, but with the addition of titanium dioxide, the porosity decreased significantly. This phenomenon indicates that when the loading of titania is less than 3wt.%, the titania nanoparticles are successfully incorporated into the polymer matrix. In general, many holes are visible in all cross-sections of the film due to the insufficient tight chain attachment in the zein/titanium dioxide film. The microstructure of the pure zein film is non-porous and has a compact network structure, and the phenomenon is that zein molecules are tightly combined together to form a film through hydrophobic interaction, but the hydrophobic interaction is very strong, so that the pure zein film is fragile and poor in flexibility. The energy of hydrogen bonds in the plasticized zein film is relatively weak, so that the structure of the zein film is looser. Thus, all composite cross-sections have many small pores after the solvent has evaporated. For T4(3 wt.%), a large amount of titanium dioxide and clusters of titanium dioxide cover the surface. The excess titanium dioxide nanoparticles are unevenly distributed in the zein/eugenol matrix, fail to introduce internal structure, and instead form many aggregates on the surface and cross-section of the composite membrane. The presence of excess titanium dioxide nanoparticles reduces the activity of the molecular chain, and intermolecular hydrogen bonding and structural regularity are affected. In general, structural uniformity, porosity, and morphology of clusters play an important role in the barrier properties of the composite.

(7) Infrared spectroscopic analysis

The FTIR spectra of the zein/titanium dioxide composite films with different amounts of added titanium dioxide are shown in fig. 16. At 3289cm^-1～2873cm^-1Wave ofIn the number range of 3289cm^-1The characteristic peaks at (a) are related to the stretching vibration of the O-H and-NH groups. At 2957cm^-1The characteristic peak at (a) is due to the stretching vibration of the aliphatic group C-H. At 2929cm^-1The peak at (c) can be considered to be due to CH₂And CH₃The asymmetric vibration of C-H in the group, while the symmetric vibration peak of methyl and the stretching vibration peak of C-H appear at 2873cm^-1. In the zein/titanium dioxide composite film, a characteristic peak related to zein appears at 1644cm^-1～1237cm^-1In the wavenumber range of (c). Wherein, the length is 1644cm^-1The peak at (a) represents the characteristic peak of-C ═ O caused by the axial deformation of the carbonyl group in amide-vi; at 1535cm^-1The next peak was found to be 1448cm with amide-I in the N-H bending and C-N stretching oscillations of amide-II^-1C-H vibration of (a); 1262cm^-1The band of (A) may correspond to an axial deformation of the amide-III-CN, 1237cm^-1The band at (a) was assigned as the characteristic peak vibration associated with zein in the N-H and C-N group planes in amide-III. Finally, at 1039cm^-1A peak occurs due to the stretching of C-N in the amide. Although less pronounced, the FTIR spectrum is still 1512cm in the FTIR spectrum due to stretching of C ═ C in the aromatic ring^-1Characteristic peaks related to eugenol exist, which indirectly shows that the eugenol has better compatibility with the zein.

In short, all film samples showed similar peaks at essentially the same wavenumber, with little change in density and little change in displacement, indicating that titanium dioxide improved many of the properties of the composite film by simple physical attachment. In the entire infrared spectrum, no characteristic peak was found in relation to titanium dioxide, probably due to the small amount of titanium dioxide added. However, the peak associated with-OH shifts slightly toward high wavenumbers, which is likely due to the increased number of-OH groups in the titanium dioxide molecule due to the increased polarity of Ti-O.

(8) Thermogravimetric analysis

TABLE 5 weight loss ratio of films with different titanium dioxide addition in the second stage of thermal degradation

The thermal properties of the composite films were studied in thermogravimetric analysis. The composite film is thermally deformed in two stages, the initial stage being from about 75 ℃ to 110 ℃ due to the evaporation of residual volatile ethanol and bound water. The second stage is in the range of 131-500 ℃, is mainly related to the degradation of zein, and is a complex process. At this stage, depolymerization, dehydration, pyrolytic decomposition of polymer chains, destruction of polymer networks, and decomposition of low molecular weight organic compounds all occur in the film internal structure. As can be seen in fig. 14 and 15, the temperature of maximum degradation rate in the DTG curve may be related to zein breakdown. As predicted, the mass loss of the composite film with the titanium dioxide added was somewhat smaller than that of the composite film without the titanium dioxide added, indicating that the addition of the titanium dioxide nanoparticles is advantageous for improving the thermal stability of the film because the titanium dioxide itself has excellent thermal stability. However, ash was also found for the T2(1 wt.%) sample with the above-described optimum tensile strength, oxygen resistance and morphology (T in table 2_eThermal degradation rate) was slightly higher than the other experimental samples. The T2 sample (1 wt.%) consistently had the highest thermal stability, and gradually became the least stable after 318 ℃. In other words, in sharp contrast to the instability of zein after 318 ℃, T2(1 wt.%) has the highest thermal stability in the temperature range associated with the degradation of low molecular weight organic compounds. To some extent, the addition of titanium dioxide nanoparticles slightly promoted thermal degradation of the composite film after the addition of 1wt.% zein.

The addition of titanium dioxide significantly reduced the porosity of the composite film compared to the control sample (T0), with the most uniform surface microstructure and the least number of micropores in the T2 sample. Since the titania nanoparticles are bonded in a saturated state at this time, the barrier properties (moisture and oxygen resistances) and tensile properties of T2 are also improved to the best extent. In terms of thermal stability, the mass loss of different amounts of titanium dioxide nanoparticles was reduced to different degrees, that is, the thermal stability was improved to different degrees, as compared to the control sample (T0).

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a zein/titanium dioxide composite film is characterized in that zein is added into an ethanol water solution to prepare a dispersion liquid, glycerol and eugenol are added into the dispersion liquid to be mixed, heating reaction is carried out, nano titanium dioxide particles and an emulsifier are added to be mixed to prepare a film forming liquid, and the film forming liquid is dried to obtain the zein/titanium dioxide composite film;

wherein the volume fraction of the eugenol which is zein is 5-25% v/v; the mass fraction of the nano titanium dioxide particles to be zein is 0.5-3 wt.%.

2. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein the volume fraction of ethanol in the ethanol aqueous solution is 60 to 90% v/v.

3. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein the volume fraction of ethanol in the ethanol aqueous solution is 79-81% v/v.

4. The method for preparing the zein/titanium dioxide composite film as claimed in claim 1, wherein the solid-to-liquid ratio of the zein to the ethanol aqueous solution is 1: 10-70 g/ml.

5. The method for preparing the zein/titanium dioxide composite film as claimed in claim 4, wherein the solid-to-liquid ratio of the zein to the ethanol aqueous solution is 1: 10-10.1, g/ml.

6. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein glycerin accounts for 10 to 40 wt.% of the mass of the zein.

7. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein glycerin accounts for 19.6 to 20.4 wt.% of the mass of zein.

8. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein the volume fraction of the eugenol to zein is 9.6 to 10.4% v/v.

9. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein the volume fraction of the eugenol to zein is 24.6 to 25% v/v.

10. The method for preparing the zein/titanium dioxide composite film according to claim 1, wherein the mass fraction of the nano titanium dioxide particles to the zein is 0.9 to 1 wt.%.

11. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein the drying temperature is 50 to 80 ℃.

12. The method of preparing a zein/titanium dioxide composite film according to claim 1, wherein the drying temperature is 79 to 81 ℃.

13. The method for preparing a zein/titanium dioxide composite film as claimed in claim 1, wherein the temperature of the heating reaction is 76-84 ℃.

14. The method for preparing a zein/titanium dioxide composite film according to claim 1, wherein the heating reaction time is 20-40 min.

15. The method of claim 1, wherein the emulsifier is tween 20.

16. The method of preparing a zein/titanium dioxide composite film as in claim 1, wherein after drying, the film is equilibrated in an environment with a relative humidity of 42-44%.

17. The method of claim 16, wherein the equilibration time is 22-26 hours.

18. A zein/titanium dioxide composite film obtained by the production method according to claim 1.

19. Use of the zein/titanium dioxide composite film of claim 18 in packaging and/or as a replacement for conventional degradable plastic articles.