Food packaging paper with high barrier oxygen and water vapor performance and preparation method and application thereof

Abstract

The application discloses food packaging paper with high oxygen and water vapor barrier properties and a preparation method and application thereof, and belongs to the technical field of papermaking. The method comprises the following steps: beating wood pulp to perform fine fiberization treatment, papermaking after the fine fiberization treatment, obtaining raw paper after drying and balancing, semi-dry pressing the raw paper, surface coating after drying and balancing, semi-dry pressing again, drying and balancing, and finally obtaining the food packaging paper. The biomass paper is prepared by the technologies of paper pulp fine fiberization, paper semi-dry pressing, TiO2 particle filling on the surface of the paper and carboxymethyl starch sodium surface coating and film forming, no synthetic polymer polymer surface film forming agent is used, the prepared packaging paper has high barrier properties to water molecules and oxygen molecules, the requirement of high oxygen and water vapor barrier properties of the food packaging paper is met, and the packaging paper is easy to degrade and green and environment-friendly.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of papermaking, and particularly relates to a food packaging paper with high oxygen and water vapor barrier properties and a preparation method and application thereof. BACKGROUND

[0002] Petroleum-based plastic films are widely used in fruit and vegetable and food packaging due to their excellent strength, barrier properties and low cost. However, they are difficult to recycle and non-biodegradable, which causes serious environmental pollution and ecological threat. Paper packaging materials made of plant fibers are abundant in resources, green and environmentally friendly, biodegradable or recyclable, and are an important development direction to replace high-molecular polymer plastic films. However, cellulose-based paper has some inherent shortcomings, such as a porous structure, poor oxygen and water vapor barrier properties, and easy contact of the inner contents with oxygen, which leads to deterioration and does not protect the inner contents. Therefore, in recent years, whether food packaging paper can truly replace high-molecular polymer plastic film packaging materials, and breakthroughs in the high barrier properties of oxygen and water molecules are the key. Improving the gas barrier properties of paper has become a hot spot for replacing plastic packaging.

[0003] The commonly used "degradable plastic packaging materials" on the market mostly only add starch to the plastic raw materials. After landfill, the large plastic will be decomposed into small pieces or even invisible fragments due to the fermentation of starch and the decomposition of bacteria, which is only a physical degradation and does not fundamentally change the chemical properties of plastic products. PE film coating, PE film covering or aluminum foil on the surface of paper indeed has excellent barrier properties of gas and oil, but has the same problems as pure plastic film. André Mazega et al. combined nanocellulose, minerals, PVA, pullulan acid, alginate and non-ionic surfactants for a multi-purpose coating formulation, which reduced the porosity while complementing the defects of these materials, but it cannot be used as a food contact layer. Jinsong Zen et al. prepared a high-barrier composite film by self-assembly of cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), montmorillonite (MMT), polyvinyl alcohol (PVA) and alkyl ketene dimer (AKD). The film shows excellent barrier properties, but still uses PVA high-molecular polymer.

[0004] Therefore, it is urgent to provide a food packaging paper with high oxygen and water vapor barrier properties and green environmental protection. SUMMARY

[0005] In view of the above problems existing in the prior art, a first technical problem to be solved by the present application is to provide a preparation method of food packaging paper with high oxygen and water vapor barrier properties, which improves the plasticity of fibers by fine fiberization of pulp fibers, reduces the pore structure of paper, improves the tightness between fibers, flattens the fibers by paper semi-dry pressing, further compresses the fiber pores, and finally coats the base paper with a surface sizing agent to fill and block the surface pores of the paper, so as to obtain food packaging paper with high oxygen and water vapor barrier properties, and the method is simple and convenient.

[0006] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of food packaging paper with high oxygen and water vapor barrier properties, first, wood pulp is beaten to perform fine fiberization treatment, paper is made after fine fiberization treatment, and base paper is obtained after drying and balancing, the base paper is semi-dry pressed, surface coated after drying and balancing, semi-dry pressed again, dried and balanced, and finally the food packaging paper is obtained.

[0008] Further, the beating degree of the fine fiberization treatment is 15-75°SR.

[0009] Further, the linear pressure of the semi-dry pressing is 2MPa or lower.

[0010] Further, the surface sizing agent used for the surface coating is a mixture of carboxymethyl sodium starch and TiO2.

[0011] Further, the mass ratio of the carboxymethyl sodium starch and TiO2 is 4:1.

[0012] Further, the solid content of the surface sizing agent is 5%.

[0013] Further, the coating amount of the surface coating is 2-8g / m 2 .

[0014] The food packaging paper with high oxygen and water vapor barrier properties prepared by the method.

[0015] Further, the water vapor transmission coefficient of the food packaging paper is 1.55x10 -10 g / m·s·Pa, and the oxygen transmission coefficient is 0.192x10 -14 cm3 cm / cm 2 s*Pa.

[0016] The food packaging paper in the field of food packaging.

[0017] Advantages: compared with the prior art, the advantages of the present application are:

[0018] (1) The present application improves the plasticity of fibers, reduces the pore structure of paper, and improves the tightness of fiber bonding by fine fiberization of pulp, then flattens the fibers by semi-dry pressing of paper, further compresses the fiber pores, and then coats the base paper with carboxymethyl sodium starch polymer with a certain proportion of titanium dioxide, which has a certain antibacterial function, can fill and block the surface pores of the paper, and the carboxymethyl sodium starch serves as both a binder for titanium dioxide particles and a film-forming agent for the surface of the paper; the food packaging paper prepared finally has high oxygen and water vapor barrier properties.

[0019] (2) The food packaging paper prepared by the present application reduces the water vapor transmission coefficient from 5.59*10 -10 g / m*s*Pa to 1.55*10 -10 g / m*s*Pa, which is 72.27% lower than that of the original paper, and the oxygen transmission coefficient is reduced from 98.3*10 -14 cm 3 / cm / cm 2 / s*Pa to 0.192*10 -14 cm 3 / cm / cm 2 / s*Pa, which is 99.8% lower than that of the original paper.

[0020] (3) The present application uses fine fiberization of pulp, semi-dry pressing of paper, TiO2 particle filling on the surface of paper, and carboxymethyl starch surface coating and film-forming technology, which does not use synthetic polymer surface film-forming agent at all, and is easy to degrade and environmentally friendly while meeting the requirements of food packaging paper for high barrier to water molecules and oxygen molecules. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Process flow chart for preparing food packaging paper of the present application;

[0022] Figure 2 Fine fiberization degree and fiber surface morphology (a: 15°SR, b: 45°SR, c: 60°SR, d: 60°SR);

[0023] Figure 3 Fine fiberization degree and paper surface morphology (a: 15°SR, b: 30°SR, c: 45°SR, d: 60°SR);

[0024] Figure 4 Effect of the degree of fibrillation on the tensile index of paper;

[0025] Figure 5 Effect of the degree of fibrillation on the burst index of paper;

[0026] Figure 6 Effect of the degree of fibrillation on the tear index of paper;

[0027] Figure 7 Effect of the degree of fibrillation on the air permeability of paper;

[0028] Figure 8 Effect of different pressure of semi-dry press on the surface topography of paper (a: 0.0 MPa, b: 0.5 MPa, c: 1.0 MPa, d: 1.5 MPa);

[0029] Figure 9 Effect of different pressure of semi-dry press on the water vapor barrier property of paper;

[0030] Figure 10 Effect of different pressure of semi-dry press on the oxygen barrier property of paper;

[0031] Figure 11 Effect of the surface sizing amount on the water vapor barrier property of paper;

[0032] Figure 12 Effect of the surface sizing amount on the oxygen barrier property of paper;

[0033] Figure 13 Effect of different processes on the surface topography of paper (a: without beating, b: semi-dry press, c: surface coating, d: coating and then calendering). DETAILED DESCRIPTION

[0034] The application will be further described below in conjunction with specific examples.

[0035] The bleached softwood pulp used in the following examples was sourced from Canada, Moon brand; titanium dioxide TiO2 was sourced from Shanghai Maikelin Biotechnology Co., Ltd.; carboxymethyl starch sodium (CMS, food grade) was sourced from Henan Jiucha Biotechnology Co., Ltd.

[0036] The method for testing the water vapor and oxygen barrier properties of the food packaging paper prepared in the following examples is as follows: the WVP value (water vapor transmission coefficient) of different papers is tested using a W3-031 water vapor transmission rate tester (W3 / 036, LABTHINK, China) at a temperature of 37±0.6°C and a relative humidity of 50±2%, and each sample is tested three times. The OP value (oxygen transmission coefficient) of the paper is tested using a pressure difference method gas permeameter (VAC-V1, LABTHINK, China) at a temperature of 23±2°C and a relative humidity of 50±10%, and three samples of each sample paper are tested to calculate the average value.

[0037] The fiber morphology observation of the food packaging paper prepared in the following examples is performed using a BX41 optical microscope, and the surface morphology of the paper is observed using a Quanta 200 SEM.

[0038] Example 1

[0039] The method for preparing the food packaging paper with high oxygen and water vapor barrier properties is as follows:

[0040] (1) Fiber fine sizing and base paper preparation: 2% concentration of bleached coniferous wood pulp is subjected to viscous beating and fiber fine sizing treatment using a ZQS2-23 Valley beater, and the fiber fine sizing treatment degree is 15°SR, 30°SR, 45°SR, 60°SR and 75°SR respectively; the paper pulp after fiber fine sizing treatment is made into a base paper with a basis weight of 38g / m 2 after drying, and the base paper is placed in an environment of 23°C and 50% RH for 24h to obtain a base paper, and the base paper is subjected to relevant paper property detection.

[0041] (2) Paper semi-dry pressing: the base paper prepared in step (1) (with a water content of 50%) is subjected to semi-dry pressing by an XLS calender, and the linear pressure is set to 0MPa, 0.5MPa, 1.0MPa, 1.5MPa and 2.0MPa respectively for semi-dry pressing treatment; the paper after semi-dry pressing is dried, placed in an environment of 23°C and 50% RH for 24h, and subjected to paper property detection.

[0042] (3) Surface coating of film-forming agent on paper: carboxymethyl sodium starch and TiO2 are mixed (mass ratio of 4:1) to prepare a surface sizing agent (solid content of 5%). The surface of the paper is coated with the surface sizing agent using a CV-TB-B2 wire bar doctor blade integrated coater, and the coating amount is 2g / m 2 , 4g / m 2 , 6g / m 2 and 8g / m 2, after coating, the paper is again subjected to a semi-dry press (same line pressure as step (1)) in a semi-dry state, and then dried in an oven at 105°C. The dried paper sample is equilibrated at 23°C and 50% relative humidity, and a food packaging paper with high oxygen and water vapor barrier properties is finally obtained. The process flow for preparing the food packaging paper is shown in Figure 1 .

[0043] Example 2

[0044] 1. Measurement of the relationship between the degree of fibrillation and the surface morphology of the paper

[0045] The pulp fibers are subjected to mechanical treatment to achieve fibrillation, and the results are shown in Figure 2 .

[0046] Figure 2 The degree of fibrillation and the surface morphology of the fibers (a: 15°SR, b: 45°SR, c: 60°SR, d: 60°SR) are shown in the figure. After mechanical treatment of the pulp, the rigid structure of the pulp is gradually reduced, and the water absorption and swelling are promoted, which causes the outer layer of the primary and secondary cell walls of the fiber to break, the inter-fiber fibril layer bonding force is weakened, and the fiber end or surface is split into a fluffy state.

[0047] To ensure the tensile and tear strength properties of the packaging paper film material, the present application adopts a long-fiber viscous beating method, and the degree of fibrillation (beating degree) of the pulp is set at 15°SR, 30°SR, 45°SR, 60°SR and 75°SR, respectively, and then the paper with a basis weight of 38g / m 2 is made, and the strength and barrier properties of the paper are analyzed. The results are shown in Figure 3 .

[0048] Figure 3 The degree of fibrillation and the surface morphology of the paper (a: 15°SR, b: 30°SR, c: 45°SR, d: 60°SR) are shown in the figure. As can be seen from the figure, Figure 3 a is the surface morphology of the paper made from the virgin pulp, the paper structure is loose, the pores are obvious, and the fiber surface is smooth. As can be seen from Figure 3 b, 3c and 3d, as the degree of fibrillation of the pulp increases, the fiber bonding tends to be tight, and the surface of the paper film becomes smoother and smoother. The reason is that the degree of fibrillation increases, the specific surface area of the pulp fiber increases, the number of hydrogen bonds between the fibers increases significantly, and the cohesion between the fibers in the paper increases, so that the fibers are more closely combined. In addition, the fine fibers can form a "bridging" effect between the fibers, reduce the average pore size of the paper, and reduce the cross-sectional area of the fiber gap, further improving the barrier properties of the paper.

[0049] 2. Measurement of the relationship between the degree of fibrillation and the mechanical and barrier properties of the paper

[0050] Paper basis weight 38g / m 2 The paper strength and barrier properties of different beating degree were measured and analyzed, and the results are shown in Figures 4 to 7

[0051] Figure 4 The influence of the degree of fibrillation on paper tensile index; Figure 5 The influence of the degree of fibrillation on paper burst index; Figure 4 5 It can be seen that with the increase of beating degree, the tensile index and burst index of paper gradually increase, the specific surface area of fiber increases, the bonding area between fibers also expands, the number of hydrogen bond between fibers increases, which makes the tensile strength and burst strength of paper increase.

[0052] Figure 6 The influence of the degree of fibrillation on paper tear index; it can be seen from the figure that the tear index of paper decreases with the increase of the degree of fibrillation, mainly because the average length of pulp fiber decreases with the increase of the degree of fibrillation.

[0053] Figure 7 The influence of the degree of fibrillation on paper air permeability; it can be seen from the figure that when the beating degree increases, the air permeability of paper gradually decreases. Because with the increase of beating degree, the fiber is fully swollen, which increases its flexibility and bonding force, so that the bonding area of paper increases, and the pore between fibers becomes smaller, and the air permeability becomes lower. When the beating degree is 60°SR, the air permeability is 10.125um / (Pa·s).

[0054] Example 3

[0055] Measurement of the relationship between paper semi-dry pressing and paper barrier properties

[0056] After mechanical fibrillation treatment, not only the coarse fibers are split, but also the inherent rigid structure of the fibers is greatly weakened, making the fibers soft and plastic. Under the condition that the moisture content of paper is 50%, semi-dry pressing is carried out by a certain line pressure of pressing roller, which makes the fiber height decrease in radial direction and expand in transverse direction, thereby reducing the pore cross-sectional area between fibers, and even blocking the pore channel, so that the paper structure is further compacted. The results are shown in Figures 8 to 10

[0057] Figure 8 The surface morphology of paper under different semi-dry pressing pressures (a: 0.0MPa, b: 0.5MPa, c: 1.0MPa, d: 1.5MPa); it can be seen from the figure that with the increase of pressing line pressure, the fiber is more flat, the paper is more compact, and the pore is less.

[0058] Figure 9 The influence of different semi-dry pressing pressures on the water vapor barrier properties of paper;​​​Figure 10 The influence of different pressure semi-dry pressing on the oxygen barrier property of paper; from Figure 9 and 10 It can be seen that when semi-dry pressing is not performed, the WVP and OP of the paper are 5.59 x 10 -10 g / m-s-Pa and 98.3 x 10 -14 cm 3 cm / cm 2 s-Pa, respectively. Before the pressure is 1.0 MPa, the water vapor and oxygen permeability of the paper is significantly reduced, and after the pressure is 1.0 MPa, the reduction speed of the water vapor and oxygen permeability of the paper begins to slow down, and the degree of reduction begins to be not obvious. When the pressure is 2 MPa, the WVP and OP of the paper reach the lowest, which are 2.5651 x 10 -10 g / m-s-Pa and 1.03 x 10 -14 cm 3 cm / cm 2 s-Pa, respectively, which are increased by 54.1% and 98.95% compared with the barrier property of the un-pressed paper. It shows that the increase of the pressure can make the water vapor and oxygen barrier property of the paper better, and the reason is that the contact between the fibers is increased due to the pressing of the fibers by the pressure, the contact area is increased, and thus the porosity is reduced, so that the barrier property of the paper is improved. When the pressure is 1 MPa, the WVP and OP of the paper are 2.74 x 10 -10 g / m-s-Pa and 1.93 x 10 -14 cm 3 cm / cm 2 s-Pa, respectively, which are increased by 50.98% and 98.04% compared with the water vapor and oxygen barrier property of the un-pressed paper. The difference between the influence on the water vapor and oxygen barrier property of the paper when the pressure is 2 MPa and 1 MPa is not large, and when the pressure is too large during the semi-dry pressing, the fibers can be crushed, which can cause the mechanical property of the fibers to be reduced. It is found in the experiment that when the pressure is too large, the paper can be wrinkled, and the creases are increased. This not only affects the appearance of the paper, but also affects the performance test and later use of the paper.

[0059] In summary, under the condition that the basis weight of the paper is 38 g / m 2 and the moisture content of the paper is 50%, it is more appropriate to select the semi-dry pressing pressure as 1 MPa. Through the semi-dry pressing technology, the combination of the fibers is more compact, and the porosity is reduced, which further confirms that the semi-dry pressing can improve the water vapor and oxygen barrier property of the paper.

[0060] Example 4

[0061] Determination of the relationship between paper surface sizing and paper barrier property

[0062] The application adopts natural high molecular carboxymethyl surface film-forming agent (CMS) to be compounded with TiO2. TiO2 and the surface film-forming agent are compounded into a surface sizing agent with solid content of 5% (w:w) according to the mass ratio of 20:80, and the surface sizing agent is used to coat the paper after semi-dry pressing, and then the paper is treated by drying and pressing again, and the influence of the surface sizing amount on the water vapor and oxygen barrier properties of the paper is determined. Figure 11 and 12 .

[0063] Figure 11 The influence of the surface sizing amount on the water vapor barrier property of the paper; Figure 12 The influence of the surface sizing amount on the oxygen barrier property of the paper, as shown in the figure, the WVP and OP of the base paper are respectively: 5.59*10 -10 g / m·s·Pa and 98.3*10 - 14 cm 3 ·cm / cm 2 ·s·Pa. After the surface sizing agent mixed with TiO2 is used to size the surface of the paper, the water vapor and oxygen barrier properties of the paper are improved, with the increase of the surface sizing amount, the water vapor and oxygen transmission rates of the paper are reduced, that is, the barrier properties are better and better, and the greater the surface sizing amount, the better the water vapor and oxygen barrier properties. When the surface sizing amount is 8 g / m 2 , the WVP of the paper is 1.55*10 -10 g / m·s·Pa, and the OP is 0.192*10 -14 cm 3 ·cm / cm 2 ·s·Pa, which is respectively increased by 72.27% and 99.8% compared with the water vapor and oxygen barrier properties of the base paper. Therefore, the surface sizing agent used for the surface sizing of the paper shows more excellent water vapor and oxygen barrier properties.

[0064] Figure 13 Fig. 13 is the surface topography of the paper with different processes and paper surface topography (a: without beating, b: semi-dry pressing, c: surface coating, d: calendering after coating), 13a is the surface topography of the paper without beating, Figure 13 b is the surface topography of the paper after semi-dry pressing, from the two figures, it can be seen that the fibers and pores on the surface of the paper are clearly visible when the paper is not beaten, when the paper is beaten and semi-dry pressed, the fibers are flattened, the contact between the fibers is increased, and the pores on the surface of the paper are reduced. Figure 13 c and d are respectively the surface of the paper coated with sizing agent 8 g / m 2And coated after calendering surface topography, it can be seen that the surface of the paper coated only pretreatment, which are in the paper surface film, block the pores of the paper. The reason is that titanium dioxide hiding power, filling the pores of the paper, and the paper surface formed a layer of titanium dioxide, carboxymethyl starch sodium has excellent film forming, can be coated on the paper surface film and form a more uniform and complete barrier layer, further reduce the capillary effect of the paper, the paper water vapor and oxygen barrier performance can be greatly improved. The surface of the paper without calendering treatment can clearly see the outline of the fiber, the paper surface is uneven, while the paper surface after calendering film forming is better, more smooth, forming a uniform and complete film, so that the paper water vapor and oxygen barrier performance is improved.

[0065] In summary, the pulp by fine fiberization treatment, in the beating degree 60°SR paper air permeability from 81.436um / (Pa·s) to 10.125um / (Pa·s), reduced by 87.56%; paper by 1MPa pressure for semi dry press treatment, the water vapor transmission coefficient from 5.59×10 -10 g / m·s·Pa to 2.74×10 -10 g / m·s·Pa, reduced by 50.98%, oxygen transmission coefficient from 98.3×10 -14 cm 3 ·cm / cm 2 ·s·Pa to 1.93×10 -14 cm 3 ·cm / cm 2 ·s·Pa, reduced by 98.04%; by titanium dioxide on the paper surface pore structure capillary filling and paper surface sizing treatment, the paper water vapor transmission coefficient from 5.59×10 -10 g / m·s·Pa to 1.55×10 -10 g / m·s·Pa, reduced by 72.27% than the original paper, oxygen transmission coefficient from 98.3×10 -14 cm 3 ·cm / cm 2 ·s·Pa reduced to 0.192×10 -14 cm 3 ·cm / cm 2 ·s·Pa, reduced by 99.8% than the original paper.

[0066] Therefore, by the pulp fine fiberization, paper semi dry press, paper surface TiO2 particle filling and carboxymethyl starch surface coating film forming combined technical method, completely without using synthetic polymer surface film forming agent, can make the paper to the water molecules and oxygen molecules high barrier of food packaging paper film performance requirements.

Claims

1. A method for preparing food packaging paper with high oxygen and water vapor barrier properties, characterized in that, First, the wood pulp is beaten and subjected to fine fiberization treatment. After fine fiberization, paper is made, dried, and balanced to obtain base paper. The base paper is then semi-dry pressed, dried, and balanced before surface coating. It is then semi-dry pressed again, dried, and balanced to finally obtain food packaging paper. The surface sizing agent used for the surface coating is a mixture of sodium carboxymethyl starch and TiO2. The mass ratio of sodium carboxymethyl starch to TiO2 is 4:

1. The solid content of the surface sizing agent is 5%.

2. The method for preparing food packaging paper with high oxygen and water vapor barrier properties according to claim 1, characterized in that, The beating degree of the fine fiber treatment is 15-75°SR.

3. The method for preparing food packaging paper with high oxygen and water vapor barrier properties according to claim 1, characterized in that, The linear pressure of the semi-dry pressing is below 2 MPa.

4. The method for preparing food packaging paper with high oxygen and water vapor barrier properties according to claim 1, characterized in that, The coating amount on the surface is 2-8 g / m². 2 .

5. Food packaging paper with high oxygen and water vapor barrier properties prepared by the method according to any one of claims 1 to 4.

6. The application of the food packaging paper according to claim 5 in the field of food packaging.

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