Degradable straw fiber packaging film and preparation method thereof

Abstract

The invention discloses a degradable straw fiber packaging film and a preparation method thereof.The preparation method comprises the following steps that 1, after rice straw is cut into small sections, the small sections are treated through a gradient steam explosion technology, and straw microfibrils are obtained; (2) mixing the straw microfibrils with a deep eutectic solvent, and synchronously performing lignin removal and cellulose esterification reaction to obtain esterified straw microfibrils; the cellulose content of the esterified straw microfibril is 30%-35%, and the ester group substitution degree is 0.5-1.2; and (3) carrying out hot calendaring molding on the esterified straw microfilaments to prepare the degradable straw fiber packaging film. The method overcomes the defects that a lignin-cellulose compact cross-linked structure in the straw is difficult to dissociate efficiently, the tensile strength of the film is low, and the cellulose microfibril interface is high in hydrophilicity, so that the fiber film is softened and loses efficacy when encountering water and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass materials, and particularly relates to a degradable straw fiber packaging film and a preparation method thereof. Background Art

[0002] Rice straw is the main waste in agricultural production, with a huge annual output. It has a high lignin content (10%-15%), a strong anti-depolymerization barrier effect, and requires 6-12 months for natural degradation. Incineration is likely to cause environmental pollution. Traditional petrochemical-based plastics (such as PP, PE) are difficult to degrade and cause soil pollution; existing biodegradable films (such as starch, PLA) have problems such as poor mechanical properties and high costs. Therefore, it is of great significance to develop a straw-based packaging film with high mechanical properties, water resistance and degradability. Summary of the Invention

[0003] The purpose of the present invention is to provide a degradable straw fiber packaging film and a preparation method thereof, so as to solve the problems in the prior art such as the difficulty in dissociating lignin-cellulose, low mechanical properties of the film, and softening when encountering water due to strong hydrophilicity.

[0004] According to one aspect of the present invention, a preparation method of a degradable straw fiber packaging film is provided, including the following steps:

[0005] (1) After cutting rice straw into small segments, it is treated by a gradient steam explosion process to obtain straw microfibrils;

[0006] (2) Mixing the straw microfibrils with a deep eutectic solvent, and simultaneously performing lignin removal and cellulose esterification reaction to obtain esterified straw microfibrils; the cellulose content of the esterified straw microfibrils is 30%-35%, and the degree of ester group substitution is 0.5-1.2;

[0007] (3) Thermally calendering and forming the esterified straw microfibrils to prepare a degradable straw fiber packaging film.

[0008] In some embodiments, the initial components of the rice straw are 25%-28% cellulose, 30%-35% hemicellulose, and 10%-15% lignin.

[0009] In some embodiments, the conditions of the gradient steam explosion in step (1) are a pressure of 1.5-3.0 MPa, a time of 5-10 minutes, a rapid pressure relief from 3.0 to 1.5 MPa within 10-30 seconds, and a low-pressure slow release to atmospheric pressure within 10 minutes; the length of the obtained straw microfibrils is 1.2-1.8 mm, the diameter is 500-1200 nm, the cellulose content is 25%-28%, the hemicellulose content is 10%-18%, and the lignin content is 6%-10%.

[0010] In some embodiments, the deep eutectic solvent in step (2) is a mixture of choline chloride and γ-valerolactone, and the molar ratio of the two is 1:1 to 1:25.

[0011] In some embodiments, the solid-liquid mass ratio of straw microfibrils to the deep eutectic solvent in step (2) is 1:10 to 1:20, and the reaction conditions are microwave heating at a temperature of 60 - 80 °C, a power of 500 - 800 W, and a time of 2 - 4 hours, and 1% - 5% of acetic anhydride or butyric anhydride is added as a catalyst.

[0012] In some embodiments, the conditions for hot calendering in step (3) are a temperature of 80 - 150 °C and a pressure of 5 - 10 MPa.

[0013] A degradable straw fiber packaging film,

[0014] The film thickness is 20 - 100 μm;

[0015] The density is 0.9 - 1.3 g / cm 3 ;

[0016] The optical transmittance is 80% - 92%;

[0017] The water vapor transmission rate is 2.15×10 -11 g·s -1 ·m -1 ·Pa -1 to 1.12×10 -12 g·cm -2 ·s -1 ·Pa -1 ;

[0018] The oxygen permeability coefficient is 1.4×10 -17 cm 3 ·cm / cm 2 ·s·Pa;

[0019] The tensile strength is 30 - 50 MPa;

[0020] The hydrophobic angle is 75 - 105°

[0021] Compared with the prior art, the beneficial effects of this application are:

[0022] This application can utilize straw resources and reduce environmental pollution;

[0023] The film of this application has high transparency (80% - 92%), excellent mechanical properties (tensile strength 30 - 50 MPa), and strong hydrophobicity (contact angle 75° - 105°);

[0024] The film of this application can be naturally degraded to avoid traditional plastic pollution;

[0025] Compared with the prior art, it solves the problems that the dense cross-linked structure of lignin-cellulose in straw is difficult to efficiently dissociate, the tensile strength of the film is low, and the hydrophilicity of the cellulose microfibril interface is strong, resulting in the softening and failure of the fiber film when it meets water. Brief Description of the Drawings

[0026] Figure 1 It is a scanning electron microscope image of the microstructure of untreated straw microfibrils (left), gradient steam explosion-treated straw microfibrils (middle), and deep eutectic solvent-treated straw microfibrils (right) in Example 1 of the present invention;

[0027] Figure 2 It is a comparison diagram of the degradation situation of the film in Comparative Example 2 of the present invention under natural conditions for 1 month. Detailed Description of the Embodiments

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] Reference Figures 1 to 2 。

[0030] Example 1:

[0031] Raw material treatment: Take rice straw with 26% cellulose, 32% hemicellulose, and 12% lignin, cut it into sections (2 - 3 cm), perform gradient steam explosion (2.0 MPa, 4 minutes), achieve rapid pressure relief from 3.0 to 1.5 MPa high pressure within 10 - 30 seconds, and achieve low-pressure slow release to atmospheric pressure within 4 minutes to obtain microfibrils (length 1.5 mm, diameter 800 nm, cellulose content 27%, hemicellulose content 15%, lignin content 8%);

[0032] Solvent reaction: Mix the microfibrils with choline chloride and γ-valerolactone (molar ratio 1:2) (solid-liquid ratio 1:15), add 3% acetic anhydride, and perform microwave reaction (70 °C, 600 W, 3 hours), with an ester group substitution degree of 0.8;

[0033] Forming: Wash and dry the esterified straw microfibrils, and then transfer them to a hot press for hot pressing (120 °C, 8 MPa) to form a film with a thickness of 50 μm and a density of 1.1 g / cm 3 , a light transmittance of 88%, a tensile strength of 40 MPa, and a hydrophobic angle of 90°.

[0034] Example 2:

[0035] Raw material treatment: Take rice straw with 25% cellulose, 35% hemicellulose, and 10% lignin, cut it into sections (1 - 2 cm), perform gradient steam explosion (1.5 MPa, 5 minutes), achieve rapid pressure relief from 3.0 to 1.5 MPa within 10 - 30 seconds, and achieve low-pressure slow release to atmospheric pressure within 5 minutes to obtain microfibrils (length 1.8 mm, diameter 1000 nm, cellulose content 25%, hemicellulose content 18%, lignin content 10%);

[0036] Solvent reaction: Mix microfibrils with choline chloride and γ-valerolactone (molar ratio 1:5) (solid-liquid ratio 1:10), add 1% butyric anhydride, and perform microwave reaction (60 °C, 500 W, 4 hours), with an ester group substitution degree of 0.5;

[0037] Forming: Wash and dry the esterified straw microfibrils, then transfer them to a hot press for hot pressing (80 °C, 10 MPa) to form a film with a thickness of 20 μm and a density of 0.9 g / cm 3 , with a light transmittance of 92%, a tensile strength of 35 MPa, and a hydrophobic angle of 75°.

[0038] Example 3:

[0039] Raw material treatment: Take rice straw with 28% cellulose, 30% hemicellulose, and 15% lignin, cut it into sections (3 - 4 cm), perform gradient steam explosion (2.5 MPa, 3 minutes), achieve rapid pressure relief from 3.0 to 1.5 MPa within 10 - 30 seconds, and achieve low-pressure slow release to atmospheric pressure within 3 minutes to obtain microfibrils (length 1.2 mm, diameter 500 nm, cellulose content 28%, hemicellulose content 10%, lignin content 6%);

[0040] Solvent reaction: Mix microfibrils with choline chloride and γ-valerolactone (molar ratio 1:10) (solid-liquid ratio 1:20), add 1% acetic anhydride, and perform microwave reaction (80 °C, 800 W, 2 hours), with an ester group substitution degree of 1.2;

[0041] Forming: Wash and dry the esterified straw microfibrils, then transfer them to a hot press for hot pressing (150 °C, 5 MPa) to form a film with a thickness of 100 μm and a density of 1.3 g / cm 3 , with a light transmittance of 80%, a tensile strength of 50 MPa, and a hydrophobic angle of 105°.

[0042] Example 4:

[0043] Raw material treatment: Take rice straw with 27% cellulose, 33% hemicellulose, and 13% lignin, cut it into sections (2 - 3 cm), and perform gradient steam explosion (2.2 MPa, 3.5 minutes). Achieve rapid pressure relief from 3.0 to 1.5 MPa within 10 - 30 seconds, and achieve low-pressure slow release to atmospheric pressure within 3.5 minutes to obtain microfibrils (length 1.4 mm, diameter 700 nm, cellulose content 26%, hemicellulose content 12%, lignin content 7%);

[0044] Solvent reaction: Mix microfibrils with choline chloride and γ-valerolactone (molar ratio 1:25) (solid-liquid ratio 1:12), add 1% butyric anhydride, and perform microwave reaction (75 °C, 700 W, 2.5 hours) with an ester group substitution degree of 1.0;

[0045] Forming: Wash and dry the esterified straw microfibrils, then transfer them to a hot press for hot pressing (130 °C, 7 MPa) to form a film with a thickness of 70 μm and a density of 1.2 g / cm 3 , with a light transmittance of 85%, a tensile strength of 45 MPa, and a hydrophobic angle of 95°.

[0046] Comparative example 1 (mechanical crushing method):

[0047] Take the same rice straw as in Example 1, use mechanical crushing instead of gradient steam explosion to obtain microfibrils with a fiber length of about 5 mm and a diameter of about 2000 nm. Subsequently, prepare a packaging film according to the deep eutectic solvent treatment and hot pressing forming steps of Example 1.

[0048] The obtained film has a thickness of about 60 μm and a density of 1.0 g / cm 3 , an optical transmittance of 65%, a tensile strength of 20 MPa, and a hydrophobic angle of 60°. Due to the larger fiber size, the transparency and mechanical properties of the packaging film are significantly lower than those of Example 1.

[0049] Conclusion: Insufficient fiber dissociation leads to performance degradation.

[0050] Comparative example 2 (without esterification treatment):

[0051] Take the same rice straw as in Example 3, perform gradient steam explosion according to Example 3, but do not use the deep eutectic solvent and esterification reaction, and directly hot press the straw microfibrils (150 °C, 5 MPa).

[0052] The obtained film has a thickness of about 80 μm and a density of 1.4 g / cm 3 , an optical transmittance of 70%, a tensile strength of 25 MPa, and a hydrophobic angle of 50°. The packaging film has poor water resistance and starts to decompose after 1 month of use.

[0053] Failure to perform lignin removal and cellulose esterification results in insufficient hydrophobicity and mechanical properties of the packaging film, unable to meet the packaging application requirements. AsFigure 1 As shown, through gradient steam explosion treatment, the fine fiber structure in rice straw becomes fluffy and the distance between the cell wall layers increases, which helps the rapid and uniform dissolution of lignin. If the residual lignin is removed directionally by deep eutectic solvent treatment, the completely delignified bamboo board has good transparency, indicating that there is no lignin residue and the structure remains intact. After hot rolling densification treatment, the film thickness decreases and the internal pore structure reduces, and the mechanical strength will be improved.

[0054] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a degradable straw fiber packaging film, characterized in that: The following steps are involved: (1) Cutting rice straw into small pieces and treating them by gradient steam explosion to obtain straw microfibrils; (2) mixing the straw microfibrils with a deep eutectic solvent, and simultaneously performing lignin removal and cellulose esterification reaction to obtain esterified straw microfibrils; the esterified straw microfibrils have a cellulose content of 30%-35% and an ester substitution degree of 0.5-1.2; (3) The esterified straw microfibrils are hot-calendered to obtain a degradable straw fiber packaging film.

2. The method for preparing the degradable straw fiber packaging film according to claim 1, characterized in that: The initial components of the rice straw are 25%-28% of cellulose, 30%-35% of hemicellulose and 10%-15% of lignin.

3. The method for preparing the degradable straw fiber packaging film according to claim 1, characterized in that: The conditions of gradient steam explosion in step (1) are as follows: pressure 1.5-3.0 MPa, time 5-10 minutes, high pressure rapid pressure relief of 3.0 to 1.5 MPa within 10-30 seconds, and low pressure slow release to normal pressure within 10 minutes; the obtained straw microfibrils have a length of 1.2-1.8 mm, a diameter of 500-1200 nm, a cellulose content of 25%-28%, a hemicellulose content of 10%-18%, and a lignin content of 6%-10%.

4. The method for preparing the degradable straw fiber packaging film according to claim 1, characterized in that: The deep eutectic solvent in step (2) is a mixture of choline chloride and γ-valerolactone, and the molar ratio of the two is 1:1 to 1:

25.

5. The method for preparing the degradable straw fiber packaging film according to claim 1, characterized in that: In step (2), the solid-liquid mass ratio of the straw microfibrils to the deep eutectic solvent is 1:10 to 1:20, the reaction conditions are microwave heating temperature of 60-80°C, power of 500-800W, time of 2-4 hours, and adding 1%-5% acetic anhydride or butyric anhydride as a catalyst.

6. The method for preparing the degradable straw fiber packaging film according to claim 1, characterized in that: The conditions for hot calendering in step (3) are a temperature of 80-150° C. and a pressure of 5-10 MPa.

7. A degradable straw fiber packaging film prepared by the method according to any one of claims 1 to 6, characterized in that: The film thickness is 20-100 μm; Density 0.9-1.3g / cm 3 ; Optical transmittance is 80%-92%; The water vapor transmission rate is 2.15×10 -11 g·s -1 ·m -1 ·Pa -1 to 1.12×10 -12 g cm -2 ·s -1 ·Pa -1 ; The oxygen permeability coefficient is 1.4×10 -17 cm 3 cm / cm 2 ·s·Pa; Tensile strength is 30-50MPa; The hydrophobic angle is 75-105°.

Images