Paper-based material with high lignin content and method for its production

Abstract

The application belongs to the field of papermaking, and particularly relates to a paper-based material with high lignin content and a preparation method thereof. The paper-based material uses alkali lignin as a filler. After lignin is added to the paper-based material, the paper structure is more compact, the barrier property is enhanced, and good mechanical properties can be maintained by using the thermoplasticity, cohesiveness and hydrophobicity of lignin after high-temperature hot pressing of the paper base. The paper-based material can be applied to packaging materials, food packaging, paper cup manufacturing, medical materials and the like, and can replace traditional petroleum-based materials and plastics.

Description

Technical Field

[0001] This invention belongs to the field of papermaking, specifically relating to a paper-based material with high lignin content and its preparation method. Background Technology

[0002] Paper-based materials are among the most widely used materials today. They are typically made primarily of plant fibers, which are then formed into paper using a papermaking machine. Fillers, besides fibers, are the largest component, accounting for 1%-60% of the paper stock, significantly reducing production costs. Inorganic minerals are commonly used fillers in papermaking, such as titanium dioxide, calcined kaolin, synthetic silica, talc, ground calcium carbonate, and precipitated calcium carbonate. Compared to plant fibers, fillers are generally less expensive, and their addition not only reduces production costs but also improves paper's whiteness, opacity, and smoothness. However, with the addition of fillers, filler particles occupy fiber gaps and spaces, hindering the bonding between plant fibers and reducing the strength of the finished paper.

[0003] Lignin, a macromolecule with a phenylpropane structure, is the second largest component of plant raw materials after cellulose. It exists in and between the cell walls of plant fibers, acting as a binder to give plants a certain strength. However, in the extraction of papermaking raw materials and the papermaking process, lignin is usually removed as a foreign substance and remains in the pulping black liquor. Currently, lignin is mostly used as fuel, burned during alkali recovery, resulting in low high-value utilization. However, lignin's unique structural characteristics and physicochemical properties give it hydrophobicity, thermoplasticity, and adhesiveness. Derived from natural wood, its application in the preparation of paper-based materials, compared to its use as fuel, effectively promotes the high-value utilization of lignin, reduces production costs and environmental pollution, and is energy-saving and environmentally friendly. Its thermoplasticity, adhesiveness, and hydrophobicity allow for a denser structure in the prepared paper-based materials, improving the generally poor mechanical strength and barrier properties of traditional paper-based materials. Furthermore, no harmful chemicals are added during the preparation process, ensuring high safety. It can be used in packaging materials and food packaging, replacing traditional plastics, making paper cups, medical materials, etc., and replacing traditional petroleum-based materials and plastics. Therefore, the application of lignin and the preparation of environmentally friendly paper-based materials have become the focus of current research. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a paper-based material with high lignin content and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A paper-based material with high lignin content, using alkali lignin as a filler.

[0007] The alkali lignin is prepared by the following method: black liquor obtained by pulping alkali lignin raw material slurry through sulfate method, caustic soda method, alkali anthraquinone method, lime method, oxyalkali method or ammonia method is separated by precipitation;

[0008] Preferably, the alkali lignin raw material pulp is at least one of softwood pulp, hardwood pulp, hemp pulp, straw pulp, bamboo pulp, sugarcane pulp, cotton pulp, and reed pulp.

[0009] The alkali lignin has a particle size of 200nm-40μm and a purity of over 85%; the particle size D50 is greater than 300 mesh.

[0010] The paper-based material comprises the following components in relative mass parts: 100 parts oven-dried pulp, 0.5-60 parts alkali lignin, and 0.1-5 parts retention and filtration aids. Preferably, the alkali lignin accounts for 5-40% of the oven-dried pulp weight; more preferably, 5-20%; preferably, the retention and filtration aids account for 0.8%-1% of the oven-dried pulp weight.

[0011] The oven-dry pulp is prepared by beating the paperboard pulp board to 15°SR-80°SR; preferably 35°SR.

[0012] The paperboard pulp board is at least one of unbleached softwood pulp board, unbleached hardwood pulp board, and unbleached straw pulp board.

[0013] The retention and filtration aid is at least one of polyaluminum chloride, alum, cationic starch, amphoteric starch, chitosan, polyethyleneimine, polyethylene oxide, polydiallyldimethylammonium chloride, polyamide polyamine-epoxychloropropane, and cationic polyacrylamide.

[0014] The present invention also includes a method for preparing the paper-based material, comprising the following steps: 1) adding alkali lignin and retention and filtration aids to oven-dry pulp, defragmenting and then forming sheets to obtain a quantitative sheet base; 2) subjecting the sheet base obtained in step 1) to surface sizing treatment; 3) subjecting the sheet base obtained in step 2) to hot pressing treatment.

[0015] Step 2) involves preparing a 6%-8% starch solution, applying it using a surface rod application method at a rate of 6 g / m². 2 The sizing temperature is 18–45°C; the starch is at least one of native starch, oxidized starch, dialdehyde starch, roasted dextrin, esterified starch, etherified starch, and grafted starch; the native starch is at least one of corn starch, potato starch, and sweet potato starch.

[0016] The quantitative requirement in step 1) is 20g / m 2 -160 g / m 2Preferably, the parameters for hot pressing in step 3) are: hot pressing temperature is 110℃-250℃, preferably 160-180℃; linear pressure during hot pressing is 2-80N / mm, preferably 20N / mm-50N / mm; and crawling speed is 0.5m / min-5m / min.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. Alkali lignin is derived from natural wood and has significant advantages over traditional inorganic mineral fillers in terms of renewability, biodegradability, energy saving and environmental protection;

[0019] 2. After the paper sheet base is hot-pressed at high temperature, the thermoplasticity, adhesiveness, and hydrophobicity of lignin are utilized to make the paper structure more compact, enhance its barrier properties, and maintain good mechanical properties.

[0020] 3. Make reasonable use of alkali lignin, a waste material removed during papermaking, to overcome the problem that most of it is used as fuel and is burned during the alkali recovery process, resulting in a low utilization rate of high-value materials.

[0021] 4. No harmful chemicals are added during the preparation of paper-based materials, making them highly safe. They can be used in packaging materials, food packaging, paper cups, medical materials, etc., replacing traditional petroleum-based materials and plastics. Attached Figure Description

[0022] Figure 1 The diagram shows the effect of the pressure resistance index in Examples 1-5;

[0023] Figure 2 The diagram shows the effect of longitudinal tensile index in Examples 1-5;

[0024] Figure 3 The diagram shows the effect of the transverse tensile index in Examples 1-5;

[0025] Figure 4 These are the effect diagrams of longitudinal folding resistance in Examples 1-5;

[0026] Figure 5 These are the effect diagrams of the lateral folding resistance of Examples 1-5;

[0027] Figure 6 This is a diagram showing the contact angle of the paper when blank sample 1 is not hot-pressed.

[0028] Figure 7 This is a diagram showing the contact angle of the paper without hot pressing in Example 5;

[0029] Figure 8 This is a diagram showing the contact angle of paper during hot pressing at 160°C for example blank sample 1.

[0030] Figure 9This is a diagram showing the effect of the contact angle of the paper during hot pressing at 160°C in Example 5. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. Unless otherwise specified, all percentage contents used in this application are mass percentages.

[0032] Unless otherwise specified, all materials used in this application were purchased from Tianjin Mujingling Biotechnology Co., Ltd.; the alkali lignin used in this application was also purchased from Tianjin Mujingling Biotechnology Co., Ltd., and its particle size distribution is as follows. Figure 1 The particle size is 200nm-40μm, and the purity is higher than 85%; the particle size D50 is greater than 300 mesh; the alkali lignin can be obtained by evaporating and concentrating the black liquor obtained after pulping by sulfate method, caustic soda method, alkali anthraquinone method, lime method, oxyalkali method or ammonia method to 3-30 Baume degree, filtering it, and then entering a centrifugal atomizer for high-temperature atomization treatment, then entering a drying tower for drying, and finally separating the alkali lignin dry powder by a cyclone separator.

[0033] Example 1

[0034] In this embodiment, alkali lignin is applied to papermaking fillers to obtain a paper-based material with high lignin content. The paper-based material is prepared in the following manner:

[0035] 1) Select natural-colored, oven-dried coniferous pulp, beat it to 35°SR using a Wali pulper, and sieve alkali lignin particles (300 mesh) through a sieve. Add the alkali lignin particles at 5% of the air-dried pulp weight, and add retention and filtration aid PE I at 0.8% of the air-dried pulp weight. After decomposition, form into sheets with a basis weight of 60 g / m³. 2 .

[0036] 2) The sheet base obtained in step 1) is surface-treated with aldehyde starch; specifically, a 3%-8% aldehyde starch solution is prepared, gelatinized at 90℃ for 30 minutes, and then surface-treated with a rod-type sizing agent at a rate of 6 g / m². 2 The application temperature is 30℃;

[0037] 3) Take the substrate obtained in step 2) and use a roller hot press to perform hot pressing treatment at a temperature of 160℃, a linear pressure of 50N / mm, and a crawling speed of 0.5m / min. Then place the prepared substrate in an international standard constant temperature and humidity environment (temperature of 23±0.5℃ and humidity of 50±5%rh) for equilibration for 24 hours before relevant tests can be performed.

[0038] Example 2

[0039] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 1 is that, in step 1), alkali lignin particles are added at 10% of the oven-dry pulp weight. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0040] Example 3

[0041] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 1 is that, in step 1), alkali lignin particles are added at 20% of the oven-dry pulp weight. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0042] Example 4

[0043] This embodiment provides a method for preparing paper-based materials. Unlike embodiment 1, in step 1), alkali lignin particles are added at 30% of the amount of air-dried pulp. The selection of other raw materials and methods are the same as in embodiment 3, and will not be repeated here.

[0044] Example 5

[0045] This embodiment provides a method for preparing paper-based materials. The difference from embodiment 3 is that, in step 1), alkali lignin particles are added at 40% of the amount of air-dried pulp. The selection of other raw materials and methods are the same as in embodiment 3, and will not be repeated here.

[0046] Blank Sample 1: Blank Sample 1 is oven-dried pulp obtained at 35°SR;

[0047] Blank Sample 2: The difference between Blank Sample 2 and Example 1 is that no lignin particles were added.

[0048] Examples 1-5 illustrate the effect of different amounts of alkali lignin added on paper-based materials. The results show that, compared with blank sample 1 and blank sample 2, Figure 1 Before hot pressing, the bursting index gradually decreased with increasing alkali lignin content, decreasing from 8.23 ​​kPa·m for blank sample 1. 2 / g decreases to 4.12 kPa.m when added at a concentration of 40%. 2 / g, because lignin particles occupy fiber gaps and fiber space, hindering the bonding between plant fibers, thus reducing its strength. After hot pressing, the bursting index increased compared to the unpressed state, and a good bursting index was maintained even with an addition amount of 5%-20%. This indicates that the partial melting of lignin during hot pressing has a positive effect on the mechanical properties and strength of paper.

[0049] Figure 2Comparing the longitudinal tensile index before and after hot pressing, the tensile index gradually decreased with the increase of alkali lignin addition before hot pressing. The tensile index decreased from 179.05 Nm / g in blank sample 1 to 91.20 Nm / g at 40% addition. The tensile strength could be maintained at more than 60% of the original tensile strength at 5-30% addition. Although the strength decreased significantly at 20%-40% addition, the adhesive properties of lignin after hot pressing restored some of the strength. The tensile index after hot pressing was higher than that before pressing. Figure 3 Comparing the transverse tensile index before and after hot pressing, the tensile index gradually decreased with the addition of alkali lignin before hot pressing, and the change in tensile index before and after hot pressing was not significant. After hot pressing, the tensile index increased slightly, and the transverse tensile index was the best after hot pressing when the addition amount was 5%-10%. Moreover, the original strength level was basically maintained when the addition amount was 10%-30%. This indicates that through hot pressing, the melting of lignin has a good effect on improving the mechanical strength of paper.

[0050] Figure 4 Comparing longitudinal folding endurance before and after hot pressing, the number of folds before hot pressing gradually decreased with the addition of alkali lignin, but it could still reach 517 times with an addition of 40%. After hot pressing, the number of folds increased with the addition of alkali lignin, reaching 891 times with an addition of 40%, which is equivalent to that of traditional plastic film. Figure 5 Comparing the transverse flexural endurance before and after hot pressing, before hot pressing, the number of flexural cycles gradually decreased with the addition of alkali lignin from 20% to 40%, but was better than the blank sample at 5% to 10%. After hot pressing, although the number of flexural cycles decreased, the transverse flexural endurance could still reach 70 times at an addition of 40%, significantly higher than the 30 times before hot pressing. The number of flexural cycles was higher when the addition was 5% to 20%.

[0051] Example 6

[0052] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 3 is that the amount of retention and filtration aid added in step 1) is 0.1% of the amount of air-dried pulp. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0053] Example 7

[0054] This embodiment provides a method for preparing paper-based materials. The difference from embodiment 3 is that the amount of retention and filtration aid added in step 1) accounts for 1% of the amount of air-dried pulp. The selection of other raw materials and methods are the same as in embodiment 3, and will not be repeated here.

[0055] Example 8

[0056] This embodiment provides a method for preparing paper-based materials. The difference from embodiment 3 is that the amount of retention and filtration aid added in step 1) accounts for 2% of the amount of air-dried pulp. The selection of other raw materials and methods are the same as in embodiment 3, and will not be repeated here.

[0057] Examples 6-8 illustrate the effects of different retention and filtration aid dosages on paper-based materials. The results show that because lignin particles are negatively charged, too little retention and filtration aid will result in fewer fine lignin particles remaining in the paper (retention <30%), while too much will cause pulp flocculation, affecting the uniformity of the paper and thus adversely affecting its mechanical properties. Therefore, 0.8%-1% is the preferred dosage.

[0058] Example 9

[0059] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 3 is that the paper hot-pressing temperature in step 3) is 80°C. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0060] Example 10

[0061] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 3 is that the paper hot-pressing temperature in step 3) is 180°C. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0062] Example 11

[0063] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 3 is that, in step 3), the paper hot-pressing temperature is 260°C. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0064] Examples 9-11 illustrate the effects of different hot-pressing temperatures on paper-based materials. The results show that when the temperature is too low, the glass transition temperature of lignin cannot be reached, thus affecting its mechanical properties. On the other hand, when the temperature is too high, the stability of the starch coating is destroyed, affecting the barrier properties of the paper after hot pressing. Therefore, a hot-pressing temperature of 160-180℃ is the preferred setting.

[0065] Example 12

[0066] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 3 is that the linear pressure of the paper hot press roller in step 3) is 5 N / mm. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0067] Example 13

[0068] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 3 is that the linear pressure of the paper hot press roller in step 3) is 20 N / mm. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0069] Example 14

[0070] This embodiment provides a method for preparing paper-based materials. The difference from Embodiment 3 is that the linear pressure of the paper hot press roller in step 3) is 60 N / mm. The selection of other raw materials and methods are the same as in Embodiment 3, and will not be repeated here.

[0071] Examples 12-14 illustrate the effects of different roll forming pressures on paper base materials. The results show that when the pressure is too low, it is impossible to work with the temperature to compress the lignin into sheets to fill the fiber gaps, thus affecting its mechanical properties. On the other hand, when the pressure is too high, it damages the fiber lumen, causing crushing, which affects the mechanical properties of the paper after hot pressing. Therefore, 20 N / mm-50 N / mm is the preferred setting.

[0072] Evaluation of the properties of the paper-based material

[0073] Various physical property tests were conducted on Examples 1 to 5, the comparison of unfilled alkali lignin particles (blanks 1 and 2), and the unpressed sheet substrate.

[0074] 1. Determination of mechanical strength of sheet metal before and after hot pressing

[0075] The mechanical properties of the substrates prepared in Examples 1 to 5 and blank samples 1 and 2 were tested before and after calendering. The substrates were placed in an international standard constant temperature and humidity environment (temperature 23±0.5℃, humidity 50±5% RH) for 24 hours before relevant tests were performed. The tensile strength was determined using a tensile strength tester (B0660005, Lorentzen & Wettre, Sweden); the number of folding cycles was determined using a folding endurance tester; and the bursting strength was determined using a bursting strength tester (Lorentzen & Wettre, Sweden). Each sample was tested three times, and the average value was recorded. Figures 1 to 5 The graph shows the measured data of bursting index, tensile index, and folding endurance of the paper before and after hot pressing in Examples 1-5 and blank samples 1 and 2.

[0076] 2. Determination of water resistance properties before and after hot pressing of sheet metal sheets

[0077] The water resistance properties of the sheet substrates prepared in Examples 1-5 and Blank Sample 2 were tested before and after calendering. The static water contact angle of the paper before and after calendering was measured at room temperature using a PGX contact angle meter (AST Products, Inc., USA).

[0078] The effects of different amounts of alkali lignin addition on the barrier properties of paper-based materials before and after hot pressing were determined. Figure 6 This is a diagram showing the contact angle of the paper when blank sample 1 is not hot-pressed. Figure 7 This is a diagram showing the contact angle of the paper without hot pressing in Example 5; Figure 8 This is a diagram showing the contact angle of paper during hot pressing at 160°C for example blank sample 1. Figure 9This is a diagram showing the effect of the contact angle of the paper during hot pressing at 160°C in Example 5.

[0079] The contact angle results showed that before hot pressing, the initial contact angle of the blank sample (blank sample 1) was 40°, and the complete water absorption time was 5s. The sample with 40% lignin (Example 5) had an initial contact angle of 58.10° and a complete water absorption time of 16s. After hot pressing, the initial contact angle of the blank sample (blank sample 1) was 91.19°, and it reached 80.53° after 10 minutes. The sample with 40% lignin had an initial contact angle of 112.49°, and the contact angle remained at 104.36° after 10 minutes. Similarly, addition amounts of 5%, 10%, 20%, and 30% all showed varying degrees of improvement in both the initial contact angle and the complete water absorption time. These results indicate that the addition of lignin can have a positive effect on the barrier properties of paper-based materials.

[0080] In summary, compared with the prior art, the technical solution of the present invention is as follows:

[0081] 1. Alkali lignin is derived from natural wood and has significant advantages over traditional inorganic mineral fillers in terms of renewability, biodegradability, energy saving and environmental protection;

[0082] 2. After the paper sheet base is hot-pressed at high temperature, the thermoplasticity, adhesiveness, and hydrophobicity of lignin are utilized to make the paper structure more compact, enhance its barrier properties, and maintain good mechanical properties.

[0083] 3. Make reasonable use of alkali lignin, a waste material removed during papermaking, to overcome the problem that most of it is used as fuel and is burned during the alkali recovery process, resulting in a low utilization rate of high-value materials.

[0084] 4. No harmful chemicals are added during the preparation of paper-based materials, making them highly safe. They can be used in packaging materials, food packaging, paper cups, medical materials, etc., replacing traditional petroleum-based materials and plastics.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A paper-based material with high lignin content, characterized in that, Alkali lignin is used as a filler; the components include the following relative mass parts: 100 parts oven-dried pulp, 5-40 parts alkali lignin, and 0.8-1 parts retention and filtration aid; The preparation method of the paper-based material includes the following steps: 1) adding alkali lignin and retention and filtration aids to oven-dry pulp, defragmenting and then forming sheets to obtain a quantitative sheet base; 2) subjecting the sheet base obtained in step 1) to surface sizing treatment; 3) subjecting the sheet base obtained in step 2) to hot pressing treatment; the parameters of the hot pressing treatment are: hot pressing temperature is 160-180℃; the linear pressure during hot pressing is 20N / mm-50N / mm; the creeping speed is 0.5m / min-5m / min.

2. The high lignin content paper-based material according to claim 1, characterized in that, The alkali lignin is prepared by the following method: black liquor obtained by pulping alkali lignin raw material slurry through sulfate method, caustic soda method, alkali anthraquinone method, lime method, oxy-alkali method or ammonia method is separated by precipitation. The alkali lignin raw material pulp is at least one of softwood pulp, hardwood pulp, hemp pulp, straw pulp, bamboo pulp, sugarcane pulp, cotton pulp, and reed pulp.

3. The high lignin content paper-based material according to claim 1, characterized in that, The alkali lignin has a particle size of 200nm-40μm and a purity of over 85%.

4. The high lignin content paper-based material according to claim 1, characterized in that, The mass percentage of alkali lignin is 5-20% of the oven-dried pulp.

5. The high lignin content paper-based material according to claim 4, characterized in that, The oven-dry pulp is prepared by beating the paperboard pulp board to 15°SR - 80°SR.

6. The paper-based material according to claim 5, characterized in that, The paperboard pulp board is at least one of unbleached softwood pulp board, unbleached hardwood pulp board, and unbleached straw pulp board.

7. The high lignin content paper-based material according to claim 4, characterized in that, The retention and filtration aid is at least one of polyaluminum chloride, alum, cationic starch, amphoteric starch, chitosan, polyethyleneimine, polyethylene oxide, polydiallyldimethylammonium chloride, polyamide polyamine-epoxychloropropane, and cationic polyacrylamide.

8. The paper-based material according to claim 1, characterized in that, Step 2) involves the following steps: preparing a starch solution, applying it using a surface rod applicator, with an application rate of 6 g / m². 2 The sizing temperature is 18–45°C; the starch is at least one of native starch, oxidized starch, dialdehyde starch, roasted dextrin, esterified starch, etherified starch, and grafted starch; the native starch is at least one of corn starch, potato starch, and sweet potato starch.

Images