A multi-component retention system for lightweight paper-based materials

Abstract

This invention relates to the field of papermaking and provides a multi-component retention aid system for lightweight paper-based materials. The multi-component retention aid system includes chitosan, cationic starch, nanocellulose, polyvinyl alcohol, and nano-TiO2. The system comprises the following steps: mixing chitosan, cationic starch, and nanocellulose, and subjecting them to magnetic stirring to obtain a composite retention aid; adding the composite retention aid, polyvinyl alcohol, and nano-TiO2 to pulp, followed by ultrasonic and high-speed shearing treatment to obtain a composite pulp; and subjecting the composite pulp to wet-end retention and web-forming processes to obtain a lightweight paper-based material. By neutralizing the charge of fibers and TiO2 particles with chitosan and cationic starch, and constructing a three-dimensional network with nanocellulose and polyvinyl alcohol, a core-shell structure is formed under ultrasonic and high-speed shearing conditions, improving the retention rate and uniform distribution of nano-TiO2, achieving lightweighting while improving the mechanical strength and surface quality of the paper-based material.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, and more specifically, to a multi-component retention aid system for lightweight paper-based materials. Background Technology

[0002] In the papermaking industry, single-component or multi-component retention aid systems are typically used to improve the retention rate of fillers and fine fiber components. While single-component polymeric retention aids can improve retention to some extent, they often struggle to balance wet web formation and high filler retention. Two-component systems, usually composed of low charge density polymers and microparticles, can improve retention and dewatering performance, but their retention efficiency for nanoscale fillers, such as nano-TiO2, remains insufficient. Therefore, there is an urgent need for a multi-component retention aid system that can achieve efficient wet-end retention of nano-TiO2 while maintaining good rheological and web-forming properties. Summary of the Invention

[0003] This invention provides a multi-component retention aid system for lightweight paper-based materials. First, positively charged chitosan and cationic starch are used to electrostatically neutralize and bridge fibers and nano-TiO2 particles. Then, a stable three-dimensional network is constructed through hydrogen bonding crosslinking of nano-cellulose and polyvinyl alcohol. Under ultrasonic and high-speed shearing, the pulp fibers become the "core" and the nano-TiO2 forms the "shell," forming a core-shell structure. This structure significantly improves the retention rate and dispersion uniformity of fillers such as nano-TiO2, and greatly enhances the whiteness and opacity of the paper-based material. At the same time, the crosslinked network structure enhances the dry strength and tear strength of the paper, achieving optimization of mechanical properties and surface quality while achieving lightweighting.

[0004] This invention provides a multi-component retention aid system for lightweight paper-based materials. The multi-component retention aid system includes chitosan, cationic starch, nanocellulose, polyvinyl alcohol, and nano-TiO2. The multi-component retention aid system includes the following steps: S100, mixing chitosan, cationic starch, and nanocellulose, and performing magnetic stirring to obtain a composite retention aid; S200, adding the composite retention aid, polyvinyl alcohol, and nano-TiO2 to pulp, and subjecting it to ultrasonic treatment and high-speed shearing to obtain a composite pulp; S300, subjecting the composite pulp to wet-end retention aid and web forming processes to obtain a lightweight paper-based material.

[0005] In any of the above technical solutions, the composite slurry in step S200 forms the following core-shell structure: a core layer comprising pulp fibers as the core carrier; and a shell layer comprising nano-TiO2 particles, at least partially encapsulating the core layer.

[0006] In any of the above technical solutions, the composite slurry further includes an interface layer, which is disposed between the core layer and the shell layer. The interface layer includes chitosan and cationic starch, which neutralize and crosslink the cationic charges and crosslink the fibers and TiO2 surface. The interface layer tightly binds the core layer and the shell layer.

[0007] In any of the above technical solutions, in step S300, the thickness of the core layer is 1-5 μm; the thickness of the shell layer is 50-200 nm.

[0008] In any of the above technical solutions, in step S100: the mass ratio of chitosan, cationic starch and nanocellulose in the composite retention aid is (0.1-1):(0.1-1):1; the magnetic stirring time is 20-40 min.

[0009] In any of the above technical solutions, in step S100, the pH value of the composite retention aid is 7-8 and the solid content is 0.8-1.2wt%.

[0010] In any of the above technical solutions, before step S100, the following steps are included: S001, pre-dissolving chitosan in an acetic acid solution with a pH value in the range of 4-5; S002, pre-dissolving cationic starch in water at 40-50℃; S003, pre-dissolving nanocellulose in deionized water.

[0011] In any of the above technical solutions, the pulp slurry includes pretreatment: S201, diluting the pulp raw material to 3-4 wt% and heating it to 30-50℃ to obtain the pulp slurry.

[0012] In any of the above technical solutions, in step S200: the mass ratio of the composite retention aid to nano-TiO2 is 1:(8-12); the ultrasonic treatment frequency is 20-40kHz, and the time is 5-15min; the high-speed shearing treatment speed is 2000-4000rpm, and the time is 45-75s.

[0013] In any of the above technical solutions, in step S300, the screen speed of the screen forming process is 200-250 m / min, and the screen temperature is 35-40℃.

[0014] The technical effects that can be achieved by adopting the technical solution of the present invention are as follows: 1. By neutralizing and bridging the charge of chitosan and cationic starch, combined with ultrasonic shearing technology, a composite structure with fiber as the core and nano-TiO2 as the shell is formed, which significantly improves the filler retention rate; 2. The synergistic system of the cationic charge of chitosan, the three-dimensional network of nanocellulose, and the hydrogen bonding crosslinking of polyvinyl alcohol can improve the dry tensile strength while reducing the basis weight of paper-based materials. 3. The combined use of ultrasonic treatment and high-speed shearing technology achieves efficient dispersion of nano-TiO2 and directional assembly of core-shell structure. Combined with a wire section temperature of 35-40℃, the dewatering efficiency is improved and the smoothness of the paper is increased. Attached Figure Description

[0015] Figure 1 This is a SEM image of the core-shell structure of the composite slurry in Embodiment 1 of the present invention; Figure 2 This is a SEM image of the composite slurry core-shell structure of Embodiment 1 of the present invention. Detailed Implementation

[0016] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0017] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0018] To make the above-mentioned objectives, features and advantages of this aspect more apparent and understandable, specific embodiments of this aspect are described in detail below.

[0019] In the papermaking industry, single-component or multi-component retention aid systems are usually used to improve the retention rate of fillers and fine fiber components. Although single-component polymeric retention aids can improve the retention effect to a certain extent, they often cannot achieve both wet web formation and high filler retention rate. Two-component systems usually consist of a combination of low charge density polymers and microparticles, which can improve retention and dewatering performance, but the retention efficiency for nanoscale fillers, such as nano TiO2, is still insufficient.

[0020] In recent years, nanocellulose has attracted attention for its high specific surface area and network toughening ability in wet end retention. However, when used alone with polymers, it is easy to cause flocculation instability and it is difficult to meet the requirements of high retention rate and good network formation at the same time. Chitosan, as a natural cationic polymer, has also been studied for pulp filler retention, but there is little research on wet end retention of nano-TiO2. Therefore, this embodiment provides a multi-component retention aid system for lightweight paper-based materials. First, positively charged chitosan and cationic starch are used to electrostatically neutralize and bridge fibers and nano-TiO2 particles. Then, a stable three-dimensional network is constructed through hydrogen bonding crosslinking of nano-cellulose and polyvinyl alcohol. Under ultrasonic and high-speed shearing, the pulp fibers become the "core" and the nano-TiO2 forms the "shell," forming a core-shell structure. This structure significantly improves the retention rate and dispersion uniformity of fillers such as nano-TiO2, and greatly enhances the whiteness and opacity of the paper-based material. At the same time, the crosslinked network structure enhances the dry strength and tear strength of the paper, achieving optimization of mechanical properties and surface quality while achieving lightweighting.

[0021] Specifically, the multi-component retention aid system of this embodiment includes chitosan, cationic starch, nanocellulose, polyvinyl alcohol, and nano-TiO2; The diversified retention system includes the following steps: S100. Chitosan, cationic starch and nanocellulose are mixed and magnetically stirred to obtain a composite retention aid. S200: The composite retention aid, polyvinyl alcohol, and nano-TiO2 are added to the pulp slurry, and the slurry is obtained by ultrasonic treatment and high-speed shearing treatment. S300: The composite pulp is subjected to wet-end retention and web-forming processes to obtain lightweight paper-based materials.

[0022] Preferably, in step S100, chitosan, cationic starch, and nanocellulose are mixed in a mass ratio of (0.1-1):(0.1-1):1 and subjected to magnetic stirring to obtain a composite retention aid. Chitosan and cationic starch carry cationic charges and can electrostatically adsorb with negatively charged fibers and fillers to form a bridging structure, thereby enhancing the retention rate of fillers in pulp. Nanocellulose has a high specific surface area and abundant hydroxyl groups, which can form hydrogen bonds with other components to construct a three-dimensional network structure, enhance the bonding force between fibers, and improve the mechanical strength of paper. The mass ratio of chitosan, cationic starch, and nanocellulose (0.1-1):(0.1-1):1) ensures that the cationic polymer forms an appropriate charge neutralization layer on the surface of fibers and fillers, while leaving enough nanocellulose for structural support, avoiding excessive aggregation or insufficient dispersion due to excessive single component. Furthermore, the appropriate ratio can adjust the chain length and branching degree of the polymer chain, thereby controlling the particle size of the formed flocs, ensuring that the micro-flocs are large enough to improve the retention rate, without clogging the wire due to excessive size. Magnetic stirring for 20-40 minutes ensures thorough mixing of different components without generating excessive shear force, forming a homogeneous colloid. This avoids uneven or excessive dispersion due to insufficient time, which could damage the polymer structure. The composite retention aid has a pH of 7-8. Chitosan maintains a certain positive charge in a weakly alkaline environment while reducing the tendency to aggregate and precipitate, giving the retention aid good aqueous stability and adsorption capacity. The solid content is 0.8-1.2 wt%, which ensures moderate slurry viscosity, maintaining the suspension stability of the retention aid without affecting pumping and stirring due to excessive viscosity, thus forming an ideal micro-flocculated structure.

[0023] Prior to this, chitosan was dissolved in acetic acid solution with a pH of 4-5, cationic starch was dissolved in water at 40-50℃, and nanocellulose was dissolved in deionized water to ensure that each component was fully dissolved and dispersed. Under weakly acidic conditions, chitosan is fully protonated and has high solubility, resulting in a uniformly dispersed cationic polymer solution and avoiding agglomeration when added directly. Dissolving cationic starch in water at 40-50℃ helps to draw out more cationic groups to participate in charge neutralization and improve retention efficiency. Pre-dissolving nanocellulose in deionized water can avoid interference from irrelevant ions on its surface charge and hydrogen bonding, forming a stable nano-network framework.

[0024] Preferably, in step S200, the composite retention aid, polyvinyl alcohol, and nano-TiO2 are added to the pulp. The pulp is first dispersed and refined by ultrasonic treatment, and then the agglomerates are broken up by high-speed shearing. Finally, an interface layer is formed with pulp fiber as the "core", nano-TiO2 as the "shell", and chitosan / cationic starch crosslinked in the middle, which firmly coats the filler on the fiber surface. This core-shell structure not only significantly improves the filler retention rate and dispersion uniformity, but also takes into account the optical properties, mechanical strength, and web forming and dewatering efficiency of the paper base material. The ultrasonic treatment frequency is 20-40kHz, and the time is 5-15min. The micro-cavitation collapse generated by the ultrasound can produce strong shear force at the microscale, which can rapidly disperse nano-TiO2 particles and retention-aiding polymers in the pulp. At the same time, it can slightly peel and refine the fiber surface, increasing the contact area and interfacial bonding force between the fiber and the filler. The subsequent high-speed shearing at 2000-4000rpm can further disperse residual micro-flocs, prevent the formation of large agglomerates, and obtain a more homogeneous composite pulp, which is conducive to uniform spreading and stable dewatering during web formation. The pulp fiber, as the "core", provides large-scale The high-strength skeleton makes the formed flocs less likely to fall off or redisperse during the papermaking process. The uniform outer layer of nano-TiO2 not only greatly improves the whiteness and opacity of the paper, but its high refractive index and nano-scattering effect also enhance printability and color reproduction. The interface layer is a neutralization layer formed by chitosan and cationic starch, which not only neutralizes the negative charge on the surface of the fiber and TiO2, but also achieves a strong "bridge" across the fiber and shell through polymer chains. Furthermore, this layer significantly improves the interfacial bonding strength between the core layer and the shell through electrostatic adsorption and hydrogen bond network, preventing the shell from falling off under subsequent drying and mechanical stress.

[0025] Furthermore, the core layer has a thickness of 1-5 μm and a size that matches the paper mesh pores, making it easy for the composite pulp to form a web on the mesh and ensuring that the dewatering channels are unobstructed without significant blockage; the shell layer has a thickness of 50-200 nm, which is thin enough to ensure the nano-scattering effect and thick enough to provide complete coating protection, while avoiding excessive thickness that would lead to a decrease in optical performance or a darker image.

[0026] Furthermore, controlling the pulp concentration at 3-4 wt% ensures that the pulp is neither too thick, making pumping, stirring, and aeration difficult, nor too thin, making it difficult for fibers to disperse evenly. Heating at 30-50℃ reduces pulp viscosity and improves fluidity, which is beneficial for the uniform dispersion of fibers and retention aids during subsequent ultrasonic and shearing treatments. Under suitable temperature and dilution conditions, the hydration layer on the fiber surface becomes looser, allowing retention polymers to penetrate and adsorb more fully. At the same time, it also forms a more stable interface layer for nano-TiO2 particles, laying the foundation for the subsequent construction of the core-shell structure. The mass ratio of composite retention aid to nano-TiO2 is 1:(8-12). On the one hand, this ensures that each unit of retention aid carries a sufficient amount of TiO2, significantly increasing the filler loading in the pulp. On the other hand, it avoids excessively high TiO2 ratios that could lead to "saturation" failure or particle agglomeration of the retention aid, thus maintaining excellent dispersibility and retention efficiency while ensuring high loading.

[0027] Preferably, in step S300, the web forming speed is 200-250 m / min, which generates sufficient centrifugal force to help the free water in the fiber web be quickly discharged. At the same time, the web temperature rises to 35-40°C, reducing the viscosity of the water and accelerating the movement and evaporation of water in the capillary action. The appropriate linear speed and temperature allow the web vacuum box and press roll system to maintain the optimal negative pressure difference, preventing excessive stretching or deviation of the fiber web, thereby ensuring uniform web formation and achieving efficient dewatering in the web forming zone in a short time. This can quickly "lock" the free water in the fibers and core-shell composite flocs in the fiber gaps, reducing redispersion or flocculent expansion caused by subsequent web speed changes. The web temperature of 35-40°C will not cause the polymer retention aid or nano-TiO2 layer to flow or become unstable, ensuring that the core-shell structure and interface layer are well protected during the dewatering process.

[0028] In summary, the core of this patent application lies in the electrostatic neutralization and bridging of fibers and nano-TiO2 by chitosan and cationic starch, and the construction of a stable three-dimensional network by hydrogen bonding crosslinking of nano-cellulose and polyvinyl alcohol. Under ultrasonic dispersion and high-speed shearing, a core-shell structure is formed with pulp fibers as the "core", nano-TiO2 as the "shell", and a chitosan / cationic starch crosslinking layer in the middle. This significantly improves the retention rate and dispersion uniformity of nano-TiO2. At the same time, the three-dimensional crosslinking network enhances the dry strength and tear strength of paper, and maintains structural stability during web formation and dehydration. This achieves simultaneous optimization of the optical and mechanical properties of lightweight paper-based materials.

[0029] Example 1

[0030] This embodiment provides a multi-component retention aid system for lightweight paper-based materials, including chitosan, cationic starch, nanocellulose, polyvinyl alcohol, and nano-TiO2; The multi-faceted retention support system includes the following steps: S001. Chitosan is pre-dissolved in an acetic acid solution with a pH value in the range of 4.5; S002. Dissolve cationic starch in water at 45°C beforehand; S003. Pre-dissolve nanocellulose in deionized water. S100. Chitosan, cationic starch, and nanocellulose are mixed in a mass ratio of 0.1:0.1:1 and magnetically stirred for 20 minutes to obtain a composite retention aid with a pH of 7 and a solid content of 0.8 wt%. S201. Dilute the pulp raw material to 3 wt% and heat it to 30°C to obtain pulp slurry; S200: The composite retention aid, nano TiO2 and polyvinyl alcohol are added to the pulp at a mass ratio of 1:8. The pulp is then subjected to ultrasonic treatment at 20kHz for 5 minutes and high-speed shearing treatment at 2000rpm for 45 seconds to obtain the composite pulp. S300: The composite pulp is wet-end retained and formed at 38°C with a web forming process at 220m / min to obtain a lightweight paper-based material.

[0031] Example 2

[0032] This embodiment provides a multi-component retention aid system for lightweight paper-based materials, including chitosan, cationic starch, nanocellulose, polyvinyl alcohol, and nano-TiO2; The multi-faceted retention support system includes the following steps: S001. Chitosan is pre-dissolved in an acetic acid solution with a pH value in the range of 4; S002. Dissolve the cationic starch in water at 40°C beforehand; S003. Pre-dissolve nanocellulose in deionized water. S100. Chitosan, cationic starch, and nanocellulose are mixed in a mass ratio of 1:1:1 and magnetically stirred for 40 minutes to obtain a composite retention aid with a pH of 8 and a solid content of 1.2 wt%. S201. Dilute the pulp raw material to 4 wt% and heat it to 50°C to obtain pulp slurry; S200: The composite retention aid, nano TiO2 and polyvinyl alcohol are added to the pulp at a mass ratio of 1:10. The pulp is then subjected to ultrasonic treatment at 40kHz for 15min and high-speed shearing treatment at 4000rpm for 75s to obtain the composite pulp. S300: The composite pulp is wet-end retained and formed at 40°C with a web forming process at 250m / min to obtain a lightweight paper-based material.

[0033] Example 3

[0034] This embodiment provides a multi-component retention aid system for lightweight paper-based materials, including chitosan, cationic starch, nanocellulose, polyvinyl alcohol, and nano-TiO2; The diversified retention system includes the following steps: S001. Chitosan is pre-dissolved in an acetic acid solution with a pH value in the range of 5; S002. Dissolve the cationic starch in water at 50°C beforehand; S003. Pre-dissolve nanocellulose in deionized water. S100. Chitosan, cationic starch, and nanocellulose are mixed in a mass ratio of 0.5:0.5:1 and magnetically stirred for 30 minutes to obtain a composite retention aid with a pH of 7.5 and a solid content of 1 wt%. S201. Dilute the pulp raw material to 3.5 wt% and heat it to 40°C to obtain pulp slurry; S200: The composite retention aid, nano TiO2 and polyvinyl alcohol are added to the pulp at a mass ratio of 1:10. The pulp is then subjected to ultrasonic treatment at 30kHz for 10min and high-speed shearing treatment at 3000rpm for 60s to obtain the composite pulp. S300: The composite pulp is wet-end retained and formed at 35°C with a web forming process at 200m / min to obtain a lightweight paper-based material.

[0035] Comparative Example 1 This comparative example provides a lightweight paper-based material multi-component retention aid system that was purchased externally.

[0036] Performance testing The core and shell thicknesses of the composite slurries from Examples 1-3 were measured, and the results are shown in Table 1. The core-shell structure of the composite slurry from Example 1 is shown below. Figure 1 , Figure 2 As shown: Table 1 The tensile strength, tear resistance, flexural endurance, and filler retention rate of Examples 1-3 and Comparative Example 1 were tested. The test results are shown in Table 2, and the test methods are as follows: Tensile strength: According to ISO 1924-2 standard, the specimen is stretched at a constant rate until fracture using a universal testing machine, and the maximum load is recorded; Tear strength: The force required to tear a single-cut specimen was measured using an ISO 1974 Elmendorf tear tester. Flexural endurance: According to ISO 5626 standard, the number of folds before the specimen breaks was recorded using the MIT flexural endurance tester under standard load; Filler retention rate: The proportion of residual ash to the original filler mass is calculated after burning the sample according to the ISO 2144 ash content test.

[0037] Table 2 As shown in Table 2, Example 2 has the highest tensile strength due to its high solid content and strong shear treatment, resulting in a tight bond between the fiber and TiO2. The uniform shell structure of Examples 1-3 enhances the interfacial toughness, and the tear resistance is significantly better than that of Comparative Example 1. The web forming process temperature of Example 2 is higher, resulting in more complete fiber cross-linking and the best folding endurance. The core-shell structure of Examples 1-3 effectively fixes the filler, and the retention rate is much higher than that of Comparative Example 1.

[0038] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A multi-component retention system for lightweight paper-based materials, characterized by The multi-component retention aid system includes chitosan, cationic starch, nanocellulose, polyvinyl alcohol, and nano-TiO2; The multi-faceted retention assistance system includes the following steps: S100. Chitosan, cationic starch and nanocellulose are mixed and magnetically stirred to obtain a composite retention aid. S200: The composite retention aid, polyvinyl alcohol, and nano-TiO2 are added to the pulp slurry, and the slurry is subjected to ultrasonic treatment and high-speed shearing treatment to obtain the composite slurry. S300. The composite slurry is subjected to wet end retention and web forming processes to obtain a lightweight paper-based material.

2. The multi-functional retention system according to claim 1, characterized in that, The composite slurry in step S200 forms the following core-shell structure: The core layer comprises a core carrier consisting of pulp fibers; The shell layer comprises nano-TiO2 particles, at least partially encapsulating the core layer.

3. The multi-functional retention system according to claim 2, characterized in that, The composite slurry further includes an interface layer, which is disposed between the core layer and the shell layer. The interface layer includes the neutralization and cross-linking of cationic charges in the chitosan and cationic starch with the fiber and TiO2 surface. The interface layer tightly binds the core layer and the shell layer.

4. The multi-functional retention system according to claim 2, characterized in that, In step S200, the thickness of the core layer is 1-5 μm; the thickness of the shell layer is 50-200 nm.

5. The multi-functional retention system according to claim 1, characterized in that, In step S100: The mass ratio of chitosan, cationic starch, and nanocellulose in the composite retention aid is (0.1-1):(0.1-1):1; The magnetic stirring process takes 20-40 minutes.

6. The multi-functional retention system according to claim 1, characterized in that, In step S100, the pH value of the composite retention aid is 7-8 and the solid content is 0.8-1.2 wt%.

7. The multi-functional retention system according to claim 1, characterized in that, The steps preceding step S100 also include: S001. The chitosan is pre-dissolved in an acetic acid solution with a pH value in the range of 4-5; S002, Dissolve the cationic starch in water at 40-50℃ beforehand; S003. Dissolve the nanocellulose in deionized water beforehand.

8. The multi-functional retention system according to claim 1, characterized in that, The pulp stock includes pretreatment: S201. Dilute the pulp raw material to 3-4 wt% and heat it to 30-50°C to obtain the pulp slurry.

9. The multi-functional retention system according to claim 1, characterized in that, In step S200: The mass ratio of the composite retention aid to the nano-TiO2 is 1:(8-12). The ultrasonic treatment frequency is 20-40kHz, and the time is 5-15min; The high-speed shearing process operates at a speed of 2000-4000 rpm for 45-75 seconds.

10. The multi-functional retention system according to claim 1, characterized in that, In step S300, the screen speed of the screen forming process is 200-250 m / min, and the screen temperature is 35-40℃.

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