Processing method of high-strength bamboo fiber non-woven fabric

Abstract

According to the processing method of the high-strength bamboo fiber non-woven fabric, the synergistic effect of physical hot pressing and calcium-tannic acid chemical coordination cross-linking is combined, and glue-free green enhancement of the natural bamboo fiber non-woven fabric is achieved through the five steps of fiber calcium-loaded plasticizing treatment, fiber web physical forming, hot-pressing melting, cross-linking preparation and hot-pressing curing cross-linking in sequence. The invention overcomes the defects in the prior art, and provides the bamboo fiber non-woven fabric which is high in strength and high in wet strength and can be completely biodegraded and the green preparation method of the bamboo fiber non-woven fabric. The non-woven fabric can be directly applied to the fields of environment-friendly filtering materials, medical hygienic products, degradable packaging materials and the like, can also be used for preparing high-performance glue-free bamboo fiber boards, pipes and other composite materials through multi-layer hot pressing, and has wide application prospects in the fields of environment-friendly manufacturing and low-carbon environment protection.

Description

Technical Field

[0001] This invention relates to the technical field of processing natural fiber application products, specifically to a method for processing high-strength natural bamboo fiber nonwoven fabric with adhesive-free green reinforcement, which is particularly suitable for preparing bamboo fiber nonwoven fabric with high dry / wet strength and complete biodegradability, and its application in high-end fields such as environmental filtration, medical hygiene, and composite materials. Background Technology

[0002] Natural bamboo fiber (also known as bamboo virgin fiber), as a renewable and biodegradable natural polymer material, possesses excellent properties such as low density, high specific strength, antibacterial properties, and breathability, making it an ideal choice to replace traditional synthetic fibers and achieve green material upgrades. However, bamboo virgin fiber itself has high crystallinity and high molecular chain rigidity, making it prone to fiber breakage and damage during textile processing such as opening and carding, resulting in poor uniformity of fiber web formation. At the same time, bamboo fiber prepared by purely physical methods relies solely on hydrogen bonds between fibers, resulting in extremely low mechanical strength, especially wet strength, which is difficult to meet the application requirements of high-performance materials.

[0003] In existing technologies, methods to improve the strength of natural fiber nonwoven fabrics mainly fall into two categories: one is to add synthetic polymer adhesives (such as polyvinyl alcohol and acrylic emulsions), but these adhesives have poor biodegradability, easily cause environmental pollution, and reduce the product's air permeability and biocompatibility; the other is to use aldehyde crosslinking agents (such as melamine-formaldehyde resin and urea-formaldehyde resin) for chemical crosslinking reinforcement. Although this can significantly improve strength, the toxic substances such as formaldehyde remaining in the crosslinking agent can harm human health and does not conform to the trend of green and environmentally friendly development.

[0004] Therefore, developing a formaldehyde-free, synthetic adhesive-free, fully green processing technology that can significantly improve the dry / wet strength of bamboo fiber nonwoven fabrics is key to breaking through the bottleneck of high-end applications of bamboo fiber materials and is of great significance to promoting the sustainable development of the natural plant fiber industry. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a green processing method for high-strength bamboo fiber nonwoven fabrics, solving the technical problems of low strength, poor wet performance, and environmentally unfriendly processing of existing natural bamboo fiber nonwoven fabrics. This invention utilizes the coordination and cross-linking effect of natural polyphenols and metal ions to construct a stable three-dimensional network within the fiber, thereby achieving formaldehyde-free green reinforcement of bamboo fiber nonwoven fabrics and expanding the application scope of bamboo fiber materials in high-end green manufacturing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for processing high-strength bamboo fiber nonwoven fabric includes the following steps: Step 1: Fiber calcium-loaded plasticizing treatment Bamboo fibers with an initial pH of 6.0-8.0 and a standard moisture regain of 10.0-11.0% are immersed in a 5-15% (w / w) calcium chloride dihydrate aqueous solution and plasticized at 50-70℃ for 20-40 minutes. Calcium ions can penetrate into the amorphous regions of the bamboo fibers, disrupting some intermolecular hydrogen bonds, causing the fibers to swell moderately, reducing fiber rigidity and improving fiber flexibility. Simultaneously, calcium ions adsorb onto the active groups (hydroxyl groups) on the fiber surface and interior, providing reaction sites for subsequent chemical cross-linking. After treatment, the fibers are directly pressed to remove excess water without washing, and then dried at 80-120℃ to the standard moisture regain to obtain plasticized bamboo fibers.

[0007] Step 2: Physical forming of the fiber web According to the preset product weight requirements (50-200g / m²), the above-mentioned plasticized bamboo fibers are opened and combed, and then a uniform fiber web is prepared by air-jet web formation, carding web formation, or wet web formation. The flexibility of calcium-loaded plasticized bamboo fibers is significantly improved, and they are not easy to break during the opening and combing process, which can effectively ensure the uniformity and integrity of the fiber web.

[0008] Step 3, Hot pressing and fusion The fiber web (fiber crossing points) undergoes hot-pressing and fusion treatment with the following process parameters: linear pressure 50-120 N•mm⁻¹, temperature 125-140 ℃, and hot-pressing time 0.5-2 minutes. Under high temperature and high pressure conditions, the amorphous areas on the fiber surface soften, and the fiber crossing points form physical fusion (welding), thus initially shaping the fiber web into a nonwoven fabric with a certain strength, providing a stable structural basis for subsequent chemical crosslinking.

[0009] Step 4, Crosslinking Preparation Prepare a tannic acid aqueous solution with a mass concentration of 2-8% and a pH value of 4.5-6.0. Treat the above-mentioned nonwoven fabric to saturation by impregnation or spraying, maintaining this state for 1 minute to ensure sufficient contact between the tannic acid and calcium ions on the fiber surface. Then, drain off excess solution and dry at 80-120℃ to the specified moisture regain. Tannic acid, as a natural polyphenol, contains a large number of phenolic hydroxyl groups in its molecule, which can undergo coordination reactions with calcium ions.

[0010] Step 5: Hot pressing for curing and crosslinking The tannic acid-treated fabric undergoes a secondary hot-press curing process with the following parameters: linear pressure 10-30 N•mm⁻¹, temperature 100-120℃, and hot-pressing time 10-30 seconds. Under hot-pressing conditions, tannic acid molecules undergo coordination cross-linking reactions with calcium ions on the fiber surface and inside, constructing a stable three-dimensional coordination network structure within the fiber and at the fiber interface. This network acts like a "molecular bridge," tightly connecting adjacent fibers and significantly improving the dry / wet strength of the nonwoven fabric.

[0011] Preferably, in step 1, the mass concentration of the calcium chloride dihydrate aqueous solution can be adjusted according to the product performance requirements: low concentration (5-8%) is suitable for preparing nonwoven fabrics with a soft feel, and high concentration (10-15%) is suitable for preparing nonwoven fabrics with high hardness and excellent strength.

[0012] Preferably, in step 4, the pH value of the tannic acid solution is adjusted with citric acid to avoid introducing other impurity ions that may affect the crosslinking effect.

[0013] The present invention also discloses a high-strength bamboo fiber nonwoven fabric prepared by the above method. Taking a product with a weight of 100g / m² as an example, its dry longitudinal tensile strength is ≥50N / 5cm, its wet longitudinal tensile strength is ≥40N / 5cm, its wet strength retention rate is ≥80%, and the product is completely biodegradable. At the same time, due to the presence of tannic acid, it has natural antibacterial and antioxidant properties.

[0014] This invention further discloses the applications of the above-mentioned high-strength bamboo fiber nonwoven fabric: it can be directly used in environmentally friendly filter materials (such as sewage treatment filter cloth, air filter cotton), medical and hygiene products (such as biodegradable medical dressings, sanitary napkin surface layer), biodegradable packaging materials and other fields; it can also be used to prepare high-performance composite materials such as glue-free bamboo fiberboard and pipes through multi-layer hot pressing, and applied in fields such as building decoration, automotive interiors, new energy, and low-altitude economy.

[0015] The present invention has the following advantages: 1. Process Innovation: A step-by-step process of "physical hot pressing followed by chemical coordination crosslinking" was creatively proposed. First, only the fibers undergo "calcium-loaded plasticization" treatment, which greatly improves the rigidity of bamboo fibers, enabling them to exhibit excellent flexibility and processability during the opening, carding, and web-forming stages, solving the industry problem of poor spinnability of pre-crosslinked fibers. Second, overall crosslinking is performed on the already formed, structurally stable fabric, ensuring the uniformity and efficiency of chemical reinforcement.

[0016] 2. Enhanced Performance: Utilizing the synergistic effect of "calcium ion plasticization" and "calcium-tannic acid coordination crosslinking," calcium ions act as plasticizers in the early stages and crosslinking nodes in the later stages. The resulting coordination network that penetrates the fibers and fiber interfaces is like constructing a "reinforced concrete" structure for the nonwoven fabric, achieving fundamental enhancement at the molecular scale, especially significantly improving wet strength.

[0017] 3. Green and environmentally friendly: No toxic cross-linking agents such as formaldehyde and phenol are used throughout the entire process. The main chemicals are natural polyphenols (tannic acid) and low-toxicity inorganic salts (calcium chloride dihydrate). Wastewater treatment is simple, and the final product is completely biodegradable, achieving greening of the entire chain from process to product.

[0018] 4. Superior performance: The resulting nonwoven fabric not only has high dry / wet strength and dimensional stability, but also possesses long-lasting natural antibacterial and antioxidant properties due to the presence of tannins, making it suitable for high-end fields with high requirements for hygiene and environmental protection.

[0019] The present invention discloses a processing method for high-strength bamboo fiber nonwoven fabric, with clear process steps and controllable parameters, which can be adapted to existing nonwoven fabric production lines for industrial production; the resulting product has high dry / wet strength, natural antibacterial properties and full biodegradability, and has a wide range of applications, with significant economic value and social benefits.

[0020] The processing method described in this invention can be applied not only to natural bamboo fiber nonwoven fabrics, but also to the preparation of other natural plant fiber nonwoven fabrics. Detailed Implementation

[0021] Example 1: Processing high-hardness, high-strength bamboo fiber nonwoven fabric.

[0022] Step 1, Calcium-loaded plasticizing treatment of fibers: Take bamboo raw fibers with an initial pH value of 7.0 and a standard moisture regain of 10.5%, immerse them in a 15% (w / w) calcium chloride dihydrate aqueous solution at 60℃, and plasticize for 30 minutes; without washing, directly press and dehydrate, and then dry at 100℃ to the standard moisture regain to obtain plasticized bamboo fibers.

[0023] Step 2, Physical forming of fiber web: After opening and combing, plasticized bamboo fiber is combed into a uniform fiber web with a weight of 100g / m².

[0024] Step 3, Hot pressing and melting: The fiber web is reinforced by hot pressing with a linear pressure of 100 N•mm⁻¹, a temperature of 130℃, and a time of 1.5 minutes to obtain the nonwoven fabric.

[0025] Step 4, Crosslinking preparation: Prepare an aqueous solution of tannic acid with a mass concentration of 8% and a pH value of 5.0. Immerse the fabric in the solution until saturated, keep it for 1 minute, drain the water, and dry it at 100°C until the specified moisture regain.

[0026] Step 5, Hot-press curing and cross-linking: The fabric is hot-pressed and cured at a linear pressure of 10 N•mm⁻¹, a temperature of 110℃, and a time of 10 seconds to obtain a high-strength bamboo fiber nonwoven fabric.

[0027] Example 2: Processing soft, high-strength bamboo fiber nonwoven fabric.

[0028] Step 1, Calcium-loaded plasticizing treatment of fibers: Take bamboo raw fibers with an initial pH value of 7.0 and a standard moisture regain of 10.5%, immerse them in a 5% (w / w) calcium chloride dihydrate aqueous solution at 60℃, and plasticize for 40 minutes; without washing, directly press and dehydrate, and then dry at 90℃ to the standard moisture regain to obtain plasticized bamboo fibers.

[0029] Step 2, Physical forming of fiber web: After the plasticized bamboo fiber is opened and combed, a uniform fiber web with a basis weight of 100g / m² is prepared by air-flow forming.

[0030] Step 3, Hot pressing and melting: The fiber web is reinforced by hot pressing with a linear pressure of 120 N•mm⁻¹, a temperature of 140℃, and a time of 1.5 minutes to obtain the nonwoven fabric.

[0031] Step 4, Crosslinking preparation: Prepare a tannic acid aqueous solution with a mass concentration of 2% and a pH value of 5.0. Spray the fabric with the solution until saturated, keep it for 1 minute, drain the water, and dry it at 90°C until the specified moisture regain.

[0032] Step 5, Hot-press curing and cross-linking: The fabric is hot-pressed and cured at a linear pressure of 30 N•mm⁻¹, a temperature of 120℃, and a time of 30 seconds to obtain a high-strength bamboo fiber nonwoven fabric.

[0033] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A processing method for high-strength bamboo fiber nonwoven fabric, characterized in that, The steps are as follows: Step 1, Fiber calcium-loaded plasticizing treatment: The initial pH value is 6.0-8.0, and the fiber is at a standard moisture regain. The bamboo fiber is impregnated in an aqueous solution containing calcium ions to allow the calcium ions to penetrate deep into the fiber. Then, it is directly pressed and dehydrated without washing, and dried to the specified moisture regain. Step 2, Physical forming of fiber web: The plasticized fibers obtained in Step 1 are formed into a fiber web according to the product weight requirements; Step 3, Hot pressing and fusion: Hot pressing and fusion of the fiber web obtained in Step 2: linear pressure 50-120 N mm⁻¹, temperature 125-140 ℃, time 0.5-2 minutes; Step 4, Crosslinking preparation: After hot pressing and melting, the fiber web obtained in step 3 is impregnated or sprayed with tannic acid solution until saturated, kept for 1 minute, then drained and dried to the specified moisture regain. Step 5, Hot-press curing and crosslinking: The non-woven fabric obtained in step 4 after being treated with tannic acid and dried is hot-pressed and cured to obtain high-strength bamboo fiber non-woven fabric, wherein the linear pressure is 10-30 N·mm⁻¹, the temperature is 100-120℃, and the time is 10-30 seconds.

2. The method according to claim 1, characterized in that, In step 1, the calcium ion-containing aqueous solution is a calcium chloride dihydrate aqueous solution with a mass concentration of 5-15%. The plasticizing treatment temperature is 50-70℃, and the treatment time is 20-40 minutes; the drying temperature is 80-120℃.

3. The method according to claim 1, characterized in that, In step 2, the fiber web is prepared by air-flow web forming, carding web forming, or wet web forming, and the fiber web basis weight is 50-200 g / m².

4. The method according to claim 1, characterized in that, In step 4, the tannic acid solution has a mass concentration of 2-8% and a pH value of 4.5-6.0; the drying temperature is 80-120℃.

5. The method according to any one of claims 1-4, characterized in that, The stated standard moisture regain is the standard moisture regain of bamboo fiber, with a value of 10.0-12.0%.