A bio-based high-elasticity knitted fabric and a preparation process thereof

Abstract

The present application relates to the technical field of textile fabric, especially to a bio-based high-elasticity knitted fabric, comprising a knitted main layer; the knitted main layer is integrally knitted by full bio-based composite elastic yarn through a circular machine; the full bio-based composite elastic yarn comprises core yarn and covering yarn, and the mass ratio of the core yarn to the covering yarn is 3:7-6:4; the core yarn is bio-based PTT elastic filament, and the covering yarn is modified bio-based cellulose fiber treated by grafting a lignin-castor oil crosslinking modifier; the knitted main layer has a transverse breaking elongation of no less than 280%, a longitudinal breaking elongation of no less than 110%, and a resilience retention rate of no less than 85% after 50 times of standard washing. The present application solves the technical problem of poor degradation, durability and resilience of the existing fabric. A preparation process of the bio-based high-elasticity knitted fabric is provided.

Description

Technical Field

[0001] This invention relates to the field of textile fabric technology, and in particular to a bio-based high-elastic knitted fabric and its preparation process, which is suitable for yoga wear, sportswear, maternity and baby underwear, biodegradable elastic medical dressings and other close-fitting elastic fabric applications. Background Technology

[0002] Currently, biodegradable and bio-based green textile materials have become the mainstream of industry research and development. Traditional high-elastic knitted fabrics generally use petroleum-based spandex and high-elastic polyester as the core elastic components, which have three inherent defects: First, the raw materials rely on non-renewable fossil resources and cannot be completely degraded after disposal, resulting in a large amount of microplastics entering the soil and water, causing long-term environmental pollution; Second, petroleum-based elastic fibers have poor water resistance, and their elasticity rapidly decreases after repeated washing, making the fabric prone to bulging and sag after stretching; Third, petroleum-based fibers have poor biocompatibility, making them prone to causing sweating when worn close to the skin and irritating sensitive skin and infants' skin.

[0003] Chinese Patent Publication No. CN202510795008.X discloses an environmentally friendly knitted elastic fabric with good softness and deformation resistance, and its preparation method. This relates to the field of fiber textile fabric technology. The fabric comprises: a core-spun composite yarn as raw material, wherein the composite yarn consists of a bio-based block copolymer spandex as the core yarn and a blended yarn of Lyocell fiber and bio-based PTT fiber as the covering layer, with a covering rate of 60%-70%; the composite yarn is woven into a fabric using a double-sided plain knitting structure, wherein the knitting structure is a double-layer structure with different stitch pitches for the surface and inner layers, the surface stitch pitch being set at 4.0 stitches / cm and the inner stitch pitch at 3.2 stitches / cm; the knitted fabric is then subjected to enzymatic softening treatment, atmospheric pressure plasma activation treatment, green cross-linking treatment, and natural plant oil finishing treatment.

[0004] Although it has achieved partial bio-based properties, it still incorporates petroleum-based polyurethane elastic additives to enhance elasticity and has not completely broken away from petrochemical elastic components. It only undergoes cross-linking treatment in the finishing process, and the non-woven yarn is modified beforehand, resulting in insufficient dry and wet rebound stability. It adopts a common plain knit structure, and the elastic yarn is prone to yarn slippage during washing and stretching, resulting in a large fabric size change rate and poor durable rebound performance. Summary of the Invention

[0005] Therefore, to address the aforementioned problems, this invention proposes a bio-based high-elastic knitted fabric, which solves the technical problems of poor degradability, durability, and resilience of existing fabrics. A preparation process for this bio-based high-elastic knitted fabric is also proposed.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a bio-based high-elastic knitted fabric, comprising a knitted main body layer; the knitted main body layer is formed by integral knitting of fully bio-based composite elastic yarn on a circular knitting machine; The fully bio-based composite elastic yarn comprises a core yarn and a covering yarn, with a core yarn to covering yarn mass ratio of 3:7 to 6:4; the core yarn is a bio-based PTT elastic filament, and the covering yarn is a modified bio-based cellulose fiber grafted with a lignin-castor oil crosslinking modifier. The knitted main body layer has a transverse breaking elongation ≥280%, a longitudinal breaking elongation ≥110%, and a resilience retention rate ≥85% after 50 standard washes.

[0007] Furthermore, the bio-based PTT elastic filament has a bio-based carbon content of ≥92%, a single filament fineness of 20-40D, and a breaking elongation of 350%-450%; the regenerated bio-based cellulose staple fiber is a binary blend of lyocell and soybean protein viscose, with a fiber fineness of 1.0-1.5D and a fiber length of 38-51mm.

[0008] Furthermore, the lignin-castor oil crosslinking modifier is composed of the following bio-based raw materials in parts by weight: 12-20 parts modified lignin, 25-35 parts epoxidized castor oil polyol, 5-10 parts chitosan, and 2-5 parts plant-based dispersant; the modifier does not contain petroleum-based monomers or petroleum-based silicone oil additives.

[0009] Furthermore, the knitted main body layer adopts a double weft loop structure with alternating long and short needles, and the all-bio-based elastic yarn used as the weft is locked inside the ground structure loop; Among them, the ground weave loop density is 45-75 loops / cm², the weaving tension of the all-bio-based elastic yarn is 8-15cN, the loop misalignment spacing is 0.1-0.3mm, and the fabric washing dimensional change rate is ≤2.5%.

[0010] Furthermore, the bio-based carbon content in the knitted main body layer is ≥85%, and the biodegradability rate is greater than 95% after 180 days under industrial composting conditions.

[0011] Furthermore, the knitted main layer exhibits a residual deformation of ≤6% in a wet state and an elasticity attenuation of ≤12% after 1000 cycles of tensile fatigue testing.

[0012] A process for preparing a bio-based high-elastic knitted fabric includes the following steps: S1. Pre-modification of bio-based cellulose fibers: Regenerated bio-based cellulose short fibers are added to a lignin-castor oil bio-modified emulsion, ultrasonically impregnated for 15-25 minutes, and dried at a low temperature of 70-85℃ to obtain modified bio-based cellulose fibers. S2. Spinning of fully bio-based composite elastic yarn: Using bio-based PTT elastic filament as core yarn and modified bio-based cellulose fiber as cover yarn, low-tension airflow covering spinning is adopted, and the covering twist is controlled at 360-420 twists / m to obtain fully bio-based composite elastic yarn. S3. Low-tension double-weft knitting: A double-sided circular knitting machine is used for segmented tension yarn feeding. The ground yarn feeding tension is 12-18cN, and the weft elastic yarn feeding tension is 8-15cN. Long and short needles are alternately arranged to weave and obtain the knitted main fabric. S4. Low-temperature pretreatment with biological enzymes: 45-60℃ biological amylase is used to remove the weaving sizing agent, followed by rinsing with clean water and low-temperature pre-drying. S5. Bio-based low-temperature cross-linking and setting: Prepare a bio-based cross-linking and setting solution, impregnate the fabric with the setting solution, and then perform low-temperature wet setting at 85-105℃ for 30-60 seconds. Low-temperature drying completes the fiber cross-linking and elasticity locking. S6. Bio-based green finishing: The basic bio-based high-elastic knitted fabric is obtained by padding with palm oil-based softening solution and drying at 75-90℃.

[0013] Furthermore, the biomodified emulsion in step S1 has a solid content of 15% to 25%, an impregnation bath ratio of 1:10 to 1:15, and an ultrasonic power of 200 to 350W.

[0014] Furthermore, in step S5, the solid content of the bio-based crosslinking shaping liquid is 8%–15%, the padding residue is 65%–80%, and the oven heating rate is ≤3℃ / min.

[0015] Furthermore, in step S3, the surface of the knitting needles is coated with a plant-based lubricating coating, the knitting speed is 22-28 m / min, and the yarn breakage rate is ≤0.8 times / km.

[0016] By adopting the aforementioned technical solution, the beneficial effects of the present invention are: 1. The core yarn uses bio-based PTT elastic filaments to provide basic high elongation capacity. After the covering yarn is modified by lignin-castor oil crosslinking, the wet rigidity of the cellulose fiber is reduced and the rebound hysteresis is improved. The two are matched with each other in a mass ratio of 3:7 to 6:4, so that when the yarn is stretched, the core yarn bears the main deformation and the covering yarn effectively transmits stress and restricts permanent slippage.

[0017] As a result, the fabric has a transverse breaking elongation of ≥280% and a longitudinal elongation of ≥110%, ensuring that the fabric can still closely conform to the human body after strenuous exercise or repeated stretching; after 50 standard washes, the elasticity retention rate is ≥85%, proving that the bio-based cross-linking network effectively resists the damage of hydrogen bonds between fibers by water molecules, solving the industry pain point that traditional bio-based fabrics are prone to loosening after washing, and the entire process does not contain petroleum-based components, which meets the purpose of carbon neutrality and biodegradability.

[0018] 2. The limited bio-based PTT filament and lyocell / soybean protein viscose binary blended short fiber can precisely match the cohesion strength and soft hand feel of the covered yarn, while ensuring high elastic recovery and increasing the coefficient of friction between fibers, making the yarn structure denser and more stable in repeated stretching performance.

[0019] 3. The modifier is a compound of modified lignin, epoxy castor oil polyol, chitosan and plant-based dispersant. It does not contain any petroleum-based monomers or silicone oil. It can form a strong covalent crosslink with cellulose through the polyphenolic hydroxyl groups of lignin, and can also use the flexible segments of castor oil to give the fiber an internal lubrication effect. While improving the resilience of elastic yarn, it ensures that the modifier itself is completely biodegradable under composting conditions, reducing microplastic pollution caused by traditional epoxy resins or organosilicon additives.

[0020] 4. The fabric adopts an alternating long and short needle double-weft loop structure, locking the elastic yarn inside the ground fabric. Combined with a ground fabric density of 45-75 yarns / cm² and a low weft tension of 8-15cN, the elastic deformation is distributed to multiple loop units rather than concentrated at the yarn nodes. The misalignment spacing of 0.1-0.3mm effectively releases internal stress, resulting in a final fabric dimensional change rate of ≤2.5% after washing, which is significantly better than the shrinkage rate of conventional elastic knitted fabrics, ensuring the dimensional accuracy of the finished garment.

[0021] 5. The overall bio-based carbon content of the fabric is ≥85% and the degradation rate of industrial composting in 180 days is >95%, ensuring that it can return to the natural carbon cycle without special recycling treatment after disposal, avoiding the persistent environmental pollution caused by the incineration or landfill of traditional spandex elastic fabrics.

[0022] 6. The residual deformation in wet rebound is ≤6% and the elasticity decreases by ≤12% after 1000 cycles of stretching, which proves that the molecular chain slippage of the cross-linked modified fiber is restricted in a wet state. This gives the fabric the unique advantage of maintaining its tightness and elasticity after sweating or washing. It is especially suitable for high-humidity usage scenarios such as sports underwear and yoga wear, and extends the product's service life.

[0023] 7. This preparation process integrates six steps: fiber pre-modification, low-tension coating spinning, double-weft weaving, enzymatic low-temperature pretreatment, bio-based low-temperature cross-linking and setting, and palm oil-based softening finishing. Each step avoids high-temperature strong alkalis or petroleum-based chemicals. Ultrasonic impregnation allows the modified emulsion to penetrate deep into the amorphous region of cellulose; low-tension airflow coating prevents excessive stretching of the PTT core yarn, thus avoiding loss of initial elastic modulus; segmented tension yarn feeding on a double-sided circular knitting machine ensures tension matching between the weft elastic yarn and the ground fabric, reducing coil skew; bio-amylase pretreatment at 45–60℃ gently removes sizing agents without damaging the surface of the bio-based fibers; low-temperature wet setting at 85–105℃ and subsequent low-temperature drying replace traditional heat setting above 190℃, significantly reducing energy consumption and avoiding PTT thermal degradation; palm oil-based softening finishing replaces silicone softeners, ensuring skin-friendliness and not inhibiting degradation.

[0024] 8. By limiting the solid content of the modified emulsion to 15%–25%, the liquor ratio to 1:10–1:15, and the ultrasonic power to 200–350W, the modifier can be uniformly penetrated and efficiently grafted without damaging the fiber morphology, avoiding excessive surface deposition that would cause the surface to harden, while ensuring reaction efficiency and industrial operability.

[0025] 9. With a cross-linking setting liquid solid content of 8% to 15%, a roll-off rate of 65% to 80%, and a heating rate of ≤3℃ / min, the bio-based cross-linking agent can form a continuous film on the fiber surface and slowly diffuse into the interior, avoiding premature surface curing caused by rapid heating and hindering moisture escape, thereby obtaining a uniform cross-linking density and achieving the best balance between fabric elasticity retention and dimensional stability.

[0026] 10. The knitting needles are coated with a plant-based lubricating coating, the machine speed is 22-28m / min and the yarn breakage rate is ≤0.8 times / km. This effectively solves the problem of fuzz and yarn breakage caused by the large surface friction coefficient of bio-based short fiber covered yarn, reduces the frequency of weaving downtime, improves the uniformity of fabric quality, and avoids the mineral oil lubricant from contaminating the yarn and affecting the effect of subsequent bio-enzyme pretreatment. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited to the following embodiments. Example 1

[0028] This embodiment provides a bio-based high-elastic knitted fabric, which includes a knitted main layer. This knitted main layer is formed by integrally knitting a fully bio-based composite elastic yarn on a circular knitting machine. The fully bio-based composite elastic yarn comprises a core yarn and a cover yarn, with a core yarn to cover yarn mass ratio of 5:5. The core yarn is selected from bio-based PTT elastic filaments, with a bio-based carbon content of 95%, a single filament fineness of 30D, and a breaking elongation of 400%. The cover yarn is a modified bio-based cellulose fiber grafted with a lignin-castor oil crosslinking modifier. This cellulose fiber is obtained by binary blending lyocell and soybean protein viscose at a mass ratio of 60:40, with a fiber fineness of 1.2D and a fiber length of 44mm.

[0029] The lignin-castor oil crosslinking modifier is prepared as follows: Weigh 16 parts of modified lignin, 30 parts of epoxidized castor oil polyol, 8 parts of chitosan, and 3 parts of plant-based dispersant by weight, and mix them evenly at room temperature to obtain a bio-modified emulsion with a solid content of 20%. This modifier does not contain any petroleum-based monomers or petroleum-based silicone oil additives.

[0030] The knitted main layer employs an alternating long and short needle double-weft loop structure, with the fully bio-based elastic yarn used as the weft thread locked inside the ground weave loops. The ground weave loop density is set at 60 loops / cm², the weaving tension of the fully bio-based elastic yarn is 12cN, and the loop misalignment distance is 0.2mm. Testing showed that the fabric obtained in this embodiment exhibited a transverse breaking elongation of 295%, a longitudinal breaking elongation of 118%, a rebound retention rate of 87% after 50 standard washes, a dimensional change rate of 2.1% after washing, an overall bio-based carbon content of 88%, a biodegradation rate of 96.5% after 180 days under industrial composting conditions, a wet rebound residual deformation of 5.2%, and an elasticity decay of 10.5% after 1000 cycles of tensile fatigue testing. Example 2

[0031] This embodiment provides a bio-based high-elastic knitted fabric, which differs from Embodiment 1 in that the core yarn to cover yarn mass ratio is 3:7, the core yarn bio-based PTT elastic filament has a single filament fineness of 20D and a breaking elongation of 450%, the cover yarn has a fiber fineness of 1.0D and a fiber length of 38mm, and the blending ratio of lyocell to soybean protein viscose is 70:30. The lignin-castor oil crosslinking modifier consists of: 12 parts modified lignin, 25 parts epoxidized castor oil polyol, 5 parts chitosan, and 2 parts plant-based dispersant. The ground weave loop density is 45 loops / cm², the weaving tension is 8cN, and the loop misalignment spacing is 0.1mm. Tests showed that the fabric obtained in this embodiment had a transverse breaking elongation of 282%, a longitudinal breaking elongation of 112%, a rebound retention rate of 85% after 50 standard washes, a washing dimensional change rate of 2.4%, a rebound residual deformation of 5.8% in the wet state, and an elasticity decay of 11.8% after 1000 cycles of tensile fatigue testing. Example 3

[0032] This embodiment provides a bio-based high-elastic knitted fabric, which differs from Embodiment 1 in that the core yarn to cover yarn mass ratio is 6:4, the core yarn bio-based PTT elastic filament has a single filament fineness of 40D and a breaking elongation of 350%, the cover yarn has a fiber fineness of 1.5D and a fiber length of 51mm, and the blending ratio of lyocell and soybean protein viscose is 50:50. The lignin-castor oil crosslinking modifier consists of: 20 parts modified lignin, 35 parts epoxidized castor oil polyol, 10 parts chitosan, and 5 parts plant-based dispersant. The ground weave loop density is 75 loops / cm², the weaving tension is 15cN, and the loop misalignment spacing is 0.3mm. Tests showed that the fabric obtained in this embodiment had a transverse breaking elongation of 310%, a longitudinal breaking elongation of 125%, a rebound retention rate of 89% after 50 standard washes, a washing dimensional change rate of 1.8%, a rebound residual deformation of 4.8% in the wet state, and an elasticity decay of 9.8% after 1000 cycles of tensile fatigue testing. Example 4

[0033] This embodiment provides a process for preparing a bio-based high-elastic knitted fabric, used to prepare the fabrics described in Embodiments 1 to 3 above. The specific steps are as follows: S1. Pre-modification of bio-based cellulose fibers: Regenerated bio-based cellulose short fibers are added to a lignin-castor oil bio-modification emulsion with a solid content of 20% and an impregnation bath ratio of 1:12. The fibers are ultrasonically impregnated for 20 minutes at an ultrasonic power of 280W, followed by low-temperature drying at 78℃ to obtain modified bio-based cellulose fibers. In this step, ultrasonic-assisted impregnation allows the modifier to fully penetrate the amorphous region of the cellulose fibers, achieving uniform grafting. If the ultrasonic power is too low or the impregnation time is insufficient, the modifier penetration will be inadequate, and the cross-linking effect will decrease; if the power is too high or the time is too long, the fiber surface structure may be damaged.

[0034] S2. Spinning a fully bio-based composite elastic yarn: Using bio-based PTT elastic filament as the core yarn and the modified bio-based cellulose fiber obtained in step S1 as the cover yarn, a low-tension airflow cover spinning technique is employed to control the cover twist at 390 twists / m, resulting in a fully bio-based composite elastic yarn. The choice of cover twist directly affects the structural stability and elasticity of the yarn. If the twist is too low, the cover layer will not be tightly bound to the core yarn; if the twist is too high, the yarn stiffness will be too great, affecting subsequent weaving and the fabric's hand feel.

[0035] S3. Low-tension double-weft knitting: A double-sided circular knitting machine is used for segmented tension yarn feeding. The ground yarn feeding tension is 15cN, and the weft elastic yarn feeding tension is 12cN. Weaving is performed using an alternating long and short needle arrangement at a knitting speed of 25m / min. The knitting needles are coated with a plant-based lubricating coating. The use of different feeding tensions for the ground and weft yarns ensures that the weft elastic yarn is embedded in the ground structure under low tension, preventing excessive pre-stretching of the elastic yarn and loss of subsequent elasticity, while also ensuring stable formation of the ground structure loops. The plant-based lubricating coating on the knitting needles effectively reduces the frictional resistance of the bio-based short fiber covered yarn during loop formation, reducing hairiness and yarn breakage. The yarn breakage rate during this step can be controlled below 0.6 times / km.

[0036] S4. Low-Temperature Bio-enzyme Pretreatment: The greige fabric is cleaned with a 52℃ bio-amylase washing solution to remove residual sizing agents and lubricants from the weaving process. After rinsing twice with clean water, it is pre-dried at a low temperature of 60℃. Compared to traditional high-temperature alkaline-oxygen pretreatment, this step uses the biocatalytic action of amylase to remove sizing agents at low temperatures, avoiding the etching of the bio-based fiber surface by high-temperature strong alkali and the damage to the elasticity of the PTT core yarn, while also reducing chemical residues in wastewater discharge.

[0037] S5. Bio-based Low-Temperature Crosslinking and Setting: Prepare a bio-based crosslinking setting solution with a solid content of 12%. Impregnate the fabric treated in step S4 with this setting solution, controlling the roll-off rate to 72%. Then, perform a low-temperature wet setting treatment at 95℃ for 45 seconds, followed by constant-temperature drying at 85℃ to complete the fiber crosslinking and elasticity locking. In this step, the solid content and roll-off rate of the crosslinking setting solution must be coordinated. If the solid content is too low, the crosslinking will be insufficient; if the solid content is too high, too many crosslinking points will form between the fibers, resulting in a stiffer hand feel. The purpose of controlling the heating rate is to allow the crosslinking agent to slowly diffuse into the fiber interior and fully react with the hydroxyl groups on the cellulose molecular chains to obtain a uniform crosslinking density distribution.

[0038] The bio-based crosslinking finishing liquid can be selected from at least one of the following systems: a bio-based crosslinking emulsion composed of lignin, castor oil polyol, and chitosan; a bio-based aqueous polyurethane crosslinking liquid synthesized from castor oil and lignin; a bio-based crosslinking finishing liquid with citric acid and chitosan as the main components; or a multifunctional crosslinking agent solution containing bio-based epoxy groups. None of the above systems contain petroleum-based monomers or petroleum-based silicone oil additives.

[0039] Among them, the bio-based cross-linking and setting liquid can be a diluted lignin-castor oil bio-modified emulsion. The two have the same formula, only the solid content and the target of application are different.

[0040] S6. Bio-based Green Finishing: The fabric is padded with a palm oil-based softening solution at a pick-up rate of 70%, and then dried at 82°C to obtain the basic bio-based high-elastic knitted fabric. The palm oil-based softener replaces the traditional petroleum-based silicone softener, giving the fabric a soft and skin-friendly feel without affecting its biodegradability, and avoiding the negative impact of silicone oil on subsequent coating, printing and other processing steps.

[0041] Fabric performance testing The fabrics obtained in the above embodiments were subjected to performance tests, and the test standards and results are as follows: The transverse elongation at break was tested in accordance with GB / T 3923.1-2013; The dimensional change rate after washing was determined after 50 washes in accordance with GB / T 8629-2017 standard. The springback retention rate was tested in accordance with FZ / T 70006-2004; The bio-based carbon content was determined in accordance with ASTM D6866 standard; The degradation rate of industrial compost was tested in accordance with ISO 14855-1 standard.

[0042] The test results of each embodiment all meet the requirements of the specifications described in the claims.

[0043] Furthermore, in step S5, A bio-based crosslinking setting solution is prepared. This setting solution uses the same formulation system as the lignin-castor oil biomodified emulsion used in step S1, namely, it contains 16 parts modified lignin, 30 parts epoxidized castor oil polyol, 8 parts chitosan, and 3 parts plant-based dispersant by weight. It is diluted with deionized water to a solid content of 12% before use. The fabric treated in step S4 is then impregnated with this setting solution, with the roll-off rate controlled at 72%, to ensure the setting solution is evenly adhered to the fabric surface and fiber gaps.

[0044] The pre-dried fiber blanks were pre-dried in a humid heat environment at 85°C for 30 seconds to allow for uniform evaporation of moisture from the fiber surface and initial penetration of the crosslinking agent. The temperature was then gradually increased to 95°C at a rate of 2.5°C / min, and held at 95°C under saturated wet steam for 45 seconds for setting. Finally, the fiber blanks were dried at a constant temperature of 85°C. The entire wet setting process was carried out in a closed humid heat environment with relative humidity controlled between 75% and 85%.

[0045] The core mechanism of this gradient heating process is as follows: in the initial low temperature stage, the crosslinking agent slowly diffuses into the amorphous region of cellulose fibers, avoiding premature film formation on the surface that hinders the penetration of the inner layer; in the subsequent high temperature and wet setting stage, the plasticizing effect of water molecules enhances the mobility of cellulose molecular chains, and the polyphenolic hydroxyl groups of lignin and cellulose hydroxyl groups undergo covalent crosslinking reaction under humid and hot conditions. The flexible long chain segments of epoxy castor oil polyol are embedded in the crosslinking network, and the amino groups of chitosan form hydrogen bonds with the phenolic hydroxyl groups of lignin to assist in crosslinking.

[0046] Compared to traditional high-temperature heat setting processes exceeding 190℃, this solution lowers the setting temperature by nearly 100℃, significantly saving energy consumption and preventing thermal degradation and elasticity loss of the bio-based PTT core yarn at high temperatures. Simultaneously, the saturated steam in the wet setting environment effectively inhibits excessive fiber shrinkage at high temperatures, ensuring fabric dimensional stability. After cross-linking and setting, a three-dimensional cross-linked elastic network is formed in the fabric, with cellulose as the main chain, lignin as rigid cross-linking points, and castor oil segments as flexible spacers. This network effectively resists the disruption of inter-fiber hydrogen bonds by water molecules during subsequent washing and use, forming the key structural basis for achieving a resilience retention rate of ≥85% after 50 washes.

[0047] Furthermore, in step S6, The fabric obtained in step S5 was impregnated and finished with a palm oil-based softening solution, with the roll-off rate controlled at 70%, and then dried at 82°C to obtain the finished bio-based high-elastic knitted fabric.

[0048] The preparation method of palm oil-based softening liquid is as follows: Weigh 8-12 parts by weight of palm oil-based ester-based quaternary ammonium salt softener, 2-4 parts by weight of plant-based emulsifier, and 84-90 parts by weight of deionized water, and emulsify in a water bath at 50-60℃ until uniform and transparent. The palm oil-based ester-based quaternary ammonium salt softener is prepared from palm oil fatty acids through esterification and quaternization reactions, and belongs to the cationic surfactant type.

[0049] The core advantages of this palm oil-based softening finish over traditional petroleum-based silicone softeners lie in three aspects: First, the long-chain alkyl groups in the softener's molecular chain can be oriented onto the fiber surface, imparting a soft and smooth feel to the fabric through intermolecular lubrication. Fabrics treated with palm oil-based softeners show superior overall scores in toughness, softness, and smoothness compared to traditional dialkyl quaternary ammonium salt softeners. Second, the ester-based quaternary ammonium salt molecular structure contains hydrolyzable ester bonds, achieving a biodegradability of over 90% within 13 days under activated sludge conditions. Unlike silicone softeners, it does not form a persistent hydrophobic film on the fiber surface, thus inhibiting the overall biodegradability of the fabric. Third, imidazoline-type palm oil-based softeners have less impact on the fabric's absorbency. Cotton knitwear treated with this softener can still maintain an absorbency height of 42mm, while the absorbency height after treatment with traditional quaternary ammonium salt softeners is only 19mm. This characteristic ensures that the final fabric maintains excellent hydrophilic and moisture-wicking properties while achieving a soft touch, meeting the comfort requirements for sportswear. Furthermore, the palm oil-based softener imparts excellent antistatic properties to the fabric, reducing the friction voltage of synthetic fiber fabrics such as polyester from 4080V to 400V, effectively preventing static electricity buildup and discomfort caused by friction during wear. The low-temperature drying at 82℃ further ensures that the elastic structure of the PTT core yarn is not damaged by high temperatures, thus preserving the full effects of the preceding processing steps.

[0050] A three-dimensional elastic network, consisting of alternating rigid crosslinking points and flexible spacers, is constructed within the fiber through a lignin-castor oil crosslinking system, achieving elasticity locking. A palm oil-based softener forms a molecular-level lubricating film on the fiber surface, resulting in a smooth hand feel. Both processes exhibit a stepped decrease in temperature window—95℃ for crosslinking setting and 82℃ for softening finishing—ensuring that elasticity locking and hand feel improvement are completed step-by-step under different temperature conditions without interference. Simultaneously, the palm oil-based softener does not affect the stability of the crosslinking network, and the crosslinking network does not hinder the spread of softener molecules on the fiber surface. The two processes achieve effective synergy in chemical compatibility and action sites, jointly ensuring the fabric possesses comprehensive properties of high elasticity, softness, and smoothness.

[0051] It should be noted that the process parameters of each step in this invention can be adjusted within the defined range according to the actual production conditions, and the different values ​​are all within the range that can be easily achieved by those skilled in the art based on the technical teachings of this invention.

[0052] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A bio-based high-elastic knitted fabric, characterized in that, Includes a knitted main body layer; the knitted main body layer is formed by integral knitting of fully bio-based composite elastic yarn on a circular knitting machine; The fully bio-based composite elastic yarn comprises a core yarn and a covering yarn, with a core yarn to covering yarn mass ratio of 3:7 to 6:4; the core yarn is a bio-based PTT elastic filament, and the covering yarn is a modified bio-based cellulose fiber grafted with a lignin-castor oil crosslinking modifier. The knitted main body layer has a transverse breaking elongation ≥280%, a longitudinal breaking elongation ≥110%, and a resilience retention rate ≥85% after 50 standard washes.

2. The bio-based high-elastic knitted fabric according to claim 1, characterized in that, The bio-based PTT elastic filament has a bio-based carbon content of ≥92%, a single filament fineness of 20-40D, and a breaking elongation of 350%-450%; the regenerated bio-based cellulose staple fiber is a binary blend of lyocell and soybean protein viscose, with a fiber fineness of 1.0-1.5D and a fiber length of 38-51mm.

3. The bio-based high-elastic knitted fabric according to claim 1, characterized in that, The lignin-castor oil crosslinking modifier is composed of the following bio-based raw materials in parts by weight: 12-20 parts modified lignin, 25-35 parts epoxidized castor oil polyol, 5-10 parts chitosan, and 2-5 parts plant-based dispersant; the modifier does not contain petroleum-based monomers or petroleum-based silicone oil additives.

4. The bio-based high-elastic knitted fabric according to claim 1, characterized in that, The knitted main body layer adopts a double weft loop structure with alternating long and short needles, and the all-bio-based elastic yarn used as the weft is locked inside the ground structure loop; Among them, the ground weave loop density is 45-75 loops / cm², the weaving tension of the all-bio-based elastic yarn is 8-15cN, the loop misalignment spacing is 0.1-0.3mm, and the fabric washing dimensional change rate is ≤2.5%.

5. The bio-based high-elastic knitted fabric according to claim 1, characterized in that, The bio-based carbon content in the knitted main layer is ≥85%, and the biodegradability rate is greater than 95% after 180 days under industrial composting conditions.

6. The bio-based high-elastic knitted fabric according to claim 1, characterized in that, The knitted main layer exhibits ≤6% residual deformation during rebound in a wet state, and ≤12% elasticity decay after 1000 cycles of tensile fatigue testing.

7. A process for preparing a bio-based high-elastic knitted fabric, applied to the bio-based high-elastic knitted fabric according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Pre-modification of bio-based cellulose fibers: Regenerated bio-based cellulose short fibers are added to a lignin-castor oil bio-modified emulsion, ultrasonically impregnated for 15-25 minutes, and dried at a low temperature of 70-85℃ to obtain modified bio-based cellulose fibers. S2. Spinning of fully bio-based composite elastic yarn: Using bio-based PTT elastic filament as core yarn and modified bio-based cellulose fiber as cover yarn, low-tension airflow covering spinning is adopted, and the covering twist is controlled at 360-420 twists / m to obtain fully bio-based composite elastic yarn. S3. Low-tension double-weft knitting: A double-sided circular knitting machine is used for segmented tension yarn feeding. The ground yarn feeding tension is 12-18cN, and the weft elastic yarn feeding tension is 8-15cN. Long and short needles are alternately arranged to weave and obtain the knitted main fabric. S4. Low-temperature pretreatment with biological enzymes: 45-60℃ biological amylase wash to remove weaving sizing material, rinse with clean water and then pre-dry at low temperature. S5. Bio-based low-temperature cross-linking and setting: Prepare a bio-based cross-linking and setting solution, impregnate the fabric with the setting solution, and then perform low-temperature wet setting at 85-105℃ for 30-60 seconds. Low-temperature drying completes the fiber cross-linking and elasticity locking. S6. Bio-based green finishing: The basic bio-based high-elastic knitted fabric is obtained by padding with palm oil-based softening solution and drying at 75-90℃.

8. The preparation process of a bio-based high-elastic knitted fabric according to claim 7, characterized in that, The biomodified emulsion in step S1 has a solid content of 15% to 25%, an impregnation bath ratio of 1:10 to 1:15, and an ultrasonic power of 200 to 350W.

9. The preparation process of a bio-based high-elastic knitted fabric according to claim 7, characterized in that, The bio-based crosslinking and shaping liquid in step S5 has a solid content of 8% to 15%, a padding and roll-off rate of 65% to 80%, and an oven heating rate of ≤3℃ / min.

10. The preparation process of a bio-based high-elastic knitted fabric according to claim 7, characterized in that, Step S3: Coat the surface of the knitting needles with a plant-based lubricating coating, knitting speed 22-28 m / min, yarn breakage rate ≤0.8 times / km.