A plant dyeing method for modified degradable polyester

Abstract

The present application provides a plant dyeing method for modified degradable polyester, comprising the following steps: S1, conducting a free radical graft polymerization reaction on ethylene terephthalate oligomers and cationic polymer compounds, and the obtained reaction products are cast and pelletized to obtain cationic modified polyester chips; the cationic polymer compounds are hydrophilic polymers; S2, incorporating biodegradable masterbatch into the cationic modified polyester chips, and performing mixed melt spinning to obtain degradable cationic modified polyester fibers; S3, mixing and adsorbing the degradable cationic modified polyester fibers with water-soluble inorganic salts, and then dyeing with plant dyes at a temperature below 100°C to obtain dyed fibers. The dyeing method of the present invention can conventionally dye the modified polyester fibers with plant dyes, and the polyester fibers can be degraded under natural conditions, thereby achieving degradation of fabric fibers and plant dyes.

Description

Technical Field

[0001] The invention belongs to the technical field of textile printing and dyeing, and specifically relates to a plant dyeing method for modified degradable polyester. Background Art

[0002] Polyester fiber has excellent properties such as high strength, wear resistance, wrinkle resistance, easy washing and quick drying, and is widely used in the field of textiles and clothing. Polyester fiber is a general term for fibers spun from polyesters generated by polycondensation of various diols and aromatic dicarboxylic acids or their esters; polyethylene terephthalate fiber is its main variety, commonly known as polyester.

[0003] Polyester fiber has a tight molecular structure and no dye affinity groups. Whether it is chemical dyes or plant dyes, it is not easy to directly bind to polyester fiber molecules. Therefore, it is difficult to dye polyester fibers under normal conditions. Generally, it must be dyed with disperse dyes at high temperatures or in the presence of carriers. The chemical dyes commonly used for ordinary polyester dyeing are disperse dyes. Under high-temperature melting conditions, disperse dyes can dye polyester fibers through affinity and the concentration difference between the inside and outside of the dye molecules.

[0004] At the same time, as the largest variety of synthetic fibers, although polyester fibers do not directly harm the environment, they are used in huge quantities, have strong resistance to the atmosphere and microorganisms, have high crystallinity, and are difficult to decompose naturally. Their waste has become a global environmental pollution. In recent years, the recycling of polyester fibers has increased significantly, but it is still very low, less than 10%. In this regard, making polyester fibers naturally degradable has become a more pragmatic and effective solution, which is in line with the current trend of low-carbon social development. Summary of the invention

[0005] The purpose of the present invention is to provide a plant dyeing method for modified degradable polyester. The dyeing method of the present invention can use plant dyes to conventionally dye the modified polyester fibers. At the same time, the polyester fibers can be degraded under natural conditions, thereby achieving the degradation of fabric fibers and plant dyes, which is beneficial to environmental protection.

[0006] The present invention provides a plant dyeing method for modified degradable polyester, comprising the following steps:

[0007] S1, conducting a free radical graft polymerization reaction on ethylene terephthalate oligomer and a cationic polymer compound, and casting and pelletizing the obtained reaction product to obtain a cationic modified polyester slice; the cationic polymer compound is a hydrophilic polymer;

[0008] S2, blending biodegradable masterbatch into the cationic modified polyester slice, and performing mixed melt spinning to obtain degradable cationic modified polyester fiber;

[0009] S3, mixing and adsorbing the degradable cationic modified polyester fiber and a water-soluble inorganic salt, and then dyeing the fiber with a plant dye at a temperature below 100° C. to obtain dyed fiber.

[0010] In an embodiment of the present invention, in step S1, the ethylene terephthalate oligomer is prepared by reacting terephthalic acid and bio-based ethanol to generate ethylene terephthalate, and then subjecting the reactant to low vacuum polycondensation.

[0011] In an embodiment of the present invention, in step S1, during the low vacuum polycondensation stage of preparing the ethylene terephthalate oligomer, a stabilizer and / or a catalyst is added, the absolute pressure of the polycondensation is below 600 Pa, the temperature is controlled at 240-270° C., and the reaction is carried out for 50-70 min.

[0012] In an embodiment of the present invention, in step S1, the cationic polymer compound is selected from one or more of amide-cationic polyacrylamide, hydroxyl-cationic starch, chitosan quaternary ammonium salt and polyepichlorohydrin amide.

[0013] In an embodiment of the present invention, in step S1, the absolute value of the pressure of the free radical graft polymerization reaction is below 100 Pa, the temperature is controlled at 270-310° C., and the reaction time is 80-120 min.

[0014] In an embodiment of the present invention, in step S2, the main components of the biodegradable masterbatch are one or two of aliphatic polylactic acid and polylactic acid-glycolic acid; the mass ratio of the cationic modified polyester chips to the biodegradable masterbatch is 55-70:30-45.

[0015] In an embodiment of the present invention, in step S2, the mixed melt spinning adopts a POY process or a FDY process.

[0016] In an embodiment of the present invention, in step S3, the metal cation in the water-soluble inorganic salt is one or more of calcium, potassium, iron and aluminum; and the plant dye is selected from one or more of polyphenols, porphyrins, anthraquinones and carotenoids.

[0017] In an embodiment of the present invention, in step S3, the degradable cationically modified polyester fiber and the water-soluble inorganic salt are mixed and adsorbed in water, the amount of the water-soluble inorganic salt is within 6% of the weight of the degradable cationically modified polyester fiber, and the temperature of the mixed adsorption is 50-90°C.

[0018] In an embodiment of the present invention, in step S3, the dyeing temperature of the plant dye is 70-90° C., and the total insulation time is 30-60 minutes.

[0019] Compared with the prior art, the present invention introduces a hydrophilic cationic polymer as the third monomer for copolymerization and grafting when forming ethylene terephthalate polyester chips, thereby obtaining cationic modified polyester chips; and with the changes in these structures, a biodegradable material is added to the modified polyester, and degradable cationic modified polyester fibers are spun; finally, the prepared degradable cationic modified polyester fibers or products are grafted with metal cations before plant dyeing by mixing water-soluble inorganic salts, and these additives can be effectively adsorbed on the fiber molecules to form corresponding ionic coordination bonds, and under conventional dyeing conditions, ionic bonds or covalent bonds are formed between the plant dye molecules and the fibers, so that the plant dyes are fixed on the fibers, thereby achieving the purpose of ultimately dyeing the fibers. The biodegradable modified polyester plant dyeing process provided by the present invention incorporates biodegradable materials and cationic modification of polyester, changes the crystallinity and orientation of polyester, increases the gaps between polyester molecules, and reduces the strength of polyester to a certain extent. Through these key processes, not only does it become possible to dye polyester fibers with plant dyes, but it can also increase the degradation rate of polyester. At the same time, the plant dye molecules are degradable biomass, and the dyed fibers can be naturally biodegraded after being finally discarded, realizing a green cycle between humans and the environment. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0021] The present invention provides a plant dyeing method for modified degradable polyester, comprising the following steps:

[0022] S1, conducting a free radical graft polymerization reaction on ethylene terephthalate oligomer and a cationic polymer compound, and casting and pelletizing the obtained reaction product to obtain a cationic modified polyester slice; the cationic polymer compound is a hydrophilic polymer;

[0023] S2, blending biodegradable masterbatch into the cationic modified polyester slice, and performing mixed melt spinning to obtain degradable cationic modified polyester fiber;

[0024] S3, mixing and adsorbing the degradable cationic modified polyester fiber and a water-soluble inorganic salt, and then dyeing the fiber with a plant dye at a temperature below 100° C. to obtain dyed fiber.

[0025] The dyeing method of the invention can perform conventional dyeing on the modified polyester fiber with plant dyes, and the polyester fiber can be degraded under natural conditions, thereby achieving degradation of fabric fiber and plant dyes, which is beneficial to environmental protection and application.

[0026] In the embodiment of the present invention, ethylene terephthalate oligomers are first prepared; preferably, terephthalic acid (PTA) and bio-based ethylene glycol (EG) are used as raw monomers, and ethylene terephthalate is generated through esterification or transesterification, which is then subjected to a certain polycondensation reaction to generate polyethylene terephthalate (PET).

[0027] In some embodiments of the present invention, terephthalic acid and bio-based ethylene glycol are used as raw materials, and ethylene terephthalate is prepared by esterification reaction under nitrogen conditions. The main reason for the bio-based ethylene glycol is that its raw materials for preparation are renewable, and the raw materials come from carbohydrates in nature, whether it is starch-based polysaccharide crops, such as corn, wheat, potatoes, sweet potatoes, beets and other high-yield crops; or monosaccharide or polysaccharide crops, such as sweet sorghum, Jerusalem artichoke and cassava, etc., all can be used as bio-based ethylene glycol raw materials. Specifically, the molar ratio of terephthalic acid to ethylene glycol is 1:1-1.5, the reaction temperature is 230-270°C, the pressure is normal temperature and pressure, and the end point of the reaction is that the distillation amount of water reaches more than 90% of the theoretical value.

[0028] The embodiment of the present invention introduces a hydrophilic cationic polymer as the third monomer when forming polyester chips, which is beneficial to the subsequent combination of plant dyes and polyester fiber dyeing; specifically, the hydrophilic polymer third monomer is introduced into the oligomer intermediate in the polyester reaction to carry out a free radical graft polymerization reaction.

[0029] In an embodiment of the present invention, the polymerization reaction includes a polycondensation low vacuum stage and a polycondensation high vacuum stage; in the low vacuum stage, preferably after adding a stabilizer and a catalyst, the intermediate of the esterification reaction starts a polycondensation reaction under negative pressure conditions, the absolute pressure value of this stage is below 600Pa, the temperature is controlled at 240-270°C, and the reaction is 50-70min to obtain ethylene terephthalate oligomers. After the reaction is completed, a third monomer hydrophilic cationic polymer is introduced, and vacuuming is continued. The pressure drops to an absolute value of less than 100Pa, the temperature is controlled at 270-310°C, and the reaction is 80-120min. Afterwards, the obtained reaction product can be cooled, cast, cooled, and pelletized to finally obtain a cationic modified polyester chip.

[0030] The stabilizer is preferably phosphite, and the amount used is 0.01% to 0.05% by weight of terephthalic acid. The preferred catalyst is stannous chloride, and the amount used is 0.01% to 0.05% by weight of terephthalic acid. Furthermore, the amount of the third monomer is preferably 1% to 10% by weight of terephthalic acid.

[0031] The hydrophilic cationic polymer third monomer introduced in the embodiment of the present invention can be a hydrophilic polymer cationic compound such as amide-cationic polyacrylamide, hydroxyl-cationic starch, chitosan quaternary ammonium salt and polyepichlorohydrin amine, which is copolymerized and grafted to form a cationic modified polyester. The hygroscopicity of this polyester fiber-forming polymer structure is higher than that of ordinary polyester, and the molecular weight, crystallinity and strength will be reduced. The reduction in crystallinity can increase the ability of the fiber to bind to the plant dye group, thereby improving the inability of plant dyes to dye polyester fibers and improving the dyeing rate.

[0032] The hydrophilic cationic polymer can be a commercial product with a solid content of 30% to 50%, a pH of 6 to 8, and a molecular weight of 8000 to 20000. The molecular weight of the modified polyester after copolymerization and grafting can be 7000 to 15000, and the crystallinity is 35% to 50%.

[0033] In the obtained cationic modified polyester chips, the biodegradable masterbatch is blended into the embodiment of the present invention for mixed melt spinning to form degradable cationic modified polyester fibers.

[0034] The main component of the biodegradable masterbatch used in the embodiment of the present invention is a combination of one or two polymers of aliphatic polylactic acid and polylactic acid-glycolic acid, which are combined with modified polyester chips by melt blending so that the dye can be evenly bound to the fiber during subsequent plant dyeing. The biodegradable masterbatch can be a commercially available degradable material or can be made by yourself. In the process of making biodegradable masterbatch in some embodiments, it is preferred to add 5-8 parts by mass of compatibilizer maleic anhydride, add 5-10 parts by mass of water, and the balance is one or more combinations of polylactic acids, mix evenly at 80-100°C in a high-speed dispersing device, and extrude through a twin-screw extruder to obtain the biodegradable masterbatch, whose molecular weight is <60000 and melt index is 2-5g / min under standard conditions.

[0035] Among them, the proportion of the mixed amount for spinning is preferably: 60 parts of cationic modified polyester chips and 40 parts of biodegradable masterbatch. The spinning process is a conventional pre-oriented yarn production (POY) process or a fully drawn yarn production (FDY) process. The POY production process is generally: melt conveying → metering extrusion yarn bundles → side blowing cooling → bundling oiling → winding forming → pre-inspection → grading → packaging → storage; the FDY production process is: melt conveying → spinning → side blowing cooling → bundling oiling → stretching → network → winding forming → pre-inspection → grading → packaging → storage. For example, the POY spinning speed is 3250m / min; the melt temperature is 290℃; the wind speed is 0.8m / s; the side blowing humidity is stable at about 75%.

[0036] After being made into degradable modified polyester, the crystallinity of polyester fiber is reduced, the hygroscopicity is improved, the hand feel is soft, high fluffy, and easy to dye. The various indexes of the obtained degradable cationic modified polyester fiber are as follows:

[0037] Linear density deviation rate dpf: 2.0% <dpf<3.5%;

[0038] Linear density coefficient of variation CV: 1.0% <CV<1.7%;

[0039] Breaking strength: 1.9 <cN / dtex<2.3;

[0040] Coefficient of variation of breaking strength: 4.5 <CV<8;

[0041] Unevenness of strips: 1.4 <CV<2.2;

[0042] Oil content: <0.4%;

[0043] Crystallinity: <5%.

[0044] After obtaining the degradable cation-modified polyester fiber, the embodiment of the present invention performs cation grafting before plant dyeing to provide dyeing sites for plant dye molecules; the prepared degradable cation-modified fiber can also be spun into yarn and fabric products, and then cation grafting is performed. The specific operation includes: the degradable cation-modified polyester fiber is mixed and adsorbed with a water-soluble inorganic salt in water, and the temperature can be raised at room temperature and kept warm for a certain period of time to complete the pre-dyeing treatment modification.

[0045] The polyester degraded fiber modified by cation has certain hydrophilicity. Before dyeing, the embodiment of the present invention forms a dyeing seat of plant dye by carrying out metal cation grafting with modified polyester fiber using water-soluble inorganic salt. Preferably, the metal cation in the water-soluble inorganic salt is one or more of calcium (Ca), potassium (K), iron (Fe) and aluminum (Al), which can be carbonate, chloride, such as CaCl2, K2CO3, FeCl3, etc. These auxiliary agents or modifiers can be effectively adsorbed on the fiber molecules to form corresponding ion coordination bonds, which are beneficial to the combination of subsequent plant dye molecules and the fiber to form ionic bonds or covalent bonds, and the plant dye is fixed on the fiber to achieve the purpose of finally dyeing the polyester fiber.

[0046] In a specific embodiment of the present invention, the amount of the water-soluble inorganic salt is within 6% of the weight of the degradable cationic modified polyester fiber, and the amount of the modifier is preferably 1% to 5% of the fiber weight. The temperature of the mixed adsorption is preferably 50 to 90°C, and the total heat preservation time is at least 60 minutes. After the grafting modification treatment is completed, it is cleaned and dyed.

[0047] In the embodiment of the present invention, plant dyes are used to conventionally dye the polyester degraded fibers after ion grafting, and the dyeing temperature is lower than 100° C. to obtain dyed fibers.

[0048] In an embodiment of the present invention, the types of the plant dye include polyphenols, porphyrins, anthraquinones, carotenoids, etc., and the representative dye raw materials include pomegranate, chlorophyll, madder, gardenia, etc., and commercially available plant dye products can be used. The plant dye molecules of these structures form ionic bonds or covalent bonds with the modified polyester fiber through the above-mentioned dyeing seat, and are combined on the fiber, thereby completing the plant dye dyeing modified polyester fiber. The plant dye molecule is a degradable biomass, and the dyeing fiber can achieve natural biodegradation after being finally abandoned. The selection combination of these materials and process additives in the embodiment of the present invention has completed the harmonious win-win situation between people and the environment, and realized green development.

[0049] The specific plant dyeing implementation process of the embodiment of the present invention includes: under normal conditions, heating at room temperature, the heating rate is 1-2°C / min, preferably rising to 70-90°C, the total heat preservation time can be 40-50min, and the overall dyeing is completed. For example, the bath ratio during immersion dyeing can be 1:10 (mass volume ratio), the amount of dye used is 1-5% of the fiber weight, and dyeing auxiliaries such as acetic acid or soda ash can be added.

[0050] Through these key processes, the embodiments of the present invention not only achieve the dyeing of polyester fibers with plant dyes under normal conditions, but also have significant advantages in terms of level dyeing, fastness index, and dyeing depth. In addition, the dyed polyester fibers produced can be naturally biodegraded after being discarded, completing the recycling of environmental resources, which is more environmentally friendly.

[0051] In order to better understand the technical content of the present invention, the following specific examples are provided to further illustrate the present invention. Among them, the source of the bio-based ethylene glycol raw material involved in the present embodiment is corn, and the specific parameters are: relative molecular weight: 62.069; melting point: -11.5℃; boiling point: 198.0℃, density 1.1128g / cm 3 ; Chroma (platinum-cobalt) ≤ 10 30 60; The third monomer of the hydrophilic cationic polymer is amide-cationic polyacrylamide.

[0052] The production process of biodegradable masterbatch: add 5 parts of compatibilizer maleic anhydride, add 5 parts of water, and the balance is aliphatic polymer, mix evenly at 80-100°C in a high-speed dispersing equipment, and extrude the biodegradable masterbatch through a twin-screw extruder.

[0053] Embodiment 1:

[0054] Using terephthalic acid and bio-based ethylene glycol as raw materials, under nitrogen conditions, ethylene terephthalate is prepared through an esterification reaction. The molar ratio of terephthalic acid to ethylene glycol is 1:1 to 1.5, the reaction temperature is 230 to 270 °C, the pressure is normal temperature and pressure, and the end point of the reaction is when the distillate amount of water reaches more than 90% of the theoretical value.

[0055] The stabilizer is: phosphite, and the dosage is 0.01% to 0.05% of the weight of terephthalic acid. The catalyst is: stannous chloride, and the dosage is 0.01% to 0.05% of the weight of terephthalic acid. After adding phosphite and stannous chloride, the intermediate of the above esterification reaction starts a low-vacuum polycondensation reaction under negative pressure conditions. The absolute pressure value at this stage is below 600 Pa, the temperature is controlled at 250 °C, and the reaction lasts for 70 min. After the reaction, a third monomer, a hydrophilic cationic polymer, is introduced, and the dosage of the third monomer is 10% of the weight of terephthalic acid. Continue to evacuate, the pressure drops to below an absolute value of 100 Pa, the temperature is controlled at 280 °C, and the reaction lasts for 120 min. After cooling, pelletizing, cooling, and granulating, cation-modified polyester chips are obtained.

[0056] Basic parameters of the chips: Viscosity: 0.64 to 0.66; DEG content: <0.13%; Moisture: <0.4%; Melting point: 253 to 256 °C; b value: <1.0.

[0057] According to the ratio of 60 parts of cation-modified polyester chips and 40 parts of biodegradable masterbatch, the biodegradable masterbatch is incorporated into the cation-modified polyester chips for mixed melt spinning. The spinning process is a conventional POY process, the spinning speed is 3250 m / min; the melt temperature is 290 °C; the wind speed: 0.8 m / s; the humidity of the side blow is stabilized at about 75%, and biodegradable cation-modified polyester fibers are prepared.

[0058] The requirements for its various indicators are as follows: Linear density deviation rate: 2.0% < dpf < 3.5%; Linear density coefficient of variation: 1.0% < CV < 1.7%; Tensile strength: 1.9 < cN / dtex < 2.3; Tensile strength coefficient of variation: 4.5 < CV < 8; Evenness variation coefficient: 1.4 < CV < 2.2; Oil content: <0.4%; Crystallinity: <5%.

[0059] The biodegradable cation-modified polyester fiber is mixed and adsorbed with water-soluble inorganic salts in water. The specific process conditions include: using the inorganic salt CaCl2, the bath ratio is 1:10, the dosage of the inorganic salt is 5% of the fiber weight, heating from room temperature, the heating rate is 2 °C / min, heating to 90 °C, and the total insulation time is 60 min; after completion, clean it.

[0060] The fibers pretreated as above are subjected to plant dyeing; the plant dye used is polyphenol dye pomegranate, the bath ratio is 1:10, the dye dosage is 5% of the fiber weight, the auxiliary agent is acetic acid, the dosage is 0.5 ml / l, the temperature is raised at room temperature, the heating rate is 2°C / min, it rises to 70°C, the insulation time is 40 minutes, and the overall dyeing is completed.

[0061] In addition, other plant dyes are used for dyeing. The following indicators are the test results of example 1 using CaCl2 for ion grafting and then dyeing with four plant dyes.

[0062] Table 1 Staining results of Example 1

[0063]

[0064]

[0065] Embodiment 2:

[0066] The preparation was carried out according to the process of Example 1, with the following differences:

[0067] The auxiliary agent K2CO3 is used with a bath ratio of 1:10. The dosage of the auxiliary agent is 3% of the fiber weight. The temperature is raised at room temperature at a rate of 2°C / min to 80°C. The total insulation time is 60 minutes, and the mixture is cleaned after completion.

[0068] Porphyrin dye chlorophyll, bath ratio 1:10, dye dosage is 1% of fiber weight, auxiliary agent is soda ash, dosage is 1g / l, heating at room temperature, heating rate is 1℃ / min, rise to 80℃, keep warm for 50min, and the whole dyeing is completed.

[0069] The following is the result of dyeing four kinds of plant dyes by ion grafting with auxiliary agent K2CO3 as example 2.

[0070] Table 2 Staining results of Example 2

[0071]

[0072] Embodiment three:

[0073] The preparation was carried out according to the process of Example 1, with the following differences:

[0074] The auxiliary agent FeCl3 used has a bath ratio of 1:10 and an auxiliary agent dosage of 1% of the fiber weight. The temperature is raised at room temperature at a rate of 1°C / min to 50°C. The total insulation time is 60 minutes and the mixture is cleaned after completion.

[0075] Anthraquinone dye madder: bath ratio 1:10, dye dosage is 3% of fiber weight, auxiliary agent is soda ash, dosage is 1g / l, heating at room temperature, heating rate is 1℃ / min, rise to 80℃, keep warm for 30min, and the whole dyeing is completed.

[0076] The following is the result of dyeing four kinds of plant dyes by ion grafting with auxiliary agent FeCl3 as example 3.

[0077] Table 3 Staining results of Example 3

[0078]

[0079] Embodiment 4:

[0080] The preparation was carried out according to the process of Example 1, with the following differences:

[0081] The auxiliary agent AlCl3 is used with a bath ratio of 1:10. The dosage of the auxiliary agent is 5% of the fiber weight. The temperature is raised at room temperature at a rate of 2°C / min to 80°C. The total insulation time is 60 minutes. After the temperature is raised, the fiber is cleaned and dyed.

[0082] Carotenoid dye gardenia, bath ratio 1:10, dye dosage is 2% of fiber weight, heating at room temperature, heating rate at 2℃ / min, rising to 90℃, keeping temperature for 30min, and the whole dyeing is completed.

[0083] The following is the dyeing results of four plant dyes by ion grafting with auxiliary agent AlCl3 as example 4

[0084] Table 4 Staining results of Example 4

[0085]

[0086] It can be seen from the above embodiments that the present invention incorporates degradable materials and cationic modification of polyester, changes the crystallinity and orientation of polyester, increases the gaps between polyester molecules, and reduces the strength of polyester to a certain extent. Through these key processes, not only does it become possible to dye polyester fibers with plant dyes, but it can also increase the degradation rate of polyester. At the same time, the plant dye molecules are degradable biomass, and the dyed fibers can be naturally biodegraded after being discarded, realizing a green cycle between humans and the environment.

[0087] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A plant dyeing method for modified degradable polyester, characterized in that: The following steps are involved: S1, copolymerization and grafting reaction of ethylene terephthalate oligomer and cationic polymer compound, the obtained reaction product is cast and pelletized to obtain cationic modified polyester slices; the cationic polymer compound is a hydrophilic polymer; the ethylene terephthalate oligomer is prepared by reacting terephthalic acid and bio-based ethylene glycol to generate ethylene terephthalate, and then undergoing low vacuum polycondensation, in which stabilizers and / or catalysts are added, the absolute pressure value of the polycondensation is below 600 Pa, the temperature is controlled at 240-270° C., and the reaction is carried out for 50-70 min; the cationic polymer compound is selected from one or more of amide-cationic polyacrylamide, hydroxyl-cationic starch, chitosan quaternary ammonium salt and polyepichlorohydrin amine; the absolute pressure value of the copolymerization and grafting reaction is below 100 Pa, the temperature is controlled at 270-310° C., and the reaction time is 80-120 min; S2, blending biodegradable masterbatch into the cationic modified polyester slice, and performing mixed melt spinning to obtain degradable cationic modified polyester fiber; S3, mixing and adsorbing the degradable cationic modified polyester fiber and a water-soluble inorganic salt, and then dyeing the fiber with a plant dye at a temperature below 100° C. to obtain dyed fiber.

2. The plant dyeing method of modified degradable polyester according to claim 1, characterized in that: In step S2, the main components of the biodegradable masterbatch are one or two of aliphatic polylactic acid and polylactic acid-glycolic acid; the mass ratio of the cationic modified polyester chips to the biodegradable masterbatch is 55-70:30-45.

3. The plant dyeing method of modified degradable polyester according to claim 2, characterized in that: In step S2, the mixed melt spinning adopts POY process or FDY process.

4. The plant dyeing method of modified degradable polyester according to claim 1, characterized in that: In step S3, the metal cations in the water-soluble inorganic salt are one or more of calcium, potassium, iron and aluminum; and the plant dye is selected from one or more of polyphenols, porphyrins, anthraquinones and carotenoids.

5. The plant dyeing method of modified degradable polyester according to claim 4, characterized in that: In step S3, the degradable cationically modified polyester fiber and the water-soluble inorganic salt are mixed and adsorbed in water, the amount of the water-soluble inorganic salt is within 6% of the weight of the degradable cationically modified polyester fiber, and the temperature of the mixed adsorption is 50-90°C.

6. The plant dyeing method of modified degradable polyester according to claim 5, characterized in that: In step S3, the dyeing temperature of the plant dye is 70-90° C., and the total insulation time is 30-60 minutes.

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