Regenerated cationic dyeable polyester composition as well as preparation method and application thereof

Abstract

The invention discloses a regenerated polyester composition and a preparation method thereof, the regenerated polyester composition is mainly composed of an aromatic dicarboxylic acid structural unit and an aliphatic dihydric alcohol structural unit, and contains sulfonate groups, and the total content of the sulfonate groups accounts for 1000-5000 ppm of the total amount of the polyester composition in terms of sulfur element; the gel rate of the polyester composition is below 20%. The regenerated polyester composition is easy to dye, few in foreign matter, low in gel rate and suitable for being applied to the fiber industry.

Description

Technical Field

[0001] The present invention relates to a recycled cation - dyeable polyester composition and a preparation method thereof. Specifically, it relates to a cation - dyeable polyester composition obtained by depolymerizing recycled polyester as a raw material, adding a sulfonate compound, and then polymerizing again. Background Art

[0002] Polyester resins are widely used in industrial fields such as clothing, industrial fibers, tapes, surface - coating films, tire meridians, and fishing nets due to their excellent mechanical and chemical properties. However, in recent years, the large - scale use of polyester has led to the accumulation of a large amount of waste polyester, environmental pollution, and the increasing depletion of petroleum resources. Therefore, its recycling has become a research hotspot.

[0003] When used as clothing fibers, in order to improve the dyeability of polyester, a dyeing site that can accommodate dyes is generally introduced during the polymerization process of polyester. Since cationic dyes have a complete chromatogram, the dyed fabrics have bright colors and high dye exhaustion rates, greatly reducing the discharge of printing and dyeing wastewater. Therefore, it is relatively common to add sulfonate compounds represented by sodium 5 - sulfoisophthalate to endow polyester with cationic dyeing properties. Chinese Patent CN115232298A discloses a method and product for preparing recycled cation - dyeable polyester chips from waste polyester materials. The main steps are to dry the waste polyester materials and then melt - extrude them into a twin - screw system, remove volatiles and impurities, obtain a polyester melt, then depolymerize it to obtain a depolymerized solution of BHET and EG, and then remove excess EG and add a SIPE solution for copolymerization reaction. Although melt - extrusion can remove some impurities, impurities such as nylon, polyphenylene sulfide, and residual catalysts doped in the waste materials cannot be removed by melt - extrusion. When heated, the amino groups in nylon will oxidize to form yellow quinone - containing substances, resulting in the yellowing of recycled polyester; polyphenylene sulfide will cross - link when heated, forming foreign substances in the recycled polyester. At the same time, the residual catalyst will cause an excessive amount of catalyst in the recycled polyester, which may subsequently promote the decomposition of impurities such as nylon / polyphenylene sulfide and recycled polyester. The aforementioned impurities that cannot be removed will lead to poor hue and high gel value of the recycled polyester, thus affecting the spinning performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a recycled cation - dyeable polyester composition with excellent hue and low gel rate and a preparation method thereof, and the polyester composition is suitable for being made into fibers.

[0005] Technical solution of the present invention:

[0006] Recycled cation-dyeable polyester composition, mainly composed of aromatic dicarboxylic acid structural units and aliphatic diol structural units. The molecular chain of the polyester composition contains sulfonate groups shown in Formula 1 and / or Formula 2, and the total content of the sulfonate groups accounts for 1000 - 5000 ppm, preferably 1000 - 3500 ppm of the total amount of the polyester composition in terms of sulfur element;

[0007]

[0008] In Formula 1, Y is an alkylene group with 2 - 20 carbon atoms, phenyl group or alkylbenzene. In Formula 1 and Formula 2, Z is Li ion, Na ion or K ion.

[0009] The gel fraction of the polyester composition is below 20%, preferably below 10%.

[0010] The present invention also discloses a preparation method of the above-mentioned recycled cation-dyeable polyester composition. First, an aliphatic diol is added to the recycled polyester for depolymerization to obtain an oligomer, and then the oligomer is subjected to a polycondensation reaction. A sulfonate compound shown in Formula 3 and / or 4 is added at any stage before the end of the polycondensation reaction. The addition amount of the sulfonate compound is 1000 - 5000 ppm, preferably 1000 - 3500 ppm of the total amount of the polyester composition in terms of sulfur element; the polycondensation reaction ends within 10 - 60 minutes after entering a high vacuum to obtain a low-viscosity polymer, and then the low-viscosity polymer is subjected to solid-phase polymerization to obtain the polyester composition.

[0011]

[0012] In Formula 3, Y is an alkylene group with 2 - 20 carbon atoms, phenyl group or alkylbenzene. X in Formula 3 and Z in Formula 4 are respectively Li ion, Na ion or K ion. M in Formula 3 and R in Formula 4 are respectively hydrogen atom, alkyl group or hydroxyalkyl group with 2 - 4 carbon atoms.

[0013] The low-viscosity polymer is subjected to solid-phase polymerization to obtain a recycled cation-dyeable polyester composition. The reaction temperature of the solid-phase polymerization is preferably 200 - 240 °C, the reaction pressure is preferably below 1000 Pa, and the reaction time is preferably below 100 hours.

[0014] The recycled polyester composition described in the present invention has excellent hue, good hydrolysis resistance, good dyeability, low gel fraction, and good spinning performance of the polyester, and can be applied in the fiber field. Detailed embodiments

[0015] The recycling and reuse of waste polyester materials reduce environmental pollution and also solve the problem of the increasing depletion of petroleum resources. For applications that require dyeing, sulfonate groups can also be introduced into the molecular chain segments of recycled polyester to endow it with cation-dyeable properties.

[0016] However, there are also a series of problems in the recycling process, especially the impurities difficult to remove in waste polyester materials (such as nylon, polyphenylene sulfide, residual catalysts, etc.). Under the influence of heating temperature and time, it is easy to cause the color tone of recycled polyester to become worse and the gel rate to become higher, ultimately affecting the spinnability of recycled polyester and the physical properties of the obtained fibers. Moreover, when preparing cation-dyeable recycled polyester, due to the influence of impurities difficult to remove and thermal oxygen decomposition, sulfonate groups are prone to generate cross-linked substances, resulting in an increase in foreign matters in the recycled polyester and a decrease in dyeability.

[0017] The present invention provides a recycled polyester composition that is cation-dyeable and has a low foreign matter content. The cation-dyeable property is achieved by introducing sulfonate groups shown in Formula 1 and / or Formula 2 into the molecular chain of the polyester composition.

[0018]

[0019] In Formula 1, Y is an alkylene group having 2 to 20 carbon atoms, a phenyl group or an alkylbenzene, and X and Z are respectively Li ion, Na ion or K ion.

[0020] The total content of sulfonate groups in the polyester composition accounts for 1000 to 5000 ppm of the total amount of the polyester composition in terms of sulfur element. When the content of the sulfate group in terms of sulfur element is less than 1000 ppm, it is difficult to achieve a satisfactory color concentration in the subsequent dyeing process of the obtained recycled polyester composition. When the content of the sulfate group in terms of sulfur element is higher than 5000 ppm, if the sulfonate group shown in Formula 1 accounts for the vast majority, since the sulfonate group shown in Formula 1 is connected to the end of the polyester molecular chain, the growth of the polyester molecular chain is inhibited in the polycondensation reaction, and the polymerization terminates before the polymerization system reaches the target viscosity, resulting in a low molecular weight and poor physical properties of the obtained recycled polyester composition; if the sulfonate group shown in Formula 2 accounts for the vast majority, since the sulfonate group shown in Formula 2 is connected to the middle position of the polyester molecular chain, the sulfonate groups in the middle of the molecular chain are prone to physical cross-linking, and the melt viscosity of the system is too high when the target molecular weight is reached in the polycondensation reaction, affecting the physical properties and spinnability of the obtained recycled polyester composition. Considering the dyeability and the physical properties of the recycled polyester composition comprehensively, the total content of the sulfonate groups is preferably 1000 to 3500 ppm of the polyester composition in terms of sulfur element.

[0021] The sulfonate groups shown in Formula 1 and Formula 2 in the recycled polyester composition can exist simultaneously or separately. Since the sulfonate group shown in Formula 1 is connected to the end of the molecular chain, reducing the physical cross-linking groups that interact with each other in the middle of the molecular chain, it can ensure that the obtained recycled polyester composition has a suitable molecular weight and good strength, so it is preferred.

[0022] Regarding reducing the content of foreign matters in a recycled polyester composition, the present invention provides a process flow for achieving this purpose. Specifically, an aliphatic diol is first added to recycled polyester for depolymerization to obtain oligomers, and then the oligomers are subjected to a polycondensation reaction, and a sulfonate compound represented by Formula 3 and / or 4 is added at any stage before the end of the polycondensation reaction. The polycondensation reaction ends within 10 to 60 minutes after entering a high vacuum to obtain a low-viscosity polymer, and then the low-viscosity polymer is subjected to solid-phase polymerization to obtain a polyester composition.

[0023] The polycondensation reaction ends within 10 to 60 minutes after entering a high vacuum, shortening the residence time of each substance in the high-temperature polycondensation kettle, and being able to inhibit the occurrence of thermal decomposition and crosslinking reactions of residual impurities (such as nylon and polyphenylene sulfide) in the recycled polyester, thereby improving the hue of the recycled polyester composition and reducing its gel rate. Since the reaction time after entering a high vacuum in the polycondensation reaction is short, only a low-viscosity polymer can be obtained and it cannot be used for spinning. Therefore, it is considered to perform solid-phase polymerization on the obtained low-viscosity polymer after the polycondensation reaction, so that transesterification reactions occur between hydroxyethyl groups in the low-viscosity polymer, and esterification reactions occur between hydroxyethyl groups and terminal carboxyl groups, thereby increasing the molecular weight of the polymer and finally obtaining a recycled polyester composition that can be industrially applied.

[0024] The preparation method of the recycled polyester composition of the present invention is specifically as follows:

[0025] First, an aliphatic diol and a depolymerization catalyst are added to recycled polyester for depolymerization treatment to obtain oligomer diethylene glycol terephthalate. The molar ratio of the recycled polyester to the aliphatic diol is 1:1.5 to 10, and the depolymerization catalyst includes but is not limited to an alkaline metal compound or an inorganic alkaline compound.

[0026] The recycled polyester of the present invention is obtained from polyester waste through a known impurity removal method. For example, it is first washed with water to remove impurities, then melt-extruded by a twin-screw extruder, and impurities that cannot pass through the metal filter screen are removed through the metal filter screen, and then pelletized.

[0027] Then, the depolymerized oligomers are transferred to a polycondensation kettle, a polycondensation catalyst is added for polycondensation reaction, a sulfonate compound represented by Formula 3 and / or Formula 4 is added, and the polycondensation reaction ends within 10 to 60 minutes after entering a high vacuum to obtain a low-viscosity polymer.

[0028]

[0029] In Formula 3, Y is an alkylene group with 2 to 20 carbon atoms, a phenyl group or an alkylbenzene, X in Formula 3 and Z in Formula 4 are respectively Li ions, Na ions or K ions, and M in Formula 3 and R in Formula 4 are respectively a hydrogen atom, an alkyl group or a hydroxyalkyl group with 2 to 4 carbon atoms.

[0030] Specifically, the sulfonate compounds shown in Formula 3 are preferably sodium 2-carboxybenzenesulfonate, potassium 2-carboxybenzenesulfonate, sodium 3-carboxybenzenesulfonate, lithium 3-carboxybenzenesulfonate, sodium 4-carboxybenzenesulfonate, methyl 2-sulfobenzoate, methyl 3-sulfobenzoate, methyl 4-sulfobenzoate, ethyl 2-sulfobenzoate, ethylene glycol potassium 2-sulfobenzoate, ethyl 3-sulfobenzoate, ethylene glycol sodium 4-sulfobenzoate, ethylene glycol lithium 3-sulfobenzoate, etc., and among them, sodium 3-carboxybenzenesulfonate is more preferred.

[0031] The sulfonate compounds shown in Formula 4 are preferably sodium 5-sulfoisophthalate, dimethyl sodium 5-sulfoisophthalate, diethyl sodium 5-sulfoisophthalate, diethylene glycol sodium 5-sulfoisophthalate, lithium 5-sulfoisophthalate, dimethyl lithium 5-sulfoisophthalate, diethyl lithium 5-sulfoisophthalate, diethylene glycol lithium 5-sulfoisophthalate, etc., and among them, dimethyl sodium 5-sulfoisophthalate or diethylene glycol sodium 5-sulfoisophthalate is more preferred.

[0032] The sulfonate compounds shown in Formula 3 and Formula 4 can be added alone or jointly. Whether used alone or simultaneously, their addition amount in terms of total sulfur element is equivalent to 1000 - 5000 ppm of the final recycled polyester composition. When the addition amount of the sulfate group compound in terms of sulfur element is less than 1000 ppm, it is difficult to achieve a satisfactory color concentration during the subsequent dyeing process of the obtained recycled polyester composition. When the addition amount of the sulfate compound in terms of sulfur element is higher than 5000 ppm, if the sulfonate compound shown in Formula 3 accounts for the vast majority, since the sulfonate compound shown in Formula 3 is connected to the end of the polyester molecular chain after reaction, it will inhibit the growth of the polyester molecular chain. Even if it is extruded at a low viscosity and then subjected to solid-phase polymerization, due to end capping, the required molecular weight cannot be achieved, and a recycled polyester composition with good physical properties cannot be obtained; if the sulfonate compound shown in Formula 4 accounts for the vast majority, since the sulfonate compound shown in Formula 4 is connected to the middle position of the polyester molecular chain, the sulfonate group in the middle of the molecular chain is prone to physical cross-linking. During the solid-phase polymerization reaction stage, the melt viscosity of the polyester composition when reaching the target molecular weight is too high, affecting the physical properties and spinnability of the obtained recycled polyester composition. Considering the dyeability and physical properties of the recycled polyester composition comprehensively, the total addition amount of the sulfonate compound is preferably 1000 - 3500 ppm of the polyester composition in terms of sulfur element.

[0033] There is no particular limitation on adding the polycondensation catalyst at this reaction stage, and it can be a conventional catalyst used in polyester polycondensation reactions in the prior art and production, such as antimony compounds, germanium compounds, titanium compounds, etc. These catalysts can be used in combination or alone.

[0034] As described above, the present invention obtains a recycled polyester composition with good hue and low foreign matter content by shortening the polycondensation reaction time and reducing the thermal decomposition and crosslinking of residual impurities in the recycled polyester. Specifically, the polycondensation reaction ends within 10 to 60 minutes after entering a high vacuum. If the polycondensation reaction ends too early, that is, it ends in less than 10 minutes after entering the high vacuum, the viscosity of the polymerization system is too low to extrude and pelletize; if the polycondensation reaction ends too late, that is, it ends more than 60 minutes after entering the high vacuum, the time of the residual impurities of the recycled polyester in the polymerization system at high temperature is too long, and thermal decomposition and the like will occur, resulting in a poor hue and a high gel rate of the recycled polyester composition.

[0035] The solid-phase polymerization method of the present invention refers to a method in which a low-viscosity polymer is polymerized in a solid state under an inert gas flow or in a vacuum state below the melting point temperature of the low-viscosity polymer. Specifically, the present invention preferably pre-crystallizes the low-viscosity polymer and then performs solid-phase polymerization under the conditions of a reaction temperature of 200 to 240 °C, a reaction pressure of 1000 Pa or less, and a reaction time of 100 hours or less to obtain a recycled polyester composition.

[0036] If the reaction temperature of the solid-phase polymerization is too low, the reaction time required to reach the target molecular weight is too long, which affects the reaction efficiency and increases the production cost; if the reaction temperature of the solid-phase polymerization is too high, this temperature is close to the melting point of the polyester composition, and the thermal decomposition reactions of impurities such as nylon and polyphenylene sulfide and the recycled polyester composition will intensify, thus affecting the hue and gel rate of the final recycled polyester composition. Therefore, the reaction temperature of the solid-phase polymerization is preferably 200 to 240 °C.

[0037] The pressure of the solid-phase polymerization needs to be controlled below a certain value. Otherwise, once the pressure is too high, small molecules are not easily extracted, which will inhibit the further transesterification reaction of the low-viscosity polymer, resulting in an extended solid-phase polymerization time and a poor hue of the obtained recycled polyester composition. The present invention preferably has the pressure of the solid-phase polymerization below 1000 Pa.

[0038] The time of the solid-phase polymerization is preferably within 100 h because too long a time will result in a poor hue and an increased gel rate of the obtained recycled polyester composition.

[0039] In addition, in order to improve the dyeing performance and strength of the recycled polyester composition, the present invention can add an aliphatic dicarboxylic acid or its esterification derivative at any stage before the end of the polycondensation reaction. The aliphatic dicarboxylic acid or its esterification derivative can increase the length of the flexible chain in the molecular chain of the recycled polyester composition, improve the mobility of the molecular chain of the recycled polyester composition, and make it easier for dye molecules to enter the interior of the recycled polyester composition, thereby improving the dyeability of the recycled polyester composition.

[0040] The aliphatic dicarboxylic acid or its esterification derivative refers to an aliphatic dicarboxylic acid or an esterification derivative of the aliphatic dicarboxylic acid. The number of carbon atoms of the aliphatic dicarboxylic acid is preferably 4 to 10. The aliphatic dicarboxylic acid or its esterification derivative can be a straight-chain aliphatic or a branched-chain aliphatic. Specifically, examples include succinic acid, adipic acid, azelaic acid, sebacic acid, 2,2-dimethyladipic acid, etc. Among them, the structural units of succinic acid and sebacic acid are preferred.

[0041] The addition amount of the aliphatic dicarboxylic acid or its esterification derivative is preferably 10.0 wt% or less relative to the total amount of the recycled polyester composition. Because if its addition amount is too high, the heat resistance of the obtained recycled polyester composition becomes poor, and thermal decomposition is likely to occur during subsequent processing, affecting the quality of the product. The addition amount of the aliphatic dicarboxylic acid or its esterification derivative is more preferably 0.5 to 8.0 wt% relative to the polyester composition.

[0042] By controlling the time of the polycondensation reaction in the present invention, the thermal decomposition, crosslinking and other reactions of the residual impurities in the recycled polyester in the reaction system caused by high temperature are reduced, so that the gel rate of the obtained recycled polyester composition is below 20%. In a preferred technical solution, the gel rate can further reach below 10%. At the same time, the recycled polyester composition has the advantages of easy dyeing, good hydrolysis resistance, less by-products of diethylene glycol and terminal carboxyl groups, and good strength retention rate after dyeing, and can be applied in fibers.

[0043] The measurement methods and evaluation methods for the various indexes of the present invention are as follows:

[0044] (1) Intrinsic viscosity (IV)

[0045] Dissolve 0.8 g of the polyester composition chips in 10 ml of o-chlorophenol solution, and use an Ubbelohde viscometer to measure its intrinsic viscosity at a water bath temperature of 25 ± 0.2 °C (take the average value after testing 5 times).

[0046] (2) Sulfur element content in the polyester composition

[0047] Quantitatively analyze the sulfur element content in the polyester composition by a SEM-EDX elemental analyzer (take the average value after testing 5 times).

[0048] (3) Hue of the polyester composition

[0049] Use a colorimeter (SUGA test machine, SM color computer type SM-T45) for testing. Test the b value in the Hunter values (take the average value after testing 5 times). The larger the b value, the worse the hue of the polyester composition.

[0050] (4) Filter pressure difference ΔPa

[0051] The test was carried out using a small filtration test machine for filter pressure testing. Under certain discharge conditions, polyester was passed through a filter screen with a pore size of 5 μm. The test temperature was the melting point of polyester + 25 °C, the discharge amount was 10 g / min. The pressure in front of the filter screen 30 min after starting the feeding was recorded as the initial pressure Pa1, and the final pressure Pa2 was recorded 6 h after starting from the initial pressure. Then the filter pressure rise value in 6 h was ΔPa = Pa2 - Pa1 (the average value was taken after 5 tests). The smaller ΔPa is, the fewer foreign substances in the polyester composition and the more stable the spinning is.

[0052] (5) Gel fraction

[0053] The polyester composition was ground into powder, 0.5 g of the powder was weighed and heat-treated at 300 °C under a mixed gas of nitrogen and oxygen for 6 h, then dissolved using hexafluoroisopropanol and filtered through a metal filter screen with 800 meshes. The ratio of the filtered amount to the original mass of 0.5 g was the gel fraction (the average value was taken after 5 tests).

[0054] (6) L value

[0055] The polyester composition was spun into drawn yarn, then the obtained drawn fibers were doubled with 2 fibers, and a stocking tube was made under the condition of 22 needle pitches. This stocking tube was dyed in a hot water bath at 130 °C with dye (Blue.TR) 3% owf, acetic acid 0.5 ml / l, sodium acetate 0.2 g / l, and bath ratio 1:100 for 60 min. The strength of the fiber before dyeing was S1, and the strength of the fiber after dyeing was S2. The strength retention rate was S2 / S1. After the dyed samples were overlapped into an opaque state, colorimetry was carried out using a spectrocolorimeter (Datacolor 650 manufactured by Datacolor AsiaPacific (H.K.) Ltd.) under the conditions of CEI standard light source D65 and 10° angle to obtain L* (the average value was taken after 5 tests).

[0056] (7) Strength-elongation product of fiber

[0057] The strength and elongation were calculated with reference to the standard of JIS L1013:2010 (Test methods for staple fibers of chemical fibers) 8.8.1. The strength and elongation were measured by an ORIENTEC Co., RTC-1225A strength-elongation tester. The strength-elongation product = strength × (elongation) 0.5 (The average value was taken after 5 tests).

[0058] The advantages of the present invention will be described in detail below with reference to the listed examples and comparative examples. The present invention is not limited to the following examples.

[0059] Example 1

[0060] Recycled polyester and ethylene glycol were added to a reaction vessel with a molar ratio of 1:1.5 between them. At the same time, tetramethylammonium hydroxide was added for depolymerization. The stirrer was started, and the temperature was raised from room temperature to 200 °C over 60 minutes and reacted for 4 hours. After the time elapsed, the reaction was terminated, and cooling and discharging were started to obtain a bis(hydroxyethyl) phthalate oligomer. Then, the bis(hydroxyethyl) phthalate oligomer was put into an esterification kettle, heated and melted at 200 °C, and then a heat stabilizer trimethyl phosphate, a catalyst antimony trioxide, a sulfonate compound sodium 3-hydroxybenzenesulfonate, and an additive titanium dioxide were added. Then, it was transferred to a polymerization kettle for polycondensation reaction at 290 °C. After the polymerization reaction entered a high vacuum for 30 minutes, discharging and pelletizing were carried out to obtain a low-viscosity polymer.

[0061] After the low-viscosity polymer was subjected to pre-crystallization treatment, solid-phase polymerization was carried out at a reaction temperature of 230 °C and a reaction pressure of 50 Pa for 30 hours to obtain a recycled polyester composition with an intrinsic viscosity IV of 0.65 dl / g. The specific physical properties are shown in Table 1.

[0062] Examples 2 to 23

[0063] The preparation method was the same as that in Example 1, and the specific conditions and physical properties are shown in Tables 1 to 3.

[0064] Comparative Example 1

[0065] Recycled polyester and ethylene glycol were added to a reaction vessel with a molar ratio of 1:1.5 between them. At the same time, tetramethylammonium hydroxide was added for depolymerization. The stirrer was started, and the temperature was raised from room temperature to 200 °C over 60 minutes and reacted for 4 hours. After the time elapsed, the reaction was terminated, and cooling and discharging were started to obtain a bis(hydroxyethyl) phthalate oligomer. Then, the bis(hydroxyethyl) phthalate oligomer was put into an esterification kettle, heated and melted at 200 °C, and then a heat stabilizer trimethyl phosphate, a catalyst antimony trioxide, a sulfonate compound sodium 3-hydroxybenzenesulfonate, and an additive titanium dioxide were added. Then, it was transferred to a polymerization kettle for polycondensation reaction at 290 °C. After the polymerization reaction entered a high vacuum for 150 minutes, discharging and pelletizing were carried out to obtain a recycled polyester composition with an intrinsic viscosity IV of 0.65 dl / g. The specific physical properties are shown in Table 4.

[0066] Due to the too long high-temperature polycondensation reaction time, impurities such as nylon / polyphenylene sulfide, thermal decomposition of polyester, and crosslinking of polyester occurred, resulting in a higher b value of the hue and gel fraction of the obtained recycled polyester composition, and a rapid increase in the filtration pressure during spinning.

[0067] Comparative Example 2

[0068] Recycled polyester and ethylene glycol were added to a reaction vessel at a molar ratio of 1:1.5, and tetramethylammonium hydroxide was added simultaneously for depolymerization. The stirrer was started, and the temperature was raised from room temperature to 200 °C over 60 minutes and reacted for 4 hours. After the time reached, the reaction was terminated, and cooling and discharging were started to obtain a bis(hydroxyethyl) phthalate oligomer. Then, the bis(hydroxyethyl) phthalate oligomer was put into an esterification kettle, heated and melted at 200 °C, and then a heat stabilizer trimethyl phosphate, a catalyst antimony trioxide, a sulfonate compound sodium 3-hydroxybenzenesulfonate, and an additive titanium dioxide were added, and then transferred to a polymerization kettle for polycondensation reaction at 290 °C. After the polycondensation reaction entered a high vacuum, discharging and pelletizing were carried out after 90 minutes to obtain a polymer. Then, the polymer was subjected to solid-phase polymerization to obtain a recycled polyester composition with an intrinsic viscosity IV of 0.65 dl / g. The specific physical properties are shown in Table 4.

[0069] Compared with Comparative Example 1, although the polycondensation reaction time was slightly shortened, it still caused impurities such as nylon / polyphenylene sulfide, thermal decomposition of polyester, and crosslinking of polyester. The obtained recycled polyester composition had a high b value of hue and gel fraction, and poor spinnability.

[0070] Comparative Examples 3-4

[0071] The addition amount of sodium 3-hydroxybenzenesulfonate was changed, and other conditions were the same as in Example 1 to prepare a recycled cationic dyeable polyester composition. The specific physical properties are shown in Table 4.

[0072] In Comparative Example 3, the addition amount of sodium 3-hydroxybenzenesulfonate was too low, resulting in poor dyeability of the obtained recycled polyester composition and inability to dye the required hue. In Comparative Example 4, the addition amount of sodium 3-hydroxybenzenesulfonate was too high. The molecular chains capped with sodium 3-hydroxybenzenesulfonate in the low-viscosity polymer obtained after polycondensation, even after solid-phase polymerization, the obtained polyester composition had a small molecular weight, poor physical properties, and low strength of the yarn.

[0073] Comparative Examples 5-6

[0074] The addition amount of sodium 5-sulfoisophthalate was changed, and other conditions were the same as in Example 1 to prepare a recycled cationic dyeable polyester composition. The specific physical properties are shown in Table 4.

[0075] In Comparative Example 5, the addition amount of sodium 5-sulfoisophthalate was too low, resulting in poor dyeability of the obtained recycled polyester composition and inability to dye the required hue. In Comparative Example 6, the addition amount of sodium 5-sulfoisophthalate was too high. At the polycondensation reaction stage, the molecular weight of the low-viscosity polyester with the same melt viscosity was low, and the strength of the final yarn was low.

[0076] Comparative Examples 7-8

[0077] Change the total addition amount of sodium 3 - hydroxybenzenesulfonate and sodium isophthalate - 5 - sulfonate, and prepare the regenerated cation - dyeable polyester composition under the same other conditions as in Example 1. The specific physical properties are shown in Table 4.

[0078] In Comparative Example 7, the total addition amount of sodium 3 - hydroxybenzenesulfonate and sodium isophthalate - 5 - sulfonate is too low, resulting in poor dyeability of the obtained regenerated polyester composition and unable to dye the required hue. In Comparative Example 8, the total addition amount of sodium 3 - hydroxybenzenesulfonate and sodium isophthalate - 5 - sulfonate is too high. Under the condition of the same molecular weight, the melt viscosity of the polyester is too large, the physical properties and spinnability are poor, and the strength of the yarn is low.

[0079]

[0080]

[0081]

[0082]

Claims

1. A regenerated cation-dyeable polyester composition mainly composed of aromatic dicarboxylic acid structural units and aliphatic diol structural units, Characterized in that: The molecular chain of the polyester composition contains sulfonate groups shown in Formula 1 and / or Formula 2, and the total content of the sulfonate groups accounts for 1000 - 5000 ppm of the total amount of the polyester composition in terms of sulfur element; the gel fraction of the polyester composition is below 20%; In Formula 1, Y is an alkylene group with 2 - 20 carbon atoms, a phenyl group or an alkylbenzene, and X and Z are respectively Li ion, Na ion or K ion.

2. The regenerated cation-dyeable polyester composition according to Claim 1, Characterized in that: The content of the sulfonate groups accounts for 1000 - 3500 ppm of the total amount of the polyester composition in terms of sulfur element.

3. The regenerated cation-dyeable polyester composition according to Claim 1 or 2, Characterized in that: The gel fraction of the polymer is below 10%.

4. A preparation method of the regenerated cation-dyeable polyester composition according to Claim 1. First, an aliphatic diol is added to the recycled polyester for depolymerization to obtain an oligomer, and then the oligomer is subjected to a polycondensation reaction. Characterized in that: A sulfonate compound shown in Formula 3 and / or 4 is added at any stage before the end of the polycondensation reaction. The addition amount of the sulfonate compound is 1000 - 5000 ppm of the total amount of the polyester composition in terms of sulfur element; the polycondensation reaction ends within 10 - 60 minutes after entering a high vacuum to obtain a low-viscosity polymer, and then the low-viscosity polymer is subjected to solid-phase polymerization to obtain the polyester composition. In Formula 3, Y is an alkylene group with 2 - 20 carbon atoms, a phenyl group or an alkylbenzene. X in Formula 3 and Z in Formula 4 are respectively Li ion, Na ion or K ion. M in Formula 3 and R in Formula 4 are respectively a hydrogen atom, an alkyl group or a hydroxyalkyl group with 2 - 4 carbon atoms.

5. The preparation method of the regenerated cation-dyeable polyester composition according to Claim 4, Characterized in that: The addition amount of the sulfonate compound is 1000 - 3500 ppm of the total amount of the polyester composition in terms of sulfur element.

6. The preparation method of the regenerated cation-dyeable polyester composition according to Claim 4 or 5, Characterized in that: The reaction temperature of the solid-phase polymerization is 200 - 240 °C, the reaction pressure is below 1000 Pa, and the reaction time is below 100 hours.

7. Application of the regenerated cation-dyeable polyester composition according to Claim 1 in fibers.

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