Polyester yarn for industrial sewing thread and preparing method thereof

Abstract

A type of polyester yarn for an industrial sewing thread and preparing method thereof are provided. The preparing method is composed of a viscosity enhancing by a solid state polycondensation and a melt spinning for a modified polyester, and the modified polyester is a product of esterification and polycondensation of evenly mixed terephthalic acid, ethylene glycol, tert-butyl branched dicarboxylic acid, trimethylsilyl branched diol and a doped Sb.sub.2O.sub.3 powder, wherein the tert-butyl branched dicarboxylic acid is selected from the group consisting of 5-tert-butyl-1,3-benzoic acid, 2-tert-butyl-1,6-hexanedioic acid, 3-tert-butyl-1,6-hexanedioic acid and 2,5-di-tert-butyl-1,6-hexanedioic acid. Moreover, the modified polyester is dispersed with a doped ZrO.sub.2 powder. An obtained fiber has an intrinsic viscosity drop of 23-28% when stored at 25° C. and R.H. 65% for 60 months.

Claims

1. A preparing method for a polyester yarn for an industrial sewing thread, comprising: manufacturing a filament from a modified polyester through a series of processes composed of viscosity enhancing by a solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the modified polyester is a product of an esterification and a polycondensation of evenly mixed terephthalic acid, ethylene glycol, a tert-butyl branched dicarboxylic acid, a trimethylsilyl branched diol and a doped Sb.sub.2O.sub.3 powder; wherein the tert-butyl branched dicarboxylic acid is selected from the group consisting of 5-tert-butyl-1,3-benzoic acid, 2-tert-butyl-1,6-hexanedioic acid, 3-tert-butyl-1,6-hexanedioic acid and 2,5-di-tert-butyl-1,6-hexanedioic acid, and wherein the trimethylsilyl branched diol has a molecular formula of: ##STR00004## wherein R stands for —CH.sub.2—, —CH(CH.sub.3)— or —C((CH.sub.3).sub.2)—; wherein the doped Sb.sub.2O.sub.3 powder is obtained through a process of evenly mixing an M.sup.x+solution and an Sb.sup.3+ solution at first, then dripping in a precipitant until a pH value of 9-10, and finally calcining a precipitate; wherein M.sup.x+ is more than one ion selected from Mg.sup.2+, Ca.sup.2+, Ba.sup.2+ and Zn.sup.2+.

2. The preparing method of claim 1, wherein the trimethylsilyl branched diol is synthesized by the steps of: (1) mixing raw material alkene, peracetic acid and dichloromethane in a molar ratio of 1:5-10:10-15 and carrying out a first reaction by stirring at 35-40° C. for 5-8 hours, after the first reaction, removing a solvent, and purifying and refining a product to obtain trimethylsilyl propylene epoxide; (2) mixing water, concentrated sulfuric acid and the trimethylsilyl propylene epoxide to obtain a first mixture, then heating the first mixture to 80-85° C. in water bath under a stirring condition and holding a temperature to carry out a second reaction for 10-15 minutes to obtain a second mixture, after the second reaction, cooling the second mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol, wherein the concentrated sulfuric acid has a mass concentration of 70%, and at a beginning of the second reaction, a molar ratio of the trimethylsilyl propylene epoxide to the water is 1:20-40, whereas the concentrated sulfuric acid usage is 0.1-0.15 wt % of the first mixture; wherein if the R in the molecular formula of the trimethylsilyl branched diol stands for —CH(CH.sub.3)— or —C((CH.sub.3).sub.2)—, accordingly the raw material alkene is 3-trimethylsilyl-3-methylpropene or 3-trimethylsilyl-3,3-dimethylpropene, respectively; wherein the 2-tert-butyl-1,6-hexanedioic acid, the 3-tert-butyl-1,6-hexanedioic acid and the 2,5-di-tert-butyl-1,6-hexanedioic acid are synthesized by means of: mixing tungstic acid and hydrogen peroxide to obtain a third mixture and stirring the third mixture at room temperature for 10-15 minutes, then adding in a raw material alcohol to carrying out a third reaction in a reflux state at 80-85° C. for 1-2 hours at first and next at 90-95° C. for 2-3 hours, after the third reaction cooling, crystallizing, washing and refining to obtain the tert-butyl branched dicarboxylic acid, wherein a molar ratio of the tungstic acid, the raw material alcohol and the hydrogen peroxide is 1:30-40:120-150; wherein the product is the 2-tert-butyl-1,6-hexanedioic acid, the 3-tert-butyl-1,6-hexanedioic acid and the 2,5-di-tert-butyl-1,6-hexanedioic acid, accordingly the raw material alcohol is 2-tert-butylcyclohexyl alcohol, 4-tert-butylcyclohexyl alcohol or 2,4-di-tert-butylcyclohexyl alcohol.

3. The preparing method of claim 2, wherein the M.sup.x+ solution is an aqueous solution with a concentration of 0.5-1.0 mol % and an anion is NO.sub.3.sup.−; wherein the Sb.sup.3+ solution is a product of dissolving 5-10 mol % of Sb.sub.2O.sub.3 in oxalic acid; wherein the precipitant is ammonia water with a concentration of 2 mol/L; wherein a molar ratio of M.sup.x+ to Sb.sup.3+ is 1-3:100 in a blending solution before a coprecipitation; wherein the calcining is preceded by a washing process and a drying process for the precipitate, and the drying process is carried out at a temperature of 105-110° C. for 2-3 hours; wherein the calcining comprises the steps of a 400° C. heating for 2-3 hours, a 900° C. heating for 1-2 hours, a cooling in air, and a grinding to obtain the doped Sb.sub.2O.sub.3 powder with an average particle size less than 0.5 micron.

4. The preparing method of claim 3, wherein the modified polyester is manufactured through the following steps: (1) the esterification, concocting the terephthalic acid, the ethylene glycol, the tert-butyl branched dicarboxylic acid and the trimethylsilyl branched diol into a slurry, then adding in the doped Sb.sub.2O.sub.3 powder, a matting agent and a stabilizer and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.1 MPa-0.3 MPa at 250-260° C., finally ending the esterification when a water distillation reaching more than 90% of a theoretical value; (2) the polycondensation, for esterification products, smoothly reducing the pressure to less than 500 Pa (absolute value) within 30-50 minutes and carrying out a third reaction at 250-260° C. for 30-50 min, successively, further reducing the pressure to less than 100 Pa (absolute value) and continuing the third reaction at 270-282° C. for 50-90 minutes.

5. The preparing method of claim 4, wherein a molar ratio of the terephthalic acid, the ethylene glycol, the tert-butyl branched dicarboxylic acid and the trimethylsilyl branched diol is 1:1.2-2.0:0.02-0.03:0.01-0.02, and an addition of the doped Sb.sub.2O.sub.3 powder, the matting agent and the stabilizer are 0.012-0.015 wt %, 0.20-0.25 wt % and 0.01-0.05 wt % of an amount of the terephthalic acid, respectively.

6. The preparing method of claim 5, wherein the matting agent is titanium dioxide, and the stabilizer is selected from the group consisting of triphenyl phosphate, trimethyl phosphate and trimethyl phosphite.

7. The preparing method claim 1, wherein the solid state polycondensation is performed to further increase a molecular weight of the modified polyester until an intrinsic viscosity of the modified polyester reaches 1.0-1.2 dL/g.

8. The preparing method of claim 1, wherein a spinning process involves technological parameters of 290-320° C. for an extruder temperature, 295-300° C. for a spin head temperature, 140_bar for a spin head pressure, 22° C. for a cross air temperature, 80±5% for a cross air humidity, 0.5-0.7 m/s for a cross air blow speed, and 2600-3600 m/min for a winding speed; and wherein the stretching and the heat setting processes involve technological parameters of 440-650 m/min for a roller 1 speed, 80±5° C. for a roller 1 temperature, 460-680 m/min for a roller 2 speed, 90-100° C. for a roller 2 temperature, 1900-2400 m/min for a roller 3 speed, 125-140° C. for a roller 3 temperature, 2700-3600 m/min for a roller 4 speed, 220-250° C. for a roller 4 temperature, 2500-3600 m/min for a roller 5 speed, and 150-170° C. for a roller 5 temperature.

9. A polyester yarn for an industrial sewing thread prepared by the preparing method of claim 1, comprising a type of a modified polyester filament; wherein the modified polyester has a molecular chain structure composed of terephthalic acid segments, ethylene glycol segments, tert-butyl branched dicarboxylic acid segments and trimethylsilyl branched diol segments; and wherein the modified polyester is further dispersed with the doped Sb.sub.2O.sub.3 powder.

10. The polyester yarn of claim 9, wherein the polyester yarn comprises performance indices of a monofilament fineness of 2-3 dtex, a multifilament fineness of 150-300 dtex, a breaking strength ≥8.0 cN/dtex, a deviation rate of a linear density of ±1.5%, a breaking strength CV value of ≤3.0%, an elongation at break of 13.0-16.5%, an elongation at break CV value of ≤8.0%, an elongation at a 4.0 cN/dtex load of 5.5-7.0%, a dry heat shrinkage of 6.8-9.2% under 177° C.×10 min×0.05 cN/dtex, an interlacing degree of (5-8)±2/m, an oil content of 0.6±0.2 wt %, as well as a dye uptake of 88.9-91.2% and a K/S value of 24.07-26.12 when dyed at 130° C.

11. The polyester yarn of claim 9, wherein the trimethylsilyl branched diol is synthesized by the steps of: (1) mixing raw material alkene, peracetic acid and dichloromethane in a molar ratio of 1:5-10:10-15 and carrying out a first reaction by stirring at 35-40° C. for 5-8 hours, after the first reaction, removing a solvent, and purifying and refining a product to obtain trimethylsilyl propylene epoxide; (2) mixing water, concentrated sulfuric acid and the trimethylsilyl propylene epoxide to obtain a first mixture, then heating the first mixture to 80-85° C. in water bath under a stirring condition and holding a temperature to carry out a second reaction for 10-15 minutes to obtain a second mixture, after the second reaction, cooling the second mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol, wherein the concentrated sulfuric acid has a mass concentration of 70%, and at a beginning of the second reaction, a molar ratio of the trimethylsilyl propylene epoxide to the water is 1:20-40, whereas the concentrated sulfuric acid usage is 0.1-0.15 wt % of the first mixture; wherein if the R in the molecular formula of the trimethylsilyl branched diol stands for —CH(CH.sub.3)— or —C((CH.sub.3).sub.2)—, accordingly the raw material alkene is 3-trimethylsilyl-3-methylpropene or 3-trimethylsilyl-3,3-dimethylpropene, respectively.

12. The polyester yarn of claim 11, wherein the M.sup.x+ solution is an aqueous solution with a concentration of 0.5-1.0 mol % and an anion is NO.sub.3.sup.−; wherein the Sb.sup.3+ solution is a product of dissolving 5-10 mol % of Sb.sub.2O.sub.3 in oxalic acid; wherein the precipitant is ammonia water with a concentration of 2 mol/L; wherein a molar ratio of M.sup.x+ to Sb.sup.3+ is 1-3:100 in a blending solution before a coprecipitation; wherein the calcining is preceded by a washing process and a drying process for the precipitate, and the drying process is carried out at a temperature of 105-110° C. for 2-3 hours; wherein the calcining comprises the steps of a 400° C. heating for 2-3 hours, a 900° C. heating for 1-2 hours, a cooling in air, and a grinding to obtain the doped Sb.sub.2O.sub.3 powder with an average particle size less than 0.5 micron.

13. The polyester yarn of claim 12, wherein the modified polyester is manufactured through the following steps: (1) the esterification, concocting the terephthalic acid, the ethylene glycol, the tert-butyl branched dicarboxylic acid and the trimethylsilyl branched diol into a slurry, then adding in the doped Sb.sub.2O.sub.3 powder, a matting agent and a stabilizer and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.1 MPa-0.3 MPa at 250-260° C., finally ending the esterification when a water distillation reaching more than 90% of a theoretical value; (2) the polycondensation, for esterification products, smoothly reducing the pressure to less than 500 Pa (absolute value) within 30-50 minutes and carrying out a third reaction at 250-260° C. for 30-50 min, successively, further reducing the pressure to less than 100 Pa (absolute value) and continuing the third reaction at 270-282° C. for 50-90 minutes.

14. The polyester yarn of claim 13, wherein a molar ratio of the terephthalic acid, the ethylene glycol, the tert-butyl branched dicarboxylic acid and the trimethylsilyl branched diol is 1:1.2-2.0:0.02-0.03:0.01-0.02, and an addition of the doped Sb.sub.2O.sub.3 powder, the matting agent and the stabilizer are 0.012-0.015 wt %, 0.20-0.25 wt % and 0.01-0.05 wt % of an amount of the terephthalic acid, respectively.

15. The polyester yarn of claim 14, wherein the matting agent is titanium dioxide, and the stabilizer is selected from the group consisting of triphenyl phosphate, trimethyl phosphate and trimethyl phosphite.

16. The polyester yarn of claim 9, wherein the solid state polycondensation is performed to further increase a molecular weight of the modified polyester until an intrinsic viscosity of the modified polyester reaches 1.0-1.2 dL/g.

17. The polyester yarn of claim 9, wherein a spinning process involves technological parameters of 290-320° C. for an extruder temperature, 295-300° C. for a spin head temperature, 140 bar for a spin head pressure, 22° C. for a cross air temperature, 80±5% for a cross air humidity, 0.5-0.7 m/s for a cross air blow speed, and 2600-3600 m/min for a winding speed; and wherein the stretching and the heat setting processes involve technological parameters of 440-650 m/min for a roller 1 speed, 80±5° C. for a roller 1 temperature, 460-680 m/min for a roller 2 speed, 90-100° C. for a roller 2 temperature, 1900-2400 m/min for a roller 3 speed, 125-140° C. for a roller 3 temperature, 2700-3600 m/min for a roller 4 speed, 220-250° C. for a roller 4 temperature, 2500-3600 m/min for a roller 5 speed, and 150-170° C. for a roller 5 temperature.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Based on above mentioned method, the following embodiments are carried out for further demonstration in the present invention. It is to be understood that these embodiments are only intended to illustrate the invention and are not intended to limit the scope of the invention. In addition, it should be understood that after reading the contents described in the present invention, those technical personnel in this field can make various changes or modifications to the invention, and these equivalent forms also fall within the scope of the claims attached to the application.

Example 1

(2) A method for preparing the polyester yarn for industrial sewing thread, comprising the steps:

(3) (1) Preparation of modified polyester

(4) (1.1) Doping modification of Sb.sub.2O.sub.3

(5) (a) evenly mixing the 1.8 mol % of Mg(NO.sub.3).sub.2 aqueous solution and the 8 mol % of Sb.sub.2O.sub.3 oxalic acid solution in a molar ratio 2:100 of Mg.sup.2+ to Sb.sup.3+;

(6) (b) depositing the mixed solution by dripping in 2 mol/L of ammonia water till pH=9, then washing and drying (at 105° C. for 2.5 hr) the precipitate;

(7) (c) after the treatments including a heating at 400° C. for 2.5 hr, a heating at 900° C. for 1.5 hr and a cooling in air, finally grinding the precipitate to obtain the doped Sb.sub.3 powder with an average particle size of 0.4 micron;

(8) (1.2) Esterification

(9) concocting terephthalic acid, ethylene glycol, 5-tert-butyl-1,3-benzoic acid and 3-trimethylsilyl-1,2-propanediol into a slurry, then adding in the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.3 MPa at 260° C., finally ending the reaction when the water distillation reaching more than 92% of the theoretical value, wherein the molar ration of terephthalic acid, ethylene glycol, 5-tert-butyl-1,3-benzoic acid and 3-trimethylsilyl-1,2-propanediol is 1:1.2:0.02:0.014, whereas the addition of the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite are 0.015 wt %, 0.20 wt % and 0.04 wt % of terephthalic acid, respectively;

(10) (1.3) Polycondensation

(11) for the esterification products, smoothly reducing the pressure to 400 Pa (absolute value) within 40 min and carrying out reaction at 250° C. for 40 min, successively, further reducing the pressure to 80 Pa (absolute value) and continuing the reaction at 272° C. for 65 min;

(12) (2) Spinning of polyester yarn for industrial sewing thread converting the modified polyester into polyester yarn for industrial sewing thread through a series of processes composed of viscosity enhancing by solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the intrinsic viscosity of the modified polyester after the solid state polycondensation is 1.0 dL/g;

(13) wherein the spinning process involves the technological parameters of 290° C. for the extruder temperature, 295° C. for the spin head temperature, 140 bar for the spin head pressure, 22° C. for the cross air temperature, 82% for the cross air humidity, 0.7 m/s for the cross air blow speed, 2600 m/min for the winding speed;

(14) wherein the stretching and the heat setting processes involve the technological parameters of 440 m/min for the roller 1 speed, 75° C. for the roller 1 temperature, 520 m/min for the roller 2 speed, 90° C. for the roller 2 temperature, 2400 m/min for the roller 3 speed, 130° C. for the roller 3 temperature, 2800 m/min for the roller 4 speed, 250° C. for the roller 4 temperature, 2500 m/min for the roller 5 speed, 155° C. for the roller 5 temperature.

(15) Finally obtained degradable polyester fiber has the following performance indices of monofilament fineness 2 dtex, multifilament fineness 150 dtex, breaking strength 8.0 cN/dtex, deviation rate of linear density −0.6%, breaking strength CV value 2.8%, elongation at break 14.05%, elongation at break CV value 8.0%, elongation at 4.0 cN/dtex load 7.0%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 7.6%, interlacing degree 5/m, oil content 0.4 wt %, as well as a dye uptake of 89.17% and a K/S value of 26.12 when dyed at 130° C.

(16) Comparison 1

(17) A method for preparing the polyester yarn for industrial sewing thread involved steps basically the same as those in Example 1, except for no addition of 5-tert-butyl-1,3-benzoic acid, 3-trimethylsilyl-1,2-propanediol and the doped Sb.sub.2O.sub.3, i.e., no modification for the polyester, from which the finally obtained polyester fiber has the following performance indices of monofilament fineness 2 dtex, multifilament fineness 150 dtex, breaking strength 8.1 cN/dtex, deviation rate of linear density −0.6%, breaking strength CV value 2.8%, elongation at break 13.75%, elongation at break CV value 8.0%, elongation at 4.0 cN/dtex load 7.0%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 7.6%, interlacing degree 5/m, oil content 0.4 wt %, as well as a dye uptake of 86.36% and a K/S value of 22.68 when dyed at 130° C.

(18) From results of Example 1 and Comparison 1, it can be found that the introducing of 5-tert-butyl-1,3-benzoic acid and 3-trimethylsilyl-1,2-propanediol can enlarge the void free volume of the polyester so as to promote the penetration of dye molecules into inner fiber and increase the dye uptake, moreover, the addition of the doped Sb.sub.2O.sub.3 can reduce the usage of polymerization catalyst so as to realize the environmental protection production while ensuring the high quality of final fiber.

(19) Comparison 2

(20) A method for preparing the degradable polyester fiber involved steps basically the same as those in Example 1, except for adopting 1,2-dodecyl glycol instead of 3-trimethylsilyl-1,2-propanediol and 5-tert-butyl-1,3-benzoic acid in step (1), from which the finally obtained polyester fiber has the following performance indices of monofilament fineness 2 dtex, multifilament fineness 150 dtex, breaking strength 8.2 cN/dtex, deviation rate of linear density −0.6%, breaking strength CV value 2.8%, elongation at break 13.53%, elongation at break CV value 8.0%, elongation at 4.0 cN/dtex load 7.0%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 7.6%, interlacing degree 5/m, oil content 0.4 wt %, as well as a dye uptake of 86.45% and a K/S value of 22.87 when dyed at 130° C.

(21) From results of Example 1 and Comparison 1, it can be found that the utilization of 3-trimethylsilyl-1,2-propanediol and 5-tert-butyl-1,3-benzoic acid will be more effective in improving the mechanical properties such as elongation intensity of the polyester fiber than 1,2-dodecyl glycol, and the reason at first is that 3-trimethylsilyl-1,2-propanediol and 5-tert-butyl-1,3-benzoic acid are mainly conducive to enlarge the void free volume whereas the 1,2-dodecyl glycol is mainly contribute to the slit free volume, on the other hand, the tert-butyl groups in 3-trimethylsilyl-1,2-propanediol and 5-tert-butyl-1,3-benzoic acid possess a higher rigidity prior to the long alkyl chains so as to seldom cause the entanglement of polymer chains, therefore, 3-trimethylsilyl-1,2-propanediol and 5-tert-butyl-1,3-benzoic acid can gain much more free volume in the polyester, which is favorable to the penetration of dye into the fiber so as to improve the dye uptake while reducing the dyeing temperature, shortening the dyeing time, reducing energy consumption.

Example 2

(22) A method for preparing the polyester yarn for industrial sewing thread, comprising the steps:

(23) (1) Preparation of modified polyester

(24) (1.1) Synthesis of 3-trimethylsilyl-3-methyl-1,2-propanediol

(25) (a) mixing 3-trimethylsilyl-3-methylpropene, peracetic acid and dichloromethane in the molar ratio of 1:5:10 and carrying out the reaction with stirring at 35° C. for 5 hr, after the reaction removing the solvent, and purifying and refining the product to obtain trimethylsilyl propylene epoxide;

(26) (b) mixing water, concentrated sulfuric acid and trimethylsilyl propylene epoxide, then heating the mixture to 80° C. in water bath under stirring condition and holding the temperature to carry out the reaction for 10 min, after the reaction cooling the mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol (R=—CH(CH.sub.3)— in Formula (I)), wherein the concentrated sulfuric acid was one with mass concentration of 70%, and at the beginning of reaction the molar ratio of trimethylsilyl propylene epoxide to water is 1:20 whereas the sulfuric acid usage is 0.1 wt % of the total mixture.

(27) ##STR00003##

(28) (1.2) Synthesis of 2-tert-butyl-1,6-hexanedioic acid

(29) mixing tungstic acid and hydrogen peroxide and stirring the mixture at room temperature for 10 min, then adding in 2-tert-butyl cyclohexanol to carrying out the reaction in reflux state at 80° C. for 1 hr at first and next at 94° C. for 2 hr, after the reaction cooling, crystallizing, washing and refining to obtain the tert-butyl branched dicarboxylic acid, wherein the molar ratio of tungstic acid, 2-tert-butyl cyclohexanol and hydrogen peroxide is 1:35:120.

(30) (1.3) Doping modification of Sb.sub.2O.sub.3

(31) (1.3.1) evenly mixing the 0.5 mol % of Ca(NO.sub.3).sub.2 aqueous solution and the 5 mol % of Sb.sub.2O.sub.3 oxalic acid solution in a molar ratio 1:100 of Ca.sup.2+ to Sb.sup.3+;

(32) (1.3.2) depositing the mixed solution by dripping in 2 mol/L of ammonia water till pH=10, then washing and drying (at 110° C. for 2 hr) the precipitate;

(33) (1.3.3) after the treatments including a heating at 400° C. for 2 hr, a heating at 900° C. for 1 hr and a cooling in air, finally grinding the precipitate to obtain the doped Sb.sub.3 powder with an average particle size of 0.4 micron;

(34) (1.4) Esterification

(35) concocting terephthalic acid, ethylene glycol, 2-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3-methyl-1,2-propanediol into a slurry, then adding in the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.3 MPa at 260° C., finally ending the reaction when the water distillation reaching more than 92% of the theoretical value, wherein the molar ration of terephthalic acid, ethylene glycol, 2-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3-methyl-1,2-propanediol is 1:1.2:0.03:0.01, whereas the addition of the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite are 0.0135 wt %, 0.25 wt % and 0.01 wt % of terephthalic acid, respectively;

(36) (1.5) Polycondensation

(37) for the esterification products, smoothly reducing the pressure to 400 Pa (absolute value) within 40 min and carrying out reaction at 250° C. for 40 min, successively, further reducing the pressure to 80 Pa (absolute value) and continuing the reaction at 270° C. for 50 min;

(38) (2) Spinning of polyester yarn for industrial sewing thread

(39) converting the modified polyester into polyester yarn for industrial sewing thread through a series of processes composed of viscosity enhancing by solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the intrinsic viscosity of the modified polyester after the solid state polycondensation is 1.1 dL/g;

(40) wherein the spinning process involves the technological parameters of 290° C. for the extruder temperature, 300° C. for the spin head temperature, 140 bar for the spin head pressure, 22° C. for the cross air temperature, 75% for the cross air humidity, 0.6 m/s for the cross air blow speed, 2900 m/min for the winding speed;

(41) wherein the stretching and the heat setting processes involve the technological parameters of 650 m/min for the roller 1 speed, 80° C. for the roller 1 temperature, 460 m/min for the roller 2 speed, 100° C. for the roller 2 temperature, 2000 m/min for the roller 3 speed, 125° C. for the roller 3 temperature, 3000 m/min for the roller 4 speed, 230° C. for the roller 4 temperature, 3600 m/min for the roller 5 speed, 160° C. for the roller 5 temperature.

(42) Finally obtained degradable polyester fiber has the following performance indices of monofilament fineness 2 dtex, multifilament fineness 300 dtex, breaking strength 8.3 cN/dtex, deviation rate of linear density −1.5%, breaking strength CV value 2.8%, elongation at break 13.0%, elongation at break CV value 7.9%, elongation at 4.0 cN/dtex load 6.5%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 7.7%, interlacing degree 3/m, oil content 0.6 wt %, as well as a dye uptake of 88.8% and a K/S value of 25.32 when dyed at 130° C.

Example 3

(43) A method for preparing the polyester yarn for industrial sewing thread, comprising the steps:

(44) (1) Preparation of modified polyester

(45) (1.1) Synthesis of 3-trimethylsilyl-3-methyl-1,2-propanediol

(46) (a) mixing 3-trimethylsilyl-3-methylpropene, peracetic acid and dichloromethane in the molar ratio of 1:10:15 and carrying out the reaction with stirring at 40° C. for 8 hr, after the reaction removing the solvent, and purifying and refining the product to obtain trimethylsilyl propylene epoxide;

(47) (b) mixing water, concentrated sulfuric acid and trimethylsilyl propylene epoxide, then heating the mixture to 85° C. in water bath under stirring condition and holding the temperature to carry out the reaction for 15 min, after the reaction cooling the mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol (R=—CH(CH.sub.3)— in Formula (I)), wherein the concentrated sulfuric acid was one with mass concentration of 70%, and at the beginning of reaction the molar ratio of trimethylsilyl propylene epoxide to water is 1:40 whereas the sulfuric acid usage is 0.15 wt % of the total mixture.

(48) (1.2) Synthesis of 2-tert-butyl-1,6-hexanedioic acid

(49) mixing tungstic acid and hydrogen peroxide and stirring the mixture at room temperature for 12 min, then adding in 2-tert-butyl cyclohexanol to carrying out the reaction in reflux state at 83° C. for 1.5 hr at first and next at 90° C. for 2 hr, after the reaction cooling, crystallizing, washing and refining to obtain the tert-butyl branched dicarboxylic acid, wherein the molar ratio of tungstic acid, 2-tert-butyl cyclohexanol and hydrogen peroxide is 1:33:120.

(50) (1.3) Doping modification of Sb.sub.2O.sub.3

(51) (1.3.1) evenly mixing the 1.0 mol % of Ba(NO.sub.3).sub.2 aqueous solution and the 10 mol % of Sb.sub.2O.sub.3 oxalic acid solution in a molar ratio 3:100 of Ba.sup.2+ to Sb.sup.3+;

(52) (1.3.2) depositing the mixed solution by dripping in 2 mol/L of ammonia water till pH=9.5, then washing and drying (at 105° C. for 3 hr) the precipitate;

(53) (1.3.3) after the treatments including a heating at 400° C. for 3 hr, a heating at 900° C. for 2 hr and a cooling in air, finally grinding the precipitate to obtain the doped Sb.sub.3 powder with an average particle size of 0.5 micron;

(54) (1.4) Esterification

(55) concocting terephthalic acid, ethylene glycol, 2-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3-methyl-1,2-propanediol into a slurry, then adding in the doped Sb.sub.2O.sub.3, titanium dioxide and triphenyl phosphate and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.2 MPa at 255° C., finally ending the reaction when the water distillation reaching more than 90% of the theoretical value, wherein the molar ration of terephthalic acid, ethylene glycol, 2-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3-methyl-1,2-propanediol is 1:1.6:0.02:0.01, whereas the addition of the doped Sb.sub.2O.sub.3, titanium dioxide and triphenyl phosphate are 0.012 wt %, 0.21 wt % and 0.03 wt % of terephthalic acid, respectively;

(56) (1.5) Polycondensation

(57) for the esterification products, smoothly reducing the pressure to 450 Pa (absolute value) within 45 min and carrying out reaction at 256° C. for 50 min, successively, further reducing the pressure to 100 Pa (absolute value) and continuing the reaction at 275° C. for 60 min;

(58) (2) Spinning of polyester yarn for industrial sewing thread

(59) converting the modified polyester into polyester yarn for industrial sewing thread through a series of processes composed of viscosity enhancing by solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the intrinsic viscosity of the modified polyester after the solid state polycondensation is 1.0 dL/g;

(60) wherein the spinning process involves the technological parameters of 300° C. for the extruder temperature, 295° C. for the spin head temperature, 140 bar for the spin head pressure, 22° C. for the cross air temperature, 80% for the cross air humidity, 0.7 m/s for the cross air blow speed, 3600 m/min for the winding speed;

(61) wherein the stretching and the heat setting processes involve the technological parameters of 440 m/min for the roller 1 speed, 80° C. for the roller 1 temperature, 460 m/min for the roller 2 speed, 90° C. for the roller 2 temperature, 1900 m/min for the roller 3 speed, 125° C. for the roller 3 temperature, 3600 m/min for the roller 4 speed, 220° C. for the roller 4 temperature, 3300 m/min for the roller 5 speed, 170° C. for the roller 5 temperature.

(62) Finally obtained degradable polyester fiber has the following performance indices of monofilament fineness 2.6 dtex, multifilament fineness 150 dtex, breaking strength 8.1 cN/dtex, deviation rate of linear density 0%, breaking strength CV value 3.0%, elongation at break 13.0%, elongation at break CV value 7.95%, elongation at 4.0 cN/dtex load 5.5%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 9.2%, interlacing degree 7/m, oil content 0.6 wt %, as well as a dye uptake of 88.8% and a K/S value of 24.07 when dyed at 130° C.

Example 4

(63) A method for preparing the polyester yarn for industrial sewing thread, comprising the steps:

(64) (1) Preparation of modified polyester

(65) (1.1) Synthesis of 3-trimethylsilyl-3-methyl-1,2-propanediol

(66) (a) mixing 3-trimethylsilyl-3-methylpropene, peracetic acid and dichloromethane in the molar ratio of 1:10:10 and carrying out the reaction with stirring at 36° C. for 6 hr, after the reaction removing the solvent, and purifying and refining the product to obtain trimethylsilyl propylene epoxide;

(67) (b) mixing water, concentrated sulfuric acid and trimethylsilyl propylene epoxide, then heating the mixture to 84° C. in water bath under stirring condition and holding the temperature to carry out the reaction for 12 min, after the reaction cooling the mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol (R=—CH(CH.sub.3)— in Formula (I)), wherein the concentrated sulfuric acid was one with mass concentration of 70%, and at the beginning of reaction the molar ratio of trimethylsilyl propylene epoxide to water is 1:30 whereas the sulfuric acid usage is 0.14 wt % of the total mixture.

(68) (1.2) Synthesis of 3-tert-butyl-1,6-hexanedioic acid

(69) mixing tungstic acid and hydrogen peroxide and stirring the mixture at room temperature for 13 min, then adding in 4-tert-butyl cyclohexanol to carrying out the reaction in reflux state at 85° C. for 2 hr at first and next at 90° C. for 3 hr, after the reaction cooling, crystallizing, washing and refining to obtain the tert-butyl branched dicarboxylic acid, wherein the molar ratio of tungstic acid, 4-tert-butyl cyclohexanol and hydrogen peroxide is 1:30:130.

(70) (1.3) Doping modification of Sb.sub.2O.sub.3

(71) (1.3.1) evenly mixing the 0.6 mol % of Zn(NO.sub.3).sub.2 aqueous solution and the 6 mol % of Sb.sub.2O.sub.3 oxalic acid solution in a molar ratio 1.2:100 of Zn.sup.2+ to Sb.sup.3+;

(72) (1.3.2) depositing the mixed solution by dripping in 2 mol/L of ammonia water till pH=10 then washing and drying (at 110° C. for 2.5 hr) the precipitate;

(73) (1.3.3) after the treatments including a heating at 400° C. for 2.5 hr, a heating at 900° C. for 1 hr and a cooling in air, finally grinding the precipitate to obtain the doped Sb.sub.3 powder with an average particle size of 0.4 micron;

(74) (1.4) Esterification

(75) concocting terephthalic acid, ethylene glycol, 3-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3-methyl-1,2-propanediol into a slurry, then adding in the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.1 MPa at 250° C., finally ending the reaction when the water distillation reaching more than 90% of the theoretical value, wherein the molar ration of terephthalic acid, ethylene glycol, 3-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3-methyl-1,2-propanediol is 1:1.7:0.025:0.02, whereas the addition of the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite are 0.012 wt %, 0.20 wt % and 0.02 wt % of terephthalic acid, respectively;

(76) (1.5) Polycondensation

(77) for the esterification products, smoothly reducing the pressure to 420 Pa (absolute value) within 50 min and carrying out reaction at 260° C. for 35 min, successively, further reducing the pressure to 85 Pa (absolute value) and continuing the reaction at 270° C. for 90 min;

(78) (2) Spinning of polyester yarn for industrial sewing thread

(79) converting the modified polyester into polyester yarn for industrial sewing thread through a series of processes composed of viscosity enhancing by solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the intrinsic viscosity of the modified polyester after the solid state polycondensation is 1.0 dL/g;

(80) wherein the spinning process involves the technological parameters of 310° C. for the extruder temperature, 296° C. for the spin head temperature, 140 bar for the spin head pressure, 22° C. for the cross air temperature, 85% for the cross air humidity, 0.5 m/s for the cross air blow speed, 2600 m/min for the winding speed;

(81) wherein the stretching and the heat setting processes involve the technological parameters of 520 m/min for the roller 1 speed, 82° C. for the roller 1 temperature, 680 m/min for the roller 2 speed, 96° C. for the roller 2 temperature, 1900 m/min for the roller 3 speed, 140° C. for the roller 3 temperature, 2700 m/min for the roller 4 speed, 220° C. for the roller 4 temperature, 3300 m/min for the roller 5 speed, 150° C. for the roller 5 temperature.

(82) Finally obtained degradable polyester fiber has the following performance indices of monofilament fineness 2.3 dtex, multifilament fineness 200 dtex, breaking strength 8.5 cN/dtex, deviation rate of linear density 1.0%, breaking strength CV value 2.8%, elongation at break 16.5%, elongation at break CV value 7.6%, elongation at 4.0 cN/dtex load 5.5%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 6.8%, interlacing degree 8/m, oil content 0.8 wt %, as well as a dye uptake of 91.2% and a K/S value of 24.07 when dyed at 130° C.

Example 5

(83) A method for preparing the polyester yarn for industrial sewing thread, comprising the steps:

(84) (1) Preparation of modified polyester

(85) (1.1) Synthesis of 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol

(86) (a) mixing 3-trimethylsilyl-3,3-dimethylpropene, peracetic acid and dichloromethane in the molar ratio of 1:8:12 and carrying out the reaction with stirring at 40° C. for 5 hr, after the reaction removing the solvent, and purifying and refining the product to obtain trimethylsilyl propylene epoxide;

(87) (b) mixing water, concentrated sulfuric acid and trimethylsilyl propylene epoxide, then heating the mixture to 85° C. in water bath under stirring condition and holding the temperature to carry out the reaction for 10 min, after the reaction cooling the mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol (R=—C((CH.sub.3).sub.2)— in Formula (I)), wherein the concentrated sulfuric acid was one with mass concentration of 70%, and at the beginning of reaction the molar ratio of trimethylsilyl propylene epoxide to water is 1:25 whereas the sulfuric acid usage is 0.12 wt % of the total mixture.

(88) (1.2) Synthesis of 3-tert-butyl-1,6-hexanedioic acid

(89) mixing tungstic acid and hydrogen peroxide and stirring the mixture at room temperature for 14 min, then adding in 4-tert-butyl cyclohexanol to carrying out the reaction in reflux state at 82° C. for 2 hr at first and next at 92° C. for 3 hr, after the reaction cooling, crystallizing, washing and refining to obtain the tert-butyl branched dicarboxylic acid, wherein the molar ratio of tungstic acid, 4-tert-butyl cyclohexanol and hydrogen peroxide is 1:40:130.

(90) (1.3) Doping modification of Sb.sub.2O.sub.3

(91) (1.3.1) evenly mixing the 0.7 mol % of Mg(NO.sub.3).sub.2 aqueous solution and the 8 mol % of Sb.sub.2O.sub.3 oxalic acid solution in a molar ratio 2:100 of Mg.sup.2+ to Sb.sup.3+;

(92) (1.3.2) depositing the mixed solution by dripping in 2 mol/L of ammonia water till pH=10 then washing and drying (at 110° C. for 2.5 hr) the precipitate;

(93) (1.3.3) after the treatments including a heating at 400° C. for 2.5 hr, a heating at 900° C. for 2 hr and a cooling in air, finally grinding the precipitate to obtain the doped Sb.sub.3 powder with an average particle size of 0.5 micron;

(94) (1.4) Esterification

(95) concocting terephthalic acid, ethylene glycol, 3-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol into a slurry, then adding in the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphate and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.3 MPa at 252° C., finally ending the reaction when the water distillation reaching more than 90% of the theoretical value, wherein the molar ration of terephthalic acid, ethylene glycol, 3-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol is 1:2.0:0.023:0.017, whereas the addition of the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphate are 0.015 wt %, 0.24 wt % and 0.01 wt % of terephthalic acid, respectively;

(96) (1.5) Polycondensation

(97) for the esterification products, smoothly reducing the pressure to 500 Pa (absolute value) within 30 min and carrying out reaction at 256° C. for 45 min, successively, further reducing the pressure to 88 Pa (absolute value) and continuing the reaction at 280° C. for 75 min;

(98) (2) Spinning of polyester yarn for industrial sewing thread

(99) converting the modified polyester into polyester yarn for industrial sewing thread through a series of processes composed of viscosity enhancing by solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the intrinsic viscosity of the modified polyester after the solid state polycondensation is 1.2 dL/g;

(100) wherein the spinning process involves the technological parameters of 320° C. for the extruder temperature, 297° C. for the spin head temperature, 140 bar for the spin head pressure, 22° C. for the cross air temperature, 83% for the cross air humidity, 0.7 m/s for the cross air blow speed, 2600 m/min for the winding speed;

(101) wherein the stretching and the heat setting processes involve the technological parameters of 600 m/min for the roller 1 speed, 85° C. for the roller 1 temperature, 550 m/min for the roller 2 speed, 96° C. for the roller 2 temperature, 2400 m/min for the roller 3 speed, 135° C. for the roller 3 temperature, 2700 m/min for the roller 4 speed, 250° C. for the roller 4 temperature, 2600 m/min for the roller 5 speed, 150° C. for the roller 5 temperature.

(102) Finally obtained degradable polyester fiber has the following performance indices of monofilament fineness 3 dtex, multifilament fineness 260 dtex, breaking strength 8.5 cN/dtex, deviation rate of linear density 1.5%, breaking strength CV value 2.7%, elongation at break 14.8%, elongation at break CV value 7.7%, elongation at 4.0 cN/dtex load 7.0%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 6.8%, interlacing degree 10/m, oil content 0.6 wt %, as well as a dye uptake of 89.29% and a K/S value of 26.12 when dyed at 130° C.

Example 6

(103) A method for preparing the polyester yarn for industrial sewing thread, comprising the steps:

(104) (1) Preparation of modified polyester

(105) (1.1) Synthesis of 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol

(106) (a) mixing 3-trimethylsilyl-3,3-dimethylpropene, peracetic acid and dichloromethane in the molar ratio of 1:10:10 and carrying out the reaction with stirring at 35° C. for 6 hr, after the reaction removing the solvent, and purifying and refining the product to obtain trimethylsilyl propylene epoxide;

(107) (b) mixing water, concentrated sulfuric acid and trimethylsilyl propylene epoxide, then heating the mixture to 80° C. in water bath under stirring condition and holding the temperature to carry out the reaction for 15 min, after the reaction cooling the mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol (R=—C((CH.sub.3).sub.2)— in Formula (I)), wherein the concentrated sulfuric acid was one with mass concentration of 70%, and at the beginning of reaction the molar ratio of trimethylsilyl propylene epoxide to water is 1:35 whereas the sulfuric acid usage is 0.14 wt % of the total mixture.

(108) (1.2) Synthesis of 2,5-di-tert-butyl-1,6-hexanedioic acid

(109) mixing tungstic acid and hydrogen peroxide and stirring the mixture at room temperature for 15 min, then adding in 2,4-di-tert-butyl cyclohexanol to carrying out the reaction in reflux state at 83° C. for 1.5 hr at first and next at 92° C. for 2.5 hr, after the reaction cooling, crystallizing, washing and refining to obtain the tert-butyl branched dicarboxylic acid, wherein the molar ratio of tungstic acid, 2,4-di-tert-butyl cyclohexanol and hydrogen peroxide is 1:40:120.

(110) (1.3) Doping modification of Sb.sub.2O.sub.3

(111) (1.3.1) evenly mixing the 0.8 mol % of Mg(NO.sub.3).sub.2 and Ca(NO.sub.3).sub.2 aqueous solutions in a weight ratio of 1:1 at first, and then blending the mixture containing M.sup.x+ ions with the 8 mol % of Sb.sub.2O.sub.3 oxalic acid solution in a molar ratio 2.5:100 of M.sup.x+ to Sb.sup.3+;

(112) (1.3.2) depositing the mixed solution by dripping in 2 mol/L of ammonia water till pH=10 then washing and drying (at 105° C. for 3 hr) the precipitate;

(113) (1.3.3) after the treatments including a heating at 400° C. for 3 hr, a heating at 900° C. for 1.5 hr and a cooling in air, finally grinding the precipitate to obtain the doped Sb.sub.3 powder with an average particle size of 0.4 micron;

(114) (1.4) Esterification

(115) concocting terephthalic acid, ethylene glycol, 2,5-di-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol into a slurry, then adding in the doped Sb.sub.2O.sub.3, titanium dioxide and triphenyl phosphate and carrying out the esterification in a nitrogen atmosphere with a pressure of normal value at 260° C., finally ending the reaction when the water distillation reaching more than 95% of the theoretical value, wherein the molar ration of terephthalic acid, ethylene glycol, 2,5-di-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol is 1:2.0:0.03:0.02, whereas the addition of the doped Sb.sub.2O.sub.3, titanium dioxide and triphenyl phosphate are 0.014 wt %, 0.21 wt % and 0.05 wt % of terephthalic acid, respectively;

(116) (1.5) Polycondensation

(117) for the esterification products, smoothly reducing the pressure to 490 Pa (absolute value) within 30 min and carrying out reaction at 260° C. for 50 min, successively, further reducing the pressure to 90 Pa (absolute value) and continuing the reaction at 275° C. for 50 min;

(118) (2) Spinning of polyester yarn for industrial sewing thread

(119) converting the modified polyester into polyester yarn for industrial sewing thread through a series of processes composed of viscosity enhancing by solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the intrinsic viscosity of the modified polyester after the solid state polycondensation is 1.2 dL/g;

(120) wherein the spinning process involves the technological parameters of 320° C. for the extruder temperature, 300° C. for the spin head temperature, 140 bar for the spin head pressure, 22° C. for the cross air temperature, 85% for the cross air humidity, 0.6 m/s for the cross air blow speed, 2600 m/min for the winding speed;

(121) wherein the stretching and the heat setting processes involve the technological parameters of 650 m/min for the roller 1 speed, 85° C. for the roller 1 temperature, 680 m/min for the roller 2 speed, 100° C. for the roller 2 temperature, 2200 m/min for the roller 3 speed, 140° C. for the roller 3 temperature, 2700 m/min for the roller 4 speed, 240° C. for the roller 4 temperature, 2800 m/min for the roller 5 speed, 150° C. for the roller 5 temperature.

(122) Finally obtained degradable polyester fiber has the following performance indices of monofilament fineness 3 dtex, multifilament fineness 300 dtex, breaking strength 8.0 cN/dtex, deviation rate of linear density −1.5%, breaking strength CV value 3.0%, elongation at break 16.5%, elongation at break CV value 7.9%, elongation at 4.0 cN/dtex load 6.5%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 6.8%, interlacing degree 8/m, oil content 0.4 wt %, as well as a dye uptake of 91.2% and a K/S value of 24.59 when dyed at 130° C.

Example 7

(123) A method for preparing the polyester yarn for industrial sewing thread, comprising the steps:

(124) (1) Preparation of modified polyester

(125) (1.1) Synthesis of 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol

(126) (a) mixing 3-trimethylsilyl-3,3-dimethylpropene, peracetic acid and dichloromethane in the molar ratio of 1:5:15 and carrying out the reaction with stirring at 37° C. for 7 hr, after the reaction removing the solvent, and purifying and refining the product to obtain trimethylsilyl propylene epoxide;

(127) (b) mixing water, concentrated sulfuric acid and trimethylsilyl propylene epoxide, then heating the mixture to 82° C. in water bath under stirring condition and holding the temperature to carry out the reaction for 12 min, after the reaction cooling the mixture to room temperature, and then neutralizing, distilling, separating and purifying to obtain the trimethylsilyl branched diol (R=—C((CH.sub.3).sub.2)— in Formula (I)), wherein the concentrated sulfuric acid was one with mass concentration of 70%, and at the beginning of reaction the molar ratio of trimethylsilyl propylene epoxide to water is 1:29 whereas the sulfuric acid usage is 0.13 wt % of the total mixture.

(128) (1.2) Synthesis of 2,5-di-tert-butyl-1,6-hexanedioic acid

(129) mixing tungstic acid and hydrogen peroxide and stirring the mixture at room temperature for 11 min, then adding in 2,4-di-tert-butyl cyclohexanol to carrying out the reaction in reflux state at 80° C. for 1 hr at first and next at 95° C. for 2.2 hr, after the reaction cooling, crystallizing, washing and refining to obtain the tert-butyl branched dicarboxylic acid, wherein the molar ratio of tungstic acid, 2,4-di-tert-butyl cyclohexanol and hydrogen peroxide is 1:35:150.

(130) (1.3) Doping modification of Sb.sub.2O.sub.3

(131) (1.3.1) evenly mixing the 0.5 mol % of Mg(NO.sub.3).sub.2, Ba(NO.sub.3).sub.2 and Ca(NO.sub.3).sub.2 aqueous solutions in a weight ratio of 1:1:1 at first, and then blending the mixture containing M.sup.x+ ions with the 10 mol % of Sb.sub.2O.sub.3 oxalic acid solution in a molar ratio 2:100 of M.sup.x+ to Sb.sup.3+;

(132) (1.3.2) depositing the mixed solution by dripping in 2 mol/L of ammonia water till pH=9 then washing and drying (at 108° C. for 2.5 hr) the precipitate;

(133) (1.3.3) after the treatments including a heating at 400° C. for 2.5 hr, a heating at 900° C. for 2 hr and a cooling in air, finally grinding the precipitate to obtain the doped Sb.sub.3 powder with an average particle size of 0.4 micron;

(134) (1.4) Esterification

(135) concocting terephthalic acid, ethylene glycol, 2,5-di-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol into a slurry, then adding in the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite and carrying out the esterification in a nitrogen atmosphere with a pressure of 0.2 MPa at 250° C., finally ending the reaction when the water distillation reaching more than 92% of the theoretical value, wherein the molar ration of terephthalic acid, ethylene glycol, 2,5-di-tert-butyl-1,6-hexanedioic acid and 3-trimethylsilyl-3,3-dimethyl-1,2-propanediol is 1:1.5:0.02:0.017, whereas the addition of the doped Sb.sub.2O.sub.3, titanium dioxide and trimethyl phosphite are 0.015 wt %, 0.25 wt % and 0.03 wt % of terephthalic acid, respectively;

(136) (1.5) Polycondensation

(137) for the esterification products, smoothly reducing the pressure to 440 Pa (absolute value) within 40 min and carrying out reaction at 260° C. for 40 min, successively, further reducing the pressure to 95 Pa (absolute value) and continuing the reaction at 282° C. for 70 min;

(138) (2) Spinning of polyester yarn for industrial sewing thread

(139) converting the modified polyester into polyester yarn for industrial sewing thread through a series of processes composed of viscosity enhancing by solid state polycondensation, melting, metering, extruding, cooling, oiling, stretching, heat setting and winding; wherein the intrinsic viscosity of the modified polyester after the solid state polycondensation is 1.0 dL/g;

(140) wherein the spinning process involves the technological parameters of 300° C. for the extruder temperature, 295° C. for the spin head temperature, 140 bar for the spin head pressure, 22° C. for the cross air temperature, 79% for the cross air humidity, 0.7 m/s for the cross air blow speed, 3000 m/min for the winding speed;

(141) wherein the stretching and the heat setting processes involve the technological parameters of 440 m/min for the roller 1 speed, 75° C. for the roller 1 temperature, 580 m/min for the roller 2 speed, 90° C. for the roller 2 temperature, 2400 m/min for the roller 3 speed, 135° C. for the roller 3 temperature, 3600 m/min for the roller 4 speed, 250° C. for the roller 4 temperature, 3000 m/min for the roller 5 speed, 170° C. for the roller 5 temperature.

(142) Finally obtained degradable polyester fiber has the following performance indices of monofilament fineness 2.5 dtex, multifilament fineness 150 dtex, breaking strength 8.2 cN/dtex, deviation rate of linear density 1.5%, breaking strength CV value 2.8%, elongation at break 15.0%, elongation at break CV value 7.8%, elongation at 4.0 cN/dtex load 7.0%, dry heat shrinkage (under 177° C.×10 min×0.05 cN/dtex) 9.2%, interlacing degree 6/m, oil content 0.6 wt %, as well as a dye uptake of 90.28% and a K/S value of 26.12 when dyed at 130° C.