Hydrophilic wear-resistant PET melt-blown non-woven fabric material and preparation method thereof

Abstract

The invention relates to a hydrophilic wear-resistant PET melt-blown non-woven fabric material and a preparation method thereof, and the PET melt-blown non-woven fabric material is prepared by the following steps: pelletizing PET copolyester, and carrying out twin-screw extrusion, melt spinning, hot air traction and receiving molding. The PET copolyester dicing is prepared from the following raw materials: terephthalic acid, adipic acid, ethylene glycol, 5-sulfoisophthalic acid sodium salt, nylon-66 salt, polyethylene glycol 3350 and a stabilizer; compared with pure PET polyester, the modified PET copolyester disclosed by the invention has the advantages that relatively good melt strength is maintained, and meanwhile, the modified PET copolyester has better flowability and a lower melting point; in consideration of the die head temperature and the drafting air temperature, compared with pure PET polyester, the modified PET copolyester has the advantages that the die head temperature and the drafting air temperature of the modified PET copolyester are lower (20-30 DEG C as low) in the melt-blowing processing process, and the processing energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical fiber preparation, and particularly relates to a hydrophilic wear-resistant PET melt-blown non-woven fabric material and a preparation method thereof. BACKGROUND

[0002] Melt-blown non-woven fabric, also known as melt-blown non-woven fabric, is a kind of non-woven material formed by high-temperature airflow super-drawing polymer melt to form micron to nanometer ultra-fine fibers and relying on self-adhesion or thermal reinforcement. Its production process includes key links such as melt extrusion, melt conveying, spinning forming, high-speed airflow drafting, fiber cooling and solidification, and web collection. This technology breaks through the traditional textile principle, has the characteristics of short process, high efficiency and low cost, and the melt-blown non-woven material has the characteristics of high adhesion, softness and skin-friendliness, and is mainly used for composite materials, filter materials, sanitary products, oil absorption materials, wiping and the like.

[0003] Although PET melt-blown non-woven fabric has high melting point, excellent mechanical strength and chemical resistance, however, the traditional PET material has high processing temperature, large energy consumption and is easy to cause thermal degradation, the fiber has large rigidity and low elongation at break, the non-woven fabric made of the fiber has rough hand feeling, the surface is hydrophobic and the post-processing cost is high, the fiber has few bonding points between fibers, is not wear-resistant and is easy to be layered and torn, which seriously limits its application in medium and high performance wiping scenarios.

[0004] CN114381860A discloses a method for manufacturing a hydrophilic PET melt-blown material, which uses PET, PEG and silicon dioxide for blending modification, and the manufactured melt-blown material is hydrophilic and aging-resistant, but ordinary PET material is used, the molecular weight is large and the melt index is low, the processing temperature is high, and yellowing and decomposition phenomena are easy to occur. CN119686023A discloses a preparation method of a hydrophilic polyester melt-blown non-woven fabric, and the process flow of the preparation method is: raw material drying → melt blowing → hot air traction → drum receiving and forming; the raw material contains 8-10wt% of coated modified inorganic nano functional powder, and the base material of the raw material is polyester; the coated modified inorganic nano functional powder includes coupling agent modified inorganic nano powder and hydrophilic hyperbranched polyester coated on the surface of the coupling agent modified inorganic nano powder, and the coupling agent modified inorganic nano powder contains amino or epoxy groups. The present application uses the coated modified inorganic nano functional powder coated with hydrophilic hyperbranched polyester to improve the melt index of the polyester base material, improve the flowability of the polyester base material, and at the same time, enhance the hydrophilicity and moisture permeability of the polyester melt-blown non-woven fabric. The present application needs many steps such as coupling agent modified inorganic nano powder, hydrophilic hyperbranched polyester, preparation of coated modified inorganic nano functional powder, preparation of hydrophilic polyester chip and finally melt-blown non-woven fabric, the process is complex, the melt-blown temperature is high, the cost is high, and the product performance is improved in hydrophilicity, but there is no improvement in wear resistance.

[0005] Therefore, there is an urgent need for a multi-component synergistic modification scheme to reduce the melting point of PET, improve the fluidity, and achieve comprehensive performance of hydrophilicity, wear resistance, and high bonding strength. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a hydrophilic and wear-resistant PET melt-blown non-woven fabric material and a preparation method thereof, which can reduce the melting point of PET, improve the fluidity, and achieve comprehensive performance of hydrophilicity, wear resistance, and high bonding strength.

[0007] The present application adopts the following technical solutions:

[0008] A hydrophilic and wear-resistant PET melt-blown non-woven fabric material is made of PET copolyester granules through double-screw extrusion, melt spinning, hot air traction, and receiving forming processes. The PET copolyester granules include the following raw materials: terephthalic acid, adipic acid, ethylene glycol, m-terephthalic acid-5-sodium sulfonate, nylon-66 salt, polyethylene glycol 3350, and a stabilizer. The molar ratio of m-terephthalic acid-5-sodium sulfonate to terephthalic acid is 0.02-0.1:1, the molar ratio of adipic acid to terephthalic acid is 0.05-0.15:1, the alcohol acid molar ratio is 1.5-2.0, the mass ratio of polyethylene glycol 3350 to terephthalic acid is 3-5wt%, the mass ratio of nylon-66 salt to terephthalic acid is 5-20wt%, and the concentration of the stabilizer is 100-300ppm.

[0009] Further, the PET copolyester granules also include the following raw materials: the stabilizer is trimethyl phosphate.

[0010] Further, the intrinsic viscosity of the PET copolyester granules is 0.50-0.55dl / g.

[0011] Further, the melting point of the PET copolyester granules is 150-180℃.

[0012] A preparation method of a hydrophilic and wear-resistant PET melt-blown non-woven fabric material includes the following steps:

[0013] Step 1, mix terephthalic acid, adipic acid, ethylene glycol, and m-terephthalic acid-5-sodium sulfonate in proportion, add a stabilizer, mix uniformly, and then beat into slurry;

[0014] Step 2, transfer the mixture obtained in step 1 to a reaction kettle, introduce nitrogen, heat, and perform esterification reaction; the reaction endpoint is determined when the esterification water distillation amount reaches the calculated value;

[0015] Step 3, after the esterification reaction is completed, under normal pressure, add a polyethylene glycol 3350 and nylon-66 salt mixed ethylene glycol solution, balance for 10min, and then perform polycondensation reaction;

[0016] Step 4, after the completion of the polycondensation reaction, the discharge flow channel of the reaction kettle is opened to extrude the product by introducing nitrogen, and the product is cut into granules after water treatment to obtain PET copolyester granules;

[0017] Step 5, the PET copolyester granules obtained in step 4 are sequentially subjected to double-screw extrusion, melt spinning, hot air drafting, and receiving molding to obtain the hydrophilic wear-resistant PE melt-blown non-woven fabric material.

[0018] Further, in step 3, the polycondensation reaction is divided into a normal pressure stage, a low vacuum stage, and a high vacuum stage; in the normal pressure stage, the temperature is controlled at 250-255℃; in the low vacuum stage, the pressure is smoothly extracted from normal pressure to below 1kpa absolute pressure, and the temperature is controlled at 255-260℃; in the high vacuum stage, the vacuum is continuously extracted to below 50Pa absolute pressure, and the reaction temperature is controlled at 260-270℃, and the end discharge temperature is strictly controlled at 270-275℃.

[0019] Further, in step 5, in the double-screw extrusion process, the screw zone 1 temperature is 230-250℃, the screw zone 2 temperature is 230-250℃, the screw zone 3 temperature is 240-260℃, and the screw zone 4 temperature is 240-260℃; the die zone 1 temperature is 250-260℃, the die zone 2 temperature is 260-265℃, the die zone 3 temperature is 260-275℃, the die zone 4 temperature is 260-275℃, and the die zone 5 temperature is 260-280℃.

[0020] Further, in step 5, the melt spinning process is specifically operated as follows: the melt is respectively subjected to melt pressure boosting, melt filtration, metering pump metering, and melt ejection through a die after being extruded by a double-screw extruder, the melt pressure boosting pump, metering pump, and filtration zone temperatures are all the same, the melt temperature is 250-260℃, and the die temperature is 250-280℃, wherein the die zone 1 temperature is controlled at 250-260℃, the die zone 2 temperature is controlled at 260-265℃, the die zone 3 temperature is controlled at 260-275℃, the die zone 4 temperature is controlled at 260-275℃, and the die zone 5 temperature is controlled at 260-280℃.

[0021] Further, in step 5, in the hot air drafting process, the hot air temperature is 270-285℃, and the drafting air pressure is 0.1-0.3MPa.

[0022] Further, in step 2, the temperature during the heating reaction is 240-250℃, the pressure is 0.1-0.2MPa, and the esterification water distillation amount is obtained by the following formula: esterification water amount (kg) = total acid component molar number in the reaction system x 36 x 98%.

[0023] From the above description of the present application, compared with the prior art, the beneficial effects of the present application are:

[0024] Firstly, the modified PET copolyester of the present application has good melt strength, better flowability and lower melting point compared with pure PET polyester; considering the die temperature and stretching air temperature, the die temperature and stretching air temperature of the modified PET copolyester in the melt blowing process are lower (20-30℃ lower) compared with pure PET polyester, thereby reducing the processing energy consumption.

[0025] Secondly, the modified PET copolyester of the present application introduces two polar groups of sulfonate and amino, which greatly improves the bonding performance of the fiber, and forms high-strength bonding points through matching with the receiving distance, melt temperature and micro-melt of the fiber surface.

[0026] Thirdly, the SIPA in the modified PET copolyester of the present application has polycondensation catalytic function and does not contain heavy metal catalyst, and the non-woven fabric material made of the SIPA is environmentally friendly and recyclable.

[0027] Fourthly, the present application solves the core defects of traditional PET melt blown fabric such as hydrophobicity, high energy consumption and low strength through the polyester modification-melt blowing process-performance oriented full-chain development path, provides a high-performance, low-cost and green solution for medium and high-end wiping materials, and has great market potential. DETAILED DESCRIPTION

[0028] The present application will be further described through specific embodiments.

[0029] A hydrophilic and wear-resistant PET melt-blown non-woven fabric material is made of PET copolyester pellets through double-screw extrusion, melt blowing, hot air traction and receiving forming processes. The PET copolyester pellets comprise the following raw materials: terephthalic acid (PTA), adipic acid (AA), ethylene glycol (EG), sodium 5-sulfonate isophthalic acid (SIPA), nylon-66 salt (PA-66 salt), polyethylene glycol 3350 (PEG3350) and trimethyl phosphate; wherein the molar ratio of sodium 5-sulfonate isophthalic acid to terephthalic acid is 0.02-0.1:1, the molar ratio of adipic acid to terephthalic acid is 0.05-0.15:1, the alcohol acid molar ratio is 1.5-2.0, the mass ratio of polyethylene glycol 3350 to terephthalic acid is 3-5wt%, the mass ratio of nylon-66 salt to terephthalic acid is 5-20wt%, and the concentration of the stabilizer is 100-300ppm; specifically, the intrinsic viscosity of the PET copolyester pellets is 0.50-0.55dl / g, and the melting point is 150-180℃.

[0030] A preparation method of a hydrophilic and wear-resistant PET melt-blown non-woven fabric material, comprising the following steps:

[0031] (1) preparing PET copolyester pellets:

[0032] Step 1, p-Phthalic acid, adipic acid, ethylene glycol, m-Phthalic acid-5-sodium sulfonate are mixed in proportion, a stabilizer is added and mixed uniformly, and then a slurry is made;

[0033] Step 2, the mixture obtained in step 1 is transferred to a reaction kettle, nitrogen is introduced, and esterification is carried out by heating. The end point of the reaction is determined when the calculated amount of esterification water is distilled off. The amount of esterification water is calculated by the following formula: esterification water amount (kg) = total moles of acid components in the reaction system x 36 x 98%; and the temperature during heating reaction is 240-250℃, and the pressure is 0.1-0.2MPa;

[0034] Step 3, after the esterification reaction is completed, under normal pressure, polyethylene glycol 3350 and nylon-66 salt mixed ethylene glycol solution are added, and after 10min of equilibration, polycondensation reaction is carried out. The polycondensation reaction is divided into a normal pressure stage, a low vacuum stage and a high vacuum stage. In the normal pressure stage, the temperature is controlled between 250-255℃; in the low vacuum stage, the pressure is smoothly extracted from normal pressure to below 1kpa of absolute pressure, and the temperature is controlled between 255-260℃; in the high vacuum stage, vacuum extraction is continued to below 50Pa of absolute pressure, and the reaction temperature is controlled between 260-270℃, with the end point discharge temperature strictly controlled between 270-275℃; and the concentration of the polyethylene glycol 3350 and nylon-66 salt mixed solution is 30-45%;

[0035] Step 4, after the polycondensation reaction is completed, the discharge flow channel of the reaction kettle is opened, nitrogen is introduced, and the product is extruded. After the product is washed with water, it is cut into granules to obtain PET copolyester granules;

[0036] (2) Double screw extrusion: PET copolyester granules are sent into a double screw extruder to form a melt. Three exhaust ports are provided on the double screw. Two exhaust ports of the machine head are connected to a three-stage series vacuum pump set, one of which is a Roots vacuum pump and the third is a water ring vacuum pump. The vacuum pump set inlet absolute pressure value is below 200Pa. The screw zone 1 temperature is 230-250℃, the screw zone 2 temperature is 230-250℃, the screw zone 3 temperature is 240-260℃, the screw zone 4 temperature is 240-260℃; the die zone 1 temperature is 250-260℃, the die zone 2 temperature is 260-265℃, the die zone 3 temperature is 260-275℃, the die zone 4 temperature is 260-275℃, and the die zone 5 temperature is 260-280℃;

[0037] (3) melt blowing: the melt is respectively introduced into a melt booster pump, a melt filter, a metering pump after being extruded by a double screw extruder, and the melt is sprayed through a die head, the temperature of the melt booster pump, the metering pump and the filter area is the same, the melt temperature is 250-260℃, and the die head temperature is 250-280℃, wherein, the temperature of the first zone of the die head is 250-260℃, the temperature of the second zone of the die head is 260-265℃, the temperature of the third zone of the die head is 260-275℃, the temperature of the fourth zone of the die head is 260-275℃, and the temperature of the fifth zone of the die head is 260-280℃;

[0038] (4) hot air traction: the melt is sprayed through a spinning die head, and then is tractioned by hot air, wherein, the hot air temperature is 270-285℃, and the traction air pressure is 0.1-0.3MPa;

[0039] (5) receiving and forming: the hot air tractioned yarn is laid on a receiving net, and is wound to form the hydrophilic wear-resistant PET melt-blown nonwoven fabric material, wherein, the receiving distance from the receiving net to the spinning die head is 10-20cm.

[0040] Seven groups of examples and three groups of comparative examples are provided in the application, the PET copolyester pellet preparation process and indexes of the examples and the comparative examples are shown in Table 1, the melt blowing process conditions are shown in Table 2, wherein, in the comparative example 1, except that no PA66 salt is added after esterification, the conditions are the same as those of the example 6; in the comparative example 2, no SIPA and PA66 salt is added, and an ethylene glycol antimony catalyst is added in the slurry preparation, the addition amount is 500PPM, and the other conditions are the same as those of the example 6; in the comparative example 3, no SIPA is added in the slurry preparation step of the raw material preparation, and the other conditions are the same as those of the example 6.

[0041] Table 1: PET copolyester pellet preparation process and index parameter table

[0042]

[0043]

[0044] Table 2: melt blowing process condition table

[0045]

[0046] The PET copolyester pellet test method is as follows: 1, intrinsic viscosity: according to the national standard GB / T14190-2008; 2, melting point: tested by a DSC differential scanning calorimeter.

[0047] The PET melt-blown non-woven fabrics prepared in Examples 1-7 and Comparative Examples 1-2 were tested, and the specific results are shown in Table 3. The test methods are as follows: 1. PET melt-blown non-woven fabric material breaking strength: GB / T 24218.3-2010 Textiles-Determination of breaking force, elongation and elongation at break of textile fabrics-Part 3: test for nonwoven fabrics; 2. PET melt-blown non-woven fabric material breaking weight per area: GB / T 24218.3-2010 Textiles-Determination of breaking force, elongation and elongation at break of textile fabrics-Part 3: test for nonwoven fabrics; 3. PET melt-blown non-woven fabric material wear resistance: GB / T 21196.3-2007 Textiles-Determination of abrasion resistance of fabrics-Martin's method-Part 3: determination of mass loss, test conditions: humidity (65±5)%, temperature (20±2)℃, pressure hammer 250g, sand wheel type A-280, friction circle number is 80 circles; 4. PET melt-blown non-woven fabric material water absorption height of wicking: JJF (Textile) 056-2013 Capillary Effect Instrument Calibration Specification, test conditions: cut the melt-blown fabric into a narrow strip with a length of 30 cm and a width of 3 cm.

[0048] Table 3 Product test index table

[0049]

[0050] As can be seen from Examples 1-4 in Table 3, the hydrophilicity (height of wicking) is increased from 47.5 mm (Example 1) to 66 mm (Example 4), an increase of 18.5 mm, and the combined hydrophilic effect of the three components of the hydrophilic group of PEG3350, sodium 5-sulfonate isophthalic acid and PA66 salt is the core driving force; the wear resistance is also significantly improved, and the mass loss rate is reduced from 0.085% (Example 1) to 0.053% (Example 4), and at the same time, the PA-66 salt and the sodium 5-sulfonate isophthalic acid jointly improve the intermolecular force, thereby improving the adhesion and reducing the wear and tear.

[0051] In addition, as can be seen from Examples 4-7, reducing the receiving distance (Example 5: 10 mm) makes the fiber deposition more compact, the weight per area is increased to 88 g / m, and the breaking strength is increased to 70 / 41 N, effectively making up for the strength loss caused by the formula, and is suitable for high mechanical requirement scenarios; increasing the hot air pressure (Example 7: 0.3 MPa) promotes fiber refinement and entanglement, and the wear resistance reaches an extreme level (0.050% mass loss), which is better than all examples, and at the same time, the height of wicking is increased to 70 mm (optimal hydrophilicity); the die temperature of Examples 1-4 and Comparative Examples 1-3 is 250-260℃, which is significantly lower than the unmodified PET melt-blown temperature (usually > 280℃), and the melt-blown fabric can be normally sprayed, which proves that the modified formula maintains the advantage of low-temperature processing.

[0052] Further comparative examples are described as follows: Comparative Example 1 (without PA-66 salt): Abrasion resistance is reduced to 0.110% (mass loss), which proves that PA-66 salt contributes greatly to the abrasion resistance. Comparative Example 2 (without PA-66 salt + without isophthalic acid-5-sodium sulfonate): Abrasion resistance is further deteriorated to 0.129%, which indicates that only adipic acid cannot compensate for the synergistic abrasion resistance of PA-66 salt and isophthalic acid, and when PA-66 salt and SIPA are not added, the hydrophilic property is decreased, and the strength of the finished product is also low. Comparative Example 3 (without isophthalic acid-5-sodium sulfonate): When SIPA is not added and no polycondensation catalyst is added, the polymerization reaction cannot be carried out, which indicates that SIPA has a catalytic effect.

[0053] In summary, the present application solves the core defects of traditional PET meltblown fabric, such as poor hydrophobicity, high energy consumption and low strength, by the polyester modification-meltblown process-performance-oriented full-chain development path, and provides a high-performance, low-cost and green solution for medium and high-end wiping materials, which has great market potential.

[0054] The above description is only a preferred embodiment of the present application, and therefore cannot limit the scope of the present application. Any equivalent changes and modifications made according to the scope and content of the present application should still be within the scope of the present application.

Claims

1. A hydrophilic and wear-resistant PET melt-blown nonwoven fabric material, characterized by: The invention is prepared by subjecting PET copolyester pellets to twin-screw extrusion, melt spinning, hot air drawing, and receiving molding processes. The PET copolyester pellets include the following raw materials: terephthalic acid, adipic acid, ethylene glycol, 5-sodium sulfoisophthalate, nylon-66 salt, polyethylene glycol 3350, and a stabilizer. The molar ratio of 5-sodium sulfoisophthalate to terephthalic acid is 0.02-0.1:1, the molar ratio of adipic acid to terephthalic acid is 0.05-0.15:1, the molar ratio of alkyd acid is 1.5-2.0, the mass ratio of polyethylene glycol 3350 to terephthalic acid is 3-5wt%, the mass ratio of nylon-66 salt to terephthalic acid is 5-20wt%, and the concentration of the stabilizer is 100-300ppm.

2. The hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 1, characterized in that: The PET copolyester pellets further include the following raw materials: the stabilizer is trimethyl phosphate.

3. The hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 1, characterized in that: The intrinsic viscosity of the PET copolyester pellets is 0.50-0.55 dl / g.

4. The hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 1, characterized in that: The melting point of the PET copolyester pellets is 150-180°C.

5. The method for preparing a hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 1, wherein: The following steps are involved: Step 1: terephthalic acid, adipic acid, ethylene glycol, and 5-sodium sulfoisophthalate are mixed in proportion, a stabilizer is added, and the mixture is mixed evenly to form a slurry; Step 2: Transfer the mixture obtained in step 1 to a reactor, introduce nitrogen, and heat to carry out esterification reaction. The reaction endpoint is determined when the amount of esterification water distilled reaches the calculated value; Step 3: After the esterification reaction is completed, polyethylene glycol 3350 and nylon-66 salt are added to a mixed ethylene glycol solution under normal pressure, and the mixture is allowed to equilibrate for 10 minutes before polycondensation reaction is carried out; Step 4: After the polycondensation reaction is completed, the discharge channel of the reactor is opened to introduce nitrogen gas to extrude the product, and the product is washed with water and then pelletized to obtain PET copolyester pellets; Step 5: The PET copolyester pellets obtained in step 4 are sequentially subjected to twin-screw extrusion, melt spinning, hot air drawing, and receiving molding to obtain the hydrophilic and wear-resistant PE melt-blown non-woven fabric material.

6. The method for preparing a hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 5, wherein: In step 3, the polycondensation reaction is divided into a normal pressure stage, a low vacuum stage and a high vacuum stage; in the normal pressure stage, the temperature is controlled between 250-255°C; in the low vacuum stage, the pressure is steadily pumped from normal pressure to below 1 kPa absolute pressure, and the temperature is controlled between 255-260°C; in the high vacuum stage, the vacuum is continued to be pumped to below 50 Pa absolute pressure, the reaction temperature is controlled between 260-270°C, and the terminal discharge temperature is strictly controlled at 270-275°C.

7. The method for preparing a hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 5, wherein: In step 5, in the twin-screw extrusion process, the temperature of screw zone 1 is 230-250°C, the temperature of screw zone 2 is 230-250°C, the temperature of screw zone 3 is 240-260°C, and the temperature of screw zone 4 is 240-260°C; the temperature of die zone 1 is 250-260°C, the temperature of die zone 2 is 260-265°C, the temperature of die zone 3 is 260-275°C, the temperature of die zone 4 is 260-275°C, and the temperature of die zone 5 is 260-280°C.

8. The method for preparing a hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 5, wherein: In step 5, the specific operation of the melt spinning process is as follows: after the melt is extruded by a twin-screw extruder, it enters the melt booster pump for pressurization, melt filtration, metering pump for metering, and the melt is ejected through the die head. The temperatures of the melt booster pump, metering pump and filtration zone are all the same, the feed temperature is 250-260°C, and the die head temperature is 250-280°C. Among them, the temperature of the die head zone 1 is controlled at 250-260°C, the temperature of the die head zone 2 is 260-265°C, the temperature of the die head zone 3 is 260-275°C, the temperature of the die head zone 4 is 260-275°C, and the temperature of the die head zone 5 is 260-280°C.

9. The method for preparing a hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 5, wherein: In step 5, in the hot air drawing process, the hot air temperature is 270-285°C, and the drawing air pressure is 0.1-0.3MPa.

10. The method for preparing a hydrophilic and wear-resistant PET melt-blown nonwoven fabric material according to claim 5, characterized in that: In step 2, the temperature during the heating reaction is 240-250° C., the pressure is 0.1-0.2 MPa, and the amount of esterification water distilled is calculated by the following formula: esterification water amount (kg) = total molar number of acid components in the reaction system × 36 × 98%.

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