Diesterified starch-based flame retardant and preparation method thereof, and starch-based flame-retardant finishing agent and preparation method and use

Abstract

A diesterified starch-based flame retardant and preparation thereof. The diesterified starch-based flame retardant is prepared by adding 9.5-10.5 parts by weight (pbw) sodium dihydrogen phosphate, 9.5

Description

[0002] Polylactic acid fiber has a wide range of sources, and its waste can be degraded into carbon dioxide and water in nature. Therefore, the polylactic acid fiber is a type of sustainable ecological fiber. However, due to flammability and burning drip characteristics, polylactic acid fibers have huge safety hazards during the production and use. Accordingly, it is necessary to study flame retardant modification of the polylactic acid fibers, which is of great significance for its wide application.

[0003] Starch has low cost, easily-available raw materials, no pollution, and easy degradation, and is widely used in flame-retardant finishing. Phosphate starch is a type of esterified starch formed by esterification on hydroxyl groups and phosphate groups in a starch glucose residue; carbamate starch is a type of starch formed by carbamate groups substituting some of the hydroxyl groups in the starch glucose residue, and introducing amide groups into a starch macromolecule. When the above two esterified starches are used alone, the starch slurry has poor gelatinization performance and low stability, resulting in an unsatisfactory flame retardant effect, and showing certain limitations during use. SUMMARY

[0004] An objective of the present disclosure is to provide a diesterified starch-based flame retardant, and a starch-based flame-retardant finishing agent and a preparation method and use thereof. In the present disclosure, the diesterified starch-based flame retardant has a remarkable flame-retardant effect, and polylactic acid fabrics treated by the flame retardant have a significantly improved flame-retardant performance, thereby effectively improving a combustion performance of the polylactic acid fabrics.

[0005] To achieve the above objective, the present disclosure provides the following technical solutions:

[0006] According to a first aspect, the present disclosure provides a preparation method of a 20 02 24 diesterified starch-based flame retardant, including the following steps:

[0007] dissolving 9.5 to 10.5 parts by mass of sodium dihydrogen phosphate, 9.5 to 10.5 parts by mass of disodium hydrogen phosphate, 9.5 to 10.5 parts by mass of ammonium chloride, and 9.5 to 10.5 parts by mass of urea into 90 to 110 parts by mass of water, and mixing an obtained solution with 95 to 105 parts by mass of corn starch to obtain a starch suspension;

[0008] filtrating the starch suspension to obtain a filter cake; and

[0009] drying the filter cake, and conducting esterification at 128°C to 130°C to obtain the diesterified starch-based flame retardant.

[0010] Preferably, the esterification is conducted for 110 min to 120 min.

[0011] Preferably, a dried filter cake has a moisture content of 10% to 12%.

[0012] Preferably, the preparation method further includes the following steps after the esterification: washing, drying, pulverizing, and sieving an esterified product in sequence.

[0013] According to a second aspect, the present disclosure provides a preparation method of a starch-based flame-retardant finishing agent, including the following steps: mixing 95 parts to 105 parts of a diesterified starch-based flame retardant, 18 parts to 20 parts of a penetrant, and 18 parts to 20 parts of urea with 1,900 parts to 2,100 parts of water to obtain a suspension; and conducting gelatinization on a starch by conducting reflux condensation and heating on the suspension to obtain the starch-based flame-retardant finishing agent; where the diesterified starch-based flame retardant is prepared by the preparation method according to the first aspect.

[0014] Preferably, the reflux condensation and heating are conducted at 88°C to 90°C for 15 min to 20 min.

[0015] According to a third aspect, the present disclosure provides use of the starch-based flameretardant finishing agent in finishing polylactic acid fabrics.

[0016] Preferably, a process of finishing polylactic acid fabric includes the following steps: placing polylactic acid fabric in the starch-based flame-retardant finishing agent to conduct padding, collecting padded polylactic acid fabric, and conducting pre-drying at 103°C to 105°C and baking at 125°C to 130°C in sequence.

[0017] In the present disclosure, the diesterified starch-based flame retardant is prepared by di esterification, where a phosphorus-nitrogen-containing starch-based flame retardant is prepared by introducing phosphate groups and amino groups into a starch macromolecule.

[0018] In the present disclosure, the diesterified starch of phosphate-carbamate, namely a phosphate-carbamate starch, can significantly reduce a gelatinization temperature of the starch, improve a stability of a paste liquid, and enhance an adhesion to the polylactic acid fibers, thereby significantly improving flame retardancy of a finished polylactic acid Tibetans Khata fabric.

[0019] In the present disclosure, the diesterified starch-based flame retardant has the advantages 20 02 24 of both phosphorus-based and nitrogen-based flame retardants, and can produce acidic substances, such as pyrophosphoric acid and polyphosphoric acid, that promote polymer char formation during combustion and degradation. Therefore, the flame retardant can form a dense and continuous carbon layer on a surface of the material, isolating external oxygen and heat to prevent the reaction of free radicals. In addition, during the combustion, phosphorus-containing free radicals generated can capture free radicals from the outside, thereby delaying the entire combustion process and achieving an effect of gas-phase flame retardancy. In addition, the diesterified starch-based flame retardant may be decomposed by heat during the combustion to release a large amount of inert gases such as NH3, NO, and N2O, diluting an oxygen concentration and a concentration of flammable volatiles on a surface of the substrate to a certain extent, thereby achieving the flameretardant effect. As a result, compared with a single phosphorus-based or nitrogen-based flame retardant, the phosphorus-nitrogen-containing and double-modified starch-based flame retardant can significantly improve a flame-retardant effect of the polylactic acid fabrics.

[0020] In the present disclosure, compared with traditional inorganic flame retardants, the diesterified starch-based flame retardant has desirable biocompatibility, has excellent adhesion to polylactic acid fibers, and is completely biodegradable. Moreover, the flame-retardant finishing agent of the present disclosure is a brand-new and natural polymer-based flame-retardant finishing agent.

[0021] In summary, the diesterified starch-based flame retardant is prepared from com starch, sodium dihydrogen phosphate, disodium hydrogen phosphate, and urea, which has a wide source of raw materials that is abundant and easily available with a low cost. The flame retardant has a simple preparation process with less equipment; and the flame retardant has few conditions for flame retardant finishing and is convenient and easy to implement, showing a desirable flameretardant effect. After finishing, polylactic acid Tibetans Khata fabrics have a limiting oxygen index increasing from 21.4 to 24.8. Meanwhile, the flame retardant can be completely degraded, causing no environmental pollution in the subsequent treatments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 shows infrared spectrograms of a diesterified starch-based flame retardant prepared in Example 1 and com starch;

[0023] FIG. 2 shows a scanning electron microscopy (SEM) image of the corn starch;

[0024] FIG. 3 shows a SEM image of a carbamate starch-based flame retardant prepared in Comparative Example 1; and

[0025] FIG. 4 shows a SEM image of the diesterified starch-based flame retardant prepared in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present disclosure provides a preparation method of a diesterified starch-based flame retardant, including the following steps:

[0027] dissolving 9.5 to 10.5 parts by mass of sodium dihydrogen phosphate, 9.5 to 10.5 parts by mass of disodium hydrogen phosphate, 9.5 to 10.5 parts by mass of ammonium chloride, and 9.5 to 10.5 parts by mass of urea into 90 to 110 parts by mass of water, and mixing an obtained solution with 95 to 105 parts by mass of corn starch to obtain a starch suspension;

[0028] filtrating the starch suspension to obtain a filter cake; and

[0029] drying the filter cake, and conducting esterification at 128°C to 130°C to obtain the diesterified starch-based flame retardant.

[0030] In the present disclosure, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art.

[0031] In the present disclosure, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium chloride, and urea are dissolved into water, and an obtained solution is mixed with corn starch to obtain a starch suspension.

[0032] In the present disclosure, 9.5 to 10.5 parts by mass of the sodium dihydrogen phosphate, 9.5 to 10.5 parts by mass of the disodium hydrogen phosphate, 9.5 to 10.5 parts by mass of the ammonium chloride, and 9.5 to 10.5 parts by mass of the urea are dissolved into 90 to 110 parts by mass of water, and the obtained solution is mixed with 95 to 105 parts by mass of the com starch to obtain the starch suspension. Further, in parts by mass, preferably 9.8 parts to 10.2 parts of the sodium dihydrogen phosphate, preferably 9.8 parts to 10.2 parts of the disodium hydrogen phosphate, preferably 9.8 parts to 10.2 parts of the ammonium chloride, and preferably 9.8 parts to 10.2 parts of the urea are dissolved into more preferably 95 parts to 105 parts of water, and the obtained solution is mixed with preferably 98 parts to 102 parts of the com starch to obtain the starch suspension. The water is preferably deionized water.

[0033] In the present disclosure, a process of mixing an obtained solution with com starch is preferably adding the corn starch into the solution. After adding the corn starch, a mixture is preferably stirred at 48°C to 50°C for 25 min to 30 min to obtain a starch suspension. A purpose of stirring at 48°C to 50°C for 25 min to 30 min is to swell the starch and fully mix the starch with a reaction agent.

[0034] In the present disclosure, the starch suspension is filtrated to obtain a filter cake.

[0035] In the present disclosure, the filtering is conducted by preferably suction filtration.

[0036] In the present disclosure, the filter cake is dried, and esterification is conducted at 128°C to 130°C to obtain the diesterified starch-based flame retardant. 20 02 24

[0037] In the present disclosure, the drying is conducted at preferably 48°C to 52°C; and there is no special requirement on a drying time, and preferably a dried filter cake has a moisture content of 10% to 12%. A purpose of controlling the moisture content of the filter cake at 10% to 12% is that: the moisture content in this range can make the reaction agent fully contact with the starch, while hydrolysis side reactions of the esterified starch may not be caused by too much water.

[0038] In the present disclosure, the esterification is conducted for preferably 110 min to 120 min. During the esterification, the starch macromolecule undergoes phosphorylation with orthophosphate under the catalysis of urea, and also reacts with amino groups to produce carbamate starch.

[0039] In the present disclosure, after the esterification, washing, drying, pulverizing, and sieving are preferably conducted on an esterified product in sequence to the diesterified starch-based flame retardant.

[0040] In the present disclosure, the washing is preferably conducted 2 to 3 times with deionized water; the drying is conducted at preferably 48°C to 50°C; and the sieving is preferably conducted through a 65-mesh (230 micron) sieve.

[0041] In the present disclosure, the diesterified starch-based flame retardant is prepared by di esterification, where a phosphorus-nitrogen-containing starch-based flame retardant is prepared by introducing phosphate groups and amino groups into a starch macromolecule.

[0042] The present disclosure further provides a diesterified starch-based flame retardant prepared by the preparation method. In the present disclosure, the diesterified starch-based flame retardant has the advantages of both phosphorus-based and nitrogen-based flame retardants, and can produce acidic substances, such as pyrophosphoric acid and polyphosphoric acid, that promote polymer char formation during combustion and degradation. Therefore, the flame retardant can form a dense and continuous carbon layer on a surface of the material, isolating external oxygen and heat to prevent the reaction of free radicals. In addition, during the combustion, phosphorus-containing free radicals generated can capture free radicals from the outside, thereby delaying the entire combustion process and achieving an effect of gas-phase flame retardancy. In addition, the flame retardant may be decomposed by heat during the combustion to release a large amount of inert gases such as NH3, NO, and N2O, diluting an oxygen concentration and a concentration of flammable volatiles on a surface of the substrate to a certain extent, thereby achieving the flameretardant effect. As a result, compared with a single phosphorus-based or nitrogen-based flame retardant, the phosphorus-nitrogen-containing and double-modified starch-based flame retardant can significantly improve a flame-retardant effect of the polylactic acid fabrics.

[0043] The present disclosure further provides a preparation method of a starch-based flameretardant finishing agent, including the following steps: mixing 95 parts to 105 parts of a 20 02 24 diesterified starch-based flame retardant, 18 parts to 20 parts of a penetrant, and 18 parts to 20 parts of urea with 1,900 parts to 2,100 parts of water to obtain a suspension; and conducting gelatinization on a starch by conducting reflux condensation and heating on the suspension to obtain the starch-based flame-retardant finishing agent; where the diesterified starch-based flame retardant is prepared by the preparation method according to the first aspect.

[0044] In the present disclosure, the reflux condensation and heating are conducted at preferably 88°C to 90°C for preferably 15 min to 20 min.

[0045] In the present disclosure, there is no special requirement on a type of the penetrant, and penetrants well known in the art can be used. The urea is to promote swelling of the polylactic acid fiber in hot water, so as to facilitate diffusion and penetration of a macromolecule of the diesterified starch-based flame retardant to the polylactic acid fiber, thereby increasing a loading rate of the flame retardant to further enhance a flame-retardant effect of polylactic acid Tibetans Khata fabrics.

[0046] The present disclosure further provides a starch-based flame-retardant finishing agent prepared by the preparation method.

[0047] The present disclosure further provides use of the starch-based flame-retardant finishing agent in finishing polylactic acid fabrics. The polylactic acid fabrics include preferably polylactic acid Tibetans Khata.

[0048] In the present disclosure, a process of finishing polylactic acid fabric includes preferably the following steps: placing polylactic acid fabric in the starch-based flame-retardant finishing agent to conduct padding, collecting padded polylactic acid fabric, and conducting pre-drying at 103°C to 105°C and baking at 125°C to 130°C in sequence.

[0049] In the present disclosure, the padding is conducted at a padding rate of preferably 200%. The pre-drying is conducted for preferably 8 min to 10 min; the baking is conducted for preferably 2 min to 3 min. The pre-drying is to remove side reactions that moisture brings to the esterification, namely hydrolysis; and the baking at 125°C to 130°C is to react with the fibers to produce a washable flame-retardant effect.

[0050] The diesterified starch-based flame retardant and the preparation method thereof, and the starch-based flame-retardant finishing agent and the preparation method and the use thereof provided by the present disclosure will be described in detail below with reference to examples, but these examples should not be construed as limiting the scope of the present disclosure.

[0051] Example 1

[0052] 10 parts for each of sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium chloride, and urea were dissolved in 100 parts of deionized water to obtain a solution, and then corn starch was added to the solution to prepare a suspension; the suspension was heated in a water bath at 50°C while stirring with a magnetic stirrer for 30 min; and a treated suspension 20 02 24 was filtered with a suction filter to obtain a filter cake and weighed; and

[0053] the filter cake was dried in an oven at 50°C until a moisture content was 10%, and then reacted at 130°C for 2 h. A product was washed with deionized water for 2 to 3 times, dried in an oven at a low temperature of 50°C, pulverized, and sieved by a 65-mesh (230 micron) sieve to obtain a powdery diesterified starch-based flame retardant.

[0054] Comparative Example 1

[0055] 10 parts for each of ammonium chloride and urea were dissolved in 100 parts of deionized water to obtain a solution, and then corn starch was added to the solution to prepare a suspension; the suspension was heated in a water bath at 50°C while stirring with a magnetic stirrer for 30 min; and a treated suspension was filtered with a suction filter to obtain a filter cake and weighed; and

[0056] the filter cake was pre-dried in an oven at 50°C until a moisture content was 10%, and then reacted at 130°C for 2 h. A product was washed with deionized water for 2 to 3 times, dried in an oven at a low temperature of 50°C, pulverized, and sieved by a 65-mesh (230 micron) sieve to obtain a powdery carbamate starch-based flame retardant.

[0057] The flame retardants prepared in Example 1 and Comparative Example 1 were characterized, and their physical and chemical properties were analyzed.

[0058] FIG. 1 showed infrared spectrograms of the diesterified starch-based flame retardant prepared in Example 1 and com starch. As shown in FIG. 1, compared with native starch, the vo-h bands at 3,500 cm'1 to 3,200 cm'1 and the SOH bands near 1,600 cm'1 of the diesterified starch-based flame retardant narrowed, with its peak intensity being weakened. This change was easily observed in the infrared spectrum, since some of hydroxyl groups in a starch molecule were consumed due to participation in the esterification, resulting in a decrease in the number of O-H bonds. In addition, a carbonyl stretching vibration absorption peak vc=o appeared around 1,750 cm'1 in the esterification, which might be due to the conversion of O-H bonds into C=O bonds during the grafting by a large number of hydroxyl groups participating in the reaction. Moreover, the spectrum peaks of stretching vibration of a middle C-N bond and P=O and P-0 bonds appeared at 1,175 cm’1 and 1,116 cm’1 to 1,007 cm’1, respectively. The above changes indicated that after the diesterification modification, amino and phosphate flame-retardant functional groups had been introduced into the natural starch macromolecule.

[0059] FIG. 2 showed a SEM image of the corn starch; FIG. 3 showed a SEM image of the carbamate starch-based flame retardant prepared in Comparative Example 1; and FIG. 4 showed a SEM image of the diesterified starch-based flame retardant prepared in Example 1. It was seen from FIG. 2 that granules of natural corn starch were mostly polygonal, with a smooth surface, regular shape, and a small particle size of 10 pm to 15 pm. It was seen from FIG. 3 that the nitrogen-containing monoesterified starch granules prepared in Comparative Example 1 had no 20 02 24 significant difference compared with the native starch, indicating a lower degree of denaturation. In contrast, as shown in FIG. 4, the phosphorous-nitrogen-containing diesterified starch-based flame retardant prepared in Example 1 had more significant changes in granules than those of the native starch; damages and holes appeared on the surface of some granules, indicating that the chemical denaturation had caused certain damages to the morphology and structure of starch granules. Meanwhile, a certain bonding appeared between the granules, the reason was that chemical denaturation led to an increase in polarity of the surface of the starch granules, such that the interaction between the granules was enhanced. The above changes were beneficial to the gelatinization of starch granules to form a stable finishing solution, so as to improve an adhesion effect to polylactic acid fibers and a flame-retardant finishing effect.

[0060] Use Example 1

[0061] The raw materials included the following components in parts by mass: 100 parts of the diesterified starch-based flame retardant, 20 parts of a penetrant, 20 parts of urea, and 2,000 parts of deionized water.

[0062] The diesterified starch-based flame retardant, the penetrant, and the urea were dissolved in the deionized water to form a suspension, and transferred to a three-necked flask; the flask was placed in a constant-temperature magnetic stirrer that was connected to a reflux condensation device, and stirred at 90°C for 20 min to gelatinize the starch to obtain a flame-retardant finishing agent.

[0063] The product was taken out, and a polylactic acid fabric was subjected to flame-retardant finishing with the product through padding at a padding rate of 200%; a treated fabric was dried in an oven at 105°C for 10 min, and then baked in an oven at 130°C for 3 min to obtain a flameretardant-treated polylactic acid fabric.

[0064] Comparative Use Example 1

[0065] A polylactic acid fabric without flame-retardant finishing was prepared.

[0066] Comparative Use Example 2

[0067] The raw materials included the following components in parts by mass: 100 parts of the carbamate starch-based flame retardant prepared in Comparative Example 1, 20 parts of a penetrant, 20 parts of urea, and 2,000 parts of deionized water.

[0068] The carbamate starch-based flame retardant, the penetrant, and the urea were dissolved in the deionized water to form a suspension, and transferred to a three-necked flask; the flask was placed in a constant-temperature magnetic stirrer that was connected to a reflux condensation device, and stirred at 90°C for 20 min to gelatinize the starch to obtain a flame-retardant finishing agent.

[0069] The product was taken out, and a polylactic acid fabric was subjected to flame-retardant finishing with the product through padding at a padding rate of 200%; a treated fabric was dried in an oven at 105°C for 10 min, and then baked in an oven at 130°C for 3 min to obtain a flame-retardant-treated polylactic acid fabric.

[0070] A limiting oxygen index test was conducted on the polylactic acid fabrics treated with the flame retardants of each example and comparative use example. The determination of the limiting oxygen index referred to "GB / T 5454-1997 Textiles-Burning behavior-Oxygen index method", and the results were shown in Table 1.

[0071] Table 1 Limiting oxygen index of use examples and comparative use examples

[0072] __________________________________________________________________________________ Test Example Limiting oxygen index (%) Use Example 1 24.8 Comparative Use Example 1 21.4 Comparative Use Example 2 22.5 20 02 24

[0073] It was seen from the test results in Table 1 that in Comparative Use Example 1, the pure-spun polylactic acid fiber-based Tibetans Khata fabric had a lower limiting oxygen index of 21.4%, indicating a higher flammability. In Comparative Use Example 2, the limiting oxygen index of polylactic acid Tibetans Khata finished with carbamate-monoesterified starch had increased to 22.5%, indicating that the flame retardancy had been improved. This was because in the monoesterification modification, due to the introduction of nitrogen-containing groups, the flame retardant might be decomposed by heat during the combustion to release a large amount of inert gases such as NHt, NO, and N2O, diluting an oxygen concentration and a concentration of flammable volatiles on a surface of the substrate to a certain extent, thereby achieving the flameretardant effect. However, in Comparative Use Example 2, the limiting oxygen index was not significantly improved, indicating that the improvement of its flame retardancy was not significant. This was because although the above gases might dilute the oxygen concentration and the concentration of flammable volatiles on the surface of the substrate to a certain extent, thereby achieving the flame-retardant effect, but there was a poor flame retardant efficiency when being used alone.

[0074] In Use Example 1, the polylactic acid Tibetans Khata fabric finished with the diesterified starch-based flame retardant had a limiting oxygen index of 24.8%, which was further improved compared with that of Comparative Use Example 2. This was because the diesterified starch-based flame retardant had both nitrogen-containing and phosphorus-containing flame-retardant groups. During combustion and degradation, acidic substances that promote polymer char formation were produced, such as pyrophosphoric acid and polyphosphoric acid during combustion and degradation. Therefore, the flame retardant can form a dense and continuous carbon layer on a surface of the material, isolating external oxygen and heat to prevent the reaction of free radicals. In addition, during the combustion, phosphorus-containing free radicals generated can capture free radicals from the outside, thereby delaying the entire combustion process. Therefore, the diesterified starch-based flame retardant of the present disclosure have the functions of agglomerated-phase flame retardancy and gas-phase flame retardancy, which was a main reason for its excellent flame retardancy for the polylactic acid Tibetans Khata fabrics.

[0075] The above descriptions are merely preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the protection scope of the present disclosure. 20 02 24 20 02 24

Claims

1. A preparation method of a diesterified starch-based flame retardant, comprising the following steps:dissolving 9.5 to 10.5 parts by mass of sodium dihydrogen phosphate, 9.5 to 10.5 parts by mass of disodium hydrogen phosphate, 9.5 to 10.5 parts by mass of ammonium chloride, and 9.5 to 10.5 parts by mass of urea into 90 to 110 parts by mass of water, and mixing an obtained solution with 95 to 105 parts by mass of corn starch to obtain a starch suspension;filtrating the starch suspension to obtain a filter cake; anddrying the filter cake, and conducting esterification at 128°C to 130°C to obtain the diesterified starch-based flame retardant.

2. The preparation method according to claim 1, wherein the esterification is conducted for 110 min to 120 min.

3. The preparation method according to claim 1, wherein a dried filter cake has a moisture content of 10% to 12%.

4. The preparation method according to claim 1, further comprising the following steps after the esterification: washing, drying, pulverizing, and sieving an esterified product in sequence.

5. A preparation method of a starch-based flame-retardant finishing agent, comprising the following steps: mixing 95 parts to 105 parts of a diesterified starch-based flame retardant, 18 parts to 20 parts of a penetrant, and 18 parts to 20 parts of urea with 1,900 parts to 2,100 parts of water to obtain a suspension; and conducting gelatinization on a starch by conducting reflux condensation and heating on the suspension to obtain the starch-based flame-retardant finishing agent; wherein the diesterified starch-based flame retardant is prepared by the preparation method according to any one of claims 1 to 4.

6. The preparation method according to claim 5, wherein the reflux condensation and heating are conducted at 88°C to 90°C for 15 min to 20 min.

7. Use of the starch-based flame-retardant finishing agent prepared by the preparation method according to claim 5 or 6 in finishing polylactic acid fabrics.

8. The use according to claim 7, wherein a process of finishing polylactic acid fabric comprises the following steps: placing polylactic acid fabric in the starch-based flame-retardant finishing agent to conduct padding, collecting padded polylactic acid fabric, and conducting pre-drying at 103°C to 105°C and baking at 125°C to 130°C in sequence.20 02 24

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