CN111764154A - A kind of method for improving the flame retardant performance of modified ramie fabric - Google Patents

Abstract

The invention discloses a method for improving the flame retardant performance of modified ramie fabric, comprising the following steps: (1) washing the ramie fabric in deionized water for 5-10 minutes, and then drying; The ramie fabric is soaked in the aldehyde-based functionalization reagent solution for 6 to 10 hours, taken out and then dried; (3) the ramie fabric treated in step (2) is soaked in the chitosan solution, and then baked; the method is based on the following steps: After the surface aldehyde group is functionalized by periodic acid or sodium periodate treatment, the surface of ramie fabric is pretreated by chemical method of Schiff base reaction between aldehyde group and amino group, and then polyethyleneimine (PEI) is used to pretreat the surface of ramie fabric. It is prepared by a layer-by-layer self-assembly method with positive charge and ammonium polyphosphate (APP) as negative charge. The process is simple, flexible and stable, and can effectively improve the flame retardant properties of ramie fabrics.

Description

A kind of method for improving the flame retardant performance of modified ramie fabric

technical field

The invention relates to the technical field of ramie fiber processing, in particular to a method for improving the flame retardancy of modified ramie fabrics.

Background technique

As a natural cellulose fiber, ramie has many advantages, such as low cost, light weight and environmental friendliness. The tensile strength of ramie fiber is 850-900N/mm2, which is much higher than other natural fibers such as flax and jute, and almost equal to glass fiber. As a composite material reinforcement, ramie fiber has been widely studied and used in systems such as polylactic acid, polypropylene, epoxy resin, phenolic resin and benzoxazine resin. However, plant fibers have poor thermal stability and easy combustion, which limit their practical applications. Therefore, researches on flame retardant modification of ramie fibers or fabrics and their use in reinforced composites have attracted much attention.

Layer-by-layer (LBL) assembly is a technique for alternately depositing multilayer films on solid surfaces based on the physical adsorption of oppositely charged polyelectrolytes. The method is simple, flexible, and stable, and is not only suitable for polyelectrolyte systems, but also for any charged species, and thus has received more and more attention. The wide adaptability of LBL technology makes it have potential application value in many fields. But so far, this method requires 15-20 double layers, or even 30 double layers to be assembled in order to obtain a satisfactory flame retardant modification effect, which limits its wide application in industry.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the above shortcomings of the prior art: to provide a method for improving the flame retardant performance of modified ramie fabrics. The surface of the ramie fabric was pretreated by the chemical method of the Schiff base reaction between the aldehyde group and the amino group, and then polyethyleneimine (PEI) was used as the positive charge and ammonium polyphosphate (APP) as the negative charge. The layer self-assembly method is prepared, the process operation is simple, flexible and stable, and the flame retardant performance of the ramie fabric can be effectively improved.

The technical solution of the present invention is as follows: a method for improving the flame retardant performance of modified ramie fabric, comprising the following steps:

(1) The ramie fabric is washed in deionized water for 5 to 10 minutes, and then dried;

(2) soaking the ramie fabric treated in step (1) in an aldehyde-based functionalization reagent solution for 6-10 hours, taking it out and drying;

(3) the ramie fabric treated in step (2) is dipped in the chitosan solution, and then baked;

(4) soak the ramie fabric treated in step (3) in the APP solution for 2 to 5 minutes, then use deionized water to wash for 1 to 3 times and dry;

(5) soaking the ramie fabric treated in step (4) in PEI solution for 2～5min, then using deionized water to wash 1～3 times and drying;

(6) The process of step (4) and step (5) describes an assembly cycle that includes a complete bilayer of PEI and APP, and the process of step (4) and step (5) is repeated until the desired number of layers is reached;

(7) drying the ramie fabric obtained in step (6) to obtain a flame retardant modified ramie fabric.

In the step (2), the aldehyde group functionalizing reagent is one of periodic acid and sodium periodate.

The concentration of the aldehyde-based functionalization reagent solution in the step (2) is 3-5 wt%.

In the step (2), the pH of the aldehyde-based functionalizing reagent solution is 5-6 wt %.

The concentration of the chitosan solution in the step (3) is 1-2 wt%.

In the step (3), the conditions for dipping and rolling are as follows: two dips and two rollings, and the overroll ratio is controlled at 70-90%.

The baking conditions in the step (3) are: baking in a baking machine with a temperature of 90-100° C. for 5-10 minutes.

The concentration of the APP solution in the step (4) is 1.0-2.0% by weight, and the concentration of the PEI solution in the step (5) is 1.0-2.0% by weight.

Drying in the steps (1) and (2) specifically refers to: drying in a blast dryer at 70 to 90°C for 5 to 10 minutes; drying in the steps (3) and (4) specifically refers to: drying the ramie fabric It was placed on a quartz piece blown dry with N ₂ , and then placed in a blast drying oven at 70-90°C for 5-10min.

The drying in the step (7) specifically refers to: placing the ramie fabric in a 50-60° C. vacuum drying oven for 15-30 minutes, and then placing it in a drying dish for 10-12 hours.

The beneficial effects of the present invention are: compared with the prior art, the present invention has the following significant advantages and beneficial effects:

(1) Using this chemical method to pretreat ramie fabrics can increase the number of positive charges on the surface of ramie fabrics, greatly improve the adsorption capacity of single-layer self-assembled flame retardants, and then reduce the assembly of layer-by-layer self-assembly. layers.

(2) Compared with the process without pretreatment, the flame retardant adsorption capacity and flame retardant effect of the ramie fabric assembled by this method are obviously improved, and the self-restoration can be realized when only 10 double layers are assembled. The assembly processing time is shortened to a certain extent, which further improves the flexibility, stability and cost of the method;

(3) The ramie fabric prepared by the method of the present invention has excellent heat resistance and carbon residue rate, and the peak heat release rate (PHRR), total heat release (THR), and average CO and _CO2 release are significantly reduced; limiting oxygen index (LOI) increased from 18.0% to 30.6%; after vertical combustion, a continuous and dense protective carbon layer structure was formed, the original orthogonal plain weave structure of the fabric was completely preserved, and the flame retardant effect with excellent self-sustaining property was achieved. ;

(4) The ramie fabric prepared by the method of the present invention is suitable for making green composite materials with high performance and high temperature resistance and flame retardancy.

Description of drawings

What is shown in Fig. 1 is the preparation process schematic diagram of the flame-retardant modified ramie fabric of the present invention;

What is shown in Fig. 2 is the scanning electron microscope picture of the ramie fabric before and after the flame-retardant modified ramie fabric of the present invention is assembled layer by layer;

Figure 3 is a photo of the flame-retardant modified ramie fabric of the present invention 5s after ignition in a vertical combustion experiment;

What is shown in Fig. 4 is the photo of the residual carbon after the vertical combustion experiment of the flame-retardant modified ramie fabric of the present invention;

What is shown in Fig. 5 is the scanning electron microscope image of the carbon residue after the vertical combustion experiment of the flame-retardant modified ramie fabric of the present invention;

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments. It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present invention. Unless otherwise defined, all scientific and technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Example 1:

The ramie fabric was washed in deionized water, taken out, and dried in a blast dryer at 90 °C for 5 min. The cleaned ramie fabric was soaked in an aldehyde-based functionalization reagent solution with a concentration of 3 wt % for 10 h, taken out, and dried in a blast dryer at 90° C. for 5 min. The aldehyde-based ramie fabric was subjected to padding treatment in a chitosan solution with a concentration of 1 wt %, with an overage rate of 90%, and was baked at 90° C. for 10 minutes. The treated ramie fabric is then immersed in APP solution with a concentration of 1.0 wt% and PEI solution with a concentration of 1.0 wt% for 5 minutes, washed and dried, which is a double-layered ramie fabric with flame retardant finishing. This process was repeated until five double-layer flame-retardant coatings were assembled on the surface of the ramie fabric, and the preparation process was shown in Figure 1. The obtained ramie fabric was dried. The content of the flame retardant coating was calculated by weighing the mass of the ramie fabric before and after treatment, and it was 18.12%. Thermal gravimetric analysis of the sample showed that the carbon residue at 600°C under nitrogen was 36.9%. The limit oxygen index of the sample was measured with an oxygen index tester, and the LOI reached 26.7%.

Example 2:

The ramie fabric was washed in deionized water, taken out, and dried in a blast dryer at 90 °C for 5 min. The cleaned ramie fabric was soaked in an aldehyde-based functionalization reagent solution with a concentration of 5 wt % for 6 hours, taken out, and dried in a blast dryer at 90° C. for 5 minutes. The aldehyde-based ramie fabric was treated by padding in a chitosan solution with a concentration of 2 wt %, with an overage rate of 70%, and was baked at 100° C. for 5 minutes. The treated ramie fabric is then immersed in the APP solution with a concentration of 2.0 wt% and the PEI solution with a concentration of 2.0 wt% for 2 minutes, washed and dried. This is a double-layered ramie fabric with flame retardant finishing. This process was repeated until 10 double-layer flame retardant coatings were assembled on the surface of the ramie fabric, and the preparation process was shown in Figure 1. The obtained ramie fabric was dried. The content of the flame retardant coating was calculated by weighing the mass of the ramie fabric before and after treatment, and it was 26.03%. The analysis result of the sample by thermogravimetric analyzer showed that the carbon residue at 600°C under nitrogen condition was 39.3%. The limit oxygen index of the sample was measured with an oxygen index tester, and the LOI reached 30.6%.

Comparative ratio

The ramie fabric was washed in deionized water, taken out, and dried in a blast dryer at 90 °C for 5 min. The cleaned ramie fabric was immersed in the APP solution with a concentration of 2.0 wt% and the PEI solution with a concentration of 2.0 wt% for 2 minutes in turn, washed and dried. This is a double-layered ramie fabric with flame retardant finishing. This process was repeated until 10 double-layer flame retardant coatings were assembled on the surface of the ramie fabric. The resulting ramie fabric ((PEI/APP) ₁₀ ) was dried. The content of the flame retardant coating was calculated by weighing the mass of the ramie fabric before and after treatment, and it was 8.29%. Thermogravimetric analyzer analysis of the sample showed that the residual carbon content at 600°C under nitrogen conditions was 28.7%, respectively. The limit oxygen index of the sample was measured with an oxygen index tester, and the LOI reached 23.6%.

Untreated ramie fabric sample: Thermal gravimetric analyzer analysis of this sample showed that the Pristineramie ramie fabric had a carbon residue of 10.5%. The limit oxygen index of the sample was measured with an oxygen index tester, and the LOI reached 18.0.

The test results are shown in Tables 1 and 2. The present invention takes Examples 1, 2 and Comparative Examples 1 to 3 and untreated raw ramie fabrics as detection objects.

Table 1 Thermal properties data of ramie fabrics before and after modification under nitrogen atmosphere

Table 2 Cone calorimetry test results of ramie fabrics before and after treatment

Note: t _ign : ignition time; t _duration : burning duration; PHRR: peak heat release rate; THR: total heat release; Y _CO :; Y _CO2 : ; Char: residual carbon;

2 is a scanning electron microscope image of the ramie fabric before and after the flame-retardant modified ramie fabric of the present invention is assembled layer by layer. Compared with the original ramie fabric, the gaps between the treated ramie fabrics were gradually filled, and the flame retardant attached to the fabric surface also increased significantly with the increase of the number of assembled layers. This shows that the PEI/APP two-component intumescent coating structure has been successfully constructed on the surface of the fabric. Compared with the results of the comparative example, a thick and dense PEI/APP two-component intumescent flame retardant coating can be obtained when 10 layers are assembled by using the preparation method of the present invention, indicating that the preparation method is beneficial to improve the performance of the flame retardant. The amount of adsorption, thereby reducing the number of layers that are self-installed.

Figures 3 and 4 show the photos of the flame-retardant modified ramie fabric of the present invention 5s after ignition in the vertical combustion experiment and the photos of the carbon residue after the vertical combustion experiment. After the original ramie fabric was ignited, the flame quickly spread from the bottom of the fabric to the top of the fabric, and almost burned out. The flame propagation rate of the control sample is obviously slowed down, and the combustion process is also milder. In the end, although the carbon residue keeps the original weave structure of the fabric, it also breaks obviously. For Examples 1 and 2, after chemical pretreatment, the ramie fabric exhibited better self-extinguishing properties only when 10 PEI/APP bilayers were assembled.

Fig. 5 is the scanning electron microscope picture of the carbon residue after the vertical combustion experiment of the flame-retardant modified ramie fabric of the present invention. The residual charcoal of the original ramie fabric retains the plain weave structure, however, during the combustion process, the fiber shrinks seriously, and the fiber surface is smooth and clean. The fiber shrinkage and voids of the comparative ramie fabric after burning were significantly reduced, and the integrity of the carbon residue was also significantly improved. There were many expanded carbon particles in the voids between the fibers. For Examples 1 and 2, after the ramie fabric was chemically pretreated, a thick and dense intumescent flame-retardant carbon layer was formed on the surface of the ramie fabric after burning when only 10 PEI/APP double layers were assembled. The carbon layer has a strong flame shielding effect on the bottom ramie fabric matrix, so that the flame retardant modified ramie fabric of the present invention shows better flame retardant effect.

Table 1 is the thermal performance data of the flame-retardant modified ramie fabric of the present invention before and after modification under nitrogen atmosphere. Compared with the original ramie fabric, the temperature (T _5% ) of all the assembled ramie fabrics at a thermal weight loss of 5 wt% decreased gradually with the increase of the flame retardant concentration and the number of assembled layers, mainly because Flame retardants PEI and APP were caused by early thermal degradation. However, the carbon residue of the treated ramie at 600℃ was significantly higher than that of the original ramie fabric. For the ramie fabrics of Examples 1 and 2 of the present invention, after chemical pretreatment, the carbon residue of the ramie fabrics at 600°C can be increased from 10.5% to 39.3% when only 10 PEI/APP double layers are assembled. Compared with the comparative example, the decomposition rate was significantly slower, and the carbon residue at 600°C was also significantly increased. It can be seen that PEI/APP flame retardant promotes ramie fabrics to have excellent carbon-forming properties, which in turn endows ramie fabrics with excellent flame retardant properties.

Table 2 is the cone calorimetry test result of the flame retardant modified ramie fabric of the present invention. For the original ramie fabric, the ignition time was the shortest, the burning duration was the longest, the heat release rate and total heat release were also the largest, and the carbon residue was the lowest. For the ramie fabric of the comparative example, the construction (PEI/APP) ₁₀ flame retardant coating can effectively prolong the ignition time, shorten the burning duration, reduce the heat release rate and total heat release amount, and increase its carbon residue. However, the ramie fabrics of Examples 1 and 2 of the present invention, after chemical pretreatment, have the longest ignition time, the shortest burning duration, and the least (PEI/APP) _n flame retardant coating layers. The heat release rate and total heat release amount, which in turn has the highest carbon residue.

The above results all show that the chemical surface pretreatment of ramie fabric can effectively improve the single-layer adsorption effect of self-assembly, significantly reduce the number of assembled layers, and increase the adsorption capacity of the flame retardant coating, thereby making it have excellent flame retardant properties. Effect.

The test standard on which the limiting oxygen index test of the present invention is based is GB/T 5454-1997, the test standard on which the vertical combustion test is based is GB/T 5455-1997, and the test standard on which the cone calorimetry test is based is ISO 5660-1 .

The above are only preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, improvements and modifications can be made without departing from the core technology of the present invention. These improvements and Retouching should also belong to the scope of patent protection of the present invention. Any changes within the meaning and scope equivalent to the claims of the present invention should be construed as being included in the scope of the claims.

Claims (10)

1. A method for improving the flame retardant property of modified ramie fabric is characterized by comprising the following steps:

(1) cleaning the ramie fabric in deionized water for 5-10 minutes, and then drying;

(2) soaking the ramie fabric treated in the step (1) in an aldehyde functional reagent solution for 6-10 h, taking out and drying;

(3) dipping the ramie fabric treated in the step (2) in a chitosan solution, and then baking;

(4) soaking the ramie fabric treated in the step (3) in an APP solution for 2-5 min, then washing for 1-3 times in deionized water, and drying;

(5) soaking the ramie fabric treated in the step (4) in a PEI solution for 2-5 min, then washing for 1-3 times in deionized water, and drying;

(6) the processes of step (4) and step (5) describe an assembly cycle comprising a complete bilayer of PEI and APP, and the processes of step (4) and step (5) are repeated until the desired number of layers is reached;

(7) and (4) drying the ramie fabric obtained in the step (6) to obtain the flame-retardant modified ramie fabric.

2. The method for improving the flame retardant property of the modified ramie fabric according to claim 1, wherein the aldehyde-based functionalizing agent in the step (2) is one of periodic acid and sodium periodate.

3. The method for improving the flame retardant property of the modified ramie fabric according to claim 2, wherein the concentration of the aldehyde-based functionalization reagent solution in the step (2) is 3-5 wt%.

4. The method for improving the flame retardant property of the modified ramie fabric according to claim 1, wherein the pH of the aldehyde-based functionalization reagent solution in the step (2) is 5-6 wt%.

5. The method for improving the flame retardant property of the modified ramie fabric according to claim 1, wherein the concentration of the chitosan solution in step (3) is 1-2 wt%.

6. The method for improving the flame retardant property of the modified ramie fabric according to claim 1, wherein the dipping treatment in the step (3) is carried out under the following conditions: and (4) carrying out secondary soaking and secondary rolling, wherein the rolling residual rate is controlled to be 70-90%.

7. The method for improving the flame retardant property of the modified ramie fabric according to claim 1, wherein the baking conditions in step (3) are as follows: the temperature is 90-100 DEG C^oAnd C, baking for 5-10min in a baking machine.

8. The method for improving the flame retardant property of the modified ramie fabric according to claim 1, wherein the concentration of the APP solution in the step (4) is 1.0-2.0 wt%, and the concentration of the PEI solution in the step (5) is 1.0-2.0 wt%.

9. The method of improving the flame retardant properties of a modified ramie fabric according to claim 1, wherein the flame retardant is a mixture of a first and a second component,the drying in the steps (1) and (2) specifically refers to: in the range of 70 to 90^oC, drying in a blast drier for 5-10 min; the drying in the steps (3) and (4) specifically refers to: placing the ramie fabric in the application N₂Drying the quartz plate, and placing the quartz plate on a 70-90 DEG air-dried quartz plate^oAnd C, drying in a forced air drying oven for 5-10 min.

10. The method for improving the flame retardant property of the modified ramie fabric according to claim 1, wherein the drying in step (7) is specifically: placing the ramie fabric in 50-60% of the total weight^oAnd C, drying in a vacuum drying oven for 15-30min, and then drying in a drying dish for 10-12 h.

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