Preparation method of para-aramid nanofibers

Abstract

The present invention relates to a preparation method of para-aramid nanofibers, and belongs to the technical field of novel polymer materials. The para-aramid nanofibers prepared in the present invention have a diameter of 10-100 nm, and a length of hundreds of microns. The preparation method includes: adding a certain amount of surfactant in a PPTA low-temperature polymerization process, and controlling aggregation of PPTA molecules along with growth of a PPTA molecule chain, thereby preparing the para-aramid fibers with a uniform size and an adjustable nano-scale diameter under assistance of other means (e.g., a coagulator and high-speed shearing dispersion). The present invention is short in production process and simple in equipment, can realize stable batch production to meet needs of large-scale production of the para-aramid nanofibers, has wide application prospects and can be applied to preparing a lithium-ion battery separator, a high-performance composite material and the like.

Claims

1. A preparation method of para-aramid nanofibers, comprising: (1) modified polymerization: under nitrogen protection, adding a dewatered solvent N-methyl pyrrolidone (NMP) with moisture content lower than 150 ppm into a reaction container; adding an solubilizing salt under stirring without the use of surfactants, wherein the solubilizing salt is calcium chloride or lithium chloride; and heating to 80-100 C. to dissolve the solubilizing salt to obtain a solution of the solubilizing salt, wherein a concentration of the solubilizing salt is 5-10 wt % and a concentration of the surfactants is 0 wt %; then cooling the solution to 0-15 C., and adding p-phenylenediamine into the reaction container for stirring and dissolving, and controlling the concentration of the p-phenylenediamine as 0.1-0.6 mol/1; continuously cooling the solution to 5-5 C., and adding terephthaloyl chloride, wherein a molar ratio of the terephthaloyl chloride to the p-phenylenediamine is (1.000-1.010):1; accelerating the stirring speed and continuously reacting for 5-30 minutes, and controlling a reaction temperature to be below 70 C.; and stopping stirring when a gel phenomenon occurs in the reaction system before reactants are completely agglomerated, thereby obtaining frozen gel; (2) dispersing into fibers: adding a dispersing agent of N-methyl pyrrolidone into the frozen gel in the above step (1) while high-speed stirring to disperse the frozen gel into a uniform gel solution, wherein a stirring speed and stirring time are regulated according to a dispersion effect and an addition amount of the dispersing agent of N-methyl pyrrolidone is 2-10 times of the solvent used in the above step (1); adding a coagulator into the above gel solution while high-speed stirring, or injecting the above gel solution into a coagulator under high-speed stirring, thereby obtaining a suspension containing the para-aramid nanofibers, wherein the stirring speed and the stirring time are regulated according to a forming effect of the nanofibers, and the use amount of the coagulator is 2-10 times of mass of the dispersing agent; and (3) washing and purification: purifying the suspension in a manner of continuous countercurrent washing or a manner of centrifugal washing to remove the solvent, the solubilizing salt and other impurities, and finally dispersing with water, thereby obtaining the pure aqueous dispersion of the para-aramid nanofibers; wherein the obtained para-aramid nanofibers have diameters, within a range of 10 to 100, adjustable according to change of formulas and processes, and have lengths of hundreds of microns; and a polymer has a logarithmic viscosity number (.sub.inh) within a range of 3.0-6.0.

2. The preparation method of para-aramid nanofibers according to claim 1, wherein the coagulator is one or a mixture of water, methanol or ethanol and other liquid alcohols according to any ratio.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a transmission electron microscope image of para-aramid nanofibers obtained in a preparation method in embodiment 1 of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) Embodiments of a method in the present invention are introduced below.

Embodiment 1

(3) steps: under nitrogen protection, adding 100 mL of a dewatered solvent N-methyl pyrrolidone with moisture content of about 100 ppm into a reaction container; adding 7.5 g of solubilizing salt of CaCl2 and 2 g of surfactant of dimethoxy polyethylene glycol (with a molecular weight of 2000) while stirring; heating to 100 C. to dissolve the solubilizing salt and the surfactant to obtain a solution of the solubilizing salt and the surfactant; cooling the solution to 15 C. in a cold bath, adding 4.326 g of p-phenylenediamine into the reaction container, and cooling the reaction container to 0 C. after the p-phenylenediamine is dissolved; and adding 8.189 g of terephthaloyl chloride, gradually accelerating the stirring speed as 2000 r/m, reacting for 5 min at a reaction temperature below 70 C., continuing to react for 2 min after a gel phenomenon occurs in the reaction system, and stopping stirring, thereby obtaining frozen gel;

(4) transferring the frozen gel into a tissue dispersion machine, adding 500 mL of dispersing agent of N-methyl pyrrolidone into the frozen gel while high-speed stirring to disperse the frozen gel into a uniform gel solution, wherein the stirring speed is 2000 r/min, and the stirring time is 5 min; and injecting the gel solution into 1000 mL of water under high-speed stirring with the stirring speed of 2000 r/min and the stirring time of 10 min, thereby obtaining uniform and stable suspension containing the para-aramid nanofibers; and

(5) washing the suspension with water on a countercurrent belt filter, and finally dispersing with water, thereby obtaining aqueous dispersion of the para-aramid nanofibers.

(6) A transmission electron microscope image of the para-aramid nanofibers prepared in the present embodiment is shown in FIG. 1. Diameters of the fibers are about tens of nanometers, and lengths of the fibers are predicted to exceed microns. It should be indicated that, distribution of the diameters of the fibers is difficult to be counted since many fibers are wound together. However, seen from most of results, the diameters of the obtained nanofibers are within 100 nm, and the lengths are also large.

Embodiment 2

(7) steps: under nitrogen protection, adding 100 mL of dewatered solvent of N-methyl pyrrolidone with moisture content of about 120 ppm into a reaction container; adding 6 g of solubilizing salt of LiCl and 1.5 g of surfactant of olyethylene glycol monomethyl ether (with a molecular weight of 2000) while stirring; heating to 80 C. to dissolve the solubilizing salt and the surfactant to obtain a solution of the solubilizing salt and the surfactant; cooling the solution to 10 C. in a cold bath, adding 2.163 g of p-phenylenediamine (PPD) into the reaction container, and cooling the reaction container to 5 C. after the p-phenylenediamine is dissolved; and adding 4.095 g of terephthaloyl chloride (TPC), gradually accelerating the stirring speed as 1500 r/min, stopping stirring after reacting for 30 min to obtain frozen gel, and controlling a reaction temperature to be below 70 C.;

(8) transferring the frozen gel into a tissue dispersion machine, adding 300 mL of dispersing agent of N-methyl pyrrolidone into the frozen gel while high-speed stirring to disperse the frozen gel into a uniform gel solution, wherein the stirring speed is 1000 r/min, and the stirring time is 5 min; and adding the gel solution into 2000 mL of methanol while strongly stirring with the stirring speed of 1500 r/min and the stirring time of 10 min, thereby obtaining uniform and stable suspension containing the para-aramid nanofibers; and

(9) repeatedly washing the uniform and stable suspension containing the para-aramid nanofibers with water for 5 times by using a centrifugal machine, and finally dispersing with water, thereby obtaining the dispersion of the para-aramid nanofibers.

Embodiment 3

(10) steps: under nitrogen protection, adding 100 mL of dewatered solvent of N-methyl pyrrolidone with moisture content of about 120 ppm into a reaction container; adding 8 g of solubilizing salt CaCl2 and 2.5 g of a surfactant amino-terminated polyethylene glycol (with a molecular weight of 2000) while stirring; heating to 90 C. to dissolve the solubilizing salt and the surfactant to obtain a solution of the solubilizing salt and the surfactant; cooling the solution to 10 C. in a cold bath, adding 6.489 g of p-phenylenediamine (PPD) into the reaction container, and cooling the reaction container to 2 C. after the p-phenylenediamine is dissolved; and adding 12.284 g of terephthaloyl chloride (TPC), gradually accelerating the stirring speed to be 1500 r/min, continuously reacting for 4 minutes, controlling a reaction temperature to be below 70 C., and immediately stopping stirring after a gel phenomenon occurs in the reaction system, thereby obtaining frozen gel;

(11) transferring the frozen gel into a tissue dispersion machine, adding 800 mL of dispersing agent of N-methyl pyrrolidone into the frozen gel while high-speed stirring to disperse the frozen gel into a uniform gel solution, wherein the stirring speed is 2000 r/min, and the stirring time is 5 min; and injecting the gel solution into 5000 mL of coagulator ethanol under high-speed stirring with the stirring speed of 3000 r/min and the stirring time of 10 min, thereby obtaining uniform and stable suspension containing the para-aramid nanofibers; and

(12) repeatedly washing the uniform and stable suspension containing the para-aramid nanofibers with water for 5 times by using a centrifugal machine, and finally dispersing with water, thereby obtaining the dispersion of the para-aramid nanofibers.

Embodiment 4

(13) steps: under nitrogen protection, adding 100 mL of dewatered solvent of N-methyl pyrrolidone with moisture content of about 60 ppm into a reaction container; adding 6 g of solubilizing salt LiCl and 1 g of surfactant of di-ester-terminated polyethylene glycol (with a molecular weight of 2000) while stirring; heating to 90 C. to dissolve the solubilizing salt and the surfactant to obtain a solution of the solubilizing salt and the surfactant; cooling the solution to 15 C. in a cold bath, adding 2.163 g of p-phenylenediamine (PPD) into the reaction container, and cooling the reaction container to 5 C. after the p-phenylenediamine is dissolved; and adding 4.095 g of terephthaloyl chloride (TPC), gradually accelerating the stirring speed to be 1500 r/min, continuously reacting for 8 minutes, controlling a reaction temperature to be below 70 C., and continuing to react for 10 min and stopping stirring after a gel phenomenon occurs in the reaction system, thereby obtaining frozen gel;

(14) transferring the frozen gel into a tissue dispersion machine, adding 400 mL of dispersing agent of N-methyl pyrrolidone into the frozen gel while high-speed stirring to disperse the frozen gel into a uniform gel solution, wherein the stirring speed is 1500 r/min and the stirring time is 5 min; and adding the gel solution into 2000 mL of water while strongly stirring with the stirring speed of 3000 r/min and the stirring time of 10 min, thereby obtaining uniform and stable suspension containing the para-aramid nanofibers; and

(15) washing the uniform and stable suspension containing the para-aramid nanofibers with water on a countercurrent belt filter, and dispersing with water again, thereby obtaining the dispersion of the para-aramid nanofibers.

Embodiment 5

(16) steps: under nitrogen protection, adding 100 mL of dewatered solvent of N-methyl pyrrolidone into a reaction container; adding 8 g of solubilizing salt of CaCl while stirring; heating to 100 C. to dissolve the solubilizing salt to obtain a solution of the solubilizing salt; cooling the solution to 15 C. in a cold bath, adding 2.163 g of p-phenylenediamine (PPD) into the reaction container, and cooling the reaction container to 0 C. after the p-phenylenediamine is dissolved; and adding 4.095 g of terephthaloyl chloride (TPC), gradually accelerating the stirring speed to be 1500 r/min, continuously reacting for 8 minutes, controlling a reaction temperature to be below 70 C., and continuing to react for 10 minutes and stopping stirring after a gel phenomenon occurs in the reaction system, thereby obtaining frozen gel;

(17) transferring the frozen gel into a tissue dispersion machine, adding 1000 mL of dispersing agent of N-methyl pyrrolidone into the frozen gel while high-speed stirring to disperse the frozen gel into a uniform gel solution, wherein the stirring speed is 2500 r/min and the stirring time is 5 min; and adding the gel solution into 8000 of water while strongly stirring with the stirring speed of 4000 r/min and the stirring time of 10 min, thereby obtaining uniform and stable suspension containing the para-aramid nanofibers; and

(18) washing the uniform and stable suspension containing the para-aramid nanofibers with water on a countercurrent belt filter, and dispersing with water again, thereby obtaining the dispersion of the para-aramid nanofibers.