Poly (p-phenylene terephthalamide) fiber is called meta-aramid fiber for short; Poly (p-phenylene terephthalamide) fiber is called para-aramid fiber.
The differences are as follows:
1, different molecular arrangements. The molecular chain arrangement of meta-aramid fiber is zigzag; Para-aramid fiber is linear in molecular chain arrangement.
2, the production process is different. The two-step imitation process of para-aramid fiber is complex, which requires high equipment and complex technology, while meta-aramid fiber only needs one step.
3. Different uses. Meta-aramid fiber is widely used as bonding fiber for making special paper-based materials. Para-aramid precipitation fiber is a new differentiated product of meta-aramid precipitation fiber, which has great application potential in the field of high-performance paper-based materials.
2. What is the preparation method of meta-aramid fiber?
1, Preparation of Poly (m-benzamide) Polycondensate Aromatic polyamide 13 13 was prepared by polycondensation of m-phthaloyl chloride (ICI) and m-phenylenediamine (MPD). There are three main methods to produce polycondensates:
(1) interfacial polycondensation method
M-phenylenediamine is dissolved in a certain amount of water, and a small amount of acid absorbent is added to become the water phase. Dissolve ICI in organic solvent, then add ICI solution into MPD aqueous solution with strong stirring, and react immediately at the interface between water and organic phase to generate polymer precipitate, and then obtain solid polymer after separation, washing and drying.
(2) Low temperature solution polycondensation method
Firstly, m-phenylenediamine is dissolved in N, N dimethylacetamide (DMAc) solvent, and m-phthaloyl chloride is added with stirring. The reaction was carried out at low temperature, and the temperature gradually increased to the end of the reaction. Then calcium hydroxide is added to neutralize the oxychloride generated by the reaction, so that the solution becomes a DMAc- calcium chloride amide salt solution system. After concentration adjustment, it can be directly used for wet spinning, or HCI generated by the reaction can be removed by alkaline ion exchange resin. Li Wei et al. studied the influence of tertiary amine additives on the polycondensation of PMIA, and found that tertiary amines with different structures have different effects on the molecular weight of PMIA, among which adding a small amount of A- methylpyridine as HCl absorbent is the most obvious way to improve the molecular weight of PMIA.
(3) emulsion polycondensation method
ICI is dissolved in water-soluble organic solvent (such as cyclohexanone), and MPD is dissolved in water containing acid absorbent, and stirred at high speed, so that the polycondensation reaction is carried out in the organic phase of emulsion system formed during stirring. This method is beneficial to heat transfer. In addition, a patent reports the preparation of aromatic polyamides by gas phase polycondensation.
Compared with interfacial polycondensation and emulsion polycondensation, low temperature solution polycondensation consumes less solvent and has higher production efficiency. When spinning, beating and making films directly with resin solution, the operations of resin precipitation, water washing and redissolution can be omitted, which is more economical in production, so low-temperature solution polymerization is widely used. Poly (m-phenylene terephthalamide) was prepared by low temperature polycondensation. When N, N- dimethylacetamide (DMAc) is used as solvent, the following factors affect the reaction: purity of isophthaloyl chloride and isophthalic diamine, molar ratio, reaction temperature, reaction time, water content in the solvent and stirring speed.
2. Preparation of aramid fiber The fiber can be prepared by dry spinning, wet spinning or dry jet wet spinning.
(1) dry spinning
In the process of dry spinning, the spinning solution obtained by polycondensation of low-temperature solution is neutralized with calcium hydroxide to obtain a viscous solution containing about 20% polymer and 9% CaCl _ 2, which is filtered and heated to 150 ~ 160℃ for dry spinning, so as to obtain a primary spinning fiber containing a large number of inorganic salts, which needs to be stretched for 4 ~ 5 times at about 300℃ after repeated water washing, or first. There are two kinds of dry spinning products: filament and staple fiber.
(2) Wet spinning
The general process of wet spinning is: before spinning, the temperature of the stock solution is controlled at about 22℃, and the stock solution enters a coagulation bath containing dimethylacetamide and CaCI2 with a volume density of 1.366, and the bath temperature is kept at 60℃. After washing with water, the as-spun fiber was stretched 2.73 times in a hot water bath, then dried at 65,438 030℃, and then heated again on a hot plate at 320℃. The Japanese Teijin adopted this method. Conex's products are mainly short fibers, and there are the following varieties: ordinary short fibers, stock solution dyed short fibers, chopped fibers and high-strength filaments. According to the patent, the wet spinning process of high strength Conex is as follows: slurry → coagulation bath → water washing → first wet drawing → second wet drawing → drying → thousand drawing → post-treatment. The tensile strength of the prepared fiber can reach 8.48 ~ 9.27 CN/dtex, the elongation is 25% ~ 28%, and the thermal shrinkage at 300℃ is 5.60% ~ 6.0%.
(3) dry-jet wet spinning method
By adopting this process, the spinning draw ratio is large, the orientation effect is good and the heat resistance is high. For example, the thermal shrinkage of wet-spun fiber is 80% at 400℃, while that of dry-spun fiber is less than 10%. The zero strength temperature of wet-spun fiber is 440℃, that of dry-spun fiber is 470℃, and the zero strength temperature of wet-spun fiber can be increased to 565,438+05℃.