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Low energy consumption reactive melt spinning process was developed to prepare polyamide 6 micro/nano fibers in Qingdao University, China

Time : 2021-12-20 Hits : 18

In the traditional chemical fiber industry, fiber forming process of melt spinning technology to polymer as raw material, owing to the high polymer melt viscosity, the fiber is usually in more than 10 microns in diameter, smaller scale (sub-micron and nanometer level) fiber usually require the electrostatic spinning technology implementation, process in addition to the required 5 ~ 40 kv high voltage, also requires a lower fluid viscosity, Easy to stretch. Therefore, in melt spinning technology, polymers are usually dissolved in organic solvents to form a spinning solution of 1%~20%, which not only reduces the yield of fiber, increases the process cost, but also brings problems of solvent recovery and environmental pollution. Therefore, it has long been a difficult problem in the industry to obtain microfibers without solvent volatilization.

In view of this, the team of Professor Ning Xin of Qingdao University designed a novel low-energy Reactive melt spinning (RMS) based on the anionic ring-opening polymerization mechanism of caprolactam, catalyst and initiator system to prepare polyamide 6 micro/nano fiber materials. Related research is titled "Forming of nylon-6 Micro/ nano-fiber Assembly through a Low Energy Reactive Melt Spinning Process "( issues published in Green Chemistry".


Figure 1. Reactive melt spinning process (RMS)

In this study, low viscosity monomer as spinning starting raw material, through the control of polymerization reaction kinetics of hybrid system viscosity matching high voltage electrostatic field force stretching, realized the low viscosity monomer mixture, anionic ring-opening polymerization, polymer crystallization, fluid extrusion stretch forming and fiber random synchronization network process. The process temperature is about 80~100℃ lower than the current commercial melt spinning process temperature, greatly reducing the energy consumption. Compared with solution spinning, this process does not use any solvent or thinner, which improves the yield and saves the cost of solvent recovery and treatment.


According to lambert-Beer law, the conversion rate of the mixed melt monomer with the ideal drawing viscosity is between 50% and 60% by monitoring the anionic ring-opening polymerization process of caprolactam catalyst initiator system by dynamic infrared spectroscopy. By optimizing the raw material formula and process parameters of the reactants, the obtained samples were solid columnar fibers with smooth surface, and formed two-dimensional porous films with random distribution. The fiber diameters were mainly distributed between 400 nm and 3 μm. DSC test results show that the fiber's melting point is 212.4℃, which can reach the melting point range of conventional NYLON 6 products (210~230℃), and its crystallinity is 26.7%, slightly lower than that of commercial nylon 6 filament (31.7%). It also has α and γ crystal forms, which are the most common of nylon 6. And under different reactant ratio and process parameters show regular mutual transformation. The average monomer conversion rate of the fiber sample calculated by weighing method can reach more than 90%. GPC test results show that the average molecular weight of the final sample is more than 50000, indicating that the reactive melt spinning process is accompanied by a very efficient and thorough polymerization reaction process.


Figure 3

In addition, the study also carried out the Life Cycle Assessment (LCA) of NYLON 6 products, from caprolactam monomer source -- synthesis of nylon 6 -- production of nylon 6 products -- degradation process of nylon 6, the overall investigation, comparison and analysis. In the production stage of nylon 6, compared with the traditional melt spinning and solution spinning, the reactive melt spinning (RMS) process may be the only way to produce fibers within the diameter of several microns and sub-microns without using solvents. The whole process is non-toxic, non-polluting, low energy consumption and high yield. RMS process combined with the route that caprolactam monomer can be synthesized by enzyme engineering of winter fern extract, and the green cycle process that nylon 6 can be degraded into caprolactam precursor, thus achieving the green cycle sustainable manufacturing process of nylon 6 micro and nano fibers in the whole life cycle shown in FIG. 4. At the same time, THE RMS process has a highly feasible commercial prospect conceptually, and is expected to realize the industrial scale production of nylon 6 micro/nano fibers. The invention of this process and related materials have been declared for patent protection.


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