Prof. Do-hyeon Kim’s research team at the department of Chemical & Biomolecular Engineering in KAIST announced the development of new mass production process of micro and nano fiber using centrifugal force on the 23rd.

Prof. Kim’s team succeeded the production of various macromolecule micro and nano fibers by developing multi centrifugal spinning system subdividing thread disk to multiple layers through upbuilding the existence centrifugal spinning process. This technology is expected to be applied to a wide range of fields by enabling the mass production of fibers as well as the manufacture of composite filters containing various kinds of fibers in one filter.

This research that Byeong-eun Kwak in the course of combined masters and doctorate program Ho-jeong Yoo in doctorate course and Eung-jun Lee in the course of combined masters and doctorate program had participated as the lead author the second and third authors was selected as a cover thesis of international academic journal ‘ACS Macro Letters’ volume 10 issue 3 in 2021. (Thesis title: Large-Scale Centrifugal Multispinning Production of Polymer Micro- and Nano fibers for Mask Filter Application with a Potential of Cospinning Mixed Multicomponent Fibers)

Macromolecule micro and nano fibers refer to a fiber that its thickness is micrometer (μm) or nanometer (nm) which is similar to the thickness of hair or 1/1000 or 1/10 thickness. Recently the demand for masks has gradually increased due to coronavirus and fine dust issues and also the demand for polymer fiber used for filter materials is increasing.

Especially macromolecule nano fiber-based mask filters with very thin thickness are emerging as important materials in the mask filter field as they can block more than 90% of fine dust and coronavirus through mechanical filtration even without static electricity.

Electrostatic-based mask filters reduce the collection efficiency of fine dust over time due to moisture contained in the breath. Nano-filter masks on the other hand rarely exhibit efficiency degradation over time. Already countries such as Europe are evaluating the performance of masks that exclude the efficiency of collection by static electricity. Thus the manufacture of nano fiber-based filters that can achieve high capture efficiency with mechanical filtration is a very important task.

The existing nano fiber manufacturing uses an electro spinning process that applies high voltage to manufacture thin fibers. However the electro spinning process uses tens of kilovolts (kV) of high voltage which makes the process less safe and makes it difficult to increase the size of the facility.

In addition the process itself is designed unfavorably for mass production so the manufacturing speed of fibers in laboratory units is only 0.01 to 1 gram (g) per hour. The multi-nozzles electro spinning and nozzleless electro spinning processes designed to overcome the limitations of this slow fiber production speed also present the problem of lower production efficiency and higher pressure than 50 kilovolts (kV) due to electrical field interference between nozzles. 

The team paid attention to centrifugal spinning to overcome the limitations of this process. Centrifugal spinning is a process that manufactures fibers through the rotation of radiated disks and is often used in cotton candy machines.

However since conventional centrifugal spinning devices also used a single spinning disk increasing the size did not produce much faster fibers than conventional electro spinning processes. Accordingly the team came up with a multi-layered centrifugal disk with multiple layers showing the possibility of mass production of fibers.

The team produced a multi-centrifugal spinning disc with three layers and confirmed that the rate of fiber production was increased proportionally as the number of layers of the discs increased. This means that in multi-centrifugal systems interference among nozzles does not result in production efficiency degradation.

Through the newly designed process the team found that the production speed of fibers with an average thickness of 1/100th of hair based on the size of the laboratory increased to 8~25 grams (g) per hour. This is about 300 times faster than conventional electro spinning processes. In addition 25 grams (g) of nano fiber is equivalent to 20 to 30 KF94 mask filters which may seem small but at the laboratory scale they produce very much over the same time.

Also the team manufactured mask filters using mass-produced nano fibers and found that it has a capture efficiency and differential pressure equivalent to commercial masks (KF80 and KF94) depending on the amount of fiber used. Furthermore the manufactured mask filters also performed very well for blocking droplets.

The lead author Byeong-eun Kwak in the course of combined masters and doctorate program said “Centrifugal spinning is a process that is not studied much even though it has distinct advantages in terms of cost and mass production than electro spinning” and “I expect that if the multi-centrifugal spinning system designed in this research is increased in industrial scales it would reduce the unit price of nano filters dramatically.”

Meanwhile this research was conducted as 2020 Global Singularity Research Project supported by KAIST.
