Peter P. Tsai

Different electrostatic methods for making electret filters

Three charging techniques (viz., corona charging, tribocharging, and electrostatic fiber spinning) were used to charge fibers or fabrics of different polymer types. Corona charging is suitable for charging monopolymer fiber or fiber blend, or fabrics. Tribocharging is only appropriate for charging fibers with dissimilar electronegativity. Electrostatic fiber spinning combines the charging of polymer and the spinning of the fibers as a one-step process. It was observed that two dissimilar fibers following tribocharging had higher filtration efficiency than the corona-charged polypropylene fibers. An electrostatic spinning process produced nanofibers exhibiting extremely high efficiency by mechanical filtration mechanisms. Little charge was retained in electrospun polyethylene oxide fibers; however, polycarbonate and polyurethane retained a great amount of charge.

Room temperature sterilization of surfaces and fabrics with a One Atmosphere Uniform Glow Discharge Plasma

We report the results of an interdisciplinary collaboration formed to assess the sterilizing capabilities of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). This newly-invented source of glow discharge plasma (the fourth state of matter) is capable of operating at atmospheric pressure in air and other gases, and of providing antimicrobial active species to surfaces and workpieces at room temperature as judged by viable plate counts. OAUGDP exposures have reduced log numbers of bacteria, Staphylococcus aureus and Escherichia coli, and endospores from Bacillus stearothermophilus and Bacillus subtilis on seeded solid surfaces, fabrics, filter paper, and powdered culture media at room temperature. Initial experimental data showed a two-log10 CFU reduction of bacteria when 2 × 102 cells were seeded on filter paper. Results showed ≥3 log10 CFU reduction when polypropylene samples seeded with E. coli (5 × 104) were exposed, while a 30 s exposure time was required for similar killing with S. aureus-seeded polypropylene samples. The exposure times required to effect ≥6 log10 CFU reduction of E. coli and S. aureus on polypropylene samples were no longer than 30 s. Experiments with seeded samples in sealed commercial sterilization bags showed little or no differences in exposure times compared to unwrapped samples. Plasma exposure times of less than 5 min generated ≥5 log10 CFU reduction of commercially prepared Bacillus subtilis spores (1 × 106); 7 min OAUGDP exposures were required to generate a ≥3 log10 CFU reduction for Bacillus stearothermophilus spores. For all microorganisms tested, a biphasic curve was generated when the number of survivors vs time was plotted in dose-response cures. Several proposed mechanisms of killing at room temperature by the OAUGDP are discussed.

Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms

The medical, industrial, and food processing industries are constantly in search of new technologies to provide improved methods of sterilization and pasteurization. Proposed techniques must deal with such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, cost, and inefficiency in performance. We report results from a newly invented plasma source, a one atmosphere uniform glow discharge plasma (OAUGDP), which is capable of operating at atmospheric pressure in air and providing antimicrobial active species at room temperature. OAUGDP exposures have reduced log numbers of bacteria (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa), bacterial endospores (Bacillus subtilis and Bacillus pumilus), and various yeast and bacterial viruses on a variety of surfaces. These surfaces included polypropylene, filter paper, paper strips, solid culture media, and glass. Experimental results showed at least a ⩾5 log10 colony forming units (CFU) reduction in bacteria...

Sterilization and plasma processing of room temperature surfaces with a one atmosphere uniform glow discharge plasma (OAUGDP)

A technique for generating active species with the one atmosphere uniform glow discharge plasma (OAUGDP) has been developed and tested in a wide range of potential plasma processing applications, including the sterilization and decontamination of surfaces. The OAUGDP is a non-thermal plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. In addition to directly exposing webs and workpieces to active species by immersion or at the plasma boundary of a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. No vacuum system or batch processing is necessary, and a wide range of applications can be accommodated. This technology is simple, cost-effective and suitable for online treatment of webs and such three-dimensional workpieces as medical instruments. We will report the use of an air OAUGDP to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a remote exposure reactor to sterilize large workpieces 20 cm or more from the plasma-generating region, and a sterilizable air filter.

Surface Modification of Fabrics Using a One-Atmosphere Glow Discharge Plasma to Improve Fabric Wettability

In industrial applications, a steady-state glow discharge capable of operating at one atmosphere would allow many plasma-related surface modification processes to be done on the production line, rather than in expensive vacuum systems that force batch processing. In this paper, we report some encouraging results from the plasma surface treatment of polypropylene meltblown nonwovens in the UTK one-atmosphere glow discharge plasma reactor. This reactor generates a large volume (up to 2.4 liters), low power (less than 150 watts), uniform glow discharge plasma in a parallel plate configuration with oval electrodes of 213 cm2 face area, the lower electrode being covered with a 3.2 mm thick insulating Pyrex surface. The plates are set up in an enclosed box that makes it possible to control the working gas used, and the spacing between the plates can be varied. This reactor is energized by a custom-made high impedance kilohertz power supply capable of supplying up to 5 kilowatts of kilohertz power at RMS voltages up to 10 kV, and over a frequency range from 1 to 100 kHz. Exposing a wide variety of polymer fabrics reveals that the wettability, wickability, printability, and surface contact angle of the materials are significantly changed in a direction that may lead to new uses for these materials.

A remote exposure reactor (RER) for plasma processing and sterilization by plasma active species at one atmosphere

We have developed a remote exposure reactor (RER) in which the active species of air and other gases responsible for sterilization and processing effects are generated on flat panels in a surface layer of one atmosphere uniform glow discharge plasma (OAUGDP). These active species are convected by forced airflow at one atmosphere and near room temperature to a remote exposure chamber in which the workpiece is located. This allows workpieces of any size or shape to be sterilized or processed without direct contact with the plasma. Here, we report operation of the RER as a sterilizer with both single-pass and recirculating active species flow through the remote exposure chamber. We used the RER to reduce the numbers of two genera of microorganisms (Esherichia coli and Staphylococcus aureus) on test samples of polypropylene fabric. When the recirculating airflow configuration was employed, the population both of E. coli and S. aureas cells was reduced by at least five decades after only 25 s of exposure. Tests in the single pass airflow configuration produced similar results, with the E. coli and S. aureas populations decreased by at least four decades after 25 s of exposure.

Strength, surface energy, and ageing of meltblown and electrospun nylon and polyurethane (PU) fabrics treated by a one atmosphere uniform glow discharge plasma (OAUGDP)

The One Atmosphere Uniform Glow Discharge Plasma (OAUGDP™) generates a normal glow electrical discharge at 1 atmosphere in air and other gases. This plasma has been used to treat meltblown and electrospun nylon and polyurethane (PU) fabrics, and has produced an increase in the surface energy/wettability in all cases. Nylon and polyurethane (PU) nanofiber fabrics can be exposed to the OAUGDP™ for up to 10 seconds, long enough to greatly increase their surface energy without significant degradation of strength. After 10 seconds of plasma exposure, the electrospun (but not the meltblown) fabric strength and color degrade to a noticeable extent. It was found that prior to plasma exposure, the strength per unit areal weight of electrospun nanofiber fabrics was (for nylon) up to ten times that of the meltblown material. We also found that the surface energy of meltblown nylon could be increased to 70 dynes cm 1 by 5 seconds of OAUGDP™ exposure, that it was durable at this level for 6 months, and that the surface energy dropped from 70 to 64 dynes cm 1 only after more than 1 year post-exposure. We also report the effects of OAUGDP™ exposure on three surface characteristics of meltblown nylon and PU fabrics: (1) the strength of the fabric as a function of the plasma exposure time; (2) the surface energy of the fabric as a function of the plasma exposure time; and (3) the surface energy/wettability of the fabric as a function of time after exposure (ageing effect). We also describe the treatment of nanofiber fabrics using recent improvements in OAUGDP™ reactor technology

The Effect of Water-quenching on the Electrostatic Charging of Fibers and Fabrics during the Melt-blowing Process

This paper considers the efficiency of electrostatic charging of water-sprayed fibers during the melt-blowing process. Two charging methods were used to charge the fibers near the die exit and the fabrics after the collector. Both showed that the charging efficiency was not affected by the water-spraying process if the amount of spraying was controlled.

Determination of mineral content in polymelt nonwoven fabrics

Minerals have been widely added to polyolefins during film- or fiber-manufacturing process to improve the processibility as well as to enhance the product properties such as thermal conductivity, surface roughness, fabric filtration efficiency, and fabric capacity of oil absorbency. Titanium dioxide has been traditionally added in PET fibers as a delustrant to reduce their transparency for some applications, e.g. clothing materials. Calcium carbonate has recently been added in polymelt – spunbond and meltblown – fibers to increase the fiber processibility and to improve the fiber properties and hence to achieve their final performance. It is crucial that the adding quantity should be controlled so the fabric strength will not be adversely reduced. Calcium carbonate is frequently over-added in polymelt fibers to take the advantage in business trading by weight. A method is essential to determine the mineral content in the polymeric materials. While trying to use the volume of the fabrics displaced by liquid to determine the density of fibers fails, we successfully used buoyant force of the fabrics in a liquid to precisely determine the volume of the fibers and to use it to calculate the mineral content in spunmelt PP fabrics. A gadget was designed to incorporate with a balance to form a density balance for this research. It was observed that only a single layer but not multiple layers of fabric is a key point to accurately determine its buoyancy in the liquid. Multiple layers contributed to a relaxation of the bending forces at the folding lines of the fabric, which attributed to an error in measuring the buoyancy of the fabric.

Processing of films and Fabrics with the MOD-VIII Roll-to-Roll One Atmosphere Uniform Glow Discharge Plasma (OAUGDP®) Reactor

Summary form only given. Industrial atmospheric pressure plasma treatment has unique advantages over vacuum plasma technology for material surface energy enhancement, surface cleaning and decontamination, sterilization, surface etching and related tasks. The MOD-VIII plasma reactor studied in this paper consists of a fabric feed system, a gas feed system, a water cooling system, and a OAUGDPreg plasma reactor. We have shown that a roll of polymer film or fabric can be run through the reactor while being exposed to the plasma generated between a flat and a cylindrical drum electrode. The fabric is cooled by contact with the stainless steel water-cooled rotating drum electrode; the fabric exposure time is precisely controlled by a belted drive system driven by a variable-speed motor; and the fabric tension is controlled by a second variable-speed motor on the take-up roll. The fabric surface charge is drained at two grounded locations after treatment. We have obtained a uniform OAUGDPreg plasma with no filaments or pin holing in the exposed fabric. Subsequent measurement of the surface energy by the sessile water drop and related tests show that the surface energy after exposure is raised to levels well above those required for industrial use. Data on the uniformity of the surface energy in the cross and machine direction will be presented. This flexible MOD-VIII plasma reactor can be used for a wide range of material surface treatment purposes.