Larry C. Wadsworth

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...

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.

Corona treatment of polyolefin films—A review

Corona discharge introduces polar groups into the polymeric surfaces and, as a consequence, improves the surface energy, wettability, and adhesion characteristics. The main chemical mechanism of corona treatment is oxidation. This article further discusses some special problems that are related to corona treatment of polyolefin films by reviewing the recent developments in this field, such as effect of corona treatment on adhesion, effect of resin additives on corona treatment, insufficient treatment and over-treatment of corona discharge, aging, and re-treatment.

Effects of melt-blowing process conditions on morphological and mechanical properties of polypropylene webs

Abstract Isotactic polypropylene (iPP) melt-blown webs have been studied in terms of the relationships among the processing conditions, structure and mechanical properties. The melt-blowing process conditions investigated in this study were die and air temperatures, die-to-collector distance ( DCD ) and attenuation air flow rate at the die. The macroscopic web structure was characterized in terms of interfibrous bonding and fibre diameter using scanning electron microscopy. The degree of fibre entanglements was found to increase with decreasing DCD , with increasing die temperature, or with increasing air flow rate. Using wide-angle X-ray diffraction and differential scanning calorimetry (d.s.c.), the microscopic molecular structure of iPP has been investigated. The fibres in a web consist of the α-form crystal, smectic phase and amorphous regions. The crystallinity of the iPP webs obtained from d.s.c. was found to be similar (39–44%) since the smectic phase transforms to crystals on heating in a d.s.c. A wide range of tensile properties and flexural rigidity values in the machine direction and cross direction were obtained at various processing conditions. The results have been analysed in terms of the degree of fibre entanglements, fibre orientation in the machine direction and the fraction of smectic phase.

Evolution of Structure and Properties in a Spunbonding Process

The inherent properties of filaments are of utmost importance in spunbonded webs. A good understanding of structure and property development in individual filaments is helpful in better comprehending the whole process. A polypropylene homopolymer and a copolymer (PP/PE) are processed on the Reicofil® spunbonding line at the Textiles and Nonwovens Development Center of the University of Tennessee. The properties of the filament samples taken before thermal bonding are determined through a variety of experimental techniques, such as differential scanning calorimetry. thermomechan ical analysis, scanning electron microscopy, density, x-ray diffraction, and mechanical properties. The performance properties of the bonded nonwoven fabrics from the same set of filaments are evaluated and the structure and properties of the fibers are compared with those of the bonded fabrics. Primary air temperature and throughput have a strong influence on the structure and properties of both filaments (before bonding) and non wovens (after bonding). As primary air temperature and throughput decrease, filament diameter tends to decrease, accompanied by a simultaneous increase in crystallinity. birefringence, tensile strength, initial modulus, thermal stability. and density.

Structure and properties of polypropylene filaments in a spunbonding process

Polypropylene homopolymer (PP) and a copolymer (P/E) were processed using the Reicofil® spunbonding line at the Textiles and Nonwovens Development Center of the University of Tennessee, Knoxville. The properties of the filament samples taken before thermal-bonding were determined through a variety of techniques such as differential scanning calorimetry, thermomechanical analysis, thermal deformation analysis and mechanical properties. The two process variables investigated, primary air temperature and throughput had a strong influence on the structure and properties of both the filaments and the bonded nonwovens. As the primary air temperature and throughput decreased, there was a tendency for decrease in filament diameter with a simultaneous increase in their crystallinity, birefringence and thermal stability. The copolymer filaments showed lower crystallinity and orientation for all the corresponding processing conditions.

Application of neural networks to meltblown process control

Process modeling is essential for the control of optimization and an on-line prediction is very useful for process monitoring and quality control. Up to now, no satisfactory methods have been found to model an industrial meltblown process since it is of highly dimensional and nonlinear complexity. In this article, back-propagation neural networks (BPNNs) were investigated for modeling the meltblown process and on-line predicting the product specifications such as fiber diameter and web thickness. The feasibility of this application was successfully demonstrated by agreement of the prediction results from the BPNN to the actual measurements of a practical case. The network inputs included extruder temperature, die temperature, melt flow rate, air temperature at die, air pressure at die, and die-to-collector distance (DCD). The output of the fiber diameter was obtained by neural computing. The network training was based on 160 sets of the training samples and the trained network was tested with 70 sets of test samples which were different from the training data. This research is preliminary and of industrial significance and especially valuable for the optimal control of advanced meltblown processes.

Development of Innovative Cotton-Surfaced Nonwoven Laminates

Cotton-based nonwovens have been developed at Textiles and Nonwovens Development Center (TANDEC), The University of Tennessee, with the cotton fibers on the surface or in the core layer laminated with meltblown (MB) and/or spunbonded (SB) webs. Both Cotton-Surfaced Nonwovens (CSN) and Cotton-Core Nonwovens (CCN) have excellent soft hand, breathability, absorbency, and tensile properties making them ideal for many medical applications such as isolation gowns, hospital drapes and gowns, shoe covers, head covers, underwear, pillowcases, diaper components (acquisition, core, back sheet), feminine hygiene pads, baby wipes, etc. In this paper, the processes to produce these cotton-surfaced nonwovens will be presented, including as-bonded, heat-stretched CSN fabrics, and foam-finished CSN nonwovens.

Processing and Property Study of Cotton-Surfaced Nonwovens

Cotton-surfaced nonwovens have been developed by thermally bonding cotton precur sor webs with unbonded spunbond (SB) PP webs on a spunbond line, with cotton on one or both sides. The novel two- or three-layered laminates have a hand similar to cotton knits or hydroentangled fabrics, and also exhibit excellent strength and elongation properties, making them more suitable for some highly desirable disposable and short-wear-cycle applications such as medical and personal hygiene products. The cotton precursor webs are thermally bonded cotton and PP staple (TCPP) webs (25-27 g/m2). Six different TCPP webs are used with three blend ratios of cotton/pp (60/40, 50/50, 40/60) and two different deniers (1.9 and 2.2 denier) and two lengths (1.0 and 1.5 inches) of PP staple fibers. A comprehensive study is made of the effect of processing conditions on the properties of the laminates as bonded on the SB line, with SB web weights of 17 and 34 g/m2.