R. M. Broughton

Mechanism of photolytic decomposition of N-halamine antimicrobial siloxane coatings.

Generally, antimicrobial N-halamine siloxane coatings can be rehalogenated repetitively upon loss of their biocidal efficacies, a marked advantage over coatings containing other antimicrobial materials. However, the N-halamine materials tend to slowly decompose upon exposure to ultraviolet irradiation as in direct sunlight. In this work the mechanism of photolytic decomposition for the N-halamine siloxanes has been studied using spectroscopic and theoretical methods. It was found that the N-chlorinated coatings slowly decomposed upon UVA irradiation, whereas the unhalogenated coatings did not. Model compound evidence in this work suggests that upon UVA irradiation, the N-Cl bond dissociates homolytically, followed by a Cl radical migration to the alkyl side chain connected to the siloxane tethering group. An alpha and/or beta scission then occurs causing partial loss of the biocidal moiety from the surface of the coated material, thus precluding complete rechlorination. NMR, FTIR, GCMS, and computations at the DFT (U)B3LYP/6-311++G(2d,p) level of theory have been employed in reaching this conclusion.

Antimicrobial Fibers Created via Polycarboxylic Acid Durable Press Finishing

An N-halamine precursor, m-aminophenyl hydantoin (m-APH), which was rendered antimicrobial through exposure to chlorine bleach, was synthesized and was applied on cotton fabric using polycarboxylic acids as crosslinking agents. Particularly, 1,2,3,4-butanetetracarboxylic acid (BTCA) with m-APH treated cotton fabric resulted in the highest increased wrinkle recovery angle and chlorine content simultaneously. Durability and rechargeability were measured through an AATCC test method and antimicrobial efficacy of BTCA/m-APH treated cotton fabric against Gram-positive and Gram-negative bacteria showed a 6 log reduction within 1 min of contact time.

N-Halamine-modified antimicrobial polypropylene nonwoven fabrics for use against airborne bacteria.

Disinfecting, nonbleaching compound 1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone (MC) was uniformly coated onto polypropylene melt-blown nonwoven fabrics having basis-weights of 22 and 50 g/m(2) in order to impart antimicrobial properties via a pad-dry technique. The antimicrobial efficacies of the tested fabrics loaded with MC compound were evaluated against bioaerosols of Staphylococcus aureus and Escherichia coli O157:H7 utilizing a colony counting method. It was determined that both types of coated fabrics exhibited superior antimicrobial efficacy upon exposure to aerosol generation for 3 h. The effect of the coating on air permeability was found to be minimal. Samples were stable for a 6 month time period when they were stored in darkness. However, when the fabrics were exposed to fluorescent light, partial chlorine loss was observed. The MC-coated fabrics exhibited great potential for use in protective face masks and air filters to combat airborne pathogens.

Structural Analysis of a Two-dimensional Braided Fabric

Two-dimensional-braid geometry is analyzed. The cover factor of a fabric braided on a particular braider depends on three variables: braid angle, helical length, and braid diameter; however, only two of the three are independent because of an equation of constraint. The cover factor of an existing braid is a function of braid angle and diameter and maintains a constant helical length between its tensile and compressive jammed states. A stable jammed state with maximum crimp is found to exist when the braid angle is 45° and the helical length is a minimum. When the braid diameter is held constant by braiding on a constant-diameter mandrel, the cover factor is increased by decreasing the helical length or increasing the braid angle. The cover factor is directly related to the fabric width as a single independent variable. When the yarn cannot be considered as a flat strip but must instead be considered to have a circular cross-section, the maximum cover factor in the jammed state is shown to be 0.82.

Preparation and application of ans-triazine-based novelN-halamine biocide for antimicrobial fibers

N-halamines serve as important antimicrobial agents. Development of this class of compounds has been shown to provide benefits especially from a biocidal point of view. A novels-triazine-basedN-heterocycle, dichloro-m-aminophenyl-hydantoinyl-s-triazine (DAPHT), which could be rendered antimicrobial through exposure to diluted chlorine bleach, was synthesized and characterized by1H NMR,13C NMR, and FT-IR. A finishing method was used to apply theN-halamine precursor onto cotton fabric, and the optimum conditions for finishing were investigated. The DAPHT-treated cotton fabric had durable antimicrobial properties up to 50 standard washing cycles and was rechargeable under normal laundry/bleaching conditions. The antimicrobial efficacy against Gram-positive and Gram-negative bacteria was demonstrated.

Recovery and Reuse of Waste PVC Coated Fabrics. Part 1: Experimental Procedures and Separation of Fabric Components

The polyester in the base fabrics (PET) and the polyvinyl chloride coating (PVC) along with plasticizers and adhesive/glue were separated from a commercial coated fabric by a scheme of chopping, grinding, and extracting with a selected preferred aqueous MEK solution. A novel recovering method called swelling method is introduced to separate and reuse waste PVC coated PET fab rics. In comparison with other recycling techniques, the swelling method is a sim ple procedure with minimal environmental impact. The selection of the swelling agent of methylethyl ketone (MEK) was made after an analysis of the physical and chemical properties of several chemicals. Phase separation was found in the MEK/water system that serves as swelling bath. The two phases exist over a wide concentration range. The behavior of the swelling system and the swelling proper ties of recovered components were investigated by parameters, such as refractive index, swelling degree, and the average particle size of recovered PVC.

Analysis of Circular Braiding Process, Part 2: Mechanics Analysis of the Circular Braiding Process and Experiment

The final structure of braid is a consequence of force interactions among yarns in the convergent zone. In Part 1, the influence of friction forces on the final braided structure was discussed via kinematic analysis. A transformation from a 3-D cone to a 2-D plane was made for the mechanics analysis. A mechanics model is proposed in this paper to determine the braid angle by considering interlacing forces. Equilibrium equations for the braiding process are deduced. A Newton-Raphson method is used to solve the nonlinear algebraic equation set. Experiments have been conducted to produce braids at different machine speeds and with different tensions, and reveal that the mechanics model is potentially a better predictor of final braid structure than the kinematic analysis.

ANTIMICROBIAL CELLULOSE: Preparation and Application of 5-methyl-5- aminomethylhydantoin

A new N-halamine precursor, 5-methyl-5-aminomethylhydantoin (AH), was synthesized. This N-halamine precursor can be coated onto cotton surfaces with the addition of the crosslinking agent butanetetracarboxylic acid (BTCA) and rendered biocidal by exposure to halogen solutions either before or after curing the coating or material. Standard washing tests show that covalently bound AH/BTCA on the cotton swatches can survive repeated washing cycles. After 50 washing cycles, chlorinated cotton swatches had lost 98.7 % of oxidative Cl+, but after rechlorination, almost 43.5 % of Cl+ was regained. Biocidal tests indicated that the cotton swatches coated with chlorinated AH/BTCA were effective against Gram positive Staphylococcus aureus and Gram negative Escherichia coli.

The Design of Optimal Lattice Structures Manufactured by Maypole Braiding

Beginning with the maypole braiding process and its inherent constraints, we develop a design methodology for the realization of optimal braided composite lattice structures. This process requires novel geometric, mechanical, and optimization procedures for comprehensive design-ability, while taking full advantage of the capabilities of maypole braiding. The composite lattice structures are braided using yarns comprised of multiple prepreg carbon fiber (CF) tows that are themselves consolidated in a thin braided jacket to maintain round cross sections. Results show that optimal lattice-structure tubes provide significant improvement over smooth-walled CF tubes and nonoptimal lattices in torsion and bending, while maintaining comparable axial stiffness (AE). [DOI: 10.1115/1.4031122]

Airlaid nonwoven panels for use as structural thermal insulation

Abstract Thermal-bonded airlaid nonwoven webs consisting of fiber glass and polyester bicomponent fibers were manufactured, and then multilayer webs were formed into composite panels using compression molding technique. The consolidation process was optimized and the effect of bulk density on air permeabilites, mechanical properties, and thermal resistance was studied. Increasing binder amount and bulk density improved the flexural and tensile strength. Thermal resistance of the panels were found to be very dependent on the bulk density such that the resistance increased exponentially with an initial increase in density, then leveled off and decreased linearly with further increment in density. Depending on the composition and bulk density, the panels provided thermal resistance between 0.52 and 0.88 Km2/W, tensile strength between 2 and 7 MPa, and flexural strength between 600 and 3500 kPa. The findings revealed that airlaid nonwoven panels can be designed to use as structural thermal insulation materials in constructions.