The relationship between surface tension and roughness is reviewed. The Cassie-Baxter model is restated in its original form, which better describes the most general cases of surface roughness. Using mechanical and chemical surface modification of nylon 6,6 woven fabric, an artificial superhydrophobic surface was prepared. A plain woven fabric mimicking the Lotus leaf was created by further grafting 1H,1H-perfluorooctylamine or octadecylamine to poly(acrylic acid) chains which had previously been grafted onto a nylon 6,6 woven fabric surface. Water contact angles as high as 168 degrees were achieved. Good agreement between the predictions based on the original Cassie-Baxter model and experiments was obtained. The version of the Cassie-Baxter model in current use could not be applied to this problem since the surface area fractions in this form is valid only when the liquid is in contact with a flat, porous surface. The angle at which a water droplet rolls off the surface has also been used to define a superhydrophobic surface. It is shown that the roll-off angle is highly dependent on droplet size. The roll-off angles of these superhydrophobic surfaces were less than 5 degrees when a 0.5 mL water droplet was applied.
Recent research on all aspects of thermally point‐bonded nonwovens has led to considerable improvements in the understanding of material requirements for these nonwovens, the changes that occur during bonding, and the mechanical properties of the resultant nonwoven materials. This article will review (1) how the thermal bonding process transforms the material properties of feed fibers, (2) the implications for material selection, and (3) the resultant failure properties of the bonded nonwoven. The formation of a bond during thermal bonding follows in sequence through three critical steps: (1) heating the web to partially melt the crystalline region, (2) reptation of the newly released chain segments across the fiber–fiber interface, and (3) subsequent cooling of the web to re‐solidify it and to trap the chain segments that diffused across the fiber–fiber interface. The time scales for these processes closely match commercial practice. In addition, adequate pressure is required to compress the fibers that form the bond spots and enhance heat transfer to these fibers. However, pressures typically used in commercial practice are insufficient to increase the melting temperature significantly or to produce significant heating due to compression of the fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006
New light-activated antimicrobial materials with a potentially wide range of possible uses in civilian settings were synthesized by the grafting of protoporphyrin IX and zinc protoporphyrin IX to nylon fibers. These fibers were shown to be active against Staphylococcus aureus at light exposures of 10,000 lux and greater and against Escherichia coli at 60,000 lux. They were ineffective against both strains in the absence of light. At 40,000 lux, these fibers showed increased antimicrobial activity against S. aureus with increasing exposure time.
Polarized Raman spectroscopy was used to determine the crystal orientation in uniaxially oriented fibers of poly(ethylene terephthalate) (PET). The Raman tensor ratios and the second-(P 2) and fourth-order (P4) Legendre polynomials of the orientation distribution function of the 998 cm -1 vibrational band are reported. We show that both P2 and P4 for this band increase more rapidly than the average chain orientation as determined by birefringence. In addition, they reach plateau values of P2 ) 0.90 ( 0.06 and P4 ) 0.55 ( 0.09 for birefringence values >0.05 in our drawn and annealed samples. Since this band has been assigned to the all-trans conformation of the glycol unit, we suggest that these P2 and P4 values correspond to the orientation of the crystalline units. This is the first time that the orientation parameters of the crystals of PET as determined by polarized Raman spectroscopy have been reported.
The relationships between the material parameters, i.e., the fiber fineness, porosity, areal density, layering sequence, and airflow resistivity with the normalincidence sound absorption coefficient of nonwoven composites consisting of three layers have been studied. The monofiber or multifiber needle-punched nonwovens included poly(lactic acid) (PLA), polypropylene (PP), glass fiber, and hemp fibers. Air flow resistivity was statistically modeled and was found to increase with decreasing fiber size and nonwoven porosity. The former models developed for glass fiber mats in the literature were found to be inconsistent with the air flow resistance of the nonwovens reported below. The effects of the layering sequence on air flow resistivity and sound absorption were obtained. It was found that when the layer including reinforcement fibers, i.e., hemp or glass fiber, faced the air flow/sound source, the air flow resistance and the absorption coefficient were higher than the case when the layer including reinforcement fibers was farthest from the air flow/sound source. The difference was more pronounced if there was a greater difference between the resistivity values of the constituent layers of the nonwoven composite. Sound absorption coefficient was statistically modeled in terms of air flow resistivity and frequency.
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