Ricardo Molina

Wettability, ageing and recovery process of plasma-treated polyamide 6

The wetting properties of polyamide 6 rods treated with radiofrequency (RF) low-temperature plasma (LTP) using three different non-polymerizing gases (air, nitrogen and water vapour) were determined using the Wilhelmy contact-angle technique. Information on the acidic or basic nature of the ionizable groups generated on the rod surface was obtained using contact-angle titration. The wettability obtained depends on the plasma gas used, and it tends to decrease with time elapsed after the treatment when the samples are kept in an air environment. However, the wettability can be recovered by immersion of the aged samples in water. The degree of recovery depends on the plasma gas used and the highest recovery was obtained with water vapour plasma treated samples. Both ageing and recovery behaviour can be attributed to the reorganisation of hydrophilic groups which tend to reversibly migrate or orient towards the bulk phase depending on the storage conditions, although other factors can also have influence.

Shrinkage Properties of Wool Treated with Low Temperature Plasma and Chitosan Biopolymer

Low temperature plasma treatments of wool modify only the cuticle surface of the fibers, improving their surface wettability, dyeability, fiber cohesion, and shrink resistance. The shrink-resist properties obtained with plasma treatment do not impart a machine-washable finish, which is an important end-user demand. However, the shrink resistance of air plasma. treated wool is suitably enhanced by a subsequent biopolymer chitosan application. Using a qualitative colorimetric method, chitosan adsorption is shown to increase after treatment with air plasma. SEM observations yield information about the etching effect and chitosan adsorp tion. Given that both kinds of treatments, air plasma and chitosan, are environmentally acceptable, a new ecological shrink-proofing process is proposed.

Shrink-resistance and wetting properties of keratin fibres treated by glow discharge

The influence of the gas type, air or nitrogen, and the treatment time in an RF glow discharge treatment on the shrink resistance properties of knitted wool fabric and wetting properties of keratin fibres were studied. Wetting properties were determined by means of contact angle measurements on single keratin fibres. This method allows measuring accurately the influence of the plasma gas type and treatment time on fibre hydrophilicity, and its modification with the time elapsed after plasma treatment. The modification of the surface properties should be taken into account, especially, when a biopolymer after-treatment is applied to achieve wool shrink resistance. Surface chemical changes were studied by means of XPS. Topographical changes in the wool fibre surface were observed by scanning electron microscopy (SEM) and surface damage was evaluated by means of the Herbig sac formation. Both air and nitrogen plasma treatments impart shrink resistance to wool fabric and hydrophilic properties to the keratin fibres. Even short exposure times are found to be enough to decrease drastically the advancing water contact angle and, therefore, to increase the shrink resistance effect. Slight differences were observed between the air and nitrogen plasma treatments. The time elapsed after the plasma treatment promotes an increase of the advancing contact angle and a decrease of chitosan adsorption. The plasma treatments studied here modify chemically the epicuticle but it is not removed.

Removal of priority pollutants from water by means of dielectric barrier discharge atmospheric plasma

Two different nonthermal plasma reactors at atmospheric pressure were assessed for the removal of organic micropollutants (atrazine, chlorfenvinfos, 2,4-dibromophenol, and lindane) from aqueous solutions (1-5 mg L(-1)) at laboratory scale. Both devices were dielectric barrier discharge (DBD) reactors; one was a conventional batch reactor (R1) and the other a coaxial thin-falling-water-film reactor (R2). A first-order degradation kinetics was proposed for both experiments. The kinetic constants (k) were slightly faster in R1 (0.534 min(-1) for atrazine; 0.567 min(-1) for chlorfenvinfos; 0.802 min(-1) for 2,4-dibromophenol; 0.389 min(-1) for lindane) than in R2 (0.104 min(-1) for atrazine; 0.523 min(-1) for chlorfenvinfos; 0.273 min(-1) for 2,4-dibromophenol; 0.294 min(-1) for lindane). However, energy efficiencies were about one order of magnitude higher in R2 (89 mg kW(-1) h(-1) for atrazine; 447 mg kW(-1) h(-1) for c hlorfenvinfos; 47 mg kW(-1) h(-1) for 2,4-dibromophenol; 50 mg kW(-1) h(-1) for lindane) than in R1. Degradation by -products of all four compounds were identified in R1. As expected, when the plasma treatment (R1) was applied to industrial wastewater spiked with atrazine or lindane, micropollutant removal was also achieved, although at a lower rate than with aqueous solutions (k = 0.117 min(-1) for atrazine; k = 0.061 min(-1) for lindane).

Improved properties of oxygen and argon RF plasma-activated polyester fabrics loaded with TiO2 nanoparticles.

The potentials of low-pressure capacitively coupled RF oxygen and argon plasmas for the activation of polyester fibers surface that can enhance the deposition of colloidal TiO(2) nanoparticles were discussed. SEM and XPS analysis confirmed the plasma-induced morphological and chemical changes on the surface of polyester fibers. Oxygen and argon plasma pretreated polyester fabrics loaded with TiO(2) nanoparticles provided maximum reduction of Gram-negative bacteria E. coli and UV blocking. The self-cleaning effects tested on blueberry juice stains and photodegradation of methylene blue in aqueous solution proved excellent photocatalytic activity of TiO(2) nanoparticles deposited onto fiber surface. Although both plasmas significantly contributed to overall improvement of properties of such nanocomposite textile material, oxygen plasma treatment, in particular, enhanced the deposition of colloidal TiO(2) nanoparticles and thus ensured superior effects.

Shrinkage Properties of Peroxide-Enzyme-Biopolymer Treated Wool

Incorporating an enzyme in the alkaline peroxide treatment bath enhances wool wet-tability and the effectiveness of subsequently applied chitosan biopolymer. Wool whiteness is also significantly enhanced. Wool knitted fabric thus treated is shrink resistant at the machine-washable level, which is one of the most important end-user demands. The formation of ionic bonds between the new sulphonic groups generated on the wool fiber surface and chitosan contribute to the shrink resistance of H2O2 + enzyme/chitosan treated wool. As a result of excessive increases in enzyme concentration in the peroxide bath, the wool surface cysteic acid content decreases, thus diminishing both the efficiency of post-applied chitosan solution and the shrink resistance.

Removal of cyanide from water by means of plasma discharge technology

Two different nonthermal plasma reactors at atmospheric pressure were assessed for the first time for cyanide removal (1 mg L(-1)) from aqueous solutions (0.025 M NaHCO(3)/NaOH buffer, pH 11) at laboratory scale. Both devices were dielectric barrier discharge (DBD) reactors; one of them was a conventional batch reactor (R1) and the other one was a coaxial thin falling water film reactor (R2). A first-order degradation kinetics was proposed for both experiments, obtaining k(R1) = 0.5553 min(-1) and k(R2) = 0.7482 min(-1). The coaxial reactor R2 yielded a removal of 99% within only 3 min. Energy efficiencies (G) were calculated, yielding 1.74 mg kW(-1) h(-1) for R1 and 127.9 mg kW(-1) h(-1) for R2. When the treatment was applied to industrial wastewaters, cyanide elimination was confirmed, although at a lower rate (above 92% removal in 90 min with R2). Therefore, plasma reactors could be a relevant alternative to established advanced oxidation techniques (UV, H(2)O(2), ozonation, etc.) for the removal of cyanide from wastewaters with low organic loads or even drinking waters.

Regulation of surface hydrophilicity of plasma treated wool fabrics

In this study, a set of experiments was carried out with the aim of gradually conferring hydrophobic properties to a low temperature plasma-treated wool fiber surface by post-reaction with hydrocarbon chains of different chain length. This study revealed the close relationship between the hydrophobic/hydrophilic properties of the wool surface with its shrinkage properties.

In situ chitosan gelation initiated by atmospheric plasma treatment.

This work reports on the feasibility of atmospheric dielectric barrier discharge (DBD) plasma as a novel synthetic pathway for the liquid phase gelation of chitosan. The DBD plasma chitosan gelation process did not significantly alter the chemical structure of the biopolymer as confirmed by FTIR study. However, the oxidation processes and local heating effect associated with the solvent evaporation during the plasma treatment could provoke both reaction of chitosan degradation and the cleavage of β-1-4-glycosidic linkages with the concomitant generation of aldehyde groups able to crosslink via Schiff-base with amino groups from other chitosan molecules. Shear viscosity measurements suggested the formation of chitosan fragments of lower molecular weight after the plasma treatment of 1% (w/v) chitosan and fragments of higher molecular weight after the plasma treatment of 2% (w/v) chitosan. The crosslinking density of hydrogels generated during the in situ DBD plasma chitosan gelation process increased as a function of the treatment time and concentration of chitosan. As of consequence of the increase of the cross-linking density, the equilibrium swelling ratio and water content decreased significantly.

Free Radical Formation in Wool Fibers Treated by Low Temperature Plasma

Electron spin resonance studies of merino wool fabrics provide evidence of the presence of stable free radicals. Ultraviolet/visible (λ > 250 nm) irradiation increases the radical concentration. Nitrogen, air, and water vapor plasma treatments on wool fabrics result in new signal bands attributed to nitrogen-centered radicals. The formation of the different additional radicals could be related to the high reactivity of the plasma species or to the vacuum-ultraviolet radiation component (λ < 200 nm) of the plasma environ ment. The presence of these radicals depends on the treatment time and the kind of gas used for plasma generation.