title: Ammonia diffusion through Nalophan double bags: effect of concentration gradient reduction.
abstract: The ammonia loss through Nalophan bags has been studied. The losses observed for storage conditions and times as allowed by the reference standard for dynamic olfactometry (EN 13725:2003) indicate that odour concentration values due to the presence of small molecules may be significantly underestimated if samples are not analysed immediately after sampling. A diffusion model was used in order to study diffusion through the bag. The study discusses the effect of concentration gradient (ΔC) across the polymeric membrane of the analyte. The ΔC was controlled by using a setup bag called "double bags." Experimental data show a reduction of ammonia percentage losses due to the effect of the external multibarrier. The expedient of the double bag loaded with the same gas mixture allows a reduced diffusion of ammonia into the inner bag. Comparing the inner bag losses with those of the single bag stored in the same conditions (T, P, u) and with equal geometrical characteristics (S/V, z), it was observed that the inner bag of the double bag displays a 16% loss while the single bag displays a 37% loss. Acting on the ΔC it is possible to achieve a gross reduction of 57% in the ammonia leakage due to diffusion.
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, 20133 Milan, Italy.
authors.forename: Selena
authors.identifier: 0000-0002-9680-6847
authors.initials: S
authors.lastname: Sironi
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, 20133 Milan, Italy.
authors.forename: Lidia
authors.identifier: 0000-0002-2319-2792
authors.initials: L
authors.lastname: Eusebio
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, 20133 Milan, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Capelli
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, 20133 Milan, Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Boiardi
authors.affiliation: Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, 20133 Milan, Italy.
authors.forename: Renato
authors.initials: R
authors.lastname: Del Rosso
mesh_terms: D000641:Ammonia / Q000032:analysis*; D004058:Diffusion; D011093:Polyethylene Terephthalates / Q000737:chemistry*; D013997:Time Factors
chemical_list: D011093:Polyethylene Terephthalates; D000641:Ammonia