Browsing by Subject "oxygen permeability"

Gas permeabilities of films used in food packaging must be well known to ensure the best conditions for packed food products. In addition to oxygen and carbon dioxide permeability as such their ratio affects the choice of packaging materials. The CO2/O2 ratio of petroleum derived plastics is normally under 6:1 but that of bio-based films is less known. The literature review of this study focused on different sources of bio-based raw-materials and their chemical structure. The aim of the experimental study was to measure oxygen and carbon dioxide permeabilities of different bio-based films and to identify the CO2/O2 ratio. Another point of interest was the realiability of used carbon dioxide permeation analyzer which was assembled from an old oxygen permeation analyzer and gas chromatography. Three of the used film types were prepared in laboratory scale from Konjac glucomannan, starch and hydroxypropyl starch with 10 % or 40 % of sorbitol (of the dry matter) due to a reduction of porosity of materials. Other bio-based films were obtained from VTT (cellulose nanofibrils, hydroxypropyl xylan, cellulose derivative, cellophane and polyglycolic acid). Almost all the films had low oxygen permeabilities (OP<2.8 [cm3 µm]/[m2 d kPa]) and replicate results did not vary much. The cellulose derivative films had higher OP of 120 (cm3 µm)/(m2 d kPa). The carbon dioxide permeabilities showed more variation and were clearly higher (CO2P was 0 to 978 [cm3 µm]/[m2 d kPa]). In addition films including 40 % of sorbitol leaked more often. The ratio of CO2/O2 varied between 7:1–329:1. Most of the measured bio-based films are suitable for packaging food products, whose preservation depends on the permeability of carbon dioxide through the packaging more than that of oxygen. Excellent applications can be found among fruits and vegetables, whose maturing have to be controlled during storage. High CO2/O2 ratios were due to rather different chemical structures of the studied bio-based films and therefore the determination of a definite CO2/O2 ratio was not possible (unlike with petroleum based films). The magnitude of carbon dioxide permeabilities were similar to those reported in literature but further research with the assembled analyzer is needed to ensure its realiability.