Food packaging

This is a typically an aesthetic characteristic of the packaging materials and one of the properties most anted and appreciated by the consumers. Even if it is hedonistic and somehow subjectiveperception, the transparency (i.e., the transmitted radiant flux measured includes only that in the same direction as that of the incident flux, whit deviation of an angle less than 0.1°) of anelectromagnetic radiation between 540 and 560 nm, central in the visible light spectrum. Actually, some confusion still exists about the optical property, which is sometimes presented as an empiricaldetermination of ‘see through clarity’. Nowadays it is easily measured objectively for the transparent material in standard conditions. Table XX gives some typical values.
Material | %T(specular transmittanceat 550 nm) |
Glass (180 m) | 92.1 |
Plypropylene biaxially oriented (28m) | 92.0 |
Cellophane (20m) | 92.0 |
Polyamide (nylon 6.6) biaxially oriented (18m) | 89.2 |
Polyvinyl chloride(40m) | 87.3 |
Polyamide (nylon 6.6) cast (50m) | 82.6 |
Polypropylene cast (40m) | 82.3 |
Polyester (25m) | 81.8 |
Polystyrene (38m) | 43.5 |
Polytetrafluoroethylene (50m) |21.4 |
Pergamine (45m) | 8.7 |
White polypropylene (36m) | 3.1 |
Vegetable parchment (78m) | 1.3 |

Transparency is inversely correlated to the thickness of the material, following Beer’sLaw: I=I0exp-kcl, where I is the intensity of the radiation, whose original intensity is I0, after passing through a thickness l (cm) of a material with a molar absorptivity of k (cm-1 M-1) and amolar concentration of c (M). The ratio II0 gives the transmission factor (T) and its percentage (%T) is termed as transmittance providing the basis for transparency definition. The transparency offlexible packaging materials is greatly affected by the degree of crystallinity, as well the thickness of some coatings like varnishes or very thin metallic layers; therefore, it can be modified, beyond...