Homogeneous plastic structures
The progress from package insert to reactive polymers, via various blends of solids (or inclusion of trapped liquid scavenger solutions), also included homogeneous solutions of reagents in polymers. This provided the opportunity for increased clarity of flexible and rigid packaging, and reduced interference with the inherent properties of the polymers used. This also had the potential to reduce limittstions on the component polymers, which might be desired in particular packaging structures.
There was the first multilayer plastic structure in which antioxidants were claimed to function as oxygen “getters”. According to Brody et al. (2001), the process involved dispersing very minor portions of conventional antioxidants in or between layers in a multilayer. The process appears not to have advanced from that point.
The first plastic to incorporate dissolved reagents with known oxidation chemistry involved the light-energized excitation of oxygen diffusing into the plastic (Rooney and Holland, 1979). The substrate for oxidation does not react with ground-state oxygen,so the oxygen to be scavenged had to be excited to the singlet state. This was achieved by including a photosensitizing dye and exposing the scavenger film to visible light. The process occurs only while the scavenger film is exposed to the light, as shown in Figure 8.1.
Figure 8.1 Effect of illumination (solid line) and darkness (dashed line) on the cumulative volume of oxygen permeating a scavenger film laminate.
Homogeneous plastic structuresThe progress from package insert to reactive polymers, via various blends of solids (or inclusion of trapped liquid scavenger solutions), also included homogeneous solutions of reagents in polymers. This provided the opportunity for increased clarity of flexible and rigid packaging, and reduced interference with the inherent properties of the polymers used. This also had the potential to reduce limittstions on the component polymers, which might be desired in particular packaging structures. There was the first multilayer plastic structure in which antioxidants were claimed to function as oxygen “getters”. According to Brody et al. (2001), the process involved dispersing very minor portions of conventional antioxidants in or between layers in a multilayer. The process appears not to have advanced from that point. The first plastic to incorporate dissolved reagents with known oxidation chemistry involved the light-energized excitation of oxygen diffusing into the plastic (Rooney and Holland, 1979). The substrate for oxidation does not react with ground-state oxygen,so the oxygen to be scavenged had to be excited to the singlet state. This was achieved by including a photosensitizing dye and exposing the scavenger film to visible light. The process occurs only while the scavenger film is exposed to the light, as shown in Figure 8.1.Figure 8.1 Effect of illumination (solid line) and darkness (dashed line) on the cumulative volume of oxygen permeating a scavenger film laminate.
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