Packaging gas permeable

Contemporary gas-permeable packaging for ethylene sterilization of Dunasul highly crosslinked UHMWPE components, used by Centerpulse, Inc. (Austin, TX). 

In the Longevity process, the UHMWPE bars are warmed, placed in a carrier on a conveyor, and are exposed to electron beam radiation, with a total dose of 100 kGy. The UHMWPE does not heat above the melt transition during the crosslinking. After irradiation, the UHMWPE is heated above the melt temperature (>135°C) for stabilization of free radicals. Components are then machined from the Longevity material, enclosed in gas-permeable packaging, and sterilized by gas plasma. 

In the Marathon process, extruded rod bar stock is irradiated with a dose of 50 kGy and then remelted at 150°C (McKellop, Shen, and Salovey 1998) (Figure 15.1). After remelting, the rods are then annealed at 120°C for 24 hours (Greer, King, and Ghan 2003). Acetabular components are machined from the processed bar stock, enclosed in gas-permeable packaging, and then gas plasma sterilized (Figure 15.5). 

The Prolong process is similar to the previously described DURASUL except that an electron beam irradiation dose of 65 kGy is used for Prolong and continuous compression-molded bars are processed as with Longevity. Components are machined from processed Prolong maferial, enclosed in gas-permeable packaging, and sterilized by gas plasma (Figure 15.6). 

FIGURE 3.10 Oxidation levels in gamma sterilized polyethylene components, adapted from [1]. Packaging was classified as gas permeable, multilayer polymer film barrier, or aluminum foil and polymer film barrier (see Table 3.4). Gamma sterilization in gas permeable packaging is the equivalent to gamma sterilization in air. The expiration date was obtained directly from the packaging. (The symbol corresponds to p < 0.05 for Mann-Whitney tests.)... 

Gas-permeable packaging continues to be used for ethylene oxide and gas plasma, which emerged at the turn of the century as industrially viable, alternative methods for sterilizing UHMWPE, especially following radiation... 

Table 15.4 illustrates that though the nitrile resins had a gas permeability much higher than has poly(acrylonitrile) the figures for oxygen and carbon dioxide are much lower than for other thermoplastics used for packaging. 

One impediment of universally applying PET in the area of packaging is its gas-barrier properties. These can be slightly improved by measures to increase the density (crystallinity) during blow molding, for example, by treatment with ultrasound. Ultrasonic treatment during injection reduces the gas permeability to a certain extent [34],... 

Fig. 5.8. Micrograph of the packaged chip. The left-hand side shows the chip attached to a T08/16 header with a partial epoxy cover. On the right-hand side, the metal cap with the gas-permeable membrane is shown...

Fig. 6.15. Photo of a packaged sensor chip. The partial epoxy cover enables free analyte access to the chemical sensor area. The metal cap with the gas-permeable membrane provides mechanical and dust protection...

Copolymers of ethylene and norbomene exhibit excellent transparency, high moisture barrier, high strength and stiffness, and low shrinkage. In comparison to poly(ethylene) (PE) and polypropylene) (PP), they show a very low gas permeability. They are used for blister packaging in pharmacy applications and for flexible films for food packaging. Multilayer films consisting of PP outer layers and a cyclic olefin copolymer are in use. 

In the area of gas permeability, the loss- crystallinity of a typical ionomer I —. IDT) results in relatively high permeability to oxygen. For packaging of fresh meat this is advantageous, but in other packaging areas, combination with a barrier layer may be required. 

A controllable biodegradability, desirable mechanical properties, suitable gas permeability and selectivity would extend the potential application areas of aliphatic polyesters not only in agriculture or in the greenhouse or packaging industry but also as a substitute for human skin. There is a need for such focused studies in the future. 

Not only can absorption alter the aroma and flavor of a product, it can also change the mechanical properties of the polymer. Swelling and gas permeability are factors that effect the physical properties of a polymer (Robertson, 2006 Sadler and Braddock, 1991 Safa and Bourelle, 1999). Swelling occurs when compounds are absorbed into the polymer and distort the shape of the package. As absorption increases there is also a subsequent increase in gas permeability. This increase in gas permeability can affect the shelf-life and sensory quality of a food by, for example, increasing oxidation. In very severe cases, absorption can affect package integrity. 

Copolymers of PE with vinylacetate, acrylic acid ester and methacrylic acid increase the heat sealability, adhesion to other materials and seal strength and they improve the polymer s cold resistance and transparency. EVA in the form of shrink films are well suited for meat packaging because of their relatively high gas permeabilities. 

Of the styrene copolymers used for food packaging the styrene-acrylonitrile copolymer known as SAN still needs to be mentioned. SAN copolymers possess better mechanical properties and better resistance to oils and aroma compounds than PS. Copolymers with acrylonitrile fractions of 20-35 % find uses as household and camping dishes. Copolymers with a higher acrylonitrile content (> 60%) have earned particular importance as barrier plastics. With an increasing acrylonitrile fraction, the gas permeability decreases sharply. 

Chemical Composition The chemical composition of the materials of construction may affect the safety of a packaging component. New materials may result in new substances being extracted into the dosage form or a change in the amount of known extractables. The chemical composition may also affect the compatibility, functional characteristics, or protective properties of packaging components by changing rheological or other physical properties (e.g., elasticity, resistance to solvents, or gas permeability). 

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