Cellulose-based packaging materials

The properties listed in Table 5.8 were responsible for the rapid replacement of cellophane or other cellulose-based packaging materials by polyethylene. Utilizing polyethylene in food packaging applications, such as fresh produce, provided much longer shelf-life and a reduction in waste and spoilage. As can be seen from the physical properties of polyethylene relative to cellulose, polyethylene was more elastic, less likely to tear, heat sealable and much less permeable to water vapor. 

The outstanding advantage the thermoplastics have over cellulose-based packaging materials is their very good barrier properties. The advantage of polyethylene in foodwrapping is without parallel over traditional wrapping materials, such as paper or metal foil, due to its resistance to moisture and mechanical stress. 

Subramaniam, 1988]. Hydrochlorination, usually carried out at about 10°C, proceeds by electrophilic addition to give the Markownikoff product with chlorine on the tertiary carbon (Eq. 9-33) [Golub and Heller, 1964 Tran and Prud homme, 1977]. Some cyclization of the intermediate carbocation (XXVI) also takes place (Sec. 9-7). The product, referred to as rubber hydrochloride, has low permeability to water vapor and is resistant to many aqueous solutions (hut not bases or oxidizing acids). Applications include packaging film laminates with metal foils, paper, and cellulose films, although it has been largely replaced by cheaper packaging materials such as polyethylene. 

Humidity. If the humidity of the packaging area is higher than that of the storage area, condensation may form on the containers, wads, or closures, and any cellulose-based materials will begin to absorb moisture. It may take days (even weeks in the case of roll materials) to reach equilibrium with the filling area. 

In this chapter, packaging materials based on cellulose or natural fibres will be discussed. They provide a major contribution to the packaging of pharmaceuticals, the size and nature of which can readily be overlooked since the number of applications is far more diverse and more paper and board is used than glass, metal or plastics. 

Natural polymers are not newcomers in food packaging. Commercial film and paper-based packaging using cellulose or starch is a big industry worldwide. The 2002 Industry Status Report of the US Flexible Packaging Association has reported that in the US alone, the flexible packaging industry, which includes food packaging materials, is worth around 20 billion US dollars. 

Gas barrier properties were evaluated to access the potential of isotropic all-cellulosic based composites for packaging applications. The mechanical properties, fiexibility and biocompatibility of these materials can be useful, in particular, for food packaging. Due to the nature of the envisaged application insoluble materials are required. This requisite is only fulfilled by cross-linked composites and, therefore, we have decided to subject only cross-Unked films for gas permeation measurements. 

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