Paper And Paperboard

Paper and paperboard are made from wood fibers composed of cellulose, hemicellulose, and polymeric residues.

Although there is no strict distinction between paper and paperboard, structures less than 0.012 in thick are generally considered to be paper. Because of their good mechanical strength, paper and paperboard are used mostly to protect the product from physical damage. However, paper and paperboard have poor gas-barrier properties, and their mechanical strength can decrease greatly in wet or humid conditions.

Many types of paper are used for food-packaging applications (1,2). Kraft paper is typically a coarse paper used in applications such as bags and wrapping where strength is required. Kraft paper is available either in unbleached brown form or in bleached form. Greaseproof paper consists of densely packed fine fibers that provide good oil and grease resistance. Greaseproof paper may be further treated with fluorochemicals or coated with polyvinylidene chloride (PVDC) to improve gas- and moisture-barrier properties. Glassine paper is produced by further processing greaseproof paper through a super-calendering operation, making the paper smoother, denser, and translucent. Waxed paper consists of a continuous layer of wax on a base paper such as greaseproof or glassine paper. The wax serves as both a moisture barrier and a heat-sealable layer.

There are also many types of paperboard used for food-packaging applications (5). Corrugated boxes are used mostly for shipping food packages. Folding cartons are used as outer boxes for packaging cereal products, cookies, snacks, frozen foods, and the like. The appearance and printing quality of paperboard can be enhanced by coating with clay and other minerals.

Paperboard is often coated or laminated with plastics or aluminum for better performance. For example, polyethylene (PE) is coated onto gable-top paperboard containers, which are commonly used to contain milk or juices. The coating protects the paperboard against moisture absorption, and it also provides the paperboard with heat sealability. Another example is the aseptic Tetra Pak juice carton, which is made from a paperboard laminate having the structure PE/paper/aluminum/PE. In this laminate structure, the inner PE layer protects the aluminum from the juice, the aluminum layer provides oxygen and a moisture barrier, the paperboard layer provides strength and rigidity, and the outer PE layer provides moisture protection for the paperboard.

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