Polypropylene, oriented

Sometimes the hazy optical properties of polypropylene are a detriment to its use in thin films. To address this problem, as well as to improve physical properties and reduce material costs, we can orient the molecular chains by stretching the polymer film after it has left the extrusion die. There are two methods of orienting films, film blowing, shown in Fig. 11.6, and tentering, shown in Fig. 19.6. 

During blown film processing, orientation is imparted to the film by both pulling the melt into the nip rollers and by increasing the circumference of the bubble vith air. By managing 

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BOPP films. See Biaxially oriented polypropylene films. 

Hard baked goods such as cookies and crackers have a relatively low water and high fat content. Water can be absorbed, and the product loses its desirable texture and becomes subject to Hpid rancidity. Packagiag for cookies and crackers includes polyolefin-coextmsion film pouches within paperboard carton sheUs, and polystyrene trays overwrapped with polyethylene or oriented polypropylene film. Soft cookies are packaged in high water-vapor-barrier laminations containing aluminum foil. 

Hard sugar candies have very low moisture content. They are sealed in low water vapor-transmission packaging such as aluminum foil or oriented polypropylene film. 

Oriented polypropylene film (OPP) may be classified as heat-set and non-heat-set, blown and tentered, coextmded and coated. Orientation improves the cold-temperature resistance and other physical properties. Heat-set biaxially oriented polypropylene film (BOPP) is the most widely used protective packagiag film ia the United States. It is used to wrap bakery products, as lamination pHes for potato and com chips, and for pastas and numerous other flexible pouch and wrapping appHcations. Nonheat-set OPP is used as a sparkling, transparent shrink-film overwrap for cartons of candy. 

Oriented polypropylene film has exceUent water-vapor barrier but poor gas barrier properties exceUent clarity, or opacity in newer forms and good heat-seal properties in packagiag appHcations. 

Poly(vinylidene chloride). Poly(viayHdene chloride) [9002-85-1] (PVDC), most of which is produced by Dow Chemical, is best known in its saran or PVC-copolymerized form (see Vinylidene chloride and poly(VINYLIDENE chloride)). As solvent or emulsion coating, PVDC imparts high oxygen, fat, aroma, and water-vapor resistance to substrates such as ceUophane, oriented polypropylene, polyester, and nylon. 

A small quantity of flexible packaging material, usually oriented polypropylene, shrink polypropylene, or polyethylene, is used to overwrap paperboard cartons. The film is wrapped around the carton and sealed by heating. Products such as boxed chocolates, candies, and cookies are overwrapped, sometimes by a printed film. 

Table 11.5 Comparison of cast, monoaxially oriented and biaxially oriented polypropylene film ...

Binder formulas for carpet backing, aluminum foil to paper, vinyl flooring, tire cord, paper labeling, masking tape, and oriented polypropylene tape applications are available from Midgley and Rea in Skiest [215]. 

Patel et al. [70] in a recent publication have explored the adhesive action of the mbber-siUca hybrid nanocomposites on different substrates. The rubber-silica hybrid nanocomposites are synthesized through in situ silica formation from TEOS in strong acidic pH within acryhc copolymer (EA-BA) and terpolymer (EA-BA-AA) matrices. The transparent nanocomposites have been apphed in between the aluminum (Al), wood (W), and biaxially oriented polypropylene (PP) sheets separately and have been tested for peel strength, lap shear strength, and static holding power of the adhesive joints. 

Oriented polypropylene is used for clear films used as food wrap. What advantageous properties do the oriented films have over standard films How can a polymer that is, typically semicrystalline be transparent ... 

Stretching a polymer in two perpendicular directions, either successively or by blowing a bubble of molten material, leads to its biaxial orientation, which strongly improves mechanical properties in the stretching directions and/or gas permeability (e.g., biaxial orientation of polypropylene leads to BOPP (for biaxially oriented polypropylene) or biaxial orientation of poly(ethylene terephthalate) gives CC>2-impermeable bottles for carbonated beverages.) (Characterisation methods for determining molecular orientation are considered in Chapter 8.)... 

The new currency substrate consists of three main components an optical film core, an oriented polypropylene (OPP) laminate applied to both surfaces, and an opaque acrylic receptor coat. A simplified diagram of this construction is shown below. 

ISO/TS 15874-7 2003 Plastics piping systems for hot and cold water installations -Polypropylene (PP) - Part 7 Guidance for the assessment of conformity ISO 17555 2003 Plastics - Film and sheeting - Biaxially oriented polypropylene (PP) films (available in English only)... 

Oriented polypropylene for easy-open bags and wraps. 

Notice that there is variation in values not only between polymer types, but within polymer type due to processing differences. Tensile strength is of most importance to the soda bottle application, since the contents are under pressure, and factors such as hoop stress (see Section 8.1) come into play. PET is obviously an excellent choice for this application from a tensile strength standpoint, as would be oriented polypropylene (OPP). 

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