Polypropylene packaging applications

High molecular weight atactic polyropylene is now available (Rexene-Huntsman). This is miscible with isotactic polypropylene in any proportion to give transparent blends of interest in packaging applications. 

The production of foamed films and sheets from polypropylene and polystyrene is discussed, with particular reference to packaging applications. Advantages of foamed materials for this application are examined, and the chemical and physical foaming processes are described. Extrusion technology for film and sheet by chemical and physical foaming processes is discussed, and recent developments in the coextrusion of multilayer packaging trays for the food industry are considered. 

Polypropylene. Polypropylene (PP) is used in packaging applications as films and in rigid containers. Battery cases could be considered another packaging application. Dead batteries are often collected at the point of sale of new batteries. In the U.S., some states have laws mandating this. Lead, acid, and plastics, particularly PP from battery casings is recovered and recycled (3). Care must be taken to limit worker exposure to lead during this process (44). PP is also recovered from bale wrap and other PP fabrics used for wrapping in the textile industry and from other containers (45). 

ILSl Europe Report Series Packaging Materials 1. Polyethylene terephthalate (PET) for food packaging applications 2. Polystyrene for food packaging applications 3. Polypropylene for food packaging applications 4. Polyethylene for food packaging applications 5. Polyvinyl chloride (PVC) for food packaging applications. 

Thermoplastics may be further subdivided into two broad categories on the basis of their cost and suitable end uses. Commodity plastics are typified by high volume production, good properties, and low resin cost. The four major commodity plastics are polyethylene, polypropylene, poly(vinyl chloride), and polystyrene. Their adequate properties and low cost have led to the extensive use of these plastics in packaging applications where they are very competitive with paper, steel, and glass. They are also used for some less demanding applications as components of durable goods (Table 22.1). 

Films. Three films were included in this study. Low density polyethylene (LDPE) was included as a representative polyolefin. It is not considered to be a barrier polymer. It has permeabilities to selected aroma compounds slightly higher than the permeabilities of polypropylene and high density polyethylene (1). A vinylidene chloride copolymer (co-VDC) film was included as an example of a barrier that is useful in both dry and humid conditions. The film was made from a Dow resin which has been designed for rigid packaging applications. A hydrolyzed ethylene-vinylacetate copolymer (EVOH) film was included as an example of a barrier film that is humidity sensitive. The polymer was a blend of resins with total composition of 38 mole% ethylene. 

Although the possible number of polymers is theoretically limitless, the economics of their production and processing, as well as the physical and chemical properties they have, restrict the number of commercial importance to a few dozen (see Fig. 2.2), and in packaging applications the number of polymers used is even smaller. The polymers most commonly used in packaging are polyolefins, specifically polyethylene and polypropylene. Polystyrene, polyvinyl chloride, and polyethylene terephthalate (PET) are also among the most commonly used packaging polymers. 

Grimm A, Weiser J. Transparent coloration of clarified polypropylene for packaging applications. Additives Colors, conference proceedings. Society of Plastics Engineers 2007. 

Polypropylene accounted for about half of the nonwoven products in industrial uses in 2001. Its share in ropes and nets was 55-60%, and 70-80% in civil construction, where polyester claimed 20-24%. In automotive applications, polypropylene shared 26-30%, nylon almost 50%, and polyester about 20%. Polypropylene contributed to over 86% of agricultural nonwoven, 100% of packaging cloth, 85% of sanitary items, and 64-70% of medical applications. The world consumption of industrial nonwoven products was 1.329 MT in 2000. Polypropylene topped all synthetic fibers with a share of over 40% in this market segment. 

Polystyrene films and polyester (polyethylene terephthalate) films are only used in the biaxially stretched form, because unstretched films are very weak and brittle. To a lesser extent this is also true for polypropylene films. Roll-quenched flat film is used for many packaging applications, but below 0°C these films become brittle. Biaxially oriented polypropylene film, on the other hand, is not brittle at a temperature as low as — 50°C and is suitable for packaging frozen foods. 

An important application for polybutylene is plumbing pipe for both commercial and residential use. The excellent creep resistance of polybutylene allows for the manufacture of thinner wall pipes compared to pipes made from polyethylene or polypropylene. Polybutylene pipe can also be used for the transport of abrasive fluids. Other applications for polybutylene include hot melt adhesives and additives for other plastics. The addition of polybutylene improves the environmental stress cracking resistance of polyethylene and the impact and weld line strength of polypropylene. Polybutylene is also used in packaging applications. 

Other applications include hot-melt adhesives and additives for other plastics. The addition of polybutylene improves the environmental stress cracking resistance of polyethylene and the impact and weld line strength of polypropylene. Polybutylene is also used in packaging applications. 

A common multilayer PP product is bi-axially oriented polypropylene (BOPP), produced on a line including a machine direction orientation unit, and a tenter frame for transverse orientation. This process commonly uses a three-manifold die that allows thin skin layers of copolymer to be applied on either side of a homopolymer base layer. The copolymer is used in this product so the film can be sealed, which is a requirement in packaging applications. Typically, the skin layer thickness is 5% of the total film thickness. The adhesive property of the copol3mier makes it difficult for the film to be processed through a tenter frame, because the film would stick to the tenter frame clips. The multimanifold die can be designed with narrower width flow channels for the skin layers, to keep the adhesive out of contact with the tenter clips, allowing the product to be extruded successfully. 

Omitting the construction and demolition debris from the calculations, the composition (by volume this time) is as follows paper and paperboard 50%, plastics 14%, metals 12%, glass 4%, organics 6%, and miscellaneous 14%. All plastic packaging (post-consumer, industrial, commercial, and institutional) represented about 8% of the overall refuse. It is a reasonable assumption that the composition of plastics discarded in landfills is a reflection of the quantities produced for packaging applications the commodity plastics polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) should be well represented (see Ethylene POLYMERS PROPYLENE Polymers (PP) Styrene Polymers Vinyl Chloride Polymers). 

Many polymers, including polyethylene, polypropylene, and nylons, do not dissolve in suitable casting solvents. In the laboratory, membranes can be made from such polymers by melt pressing, in which the polymer is sandwiched at high pressure between two heated plates. A pressure of 8-15 MPa (1000-2000 psi) is applied for 0.5-5 min, at a plate temperature just above the melting point of the polymer. Melt forming is commonly used to make dense films for packaging applications, either by extmsion as a sheet from a die or as blown film. 

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