Polyolefins polyethylene packaging

A large-volume intraocular solution (for irrigation) may be packaged in a polyolefin (polyethylene and/or polypropylene) container. 

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. 

The commodity thermoplastics are the most-used plastics in this sector, accounting for 95% of all thermoplastic packaging. Polyolefins are the most important, accounting for more than 65% of the total plastic weight. Polyethylene terephthalate, polystyrene and PVC are also commonly used. 

Uses. As an antioxidant in the rubber and plastics industry as a stabilizer in polyethylene and polyolefin packaging materials for foodstuffs... 

Harden s (27) market survey of the growth of polyolefin foams production and sales shows that 114 x 10 kg of PE was used to make PE foam in 2001. The growth rate for the next 6 years was predicted as 5-6% per year, due to recovery in the US economy and to penetration of the automotive sector. In North America, 50% of the demand was for uncrosslinked foam, 24% for crosslinked PE foams, 15% for EPP, 6% for PP foams, 3% for EVA foams and 2% for polyethylene bead (EPE) foam. As protective packaging is the largest PE foam use sector, PE foam competes with a number of other packaging materials. Substitution of bead foam products (EPP, EPE, ARCEL copolymer) by extruded non-crosslinked PE foams, produced by the metallocene process was expected on the grounds of reduced costs. Compared with EPS foams the polyolefin foams have a lower yield stress for a given density. Compared with PU foams, the upper use temperature of polyolefin foams tends to be lower. Eor both these reasons, these foams are likely to coexist. 

So far, emphasis has been placed on the treatment of polyolefins to improve printability, but the same treatments affect also other processes. As an example, while an untreated polyethylene surface will not retain an adhesive the treated and modified surfaces are receptive to adhesives. A field of increasing importance for packaging is the production of laminates of film with other materials and, as examples, suitably pre-treated polyethylene film can be bonded securely to substrates such as cellulose or polyester films and aluminium foil, using standard adhesives, whereas this cannot be achieved without pre-treatment. 

The majority of packaging plastic materials consists of polyolefins and vinyl polymers, namely polyethylene (PE), polypropylene (PP), polystyrene (PS) and poly(vinyl chloride) (PVC). Obviously, these polymers have many other applications not only as packaging materials. Chemically they are all composed of saturated hydrocarbon chains of macro-molecular size their typical thermal decomposition pathway is free radical one initiated by the homolytic scission of a backbone carbon-carbon bond. In spite of the basic similarity of the initial cleavage, the decomposition of the hydrocarbon macroradicals is strongly influenced by fhe nafure of the side groups of the main chain. 

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