Polypropylene barrier properties

Some cast (unoriented) polypropylene film is produced. Its clarity and heat sealabiUty make it ideal for textile packaging and overwrap. The use of copolymers with ethylene improves low temperature impact, which is the primary problem with unoriented PP film. Orientation improves the clarity and stiffness of polypropylene film, and dramatically increases low temperature impact strength. BOPP film, however, is not readily heat-sealed and so is coextmded or coated with resins with lower melting points than the polypropylene shrinkage temperature. These layers may also provide improved barrier properties. 

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. 

Barrier Properties. VinyUdene chloride polymers are more impermeable to a wider variety of gases and Hquids than other polymers. This is a consequence of the combination of high density and high crystallinity in the polymer. An increase in either tends to reduce permeabiUty. A more subtle factor may be the symmetry of the polymer stmcture. It has been shown that both polyisobutylene and PVDC have unusually low permeabiUties to water compared to their monosubstituted counterparts, polypropylene and PVC (88). The values Hsted in Table 8 include estimates for the completely amorphous polymers. The estimated value for highly crystalline PVDC was obtained by extrapolating data for copolymers. 

This stretching, similar to the drawing of fibres, which promotes orientation and crystallite formation, is called biaxial orientation. It gives the film added strength and gas-barrier properties. In some processes, monoaxial (uniaxial) drawing is employed, e.g., polypropylene, which is then slit into thin strips and fabricated into heavy duty sacks, carpet backing, etc. The stenter process is used to make biaxial oriented poly(vinylidene dichloride) ("ding" film), polyester, polyamide and polypropylene films. 

Barrier properties -ofparylenes [XYLYLENE POLYMERS] (Supplement) -of PP films [OLEFIN POLYMERS - POLYPROPYLENE] (Vol 17) -ofPTFE [FLUORINE COMPOUNDS, ORGANIC - POLYTETRAFLUOROETHYLENE] (Vol 11) -of vinylidene chloride polymers [VINYLIDENE CHLORIDEMONOMERAND POLYMERS] (Vol 24)... 

EVOH have superior gas barrier properties.80 89 They are often used as the internal layer in multilayer food packaging films, blow molded rigid containers, gasoline tanks for automobiles for a variety of purposes, etc. EVOH can be fabricated by the usual melt processing methods. The barrier properties of films decrease in the presence of moisture, so multilayer with protective polypropylene (especially biaxially oriented material), low-density polyethylene, nylons, or other moisture barrier films provides films or products that are useful even with liquids. The... 

Many thermoplastics can be thermoformed, including polystyrene, polypropylene, APET, CPET, and PVC. EVOH is commonly incorporated into a co-extrusion for its superior barrier properties in food. Co-extrusions of these materials are commonly used to provide precise properties for specific applications. 

In this review article, an account will be presented of the diffia t methods by which high modulus materials have been produced from flexible polymers. Much of the discussion will be concerned with polyethylene, although comparable results have been obtained fot polypropylene and polyoxymethylene, and these will also be considered. The initial stimulus to this research came from the quest for high stiffness, but other properties have also been enhanced, including strength, thermal and chemical stability, and barrier properties. The present article updates and extends previous reviews of progress in this exciting new area of polymer science. 

Shrink sleeving made from lay flat tubing or welded tubing is widely used as a tamperevident overwrap to enclose either a whole container or neck and closure. Materials include PVC, polypropylene and polyester. Shrink sleeving can improve container barrier properties or light exclusion. 

Information on how orientation during melt crystallization affects the transport properties of polymers is sparse however, increases in the permeability have been attributed to the "shish kebab" morphology (ill). Most of the work involving barrier properties of oriented semicrystalline polymers has dealt with materials drawn at temperatures well below the melting point. The transport properties of cold-drawn polyethylene (34f 42-46), polypropylene (42,42), poly(ethylene terephthalate) (12,42-4 9), and nylon 66 (22) among others have been reported. 

Monomers which have also been demonstrated to have been grafted to polyethylene and polypropylene film by this process include styrene and various acrylated esters, mixtures of acrylated esters, and acrylonitrile. The application of this technology to improving the barrier properties of films is discussed. Some initial data on the O2 barrier, fragrance/aroma, and haze performance of these graft modified films indicate substantial Improvement and place them in the high barrier range where dry Oo permeabilities of less than 1 cc/100 ln /24 hrs. are ootained. 

It Is known that most radiation Initiated polymerization processes are Initiated by Che free radicals created by radlolysls of Che monomers. If a monomer or a mixture of monomers Is Irradiated In Che presence of a polymer, a graft copolymer Is formed which has different physical properties. For example. If a second polymer like polyacrylonitrile or polyvlnylldlne chloride, which possess superior barrier properties against permeation by oxygen, carbon dioxide, water vapor etc.. Is grafted to a polyolefin film like polyethylene, polypropylene, etc., the barrier properties of the composite film are greatly enhanced compared with Che polyolefin film. 

Tests on the fragrance/flavor barrier properties of slloxane coated polyethylene and polypropylene film, using the ASTM test method D-1653 are given In Table II, which show excellent performance for the primed film. ... 

Barrier Properties Ticona Topas COCs provide excellent moisture control. They have roughly double the moisture barrier of HDPE, triple that of LDPE, and seven times that of unoriented polypropylene (PP). They also provide high clarity and stiffness. Grades are available with the heat resistance to withstand hot-fill and microwave processes. ... 

Kraton polymers blended with polypropylene can provide films with elasticity and strength, puncture resistance, low permanent set to prevent finger marks and indentation due to handling, high oxygen permeability, moisture-barrier properties, and clingJ ]... 

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