High barrier properties

Homo and copolymers of vinylidene chloride (VDC) possess extremely high barrier properties to gases, water and aromas as well as good resistance to water and solvents. The barrier properties of polyvinylidene chloride (PVDC) come from the dense packing of its polymer chains (without voids or branching) which are crystalline in their stable form. The chlorine content of the high density polymer is 73 % (1.80-1.97 g/cm3, crystalline). 

Structures 2 and 3 are considered as having high barrier properties. The second structure has EVOH as a barrier and the third is a face-to-face metallized polyester. The latter structure is very stiff due to the face-to-face lamination of the metallized polyester. 

Coextrusion is the simultaneous extrusion of two or more layers of different polymers to make a film. Coextruded films have three main advantages over other types of film they have very high barrier properties, similar to laminates but produced at a lower cost they are thinner than laminates and are therefore easier to use on filling equipment and the layers do not separate. There are three main groups of polymers that are coextruded ... 

Silica layered Nation membranes prepared by olasma enhanced chemical vapour deposition [45] also exhibit a moderate reduction of permeability (F, =0.33) by those membranes fabricated by dip-coating [38] show extremely high barrier properties to methanol permeation, with 0.002 < P < 0.005. However, it should be noted that the permeability reported for the Nation 117 without silica layers is more than one order of magnitude higher than the values reported by several authors, including those shown in Fig. 6.18. 

High barrier film users are currently looking for alternatives to polyvinyli-dene chloride as a barrier layer because of problems cited in melt recycling or burning PVDC. LCP laminates and coextruded films are being evaluated because evidence suggests they can be burned as easily as PLT, and their high barrier properties mean that LCP layers will be four to five times thinner than PVDC for equivalent barrier performance. 

The excellent properties of EVOH resins in terms of high gas, hydrocarbon and aroma barrier and transparency have allowed them to become widely implemented in many commercial applications where high barrier properties are needed to minimise product losses due to deterioration. Despite the excellent performance of these materials in high barrier food packaging applications, the materials are easily plasticised by moisture and, consequently, in most packaging applications are commonly encapsulated in multi-layer structures between hydrophobic polymers such as PP or PE. 

The intimacy of the filler/matrix bond is the main key to the performance of fillers and. with the latest technology, it is possible to achieve very good dispersion and an almost molecular bond. Tiny filler particles - sub-microscopic and also nanosized - have been shown to produce better mechanical properties at considerably lower loadings, and also give better flow, high barrier properties, inherent flame retardancy, and different surface textures in the same moulded part. 

Major polymer applications housings for electronic and electrical applications, instrument lenses packaging for high barrier properties, bottles, pliances (housings, air conditioner parts, refrigerator shelves, blenders, lenses), house-wares (eating utensils, beverage/food containers, display boxes), automotive (dashboard, battery cases)... 

The film-forming properties of corn zein have also been investigated in detail [2, 44-55]. Zein films are water-insoluble, relatively shiny and greaseproof, but they sometimes have unsuitable organoleptic properties (off-odour, chewiness and so on). Zein-based films and coatings improve food shelf life, via their high barrier properties (to water vapour or especially to oxygen (O2)), or their retention or controlled release properties of active additives on the food surface. These films have been successfully used to protect dry fruits and various parts of frozen or intermediate moisture foods. 

The incorporation of cellulose nanostructure into PLA creates a great effect that includes improvement in barrier properties, nucleation effects and foam formation. Sanchez-Garcia et al. [57] have reported the barrier properties of PLA/cellulose nanowhisker composites showing that the addition of 3 wt% of cellulose nanowhiskers into PLA was able to reduce the water and oxygen permeabilities by 82% and 90%, respectively. Cellulose nanowhiskers acted as a shield in PLA and caused the increment of the crystallinity degree, resulting in high barrier properties [57]. 

This is a very thin plastic film in the order of 10 microns and is commonly used for covering food items. It does not possess veiy high barrier properties and often used for covering the items for avoiding their direct contact with foreign substances for short durations especially for food items. 

Beverages Acid resistant, high barrier properties... 

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