Kendall Packaging is proud of the strong technical alliances that we've built with our key suppliers.  Our partnerships allow us to leverage the knowledge and capabilities of the leading suppliers in the industry.  Many of the technologies that we use to continuously improve our customer's products come directly from our suppliers.  The article below is an example of the resin technologies applied to improving sealant performance in our laminated structures.  Thanks to Appleton Performance Films for allowing us to reprint this article. 

"Linear Low Density PE (LLDPE) resins are made using multi-site catalyst technology.  This technology produces a product that has, on a chain, different lengths and shapes.  This range of chain lengths, or molecular weights, can be both an advantage and a hindrance for the use LLDPE's in some packaging applications.

Metallocene resins differ in the way they are produced.  They are manufactured using a "single site" catalyst, which gives the polymer scientists greater control over how the polymer grows.  Molecularly they can control the length of the chain (molecular weight) as well as placement and length of the side chain branches.  Each and every polymer chain can be made virtually identical to the next.  For example, by tightening the molecular weight distribution (eliminating the low molecular weight fraction that would normally be mobile), metallocene products are able to meet FDA extractable guidelines at very low densities, as low as 0.895.

Metallocene products can be broken out in to two categories, metallocene linear low density PE's (MLL) and plastomer metallocenes (POP).  These categories are determined by the polymer's density.  Generally metallocene linear low materials have densities above 0.915.  Plastomer resins have a density in a range from 0.870 to 0.915.

These density differences correlate readily to differences in physical properties between the two product types in film form.  They can also be set apart then compared to LLDPE materials, which have a density of 0.915 and greater.  Since the linear low density range overlaps that of the metallocene linear low, many, but not all of the physical properties will be similar.  The largest differences are that the MLL resins have better clarity, lower MD tear strength and lower extractables than LLDPE resins.

As a general rule of thumb, the benefits of the POP resins are as follows:

• Secant Modulus - Lower density equates to lower crystallinity and thus a softer material, as measured by a lower secant modulus.  POP materials have the lowest secant modulus.  These soft films can sometimes be difficult to work with.
• Elongation - Plastomers will have higher elongation than the other materials.  The stretchy nature of the plastomers can sometimes make it difficult for converters to handle on their equipment.
• Haze - Plastomer products will have lower haze in film form than LLDPE's and MLL's, as haze is partly a function of density.
• Seal Strength - Seal strength for all of these materials will be high, but the plastomers will have a much lower heat seal initiation temperature and a wider heat seal window.
• Hot Tack - Octene LLDPE and the metallocene linears have been known for their exceptional hot tack strength and this hot tack is seen over a much wider temperature range.
• Dart Impact - Plastomer products are very stretchy and often times they don't break during a dart impact test.  While linear low and MLL products are strong, plastomers exhibit the highest puncture resistance of the three.
• Oxygen Transmission Rate - The OTR of a film is largely determined by its density.  Since the density of the plastomers is the lowest, they would have a higher OTR than that of the other materials.
• Cost - The cost associated with Octene LLDPE materials and MLL materials are similar.  Plastomers, on the other hand, tend to be more expensive.  In many cases, the benefits gained by their use outweigh the added cost. For more cost sensitive applications, blending resins can help to reduce costs, while maintaining specific film properties."

Written by: Appleton Performance Films