Nanocomposites, defined as polymers bonded with nanoparticles to produce materials with enhanced properties, have been in existence for years but are recently gaining momentum in mainstream commercial packaging use.

Modification technology is an innovation in polymer nanocomposite technology which holds the key to future advances in flexible packaging recycling.

Silicon based nanocomposites of the modifier are constructed by dispersing a filler material into nanoparticles that form flat platelets. Initially, the Modifying Agent reacts with the most active, low molecular weight pieces of polymer chain. Symmetrical nanocomposites allow the reaction to occur at 2, 3 or 4 active ends of the Silicon molecule. As a result, the modified PET molecular chain Molecules of the Modifying Agent that represent symmetrical silicones react with the molecular chains of PET. Initially, the Modifying Agent reacts with the most active, low molecular weight pieces of polymer chain. These platelets are then distributed into a polymer matrix creating multiple parallel layers which regenerate the physic mechanical properties of PET post consumer waste. Symmetrical silicones allow the reaction to occur at 2, 3 or 4 active ends of the Silicon molecule. As a result,, the modified PET molecular chain becomes both “longer” and “branched”.

We can compare this process to a re-synthesis of PET. However, instead of PET monomers, the PET-MTM process uses oligomers of post-consumer PET. Silicon-based modifier plays the role of a catalyst in the process.

This mechanism performs a dual effect. On one hand, toxic, low molecular weight particles are integrated back into the PET chain. Simultaneously, there is a significant growth in average molecular weight of the polymer. The dual effect results in restoring mechanical and other properties of the resin. As the result, UV barrier properties and elasticity are improved. 35 g pre-form normally used for 1.5 liter bottle production can be easily stretched and blown into 2 liter bottle

There are three mechanisms that are involved in “cleaning” or “purifying” post-consumer material that goes through the PET-MTM technological process. These three mechanisms can be described as (1)biological, (2) mechanical, and (3) chemical

BIOLOGICAL

Biological purification aimed to purify the material from the biologically active substances like bacteria and viruses that could have survived washing procedures. It is succeeded due to thermal treatment of the material during its presence in the mixing reactor (140 °C, 90 min) and extrusion (260-280 C, 6-10 minutes).

MECHANICAL

Mechanical purification aimed to remove the mechanical impurities that could have left after washing procedures. It is succeed during the mixing process which is combined with intensive blowing of hot air. Next step is high vacuum degassing, and the last step is filtration of molten material through 58 micron filter after the extrusion.

CHEMICAL

Chemical purification aimed to remove migrating, toxic and chemically active substances like low molecular weight chains of PET molecules. It is succeeded by introduction of the modifying agent, which reacts with the most active, short chains of PET molecules. It provides for binding those chains into long linear or ramified polymers which are not toxic and do not migrate from the material into foodstuffs. The effectiveness of this method is proved by the results of the analyses of PET-M performed by Czech Institute for Testing and Certification (Zlin, CZ). www.itczlin.cz