Bio-based Polyester-amide / Cellulose Nanocrystal Nanocomposites for Food Packaging

The worldwide plastic waste production is steadily increasing, since the use of polymeric materials continues to rise. One area of particular high plastic consumption is food packaging. Flexible and rigid packaging films are typically made from petrochemical-sourced polymers, which are utilized because of their low cost, ductility, melt-processability, and gas barrier proper­ties, but a major downside is their inability to biodegrade in a reasonable time. We here report, packaging-relevant properties of nanocomposites based on polyester-amides (PEAs), which were chosen on account of their tunable crystallinity, bio-based starting materials, and bio­degradability. These polymers were synthesized via melt polycondensation of a building block made from caprolactone and 1,4-diaminobutane, with the addition of 1,4-butanediol, and dimethyl adipate. The fraction of the amide segment was varied between 25 and 75 mol%. The oxygen trans­mission rate (O₂TR) drops upon increasing the amide content from 1.6x10⁵ to 2.9x10­⁴ cm³m^-2d^-1 on account of increasing crystallinity. In order to improve the gas barrier properties further, nanocomposites of the PEAs and 1-10 wt% cellulose nanocrystals (CNCs) were prepared. These nanocomposites have indeed lower O­₂TR values than the neat PEAs, with reductions of as much as 50% for a CNC content of 10 wt%.