Effect of ultrasonic processing on the physical-chemical properties and migration of metallized flexible packaging materials

Abstract

Flexible polymeric packaging can be used for ultrasonic processing of food inside the package. However, the effects of ultrasound on packaging materials are not well understood and require further research to ensure their performance and safety. This research explores the effects of ultrasonic processing on the physical-chemical and migration behavior of metallized flexible packaging used for acidic food products. Two types of metallized flexible packaging (PETmet/PE and PETmet/PP – PET: polyethylene terephthalate, met: metallized, PE: polyethylene, and PP: polypropylene) were filled with acidic food simulant and processed to varying conditions in an ultrasonic bath (with frequency of 25 kHz, volumetric power of 8.75 W/L, temperature of 25 °C and 60 ºC for 60 min). The materials underwent comprehensive evaluations regarding their structural integrity, performance properties and migration potential. Results indicate that ultrasonic treatment influenced the crystallinity index, with reductions observed from 69.3 to 67.0% for PETmet/PE and from 56.4 to 46.7% for PETmet/PP films. Moreover, a discontinuity in the metallization of the outer layer was observed as a result of ultrasound processing, using SEM at 10,000× magnification. This defect led to a significant increase in the oxygen transmission rate of the films significantly in ten times (p < 0.05). Additionally, there was a noticeable decrease in moisture barrier properties following ultrasonic treatment. The PETmet/PP sample exhibited a reduction in seal strength. Chemical analyses, including FT-IR and DSC, revealed minimal alterations in melting temperature, chemical groups, and tensile strength. Migration of aluminum and antimony to the interior of the package was also assessed, showing no significant increase post-ultrasound. In conclusion, our findings caution against the use of these metallized materials for ultrasonic food treatment due to the detrimental effects on metallization continuity and barrier properties, revealing significant limitations in this processing approach. This research highlights critical considerations for the future of food packaging in the context of advanced processing techniques.