# Analysis of the Delamination Process with Nitric Acid in Multilayer Composite Food Packaging
## 4 Discussion and Conclusions  
Multilayer food packaging is prevalent in global industries due to its adaptability in packaging diverse products. Nonetheless, the non-recyclable, multi-material structure of such packaging has raised concerns regarding its environmental impact [17]. In response, delamination of multilayer packaging can be achieved using methods such as selective melting, micro-perforation, and ultrasound. In this study, we have chosen the latter approach. Additionally, making polymers in compatible packaging can help reduce waste.  
Our delamination method employs nitric acid, temperature, stirring, and ultrasound to separate the packaging layers while preserving the polymer layers. One notable advantage of our method is that it enables the separation of dissolved aluminum from the liquid medium through further investigation. We successfully recovered three distinct polymers that can be recycled and used for producing new products through utilizing nitric acid,  
Figure 5: Response contour plot comparing ultrasound influence on duration (minutes).  
temperature, mixing, and ultrasound. Aluminum can also be reused to its full potential, considering the existing abundance of aluminum in the market.  
The foundation of our method lies in the degradation of adhesive layers. For example, if PU adhesive layers are present, they can be decomposed by a strong oxidizing agent, such as nitric acid. PU comprises soft and hard segments, and monomers are formed when the polymer is oxidized by acid. These monomers are subsequently removed from the multilayer packaging structure by mixing, breaking down the packaging structure, and separating the polymers. The use of non-concentrated nitric acid further enables the dissolution of aluminum from the packaging. However, controlling gas emissions remains a significant challenge in the delamination process, warranting further research.  
We conducted 24 experiments using the Mode 13.0.1 (Umetrics) program to identify the factors influencing the process. The results revealed that ultrasound has the most substantial impact on the process with temperature and acid concentration exhibiting no significant statistical correlation. Ultrasound application enhanced the process's efficiency, and the width of the packaging strips emerged as a crucial factor in the process's success. The contour plots demonstrated that acid concentration and temperature are equally important when the strips are 1 cm and 1.5 cm wide. In contrast, when the strips are 0.5 cm wide, the influence of concentration outweighs that of temperature. The situation alters when ultrasound is applied, rendering the influence of temperature insignificant when the width of the packaging strips is 1.5 cm.  
In conclusion, based on the presented results, we successfully separated the packaging layers and recovered three polymers with the potential for aluminum deposition. All chosen process parameters, including acid concentration, temperature, the width of MLPW strips, and ultrasound, were vital for the final outcome. Although the process is effective without ultrasound, ultrasound is the most critical factor in achieving faster results.  
Conceptualization, A.S. and G.D.; methodology, A.S.; software, A.S.; validation, A.S., T.M. and G.D.; formal analysis, T.M.; investigation, A.S.; resources, T.M.; data curation, A.S.; writing--original draft preparation, A.S.; writing--review and editing, G.D.; visualization, A.S. and T.M.; supervision, G.D.; project administration, G.D.; funding acquisition, T.M. All authors have read and agreed to the published version of the manuscript.  
Research is carried out with EU financial support, implemented in the frame of GRMP, EU fellowships for Georgian researchers, 2023 (57655523).  
Not applicable.