# Analysis of the Delamination Process with Nitric Acid in Multilayer Composite Food Packaging
## 1 Introduction  
Multilayer packaging, commonly referred to as composite materials, is extensively utilized in food storage, distribution, and consumption. This type of packaging consists of multiple materials, including paper, plastic, and metal, combined to form a sandwich-like structure [1]. The package's polymer is laminated with other polymers, aluminum foil, and/or cardboard to provide various functions, such as tensile strength, satisfactory sealing, and protection from moisture, light, other flavors and odors, and oxygen [2]. Each layer of packaging serves a distinct purpose in achieving the desired technological functionality. Typical polymers employed in food packaging include polypropylene (PP), polyethylene terephthalate (PET), low-density polyethylene (LDPE), polyamide (PA), polyvinylidene chloride (PVdC), and ethylene vinyl alcohol (EVOH) [3]. The thickness of the polymer layers varies based on their intended use. For instance, PP and PET generally range between 15-55 \(\upmu\)m and 12-50 \(\upmu\)m, respectively. LDPE is a thicker polymer utilized in packaging with thicknesses ranging from 25-100 \(\upmu\)m. Thinner polymers, such as PA, PVdC, and EVOH, can range from 12-30 \(\upmu\)m, 32 \(\upmu\)m, and 2-10 \(\upmu\)m, respectively. The remaining thickness of the packages results from the aluminum foil, adhesive layers, ink, and paper (if used). The thickness of the aluminum foil can be up to 12 \(\upmu\)m [4]. However, the use of plastic packaging composed of multiple layers of polymers, ink, paper, and metal has sparked concerns about its adverse environmental impact. Separating the layers for recycling purposes is technically challenging and financially burdensome due to the thermodynamic incompatibility of the materials. According to Eurostat Statistics Explained, the generation of packaging waste in the European Union amounted to79 \(\pm\) 1.25 million tons annually between 2007 and 2016, constituting approximately 17% of all co-collected waste, including multilayer composites [5]. In light of this, substantial research and resources should be dedicated to developing innovative recycling techniques capable of enhancing the recycling rate of multilayer packaging while focusing on achieving high recovery rates. Delamination is considered an effective solution for multilayer plastic waste (MLPW) recycling. Several methods can be employed to achieve delamination, such as selectively dissolving polymers [6]. However, this method requires an in-depth understanding of the chemical properties of polymers, making it difficult to apply to a mixture of packaging waste from a recycling center. Another option involves delamination through micro-perforation, which expedites the process by creating small holes in the polymers [7]. It is advised to remove the aluminum layer before initiating the delamination process, for instance, by dissolving it in an alkali solution. In addition to delamination, compatibilization represents another feasible recycling approach that involves the incorporation of additives to combine and stabilize different polymers [8]. Nevertheless, this method is currently inefficient due to differences in material composition. Recent studies have concentrated on developing novel, sustainable packaging materials to replace multilayer composite packaging. For example, researchers have developed biodegradable packaging materials from cellulose nanocrystals, chitosan, and starch [9]. These materials exhibit exceptional oxygen and moisture barrier properties, and can be employed in food product packaging. This study aims to determine the efficiency of MLPW in separating polymer layers by analyzing the resulting surface morphology and chemical composition of the separated layers. The study also seeks to optimize the conditions for the separation process, such as the concentration of nitric acid, exposure time, and temperature.