PEER-REVIEWED ARTICLE bioresources.com Kuzmin et al. (2023). “Carton in HDPE composites,” BioResources 18(2), 2815-2825. 2815 Effect of Content and Particle Size of Used Beverage Carton Pieces on the Properties of HDPE Composites Anton Michailovich Kuzmin, a Nadir Ayrilmis, b Ferhat Özdemir, c and Gürdal Kanat d, * This study investigated the tensile properties and thermal behavior of virgin and hot press molded HDPE composites filled with different particle size and content of used beverage cartons which were the Tetra Pak ® cartons. The mechanical properties of the composites were positively influenced by particle size of the used beverage carton, such that the smallest particle size gave the highest tensile strength and tensile modulus. The tensile strength of the specimens decreased with increasing filler content (40 to 70 wt%), while the tensile modulus rose. Furthermore, the filler size and its content affected the thermal behavior of the specimens. Calorimetry analysis of composite specimens showed that melting temperature and enthalpy values of virgin HDPE and recycled- HDPE decreased with increasing Tetra Pak ® content. In all composite groups produced by adding Tetra Pak ® , the degree of crystallinity decreased as a function of Tetra Pak ® addition compared to the pure HDPE. Increasing particle size adversely affected the crystallization degree, which decreased with increasing particle size while the HDPE maintained its crystalline form. As for the recycled-HDPE composites, the degree of crystallization was reduced by increasing the Tetra Pak ® content, but this was still noticeably higher than that of the HDPE. DOI: 10.15376/biores.18.2.2815-2825 Keywords: Tetra Pak; Filler; Thermal behavior; Strength; Particle size; Filler content Contact information: a: Assoc. Prof. Dr., Institute of Mechanics and Power Engineering, National Research Mordovia State University, Bolshevistskaya st., 68, 430005, Saransk, Republic of Mordovia, Russia; b: Prof. Dr., Department of Wood Mechanics and Technology, Forestry Faculty, Istanbul University-Cerrahpasa, Bahcekoy, Sariyer, 34473, Istanbul, Turkey; c: Assoc. Prof. Dr., Department of Wood Chemistry and Technology, Faculty of Forestry, Kahramanmaras Sutcu Imam University, Onikisubat, 46050, Kahramanmaras, Turkey; d: Assoc. Prof. Dr., Department of Environmental Engineering, Faculty of Civil Engineering, Yildiz Technical University, 34220, Esenler, Istanbul, Turkey; * Corresponding author: kanat@yildiz.edu.tr INTRODUCTION Paper and cardboard packaging is the largest proportion by weight with 33.2%, followed by flexible plastics 25.5%, rigid plastics 18.7%, metal 12.1%, glass 5.8%, 4.7 other packaging materials (Fernandez 2022). Recently, in addition to the virgin thermoplastics, the use of multilayer beverage cartons (Tetra Pak ® ) is composed of three materials organized in six layers: paper (75 wt%), low density polyethylene (LDPE, 20 wt%), and aluminum (5 wt%) (Ayrilmis et al. 2008). However, the amount of their waste has increased more and more. A thin aluminum sheet is also incorporated in the composition to improve UV resistance and oxygen barrier for aseptic cartons (Avella et al. 2009). Several studies were published on the utilization of used beverage carton in the production of high value-added products (Ayrilmis et al. 2008, 2013a; Selim et al. 2010;