3D printing to optimize the dry forming of thermomechanical pulp and chemi-thermomechanical pulp trays for food packaging

Environmental concerns over plastic pollution have intensified the search for alternative materials for single-use products, such as trays for food packaging. Dry forming, using wood pulp fibres, is a promising technology for the fabrication of various single-use products. However, the fabrication of trays with relatively complex geometry is challenging. In this study, an approach is introduced where trays are pre-formed in tailored three-dimensional (3D) printed meshes with varying distances between the printed lines in the side walls (1.5 mm, 1.8 mm and 2.0 mm) and bottom (1.0 mm) of the trays. This was expected to facilitate the deposition of wood pulp fibres during formation of a given tray geometry and subsequently yield trays with adequate grammage and mechanical properties. The approach was tested with thermomechanical pulp (TMP) and chemi-thermomechanical pulp fibres (CTMP). Both fibres have similar chemical composition (carbohydrates and lignin), but differed with respect to the structural properties. TMP fibres revealed higher fraction of disrupted fibres and fibrils on the fibre surfaces. These characteristics increased the densification of the TMP trays during thermoforming and thus provided higher mechanical properties, compared with the corresponding CTMP trays. A tray demonstrator was developed, with tray depth of 50 mm and side wall angles of 65°. Thermopressed trays (pressure and temperature of 40 MPa and 200 °C, respectively) yielded strength and modulus of 1–10 MPa and 400–1600 MPa, respectively. The mechanical performance depended on the type of fibre (TMP or CTMP) and on the area of measurement in the trays (side walls or bottom).