Effects of dry forming parameters on density, tensile properties, and their relationship in air-laid paper

Abstract Cellulose-based materials are increasingly used as sustainable alternatives to conventional packaging materials. Among emerging technologies, dry forming of air-laid fiber networks offers improved formability compared to conventional paperboard forming processes and reduced energy consumption compared to wet molding. However, the effect of process conditions on densification, mechanical property development, and their interrelationship remains relatively unexplored, particularly under industrially relevant combinations of temperature, pressure, and moisture content. Here we investigate how temperature, moisture content, pressure, and holding time, both individually and in combination, affect the density, tensile modulus, and tensile strength of dry-formed air-laid paper. A three-level factorial split-plot design combined with linear mixed-effects modeling was used to systematically evaluate parameter effects. Temperature was identified as the dominant parameter, strongly influencing both densification and tensile properties. While density exhibited saturation behavior, tensile properties continued to increase with temperature, indicating ongoing bond development. Moisture content enhanced consolidation but introduced steam-related effects at high temperature-moisture combinations. Importantly, identical density levels were associated with different mechanical properties depending on process conditions. These findings improve understanding of densification and process-property relationships in dry forming while highlighting limitations of density-based descriptions of material behavior.