Property Variations of Binder-Free Lignin-Rich Fiber Networks Driven by Forming Processes and Hot Pressing

Area of Science:

• Materials Science
• Wood Chemistry
• Fiber Engineering

Background:

• Lignin-rich fibers can form self-bonding sheets via hot pressing, eliminating the need for external binders.
• Understanding the influence of web formation methods on the properties of these novel materials is crucial for their application.

Purpose of the Study:

• To investigate the impact of air-laid, foam-laid, and water-laid web formation methods on the physical properties of hot-pressed lignin-based fiber sheets.
• To analyze the effects of initial moisture content and hot-pressing parameters on sheet characteristics.
• To correlate structural features with mechanical and physical properties.

Main Methods:

• Chemi-thermomechanical softwood fibers were used to create sheets via three web formation methods.
• Sheets were hot-pressed under varying conditions (5 MPa, 100-260 °C, 1-60 s).
• Structural characterization (X-ray microtomography) and property measurements (air permeance, water contact angle, tensile strength, in-plane compression) were performed.

Main Results:

• Web formation characteristics persisted after hot pressing, influencing final sheet properties.
• Air-laid sheets exhibited high air permeance and small mean pore size, suitable for particle filtration.
• Foam-laid sheets were weaker than water-laid sheets at moderate pressing but achieved similar high strengths under extreme conditions due to polymer interdiffusion.

Conclusions:

• The choice of web formation method significantly impacts the properties of hot-pressed lignin-based fiber sheets.
• Air-laid sheets are promising for filtration applications.
• Under severe hot-pressing, polymer interdiffusion becomes a key factor in achieving high mechanical strength, overriding initial forming effects.