Lignin-Containing Coatings for Packaging Materials-Pilot Trials.

Area of Science:

• Materials Science
• Polymer Chemistry
• Sustainable Packaging

Background:

• Biopolymers used in packaging often suffer from high water solubility, limiting their application.
• Kraft lignin addition to starch coatings can decrease starch's water solubility.
• Lignin migration into aqueous solutions remains a concern for lignin-containing coatings.

Purpose of the Study:

• To investigate the effect of pH on the solubility of LignoBoost kraft lignin.
• To evaluate the impact of ammonium zirconium carbonate (AZC) on lignin solubility and coating properties.
• To assess the water stability and defect formation in starch-lignin coated paper at varying pH levels.

Main Methods:

• Kraft lignin isolated via the LignoBoost process was used.
• Machine-glazed (MG) paper was coated using a pilot coating machine; lab samples served as reference.
• Solubility, migration, water vapor transmission rate (WVTR), water contact angle, and pinhole defects were measured.

Main Results:

• Kraft lignin solubility in water decreased at lower pH levels when starch was present, due to starch-lignin interactions.
• Reduced pH of coating solutions increased water stability, decreasing lignin migration.
• AZC addition reduced lignin migration and increased water contact angle but also increased pinholes in pilot-coated samples.

Conclusions:

• Lowering the pH of starch-lignin coating solutions enhances water stability by reducing lignin migration.
• AZC can improve water resistance but may negatively impact coating integrity (pinholes).
• Optimizing pH and considering additives like AZC are crucial for developing water-resistant biopolymer packaging.