How Different Carryover Pitch Extractive Components are Affecting Kraft Paper Strength

Area of Science:

• Pulp and Paper Science
• Wood Chemistry
• Material Science

Background:

• Unbleached softwood Kraft pulp contains wood extractives that can negatively impact paper properties.
• Carryover pitch extractives (CPEs) are a known issue in papermaking, affecting product quality.
• Understanding the specific impact of different extractive compounds is crucial for process optimization.

Purpose of the Study:

• To investigate the detrimental effects of various wood extractives in CPEs on the strength of packaging papers and boards.
• To identify the most harmful extractive compounds and their mechanisms of action.
• To evaluate the efficacy of cationic starch in mitigating these negative effects.

Main Methods:

• Simulated industrial papermaking conditions using laboratory-scale handsheet production.
• Analysis of CPE composition and its correlation with paper strength properties.
• Comparative testing of handsheets with varying extractive content and addition of cationic starch.

Main Results:

• Fatty acids were identified as the most abundant and detrimental CPE compounds, significantly reducing fiber-fiber bonding strength.
• Oleic acid (an unsaturated fatty acid) was particularly harmful, even impairing cationic starch performance.
• Cationic starch addition generally improved paper strength but struggled with highly unsaturated fatty acids.

Conclusions:

• Fatty acids, especially unsaturated ones, are the primary contributors to reduced paper strength and cationic starch inefficiency in unbleached softwood Kraft paper.
• Current practices of precipitating CPEs onto pulp fibers for water treatment can be detrimental to final paper strength.
• Targeted removal or management of specific fatty acids could improve paper quality and process efficiency.