Lignin as promising building blocks for pressure-sensitive adhesives

A new peer-reviewed study has explored how lignins produced with CH-Bioforce’s Bioforsense® technology can be transformed into soft, functional materials for pressure-sensitive adhesives (PSA). These adhesives are widely used in everyday products such as sticky notes, labels, tapes and the well-known Blu Tack® .
The research investigated lignins from birch, spruce and wheat straw, all produced with the CH-Bioforce process, and evaluated how they perform when grafted with poly(n-butyl acrylate) (PnBA). The work highlights how bio-based lignin can replace fossil-based polymers in entirely new adhesive applications.

MODIFIED LIGNINS SUCCESSFULLY GRAFTED WITH POLYACRYLATE
The researchers first prepared lignin-based macroinitiators and then grafted them with PnBA using ATRP polymerisation. The study confirmed:
– successful lignin–polyacrylate grafting, verified through FTIR, NMR and SEC/GPC.
– Clear differences between hardwood, softwood and straw lignins in macroinitiator formation and polymerisation efficiency.
– Birch and spruce lignins showed the most effective copolymerisation behaviour, while wheat straw lignin displayed lower reactivity due to structural complexity.
Gel permeation chromatography further demonstrated clear molecular-weight shifts, distinguishing true copolymers from simple blends.

THERMAL AND RHEOLOGICAL PROPERTIES SUPPORT ADHESIVE PERFORMANCE
The resulting lignin-g-PnBA copolymers displayed:
– increased glass-transition temperatures compared to pure polyacrylate.
– Structural differences between lignin sources reflected in their thermal decomposition profiles.
– Strong viscoelastic behaviour, with birch-based copolymers showing particularly good performance in rheology tests.
– Compliance with the Dahlquist criterion, the established requirement for pressure-sensitive adhesives (low modulus under deformation).
Notably, birch-lignin-based materials (BLNBA2 and BLNBA4) showed adhesive behaviour comparable to commercial Blu Tack® , confirming excellent tack and softness in real-world use.

LIGNIN AS A RENEWABLE ROUTE TO SOFT, FUNCTIONAL ADHESIVE MATERIALS
This study provides strong evidence that CH-Bioforce lignins can be converted into soft, elastic materials suitable for PSA applications. Unlike conventional petroleum-based polymers, lignin offers: Rapid renewability, a high-value outlet for side streams, the potential to reduce fossil-based content in consumer products and a compatibility with circular economy principles. By demonstrating high-performing, lignin-based PSA materials, the research opens the door to sustainable alternatives for everyday adhesive products.

ACKNOWLEDGMENT
Doctoral thesis (Åbo Akademi University), Bhadane, Rupali: “Structure and Properties of Lignin from Biomass Waste and Engineering of Sustainable Acrylic Adhesives”, https://urn.fi/URN:ISBN:978-952-12-4720-0.