Molecular design and characterization of adaptive polymers derived from biomass

shifted with 100 °C to higher temperatures. This immense increase was attributed to the
antioxidant activity of the remaining phenolic OH groups onto F-KLEMK (11%) as confirmed by
the DPPH assay. In turn, additional lignin structure-property-related experiments were
performed to study the hydrophobicity, flame-retardancy, UV stability, and the ability to resist
microbial attacks and static energy. This led ultimately to the understanding that lignin brings
structure-related stability into the network formulations which is extremely beneficial in
application purposes.
However, the 3-component network formulation was not stable against prolonged heating or
multiple heating cycles due to the incompatibility between lignin and F5000, limiting their usage
for adhesive formulations. Therefore, a 2-component formulation was designed where F-KLEMK
was reacted with two different amorphous bismaleimides; a polyether-based bismaleimide
(PPO-6) and a vegetable oil-based bismaleimide (BMI-689). Here, the maleimide-furan ratio was
adapted to allow increasing lignin concentrations into the network formulations. Similarly to
the 3-component system, the mechanical properties in both PPO-6-based (L-PPO) and BMI-689-
based (L-BMI) networks increased significantly with increasing lignin content. Formulation
L-BMI-0.8 (containing a maleimide to furan ratio of 0.8), displayed the highest toughness
(2.1 MJ.m-3) and a desirable Young’s modulus (420 MPa), making it a prime candidate for
adhesive evaluation. Consequently, L-BMI-0.8 was comprehensively studied regarding its
thermal stability upon multiple heat-cool cycles, viscosity, stress relaxation and creep behaviour,
substantiating its potential for reversible adhesive applications.
As a result, L-BMI-0.8 was used as an adhesive on two different surfaces (wood and metal) and
showed strong adhesive properties at room temperature which could rapidly and repeatedly
switch on-demand into a non-adhesive liquid state upon heating. Shear stresses of 2.8 MPa and
5.5 MPa were achieved for wood-wood adhesion (substrate failure) and metal-metal adhesion
(adhesion failure) respectively. After two repeating un/reglue cycles, the mechanical properties
of the adhesives were completely restored. In addition, the material maintained its strong
adhesive properties after submersion in water for 24 h, clearly showing the stability of the glue.
These promising outcomes underscored L-BMI-0.8's potential as a biobased reversible adhesive,
supported by some proof-of-concept examples.
In contrast to the elaborated DA study, only a preliminary study regarding lignin-incorporated
ureidopyrimidinone (UPy)-based supramolecular network blends was performed to study the
influence of lignin on the properties of the final materials. Adapting the concentration of UPy
allowed us to tune the crystallinity of the supramolecular networks. Subsequently, when lignin
was added as a filler, the properties of the network blends were further influenced, especially
when low UPy concentrations were added. This study clearly contributes to a better
understanding of the influence of lignin on the supramolecular network properties.
In this thesis, we show the potential of lignin to be used as a valuable building block in the design
of reversible polymers and subsequently their application strategies. In this way, we contribute
towards the design of sustainable materials, a concept which is becoming extremely important
in our current society.