Although lignin is
currently an under-utilized biopolymer, it has
the potential to be valorized through different modification pathways
to yield alternative products to petroleum-based ones. In this work,
hydrolysis lignin (HL) was copolymerized with acrylamide (AM) and
acrylic acid (AA) under acidic conditions to generate the lignin/AM
polymer (HM), lignin/AA polymer (HA), and lignin/AM/AA copolymer (HAM)
with different negative charge densities and molecular weights. Lignin-based
polymers characterized by advanced tools, such as proton nuclear magnetic
resonance (1H NMR), gel permission chromatography (GPC),
and elemental analysis confirmed the successful polymerization of
HL with AM, AA, or AM/AA monomers. The adsorption analysis using a
quartz crystal microbalance (QCM) revealed that compared to diblock
HM and HA, the triblock copolymers of HAM adsorbed more on the Al2O3 surface and generated a bulkier adsorbed layer,
which is important for lignin-based coating formulation. HAM1 with
a lower charge density yielded a higher surface excess density, while
HAM2 with a larger R
h occupied more space
(153.7 Å2) at the interface of water and Al2O3. In suspension systems, because of the higher M
w, R
h, and adsorption
affinity, the bridging performance of HAM2 was more remarkable than
that of the other lignin derivatives for Al2O3 particles via forming stronger flocs (with a deflocculation parameter, T
df, of 80.6 s). However, the diblock lignin–AA
(HA1) polymer showed the fastest floc regrowth capability after reducing
the shear forces (with a reflocculation parameter, T
rf, of 62.5 s). The high thermal stability, T
g, and rheological characteristics of the HAM copolymer
proved that it can be an excellent material for coating formulations
and flocculants for wastewater treatment systems.