This work demonstrates the feasibility of superhydrophilic polyelectrolyte brush coatings for anti-icing applications. Five different types of ionic and nonionic polymer brush coatings of 25-100 nm thickness were formed on glass substrates using silane chemistry for surface premodification followed by polymerization via the SI-ATRP route. The cationic [2-(methacryloyloxy)ethyl]trimethylammonium chloride] and the anionic [poly(3-sulfopropyl methacrylate), poly(sodium methacrylate)] polyelectrolyte brushes were further exchanged with H+, Li+, Na+, K+, Ag+, Ca2+, La3+, C16N+, F-, Cl-, BF4-, SO4(2-), and C12SO3- ions. By consecutive measurements of the strength of ice adhesion toward ion-incorporated polymer brushes on glass it was found that Li+ ions reduce ice adhesion by 40% at -18 °C and 70% at -10 °C. Ag+ ions reduce ice adhesion by 80% at -10 °C relative to unmodified glass. In general, superhydrophilic polyelectrolyte brushes exhibit better anti-icing property at -10 °C compared to partially hydrophobic brushes such as poly(methyl methacrylate) and surfactant exchanged polyelectrolyte brushes. The data are interpreted using the concept of a quasi liquid layer (QLL) that is enhanced in the presence of highly hydrated ions at the interface. It is suggested that the ability of ions to coordinate water is directly related to the efficiency of a given anti-icing coating based on the polyelectrolyte brush concept.
Recent
years have seen an increased interest toward utilizing biobased
and biodegradable materials for barrier packaging applications. Most
of the abovementioned materials usually have certain shortcomings
that discourage their adoption as a preferred material of choice.
Nanocellulose falls into such a category. It has excellent barrier
against grease, mineral oils, and oxygen but poor tolerance against
water vapor, which makes it unsuitable to be used at high humidity.
In addition, nanocellulose suspensions’ high viscosity and
yield stress already at low solid content and poor adhesion to substrates
create additional challenges for high-speed processing. Polylactic
acid (PLA) is another potential candidate that has reasonably high
tolerance against water vapor but rather a poor barrier against oxygen.
The current work explores the possibility of combining both these
materials into thin multilayer coatings onto a paperboard. A custom-built
slot-die was used to coat either microfibrillated cellulose or cellulose
nanocrystals onto a pigment-coated baseboard in a continuous process.
These were subsequently coated with PLA using a pilot-scale extrusion
coater. Low-density polyethylene was used as for reference extrusion
coating. Cationic starch precoating and corona treatment improved
the adhesion at nanocellulose/baseboard and nanocellulose/PLA interfaces,
respectively. The water vapor transmission rate for nanocellulose
+ PLA coatings remained lower than that of the control PLA coating,
even at a high relative humidity of 90% (38 °C). The multilayer
coating had 98% lower oxygen transmission rate compared to just the
PLA-coated baseboard, and the heptane vapor transmission rate reduced
by 99% in comparison to the baseboard. The grease barrier for nanocellulose
+ PLA coatings increased 5-fold compared to nanocellulose alone and
2-fold compared to PLA alone. This approach of processing nanocellulose
and PLA into multiple layers utilizing slot-die and extrusion coating
in tandem has the potential to produce a barrier packaging paper that
is both 100% biobased and biodegradable.
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