2 research outputs found
Hydrazide-Derivatized Microgels Bond to Wet, Oxidized Cellulose Giving Adhesion Without Drying or Curing
Hydrazide-derivatized
polyÂ(<i>N</i>-isopropylacrylamide-<i>co</i>-acrylic
acid) microgels gave strong adhesion to wet, TEMPO oxidized, regenerated
cellulose membranes without a drying or heating step. Adhesion was
attributed to hydrazone covalent bond formation with aldehyde groups
present on the cellulose surfaces. This is one of only three chemistries
we have found that gives significant never-dried adhesion between
wet cellulose surfaces. By contrast, for cellulose joints that have
been dried and heated before wet testing, the hydrazide-hydrazone
chemistry offers no advantages over standard paper industry wet strength
resins. The design rules for the hydrazide-microgel adhesives include:
cationic microgels are superior to anionic gels; the lower the microgel
cross-link density, the higher the adhesion; longer PEG-based hydrazide
tethers offer no advantage over shorter attachments; and, adhesion
is independent of microgel diameter. Many of these rules were in agreement
with predictions of a simple adhesion model where the microgels were
assumed to be ideal springs. We propose that the unexpected, high
cohesion between neighboring microgels in multilayer films was a result
of bond formation between hydrazide groups and residual NHS-carboxyl
esters from the preparation of the hydrazide microgels
Comparing Soft Semicrystalline Polymer Nanocomposites Reinforced with Cellulose Nanocrystals and Fumed Silica
This
work compares solvent-cast polyÂ(ethylene oxide) (PEO) nanocomposites
reinforced with cellulose nanocrystals (CNCs) and fumed silica. Mechanical
properties and crystallization behavior were investigated over a range
of polymer molecular weights (10 000–100 000
g/mol) and particle loadings (1–10 wt %). Polymer adsorption
to CNCs and fumed silica was found to alter PEO undercooling and inhibit
crystal nucleation. Atomic force microscopy revealed PEO adsorbs to
CNCs in a shish-kebab morphology that is readily incorporated into
the crystalline domains of the polymer. Tensile testing and nanoindentation
showed that Young’s modulus increased by more than 60% for
CNC reinforced nanocomposites, and that the Halpin–Kardos model
could effectively describe the mechanical properties. Fumed silica
reinforced nanocomposites were fit to the Guth–Gold micromechanical
model using effective particle volume fractions. Although only solvent-cast
nanocomposites were investigated, this work provides new insight into
the interactions that control dispersion, crystallization, and mechanical
reinforcement