6 research outputs found
Rapid Development of Wet Adhesion between Carboxymethylcellulose Modified Cellulose Surfaces Laminated with Polyvinylamine Adhesive
The surface of regenerated cellulose
membranes was modified by irreversible adsorption of carboxymethylcellulose
(CMC). Pairs of wet CMC-modified membranes were laminated with polyvinylamine
(PVAm) at room temperature, and the delamination force for wet membranes
was measured for both dried and never-dried laminates. The wet adhesion
was studied as a function of PVAm molecular weight, amine content,
and deposition pH of the polyelectrolyte. Surprisingly the PVAm–CMC
system gave substantial wet adhesion that exceeded that of TEMPO-oxidized
membranes with PVAm for both dried and never-dried laminates. The
greatest wet adhesion was achieved for fully hydrolyzed high molecular
weight PVAm. Bulk carboxymethylation of cellulose membranes gave inferior
wet adhesion combined with PVAm as compared to CMC adsorption which
indicates that a CMC layer of the order of 10 nm was necessary. There
are no obvious covalent cross-linking reactions between CMC and PVAm
at room temperature, and on the basis of our results, we are instead
attributing the wet adhesion to complex formation between the PVAm
and the irreversibly adsorbed CMC at the cellulose surface. We propose
that interdigitation of PVAm chains into the CMC layer is responsible
for the high wet adhesion values
Direct Adhesive Measurements between Wood Biopolymer Model Surfaces
For the first time the dry adhesion was measured for
an all-wood
biopolymer system using Johnson–Kendall–Roberts (JKR)
contact mechanics. The polydimethylsiloxane hemisphere was successfully
surface-modified with a Cellulose I model surface using layer-by-layer
assembly of nanofibrillated cellulose and polyethyleneimine. Flat
surfaces of cellulose were equally prepared on silicon dioxide substrates,
and model surfaces of glucomannan and lignin were prepared on silicon
dioxide using spin-coating. The measured work of adhesion on loading
and the adhesion hysteresis was found to be very similar between cellulose
and all three wood polymers, suggesting that the interaction between
these biopolymers do not differ greatly. Surface energy calculations
from contact angle measurements indicated similar dispersive surface
energy components for the model surfaces. The dispersive component
was dominating the surface energy for all surfaces. The JKR work of
adhesion was lower than that calculated from contact angle measurements,
which partially can be ascribed to surface roughness of the model
surfaces and overestimation of the surface energies from contact angle
determinations
Hydrazide-Derivatized Microgels Bond to Wet, Oxidized Cellulose Giving Adhesion Without Drying or Curing
Hydrazide-derivatized
poly(<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
Relating Redox Properties of Polyvinylamine‑<i>g</i>‑TEMPO/Laccase Hydrogel Complexes to Cellulose Oxidation
The
structure and electrochemical properties of adsorbed complexes
based on mixtures of polyvinylamine-<i>g</i>-TEMPO (PVAm-T)
and laccase were related to the ability of the adsorbed complexes
to oxidize cellulose. PVAm-T10 with 10% of the amines bearing TEMPO
moieties (i.e., DS = 10%), adsorbed onto gold sulfonate EQCM-D sensor
surfaces giving a hydrogel film that was 7 nm thick, 89% water, and
encasing laccase (200 mM) and TEMPO moieties (33 mM). For DS values
>10%, all of the TEMPOs in the hydrogel film were redox-active
in
that they could be oxidized by the electrode. With hydrogel layers
made with lower-DS PVAm-Ts, only about half of the TEMPOs were redox-active;
10% DS appears to be a percolation threshold for complete TEMPO-to-TEMPO
electron transport. In parallel experiments with hydrogel complexes
adsorbed onto regenerated cellulose films, the aldehyde concentrations
increased monotonically with the density of redox-active TEMPO moieties
in the adsorbed hydrogel. The maximum density of aldehydes was 0.24
μmol/m<sup>2</sup>, about 10 times less than the theoretical
concentration of primary hydroxyl groups exposed on crystalline cellulose
surfaces. Previous work showed that PVAm-T/laccase complexes are effective
adhesives between wet cellulose surfaces when the DS is >10%. This
work supports the explanation that TEMPO-to-TEMPO electron transport
is required for the generation of aldehydes necessary for wet adhesion
to PVAm
Robust and Tailored Wet Adhesion in Biopolymer Thin Films
Model layer-by-layer (LbL) assemblies
of poly(allylamine hydrochloride)
(PAH) and hyaluronic acid (HA) were fabricated in order to study their
wet adhesive behavior. The film characteristics were investigated
to understand the inherent structures during the assembly process.
Subsequently, the adhesion of these systems was evaluated to understand
the correlation between the structure of the film and the energy required
to separate these LbL assemblies. We describe how the conditions of
the LbL fabrication can be utilized to control the adhesion between
films. The characteristics of the film formation are examined in the
absence and presence of salt during the film formation. The dependence
on contact time and LbL film thickness on the critical pull-off force
and work of adhesion are discussed. Specifically, by introducing sodium
chloride (NaCl) in the assembly process, the pull-off forces can be
increased by a factor of 10 and the work of adhesion by 2 orders of
magnitude. Adjusting both the contact time and the film thickness
enables control of the adhesive properties within these limits. Based
on these results, we discuss how the fabrication procedure can create
tailored adhesive interfaces with properties surpassing analogous
systems found in nature
Redox Properties of Polyvinylamine‑<i>g</i>‑TEMPO in Multilayer Films with Sodium Poly(styrenesulfonate)
Layer-by-layer (LbL) assemblies of
polyvinylamine with grafted
TEMPO moieties (PVAm-T) with sodium polystyrenesulfonate (PSS) were
prepared on gold-sulfonate surfaces, and the redox properties were
measured by cyclic voltammetry. LbL compositions were probed by quartz
crystal microbalance (wet) and ellipsometric (dry) film measurements.
Approximately 30% of the TEMPO moieties in the LbL assemblies were
redox-active when the total TEMPO coverage was varied up to 6 μmol/m<sup>2</sup>, by either varying the TEMPO content in PVAm-T or by varying
the number of LbL bilayers. Three non-redox-active PVAm/PSS blocking
bilayers were required to prevent the electrode from oxidizing PVAm-T
in the exterior LbL layer. This suggests significant intermixing between
the layers in the LbL film. In addition to contributing to the small
but growing body of work on redox polymers based on grafted TEMPO,
this work serves as a reference point for understanding the redox
properties of colloidal PVAm-T-laccase complexes in future work