13 research outputs found
Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams
Polymeric
foams used in furniture and automotive and aircraft seating applications
rely on the incorporation of environmentally hazardous fire-retardant
additives to meet fire safety norms. This has occasioned significant
interest in novel approaches to the elimination of fire-retardant
additives. Foams based on polymer nanocomposites or based on fire-retardant
coatings show compromised mechanical performance and require additional
processing steps. Here, we demonstrate a one-step preparation of a
fire-retardant ice-templated inorganic/polymer hybrid that does not
incorporate fire-retardant additives. The hybrid foams exhibit excellent
mechanical properties. They are elastic to large compressional strain,
despite the high inorganic content. They also exhibit tunable mechanical
recovery, including viscoelastic âmemoryâ. These hybrid
foams are prepared using ice-templating that relies on a green solvent,
water, as a porogen. Because these foams are predominantly comprised
of inorganic components, they exhibit exceptional fire retardance
in torch burn tests and are self-extinguishing. After being subjected
to a flame, the foam retains its porous structure and does not drip
or collapse. In micro-combustion calorimetry, the hybrid foams show
a peak heat release rate that is only 25% that of a commercial fire-retardant
polyurethanes. Finally, we demonstrate that we can use ice-templating
to prepare hybrid foams with different inorganic colloids, including
cheap commercial materials. We also demonstrate that ice-templating
is amenable to scale up, without loss of mechanical performance or
fire-retardant properties
Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams
Polymeric
foams used in furniture and automotive and aircraft seating applications
rely on the incorporation of environmentally hazardous fire-retardant
additives to meet fire safety norms. This has occasioned significant
interest in novel approaches to the elimination of fire-retardant
additives. Foams based on polymer nanocomposites or based on fire-retardant
coatings show compromised mechanical performance and require additional
processing steps. Here, we demonstrate a one-step preparation of a
fire-retardant ice-templated inorganic/polymer hybrid that does not
incorporate fire-retardant additives. The hybrid foams exhibit excellent
mechanical properties. They are elastic to large compressional strain,
despite the high inorganic content. They also exhibit tunable mechanical
recovery, including viscoelastic âmemoryâ. These hybrid
foams are prepared using ice-templating that relies on a green solvent,
water, as a porogen. Because these foams are predominantly comprised
of inorganic components, they exhibit exceptional fire retardance
in torch burn tests and are self-extinguishing. After being subjected
to a flame, the foam retains its porous structure and does not drip
or collapse. In micro-combustion calorimetry, the hybrid foams show
a peak heat release rate that is only 25% that of a commercial fire-retardant
polyurethanes. Finally, we demonstrate that we can use ice-templating
to prepare hybrid foams with different inorganic colloids, including
cheap commercial materials. We also demonstrate that ice-templating
is amenable to scale up, without loss of mechanical performance or
fire-retardant properties
Mechanically Stable Thermally Crosslinked Poly(acrylic acid)/Reduced Graphene Oxide Aerogels
Graphene oxide (GO) aerogels, high
porosity (>99%) low density
(âź3â10 mg cm<sup>â3</sup>) porous materials with
GO pore walls, are particularly attractive due to their lightweight,
high surface area, and potential use in environmental remediation,
superhydrophobic and superoleophilic materials, energy storage, etc.
However, pure GO aerogels are generally weak and delicate which complicates
their handling and potentially limits their commercial implementation.
The focus of this work was to synthesize highly elastic, mechanically
stable aerogels that are robust and easy to handle without substantially
sacrificing their high porosity or low density. To overcome this challenge,
a small amount of readily available and thermally cross-linkable polyÂ(acrylic
acid) (PAA) was intermixed with GO to enhance the mechanical integrity
of the aerogel without disrupting other desirable characteristic properties.
This method is a simple straightforward procedure that does not include
multistep or complicated chemical reactions, and it produces aerogels
with mass densities of about 4â6 mg cm<sup>â3</sup> and
>99.6% porosity that can reversibly support up to 10âŻ000
times
their weight with full recovery of their original volume. Finally,
pressure sensing capabilities were demonstrated and their oil absorption
capacities were measured to be around 120 g oil per g aerogel<sup>â1</sup> which highlights their potential use in practical
applications
Bioinspired Catecholic Copolymers for Antifouling Surface Coatings
We
report here a synthetic approach to prepare polyÂ(methyl methacrylate)-polydopamine
diblock (PMMA-PDA) and triblock (PDA-PMMA-PDA) copolymers combining
mussel-inspired catecholic oxidative chemistry and atom transfer radical
polymerization (ATRP). These copolymers display very good solubility
in a range of organic solvents and also a broad band photo absorbance
that increases with increasing PDA content in the copolymer. Spin-cast
thin films of the copolymer were stable in water and showed a sharp
reduction (by up to 50%) in protein adsorption compared to those of
neat PMMA. Also the peak decomposition temperature of the copolymers
was up to 43°C higher than neat PMMA. The enhanced solvent processability,
thermal stability and low protein adsorption characteristics of this
copolymer makes it attractive for variety of applications including
antifouling coatings on large surfaces such as ship hulls, buoys,
and wave energy converters
Polyhedral Oligomeric Silsesquioxane-Containing Thiolâene Fibers with Tunable Thermal and Mechanical Properties
Polyhedral
oligomeric silsesquioxanes (POSS) are versatile inorganicâorganic
hybrid building blocks that have potential applications as reinforcement
nanofillers, thermal stabilizers, and catalyst supports for metal
nanoparticles. However, fabrication of fibrous materials with high
POSS content has been a challenge because of the aggregation and solubility
limits of POSS units. In this paper, we describe a robust and environmentally
friendly fabrication approach of inorganicâorganic hybrid POSS
fibers by integrating UV initiated thiolâene polymerization
and centrifugal fiber spinning. The use of monomeric liquids in this
approach not only reduces the consumption of heat energy and solvent,
but it also promotes homogeneous mixing of organic and inorganic components
that allows integration of large amount of POSS (up to 80 wt %) into
the polymer network. The POSS containing thiolâene fibers exhibited
enhanced thermomechanical properties compared to purely organic analogs
as revealed by substantial increases in residual weight and a factor
of 4 increase in modulus after thermal treatment at 1000 °C.
This simple fabrication approach combined with the tunability in fiber
properties afforded by tailoring monomer composition make POSS containing
thiolâene fibers attractive candidates for catalyst supports
and filtration media, particularly in high-temperature and harsh environments
ThiolâEne Chemistry: A Greener Approach to Making Chemically and Thermally Stable Fibers
Fibers of micrometer and submicrometer diameters have been of significant interest in recent years owing to their advanced applications in diverse fields such as optoelectronics, regenerative medicine, piezoelectrics, ceramic materials, etc. There are a number of processes to make thin fibers including electrospinning, melt blowing, and recently developed Forcespinning. However, use of solvents or heat to lower viscosity for processing is common to all existing polymer fiber manufacturing methods, and a greener approach to making fibers remains a challenge. Interestingly, nature has engineered spiders and silkworms with a benign way of making mechanically strong and tough fibers through an intricate self-assembly of protein constituents during the fiber formation process. Comprehending the biosynthetic process and precisely replicating it has been a challenging task. However, we find that extruding small functional segments into solid fibrillar structures, through mediation of chemical interactions between the subunits, is a design approach that can be broadly adapted from nature to realize a greener fiber manufacturing process. Using the robust chemistry of thiolâene photopolymerization, we demonstrate here that a photocurable mixture of a multifunctional acrylate, a tetrafunctional thiol, and a photoinitiator can be processed into continuous fibers by <i>in situ</i> photopolymerization during electrospinning under ambient conditions. The fibers are mechanically robust and have excellent chemical and thermal stability. While electrospinning has been used to demonstrate this concept, the chemistry could be broadly adapted into other fiber manufacturing methods to produce fibers without using solvents or heat
Water-Triggered Modulus Changes of Cellulose Nanofiber Nanocomposites with Hydrophobic Polymer Matrices
Biomimetic, stimuli-responsive nanocomposites were made
using either
polyÂ(styrene-<i>co</i>-butadiene) (SBR) or polybutadiene
(PBD) as the hydrophobic, low-modulus matrix and hydrophilic cellulose
whiskers isolated from tunicates (TW) as the high-modulus filler.
These materials were prepared using a template approach, which involves
the formation of a percolating TW network and filling this template
with either of the matrix polymers. Dynamic mechanical analysis (DMA)
studies of the dry nanocomposite films reveal that the incorporation
of TWs into the rubbery polymers increases the tensile storage modulus <i>E</i>Ⲡsignificantly. The reinforcement is attributed
to the formation of a three-dimensional TW network within the SBR
and PBD matrices. The incorporation of the TWs did not affect the
main relaxation temperature of the matrix SBR polymer, suggesting
weak nanofillerâpolymer interactions. Thus, the reinforcement
is primarily on account of the nanofillerânanofiller interactions,
which involve hydrogen bonding. Interestingly, submersion of these
hydrophobic matrix nanocomposites in water results in dramatic softening,
consistent with disengagement of the TW network as a consequence of
competitive hydrogen bonding with water. The kinetics of the modulus
change and the amount of water uptake were shown to depend on the
TW content. Given the hydrophobic nature of the matrices, it is proposed
that the TWs create a percolating network of hydrophilic channels
within the hydrophobic SBR and PBD matrices
Soybean Oil Based Fibers Made Without Solvent or Heat
Thiolâene chemistry was harnessed to enable production
of
thermochemically stable thermoset fibers containing 50â87 wt
% acrylated epoxidized soybean oil and 49â72% biobased carbon
without using solvent or heat. In this demonstration, the fibers were
made by simultaneous electrospinning and photocuring of a liquid monomer
mixture, which could be translated to other fiber manufacturing processes
such as melt blowing or Forcespinning. Scanning electron micrographs
illustrate the fiber quality and an average diameter of about 30 Îźm.
Photochemical conversion kinetics of functional groups during light
exposure were measured by real-time Fourier transform infrared spectroscopy,
providing insight into the advantages of using high-functionality
monomers and thiolâene chemistry in this application
pH-Responsive Cellulose Nanocrystal Gels and Nanocomposites
We show that functionalization of the surface of cellulose
nanocrystals
(CNCs) with either carboxylic acid (CNCâCO<sub>2</sub>H) or
amine (CNCâNH<sub>2</sub>) moieties renders the CNCs pH-responsive.
At low pH, where the amine groups are protonated, CNCâNH<sub>2</sub> forms aqueous dispersions in water on account of electrostatic
repulsions of the ammonium moieties inhibiting aggregation. However,
a transition to hydrogels is observed at higher pH where the CNCâNH<sub>2</sub> are neutral and the attractive forces based on hydrogen bonding
dominate. The opposite behavior is observed for CNCâCO<sub>2</sub>H, which are dispersible at high pH and form gels in an acidic
environment. We further show that these pH-responsive CNCs can be
incorporated into a polyÂ(vinyl acetate) matrix to yield mechanically
adaptive pH-responsive nanocomposite films
Synthesis of Amphiphilic Naturally-Derived Oligosaccharide-<i>block</i>-Wax Oligomers and Their Self-Assembly
Self-assembly
characteristics of amphiphilic macromolecules into
micelles, nanoparticles and vesicles has been of fundamental interest
for many applications including designed nanoscale therapeutic delivery
systems and enzymatic reactors. In this work, a class of amphiphilic
block oligomers was synthesized from naturally occurring oligosaccharides
and aliphatic alcohol precursors, which are all currently prominent
in the pharmaceutical, food, and supplement industries. These block
oligomer materials were synthesized by functionalization of the precursor
materials followed by subsequent coupling by azideâalkyne cycloaddition
and their bulk self-assembly was investigated after solvent vapor
annealing. Self-assembly of the amphiphilic materials into liposomes
in aqueous solution was also investigated after preparing solutions
using a nanoprecipitation method. Encapsulation of hydrophobic components
was demonstrated and verified using dynamic light scattering, transmission
electron microscopy, and fluorescence spectroscopy experiments