3 research outputs found
Grafting of Bacterial Polyhydroxybutyrate (PHB) onto Cellulose via In Situ Reactive Extrusion with Dicumyl Peroxide
Polyhydroxybutyrate (PHB) was grafted
onto cellulose fiber by dicumyl
peroxide (DCP) radical initiation via in situ reactive extrusion.
The yield of the grafted (cellulose-<i>g</i>-PHB) copolymer
was recorded and grafting efficiency was found to be dependent on
the reaction time and DCP concentration. The grafting mechanism was
investigated by electron spin resonance (ESR) analysis and showed
the presence of radicals produced by DCP radical initiation. The grafted
copolymer structure was determined by nuclear magnetic resonance (NMR)
spectroscopy. Scanning electronic microscopy (SEM) showed that the
cellulose-<i>g</i>-PHB copolymer formed a continuous phase
between the surfaces of cellulose and PHB as compared to cellulose-PHB
blends. The relative crystallinity of cellulose and PHB were quantified
from Fourier transform infrared (FTIR) spectra and X-ray diffraction
(XRD) results, while the absolute degree of crystallinity was evaluated
by differential scanning calorimetry (DSC). The reduction of crystallinity
indicated the grafting reaction occurred not just in the amorphous
region but also slightly in crystalline regions of both cellulose
and PHB. The smaller crystal sizes suggested the brittleness of PHB
was decreased. Thermogravimetric analysis (TGA) showed that the grafted
copolymer was stabilized relative to PHB. By varying the reaction
parameters the compositions (%PHB and %cellulose) of resultant cellulose-<i>g</i>-PHB copolymer are expected to be manipulated to obtain
tunable properties
Lignin-Containing Cellulose Nanofibril-Reinforced Polyvinyl Alcohol Hydrogels
Two lignin-containing cellulose nanofibril
(LCNF) samples, produced
from two unbleached kraft pulps with very different lignin contents,
were used to produce reinforced polyvinyl alcohol (PVA) hydrogels.
The effects of LCNF loading (0.25–2 wt %) and lignin content
on the rheological and mechanical properties of the reinforced hydrogels
were investigated. The 2 wt % LCNF-reinforced PVA hydrogels exhibited
up to a 17-fold increase in storage modulus and a 4-fold increase
in specific Young’s modulus over that of pure PVA hydrogel.
Both the mechanical and rheological properties of LCNF-reinforced
PVA hydrogels can be tuned by varying LCNF loading and LCNF lignin
content. During LCNF production, lignin reduced cellulose depolymerization,
resulting in LCNF with high aspect ratios that promoted entanglement
and physical bridging of the hydrogel network. Free lignin particles
generated during LCNF production acted as multifunctional nanospacers
that increased porosity of the hydrogels. Because LCNFs were produced
from unbleached chemical pulps, which have high yields and do not
require bleaching, this study provides a more sustainable approach
to utilize lignocelluloses to produce biomass-based hydrogels than
by methods using commercial bleached pulps
Controlled Shape Memory Behavior of a Smectic Main-Chain Liquid Crystalline Elastomer
A smectic
main-chain liquid crystalline elastomer (LCE), with controlled
shape memory behavior, is synthesized by polymerizing a biphenyl-based
epoxy monomer with an aliphatic carboxylic acid curing agent. Microstructures
of the LCEs, including their liquid crystallinity and cross-linking
density, are modified by adjusting the stoichiometric ratio of the
reactants to tailor the thermomechanical properties and shape memory
behavior of the material. Thermal and liquid crystalline properties
of the LCEs, characterized using differential scanning calorimetry
and dynamic mechanical analysis, and structural analysis, performed
using small-angle and wide-angle X-ray scattering, show that liquid
crystallinity, cross-linking density, and network rigidity are strongly
affected by the stoichiometry of the curing reaction. With appropriate
structural modifications it is possible to tune the thermal, dynamic
mechanical, and thermomechanical properties as well as the shape memory
and thermal degradation behavior of LCEs