2 research outputs found
Analysis of the Porous Architecture and Properties of Anisotropic Nanocellulose Foams: A Novel Approach to Assess the Quality of Cellulose Nanofibrils (CNFs)
Cellulose
nanofibrils (CNFs) are a unique nanomaterial because
of their abundant, renewable, and biocompatible origin. Compared with
synthetic nanoparticles, CNFs are commonly produced from cellulose
fibers (e.g., wood pulp) by repetitive high-shear mechanical disintegration.
Yet, this process is still highly demanding in energy and costly,
slowing down the large-scale production and commercialization of CNFs.
Reducing the energy consumption during fibers fibrillation without
using any chemical or enzymatic pretreatments while sustaining the
CNF quality is challenging. Here, we show that the anisotropic properties
of the CNF foams are directly connected to the degree of nanofibrillation
of the cellulose fibers. CNFs were produced from wood pulps using
a grinder at increasing specific energy consumptions. The anisotropic
CNF foams were made by directional ice templating. The porous architecture,
the compressive behavior of the foams, and the CNF alignment in the
foam cell walls were correlated to the degree of fibrillation. A particular
value of specific energy consumption was identified with respect to
the highest obtained foam properties and CNF alignment. This value
indicated that the optimal degree of fibrillation, and thus CNF quality,
was achieved for the studied cellulose pulp. Our approach is a straightforward
tool to evaluate the CNF quality and a promising method for the benchmarking
of different CNF grades
Shape-Anisotropic Polyimide Particles by Solid-State Polycondensation of Monomer Salt Single Crystals
Shape-anisotropic
particles are of broad interest, e.g., for colloidal
crystals or applications at interfaces such as particle-stabilized
emulsions. Despite the wealth of accessible shapes of inorganic particles,
anisotropic homopolymer particles are to date mostly limited to objects
derived from spheres (e.g., ellipsoidal or disk-shaped particles).
Here, we report the synthesis of shape-anisotropic, angular polyimide
particles by thermal solid-state polycondensation (SSP) of monomer
salts. We prepare monomer salt single crystals of relatively narrow
size and shape distribution by growth inside hydrogels, and solve
their crystal structure. Polyimide particles are obtained by simple
heating and retain the shape of the initial salt crystals. Using high-temperature
X-ray diffraction, thermal analyses and microscopy techniques, we
investigate the mechanism of the transformation. The obtained polyimide
particles are temperature-stable up to 640 Ā°C and virtually insoluble
in any solvent. This work sheds more light on the mechanism of SSP
of monomer salts and reports a new methodology for accessing nonspherical
homopolymer particles, which are due to their outstanding stability
potentially of interest for applications under extreme conditions