Four
inorganic chlorides were introduced into hydrochloric acid hydrolysis
to extract cellulose nanocrystals (CNCs) from microcrystalline celluloses
(MCC) under hydrothermal conditions. The as-prepared CNCs were investigated
by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier
transform infrared (FT–IR), and thermogravimetric analysis
(TGA). The role of inorganic chlorides including ferric chloride hexahydrate
(FeCl3·6H2O), copper chloride dihydrate
(CuCl2·2H2O), aluminum chloride (AlCl3), and manganese chloride tetrahydrate (MnCl2·4H2O) in the extraction and properties of high quality CNCs was
determined. It is observed that the introduction of inorganic chlorides
obviously enhanced the hydrolysis process through faster degradation
of the disordered region of cellulose. Compared with those for pure
hydrochloric acid hydrolysis, smaller diameter and a larger length
to diameter ratio of CNCs could be obtained through salt-catalyzed
hydrolysis, which could contribute to greater enhancement on the mechanical
properties of polylactic acid (PLA) nanocomposite films. Moreover,
it is found that the highest reinforcing effects for the PLA matrix
as well as the best transparency among all the nanocomposites were
achieved in the presence of ferric chlorides, benifiting from the
largest length to diameter ratio and most white of the corresponding
CNCs. These results show that the use of salt-catalyzed hydrolysis
especially ferric chloride has a significant improvement in achieving
the energy-efficient and cost-effective conversion of cellulose starting
materials into high quality CNCs.
To achieve a better balance between the refractive index and Abbe number, the thiol-functionalized polyhedral oligomeric silsesquioxane (POSS−SH) was incorporated as both nanoreinforcement and cross-linking reagent into high-refractive index polythiourethane (PTU). The influences of the POSS−SH on the microstructures and properties of PTU were investigated. It is found that all the nanocomposites exhibited a dense network structure and high structural homogeneity even at the POSS−SH loading up to 10 wt %. Besides great improvements in the thermal stability and mechanical property, the nanocomposite containing 1.5 wt % POSS− SH revealed a slight reduction in the refractive index from 1.6568 for neat PTU to 1.6557 but a significant increase in the Abbe number from 28 to 35, accompanied by excellent optical transparency. These results indicate that the covalent incorporation of bifunctional POSS− SH into the PTU network will be helpful for the rational design of advanced optical and optoelectronic materials.
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