Mechanical and thermal properties of waterborne epoxy composites containing cellulose nanocrystals

Direct Ink Write (DIW) 3D Printed Cellulose Nanocrystal Aerogel Structures

Pure cellulose nanocrystal (CNC) aerogels with controlled 3D structures and inner pore architecture are printed using the direct ink write (DIW) technique. While traditional cellulosic aerogel processing approaches lack the ability to easily fabricate complete aerogel structures, DIW 3D printing followed by freeze drying can overcome this shortcoming and can produce CNC aerogels with minimal structural shrinkage or damage. The resultant products have great potential in applications such as tissue scaffold templates, drug delivery, packaging, etc., due to their inherent sustainability, biocompatibility, and biodegradability. Various 3D structures are successfully printed without support material, and the print quality can be improved with increasing CNC concentration and printing resolution. Dual pore CNC aerogel scaffolds are also successfully printed, where the customizable 3D structure and inner pore architecture can potentially enable advance CNC scaffold designs suited for specific cell integration requirements.

Influence of particle size of isotactic polypropylene (iPP) on barrier property against agglomeration of homogenized microcrystalline cellulose (HMCC) in iPP/HMCC composites

Isotactic polypropylene (iPP) powders were treated by a colloid mill for different times to obtain a series of particle sizes ranging from 682 μm to 89 μm. The relative crystallinity degree index (Xc, %) calculated by X-ray diffraction, and the initial degradation temperature measured by thermogravimetry, were all reduced after the milling process, which revealed that the structure of iPP molecular chains was destroyed during the powerful shearing and friction action. Furthermore, the increasing melt flow rate (MFR) index indicated that the molecular weight of iPP had reduced during the mechanical treatment. Scanning electron micrographs showed the inevitable agglomeration of homogenized microcrystalline cellulose (HMCC) fibers after being dried directly without iPP powders. However, the addition of achieved superfine iPP powders presented a good barrier property against the agglomeration phenomenon and consequent improvement in mechanical performance of the iPP/HMCC composites.

Mechanical, morphological and structural properties of cellulose nanofibers reinforced epoxy composites

Present study, deals about isolation and characterization of cellulose nanofibers (CNFs) from the Northern Bleached Softwood Kraft (NBSK) pulp, fabrication by hand lay-up technique and characterization of fabricated epoxy nanocomposites at different filler loadings (0.5%, 0.75%, 1% by wt.). The effect of CNFs loading on mechanical (tensile, impact and flexural), morphological (scanning electron microscope and transmission electron microscope) and structural (XRD and FTIR) properties of epoxy composites were investigated. FTIR analysis confirms the introduction of CNFs into the epoxy matrix while no considerable change in the crystallinity and diffraction peaks of epoxy composites were observed by the XRD patterns. Additions of CNFs considerably enhance the mechanical properties of epoxy composites but a remarkable improvement is observed for 0.75% CNFs as compared to the rest epoxy nanocomposites. In addition, the electron micrographs revealed the perfect distribution and dispersion of CNFs in the epoxy matrix for the 0.75% CNFs/epoxy nanocomposites, while the existence of voids and agglomerations were observed beyond 0.75% CNFs filler loadings. Overall results analysis clearly revealed that the 0.75% CNFs filler loading is best and effective with respect to rest to enhance the mechanical and structural properties of the epoxy composites.

Simultaneously Tailoring Surface Energies and Thermal Stabilities of Cellulose Nanocrystals Using Ion Exchange: Effects on Polymer Composite Properties for Transportation, Infrastructure, and Renewable Energy Applications

Cellulose nanocrystals (CNCs) have great potential as sustainable reinforcing materials for polymers, but there are a number of obstacles to commercialization that must first be overcome. High levels of water absorption, low thermal stabilities, poor miscibility with nonpolar polymers, and irreversible aggregation of the dried CNCs are among the greatest challenges to producing cellulose nanocrystal-polymer nanocomposites. A simple, scalable technique to modify sulfated cellulose nanocrystals (Na-CNCs) has been developed to address all of these issues. By using an ion exchange process to replace Na⁺ with imidazolium or phosphonium cations, the surface energy is altered, the thermal stability is increased, and the miscibility of dried CNCs with a nonpolar polymer (epoxy and polystyrene) is enhanced. Characterization of the resulting ion exchanged CNCs (IE-CNCs) using potentiometry, inverse gas chromatography, dynamic vapor sorption, and laser scanning confocal microscopy reveals that the IE-CNCs have lower surface energies, adsorb less water, and have thermal stabilities of up to 100 °C higher than those of prepared protonated cellulose nanocrystals (H-CNCs) and 40 °C higher than that of neutralized Na-CNC. Methyl(triphenyl)phosphonium exchanged cellulose nanocrystals (MePh₃P-CNC) adsorbed 30% less water than Na-CNC, retained less water during desorption, and were used to prepare well-dispersed epoxy composites without the aid of a solvent and well-dispersed polystyrene nanocomposites using a melt blending technique at 195 °C. Predictions of dispersion quality and glass transition temperatures from molecular modeling experiments match experimental observations. These fiber-reinforced polymers can be used as lightweight composites in transportation, infrastructure, and renewable energy applications.

Epoxy Monomers Cured by High Cellulosic Nanocrystal Loading

The present study focuses on the use of cellulose nanocrystals (CNC) as the main constituent of a nanocomposite material and takes advantage of hydroxyl groups, characteristic of the CNC chemical structure, to thermally cross-link an epoxy resin. An original and simple approach is proposed, based on the collective sticking of CNC building blocks with the help of a DGEBA/TGPAP-based epoxy resin. Scientific findings suggest that hydroxyl groups act as a toxic-free cross-linking agent of the resin. The enhanced protection against water degradation as compared to neat CNC film and the improvement of mechanical properties of the synthesized films are attributed to a good compatibility between the CNC and the resin. Moreover, the preservation of CNC optical properties at high concentrations opens the way to applying these materials in photonic devices.

Site-Selective Modification of Cellulose Nanocrystals with Isophorone Diisocyanate and Formation of Polyurethane-CNC Composites

The unequal reactivity of the two isocyanate groups in an isophorone diisocyante (IPDI) monomer was exploited to yield modified cellulose nanocrystals (CNCs) with both urethane and isocyanate functionality. The chemical functionality of the modified CNCs was verified with ATR-FTIR analysis and elemental analysis. The selectivity for the secondary isocyanate group using dibutyl tin dilaurate (DBTDL) as the reaction catalyst was confirmed with (13)C NMR. The modified CNCs showed improvements in the onset of thermal degradation by 35 °C compared to the unmodified CNCs. Polyurethane composites based on IPDI and a trifunctional polyether alcohol were synthesized using unmodified (um-CNC) and modified CNCs (m-CNC). The degree of nanoparticle dispersion was qualitatively assessed with polarized optical microscopy. It was found that the modification step facilitated superior nanoparticle dispersion compared to the um-CNCs, which resulted in increases in the tensile strength and work of fracture of over 200% compared to the neat matrix without degradation of elongation at break.

Composites of graphene oxide and epoxy resin assuming a uniform 3D graphene oxide network structure

The curing reactions and formation mechanism of 3D GO network.

Thermally flexible epoxy/cellulose blends mediated by an ionic liquid

Blends between the widely used thermoset resin, epoxy, and the most abundant organic material, natural cellulose are demonstrated for the first time.