Melt Processing of Cellulose Nanocrystal-Filled Composites: Toward Reinforcement and Foam Nucleation

Synthesis of carboxylated cellulose nanocrystal/ZnO nanohybrids using Oxytenanthera abyssinica cellulose and zinc nitrate hexahydrate for radical scavenging, photocatalytic, and antibacterial activities

The extremely low antioxidant, photocatalytic, and antibacterial properties of cellulose limit its application in the biomedical and environmental sectors. To improve these properties, nanohybrides were prepared by mixing carboxylated cellulose nanocrystals (CCNCs) and zinc nitrate hexahydrate. Data from FTIR, XRD, DLS, and SEM spectra showed that, ZnO nanoparticles, with a size ranging from 94 to 351 nm and the smallest nanoparticle size of 164.18 nm, were loaded onto CCNCs. CCNCs/ZnO1 nanohybrids demonstrated superior antibacterial, photocatalytic, and antioxidant performance. More considerable antibacterial activity was shown with a zone of inhibition ranging from 26.00 ± 1.00 to 40.33 ± 2.08 mm and from 31.66 ± 3.51 to 41.33 ± 1.15 mm against Gram-positive and Gram-negative bacteria, respectively. Regarding photodegradation properties, the maximum value (∼91.52 %) of photocatalytic methylene blue degradation was observed after 75 min exposure to a UV lamp. At a concentration of 125.00 μm/ml of the CCNC/ZnO1 nanohybrids sample, 53.15 ± 1.03 % DPPH scavenging activity was obtained with an IC50 value of 117.66 μm/ml. A facile, cost-effective, one-step synthesis technique was applied to fabricate CCNCs/ZnO nanohybrids at mild temperature using Oxytenanthera abyssinica carboxylated cellulose nanocrystals as biotemplate. The result showed that CCNCs/ZnO nanohybrids possess potential applications in developing advanced functional materials for dye removal and antibacterial and antioxidant applications.

Nano Boron Oxide and Zinc Oxide Doped Lignin Containing Cellulose Nanocrystals Improve the Thermal, Mechanical and Flammability Properties of High-Density Poly(ethylene)

The widely used high-density polyethylene (HDPE) polymer has inadequate mechanical and thermal properties for structural applications. To overcome this challenge, nano zinc oxide (ZnO) and nano boron oxide (B2O3) doped lignin-containing cellulose nanocrystals (L-CNC) were blended in the polymer matrix. The working hypothesis is that lignin will prevent CNC aggregation, and metal oxides will reduce the flammability of polymers by modifying their degradation pathways. This research prepared and incorporated safe, effective, and eco-friendly hybrid systems of nano ZnO/L-CNC and nano B2O3/L-CNC into the HDPE matrix to improve their physio-mechanical and fire-retardant properties. The composites were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, thermo-gravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, horizontal burning test, and microcalorimetry test. The results demonstrated a substantial increase in mechanical properties and a reduction in flammability. The scanning electron microscope (SEM) images showed some agglomeration and irregular distribution of the inorganic oxides.

Poly(butylene succinate)/cellulose composite monofilaments with microelastic response based on interfacial bonding

Biodegradable fibers have been widely developed for advanced textile fields, but their practical applications are limited by large plastic deformation. To solve this problem, we developed a solvent-free melt spinning method to prepare poly(butylene succinate)/microcrystalline cellulose (PBS/MCC) composite monofilaments. The high modulus and rigidity of MCC limit PBS plastic deformation and the in-situ formed hydrogen bonds between MCC and amorphous PBS improved MCC dispersion and led to the formation of rigid MCC physical crosslink points. The composite monofilaments with 10-25 wt% of MCC after multi-stage and high-ratio hot stretching showed a double yielding behavior and microelastic response, indicating the permanent deformation resistance of the composite monofilaments under small deformation. Moreover, the addition of MCC improved the biodegradability of the composite monofilaments after 60 days buried in soil. Therefore, our study provides a design strategy of microelastic composite monofilaments for maintaining dimensional stability during use and accelerating degradation during waste.

Masterbatch of Chitosan Nanowhiskers for Preparation of Nylon 6,10 Nanocomposite by Melt Blending

Composite materials have been extensively studied to optimize properties such as lightness and strength, which are the advantages of plastics. We prepared a highly concentrated (30 wt %) nylon/chitosan nanowhisker (CSW) masterbatch by blending nylon 6,10 and CSW by solvent casting to achieve high dispersion efficiency while considering an industrial setting. Subsequently, 0.3 wt % nylon/CSW nanocomposites were prepared with a large quantity of nylon 6,10 via melt blending. During preparation, the materials were stirred in the presence of formic acid at different times to investigate the effect of stirring time on the structure of the CSW and the physical properties of the composite. The formation of nanocomposites by the interactions between nylon and CSW was confirmed by observing the change in hydrogen bonding using FT-IR spectroscopy and the rise in melting temperature and melting enthalpy through differential scanning calorimetry. The results demonstrated increases in complex viscosity and shear thinning. The rheological properties of the composites changed due to interactions between CSW and nylon, as indicated by the loss factor. The mechanical properties produced by the nanocomposite stirred for 1.5 h were superior, suggesting that formic acid caused minimal structural damage, thus verifying the suitability of the stirring condition.

Cellulose I nanocrystals (CNCs I) prepared in mildly acidic lithium bromide trihydrate (MALBTH) and their application for stabilizing Pickering emulsions

This study proposed a sustainable method to prepare cellulose I nanocrystals (CNCs I) from microcrystalline cellulose (MCC) in a mildly acidic lithium bromide trihydrate (MALBTH) system, a concentrated (50 wt%) solution of LiBr in water with recyclable formic acid (FA). First, the MCC was treated in the MALBTH system to generate CNCs with a uniform size, yield higher than 68.49% and crystallinity of 84.02%. Then, the CNCs could application for stabilizing Pickering emulsions for at least 15 days. Furthermore, FA was easily recycled from the MALBTH system, and the yield of the CNCs produced from the hydrolysis of MCC by using the recycled FA was still higher than 60%. Finally, this study provided a sustainable and green production of CNCs. A low-cost and environmentally friendly pathway to recover FA from the MALLBTH system at a high yield was still realized.

Grafting PEG on cellulose nanocrystals via polydopamine chemistry and the effects of PEG graft length on the mechanical performance of composite film

In this study, cellulose nanocrystals (CNCs) with PEG grafts of various lengths (1 k, 2 k, 5 k, and 10 kDa) were prepared via a polydopamine (PDA) mediated method in the aqueous solution. The prepared CNC-PEGs were further used to reinforce the polyvinyl alcohol (PVA) at the loading of 0, 1, 3, 5, and 7 wt% in order to demonstrate the effects of the PEG length on the properties of the PVA/CNC nanocomposites. PEG surface modification resulted in simultaneous improvements in stiffness and toughness. The graft lengths have noticeable impacts on the properties of composites. The shorter graft yields better enhancement in strength and stiffness, attributable to the high efficiency in the stress transfer and high interface adhesion. The longer PEG graft length yields high graft-matrix entanglement, forming a thicker rubbery coating layer that enhances the toughness of PVA/CNC composites.

Polylactic Acid Cellulose Nanocomposite Films Comprised of Wood and Tunicate CNCs Modified with Tannic Acid and Octadecylamine

Herein, a one-pot strategy was used to prepare hydrophobic cellulose nanocrystals (CNCs) surface-modified with tannic acid and octadecylamine. By this strategy, CNCs derived from wood (W-CNC) and tunicates (T-CNC) were modified in situ and incorporated into a polylactic acid (PLA) matrix using two methods, without first drying the CNCs. Films of PLA-CNC nanocomposites were prepared both by solution casting and by wet compounding in a thermo-kinetic mixer, followed by melt extrusion. Various properties of these PLA nanocomposites were evaluated herein, along with an assessment of how these properties vary with the type of CNC reinforcement. Cast films with a hybrid mixture of wood and tunicate CNCs displayed improved mechanical properties compared to either wood or tunicate CNCs, but extruded films did not show this hybrid effect. The water vapor permeability of the extruded nanocomposite films with 1% CNCs was reduced by as much as 60% compared to the PLA films. The composite films also showed enhanced biodegradation compared to neat PLA films. These results demonstrate that wet compounded PLA composites produced with wood or tunicate CNCs modified using a one-pot, water-based route have improved barrier and biodegradation properties, indicating a potential for packaging applications without having to dry the CNCs.

Impact and Tensile Properties of Polyester Nanocomposites Reinforced with Conifer Fiber Cellulose Nanocrystal: A Previous Study Extension

In a recent paper, novel polyester nanocomposites reinforced with up to 3 wt% of cellulose nanocrystals (CNCs) extracted from conifer fiber were characterized for their crystallinity index, water absorption, and flexural and thermal resistance. The use of this novel class of nanocomposites as a possible substitute for conventional glass fiber composites (fiberglass) was then suggested, especially for the 1 and 2 wt% CNC composites due to promising bending, density, and water absorption results. However, for effective engineering applications requiring impact and tensile performance, the corresponding properties need to be evaluated. Therefore, this extension of the previous work presents additional results on Izod and tensile tests of 1 and 2 wt% CNC-reinforced polyester composites, together with a comparative cost analysis with fiberglass. The chemical effect caused by incorporation of CNCs into polyester was also investigated by FTIR. In comparison to the neat polyester, the Izod impact energy increased 50% and 16% for the 1 and 2 wt% composites, respectively. On the other hand, the tensile strength and Young's modulus remained constant within the ANOVA statistical analysis. FTIR analysis failed to reveal any chemical modification caused by up to 2 wt% CNC incorporation. The present impact and tensile results corroborate the promising substitution of a polyester composite reinforced with very low amount of CNCs for common fiberglass in engineering application.

Sustainable preparation of bifunctional cellulose nanocrystals via mixed H2SO4/formic acid hydrolysis

In this work, a sustainable and highly efficient approach for preparing bifunctional cellulose nanocrystals (CNCs) was proposed through a mixed acid system of sulfuric acid and formic acid (FA). It was found that low-concentration (5-10 wt%) sulfuric acid can significantly improve the hydrolysis efficiency of FA (65-80 wt%), which enabled the highly efficient preparation of CNCs, i.e., the maximum yield of CNCs reached up to 70.65%. The obtained CNCs exhibited a rod-like shape with high crystallinity, and good dispersibility in both water and some organic phases. Moreover, the as-prepared CNCs exhibited high thermal stability, which is much higher than that of the traditionally sulfuric acid hydrolyzed ones. In addition, it was demonstrated that the bifunctional CNCs were able to stabilize various oils to form stable Pickering emulsion gels. Thus, this work provides a promising approach for sustainable preparation of bifunctional CNCs, which may find high-end applications in diverse fields.