Cellulose nanofibrils-graphene hybrids: recent advances in fabrication, properties, and applications

On the versatility of graphene-cellulose composites: An overview and bibliometric assessment

Practical benefits of graphene-cellulose composites (GCC) are categorical. Diverse salient features like thermal and electrical conductivity, mechanical strength, and durability make GCC advantageous for widespread applications. Despite extensive studies the basic understanding of various fundamental aspects of this novel complex remains deficient. Based on this fact, a critical overview and bibliometric analysis involving the overall prospects of GCC was made wherein a total of 1245 research articles from the Scopus database published during the year 2002 to 2020 were used. For the bibliometric assessment, various criteria including the publication outputs, co-authorships, affiliated countries, and co-occurrences of the authors' keywords were explored. Environmental amiability, sustainability, economy, and energy efficiency of GCC were emphasized. In addition, the recent trends, upcoming challenges, and applied interests of GCC were highlighted. The findings revealed that the studies on GCC related to the energy storage, adsorption, sensing, and printing are ever-increasing, indicating the global research drifts on GCC. The bibliometric map analysis displayed that among the researchers from 61 countries/territories, China alone contributed about 50 % of the international publications. It is asserted that the current article may offer taxonomy to navigate into the field of GCC wherein stronger collaboration networks can be established worldwide through integrated research activities desirable for sustainable development.

Nanocellulose extraction from acai bagasse through mixed acid hydrolysis and oxidative techniques

Exploring new biomass sources for nanocellulose (NC) extraction is crucial in elevating the economic value of readily available renewable resources. This study compares NC extracted from acai (Euterpe oleracea) bagasse using different methods: mixed acid hydrolysis, 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) mediation, and ammonium persulfate (APS) oxidations. A comprehensive analysis investigates the impact of each treatment on the physical-chemical properties of the nanoparticles, including chemical structure, crystallinity, morphology, and thermal and suspension stability. NCs obtained through mixed acid hydrolysis exhibit the highest crystallinity (62 %) and low sulfate groups on their surfaces. Consequently, they demonstrate excellent thermal stability but poor colloidal stability in water. Oxidized NCs undergo chemical modification, converting alcoholic groups into carboxyl, resulting in NCs with zeta potentials ranging between -25.30 ± 0.81 and - 27.49 ± 1.07 mV. APS oxidation produces nanoparticles with superior thermal stability compared to TEMPO oxidation. Atomic Force Microscopy (AFM) images reveal that all nanocelluloses share characteristics of nanofibers (CNFs). This comprehensive characterization highlights the potential of acai bagasse for yielding high-added-value bioproducts suitable for versatile applications.

Cellulose microfiber extraction from leftover celery pulp: Chemomechanical treatments, structural, morphological, and thermal characterization

Based on the variety of attractive applicability and structural advantages, cellulose is suggested as a sustainable and environmentally-friendly replacement for petroleum-based materials. Therefore, the current study proposed two chemo-mechanical treatments including bleaching with sodium chlorite and sodium hypochlorite for pure cellulose extraction from leftover celery pulp (Apium graveolens var. dulce). The characterizations of the extracted cellulose fibers were measured and analyzed, by using FT-IR, XRD, optical microscopy, FE-SEM, and TGA analysis. FTIR analysis confirmed the successful removal of non-cellulosic and impurities materials by chemical treatments. Analyzing the X-ray diffraction showed that the proposed chemo-mechanical procedures did not have damaging impacts on the cellulose crystalline structure. Microscopies analysis within optical microscopy and FE-SEM indicated that the diameters of the untreated fibers generally ranged from 100 to 150 μm, while for the treated ones, they ranged from 10 to 15 μm. The TGA results illustrated the higher initial degradation temperatures for the treated samples which led to significant improvement in their thermal stabilities.

Fit-for-Use Nanofibrillated Cellulose from Recovered Paper

The cost-effective implementation of nanofibrillated cellulose (CNF) at industrial scale requires optimizing the quality of the nanofibers according to their final application. Therefore, a portfolio of CNFs with different qualities is necessary, as well as further knowledge about how to obtain each of the main qualities. This paper presents the influence of various production techniques on the morphological characteristics and properties of CNFs produced from a mixture of recycled fibers. Five different pretreatments have been investigated: a mechanical pretreatment (PFI refining), two enzymatic hydrolysis strategies, and TEMPO-mediated oxidation under two different NaClO concentrations. For each pretreatment, five high-pressure homogenization (HPH) conditions have been considered. Our results show that the pretreatment determines the yield and the potential of HPH to enhance fibrillation and, therefore, the final CNF properties. These results enable one to select the most effective production method with the highest yield of produced CNFs from recovered paper for the desired CNF quality in diverse applications.

Graphene in Polymeric Nanocomposite Membranes—Current State and Progress

One important application of polymer/graphene nanocomposites is in membrane technology. In this context, promising polymer/graphene nanocomposites have been developed and applied in the production of high-performance membranes. This review basically highlights the designs, properties, and use of polymer/graphene nanocomposite membranes in the field of gas separation and purification. Various polymer matrices (polysulfone, poly(dimethylsiloxane), poly(methyl methacrylate), polyimide, etc.), have been reinforced with graphene to develop nanocomposite membranes. Various facile strategies, such as solution casting, phase separation, infiltration, self-assembly, etc., have been employed in the design of gas separation polymer/graphene nanocomposite membranes. The inclusion of graphene in polymeric membranes affects their morphology, physical properties, gas permeability, selectivity, and separation processes. Furthermore, the final membrane properties are affected by the nanofiller content, modification, dispersion, and processing conditions. Moreover, the development of polymer/graphene nanofibrous membranes has introduced novelty in the field of gas separation membranes. These high-performance membranes have the potential to overcome challenges arising from gas separation conditions. Hence, this overview provides up-to-date coverage of advances in polymer/graphene nanocomposite membranes, especially for gas separation applications. The separation processes of polymer/graphene nanocomposite membranes (in parting gases) are dependent upon variations in the structural design and processing techniques used. Current challenges and future opportunities related to polymer/graphene nanocomposite membranes are also discussed.

A review of environmental friendly green composites: production methods, current progresses, and challenges

The growing concern about environmental damage and the inability to meet the demand for more versatile, environmentally friendly materials has sparked increasing interest in polymer composites derived from renewable and biodegradable plant-based materials, mainly from forests. These composites are mostly referred to as "green" and they can be widely employed in many industrial applications. Green composites are less harmful to the environment and could be potential substitutes for petroleum-based polymeric materials. It is helpful to limit usage of fossil oil assets by developing biopolymer matrices such as cellulose-reinforced biocomposites using renewable assets such as plant oils, carbohydrates, and proteins. This paper focuses on green composites processing utilizing a variety of naturally available resources, sustainable materials which are not detrimental to the environment, new scientific signs of progress in achieving green sustainable development, as well as nanotechnology and its environmental consequences. Additionally, the environmental impacts of different composite materials are examined in this paper, along with their production from eco-friendly materials. Moreover, the manufacturing aspects of green composites and some concerns related to their production are also discussed. The merits of green composite materials and valid reasons why they are a valuable substitute for the traditionally used composite materials are also covered.

Cellulosic pine needles-based biorefinery for a circular bioeconomy

Pine needles (PNs) are one of the largest bio-polymer produced worldwide. Its waste, i.e., fallen PNs, is mostly responsible for forest fires and is a major challenge. In present article, we have reviewed differenteffortsmadeto tackle this situation. PNs have been used in various fields such asin composite, water purification industries,electronic devices, etc. Gasification is one of the appealing processes for turning PNs into bio-energy; pyrolysis technique has been employed to create various carbon-based water purification materials; saccharification combined with fermentation produced good yields of bio-ethanol; Pd or Ni/PNs biocatalyst showed good catalytic properties in variousreactionsand pyrolysis with or without catalyst is an alluring technique to prepare bio-fuel. Nano cellulose extracted from PNs showed appealing thermal and mechanical strength. The air quality of nearbyenvironment was examinedby studying the magnetic properties of PNs. Packing materials made of PNs showed exceptional ethylene scavenging abilities.