Cellulosic Bionanocomposites: A Review of Preparation, Properties and Applications

Polysaccharides for tissue engineering: Current landscape and future prospects

Biological studies on the importance of carbohydrate moieties in tissue engineering have incited a growing interest in the application of polysaccharides as scaffolds over the past two decades. This review provides a perspective of the recent approaches in developing polysaccharide scaffolds, with a focus on their chemical modification, structural versatility, and biological applicability. The current major limitations are assessed, including structural reproducibility, the narrow scope of polysaccharide modifications being applied, and the effective replication of the extracellular environment. Areas with opportunities for further development are addressed with an emphasis on the application of rationally designed polysaccharides and their importance in elucidating the molecular interactions necessary to properly design tissue engineering materials.

Dimensionally stable cellulosic aerogels functionalized by titania

The study is aimed at imparting dimensional stability and some functionalities to cellulosic aerogels. The polysaccharide suffers from mechanical strength loss in wetted state that restricts its application. Improvement is achieved by mean of microfibrillation of cellulosic fibers combining intense mechanical treatment with freeze-thawing. Addition of the latter decreases the number of cycles. Aerogels prepared from microfibrillated cellulose by freeze-drying hold their dimensional stability in solutions that makes possible treating them chemically without loss in shape. Here a method of directional sol-gel processing is applied to mineralize such aerogels by titania. Owing to covalent bonds to cellulose macromolecules formed via the condensation reactions, titania coating possesses good adhesion, not separating at heating when it is transferred in anatase form. Its photocatalytic activity results in self-cleaning of cellulose aerogels under outdoor sunlight irradiation. Calcination in air or carbonization in an inert gas atmosphere can serve to prepare metal oxide or composites with carbon of various shape and dimensionality.

A review on processing techniques of bast fibers nanocellulose and its polylactic acid (PLA) nanocomposites

The utilization of nanocellulose has increasingly gained attentions from various research fields, especially the field of polymer nanocomposites owing to the growing environmental hazardous of petroleum based fiber products. Meanwhile, the searching of alternative cellulose sources from different plants has become the interests for producing nanocellulose with varying characterizations that expectedly suit in specific field of applications. In this content the long and strong bast fibers from plant species was gradually getting its remarkable position in the field of nanocellulose extraction and nanocomposites fabrications. This review article intended to present an overview of the chemical structure of cellulose, different types of nanocellulose, bast fibers compositions, structure, polylactic acid (PLA) and the most probable processing techniques on the developments of nanocellulose from different bast fibers especially jute, kenaf, hemp, flax, ramie and roselle and its nanocomposites. This article however more focused on the fabrication of PLA based nanocomposites due to its high firmness, biodegradability and sustainability properties in developed products towards the environment. Along with this it also explored a couple of issues to improve the processing techniques of bast fibers nanocellulose and its reinforcement in the PLA biopolymer as final products.

Co-Production of Cellulose Nanocrystals and Fermentable Sugars Assisted by Endoglucanase Treatment of Wood Pulp

In this study, fermentable sugars and cellulose nanocrystals (CNCs) were co-produced from endoglucanase treatment of wood pulp, followed by acid hydrolysis. Enzymatic hydrolysis was performed using two endoglucanases differentiated by the presence or absence of a cellulose-binding domain (CBD). The enzyme with an intact CBD gave the higher glucan conversion (up to 14.1 ± 1.2 wt %) and improved the degree of crystallinity of the recovered wood pulp fiber (up to 83.0 ± 1.0%). Thus, this endoglucanase-assisted treatment successfully removed amorphous content from the original cellulosic feedstock. CNC recovery (16.9 ± 0.7 wt %) from the feedstock going into the acid hydrolysis was improved relative to untreated pulp (13.2 ± 0.6 wt %). The mass loss from enzymatic treatment did not cause a decrease in the CNC yield from the starting material. The characteristics of CNCs obtained through acid hydrolysis (with or without enzyme treatment of pulp) were analyzed using X-ray diffraction, transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, and differential scanning calorimetry as characterization techniques. The CNCs generated through acid hydrolysis of endoglucanase-treated wood pulp displayed comparable properties relative to those generated using untreated pulp. Thus, endoglucanase treatment can enable co-production of CNCs and sugars for biofuel fermentation.

Bacterial Exopolysaccharides as Reducing and/or Stabilizing Agents during Synthesis of Metal Nanoparticles with Biomedical Applications

Bacterial exopolysaccharides (EPSs) are biomolecules secreted in the extracellular space and have diverse biological functionalities, such as environmental protection, surface adherence, and cellular interactions. EPSs have been found to be biocompatible and eco-friendly, therefore making them suitable for applications in many areas of study and various industrial products. Recently, synthesis and stabilization of metal nanoparticles have been of interest because their usefulness for many biomedical applications, such as antimicrobials, anticancer drugs, antioxidants, drug delivery systems, chemical sensors, contrast agents, and as catalysts. In this context, bacterial EPSs have been explored as agents to aid in a greener production of a myriad of metal nanoparticles, since they have the ability to reduce metal ions to form nanoparticles and stabilize them acting as capping agents. In addition, by incorporating EPS to the metal nanoparticles, the EPS confers them biocompatibility. Thus, the present review describes the main bacterial EPS utilized in the synthesis and stabilization of metal nanoparticles, the mechanisms involved in this process, and the different applications of these nanoparticles, emphasizing in their biomedical applications.

Effect of cellulose nanocrystals on crystallization kinetics of polycaprolactone as probed by Rheo-Raman

The development of biocompatible polymer nano-composites that enhance mechanical properties while maintaining thermoplastic processability is a longstanding goal in sustainable materials. When the matrix is semi-crystalline, the nanoparticles may induce significant changes to crystallization kinetics and morphology due to their ability to act as nucleating agents. To fully model this behavior in a process line, an understanding of the relationship between crystallinity and modulus is required. Here, we introduce a scalable model system consisting of surface-compatibilized cellulose nanocrystals (CNC) dispersed into poly(ε-caprolactone) (PCL) and study the effects of nanoparticle concentration on isothermal crystallization kinetics. The dispersion is accomplished by exchange of the Na⁺ of sulfated cellulose nanocrystals by tetra-butyl ammonium cations (Bu₄N⁺) followed by melt mixing via twin-screw extrusion. Crystallization kinetics are measured through the recently developed rheo-Raman instrument which extracts the relationship between the growth of the transient mechanical modulus and that of crystallinity. With extrusion and increasing CNC content, we find the expected enhancement of crystallization rate, but we moreover find a significant change in the relative kinetics of increase in modulus versus crystallinity. We analyze this via generalized effective medium theory which allows computation of a critical percolation threshold ξ _c and discuss the results in terms of a change in nucleation density and a change in the anisotropy of crystallization.

Dynamics of Cellulose Nanocrystal Alignment during 3D Printing

The alignment of anisotropic particles during ink deposition directly affects the microstructure and properties of materials manufactured by extrusion-based 3D printing. Although particle alignment in diluted suspensions is well described by analytical and numerical models, the dynamics of particle orientation in the highly concentrated inks typically used for printing via direct ink writing (DIW) remains poorly understood. Using cellulose nanocrystals (CNCs) as model building blocks of increasing technological relevance, we study the dynamics of particle alignment under the shear stresses applied to concentrated inks during DIW. With the help of in situ polarization rheology, we find that the time period needed for particle alignment scales inversely with the applied shear rate and directly with the particle concentration. Such dependences can be quantitatively described by a simple scaling relation and qualitatively interpreted in terms of steric and hydrodynamic interactions between particles at high shear rates and particle concentrations. Our understanding of the alignment dynamics is then utilized to estimate the effect of shear stresses on the orientation of particles during the printing process. Finally, proof-of-concept experiments show that the combination of shear and extensional flow in 3D printing nozzles of different geometries provides an effective means to tune the orientation of CNCs from fully aligned to core-shell architectures. These findings offer powerful quantitative guidelines for the digital manufacturing of composite materials with programmed particle orientations and properties.

The Effect of Cellulose Nanocrystals (CNC) on Isothermal Crystallization Kinetics of LLDPE and HDPE

Highly porous agglomerates of spray freeze dried cellulose nanocrystals (SFD-CNC) were prepared, starting with sonicated aqueous suspensions of spray-dried cellulose nanocrystals powder (SD-CNC). Subsequently, SFD-CNC together with the SD-CNC (used as a reference) were incorporated into LLDPE and HDPE via melt compounding in a batch mixer to produce nanocomposites containing 0.5 wt.° and 2 wt.° CNC. Differential scanning calorimetry (DSC) was used to study the thermal properties and the isothermal crystallization kinetics of the polyethylenes and the nanocomposites. Polarized light microscopy (PLM) was used to evaluate the growth kinetics and spherulitic structure of polyethylene in both the filled and unfilled polymers. Avrami crystallization kinetics models were employed to analyze the DSC results. It was observed that CNC acts as a heterogeneous nucleating agent in LLDPE nanocomposites, thus yielding nucleation controlled crystallization. On the other hand, in the HDPE systems (polymer and nanocomposites) heterogeneous nucleation was followed by 3-D growth. It was observed that CNC slightly hindered the formation of chain folding for the HDPE, similar to previous studies on the polypropylene and its nanocomposites. Spray freeze drying produced twice as many nucleation sites compared to spray dried samples and it enhanced the overall crystallization rate and the crystallinity.

Cellulose Aerogels: Synthesis, Applications, and Prospects

Due to its excellent performance, aerogel is considered to be an especially promising new material. Cellulose is a renewable and biodegradable natural polymer. Aerogel prepared using cellulose has the renewability, biocompatibility, and biodegradability of cellulose, while also having other advantages, such as low density, high porosity, and a large specific surface area. Thus, it can be applied for many purposes in the areas of adsorption and oil/water separation, thermal insulation, and biomedical applications, as well as many other fields. There are three types of cellulose aerogels: natural cellulose aerogels (nanocellulose aerogels and bacterial cellulose aerogels), regenerated cellulose aerogels, and aerogels made from cellulose derivatives. In this paper, more than 200 articles were reviewed to summarize the properties of these three types of cellulose aerogels, as well as the technologies used in their preparation, such as the sol⁻gel process and gel drying. In addition, the applications of different types of cellulose aerogels were also introduced.

Recent Advances in Nanocellulose Composites with Polymers: A Guide for Choosing Partners and How to Incorporate Them

In recent years, the research on nanocellulose composites with polymers has made significant contributions to the development of functional and sustainable materials. This review outlines the chemistry of the interaction between the nanocellulose and the polymer matrix, along with the extent of the reinforcement in their nanocomposites. In order to fabricate well-defined nanocomposites, the type of nanomaterial and the selection of the polymer matrix are always crucial from the viewpoint of polymer⁻filler compatibility for the desired reinforcement and specific application. In this review, recent articles on polymer/nanocellulose composites were taken into account to provide a clear understanding on how to use the surface functionalities of nanocellulose and to choose the polymer matrix in order to produce the nanocomposite. Here, we considered cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) as the nanocellulosic materials. A brief discussion on their synthesis and properties was also incorporated. This review, overall, is a guide to help in designing polymer/nanocellulose composites through the utilization of nanocellulose properties and the selection of functional polymers, paving the way to specific polymer⁻filler interaction.

Nanofiller Reinforced Biodegradable PLA/PHA Composites: Current Status and Future Trends

The increasing demand for environmental protection has led to the rapid development of greener and biodegradable polymers, whose creation provided new challenges and opportunities for the advancement of nanomaterial science. Biodegradable polymer materials and even nanofillers (e.g., natural fibers) are important because of their application in greener industries. Polymers that can be degraded naturally play an important role in solving public hazards of polymer materials and maintaining ecological balance. The inherent shortcomings of some biodegradable polymers such as weak mechanical properties, narrow processing windows, and low electrical and thermal properties can be overcome by composites reinforced with various nanofillers. These biodegradable polymer composites have wide-ranging applications in different areas based on their large surface area and greater aspect ratio. Moreover, the polymer composites that exploit the synergistic effect between the nanofiller and the biodegradable polymer matrix can lead to enhanced properties while still meeting the environmental requirement. In this paper, a broad review on recent advances in the research and development of nanofiller reinforced biodegradable polymer composites that are used in various applications, including electronics, packing materials, and biomedical uses, is presented. We further present information about different kinds of nanofillers, biodegradable polymer matrixes, and their composites with specific concern to our daily applications.

Current characterization methods for cellulose nanomaterials

A new family of materials comprised of cellulose, cellulose nanomaterials (CNMs), having properties and functionalities distinct from molecular cellulose and wood pulp, is being developed for applications that were once thought impossible for cellulosic materials. Commercialization, paralleled by research in this field, is fueled by the unique combination of characteristics, such as high on-axis stiffness, sustainability, scalability, and mechanical reinforcement of a wide variety of materials, leading to their utility across a broad spectrum of high-performance material applications. However, with this exponential growth in interest/activity, the development of measurement protocols necessary for consistent, reliable and accurate materials characterization has been outpaced. These protocols, developed in the broader research community, are critical for the advancement in understanding, process optimization, and utilization of CNMs in materials development. This review establishes detailed best practices, methods and techniques for characterizing CNM particle morphology, surface chemistry, surface charge, purity, crystallinity, rheological properties, mechanical properties, and toxicity for two distinct forms of CNMs: cellulose nanocrystals and cellulose nanofibrils.

Incorporation of microfibrillated cellulose into collagen-hydroxyapatite scaffold for bone tissue engineering

In this study, the composite of Collagen-Hydroxyapitite (COL-HA) with microfibrillated cellulose (MFC) was developed as a new bone substitute material. COL-HA was prepared by in-situ method and modified by dehydrothermal treatment. Microfibrillated cellulose (MFC), a nature polysaccharide with plenty of hydroxyl groups, was incorporated into COL-HA composites to improve the properties. The novel COL-HA-MFC scaffold with different ratios of COL-HA and MFC were fabricated by cold isostatic pressing technique and freeze-drying technology. During the forming process, a three-dimensional bone-like structure was shaped in hybrid scaffolds. The microstructural transitions of COL-HA-MFC composites were examined by Fourier transform infrared spectroscope (FTIR), Ultraviolet-visible spectrophotometer (UV), and X-ray diffraction (XRD), which indicated that HA deposited on collagen molecules and MFC bonded with COL-HA. Hydrophilicity, swelling property, mechanical property, and degradability of COL-HA-MFC composites were investigated. Biological properties, such as cytotoxicity and hemolysis, were also studied. The results showed a good swelling capacity for the scaffolds, keeping their original shapes after swelling. The compression strength and degradability of the scaffold materials could be regulated by the MFC content. The compression strength of COL-HA-MFC composite scaffords increased to 20-40 MPa, closing to that of the nature bone (1-200 MPa). The obtained scaffolds are good in biocompatibility with high level of cell growth rate (>70%) and suitable hemolysis rate (≦5%). The work might provide an efficient and alternative approach for collagen-based biomaterials with necessary properties. The COL-HA-MFC composite scaffold showed a potential application in bone tissue engineering.

Elaboration of Cellulose Nanocrystal/Ge-Imogolite Nanotube Multilayered Thin Films

Multilayered thin films combining two oppositely charged nanoparticles (NPs), i.e., cellulose nanocrystals (CNCs) and Ge-imogolites, have been successfully obtained by the layer-by-layer method. CNC/Ge-imogolite (NP/NP) film growth patterns were studied by comparing growth mode of all of the nanoparticles thin films to that of films composed of CNC or Ge-imogolites combined with polyelectrolytes (PEs), i.e., cationic poly(allylamine hydrochloride) and anionic poly-4-styrene sulfonate (NP/PE films). NP/NP and NP/PE films growth patterns were found to be different. To get a deeper understanding of the growth mode of NP/NP, impact of different parameters, such as imogolites aspect ratio, adsorption time, ionic strength, and repeated immersion/drying, was evaluated and influence of the drying step is emphasized. The aspect ratio of imogolites was identified as an important feature for the film's architecture. The short Ge-imogolites form denser films because the surface packing was more efficient.

Development of high throughput, high precision synthesis platforms and characterization methodologies for toxicological studies of nanocellulose

Cellulose is one of the most abundant natural polymers, is readily available, biodegradable, and inexpensive. Recently, interest is growing around nanoscale cellulose due to the sustainability of these materials, the novel properties, and the overall low environmental impact. The rapid expansion of nanocellulose uses in various applications makes the study of the toxicological properties of these materials of great importance to public health regulators. However, most of the current toxicological studies are highly conflicting, inconclusive, and contradictory. The major reasons for these discrepancies are the lack of standardized methods to produce industry-relevant reference nanocellulose and relevant characterization that will expand beyond the traditional cellulose characterization for applications. In order to address these issues, industry-relevant synthesis platforms were developed to produce nanocellulose of controlled properties that can be used as reference materials in toxicological studies. Herein, two types of nanocellulose were synthesized, cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) using the friction grinding platform and an acid hydrolysis approach respectively. The nanocellulose structures were characterized extensively regarding their physicochemical properties, including testing for endotoxins and bacteria contamination.

Strategy for the Improvement of the Mechanical Properties of Cellulose Nanofiber-Reinforced High-Density Polyethylene Nanocomposites Using Diblock Copolymer Dispersants

Cellulose nanofibers (CNFs) hold great potential as sustainable reinforcement fillers with excellent mechanical, thermal, and chemical properties. However, in polyolefin nanocomposite materials, the rational control of dispersion and the improvement of interfacial strength remain challenging. Herein we propose the tuning of the interface between CNF and high-density polyethylene by the design of polymer dispersants on the basis of surface free energy and the glass transition temperature. The former is related to the wettability against the polymer matrix and is therefore critical to the dispersion of CNF whereas the latter is related to the interfacial strength between CNF and HDPE. As a result of this investigation, we discovered a suitable dispersant for CNFs, poly(dicyclopentenyloxyethyl methacrylate)-block-poly(2-hydroxyethyl methacrylate), which played a pivotal role in achieving both a uniform dispersion of CNF and greatly improved mechanical properties, including a 4-fold increase of the Young's modulus over that of neat HDPE with 10 wt % CNF loading.

Preparation, Characterization and Application of Polysaccharide-Based Metallic Nanoparticles: A Review

Polysaccharides are natural biopolymers that have been recognized to be the most promising hosts for the synthesis of metallic nanoparticles (MNPs) because of their outstanding biocompatible and biodegradable properties. Polysaccharides are diverse in size and molecular chains, making them suitable for the reduction and stabilization of MNPs. Considerable research has been directed toward investigating polysaccharide-based metallic nanoparticles (PMNPs) through host⁻guest strategy. In this review, approaches of preparation, including top-down and bottom-up approaches, are presented and compared. Different characterization techniques such as scanning electron microscopy, transmission electron microscopy, dynamic light scattering, UV-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and small-angle X-ray scattering are discussed in detail. Besides, the applications of PMNPs in the field of wound healing, targeted delivery, biosensing, catalysis and agents with antimicrobial, antiviral and anticancer capabilities are specifically highlighted. The controversial toxicological effects of PMNPs are also discussed. This review can provide significant insights into the utilization of polysaccharides as the hosts to synthesize MPNs and facilitate their further development in synthesis approaches, characterization techniques as well as potential applications.

The Preparations and Water Vapor Barrier Properties of Polyimide Films Containing Amide Moieties

Flexible displays are a systematic revolution in the field of display, in which high-performance and high-barrier polymer substrates are considered to be one of the most important key materials. In this work, high water vapor barrier polyimides containing amide moieties were synthesized via the ternary polymerization of 4,4'-diaminobenzailide (DABA), 4,4'-diaminodipheny ether (ODA), and 3,3',4,4'-biphenyl-tetracarboxylic acid dianhydride (BPDA) followed by thermal imidization. The relationship between the content of amide moieties and the water vapor barrier property of the prepared polyimides was studied by means of density test, water absorbing test, water contact angle test, water vapor permeation test, fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), thermogravimetry coupled with fourier transform infrared spectrometry (TG-FTIR), wide-angle X-ray diffraction analysis (WXRD), mechanical performance test, etc. The results show that the introduction of amide groups into polyimide (PI) main chains can improve the water vapor barrier properties of the polyimides effectively. The water vapor transmission rate (WVTR) of the polyimide films can be improved from 8.2365 g·(m²·24 h)-1 to 0.8670 g·(m²·24 h)-1 with the increasing content of amide moieties.

Post-sulfonation of cellulose nanofibrils with a one-step reaction to improve dispersibility

Cellulose nanofibrils (CNF) were sulfonated and the dispersion quality was compared to unfunctionalized and 2,2,6,6-tetramethylpiperdine-1-oxyl radical (TEMPO) post-oxidation treatment of existing CNF (mechanically fibrillated pulp). A post-sulfonation treatment on existing CNF in chlorosulfonic acid and dimethylformamide (DMF) resulted in sulfonated CNF that retained a fibril-like morphology. There was a small decrease in the cellulose crystallinity index for the sulfonated CNF, but this was much lower than the reported regioselective oxidative bisulfite pretreatment method used to make sulfonated CNF. The current approach was extremely quick, and 5min of reaction time was sufficient to result in significant improvements in dispersibility compared to unfunctionalized CNF. The sulfonated CNF and TEMPO oxidized CNF had better dispersibility compared to the unfunctionalized CNF when dispersed in DMF and water, and in many cases the sulfonated CNF had better dispersibility than the TEMPO CNF. It was found that when CNF was dispersed in DMF the TEMPO CNF formed carboxyl dimethylammonium groups, while the sulfonated CNF formed formate groups.