Comparing Soft Semicrystalline Polymer Nanocomposites Reinforced with Cellulose Nanocrystals and Fumed Silica

Exploring nanocellulose frontiers: A comprehensive review of its extraction, properties, and pioneering applications in the automotive and biomedical industries

Material is an inseparable entity for humans to serve different purposes. However, synthetic polymers represent a major category of anthropogenic pollutants with detrimental impacts on natural ecosystems. This escalating environmental issue is characterized by the accumulation of non-biodegradable plastic materials, which pose serious threats to the health of our planet's ecosystem. Cellulose is becoming a focal point for many researchers due to its high availability. It has been used to serve various purposes. Recent scientific advancements have unveiled innovative prospects for the utilization of nanocellulose within the area of advanced science. This comprehensive review investigates deeply into the field of nanocellulose, explaining the methodologies employed in separating nanocellulose from cellulose. It also explains upon two intricately examined applications that emphasize the pivotal role of nanocellulose in nanocomposites. The initial instance pertains to the automotive sector, encompassing cutting-edge applications in electric vehicle (EV) batteries, while the second exemplifies the use of nanocellulose in the field of biomedical applications like otorhinolaryngology, ophthalmology, and wound dressing. This review aims to provide comprehensive information starting from the definitions, identifying the sources of the nanocellulose and its extraction, and ending with the recent applications in the emerging field such as energy storage and biomedical applications.

Recent advances in qualitative and quantitative characterization of nanocellulose-reinforced nanocomposites: A review

Nanocellulose has received immense consideration owing to its valuable inherent traits and impressive physicochemical properties such as biocompatibility, thermal stability, non-toxicity, and tunable surface chemistry. These features have inspired researchers to deploy nanocellulose as nanoscale reinforcement materials for bio-based polymers. A simple yet efficient characterization method is often required to gain insights into the effectiveness of various types of nanocellulose. Despite a decade of continuous research and booming growth in scientific publications, nanocellulose research lacks a measuring tool that can characterize its features with acceptable speed and reliability. Implementing reliable characterization techniques is critical to monitor the specifications of nanocellulose alone or in the final product. Many techniques have been developed aiming to measure the nano-reinforcement mechanisms of nanocellulose in polymer composites. This review gives a full account of the scientific underpinnings of techniques that can characterize the shape and arrangement of nanocellulose. This review aims to deliver consolidated details on the properties and characteristics of nanocellulose in biopolymer composite materials to improve various structural, mechanical, barrier and thermal properties. We also present a comprehensive description of the safety features of nanocellulose before and after being loaded within biopolymeric matrices.

Dispersibility Characterization of Cellulose Nanocrystals in Polymeric-Based Composites

Cellulose nanocrystals (CNCs) are hydrophilic nanoparticles extracted from biomass with properties and functions different from cellulose and are being developed for property-oriented applications such as high stiffness, abundant active groups, and biocompatibility. It has broad application prospects in the field of composite materials, while the dispersibility of the CNC in polymers is the key to its application performance. Many reviews have discussed in-depth the modification strategies to improve the dispersibility of the CNC and summarized all characterization for the CNC, but there are no reviews on the in-depth exploration of dispersion characterization. This review is a comprehensive summary of the characterization of CNC dispersion in the matrix in terms of direct observation, indirect evaluation, and quantified evaluation, summarizing how and why different characterization tools reveal dispersibility. In addition, "decision tree" flowcharts are presented to provide the reader with a reference for selecting the appropriate characterization method for a specific composite.

Anisotropy and Nanomechanics of Cellulose Nanocrystals/Polyethylene Glycol Composite Films

The influence of shear flow on the nanomechanical properties of cellulose nanocrystal (CNC)/polyethylene glycol (PEG) composite films and the distribution of anisotropic phases are investigated at various CNC/PEG ratios. Here, the drying process of CNC/PEG mixed suspensions is systematically traced by rheology, followed by the spatial mapping of local mechanical properties of CNC/PEG films by nanoindentation. The detailed study of the morphology of CNC/PEG films by polarized optical microscopy (POM) and image analysis revealed the link between the mechanical properties and the influence of shear flow. A comparison of the data obtained for shear-dried films with nonsheared films showed the improved reduced Young's modulus (E_r) and hardness (H), and suppression of microphase separation in the shear-dried films. Based on this experimental evidence, a mechanism is proposed to explain the microstructural transition during the shear-drying process leading to the generation of the anisotropic domains containing the shear-induced assembled structure of CNC particles coexisting with the elongated PEG microphases.

Direct Comparison of Three Buckling-Based Methods to Measure the Elastic Modulus of Nanobiocomposite Thin Films

To engineer tunable thin-film materials, the accurate measurement of their mechanical properties is crucial. However, characterizing the elastic modulus with current methods is particularly challenging for sub-micrometer thick films and hygroscopic materials because they are highly sensitive to environmental conditions and most methods require free-standing films which are difficult to prepare. In this work, we directly compared three buckling-based methods to determine the elastic moduli of supported thin films: (1) biaxial thermal shrinking, (2) uniaxial thermal shrinking, and (3) the mechanically compressed, strain-induced elastic buckling instability for mechanical measurements (SIEBIMM) method. Nanobiocomposite model films composed of cellulose nanocrystals (CNCs) and polyethyleneimine (PEI) were assembled using layer-by-layer deposition to control composition and thickness. The three buckling-based methods yielded the same trends and comparable values for the elastic moduli of each CNC-PEI film composition (ranging from 15 to 44 GPa, depending on film composition). This suggests that the methods are similarly effective for the quantification of thin-film mechanical properties. Increasing the CNC content in the films statistically increased the modulus; however, increasing the PEI content did not lead to significant changes. For the CNC-PEI system, the standard deviation of elastic moduli determined from SIEBIMM was 2-4 times larger than that for thermal shrinking, likely due to extensive cracking due to the different stress applied to the film when subjected to compression of a relaxed substrate versus the shrinking of a pre-strained substrate. These results show that biaxial thermal shrinking is a reliable method for the determination of the mechanical properties of thin films with a simple implementation and analysis and low sensitivity to small deviations in the input parameter values, such as film thickness or substrate modulus.

Cellulose hydrolysis using ionic liquids and inorganic acids under dilute conditions: morphological comparison of nanocellulose

The preparation of cellulose nanocrystals (CNCs) from cellulose extracted from cotton gin motes (CGM) using an ionic liquid (1-butyl-3-methylimidazolium chloride, [BMIm]Cl) under dilute conditions is reported. The concurrent process involves minimal swelling of cellulose with an ionic liquid and hydrolysis of the cellulose initiated by the addition of either phosphoric (H3PO4), hydrochloric (HCl), or sulfuric (H2SO4) acid. The obtained nanocrystals had similar physical properties (e.g. crystallinity) to the counterparts prepared under conventional conditions and exhibited superior thermal properties for sulfate CNCs. Additionally, the obtained CNCs had low surface functionalization, yet were colloidally stable for >90 days, which is a desirable trait for post-functionalization of CNCs. This process represents a general strategy utilizing dilute ionic liquids in the preparation of nanocellulose under mildly acidic conditions.

Use of Synergistic Interactions to Fabricate Transparent and Mechanically Robust Nanohybrids Based on Starch, Non-Isocyanate Polyurethanes, and Cellulose Nanocrystals

Materials based on petroleum-based resources have aroused widespread concern because of their environmental and healthcare footprints. Cellulose nanocrystals (CNCs) are at the cutting edge of current research because of their great promise in developing sustainable and high-performance materials. To establish a comprehensive understanding of the synergistic reinforcement effect of CNCs, we introduced a new method to fabricate all-green, transparent, and mechanically robust nanohybrid materials using CNCs in conjunction with gelatinized starch (GS) and polyhydroxyurethanes (PHUs). The synergistic interaction between the CNC skeleton and the GS/PHU network enabled us to span exceptionally stiff nanohybrids that could withstand up to 8.5 MPa tensile strength. The tunable mechanical properties and enhanced thermal stability in these nanohybrids primarily arise from the presence of dense hydroxyl groups on the CNCs' surface, which offer a robust scaffold for fortified hydrogen bonds to form with GS/PHU domains. The multiple intramolecular hydrogen bonds synergistically served as highly stable associations and concurrently facilitated energy dissipation and transferred the stress across the interfacial region. The rational design of the molecular interactions presented in this work provided increased opportunities to build nanohybrids with outstanding mechanical performance. More broadly, the insights afforded by this study not only delivered a better understanding on the molecular-level interactions in the CNC/GS/PHU system but also enriched the potential for the commercial exploration of tunable cellulosic nanohybrid materials.

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.