Non-cytotoxic, highly functionalized cellulose nanocrystals with high crystallinity and thermal stability derived from a novel agromass of Elettaria cardamomum, using a soft and benign mild oxalic acid hydrolysis

Non-cytotoxic, highly crystalline, and functionalized, thermally stable cellulose nanocrystals are extracted from the stems of Elettaria cardamom, a novel underutilised agromass, by employing a neat green, mild oxalic acid hydrolysis. The protocol involves a chemo-mechanical strategy of coupling hydrolysis with steam explosion and homogenization. The obtained CNC showed a crystallinity index of 81.51 %, an aspect ratio of 17.80 ± 1.03 and a high degradation temperature of about 339.07 °C. The extraction procedure imparted a high negative surface functionalization with a zeta potential value of -34.244 ± 0.496 mV and a polydispersity of 16.5 %. The CNC had no antibacterial activity, according to non-cytotoxic experiments conducted on four bacterial strains. This supports the notion of "One Health" in the context of AMR by demonstrating the safety of antibiotic resistance due to consistent exposure upon environmental disposal. The as-extracted nanocellulose crystals can be a potential candidate for commercial application in wide and diversified disciplines like food packaging, anti-infective surfaces for medical devices, biosensors, bioelectronics etc.

Enhancing Stiffness and Oil Resistance of Fluorosilicone Rubber Composites through Untreated Cellulose Reinforcement

Fluorosilicone rubber, essential in automotive and aerospace owing to its excellent chemical resistance, plays a pivotal role in sealing technology, addressing the industry's evolving demands. This study explores the preparation and properties of fibrillated cellulose-reinforced fluorosilicone rubber composites to enhance their stiffness and oil resistance. Fibrillated cellulose sourced as a wet cake and subjected to processing and modification is incorporated into a fluorosilicone rubber matrix. The resulting composites are analysed by tensile and compression tests, along with compressive stress-relaxation testing in air and in an oil-immersed environment. The findings demonstrate significant improvements in the mechanical properties, including an increased Young's modulus and elongation at break, whereas the tensile strength remained uncompromised throughout the testing procedures. Morphological analysis of the fracture surfaces revealed a remarkable interfacial affinity between the fibrillated cellulose and rubber matrix, which was attributed in part to the modified fatty acids and inorganic nanoparticles. The presence of fibrillated cellulose enhanced the stress-relaxation characteristics under oil-immersion conditions. These results contribute to the domain of advanced elastomer materials, with potential for applications requiring enhanced mechanical properties and superior oil resistance.

Nanocellulose reinforced lightweight composites produced from cotton waste via integrated nanofibrillation and compounding

Cotton is a natural fiber containing more than 95% of cellulose. With worldwide cotton consumption continuously increasing, the amount of cotton waste generated is enormous. Most of the cotton waste ends up in landfill or incinerators, resulting in a huge waste of this excellent natural resource. In this project, cotton waste was recycled to produce polypropylene nanocomposites. Instead of using the traditional two-step nanofiber extraction and compounding technique, an integrated process was adopted to combine nanofibrillation and compounding into one step. Results showed that cotton fibers with a slight prefibrillation and hydrophobic surface modification were successfully fibrillated into tens to hundreds of nanometers in width during compounding. The nanofibers reinforced polypropylene composites exhibited significantly enhanced tensile and flexural strength and moduli. For instance, when 30% fibers from bleached white and indigo-dyed denim fabrics were introduced, the tensile moduli of the resultant composites reached 4.57 and 4.59 GPa, respectively, compared to 1.60 GPa, the modulus of neat PP. Meanwhile, denim fabrics had a remarkable reinforcing effect on the composites' impact strength attributing to the hydrophobic indigo dyes that improved the interfacial bonding between cotton fibers and the matrix. The highest impact strength of denim reinforced composites was 4.96 kJ/m² with 20% fiber loading; while the impact strength of neat polypropylene was 2.46 kJ/m². The low water uptake of the composites further indicated the excellent adhesion at the filler/matrix interface. In general, a very promising processing technique to recycle cotton waste for high-value products was demonstrated.

Shape memory polymer composites (SMPCs) using interconnected nanowire network foams as reinforcements

Shape memory polymers (SMPs), although offer a suite of advantages such as ease of processability and lower density, lag behind their shape memory alloy counterparts, in terms of mechanical properties such as recovery stress and cyclability. Reinforcing SMPs with inorganic nanowires and carbon nanotubes (CNTs) is a sought-after pathway for tailoring their mechanical properties. Here, inorganic nanowires also offer the added advantage of covalently binding the fillers to the surrounding polymer matrices via organic molecules. The SMP composites (SMPCs) thus obtained have well-engineered nanowire-polymer interfaces, which could be used to tune their mechanical properties. A well-known method of fabricating SMPCs involving casting dispersions of nanowires (or CNTs) in mixtures of monomers and crosslinkers typically results in marginal improvements in the mechanical properties of the fabricated SMPCs. This is owed to the constraints imposed by the rule-of-mixture principles. To circumvent this limitation, a new method for SMPC fabrication is designed and presented. This involves infiltrating polymers into pre-fabricated nanowire foams. The pre-fabricated foams were fabricated by consolidating measured quantities of nanowires and a sacrificial material, such as (NH₄)₂CO₃, followed by heating the consolidated mixtures for subliming the sacrificial material. Similar to the case of traditional composites, use of silanes to functionalize the nanowire surfaces allowed for the formation of bonds between both the nanowire-nanowire and the nanowire-polymer interfaces. SMPCs fabricated using TiO₂nanowires and SMP composed of neopentyl glycol diglycidyl ether and poly(propylene glycol) bis(2-aminopropyl ether) (Jeffamine D230) in a 2:1 molar ratio exhibited a 300% improvement in the elastic modulus relative to that of the SMP. This increase was significantly higher than SMPC made using the traditional fabrication route. Well-known powder metallurgy techniques employed for the fabrication of these SMPCs make this strategy applicable for obtaining other SMPCs of any desired shape and chemical composition.

A Review on Fully Bio-Based Materials Development from Polylactide and Cellulose Nanowhiskers

This review covers the development of eco-friendly, bio-based materials based on polylactide (PLA) and cellulose nanowhiskers (CNWs). As a biodegradable polymer, PLA is one of the promising materials to replace petroleum-based polymers. In the field of nanocomposites, CNWs offer many advantages; they are made from renewable resources and exhibit beneficial mechanical and thermal properties in combination with polymer matrix. A wide range of surface modifications has been done to improve the miscibility of CNW with the PLA homopolymer, which generally gives rise to hydrophobic properties. PLA–CNW nanocomposite materials are fully degradable and sustainable and also offer improved mechanical and thermal properties. Limitations pertaining to the miscibility of CNWs with PLA were solved through surface modification and chemical grafting on the CNW surfaces. Further development has been done by combining PLA-based material via stereocomplexation approaches in the presence of CNW particles, known as bio-stereo-nanocomposite PLA–CNW. The combination of stereocomplex crystalline structures in the presence of well-distributed CNW particles produces synergetic effects that enhance the mechanical and thermal properties, including stereocomplex memory (melt stability). The bio-based materials from PLA and CNWs may serve as eco-friendly materials owing to their sustainability (obtained from renewable resources), biodegradability, and tunability properties.

An innovative model for conductivity of graphene-based system by networked nano-sheets, interphase and tunneling zone

This study presents a simple equation for the conductivity of graphene-filled nanocomposites by considering graphene size, amount of filler in the net, interphase deepness, tunneling size, and properties of the net. The amount of nanoparticles in the net is related to the percolation threshold and effective filler content. The novel model is analyzed using the measured conductivity of numerous examples and the factors' impacts on the conductivity. Both experienced data and parametric examinations verify the correctness of the novel model. Among the studied factors, filler amount and interphase deepness implicitly manage the conductivity from 0 to 7 S/m. It is explained that the interphase amount affects the operative quantity of nanofiller, percolation threshold, and amount of nets.

How hydrogen-bonding interactions and nanocrystal aspect ratios influence the morphology and mechanical performance of polymer nanocomposites reinforced with cellulose nanocrystals

The performance of polymer nanocomposites reinforced with cellulose nanocrystals (CNCs) is complicated by several factors, primarily CNC-polymer and polymer-polymer interactions. Our current work specifically seeks to address the effects of CNC geometry, CNC-polymer and polymer-polymer interactions on the structure and non-linear mechanical performance of nanocomposites prepared using two water-soluble polymers, polyethylene oxide (PEO) and polyvinyl alcohol (PVA), having different morphological and structural characteristics. PEO and PVA are chosen since they are compatible with CNCs, however, they interact quite differently with CNCs and result in different reinforcement mechanisms. PEO and PVA interact with CNCs via a nucleating effect and H-bonding, which influence the polymer structure in two opposite directions. The nucleating effect tends to lead the polymer chains to form more ordered structures, whereas H-bonding interactions restrict the mobility of the polymer chains. Since PEO has weaker interactions amongst molecular chains than PVA, the properties of PEO are more significantly influenced by CNCs.

Nanocellulose for Sustainable Water Purification

Nanocelluloses (NC) are nature-based sustainable biomaterials, which not only possess cellulosic properties but also have the important hallmarks of nanomaterials, such as large surface area, versatile reactive sites or functionalities, and scaffolding stability to host inorganic nanoparticles. This class of nanomaterials offers new opportunities for a broad spectrum of applications for clean water production that were once thought impractical. This Review covers substantial discussions based on evaluative judgments of the recent literature and technical advancements in the fields of coagulation/flocculation, adsorption, photocatalysis, and membrane filtration for water decontamination through proper understanding of fundamental knowledge of NC, such as purity, crystallinity, surface chemistry and charge, suspension rheology, morphology, mechanical properties, and film stability. To supplement these, discussions on low-cost and scalable NC extraction, new characterizations including solution small-angle X-ray scattering evaluation, and structure-property relationships of NC are also reviewed. Identifying knowledge gaps and drawing perspectives could generate guidance to overcome uncertainties associated with the adaptation of NC-enabled water purification technologies. Furthermore, the topics of simultaneous removal of multipollutants disposal and proper handling of post/spent NC are discussed. We believe NC-enabled remediation nanomaterials can be integrated into a broad range of water treatments, greatly improving the cost-effectiveness and sustainability of water purification.

Unravelling the Mechanism of Viscoelasticity in Polymers with Phase-Separated Dynamic Bonds

Incorporation of dynamic (reversible) bonds within polymer structure enables properties such as self-healing, shape transformation, and recyclability. These dynamic bonds, sometimes refer as stickers, can form clusters by phase-segregation from the polymer matrix. These systems can exhibit interesting viscoelastic properties with an unusually high and extremely long rubbery plateau. Understanding how viscoelastic properties of these materials are controlled by the hierarchical structure is crucial for engineering of recyclable materials for various future applications. Here we studied such systems made from short telechelic polydimethylsiloxane chains by employing a broad range of experimental techniques. We demonstrate that formation of a percolated network of interfacial layers surrounding clusters enhances mechanical modulus in these phase-separated systems, whereas single chain hopping between the clusters results in macroscopic flow. On the basis of the results, we formulated a general scenario describing viscoelastic properties of phase-separated dynamic polymers, which will foster development of recyclable materials with tunable rheological properties.

Comparing Percolation and Alignment of Cellulose Nanocrystals for the Reinforcement of Polyurethane Nanocomposites

The reinforcement of polymer nanocomposites can be achieved through alignment or percolation of cellulose nanocrystals (CNCs). Here, we compare the efficacy of these reinforcement mechanisms in thermoplastic polyurethane (PU) elastomer nanocomposites containing thermally stable cotton CNCs. CNC alignment was achieved by melt spinning nanocomposite fibers, while a percolating CNC network was generated by solvent casting nanocomposite films with CNC contents up to 20 wt %. While in films both the CNCs and the PU matrix were entirely isotropic at all concentrations as confirmed by wide-angle X-ray scattering and birefringence analysis, the CNCs in the fibers exhibited a preferential orientation, which improved with increasing CNC concentration. Increasing the CNC concentration in the fibers reduces, however, the alignment of the PU chains, resulting in an entirely isotropic PU matrix at high CNC contents. The mechanical properties of films and fibers were evaluated using stress-strain measurements. Nanocomposite fibers with low CNC content exhibited superior stiffness, extensibility, and strength compared to the films, while the films displayed superior mechanical properties at high CNC concentrations. These findings are rationalized using common semiempirical models describing the reinforcing effects of CNC alignment in fibers (Halpin-Tsai) and CNC percolation in films (percolation model). The formation of a percolating CNC network leads to a stronger reinforcement than CNC alignment, as the reinforcing effect of the latter is limited by the comparably low aspect ratio of CNCs extracted from cotton. As a consequence, above the percolation threshold for cotton CNCs, isotropic nanocomposite PU films show a higher stiffness than aligned nanocomposite PU fibers.

Understanding the Mechanical Reinforcement of Metal-Organic Framework-Polymer Composites: The Effect of Aspect Ratio

The aspect ratio (AR) of filler particles is one of the most critical determinants for the mechanical properties of particle-reinforced polymer composites. However, it has been challenging to solely study the effect of particle AR due to the difficulties of controlling AR without altering the physical and chemical properties of the particle. Herein, we synthesized PCN-222, a zirconium-based porphyrinic metal-organic framework (MOF) with preferential longitudinal growth as a series of particles with ARs increasing from 3.4 to 54. The synthetic MOF conditions allowed for the chemical properties of the particles to remain constant over the series. The particles were employed as reinforcers for poly(methyl methacrylate) (PMMA). MOF-polymer composite films were fabricated using doctor-blading techniques, which facilitated particle dispersion and alignment in the PMMA matrix, as revealed by optical microscopy and wide-angle X-ray diffraction. Mechanical measurements showed that both elastic and dynamic moduli increased with particle AR and particle concentrations but started to decrease as particle loading increased beyond 0.5 wt % (1.12 vol %). The data obtained at low particle loadings were fitted well with the Halpin-Tsai model. In contrast, the percolation model and the Cox model were unable to adequately fit the data, indicating the mechanical reinforcement in our system mainly originated from efficient load transfer between particles and the matrix in the particle orienting direction. Finally, we showed that the thermal stability of composite films increased with the addition of MOF particles because of the high thermal degradation temperature and restricted polymer chain mobility.

Effect of Nanoscale Confinement on Polymer-Infiltrated Scaffold Metal Composites

Most research on polymer composites has focused on adding discrete inorganic nanofillers to a polymer matrix to impart properties not found in polymers alone. However, properties such as ion conductivity and mechanical reinforcement would be greatly improved if the composite exhibited an interconnected network of inorganic and polymer phases. Here, we fabricate bicontinuous polymer-infiltrated scaffold metal (PrISM) composites by infiltrating polymer into nanoporous gold (NPG) films. Polystyrene (PS) and poly(2-vinylpyridine) (P2VP) films are infiltrated into the ∼43 nm diameter NPG pores via capillary forces during thermal annealing above the polymer glass transition temperature (T_g). The infiltration process is characterized in situ using spectroscopic ellipsometry. PS and P2VP, which have different affinities for the metal scaffold, exhibit slower segmental dynamics compared to their bulk counterparts when confined within the nanopores, as measured through T_g. The more attractive P2VP shows a 20 °C increase in T_g relative to its bulk, while PS only shows a 6 °C increase at a comparable molecular weight. The infiltrated polymer, in turn, stabilizes the gold nanopores against temporal coarsening. The broad tunability of these polymer/metal hybrids represents a unique template for designing functional network composite structures with applications ranging from flexible electronics to fuel cell membranes.

Tailoring renewable materials via plant biotechnology

Plants inherently display a rich diversity in cell wall chemistry, as they synthesize an array of polysaccharides along with lignin, a polyphenolic that can vary dramatically in subunit composition and interunit linkage complexity. These same cell wall chemical constituents play essential roles in our society, having been isolated by a variety of evolving industrial processes and employed in the production of an array of commodity products to which humans are reliant. However, these polymers are inherently synthesized and intricately packaged into complex structures that facilitate plant survival and adaptation to local biogeoclimatic regions and stresses, not for ease of deconstruction and commercial product development. Herein, we describe evolving techniques and strategies for altering the metabolic pathways related to plant cell wall biosynthesis, and highlight the resulting impact on chemistry, architecture, and polymer interactions. Furthermore, this review illustrates how these unique targeted cell wall modifications could significantly extend the number, diversity, and value of products generated in existing and emerging biorefineries. These modifications can further target the ability for processing of engineered wood into advanced high performance materials. In doing so, we attempt to illuminate the complex connection on how polymer chemistry and structure can be tailored to advance renewable material applications, using all the chemical constituents of plant-derived biopolymers, including pectins, hemicelluloses, cellulose, and lignins.

Development and Characterization of Electrospun Fiber-Based Poly(ethylene-co-vinyl Alcohol) Films of Application Interest as High-Gas-Barrier Interlayers in Food Packaging

In the present study, poly(ethylene-co-vinyl alcohol) with 44 mol % ethylene content (EVOH44) was managed to be processed, for the first time, by electrospinning assisted by the coaxial technology of solvent jacket. In addition to this, different suspensions of cellulose nanocrystals (CNCs), with contents ranging from 0.1 to 1.0 wt %, were also electrospun to obtain hybrid bio-/non-bio nanocomposites. The resultant fiber mats were thereafter optimally annealed to promote interfiber coalescence at 145 °C, below the EVOH44 melting point, leading to continuous transparent fiber-based films. The morphological analysis revealed the successful distribution of CNCs into EVOH44 up to contents of 0.5 wt %. The incorporation of CNCs into the ethylene-vinyl alcohol copolymer caused a decrease in the crystallization and melting temperatures (TC and Tm) of about 12 and 7 °C, respectively, and also crystallinity. However, the incorporation of CNCs led to enhanced thermal stability of the copolymer matrix for a nanofiller content of 1.0 wt %. Furthermore, the incorporation of 0.1 and 0.5 wt % CNCs produced increases in the tensile modulus (E) of ca. 38% and 28%, respectively, but also yielded a reduction in the elongation at break and toughness. The oxygen barrier of the hybrid nanocomposite fiber-based films decreased with increasing the CNCs content, but they were seen to remain high barrier, especially in the low relative humidity (RH) regime, i.e., at 20% RH, showing permeability values lower than 0.6 × 10-20 m3·m·m-2·Pa-1·s-1. In general terms, an optimal balance in physical properties was found for the hybrid copolymer composite with a CNC loading of 0.1 wt %. On the overall, the present study demonstrates the potential of annealed electrospun fiber-based high-barrier polymers, with or without CNCs, to develop novel barrier interlayers to be used as food packaging constituents.

Photonic Thin Films Assembled from Amphiphilic Cellulose Nanofibrils Displaying Iridescent Full-Colors

Self-assembly of nanoparticles (NPs) to form structural colors offers promising opportunities for developing electronic, optoelectronic, and magnetic devices. In this regard, we reported co-assembly of cellulose nanofibrils (CNFs) and graphene to produce colored thin films. We demonstrated that biomimetic iridescent "peacock feather"-like full-color thin films can be generated by simple evaporation of aqueous suspensions on a surface tension confined, optically symmetric indium tin oxide-coated polyethylene terephthalate substrate. Amphiphilic CNFs serve dual functions to attract hydrophobic graphene via van der Waals interactions and to disperse hydrophilically and anionically CNF-tethered graphene while regulating surface tension to induce capillary and Marangoni flows in the force fields and construct thickness variation during dewetting. These CNF-graphene thin films exhibit full-color patterns and function as tunable light and moisture actuators. This approach has high potential to be applied to assemble other metal or metal oxide NPs for fast, simple, and robust fabrication without involving any complex lithography and external fields.

Preparation of collagen/cellulose nanocrystals composite films and their potential applications in corneal repair

As the main component of the natural cornea, collagen (COL) has been widely applied to the construction of corneal repair materials. However, the applications of collagen are limited due to its poor mechanical properties. Cellulose nanocrystals (CNCs) possess excellent mechanical properties, optical transparency and good biocompatibility. Therefore, in this study, we attempted to introduce cellulose nanocrystals into collagen-based films to obtain corneal repair materials with a high strength. CNCs were incorporated at 1, 3, 5, 7 and 10 wt%. The physical properties of these composite films were characterized, and in vitro cell-based analyses were also performed. The COL/CNC films possessed better mechanic properties, and the introduction of CNCs did not affect the water content and light transmittance. The COL/CNC films demonstrated good biocompatibility toward rabbit corneal epithelial cells and keratocytes in vitro. Moreover, the collagen films with appropriate ration of CNCs effectively induced the migration of corneal epithelial cells and inhibited the myofibroblast differentiation of keratocytes. A collagen film with 7 wt% CNCs displayed the best combination of physical properties and biological performance in vitro among all the films. This study describes a nonchemical cross-linking method to enhance the mechanical properties of collagen for use in corneal repair materials and highlights potential application in corneal tissue engineering.

Well-Dispersed Cellulose Nanofiber in Low Density Polyethylene Nanocomposite by Liquid-Assisted Extrusion

Two different liquid assisted processing methods: internal melt-blending (IMB) and twin-screw extrusion (TWS) were performed to fabricate polyethylene (PE)/cellulose nanofiber (CNF) nanocomposites. The nanocomposites consisted maleic anhydride-grafted PE (PEgMA) as a compatibilizer, with PE/PEgMA/CNF ratio of 97/3/0.5–5 (wt./wt./wt.), respectively. Morphological analysis exhibited that CNF was well-dispersed in nanocomposites prepared by liquid-assisted TWS. Meanwhile, a randomly oriented and agglomerated CNF was observed in the nanocomposites prepared by liquid-assisted IMB. The nanocomposites obtained from liquid-assisted TWS exhibited the best mechanical properties at 3 wt.% CNF addition with an increment in flexural strength by almost 139%, higher than that of liquid-assisted IMB. Results from this study indicated that liquid feeding of CNF assisted the homogenous dispersion of CNF in PE matrix, and the mechanical properties of the nanocomposites were affected by compounding method due to the CNF dispersion and alignment.

Bacterial cellulose micro-nano fibres for wound healing applications

Bacterial cellulose (BC) is cellulose produced by a few limited species of bacteria in given conditions. BC has many remarkable properties such as its attractive mechanical properties, water uptake ability and biocompatibility which makes it a very desirable material to be used for wound healing. Inherently due to these important properties, the material is very resistant to easy processing and thus difficult to produce into useful entities. Additionally, being rate limited by the dependency on bacterial production, high yield is difficult to obtain and thus secondary material processing is sought after. In this review, BC is explained in terms of synthesis, structure and properties. These beneficial properties are directly related to the material's great potential in wound healing where it has also been trialled commercially but ultimately failed due to processing issues. However, more recently there has been increased frequency in scientific work relating to BC processing into hybrid polymeric fibres using common laboratory fibre forming techniques such as electrospinning and pressurised gyration. This paper summarises current progress in BC fibre manufacturing, its downfalls and also gives a future perspective on how the landscape should change to allow BC to be utilised in wound care in the current environment.

Development of Expanded Takayanagi Model for Tensile Modulus of Carbon Nanotubes Reinforced Nanocomposites Assuming Interphase Regions Surrounding the Dispersed and Networked Nanoparticles

In this paper, we consider the interphase regions surrounding the dispersed and networked carbon nanotubes (CNT) to develop and simplify the expanded Takayanagi model for tensile modulus of polymer CNT nanocomposites (PCNT). The moduli and volume fractions of dispersed and networked CNT and the surrounding interphase regions are considered. Since the modulus of interphase region around the dispersed CNT insignificantly changes the modulus of nanocomposites, this parameter is removed from the developed model. The developed model shows acceptable agreement with the experimental results of several samples. "ER" as nanocomposite modulus per the modulus of neat matrix changes from 1.4 to 7.7 at dissimilar levels of "f" (CNT fraction in the network) and network modulus. Moreover, the lowest relative modulus of 2.2 is observed at the smallest levels of interphase volume fraction ( ϕ i < 0.017), while the highest " ϕ i " as 0.07 obtains the highest relative modulus of 11.8. Also, the variation of CNT size (radius and length) significantly changes the relative modulus from 2 to 20.

Cellulose nanocrystal-reinforced poly(5-triethoxysilyl-2-norbornene) composites

We demonstrate the reinforcement of a previously inaccessible norbornene-silane with a stiff, bio-based nanofiller.

Novel Polyvinyl Alcohol (PVA)/Cellulose Nanocrystal (CNC) Supramolecular Composite Hydrogels: Preparation and Application as Soil Conditioners

In this work, cellulose nanocrystal (CNC) was modified by an ureido-pyrimidinone (UPy) system based on quadruple hydrogen bondings, and CNC-UPy was obtained. Then, this powder was added into polyvinyl alcohol (PVA), and PVA/CNC-UPy composite membranes and hydrogels were prepared. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarizing optical microscopy (POM) and particle size distribution (PSD) were used to characterize CNC-UPy. From the FTIR results, the characteristic peaks of NCO group sat 2270 cm⁻¹ disappeared, indicating the successful synthesis of CNC-UPy. XRD results showed that the modification by UPy may change the structure of CNC and its degree of crystallinity was increased. PSD analysis showed that the particle size of CNC was increased and its size distribution became narrower after modification by UPy groups. The structure and properties of the composite membranes and hydrogels were studied by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA) together with investigation of swelling, sustained release and self-healing performances. DSC curves depicted that the glass transition temperature, T_g, of different PVA membranes was increased with addition of different proportions of CNC-UPy. TGA data showed that the temperature of maximum weight loss rate was increased, which illustrated the enhanced thermal stability of PVA/CNC-UPy composites. Meanwhile, it was also revealed that the PVA/CNC-UPy composite hydrogels possess good self-healing and better sustained release behavior for the soil conditioner, fulvic acid (FA).

Development of mechanical properties in dental resin composite: Effect of filler size and filler aggregation state

The aim of this work was to study the effect of filler size and filler aggregation state on the mechanical properties of dental resin composites evaluated at filler loadings between 20 wt% and up to 76.5 wt%. Non-aggregated silica nanoparticles (SiNP_MPS) (80 nm), doughnut-shaped silica nanoclusters obtained by spray drying (SDSiNP_MPS) (3.5 μm) and amorphous barium-alumina borosilicate microparticles (BaAlBoSi_MPS) (1.0 μm), functionalized by 3-methacryloxypropyl trimethoxysilane (MPS), were the fillers incorporated into resin matrix dental composites composed of triethylene glycoldimethacrylate (TEGDMA), urethane dimethylacrylate (UDMA), bisphenol A polyethylene glycol diether dimethacrylate (Bis EMA), and bisphenol A glycidyl methacrylate (BisGMA) (0.3:0.7:1:1 weight ratio, respectively). The mechanical properties developed in the resin composites were correlated with the formation of percolated-like particle networks, as observed by scanning electron microscopy (SEM), and volume fraction percolation thresholds (ϕ_c) calculated from a percolation model. Resin composites with non-aggregated SiNP_MPS showed an apparent percolation threshold ϕ_c = 0.15 (i.e. 27 wt%); above this filler concentration and up to a volume fraction of particles (ϕ_P) of 0.24 (i.e. 40 wt%) there was an increase in the flexural modulus and the compressive strength of the resin composite. However, a further increase in filler concentration diminished all its mechanical properties due to a decrease in the particle-matrix adhesion strength, demonstrated by the increase in surface roughness and fracture steps as observed by SEM images. On the other hand, a resin composite filled with doughnut-shaped silica nanoclusters (SDSiNP_MPS) showed an apparent percolation threshold ϕ_c = 0.41 (i.e. 60 wt%); increasing filler loading over this concentration generated an improvement in its mechanical properties, except the flexural strength also due to a decrease in the particle-matrix adhesion strength. The resin composites obtained with amorphous individual BaAlBoSi_MPS microparticles (1.0 μm) and BaAlBoSi_MPS microparticle aggregates (ca. 40.0 μm) showed an apparent percolation threshold ϕ_c = 0.41 (i.e. 64 wt%) that promoted an improvement in all their mechanical properties. SEM image of BaAlBoSi_MPS resin composite at high filler loading (≥ 60 wt%) showed a decrease in fracture steps and no presence of voids, indicating a better adhesion between amorphous BaAlBoSi_MPS particles and the polymeric matrix, which explains the improvement of mechanical properties. Resin composites filled exclusively with silica doughnut-shape nanoclusters or amorphous BaAlBoSi_MPS microparticles could develop mechanical properties similar to or even better than those obtained by mixing nanofillers with spherical nanoclusters, which are commonly used in commercial resin composites.

Higher-Order Structure in Amorphous Poly(ethylene terephthalate)/Graphene Nanocomposites and Its Correlation with Bulk Mechanical Properties

Graphene of two different aspect ratios, A _f, was melt mixed with poly(ethylene terephthalate) (PET) to form amorphous PET/graphene composites with less than 5% crystallinity. The higher-order structure and mechanical properties of poly(ethylene terephthalate) (PET) in these composites were investigated using techniques such as differential scanning calorimetry and dynamic mechanical analysis, whereas transmission electron microscopy, melt rheology, and electrical conductivity were used to study the graphene dispersion. A decrease in heat capacity changes, ΔC _p, of PET in nanocomposites at the glass transition temperature, T _g, without T _g change suggests that a rigid amorphous fraction (RAF) of PET was formed at the PET/graphene interface. The stiffening effect of graphene below 1 wt % loading is quite small in the glassy state region and independent of the A _f of graphene. Above 2 wt %, graphene forms a mechanical percolation network with the RAF of PET and the PET chains are geometrically restricted by the incorporation of graphene with a high A _f, resulting in an unexpectedly higher modulus of nanocomposites both below and above T _g.

Five different chitin nanomaterials from identical source with different advantageous functions and performances

Chitin is a renewable and sustainable biomass material that can be converted into various one-dimensional crystalline nanomaterials different in 1) length, 2) diameter, 3) charge density, 4) type of charge, and 5) crystallinity via diverse top-down synthetic methods. These nanomaterials have great potential as sustainable reinforcing and biologically functional materials. The proper design of chitin nanomaterials maximizes their performances in specific applications. Extensive efforts are devoted to understanding each type of chitin nanomaterial produced from different chitin sources; however, few studies have compared different chitin nanomaterials. Herein, we synthesize five different types of chitin nanomaterials from identical sources and compare their physical and chemical properties, including suitability for assorted purposes. Factors 1)-5) are discussed regarding their dominance in determining functionality depending on the specific goals of a) gas barriers, b) mechanical reinforcements, c) dispersibility in various pH aqueous buffers, d) thermal dimensional stability, and e) antibacterial activity. This study gives insights to design new chitin nanomaterial-based materials.

RIGID GRAPH COMPRESSION: MOTIF-BASED RIGIDITY ANALYSIS FOR DISORDERED FIBER NETWORKS

Using particle-scale models to accurately describe property enhancements and phase transitions in macroscopic behavior is a major engineering challenge in composite materials science. To address some of these challenges, we use the graph theoretic property of rigidity to model mechanical reinforcement in composites with stiff rod-like particles. We develop an efficient algorithmic approach called rigid graph compression (RGC) to describe the transition from floppy to rigid in disordered fiber networks ("rod-hinge systems"), which form the reinforcing phase in many composite systems. To establish RGC on a firm theoretical foundation, we adapt rigidity matroid theory to identify primitive topological network motifs that serve as rules for composing interacting rigid particles into larger rigid components. This approach is computationally efficient and stable, because RGC requires only topological information about rod interactions (encoded by a sparse unweighted network) rather than geometrical details such as rod locations or pairwise distances (as required in rigidity matroid theory). We conduct numerical experiments on simulated two-dimensional rod-hinge systems to demonstrate that RGC closely approximates the rigidity percolation threshold for such systems, through comparison with the pebble game algorithm (which is exact in two dimensions). Importantly, whereas the pebble game is derived from Laman's condition and is only valid in two dimensions, the RGC approach naturally extends to higher dimensions.

Nanocomposites of LLDPE and Surface-Modified Cellulose Nanocrystals Prepared by Melt Processing

Cellulose nanocrystals (CNCs) were surface modified by esterification in tetrahydrofuran (THF) at 25 °C using different catalysts and anhydrides bearing different alkyl side chain lengths. Unmodified and acetic anhydride (AcAnh)-modified CNCs were studied as potential nanofillers for linear low-density poly(ethylene) (LLDPE). Nanocomposites were prepared by melt processing. Determination of the size and size distribution of CNCs in the nanocomposites by SEM revealed an enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, since the average size of the aggregates of the modified CNCs (0.5⁻5 μm) was smaller compared to that of the unmodified CNCs (2⁻20 μm). Tensile test experiments revealed an increase in the nanocomposites' stiffness and strain at break-by 20% and up to 90%, respectively-at the CNC concentration of 5 wt %, which is close to the critical percolation concentration. Since the CNC nanofiller simultaneously reduced LLDPE crystallinity, the reinforcement effect of CNCs was hampered. Therefore, the molding temperature was increased to 120 °C, and, in this way, the greatest increase of the Young's modulus was achieved (by ~45%). Despite the enhanced compatibility of the AcAnh-modified CNCs with the LLDPE matrix, no additional effect on the mechanical properties of the nanocomposites was observed in comparison to the unmodified CNC.