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Three types of wood pulp feedstocks were disk refined to produce cellulose nanofibrils at different fineness levels ranging from 50 to 100%, and the resulting aqueous suspensions of cellulose nanofibrils were spray dried. The spray drying experiments were carried out to examine different processing conditions for the different CNF feedstock types and fines level at various suspension concentrations to produce dry samples with free-flowing powder morphologies. The fineness levels and solids contents of CNF suspensions were set to 80% or more and 1.8% or less, respectively. If the solids content of the CNF solutions was high and the fibrillation level was low, plugging was experienced in the spray head because of the high viscosity of the suspensions, resulting in production of poor-quality powders. In terms of energy savings, even if the CNF suspension solids content was increased to 1.5 wt.%, the powder quality and the production yields were excellent. It was confirmed that high-quality powder under 20 µm were produced at a 90% fibrillation level of all CNF feedstocks. The resulting dry CNF powders were characterized to determine particle size distributions and morphological properties via a scanning electron microscope and a laser diffraction particle size analyzer. The particle sizes were smaller at higher fibrillation levels and lower solids content of the CNF suspensions. CNF suspension derived from bleached kraft pulp, the average particle size decreased by 43% and 33% with the lowered solids contents from 1.8–1%, and the increased fineness levels from 80–100%, respectively.

In nature, cellulose nanofibers form hierarchical structures across multiple length scales to achieve high-performance properties and different functionalities. Cellulose nanofibers, which are separated from plants or synthesized biologically, are being extensively investigated and processed into different materials owing to their good properties. The alignment of cellulose nanofibers is reported to significantly influence the performance of cellulose nanofiber-based materials. The alignment of cellulose nanofibers can bridge the nanoscale and macroscale, bringing enhanced nanoscale properties to high-performance macroscale materials. However, compared with extensive reviews on the alignment of cellulose nanocrystals, reviews focusing on cellulose nanofibers are seldom reported, possibly because of the challenge of aligning cellulose nanofibers. In this review, the alignment of cellulose nanofibers, including cellulose nanofibrils and bacterial cellulose, is extensively discussed from different aspects of the driving force, evaluation, strategies, properties, and applications. Future perspectives on challenges and opportunities in cellulose nanofiber alignment are also briefly highlighted.

The stiffness and tensile strength of biopolymers (e.g., polylactic acid (PLA)) are less than desirable for load-bearing applications in their neat form. The use of natural fibers as reinforcements...

The development of new polymer composites is highly dependent on the design of novel fillers that can bring more benefits in the design and control of structure–property–function than conventional ...

In recent years there has been growing interest in developing recycling technologies for composites manufacturing scrap, process waste and end-of-life parts. The focus of this work was to establish processing routes and mechanical property bounds for glass-polypropylene (PP-GF) scrap from the production of parts for truck trailers, automobiles, and rail cars. This study considered PP-GF scrap and demonstrated extrusion-compression molding (ECM) as a viable route for the closed-loop manufacture of composite parts. The results were promising in terms of the strength and modulus retention of the PP-GF recyclate. The tensile strength and modulus was the highest for 50% and 66% recycled content, compared with 100% and 83% recycle content. The flexural strength and modulus of the 100% and 83% recycled compositions was higher than the 66% and 50% recycled content, respectively. The impact energy absorption of the PP-GF recyclate at at all fiber loadings was superior in absorbing energy compared with the incumbent (benchmark) plywood. This work is useful to designers seeking to incorporate recycled materials in their products.

The economic viability of the biofuel industry could be improved by adding a high-value revenue stream for biomass supply chains: bioderived composites for the rapidly expanding large-scale additive manufacturing industry (i.e., 3D printing). Using fibrillated fibers derived from biomass (e.g.

Cellulose nanofibrils (CNFs) have been exploited for different applications, such as nanocomposites, gas separation, flexible electronics, and fuel cells, due to their unique properties. To fulfill...

Microfibrillated cellulose (MFC) is widely used as a reinforcement filler for biocomposites due to its unique properties. However, the challenge of drying MFC and the incompatibility between nanocellulose and polymer matrix still limits the mechanical performance of MFC-reinforced biocomposites. In this study, we used a water-based transesterification reaction to functionalize MFC and explored the capability of oven-dried MFC as a reinforcement filler for polylactic acid (PLA). Remarkably, this oven-dried, vinyl laurate-modified MFC improved the tensile strength by 38 % and Young's modulus by 71 % compared with neat PLA. Our results suggested improved compatibility and dispersion of the fibrils in PLA after modification. This study demonstrated that scalable water-based surface modification and subsequent straightforward oven drying could be a facile method for effectively drying cellulose nanomaterials. The method helps significantly disperse fibrils in polymers and enhances the mechanical properties of microfibrillar cellulose-reinforced biocomposites.

While PLA possesses modest to good strength and stiffness, broader application is hindered by its brittle nature. The aim of this study was to develop strong and tough polymeric materials from renewable biomaterials and understand the underlying interactions and mechanisms. Cellulose nanofibrils (CNFs) and epoxidized soybean oil (ESO) were compounded with poly(lactic acid) (PLA) to create a PLA-CNF-ESO tertiary nanocomposite system. Tensile and dynamic mechanical analyses were performed to see how variations in ESO and CNF content affect mechanical properties such as strength, modulus, ductility, and toughness. It was found that at low CNF levels (10 wt%) the addition of ESO can improve the ductility of the nanocomposites 5- to 10-fold with only slight losses in strength and modulus, while at higher CNF levels (20 and 30 wt%), ESO exhibited little effect on mechanical properties, possibly due to percolation of CNFs in the matrix, dominating stress transfer. Therefore, it is important to optimize CNF and ESO amounts in composites to achieve materials with both high strength and high toughness. Efforts have been made to understand the underlying mechanisms of the mechanical behavior of one class of these composites via thermal, dynamic mechanical, rheological, morphological, and Raman analyses.

Large amounts of plastics are discarded worldwide each year, leading to a significant mass of waste in landfills and pollution to soil, air, and waterways. Upcycling is an efficient way to transform plastic waste into high-value products and can significantly lessen the environmental impact of plastic production/consumption. In this article, current advances and future directions in plastic waste upcycling technologies are discussed. In particular, this review focuses on the production of high-value materials from plastic waste conversion methods, including pyrolysis, gasification, photoreforming, and mechanical reprocessing. Plastic waste compositions, conversion products, reaction mechanisms, catalyst selection, conversion efficiencies, polymer design, and polymer modification are also explored. The main challenges facing the adoption and scale-up of these technologies are highlighted. Suggestions are given for focusing future research and development to increase the efficiency of upcycling practices.

Brittleness is a key barrier for poly(lactic acid) (PLA) toward broader applications. Supertough PLA was achieved by simply mixing a low amount (0.5–1 wt %) of organoalkoxysilane with PLA. Three organosilanes, (3-aminopropyl)triethoxysilane (APTES), 3-(triethoxysilyl)propyl isocyanate (ICPTES), and trimethoxymethylsilane (MTMS), were selected for this study to understand how the functional group on a silane affects the behavior of the PLA-silane hybrids. Remarkable improvements in ultimate tensile strain (up to 12 folds) and tensile toughness (up to 10 folds) were observed in APTES- and ICPTES-modified PLA without any loss in tensile strength and modulus. Glass transition temperatures measured by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) did not show any obvious decrease. We propose that in situ condensation of organosilane and grafting of PLA to form a silica-PLA core–shell nanocomplex may be the reason for the improved mechanical properties. Scanning electron microsco...

Advanced templating techniques have enabled delicate control of both nano- and microscale structures and have helped thrust functional materials into the forefront of society. Cellulose nanomaterials are derived from natural polymers and show promise as a templating source for advanced materials. Use of cellulose nanomaterials in templating combines nanoscale property control with sustainability, an attribute often lacking in other templating techniques. Use of cellulose nanofibers for templating has shown great promise in recent years, but previous reviews on cellulose nanomaterial templating techniques have not provided extensive analysis of cellulose nanofiber templating. Cellulose nanofibers display several unique properties, including mechanical strength, porosity, high water retention, high surface functionality, and an entangled fibrous network, all of which can dictate distinctive aspects in the final templated materials. Many applications exploit the unique aspects of templating with cellulose nanofibers that help control the final properties of the material, including, but not limited to, applications in catalysis, batteries, supercapacitors, electrodes, building materials, biomaterials, and membranes. A detailed analysis on the use of cellulose nanofibers templating is provided, addressing specifically how careful selection of templating mechanisms and methodologies, combined toward goal applications, can be used to directly benefit chosen applications in advanced functional materials.

Cellulose nanomaterials (CNMs) naturally exist in plant biomass. The success of extraction of CNMs opened up a new era of using plant biomass for innovative industrial applications. Because CNMs are abundant, renewable, biodegradable, transparent, light weight and low in cost, they are ideal materials for large volume applications such as packaging, automotive, building and infrastructure. In many potential application areas, CNM-enabled products appear in a composite form, mostly polymer composites. The industrial-scale manufacturing of CNM/thermoplastic composites remains as a set of unsolved problems for academia and industry. A prime challenge in applications is the nanoscale dispersion of CNMs in thermoplastic matrices during melt processing. Both bench-scale and pilot-scale studies have been conducted to solve the dispersion issue of CNMs. In this article, research related to the dispersion of CNMs in thermoplastic matrices during melt processing were critically reviewed. All research papers were classified into three groups: chemically-aided dispersion, physically-aided dispersion and mechanically-aided dispersion. Numerous factors affect the CNM dispersion and the mechanical performance of its nanocomposites. There are material-related factors, including CNM types and forms, polymer matrices, surface modification, coupling agents, etc. Extrusion processing parameters also play a significant role, covering screw rotation speed, extrusion barrel temperature settings and screw design. In addition, the material-related factors interact with the processing-related factors. Understanding all factors and their interactions are important for moving CNM nanocomposites research a step further towards industrial-relevant production, which is the final ambitious goal of this manuscript.

Advanced biocomposites reinforced by abundant biomass-derived fillers can add a revenue stream to enhance the economic viability of biofuel production chains and the energy efficiency of the composite industry. However, the low stiffness of biopolymers limits their use in structural applications. Poplar fibers (mesh size: l -lysine). As a benefit of the amino acid treatment, the tensile Young's moduli of the lysine/poplar/PLA composites increased by up to 68% with the addition of a small amount of lysine, compared with neat PLA. At the same time, the tensile strength, failure strain, and Young's modulus of the poplar/PLA composites all increased after adding only 0.1 wt % of lysine. It has been observed that the lysine content has a significant effect on the decomposition temperature, complex viscosity, storage modulus, crystallization temperature, and crystallinity of composites. The fracture surfaces of the composites with an optimum lysine content had fewer voids and were more compact compared with composites without any lysine. The pores on the surfaces of poplar fibers became more available for the penetration of PLA molecules as a result of lysine addition. Therefore, this study presents a facile method for reinforcing biocomposites with extremely low-cost and environmentally friendly biofillers.

Cellulose nanocrystal (CNC)-based composite films were prepared as a solid electrolyte for alkaline fuel cells. Poly(vinyl alcohol) (PVA) and silica gel hybrid were used to bind the CNCs to form a robust composite film. The mass ratio (i.e., 1 : 1, 1 : 2) of PVA and silica gel was tuned to control the hydrophobicity of the resulting films. Composite films with a range of CNC contents (i.e., 20–60%) were prepared to demonstrate the impact of CNCs on the performance of these materials as a solid electrolyte for alkaline fuel cells. Different from previously reported cross-linked polymer films, CNC-based composite films with 40% hydrophobic binder (i.e., PVA : silica gel = 1 : 2) exhibited simultaneous low water swelling (e.g., ∼5%) and high water uptake (e.g., ∼80%) due to the hydrophilicity and extraordinary dimensional stability of CNCs. It also showed a conductivity of 0.044 and 0.065 S cm−1 at 20 and 60 °C, respectively. To the best of our knowledge, the film with 60% CNC and 40% binder is characterized by the lowest hydroxide conductivity-normalized swelling ratio. Decreased CNC contents (i.e., 40 and 20%) resulted in comparable hydroxide conductivity but a greater swelling ratio. These results demonstrate the advantage of CNCs as a key component for a solid electrolyte for alkaline fuel cells over conventional polymers, suggesting the great potential of CNCs in improving the dimensional stability while maintaining the conductivity of existing anion exchange membranes.

While polymer additive manufacturing (AM) has advanced significantly over the past few decades, the limitations in material properties, speed of manufacture, and part size have relegated this technology to the space of rapid prototyping rather than the legitimate manufacture of end-use parts. Carbon fiber offers a low density, a low coefficient of thermal expansion, and high thermal conductivity and is an ideal material for bringing polymer-based AM from the realm of form and fit to that of form, fit, and function. Use of carbon fiber in AM can improve material properties, reduce the time required to manufacture functional parts compared with traditional subtractive technologies, and reduce warping, thereby enabling a larger possible build envelope. Therefore, the addition of carbon fiber to various AM technologies is of increasing interest in academic and industrial communities. This paper examines the work performed in this fast-growing area to date. Specifically, the effects of fiber reinforcement on the structure and mechanical properties of 3D printed parts are investigated within the body of literature. Upper bounds for tensile properties of carbon fiber composites are theoretically evaluated and compared with experimentally measured values. Moreover, current and potential applications of additively manufactured carbon fiber composites in the context of desktop 3D printing and big area AM are discussed. Recent innovations and industry breakthroughs in this field are also examined. This review is intended to organize and synthesize the present body of work surrounding AM of carbon fiber reinforced plastics, identify the most promising technologies, and prescribe viable research and development paths forward to advance AM from the application space of rapid prototyping to that of functional, load-bearing, end-use parts.

Additive manufacturing, diverging from traditional manufacturing techniques, such as casting and machining materials, can handle complex shapes with great design flexibility without the typical waste. Although this technique has been mainly used for rapid prototyping, interest is growing in using this method to directly manufacture actual parts of complex shape. To use 3D-printing additive manufacturing in wide spread applications, the technique and the feedstock materials require improvements to meet the mechanical requirements of load-bearing components. Thus, we investigated the short fiber (0.2 mm to 0.4 mm) reinforced acrylonitrile-butadiene-styrene composites as a feedstock for 3D-printing in terms of their processibility, microstructure and mechanical performance; and also provided comparison with traditional compression molded composites. The tensile strength and modulus of 3D-printed samples increased ~115% and ~700%, respectively. 3D-printer yielded samples with very high fiber orientation in printing direction (up to 91.5 %), whereas, compression molding process yielded samples with significantly less fiber orientation. Microstructure-mechanical property relationships revealed that although the relatively high porosity is observed in the 3D-printed composites as compared to those produced by the conventional compression molding technique, they both exhibited comparable tensile strength and modulus. Furthermore, this phenomena is explained based on the changes in fiber orientation, dispersion andmore » void formation.« less

ORNL worked with American Process Inc. to demonstrate the potential use of bio-based BioPlus® lignin-coated cellulose nanofibrils (L-CNF) as a reinforcing agent in the development of polymer feedstock suitable for additive manufacturing. L-CNF-reinforced polylactic acid (PLA) testing coupons were prepared and up to 69% increase in tensile strength and 133% increase in elastic modulus were demonstrated.

Among the various stationary-storage technologies under development, redox flow batteries (RFBs) offer the greatest potential to deliver inexpensive, scalable, and efficient grid-scale electrical-energy storage. Unlike traditional sealed batteries, in a flow battery power and energy are decoupled. Cell area and cell count in the stack determine the device power, and the chemical storage volume determines the total energy. Grid-scale energy-storage applications require megawatt-scale devices, which require the assembly of hundreds of large-area, bipolar cells per power plant. The cell-stack is the single system component with the largest impact on capital cost (due to the large number of highly engineered components) and operating costs (determined by overall round-trip efficiency).