ABSTRACT
Graphene oxide (GO) is a promising membrane material for chemical separations, including water treatment. However, GO has often required postsynthesis chemical modifications, such as linkers or intercalants, to improve either the permeability, performance, or mechanical integrity of GO membranes. In this work, we explore two different feedstocks of GO to investigate chemical and physical differences, where we observe up to a 100× discrepancy in the permeability-mass loading trade-off while maintaining nanofiltration capacity. GO membranes also show structural stability and chemical resilience to harsh pH conditions and bleach treatment. We probe GO and the resulting assembled membranes through a variety of characterization approaches, including a novel scanning-transmission-electron-microscopy-based visualization approach, to connect differences in sheet stacking and oxide functional groups to significant improvements in permeability and chemical stability.
ABSTRACT
A sustainable closed-loop manufacturing would become reality if commodity plastics can be upcycled into higher-performance materials with facile processability. Such circularity will be realized when the upcycled plastics can be (re)processed into custom-designed structures through energy/resource-efficient additive manufacturing methods, especially by approachable and scalable fused filament fabrication (FFF). Here, we introduce a circular model epitomized by upcycling a prominent thermoplastic, acrylonitrile butadiene styrene (ABS) into a recyclable, robust adaptive dynamic covalent network (ABS-vitrimer) (re)printable via FFF. The full FFF processing of ABS-vitrimer overcomes the major challenge of (re)printing cross-linked materials and produces stronger, tougher, solvent-resistant three-dimensional objects directly reprintable and separable from unsorted plastic waste. This study thus offers an imminently adoptable approach for advanced manufacturing toward the circular plastics economy.
ABSTRACT
Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm3, and the room temperature magnetic properties are: intrinsic coercivity Hci = 688.4 kA/m, remanence Br = 0.51 T, and energy product (BH)max = 43.49 kJ/m3 (5.47 MGOe). In addition, tensile tests performed on four dog-bone shaped specimens yielded an average ultimate tensile strength of 6.60 MPa and an average failure strain of 4.18%. Scanning electron microscopy images of the fracture surfaces indicate that the failure is primarily related to the debonding of the magnetic particles from the polymer binder. The present method significantly simplifies manufacturing of near-net-shape bonded magnets, enables efficient use of rare earth elements thus contributing towards enriching the supply of critical materials.
ABSTRACT
One of the main factors responsible for the mechanical and physical properties of nanocomposites is the effectiveness of the interfacial region to transfer loads and mechanical vibrations between the nano-reinforcements and the matrix. Surface functionalization has been the preferred approach to engineer the interfaces in polymer nanocomposites in order to maximize their potential in structural and functional applications. In this study, amine-functionalized cellulose nanofibrils (mCNF-G1) were synthesized via silylation of the hydroxyl groups on the CNF surface using 3-aminopropyltrimethoxysilane (APTMS). To further increase the amine density (mCNF-G2), dendritic polyamidoamine (PAMAM) was grafted onto mCNF-G1 by the Michael addition of methacrylate onto mCNF-G1, followed by the transamidation of the ester groups of methacrylate using ethylenediamine. Compared to native CNF-reinforced, poly(l-lactide) (PLLA) nanocomposites, amine-functionalized CNF exhibited significantly improved dispersion and interfacial properties within the PLLA matrix due to the grafting of PLLA chains via aminolysis. It is also a more effective nucleating agent, with 15% mCNF-G1 leading to a crystallinity of 32.5%, compared to 0.1 and 8.7% for neat PLLA and native CNF-reinforced composites. We have demonstrated that APTMS-functionalized CNF (mCNF-G1) significantly improved the tensile strength compared to native CNF, with 10% mCNF-G1 being the most effective (i.e., >100% increase in tensile strength). However, we also found that excessive amines on the CNF surface (i.e., mCNF-G2) resulted in decreased tensile strength and modulus due to PLLA degradation via aminolysis. These results demonstrate the potential of optimized amine-functionalized CNF for future renewable material applications.
