Enhancing the Matrix-Fiber Interface with a Surfactant Leads to Improved Performance Properties of 3D Printed Composite Materials Containing Cellulose Nanofibrils.

Cellulose nanofibrils (CNFs) exhibit characteristics that make them a desirable addition to new composite materials. CNFs are usable in a wide variety of applications such as coatings, personal and healthcare products, packaging, and advanced structural materials. They can also help overcome some performance issues with objects 3D printed by stereolithography (SLA) including dimensional instability and poor mechanical properties. However, CNFs are hydrophilic, making their dispersion in hydrophobic resins common to SLA difficult. Therefore, improvement of performance properties will not be fully realized. In this work, we treated TEMPO-oxidized CNFs (TOCNFs) with the hydrochloride salt of lauroyl arginate ethyl ester (LAE·HCl), a cationic surfactant, to investigate how this coating would affect the performance properties of multicomponent uncured SLA resins and subsequently printed objects. We hypothesized this coating would enhance the dispersion of the cellulose nanomaterials when compared to their uncoated counterparts, which would lead to quantifiable differences among the sample groups. We found that the viscosity of a commercial 3D printing resin (0.34 Pa·s at 30 Hz) increased by nearly an order of magnitude upon addition of even 1 wt % uncoated TOCNFs (2.96 Pa·s at 30 Hz). Moreover, the tensile strength (19.9(5) MPa) and modulus (0.65(5) GPa) of objects printed from the commercial resin decreased when adding 4 wt % uncoated TOCNF (12.5(2) MPa and 0.58(8) GPa, respectively). In contrast, resins having 4 wt % TOCNFs coated with LAE were less viscous (1.25 Pa·s at 30 Hz), and objects printed from them had enhanced tensile strength (24.7(7) MPa) and modulus (0.78(8) GPa) when compared to both the unadulterated resin and that having uncoated TOCNFs. Our findings show the general utility of using a surfactant with cellulose nanomaterials to homogenize multicomponent resins for 3D printing composite materials with enhanced performance properties.

Improving UV Curing in Organosolv Lignin-Containing Photopolymers for Stereolithography by Reduction and Acylation.

Despite recent successes in incorporating lignin into photoactive resins, lignin photo-properties can be detrimental to its application in UV-curable photopolymers, especially in specialized engineered resins for use in stereolithography printing. We report on chemical modification techniques employed to reduce UV absorption by lignin and the resulting mechanical, thermal, and cure properties of these modified lignin materials. Lignin was modified using reduction and acylation reactions and incorporated into a 3D printable resin formulation. UV-Vis absorption at the 3D printing range of 405 nm was reduced in all modified lignins compared to the unmodified sample by 25% to ≥ 60%. Resins made with the modified lignins showed an increase in stiffness and strength with lower thermal stability. Studying these techniques is an important step in developing lignin for use in UV-curing applications and further the effort to valorize lignin towards commercial use.

Mechanochemically directed metathesis in group 2 chemistry: calcium amide formation without solvent.

Ball milling CaI2 and [KN(SiMe3)2] in a 1 : 1 ratio without solvent, and then extracting the ground material with toluene, yields the synthetically valuable neutral amide [Ca(N(SiMe3)2)2] in good yield, without the contamination by calciate species that complicates solution metathesis routes. The effects on yield of grinding time, milling frequency, and calcium halide identity are also examined.

Dual-emitting film with cellulose nanocrystal-assisted carbon dots grafted SrAl2O4, Eu2+, Dy3+ phosphors for temperature sensing.

In this study, we synthesized a novel dual-emitting fluorescent phosphor from cellulose nanocrystal (CNC)-assisted carbon dots (CDs)-grafted SrAl2O4, Eu2+, Dy3+ (SAO) through a facile core-shell process. The CNC-CDs-coated SAO presents excellent scattered dual-emission and improved water resistance without destruction of the SrAl2O4 crystals. The phosphors were then reacted with coupling amino-silane and assembled with nanofibrillated cellulose skeletons to create flexible isotropic films. The obtained phosphors and hybrid films were characterized via electron microscopy, photoluminescence analysis, and X-ray photoelectron spectroscopy. The results demonstrate that the optical signals of phosphors can be controlled by CDs content. The assembled cellulose films exhibit strong temperature responses, high light-induced scattering, and good flexibility. The luminescent emission of films is highly sensitive to surrounding temperature variation (243-383 K) and good linearity behavior was obtained for such a sensitive sensor. Such flexible nanofibrillated cellulose films are excellent candidates for temperature sensor devices in industrial applications.

Structural changes in lignocellulosic biomass during activation with ionic liquids comprising 3-methylimidazolium cations and carboxylate anions.

BACKGROUND: Lignocellulosic biomass requires either pretreatment and/or fractionation to recover its individual components for further use as intermediate building blocks for producing fuels, chemicals, and products. Numerous ionic liquids (ILs) have been investigated for biomass pretreatment or fractionation due to their ability to activate lignocellulosic biomass, thereby reducing biomass recalcitrance with minimal impact on its structural components. In this work, we studied and compared 1-allyl-3-methylimidazolium formate ([AMIM][HCOO]) to the commonly used 1-ethyl-3-methylimidazolium acetate ([EMIM][CH3COO]) for its potential to activate hybrid poplar biomass and enable high cellulose and hemicellulose enzymatic conversion. Although [EMIM][CH3COO] has been widely used for activation, [AMIM][HCOO] was recently identified to achieve higher biomass solubility, with an increase of 40% over [EMIM][CH3COO]. RESULTS: Since IL activation is essentially an early stage of IL dissolution, we assessed the recalcitrance of [EMIM][CH3COO] and [AMIM][HCOO]-activated biomass through a suite of analytical tools. More specifically, Fourier transform infrared spectroscopy and X-ray diffraction showed that activation using [AMIM][HCOO] does not deacetylate hybrid poplar as readily as [EMIM][CH3COO] and preserves the crystallinity of the cellulose fraction, respectively. This was supported by scanning electron microscopy and enzymatic saccharification experiments in which [EMIM][CH3COO]-activated biomass yielded almost twice the cellulose and hemicellulose conversion as compared to [AMIM][HCOO]-activated biomass. CONCLUSION: We conclude that the IL [AMIM][HCOO] is better suited for biomass dissolution and direct product formation, whereas [EMIM][CH3COO] remains the better IL for biomass activation and fractionation.

Lignin-Containing Photoactive Resins for 3D Printing by Stereolithography.

Generating compatible and competitive materials that are environmentally sustainable and economically viable is paramount for the success of additive manufacturing using renewable materials. We report the successful application of renewable, modified lignin-containing photopolymer resins in a commercial stereolithography system. Resins were fabricated within operable ranges for viscosity and cure properties, using up to 15% modified lignin by weight. A 4-fold increase in ductility in cured parts with higher lignin concentration is noted compared to commercial stereolithography resins. Excellent print quality was seen in modified lignin resins, with good layer fusion, high surface definition, and visual clarity. These materials can be used to generate new products for additive manufacturing applications and help fill vacant material property spaces, where ductility, sustainability, and application costs are critical.

Sustainable Hydrogels Based on Lignin-Methacrylate Copolymers with Enhanced Water Retention and Tunable Material Properties.

Synthesizing lignin-based copolymers would valorize a major coproduct stream from pulp and paper mills and biorefineries as well as reduce the dependence on petrochemical-based consumer goods. In this study, we used organosolv lignin isolated from hybrid poplar ( Populus trichocarpa × P. deltoides) to generate lignin-containing methacrylate hydrogels. The copolymer hydrogels were synthesized by first grafting 2-hydroxyethyl methacrylate (HEMA) onto lignin (OSLH) via esterification and then by free radical polymerization of OSLH with excess HEMA. The copolymer hydrogels were prepared with different stoichiometric ratios of OSLH (e.g., 0, 10, 20, and 40 wt %) with respect to HEMA. Copolymerization with OSLH led to an increase in cross-linking density, which in turn enhanced the hydrogel's material properties; we report up to 39% improvement in water retention, 20% increase in thermostability, and up to a 3 order increase in magnitude of the storage modulus ( G'). The copolymer's properties, such as water retention and glass transition temperature, could be tuned by altering the percent functionalization of lignin OH groups and the ratio of OSLH to HEMA.

Relationship between lignocellulosic biomass dissolution and physicochemical properties of ionic liquids composed of 3-methylimidazolium cations and carboxylate anions.

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIM]Acetate) has been widely used for biomass processing, i.e., to pretreat, activate, or fractionate lignocellulosic biomass to produce soluble sugars and lignin. However, this IL does not achieve high biomass solubility, therefore minimizing the efficiency of biomass processing. In this study, [EMIM]Acetate and three other ILs composed of different 3-methylimidazolium cations and carboxylate anions ([EMIM]Formate, 1-allyl-3-methylimidazolium ([AMIM]) formate, and [AMIM]Acetate) were analyzed to relate their physicochemical properties to their biomass solubility performance. While all four ILs are able to dissolve hybrid poplar under fairly mild process conditions (80 °C and 100 RPM stirring), [AMIM]Formate and [AMIM]Acetate have particularly increased biomass solubility of 40 and 32%, respectively, relative to [EMIM]Acetate. Molecular dynamics simulations suggest that strong interactions between IL and specific plant biopolymers may contribute to this enhanced solubilization, as the calculated second virial coefficients between ILs and hemicellullose are most favorable for [AMIM]Formate, matching the trend of the experimental solubility measurements. The simulations also reveal that the interactions between the ILs and hemicellulose are an important factor in determining the overall biomass solubility, whereas lignin-IL interactions were not found to vary significantly, consistent with literature. The combined experimental and simulation studies identify [AMIM]Formate as an efficient biomass solvent and explain its efficacy, suggesting a new approach to rationally select ionic liquid solvents for lignocellulosic deconstruction.

Structural distortions in M[E(SiMe3)2]3 complexes (M = group 15, f-element; E = N, CH): is three a crowd?

The tris(bistrimethylsilylamido) species P[N(SiMe3)2]3 (1) and As[N(SiMe3)2]3 (2) have been prepared through halide metathesis in high yield. Their single crystal X-ray structures, along with that of Sb[N(SiMe3)2]3 (3), complete the series of structurally authenticated group 15 M[N(SiMe3)2]3 complexes (the bismuth analogue (4) has been previously reported). All four complexes possess the expected pyramidal geometries, with progressively longer M-N bond distances from P to Bi but closely similar N-M-N angles (107-104°). The structures of 1-4 also display distortions that are similar to those in f-element M[N(SiMe3)2]3 and M[CH(SiMe3)2]3 complexes, in which M···(ß-Si-C) interactions have been identified. Such structural features include distorted M-(N,CH)-Si and (N,CH)-Si-C angles and close M···C and M···Si contacts. DFT calculations confirm that there are no M···(ß-Si-C) interactions in 1-4; the bond distortions appear to result from the particular steric crowding that arises in pyramidal M[(N,CH)(SiMe3)2]3 complexes. This is likely the source of the most of the distortions in the structures of the f-element analogues as well, even though the latter possess attractive M···Si-C interactions.

Reaction of platinum(II) diamine and triamine complexes with selenomethionine.

We have reacted [Pt(dien)Cl]Cl, [Pt(en)(D(2)O)(2)](2+), and [Pt(Me(4)en)(D(2)O)(2)](2+) [Me(4)en = N,N,N',N'-tetramethylethylenediamine] with selenomethionine (SeMet). When [Pt(dien)Cl]Cl is reacted with SeMet, [Pt(dien)(SeMet-Se)](2+) is formed; two Se-CH(3) resonances are observed due to the different chiralities at the Se atom upon platination. In a reaction of [Pt(dien)Cl]Cl with an equimolar mixture of SeMet and Met, the SeMet product forms more quickly though a slow equilibrium with approximately equal amounts of both products is reached. [Pt(Me(4)en)(D(2)O)(2)](2+) reacts with SeMet to form [Pt(Me(4)en)(SeMet-Se)(D(2)O)](2+) initially but forms [Pt(Me(4)en)(SeMet-Se,N)](+) ultimately. One stereoisomer of the chelate, assigned to the R chirality at the Se atom, dominates within the first few minutes of reaction. [Pt(en)(D(2)O)(2)](2+) forms a variety of products depending on reaction stoichiometry; when one equivalent or less of SeMet is added, the dominant product is [Pt(en)(SeMet-Se,N)](+). In the presence of excess SeMet, [Pt(en)(SeMet-Se)(2)](2+) is the dominant initially, but displacement of the en ligand occurs leading to [Pt(SeMet-Se,N)(2)] as the eventual product. Displacement of the en ligand from [Pt(en)(SeMet-Se,N)](+) does not occur. In reactions of K(2)PtCl(4) with two equivalents of SeMet, [Pt(SeMet-Se,N)(2)] is formed, and three sets of resonances are observed due to different chiralities at the Se atoms. Only the cis geometric isomers are observed by (1)H and (195)Pt NMR spectroscopy.

Classical versus bridged allyl ligands in magnesium complexes: the role of solvent.

Magnesium allyl complexes are regularly isolated with classical, sigma-bonded ligands, and this has been thought to be their preferred mode of bonding. Density functional theory calculations confirm that such bonding is the most stable mode when coordinated bases are present, but in their absence, pi-bonded forms are expected to be lower in energy. The isolation of the unsolvated [Mg{C(3)(SiMe(3))(2)H(3)}(2)](2) complex supports this prediction, as it is a dinuclear species in which two allyl ligands bridge the metals and display cation-pi interactions with them.

Solution interaction of potassium and calcium bis(trimethylsilyl)amides; preparation of Ca[N(SiMe3)2]2 from dibenzylcalcium.

Ca[N(SiMe(3))(2)](2) (1) is isolated in nearly quantitative yield from the room temperature reaction of Ca(CH(2)Ph)(2)(THF) and HN(SiMe(3))(2) in toluene. A commonly used preparation of 1 involving the reaction of potassium bis(trimethylsilyl)amide, K[N(SiMe(3))(2)] (2), with CaI(2) can produce material that contains substantial amounts of potassium, probably in the form of a calciate such as K[Ca{N(SiMe(3))(2)}(3)]. The favorable formation of K[Ca{N(SiMe(3))(2)}(3)] from 1 and 2 was confirmed with density functional theory calculations. Deliberate doping of solutions of 1 with 2 initially causes only an upfield shift in the single (1)H NMR resonance observed for 1; not until K/Ca ratios exceed 1:1 is the presence of the added potassium obvious by the appearance of an additional peak in the spectrum.