Liquid crystalline properties of symmetric and asymmetric end-grafted cellulose nanocrystals

The hydrophilic polymer poly[2-(2-(2-methoxy ethoxy)ethoxy)ethylacrylate] (POEG3A) was grafted onto the reducing end-groups (REGs) of cellulose nanocrystal (CNC) allomorphs, and their liquid crystalline properties were investigated. The REGs on CNCs extracted from cellulose I (CNC-I) are exclusively located at one end of the crystallite, whereas CNCs extracted from cellulose II (CNC-II) feature REGs at both ends of the crystallite, so that grafting from the REGs affords asymmetrically and symmetrically decorated CNCs, respectively. To confirm the REG modification, several complementary analytical techniques were applied. The grafting of POEG3A onto the CNC REGs was evidenced by Fourier transform infrared spectroscopy, atomic force microscopy, and the coil–globule conformational transition of this polymer above 60 °C, i.e., its lower critical solution temperature. Furthermore, we investigated the self-assembly of end-tethered CNC-hybrids into chiral nematic liquid crystalline phases. Above a critical concentration, both end-grafted CNC allomorphs form chiral nematic tactoids. The introduction of POEG3A to CNC-I does not disturb the surface of the CNCs along the rods, allowing the modified CNCs to approach each other and form helicoidal textures. End-grafted CNC-II formed chiral nematic tactoids with a pitch observable by polarized optical microscopy. This is likely due to their increase in hydrodynamic radius or the introduced steric stabilization of the end-grafted polymerPeer ReviewedPostprint (author's final draft

The effect of cellulose nanocrystals on latex and adhesive properties in emulsion- based polymer nanocomposites

Pressure sensitive adhesives (PSAs) adhere quickly and firmly to surfaces with the application of light pressure, and can be removed without leaving a residue. Their mechanical performance is measured by tack, peel strength and shear strength. A balanced combination between the three mechanical performance measurements depends on the specific end-use application and is challenging to achieve. This is particularly so when replacing solvent-based technologies with more sustainable, water-based (i.e., emulsion polymerization) technologies. PSAs synthesized using emulsion polymerization tend to have a lower shear strength due to poor gel network formation. As a result, conventional emulsion-based PSAs suffer from the inability to increase certain adhesive properties (e.g., tack and peel strength) while simultaneously increasing shear strength. Nanomaterials are often used in polymer composites to improve polymer properties (e.g., tensile strength). They are particularly effective in low quantities (e.g., \u3c2 \u3ewt.%) because of their high surface area. Cellulose nanocrystals (CNCs) are a “green alternative” to common nanomaterials and are isolated from natural cellulose. CNCs have been used more commonly, in the past, as rheological modifiers and interface stabilizers.[1] Because CNCs form colloidally stable dispersions in water, they can be incorporated/processed in water-based systems, eliminating the need for organic solvents.[2] The most common method to produce CNCs is through acid hydrolysis with sulfuric acid; this process preferentially degrades the disordered cellulose regions and leaves behind the crystalline CNCs with grafted anionic sulfate half ester groups.[1] The resulting nanoparticles are whisker-shaped and have a high aspect ratio.[3] CNCs provide composite material reinforcement in the range of other nanomaterials. In the past, CNCs have been blended with polymers and significant strength improvements were noted.[4] Our studies demonstrate how to incorporate CNCs in a nanocomposite using an in situ semi-batch emulsion polymerization protocol.[5] PSA nanocomposite films were generated for a broad variety of copolymer systems including monomers such as iso-butyl acrylate, n-butyl acrylate, 2-ethyl hexyl acrylate, methyl methacrylate, styrene and vinyl acetate. In all cases, the monomer composition of the reaction formulations was manipulated to achieve a suitable range of polymer glass transition temperatures. CNC loadings were varied from 0 to 0.5 to 1 wt.% (based on monomer weight). The addition of CNC was shown to significantly and simultaneously increase tack, peel strength, and shear strength.[6] References [1] Dufresne, A., Nanocellulose, De Gruyter, Saint Martin D’Heres Cedex, France 2012. [2] Flauzino Neto, W. P., Mariano, M., da Silva, I. S. V., Silvério, H. A., Putaux, J.-L., Otaguro, H., Pasquini, D., Dufresne, A., Carbohydr. Polym. 2016, 153, 143. [3] Moon, R. J., Martini, A., Nairn, J., Simonsen, J., Youngblood, J., Chem. Soc. Rev., 2011, 40, 3941. [4] Rajisha, K. R., Maria, H. J., Pothan, L. A., Ahmad, Z., Thomas, S., Int. J. Biol. Macromol., 2014, 67, 147. [5] Dastjerdi, Z., Cranston, E. D., Dubé, M. A., Macromol. React. Eng., 2018, in press. [6] Dastjerdi, Z., Cranston, E. D., Dubé, M. A., Int. J. Adh. Adh. 2018, 81, 36-42

Pressure sensitive adhesives produced by in-situ emulsion polymerization of cellulose nanocrystal-poly(nBA-VAc)

Pressure sensitive adhesives (PSAs) are conventionally produced using a variety of polymerization methods such as emulsion, solution, or radiation curing. Environmental concerns favor the development of emulsion polymerization based PSAs.[1] However, maintaining and controlling the PSA properties achievable from solution polymerization in PSAs produced by emulsion polymerization remains challenging. Depending on the particular adhesive application, PSA properties are largely guided by the polymer glass transition temperature and the polymer microstructure. The latter is controlled in a variety of ways but typically via the addition of chain transfer agents and crosslinkers.[2] During the last decades, efforts in PSA property manipulation have included the preparation of nanocomposite latexes by introducing nanomaterials such as titanium dioxide, silica, and carbon nanotubes into the formulations.[3] On the other hand, utilizing cellulose nanocrystals (CNCs) as a sustainable source of reinforcement in polymers is emerging rapidly.[4] CNCs are the product of controlled hydrolysis of plant based tissues, through which crystalline domains of cellulose are isolated from the disordered parts of the raw material. High aspect ratio, surface activity and modulus, as well as non-toxic nature of CNCs make them ideal candidates for use in nanocomposite formulations. More recently, our group have prepared CNC nanocomposite PSAs which were revealed to significantly and simultaneously improve tack, peel strength and shear strength in the PSA films.[5] The ability to improve tack and peel strength without decreasing shear strength overcomes a major challenge in PSA formulation. We will present results from emulsion polymerization of n-butyl acrylate/vinyl acetate/CNC nanocomposite PSAs. We will identify the location of the CNCs relative to the latex particles and show their effect on latex viscosity, gel content, and PSA properties. The goal of these new results is to show how the manipulation of the reaction formulation (e.g., monomer feed ratio, surfactant type) will affect the distribution and relative location of the CNCs in the polymer latex and ultimately the PSA properties. [1] Jovanović, R., Dubé, M. A., J. Macromol. Sci., Part C, 44:1, 1-51, 2004. [2] Qie, L., Dubé, M. A., 46, 1225–1236, 2010. [3] Dastjerdi, Z., Cranston, E. D., Berry, R. Fraschini, C., Dubé, M. A., J. Matls. Sci., submitted January 2018. [4] Lee, K-Y., Aitomäki, Y., Berglund, L. A., Oksman, K., Bismarck, A., Compos. Sci. Technol. 105, 15–27, 2014. [5] Dastjerdi, Z., Cranston, E. D., Dubé, M. A., Macromol. React. Eng., 11, 1700013, 2017. [6] Dastjerdi, Z., Cranston, E. D., Dubé, M. A., Int. J. Adh. Adh., 81, 36-42, 201

Challenges in synthesis and analysis of asymmetrically grafted cellulose nanocrystals via atom transfer radical polymerization

When cellulose nanocrystals (CNCs) are isolated from cellulose microfibrils, the parallel arrangement of the cellulose chains in the crystalline domains is retained so that all reducing end-groups (REGs) point to one crystallite end. This permits the selective chemical modification of one end of the CNCs. In this study, two reaction pathways are compared to selectively attach atom-transfer radical polymerization (ATRP) initiators to the REGs of CNCs, using reductive amination. This modification further enabled the site-specific grafting of the anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) from the CNCs. Different analytical methods, including colorimetry and solution-state NMR analysis, were combined to confirm the REG-modification with ATRP-initiators and PSS. The achieved grafting yield was low due to either a limited conversion of the CNC REGs or side reactions on the polymerization initiator during the reductive amination. The end-tethered CNCs were easy to redisperse in water after freeze-drying, and the shear birefringence of colloidal suspensions is maintained after this process.Peer ReviewedPostprint (author's final draft

Phylesystem: a git-based data store for community-curated phylogenetic estimates

Motivation: Phylogenetic estimates from published studies can be archived using general platforms like Dryad (Vision, 2010) or TreeBASE (Sanderson et al., 1994). Such services fulfill a crucial role in ensuring transparency and reproducibility in phylogenetic research. However, digital tree data files often require some editing (e.g. rerooting) to improve the accuracy and reusability of the phylogenetic statements. Furthermore, establishing the mapping between tip labels used in a tree and taxa in a single common taxonomy dramatically improves the ability of other researchers to reuse phylogenetic estimates. As the process of curating a published phylogenetic estimate is not error-free, retaining a full record of the provenance of edits to a tree is crucial for openness, allowing editors to receive credit for their work and making errors introduced during curation easier to correct. Results: Here, we report the development of software infrastructure to support the open curation of phylogenetic data by the community of biologists. The backend of the system provides an interface for the standard database operations of creating, reading, updating and deleting records by making commits to a git repository. The record of the history of edits to a tree is preserved by git’s version control features. Hosting this data store on GitHub (http://github.com/) provides open access to the data store using tools familiar to many developers. We have deployed a server running the ‘phylesystem-api’, which wraps the interactions with git and GitHub. The Open Tree of Life project has also developed and deployed a JavaScript application that uses the phylesystem-api and other web services to enable input and curation of published phylogenetic statements

Challenges in Synthesis and Analysis of Asymmetrically Grafted Cellulose Nanocrystals via Atom Transfer Radical Polymerization

When cellulose nanocrystals (CNCs) are isolated from cellulose microfibrils, the parallel arrangement of the cellulose chains in the crystalline domains is retained so that all reducing end-groups (REGs) point to one crystallite end. This permits the selective chemical modification of one end of the CNCs. In this study, two reaction pathways are compared to selectively attach atom-transfer radical polymerization (ATRP) initiators to the REGs of CNCs, using reductive amination. This modification further enabled the site-specific grafting of the anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) from the CNCs. Different analytical methods, including colorimetry and solutionstate NMR analysis, were combined to confirm the REG-modification with ATRP-initiators and PSS. The achieved grafting yield was low due to either a limited conversion of the CNC REGs or side reactions on the polymerization initiator during the reductive amination. The end-tethered CNCs were easy to redisperse in water after freeze-drying, and the shear birefringence of colloidal suspensions is maintained after this process.Peer reviewe

Structural Variations in Hybrid All-Nanoparticle Gibbsite Nanoplatelet/Cellulose Nanocrystal Multilayered Films

Cellulose nanocrystals (CNCs) are promising bio-sourced building blocks for the production of high performance materials. In the last ten years, CNCs have been used in conjunction with polymers for the design of multilayered thin films via the layer-by-layer assembly technique. Herein, polymer chains have been replaced with positively charged inorganic gibbsite nanoplatelets (GN) to form hybrid “nanoparticle-only” composite films. A combination of atomic force microscopy and neutron reflectivity experiments was exploited to investigate the growth and structure of the films. Data show that the growth and density of GN/CNC films can be tuned over a wide range during preparation by varying the ionic strength in the CNC suspension and the film drying protocol. Specifically, thin and dense multilayered films or very thick, more porous mixed slabs, as well as intermediate internal structures could be obtained in a predictable manner. The influence of key physicochemical parameters on the multilayer film build up was elucidated and the film architecture was linked to the dominating interaction forces between components. The degree of structural control over these hybrid nanoparticle-only films is much higher than that reported for CNC/polymer films, which offers new properties and potential applications as separation membranes or flame retardant coatings

Phylotastic! Making Tree-of-Life Knowledge Accessible, Reusable and Convenient

Scientists rarely reuse expert knowledge of phylogeny, in spite of years of effort to assemble a great "Tree of Life" (ToL). A notable exception involves the use of Phylomatic, which provides tools to generate custom phylogenies from a large, pre-computed, expert phylogeny of plant taxa. This suggests great potential for a more generalized system that, starting with a query consisting of a list of any known species, would rectify non-standard names, identify expert phylogenies containing the implicated taxa, prune away unneeded parts, and supply branch lengths and annotations, resulting in a custom phylogeny suited to the user's needs. Such a system could become a sustainable community resource if implemented as a distributed system of loosely coupled parts that interact through clearly defined interfaces. Results: With the aim of building such a "phylotastic" system, the NESCent Hackathons, Interoperability, Phylogenies (HIP) working group recruited 2 dozen scientist-programmers to a weeklong programming hackathon in June 2012. During the hackathon (and a three-month follow-up period), 5 teams produced designs, implementations, documentation, presentations, and tests including: (1) a generalized scheme for integrating components; (2) proof-of-concept pruners and controllers; (3) a meta-API for taxonomic name resolution services; (4) a system for storing, finding, and retrieving phylogenies using semantic web technologies for data exchange, storage, and querying; (5) an innovative new service, DateLife.org, which synthesizes pre-computed, time-calibrated phylogenies to assign ages to nodes; and (6) demonstration projects. These outcomes are accessible via a public code repository (GitHub.com), a website (www.phylotastic.org), and a server image. Conclusions: Approximately 9 person-months of effort (centered on a software development hackathon) resulted in the design and implementation of proof-of-concept software for 4 core phylotastic components, 3 controllers, and 3 end-user demonstration tools. While these products have substantial limitations, they suggest considerable potential for a distributed system that makes phylogenetic knowledge readily accessible in computable form. Widespread use of phylotastic systems will create an electronic marketplace for sharing phylogenetic knowledge that will spur innovation in other areas of the ToL enterprise, such as annotation of sources and methods and third-party methods of quality assessment.NESCent (the National Evolutionary Synthesis Center)NSF EF-0905606iPlant Collaborative (NSF) DBI-0735191Biodiversity Synthesis Center (BioSync) of the Encyclopedia of LifeComputer Science

Liquid-state NMR analysis of nanocelluloses

Recent developments in ionic liquid electrolytes for cellulose or biomass dissolution has also allowed for high-resolution 1H and 13C NMR on very high molecular weight cellulose. This permits the development of advanced liquid-state quantitative NMR methods for characterization of unsubstituted and low degree of substitution celluloses, for example, surface-modified nanocelluloses, which are insoluble in all molecular solvents. As such, we present the use of the tetrabutylphosphonium acetate ([P4444][OAc]):DMSO-d6 electrolyte in the 1D and 2D NMR characterization of poly(methyl methacrylate) (PMMA)-grafted cellulose nanocrystals (CNCs). PMMA-g-CNCs was chosen as a difficult model to study, to illustrate the potential of the technique. The chemical shift range of [P4444][OAc] is completely upfield of the cellulose backbone signals, avoiding signal overlap. In addition, application of diffusion-editing for 1H and HSQC was shown to be effective in the discrimination between PMMA polymer graft resonances and those from low molecular weight components arising from the solvent system. The bulk ratio of methyl methacrylate monomer to anhydroglucose unit was determined using a combination of HSQC and quantitative 13C NMR. After detachment and recovery of the PMMA grafts, through methanolysis, DOSY NMR was used to determine the average self-diffusion coefficient and, hence, molecular weight of the grafts compared to self-diffusion coefficients for PMMA GPC standards. This finally led to a calculation of both graft length and graft density using liquid-state NMR techniques. In addition, it was possible to discriminate between triads and tetrads, associated with PMMA tacticity, of the PMMA still attached to the CNCs (before methanolysis). CNC reducing end and sulfate half ester resonances, from sulfuric acid hydrolysis, were also assignable. Furthermore, other biopolymers, such as hemicelluloses and proteins (silk and wool), were found to be soluble in the electrolyte media, allowing for wider application of this method beyond just cellulose analytics.Peer reviewe