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

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

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

Nanocellulose as a natural source for groundbreaking applications in materials science: Todays state

Nanocelluloses are natural materials with at least one dimension in the nano-scale. They combine important cellulose properties with the features of nanomaterials and open new horizons for materials science and its applications. The field of nanocellulose materials is subdivided into three domains: biotechnologically produced bacterial nanocellulose hydrogels, mechanically delaminated cellulose nanofibers, and hydrolytically extracted cellulose nanocrystals. This review article describes todays state regarding the production, structural details, physicochemical properties, and innovative applications of these nanocelluloses. Promising technical applications including gels/foams, thickeners/stabilizers as well as reinforcing agents have been proposed and research from last five years indicates new potential for groundbreaking innovations in the areas of cosmetic products, wound dressings, drug carriers, medical implants, tissue engineering, food and composites. The current state of worldwide commercialization and the challenge of reducing nanocellulose production costs are also discussed.Dana Kralisch and Dagmar Fischer gratefully acknowledge the Free State of Thuringia and the European Social Fund (2016 FGR 0045) for funding. Dagmar Fischer would like to thank Yvette Pötzinger and Berit Karl for the excellent editorial support. Dieter Klemm, Friederike Kramer and Katrin Petzold-Welcke are grateful for the support by the Federal Ministry of Economic Affairs and Energy, ZIM (KF2748903MF4 and KF2386003MF3). Thanks are due to the employees of Jenpolymer Materials Ltd. & Co. KG and the Polymet Jena Association, especially Priv.-Doz. Dr. Wolfgang Fried, and Prof. Dr. Raimund W. Kinne, Experimental Rheumatology Unit, Department of Orthopedics, Jena University Hospital, Germany as well as to Dr. Detlef Gorski and Elke Langhammer, SuraChemicals GmbH, Jena, Germany for effective and helpful cooperation and stimulating interaction. Dieter Klemm and Friederike Kramer would like to thank Katharina Horn for the excellent editorial support. Miguel Gama acknowledges the funding from QREN (“Quadro de Referência Estratégica Nacional”) through the BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020-Programa Operacional Regional do Norte. Tom Lindström acknowledges RISE Bioeconomy for support and permission to publish. Emily Cranston and Stephanie Kedzior are thankful for funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) in the form of a Discovery Grant (RGPIN 402329) and PGSD graduate student scholarship, as well as support from the Faculty of Engineering at McMaster University.info:eu-repo/semantics/publishedVersio

Current characterization methods for cellulose nanomaterials

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Polyelectrolyte multilayer films containing nanocrystalline cellulose

In the past decade, electrostatic layer-by-layer (LBL) assembly has gained attention because it is a facile and robust method to prepare thin polymer films. Due to the industrial importance and natural abundance of cellulose, its incorporation into LBL films is of particular interest. This thesis examines the use of nanocrystalline cellulose, prepared by sulfuric acid hydrolysis of cotton, in polyelectrolyte multilayer films. Conventional solution-dipping and a spin-coating variant of LBL assembly both resulted in chemically defined, reproducible, and smooth films with adjustable properties. Surface morphology was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and film growth was monitored by X-ray photoelectron spectroscopy (XPS) and optical techniques. Orientation of the rod-like cellulose nanocrystals imparted anisotropic film properties, and birefringence was calculated from angle dependent and wavelength dependent optical reflectometry measurements. While spin-coating resulted in radial orientation of the nanocrystals, electrostatic adsorption in a magnetic field led to linear alignment. The internal structure, surface orientation and wettability of these materials were investigated. The attractive and repulsive forces acting close to the surface of the multilayer films in aqueous media were measured by colloid-probe AFM and the interaction forces between the film surfaces and charged colloidal-probes were compared to the predictions of the DLVO theory. The applications and advantages of polyelectrolyte multilayers containing nanocrystalline cellulose and their potential as model cellulose surfaces are discussed

Bottom-up Assembly of Nanocellulose Structures

Nanocelluloses, both cellulose nanofibrils and cellulose nanocrystals, are gaining research traction due to their viability as key components in commercial applications and industrial processes. Significant efforts have been made to understand both the potential of assembling nanocelluloses, and the limits and prospectives of the resulting structures. This Review focuses on bottom-up techniques used to prepare nanocellulose-only structures, and details the intermolecular and surface forces driving their assembly. Additionally, the interactions that contribute to their structural integrity are discussed along with alternate pathways and suggestions for improved properties. Six categories of nanocellulose structures are presented: (1) powders, beads, and droplets; (2) capsules; (3) continuous fibres; (4) films; (5) hydrogels; and (6) aerogels and dried foams. Although research on nanocellulose assembly often focuses on fundamental science, this Review also provides insight on the potential utilization of such structures in a wide array of applications.Peer reviewe