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1.
ACS Omega ; 5(45): 29243-29256, 2020 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-33225155

RESUMO

Herein, colloidal dispersions of alkaline nanoparticles (NPs: CaCO3 and Mg(OH)2) are stabilized by trimethylsilyl cellulose (TMSC) in hexamethyldisiloxane and employed to treat historical wood pulp paper by an effortless dip-coating technique. Both alkaline NPs exhibit high stability and no size and shape changes upon stabilization with the polymer, as shown by UV-vis spectroscopy and transmission electron microscopy. The long-term effect of NP/TMSC coatings is investigated in detail using accelerated aging. The results from the pH-test and back-titration of coated papers show a complete acid neutralization (pH ∼ 7.4) and introduction of adequate alkaline reserve even after prolonged accelerated aging. Scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and infrared and water contact angle measurements showed the introduction of a thin and smooth hydrophobic NP/TMSC coating on the paper fibers. Acid-catalyzed desilylation of TMSC was observed by declining C-Si infrared absorbance peaks upon aging. The CaCO3 coatings are superior to Mg(OH)2 with respect to a reduced yellowing and lower cellulose degradation upon aging as shown by colorimetric measurements and degree of polymerization analysis. The tensile strength and folding endurance of coated and aged papers are improved to 200-300 and 50-70% as illustrated by tensile strength and double folding endurance measurements.

2.
Materials (Basel) ; 13(12)2020 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-32560465

RESUMO

Ultrasonic liquid penetration (ULP) measurements of porous sheets have been applied for a variety of purposes ranging from determining liquid absorption dynamics to surface characterization of substrates. Interpretation of ULP results, however, is complex as the ultrasound signal can be affected by several mechanisms: (1) air being replaced by the liquid in the substrate pores, (2) air bubbles forming during penetration, and (3) structural changes of the substrate due to swelling of the substrate material. Analyzing tailored liquids and substrates in combination with contact angle measurements we are demonstrating that the characteristic shape of the ULP measurement curves can be interpreted in terms of the regime of liquid uptake. A fast and direct decline of the curve corresponds to capillary penetration, the slope of the curve indicates the penetration speed. A slow decline after a previous maximum in the signal can be related to diffusive liquid transport and swelling of the substrate material.

3.
Carbohydr Polym ; 235: 115946, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32122482

RESUMO

Atomistic modelling of cellulose has widely been investigated for years using molecular dynamics simulations. In this paper, we model Iß crystalline cellulose as well as develop a model including dislocations in between the crystal regions. The model including dislocations shows a tensile modulus of 109 GPa, 25% lower than that of the fully crystalline model (146 GPa). The change in dihedral angle preferences is analysed, and its effect on hydrogen bonding pattern is assessed. How presence of hydrogen bonds contributes to elastic properties of cellulose nano-fibrils is shown. Effect of water on the elastic modulus of fibrils is also investigated. Moreover, an illustration is given of how the tensile behaviour of fibrils is controlled by a synergy between the geometry changes occurring at the glycosidic linkage, reflected by specific torsional and glycosidic angles. These findings can be useful in further modelling of cellulosic fibrils at the atomistic and coarse-grained scales.

4.
Carbohydr Polym ; 235: 115964, 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32122498

RESUMO

This review focuses on cationic starches with a low degree of substitution (<0.06) which are mainly used for production of paper-based products. After a brief introduction on starch in general, cationization pathways and importance of cationic starches in paper production, this review emphasizes on the analytical challenges from different perspectives. These include the different length scales of starches when in solution: the macromolecular level, their assembly into nm aggregates and finally hydrocolloids with hundreds of nanometers of diameter. We give an overview on the current state of the art on the analysis of such challenging samples and aim at providing a guideline for obtaining and presenting reliable analytical data.


Assuntos
Papel , Amido/análise , Cátions/análise , Estrutura Molecular , Tamanho da Partícula , Propriedades de Superfície
5.
PLoS One ; 15(2): e0228543, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32045426

RESUMO

Two molecules, 7-(diethylamino)coumarin-3-carbohydrazide (DCCH) and fluorescein-5-thiosemicarbazide (FTSC) were investigated in different solvents, under varying pH conditions regarding their spectroscopic properties for the usage as a Förster Resonance Energy Transfer (FRET) pair to study the molecular interaction between cellulosic surfaces. All the relevant spectroscopic properties to determine the Förster distance were measured and the performance as a FRET system was checked. From the results, it is clear that the environmental conditions need to be accurately controlled as both, but especially the FTSC dyes are sensitive to changes. For high enough concentrations positive FRET systems were observed in DMF, DMSO, H2O, THF and alkaline DMF. However due to the low quantum yield of the unmodified DCCH throughout the investigated parameter range and the strong environmental dependency of FTSC, both dyes are not preferable for being used in a FRET system for studying interaction between cellulosic surfaces.


Assuntos
Cumarínicos/química , Fluoresceínas/química , Transferência Ressonante de Energia de Fluorescência/métodos , Hidrazinas/química , Solventes/química , Análise Espectral/métodos , Transferência de Energia/efeitos dos fármacos , Concentração de Íons de Hidrogênio , Solventes/farmacologia , Espectrometria de Fluorescência/métodos , Espectrofotometria Ultravioleta/métodos
6.
Front Chem ; 7: 251, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31041311

RESUMO

An approach for the multilayer density analysis of polysaccharide thin films at the example of cellulose is presented. In detail, a model was developed for the evaluation of the density in different layers across the thickness direction of the film. The cellulose thin film was split into a so called "roughness layer" present at the surface and a "bulk layer" attached to the substrate surface. For this approach, a combination of multi-parameter surface plasmon resonance spectroscopy (SPR) and atomic force microscopy (AFM) was employed to detect changes in the properties, such as cellulose content and density, thickness and refractive index, of the surface near layer and the bulk layer. The surface region of the films featured a much lower density than the bulk. Further, these results correlate to X-ray reflectivity studies, indicating a similar layered structure with reduced density at the surface near regions. The proposed method provides an approach to analyse density variations in thin films which can be used to study material properties and swelling behavior in different layers of the films. Limitations and challenges of the multilayer model evaluation method of cellulose thin films were discussed. This particularly involves the selection of the starting values for iteration of the layer thickness of the top layer, which was overcome by incorporation of AFM data in this study.

7.
Polymers (Basel) ; 10(11)2018 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-30961157

RESUMO

Chitosan is a versatile biopolymer with many interesting functionalities. Its effects on the barrier and mechanical properties of single- or double-coated fibre-based packaging papers in dependence on the applied drying regime were successfully tested. Our investigations revealed chitosan to be a highly robust biopolymer, since the different drying regimes did not alter its contribution to the development of strength and barrier properties of the coated packaging papers. These properties showed a stronger influence of the applied coat weights than of the different drying regimes. The effect of chitosan coatings were quantified by measuring tensile strength (TS), burst strength (BS) and tensile energy absorption (TEA). These revealed that TS, BS and TEA of the coated papers increased significantly. Moreover, the chitosan-coated papers were less permeable against water vapor and air. High grease resistance was observed for double-coated papers, irrespective of the drying regimes. The coated paper surface showed a more hydrophilic character, resulting in lower contact angles and higher water absorption properties. In this study, industrially produced chitosan has been proven to be a renewable, robust biopolymer that can be utilized as an additive to increase strength and the barrier properties of fibre-based materials.

8.
Carbohydr Polym ; 179: 290-296, 2018 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-29111054

RESUMO

Industrially relevant, commercially available cationic starches have been investigated towards their interaction capacity with cellulose thin films derived from trimethylsilyl cellulose (TMSC). The starches used in this study stem from different sources (potato, pea, corn) and featured rather low degrees of substitution ranging from 0.030 to 0.062. The interaction of those starches with cellulose thin films was studied by surface plasmon resonance spectroscopy under flow conditions using concentrations of 1.0mgml-1 and a flow rate of 25µlmin-1. All the investigated starches employed in this study were capable to efficiently interact with the slightly negatively charged cellulose surface leading to irreversible deposition on the surface. As complementary techniques atomic force microscopy and x-ray photoelectron spectroscopy were used to confirm the presence of the starches on the cellulose film surface. Further, dynamic light scattering and size exclusion chromatography measurements were performed to correlate adsorbed amount, particle size and molecular weight of the starches to their interaction behavior.

9.
Soft Matter ; 14(1): 140-150, 2017 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-29220057

RESUMO

Viscoelastic properties are often measured using probe based techniques such as nanoindentation (NI) and atomic force microscopy (AFM). Rarely, however, are these methods verified. In this article, we present a method that combines contact mechanics with a viscoelastic model (VEM) composed of springs and dashpots. We further show how to use this model to determine viscoelastic properties from creep curves recorded by a probe based technique. We focus on using the standard linear solid model and the generalized Maxwell model of order 2. The method operates in the range of 0.01 Hz to 1 Hz. Our approach is suitable for rough surfaces by providing a defined contact area using plastic pre-deformation of the material. The very same procedure is used to evaluate AFM based measurements as well as NI measurements performed on polymer samples made from poly(methyl methacrylate) and polycarbonate. The results of these measurements are then compared to those obtained by tensile creep tests also performed on the same samples. It is found that the tensile test results differ considerably from the results obtained by AFM and NI methods. The similarity between the AFM results and NI results suggests that the proposed method is capable of yielding results comparable to NI but with the advantage of the imaging possibilities of AFM. Furthermore, all three methods allowed a clear distinction between PC and PMMA by means of their respective viscoelastic properties.

10.
Sci Rep ; 5: 10503, 2015 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-26000898

RESUMO

The process of papermaking requires substantial amounts of energy and wood consumption, which contributes to larger environmental costs. In order to optimize the production of papermaking to suit its many applications in material science and engineering, a quantitative understanding of bonding forces between the individual pulp fibers is of importance. Here we show the first approach to quantify the bonding energies contributed by the individual bonding mechanisms. We calculated the impact of the following mechanisms necessary for paper formation: mechanical interlocking, interdiffusion, capillary bridges, hydrogen bonding, Van der Waals forces, and Coulomb forces on the bonding energy. Experimental results quantify the area in molecular contact necessary for bonding. Atomic force microscopy experiments derive the impact of mechanical interlocking. Capillary bridges also contribute to the bond. A model based on the crystal structure of cellulose leads to values for the chemical bonds. In contrast to general believe which favors hydrogen bonding Van der Waals bonds play the most important role according to our model. Comparison with experimentally derived bond energies support the presented model. This study characterizes bond formation between pulp fibers leading to insight that could be potentially used to optimize the papermaking process, while reducing energy and wood consumption.

11.
Sci Rep ; 3: 2432, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23969946

RESUMO

Paper, a man-made material that has been used for hundreds of years, is a network of natural cellulosic fibres. To a large extent, it is the strength of bonding between these individual fibres that controls the strength of paper. Using atomic force microscopy, we explore here the mechanical properties of individual fibre-fibre bonds on the nanometre scale. A single fibre-fibre bond is loaded with a calibrated cantilever statically and dynamically until the bond breaks. Besides the calculation of the total energy input, time dependent processes such as creep and relaxation are studied. Through the nanometre scale investigation of the formerly bonded area, we show that fibrils or fibril bundles play a crucial role in fibre-fibre bonding because they act as bridging elements. With this knowledge, new fabrication routes can be deduced to increase the strength of an ancient product that is in fact an overlooked high-tech material.


Assuntos
Nanopartículas/química , Nanopartículas/ultraestrutura , Papel , Adsorção , Teste de Materiais , Tamanho da Partícula
12.
J Phys Condens Matter ; 25(4): 045002, 2013 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-23220767

RESUMO

The surface topography of paper fibers is studied using atomic force microscopy (AFM), and thus the surface roughness power spectrum is obtained. Using AFM we have performed indentation experiments and measured the effective elastic modulus and the penetration hardness as a function of humidity. The influence of water capillary adhesion on the fiber-fiber binding strength is studied. Cellulose fibers can absorb a significant amount of water, resulting in swelling and a strong reduction in the elastic modulus and the penetration hardness. This will lead to closer contact between the fibers during the drying process (the capillary bridges pull the fibers into closer contact without storing up a lot of elastic energy at the contacting interface). In order for the contact to remain good in the dry state, plastic flow must occur (in the wet state) so that the dry surface profiles conform to each other (forming a key-and-lock type of contact).


Assuntos
Celulose/química , Papel , Adesividade , Elasticidade , Humanos , Ligação de Hidrogênio , Microscopia de Força Atômica/métodos , Modelos Estatísticos , Pele/patologia , Propriedades de Superfície , Água/química
13.
Rev Sci Instrum ; 83(7): 073902, 2012 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-22852699

RESUMO

We are introducing a method to measure tensile strength of individual fiber-fiber bonds within a breaking force range of 0.01 mN-1 mN as well as the energy consumed during breaking. Until now, such a method was not available. Using a conventional atomic force microscope and a specifically designed sample holder, the desired force and the breaking behavior can be analyzed by two different approaches. First, dynamic loading can be applied, where force-versus-distance curves are employed to determine the proportions of elastic energy and energy dissipated in the bond. Second, static loading is utilized to study viscoelastic behavior and calculate viscoelastic energy contributions. To demonstrate the capability of the proposed method, we are presenting results for breaking strength of kraft pulp fiber-fiber bonds in tensile opening mode. The procedure is by no means restricted to cellulose fibers, it has the potential to quantify joint strength of micrometer-sized fibers in general.

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