Paper is susceptible to chemical degradation through hydrolysis and oxidation, resulting in embrittlement and failure. Understanding the embrittlement process is important to ensure the preservation and longevity of historical paper-based documents. However, the complex and architectured paper microstructure is a major challenge for fully understanding this process. Two papers with different microstructures were artificially aged under hydrolytic and oxidative exposure conditions, and the consequences of ageing were studied. The fibre embrittlement, the fibre–fibre bonds deterioration, and the evolution of paper microstructure upon ageing are evaluated through macroscopic and localised mechanical tests, as well as through morphological observations at the microscopic scale. It was concluded, from the different tests in the two principal orientations of the paper, that fibre embrittlement plays a more significant role in the embrittlement process than fibre–fibre bonds deterioration. Specifically, the cellulose chain scissions led to fibre embrittlement, irrespective of the oxidative or hydrolytic nature of the chemical degradation mechanism. Furthermore, we identify a critical degree of polymerisation for cellulose ( DP c ~ 750) below which the evolution of mechanical properties accelerates significantly, regardless of the type of mechanical testing performed. Fibre analysis suggests that the decline in fibre resistance results in fractures occurring under stress at weak points of the fibres, such as kinks or twists.

Microscale measurements of halftone dots allow us to investigate the ink transmittance as a function of the position on the halftone dots and to characterize the edges of the halftone dots. In this work, an optical microscope mounted with a commercial camera and a High Dynamic Range (HDR) capture method were combined to measure accurately the printed dots at the microscale. Each stage of the method development has been quantified and compared to simple imaging. On the equipment, the parameters of acquisition have been optimized: size of the observed area under the microscope, exposure time, and fusion of different images resulting from the HDR method. The development of this method allowed comparing three types of printing: offset, inkjet, and electrophotography. The interest of microscopic analysis is to retrieve information that is not accessible at the macroscopic level: descriptors of the ink dot shape and a more precise model of the light diffusion in paper. Furthermore, variables classically measured at the macroscopic level can be assessed: optical densities and colorimetric values. Compared to the single method, the HDR method makes it possible to measure accurately the print characteristics. The coefficient of variation is reduced from 30% to 5%. The perspective of this work is to provide additional information for authenticating printed documents.

The present study focuses on the extraction and characterization of natural cellulosic tissues from the cactus Opuntia ficus-indica. A major goal is the establishment of a "green" process for fibrous networks extraction that allows for biomass valorization using sustainable plant fibers. This process shall contribute to the eco-friendly concept. Numerous separated fibrous layers (tissues) with intricate structures were obtained from different parts of the plant. Bulk density and thicknesses of the fibrous layers were determined including evaluation of fiber swelling (water uptake test) and detailed arrangement of the fibrous layers according to thickness was given. A good layer distribution and different values of bulk density were obtained for the studied tissues. The macrostructure (topology and geometric parameters) and microstructure (internal and anatomical structures) of fibrous networks were studied using both bright-field microscopy and scanning electron microscopy. A high diversity of fibers having a complex hierarchical structure was observed. The study of the fibrous-networks crystallinity and the thermostability indicate that water-immersion processing ameliorated the thermal stability in some temperature regions. The fibrous networks mechanical studies were examined, and the results showed a good response strength, especially for uniaxial tensile layers, which has led to the highest strength and elastic modulus.

The effect of chitosan additives on the mechanical and hydrophobic properties, and air permeability of paper sheets was investigated. As chitosan additives, molecular chitosan and nanochitosan were used. Molecular chitosan was obtained by dissolving chitosan in 1% acetic acid. Nanochitosan was obtained using a thermocatalytic destruction method. It has been established that chitosan additives improve the mechanical properties of paper sheets (tensile strength in dry and wet states, burst strength). In the case of molecular chitosan, tensile index in dry and wet states increases with increasing chitosan dosage till 2.5-3.0% and then remains constant. It can be explained by the fact that chitosan forms ionic bonds and polyelectrolyte complexes with hemicelluloses and cellulose. At the dosage of 2.5-3.0%, all possible ionic bonds are already formed and further chitosan can form only hydrogen bonds by amino groups with cellulose. In the case of micro-nanochitosan, micro-nanoparticles fill also the submicroscopic voids in the porous structure of paper and create additional bonds. Chitosan additives also improve the hydrophobic properties (decrease of water adsorption, and increase of wetting time) and air permeability of paper sheets.

AbstractThe swelling of dissolving pulps has been investigated by a new method based on the MorfiRanalyser, which is measuring the width variation of thousands of fibres in a cupriethylenediamine (CUEN) solution in a few minutes. Pulps from various origins were analysed coming from softwood, birch wood, eucalyptus wood, kraft pulps, sulphite pulps and ECF and TCF bleached pulps, which were modified by several treatments including chemical (cold caustic extraction, hypochlorite) or enzymatic (cellulase) methods. The swelling was much affected by the crystalline form of cellulose and the hemicellulose content but did not depend neither on the cellulose DP nor on the fibre structure (hardwood vs. softwood). The dissolving pulp reactivity in the viscose process was also assessed by swelling in dilute solutions of cupriethylenediamine (CUEN) instead of the Fock’s method.

Date palm seeds (DS) were subjected to mechanical grinding and then to sodium hydroxide delignification and sodium chlorite single step bleaching. The obtained holocellulose was treated with potassium hydroxide to extract cellulose. The structural features of the isolated cellulosic samples were examined by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The morphological characteristics of the cellulosic preparation were investigated with a fiber morphology analyser (MorFi). The degree of polymerization (DP) was determined by the standard test method for intrinsic viscosity. It was found that cellulose extracted from date seeds (CDS) contained fines (elements with the length under 100 gm and width under 5 m) with a degree of polymerization of 950. The extracted cellulose (CDS) was composed of 90% of amorphous phase and had a monoclinic crystal structure Ip. FTIR spectra showed that the extracted cellulose was free from lignin and hemicelluloses.

The general context of this study is to establish recommendations for the development of digital models in the framework of counterfeiting. To achieve this goal, printed 2D codes were investigated. Visual Basic tools have been developed in order to automate tasks. The present paper allows characterizing the printing process used (conventional and waterless offset); sensitive results were also obtained regarding the kind of printed substrate (coated and uncoated paper). Histograms of area classes were plotted and they revealed that the printing process induced the raise of a new class of small dots not present on the digital file. In addition, two types of counterfeiting methods were carried out and they pointed out that the histograms of the counterfeit codes were different from the original printed code, whatever the attempt of counterfeiting. Furthermore, in these cases, small dots tend to agglomerate and form new area classes of bigger size. The method developed in this study thus allows the identification of the printing process as well as the distinction of true and counterfeit 2D codes.

This study pursued two objectives related to deinking. The first objective deals with the application of fractionation for deinking operations rationalization, which requires all free ink separation in one fraction and treatment in ink removal operations. Following accomplishment of the first objective, the second objective was fractions generation for stratified sheet formation. The first objective requires separation based on length, and the second requires separation by development of surface characteristics. The experimental plan was focused on selective fines separation and further valorization of fiber and fines fractions. It was shown that fractionation by a pressure screening system equipped with a smooth hole basket with 0.25mm perforations was very selective towards fines (free ink, fillers, cellulosic fines) separation in the accepts. Long fibers, as well as specks, were retained in the rejects fraction. Due to the higher selectivity of the micro-hole screen, fibers are retained on the screen basket. Hence, they are not subjected to flotation operations, thereby effectively reducing their probability of being lost during flotation. This essentially translated into a fractionation-deinking concept. It was also shown that 1-stage micro-hole fractionation and fines flotation provided higher yield than conventional direct pulp flotation, though the final residual ink content was high. A multistage fractionation process would allow further reduction in long fiber residual ink. The second objective was achieved by applying hydrocyclone fractionation on the fine and fiber fractions generated.Separation was based on fiber and fines development. This new fractionation strategy allowed production and characterization of four different fractions: well developed fibers/coarse fibers and fibrillar/flake type fines.

In this study, an attempt has been made to determine the mechanical properties of the wood pulp cell wall after pulping, bleaching and refining by means of nanoindentation in comparison with flax and lyocell fibres. Based on the indents performed on single fibre cell wall cross-sections, it has been found that bleaching and refining processes are causing reduction in indentation modulus and hardness values. It is assumed that the reduction is attributed to the change in lignin content as well as microfibril angle. Surprisingly, refined pulp fibres and lyocell have the same hardness and indentation modulus, which conforms that no residual lignin is present in the refined pulp. The bast fibre, flax, extracted without Kraft cooking revealed higher indentation modulus (23 GPa) and hardness (0.50 GPa) compared to wood pulp fibres.

In this work, Ailanthus altissima (tree-of-heaven) wood was analyzed for its chemical, morphological and papermaking properties. The A. altissima wood was cooked under kraft conditions using different active alkali charges and then handsheets were produced with the pulps having a kappa number of 16. Based on structural, strength and optical data it was found that the kraft pulp of A. altissima is not suitable to be used alone for the production of printing and writing papers. Notwithstanding, the handsheets exhibit a favorable value of brightness in comparison to those produced from Eucalyptus globulus pulp (with similar kappa number). Therefore, the wood of A. altissima seems to have a good potential to be used as a partial substitute of the main raw material of the Portuguese pulp industry. In fact, the results showed that when beaten E. globulus and A. altissima pulps were mixed (50:50, w/w), the papermaking properties were comparable to those of beaten eucalypt kraft pulps. Therefore, the use of A. altissima wood seems promising for the production of uncoated wood-free papers, which has advantages both from an economical and environmental perspective.

Paper is constituted of natural fibers and represents a perfect example of structural multifunctional materials. Indeed, its fibrous structure is engineered to fit the different end use properties: both optical and mechanical properties are usually required. These requirements may lead to contradictory needs in terms of structure. The influence of the structure on the physical properties is classically tackled based on standard methods such as the estimation of the porosity. However, this macroscopic property is not sufficient in terms of optimization of the fibrous network. For example, fluid transport has to be controlled either in the bulk of the material or only at its surface in the case of health or printing applications. Consequently, the characterization at the macro-level of the structure has to be complemented with an experimental measurement at the fiber level. The X-ray synchrotron micro-tomography, an imaging technique, is based on X-ray transmission. It allows the structure to be analyzed in 3D. It was carried in a large instrument (ESRF, France). The characterization of samples containing different recycled fibers was carried out. In particular, the influence of the number of cycles of drying-pulping is studied. Both qualitative and quantitative characterizations are obtained.The use of recycled fibers may also be included in the elaboration of materials, taking into account the modification of the fibers in terms of morphology and mechanical properties, essentially flexibility. Mechanical properties (tensile and deformation) constitute the main examples of the analysis showing the effect of the recycling of natural fibers: the decrease in mechanical resistance of the fibrous network is explained in terms of the increase of the global porosity, essentially in the bulk of the materials. The profile of porosity in the thickness direction is found to be essential to understand the evolution of physical properties.

From before 250 years BC until today, paper has been made mainly with natural fibres and always with the same operation units even if production processes have evolved greatly. This chapter highlights the origin of natural fibres and their uses in paper- or boardmaking. Pulp and paper processes are briefly described below in order to give an overview. Main end-use characteristics are then discussed and two paper analyses are explained to illustrate relationships between end-use characteristics, raw material and applied processes. To conclude, some information about the future of board and paper is given.

Unrefined chemical pulps of bleached and unbleached softwood (Scots pine, Pinus sylvestris) and hardwood (Eucalyptus, Eucalyptus globulus) were subjected to indentation tests using a nanoindenter equipped with an AFM scanner. Tests on unbleached pulps revealed no difference in hardness values between softwood and hardwood, but bleaching treatment decreased the hardness values of both pulps. Indentation modulus of 12 GPa was observed for unbleached softwood pulps, which is 25% higher than unbleached hardwood pulps. Bleaching treatment again decreased the indentation modulus of the softwood pulps, whereas it slightly increased the indentation modulus of the hardwood pulps. After bleaching and drying processes, only negligible difference was observed in cell wall mechanical properties (hardness and indentation modulus) between hardwood and softwood pulps. This study is based on latewood pulp fibres.

The present paper discusses the use of Inverse Gas Chromatography (IGC) in characterizing the specific surface of cellulose fibers. Thus, the adsorption capacities of microcrystalline Avicel and of the fibers obtained from bleached kraft hardwood (BHK) were determined, which permitted calculation of the specific surface area of these materials by applying both the Brunauer-Emmett-Teller (BET) equations and the iterative approach. Measurements were carried out in finite concentration conditions. The values obtained, agreeing with those reported in the literature for similar materials, were of about 1.4 and 1.2 m(2)/g, for Avicel and BHK fibers, respectively.

The strength potential of softwood reinforcement pulp is primarily determined by the quality of wood raw material, but it is also highly affected by the fiber damage occurring during pulp processing. This paper presents basic observations on industrial fiber damage, its appearance, quantification, and effects on pulp strength properties in order to provide practical documentation and understanding of fiber damage for future studies. The work was carried out using scanning electron microscopy, commercial fiber deformation analyses, fiber porosity measurements, and pulp strength analyses. According to the SEM images, pulp fibers are quite intact after the blow valve in the studied kraft pulp mill. After this, the damage develops gradually in downstream brown stock processes, and is seen as increased raggedness, increasingly loose texture of the fibers, fiber cell wall porosity, and changes in the fiber form. Strength analyses showed that each process stage has characteristic effects on the deterioration of pulp strength, i.e. brown stock washing induces deformations and physical fiber cell wall damage resulting in a decrease in tear-tensile strength, and oxygen delignification results in a decrease in tear tensile strength but also in a decrease in wet zero span due to the degradation of the hemicellulose-lignin matrix.

Two commercial papers used in industrial applications for pet food packaging were studied. In particular, the grease proof efficiency was determined by standard and home-made industrial methods. The differences in grease-barrier behaviour could be explained by the fluorine atom distribution in the thickness of the samples. The results showed that the concentration and distribution homogeneity of fluorine atoms could lead to different grease proof efficiencies, but also to different physico-chemical properties of the paper surface. which were detrimental to printability.