Estimation of the in-situ elastic constants of wood pulp fibers in freely dried paper via AFM experiments

Atomic force microscopy-based nanoindentation (AFM-NI) enables characterization of the basic mechanical properties of wood pulp fibers in conditions representative of the state inside a paper sheet. Determination of the mechanical properties under different loads is critical for the success of increasingly advanced computational models to understand, predict and improve the behavior of paper and paperboard. Here, AFM-NI was used to indent fibers transverse to and along the longitudinal axis of the fiber. Indentation moduli and hardness were obtained for relative humidity from 25 % to 75 %. The hardness and the indentation modulus exhibit moisture dependency, decreasing by 75 % and 50 %, respectively, over the range tested. The determined indentation moduli were combined with previous work to estimate the longitudinal and transverse elastic modulus of the fiber wall. Due to the relatively low indentation moduli, the elastic constants are also low compared to values obtained via single fiber testing

INFLUENCE OF RAW MATERIAL CHARACTERISTICS ON THE PULP MOLDING PROCESS

<p><i>Due to the negative impact of fossil-based, plastic packaging on the environment and the demand for sustainability, the molded pulp industry has been growing tremendously in recent years. The sustainable qualities of these packaging materials, as well as certain government regulations and the growing customer demands for a more 'green packaging', is making companies eager to find suitable alternatives to those currently used oil-based forms of packaging. Molded pulp packaging is produced from biodegradable lignocellulosic fibers like wood-based fibers, hemp fibers or other fibrous materials, therefore, it became focus of research and gained importance in industrial applications. Although molded pulp packaging is a rather old technology, as it has been around for over a hundred years now, scientific understanding of the whole process and the needed material properties is incomplete. Here, an overview of the different production procedures will be given. Furthermore, first results of measurements obtained for the so-called thermoforming process will be presented. The goal of this work was to emphasize the importance of understanding the characteristics of the used raw materials in order to optimize the molding process. For this reason, different types of fibrous materials, which are already being used in pulp molding processes and their characteristics, like the lignin content, fiber length distribution, ash content and drainage level, have been compared. </i></p&gt

Fine Cellulosic Materials Produced from Chemical Pulp: the Combined Effect of Morphology and Rate of Addition on Paper Properties

International audienceAmong bio-based reinforcement additives for paper existing on the market, microfibrillated cellulose (MFC) turned out to be a promising material, showing outstanding potential in composites science. Its relevance in papermaking as a new family of paper components was suggested more recently. There remains a number of constraints limiting the promotion of their use in papermaking, mostly related to their high cost and effect on dewatering resistance. Also, contrasting results reported in the literature suggest that the effect of fibrillation rate and quantity of such cellulosic additives in a furnish on the technological paper properties needs further research. The purpose of this study is to produce and characterize different MFC-like fine fibrous materials of varying particle size and degree of fibrillation from the same batch of pulp through mechanical treatment or fractionation. The effect of the thus obtained fine fibrous materials on paper properties is evaluated with respect to their concentration within a fiber furnish. We compared: (i) a mixture of primary and secondary fines isolated from the pulp by means of a purpose-built laboratory pressure screen; (ii) MFC-like fine fibrous materials of increasingly fibrillar character obtained by refining and subsequent steps of high-pressure homogenization. The morphology of the different materials was first characterized using flow cell based and microscopic techniques. The thus obtained materials were then applied in handsheet forming in blends of different proportions to evaluate their influence on paper properties. The results of these experiments indicate that all these products lead to a substantial decrease in air permeability and to improved mechanical properties already at low concentration, independent of the type and morphological character of the added fine cellulosic material. At higher addition rates, only highly fibrillated materials allowed a further considerable increase in tensile and z-strength. These observations should help to allow a more targeted application of this new generation of materials in papermaking, depending on the desired applicatio