STRUCTURE AND PROPERTIES OF SOME NATURAL CELLULOSIC FIBRILS

This study examines the properties of cellulosic fibrillar fines manufactured from different pulp raw materials, bleached softwood kraft (bswk), themomechanical (TMP), and non-wood sisal. Chemical characterisation showed that the carbohydrate and lignin contents of sisal were between those of bswk and TMP. Sisal was found to contain about three times more calcium than bswk and TMP. Measurements from the immobilization kinetics showed that the solids content after immobilization was highest for the sisal suspension followed by TMP and bswk. This indicates that the dewatering ability of the fines suspension increases in the order bswk<TMP<sisal. The loss modulus (G'') was maxmium with bswk, indicating that the greatest viscous dissipation before immobilisation took place in the bswk suspension. The strength properties of fines sheets decreased in the order bswk>TMP>sisal. This is due to the highly fibrillated nature of bswk fines, as illustrated by fibre saturation point (FSP), differential scanning calorimetric (DSC), and hydrodynamic specific volume (HSV) measurements

EffEct of ionic form on fibrillation and thE dEvElopmEnt of thE fibrE nEtwork strEngth during thE rEfining of thE kraft pulps

abstract the refining of unbleached kraft pulps in their na + -form has shown energy saving potential. in this study, the fibre network strength of unrefined and laboratory refined samples of an unbleached neverdried kraft pulp in different ionic forms was studied. the external fibrillation and the fibre flexibility were also studied. the objective was to investigate whether the improved refinability of fibres in the na + -form could be related to the floc network strength or to fibrillation characteristics. the results showed that the rheological properties may not explain the improved refinability of fibres in the na + -form, since fibres showed similar rheological properties regardless of their ionic form. measurements using the mms (pulp measuring system) showed that fibres refined in the na + -form have a larger amount of external fibrillation, and microscopic investigation confirmed that the characteristics of the fibrils are different for fibres refined in the na + -form from those of fibres refined in the h + -or ca 2+ -forms. the observed differences in fibrillation and improved refinability may be explained by the co-operation of electrostatic interactions of the fibre wall and the mechanical forces applied during refining

Mechanical and thermal behavior of natural fiber-polymer composites without compatibilizers

The present study aims at understanding the mechanical and thermal properties of natural fibers in a polymer matrix without strong adhesionbetween the two constitutes. For this purpose, four types of pulps, which arerefined and unrefined pine and birch kraft pulps,were used together with polypropylene without any compatibilizer. One constituent pulpbasedand composite pulp fiber-polypropylene handsheets were prepared by standard laboratory sheet preparation method followed by hot pressing process. In addition to these handsheets, pure polypropylene sheets were also formed as the reference. The produced handsheets were testedtodetermine their tensile properties following the ISO 1924-2 standard for paper and board. During these tests, infrared thermal imaging was also carried out with FLIR A655SC thermal camera with frame rate of 200 Hz and thermal resolution of 50 mK so as to investigate the thermal behavior. As a result of the experiments, it was deducedthat the chosen methods produced composites with unsatisfactory properties. In addition, microstructures of the investigated handsheets were analyzed with scanning electronmicroscopy (SEM)indicating theheterogeneous mixing of constituents and existence of material defects, whichwas mainly due to the inherent incompatibility of hydrophilic natural fibers and hydrophobic thermoplastics. The study aims at pavinga way for improved naturalfiber-polymer composite manufacturing methods, a requirement for better understanding the natural fiberand polymer matrix bonding practices.Peer reviewe

On the computational homogenization of three-dimensional fibrous materials

Fibrous materials such as paper, nonwovens, textiles, nanocellulose based-biomaterials, polymer networks and composites are widely used versatile engineering materials. Deformations at the fiber network scale have direct role in their effective mechanical behavior. However, computational description of the deformations is a challenge due to their stochastic characteristics. In consideration to this issue, the current study presents a computational homogenization framework at the fiber network scale to investigate how the fiber properties affect the mechanical properties at material scale. Methodology is based on (I) geometrical, spatial and mechanical modelling of fibers and fiber-to-fiber interactions, (II) formation of fiber network solution domain, boundary nodes on the solution domain and control nodes of the domain bounding the solution domain. The boundary value problem is then defined at the fiber network scale and solved with the proposed framework using the Euclidean bipartite matching coupling the boundary nodes and the control nodes represented in the form of corner, edge and surface nodes. The computed results show that the framework is good at capturing the fibrous material characteristics at different scales and applicable to the solution domains generated with stochastic modelling or image-reconstruction methods resulting in non-conformal meshes with non-matching boundary node distributions.Peer reviewe

Geometrical and spatial effects on fiber network connectivity

For fibrous materials such as nonwoven fabrics, paper and paperboards, inter-fiber bonds play a critical role by holding fibers, thus providing internal cohesion. Being a physical phenomenon, inter-fiber bonds occur at every fiber crossing and can be also geometrically detected. In relation to the idea, a statistical geometrical model was developed to investigate the effects of fiber geometry, (i.e. length and cross-sectional properties), spatial distribution, (i.e. location and orientation), and specimen size on fiber network connectivity, which refers to inter-fiber bonds at fiber crossings. In order to generate the fiber network, a geometrical fiber deposition technique was coded in Mathematica technical computing software, which is based on the planar projections and intersections of fibers and provided as supplementary material to the present article. According to this technique, fiber geometries in discrete rectangular prismatic segments were generated by using uniform distributions of the geometrical and spatial parameters and projected onto the transverse plane. Then, projected geometries were trimmed within the transverse boundaries of the specified specimen shape, rectangular prism in this particular study. After this step, fiber crossings were determined through a search algorithm, which was also used as the basis for the fiber spatial regeneration. Thereafter, fibers were accumulated on top of each other by taking fiber crossings into account and eventually fiber networks based on selected properties were formed. By means of the proposed technique, a series of simulation experiments were conducted on paper fiber networks to investigate the correlation between the fiber network connectivity and fiber length, cross-sectional properties, orientation and specimen length, width and thickness.Peer reviewe

Data-Driven Computational Homogenization Method Based on Euclidean Bipartite Matching

Image processing methods combined with scanning techniques - for example, microscopy or microtomography - are now frequently being used for constructing realistic microstructure models that can be used as representative volume elements (RVEs) to better characterize heterogeneous material behavior. As a complement to those efforts, the present study introduces a computational homogenization method that bridges the RVE and material-scale properties in situ. To define the boundary conditions properly, an assignment problem is solved using Euclidean bipartite matching through which the boundary nodes of the RVE are matched with the control nodes of the rectangular prism bounding the RVE. The objective is to minimize the distances between the control and boundary nodes, which, when achieved, enables the bridging of scale-based features of both virtually generated and image-reconstructed domains. Following the minimization process, periodic boundary conditions can be enforced at the control nodes, and the resultingboundary value problem can be solved to determine the local constitutive material behavior. To verify the proposed method, virtually generated domains of closed-cell porous, spherical particle-reinforced, and fiber-reinforced composite materials are analyzed, and the results are compared with analytical Hashin-Shtrikman and Halpin-Tsai methods. The percent errors are within the ranges from 0.04% to 3.3%, from 2.7% to 14.9%, and from 0.5% to 13.2% for porous, particle-reinforced, and fiber-reinforced composite materials, respectively, indicating that the method has promising potential in the fields of image-based material characterization and computational homogenization.Peer reviewe

The Development and Validation of a Biomechanical Model to Describe Golf Swings: A Focus on Rotational Mechanics and Performance

This work presents the creation, validation, and utility of a new full body biomechanical model to describe the golf swing. The model used 47 retroreflective markers to capture swing data with a 12-camera Vicon MX motion capture system. Motion data was collected at 250Hz, the data was processed, and a 17 segment custom biomechanical model was constructed in Visual3D (c-motion, Derwood, MD). Data from 10 subjects was collected. The swing was divided by 4 event times—Address, Peak Backswing, Impact, and Follow Through—at which the kinematics of the swing were analyzed. Validation results indicated excellent agreement between expected joint angles and joint angles calculated by the Visual3D model (R = 0.999). Kinematic results indicated that X-Factor at Peak Backswing = -43 ± 5°, Lead Shoulder Adduction at Peak Backswing = 76 ± 14°, and Lead Knee Flexion at Impact = 10 ± 9°. Additionally, Trunk Rotation at Address was found to be positively associated with ball carry and clubhead progression at Impact (p = 0.0497 and p = 0.0209, respectively), X-Factor at Peak Backswing and Impact were found to be positively associated with clubhead speed at Impact (p = 0.0028 and p = 0.0013, respectively), and Lead Shoulder Adduction at Peak Backswing and Impact were found to be positively associated with clubhead speed at Impact (p = 0.0093 and p = 0.0459, respectively). The groundwork has been laid for future studies concerning the golf swing. Performance enhancement and injury prevention remain long-term goals