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Natural Additive for Reducing Formaldehyde Emissions in Urea-Formaldehyde Resins
Get PDFThis work studies the use of soy protein as a natural formaldehyde scavenger in wood particleboard production. The protein is incorporated in two forms: a) as a powder, during the blending process of wood particles with urea-formaldehyde binder resin, and b) as an aqueous solution, added at different times during resin synthesis. Analysis of variance (ANOVA) was used to evaluate the signifi cance level of two effects (amount of added soy and time of addition) on internal bond strength, thickness swelling, and formaldehyde content of the resulting panels. The results showed that soy protein can contribute to decrease the formaldehyde content of particleboard panels. Addition in powder form or in solution during the resin condensation step leads to the highest formaldehyde reduction, without signifi cantly affecting the physical properties of the panels
Improved Permeability Properties for Bacterial Cellulose/ Montmorillonite Hybrid Bionanocomposite Membranes by In-Situ Assembling
Get PDFBacterial cellulose/montmorillonite (BCMMT) hybrid bionanocomposite membranes were prepared by in-situ assembling or one-step biosynthesis process. The presence of MMT in BC membranes was confi rmed by thermogravimetric analysis and quantifi ed by mass spectrometry, resulting in bionanocomposites with MMT contents between 7–13 wt%. The incorporation of MMT during BC biosynthesis modifi ed BC morphology and led to lower porosity, even though higher water holding capacity was achieved. Bionanocomposites showed improved thermal stability and water vapor and oxygen gas barrier properties up to 70 and 80% with respect to neat BC membranes. This improvement was related to the tortuous path of gas diffusion created by MMT nanoplatelets due to the high extent of dispersion achieved, as observed by XRD. SEM micrographs confi rmed MMT was fi nely dispersed between BC nanofi brils and a more compact structure was observed as MMT content increased. Thus, the in-situ process can be used as an alternative method to obtain cellulose/MMT hybrid bionanocomposite that would have potential applications as reinforcing element
Mineralization of Poly(lactic acid) (PLA), Poly(3-hydroxybutyrate-co-valerate) (PHBV) and PLA/PHBV Blend in Compost and Soil Environments
Get PDFThe present study investigates the mineralization of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-covalerate) (PHBV), and PLA/PHBV blend in compost and soil burial environments. The mineralization was assayed on the basis of carbon dioxide (CO2) release from the test materials incubated in compost and soil for a period of 200 days. The degradation was followed by means of fragmentation, thermogravimetric (TGA), FTIR spectroscopy and scanning electron microscopy (SEM) analyses. The results showed that PLA, PHBV and blend of PLA/PHBV achieved almost 90% biodegradation under composting conditions, while PHBV, PLA/PHBV blend and PLA respectively achieved only 35%, 32% and 4% biodegradation under soil burial conditions. The results of crystallinity, thermal degradation, microstructure and surface morphology analyzed by TGA, FTIR and SEM indicated that the blending approach and different environmental conditions in soil and compost were the most influencing parameters for the ultimate biodegradation of these biobased polymers
Characterization Methodology for Biological Plywoods Based on Characteristic Cross-Section Patterns
Get PDFBiological plywoods are solid analogues of liquid crystalline phases whose building blocks, including cellulose, collagen and chitin, present multifunctionality, providing in some cases protection, camouflage, self-healing and/or adaptability to the surrounding environment. The 3D ordered structure is the main factor for these fascinating properties, and the assessment of the structure-property relationship will be a powerful tool in terms of future material design and innovation. Cross-section observations lead to characteristic patterns depending on the specific arrangement of the plywood’s building blocks. Twisted plywood architectures, known as the Bouligand structure, lead to the widely observed arced patterns which can be ideal or nonideal depending on whether the relationship between the twist angle and the spatial coordinate is linear or not. The latter is the case of nonideal and the projected arcs to the incision plane do not have a constant periodicity. On the other hand, orthogonal plywoods project into herringbone patterns when the incision angle is adequate. In either case, arcs or herringbones, key characteristic variables, have been identified that provide quantitative means that relate them to structural variables such as the pitch and the helix location. Based on this quantitative information we proposed a methodology to characterize the plywoods when these characteristic patterns are accessible. The method has been validated using in-vivo and in-silico observations, where the latter were obtained using Mayavi, a general purpose 3D visualization software. In this article we present a new analysis of plywoods’ mechanics using Krenchel’s formalism and we give a broad and unifying vision of our recent findings regarding cross-section reconstruction techniques of several biological plywoods along with recommendations that increase accuracy in the predictions
Introduction to the Special Issue on Nanocellulose Composites
Get PDFCellulose nanomaterials (CNs) are at the convergence
of nanotechnology and bio-sourced material trends
and are currently of considerable interest. CNs are
a new class of nano-scale, cellulose-based building
blocks extracted from trees and plants as well as certain
animals, bacteria, and algae. CNs are not a single
material type but a family of materials with different
characteristics, which largely result from differences in
source and preparation methodology. Here we focus
on plant- and tree-derived CNs
Multidirectional Gaussian Mixture Models for Nonlinear Uncertainty Propagation
Get PDFMonte Carlo simulations are an accurate but computationally expensive procedure for approximating the resultant non-Gaussian probability density function (PDF) after propagation of an initial Gaussian PDF through a nonlinear function. Univariate splitting libraries for Gaussian Mixture Models (GMMs) exist with up to five elements in the literature. The number of splits are extended in the present work by generating three homoscedastic univariate splitting libraries with up to 39 elements. Mulitvariate GMMs are typically handled with splits along a single direction. Instead, we generate a regular multidirectional grid over the initial multivariate Gaussian distribution by recursively applying the splitting library along multiple directions. The splitting direction is arbitrary and no longer limited to directions parallel to the columns of the square-root of the covariance matrix. A second order Stirling's interpolation of the nonlinear function evaluated at the mean of the initial Gaussian distribution is used to quantify nonlinearity along candidate splitting directions. The directions with the highest nonlinearity benefit most from splitting. The Multidirectional GMM (MGMM) has applications for uncertainty quantification with computationally intensive nonlinear functions. The variable number of splits in each direction allows for a spectrum of models in the accuracy versus compute time design space, filling the gap between expensive Monte Carlos and fast linearized models. The multidirectional method is demonstrated with four test cases, including an orbit uncertainty propagation case, to illustrate the benefit of splitting along multiple directions and of ranking the splitting directions
Stable and Minimum Energy Configurations in the Spherical, Equal Mass Full 4-Body Problem
Get PDFThe minimum energy and stable configurations in the spherical, equal mass full 4-body problem are investigated. This problem is defined as the dynamics of finite density spheres which interact gravitationally and through surface contact forces. This is a variation of the gravitational n-body problem in which the bodies are not allowed to come arbitrarily close to each other (due to their finite density), enabling the existence of resting configurations in addition to orbital motion. Previous work on this problem has outlined an efficient and simple way in which the stability of configurations in this problem can be defined. This methodology is applied to the 4-body problem, where we find multiple resting equilibrium configurations and outline the stability of a number of these. The study of these configurations is important for understanding the mechanics and morphological properties of small rubble pile asteroids. These results can also be generalized to other configurations of bodies that interact via field potentials and surface contact forces
Analysis and Numerical Simulation for Tunnelling Through Coal Seam Assisted by Water Jet
Get PDFTunnel though coal seam is one of the most difficult tunnels since its risk of coal and gas outburst and the complex geological conditions. According to the directional cutting of water jet and the characteristic of the coal seam and rock mass, this paper presents a new method of tunnelling though coal seam assisted by water jet slotting, which can be divided into improving permeability of coal seam and directional cracking in the rock mass. The mechanism of improving permeability of coal seam was stated, and the crack criterion of rock during blasting was established based on fracture theory. Then, the evolution law of pressure wave and the crack propagation were simulated by FEM software ANSYS/LS-DYNA, the results show that the shape of the crush zone formed by stress wave is different between the normal borehole blasting and the slotted borehole blasting, and the tension is the main factor which let crack propagation. What is more, for normal borehole blasting, the tension concentration occurred along the direction of 45 degrees and let crack expand, while for slotted borehole blasting the tension concentration occurred along the direction of 0 degrees and 90 degrees, and the maximum tension along the direction of 0 degrees is larger than the maximum tension along the direction of 90 degrees, and the main crack expand along the direction of 0 degrees, which prove that the existence of the slot play a good role of orientation for directional cracking
Are “Higher-Order” and “Layer-wise Zig-Zag” Plate & Shell Theories Necessary for Functionally Graded Materials and Structures?
Get PDFSimilar to the very vast prior literature on analyzing laminated composite structures, "higher-order" and "layer-wise higher-order" plate and shell theories for functionally-graded (FG) materials and structures are also widely popularized in the literature of the past two decades. However, such higher-order theories involve (1) postulating very complex assumptions for plate/shell kinematics in the thickness direction, (2) defining generalized variables of displacements, strains, and stresses, and (3) developing very complex governing equilibrium, compatibility, and constitutive equations in terms of newly-defined generalized kinematic and generalized kinetic variables. Their industrial applications are thus hindered by their inherent complexity, and the fact that it is difficult for end-users (front-line structural engineers) to completely understand all the newly-defined generalized DOFs for FEM in the higher-order and layer-wise theories. In an entirely different way, very simple 20-node and 27-node 3-D continuum solid-shell elements are developed in this paper, based on the simple theory of 3D solid mechanics, for static and dynamic analyses of functionally-graded plates and shells. A simple Over-Integration (a 4-point Gauss integration in the thickness direction) is used to evaluate the stiffness matrices of each element, while only a single element is used in the thickness direction without increasing the number of degrees of freedom. A stress-recovery approach is used to compute the distribution of transverse stresses by considering the equations of 3D elasticity in Cartesian as well as cylindrical polar coordinates. Comprehensive numerical results are presented for static and dynamic analyses of FG plates and shells, which agree well, either with the existing solutions in the published literature, or with the computationally very expensive solutions obtained by using simple 3D isoparametric elements (with standard Gauss Quadrature) available in NASTRAN (wherein many 3D elements are used in the thickness direction to capture the varying material properties). The effects of the material gradient index, the span-to-thickness ratio, the aspect ratio and the boundary conditions are also studied in the solutions of FG structures. Because the proposed methodology merely involves: (2) standard displacement DOFs at each node, (2) involves a simple 4-point Gaussian over-integration in the thickness direction, (3) relies only on the simple theory of solid mechanics, and (4) is capable of accurately and efficiently predicting the static and dynamical behavior of FG structures in a very simple and cost-effective manner, it is thus believed by the authors that the painstaking and cumbersome development of "higher-order" or "layer-wise higher-order" theories is not entirely necessary for the analyses of FG plates and shells
Applying a Step Approach Method in Solving the Multi-Frequency Radiation From a Complex Obstacle
Get PDFIn this paper, a step approach method in the time domain is developed to calculate the radiated waves from an arbitrary obstacle pulsating with multiple frequencies. The computing scheme is based on the Boundary Integral Equation and derived in the time domain; thus, the time-harmonic Neumann boundary condition can be imposed. By the present method, the values of the initial conditions are set to zero, and the approach process is carried forward in a loop from the first time step to the last. At each time step, the radiated pressure on each element is updated. After several loops, the correct radiated pressures can be obtained. A sphere pulsating with a monopole frequency in an infinite acoustic domain is calculated first. This result is compared with the analytical solution, and both of them are in good agreement. Then, a complex-shaped radiator is taken as the studied case. The pulsating frequency of this case is multiple, and the waves propagate in half space. It is shown that the present method can treat multiple-frequency pulsation well, even when the radiator is a complex shape, and a robust convergence can be attained quickly