关键词： Nanocomposites   Plant polymer   Flammability   Thermal stability   Activation energy  

摘要： Melamine formaldehyde-furfuryl alcohol copolymer was impregnated into softwood in combination with 1,3-dimethylol-4,5-dihydroxy ethyleneurea, a crosslinking agent, nanoclay, and a renewable polymer, collected as gum from a local plant (Moringa oleifera) under vacuum condition and polymerized by catalyst heat treatment. Fourier-transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy were used to characterize the nanocomposites. Transmission electron microscopy showed uniform distribution of nanoclay in the composites. The mechanical properties were improved after the addition of plant polymer. The plant polymer had a marked influence on the flammability and thermal stability of the prepared composites. The apparent activation energy was determined by Ozawa-Flynn-Wall's and Vyazovkin methods. The activation energy of the composites decreased up to a certain decomposed fraction thereafter it remained constant. Higher the plant polymer content higher was the activation energy of the prepared composites which indicated a better interfacial adhesion and thermal stability.

关键词： Lignocellulosic wastes   particleboards   properties   residues   Tetra Pak   tropical species  

摘要： Lignocellulosic wastes resulting from agricultural activities as well as Tetra Pak residues from urban centres can cause significant levels of pollution. A possible action to minimize this problem is to use them in the production of particleboards. The purpose of this study was to evaluate the physical, mechanical, and hydration properties of particleboards manufactured with the mixture of woody biomass (Cupressus lusitanica, Gmelina arborea, and Tectona grandis) and either agricultural wastes [pineapple leaves (Ananas comosus) and palm residues (Elaeis guineensis)] or Tetra Pak residues (TP). The results show that the particleboards prepared with TP and woody biomass can reduce the swelling and water absorption in up to 40% and 50% compared with particleboards without TP. Also, these particleboards had increased flexure resistance and shear stress (up to 100%) compared with those without TP. On the contrary, particleboards prepared with pineapple leaves in combination with woody biomass showed the lowest mechanical properties, particularly for tensile strength, hardness, glue-line shear, and nail and screw evaluation.

关键词： Nano-wire   Molecular dynamics simulation   Mechanical properties   Size effect   Tensile test   Surface effect  

摘要： In this study we have used atomistic simulations to investigate the role of surface on the size-dependent mechanical properties of nano-wires. In particular, we have performed computational investigation on single crystal face-centered cubic copper nano-wires with diameters ranging from 2 to 20 nm. The wire axis for all the nano-wires are considered along the [001] direction. Characterization of the initial optimized structures revealed clear differences in interatomic spacing, stress, and potential energy in all the nano-wires. The mechanical properties with respect to wire diameter are evaluated by applying tension along the [001] direction until yielding. We have discussed the stress-strain relationships, Young's modulus, and the variation in potential energy from surface to the center of the wire for all the cases. Our results indicate that the mechanical response (including yield strain, Young's modulus, and resilience) is directly related to the proportion of surface to bulk type atoms present in each nano-wire. Thus the sizedependent mechanical properties of single crystal copper nano-wire within elastic region are attributed to the surface to volume ratio (surface effect). Using the calculated response, we have formulated a mathematical relationship, which predicts the nonlinear correlation between the mechanical properties and the diameter of the wire. (C) 2013 Elsevier B.V. All rights reserved.

关键词： CRYSTALLIZATION -- Kinetics   BLOCK copolymers   TEMPERATURE effect   SEPARATION (Technology)   CRYSTAL growth   MATERIALS -- Mechanical properties  

摘要： Two olefinic blocky copolymers (OBCs) were quenched from different mixing states in the melt, and crystallization kinetics and morphology at various crystallization temperatures (T(c)s) and corresponding mechanical properties were studied. It is observed that, at lower T(c)s, premesophase separation in the melt accelerates crystallization of OBC-A with a weak segregation strength and a larger fraction of the crystalline hard blocks due to enrichment of the hard blocks in the hard-block-rich domains. By contrast, premesophase separation retards crystallization of OBC-B with a stronger segregation strength and lower fraction of the hard blocks because of the prevailing confinement effect at lower T(c)s. Moreover, since the hard blocks dissolved in the soft-block-rich domains can crystallize at lower T(c)s, which can bridge the crystals formed in different hard-block-rich domains, the crystal growth is not restricted. At higher T(c)s, OBC-A crystallizes more slowly from the premesophase-separated melt than that from the homogeneous melt, which is attributed to the weaker crystallizability of the hard blocks dissolved in the soft-block-rich domains and thus the restricted crystal growth. Nevertheless, mesophase separation always takes place prior to crystallization at higher T(c)s for OBC-B because of the faster rate of mesophase separation. Therefore, the mixing state in the melt has little effect on crystallization and morphology of OBC-B at higher T(c)s. It is found that the mechanical properties of OBCs can be regulated in a wide range by alteration of crystallization conditions. Better mechanical properties can be achieved when OBCs crystallize from the homogeneous melt and at a lower T-c.

关键词： Curing  

摘要： A silicone-contained biphenol type monomer, 4,4′-(1,3-dipropyl- tetramethyldisiloxane)bis-2-methoxyphenol(SIE), was used to modify phenolic novolac resin by being copolymerized with phenol and formaldehyde to yield SIE-modified phenolic resins (SPNs). The curing behavior of SPNs with hexamethyleneteramine (HMTA) was analyzed by DSC tests, and the non-isothermal curing kinetics were analyzed using the model-fitting and model-free isoconversional methods. Then, SPN/HMTA was used as the resin matrix, while surface-treated chopped sisal fiber was used as the reinforced filler to produce the silicon modified phenolic molding composites (SIEC). The finished composites expressed improved mechanical and thermal resistance properties compared with unmodified composites. © 2013 Elsevier B.V. All rights reserved.

关键词： MECHANICAL properties of metals   BORON nitride   MOLECULAR dynamics   RESEARCH   MONOMOLECULAR films   WAVELENGTHS  

摘要： The mechanical properties, including wrinkling patterns and fracture behavior, of monolayer h-BN sheets have been investigated using classic molecular dynamics simulations and continuum model. The wrinkling pattern formation and evolution have been first explored. The dependences of the wrinkling shape, amplitude, and wavelength, as well as wrinkling number on shear displacement are extensively elucidated. The influences of geometry and shear load direction, as well as temperature, on the fracture behavior have also been studied to obtain further insights into the properties of the monolayer h-BN sheets. (C) 2014 AIP Publishing LLC.

关键词： exports   Korea   machinery   manufacturing   trade fairs  

摘要： With heightened global competition, many manufacturers export as a process by which to increase sales and expand into new markets. South Korean manufacturers export in order to expand outside of a small domestic market, but confront the constraints of many exporters (especially smaller firms), including access to market intelligence and geographically distant prospective customers. This article examines efforts by machine tool manufacturers to minimize the friction of distance involved with exporting through the use of international trade fairs. Analytical emphases are placed on the influence of individual export destinations and on the role of firm size vis-a-vis firm export intensities and overall export strategies and motivations.

关键词： dynamics   non-smooth mechanics   multi-body systems   unilateral constraints   impact   contact   non-linear vibrations  

摘要： The paper deals with mathematical description and computer simulation of multi-body dynamical systems with constraints imposed on displacements and velocities. Such mechanical systems contain a finite number of material points, whose motion is limited by unilateral constraints. The mathematical description of the problem, concerning the interaction between material points and unilateral constraints, is presented. The dynamic problem was defined in order to evaluate accelerations of elements and reactions of constraints. Moreover, the impact problem was formulated. The solution of the impact problem determines non-continuous change in velocities of elements and impulses of constraints’ reactions.