Dynamic arrest in polymer melts: competition between packing and intramolecular barriers

We present molecular dynamics simulations of a simple model for polymer melts with intramolecular barriers. We investigate structural relaxation as a function of the barrier strength. Dynamic correlators can be consistently analyzed within the framework of the mode coupling theory of the glass transition. Control parameters are tuned in order to induce a competition between general packing effects and polymer-specific intramolecular barriers as mechanisms for dynamic arrest. This competition yields unusually large values of the so-called mode coupling theory exponent parameter and rationalizes qualitatively different observations for simple bead-spring and realistic polymers. The systematic study of the effect of intramolecular barriers presented here also establishes a fundamental difference between the nature of the glass transition in polymers and in simple glass formers.

Globaalin hankintastrategian komponentit, case: Joptek Oy Composites

Viimeiset vuosikymmenet ovat olleet voimakasta kansainvälistymisen aikaa liiketoiminnassa, jonka myötä globaalista hankinnasta on tullut yhä enenevässä määrin hyvin merkittävä osa yritysten hankintastrategiaa. Kansainvälisten hankintapäätösten tekeminen vaatii yritykseltä kansainvälistymisen asteesta riippuen taloudellisia-, ajallisia- ja henkilöresursseja. Suhteessa näihin panoksiin nähden kansainvälisestä hankinnasta on saavutettavissa merkittäviä etuja, joista tärkeimpiä ovat kustannussäästöt, kilpailuetu sekä laatu- ja teknologiaedut. Projektiluontoisessa liiketoiminnassa hankintastrategian muodostamiseen ja hankintaprosesseihin vaikuttavat yksittäisten projektien ominaisuudet ja niille asetetut tavoitteet. Projektitoiminnassa hankintastrategian mukauttaminen kulloinkin vallitseviin olosuhteisiin, tavoitteisiin ja asiakkaiden tarpeisiin on projektien onnistumisen kannalta tärkeää. Tutkielman teoriaosassa tarkasteltiin projektihankintaprosesseja sekä projekteihin perustuvan liiketoiminnan ominaispiirteitä ja niiden vaikutuksia hankintaan. Teorian keskeisimpänä asiakokonaisuutena on kansain-välinen hankintastrategia osana yrityksen kokonaisvaltaista hankinta-strategiaa. Globaalia hankintastrategiaa on tarkasteltu investointien, kilpailuedun, strategian muodostuksen, motiivien ja esteiden sekä sen eri komponenttien osalta. Empiiriaosassa tutkittiin tutkielman case –yrityksen ja toimeksiantajan, Joptek Oy Compositesin hankinnan nykytilaa sekä kansainvälisen hankintastrategian eri osa-alueita. Haastattelun avulla suoritetun tutkimuksen mukaan Joptek Oy:n liiketoimintaympäristö edellyttää yrityksen entistä aktiivisempaa panostamista kansainväliseen hankintaan. Projektiliiketoiminnassa kansainvälisen hankintastrategian muodostamisessa on pyrittävä yrityksen tarpeisiin vastaaviin räätälöityihin ratkaisuihin, huomioiden erillisten projektien muutokset ja riskitekijät.

Investigating ferromagnetism and charge order in Bi1-xSrxMnO3(x<0.3)ceramic oxides.

The possible coexistence of ferromagnetism and charge/orbital order in Bi3/4Sr1/4MnO3 has been investigated. The manganite Bi0.75Sr0.25MnO3, with commensurate charge balance, undergoes an electronic transition at TCO~600 K that produces a longrange modulation with double periodicity along a and c axis, and unusual anisotropic evolution of the lattice parameters. The previously proposed ferromagnetic properties of this new ordered phase were studied by magnetometry and diffraction techniques. In zero field the magnetic structure is globally antiferromagnetic, ruling out the apparition of spontaneous ferromagnetism. However, the application of magnetic fields produces a continuous progressive canting of the moments, inducing a ferromagnetic phase even for relatively small fields (H<<1 T). Application of pulsed high fields produces a remarkable and reversible spin polarization (under 30 T, the ferromagnetic moment is ~3 ¿B/Mn, without any sign of charge order melting). The coexistence of ferromagnetism and charge order at low and very-high fields is a remarkable property of this system.

Macroporous Scaffolds for Bone Engineering. Studies on Cell Culture and Ectopic Bone Formation

Bone engineering is a rapidly developing area of reconstructive medicine where bone inducing factors and/or cells are combined with a scaffold material to regenerate the structure and function of the original tissue. The aim of this study was to compare the suitability of different macroporous scaffold types for bone engineering applications. The two scaffold categories studied were a) the mechanically strong and stable titanium fiber meshes and b) the elastic and biodegradable porous polymers. Furthermore, bioactive modifications were applied to these basic scaffold types, and their effect on the osteogenic responses was evaluated in cell culture and ectopic bone formation studies. The osteogenic phenotype of cultured cell-scaffold constructs was heightened with a sol-gel derived titania coating, but not with a mixed titania-silica coating. The latter coating also resulted in delayed ectopic bone formation in bone marrow stromal cell seeded scaffolds. However, the better bone contact in early implantation times and more even bone tissue distribution at later times indicated enhanced osteoconductivity of both the coated scaffold types. Overall, the most promising bone engineering results were obtained with titania coated fiber meshes. Elastic and biodegradable poly(ε-caprolactone/D,L-lactide) based scaffolds were also developed in this study. The degradation rates of the scaffolds in vitro were governed by the hydrophilicity of the polymer matrix, and the porous architecture was controlled by the amount and type of porogen used. A continuous phase macroporosity was obtained using a novel CaCl2 • 6H2O porogen. Dynamic culture conditions increased cell invasion, but decreased cell numbers and osteogenicity, within the scaffolds. Osteogenic differentiation in static cultures and ectopic bone formation in cell seeded scaffolds were enhanced in composites, with 30 wt-% of bioactive glass filler.

L'ús de materials compostos en el reforç intern d'estructures de formigó

L’ús de materials compostos de matriu polimèrica (FRP, Fibre Reinforced Polymer) en el reforç intern d'estructures de formigó

Plant uses in different bronze and iron age settlements from the Nuoro province (Sardinia). The results of phytolith analyses from several ceramic fragments and grinding stones.

Ceramic vessels and milling stones are important components of the archaeological record in several Nuraghi from the Pranemuru Plateau (Sardinia). To obtain information on the possible uses of the milling stones and the content vessels is of great interest to understand the economical activities carried out in these sites by these populations. One of the approaches to obtain information on the plant uses was the phytolith analyses of the sediment adhered both to the surface of the milling stones and to the surface of the vessel content. In total we analyzed eleven archaeological samples and two control samples collected from five different Nuraghi in the Pranemuru Plateau (Nuoro Province, Sardinia). The Nuraghi were located in an area of 10 km radius from nuraghe Arrubiu and were chronologically ascribed to the Bronze Age and one site -Pranu Illixi- to the Iron Age.

Síntese de polímeros condutores em matrizes sólidas hospedeiras

This review discusses the methods used to prepare conductive polymers in confined environments. This spatial restriction causes formation of defect-free polymer chains in the interlayer as porous cavities of inorganic hosts. The properties of the different composites obtained are a synergist combination of the characteristics of the inorganic host and the polymer. This opens new perspectives for the preparation of these materials and widens its potential applications.

Calcium phosphate glasses: silanation process and effect on the bioactivity behavior of Glass-PMMA composites

This article presents the results of a study of the efficiency of silanation process of calcium phosphate glasses particles and its effect on the bioactivity behavior of glasspoly( methyl methacrylate) (PMMA) composites. Two different calcium phosphate glasses: 44.5CaO-44.5P2O5-11Na2O (BV11) and 44.5CaO-44.5P2O5-6Na2O-5TiO2 (G5) were synthesized and treated with silane coupling agent. The glasses obtained were characterized by Microprobe and BET while the efficiency of silanation process was determined using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Thermal Analysis (DTA and TG)techniques. The content of coupling agent chemically tightly bond to the silanated glasses ascended to 1.69 6 0.02 wt % for BV11sil glass and 0.93 6 0.01 wt % for G5sil glass. The in vitro bioactivity test carried out in Simulated Body Fluid (SBF) revealed certain bioactive performance with the use of both silanated glasses in a 30% (by weight) as filler of the PMMA composites because of a superficial deposition of an apatite-like layer with low content of CO3 22 and HPO4 22 in its structure after soaking for 30 days occurred. VC 2013 Wiley Periodicals,Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000-000, 2013.

Cleaning of ceramic filter plates

In this thesis, cleaning of ceramic filter plates clogged by iron oxides was studied. Oxalic acid is considered as the most effective cleaning agent for the plates fouled by iron oxides, but when using oxalic acid, sparingly soluble calcium oxalate may be formed and it can blind the filter media. Suitability of another chemical for cleaning the plates clogged by iron oxides was studied in this thesis. The literature part was mostly about the properties of the chemical, about its reactions, industrial uses, safety issues etc. In the experimental part, the efficiency of the chemical for cleaning of the ceramic plates clogged by iron oxides was studied. Two kinds of plates were used in the experiments; the others were clogged by hematite and the others by magnetite. Both soaking and flow-through experiments were done. A suitable concentration, pH and temperature were tried to find in the experiments. Also the effect of ultrasound was studied. The efficiency of the cleaning was examined by measuring the permeability of the plates during the experiments. ICP-OES analysis was performed for determining the amount of dissolved iron in the washing solution. Some experiments were also done with oxalic acid. The results from the oxalic acid experiments were compared to the results from the experiments with the other chemical. In the experiments with the other chemical, the permeability increased more and the amounts of dissolved iron were larger. According to the results from the experiments, the method of application of the washing solutions had an impact on the washing results.

High-Performance-Tensile-Strength Alpha-Grass Reinforced Starch-Based Fully Biodegradable Composites

Though there has been a great deal of work concerning the development of natural fibers in reinforced starch-based composites, there is still more to be done. In general, cellulose fibers have lower strength than glass fibers; however, their specific strength is not far from that of fiberglass. In this work, alpha-fibers were obtained from alpha-grass through a mild cooking process. The fibers were used to reinforce a starch-based biopolymer. Composites including 5 to 35% (w/w) alpha-grass fibers in their formulation were prepared, tested, and subsequently compared with those of wood- and fiberglass-reinforced polypropylene (PP). The term “high-performance” refers to the tensile strength of the studied composites and is mainly due to a good interphase, a good dispersion of the fibers inside the matrix, and a good aspect ratio. The tensile strength of the composites showed a linear evolution for fiber contents up to 35% (w/w). The strain at break of the composites decreased with the fiber content and showed the stiffening effects of the reinforcement. The prepared composites showed high mechanical properties, even approaching those of glass fiber reinforced composites

Analysis of the tensile modulus of polypropylene composites reinforced with stone groundwood fibers

One of the most relevant properties of composite materials to be considered is stiffness. Fiberglass has been used traditionally as a fibrous reinforcing element when stiff materials are required. However, natural fibers are been exploited as replacements for synthetic fibers to satisfy environmental concerns. Among the different natural fibers, wood fibers show the combination of relatively high aspect ratio, good specific stiffness and strength, low density, low cost, and less variability than other natural fibers of such those from annual crops. In this work, composites from polypropylene and stone groundwood fibers from softwood were prepared and mechanically characterized under tensile loads. The Young’s moduli of the ensuing composites were analyzed and their micromechanics aspects evaluated. The reinforcing effect of stone groundwood fibers was compared to that of conventional reinforcement such fiberglass. The Halpin-Tsai model with the modification proposed by Tsai-Pagano accounted fairly for the behavior of PP composites reinforced with stone groundwood fibers. It was also demonstrated that the aspect ratio of the reinforcement plays a role in the Young’s modulus of injection molded specimens

Bio-based composites from stone groundwood applied to new product development

This paper deals with the product design, engineering, and material selection intended for the manufacturing of an eco-friendly chair. The final product is expected to combine design attributes with technical and legal feasibility with the implementation of new bio-based materials. Considering the industrial design, a range of objectives and trends were determined after setting the market requirements, and the final concept was proposed and modeled. The product geometry, production technology, and legal specifications were the input data for product engineering. The material selection was based on the technical requirements. Polypropylene (PP) composite materials based on coupled-fiberglass, sized-fiberglass, and coupled-stone ground wood reinforcements were prepared and characterized. Final formulations based on these PP composites are proposed and justified

Research on the suitability of organosolv semi-chemical triticale fibers as reinforcement for recycled hdpe composites

The main objective of this research was to study the feasibility of incorporating organosolv semi-chemical triticale fibers as the reinforcing element in recycled high density polyethylene (HDPE). In the first step, triticale fibers were characterized in terms of chemical composition and compared with other biomass species (wheat, rye, softwood, and hardwood). Then, organosolv semi-chemical triticale fibers were prepared by the ethanolamine process. These fibers were characterized in terms of its yield, kappa number, fiber length/diameter ratio, fines, and viscosity; the obtained results were compared with those of eucalypt kraft pulp. In the second step, the prepared fibers were examined as a reinforcing element for recycled HDPE composites. Coupled and non-coupled HDPE composites were prepared and tested for tensile properties. Results showed that with the addition of the coupling agent maleated polyethylene (MAPE), the tensile properties of composites were significantly improved, as compared to non-coupled samples and the plain matrix. Furthermore, the influence of MAPE on the interfacial shear strength (IFSS) was studied. The contributions of both fibers and matrix to the composite strength were also studied. This was possible by the use of a numerical iterative method based on the Bowyer-Bader and Kelly-Tyson equations

Determination of corn stalk fibers' strength through modeling of the mechanical properties of its composites

Worldwide cultivation of corn is expanding, due in part to the increasing production of bioethanol. In consequence, huge amounts of corn stalks residues are been produced. Instead of incineration, we transformed the corn stalks into a semichemical pulp and successfully applied it as reinforcement in polypropylene composites. PP composites reinforced with 40% wt corn stalk single fibers were prepared, and their mechanical properties were evaluated. Through mechanical properties modeling of the composites, the intrinsic tensile strength of the cellulosic fibers that constitute the corn stalk have been determined