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Locs J.,Riga Technical University | Berzina-Cimdina L.,Riga Technical University | Zhurinsh A.,Latvian State Institute of Wood Chemistry | Loca D.,Riga Technical University
Journal of the European Ceramic Society | Year: 2011

Pine (Pinus silvestris) wood samples were dried and impregnated with a SiO2 sol from a sol-gel process. The impregnation involved a two step process in a custom-made apparatus. Impregnated samples were dried and pyrolised at 500°C under an oxygen-free atmosphere. SiC synthesis was performed in a high-temperature furnace in an argon atmosphere at a temperature of 1600°C for 2, 4 and 8h. The samples were investigated with X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The changes in the SiC synthesis time at the maximum temperature lead to changes in the microstructure and crystalline phase composition. An increase in the synthesis time opens up the possibility to produce mainly α-SiC crystalline modification containing porous SiC ceramics. © 2010 Elsevier Ltd. Source


Kukle S.,Riga Technical University | Gravitis J.,Latvian State Institute of Wood Chemistry | Putnina A.,Riga Technical University
Journal of Biobased Materials and Bioenergy | Year: 2012

In recent years, an increasing number of researches are dedicated to the identification of local cellulose sources to understand their specifics and develop environmentally friendly technologies according to the field of usage. Since the cellulose mass in hemp cells varies from 45% to 70%, hemp stems and their processing products can be considered as the raw material for various products, including cellulose. The article analyses the phloem fiber variety of a hemp sort grown in Latvia named Bialobrzeskie. Treatment in sodium alkali solution and steam explosion technology have been applied to split technical fibers into elementary fibers. This has the aim to find the best way to produce fiber without using environmentally harmful chemical treatments and to solve problems for further environmentally friendly nano-level disintegration of cellulose with further integration into the structure of composite materials. The influence of the treatment intensity on the residue carried out in the first stage of research is reflected and an analysis of the steam explosion process temperature and pressure influence on the fiber chemical component proportion changes during different treatments are carried out. Copyright © 2012 American Scientific Publishers. Source


Zoldners J.,Latvian State Institute of Wood Chemistry | Kiseleva T.,Latvian State Institute of Wood Chemistry
Holzforschung | Year: 2013

Polycarboxylic acids (PCAs) aroused interest as crosslinking agents for natural polymers, such as cellulose, starch, chitosan, and hemicelluloses (HC), for improving their water resistance and imparting them new properties. Here, PCAs were studied for the crosslinking of HC films. HCs were isolated from gray alder (Alnus incana L.) wood as a water-soluble fraction by sawdust extraction with 7% potassium hydroxide. Citric acid (CA), maleic acid (MA), and butane tetracarboxylic acid (BTCA) served as crosslinking agents in the presence of sodium hypophosphite as a catalyst. The crosslinking reaction was followed by the analysis of free and esterified COOH groups in HC films. At temperatures below 100-110 C, the HC esterification process with BTCA proceeded very slowly. At 140 C, most of the acids' COOH groups reacted with HC during 1-1.5 h. BTCA had a higher esterification activity than CA and MA. The obtained films retained their form on immersing in water and subsequent drying in the open air. The water retention value of films followed the reaction kinetics, that is, decreased with increasing reaction time. Water-resistant films were obtained with no <10-11% of BTCA and 20% of CA based on the weight of HC. The water vapor sorption capacity of the films after modification with 10% BTCA decreased approximately twice in the whole range of the relative humidity of air compared with the case of unmodified HC films. © 2013 by Walter de Gruyter Berlin Boston 2013. Source


Kuranska M.,Cracow University of Technology | Aleksander P.,Cracow University of Technology | Mikelis K.,Latvian State Institute of Wood Chemistry | Ugis C.,Latvian State Institute of Wood Chemistry
Composites Science and Technology | Year: 2013

The rigid polyurethane (PUR) composites with an apparent density of ca. 300kg/m3 were prepared using 4,4-diphenylmethane di-isocyanate, polyether polyols, an amine catalyst, silicone surfactant and water as a chemical blowing agent. This reference petrochemical formulation was modified with renewable components such as rapeseed oil-based polyols and flax fibers. The effects of the different contents of the two types of the bio-polyols and flax fibers on the mechanical and thermal properties, dimensional stability and water absorption of foamed PUR composites were investigated. The modification showed that the incorporation of bio-components may improve mechanical and thermal properties of final products. © 2012 Elsevier Ltd. Source


Pietrzak K.,Warsaw University of Technology | Kirpluks M.,Latvian State Institute of Wood Chemistry | Cabulis U.,Latvian State Institute of Wood Chemistry | Ryszkowska J.,Warsaw University of Technology
Polymer Degradation and Stability | Year: 2014

As part of this work, the test results for ureaurethane elastomers (PUURs) manufactured with the use of tall oil (TO)-based polyols with a rosin acid content ranging from 2 to 20% are presented. The goal of this study was to verify the thermal and mechanical properties of bio-based PUURs. The physicomechanical properties of PUURs were tested along with the strength (static tensile test) and thermal properties: thermogravimetry (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). A structural analysis of the materials was also carried out via Fourier transform infrared (FTIR) spectroscopy. The replacement of the chain extender with tall oil-based polyols resulted in materials with different properties, different chemical constitutions and different thermal decomposition patterns. PUURs with TO polyols had a higher thermal resistance, and this resistance increased for higher isocyanate numbers (INCO). The thermal decomposition of the tested PUURs with TO polyols increased with the increase in the rosin acid content. The mechanical properties of the PUURs show that changing the chain extender with the TO polyols causes an increase in the storage modulus. © 2014 Elsevier Ltd. All rights reserved. Source

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