The effect of chemical treatment of hemp hurds slices in three solutions (EDTA (Ethylenediaminetetraacetic acid), NaOH and Ca(OH)2) on the properties of natural material was discussed in this paper. Changes in the morphology, chemical composition and structure as well as thermal stability of hemp hurds before and after their modification were investigated by using FTIR (Fourier transform infrared spectroscopy), XRD (X-ray powder diffraction analysis) and TG (thermogravimetry)/DSC (differential scanning calorimetry). Size exclusion chromatography (SEC) measurements were used for determination of degree of cellulose polymerization of hemp hurd samples. Chemical modification is related to the partial removal of non-cellulosic components of lignin, hemicellulose and pectin as well as waxes from the surface of hemp hurd slices. Another effect of the chemical treatment applied is connected with increasing the crystallinity index of cellulose determined by FTIR and XRD methods. Decrease in degree of cellulose polymerization and polydispersity index in chemically modified hemp hurds compared to the original sample was observed. Increase in thermal stability of treated hemp hurd was found. The most significant changes were observed in alkaline treated hemp hurds by NaOH.

Sustainability goals are essential driving principles for the development of innovative materials in the construction industry. Natural fibers represent an attractive alternative as reinforcing material due to good mechanical properties and sustainability prerequisites. The study has been focused on the comparative investigation of chemical and physical treatments of hemp hurds and their influence on the thermal behavior of main hemp constituents in air and nitrogen atmosphere. Thermal decomposition of hemp hurds involves several parallel reactions related to heat and mass transfer processes. A comparison of DSC and TG/ DTG results of hemp hurds samples before and after treatments demonstrates a better thermal stability for treated samples. It is caused by changes in chemical composition due to a partial removal of non-cellulosic components from hemp hurds structure, an increase in cellulose content and decrease in its degree of polymerization. The results show different thermal behavior of the hurds samples heated under nitrogen and air atmosphere. Based on DTG records, several-stage process of mass loss has been found for the samples under air, whereas only two-stage process under nitrogen.

In this paper, water sorption behavior of 28 days hardened composites based on hemp hurds and inorganic binder was studied. Two kinds of absorption tests on dried cube specimens in deionized water bath at laboratory temperature were performed. Short-term (after one hour water immersion) and long-term (up to 180 days) water absorption tests were carried out to study their durability. Short-term water sorption behavior of original hemp hurds composites depends on mean particle length of hemp and on binder nature. The comparative study of long-term water sorption behavior of composites reinforced with original and chemically modified hemp hurds in three reagents confirmed that surface treatment of filler influences sorption process. Based on evaluation of sorption curves using a model for composites based on natural fibers, diffusion of water molecules in composite reinforced with original and chemically modified hemp hurds is anomalous in terms of the Fickian behavior. The most significant decrease in hydrophility of hemp hurds was found in case of hemp hurds modified by NaOH and it relates to change in the chemical composition of hemp hurds, especially to a decrease in average degree of cellulose polymerization as well as hemicellulose content.

A direct method of measuring the pH value of wood substance is proposed in the paper. The achieved results were completed by determining the pH value on the wood surface using the contact method. Moreover, the results were compared to the results achieved using the indirect methods to determine the pH value in cold water, as well as hot water, extract of wood. Using the direct method for measuring the pH value in drilled fresh sawdust, the pH value of beech was 5.11, of birch was 5.29, of alder was 4.88, and of maple was 4.65. Following the achieved results, the possibility to measure the pH value using a fast, accurate method useful in practice complying with the condition of the minimum free water in wood (moisture content of wood above the fibre saturation point) was presented. The results of measurements of the pH value using the contact method on the wood surface showed that this method can be used in the case of coniferous as well as broadleaved trees with heartwood. The value of pH measured on the surface of pine was 4.50, of spruce was 4.79, of the heartwood of oak was 3.46, and of the sapwood of oak 5.04. The measurement of pH values of water extracts confirmed great dependence of measured values on the conditions of wood extraction.

No abstract

The aim of this work was to evaluate the changes of the chemical components in birch wood (Betula pendula Roth) caused by steaming with saturated steam at three temperatures—105 °C, 125 °C and 135 °C. In the samples of the original wood and wood after steaming, select chemical characteristics were determined, and wood, isolated holocellulose and Seiferts’s cellulose were analysed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The greatest changes in the birch wood characteristics were observed in steaming mode III (135 °C). The differential spectra of the birch wood samples indicated that the hemicelluloses were significantly degraded and that the dehydration reactions were able to proceed. A clear increase in both unconjugated and conjugated carbonyls was seen only in mode III. The findings also confirmed the greater sensitivity of the guaiacyl lignin contained in broadleaves to elevated steaming temperatures, as well as the course of the thermal oxidation reactions and the formation of new carboxyls in mode III. The decrease in the ratio of absorbances H 1732/2900 and H 1243/2900 demonstrated the cleavage of acyl (acetyl and formyl) groups from birch wood hemicelluloses. The qualitative and quantitative changes of the hemicelluloses and extractive substances in birch wood during steaming were well-correlated with the measured pH values and wood colour.

An engineering approach for the calculation of the specific mass energy consumption, which is needed for defrosting and the subsequent heating of the frozen wood chips above the hydroscopic range, (in kWh·t-1), has been suggested. Equations for easy calculation of have been derived, depending on the wood moisture content u, on the fiber saturation points of the wood species at 20 °C and at –2 °C (i.e. at 293.15 K and at 271.15 K), and respectively, on the initial chips’ temperature, T0 , and on the final temperature of the heated after their defrosting chips, T1.For the calculation of the according to the suggested approach and equations a software program has been prepared in MS Excel 2010. With the help of the program calculations have been carried out for the determination of the energy consumption , which is needed for defrosting and subsequent heating of oak, acacia, beech, and poplar frozen chips with moisture content in the range from u = 0.4 kg·kg-1 to u = 1.0 kg·kg-1, initial temperature t0 = –20 °C and t0 = –10 °C until reaching of the chips‘ mass temperature of t1 = 80 °C, t1 = 100 °C, and t1 = 120 °C at the end of the heating.

The aim of this study was to characterize two types of cellulosic fibers obtained from bleached wood pulp and unbleached recycled waste paper with different cellulose content (from 47.4 percent up to 82 percent), to compare and to analyze the potential use of the recycled fibers for building application, such as plastering mortar. Changes in the chemical composition, cellulose crystallinity and degree of polymerization of the fibers were found. The recycled fibers of lower quality showed heterogeneity in the fiber sizes (width and length), and they had greater surface roughness in comparison to high purity wood pulp samples. The high purity fibers (cellulose content > 80.0 percent) had greater crystallinity and more homogeneous and smooth surfaces than the recycled fibers. The presence of calcite and kaolinite in all of the recycled cellulosic fibers samples was confirmed, whereas only one wood pulp sample contained calcite. The influence of the chemical composition was reflected in the fiber density values. Changes in the chemical composition and cellulose structure of the fibers affected the specific surface area, porosity and thermo physical properties of the fibers. More favorable values of thermal conductivity were reached for the recycled fibers than for the wood pulp samples. Testing the suitability of the recycled fibers with inorganic impurities originating from the paper-making processes for their use as fillers in plastering mortars (0.5 wt.% fiber content of the total weight of the filler and binder) confirmed their application by achieving a compressive strength value of 28 day-cured fiber-cement mortar required by the standard as well as by measured more favorable value of capillary water absorption coefficient.