Mark Irle

Processing roughness of sanded wood surfaces

Any quantitative evaluation of a sanded surface requires that the data be filtered to remove form errors and waviness. Wood surfaces contain irregularities due to both the sanding process and the anatomy, so the anatomical roughness must be excluded from any measurement of the surface if the processing roughness is to be properly evaluated. The efficacy of a number of standard filters was examined to see if they were suitable for oak, beech and spruce surfaces sanded with P1000 grit. Filters in current standards introduced distortions, but a robust Gaussian filter, contained in a draft standard, appeared to give roughness profiles free of distortions. The processing roughness and anatomical roughness, contained in the filtered profile, were separated with an algorithm based on a threshold defined in the material ratio curve. Work is continuing to compare the properties of different grit size and species combinations.ZusammenfassungAlle quantitativen Untersuchungen einer abgeschliffenen Oberfläche setzen voraus, dass die Daten gefiltert werden, um Formfehler und Schwankungen zu vermeiden. Holzoberflächen besitzen aufgrund des Schleifprozesses und ihrer Zusammensetzung Unregelmäßigkeiten; diese müssen bei jeder Messung der Oberfläche ausgeschlossen werden, damit der durch den Schleifprozess hervorgerufene Rauheitsgrad korrekt bestimmt werden kann. Die Wirksamkeit einer Reihe üblicher Filter wurde untersucht, um festzustellen, ob sie für Eichen-, Birken- und Fichtenholz geeignet sind, die jeweils mit P1000 Körnung bearbeitet worden waren. Filter, die gegenwärtigen Standards entsprachen, führten zu Verformungen, ein robuster Gaussfilter schien jedoch ein verformungsfreies Profil zu liefern. Verarbeitungs- und materialbedingte Rauhigkeit wurden im Filterprofil berücksichtigt und herausgerechnet. Die Arbeit wird fortgesetzt, um die Eigenschaften bei Kombination unterschiedlicher von Körnung und Materialien zu untersuchen.

Influence of granule properties and concentration on cork-cement compatibility

Cork granules are produced as by-products and waste by the cork processing industries that make ‘bottle stoppers’ as a main product. These granules are of low density and could be used as lightweight aggregates for making concrete. This paper describes an investigation carried out to assess the compatibility of cork granules with cement for the manufacture of lightweight cementitious composites. Five different grades of cork granules varying in terms of size and density were investigated. The effects of extractives, particle size and density of the cork granules were studied. The results indicate that these parameters affect cement hydration in a complex way. At lower concentrations of cork (10%), only the extractives have an influence on hydration behaviour. At higher cork concentrations (20% and 30%), however, particle size and density also affect the compatibility. Nevertheless, cork granules are found to be compatible with cement. ZusammenfassungKorkgranulat entsteht in der korkverarbeitenden Industrie als Neben- und Abfallprodukt bei der Herstellung von Flaschenkorken. Korkgranulat hat eine geringe Dichte und könnte als Leichtzuschlagstoff für die Herstellung von Beton verwendet werden. In diesem Artikel werden die Ergebnisse einer Untersuchung zur Beurteilung der Kompatibilität von Korkgranulat und Zement zur Herstellung von zementgebundenen Verbundwerkstoffen vorgestellt. Unter Verwendung von fünf Korkgranulatarten unterschiedlicher Grösse und Dichte wurde die Wirkung von Extraktstoffen, der Partikelgrösse und der Dichte untersucht. Es zeigte sich, dass sich diese Parameter in komplexer Weise auf die Zementhydration auswirken. Bei geringem Korkanteil (10%) wirken sich nur die Extraktstoffe auf das Hydrationsverhalten aus. Bei höheren Korkanteilen (20 und 30%) beeinflussen jedoch auch die Partikelgrösse und die Dichte die Kompatibilität. Insgesamt gesehen erwies sich Korkgranulat als mit Zement kompatibel.

Assessment of wood-cement compatibility: A new approach

Summary The influence of wood upon the setting of cement is generally assessed by conducting semi-adiabatic hydration tests. The existing methods to quantify wood-cement compatibility are based on the maximum hydration temperature (Tmax ), the time (tmax ) to reach it or the heat evolved in a specified period. Results obtained by these methods at higher wood-cement ratios are not convincing and show inconsistencies for various reasons. This paper discusses these reasons and suggests an alternative method based on a maturity function. The results from the new calculation method are compared with those of the existing methods and demonstrate the superiority of this new method at higher wood-cement ratios.

The Mechanisms Behind the Improved Dimensional Stability of Particleboards Made from Steam-Pretreated Particles

Summary The mechanisms which cause an improvement in the dimensional stability of particleboards made from steam pretreated particles were investigated from the aspects of potential thickness recoveries of densified wood particles and the breakage of the adhesive bond network in particleboards. Since the latter would depend on the balance between bond strengths and stresses imposed on the adhesive bond, the effects of steaming temperature (160 to 220°C) on bond quality, recovery stress of compressed wood and in-plane swelling stress were investigated. Steam pretreatment was found: 1) to reduce thickness recoveries of densified wood particles, steaming temperatures above 190°C are especially effective, 2) not to cause a significant reduction in bond strength when steaming below 210°C or if relatively high press pressures of 1.5MPa are employed, 3) to reduce recovery stress of compressed wood, which is mainly caused by the increase in wood compressibility, 4) to reduce in-plane swelling stress of particles, which was found to correlate with reductions in both hygroscopicity and elasticity.

Characterizing the setting of cement when mixed with cork, blue gum, or maritime pine, grown in Portugal I: temperature profiles and compatibility indices

Data are presented on the effects that cork, blue gum, or maritime pine, all grown in Portugal, have on cement setting. These materials were mixed with cement either without any treatment or after being extracted previously with a range of solvents (ranging from nonpolar to very polar). Other experiments were carried out in which extractives or calcium chloride were added to the cement paste. All lignocellulosic substrates have detrimental effects on cement setting, which is mostly seen by a delay in attaining the maximum temperature in the process. However, the addition of calcium chloride was able to overcome this disadvantage. Extraction of the substrates with some polar extraction agents before addition to the cement paste only slightly improved compatibility, and the addition of water-based extractives to a cement paste affects the setting much less than the lignocellulosic material by itself. Several thermal compatibility indices, including a new index proposed in this article, were calculated from data taken from temperature profiles, and conclusions are presented on the performance of the setting systems, as compared with a neat cement paste. In addition, comments are expressed on the level of accuracy offered by the indices applied in this study, and how such accuracy can be checked or improved by matching them to the physical properties of the wood-cement composites.

Thermal forming of chemically modified wood to make high-performance plastic-like wood composites

Abstract Chemically modified wood composites were obtained via the compression moulding of thermoplasticised Aspen (Populus tremula) sawdust. This sawdust was previously prepared by esterification with maleic anhydride (MA) and subsequent oligoesterification with maleic anhydride and glycidyl methacrylate (GMA). The thermoplastic properties of the chemically modified wood resulting from different modification procedures were confirmed and compared by compression-moulding experiments leading to preliminary and final products. An SEM study of the resulting products clearly showed that the oligoesterified wood had partially melted under pressure and temperature, such that the overlapping and surface melting of particles ensured adhesive bonding between those particles. A new type of wood/thermoplastic-wood composite was obtained. In these composites, the melted part of the modified wood plays the role of the cohesive matrix whilst none-melted wood remains as a fibrous reinforcing material. FTIR spectra suggested that changes in the chemical structure of the modified wood are possible during the thermal forming process (e.g. polymerisation of C=C double bonds). The final composites were yellowish-brown, glossy, plastic-like products that showed interesting physical, mechanical and biological properties. They are water-resistant and dimensionally stable and display good electrical insulating behaviour. Their mechanical properties (bending strength of ca. 64 MPa and tensile strength of ca. 36 MPa) are in the typical range for plastics and conventional wood-fibre/plastic composites, and are superior to common wood products such as fibreboards and particleboards. Furthermore, the outstandingly high internal bond (ca. 3.0 MPa) highlights the totally different adhesion mechanism operating in these new types of composites. Although the novel composites are much more resistant to decay than the original unmodified wood, they remain ultimately biodegradable plastic-like composites.

Preparation of Wood with Thermoplastic Properties, Part 1. Classical Synthesis

Summary Aspen wood (Populus tremula) as sawdust was chemically modified through a two-step procedure: esterification with maleic anhydride and subsequent oligoesterification with glycidyl methacrylate and maleic anhydride. Chemical analyses and infra-red spectroscopy revealed the differences in the chemical composition and structure of wood as a result of this treatment. These changes were also reflected by a hygroscopicity test and thermal analyses such as thermogravimetry and thermomechanical analysis. The esterified wood showed an increased hygroscopicity and a decreased thermal stability compared to unmodified wood. In contrast, the oligoesterified wood demonstrated a reduced hygroscopicity and a comparable thermal stability up to about 200°C. The thermomechanical analysis of oligoesterified wood clearly showed a significant softening phenomenon in the range 80–140°C, a direct evidence of the thermoplastic properties gained by this chemical modification.

Preparation of wood with thermoplastic properties: Part 2. Simplified technologies.

Summary Aspen wood (Populus tremula) as sawdust was chemically modified through a two-step procedure: esterification with maleic anhydride and subsequent oligoesterification with glycidyl methacrylate and maleic anhydride. Simplified techniques consisting of impregnation by immersion followed by thermal treatment using conventional or microwave heating were employed. Chemical analyses and infra-red spectroscopy showed some differences in the chemical composition and structure of the resulting oligoesterified wood depending on the synthesis technique. However, the thermoplastic properties, clearly revealed by thermomechanical analysis, were quite similar and comparable to those exhibited by the oligoesterified wood resulting via classical synthesis. Moreover, similar degrees of chemical modification were obtained for a significantly shorter duration of the process when microwave heating was employed instead of conventional heating.

Characterizing the setting of cement when mixed with cork, blue gum, or maritime pine, grown in Portugal II: X-ray diffraction and differential thermal analyzes

It is already known by the scientific and industrial communities that lignocellulosic substrates are, to a certain extent, inhibitors of the hydration reaction of cement. The extent to which and how they influence such reactions is still a matter of debate. Several techniques, such as calorimetry, i.e., the measurement of the heat evolved or obtaining temperature profiles during the hydration, the determination of extractive contents of lignocellulosic substrates and their relation with the characteristics of the hydration curves, or even testing of the mechanical properties of the wood-cement composites, have been used in previous research. This study complements past research using two techniques that have been used in the analysis of cement hydration but are not usually applied to lignocellulose-cement mixes, namely X-ray diffraction (XRD) and differential thermal analysis (DTA). The raw materials for this study were three lignocellulosic materials of Portuguese origin: cork (the bark of Quercus suber L.), blue gum (Eucalyptus globulus Labill.), and maritime pine (Pinus pinaster Ait); and Portland cement. The two techniques allowed tracking of the evolution of the main cement constituents during hydration. It was found that all the lignocellulosic substrates had detrimental effects on cement hydration. The blue gum exhibited the fastest hydration kinetics in the initial stage of reaction, but was then overtaken by cork, which at the end gave the highest hydration conversion amongst the three lignocellulosic substrates. Although pine caused the slowest initial hydration kinetics, with the passage of time its effect approached that of blue gum. At the end of the hydration period, specimens containing either species had similar quantities of hydration reaction products. The DTA and XRD results were consistent and are in good agreement with the temperature profiles and compatibility indexes reported in a previous work.

Formulating preliminary design optimization problems using expert knowledge: Application to wood-based insulating materials

Abstract The design of wood-fiber based thermal insulating material with optimized properties and characteristics requires a good scientific knowledge of the latter. Currently, the technical, economic and ecological characteristics of a wood-fiber based composite mat are not well known. This article presents a methodology for the acquisition of expert knowledge so that the properties and characteristics can be modeled. The knowledge domain is multidisciplinary and it was delimited and decomposed into disciplines and domains of expertise. A panel of seven experts was constituted to cover the various disciplines and domains of expertise of the knowledge domain. Knowledge acquisition sessions, guided by the estimated importance and the availability of knowledge, were conducted using semi-structured interviews and the mapping of the existing causal relations between variables. A causal map was established to represent the causal knowledge of each of the experts and then, the established causal maps were assembled into a unique global causal map, which was subsequently validated by the experts. It contains the information necessary for formulating the properties and characteristics to be optimized, which were: thermal conductivity; thickness recovery of the material; the manufacturing cost and the products environmental impact. Properties and characteristics are function of raw material type, their morphological properties and the manufacturing process variables. This methodology makes it possible to establish which objectives to optimize and which variables influence each objective. Consequently, the objective functions of the optimization problem can be clarified, specified and modeled.