Efecto de la humedad de equilibrio en la rugosidad de tableros de fibras de densidad media (MDF)

La rugosidad superficial es primariamente una función de las propiedades de la materia prima, pero otros factores como la cantidad y el tipo de resina, ciclo de prensado, lijado y contenido de humedad de los tableros pueden afectar la rugosidad y otras propiedades de la superficie. En este estudio los efectos del contenido de humedad de equilibro en superficies de tableros de densidad media (MDF), fueron evaluados usando diferentes materias primas en sus superficies como también diferentes adhesivos. El análisis estadístico confirma que la relación entre el contenido de humedad de equilibrio y la rugosidad media es una compleja función de interacciones entre muchas variables, pero donde tiene un papel relevante desde el punto de vista practico el tipo de adhesivos. AbstractThe surface roughness is primarily a function of the raw material properties, but other factors like type and amount of resin, press cycle, sanding and moisture content of the boards may also affect the roughness and other surface properties. In this study the effect of the equilibrium moisture content on medium density fiberboards (MDF) surfaces was evaluate using different raw materials in their surface layers as well as different binders. The statistical analysis confirmed that the relationship between equilibrium moisture content and average roughness are a complex function of interactions between many variables

Thinning wood properties of Nothofagus alpina under three different silvicultural conditions

The main objective of this study was to assess the properties of Nothofagus alpina wood from thinning that originates from two sites with intensive silviculture and one similar to a secondary growth forest, with different soil, climatic conditions and age. To achieve this, some mechanical, physical and chemical-crystalline properties were characterized; studying the differences from pith to bark and between the selected trees that were taken from the thinning of the three plantations. Among the studied plantation sites, there were statistical differences in equilibrium moisture content, density and modulus of elasticity. Furthermore, FT-IR was able to differentiate the chemical-crystalline compositions from pith to bark and between plantations, while the X-Ray Diffraction showed differences in the crystallinity index. It was possible to differentiate between the sites with a more intense silvicultural intervention and the one with more variable growth conditions

Utjecaj hidrotermičke i higrotermičke obrade na promatrana svojstva drva bora (Pinus radiata) i duglazije (Pseudotsuga menziesii)

Heat treatments are related to the action of temperature in successive stages and under controlled conditions, changing the chemical structure of wood. However, the method of treatment used may have a significant effect on the properties of the heat treated wood. In order to assess the effect of the heat treatments on the wood properties, two conifer species were considered, as well as the absence of the air through water and vapor and three levels of temperature (130, 145 and 160 °C). The experiments resulted in twelve treatments or interactions plus controls. This study describes the changes in chemical composition of wood at relatively low temperatures and its interactions with the physical and mechanical properties of the new thermally-modified wood. The analysis of the results indicates that the extractives and degradation products that remain in the wood processed in a closed reactor seem to be a very important factor affecting the results.Toplinske obrade povezane su s djelovanjem temperature u kontroliranim uvjetima pri čemu se mijenja kemijska struktura drva. Međutim, upotrijebljena metoda toplinske obrade može imati znatan učinak na svojstva toplinski obrađenog drva. Kako bi se procijenio učinak toplinske obrade na svojstva drva, napravljen je eksperiment na dvije vrste drva četinjača, koje su obrađene uz odsutnost zraka upotrebom vode i pare te pri tri različite temperature (130, 145 i 160 °C). Eksperiment je napravljen uz dvanaest kombinacija uvjeta obrade te na kontrolnom uzorku. U radu se opisuju promjene kemijskog sastava drva pri relativno niskim temperaturama i interakcije tih promjena s promjenama fi zikalnih i mehaničkih svojstava toplinski modifi ciranog drva. Analiza rezultata pokazuje da su ekstraktivne tvari i tvari nastale u drvu pri procesu toplinske modifi kacije vrlo važni činitelji koji utječu na fizikalna i mehanička svojstva drva

Cutting distance as factor to evaluate the quality of wood machined surfaces: A preliminary study

Surface quality of solid wood products is an important subject of study since it influences further manufacturing processes, such as finishing or strength of adhesive joint. In this study, the surface quality of the machined surfaces was evaluated through the cutting distance, which is defined as the accumulated linear meters of wood processed by a cutting tool. The roughness (Rz) and wetting (contact angle) behaviour on wood machined surfaces have been assessed each 2000 meters respectively, from 0 to 10000 meters. In Pinus radiata samples, machined using a three hydro centred mounting cutter-headsof 6 knives HSS (High Speed Steel) 6 % W (Wolfram) and a rake angle of 15° each, similar contact angles were found associated to different values of Rz through the cutting distance. This study verifies that a wide spectrum of cutting distance allows an accurate evaluation of roughness and wettability behaviour surface characteristics

Mechanical properties and electrical surface charges of microfibrillated cellulose/imidazole-modified polyketone composite membranes

In the present work, microfibrillated cellulose (MFC) suspensions were produced by high-pressure homogenization and subsequently used to fabricate MFC membranes (C-1) by vacuum filtration followed by hot-pressing. A polyketone (PK50) was chemically modified by Paal-Knorr reaction to graft imidazole (IM) functional groups along its backbone structure. The resulting polymer is referred to as PK50IM80. By solution impregnation, C-1 was immersed in an aqueous solution of PK50IM80 and subsequently hot pressed, resulting in the fabrication of MFC/PK50IM80 composite membranes (C-IMP). Another method, referred to as solution mixing, consisted in adding MFC into an aqueous solution of PK50IM80 followed by vacuum filtration and hot-pressing to obtain MFC/PK50IM80 composite membranes (C-MEZC). C-IMP and C-MEZC were characterized by a wide range of analytical techniques including, X-ray photoelectron spectroscopy, Fourier-transform infrared chemical imaging, scanning electron microscopy, atomic force microscopy, dynamical mechanical analysis, tensile testing as well as streaming zeta potential, and compared to C-1 (reference material). The results suggested that C-IMP possess a more homogeneous distribution of PK50IM80 at their surface compared to C-MEZC. C-IMP was found to possess significantly enhanced Young's modulus compared to C-1 and C-MEZC. The tensile strength of C-IMP was found to improve significantly compared to C-1, whereas C-1 possessed significantly higher tensile index than C-IMP and C-MEZC. Furthermore, the presence of PK50IM80 at the surface of MFC was found to significantly shift the isoelectric point (IEP) of the membranes from pH 2.3 to a maximum value of 4.5 for C-IMP. Above the IEP, C-IMP and C-MEZC were found to possess significantly less negative electrical surface charges (plateau value of -25 mV at pH 10) when compared to C-1 (plateau value of -42 mV at pH 10). Our approach may have implication to broaden the range of filtration applications of MFC-based membranes

Charakterisierung von Holzwerkstoffoberflächen mittels Tastschnittverfahren und optischer Verfahren

Eine ideale und fehlerfreie Oberfläche ist absolut plan, selbst künstlich ist sie mit modernster Fertigungstechnik nicht herstellbar. Im Vergleich zu dieser theoretischen Idealoberfläche zeichnen sich insbesondere natürliche Stoffe wie Holz oder auch Holzwerkstoffe durch vielfältige Gestaltsabweichungen aus (Rauhigkeit, Welligkeit, Form). Zu den wichtigsten Kenngrößen zur Charakterisierung der Oberflächeneigenschaften von Holzwerkstoffen gehört die Oberflächen-Rauhigkeit. Hohe Oberflächen-Rauhigkeiten von Rohplatten können sich auf die Beschichtungsqualität negativ auswirken. Insbesondere kann sich durch Beschichtung sehr rauher Rohplatten mit dünnen Beschichtungsmaterialien die Oberflächentextur der Rohplatte durch die Folie abzeichnen, was letztendlich zu Reklamationen seitens der Kunden führen würde. Andererseits bietet eine zu glatte Oberfläche womöglich zu wenige Haftungspunkte für eine Beschichtung mit Folien bzw. für die Haftung von Farben und Lacken.Der Grad der Oberflächen-Rauhigkeit von Holzwerkstoffen ist von mehreren Faktoren abhängig. Zu den wichtigsten zählen die Eigenschaften des eingesetzten Rohstoffs (Holzart, Spanfraktion und Spangeometrie bei Spanplatten, Faserfraktion bei mitteldichten Faserplatten (MDF)), die Herstellungsbedingungen beim Pressen der Platten (Feuchtegehalt beim Pressen, Bindemittelart und -menge, Presszeit) sowie die verwendete Körnung beim Schleifen der Platten.Die gebräuchlichste Methode zur Charakterisierung der Rauhigkeit von Oberflächen wie Metallen, Holz und Holzwerkstoffen ist das sog. Tastschnittverfahren (Kontaktverfahren) gemäß DIN 4768. Nachteilig an diesem Verfahren ist der relativ hohe Zeitaufwand zur Durchführung der Messungen, sowie die relativ eingeschränkte Aussagekraft des Verfahrens, da von nur jeweils einer geringen Anzahl kurzer Tastschnittstrecken auf der Werkstoffoberfläche auf das gesamte Oberflächenprofil (Gesamtfläche) des zu prüfenden Werkstoffes geschlossen wird.Es überrascht deshalb nicht, dass in den vergangenen Jahrzehnten viel Forschungsarbeit auf dem Gebiet der Entwicklung alternativer und effizienterer optischer Messverfahren (Bildanalyseverfahren) geleistet wurde. Mit Hilfe optischer Messverfahren kann die Oberflächestruktur von Prüfkörpern bestimmt und charakterisiert werden. Das Messprinzip beruht darauf, dass von einer Lichtquelle aus gebündeltes Licht mit einem definierten Winkel auf eine Werkstoffoberfläche gestrahlt wird. Das Licht wird in Abhängigkeit von der Textur der Oberfläche (Oberflächen-Rauhigkeit) mehr oder weniger stark gestreut bzw. abgelenkt und von einem Lichtdetektor einer analogen Kamera teilweise wieder aufgefangen. Der Grad der Lichtstreuung ist eine Funktion der Oberflächen-Rauhigkeit des zu prüfenden Werkstoffs. Das von der Oberfläche reflektierte Licht wird in Videosignale (Grauwerte) digital konvertiert und statistisch ausgewertet. Optische Messmethoden haben u. a. den Vorteil, dass sie Messzeit ersparen, Material schonend arbeiten, sowie große Datenmengen bezogen auf eine relativ große Untersuchungsfläche liefern

Efecto de la humedad de equilibrio en la rugosidad de tableros de fibras de densidad media (MDF)

The surface roughness is primarily a function of the raw material properties, but other factors like type and amount of resin, press cycle, sanding and moisture content of the boards may also affect the roughness and other surface properties. In this study the effect of the equilibrium moisture content on medium density fiberboards (MDF) surfaces was evaluate using different raw materials in their surface layers as well as different binders. The statistical analysis confirmed that the relationship between equilibrium moisture content and average roughness are a complex function of interactions between many variables.La rugosidad superficial es primariamente una función de las propiedades de la materia prima, pero otros factores como la cantidad y el tipo de resina, ciclo de prensado, lijado y contenido de humedad de los tableros pueden afectar la rugosidad y otras propiedades de la superficie. En este estudio los efectos del contenido de humedad de equilibro en superficies de tableros de densidad media (MDF), fueron evaluados usando diferentes materias primas en sus superficies como también diferentes adhesivos. El análisis estadístico confirma que la relación entre el contenido de humedad de equilibrio y la rugosidad media es una compleja función de interacciones entre muchas variables, pero donde tiene un papel relevante desde el punto de vista practico el tipo de adhesivos.

Cutting distance as factor to evaluate the quality of wood machined surfaces: A preliminary study

Surface quality of solid wood products is an important subject of study since it influences further manufacturing processes, such as finishing or strength of adhesive joint. In this study, the surface quality of the machined surfaces was evaluated through the cutting distance, which is defined as the accumulated linear meters of wood processed by a cutting tool. The roughness (Rz) and wetting (contact angle) behaviour on wood machined surfaces have been assessed each 2000 meters respectively, from 0 to 10000 meters. In Pinus radiata samples, machined using a three hydro centred mounting cutter-headsof 6 knives HSS (High Speed Steel) 6 % W (Wolfram) and a rake angle of 15° each, similar contact angles were found associated to different values of Rz through the cutting distance. This study verifies that a wide spectrum of cutting distance allows an accurate evaluation of roughness and wettability behaviour surface characteristics.La degradación superficial en madera de exteriores se debe a una combinación de factores meteorológicos inherentes al entorno de exposición y a la colonización de organismos xilófagos. Desde un punto de vista técnico y económico se trata de uno de los principales problemas para la industria de productos y materiales hechos a partir de la madera. El objetivo del presente trabajo es el de monitorizar la degradación superficial de las maderas de Corymbia citriodora y Eucalyptus tereticornis originarias de plantaciones de rápido crecimiento de Brasil, las cuales han sido expuestas a ensayos de intemperismo natural en tres entornos ambientales distintos. La monitorización de los cambios en el material fue realizada mediante estimaciones del color (método CIEL*a*b*), en ciclos de 45 días, hasta completar un periodo de 360 días de exposición. Los resultados mostraron que el material expuesto al entorno forestal fue menos afectado por los factores ambientales, lo que ha sido probablemente debido al aislamiento térmico y solar que proporciona este tipo de ecosistema. A su vez, se observó que las probetas de madera de Corymbia citriodora presentaron mayor resistencia al deterioro que las probetas de madera de Eucalyptus tereticornis, posiblemente debido a ciertas diferencias en su constitución químic

Promjene hrapavosti i svojstva kvašenja površine: utjecaj duljine rezanja tijekom blanjanja borovine

The variation of the machined surface properties is usually described in terms of changes in cutting parameters. However, the effect of the cutting distance should be considered, as it further shows the influence of the cutting tool wear. In order to assess the effect of the cutting distance on roughness and wettability of Pinus radiata wood surfaces, three conditions of feed speed and cutting speed were applied on cutting distance of 0 to 10000 meters. This study describes the effect of machining parameters on the behavior of roughness and wettability through the cutting distance, and the interaction of both surface properties is also discussed. The variation of surface roughness in function of the cutting distance is not directly related to variations in the surface wettability. It was, therefore, concluded that is was not reliable to consider only the surface roughness to explain the wetting behavior of a heterogeneous surface such as wood.Varijacije svojstava obrađene površine drva obično se opisuju kao posljedica promjene parametara obrade. Međutim, treba uzeti u obzir i učinak duljine rezanja jer to dodatno pokazuje utjecaj istrošenosti reznog alata. Kako bi se procijenio učinak duljine rezanja na hrapavost i svojstvo kvašenja površine drva bora (Pinus radiate), pri blanjanju na duljini od 0 do 10 000 metara primijenjene su tri različite posmične brzine i brzine rezanja. U radu se opisuje utjecaj parametara obrade na hrapavost i svojstvo kvašenja obrađene površine u ovisnosti o duljini rezanja, a objašnjena je i interakcija tih dvaju svojstava obrađene površine. Varijacije hrapavosti površine u ovisnosti o duljini rezanja nisu izravno povezane s varijacijama svojstva kvašenja površine. Zaključeno je da za određivanje svojstva kvašenja heterogene površine materijala kao što je drvo nije pouzdano uzimati u obzir samo hrapavost njegove površine