ESTGV - DEM - Artigo em revista científica, indexada ao WoS/Scopus
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- Pulping yield and delignification kinetics of heartwood and sapwood of maritime pinePublication . Esteves, Bruno; Gominho, J.; Rodrigues, J.C.; Miranda, I.; Pereira, H.In maritime pine (Pinus pinaster Ait.), heartwood represents a substantial part of the tree stem at final harvest age (80 years) corresponding to 42% at the base of the stem wood diameter and decreasing upward. The rate of heartwood formation was estimated at 0.35 rings/year, beginning at 18 years of age. Differences in the chemical composition between heartwood and sapwood were mainly in the extractives, 19.7% and 5.8%, respectively. The lignin content was 23.1% and 24.5% in the heartwood and sapwood, respectively. Pulping yield of the heartwood was lower than that of the sapwood (40.0% vs. 49.7%) and was negatively correlated with the extractives content. Extraction of heartwood prior to pulping increased the pulp yield and the delignification (lower residual lignin in pulps). Pulping kinetics showed lower yields for heartwood at all pulping stages, the difference occurring especially in the initial reaction phase. However, delignification rate constants were similar for heartwood and sapwood (3.1 1022 min21 and 2.7 1022 min21 for the main delignification phase for sapwood and heartwood, respectively), with a lower activation energy for sapwood (68.3 vs. 90.0kJ.mol21). The presence of heartwood decreases the raw-material quality for pulping and this should be taken into account when harvesting trees for pulping processes.
- Chemistry and ecotoxicity of heat-treated pine wood extractivesPublication . Esteves, Bruno; Videira, Romeu; Pereira, HelenaPine (Pinus pinaster) wood was heat treated in an autoclave for 2-12 hours at 190-210 ºC. Hemicelluloses were the first compounds affected by the treatment. In general, the sugar decrease was higher for arabinose and galactose followed by xylose and mannose. Lignin started to degrade for small mass losses but at a slower rate than hemicelluloses, and cellulose only degraded significantly for severe treatments. Almost all of the original extractives disappeared and new compounds arose like anhydrosugars and phenolic compounds. The compounds that might leach from heat treated wood were mainly those identified in the water and ethanol extracts, all of which were not harmful at the existing concentrations, thereby reinforcing the wood heat treatment as an environmental benign process.
- Chemical changes of heat treated pine and eucalypt wood monitored by FTIRPublication . Esteves, B.; Velez Marques, A.; Domingos, I.; Pereira, H.A hardwood, Eucalyptus globulus Labill., and a softwood Pinus pinaster Aiton., were heat treated at temperatures between 170 and 210ºC in an oven and in an autoclave. The samples were pre-extracted with dichloromethane, ethanol and water and ground prior to Fourier Transform Infrared (FTIR) spectroscopic analysis. The heat treatment caused significant changes in the chemical composition and structure of wood, in lignin and polysaccharides. Hemicelluloses were the first to degrade as proved by the initial decrease of the 1730 cm-1 peak due to the breaking of acetyl groups in xylan. Hardwood lignin changed more than softwood lignin, with a shift of maximum absorption from 1505 cm-1 to approximately 1512 cm-1 due to decrease of methoxyl groups, loss of syringyl units or breaking of aliphatic side-chains. The macromolecular structure becomes more condensed and there is a clear increase of non-conjugated (1740 cm-1) in relation to conjugated groups (1650 cm-1). However, the changes induced by the thermal treatment are difficult to monitor by FTIR spectroscopy due to the different chemical reactions occurring simultaneously.
- Comparison between heat treated sapwood and heartwood from Pinus pinasterPublication . Esteves, Bruno; Nunes, Lina; Domingos, Idalina; Pereira, HelenaSapwood and heartwood samples of Pinus pinaster were treated in an oven at 190ºC and 200ºC for 2-6h. Dimensional stability, measured as Anti Shrinking Efficiency (ASE) between 0% and 65% relative humidity, durability against fungi, mechanical resistance (MOE and MOR), hardness and chemical composition were determined for treated and untreated sapwood and heartwood. Radial ASE reached 52% for sapwood and 50% for heartwood while tangential ASE reached 50% and 40% respectively. MOE increased slightly at the beginning of the treatment decreasing afterwards. No significant differences were found between sapwood and heartwood. MOR decreased by 50% and 30% for sapwood and heartwood respectively. A significant increase in durability against Rhodonia placenta was found for both heartwood and sapwood at the higher temperature and for heartwood only at 190º for 4h.
- Improvement of termite resistance, dimensional stability and mechanical properties of pine wood by paraffin impregnationPublication . Esteves, Bruno; Nunes, Lina; Domingos, Idalina; Pereira, HelenaParaffin has been used as surface protection of wood throughout the ages but its use for impregnation to improve wood resistance to biodegradation is recent. This study determined the main improvements on wood properties with paraffin impregnation. Healthy Pinus pinaster Ait. wood was impregnated with paraffin at different levels using a hot–cold process. Weight gain, equilibrium moisture content and dimensional stability (ASE) at 35 and 65 % relative humidity, termite durability against Reticulitermes grassei (Clément), bending strength, bending stiffness (MOE) and Janka hardness were determined. Density increased from 0.57 to 0.99, ASE ranged between 38–96 % and 16–71 % for 35 and 65 % relative humidity, respectively. Equilibrium moisture content decreased from 9.9 and 12.0 % to 0.8 and 3.6 % for 35 and 65 % relative humidity. Termite durability improved from level 4 to level 3 of attack, and higher termite mortality was found in treated wood (52 % against 17 %). Bending strength (MOR) increased with paraffin weight gain, reaching a 39 % increase. MOE also increased by about 13 % for wood with a weight gain around 80 %. Janka hardness increased significantly reaching about 40 % for wood with 80 % weight gain. Paraffin impregnated wood has improved properties with regard to equilibrium moisture content, dimensional stability and density, bending strength and Janka hardness, and resistance against termites.
- Liquefied wood as a partial substitute of melamine-urea-formaldehyde and urea-formaldehyde resinsPublication . Esteves, Bruno; Martins, João; Martins, Jorge; Cruz-Lopes, Luísa; Vicente, José; Domingos, IdalinaMaritime pine (Pinus pinaster) sawdust was used to produce liquefied wood by the polyhydric method with acid catalysis. The process was optimized to produce the highest amount of liquefied wood. Wood liquefied at 160ºC for 90 min was used in the adhesion tests. The bond strength of veneer glued with urea-formaldehyde and melamine-urea-formaldehyde resins and several mixtures of liquefied wood with urea- formaldehyde and melamine-urea-formaldehyde wasevaluated by automated bonding evaluation system. With the increase in liquefied wood content the bond strength decreased. Nevertheless for 20% liquefied wood the reduction of internal bond strength is relatively small and still within the minimum standards required. When 70% of liquefied wood is employed there is a significant decrease in bond strength. In conclusion it is possible to use a small amount of maritime pine sawdust liquefied wood as a partial substitute of urea-formaldehyde and melamine-urea-formaldehyde resins in the particleboard production, thus decreasing the formaldehyde content.
- Life Cycle Assessment as a tool to promote sustainable Thermowood boards: a Portuguese case studyPublication . Ferreira, J.; Esteves, B.; Nunes, L.; Domingos, I.The present work aims to develop the Life Cycle Assessment study of thermo-modified Atlanticwood® pine boards based on real data provided by Santos & Santos Madeiras company. Atlanticwood® pine boards are used mainly for exterior decking and cladding facades of buildings. The LCA study is elaborated based on ISO 14040/44 standard and Product Category Rules for preparing an environmental product declaration for Construction Products and Construction Services. The inventory analysis and, subsequently, the impact analysis have been performed using the LCA software SimaPro8.0.4. The method chosen for impact assessment was EPD (2013) V1.01. The results show that more than ¾ of ‘Acidification’, ‘Eutrophication’, ‘Global warming’ and ‘Abiotic depletion’ caused by 1 m3 of Atlanticwood® pine boards production is due to energy consumption (electricity + gas + biomass). This was to be expected since the treatment is based on heat production and no chemicals are added during the heat treatment process.
- Densification and heat treatment of maritime pine woodPublication . Esteves, Bruno; Ribeiro, Fábio; Cruz-Lopes, Luísa; Ferreira, José; Domingos, Idalina; Duarte, Marta; Duarte, Sónia; Nunes, LinaPine (Pinus pinaster Ait.) wood samples were subjected to a combined treatment by densification and heat treatment. Samples were densified before and after heat treatment. The heat treatment was made inside an oven at 190ºC during 2 to 6 h and wood densification was made in a hot press at around 48 bar pressure and temperatures between 160ºC and 200ºC for 30 min. Compression-set, compression-set recovery after three cycles of water soaking followed by oven drying, density, hardness, bending strength and stiffness and durability against subterranean termites were determined after the treatment. Results show that densification increases density, hardness, bending strength, stiffness and durability against termites. Heat treatment applied after the densification is more effective in reducing compression-set recovery than if applied before.
- Optimizing Douglas-fir bark liquefaction in mixtures of glycerol and polyethylene glycol and KOHPublication . Esteves, Bruno; Cruz-Lopes, Luísa; Ferreira, José; Domingos, Idalina; Nunes, Lina; Pereira, HelenaThe outer bark of Douglas-fir (Pseudotsuga menziesii) has a significant amount of cork tissue that may be an important source of chemicals derived from its natural polymers, suberin, cellulose, hemicelluloses and lignin. The present work focuses on the polyalcohol liquefaction of Douglas-fir bark with glycerol and polyethylene glycol (PEG) in order to obtain a liquid that can be further processed to other chemicals and products. The results show that Pseudotsuga bark can be liquefied in a significant percentage in presence of alkali. The best liquefaction yield was obtained with 6% KOH as agents. Although the use of a cosolvent is favorable, good liquefaction yields can also be obtained by glycerol alone. Lower temperatures are favorable as they lead to acceptable liquefaction yields. FTIR-ATR studies showed that all the structural compounds of the bark were attacked and depolymerized. The process tested has a high potential for generation of value-added products from liquefied Douglas-fir bark.
- Determination of decay resistance against Pleurotus ostreatus and Coniophora puteana fungus of heat-treated scotch pine, oak and beech wood speciesPublication . Ayata, Umit; Akcay, Caglar; Esteves, BrunoThe objective of this study, to investigate decay resistance against Pleurotus ostreatus and Coniophora puteana fungus of heat - treated (ThermoWood method) Scotch pine, oak and beech wood species. Scotch pine ( Pinus sylvestris ), oak ( Quercus petreae ) and beech ( Fagus orientalis ) wood species were heat treated at 190°C for 2 h, 212°C for 1 h and 2 h by the ThermoWood® method. Untreated and heat - treated specimens were exposed to white - rot fungus ( Pleurotus ostreat us ) and brown - rot fungus ( Coniophora puteana ) for 12 weeks according to procedures defined in JIS K 1571 standard. After weight losses of all specimens were calculated. According to the results, least weight loss was determined on heat treated at 212°C for 2 h. Heat treatment can be used effectively against fungal attack for Scotch pine, oak and beech wood species.