RESUMEN
An issue in engineered wood products, like oriented strand lumber (OSL), is the low thermal conductivity coefficient of raw material, preventing the fast transfer of heat into the core of composite mats. The aim of this paper is to investigate the effect of sepiolite at nanoscale with aspect ratio of 1:15, in mixture with urea-formaldehyde resin (UF), and its effect on thermal conductivity coefficient of the final panel. Sepiolite was mixed with UF resin for 20 min prior to being sprayed onto wood strips in a rotary drum. Ten percent of sepiolite was mixed with the resin, based on the dry weight of UF resin. OSL panels with two resin contents, namely 8% and 10%, were manufactured. Temperature was measured at the core section of the mat at 5-second intervals, using a digital thermometer. The thermal conductivity coefficient of OSL specimens was calculated based on Fourier's Law for heat conduction. With regard to the fact that an improved thermal conductivity would ultimately be translated into a more effective polymerization of the resin, hardness of the panel was measured, at different depths of penetration of the Janka ball, to find out how the improved conductivity affected the hardness of the produced composite panels. The measurement of core temperature in OSL panels revealed that sepiolite-treated panels with 10% resin content had a higher core temperature in comparison to the ones containing 8% resin. Furthermore, it was revealed that the addition of sepiolite increased thermal conductivity in OSL panels made with 8% and 10% resin contents, by 36% and 40%, respectively. The addition of sepiolite significantly increased hardness values in all penetration depths. Hardness increased as sepiolite content increased. Considering the fact that the amount of sepiolite content was very low, and therefore it could not physically impact hardness increase, the significant increase in hardness values was attributed to the improvement in the thermal conductivity of panels and subsequent, more complete, curing of resin.
RESUMEN
The aim of this work is to investigate the effect of the fortification level of nanowollastonite on urea-formaldehyde resin (UF) and its effect on mechanical and physical properties of oriented strand lumbers (OSL). Two resin contents are applied, namely, 8% and 10%. Nanowollastonite is mixed with the resin at two levels (10% and 20%). It is found that the fortification of UF resin with 10% nanowollastonite can be considered as an optimum level. When nanowollastonite content is higher (that is, 20%), higher volume of UF resin is left over from the process of sticking the strips together, and therefore is absorbed by wollastonite nanofibers. The mechanism involved in the fortification of UF resin with nanowollastonite, which results in an improvement of thickness swelling values, can be attributed to the following two main factors: (i) nanowollastonite compounds making active bonds with the cellulose hydroxyl groups, putting them out of reach for bonding with the water molecules and (ii) high thermal conductivity coefficient of wollastonite improving the transfer of heat to different layers of the OSL mat, facilitating better and more complete resin curing. Since nanowollastonite contributes to making bonds between the wood strips, which consequently improves physical and mechanical properties, its use can be safely recommended in the OSL production process to improve the physical and mechanical properties of the panel.