Análise fisico-química e molhabilidade da superfície de madeiras amazônicas

Abstract

Fhysical (cell morphology, surface roughness, density) and chemical (mainly extractives) characteristics determine the wettability of the wood surface, which is directly related to the adhesion and coating process. Surface roughness depends on the machining conditions, cellular structure and interaction between both. The principal objective of this study was to evaluate the physico-chemical characteristics and surface wettability of Amazonian woods from Acre Staty. The specific objectives were: (i) to evluate the wood surface quality through visual and microscopic methods; (ii) to evaluate the effect of surface preparation conditions (planning and sanding) and the anatomical features on the surface roughness, by a texture and vessels measurements approach; (iii) to evaluate the effect of physical characteristics (surface roughness, texture and apparent density) on the surface wettability; and (iv) to evaluate the effect of aging on the surface inactivation and the its interaction with the nature and content of the extractives. Eight woods were studied: abiurana (Pouteria guianensis), garapeira (Apuleia molaris), jequitibá (Cariniana sp.), cedro (Cedrela odorata), angelim (Parkia pendula), angelim pedra (Hymenolobium excelsum), cerejeira (Amburana acreana) and cumaru (Dipteryx odorata). Woods were classified according to the texture (fine, medium and coarse) and the apparent density determined according to ASTM D 2395-93 standard. The visual evaluation was made according to the ASTM D 1666-2011 standard. Microscopic analyzes were performed through digital images by the Image-Pro® Plus software and by scanning electron microscopy using HITACHI TM300 apparatus. Amplitude parameters (Ra, Rz, Rt, Rp and Rv) were determined by the needle type roughmeter model TR 200 according to NBR ISO 4287:2002 standard. Contact angle was determined by the Drop Shape Analyser DSA 100. Surface inactivation was evaluated after 7, 14 and 21 days of aging in controlled conditions. Fourier transform infrared (FT-IR) spectroscopy analysis were performed using the VARIAN 640-IR FT-IR spectrometer in transmittance mode. Sanding reduced the surface roughness of woods, except for the Rv parameter of angelim pedra and cumaru woods. Wood texture affected the roughness and wettability. The visual evaluation had a significantly correlationship with Ra parameter. The type of surface preparation (planning x sanding) affected the contact angle. Roughness parameters had significant and negative correlations with the contact angle on the sanded surface in which roughened surfaces had lower angle, probably due to the greater penetration of the liquid by capillarity. Wood apparent density has an impact on the surface wettability, however, it did not explain the different wettability behavior among species within the same texture class. FT-IR analysis of wood extracts showed the presence of alcohols, ethers, esters, carboxylic acids, alkanes, alkenes, amines and amides, aldehydes, ketones, aromatic ring, fluorinated aliphatic and nitrogen compounds; and that the angelim and cumaru species had less hydrophobic compounds inducing a lower chemical inactivation of the wood surface