Analysis of glue line and correlations between anatomical characteristics of Eucalyptus grandis × Eucalyptus urophylla glued-laminated timber

Abstract

27The main goal of this study was to analyze glue line on eucalyptus wood. In order to do 28 that, thickness of main and secondary glue lines were measured as well their interaction 29 with apparent density of elements glued with resorcinol-formaldehyde (RF) and castor 30 polyurethane (CP) adhesives. Anatomical wood characterization of Eucalyptus grandis 31 × Eucalyptus urophylla was performed by correlating glue line thickness. According to 32 normative instruction, specimens were produced for delamination tests. The experiment 33 was conducted in a completely random 2 × 2 design factorial scheme (two classes of 34 apparent density and two adhesives). Pearson correlation (t < 0.01) was performed 35 among variables. It was found that there was adhesive penetration into wood pots and 36 rays. Glue line thickness was higher in woods with density higher than 0.58 g cm -3 glued 37 with RF adhesive. There was low correlation among density, vessel diameter, main and 38 secondary glue lines (t < 0.01). 39 40 Keywords: apparent density; resorcinol-formaldehyde; castor polyurethane; laminated 41 wood; delamination 42 43 Introduction 44Glued laminated timber (Glulam) is a structural product obtained by gluing 45 pieces of timber with fibers parallel to each other [1]. The market still needs to know 46 more information about the mechanical resistance of this product; for that reason, to 47 understand how glulam will work it is important to evaluate the behavior of some 48 variables, such as, apparent density and timber glued with adhesive. 49Wood density provides information to support methods that should be adopted 50 during the gluing process. By its determination, it is possible to correlate adhesion 3 51 resistance with anatomic elements. Proportion of empty spaces combined with 52 dimensions and arrangement of cellular elements have influence on adhesive's mobility 53 and penetration into timber structure as well in the resistance of glue line to 54 delamination [2, 3, 4, 5,6, 34]. When low density (higher frequency and vessel 55 diameters, with high and wide radii), it may allow excessive penetration of adhesive, if it 56 does not present an ideal viscosity and formation of ravenous glue line [7, 8]. 57When species are anatomically unfavorable for gluing, there will be low 58 adhesive penetration and formation of a thick glue line [8, 9]. Both types of glue lines 59 are undesirable, because they reduce mechanical strength of glued joints causing 60 separation of adjacent layers. Variations on adhesive viscosity can correct this problem 61 [3]. 62 Physico-chemical adhesion phenomenon predicts an interaction mechanism 63 between solid surfaces glued by adhesive and the capacity of holding other materials 64 together [10]. Adhesives are used to join elements by flowing and filling empty spaces 65 between them. Thus, they can reduce distances and create interactions among glued 66 elements [11]. 67 It is important to understand the interaction between wood and adhesive, because 68 it helps to evaluate glueing quality [7],...