Preparation of Polyurethane Adhesives from Crude and Purified Liquefied Wood Sawdust

Polyurethane (PU) adhesives were prepared with bio-polyols obtained via acid-catalyzed polyhydric alcohol liquefaction of wood sawdust and polymeric diphenylmethane diisocyanate (pMDI). Two polyols, i.e., crude and purified liquefied wood (CLW and PLW), were obtained from the liquefaction process with a high yield of 99.7%. PU adhesives, namely CLWPU and PLWPU, were then prepared by reaction of CLW or PLW with pMDI at various isocyanate to hydroxyl group (NCO:OH) molar ratios of 0.5:1, 1:1, 1.5:1, and 2:1. The chemical structure and thermal behavior of the bio-polyols and the cured PU adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Performance of the adhesives was evaluated by single-lap joint shear tests according to EN 302-1:2003, and by adhesive penetration. The highest shear strength was found at the NCO:OH molar ratio of 1.5:1 as 4.82 ± 1.01 N/mm2 and 4.80 ± 0.49 N/mm2 for CLWPU and PLWPU, respectively. The chemical structure and thermal properties of the cured CLWPLW and PLWPU adhesives were considerably influenced by the NCO:OH molar ratio.

Examination of wood adhesive bonds via MicroCT: The influence of pre-gluing surface machining treatments for southern pine, spotted gum, and Darwin stringybark timbers

The successful manufacturing of glulam from several important Australian commercial timbers is quite challenging due to difficulties in gluing. Improvements in adhesive bond performance of spotted gum, Darwin stringybark, and southern pine timber have been achieved using alternative pre-gluing surface machining methods, e.g., face milling and sanding-post planing, when compared to conventional planing methods. In order to improve the understanding of the effects that different surface machining methods have on adhesive bond performance, this study used micro X-ray computed tomography and microscopy to assess key adhesive bond criteria. There was a considerable loss in the amount of adhesive after the wet and dry test cycles for all species. There was also an extremely high frequency of voids in the glue lines for all species, which would negatively impact bond strength and durability. Face mill prepared timber boards resulted in thicker glue lines and greater resistance to adhesion loss, compared to boards prepared via planing. For the two hardwood species, face milling also resulted in greater adhesive penetration; however, for southern pine, there were no significant differences in adhesive penetration between the three surface machining treatments. Adhesive penetration was much deeper in southern pine compared to spotted gum and Darwin stringybark.

Characteristics of adhesive bonding with enamel deproteinization

ABSTRACT Objective: To evaluate the effect of using sodium hypochlorite (NaOCl) on the bond characteristics of orthodontic metal brackets bonded to enamel surface using three adhesive systems. Methods: One hundred twenty premolars were selected and randomly divided into two equal groups of 60 teeth/ each (Groups I and II). The teeth of Group I were left untreated while those of Group II were exposed to 5.25% NaOCl for 1 minute. The teeth in either group were randomly subdivided into three equal subgroups of 20 teeth/ each (A, B and C), according to the type of adhesive system used to bond the brackets. In Subgroup A, phosphoric acid + Transbond XT primer and adhesive were used. In subgroup B, Transbond Plus self-etching primer (SEP) + Transbond XT adhesive were utilized. In subgroup C, phosphoric acid + SmartBond LC adhesive were used. The shear bond strength (SBS) and the degree of adhesive penetration to enamel surface were assessed. Data analyses were performed using ANOVA, post-hoc (LSD), t and chi-square test. Results: Transbond XT had significantly higher SBS than SmartBond LC (p< 0.05). Phosphoric acid provided significantly higher SBS and degree of adhesive penetration than SEP (p< 0.05). NaOCl significantly increased SBS and degree of adhesive penetration in Subgroups B and C (p< 0.05). Conclusion: Adhesion quality of Transbond XT adhesive is better than SmartBond LC. Phosphoric acid is more effective than SEP. NaOCl enhances the bond characteristics.

Surface Bonding Graphene-Based Elastomeric Sensor: Preliminary Characterization of Adhesion Strength

This research intends to propose a structural integration methodology for a strain sensor based on nano-filled elastomer and its preliminary bonding strength characterization. To provide a good strength adhesion onto a structural component, a special mould was designed, made of Acrilonitrile butadiene styrene (ABS) material and realised with a 3D printing. This specific texture provided the lower surface of the elastomer (PDMS-matrix) with a special micro voids allowing for the adhesive penetration. The electrodes were made by simple conductive paste. To have a chemically compliant coupling between the elastomer and this paste, an off-the-shelf cheap neutral silicone was used. This paste was then made conductive by adding a low-cost graphite powder, obtained from a pencil lead. The test was realized with an aluminium beam in cantilever configuration. The load were applied at the free edge by means of calibrated masses of increasing weights. For each mass, the values of tip displacement and the resistance provided by the nano-filled elastomer and a reference strain gauge were logged for a set of 10 cycles. Obtained data clearly revealed that, all sensors exhibit coherent readouts with respect to the reference strain gauges and a quasi linear sensitivity curve in the whole range.

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

The main goal of this study was to analyze glue line on eucalyptus wood. In order to do that, thickness of main and secondary glue lines were measured as well their interaction with apparent density of elements glued with resorcinol-formaldehyde (RF) and castor polyurethane (CP) adhesives. Anatomical wood characterization of Eucalyptus grandis × Eucalyptus urophylla was performed by correlating glue line thickness. According to normative instruction, specimens were produced for delamination tests. The experiment was conducted in a completely random 2 × 2 design factorial scheme (two classes of apparent density and two adhesives). Pearson correlation (t < 0.01) was performed among variables. It was found that there was adhesive penetration into wood pots and rays. Glue line thickness was higher in woods with density higher than 0.58 g cm−3 glued with RF adhesive. There was low correlation among density, vessel diameter, main and secondary glue lines (t < 0.01).

Effect of atmospheric plasma torch on ballistic woven aramid

Atmospheric pressure plasma torch (APPT) is a cold plasma technique that can be used to treat materials with a polymeric surface in an environmentally friendly way. The treatment modifies the topography and chemistry of the surfaces. The effect of APPT on woven aramid is studied with the aim of enhancing its impact strength for ballistic applications. The shielding, laminated with several layers of woven and resin, can better resist projectile penetration. Woven aramid has low wettability due to its low polarity. Therefore adhesives penetrate the woven fibers with difficulty. APPT treatment considerably increases the polar component of the surface energy and the wettability is improved. Changes in the micro-topography and chemical composition that generate enhanced adhesion are investigated. The adhesion ability was determined by adhesion pull-off test, T-peel test, and impact test. Two types of adhesives were used: an elastic one (polyurethane-based, with elastoplastic mechanical behavior) and a rigid one (epoxy-based). Composites made with woven aramid treated with APPT exhibit an enhanced resistance to impact in terms of elastic energy recovery due to the greater degree of adhesive penetration between the woven fibers of each layer and better transfer of loads.