This paper presents a systematical approach to the properties of wood impregnated with different waterbased melamine resins, to provide a basis for further research. Therefore, ten commercially available methylated melamine formaldehyde resins with increasing ratios of melamine to formaldehyde have been compared in respect of their influence in dimension stabilisation, sorption behaviour, formaldehyde emissions, and water repellency of the treated wood. The dimension stabilisation caused by resin molecules that penetrated the wooden cell wall correlated with the molar mass of the resins used for impregnation. The changes in the sorption isotherms were attributed to a bulking effect. Formaldehyde emissions during and after curing increased with an increasing ratio of formaldehyde to melamine in the resins
Observations of Hylotrupes bajulus in kiln-dried timber are very rare. In Germany, this has often been attributed to a preventive effect of the drying process. Commonly assumed explanations for a preventive effect are the loss of substances that attract the insects and the decline in nutrients caused by kiln drying. A review of the literature has been undertaken and these explanations are not well supported. Seemingly, the main direct effect of kiln drying at temperatures below 100°C is the killing of all larvae present in the timber before drying. Some indirect effects may also contribute to the reduced risk of infestations in kiln-dried timber, namely kiln-dried timber is often free of wane and therefore free of outer sapwood; it shows a low number of cracks and has a planed surface. Especially the absence of wane may contribute to the scarcity of Hylotrupes in kiln-dried timber
The wet adhesion of water borne acrylic dispersions is a crucial factor on the performance of outdoor coatings on wood. Pine sapwood was treated with several methods for surface activation to increase the wet adhesion of water borne acrylic dispersions. The wet adhesion was measured by pull‐off tests as well as with a modified cross‐cut test. Atmospheric plasma, corona treatment and fluorination increased the wet adhesion of the coating which is attributed to the increasing polar portion of the surface free energy. Other ways of improving the wet adhesion are the addition of promotors, the use of primers and organisational improvements.
Bond line openings while an adhesive is still viscous (liquid or paste-like) leave characteristic marks. Air fingers and cavitation develop on the surface of the adhesive when joint parts are fully or partially separated before solidifying of the adhesive. Therefore, the observation of air fingers or cavitation provides important clues on the root cause of the failure of bond lines. There is still limited knowledge about the factors that lead to the formation of either air fingers or cavitation. Additionally, a resoftening of thermoplastic adhesives by high temperatures may be confused with air fingers or cavitation that developed before the initial curing. To improve the understanding of the adhesive structures, we assemble some experiments on this phenomenon. Air fingers dominate when air easily penetrates the adhesive, the adhesive thickness is high, and the adhesive has a low viscosity (early in the process). Cavitation dominates when the adhesive layer is thin, when the viscosity is high (late in the process) or when the air ingress is restricted.
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