Hybrid silane-crosslinking polymers: a potential alternative to polyurethane wood adhesives? A preliminary investigation by TMA
In the last years, the research on wood adhesives has focused on matching technical performance with low health and environmental impacts. This study presents the first development of a new adhesive technology based on hybrid silane-crosslinking polymers that can combine both silicone’s and polyurethane’s adhesive properties. The advantage of hybrid silane-crosslinking polymers is the absence of potential harmful chemicals, such as isocyanates and solvents. Two hybrid formulations were characterized by thermo-mechanical analysis (TMA) and glued wood product elasticity is discussed in this brief original.
Comparison of TMA and ABES as forecasting systems of wood bonding effectiveness
Materials and methods Commercial pine (Pinus radiata) and mimosa (Acacia mearnsii) bark tannin extracts solutions in water were tested by thermomechanical analysis (TMA) at different temperatures and at different percentage paraformaldehyde hardener addition both under isothermal conditions and at a constant temperature rate of increase of 10 C/minute up to the hardening of the tannin resin glue-mix according to techniques already reported [1] and the Young’s modulus as a function of time and temperature for each of the cases tested was calculated and reported. Triplicate samples of beech wood alone, these being sliced decorative beech veneers of 0.6 mm thickness, and of two beech wood plys of the same type and dimensions bonded with the resins as a layer of 350 lm, for a total samples dimension of 21 · 6 · 1.2 mm were tested with a Mettler 40 TMA apparatus in three points bending on a span of 18 mm exercising a force cycle of 0.1/0.5 N on the specimens with each force cycle of 12 seconds (6 s/ 6 s). Samples of pine wood of dimensions 120 · 20 · 0.8 mm were then bonded two by two by an overlap of 20 · 20 mm by both hot-pressing them and immediately testing them in an Automated Bond Evaluation System (ABES) [2,3] by using the same tannin adhesives used for the TMA experiments. The concentrations of formaldehyde used were of 0%, 2%, 4%, 6%, 7%, 8%, 10%, 12% and 14% paraformaldehyde fine powder hardener on tannin solids at ABES temperatures of 75 C, 90 C, 100 C, 110 C, 120 C, and at pHs of 4.5, 5.4, 6.1, 6.8, 6.9, 7.0, 7.4, 7.6, 8.0, 8.6. The correlation results between the two techniques are reported in Figs. 1 and 2. In the figures Y 1⁄4 TMA MOE in MPa. X 1⁄4 ABES joint tensile strength in MPa.
Palaeomicrobiology: current issues and perspectives
Palaeomicrobiology is an emerging field that is devoted to the detection, identification and characterization of microorganisms in ancient remains. Data indicate that host-associated microbial DNA can survive for almost 20,000 years, and environmental bacterial DNA preserved in permafrost samples has been dated to 400,000–600,000 years. In addition to frozen and mummified soft tissues, bone and dental pulp can also be used to search for microbial pathogens. Various techniques, including microscopy and immunodetection, can be used in palaeomicrobiology, but most data have been obtained using PCR-based molecular techniques. Infections caused by bacteria, viruses and parasites have all been diagnosed using palaeomicrobiological techniques. Additionally, molecular typing of ancient pathogens could help to reconstruct the epidemiology of past epidemics and could feed into current models of emerging infections, therefore contributing to the development of appropriate preventative measures.