Search

Aminated tannins were prepared by reacting mimosa condensed tannin extract with ammonia yielding the substitution of many, if not all of the tannin hydroxyl groups with -NH2 groups. A tannin-aminated tannin (ATT) particleboard coating was then prepared by reacting raw tannin extract with aminated tannin extract and thus cross-linking the two by substituting tannin's hydroxyl groups with the -NH2 groups on the aminated tannin to form -NH-bridges between the two. The resulting particleboard coating gave encouraging results when pressed at 180°C for 3 min. Conversely, the system in which tannin was reacted/cross-liked with urea (ATU) by a similar amination reaction did not perform as well as the ATT system, and this even when a higher curing temperature and longer hot press time were used. In particular its water repellence was worse probably due to the presence of urea and such a system with lower reactivity. Nonetheless, substituting the tannin -OHs with the urea -NH2 groups appeared to also take place. ATT gave better results than ATU as regards water repellence and mechanical resistance as shown by the cross cut test. The ATT system was shown to be between 95% and 98% biosourced. The difference appeared to be due, by TMA analysis, to the much faster formation of the ATT hardened network leading to a better cross-linked polymer coating. The chemical species formed for both the ATT and ATU system were studied by MALDI ToF and CP MAS 13C NMR. [ABSTRACT FROM AUTHOR]

Melamine-dialdehyde starch resins used for wood surface finishes have been developed. The reaction of melamine with dialdehyde starch has been shown to occur by FTIR and MALDI ToF spectrometry, with several oligomer species due to the reaction of the two materials being identified, and the resin thermal stability was studied by thermogravimetric analysis. The resins were prepared by two different procedures when it was realized that dialdehyde starch is sensitive to too high a temperature for prolonged times. The melamine-dialdehyde starch resins were applied on particleboard supports as a direct liquid surface finish and a resin-impregnated paper. The surface finishes were tested for adhesion by the cross-cut test, their initial sessile drop contact angle, and the contact angle evolution as a function of time. The best results were obtained by the resins catalyzed by 2% ammonium sulfate and applied to the support surface as a resin-impregnated paper hot pressed for 3 min at 200°C, although the results at 180°C also looked promising. [ABSTRACT FROM AUTHOR]

Screw connection is a type most commonly applied to timber structures. As important commercial tree species in China, Masson pine and Chinese fir have the potential to prepare wood structures. In this study, the effects of the diameter of the self-tapping screw and the guiding bores on the nail holding performance on different sections of Masson pine and Chinese fir dimension lumbers were mainly explored. The results showed that: (1) The nail holding strength of the tangential section was the maximum, followed by that of the radial section, and that of the cross section was the minimum. (2) The nail holding strength of Masson pine was higher than that of Chinese fir. (3) The nail holding strength grew with the increase in the diameter of self-tapping screws, but a large diameter would lead to plastic cracking of the timber, thus further affecting the nail holding strength. Masson pine and Chinese fir reached the maximum nail holding strength when the diameter of self-tapping screws was 3.5 mm. (4) Under a large diameter of screws, prefabricated guiding bores could mitigate timber cracking and improve its nail holding strength. (5) Prefabricated guiding bores were more necessary for the screw connection of Masson pine. The results obtained could provide a scientific basis for the screw connection design of Masson pine and Chinese fir timber structures. [ABSTRACT FROM AUTHOR]

To study the static bending creep properties of glass fiber reinforced wood, glass fiber reinforced poplar (GFRP) specimens were obtained by pasting glass fiber on the upper and lower surfaces of Poplar (Populus euramevicana, P), the performance of Normal Creep (NC) and Mechanical Sorptive Creep (MSC) of GFRP and their influencing factors were tested and analyzed. The test results and analysis show that: (1) The MOE and MOR of Poplar were increased by 17.06% and 10.00% respectively by the glass fiber surface reinforced composite. (2) The surface reinforced P with glass fiber cloth only exhibits the NC pattern of wood and loses the MSC characteristics of wood, regardless of the constant or alternating changes in relative humidity. (3) The instantaneous elastic deformation, viscoelastic deformation, viscous deformation and total creep deflection of GFRP are positively correlated with the stress level of the external load applied to the specimen. Still, the specimen's creep recovery rate is negatively correlated with the stress level of the external load applied to the specimen. The static creep deflection and viscous deformation of GFRP increase with the increase of the relative humidity of the environment. (4) The MSC maximum creep deflection of GFRP increased by only 7.41% over the NC maximum creep deflection, but the MSC maximum creep deflection of P increased by 199.25% over the NC maximum creep deflection. (5) The Burgers 4-factor model and the Weibull distribution equation can fit the NC and NC recovery processes of GFRP well. [ABSTRACT FROM AUTHOR]