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Prepolymers containing hexamethoxymethyl melamine and either sucrose (Suc-HMMM) or polyvinyl alcohol (PVA-HMMM) were prepared by acid catalysis under reaction conditions optimised with respect to stiffening effect when introduced into Pinus radiata veneers by vacuum impregnation and cured by hot pressing at 150 C. Maximum increases in MOE were 20%...
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Context 1
... it is fortunate that the two treated panels counterbalance rather than augment each other, the addition of a second treated veneer would be an expensive solution to problems of bow or warp. A valuable increase in surface hardness was evident in all of the treated surface veneers (Table 2). Surface hardening, measured as indentation after dropping a 500 g ball from a height of 400, 500 or 600 mm, was influenced most significantly by the strength of the P-H:S-H treatment solution with the immersion time, 30 or 60 minutes, having a lesser contributory effect (Table 2). ...Context 2
... valuable increase in surface hardness was evident in all of the treated surface veneers (Table 2). Surface hardening, measured as indentation after dropping a 500 g ball from a height of 400, 500 or 600 mm, was influenced most significantly by the strength of the P-H:S-H treatment solution with the immersion time, 30 or 60 minutes, having a lesser contributory effect (Table 2). ...Citations
... In an accompanying paper (Molloy et al. 2011) we describe the development of a wood modification method utilising a mixture of prepolymers (P-H:S-H) containing the amino resin hexamethoxymethyl melamine as the principal crosslinking component. Modification of veneers and fibres using P-H:S-H produced engineered wood products such as LVL and MDF with significantly improved physical properties. ...
... The preparation of the wood modifying mixture denoted as P-H:S-H, and manufacture of modified LVL is described elsewhere (Molloy et al. 2011). Briefly, P-H:S-H contained prepolymers prepared from a) polyvinyl alcohol reacted under acidic conditions with hexamethoxymethyl melamine for 30 min at 20 C, and b) sucrose reacted with hexamethoxymethyl melamine for 24 h, wherein a) and b) were combined in a 1:1 weight ratio. ...
... Twelve treated veneers were laid up with PF resin (200 g/m 2 ) and hot pressed (37 mm thickness, 30 min, 160 C). This is the "complete" LVL arrangement described elsewhere (Molloy et al. 2011). As an untreated control LVL was made from untreated veneers using the same glue spread rate and hot press conditions as described above. ...
An investigation of the effects on decay and termite resistance of a wood modification process involving prepolymers of hexamethoxymethyl melamine (HMMM) was conducted using LVL as a model engineered wood product. Dry Pinus radiata veneers were vacuum-impregnated with a wood modification formulation containing a mixture (P-H:S-H) of two separate prepolymerisation reactions containing polyvinyl alcohol and HMMM, and sucrose and HMMM. Veneers were re-dried at 30 C, assembled as 12-ply lay up and hot pressed at 160 C for 30 min. Test specimens subjected to laboratory decay tests performed according to AWPC showed either no change or small decreases in susceptibility to three brown rot fungi Coniophora puteana, Fomitopsis lilacino-gilva and Tyromyces palustris when compared to unmodified controls. The inhibitory effects were generally more apparent in leached veneers. Modified LVL specimens exposed to Coptotermes acinaciformis termites showed only a small degree of protection and no change in surface grazing of superficial veneers. Therefore, although P-H:S-H modification of engineered wood products produces significant performance benefits with respect to physical properties, it can not be used in the field without the addition of wood preservatives. The biological effects of P-H:S-H modification are compared with a number of other wood modification processes.
Current research trends of non-copper wood preservatives for enhancing durability was reviewed; as a follow-up of the review in 2012 on copper-based wood preservatives. Main environmental friendly non-copper wood preservatives studied by many scientists were boron-based compounds, synthetic compounds from natural products, and pyrethroids family of chemicals, etc. The critical issue regarding treated woods with boron-based compounds used outdoors was the leaching of boron. Many studies mainly focused on boron fixation improvement using variety of polymers. Moreover, the studies showed notable increases in attempts to use natural products used commonly in the medical fields as wood preservatives as well as outdoor use of chemical modified such as acetylated wood developed in purpose of stabilizing dimension.
