Improvement mechanism of bondability in UF-bonded reed and wheat straw boards by silane coupling agent and extraction treatments

The effects of silane coupling agents and extractives on the wettability of reed and wheat straws were investigated. The inherent wettability of these materials was low but could be significantly improved by treating with sil ane coupling agents. The degree of improvement achieved by each silane coup ling agent was different: Vinyl silane had almost no effect on wettability, epoxide silane was found to be more effective for reed straw, and amino si lane was better for wheat straw. The wettability of these materials could a lso be improved by ethanol-benzene extraction, which resulted in more impro vement in wheat straw than reed straw. The analyses of untreated reed and w heat straws by electron spectroscopy for chemical analysis (ESCA) revealed that there was much silicon on both the outer and inner surfaces of the for mer but only on the outer surface of the latter. The influence of hot-water extractives and silane coupling agents on the gelation time and pH of urea formaldehyde (UF) resin was also examined. The addition of extractives was found to increase the gelation time. Amino silane greatly retarded the gel ation of UF resin, whereas epoxide and vinyl silanes had no influence on re sin gelation. This retardation was found to be due to an increase in the pH of the resin.