甲醛中甲醇含量对低摩尔比脲醛树脂胶性能影响的研究

STUDY ON INFLUENCE OF METHANOL CONTENT ON PROPERTIES OF LOW-FORMALDEHYDE UF RESIN

研究了原料甲醛中甲醇含量对低醛化(低摩尔比)脲醛树脂性能的影响。结果表明:甲醇含量提高,甲醛原料贮存期增长,树脂贮存稳定性提高,但同时导致树脂中游离甲醛升高,板材甲醛释放量上升。树脂用NH4Cl作固化剂适用期(活性期)和固化时间随甲醇含量的升高而缩短,但适用期和固化时间太长,不适合直接做固化剂。而用草酸和10%HCl作固化剂,适用期和固化时间随甲醇含量的升高而延长。对胶合强度的进一步测试表明:原料甲醛中甲醇含量提高,胶合板湿强度和木破率明显下降,当摩尔比(U∶F)为1∶1.1、甲醇含量>6.0%时,杨木芯板胶合强度就达不到GB/T9846-1988标准0.7MPa的要求,柳桉芯板胶合强度也显著HNMR核磁共振谱证实,原料甲醛中甲醇含量高,树脂中水合下降,而干状胶合强度几乎无影响。用400Hz1甲醛含量亦高,—OCH3基也多。扫描电子显微镜(SEM)图显示,甲醇含量低时树脂固化成树状物,甲醇含量高时树脂固化成松散状。

Influence of methanol content in formaldehyde used as raw material for preparing low-formaldehyde(low molecular ratio) UF resin was studied.Results showed that high content of methanol in formaldehyde led to prolonged storage time of formaldehyde,increased storage stability of resin,higher free formaldehyde content in the resin and higher formaldehyde emission from plywood.Pot life and gelation time of the resin would be shortened by using NH_4Cl as curing agents but pot life and curing time were still to long to adopt NH_4Cl directly as suitable curing agent on the other hand,pot life and gelation time would be prolonged by using oxalic acid or 10% HCl as curing agents.Further tests on bond strength showed that higher content of methanol led to lower wet strength of plywood and lower wood (failure) ratio.When synthetic resin made with 1∶1.1 mol ratio(U∶F) and formaldehyde with methanol content higher than 6.0%,wet bond strength of poplar-core plywood could not reach 0.7 MPa level specified by GB/T 9846-1998,and wet bond strength of lauan-core plywood also decreased greatly,while dry bond strength was influenced insignificantly.Four hundred Hz ~1H NMR spectra showed that high content of methanol would lead to higher content of (hydrated) formaldehyde in the resin and increased content of —OCH_3 group.SEM results showed that cured resin graph was in tree shape for (resin) with lower methanol content in formaldehyde,while in loose shape for resin with (higher) methanol content in formaldehyde.