【作者】 赵佳宁；

【导师】 顾继友；

【作者基本信息】 东北林业大学 ， 生物材料工程， 2010， 博士

【摘要】 本论文利用现代仪器分析方法(FTIR、13CP/MAsNMR、DSC和LC-ESI/MS)研究弱酸性起始合成脲醛(UF)树脂机理和弱酸性起始合成三聚氰胺-尿素-甲醛(MUF)树脂凝胶机理,并使用响应曲面法优化弱酸性条件起始合成UF树脂工艺。探讨碱性加成阶段尿素添加次数和间隔时间对弱酸性条件起始合成UF树脂固化动力学和不同树种对弱酸性起始合成UF和MUF树脂固化的影响。研究发现弱酸性条件起始合成的UF树脂,在弱酸性条件下,质子化甲醛中碳的正电荷增多,有利于酸性条件下甲醛与尿素亲电取代反应进行。在弱酸性起始反应阶段离子化甲醛是反应主体,3价C+正离子与尿素分子中N原子上孤对电子形成化学键的同时H+发生脱离,生成羟甲基脲。酸性起始阶段生成的羟甲基脲之间发生缩聚反应,生成醚键连接的长链分子。弱酸性反应起始阶段就生成少量分子量1000以上的长链醚键分子。碱性加成阶段尿素与甲醛进行亲核取代反应,在碱性条件下,尿素是反应主体,尿素负离子与极化甲醛反应生成羟甲基脲；而且碱性加成阶段反应液中羟甲基数量开始减少,同时生成少量Uron环。随着亲核取代反应的进行,羟甲基数量减少越多,这证明羟甲基之间发生了缩聚反应,通过13C-NMR谱图证明生成了线性和支链型醚键。碱性加成阶段形成的树脂主要是各种长链羟甲基脲和醚键连接的长分子链混合物。酸性缩聚阶段RCONHCH2OH是反应主体,当RCONHCH2OH与H+结合生成RCONHCH2OH2+时,通过HMO计算,发现CH2+和OH2+都带正电荷；这种结构是不稳定的,容易脱去H20生成RCONHCH2+, RCONHCH2+与其它分子链段上N或者O原子的孤对电子发生亲电取代反应生成亚甲基和醚键相连接的长分子链结构。酸性缩聚阶段生成分子量超过1000大分子数量虽有增加,但不是主要部分。最后碱性阶段,加入的尿素与甲醛反应与碱性加成阶段反应机理相同,尿素与甲醛反应生成羟甲基脲混合物,使树脂分子量平均化。总之,弱酸性起始合成UF树脂是酸碱催化并且酸碱都参与反应进程的高分子合成反应。响应曲面法优化弱酸性起始合成UF树脂工艺发现,碱性加成阶段尿素添加次数和尿素添加的间隔时间对UF树脂的固体含量及固化时间影响不大,而对黏度、树脂中羟甲基含量、游离甲醛含量、各主要基团含量和板材的性能有很大的影响。树脂合成工艺中2次添加尿素,间隔时间20mmin时,树脂和板材性能都比较好。尿素添加次数和添加尿素的间隔时间对UF固化反应过程有显著影响,随着尿素添加次数和添加尿素间隔时间增加,UF树脂固化活化能降低。弱酸性条件下合成UF树脂的固化反应是介于0级和1级之间的反应。不同树种影响弱酸性起始合成UF树脂和MUF树脂固化,不同树种木粉与UF树脂和MUF树脂混合后,混合物的固化反应活化能低于UF树脂和MUF树脂,而且碰撞因子也降低。相同条件下,UF树脂和MUF树脂与木粉混合物固化程度低于UF树脂和MUF树脂；在180℃热压后通过FTIR分析表明,木材没有与UF或者MUF树脂发生化学反应。这说明树脂与木材胶合时,主要是树脂成分发生改变,而且木粉与UF树脂或者MUF树脂的固化反应也是介于0级和1级之间的非基元反应。通过对弱酸性起始合成MUF树脂研究发现,三聚氰胺加入量影响MUF树脂的耐水性。随着三聚氰胺加入量增多树脂胶接制品耐水性提高,这主要是因为三聚氰胺加入量增多,树脂中三嗪环增多导致树脂固化时交联密度提高；而且三聚氰胺加入量增多树脂酸性水解常数降低,提高了树脂耐水性。弱酸性条件下合成MUF树脂的结构特殊,这对MUF树脂储存稳定性产生影响。弱酸性起始合成MUF树脂在储存过程中树脂中羟甲基数量减少,并发生化学反应导致树脂中分子链的连接发生变化。MUF树脂储存期间,树脂分子链上胺基等活性基团之间或者活性基团与水之间通过氢键力连接的弱聚合体而形成分子链的聚集体是形成分子链团簇的主要原因,而且通过显微镜观察凝胶树脂其胶粒形状几乎都相同.更多还原

【Abstract】 In this paper the synthesis mechanism of UF resin as well as the storage stability mechanism of MUF resin were studied by FTIR,13CP/MAsNMR, DSC and LC-ESI/MS. The UF resin and MUF resin were synthesized at initial weak acid condition. The technology of UF resin was optimized by response surface method. The curing dynamic of UF resin was affected by the times of urea addition and interval time at base addition phase, and the effect of different wood species on the curing of UF resin and MUF resin were also investigated. It was found that the carbocation of protonation formaldehyde increased under weak acid condition. This condition favored to the electrophilic substitution. The protonation formaldehyde was the main reaction body and three valence carbocation reacted with lone-pair electron N of urea of forming chemical bond. Meantime, H+ broke away and gave birth to methylolurea. A little of exceeded 1000 (molecular weight) long chain molecular was formed, which was linked by ether bond. Urea and formaldehyde processed nucleophilic substitution at base addition phase. Urea was the main reaction body at alkali condition, under which the reaction of negative ion urea and polarization formaldehyde formed methylolourea. Moreover, the amount of methylolurea began to reduce in the reaction solution and a little Uron generated. Besides, with the decreasing of amount of methylolurea, the condensation between methylolurea and methylolurea occurred. The 13C-NMR spectrum proved the condensation generated lined and branched ether. The resin was mainly composed of mixture of various long chain methylolurea and ether compound at addition phase. RCONHCH2OH was the main reaction body at acidic phase. When the integration of RCONHCH2OH and H+ formed RCONHCH2OH2+, The HMO calculation showed the structure of the positive ion CH2+ and OH2+ were not stable. The structure was prone to keep off H2O and finally formed RCONHCH2+. The electrophilic substitution of RCONHCH2+ with N or O of molecular chain brought to methylene and dimethylene linked macromolecule chain. The amount of molecular weight of macromolecule exceeded 1000 with the increasing of acid condensation, which was not the main component. The reaction mechanism of last addition urea and formaldehyde was the same to base addition phase. The reaction of urea and formaldehyde made to the equilibration molecular weight of resin, which formed to mixture of methylolurea. The UF resin was catalysed by acid and base. Moreover, acid and base participated in process of macromolecule synthesis reaction, which was synthesized under initial weakly acid.The synthetic technology of UF resin was optimized by response surface method. It was found that the solid content and curing time of UF resin could not be dramatically affected by the times of additions, the interval of urea, and the viscosity and hydromethyl content, free formaldehyde content of the UF resin and properties of plywood were prominently affected by the number of additions and the interval between additions of urea. The main chemical groups of UF resin were influenced by the number of additions and the interval of urea. When the times of addition was two and the interval of urea was 20 min, the performance of urea-formaldehyde resins and the properties of plywood were much better. The addition times and interval notably affected curing reaction. With the increase of the additional and interval, times, the apparent activation energy of curing system of resin was reduced. The curing reaction grade of UF resin was between 0 and 1, when the UF resin was synthesized under initial weak acidity condition. Different wood species affected the curing of UF resin and MUF resin. After different wood species powder mixed with UF resin and MUF resin, the curing activation energy of compound was lower than UF resin and MUF resin. Furthermore, collision factor of compound decreased. The curing degree of compound was also lower than UF resin and MUF resin, which was the UF resin and MUF resin mixed with wood powder. After the compound was heared to 180℃, the compound was investigated by FTIR. The result showed that wood powder did not react with UF resin and MUF resin. When wood was glued by resin, resin component mainly changed. The curing reaction grade of compound was between 0 and 1 non-elementary reaction.It was found that melamine content affected the water resistance of MUF resin. With the melamine content increased, the water resistance of MUF resin bonded product improved. Moreover, the curing crosslinking density of MUF resin was enhanced, owing to the increasing of triazine. Meantime, the reduction of acidic hydrolysis constant of resin improved the water resistance. The structure of MUF resin was special, which was synthesized under initial weak acidity. This impacted on storage stability of MUF resin. The amount of methylol decreased, which was resulted to the chemical reaction at MUF resin storage. The chemical reaction leaded to the change of linking molecular chain. The weak aggregates molecular chain was the main reason of forming molecular cluster, which was connected by hydrogen bond among the amine group in the molecular chain, or active group and water. The results showed the shape of colloidal particle was the same through microscope examined the MUF resin.更多还原