采用胶体化学的方法对Fe~(2+)/H_2O_2影响脲醛树脂(UF)胶ζ电位及其稳定性的因素进行了研究.结果表明,在pH=8.0时,脲醛树脂胶粒的ζ电位平均值约-32.5 mV,粒子带负电,并以单分散形式存在.随着Fe~(2+)离子或H_2O_2加入量的增加,脲醛树脂胶ζ电位的绝对值迅速减小,从而使胶粒间排斥势垒降低,胶粒发生聚集,体系粘度随之增大并最终产生凝胶.其中,Fe~(2+)离子对脲醛树脂胶粒的ζ电位和粘度η变化的影响幅度比H_2O_2更为明显.pH值对胶体稳定性的影响主要表现在,pH值约为9时,体系具有最大的ζ电位,除此之外,pH值增大或减小ζ电位的绝对值均迅速减小,其中pH＞9时ζ电位的绝对值下降幅度更为明显.采用胶体的双电层理论对Fe~(2+)/H_2O_2影响脲醛树脂胶稳定性的机理进行了探讨.
The influences of Fe~(2+)/H_2O_2 on the ζ potential and stability of colloidal urea-formaldehyde(UF) resins were studied by means of a colloidal chemistry method. The results show that the average ζ potential of urea-formaldehyde colloidal particles is about -32.5 mV at a pH value of 8.0 and they exist in monodisperse state. The ζ potential is decreased rapidly with the addition of ferrous ions or hydrogen peroxide, which causes a decrease of expulsion potential, the aggregation of colloidal particles, an increase of viscosity and eventually the formation of stable UF resin gels. However, the influences of hydrogen peroxide on ζ potential and the viscosity η of UF colloidal particles are much less than those of the ferrous ions. pH value plays an important role in keeping the stability of the colloidal particles. The system has the highest ζ potential at pH≈9. When pH＞9, the absolute value of ζ potential decreases more significantly. The mechanism of Fe~(2+)/H_2O_2 affecting the stability of UF adhesive was discussed based on colloidal electric double layers theory.
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