摘要
用热机械分析（ＴＭＡ）方法研究了三聚氰胺－尿素－甲醛树脂固化初期胶层粘度的变化。将少量胶粘剂涂于两个直径为１０ｍｍ的木片表面，使涂胶面相对组合成一个胶层粘度测量模型，胶层厚度０．１５～０．２５ｍｍ。测量时，将模型加热使温度随时间线性升高（１０℃／ｍｉｎ），同时在模型上施以恒定的压力。根据胶层厚度的变化，可以计算出胶层的粘度。试验结果表明，在常温下陈化，由于水分和小分子树脂渗入木材内部以及水分的蒸发，胶层粘度急剧升高，３０ｍｉｎ后达到１０４Ｐａ·ｓ以上。在加热过程中，胶层粘度随温度和时间的变化可用二重指数方程描述。随着温度的升高，胶层粘度先降低达到一个最小值，此后由于固化反应速度加快，粘度急剧增加并迅速达到∞。固化剂用量对胶层的流变性能有重要影响，加入０．５、１．５和３％的氯化铵，胶层粘度由下降变为上升的转折点温度分别为８７、７６和７１℃。加入２０％的填料（淀粉），可以增加胶层的初始粘度。
Viscosity change of melamine urea formaldehyde glue line was investigated with a thermo mechanical analyzer (TMA) used as a parallel plates rheometer. A small quantity of adhesive was placed between two wood disks of 10 mm in diameter and the initial glue line thickness was about 0.15 to 0.25 mm. During measuring process, the testing model was heated so that its temperature increased linearly with time at a rate of 10 ℃/min. In the meantime a constant force of 0.5 N was applied on the top of model to compress the glue line and some of the adhesive was squeezed out between the wood disks. The experimental results showed that the initial glue line viscosity (30 min at room temperature) was more than 10 4 Pa·s, much higher than that of a liquid resin. The viscosity change of a glue line with temperature and time could be described qualitatively by a dual equation. With the increase of temperature, the glue line viscosity decreased until a minimum viscosity was reached, after which rapid viscosity increase occurred due to the advancement of cure reaction. From the viscosity temperature curves, two important temperatures related to the hot pressing process of wood composites were obtained, i.e. viscosity inflection temperature T c, corresponding to the minimum viscosity, and gel temperatue T gel . The quantity of hardener played an important role in the glue line viscosity change. With 0.5, 1.5 and 3% NH 4Cl, T c were respectively 87, 76 and 71℃. Addition of a filler(starch) could modify rheological behavior of the glue line, which was demonstrated by an increase of the initial glue line viscosity and an augmentation of the viscosity inflection temperature T c. This research indicated that TMA was suitable for modeling hot pressing process and measuring in situ the glue line viscosity change during early stage of cure.
出处
《木材工业》
北大核心
1997年第3期3-6,共4页
China Wood Industry
