Poraj-Kozminski Agatha, Hill Reghan J, van de Ven Theo G M
Department of Chemical Engineering, Pulp and Paper Research Centre, McGill University, Montreal, Quebec H3A 2A7, Canada.
J Colloid Interface Sci. 2007 May 1;309(1):99-105. doi: 10.1016/j.jcis.2007.01.031. Epub 2007 Feb 12.
In papermaking, many colloidal particles are added to a pulp fiber suspension to improve paper properties. Given the right conditions, these different colloids can interact and flocculate. Examples of papermaking colloids are fillers and internal sizing agents, which improve opacity and hydrophobicity of paper, respectively. Internal sizing agents (added at the wet end of a paper machine) are commonly solidified emulsion droplets, stabilized by cationic starch and other stabilizers. We studied the interaction of a common internal sizing agent, alkyl ketene dimer (AKD), with calcium carbonate fillers. AKD is a liquid above 50-65 degrees C (depending on alkyl chain length), which can be emulsified above its melting point in the presence of a stabilizer, resulting, after cooling, in solid colloidal particles close to 1 microm in size. We investigated the interaction of AKD particles, stabilized by cationic starch, with precipitated calcium carbonate (PCC) particles. Pure PCC particles are positively charged, but they become negative in process waters. Flocculation experiments with positively charged AKD and negatively charged PCC were performed using a photometric dispersion analyzer. Instead of the expected heteroflocculation between AKD and PCC, we observed PCC homoflocculation and AKD homoflocculation, results confirmed by SEM. The results are explained by the transfer of starch from AKD to PCC, resulting in PCC flocculation by starch and AKD destabilization due to depletion of the stabilizer.
在造纸过程中，会向纸浆纤维悬浮液中添加许多胶体颗粒以改善纸张性能。在合适的条件下，这些不同的胶体可以相互作用并絮凝。造纸胶体的例子有填料和内部施胶剂，它们分别提高纸张的不透明度和疏水性。内部施胶剂（在造纸机的湿部添加）通常是固化的乳液滴，由阳离子淀粉和其他稳定剂稳定。我们研究了一种常见的内部施胶剂烷基烯酮二聚体（AKD）与碳酸钙填料的相互作用。AKD在50 - 65摄氏度以上是液体（取决于烷基链长度），在稳定剂存在下可在其熔点以上乳化，冷却后形成尺寸接近1微米的固体胶体颗粒。我们研究了由阳离子淀粉稳定的AKD颗粒与沉淀碳酸钙（PCC）颗粒的相互作用。纯PCC颗粒带正电荷，但在工艺用水中会带负电荷。使用光度分散分析仪对带正电荷的AKD和带负电荷的PCC进行了絮凝实验。我们观察到的不是预期的AKD和PCC之间的异质絮凝，而是PCC的同质絮凝和AKD的同质絮凝，扫描电子显微镜（SEM）证实了这一结果。结果的解释是淀粉从AKD转移到PCC，导致PCC因淀粉而絮凝，以及由于稳定剂耗尽导致AKD失稳。
