Laboratory of Physical Chemistry and Colloid Science, Dreijenplein 6, Wageningen University, Wageningen, The Netherlands.
Adv Colloid Interface Sci. 2012 Jul 15;175:11-24. doi: 10.1016/j.cis.2012.03.005. Epub 2012 Mar 26.
Liquid CO(2) is a viable alternative for the toxic and environmentally harmful solvents traditionally used in dry-cleaning industry. Although liquid CO(2) dry-cleaning is being applied already at a commercial scale, it is still a relatively young technique which poses many challenges. The focus of this review is on the causes of the existing problems and directions to solve them. After presenting an overview of the state-of-the-art, we analyze the detergency challenges from the fundamentals of colloid and interface science. The properties of liquid CO(2) such as dielectric constant, density, Hamaker constant, refractive index, viscosity and surface tension are presented and in the subsequent chapters their effects on CO(2) dry-cleaning operation are delineated. We show, based on theory, that the van der Waals forces between a model soil (silica) and model fabric (cellulose) through liquid CO(2) are much stronger compared to those across water or the traditional dry-cleaning solvent PERC (perchloroethylene). Prevention of soil particle redeposition in liquid CO(2) by electrostatic stabilization is challenging and the possibility of using electrolytes having large anionic parts is discussed. Furthermore, the role of different additives used in dry-cleaning, such as water, alcohol and surfactants, is reviewed. Water is not only used as an aid to remove polar soils, but also enhances adhesion between fabric and soil by forming capillary bridges. Its role as a minor component in liquid CO(2) is complex as it depends on many factors, such as the chemical nature of fabrics and soil, and also on the state of water itself, whether present as molecular solution in liquid CO(2) or phase separated droplets. The phenomena of wicking and wetting in liquid CO(2) systems are predicted from the Washburn-Lucas equation for fabrics of various surface energies and pore sizes. It is shown that nearly complete wetting is desirable for good detergency. The effect of mechanical action and fluid dynamic conditions on dry-cleaning is analyzed theoretically. From this it follows that in liquid CO(2) an order of magnitude higher Reynold's number is required to exceed the binding forces between fabric and soil as opposed to PERC or water, mainly due to the strong van der Waals forces and the low viscosity of CO(2) at dry-cleaning operational conditions.
液态 CO2 是一种替代传统干洗行业中有毒且对环境有害的溶剂的可行选择。尽管液态 CO2 干洗技术已经在商业规模上得到应用，但它仍然是一种相对较新的技术，存在许多挑战。本综述的重点是现有问题的原因和解决方向。在介绍最新技术的概述之后，我们从胶体和界面科学的基本原理分析了去污剂的挑战。介绍了液态 CO2 的介电常数、密度、哈马克常数、折射率、粘度和表面张力等性质，并在随后的章节中阐述了它们对 CO2 干洗操作的影响。我们基于理论表明，通过液态 CO2，模型土壤（二氧化硅）和模型织物（纤维素）之间的范德华力比穿过水或传统干洗溶剂 PERC（全氯乙烯）时的范德华力强得多。通过静电稳定防止土壤颗粒在液态 CO2 中重新沉积是具有挑战性的，并且讨论了使用具有大阴离子部分的电解质的可能性。此外，还回顾了干洗中使用的不同添加剂，如水、酒精和表面活性剂的作用。水不仅用于去除极性污垢，还通过形成毛细桥来增强织物和污垢之间的附着力。水在液态 CO2 中的作用是复杂的，因为它取决于许多因素，例如织物和污垢的化学性质，以及水本身的状态，是处于液态 CO2 中的分子溶液还是相分离的液滴。根据 Washburn-Lucas 方程，预测了各种表面能和孔径的织物在液态 CO2 系统中的吸吮和润湿现象。结果表明，完全润湿对于良好的去污效果是理想的。从理论上分析了机械作用和流体动力学条件对干洗的影响。由此可知，与 PERC 或水相比，在液态 CO2 中需要大一个数量级的 Reynold 数才能超过织物和污垢之间的结合力，这主要是由于范德华力强和 CO2 在干洗操作条件下的低粘度。
