环境对改性塑料表面亲/疏水转变的作用机制

塑料制品因其质量轻、性质稳定等优点而得到广泛使用，但大部分废旧塑料未被合理回收而成为污染物，对环境造成了危害。因此，废旧塑料回收、再加工成为保护环境和资源利用的有效途径。而分离是废旧塑料能进行再加工的重要环节，目前已经发展了丰富的分离方法，其中塑料浮选法因具有工艺简单、污染少的特点而受到人们的青睐。但在塑料浮选中，其表面亲疏水性受环境的影响，该过程进一步恶化分离效果。为了避免分离过程的波动性，急需探究环境因素对亲疏水性的作用。基于此，本文选取了ABS、PC、PS三种废旧塑料，探究环境对浮选分离及表面亲疏水性基团重构的影响。结果表明：氧化改性后的ABS、PC、PS处于极性环境时，塑料可浮性基本未发生改变，接触角发生轻微浮动，表面仍保持亲水性。处于乙醇环境中，塑料可浮性上升，其接触角上升至75°左右，表面疏水性恢复速度大于极性环境。而在非极性环境中，塑料可浮性上升速度较快，表面完全恢复为未改性前的疏水性。在极性环境中，亲水基团更容易停留在表面，随着极性的减小，亲水基团逐渐迁移至本体，塑料表面恢复为疏水。因此，极性环境更有利于塑料表面保持亲水性。

Mechanism of environmental effect on hydrophilic/hydrophobic conversion of modified plastics surface

Plastic products have been widely used because of their advantages of light weight and stable nature, but most waste plastics have not been properly recycled and become pollutants, causing harm to the environment. Therefore, recycling and reprocessing of waste plastics have become an effective way to protect the environment and utilize the resources. Separation is an important link for waste plastics to be reprocessed. At present, a variety of separation methods have been developed, among which plastic flotation method is favored by people because of its simple process and less pollution. However, in plastic flotation, the surface hydrophilicity and hydrophobicity are affected by the environment, which further deteriorates the separation effect. In order to avoid the fluctuation of separation process, it is urgent to explore the effect of environmental factors on hydrophilicity and hydrophobicity. Based on this, this paper selected three kinds of waste plastics, namely ABS, PC and PS, to explore the influence of environment on flotation separation and surface hydrophilic and hydrophobic group reconstruction. The results showed that when ABS, PC and PS after oxidation modification were in polar environment, the floatability of the plastics remained unchanged, the contact angle fluctuated slightly, and the surface remained hydrophilic. In the ethanol environment, the floatability of plastics increased, the contact angle rose to about 75°, and the recovery speed of surface hydrophobicity was faster than that of polar environment. In the non-polar environment, the floatability of the plastic enhanced faster, while the surface was completely restored to the hydrophobicity before modification. In the polar environment, the hydrophilic groups were more likely to stay on the surface. With the decrease of polarity, the hydrophilic groups gradually migrated to the body and the plastic surface resumed to be hydrophobic. Therefore, polar environment was more conducive to maintaining hydrophilic surface of plastics.