Chemical Engineering Department, University of Alicante, San Vicente del Raspeig Road, s/n, 03690 San Vicente del Raspeig, Alicante, Spain.
Olax22 SL, Artesanos Street, 4A, 03690, San Vicente del Raspeig, Alicante, Spain.
Waste Manag. 2018 Oct;80:211-217. doi: 10.1016/j.wasman.2018.09.015. Epub 2018 Sep 17.
Dewatering of plastic films is a highly energy-consuming recycling operation that largely affects the quality of the recycled product. Despite the importance of good drying, this operation has not been studied at laboratory or pilot plant scale. In this work, the mechanical dewatering of blown film grade high density polyethylene has been assessed by using a laboratory centrifuge. It is suggested that a plastic cake is formed under the centrifugal forces similar to the sludge cake after the filtration process. The water is retained within the plastic cake due to three phenomena: free water within the cake pores and voids, water maintained by capillarity (superficial and pendular) and water trapped due to the tortuosity of the plastic mass. The total moisture is a sum of an equilibrium moisture and a transient moisture. The equilibrium moisture depends on the centrifugal force (G) but it is independent of time. Conversely, the transient moisture is reliant on both the G-force and the centrifugation time. The experimental results showed that an optimum side length exists. The moisture content is minimized when the flake side lies between 1 and 2 cm. Finally, it has been found that the moisture content is a function of the plastic surface. Hence, the specific moisture content (the mass of water per total plastic surface) should be calculated to compare films with uneven thickness or made of different materials. In sum, the outcomes of this study may be fundamental for the further and more extensive research into the plastic films dewatering processes.
塑料薄膜的脱水是一个高能耗的回收操作，对回收产品的质量有很大的影响。尽管干燥过程很重要，但这个操作在实验室或中试规模上还没有得到研究。在这项工作中，使用实验室离心机评估了吹塑薄膜级高密度聚乙烯的机械脱水。研究表明，在离心力的作用下，形成了类似于过滤过程后的污泥饼的塑料饼。由于三种现象，水被保留在塑料饼内：饼内的自由水和空隙、由毛细作用（表面和悬垂）保持的水以及由于塑料质量的曲折而被困的水。总水分是平衡水分和瞬态水分的总和。平衡水分取决于离心力（G），但与时间无关。相反，瞬态水分取决于 G 力和离心时间。实验结果表明存在最佳边长。当薄片边长在 1 到 2 厘米之间时，水分含量最小。最后，发现水分含量是塑料表面的函数。因此，应该计算特定的水分含量（每单位总塑料表面积的水量），以比较厚度不均匀或由不同材料制成的薄膜。总之，这项研究的结果可能对进一步更广泛的塑料薄膜脱水过程研究具有基础性意义。
