塑膠顆粒吸附水中有機化合物之研究

Abstract

廢棄塑膠顆粒及人工合成的新興有機化合物常共同存在許多水相環境中，然而對於塑膠顆粒與有機化合物間的吸附作用尚不完全清楚。本研究採用十二種塑膠顆粒進行吸附試驗，並藉由比表面積分析儀、X光繞射儀 (X-Ray diffraction, XRD)、衰減全反射傅立葉紅外線光譜儀 (attenuated total reflectance-fourier transform infrared spectrophotometer, ATR-FTIR) 等儀器進行塑膠材料特徵分析，瞭解比表面積、平均孔隙直徑、結晶度及顆粒表面官能基等特性，發現本研究採用的塑膠顆粒尺寸大及比表面積小，導致本研究採用的塑膠顆粒吸附有機化合物量較小，幾乎偵測不到高密度聚乙烯(high-density polyethylene, HDPE)、低密度聚乙烯(low-density polyethylene, LDPE)、線型低密度聚乙烯(linear low density polyethylene, LLDPE)、單聚聚丙烯(mono-material polypropylene, Mono PP)及通用級聚苯乙烯(general purpose polystyrene, GPPS)塑膠顆粒發生吸附作用，並使得吸附平衡時間長達至少14天以上。另其中軟質聚氯乙烯(flexible PVC, FPVC)及修飾型聚苯乙烯(modified PS, MPS)兩種材料具有不同於典型塑膠的單體結構，如C=O官能基及O-H官能基。探討bisphenol A (BPA)、phenol (PEN)及sulfamethoxazole (SMX)三種有機化合物與乙烯-醋酸乙烯酯共聚物(ethylene vinyl acetate copolymer, EVA)、Nylon 6、Nylon 66及FPVC四種塑膠顆粒進行靜置條件及震盪條件下的25℃吸附動力學結果，發現震盪條件會相對於靜置條件縮短吸附平衡時間。其中除了SMX無法偵測到被EVA吸附外，擬一階模型適用於SMX吸附速率，依序為Nylon 6 (0.550 day-1) > Nylon 66 (0.484 day-1) > FPVC (0.254 day-1)。擬二階模型則適用於BPA的吸附速率，排序為EVA (0.066 g/mg·day) > Nylon 66 (0.044 g/mg·day) > Nylon 6 (0.038 g/mg·day) > FPVC (0.025 g/mg·day)。而在phenol則在兩種模型具相同吸附速率的推測，排序皆為EVA > FPVC > Nylon 6 > Nylon 66。另進行不同塑膠顆粒對九種弱疏水性芳香族有機化合物的25℃等溫吸附平衡實驗，可觀察到在本研究採用的初濃度範圍內之等溫吸附曲線平衡曲線圖皆呈高度線性相關，Linear模型具高相關性(相關係數範圍0.899~0.998)，判定大部分吸附機制皆發生以凡德瓦爾力所主導的分配作用。並利用線性模型估算的Kd值作為吸附親和性的比較發現，塑膠顆粒對於有機化合物的吸附會強於河川底泥或土壤等環境基質。其中影響吸附親和性的塑膠特性主要為比表面積及極性，而有機化合物則主要為疏水性質。最終藉由多參數線性自由能關係 (polyparameter linear free energy relationships, pp-LFER)的吸附劑物化參數，表述塑膠顆粒在吸附作用中發生的不同交互作用力，以本研究的實驗結果分析可知，EVA、Nylon 6、Nylon 66、FPVC及MPS五種塑膠顆粒的v值皆具最大正值，Nylon 6、Nylon 66及FPVC的a值為較大負值，EVA的s值為正值而b值為較大負值。

Waste plastic particles and synthetic emerging organic compounds often coexist in many aqueous environments, but the sorption between plastic particles and organic compounds is not completely clear. In this study, 12 kinds of plastic particles were used for sorption test, and specific surface area analyzer, X-Ray diffraction (XRD), Attenuated Total Reflection-Fourier Transform Infrared Spectrometer (ATR-FTIR) were used to analyze the characteristics of plastic materials, and the characteristics of specific surface area, average pore diameter, crystallinity and functional groups of particles were known. It is found that the plastic particles used in this study have large size and small specific surface area, which leads to the small amount of organic compounds adsorbed by the plastic particles used in this study. The sorption of high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low density polyethylene (LLDPE), mono-material polypropylene (Mono PP) and general purpose polystyrene (GPPS) can hardly be detected, and the sorption equilibrium time is at least 14 days. In addition, flexible PVC (FPVC) and modified PS (MPS) have different monomer structures from typical plastics, such as C=O functional group and O-H functional group. The sorption kinetics of bisphenol A (BPA), phenol (PEN), sulfamethoxazole (SMX) with ethylene vinyl acetate copolymer (EVA), Nylon 6, Nylon 66 and FPVC at 25℃ under static condition and shaking condition was discussed. It was found that shaking condition could shorten the sorption equilibrium time compared with static condition. Except that SMX can't be detected by EVA, the pseudo-first-order model is suitable for SMX sorption rate, and the order is Nylon 6 (0.550day-1) > Nylon 66 (0.484day-1) > FPVC (0.254day-1). The pseudo-second order model is suitable for the sorption rate of BPA, and the order is EVA (0.066g/mg day) > Nylon 66 (0.044g/mg day) > Nylon 6 (0.038g/mg day) > FPVC (0.025g/mg day). On the other hand, PEN has the same sorption rate in the two models, and the order is EVA > FPVC > Nylon 6 > Nylon 66. In addition, the isotherm experiment of nine weakly hydrophobic aromatic organic compounds by different plastic particles at 25℃ shows that the equilibrium curves of isotherm in the initial concentration range used in this study are highly linearly correlated, and the linear model has high correlation (correlation coefficient range 0.899~0.998), which indicates that most sorption mechanisms have partition dominated by van der waals force. The Kd value estimated by the linear model is used as the comparison of sorption affinity. It is found that the sorption of organic compounds by plastic particles is stronger than that of environmental substrates such as river sediment or soil. Among them, the characteristics of plastics that affect sorption affinity are mainly specific surface area and polarity, while organic compounds are mainly hydrophobic. Finally, according to the physical and chemical parameters of the adsorbent with polyparameter linear free energy relationships (pp-LFER), the different interaction forces of plastic particles in sorption are expressed. According to the analysis of the experimental results of this study, The v values of EVA, Nylon 6, Nylon 66, FPVC and MPS all have maximum positive values, and the a values of Nylon 6, Nylon 66 and FPVC are relatively negative, while the s values of EVA are positive and the b values are relatively negative.