Biodeterioration of plasma pretreated LDPE sheets by <i>Pleurotus ostreatus</i>

Low-density polyethylene (LDPE) waste generates an environmental impact. To achieve the most suitable option for their degradation, it is necessary to implement chemical, physical and biological treatments, as well as combining procedures. Best treatment was prognosticated by Plackett-Burman Experimental Design (PB), evaluating five factors with two levels (0.25 mM or 1.0 gL-1 glucose, 1.0 or 2.0 mM CuSO4, 0.1 or 0.2 mM ABTS [2, 20-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)], pH 4.5 ± 0.2 or 7.0 ± 0.2 and 30 or 90 day incubation), which was reproduced for 150 days. Therefore, PB identified a sequential treatment (plasma followed by fungus) for partial LDPE biodeterioration. Sheets were pretreated with glow discharge plasma (O2, 3.0 x 10−2 mbar, 600 V, 6 min.), followed by Pleurotus ostreatus biodeterioration. Fungus growth, colonization percentage, and pigment generation followed. Laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP) activities were appraised. Additionally, contact angle (CA), functional group presence and changes and carbonyl and vinyl indices (Fourier transformed infrared spectroscopy) were evaluated. LDPE surface changes were assessed by Young’s modulus, yield strength, scanning electronic microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Plasma discharge increased hydrophilicity, decreasing CA by 76.57% and increasing surface roughness by 99.81%. P. ostreatus colonization was 88.72% in 150 days in comparison with untreated LDPE (45.55%). After this treatment carbonyl groups (C = O), C = C insaturations, high hydrophilicity CA (16 ± 4) °, and low surface roughness (7 ± 2) nm were observed. However, the highest Lac and LiP activities were detected after 30 days (Lac: 2.817 U Lac g-1 and LiP: 70.755 U LiP g-1). In addition, highest MnP activity was observed at day 120 (1.097 U MnP g-1) only for P. ostreatus treated LDPE. Plasma favored P. ostreatus adsorption, adherence, growth and colonization (88.72%), as well as partial LDPE biodeterioration, supported by increased hydrophilicity and presence of specific functional chemical groups. The approximate 27% changes in LDPE physical properties support its biodeterioration.低密度聚乙烯（Low-density polyethylene, LDPE）废弃物会造成环境负荷。为筛选出最适配其降解的处理方案，需采用化学、物理及生物处理手段，亦可结合多种处理流程。本研究采用普拉克特-伯曼实验设计（Plackett-Burman Experimental Design, PB）预测最优处理方案，评估了5个两水平因子：0.25 mM或1.0 g·L⁻¹葡萄糖、1.0或2.0 mM硫酸铜（CuSO₄）、0.1或0.2 mM ABTS[2,2'-连氮基-双(3-乙基苯并噻唑啉-6-磺酸)]、pH 4.5±0.2或7.0±0.2，以及30或90天的培养周期，整个实验周期为150天。通过普拉克特-伯曼实验设计，本研究确定了一套用于部分LDPE生物降解的序贯处理工艺：先经辉光放电等离子体（氧气氛围，3.0×10⁻² mbar，600 V，6分钟）预处理LDPE薄膜，随后接入糙皮侧耳（Pleurotus ostreatus）进行生物降解。后续依次监测了真菌生长情况、定殖率及色素生成量，并对漆酶（Laccase, Lac）、锰过氧化物酶（Manganese peroxidase, MnP）及木质素过氧化物酶（Lignin peroxidase, LiP）的酶活进行了测定。此外，还通过傅里叶变换红外光谱法测定了接触角（Contact Angle, CA）、官能团的存在与变化，以及羰基与乙烯基指数。LDPE的表面形貌与性能变化则通过杨氏模量、屈服强度、扫描电子显微镜（Scanning Electronic Microscopy, SEM）、傅里叶变换红外光谱（Fourier transformed infrared spectroscopy, FTIR）及原子力显微镜（Atomic Force Microscopy, AFM）进行表征。实验结果显示，等离子体处理可提升材料表面亲水性，使接触角降低76.57%，同时表面粗糙度提升99.81%。相较于未处理的LDPE（定殖率为45.55%），糙皮侧耳在150天内对经等离子体预处理的LDPE的定殖率可达88.72%。经该序贯处理后，可检测到羰基（C=O）、碳碳不饱和双键（C=C）的存在，以及16±4°的高亲水性接触角与7±2 nm的低表面粗糙度。不过，漆酶与木质素过氧化物酶的最高活性均出现在第30天，其中漆酶活性为2.817 U·g⁻¹，木质素过氧化物酶活性为70.755 U·g⁻¹。此外，仅在经糙皮侧耳处理的LDPE样本中，锰过氧化物酶的最高活性出现在第120天，活性值为1.097 U·g⁻¹。等离子体预处理可促进糙皮侧耳的吸附、附着、生长与定殖（定殖率达88.72%），同时推动LDPE的部分生物降解，这一结论得到了表面亲水性提升与特定官能团出现的佐证。LDPE物理性质约27%的变化也进一步证实了其生物降解程度。