Abstract
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.
Highlights
Low-density polyethylene (LDPE) is one of the most used polymers for synthetic material production, such as plastic bags [1], bottles, pipes and various laboratory materials [2], among others
Significant differences were observed between PBBT150 and BT2 (p = 0.004). These results suggest LDPE presence in treatments generated an oxidative stress for P. ostreatus with greater growth in C3, greater Lac semi-quantitative activity for PBBT150 and greater pigment production for BT2
Positive significant correlations were observed between Ico and biomass (ρ = 0.6933, p = 0.0124), Ico and Lac activity (ρ = 0.6010, p = 0.0387), Ico and manganese peroxidase (MnP) activity (ρ = 0.8577, p < 0.0001, Ico and lignin peroxidase (LiP) activity (ρ = 0.7002, p =
Summary
Low-density polyethylene (LDPE) is one of the most used polymers for synthetic material production, such as plastic bags [1], bottles, pipes and various laboratory materials [2], among others. At present biodegradable plastic bags are available, made-up of natural polymers degraded by microorganisms. Other alternatives include oxo-biodegradable polymers derived from petroleum that contain special additives, such as totally degradable plastic additive TDPATM. To facilitate LDPE degradation a master batch containing polymers and dispersed additives on a carrier resin, such as d2wTM has been implemented [4]. Despite these efforts, use of biodegradable bags is not popular in many countries, since its availability is restricted to certain sectors of society [5]
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