FTIR Spectroscopic Characterization of Low-Density Polyethylene (LDPE) Using the KBr (Potassium Bromide) Pellet Method

Background: Low-Density Polyethylene (LDPE) is a ubiquitous thermoplastic which are usually derived from ethylene monomers, and occupies a prominent position among plastic polymers, and it presents a persistent ecological challenge due to improper disposal and environmental accumulation. Despite its recalcitrance, certain microbial populations have evolved or emerge with the metabolic capacity to utilize LDPE as a primary carbon and energy source, thus offering a potential biotechnological pathway for waste remediation. Despite its enormous utility, the very properties that make LDPE commercially desirable, chemical stability and resistance to biological and environmental degradation render it a persistent and accumulating pollutant in terrestrial and aquatic ecosystems. The continuous and indiscriminate disposal of LDPE waste has resulted in its progressive accumulation in the environment, including in soils, freshwater systems, and marine environments, where it poses a severe ecological threat to biota, biodiversity, and ecosystem function (16). The recalcitrant nature of LDPE to conventional degradation pathways is attributed its high molecular weight, hydrophobic character, and the absence of functional groups that would render it susceptible to enzymatic hydrolysis under ambient environmental conditions (17, 6). Consequently, LDPE and related polyolefin may persist in the environment for centuries, fragmenting progressively into micro plastics and Nano plastics that infiltrate food chains and accumulate in living organisms (2).
Methodology: This research investigated the biodegradation of LDPE by isolating and characterizing specialized microorganisms from plastic-polluted dumpsite soils. Using enrichment techniques, the isolates were cultivated in both axenic (single) and consortium (mixed) cultures containing pre-treated LDPE strips in aseptically method. The degradation process was conducted at room temperature under a constant agitation of (120 rpm). The extent to which the polymer degraded was quantified through microbial load monitoring and gravimetric weight loss analysis, while the structural modifications were determined and identified via Fourier Transform Infrared (FTIR) spectroscopy.
Results: Thirteen distinct isolates were identified, belonging to the genera Bacillus (5), Aspergillus (5), Penicillium (2), and Fusarium (1). Among these isolates identified, Pseudomonas aeruginosa, Penicillium chrysogenum, Aspergillus niger, and Fusarium oxysporum demonstrated superior survival traits during the preliminary biodegradative screening. P. chrysogenum exhibited the highest individual microbial load of (1.9084 to 2.1762 Log CFU/mL), whereas the Aspergillus niger and Pseudomonas aeruginosa consortium showed the highest overall density of (2.7958 to 2.6883 Log CFU/mL). The highest gravimetric weight loss (5%) was recorded for both A. niger in isolation and the A. niger/P. aeruginosa consortium. FTIR spectra established and strengthened these findings, with A. niger producing the most significant peak reduction at 3801.82 cm-1, which is followed closely by P. aeruginosa at 3840.28 cm-1.
Conclusion: The synergistic action of the Aspergillus niger and Pseudomonas aeruginosa mixed culture proved highly effective in altering the polymer’s structural integrity. These findings suggest that these specific microbial strains hold significant promise for mitigating the environmental impact of polyethylene waste accumulation.