Chemoenzymatic Modification of Polyolefins: Surface Oxidation and Identification of Degradation Products

Abstract

Global plastic production exceeds 400 million tons annually, with polyolefins accounting for nearly half. Their highly stable hydrocarbon backbone makes them highly resistant to degradation, leading to environmental accumulation and significant contributions to plastic pollution. Conventional recycling methods are insufficient to address these challenges, highlighting the need for more sustainable alternatives. This study investigates chemoenzymatic modification of polyolefin films, including LDPE, LDPEa (LDPE with antioxidants), LLDPE and HDPE. Chemical pretreatments, KMnO4/HCl, Fenton oxidation and UVC-Fenton were combined with enzymatic treatment using bacterial (Bacillus Subtils, L.CotA) and fungal (Myceliophthora thermophila, L.MT), laccases in a TEMPO-mediated system. The resulting modifications of the polymer backbone, surface morphology, elemental composition and thermal properties were evaluated using FTIR, SEM, EDX, DSC, HPLC and GC-MS. Following chemoenzymatic treatment, FTIR revealed oxidation of the polymer backbone. The highest calculated carbonyl index values were 2.50 for KMnO4/HCl combined with L.CotA and 2.01 for Fenton oxidation combined with L.MT. Additionally, UVC treatment enhanced Fenton oxidation and enzymatic treatment with both L.CotA and L.MT. SEM analysis revealed visible surface modification in the form of cracks and particle clusters, EDX confirmed an increase in oxygen content and DSC measurements indicated slight decreases in melting temperature and crystallinity. GC-MS analysis of the reaction mixtures identified oxidised degradation products ranging from C2-C20. L.CotA primarily generated longer oxidised oligomers, suggesting more surface limited modification, whereas L.MT produced a broader range of compounds, including short chain hydroxy acids and polyoxidised intermediates, indicating more extensive modification. These degradation products demonstrated great potential for upcycling into biodegradable polymer or other industrial applications. Overall, LDPE and LDPEa films proved most susceptible to the modification.

Popular Abstract

Every year, global plastic production exceeds hundreds of millions of tonnes, reflecting the strong dependency on plastic materials today. This is a direct result of their superior properties, including high durability, low cost and light weight. However, the same properties that make plastics invaluable in countless applications also make them highly resistant to degradation. Among the most challenging plastics to degrade are polyolefins, which account for around half of global production. Their resistance to degradation stems from their simple chemical structure, consisting entirely of strong saturated C-C and C-H bonds. The most common polyolefins are polyethylene (PE) and polypropylene (PP). These materials are widely used in everyday life and are found in countless products, including plastic bags, food packaging and containers. This widespread use of single-use plastics generates large amounts of plastic waste. Today, only a small fraction of this waste is collected for recycling and most of it is mechanically recycled into products with lower quality and performance than the original material. This has led to large-scale environmental accumulation, contributing to one of the most significant global environmental challenges, plastic pollution. Hence, conventional recycling methods alone are insufficient to address these challenges, highlighting the need for more sustainable alternatives. One possible solution is biotechnological recycling, which utilises microorganisms and enzymes, proteins that catalyse biochemical reactions, to break down plastic polymers into smaller molecules. These molecules can potentially be upcycled and reused in the production of new materials, contributing to a more sustainable and circular plastic economy. Therefore, this study investigated the chemoenzymatic modification of the major types of PE, including high-density polyethylene (HDPE), low-density polyethylene (LDPE), low-density polyethylene containing antioxidants (LDPEa) and linear low-density polyethylene (LLDPE). The aim was to optimise the treatment by combining two distinct chemical oxidation methods with enzymatic treatment and to identify the potential degradation products formed during the reaction. The chemical pretreatments used were potassium permanganate oxidation and Fenton oxidation. To further enhance the oxidation process, Fenton oxidation was also combined with UVC irradiation. After these treatments, new oxygen containing functional groups were introduced to the polymer backbone, indicating that oxidation had successfully occurred. The PE polymers were then treated with laccase, an enzyme known to oxidise PE. Laccase enzymes from both fungal and bacterial sources were used to investigate how the enzyme source influences the reaction. Following the enzymatic treatment, multiple oxygenated functional groups were introduced to the polymer backbone. Microscopy revealed clear surface modifications, including cracks and particle accumulations, while elemental analysis confirmed the presence of oxygen and nitrogen on the surface. In addition, the melting temperature and crystallinity generally decreased, indicating structural changes in the material. The study revealed that LDPE and LDPEa were most susceptible to modification. Furthermore, the bacterial laccase worked with both pretreatments but performed best with permanganate, while the fungal laccase worked better with Fenton chemistry. Combining UVC with Fenton further enhanced the chemoenzymatic oxidation. The released oxidative degradation products could be detected and identified, revealing that the bacterial laccase predominantly produced longer fatty acids. In contrast, the fungal laccase generated a broader range of products, from shorter hydroxy acids, polyoxidised intermediates and longer fatty acids. These products have the potential to be converted into high value chemicals and building blocks. For example, in the synthesis of biodegradable bioplastics, medical devices or cosmetics. Overall, this study further supports the potential of biotechnological recycling as a more sustainable alternative to conventional methods, transforming waste that causes significant environmental issues into valuable, sustainable resources.

• author: Melin, Clara
• supervisor: Sang-Hyun Pyo; Mohamed Ismail; Åsa Olsson
• organization: Biotechnology (MSc); Biotechnology (M.Sc.Eng.)
• course: KBTM05 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Polyethylene (PE), enzymatic modification, Laccase enzyme, Biotechnology
• language: English
• id: 9237025
• date added to LUP: 2026-08-11 09:03:32
• date last changed: 2026-08-11 09:03:32