The membrane technology has been demonstrated to be one of the most effective methods for the separation of oil from oil-water mixtures, and it has found extensive application in various industries, including food processing, pharmaceuticals, desalination, and fuel cells. When compared to traditional methods such as chemical treatment [1]-[3], membrane separation technology provides superior oil removal efficiency, consistent effluent quality, and reduced energy costs. Consequently, it is regarded as one of the most efficient approaches for separating oil-water mixtures across a diverse array of industrial effluents [4] [5].

Electrospinning is a widely utilized technique for the fabrication of porous polymeric matrices composed of submicron fibers. Poly(e-caprolactone) (PCL) is a polyester characterized by its considerable mechanical strength and flexibility, in addition to its biodegradable, biocompatible, and non-toxic properties [6]-[8]. Similarly, Poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) exhibits biodegradability and biocompatibility, making it applicable in diverse fields, including the plastic products and drug releasing systems [9]. However, despite these advantageous characteristics, PHBV presents certain limitations that hinder its application in load-bearing contexts, notably its insufficient flexibility and high brittleness. To enhance the mechanical properties of PHBV and expand its range of applications, the incorporation of other polymers is warranted. The blending of PCL with PHBV represents a promising strategy to create a structure that is relatively elastic, physically stable, and better platform of cellular activities, thereby broadening its potential applications.

Recent research in oil-water separation technology has increasingly focused on the application of electrospinning techniques to develop nanofibrous absorbent and filtration membranes [10]. Over the past three decades, these electrospun nanofibers have garnered significant attention for their utility in oil-water separation processes [11]. The unique characteristics of electrospun nanofibers, including their high specific surface areas [12], interconnected pore structures, nanoscale pore sizes, and the ability to merge active chemical functionalities at the nanoscale [13], contribute to their effectiveness. Furthermore, these membranes exhibit low initial solid densities, which enhances their permeability during oil-water separation process. This combination of properties not only improves separation efficiency but also simplifies the process requirements. Additionally, the ability to control fiber diameters, which can range from tens of nanometers to micrometer scale, makes electrospun fibrous membranes particularly valid for oil-water separation.

The development of efficient and straightforward methods for the separation of oil/water mixtures continues to pose significant challenges that remain unresolved. Recent literature has documented advancements involving polymer-based filtration membranes created through phase separation techniques with adjustable pore sizes [14]-[16]. However, these membranes are hindered by issues related to low flux and fouling. Recently, nanofibrous membranes, characterized by high porosity and surface area to volume ratio, have demonstrated considerable capacity for the separation of emulsified oil/water phase structure [17]-[19]. Various fabrication methods for nanofibrous membranes exist, with electrospinning emerging as the preferred technique due to its relative simplicity. Electrospun nanofiber membranes represent a leading category of advanced fibrous materials, offering advantages such as tuneable wettability, extensive surface area, and high porosity [20] [21].

Huang et al. proposed an innovative and scalable methodology for the synthesis of in situ superhydrophobic and superoleophilic electrospun nanofibrous membranes, which effectively facilitate the separation of water-in-oil micro-emulsions. These membranes exhibit exceptionally high flux, favorable antifouling characteristics, thermal stability, and endurance [11]. Subsequently, Tang et al. developed a membrane characterized by high thermal stability and outstanding mechanical properties, achieved through a straightforward integration of electrospun poly(m-phenylene isophthalamide) (PMIA) nanofibers with an in situ polymerized F-PBZ functional layer that incorporated SiO₂ nanoparticles for gravity-driven oil-water separation [22]. In addition, nanofibrous membrane exhibiting superhydrophilicity and underwater superoleophobicity, which was fabricated by electrospinning cellulosic modified polyvinylidene fluoride-co-hexafluoropropylene (PVDF?HFP) [23]. Furthermore, a superhydrophobic and superoleophilic electrospun nanofibrous membrane that exhibited remarkable oil/water separation behaviour, featuring a self-cleaning surface and commendable recyclability [24].

In this study, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was chosen for its potential to enhance oil-water separation performance when combined with Polycaprolactone (PCL). Among various promising alternatives, PHBV is notable for its production via bacterial fermentation of biomass. This linear isotactic polyester is formed from hydroxy acid units and is capable of undergoing composting in industrial environments; it also demonstrates degradability in specific ecological contexts, which increases its attractiveness in terms of sustainability. Furthermore, the composition, chain length, and physicochemical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) can be altered by manipulating bacterial strains, nutrient resources, and cultivation conditions. resulting in a diverse array of mechanical and thermal properties.

The objective of this research was to fabricate a PHBV membrane blended with the bio-polyester PCL in a weight ratio of 3:1 through the electrospinning technique, with the intention of reducing energy consumption and mitigate thermal degradation during the processing phase. Polycaprolactone (PCL) was selected as the blending polymer owing to its advantageous miscibility with polyhydroxybutyrate-co-valerate (PHBV) and co-solubilization in chloroform. Additionally, a review of the existing literature reveals a lack of studies concerning polymer membrane composed of both PHBV and PCL.

This research utilized bio-based polycaprolactone (PCL) and polyhydroxybutyrate-co-valerate (PHBV) to effectively fabricate biodegradable composite membranes through an electrospinning technique. The resulting membranes exhibited remarkable performance in oil-water separation. The adsorption capacity was measured at 10 grams of oil per gram of membrane, while the membranes demonstrated minimal adsorption of deionized water. Furthermore, the foams exhibited exceptional cyclic durability, maintaining at least 95% of their initial adsorption capacity after 10 seconds of stirring. This study presents an ecological friendly and simple approach in the preparation of bio-based biodegradable membranes with outstanding oil-water separation capabilities.

The work described in this study was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (UGC/FDS25/E06/22) awarded to Technological and Higher Education Institute of Hong Kong and The Hong Kong Polytechnic University (grant code: ZDCC).

The authors declare no conflicts of interest regarding the publication of this paper.