Extraction and assessing the reinforcing properties of collagen derived from fish on the mechanical properties of polymeric composite : a case of epoxy resin and polyurethane

Abstract

Epoxy resin and polyurethane are among the commonly and widely used polymeric materials. However, the high brittleness of cured epoxy polymers promotes crack propagation and limits their impact resistance. Polyurethane (PU), on the other hand, while prized for its flexibility and biocompatibility, is mainly made from petrochemicals, which are now facing environmental concerns. In addition, natural biobased PU foams reportedly have a relatively low mechanical strength. To overcome this, reinforcing epoxy and PU with toughening agents such as collagen is proposed in the literature to enhance its mechanical properties. The fish scale has tremendous unexploited potential for adding these values to waste. Particularly, the fish scale consists of a high amount of collagen, a valuable biomaterial that has found many applications in many fields, including biomedical and pharmaceutical industries. Hence, fish scale-derived collagen has emerged as a promising natural filler, offering eco-friendly, cost-effective, high-performance reinforcement for polymeric composites. The study aims to extract fish scale-derived collagen (FSC) and assess its reinforcing properties as a filler on polymeric composite with special emphasis on epoxy and polyurethane. A quantitative approach following an experimental research design was adopted in this study. The research design comprises three phases. In the first phase, collagen and milled fish scale powder were extracted from fish scale bio-waste using acid hydrolysis and ball-milling techniques, respectively. The extracted collagen was optimised by varying the extraction time, solvent concentration, solvent volume, and tris-glycine buffer. In the second phase, the extracted collagen (FSC) and milled fish scales powder (FS) were characterised with techniques such as X-ray diffraction, Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy, and High-Transmission Electron Microscopy. Additionally, amino acid analysis was conducted to quantify and identify the type and amount of collagen extracted. In the third phase, epoxy (5, 10, 15, 20, and 25 wt.%) and polyurethane (0.5 and 1 wt.%), as well as laminates containing 2.5, 5, and 10 wt.%, were produced following ASTM standards. Mechanical properties, including tensile strength, elongation at break, tear resistance, and flexural strength, were evaluated according to ASTM standards for testing polymeric materials. The thermal stability of the composites was analysed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). One-way analysis of variance (ANOVA) was performed to assess differences in reinforcing properties (α = .05). The validity of the study was verified using ASTM standards, while reliability was ensured through the processes of repeatability and reproducibility. Paper 1 investigates the incorporation of milled fish scales (MFS) into ether-based polyurethane foam (PUF), revealing enhancements in mechanical properties such as tensile strength, elongation at break, and tear resistance, especially under heat-aging conditions. Paper 1 established that 0.5 wt.% FS improved tensile strength by 18.8% and tear resistance by 22% at elevated temperatures. Additionally, the composites demonstrated reduced density and enhanced flame-retardant properties, underscoring the material's suitability for lightweight and thermally resilient applications. Paper 2 evaluates fish scale collagen (FSC) as a filler, highlighting its amino acid composition and superior mechanical performance. Paper 2 established that the addition of 2.5 wt.% FSC increased tensile strength by 12.66% during heat aging, while 5 wt.% FSC enhanced elongation by 6.65% at standard temperatures. Comparative analysis with traditional fillers, such as calcium carbonate, revealed that FSC could serve as a sustainable substitute without compromising mechanical properties. However, excessive FSC content negatively impacted material flexibility and strength, indicating an optimal concentration of 2.5 wt.%. Paper 3 investigates the reinforcement of epoxy resin composites with fish scale-derived collagen (FSC) to enhance their mechanical and thermal properties. Results indicated significant improvements in tensile strength, Young's modulus, and thermal stability at lower FSC concentrations (5 and 10 wt.%), attributed to effective stress transfer and good interfacial bonding. Overall, this research highlights the potential of natural materials to enhance mechanical properties while addressing sustainability concerns. The findings contribute to the development of eco-friendly and cost-effective materials for various applications, from construction to consumer products.