Epoxy Phase-Change Materials Based on Paraffin Wax Stabilized by Asphaltenes

Phase-change materials (PCMs) are widely used for thermal energy storage due to their ability to absorb and release latent heat during phase transitions. However, a major limitation of PCMs is their tendency to lose structural integrity when heated, leading to leakage or migration of the melt. Traditional solutions involve encapsulation within polymer matrices, but achieving stable dispersion of the PCM within the matrix remains a challenge. Prior research has demonstrated that encapsulating PCMs in polymers can improve stability, but the process often affects the PCM's thermal properties. This gap motivated researchers to explore alternative stabilization methods that preserve both the structural and functional properties of the PCM. Theoretical and experimental studies have shown that surface-active agents can stabilize dispersed PCM droplets, but their compatibility with the polymer matrix is often limited. No prior work had resolved how to maintain droplet stability during polymer curing without compromising thermal performance. This study addresses these limitations by proposing a novel stabilization approach using asphaltenes as natural stabilizers in an epoxy matrix.

The aim of this study was to develop a stable phase-change material by dispersing paraffin wax in an epoxy resin matrix using asphaltenes as stabilizers. The researchers sought to determine whether asphaltenes could form a Pickering emulsion with paraffin wax in an epoxy medium, ensuring droplet stability during the curing process. A key challenge was to maintain the structural integrity of the wax droplets while allowing the epoxy to cure properly. The motivation stemmed from the need for PCMs that retain their thermal properties without requiring complex encapsulation techniques. The study also aimed to assess how the presence of wax and asphaltenes affects the rheological behavior of the epoxy during curing. By addressing these questions, the researchers hoped to create a PCM with improved stability and thermal efficiency. The approach involved a combination of theoretical modeling and experimental validation to ensure the feasibility of the proposed method. Ultimately, the study sought to advance the design of PCMs by leveraging natural stabilizers to enhance dispersion and performance.

The researchers used a combination of theoretical modeling and experimental analysis to study the behavior of paraffin wax in an epoxy matrix stabilized by asphaltenes. They first extracted asphaltenes from heavy crude oil and mixed them with paraffin wax and epoxy resin. Theoretical calculations were employed to model the equilibrium interactions among the three components, focusing on their solubility and interfacial behavior. Rheological tests were conducted to evaluate the viscoplastic properties of the mixture at room temperature and after heating. The wax droplet size was measured using optical microscopy to assess dispersion stability. The effect of wax and asphaltenes on the epoxy's curing process was analyzed using differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The degree of wax crystallinity was determined using X-ray diffraction (XRD) to evaluate how dispersion affected thermal performance. The study also monitored changes in the glass transition temperature of the cured epoxy to confirm that cross-linking was not inhibited. These methods provided a comprehensive understanding of the system's behavior and its suitability for PCM applications.

The study found that asphaltenes effectively stabilized paraffin wax droplets in an epoxy matrix, forming a Pickering emulsion. Theoretical calculations confirmed the complex equilibrium in the epoxy/wax/asphaltene system due to low mutual solubility. Rheological measurements showed that the dispersion exhibited viscoplastic behavior at 25°C, which disappeared upon heating and melting of the wax. The wax and asphaltenes increased the viscosity of the epoxy during curing but did not prevent cross-linking or lower the glass transition temperature of the cured polymer. The resulting phase-change material contained up to 45% paraffin wax, with droplet sizes ranging from 0.2 to 6.5 μm. The small droplet size reduced the wax's crystallinity to 13–29% of its original value, which may impact thermal efficiency. The study also showed that the presence of wax and asphaltenes did not significantly alter the epoxy's curing kinetics. These findings suggest that asphaltenes can serve as effective stabilizers for PCM dispersions without compromising the polymer matrix's structural properties.

The authors concluded that asphaltenes extracted from heavy crude oil can effectively stabilize paraffin wax droplets in an epoxy matrix, forming a Pickering emulsion. This approach allows for the creation of phase-change materials with up to 45% paraffin wax content. The study demonstrated that wax and asphaltenes increase the viscosity of the epoxy during curing but do not inhibit cross-linking or reduce the glass transition temperature. The resulting dispersions exhibited viscoplastic behavior at room temperature, which disappeared upon heating. However, the small droplet size of the wax reduced its crystallinity, potentially affecting thermal performance. The researchers propose that this method offers a viable alternative to traditional encapsulation techniques for PCM stabilization. The findings suggest that asphaltenes can serve as natural stabilizers in polymer-based PCMs without compromising the matrix's structural integrity. The study highlights the potential of using low-cost, naturally occurring materials like asphaltenes to improve PCM stability and performance.