Thermal Energy Storage Using Poly(ethylene glycol) Incorporated Hyperbranched Polyurethane as Solid–Solid Phase Change Material

Intrinsic Flame Retardancy and Flexible Solid-Solid Phase Change Materials with Self-Healing and Recyclability

Conventional polymeric phase change materials (PCMs) have been widely used due to their high heat storage density, small temperature variation, and nontoxicity. However, the high flammability and unrecyclable problems restrict their applications in energy storage devices (ESDs). Although it is facile to introduce a flame retardant into phase change materials to improve fire resistance, the physical blending will deteriorate the mechanical performance and thermal stability of PCMs. Herein, flame-retardant solid-solid PCMs (FRPCMs) with intrinsic flame retardancy, phase change property, self-healing, and recyclability were synthesized by simultaneously integrating tetrabromobisphenol A (TBBPA) and poly(ethylene glycol) (PEG) into polyurethane network skeletons. PEG ingredients acted as phase change materials, and TBBPA not only worked as an efficient flame retardant but also provided dynamic covalent bonds for thermally induced self-healing and recyclability. FRPCMs possess the highest latent heat of 124.7 J/g, high self-healing ability, and high thermal reliability and recyclability. Besides, with the introduction of TBBPA, the limiting oxygen index (LOI) value and char residue significantly increased, the heat release rate (HRR) and total heat release (THR) values decreased, and most of the FRPCMs reached UL94 V-2 rating as well. Hence, the synthesized FRPCMs could expand the application scope of PCMs for thermal energy storage.

Synthesis and characterization of biopolyurethane crosslinked with castor oil-based hyperbranched polyols as polymeric solid-solid phase change materials

Novel crosslinking bio polyurethane based polymeric solid-solid phase change materials (SSPCM) were synthesized using castor oil (CO) based hyperbranched polyols as crosslinkers. CO-based hyperbranched polyols were synthesized by grafting 1-mercaptoethanol or α-thioglycerol via a thiol-ene click reaction method (coded as COM and COT, respectively). Subsequently, the three SSPCMs were synthesized by a two-step prepolymer method. Polyethylene glycol was used as the phase change material in the SSPCMs, while the CO-based hyperbranched polyols and two types of diisocyanate (hexamethylene diisocyanate (HDI) and 4,4'-diphenylmethane diisocyanate) served as the molecular frameworks. Fourier transform infrared spectroscopy indicated the successful synthesis of the SSPCMs. The solid-solid transition of the prepared SSPCMs was confirmed by X-ray diffraction analysis and polarized optical microscopy. The thermal transition properties of the SSPCMs were analyzed by differential scanning microscopy. The isocyanate and crosslinker types had a significant influence on the phase transition properties. The SSPCM samples prepared using HDI and COT exhibited the highest phase transition enthalpy of 126.5 J/g. The thermal cycling test and thermogravimetric analysis revealed that SSPCMs exhibit outstanding thermal durability. Thus, the novel SSPCMs based on hyperbranched polyols have great potential for application as thermal energy storage materials.

Recyclable, Self-Healing, and Flame-Retardant Solid-Solid Phase Change Materials Based on Thermally Reversible Cross-Links for Sustainable Thermal Energy Storage

Conventional polymeric phase change materials (PCMs) exhibit good shape stability, large energy storage density, and satisfactory chemical stability, but they cannot be recycled and self-healed due to their permanent cross-linking structure. Additionally, the high flammability of organic PCMs seriously restricts their applications for thermal energy storage (TES). Therefore, it is urgently required to explore PCM composites exhibiting superior recyclability, good self-healing capability, and excellent flame retardancy simultaneously. Herein, tri-maleimide end-capped cyclotriphosphazene flame retardant (TMCTP) was synthesized via the nucleophilic substitution between 1,3,5,2,4,6-triazatriphosphorine-2,2,4,4,6,6-hexachloride and N-(2-hydroxyethyl)maleimide. Then, novel dynamically cross-linked PCM composites (FPCMs) with superior recyclability, good self-healing capability, and excellent flame retardancy were fabricated by bonding PEG and TMCTP to polymeric skeleton via reversible furan/maleimide Diels-Alder (DA) reaction. TMCTP, which covalently and dynamically binding in the polymeric FPCMs, acted not only as an efficient flame retardant for reducing the flammability of PCM composites but also as dynamic cross-linking skeletons for thermally induced self-healing and recycling. Differential scanning calorimetry (DSC) analysis confirmed the reversible energy storage and release ability of FPCMs. Due to its reversible DA covalent bonds, the introduction of TMCTP endowed the FPCMs with considerably increased self-healing efficiency (up to 93.1%) and recyclability efficiency (94.6%). Moreover, with the introduction of TMCTP into FPCMs, the heat release rate (HRR) and total heat release (THR) significantly decreased, while the char residue and limiting oxygen index (LOI) value increased, confirming that the flame retardancy of FPCMs greatly improved. Hence, the synthesized FPCMs show enormous potential in TES applications.

Novel Bio-Based Pomelo Peel Flour/Polyethylene Glycol Composite Phase Change Material for Thermal Energy Storage

Abstract: A series of novel bio-based form stable composite phase-change materials (fs-CPCMs) for solar thermal energy storage and management applications were prepared, using the pomelo peel flour (PPF) as the supporting matrix and poly (ethylene glycol) (PEG) or isocyanate-terminated PEG to induce a phase change. The microscopic structure, crystalline structures and morphologies, phase change properties, thermal stability, light-to-thermal conversion behavior, and thermal management characteristics of the obtained fs-CPCMs were studied. The results indicate that the obtained fs-CPCM-2 presented remarkable phase-change performance and high thermal stability. The melting latent heat and crystallization heat for fs-CPCM-2 are 143.2 J/g and 141.8 J/g, respectively, and its relative enthalpy efficiency (λ) is 87.4%, which are higher than most reported values in the related literature. The obtained novel bio-based fs-CPCM-2 demonstrated good potential for applications in solar thermal energy storage and waste heat recovery.

Advanced Polymers for Reduced Energy Consumption in Architecture

In an effort to slow the progress of climate change, the current scientific community has focused on the reduction of greenhouse gases in order to limit the global average temperature inflation to less than 2 °C. The improvement of thermally controlled construction materials can potentially result in lower energy homes/reduced emissions, and lowering the thermal conductivity of insulation materials improves home energy efficiency. Nanoporous insulation foams impart a drastic decrease in thermal conductivity but many polymer properties must be assessed to produce these materials. Passive phase-change materials also represent another key energy-saving device to control heat flux within a living space. Research into unique polymeric systems provides a novel means of encapsulation or creating polymeric cross-linked matrices to prevent leakage and improve mechanical robustness. These two areas of polymer research in architecture represent key advancements for construction materials aimed toward energy savings and energy-related emissions control.