• Energy Research

Abstract Novel polymeric solid-solid phase change materials (SSPCMs) were prepared through solvent-free bulk polymerization by employing polyethylene glycol (PEG) as phase change functional segments, diphenylmethane diisocyanate (MDI) as coupling agent and xylitol as curing agent. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarizing optical microscopy (POM), differential scanning calorimetry (DSC), accelerated thermal cycling testing and thermogravimetric analysis (TG) were conducted to study the chemical structure, crystalline properties, phase change properties, thermal reliability and stability of SSPCMs, respectively. The crosslinked structure gave the obtained SSPCMs solid-solid phase change process. XRD and POM results showed that SSPCMs have the same crystalline structure, lower degree of crystallinity and smaller crystal size with pure PEG. DSC results indicated that SSPCMs are capable of reversible storing and releasing latent heat in the temperature of −10 to 60 °C through phase transitions. Thermal cycling tests demonstrated that SSPCMs have good thermal reliability and chemical stability. TG results testified the thermal stability of SSPCM. The obtained SSPCMs exhibited great potential application in the field of thermal energy storage.

Abstract PEG based thermosetting phase change materials (PCMs) have been frequently employed for thermal energy storage in building and other fields due to the low cost, no toxic, no corrosive, good thermal properties and no leakage in phase change process. In this article, thermosetting PCMs with polyethylene glycol (PEG) as phase change functional chain and polyaryl polymethylene isocyanate terminated polycarbonatediol (PCD) as curing agent were prepared through a facile and solvent-free bulk polyaddition. This preparation strategy can provide novel mean to design and synthesize PEG based thermosetting PCMs with different structure and performances according to the specific requirement. Moreover, the introduction of PCD will further improve the performance of PCMs. The chemical structure, crystalline properties, phase change properties, thermal reliability and stability of prepared PCMs were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), polarizing optical microscopy (POM), differential scanning calorimetry (DSC), accelerated thermal cycling testing and thermogravimetric analysis (TGA), respectively. FTIR spectra showed that the PEG based thermosetting PCMs were successfully synthesized. XRD and POM results indicated the similar spherulite structure of virgin PEG and prepared PCMs, and the crystallinity and crystal size of PCMs are affected by the introduction of curing agent. Meanwhile, DSC measurements showed that prepared PCMs have good phase change properties. Accelerated thermal cycling and TGA testing proved the excellent thermal reliability and thermal stability of prepared PCMs.

Abstract Generally, the chemically crosslinking solid-solid phase change materials (PCMs) are fabricated to address the issues of leakage and poor mechanical properties of traditional PCMs. However, the solid-solid PCMs also bring environmental pollution and resources waste as the permanent chemically crosslinking polymers cannot be recycled and reprocessed once molded. Herein, we reported a dynamic-covalent- crosslinking PCMs (V-PCMs) consisting of polyethylene glycol (PEG) as phase change ingredient, polyaryl polymethylene isocyanate (PAPI) as crosslinking points and disulfide as dynamic bonds. The as-prepared V-PCMs can reversibly store and release heat via melting and crystallization of PEG chains, and exhibit anti-leakage performance and solid-solid phase change merit due to chemically crosslinking networks even above melting point (Tm) of PEG. Besides, the V-PCMs show recycling and reprocessing ability from association mechanism of dynamic disulfide bonds. Also, the recycled V-PCMs can reversibly store and release heat and exhibit solid-solid phase change characteristic as original V-PCMs. This method provides a promising way for the fabrication of chemically crosslinking solid-solid PCMs with recyclability and multi-functionalization.

In this study, the hollow glass microsphere (HGS)/stearic acid (SA) composites were prepared as form stable phase change materials (FSPCMs) for thermal energy storage via directly impregnation. In prepared FSPCMs, SA acted as the phase change substance and the HGS functioned as the supporting materials to prevent the leakage of melted SA. The special structure and large surface of HGS had strong absorption ability for SA. The chemical structure, surface morphology, crystalline properties, phase change properties, thermal reliability and stability of prepared FSPCMs were extensively studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermal cycling test and thermogravimetric analysis (TGA), respectively. FTIR results showed that only physical interaction occurs between HGS and SA, and the SEM images showed the SA is adhered on the surface and internal surface of HGS through physical interaction. The XRD pattern exhibited that the crystalline properties of FSPCMs are not affected by the introduction of HGS. FSPCMs also exhibited good phase change properties with the latent heat in the range of 48.77–133.8 J g−1 and the phase change temperature in the range of 50.20–51.54 °C, and the supercooling degree was lower than 2 °C. The special structure of HGS imparted FSPCMs with good thermal reliability reflected by slightly variation of latent heat and phase change temperature after 100 thermal cycles. TGA results showed the FSPCMs have good thermal stability, which will meet the requirement of application. In conclusion, the prepared FSPCMs had great value in the field of thermal energy storage.

Abstract To overcome the leakage of phase change materials (PCMs) above melting temperature, PCMs are commonly encapsuled by chemically crosslinked networks, which bring the issues of reparability, reprocess-ability and recyclability making for the environment pollution and resource waste. Herein, a reversible aromatic disulfide is adopted to form dynamic epoxy networks which not only encapsulate polyethylene glycol (PEG) as the shape-stabilized PCMs (SSPCMs) but also address the issues about the un-recyclability of traditional SSPCMs. The PEG was well encapsulated and uniformly dispersed in disulfide-based epoxy due to the elaborate molecular design. The obtained SSPCMs (named EXAP2) shows typical solid–solid phase transitions characteristic and thermal reliability with high latent heat value of 82.7 J/g. Besides, the EXAP2 exhibit dynamic performance and can be reprocessed by hot press via the disulfide bonds exchange reaction above topology freezing temperature (Tv). And the reprocessed EXAP2 exhibits close phase change properties with the original sample, implying the reprocessing does not affect the crystalline structure and encapsuling capability of disulfide crosslinked networks. This strategy prove a significant way for fabricating the novel SSPCM with recyclability, reprocessability and reliability.

In this article, the hollow glass microsphere (HGS)/polyethylene glycol (PEG) composites were prepared as form-stable phase change materials (FSPCMs) for thermal energy storage (TES) via direct impregnation method. In the prepared composites, the PEG functioned as phase change substance and the HGS acted as supporting materials, which will prevent the leakage of PEG in phase change process. The chemical structure, surface morphology, crystalline properties, phase change properties, thermal reliability and stability of obtained composites were extensively studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermal cycling test and thermogravimetric analysis. FTIR spectra showed that there was no chemical reaction between HGS and PEG. The SEM images exhibited that the special structure and large surface of HGS had the ability of preventing the leakage of the melting PEG. XRD and DSC curves demonstrated the good crystalline properties of prepared composites with latent heat reach up to 124.8 J/g. Meanwhile, the prepared composites had excellent thermal reliability and stability. The prepared composites can be used as FSPCMs and have great potential in TES.

Abstract Solid-solid phase change materials (SSPCMs) with small volume change and leak-proof characteristic during the whole process of phase change play a vital role in development of PCM for thermal energy storage (TES). However, the non-recyclability of the materials due to their permanent cross-linking networks limited their practical application. Herein, a dynamic urethane bond cross linked SSPCM with PEG as phase change functional segments was successfully fabricated which was in solid state even at 130°C.Meantime, it exhibited excellent solid-state plasticity, resulting from dynamic urethane bond exchange. Moreover, the dynamic behavior of urethane bond in SSPCMs was firstly investigated. The topology freezing transition temperature (Tv) is about 113°C and the relaxation activation energy of SSPCM is calculated to be about 90 kJ/mol. The crystalline PEG endows SSPCM with high enthalpy value (reached up to 85 J/g), meantime, the cross-linked structure endows SSPCMs with remarkable mechanical flexibility (possess ultra-stretchability of 600%), thermal reliability and chemical stability. The combined thermal storage ability, appealing recyclability and flexibility endow the SSPCM promising application in the field of TES.

Abstract The solid–solid phase change materials (SSPCMs) have become the preferred materials in thermal energy storage via absorbing latent heat from ambient environment. However, the trade-off between the mechanical properties, stability and recyclability is still the obstacle and barrier for development of SSPCMs. Herein, we proposed a facile and novel strategy to prepare SSPCMs for address above issues by introducing π-π stacking to form physical crosslinking points in linear polyethylene glycol (PEG). The strong intermolecular forces formed by π-π stacking not only prevented leakage of the PEG even at 130 °C but imparted high temperature stability and excellent toughness (172.44 MJ/m3) to fabricated SSPCMs. It is worth mentioning that the prepared PCMs can be added with CNT in a simple process way to improve the photo-thermal conversion ability and thermal conductivity of SSPCMs. Besides, the as-prepared SSPCMs exhibited excellent flexibility, and were expected to be excellent thermal/photo energy storage materials for human thermal management and wearable devices.