石蜡/碱改性硅藻土/膨胀石墨复合相变储热材料的制备及性能

通过碱处理,优化了硅藻土(DIA)的孔隙结构,提高了孔隙率,增加了石蜡(paraffin)负载量。通过直接浸渍法制备了新型性状稳定的石蜡/碱改性DIA/膨胀石墨(EG-alDIAP)复合材料,并研究了其结构与性能的关系。结果表明,复合相变材料的石蜡负载量从47.4%提高到了61.1%,进而提高了复合材料的储热性能;向改性DIA中添加膨胀石墨(EG)提高了复合材料的传热能力,添加质量分数10%EG时导热系数提高了113%(从0.276 W·m^-1·K^-1提高到了0.589 W·m^-1·K^-1)。随着EG含量的升高,复合相变材料的相变潜热有所增加,但化学相容性、稳定性等无明显变化。含 10%EG的石蜡/碱改性 DIA复合材料具有可靠的储能性能、良好的温度调节性能和蓄放热能力。     

石蜡/碱改性硅藻土/膨胀石墨复合相变储热材料的制备及性能

通过碱处理,优化了硅藻土(DIA)的孔隙结构,提高了孔隙率,增加了石蜡(paraffin)负载量。通过直接浸渍法制备了新型性状稳定的石蜡/碱改性DIA/膨胀石墨(EG-alDIAP)复合材料,并研究了其结构与性能的关系。结果表明,复合相变材料的石蜡负载量从47.4%提高到了61.1%,进而提高了复合材料的储热性能;向改性DIA中添加膨胀石墨(EG)提高了复合材料的传热能力,添加质量分数10%EG时导热系数提高了113%(从0.276 W·m^-1·K^-1提高到了0.589 W·m^-1·K^-1)。随着EG含量的升高,复合相变材料的相变潜热有所增加,但化学相容性、稳定性等无明显变化。含10%EG的石蜡/碱改性DIA复合材料具有可靠的储能性能、良好的温度调节性能和蓄放热能力。     

Thermal-Conductivity-Enhancing Copper-Plated Expanded Graphite/Paraffin Composite for Highly Stable Phase-Change Materials

Paraffin (PA)/expanded graphite (EG) is an important composite phase change material with low cost, high heat storage, good thermal conductivity and cycling stability. Its thermal conductivity needs to be further improved for application in the thermal management system of power lithium-ion batteries. In this paper, copper plated expanded graphite (CPEG) with 3D porous structure was prepared by electroless copper plating method, which was used as thermal conductivity enhancing material to replace part of EG in PA/EG composite materials. For the optimized phase change material composed of 80 %PA-14 %EG-6 %CPEG, the copper content is very low (0.768 wt %), but its thermal conductivity can be significantly improved without loss of latent heat and thermal cycling stability. Its thermal conductivity is increased from 11 times to 16.5 times that of paraffin while compared with the copper-free composite material (80 %PA-20 %EG). The PA/EG/CPEG composite material exhibits good temperature control effect on power lithium-ion batteries.     

Nanocrystalline MgO samples (11.5 and 12.6 nm) derived from two different precursors: characterization and catalytic activity

Decanoic acid/expanded graphite composite phase change materials (DA/EG-PCMs) with high stability and excellent thermal conductivity were fabricated by blending expanded graphite (EG) and decanoic acid (DA). The structure, thermo-physical properties, and the formation mechanism of DA/EG-PCMs were investigated. The obtained results demonstrate that EG exhibits a network-like porous structure, which is superimposed of 10–50 μm thick graphite sheet. Therefore, DA can be effectively encapsulated through the binding between micropores and the surface adsorption of EG resulting in a relatively smaller DA/EG-PCMs particle with better dispersibility. In addition, adding EG into DA also increased both the thermal stability and the thermal conductivity while decreasing the charging and discharging time, which resulted in improved thermal efficiencies. Although adding EG can negatively influence the phase change behavior of DA, the temperature and enthalpy of phase change were still as high as 34.9 °C and 153.1 J g^?1, respectively. Based on a combination of experimental results and a comprehensive analysis of the phase transformation kinetics, it is concluded that DA/EG-PCMs with 10 mass% EG with improved thermal properties can meet the requirements for efficient temperature control in low-to-medium environments.     

Polypropylene as a potential matrix for the creation of shape stabilized phase change materials

Phase change materials, based on isotactic polypropylene (PP) blended with soft and hard Fischer−Tropsch paraffin wax respectively, were studied in this paper. DSC, DMA, TGA and SEM were used to determine the structure and properties of the blends. While paraffin waxes in the blend changed state from solid to liquid, the PP matrix kept the material in a compact shape. Strong phase separation was observed in both cases, which was more pronounced in the case of soft paraffin wax. Despite the fact that both grades of paraffin wax are not miscible with PP due to different crystalline structures, it was shown that the hard Fischer−Tropsch paraffin wax is more compatible with PP than the soft one. Both waxes plasticized the PP matrix. TGA showed that PP blended with the hard Fischer−Tropsch wax degrades in just one step, whereas blends containing soft paraffin wax degrade in two distinguishable steps. SEM exposed a completely different morphology for the two paraffin waxes and confirmed the lower compatibility of PP and soft paraffin wax. The soft and hard characters of the waxes were manifested in the viscoelastic properties, where the blends containing soft paraffin wax exhibited a lower elastic modulus than pure polypropylene, whereas the hard Fisher−Tropsch paraffin wax solidified the matrix. However, both kinds of blends were able to sustain the dynamic forces applied by the DMA within five cycle runs implying good shape stability.     

三元脂肪酸/膨胀石墨复合相变材料的制备、包覆定形及热性能

采用癸酸、 月桂酸和棕榈酸的三元共晶混合物作为相变材料, 以膨胀石墨为基体, 通过膨胀石墨多孔结构的毛细吸附和复合涂饰剂的包覆定形, 将多元相变材料固定在膨胀石墨的孔道结构中, 制备出结构稳定、 密封性能优异、 热稳定性好和高导热的新型三元脂肪酸/膨胀石墨复合定形相变材料. 膨胀石墨具有膨胀疏松的多孔结构和良好的吸附性能; 其熔融潜热为95.6 J/g, 结晶焓为82.8 J/g, 说明其具有很好的相变蓄热特性和热循环稳定性; 材料的导热性能可增加至0.738 W/(m·K), 与脂肪酸相比得到大幅度提高.     

Preparation and thermal properties of expanded graphite/paraffin/organic montmorillonite composite phase change material

Expanded graphite (EG)/paraffin/organic montmorillonite (OMMT) composite phase change material (PCM) was prepared by using melt intercalation method. The microstructure of EG/paraffin/OMMT is observed by scanning electron microscope (SEM). The thermal properties are investigated by differential scanning calorimetry (DSC). The mass loss of EG/paraffin/OMMT after 50 heating cycles was measured for investigating the influence of EG and OMMT on the thermal properties of paraffin. The results show that EG and OMMT have the ability of adsorption and shape-stability. The melting point EG/paraffin/OMMT is decreased slightly with an addition of paraffin and the latent heat of EG/paraffin/OMMT is determined by the mass ratio of paraffin. The heat transfer efficiency of EG/paraffin/OMMT is strengthened and the heating time is decreased to one-sixth of that of paraffin by addition of EG and OMMT. The thermal stability of EG/paraffin/OMMT is improved by addition of OMMT.     

Improvement in thermodynamic characteristics of sodium acetate trihydrate composite phase change material with expanded graphite

In this study, three different volume expansion ratios of expanded graphite (EG) are prepared and investigated to enhance the heat transfer efficiency of the sodium acetate trihydrate (SAT) composites. A series of SAT composite phase change materials (CPCMs) with EG were prepared. The influence of volume expansion ratio and mass fraction of EG on thermodynamic characteristics of SAT CPCMs was examined, including thermal conductivity, phase change temperature, enthalpy, latent heat storage and release time, and the degree of supercooling. Results showed that SAT CPCMs can be absorbed adequately by EG, and EG could enhance the heat transfer efficiency effectively. But it also brought some problems with the addition of all the three volume expansion ratios of EG, such as the poor enthalpy and serious supercooling. Particularly, the situation gets worse with the increase in mass and expansion ratio of EG. Therefore, it is better to choose the EG with proper expansion ratio or reduce the proportion of the EG which possesses higher expansion ratio. Besides, thermal cycling test and thermogravimetric analysis revealed that the SAT CPCMs with 3 mass% EG showed a good thermal stability.

     

石蜡/膨胀石墨/石墨烯复合相变储热材料的制备及性能

以石蜡(PA)作为相变储热材料、 膨胀石墨(EG)作为主导热材料和支撑材料, 石墨烯气凝胶(GA)作为导热增强材料和辅支撑材料制备了PA/EG/GA复合相变材料, 研究了GA添加量对复合相变材料相变温度、 相变潜热、 导热性能以及循环稳定性的影响. 结果表明, 所制备的80%PA-17%EG-3%GA复合相变材料导热性能良好, 循环稳定性出色. 与80%PA-20%EG复合材料相比, 该材料的相变温度、 相变潜热以及循环稳定性无明显变化, 但导热系数由4.089 W/(m·K)提升到了5.336 W/(m·K), 显示出良好的应用前景.     

Comparisons Among Electrical and Rheological Properties of Melt-Mixed Composites Containing Various Carbon Nanostructures

The present investigation compares different carbon-based nanoscaled materials with regard to their effectiveness in producing thermoplastic polymers with antistatic and electrically conductive behavior. The dispersed phases are carbon black (CB) as spherical particles, multiwalled carbon nanotubes (MWNT) as fiber-like filler, and expanded graphite (EG) as platelet-like filler. Each was incorporated into polycarbonate by small-scale melt mixing. The electrical percolation concentrations were found to be 2 wt% for MWNT, 4 wt% for EG, and 8.75 wt% for CB which parallels the aspect ratios of the fillers. For EG a strong dependence of morphology and electrical resistivity on mixing time was observed, indicating a structural change/destruction during intensive shear mixing. Rheological percolation thresholds were found to be lower than electrical percolation threshold for the MWNT and CB, but similar in the case of EG. The general impact on complex melt viscosity decreases in the order MWNT, CB, EG. For EG, at higher loadings (above 4wt%) the viscosity increase with filler content is delayed as is the decrease in resistivity.     

Additive manufacturing of fire‐retardant ethylene‐vinyl acetate

Thermocompression (with also extrusion and injection molding) is a classical polymer shaping manufacturing, but it does not easily allow designing sophisticated shapes without using a complex mold, on the contrary to 3D printing (or polymer additive manufacturing), which is a very flexible technique. Among all 3D printing techniques, fused deposition modeling is of high potential for product manufacturing, with the capability to compete with conventional polymer processing techniques. This is a quite low cost 3D printing technique, but the range of filaments commercially available is limited. However, in some specific 3D printing processes, no filaments are necessary. Polymers pellets feed directly the printing nozzle allowing to investigate many polymeric matrices with no commercial limitation. This is of high interest for the design of flame‐retarded materials, but literature is scarce in that field. In this paper, a comparison between thermocompression and 3D printing processes was performed on both neat ethylene‐vinyl acetate (EVA) copolymer and EVA flame retarded with aluminum triHydroxyde (ATH) containing different loadings (30 or 65 wt%) and with expandable graphite (EG), ie, EVA/ATH (30 wt%), EVA/ATH (65 wt%), and EVA/EG (10 wt%), respectively. Morphological comparisons, using microscopic and electronic microprobe analyses, revealed that 3D printed plates have lower apparent density and higher porosity than thermocompressed plate. The fire‐retardant properties of thermocompressed and 3D printed plates were then evaluated using mass loss calorimeter test at 50 kW/m². Results highlight that 3D printing can be used to produce flame‐retardant systems. This work is a pioneer study exploring the feasibility of using polymer additive manufacturing technology for designing efficient flame‐retarded materials.     

Synergistic effect between expandable graphite and ammonium polyphosphate on flame retarded polylactide

Synergistic effect was observed between expandable graphite (EG) and ammonium polyphosphate (APP) on flame retarded polylactide (PLA) in this paper using limiting oxygen index (LOI), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray spectroscopy (XPS) and cone calorimeter tests etc. In the experiments, PLA composites with 15 wt% of APP/EG(1:3) combinations showed a LOI value of 36.5 and V-0 rating in UL-94 tests, greatly improved flame retardant properties from composites with APP or EG alone. Results from TGA and cone calorimeter demonstrated that APP/EG combination could retard the degradation of polymeric materials above the temperature of 520 °C by promoting the formation of a compact char layer. This char layer protects the matrix effectively from heat penetrating inside and prevents its further degradation, resulting in lower weight loss rate and better flame retarded performance.     

Evaluation of PCM/diatomite composites using exfoliated graphite nanoplatelets (xGnP) to improve thermal properties

This paper deals with the thermal performances of shape-stabilized phase change materials (SSPCM) for energy saving in various fields. This study enhanced thermal properties of SSPCM using exfoliated graphite nanoplatelets (xGnP). SSPCM, which contains the xGnP, was prepared by mixing and melting techniques for high dispersibility, thermal conductivity, and latent heat storage. In the experiment, we used hexadecane, octadecane, and paraffin as phase change materials (PCMs), and they have 254.7, 247.6, and 144.6 J g^?1 of latent heat capacity, and melting points of 20.84, 30.4, and 57.09 °C, respectively. The characteristics of SSPCMs were determined using SEM, DSC, FTIR, TG, TCi, and Energy simulation. SEM morphology showed homogenous dispersion of PCM and xGnP in the porous diatomite. DSC analysis results showed the latent heat capacity of SSPCM and SSPCM/xGnP composites, and TG analysis results showed the thermal reliability of the samples. Also, we checked the thermal conductivity of the SSPCM that contains xGnP, by TCi analysis.     

Phase change materials based on low-density polyethylene/paraffin wax blends

Phase change materials, based on low-density polyethylene blended with soft and hard paraffin waxes respectively, were studied in this paper. DSC, DMA, TGA and SEM were employed to determine the structure and properties of the blends. The blends were able to absorb large amounts of heat energy due to melting of paraffin wax, whereas the LDPE matrix kept the material in a compact shape on macroscopic level. The hard paraffin wax was, however, much more miscible with LDPE because of co-crystallization than the soft paraffin wax. LDPE blended with hard paraffin wax degrades in just one step, while blends containing soft paraffin wax degrade in two distinguishable steps. SEM showed completely different morphology for the two paraffin waxes and confirmed the lower miscibility of LDPE and soft paraffin wax. DMA analyses demonstrated the toughening effect of the waxes on the polymer matrix. This technique was also used to follow the thermal expansion as well as the dimensional stability of the samples during thermal cycling. The most visible expansion could be seen in the first cycle, probably due to a totally different thermal history of the sample. With further cycling the dimensions stabilized after two and four cycles for soft and hard paraffin wax, respectively. Controlled force ramp testing on DMA confirmed poor material strength of the blends containing soft wax, especially at temperatures above wax melting.     

Influence of char residues on flammability of EVA/EG, EVA/NG and EVA/GO composites

Graphite (expanded graphite(EG), natural graphite (NG) and graphite oxide (GO)) flame retardant poly(ethylene-co-vinyl acetate) copolymer (EVA) composites (EVA/EG, EVA/NG and EVA/GO) have been prepared by melt compounding. The flammability, the combustion process, the quantity of the residual char, the morphology of the residual chars and the thermal stability of the chars were investigated by cone calorimeter, SEM and TGA. The results indicate that heat release rate (HRR), total heat released (THR) and total smoke release (TSR) of EVA/EG (EG 30 phr) composite decrease to about 21%, 42% and 28% of that of pure EVA, respectively. The orders of the three kinds of graphite on the reduction effect of THR and TSR are EG > NG > GO. The higher the quantity, the higher is the thermal stability of the char residue and the more compact and porous char structure may be the main reasons for the phenomenon above. It has been found that the flame retardance of EVA vulcanisates is improved and the fire jeopardizing is dramatically reduced due to the addition of the graphite, especially for EG, which can give some advice to design formulations for practical applications as the jackets of cables.     

Preparation and characterization of pavement materials with phase-change temperature modulation

A kind of pavement crack repairing material with temperature regulation property was successfully prepared through one-step method, in which the paraffin was incorporated into the polyurethane/epoxy resin-interpenetrating polymer networks. Differential scanning calorimeter results indicated that the phase-change latent heat of sample A was 14.4 kJ kg^?1, and the phase transition temperature was ??0.3 °C. FTIR and thermogravimetry measurements verified that the paraffin was successfully incorporated into the interpenetrating polymer network without leakage and reacted with the carrier, which exhibited high thermal stability above 300 °C. After 1 year of road test, there was no breakage for the repairing pavement with paraffin–polyurethane/epoxy resin-interpenetrating polymer networks, and there was almost no change for the accumulated attenuation of phase-change latent heat. Therefore, the materials of paraffin–polyurethane/epoxy resin-interpenetrating polymer networks have good chemical stability and thermal stability.

     

Synthesis and properties of bulk-biodegradable phase change materials based on polyethylene glycol for thermal energy storage

The bulk-biodegradable solid–solid phase change materials (SSPCMs) based on phase change polyethylene glycol (PEG) were synthesized by solvent-free polyaddition. On the basis of the fact that the water absorption is up to 800 mass% and that the poly(ethylene oxide) molecular chains can be degraded by microorganisms, the bulk-biodegradable mechanism of SSPCMs was put forward and studied. The X-ray diffraction patterns and the polarizing optical microscopy images show the SSPCMs possess the defective crystal and small grain compared with PEG. The differential scanning calorimetry data demonstrate the melting temperature and enthalpy of the synthesized SSPCMs are, respectively, 41 °C and 128 J g^?1. The bulk-biodegradable SSPCMs have the preeminent thermal reliability and the high thermal stability due to the onset thermal degradation temperature above 302 °C, which will give a good insight into bulk-biodegradable PCM system.     

Preparation and Rheological Characterization of Polymer Nanocomposites Based on Expanded Graphite

A new type of conductive filler, namely expanded graphite (EG), was used to prepare novel nanocomposites. The EG was incorporated into several rather different polymers, specifically polycarbonate (PC), low‐density polyethylene (LDPE), isotactic polypropylene (PP), and polystyrene (PS), using melt mixing in a small‐scale DACA‐Microcompounder. The EG content was varied between 1 and 20 wt%. The rheological properties and morphologies of the nanocomposites were characterized by melt rheology and scanning electron microscopy (SEM), respectively. The melt‐state linear viscoelastic properties were investigated using an ARES rheometer, with the measurements performed in the dynamic mode at various temperatures over a wide range of frequencies. Addition of the EG increased the linear dynamic moduli and melt viscosity of the materials. Up to a certain critical concentration of EG, the materials exhibited a simple liquid‐like behavior. Above this concentration, however, significant changes in the frequency dependences of the moduli and viscosity were observed. In addition, the moduli showed a liquid‐solid transition resulting in a second plateau in the low frequency‐regime, and the complex viscosity revealed shear‐thinning behavior. Specific values of this percolation concentration were found to be at around 4 wt% in the case of PC/EG, 9 wt% for PP/EG and PS/EG, and 12 wt% for PE/EG. This critical concentration was correlated to a network‐like structure formed through interactions between the EG platelets and the polymers. The extent of these complications was found to vary from polymer to polymer, presumably due to different degrees of EG exfoliation and dispersion arising from different EG‐polymer interactions and from variable shearing forces dependent on the polymer viscosities. The formation of network‐like structures is very sensitively displayed using van Gurp‐Palmen plots, which are most suitable for identifying “rheological percolation” in our investigated systems.     

Hugely enhanced flame retardancy and smoke suppression properties of UHMWPE composites with silicone‐coated expandable graphite

In this paper, silicone‐coated intumescent flame retardants was prepared by an efficient and simple approach, aiming at enhancing the flame‐retardant efficiency and smoke suppression properties. The surface of expandable graphite (EG) was treated prior to the coverage of nonflammable silicone. The resultant silicone‐modified EG hybrid (SEG) was combined with ammonium polyphosphate (APP) and applied as a flame‐retardant and smoke‐suppressant for ultrahigh molecular weight polyethylene (UHMWPE). Compared with UHMWPE/APP/EG (with 15 wt% APP/EG), UHMWPE/APP/SEG (with 15 wt% APP/SEG) gives decrement by 18.5% in the peaks of the heat release rate, 6.33% in total heat release and 13.6% in total smoke release, whereas increment by 23% in tensile strength and 12.1% in elongation at break, respectively. It is suggested that the introduction of silicone on the surface of EG can improve the interfacial compatibility between EG and UHMWPE. Moreover, it can lead to forming more char residue and reducing the release of smoke particulates during combustion process of the composites.     

Influence of thermal and UV treatment on the polypropylene/graphite composite

Electrically conductive polypropylene/graphite (PP/graphite) composites were prepared via blending granulated PP with maleic anhydride grafted PP and natural graphite. Electrical conductivity of prepared samples containing either 65, 70, or 75 wt% of graphite was measured and the most conductive sample containing 75 wt% of graphite was exposed to UV irradiation for 1 and 24 h or thermally treated at 170 °C for 1 h. The influence of thermal and UV exposure on the structural and electrical changes in such treated samples was studied. Local current measurements on the surface were made using scanning spreading resistance microscopy and morphology of the surface was studied by atomic force microscopy. X-ray diffraction analysis, infrared and Raman spectroscopy were also used for the structural characterization. Properties of treated and untreated samples are compared and differences are discussed.