Synergistic effects of expandable graphite and dimethyl methyl phosphonate on the mechanical properties, fire behavior, and thermal stability of a polyisocyanurate-polyurethane foam

In this study, a series of flame-retardant polyisocyanurate-polyurethane (PIR-PUR) foams were prepared using various concentrations (0-25% by weight) of expandable graphite (EG) and dimethyl methyl phosphonate (DMMP) (0-7% by weight). The effect of these additives on the properties of the PIR-PUR foams, including physico-mechanical, morphological, flame retardancy, and thermal stability, was studied. Increasing amounts of EG in the PIR-PUR foam caused a significant drop in the compression strength. However, DMMP caused the mechanical properties of PIR-PUR foam to improve compared to foam filled with EG alone. The flame retardancy of PIR-PUR foams containing both EG and DMMP was enhanced significantly compared to EG filled foams. Thermogravimetric analysis (TGA) indicated that EG enhances the thermal stability of PIR-PUR foams but that DMMP decreased it. The morphology of the residual char provided conclusive evidence for the weak thermal stability of foams filled with DMMP.

Palmitic Acid-Lauric Acid/Expanded Graphite as Form-Stable Composite Phase Change Material for Low-Temperature Energy Storage Applications

Low thermal conductivity of binary fatty acid mixture of palmitic and lauric acids(PA-LA)within the value range of 0.15-0.17 W/(m·K)restricts its wide utilization as thermal energy storage material in the active regime of solar heating applications at low operating temperatures.Nevertheless,this mixture as phase change material(PCM)has a suitable phase-change temperature and heat of 36℃and 176.3 J/g,respectively.Hence,the objective of this study is to formulate a novel form-stable composite PCM with the PA-LA mixture and expanded graphite(EG)as a thermal enhancer.PA-LA eutectic mixture with varied concentrations of EG was prepared and characterized.The thermal conductivity of PA-LA/EG increased gradually with the mass of EG.Optimum thermal properties were observed in PA-LA/(5%EG)composite,where its melting(T_(m)),freezing temperature(T_(t)),latent melting heat and thermal conductivity was 35.53℃,34.84℃,174 J/g,and 1.19 W/(m·K),respectively.Also,the composite PCM is characterized by good chemical-thermal stability and thermal reliability for long-term usage.In conclusion,it can be utilized as a prospective form-stable PCM for thermal energy storage in solar heating systems,overheat treatment systems,and other thermal storage applications at low operating temperatures.

Multiple structure graphite stabilized stearic acid as composite phase change materials for thermal energy storage

This paper used 3 types of graphite with different physical structures as the porous matrix to prepare composite phase change materials(PCMs),and investigated their photo-thermal conversion performance and application in battery thermal management.Multiple structure graphite minerals,including microcrystalline graphite(MG),scale graphite(SG),and expanded graphite(EG)were used as porous matrix,while stearic acid(SA)acts as the phase change material.The vacuum impregnation method was applied to prepare SA/MG,SA/SG,SA/EG,and SA/MG1,and SA/EG1was/were prepared by the ethyl alcohol method.Results show that the thermal conductivities of all composite phase change materials were 10.82 to 22.06 times higher than that of the pure SA.Thermogravimetric(TG)analysis showed that the loadages of SA were 43.61%,18.74%,and 92.66%for SA/MG,SA/SG,and SA/EG respectively.The load rates of SA were 18.98%and 18.88%for SA/MG1 and SA/EG1,respectively.For the 3 types of graphite materials of different dimensions,the BET(Brunauer,Emmett,and Teller)surface area determines the maximum load of SA.The Fourier-transform infrared(FTIR)and X-ray diffraction(XRD)results indicated that there was good compatibility between the SA and the supports.The SA/EG1 has better thermophysical properties in heat energy storage and release process.The thermal infrared images show that SA/EG1 has higher sensitivity to the temperature changes.SA/EG1 has better photo-heat conversion performance than SA/SG and SA/MG1 attributed to the multilayer structure of EG.SA/EG has better thermal management performance in the Li-ion batteries discharge process.

Poly(lactic acid)-starch/Expandable Graphite (PLA-starch/EG) Flame Retardant Composites

This work reports on the effect of commercial expandable graphite(EG)on the flammability and thermal decomposition properties of PLA-starch blend.The PLA-starch/EG composites were prepared by melt-mixing and their thermal stability,volatile pyrolysis products and flammability characteristics were investigated.The char residues of the composites,after combustion in a cone calorimeter,were analyzed with environmental scanning electron microscopy(ESEM).The thermal decomposition stability of the composites improved in the presence of EG.However,the char content was less than expected as per the combination of the wt%EG added into PLA-starch and the%residue of PLA-starch.The flammability performance of the PLA-starch/EG composites improved,especially at 15 wt%EG content,due to a thick and strong worm-like char structure.The peak heat release rate(PHRR)improved by 74%,the total smoke production(TSP)by 40%and the specific extinction area(SEA)by 55%.The improvements are attributed to the ability of EG to exfoliate at increased temperatures during which time three effects occurred:(i)cooling due to an endothermic exfoliation process,(ii)dilution due to release of H2O,SO2 and CO2 gases,and (iii)formation of a protective intumescent char layer.However,the CO and CO2 yields were found to be unfavorably high due to the presence of EG.

Thermal Property Enhancement of a Novel Shape-Stabilized Sodium Acetate Trihydrate-Acetamide/Expanded Graphite-Based Composite Phase Change Material

Phase change materials(PCMs)are a kind of highly efficient thermal storage materials which have a bright application prospect in many fields such as energy conservation in buildings,waste heat recovery,battery thermal management and so on.Especially inorganic hydrated salt PCMs have received increasing attention from researchers due to their advantages of being inexpensive and non-flammable.However,inorganic hydrated salt PCMs are still limited by the aspects of inappropriate phase change temperature,liquid phase leakage,large supercooling and severe phase separation in the application process.In this work,sodium acetate trihydrate was selected as the basic inorganic PCM,and a novel shape-stabilized composite phase change material(CPCM)with good thermal properties was prepared by adding various functional additives.At first,the sodium acetate trihydrate-acetamide binary mixture was prepared and the melting point was adjusted using acetamide.Then the binary mixture was incorporated into expanded graphite to synthesize a novel shape-stabilized CPCM.The thermophysical properties of the resultant shape-stabilized CPCM were systematically investigated.The microscopic morphology and chemical structure of the obtained shape-stabilized CPCM were characterized and analyzed.The experiment results pointed out that acetamide could effectively lower the melting point of sodium acetate trihydrate.The obtained shape-stabilized CPCM modified with additional 18%(mass fraction)acetamide and 12%(mass fraction)expanded graphite exhibited good shape stability and thermophysical characteristics:a low supercooling degree of 1.75℃and an appropriate melting temperature of 40.77℃were obtained;the latent heat of 151.64 kJ/kg and thermal conductivity of 1.411 W/(m·K)were also satisfactory.Moreover,after 50accelerated melting-freezing cycles,the obtained shape-stabilized CPCM represented good thermal reliability.

Structure,Characterization and Thermal Properties of the Form-Stable Paraffin/High-Density Polyethylene/Expanded Graphite/Epoxy Resin Composite PCMs for Thermal Energy Storage

The form-stable paraffin/high-density polyethylene/expanded graphite/epoxy resin composite phase change materials(CPCMs),exhibiting suitable thermal properties,including low melting temperature,high conductivity and high phase change enthalpy,was developed in this work.Herein,paraffin(PA)was utilized as a core PCM.High-density polyethylene(HDPE)was utilized for the shape stabilization and preventing the PCMs leakage.Expanded graphite(EG)was used to increase its thermal conductivity and act also in the porous supporting material.Epoxy resin(ER)was used to provide flexible encapsulated scaffold morphology and keep a highly tight network structure of the PCMs.However,the physical architecture,the chemical architecture and thermal behavior properties of specimens were investigated by using the spectroscopy and calorimetry techniques.The scanning electron microscope(SEM),X-ray diffraction(XRD)and fourier transform infrared spectrometer FTIR tests have shown good uniformity structure and good compatibility of components.In addition,the thermal conductivity tests revealed that the thermal conductivity of PA,initially 0.31 W/(m·K)improved up to 1.9 times by adding the 6 wt%mass fraction of EG in composite PCMs.Furthermore,the differential scanning calorimeter(DSC)measurements indicated that PA melting enthalpy,initially 231 J/g decreased up to 125 J/g with the increase of the amount of HDPE which was due to the limitation caused by the atomic network constructed by the base material.The thermogravimetric analyzer(TGA)and leakage-proof revealed the enhancement of the degradation of PA with the raise of amount of the HDPE into the CPCMs.Therefore,the proposed form-stable CPCMs are a great candidate for the thermal regulation and thermal energy storage employment.

Preparation and Thermal Properties of a Novel Modified Ammonium Alum/Expanded Graphite Composite Phase Change Material

Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal energy storage(LTES)systems is hampered due to its high supercooling and low thermal conductivity.In this work,modified A-alum(M-PCM)containing different nucleating agents was prepared and further adsorbed in expanded graphite(EG)to obtain composite phase change material(CPCM)to overcome the disadvantages of A-alum.Thermal properties,thermal cycle stability,microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry,thermal constant analysis,scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The cold rewarming phenomenon of CPCM was established and explained.Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54℃,respectively.The supercooling of CPCM decreased by 9.61℃,and thermal conductivity increased by 27 times compared with pure A-alum.Heat storage and release tests indicated that 2 wt%calcium chloride dihydrate(CCD,CaCl_(2)·2H_(2)O)was the optimum nucleating agent for A-alum.The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature.The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.

Design of a stearic acid/boron nitride/expanded graphite multifiller synergistic composite phase change material for thermal energy storage

In order to solve the problems of low thermal conductivity and easy liquid leakage of a stearic acid(SA),the composite phase change material(PCM)was prepared by adding boron nitride(BN)and expanded graphite(EG)to melted SA,and its thermal conductivity,crystal structure,chemical stability,thermal stability,cycle stability,leakage characteristics,heat storage/release characteristics,and temperature response characteristics were char-acterized.The results showed that the addition of BN and EG significantly improved the thermal conductivity of the material,and they efficiently adsorbed melted SA.The maximum load of SA was 76 wt.%and there was almost no liquid leakage.Moreover,the melting enthalpy and temperature were 154.20 J·g^(−1) and 67.85℃,re-spectively.Compared with pure SA,the SA/BN/EG composite showed a lower melting temperature and a higher freezing temperature.In addition,when the mass fraction of BN and EG was 12 wt.%,the thermal conductivity of the composite was 6.349 W·m^(−1)·K^(−1),which was 18.619 times that of SA.More importantly,the composite showed good stability for 50 cycles of heating and cooling,and the SA/BN/EG-12 hardly decomposes below 200℃,which implies that the working performance of the composite PCM is relatively stable within the tem-perature range of 100℃.Therefore,the composite can exhibit excellent thermal stability in the field of building heating.

Preparation and Properties of Ultrathin Flexible Expanded Graphite Film via Adding Natural Rubber

Expanded graphite(EG) films exhibit potential use in a wide field including thermal management, conductive applications,and electromagnetic interference(EMI) shielding. However, their poor tensile strength and brittleness are crucial deficiencies for commercial applications. To address these defects, in our work, natural rubber(NR) is employed to improve EG films for better mechanical strength and flexibility. The origin of the strengthening effect of EG films by the addition of natural rubber mainly arises from the formation of a simulate shell structure. Compared to the neat EG films, the addition of merely 2 wt% NR can give rise to superior ductility. Further, the loading of 10 wt% NR realizes a significant mechanical enhancement of the EG/NR films, i.e., 2.4 and 11.4 times increase in tensile strength and elongation at break, respectively. Besides, EG/NR films containing 10 wt% NR can still sustain excellent thermal and electric conductivities of 173 W·m^-1·K^-1 and 75 S·cm^-1, respectively. Furthermore, a very high EMI of 41.4 dB is achieved as the film thickness reaches 50 μm. Thus, the lightweight EG/NR films with comprehensive performance as well as their virtue of green and simple large-scale preparation endow them with the possibility of designing next-generation flexible electronics.

Comparison on Thermal Conductivity and Permeability of Granular and Consolidated Activated Carbon for Refrigeration

This paper focuses on the development of three types of activated carbon （AC） adsorbents, i.e. granular AC, consolidated AC with chemical binder, and consolidated AC with expanded natural graphite （ENG）. Their thermal conductivity was investigated with the steady-state heat source method and the permeability was tested with nitrogen as the gas source. Results show that the thermal conductivity of granular AC with different sizes al-most maintains a constant at 0.36 W-（m.K）-＇, while the value modestly increases to 0.40 W.（m.K）-＇ for the con- solidated AC with chemical binder. The consolidated AC with ENG at the density of 600 kg. m-3 shows the best heat transfer performance and their thermal conductivity vary from 2.08 W-（m.K）- to 2.61 W. （m.K）-1 according toits fraction of AC. However, the granular AC and consolidated AC with chemical binder show the better permeabil- ity performance than consolidated AC with ENG binder whose permeability changes from 6.98x10-13 m2 to 5.16x10TM m2 and the maximum occurs when the content of AC reaches 71.4% （by mass）. According to the differ- ent thermal properties, the refrigeration application of three types of adsorbents is analyzed.

Processing Compressed Expanded Natural Graphite for Phase Change Material Composites

Phase change materials(PCMs)are used in various thermal energy storage applications but are limited by their low thermal conductivity.One method to increase conductivity involves impregnating organic PCMs into highly porous conductive matrix materials.Of these materials,compressed expanded natural graphite(CENG)matrices have received the most attention.Despite this attention,the effect that CENG processing has on PCM saturation and overall matrix thermal conductivity has not been fully investigated.Therefore,the effect of the heat treatment process used to expand intercalated graphite flakes is evaluated here.Higher heat treatment temperatures yielded higher saturation rates and overall saturation at similar matrix porosities.For example,increasing temperature from 300℃to 700℃resulted in approximately 60%-70%increase in pore saturation after 100 minutes of soaking.The exposure time to heat treatment had less of an effect on PCM saturation.The exposure time had negligible effect above 30 min and above 500℃heating temperatures.However,because the expanded graphite was found to oxidize around 700℃,the use of longer exposure time in manufacturing applications can be beneficial if a shortened impregnation time is needed.Heat treatment conditions did not impact thermal conductivity.The composite latent heat of fusion was also reduced approximately proportionally to the PCM mass fraction.A local maximum in axial thermal conductivity was observed at around 83%porosity,which is similar to previous studies.The observed conductivity at this maximum was a factor of 81 times greater than the conductivity of the PCM.

膨胀石墨基相变储能材料的制备及性能研究

以膨胀石墨作为主导热材料,石蜡作为相变储热材料,通过真空浸渍法制备了膨胀石墨-石蜡复合相变储能材料,研究了石蜡质量分数对复合相变储能材料微观形貌、物相结构及热性能的影响。结果表明,膨胀石墨和石蜡反应后生成的复合相变储能材料主要依靠物理吸附结合,石蜡均匀覆盖在膨胀石墨的表面以及孔隙中,当石蜡质量分数为91%时,复合相变储能材料的密封性和结构致密性最佳,几乎不发生泄露。随着石蜡质量分数的增加,复合相变储能材料的熔点逐渐增大,热分解温度逐渐提高,石蜡质量分数91%的复合相变储能材料相比石蜡质量分数85%的相变材料热分解温度提高了约15℃。随着石蜡质量分数的增大,复合相变储能材料的导热系数和热扩散系数持续降低,密度先降低后增加,比热持续增大。当石蜡质量分数为94%时,复合相变储能材料的导热系数和热扩散系数均为最低值,分别为2.492 W/(m·K)和0.605 mm^(2)/s;当石蜡质量分数为91%时,复合相变储能材料的密度为最小值0.794 g/cm^(3),对应比热为5.462 J/(g·K)。分析可得,石蜡质量分数为91%的复合相变储能材料的综合性能最佳。

各向异性膨胀石墨双极板对燃料电池性能的影响

该文分析了膨胀石墨双极板(EGBPs)各向异性结构对燃料电池水热管理与输出性能的影响。建立了三维两相非等温数值模型,对比了4种典型复合材料结构下温度、电流密度、水含量等参数的分布特征,揭示了双极板传热特性与输出性能的耦合效应。结果表明:沿质子传递方向热导率(k_z)对燃料电池性能具有显著影响,在2.2 A cm^(-2)电流密度下,将k_z从常规结构的5 W·m^(-1)·K^(-1)提升至280 W·m^(-1)·K^(-1),可以使输出性能提高22 m V;沿流道气体流动方向的热导率(k_y)是影响散热能力的关键因素,将k_y与k_z提高至280 W·m^(-1)·K^(-1),或者实现各向同性结构(k_x=k_y=k_z=20 W·m^(-1)·K^(-1)),均能够使膜电极组件(MEA)核心区域的温度降低2℃左右。因此,提高k_y与k_z并实现各向同性结构是膨胀石墨双极板技术的未来发展目标之一。

相变辅助PE-LD/EG共混物制备与性能

针对层状填料在聚合物基体中剥离与分散困难的问题,将水引入层状填料层间并冷冻成冰,相同质量的水从液态变为固态体积增大,使填料的层间距增大,在熔融共混过程中,高温作用下填料层间的冰迅速转变为水蒸气并产生瞬时高压,进而实现层状填料的原位剥离;由此提出一种相变辅助熔融共混制备低密度聚乙烯(PE-LD)/膨胀石墨(EG)复合材料的新工艺方法,研究新工艺对复合材料微观形貌、结晶性能和导热性能的影响。相变辅助制备的PE-LD/EG复合材料的扫描电子显微镜图像呈现出更薄的片材堆叠结构,X射线衍射线表现出更低的(002)衍射峰强度,说明相变效应可以有效地促进EG的原位剥离;动态扫描量热分析结果表明,剥离后的EG片层可以作为异相成核点促进PE-LD结晶,复合材料的结晶度从23.47%提高到28.44%;导热性能测试结果表明,PE-LD/EG复合材料的热导率随EG含量的增加而增加,且相变辅助制备的复合材料热导率大于常规熔融共混制备,最大值达0.715W/(m·K)。引入相变效应制备的PE-LD/EG复合材料中的EG剥离程度更高,分散效果更好,有助于EG片层相互搭接形成导热通路,从而提高复合材料的导热性能。

聚乙二醇基相变材料用于电池热管理

因不适宜的温度带来的锂离子电池热灾害问题一直未得到解决,有效的电池热管理技术显得尤为重要。以聚乙二醇(PEG)和膨胀石墨为原料,通过熔融共混法制备复合相变材料,研究材料的热物理性质和电池热管理性能。随着膨胀石墨添加量的增加,相变材料的熔点和热焓均降低,而导热系数增加。当膨胀石墨的质量分数为10%时,熔点、热焓和导热系数分别为46.8℃、116.6 J/g和1.379 W/(m·K)。相变材料冷却能很好地控制电池的温度,在2.0 C放电倍率下,与风速为2.3 m/s的强制空气冷却相比,单体电池和电池组的最高温度分别降低了7.15℃、10.98℃。

一种BIPV 光伏建筑材料制备及应用性能试验

为降低建筑能耗,试验以石蜡为相变材料,与膨胀石墨相结合制备一种复合相变材料的BIPV光伏建筑材料并研究其性能。试验结果表明,在水泥中掺入复合相变材料,会降低其力学性能,但可以提高相变温度T_(peak)和相变潜热DH,使BIPV光伏建筑材料具备良好的相变储能效果;试验中最佳复合相变材料掺量为30%,制备的BIPV光伏建筑材料在保证一定抗压强度、抗折强度下,相变潜热DH达到28.7 kJ/kg,且热稳定性较好;在实际应用方面,以BIPV光伏建筑材料制备的相变储能地板具备的储能效果,可以起到保暖、节能等作用。

太阳能相变蓄热炕的实验及数值模拟研究

为实现太阳能相变蓄热炕的快速升温,采用毛细管网及配置高导热复合相变材料来提高炕体的热响应时间,通过数值模拟与实验研究相结合的方法对炕体的热工性能进行研究。本文首先对比不同熔点石蜡的差示扫描量热(differential scanning calorimetry,DSC)曲线,选取35#石蜡作为研究对象,采用熔融混合法制备不同配比的石蜡-膨胀石墨复合定形相变材料;并通过渗漏测试确定最佳配比。实验表明:当膨胀石墨质量分数为8%时,复合定形相变材料渗漏率较低,为兼顾储热、导热性能的最佳配比。将石蜡复合相变材料应用于太阳能相变蓄热炕,通过计算流体动力学(computational fluid dynamics,CFD)建立三维非稳态传热模型,对炕体进行24 h供热模拟设计;模拟表明:太阳能相变蓄热炕在昼间垫面温度达到24.2℃,夜间垫面温度达到30.2℃。通过Trnsys(transient system simulation program)软件对组合式系统进行运行模拟发现:组合系统均可达到设计的45℃及以上;另外,组合式系统全年节电量为2974.7 kW·h,或节省标准煤469.9 kg,或减少二氧化碳1240.5 kg、一氧化碳70.9 kg、PM_(10)6.8 kg等,节能减排量显著。

石蜡/膨胀石墨复合相变材料的结构与热性能

以有机物石蜡为相变材料、膨胀石墨为支撑结构,利用膨胀石墨的多孔吸附特性,制备出了石蜡含量分别为50%(质量分数,下同),60%,70%和80%的石蜡/膨胀石墨复合相变储热材料.采用扫描电镜(SEM)和差示扫描量热分析(DSC)对复合相变储热材料的结构和热性能进行了表征.结果表明:膨胀石墨吸附石蜡后仍然保持了原来疏松多孔的蠕虫状形态,石蜡被膨胀石墨微孔所吸附;复合相变储热材料的相变温度与石蜡相似,其相变潜热与基于复合材料中石蜡含量的潜热计算值相当.储(放)热性能测试结果表明,含80%石蜡的复合相变储热材料其储热时间比石蜡减少69.7%,放热时间减少80.2%.

月桂酸-棕榈酸-硬脂酸/膨胀石墨复合相变材料的制备及性能

以理论计算为基础,制备了月桂酸-棕榈酸-硬脂酸三元低共熔混合物(LA-PA-SA)。利用膨胀石墨(EG)的网状多孔结构,制备了最佳质量配比为15:1(LA-PA-SA:EG)的LA-PA-SA/EG复合相变材料。综合利用FT-IR、SEM、DSC、冷热加速循环和蓄放热实验等对复合相变材料的结构和性能进行了研究。结果表明:LAPA-SA通过物理吸附作用均匀分布于EG的多孔结构中;复合相变材料的熔化和凝固温度分别为32.1℃和30.3℃,熔化和凝固潜热分别为143.2J·g-1和143.1J·g-1;经过1000次冷热循环后具有良好的热稳定性和化学稳定性;EG的高导热性加快了复合相变材料的蓄放热速率。

可发性聚苯乙烯复合保温材料的阻燃性能

目的研究十溴联苯醚/三氧化二锑和可膨胀石墨对发泡聚苯乙烯复合保温材料的协同阻燃效应、保温性能和力学性能的影响.为开发建筑节能保温材料提供参考.方法制备发泡聚苯乙烯复合保温材料,采用预先共混法将复合阻燃剂包裹在预发泡聚苯乙烯珠粒表面,通过蒸气热压成型聚苯乙烯复合板材,采用扫描电镜观察、差热分析、阻燃性能测试、导热系数和力学性能测试,对复合板材性能进行综合评价与分析.结果添加十溴联苯醚/三氧化二锑/可膨胀石墨的聚苯乙烯复合板材具有优异的阻燃性能(离火自熄时间仅为1.3 s),是由于膨胀石墨的多孔结构可对溴系阻燃剂分解的不燃气体产生有效束缚、显著提高阻燃效率所致.同时,聚苯乙烯复合板材具有较优的保温性能和力学性能.综合考虑复合阻燃剂的加入对力学性能和工艺性能的影响,阻燃剂加入量以十溴联苯醚/三氧化二锑15%(质量分数)、可膨胀石墨11%为宜.结论通过阻燃剂包覆法制得的聚苯乙烯复合板材具有阻燃效果明显、操作方便、性能可控性好的显著优点.