Electrical conductivity and EMI shielding effectiveness of polyurethane foam–conductive filler composites

The morphological, electrical, and thermal properties of polyurethane foam (PUF)/single conductive filler composites and PUF/hybrid conductive filler composites were investigated. For the PUF/single conductive filler composites, the PUF/nickel‐coated carbon fiber (NCCF) composite showed higher electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) than did the PUF/multiwall carbon nanotube (MWCNT) and PUF/graphite composites; therefore, NCCF is the most effective filler among those tested in this study. For the PUF/hybrid conductive fillers PUF/NCCF (3.0 php)/MWCNT (3.0 php) composites, the values of electrical conductivity and EMI SE were determined to be 0.171 S/cm and 24.7 dB (decibel), respectively, which were the highest among the fillers investigated in this study. NCCF and MWCNT were the most effective primary and secondary fillers, and they had a synergistic effect on the electrical conductivity and EMI SE of the PUF/NCCF/MWCNT composites. From the results of thermal conductivity and cell size of the PUF/conductive filler composites, it is suggested that a reduction in cell size lowers the thermal conductivity of the PUF/conductive filler composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44373.     

Studies on thermal degradation kinetics and dielectric properties of polyether imide foam/nanosilica-based nanocomposites

ABSTRACT

In this paper, polyether imide (PEI) having properties such as a high glass transition temperature of 216°C, high heat resistance, high flame resistance, low smoke generation and a high melting point within the range of 400°C, having low thermal conductivity and low dielectric constant was chosen to be a polymeric foam. Water vapor-induced phase separation method was used to prepare PEI foams. PEI foams were reinforced with nano-silica (weight 1, 3 and 5%) in order to alter the dielectric properties, thermal conductivity and degradation kinetics of foamed polymer. The tested samples showed a reduction in dielectric constant than that of solid PEI but at a higher loading, it showed a higher value due to threshold percolation and a reduction in thermal conductivity was observed for foamed PEI. From thermogravimetric analysis, we can conclude that PEI with 3% filler loading showed better thermal stability compared to other PEI foam compositions.     

导热绝缘PE-LD/PE-g-MAH/h-BN泡沫塑料的制备及性能研究

采用熔融共混法制备了一系列导热绝缘的低密度聚乙烯/马来酸酐接枝聚乙烯/六方氮化硼(PE-LD/PE-g-MAH/h-BN新型泡沫塑料,研究了相容剂PE-g-MAH的加入、h-BN含量对PE-LD/PE-g-MAH/h-BN泡沫体系导热性能、绝缘性能、力学性能及热稳定性的影响。结果表明,PE-g-MAH有利于增加PE?LD与h?BN的界面黏结,增强泡沫体系拉伸强度和断裂伸长率,显著提高其热导性能;当h-BN含量为30 %时, PE-LD/PE-g-MAH/h-BN泡沫体系的导热率为0.256 W/(m·K),相对于PE-LD/h-BN泡沫体系的0.217 W/(m·K) 和纯PE-LD泡沫体系的0.039 W/(m·K),热导率分别提高1.18和6.57倍,同时保持较好的绝缘性和热稳性。     

Pulverized polyurethane foam particles reinforced rigid polyurethane foam and phenolic foam

Polyurethane consumption has been increasing in recent years, raising concerns about how to deal with the polymer waste. Post‐consumer rigid polyurethane foams or polyurethane foam scraps (PPU) ground into particles were utilized to strengthen mechanical properties of rigid polyurethane foam (PUF) and phenolic foam (PF). Viscosity of prepolymer with PUF was measured and PPU was well dispersed in prepolymer, as observed by optical microscope. Microstructures and morphologies of the reinforced foam were examined with scanning electron microscope (SEM) while cell diameter and density were measured by Scion Image software. Universal testing machine was employed to optimize compressive properties at various weight ratios of PPU. Both PUF and PF with 5 wt % PPU, respectively, exhibited considerable improvement in mechanical properties especially compressive property. The compressive modulus of PUF with 5 wt % PPU was 12.07 MPa, almost 20% higher than pure PUF while compressive strength of PF with 5 wt % PPU reached 0.48 MPa. The thermal stability of the reinforced foam was tested by thermal gravity analysis (TGA) and the result shows no obvious impact with PPU. The decomposition temperatures of PUF with PPU and PF with PPU were 280°C, because PPU has relatively weak thermal stability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39734.     

Effect of foam density on the properties of water blown rigid polyurethane foam

Density is an important parameter that influences the properties and performances of rigid polyurethane foam (PUF). Rigid PUF with different densities were prepared by varying the amount of distilled water as blowing agent. This investigation reports the mechanical, morphological, water absorption, thermal conductivity, and thermal behavior of rigid PUF varying with the density, which controls the foam architecture. The density of the PUF decreased from 116 to 42 kg/m³ with an increase in the amount of water from 0.1 to 3.0 parts per hundred polyol by weight (phr), respectively. It was found that the mechanical properties of the PUFs changed with the foam density. The results of water absorption of the PUFs showed that water absorption increased with decrease in density, due to increase in the cell size and decrease in the cell‐wall thickness. The thermal conductivity measurements showed that the thermal conductivity decreased with increase in density. It was due to the decrease in cell size. The thermal analysis of the PUFs shows that the glass transition temperature increases with the decrease in foam density, but the thermal stability decreases with the decrease in foam density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of ultrasound on the synthesis and properties of polyurethane foam/clay nanocomposites

Polyurethane foam (PUF)/clay nanocomposites were synthesized with clay modified by polymeric 4,4′‐diphenylmethane diisocyanate (PMDI) with the application of ultrasound. Transmission electron micrographs showed that the interlayer distance increased for the polyurethane (PU)/clay nanocomposites where ultrasound was applied. The results of the transmission electron microscopy and X‐ray measurements suggest that the application of ultrasound to the clay modification with PMDI improved the efficiency of the clay modification by the effective breakup of the clay agglomerates and intercalation of the silicate layers. In the mechanical tests of the PUF/clay nanocomposites, the flexural and tensile strengths of the PUF/clay nanocomposites showed the maximum value at 3.0 wt % clay content based on PMDI. These results suggest that the increases in the flexural and tensile strengths were perhaps due to the uniform dispersion of the clay by the application of ultrasound. At the same modified clay content, the fire resistance properties were increased for the PUF/clay nanocomposites with the application of ultrasound compared to the PUF/clay nanocomposites without the application of ultrasound. The cell size and thermal conductivity were decreased for the PUF/clay nanocomposites with the application of ultrasound compared to the PUF/clay nanocomposite without the application of ultrasound. Because of these results, we suggest that the smaller cell size and lower thermal conductivity of the PUF/clay nanocomposites were mainly due to the enhanced dispersion of the clay by the application of ultrasound to the mixture of PMDI and clay. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3764–3773, 2006     

Effect of expandable graphite on the properties of intumescent flame‐retardant polyurethane foam

Water‐blown rigid polyurethane foam (PUF) with two different particle sizes (180 and 300 μm) of expandable graphite (EG) as a flame‐retardant additive were prepared, and the effects on the mechanical, morphological, water absorption, thermal conductivity, thermal, and flame‐retardant properties were studied. In this investigation, EG content was varied from 5 to 50 php by weight. The mechanical properties of PUF decreased with increasing EG loading in both cases. The water absorption of the PUF increased with an increase in the EG loading mainly because of the collapse of foam cells, as evidenced from the scanning electron microscopy pictures. The thermal conductivity of the EG‐filled PUF showed that the insulation properties decreased with EG loading. The flame‐retardant properties (limiting oxygen index and char yield measurement) of the PUF improved with increasing EG loading. PUF filled with the higher particle size EG showed better mechanical properties and fire‐retardant properties than the PUF filled with the lower particle size EG. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Analysis of mechanical,thermal, electrical and EMI shielding properties of graphite/carbon fiber reinforced polypropylene composites prepared via a twin screw extruder

The present research focuses on the preparation of an efficient material that acts as a deterrent to electromagnetic pollution. In this study, graphite and carbon fiber (CF) reinforced polypropylene (PP) composites (GCF) are prepared using a melt processing technique via a twin-screw extruder. The prepared composites were evaluated for mechanical, thermal, DC conductivity, and EMI shielding properties. There is a rise in the tensile strength (4.32%) and thermal stability (6.57%) of composites were recorded as compared to pure PP. The fractured morphology of the composites showed the breakdown of CF, leading to the improvement in the tensile strength of the composites. An increase in electrical conductivity was seen at maximum (GCF4) filler loading indicating 2.31 × 10^?4 S/cm which is much better than the pure PP value (2.07 × 10^?10 S/cm). The maximum value of shielding effectiveness is achieved at the maximum weight percentage of filler loading which is ?44.43 dB with a thickness of 2 mm covering the X-band (8.2–12.4 GHz).     

聚偏氟乙烯/类基体基团修饰石墨烯导热复合材料研究

采用含类基体基团的乙烯基三甲氧基硅烷修饰氧化石墨烯(GO),再用"一锅法"将其还原得到功能化石墨烯(F-GE),通过溶剂浇注法制备出界面性能优良的聚偏氟乙烯导热复合材料(PVDF/F-GE).利用红外光谱仪(FTIR)、扫描电子显微镜(SEM)、热导率测试仪、电子拉力试验机对复合材料的改性状态、微观形貌、导热性能和力学...     

Study on thermal properties of stearyl alcohol modified graphene oxide/ n-octadecane composite phase change materials

Adding high thermal conductivity fillers to n-octadecane to form a composite phase change material(PCM) can improve its thermal conductivity. At the same time, to ensure high thermal conductivity, dispersion stability and recycling reliability of PCM, a type of composite PCM has been fabricated by grafting stearic alcohol onto graphene oxide (GO). The modified graphene/n-octadecane composite PCMs with 0, 1%, 2%, 3% and 4%(mass) of modified graphene were prepared to characterize and study of feature structure and thermophysical properties by means of scanning electron microscope, infrared spectrum analysis, differential scanning calorimetry and thermal conductivity analysis, etc. Experiments show that the modified graphene/n-octadecane composite PCMs prepared in this paper has good dispersion stability. When the mass fraction of modified graphene reaches 4%, the thermal conductivity of composite PCMs is 131.9% higher than that of pure n-octadecane.     

硬脂醇改性的氧化石墨烯/正十八烷复合相变材料的热物性研究

向正十八烷中加入高导热填充物形成复合相变材料（PCM）,可以很好地提升其导热性能,同时,为了保证符合相变材料的高热导率、分散性和再循环可靠性,利用硬脂醇修饰氧化石墨烯（GO）,形成改性石墨烯（MG）与正十八烷的复合相变材料。分别制备了改性石墨烯质量分数为0、1%、2%、3%、4%（质量）的改性石墨烯/正十八烷复合相变材料,并经过扫描电镜测试、红外光谱分析、差示扫描量热实验及导热分析等测试对其形貌结构及热物性进行表征和研究。实验表明制备的改性石墨烯/正十八烷复合相变材料具有很好的分散性;当纳米石墨烯片的质量分数达到4%时,复合相变材料的热导率相对于纯正十八烷高出了131.9%。     

纳米二氧化硅与SBR复合改性乳化沥青的性能研究

用差示扫描量热法（DSC）对纳米二氧化硅与SBR复合改性乳化沥青蒸发残留物的热性能进行研究。结果表明，加入SBR乳液、纳米二氧化硅后样品的温度稳定性和耐高温性能均得到提高；其中SBR（质量分数0．03）加纳米二氧化硅（质量分数0．0005）复合改性效果最佳。纳米二氧化硅与SBR形成网状结构以及SBR在体系中吸附油分后的溶胀作用是沥青性能改善的主要原因。     

Halogen‐free flame‐retardant rigid polyurethane foams: Effect of alumina trihydrate and triphenylphosphate on the properties of polyurethane foams

Rigid polyurethane foam (PUF) filled with mixture of alumina trihydrate (ATH) and triphenyl phosphate (TPP) as fire retardant additive was prepared with water as a blowing agent. In this study, the ATH content was varied from 10 to 100 parts per hundred polyol by weight (php), and TPP was used at a higher loading of ATH (75 and 100 php) in a ratio of 1 : 5 to enhance the processing during PUF preparation. The effects of ATH on properties such as density, compressive strength, morphological, thermal conductivity, thermal stability, flame‐retardant (FR) behavior, and smoke characteristics were studied. The density and compressive strength of the ATH‐filled PUF decreased initially and then increased with further increase in ATH content. There was no significant change in the thermal stability with increasing ATH loading. We determined the FR properties of these foam samples by measuring the limiting oxygen index (LOI), smoke density, rate of burning, and char yield. The addition of ATH with TPP to PUF significantly decreased the flame‐spread rate and increased LOI. The addition of TPP resulted in easy processing and also improved FR characteristics of the foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of the addition of wood flours on the properties of rigid polyurethane foam

The objective of this study is to investigate an appropriate process to fabricate the wood‐polyurethane hybrid composites [wood‐polyurethane foam (PUF)]. Rigid PUFs that contain up to 20% wood flours were successfully fabricated from polymeric 4,4‐diphenylmethane diisocyanate, polyols, silicone surfactant, dibutin dilaurate/dimethylethanolamine catalysts, and distilled water (chemical blowing agent). The effects of hydroxyl value of polyols, wood flour particle size, wood flour content, isocyanate index, and water amount on the compressive property of foam were investigated. The morphology of the cell was observed with a scanning electron microscope. Wood‐PUF with different densities were prepared at different water contents in the wood flours. The relationship between the compressive property and density was established following the Power law. The incorporation of wood flour improved the compressive property of PUF, whereas its tensile and flexural properties were reduced. The thermal stability of the PUF was improved with the addition of wood flour. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

高性能定形复合相变储能材料的制备及热性能

对现有定形复合相变材料的制备方法进行改进,采用“熔融吸附-模压成型”的方法,以硬脂酸(stearic acid,SA)为相变材料,膨胀石墨(expanded graphite,EG)为多孔基体,制备了16种不同参数的样品,并对其进行了微观形貌表征、热物性测试、热稳定性研究及热性能分析。相关研究表明:SEM微观形貌显示样品内部出现致密的石墨片层结构,SA均匀分布在石墨片层中,且压块密度越大,片层结构形态越规则;DSC测试结果显示样品几乎没有过冷度,EG的加入与压块处理对SA本身的相变潜热和相变温度几乎没有影响;Hot Disk测试结果显示EG的加入显著提高了样品的轴向和径向热导率,随着EG含量的增加,径向热导率高达23.77 W·m^-1·K^-1,发现两个方向上热导率的差异随压块密度的增加而增大,最大相差5.4倍;储/放热循环实验发现压块密度越大、EG含量越低的样品,SA越容易发生泄漏;通过成型密度及质量配比的优化可实现对复合材料的热稳定性调控,发现EG质量分数为25%、密度为950 kg·m^-3的样品具有较好的综合性能。与传统定形复合相变材料的成型方法相比,该方法可进一步提高复合相变材料的综合热性能,与纯相变材料相比其热导率可提高130倍以上,且具有简单易操作的特点。     

低醛酮挥发物聚氨酯泡沫的制备研究

采用金属盐混合物,将氯化铜(CuCl2),氯化锌(ZnCl2)与硫氰酸钾(KSCN),碘化钾(KI)混合,然后对聚氨酯泡沫(PUF)进行改性.利用压缩测试、扫描电子显微镜(SEM)、傅立叶红外光谱仪(FIR)、热重分析(TG)和醛酮挥发物测试对所有样品进行分析.结果表明,改性后的PUF具有较高的压应力,改善的氧化稳定性...     

Thermal degradation and physical aging of poly(lactic acid) and its blends with starch

Poly(lactic acid) (PLA) and its blends with starch and methylenediphenyl diisocyanate (MDI) were extruded in a twin‐screw extruder and compress‐molded in a dog‐bone shaped tensile bars to form test specimens. The thermalgravimetric profile and thermal endurance of these samples were characterized. The effect of physical aging on mechanical and thermal properties of these samples was evaluated. For the aging study, samples were stored at 25°C and relative humidity fluctuating between 90 and 30%, from 2 to 180 days, with or without a polyethylene bag as a moisture barrier. Physical aging of pure PLA samples stored in a controlled environment from 2 to 360 days was also evaluated. The presence of MDI in the PLA/starch composite did not affect the thermal decomposition profile. The PLA showed the highest Arrhenius activation energy and strongest thermal endurance of all samples, followed by PLA/starch/MDI and PLA/starch. Exposure of the samples to storage conditions with fluctuating relative humidity (RH) significantly affects thermal‐mechanical performance of PLA and its composites. But, the samples stored in plastic bags can minimize such effects. Mechanical properties of PLA and PLA/starch‐based composites sealed in plastic bags had no significant change during 30‐day storage in fluctuating humidity conditions (30–90% RH). POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

硬脂醇/膨胀石墨复合相变材料的制备及储热性能

相变储热技术是解决热量在时空上分配不平衡问题的有效手段之一,研制高性能的复合相变材料（phase change material, PCM）成为当前研究者关注的重点。硬脂醇（stearyl alcohol, SAL）等有机PCM目前主要存在热导率偏低以及循环稳定性较差等问题而限制了实际应用。以SAL作为PCM,膨胀石墨（expanded graphite, EG）为高导热多孔基质,采用吸附定形工艺制备了16种SAL/EG复合PCMs[EG含量为7%、14%、21%、28%（质量）;样品密度为700kg/m³、800kg/m³、900kg/m³、1000kg/m³]。对复合PCMs样品的微观结构、储热能力、导热性能、循环稳定性及充放热性能进行研究与分析。结果表明：SAL完全填充于EG的多孔网络。当样品密度为900kg/m³,EG质量分数为28%的水平热导率最高,其值为28.58W/(m ? K),相比于纯SAL[0.38W/(m ? K)]提高了74倍,该值大约是相对应垂直热导率[5.99W/(m ? K)]的4.8倍。另外在构建的充放热性能试验台上研究了样品中心位置的储/放热性能,结果显示样品密度为900kg/m³,EG质量分数为28%的样品充放热速率最大,固-液潜热吸热和放热阶段所经历的时间分别为53min和20min。与此同时验证了样品的导热性能和熔化-凝固特性,说明SAL/EG复合PCMs具有稳定可靠的储/放热性能。     

Thermal insulation behaviour of Ethylene propylene diene monomer rubber/kevlar fiber based hybrid composites containing Nanosilica for solid rocket motor insulation

The current research discusses the properties of an elastomeric heat-shielding material, based on nano-silica (NS) filled ethylene propylene diene monomer (EPDM) rubber/Kevlar fiber (KF) hybrid composites. The developed elastomeric insulating material consists of an aromatic polyamide fiber (KF) and silica nanoparticles. An in-depth analysis of mechanical properties, density, coefficient of thermal expansion, thermal conductivity, thermogravimetric analysis, and heat release rate of the insulating materials -was performed. TEM micrograph represents an excellent distribution of nanoparticles in the EPDM matrix. The improvement in the mechanical and the flame retardancy of the NS filled EPDM/KF hybrid composite insulations is based on the fiber/matrix adhesion. Maleic anhydride grafting confers polarity to the nonpolar rubber matrix. The char residues of the insulations inspected by scanning electron microscopy and energy dispersive spectroscopy are depicting a rigid and rough surface by the optimal composites, which can aid in better insulation. The optimal formulation of the hybrid composites exhibited a 220% enhancement in char residue with improved thermal stability and mechanical properties.     

碳纳米管分散强化PVDF复合薄膜导热性能探究

采用多巴胺（DA）和3?氨基丙基?三甲氧基硅烷（APTMS）对碳纳米管（CNTs）进行DA辅助共修饰,并用溶剂浇铸法制备具有优异热性能和力学性能的聚偏氟乙烯（PVDF）复合薄膜;采用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、差示扫描量热仪（DSC）、X射线光电子能谱仪（XPS）、热常数分析仪和电子单纱强力仪等对材料的微观形貌、结晶度、导热性能和力学性能进行了表征。结果表明,经DA和APTMS共修饰后的PDA?CNTs?NH₂具有良好的分散性能;PDA?CNTs?NH₂的加入,有利于改善PVDF复合薄膜的热稳定性;与纯PVDF薄膜和PVDF/CNTs复合薄膜相比,PVDF/PDA?CNTs?NH₂复合薄膜的导热性能和力学性能显著增强,在8 %（质量分数,下同） PDA?CNTs?NH₂的填料负载下,其热导率达到0.337 9 W/（m·K）,是纯PVDF薄膜的1.78倍,其拉伸强度为52.67 MPa,是纯PVDF复合薄膜的1.36倍。