导电炭黑填充硅橡胶的电阻温度系数

以炭黑(CB3100)为导电相,硅橡胶为基质制备导电复合材料。研究导电橡胶中炭黑质量分数对电阻温度系数的影响,并用填料对电阻温度系数的影响。以隧道效应理论为基础,给出了导电炭黑填充橡胶的电阻温度系数计算模型,结合实验得到温度对导电炭黑/硅橡胶电阻温度系数的影响主要体现在对其电阻率的影响;基体的体积热膨胀提高复合材料的电阻率,提高了正电阻温度系数;炭黑粒子间的隧道效应降低复合材料的电阻率,增强了负电阻温度系数;在炭黑/硅橡胶中加入少量碳纳米管,利用碳纳米管和炭黑的协同补强效应,使复合材料的导电性和稳定性提高。     

Development of high performance EMI shielding material from EVA,NBR, and their blends: effect of carbon black structure

The conductive composites were prepared using two different types of conductive black (Conductex and Printex XE2) filled in matrices like EVA and NBR and their different blends. The electromagnetic interference shielding effectiveness (EMI SE) of all composites was measured in the X band frequency range 8–12 GHz. Both conductivity and EMI SE increase with filler loading. However, Printex black shows higher conductivity and better EMI SE at the same loading compared to Conductex black, and this can be used as a material having high EMI shielding effectiveness value. The conductivity of different blends with same filler loading generally found to increase slightly with the increase in NBR concentration. However, EMI SE has some dependency on blend composition. EMI SE increases linearly with thickness of the sample. EMI SE versus conductivity yields two master curves for two different fillers. EMI SE depends on formation of closed packed conductive network in insulating matrix, and Printex black is better than Conductex black in this respect. Some of the composites show appreciably high EMI SE (>45 dB).     

填充型聚合物基复合材料的导电和导热性能

研究了高密度聚乙烯为基体、炭黑和炭纤维为填料复合体系的导电和导热性能。发现当导电填料的含量达到渗流阈值时,复合材料的电导率急剧升高;而在渗流阈值附近,其热导率未出现突变。这表明电导渗流现象不完全是由导电粒子通过物理接触生成导电链所致。其导电机制是相当数量的导电粒子相互发生隧道效应。     

Gamma irradiation aging of NBR/CSM rubber nanocomposites

The effect of gamma-irradiation on the acrylonitrile butadiene/chlorosulphonated polyethylene rubber blends (NBR/CSM) based nanocomposites containing carbon black (CB) and silica filler (Si) were investigated by TG-DTG and ATR-FTIR techniques. The silica (with primary particle size of 22 nm) was added in content of 0, 10, 20 and 30 phr and carbon black (with primary particle size 40–48 nm) was added in content of 30 phr and rubber blend compounds were prepared. The obtained elastomeric materials were aging to different γ-irradiation doses (100, 200 and 400 kGy). The cure and mechanical properties of obtained nanocomposites were determined. Incorporating 20 phr of silica to the control NBR/CSM rubber blends containing 30 phr CB resulted 152% increase in tensile strength, 116%, in elongation at break and 142% modulus at 100% elongation, according to synergistic effect between the fillers. FTIR measurements of aged samples estimated the formation of alcohols, ethers and small amounts of lactones, anhydrides, esters and carboxylic acids after exposure to lower doses of γ-radiation (100 kGy). On the basis of the obtained spectra the formation of shorter polyene sequences and aromatic rings in aged elastomeric samples are assumed. The results show that 30 phr of carbon black (CB) and 20 phr of silica are needed for the best gamma aging resistance of NBR/CSM rubber nanocomposites. The result of radiation exposure is decrease in mechanical properties. The dose at which ultimate mechanical properties decreased was at 200 kGy. TG-DTG measurements estimated decrease in thermal stability of gamma-irradiated NBR/CSM rubber blend based nanocomposites. Silica reinforced NBR/CSM rubber blend had better radiation resistant than carbon black. Rough and heterogeneity of fracture surfaces has been observed for NBR/CSM rubber blends filled with silica. More uniform morphology of fracture surfaces according to high polymer–filler interaction and low filler–filler interaction has been observed for CB/Si filled NBR/CSM rubber blend.     

Electrical properties and morphology of carbon black filled PP/EPDM blends: effect of selective distribution of fillers induced by dynamic vulcanization

The roles of dynamic vulcanization process in the electrical properties, morphology, and rheology of carbon black (CB)-filled polypropylene (PP)/ethylene–propylene-diene rubber (EPDM) blends have been investigated. With the addition of CB, the uncross-linked (TPE) and dynamically vulcanized (TPV) composites showed a notable difference in the electrical properties, which is mainly caused by different distributions of CB particles resulting from the dynamic vulcanization process. Particularly, it was found that the CB particles in the TPE composites tended to distribute in EPDM phase, whereas the CB particles in the TPV composites were almost located in the PP matrix. The rheological behavior of the TPE and TPV composites was significantly changed with the incorporation of CB particles. Due to the selective distribution caused by the dynamic vulcanization process, the formation of the conductive network for the TPE composites is caused by the double percolation effect, while for the TPV composite, the formation of the conductive network is caused by the excluded volume effect.     

低压缩永久变形导电炭黑/硅橡胶复合材料的制备与性能

为获得一种低压缩、永久变形及高回弹的导电屏蔽硅橡胶密封材料,以经偶联剂表面处理的炭黑作补强剂及导电填料,乙烯基硅橡胶生胶作基料,制备出一种导电炭黑/硅橡胶复合材料。研究了不同炭黑含量的导电炭黑/硅橡胶复合材料的力学性能、弹性、分散性以及电性能,采用SEM观察了炭黑在硅橡胶基体中的分布形貌,分析了导电炭黑/硅橡胶复合材料的导电机制及屏蔽机制。结果表明:随着炭黑含量的增加,导电炭黑/硅橡胶复合材料的Shore A硬度由31增至70;拉伸强度先由3.31 MPa增至5.28 MPa,而后趋于稳定;拉断伸长率先由198%增至297%,然后再减小至210%;恒定压缩永久变形量先减小后增大,瞬间回弹率逐渐减小;由于"炭黑簇"的形成及导电通路的完善,导电炭黑/硅橡胶复合材料的导电性能及屏蔽效能增强。     

Pressure-sensitive electrically conductive nitrile rubber composites filled with particulate carbon black and short carbon fibre

The electrical conductivity of pressure-sensitive nitrile rubber composites, containing different loadings of particulate carbon black filler and short carbon fibre, have been studied. The conductivity of composites increases with increasing of filler concentration as well as with increased applied pressure up to a certain limit. The composites containing particulate fillers register low conductivity as compared to composites containing short carbon fibres, due to easy formation of an interconnecting network in the latter case. The effect of the orientation of short carbon fibre with respect to an applied electric field has also been studied. The pressure dependence of composites with transversely oriented carbon fibres with respect to electric fields is higher than that of composites with longitudinally oriented carbon fibres. The results are interpreted on the basis of the formation of interconnecting continuous conducting networks.     

炭黑填充聚合物体系渗流转变过程中的介电性能

采用熔融共混的方法制备了导电炭黑填充乙烯-醋酸乙烯酯共聚物复合体系,分别通过添加填料粒子和熔融态等温处理促进粒子凝聚成网两种方法研究了体系在渗流转变过程中的电性能变化,发现在该过程中材料的导电性能和介电性能均持续上升,伏安特性和相位角分析表明粒子间始终为非欧姆接触。动态渗流测试发现,复合体系从绝缘体到导体的整个渗流转变过程中介电常数是持续增加的。因此渗流理论所预测的介电常数极大值很可能发生在临界含量的上限值,此时材料的导电机理转变为欧姆传导。     

DC electrical conductivity of poly(methyl methacrylate)/carbon black composites at low temperatures

The study deals with the dc electrical conduction of poly(methyl methacrylate)/carbon black composites of different carbon black (CB) filler concentrations (2, 6, 12 wt%). The dc electrical conductivity was studied as a function of filler concentration, and temperature in the range (20–290 K). It was found that the composites exhibit negative temperature coefficient of resistivity (NTCR) at low temperatures and enhancement in the dc electrical conductivity with both temperature and CB concentration. The observed increase of conductivity with CB concentration was interpreted through the percolation theory. The dependence of the electrical conductivity of the composites in low temperatures was analyzed in term of a formula in consistence with Mott variable rang hopping (VRH) mechanism. The observed overall mechanism of electrical conduction has been related to the transfer of electrons through the carbon black aggregations distributed in the polymer matrix.     

Effect of extensional strain on the resistivity of electrically conductive nitrile-rubber composites filled with carbon filler

The resistivity and mechanical properties of nitrile-rubber based conductive composites filled with short carbon fibres (SCFs) and mixed filler system (SCF + carbon black) are studied as functions of the extensional strain and the strain rate. It has been observed that both strain and strain rate have a strong influence on the resistivity of the composites. The sensitivity of the change in resistivity against the strain and strain rate depends on the concentration as well as the type of conductive filler. SCFs impart higher conductivity to the composite than a blend of SCFs and carbon black at the same level of loading parts per hundred of rubber (p.h.r.). Composites filled with a mixed filler system show high mechanical properties in contrast to those of SCF-filled composites. The change in resistivity with the degree of strain is less pronounced in mixed-filler-filled composites than in only carbon-fibre-filled composites. The mechanical properties of the composites are dependent on the polymer-filler interaction whereas change in resistivity is dependent on the transient arrangement of the conducting components in the polymer matrix. A good correlation exists between mechanical and electrical response to the strain sensitivity.     

Micromechanism of failure of thermoplastic rubber

The fracture surface morphology of various thermoplastic rubber and rubber vulcanizates based on natural rubber (NR), ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), polyethylene (PE) and polypropylene (PP), namely NR-PE, NR-PP, EPDM-PE, EPDM-PP and NBR-PP, has been studied over a range of blend ratios, levels of interaction, rates, temperatures and modes of testing. The fracture surface changes with changes in blend ratio. Incorporation of a third component like EPDM or chlorinated polyethylene (CPE) to a certain percentage does not change the fracture morphology. Sulphur curing in the NR-PE blend generates a ductile matrix like rubber whereas large fissures are observed for peroxide-cured systems. Modification of both rubber and plastic also changes the surface morphology. The samples tested at various temperatures, rates and modes show similar features on the fracture surface.     

Quantitative mapping of surface elastic moduli in silica-reinforced rubbers and rubber blends across the length scales by AFM

The surface elastic moduli of silica-reinforced rubbers and rubber blends were investigated by atomic force microscopy (AFM)-based HarmoniX material mapping. Styrene–butadiene rubbers (SBR) and ethylene–propylene–diene rubbers (EPDM) and SBR/EPDM rubber blends with varying concentrations of silica nanoparticles (0, 5, 10, 20, 50 parts per hundred rubber, phr) were prepared to investigate the effect of different composition on the resulting morphology, filler distribution and elastic moduli of a specific rubber or rubber blend sample. For SBR, the elastic modulus values varied from 0.5 MPa for unfilled SBR to 5 MPa for 50 phr reinforced SBR with the increase in the concentration of filler. For EPDM, the corresponding values increased from 1.4 MPa for unfilled EPDM to 4.5 MPa for 50 phr reinforced EPDM. Local stiff and soft domains in silica-reinforced SBR and EPDM rubbers and rubber blends were identified by HarmoniX AFM imaging. While the stiff silica particles show modulus values as high as 2 GPa, the rubber matrix reveals modulus values in the range of ca. 30 MPa for the rubber blends to ca. 300 MPa for the unfilled rubbers. The lower value of elastic modulus of the EPDM phase in the blend, compared to the blank EPDM compound can be attributed to the presence of Sunpar oil in the compound which has a very good affinity with EPDM and decreases the rubber modulus. The elastic moduli maps revealed an increase of the areal fraction of silica particles showing an intrinsic surface modulus value with rising silica content in the compound preparation mixture. HarmoniX AFM measurements revealed the formation of larger silica aggregates in EPDM in contrast to SBR where isolated silica particles were observed. For silica-reinforced rubber blends a phase separation into a soft (ca. 40 MPa) and a significantly harder phase could be observed (ca. 500 MPa–1.5 GPa) indicating the incorporation of silica particles in the SBR phase. Using HarmoniX AFM imaging significantly higher surface elastic moduli were observed compared to those obtained by bulk tensile testing. Possible reasons for the observed differences between bulk modulus values and those measured by AFM are discussed in detail, including the aspect of different averaging procedures like inherent to surface probing by AFM versus bulk tensile testing, different filler distributions in SBR and EPDM and the AFM modulus calibration procedures.     

具有隔离结构的超高分子量聚乙烯/镍高导电复合材料

采用化学镀手段制备金属镍包覆的超高分子量聚乙烯复合粒子,通过热压成型方法制得具有隔离结构的超高分子量聚乙烯(UHMWPE)/镍(Ni)高导电复合材料。通过调节金属(镍)镀层厚度及加工温度考察不同Ni含量及加工温度对复合材料导电性能的影响。结果表明,复合材料具有明显的导电逾渗行为;通过化学镀工艺可有效提高金属填料与基体的结合力,同时实现金属镍在聚合物基体中的选择性稳定分布,构建具有隔离结构的导电网络,使得复合材料的逾渗值降低至1.02%(体积分数)。基于金属填料优异的导电性能,在Ni体积分数仅为2.53%时,复合材料的电导率达到2648S/m。此外,降低复合材料的加工成型温度有助于减少加工过程对导电网络的破坏作用,从而有效降低复合材料的导电逾渗值,对提高复合材料导电性能具有重要意义。     

The role of tackifiers on the auto-adhesion behavior of EPDM rubber

The article describes the effect of hydrocarbon (HC) and coumarone-indene (CI) resin tackifiers on autohesion behavior of ethylene propylene diene polymethylene (EPDM) rubber. The viscoelastic behavior and nature of compatibility of EPDM/tackifier blends were studied by means of dynamic mechanical analysis. Furthermore, scanning electron microscopy and atomic force microscopy were used to understand the compatibility of the EPDM/tackifier blends. The HC tackifying resin modified the viscoelastic properties of the EPDM rubber in such a way that it behaved as a plasticizer at lower frequency by reducing the storage modulus and filler at higher frequency by increasing the storage modulus. On the contrary, the CI modified EPDM rubber did not show similar behavior; the modulus enhanced throughout the entire frequency range. The viscosity of the matrix was found to be highly governed by the compatibility as well as amount of tackifier present in the blend. In order to explain the tack behavior, several tack governing factors such as green strength, creep compliance, entanglement molecular weight, relaxation time, self-diffusion coefficient, and monomer friction coefficient (ζ₀) were investigated. The tack strength increased with HC tackifier loading up to 24 parts per hundred grams of rubber (phr), beyond which a plateau region was observed. A maximum of 196% improvement was observed at 24 phr HC loaded sample as compared to gum EPDM rubber devoid of tackifier. Conversely, there was a marginal improvement of tack strength (36%) up to 8 phr loading for the system containing CI, beyond which it dropped.     

炭黑填充型导电复合材料的聚集体结构模型

分析了炭黑填充聚合物导电复合材料的非线性导电行为和机理,基于有效介质理论及以炭黑聚集体的等效球形单元为基本单元,建立了描述其非线性导电行为的聚集体结构模型。进而推导出复合体系导电率与炭黑体积分数之间的关系式及其逾渗阈值的计算式,克服了有效介质理论只能得到逾渗阈值为1/3而不能解释低于1/3的逾渗阈值的不足。应用这些表达式预测了导电复合体系的导电率和逾渗阈值,并与实验结果进行了比较,结果表明:预测值与实验结果有较好的一致性。     

PTC effect of carbon fiber filled EPDM rubber composite

Conductive ethylene-propylene-diene (EPDM) rubber composites filled with carbon fiber (CF) and carbon black (CB) were prepared by the conventional melt-mixing method. Optical microscope was used to observe the formation of the conductive pathways in the CF-filled composite. A model based on thermal expansion and electron tunneling theory was proposed to explain the PTC effect of CF-filled composite. The resistivity-temperature behavior of filled EPDM composites depended on the shape of carbonaceous fillers, CF/EPDM composite showed a positive temperature coefficient (PTC) effect, while CB/EPDM composite showed a negative temperature coefficient (NTC) effect.     

Master curve of filler localization in rubber blends at an equilibrium state

In this study, the phase-specific localization of filler in NBR/NR blends was characterized by means of the selective extraction method and wetting concept. A strong dependence of silica localization on the filler loading was found. A model based on thermodynamic data was proposed for a quantitative prediction of filler localization in rubber blends. The filler localization can be described by a master curve demonstrating a characteristic behavior in dependence on the filler surface tension data of blend components and filler. The effect of filler loading on the silica localization is sufficiently explained by this model by taking into consideration the deactivation of the silanol groups on the silica surface by adsorbed curing additives. Using the master curve, the surface tension of filler affected by curing additives and silane addition can be estimated that may be useful for evaluation and comparison of the effect of different coupling agents. Surface tension values of different fillers were estimated by means of the master curve and they lie in the same order compared to those reported in literature. A potential transfer of filler within a rubber blend can be also quantitatively predicted.     

碳纳米管/丁苯橡胶复合材料的电学性能

采用喷雾干燥法可制备不同配比的碳纳米管（Carbon nanotubes,CNTs）/粉末丁苯橡胶复合材料,观察CNTs在橡胶基体中的分散情况,检测复合材料的导电性能及介电性能,并进行了简要的理论分析。结果表明:CNTs在橡胶基体中获得了充分均匀的分散,有利于CNTs改性补强作用的发挥。与纯胶样品及填充炭黑（Carbon black,CB）样品相比, 填充CNTs样品在8~18GHz下具有较高的介电常数及低介电损耗。随着CNTs加入量的增加,CNTs/粉末丁苯橡胶复合材料的电导率逐渐升高,当CNTs加入量为60phr（per hundred rubber）时,与纯胶样品及添加60phr CB样品相比,电导率提高近10个数量级;复合材料内部导电同时存在隧道导电机制和渗逾导电机制。采用喷雾干燥法制备的CNTs/粉末丁苯橡胶复合材料,将是一种综合性能良好的新型纳米复合材料,有望在抗静电橡胶、电磁屏蔽及介电材料等领域获得应用。      

炭黑填充多组分高分子导电复合材料的研究进展

基体为多组分高分子的填充型导电复合材料中存在“双逾渗”行为,能有效地降低导电填料的逾渗阈值,克服由填料含量过高而导致的材料加工性和力学性能下降的缺点,并能削弱材料的负温度系数(NTC)效应。本文基于国内外炭黑(CB)填充多组分高分子导电复合材料的研究进展,对CB分布、多组分高分子基体对材料体系导电性的影响、导电机理以及电导-温度依赖性等方面进行评述。