Comparative Properties of Styrene-Butadiene Rubbers (SBR) Containing Pyrolytic Carbon Black,Conventional Carbon Black,and Organoclay

To evaluate the reinforcing potential of pyrolytic carbon black, styrene-butadiene rubber (SBR) was filled with pelletized pyrolytic carbon black (pCB_p), N660 industrial CB, their blend in a 1/1 ratio, and the latter also in the absence and presence of additional organoclay (OC). The Shore A hardness of the filled SBR gums was 65 ± 2°. Effects of the compositions on the filler dispersion, cure behavior, dynamic mechanical thermal parameters (including the Payne effect), tensile mechanical (including the Mullins effect), and fracture mechanical (making use of the J-integral concept) properties were studied and discussed. Though pCB_p had a higher specific surface weight than CB, the latter proved to be a more active filler with respect to the tensile strength. The opposite tendency was found for the tear strength and fracture mechanics characteristics (J-integral at crack tip opening, tearing modulus, and trouser tear strength). This was traced to an enlargement in the crack tip damage zone supported by the dispersion characteristics of the pCB_p. The performance of pCB_p was similar to that of CB with respect to some other properties. OC supported the filler networking which positively affected the resistance to crack initiation.     

Study of the road surface properties that control the acoustic performance of a rubberised asphalt mixture

Simultaneously with the fact that vehicle industry has been able to lower the noise emission from driving vehicles, tire/pavement noise has become the most significant source of traffic noise. In order to reduce it, low noise surfaces are seen as a practical solution. One of these types of surfaces may be elaborated with bituminous mixtures with crumb tire rubber added to the binder in high content by a wet process. However, the generation mechanisms involved in the tire/pavement sound and the reasons of the noise attenuation achieved with these mixtures are not so clear. This study analyses the different generation mechanisms that take place in the tire/pavement sound generation in these crumb tire rubber pavements. The surface properties of the in-service pavement, which are most important in controlling the acoustic performance (texture, acoustic absorption and dynamic stiffness or mechanical impedance), have been measured for the characterization of a test track constructed with and without crumb tire rubber. After results correlation of these surface characteristics in a pavement with crumb tire rubber added by a wet process, it seems that the parameters of roughness and texture could have a relevant role in the global tire/pavement sound emission, whereas dynamic stiffness influence is relatively minor.     

橡胶聚合物在碳氢溶剂中的膨胀特性

为了验证碳氢有机溶剂在橡胶中的运输机理及运输特性,并为后期研究吸热型碳氢燃料与橡胶的相容性做准备,用浸泡/称量法对硫磺硫化体系(分别填充快压出炭黑和SiO2)、过氧化物硫化体系和混合硫化体系的天然橡胶在有机溶剂中的膨胀现象进行了研究。膨胀达到平衡时,快压出炭黑填充的硫磺硫化体系具有最小的溶剂吸收量,过氧化物硫化体系具有最大的溶剂吸收量。分别研究了交联密度、溶剂分子和温度对有机溶剂在橡胶中扩散的影响规律,并从热力学角度进行了详细分析。结果表明:实验所用橡胶-溶剂系统中,扩散结果偏离了Fick模型,为无规则扩散,且扩散系数随溶剂摩尔体积、相对分子质量、分子链的长度增加而减小;交联密度增加时溶剂的扩散减少,橡胶吸收溶剂的量减小;对二甲苯和丙苯比实验所用的烷烃有机溶剂更易使橡胶膨胀;在实验温度范围内,温度升高时橡胶的吸收量增加。     

线形低密度聚乙烯／废胶粉热塑弹性体动态硫化性能研究

利用动态硫化法制备了线形低密度聚乙烯(LLDPE)/废胶粉(GTR)热塑弹性体。重点研究了两种交联剂:硫和过氧化二异丙苯(DCP)对共混物性能的影响。加入一定量的苯乙烯-丁二烯-苯乙烯(SBS)共聚物作为增容剂。结果表明,经过DCP动态硫化后的共混物的力学性能比简单共混的共混物有明显的提高,而加入硫磺体系对共混物力学性能影响不大甚至有所下降。通过红外光谱、热分析(DSC)和扫描电镜(SEM)对共混物的热行为和表面形态研究表明,加入DCP交联剂使LLDPE、SBS和胶粉之间发生了交联反应,从而增加了胶粉颗粒与LLDPE间的界面相容性,使其热塑性弹性体的力学性能得以提高。     

Dynamic mechanical properties of epoxy/novolac system modified with reactive liquid rubber and carbon filler

This paper reports on the work carried out to evaluate the frequency dependent viscoelastic properties of epoxy/novolac compositons modified with a liquid reactive rubber and carbon filler. For epoxy systems modified with elastomer, three typical transitions were observed: the α-relaxation deeply related to the glass transition of epoxy, the β-transition of epoxy, and the glass transition of rubber appeared near to the β-relaxation of epoxy resin. Considering an Arrhenius equation, the activation energies of β-relaxation were estimated. In the region of glass transition and rubbery state the temperature dependence of the shift factor (α_T) was determined through Williams-Landel-Ferry (WLF) equation.     

Reactive incompatibility of DTBP mixed with two acid solutions

Organic peroxides are commonly employed as an initiator for polymerization, a source of free radicals, a hardener, and a linking agent. Due to its relatively weak oxygen-oxygen bond, di-tert butyl peroxide (DTBP) has been categorized as flammable type or Class III by the National Fire Protection Association (NFPA). The transport of dangerous goods (TDG) has published a warning against DTBP that it could potentially induce violent heat, explosion, fire and self-ignition under certain circumstances. DTBP has been recommended as an international standard sample for estimating the performance of several calorimeters, such as glass tube tests, differential scanning calorimetry (DSC), and vent sizing package 2 (VSP2). In this study, we measured the precise temperature changes and heat flow with the above-mentioned testing instruments. However, some runaway incidents caused by DTBP have demonstrated the reaction temperature could be as low as ambient temperature. The reactivity and the hazardous incompatibility with sulfuric acid (H₂SO₄) and hydrochloric acid (HCl) of DTBP have not been evident, and the runaway hazards involved in different processing conditions were clarified in this study by implementing the two calorimeters. Acid-catalyzed characteristics and reaction hazards of DTBP could be acquired, such as heat of decomposition (ΔH _d) and exothermic onset temperature (T ₀).     

Characterization of natural rubber concerning its components and molecular weight in Taraxacum kok-saghyz Rodin using pyrolysis gas chromatography-mass spectrometry

Taraxacum kok-saghyz Rodin (TKS) has abundant natural rubber in its root and the molecular weight of its natural rubber is higher than that in Hevea brasiliensis. Thus, TKS is an excellent alternative for the commercial production of natural rubber. The content and molecular weight of natural rubber are two qualitative indicators. Efficient determination for both indicators is still a challenge. In this study, we developed a method to simultaneously determine the content and molecular weight of natural rubber in TKS with pyrolysis－gas chromatography-mass spectrometry. The content of natural rubber was quantified by internal standard method. We optimized the pyrolysis temperature and chromatographic method during content determination. The limits of detection and quantification were 0.47 and 1.56 μg, respectively. In addition, the arachidonic acid methyl ester, an unsaturated fatty acid proposed from the α-end group of natural rubber, was quantified to obtain the number of natural rubber polymers. Based on the content and the polymer number, we also quantified the molecular weight of natural rubber. Thus, the content and molecular weight of natural rubber were simultaneously determined in TKS. Our study provides a new perspective for the high throughput analysis of natural rubber.     

Carbon-based conductive rubber composite for 3D printed flexible strain sensors

Polymeric-based flexible electronic devices are in high demand due to its wide range of applications. Natural rubber (NR) shows a great potential as matrix phase for flexible conductive polymer composites with its high elasticity and fatigue resistance. In this study, a new 3D printable conductive NR (CNR) composite was developed for strain sensor applications. Different contents of conductive carbon black (CCB) were mixed with NR latex to investigate the effect of the filler content on electrical and mechanical properties of the composites. The best-known CNR composite with the CCB content of 12 phr was selected in order to produce the feedstock for the stereolithography process (SLA). The morphological, electrical, and mechanical properties of cast and 3D-printed samples were investigated and compared. Although the 3D-printed CNR sample had slightly lower conductivity than the cast one, it possessed comparable tensile strength and elongation at break, with values of 12.4 MPa and 703%, respectively. In addition, electrical responses of the CNR samples were investigated to demonstrate the electromechanical property of the material as a strain sensor. The 3D-printed CNR sample exhibited the highest electromechanical sensitivity with a gauge factor (GF) of 361.4 (ε = 210%–300%) and showed good repeatability for 500 cycles. In conclusion, the development of this 3D printable functional material with great sensing capability will pave the way for innovative designs of personalized sensing textiles and other smart wearable devices.     

Recent progress in bio-based elastomers with intrinsic self-healing mechanisms - part I: Natural rubber modifications

This review is focused on recent achievements in bio-based self-healable elastomeric materials with special regard to elastomers made of natural rubber (NR) and its modified forms, including epoxidized natural rubber (ENR), oxidized natural rubber (oNR) or carbonated natural rubber (CNR). Besides natural rubber, also Eucommia ulmoides gum (EUG), which is an isomer of cis-1,4-polyisoprene, is a material of great interest to obtain bio-based self-healable elastomers. The paper attempts to describe the main classification of the most important intrinsic self-repairing mechanisms, including different types of reversible non-covalent interactions (such as hydrogen bonding, ionic interactions, metal–ligand coordination, shape-memory ability), dynamic covalent bonds (for instance Diels-Alder reversible bonds, dynamic sulfur-sulfur bonds, dynamic ester bonds, boronic-ester exchangeable bonds, dynamic imine bonds, silyl ether exchangeable bonds) and their combinations, which are found in self-healing elastomers. Furthermore, examples of NR-based elastomeric materials are provided and the potential applications proposed by researchers are also presented.     

An elastomeric conducting composite based on polyaniline coated nylon fiber and chloroprene rubber

Chloroprene rubber-polyaniline (PANI) coated nylon fiber composites containing PANI powder were prepared by mechanical mixing on a two-roll mill. PANI was synthesized by chemical polymerization of aniline in presence of hydrochloric acid. PANI coated nylon fiber was prepared by in situ polymerization of aniline on nylon fiber. The cure parameters cure kinetics, filler dispersion, mechanical properties, DC electrical conductivity and thermal degradation parameters of the composites were evaluated. Cure rate index and cure reaction constants indicated that the rate of cure reaction changes on filler addition. Filler addition at higher loadings led to agglomeration. The tensile strength and modulus values increased suggesting a reinforcement effect. The conductivity, thermal characteristics and thermal degradation kinetic parameters are also presented.