Ageing in modified bitumen using FTIR spectroscopy

Modified binders exhibit complex rheological behaviour due to the interaction of the modifiers with the base binder and the manner in which they age during field applications. Quantification of the interaction and the ageing of such modified binders is currently a necessity. In this investigation, three modified binders (elastomer, plastomer, and crumb rubber) and the base bitumen were subjected to different ageing conditions and the evolution of the chemical functionalities during ageing were tracked using FTIR spectroscopy. Analysis of the spectra of modified binders immediately after the production process showed that while the elastomer modified binders exhibited physical interaction, the plastomer and crumb rubber modified binders exhibited physical and chemical interactions. During ageing, there was no subsequent evolution of the interactions and one could only see chemical functionalities related to oxidation. Analysis of the spectra showed that the carbonyl and sulphoxide exhibit identical trends whereas aliphaticity and aromaticity deviate drastically.     

Effect of the microstructure of a filled rubber on its overall mechanical properties

Mechanical behavior of filled rubber is very different from the corresponding unfilled gum rubber. To understand such difference, a multiscale material model of a filled rubber, which combines molecular mechanics, statistical mechanics and micromechanics, has been developed. The model has been used to explore how filler particles and filler–elastomer bond strength influence the overall elastic properties of a filled rubber. The model confirmed the well-established phenomena such as non-uniform strain amplification, but now, the model added much more detailed molecular information such as cross-linking density, bond strength at filler–elastomer interface, etc. to the whole phenomena. This capability enables us to investigate the influences of the factors on the overall mechanical properties of filled rubber. The results revealed that the degree of stretching is significantly amplified in elastomer chains that locate in between the filler particles along the loading direction. The degree of non-uniform stretching increases with filler volume fraction. The fully stretched elastomer chains contribute significantly greater force and stiffness than those that are stretched less. Both the Mullins effect and the Payne effect come from the non-uniform filler size and/or spatial distribution. Reducing non-uniformity of filler size and spatial distribution can decrease the degree of the Mullins effect and the Payne effect. Improving bond strength at filler–elastomer interface can delay the Mullins effect and the Payne effect but cannot eliminate them.     

Stability of dielectric elastomer/carbon nanotube composites coupling electrostriction and polarization

Experiments are conducted to test the permittivity of dielectric elastomer composites adulterated with multi-walled carbon nanotube (MWCNT). The results show that the permittivity of dielectric elastomer composites can be significantly improved by adding MWCNT conductive particles. A thermodynamic model is presented to investigate the stability of MWCNT particle-doped dielectric elastomer composites. The theoretical investigation proves that the polarization of MWCNT, the electrostriction deformation and material constants of the elastomer significantly affect the stability of the thermodynamic system. The numerical analysis shows that comparing to ideal dielectric elastomer, the stability of dielectric elastomer composites filled with MWCNT coupling between electrostriction and polarization can be significantly enhanced.     

取向磁场对钴颗粒填充硅橡胶磁流变弹性体动态黏弹性的影响

为了研究取向磁场强度对磁流变弹性体（MRE）动态黏弹性的影响规律及影响机制,采用溶剂热法制备球状钴颗粒,SEM和XRD表征结果显示,其粒径为1~2 μm,呈密排六方结构。以硅橡胶为基体,以钴颗粒为填充相,分别在0 mT、480 mT、1 154 mT取向磁场强度下制备MRE,并在不同工况下测试其动态黏弹性。实验结果表明,Co颗粒填充的MRE微观结构的有序性随取向磁场强度增大而增加,其储能模量G'、损耗模量G ″和磁流变效应也随之提高;当取向磁场强度增大到一定程度,由于有序结构趋于稳定,动态黏弹性随取向磁场的变化较小。     

Evolution of bituminous mix behaviour submitted to UV rays in laboratory compared to field exposure

Laboratory methods to simulate the short and long term ageing occurring during the service life of pure and polymer modified bitumens in a pavement are standardized but none of them takes into account the influence of ultraviolet (UV) radiations. Recently, attentions have been paid to the laboratory ageing tests with UV radiation applied to the bituminous binders. Even if this effect of UV radiation on binder’s films have been largely demonstrated and studied, however there are few studies dealing with the photo-oxidation of binders in a bituminous mix in relation with voids, film thickness and permeability. So, the aim of our study was to investigate whether the influence of UV light on bitumen ageing might be assessed in the bituminous mixes using an experimental apparatus dedicated to the ageing of paint. The results show that the influence of UV radiation on the ageing of bituminous mixes containing an elastomer modified bitumen can not be totally ignored: compared with thermal aging, the UV impact can be distinguished and found to be dominant for the production of carbonyl functions, the disappearance of C=C double bond of SBS and the increase of binder’s hardening. So, this study has highlighted, on the one hand, that inside the bituminous mix, the UV radiations do increase the rate of oxidation and, on the other hand, that the evolution’s kinetics due to a pure thermal oxidation or a photo-oxidation processes are different: the evolution due to 44 months of on site ageing is better assessed by photo-oxidation process than by pure thermal oxidation. Consequently, the UV exposure may affect the bitumen’s properties of pavement upper layers more strongly than the PAV simulation in laboratory (without UV action) does.     

Effect of ageing on the morphology and creep and recovery of polymer-modified bitumens

Polymer additives are used to improve the properties of road bitumens including their oxidative resistance. However, their usage as anti-oxidative materials remains relatively unclear. This study aims to investigate the changes in the morphology and the rheological response of polymer modified bitumens used in road pavement construction caused by ageing. An elastomer (radial styrene butadiene styrene, SBS) and a plastomer (ethyl vinyl acetate, EVA) polymer were mixed with one base bitumen at three polymer concentrations. The bitumens were RTFO and PAV aged. The morphology of the bitumens was captured by fluorescence microscopy while the rheological properties were measured by means of the multiple stress creep and recovery (MSCR) test. The results show that the morphology of the SBS modified bitumen degrades with ageing as a function of polymer concentration and dispersion, with higher dispersion being more resistant. The morphology of the EVA modified bitumen has a low ageing susceptibility irrespective of polymer concentration. The MSCR response of EVA modified bitumens does not differ from that found for unmodified bitumen, where the hardening produces a decrease in the non-recoverable compliance. In the case of SBS modified bitumen, the degradation of the polymer backbone affects the bitumen hardening as much as the polymer phase dispersed and networked in the bitumen phase. Furthermore, in the case of the elastomer, the average percent recovery is in agreement with the variation of the morphology with ageing. Therefore, the use of the average percent recovery as a valuable rheological index of the integrity of the polymer network can be advocated.     

高填充聚丙烯材料的增强和增韧

研究了本室研制的柔性分子链界面改性剂包覆的高岭土（ｋａｏｌｉｎ）刚性粒子增韧的短切玻璃纤维（ＣＦ）增强的混杂复合方式，对聚丙烯／高岭土（ＰＰ／ｋａｏｌｉｎ）填充材料强度和韧性的影响。     

Effect of elastomer interfacial agents on tensile and impact properties of CaCO3 filled HDPE

This work focuses on the modification of the tensile yield strength of CaCO3 filled HDPE brought about by the incorporation of SEBS elastomers. Two types of SEBS elastomers were used, grafted and ungrafted with maleic anhydride functions. The grafted elastomer encapsulates the filler particles in-situ and creates an adhesive interphase. The tensile yield stress was increased with increasing content of grafted elastomer until a maximum value. The influence of the interfacial area and the volume fraction of filler were studied. It was shown that the relative increase in tensile yield stress when increasing amount of interfacial agent was added, both depends on the volume of filler and the interfacial area.     

Preparation of polystyrene–polyisoprene core–shell nanoparticles for reinforcement of elastomers

Latex-formed core–shell nanoparticles composed of cross-linked polystyrene (PS) core and polyisoprene (PI) shell were successfully synthesized by means of a two-stage emulsion polymerization. The PS core possessed a Z-average diameter of 50.3 nm, and the PS–PI particles took a spherical shape with a Z-average size of 50–70 nm in diameter. Shell thickness was controlled by varying isoprene loading. Necessary interphase interactions between the core and shell domains were also achieved by grafting and swelling polymerization. Latex compounding method was employed to prepare the filled elastomer compounds. As expected, the PS–PI core–shell nanoparticles exhibited excellent reinforcement to elastomeric matrix, enhancing the tensile strength of the styrene–butadiene rubber by approximately 400%. The lower density, better interfacial interactions, and latex compounding process would benefit the PS–PI nanoparticles reinforced elastomer nanocomposites in energy saving.     

Effect of morphology on the behaviour of ternary composites of polypropylene with inorganic fillers and elastomer inclusions

The effects of phase morphology, interfacial adhesion, rigid filler particle shape and elastomer volume fraction on the tensile yield strength of polypropylene (PP) filled with inorganic filler (CaCO₃ or Mg(OH)₂) and ethylene-propylene elastomer (EPR) were investigated. Separation of the filler and elastomer particles was achieved using maleic-anhydride-grafted PP (MPP) to enhance the filler-matrix adhesion. Encapsulation of the rigid filler by the elastomer was achieved using maleic-anhydride-grafted EPR (MEPR) to increase the filler-elastomer adhesion. The two limiting morphologies differ significantly in mechanical properties under tensile loading at the same material composition. Elastomer particles separately dispersed in the matrix enhance the shear banding in the bulk matrix which prevents the crazes growing from the filler surface from becoming unstable and, thus, increases the ductility of the material. Encapsulation by an elastomer layer on the filler surface relieves triaxial stresses at the filler surface, changing the major local failure mechanism from crazing to shear yielding and, hence, increasing the ductility of the material. Increase of the elastomer volume fraction also causes, in both cases, an increase in matrix ductility. Composite models are used to predict upper and lower limits of yield strength (_y) for the two limiting morphologies over an interval of elastomer volume fractions (V _e) from 0 to 0.2 at a constant filler loading of 30 vol.% and over a filler volume fraction from 0 to 0.4 at a constant EPR content in the matrix. Satisfactory agreement was found between the experimental data and theoretical predictions.     

Economos helps GlaxoSmithKline find the right seal

This brief case study describes the problems encountered by GlaxoSmithKline with the polytetrafluoroethylene seals that were fitted on machines that filled tubes with the anti-viral cream Zovirax. These problems were solved by using a hydrolysis-resistant polyurethane elastomer seal.     

Development of a Morphing Skin Based on the Honeycomb Reinforced Elastomer

The morphing skin has been a main obstacle in the real-world implementation of morphing aircrafts. This paper presents a morphing skin made of the elastomer reinforced by the honeycomb structure. A matrix made from elastomer provides possibilities to configure the morphing skin and the honeycomb structure with smaller in-plane modulus and larger out-of-plane modulus is thought to be suitable to reinforce the elastomer. The polyurethane elastomer is selected and synthesized by the casting method with the prepolymer approach, after which a tensile test is conducted to get its stress-strain relationship. To decrease the skin depth and diminish the local deformation in the honeycomb cell, the elastomer is filled into the honeycomb core rather than just working as the flexible face sheets, which leads to the so-called honeycomb reinforced elastomer. To present its mechanical properties finite element method is applied to analyze the morphing skin with a plug-in of commercial software Abaqus developed to model the skin in details. Different geometry and material parameters are taken into consideration with three kinds of results calculated namely, the equivalent tensile modulus, the non-dimensionalized equivalent three-point bending stiffness and the linear strain capacity. After the simulation analysis, samples of the morphing skins are fabricated by the compression molds method and the tensile tests have verified both the concept and the simulation results. At last, an optimization performed has shown a significant decline of the tensile modulus and out-of-plane displacement of the morphing skin.     

改性石墨烯/介电弹性体的制备及传感性能

目的制备具有优异介电性能,可用于传感器的热塑性聚氨酯弹性体复合材料。方法使用十八烷基胺修饰氧化石墨烯片层,通过热处理工艺部分还原改性后的氧化石墨烯,利用溶液混合法将改性石墨烯分散到热塑性聚氨酯的基体中,通过絮凝-热压的方法成形,并测试其结构、介电性能及传感性能。结果十八烷基胺通过共价键的形式接枝到氧化石墨烯表面,X射线衍射表明,十八烷基胺通过表面接枝改性,增大了石墨烯片层的层间距。结论改性石墨烯填充的介电弹性体具有较高的介电常数和较低的介电损耗,且表现出良好的弯曲形变-介电敏感响应。     

Some results on the ageing of wire chambers with dimethyl ether

Ageing results of three test wire detectors when filled with dimethyl ether (DME) are presented. DME gas was analyzed before and during the tests for the presence of electronegative impurities, such as Freons. A strong dependence of the rate of ageing on the wire composition was observed. The resistive wires, such as Stablohm and Nicotin, produced fast ageing. Also, even the best available purified DME, as of today, used with gold-plated wires, produced some slow ageing. The rate of amplitude decrease depended on the Freon impurity level.     

麦秸秆粉/PP木塑复合材料紫外线加速老化性能

以麦秸秆粉为填充材料(质量分数50%),以聚丙烯(PP)膜为基体材料,采用混炼模压成型制备麦秸秆/PP木塑复合材料,对其进行紫外线加速老化实验,对比研究不同填充材料的木塑复合材料老化前后的力学性能和颜色变化,用FTIR分析探讨了复合材料老化机制,用SEM观察其表面微观形貌。结果表明,紫外线加速老化会导致麦秸秆/PP复合材料力学性能降低,当老化时间小于960 h时,麦秸秆/PP木塑复合材料弯曲强度、拉伸强度下降幅度较小,老化时间大于960 h时,力学性能下降幅度较大,材料褪色明显; 老化1200 h其弯曲强度、拉伸强度、冲击强度分别下降67.2%、47.89%、32.41%; 麦秸秆纤维中羟基加速了PP的紫外光降解,最终材料表面出现明显裂纹,部分纤维剥落并伴随有PP粉化现象。     

Thermoplastic film infusion process for long-fiber reinforced composites using thermally expandable elastomer tools

Thermoplastic film infusion process was investigated by using thermally expandable elastomer tools, which effectively compensated for the pressure loss caused by polymer infusion into porous fiber beds. In this process, the thermally expandable elastomer tool was incorporated in a fixed-volume mold with polymer-film and dry fabric layers, and upon heating, the polymer melt was forced to infuse into the dry fabric by the thermal expansion of the elastomer tool. The elastomer tool produced sufficiently high elastic force up to 7.5 MPa by the thermal expansion and sustained the mold pressure above 6.5 MPa during the resin impregnation in the flash-land compressing processing. Combining the D'Arcy's law and the compressibility of the elastomer tool and the elastic fiber bed, a film infusion model was developed to predict the resin infusion rate and impregnation pressure as a function of time during resin infusion.     

聚氨酯弹性体的合成和水下声学性能

用甲苯-2,4-二异氰酸酯(2,4-TDI)、聚醚二醇(PPO)和3,3’-二氯-4,4’-二氨基二苯基甲烷(MOCA)等原料合成了聚氨酯弹性体,在脉冲声管中测试了合成试样的声压反射系数和吸声系数,研究了合成工艺参数对其水下声学性能的影响。测试结果表明,TDI-PPO-MOCA合成型聚氨酯弹性体是一种良好的水下吸声材料,其吸声性能受到固化温度,扩链剂含量等参数的影响。加入填料和改变其结构可以进一步改善聚氨酯弹性体的水下声学性能,因此合理地设计实验工艺参数,可以得到水下声学性能更佳的聚氨酯弹性体。为工业生产提供了理论参考。     

Modeling and Prediction of Thermal Cycle Induced Failure in Epoxy-Silica Composites

Epoxy resins filled with dielectric mineral particles are frequently used as insulating materials in power industry applications. Due to their excellent dielectric properties and relatively good thermal performance (resistance, ageing and conductivity) their usability is common and extensive. However, the mechanical performance of the resins is influenced by several factors such as resistance to crack propagation, especially in low temperature applications. This phenomenon is normally linked with appearance of two phase systems where particle filled epoxy material interacts with metallic inserts having significantly different thermal expansion coefficients. This kind of epoxy-metal interface can produce relatively high stresses in the product structure during thermal cycle loading. The paper deals with mechanical problems of power industry products and introduces the methodology for numerical modeling of failure in silica filled epoxy systems subjected to severe temperature gradients. Various aspects of material behavior modeling are covered in this article, including polymerization process, viscoelastic stress relaxation as well as stochastic cracking.     

聚酰胺类热塑性弹性体的合成与发展现状

聚酰胺类热塑性弹性体 (TPAE)是一种新型热塑性弹性体 ,具有突出的性能优势 ,其合成方法主要有二元酸法和异氰酸酯法 ,应用领域广泛 ,有着良好的发展前景。     

Fracture toughness and failure assessment for particulate reinforced composites considering viscoelasticity

Fracture mechanics models which are appropriate to describe failure behavior of highly filled elastomers were discussed, and then the strip‐yield and the inherent flaw models were applied to them. In order to generate failure assessment diagrams, the two models were moderately modified, and the experiments of fracture mechanics were conducted using center cracked tension (CCT) specimens made of a highly filled elastomer applying the ASTM E399 standard. The failure assessment diagram of the modified inherent flaw model was normalized to compare with that of the modified strip‐yield model. From the comparison between two failure assessment diagrams, it was found that the failure assessment diagram of the modified inherent flaw model more conservatively assesses the failure than that of the modified strip‐yield model.