Structural silicone sealants after exposure to laboratory test for durability assessment

During the service life of structural sealant glazing (SSG) facades, the load-bearing capacity of the silicone bonds needs to be guaranteed. Laboratory tests can assess the durability of SSG-systems based on mechanical characteristics of the bond after simultaneous exposure to both climatic and mechanical loads. This article studies how the material characteristics of two common structural sealants are affected by laboratory and field exposure. Dynamic mechanical analysis (DMA) confirms a reduction in the dynamic modulus of exposed silicone samples. Results from thermogravimetric analysis, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and small-angle X-ray scattering/wide-angle X-ray scattering show differences between the two sealants and indicate no/minor changes in the composition and morphology of the laboratory and field exposed sealants. Mechanical characterization methods, such as DMA, and tensile and shear testing of the structural bond, are shown to be sensitive toward the combined climatic and mechanical loadings, and are hence suitable for studying degradation mechanisms of structural sealants.     

Spreading and Curing Behaviors of a Thermosetting Droplet-Silicone on a Heated Surface

Thermosetting materials are widely used as encapsulation in the electrical packaging to protect the core electronic components from external force, moisture, dust, and other factors. However, the spreading and curing behaviors of such kind of fluid on a heated surface have been rarely explored. In this study, we experimentally and numerically investigated the spreading and curing behaviors of the silicone(OE6550 A/B, which is widely used in the light-emitting diode packaging) droplet with diameter of ～2.2 mm on a heated surface with temperature ranging from 25 ℃ to 250 ℃. For the experiments, we established a setup with high-speed camera and heating unit to capture the fast spreading process of the silicone droplet on the heated surface. For the numerical simulation, we built a viscosity model of the silicone by using the Kiuna's model and combined the viscosity model with the Volume of Fluid(VOF) model by the User Defined Function(UDF) method. The results show that the surface temperature significantly affected the spreading behaviors of the silicone droplet since it determines the temperature and viscosity distribution inside the droplet. For surface temperature varied from 25 ℃ to 250 ℃, the final contact radius changed from ～2.95 mm to ～1.78 mm and the total spreading time changed from ～511 s to ～0.15 s. By further analyzing the viscosity evolution of the droplet, we found that the decreasing of the total spreading time was caused by the decrease of the viscosity under high surface temperature at initial spreading stage, while the reduction of the final contact radius was caused by the curing of the precursor film. This study supplies a strategy to tuning the spreading and curing behavior of silicone by imposing high surface temperature, which is of great importance to the electronic packaging.     

Enhancing the Yield Stress in Liquid Polydimethylsiloxane to Allow Its 3D Printing: Hydrogels as Removable Fillers

For manufacturing parts of very soft materials by liquid deposition modeling (e.g., to mimic living soft tissues), formulations of 3D-printable polydimethylsiloxane have been developed, with the aim of increasing the yield stress of the liquid and reducing the final mechanical modulus. In the present work, suspensions of solid-like hydrogel particles, which are easily 3D-printable, are prepared in order to generate yield stress, and the suspended phase is removed after manufacturing by taking advantage of the thermo-reversibility of the hydrogel behavior, resulting in porosity, which reduces the final rigidity. The reported approach is even more efficient than a previous approach based on emulsion formulations.     

Influence of thermal runaway in styrene–acrylonitrile bulk copolymerization revealed by computational fluid dynamics modeling

The computational fluid dynamics (CFD) and kinetic-based moment methods coupled approach is adopted to simulate the bulk copolymerization of styrene–acrylonitrile (SAN) in a stirred tank reactor. Numerical simulations are carried out to investigate the impacts of impeller speed, monomer ratio, initiator ratio, and initial reaction temperature on the copolymerization process and product properties. Particularly, the Chaos theory is selected as a criterion for evaluating the occurrence of the thermal runaway. The Flory's and Stockmayer's distributions are employed to calculate chain length distribution and copolymer composition distribution of copolymer. The simulation results highlight that the appearance of thermal runaway can be postponed by properly increasing the rotation speed, decreasing the initiator loadings, initial acrylonitrile contents and initial reactor temperature. Furthermore, significant differences exist in the product properties that predicted by the ideal and non-ideal models, which demonstrates that the temperature heterogeneity plays a crucial role in SAN copolymerization. This study could offer references for the safe operation and design of polymerization processes.     

Effect of comb-type copolymer on crystallization of paraffin from waxy oils and methyl ethyl ketone (MEK) -toluene dewaxing

In this research, maleic anhydride-α-octadecene copolymer and its derivative with phenylethylamine was synthesized and its effect on the crystallization of paraffins was investigated. This derivative, when added into second cut of vacuum gas oil and forth cut of vacuum gas oil, increases the size and improves aggregation of paraffin crystals observed by polarizing light microscopy, increases onset temperature and enthalpy of paraffin crystallization determined by differential scanning calorimetry, improves the dewaxing efficiency with dosage of 100?ppm explored by MEK-toluene dewaxing.     

Poly(L-lysine)-poly(ethylene glycol) layers with different structure and their influence on silica suspension stability

The effects of the structure of di- and triblock copolymers of poly(L-lysine) – LYS with poly(ethylene glycol) – PEG as well as the length of nonionic fragment in the LYS-PEG macromolecule on the copolymer chains conformation in the adsorption layer formed on the colloidal silica (SiO2) surface were examined. Spectrophotometry and turbidimetry were applied for the determination of copolymer adsorbed amounts and stability coefficients of silica aqueous suspensions. The electrokinetic parameters such as solid surface charge density and zeta potential were also estimated. The adsorption of LYS-PEG was proved to be the highest at pH 10 whereas the lowest adsorption on the solid surface was found for the triblock copolymer with long fragments of LYS at the same pH value.     

基于有限元仿真的发泡硅橡胶老化规律研究

通过力学性能测试得到发泡硅橡胶应力应变曲线,结合Ogden(Foam) 3阶超弹本构模型,建立发泡硅橡胶静密封系统的有限元仿真模型,得到大压缩量下发泡硅橡胶的von Mises应力及接触压力分布情况。仿真结果表明:大压缩量下发泡硅橡胶对称中心线位置的von Mises应力、接触压力值较大,在橡胶边缘和靠近限位环处接触应力数值有突增。开展140℃热空气老化试验,测定老化后发泡硅橡胶应力应变曲线,结合有限元仿真模型分析发泡硅橡胶老化后von Mises应力、接触压力的变化规律。结果表明:经过热空气老化后,在一定载荷下发泡硅橡胶等效应力和接触压力均呈增大的趋势。     

聚苯乙烯/交联丙烯酸甲酯共混物的制备及其发泡性能研究

将聚苯乙烯（PS）颗粒溶解到二乙烯基苯（DVB）、丙烯酸甲酯（MA）与偶氮二异丁腈（AIBN）的混合物中，通过加热引发MA聚合，获得PS/交联PMA共混物, 采用釜压法制备了PS/交联PMA共混物泡沫。采用全自动视频光学接触角测试仪、差示扫描量热仪、傅里叶变换红外光谱仪、动态力学分析仪对PS/交联PMA共混物的结构和性能进行了表征，并通过扫描电子显微镜对PS/交联PMA共混物泡沫的结构进行了表征。结果表明，交联PMA的引入能提高体系的成核效率，随着MA用量的增加，PS/交联PMA共混物的接触角从PS的100.5 °降至86.1 °；当MA的用量为9.6份（质量份，下同）时，PS/交联PMA共混物的泡孔尺寸主要分布在40~60 μm之间，泡孔尺寸分布明显变窄，泡孔密度达到了1.2×10⁸ 个/cm³。     

偶联剂对PLA/PBAT/WF复合材料3D打印性能的影响

以聚乳酸（PLA）和聚己二酸/对苯二甲酸丁二酯（PBAT）为基体，杨木粉（WF）为填充增强材料，使用混炼机熔融共混制备PLA/PBAT/WF复合材料，采用熔融沉积成型（FDM）技术制备标准实验试样，通过扫描电子显微镜、红外光谱分析、旋转流变测试以及力学试验等方法，研究不同含量的硅烷偶联剂KH550对PLA/PBAT共混物以及PLA/PBAT/WF的相容性、流变性及力学性能的影响。结果表明，在偶联剂用量为3 %（质量分数，下同）时，拉伸强度提高了136 %；偶联剂KH550与 PLA和PBAT共价键偶联生成接枝聚合物，二者相容性得到提高；同时偶联剂与WF表面羟基发生缩聚反应有效的改善了其与PLA/PBAT的基体相容性，PLA/PBAT/WF复合材料的FDM的制件力学性能得到较大提升；复合材料的黏度随偶联剂含量的增加呈下降的趋势，含量为3 %时线材的综合打印性能及制品质量最佳。     

MAPP/EAA处理对聚丙烯/小麦秸秆粉复合材料性能的影响

研究了马来酸酐接枝聚丙烯（MAPP）、乙烯丙烯酸共聚物（EAA）处理对聚丙烯（PP） /小麦秸秆粉（WSP）复合材料性能的影响。结果表明，随着体系中MAPP质量份数的增加，PP/WSP的拉伸强度和弯曲强度均逐渐增大，但冲击强度却先增加后减小，复合材料达到塑化峰的时间逐渐延长；使用EAA后，无论体系中是否已经使用了MAPP，PP/WSP的拉伸、弯曲和冲击强度均可得以提高，特别对于未使用MAPP的体系，效果更加明显，可分别提高65.04 %、45.42 %和6.75 %，储能模量增加，表面疏水性增强，平衡扭矩从13.9 N·m降至11.8 N·m，吸水尺寸变化率及吸水率下降，吸水平衡时间缩短；使用EAA可改善PP/WSP中WSP与PP间的界面结合，改善PP/WSP力学性能、热稳定性能、表面疏水性能、尺寸稳定性能和加工性能，降低其吸水率。