Microcellular silicone rubber foams: The influence of reinforcing agent on cellular morphology and nucleation

A series of microcellular silicone rubber foams were prepared by supercritical carbon dioxide (scCO₂). The effect of reinforcing agent (silica) on the rheological behavior, cellular morphology and nucleation of silicone rubber composites was investigated. The results show that the silica not only acts as reinforcing agent but also plays an important role in the cellular nucleation. When the content of silica increases from 40 phr to 70 phr, the range of the calculated surface tension of silicon rubber composites/scCO₂ (γ_mix) and radius of the critical nucleus (r*) are 158.95～1,092.74 nN/m and 14.45–99.34 nm, respectively. Meanwhile, aggregated silica has good heterogeneous nucleation as the diameter of aggregated silica particles is approximate to twice r*. The smallest cell diameter and the highest cell density of the silicone rubber foam can reach to 708 nm and 1.02 × 10¹¹ cells/cm³, which indicate that the silicone rubber nanofoams can be obtained by means of the supercritical foaming technology. POLYM. ENG. SCI., 59:5–14, 2019. © 2018 Society of Plastics Engineers     

Solid‐state microcellular high temperature vulcanized (HTV) silicone rubber foam with carbon dioxide

A series of microcellular high temperature vulcanized (HTV) silicone rubber foams were prepared using CO₂ as a physical blowing agent. Rheological properties, gas diffusive behavior, and foaming parameters of silicone rubber were investigated. The results show that saturation pressure has a significant effect on the diffusivity of CO₂ in HTV silicone rubber matrix. The gas concentration and diffusivity increase from 2.45 wt % to 3.24 wt %, and from 1.62 × 10^?5 cm²/s to 7.83 × 10^?5 cm²/s as the saturation pressure increases from 2 MPa to 5 MPa, respectively. The value of the gas diffusivity in HTV silicone rubber is almost 1000 times higher than that of the gas diffusivity in polyetherimide (PEI) matrix. Additionally, microcellular HTV silicone rubber foams with the smallest cell diameter of 9.8 μm and cell density exceeding 10⁸ cells/cm³ are achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44807.     

Peroxide vulcanized EPDM rubber/polyhedral oligomeric silsesquioxane nanocomposites: Vulcanization behavior,mechanical properties,and thermal stability

Effects of two different polyhedral oligomeric silsesquioxane (POSS), an acrylisobutyl POSS (AIBuPOSS) containing an acrylate group along with seven isobutyl group on its cage and an octaisobutyl POSS where the acrylate group is absent, on vulcanization behavior, mechanical properties, and thermal stability of peroxide vulcanized ethylene‐propylene‐diene rubber (EPDM) were investigated. The POSS was incorporated into the EPDM by melt mixing with POSS content of 0–10 part per hundred of rubber (phr). Oscillating disk rheometer analysis revealed that the acrylate group of the POSS are activated by dicumyl peroxide and improves the peroxide crosslinking efficiency of EPDM rubber. Solid state ²⁹Si‐nuclear magnetic resonance spectroscopy analysis and field emission scanning electron microscopy with energy dispersive X‐ray analysis of the EPDM/POSS vulcanizates showed that the AIBuPOSS are covalently grafted onto the EPDM chain during vulcanization and are dispersed uniformly at the nanometer scale in the rubber matrix. The EPDM/AIBuPOSS nanocomposites exhibit great improvement in tensile, tear strength, and modulus with a concurrent increase in elongation‐at‐break. Enhanced thermal stability in the nanocomposite was also observed. POLYM. ENG. SCI., 55:2814–2820, 2015. © 2015 Society of Plastics Engineers     

Solid-state polyetherimide (PEI) nanofoams: the influence of the compatibility of nucleation agent on the cellular morphology

The introduction of polyhedral oligomeric silsesquioxane (POSS) particles which act as heterogeneous nucleation agent was applied to improve the cellular morphology of nanocellular polyetherimide (PEI) foams. The loading of POSS particles increases the solubility and diffusivity characteristics of gases in nanocomposite sheets by changing the distribution of the free volume and enlarging the unoccupied volume in polymer matrix. When the range of content of POSS particles is 0.2?~?1.0 wt. %, the range of the calculated surface tension of PEI/scCO₂ (γ _mix ) and radius of the critical nucleus (r*) are 30.98?~?28.14 mN/m, and 6.88?~?6.25 nm, respectively. However, the small aggregated POSS particles are favour of heterogeneous nucleation bacause the actual diameter of the aggregated POSS particles is approximate to twice r*, so the addtion of 0.5 wt. % POSS to PEI matrix presents excellent heterogeneous nucleation performance for foaming. The average cell size of 0.5 wt. % POSS/PEI nanofoams compared with neat PEI decreases from 108 to 66 nm and the cell density increses from 5.96?×?10¹⁴ to 3.34?×?10¹⁵ cells/cm³.     

Microcellular foaming of silicone rubber with supercritical carbon dioxide

In spite of great concern on the industrial application of microcellular silicone rubber foams, such as in electric and medical devices, only a few works can be found about the foaming of silicone rubber. In this study, microcellular silicone rubber foams with a cell size of 12 μm were successfully prepared with curing by heat and foaming by supercritical CO₂ as a green blowing agent. The microcellular silicone rubber foams exhibited a well-defined cell structure and a uniform cell size distribution. The crosslinking and foaming of silicone rubber was carried out separately. After foaming, the silicone rubber foam was cross-linked again to stabilize the foam structure and further improve its mechanical properties. Foaming process of cross-linked silicone rubber should be designed carefully based on the viscoelastic properties because of its elastic volume recovery in the atmosphere. The basic crosslinking condition for small cell size and high cell density was obtained after investigating the rheological behavior during crosslinking.     

The grafting reaction of epoxycyclohexyl polyhedral oligomeric silsesquioxanes with carboxylic methoxypolyethylene glycols and the properties of composite solid polymer electrolytes with the graftomer

A novel organic–inorganic hybrid of epoxycyclohexyl polyhedral oligomeric silsesquioxane (e‐POSS)–grafted carboxylic methoxypolyethylene glycols (mPEG‐COOH), that is, a POSS‐mPEG graftomer, was synthesized. The grafting reaction of e‐POSS and mPEG‐COOH was characterized by Fourier transform infrared (FTIR) and ¹H‐NMR spectroscopy. Then the graftomer was used to develop new composite solid polymer electrolyte (SPE) films with a carboxylated nitrile rubber–epoxidized natural rubber (XNBR‐ENR) self‐crosslinked blend system as a dual‐phase polymer matrix. The self‐crosslinked reaction of the XNBR‐ENR matrix was investigated using ATR‐FTIR. The morphology of the SPE films and the distribution of lithium salt were investigated using field emission scanning electron microscopy and X‐ray diffraction, and the result illustrated that the addition of POSS‐mPEG could promote and accelerate the dissociation of LiClO₄. The best effect within the range of this study was achieved when 25 phr POSS‐mPEG was involved. The differential scanning calorimetry analysis proved that the glass‐transition temperature of the composite SPE films was reduced with the increase of POSS‐mPEG. The ionic conductivity of the composite SPE films was investigated by electrochemical impedance spectroscopy. The highest ionic conductivity in this study of 2.57 × 10^?5 S cm^?1 was obtained with 25 phr POSS‐mPEG loading. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44460.     

Morphology and properties of the PA66/PC/silicone rubber composites

The research focused on the PA66/PC/silicone rubber composites. By adding silicone rubber as a toughener, the composites were prepared via dynamic vulcanization. The morphology and properties of the composites were characterized by FTIR, TEM, SEM, XRD, etc. The FTIR spectrum of the composites presented an increase of the 1730, 1240, and 1450 cm^?1 that can be due to the C?O interaction and the presence of the O? CO? O group, and this fact can mean the formation of the PA66–PC copolymer. The crosslinking of silicone rubber in the PA66/PC matrix formed the net‐like structure like semi‐IPN, which is propitious to enhance the interaction between PA66 matrix and PC and in further makes the PC particles embed in PA66 matrix closely. Novel composites are gained with outstanding mechanical properties and high temperature resistance, so the combine toughening by silicone rubber and PC is an ideal toughening system owing to the synergistic effect. In addition, the PA66/PC/silicone rubber/OMMT composite exhibits better flexile strength and flexile modulus without weakening other mechanical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

功能化POSS对硅橡胶力学性能的影响及机理研究

研究了八聚笼型倍半硅氧烷(POSS)功能化侧基的种类和用量对硅橡胶力学性能的影响。结果表明,POSS的加入使硅橡胶的拉伸强度和断裂伸长率均下降,硬度均提高。乙烯基POSS的加入显著延长了硅橡胶的正硫化时间。POSS的加入能显著降低硅橡胶的压缩永久变形,乙烯基POSS的效果比甲基POSS好;且乙烯基含量越高,压缩永久变形越小。分析了功能化POSS对硅橡胶力学性能的影响机理。     

Liquid polyoctahedral silsesquioxanes as an effective and facile reinforcement for liquid silicone rubber

Acrylo polyoctahedral silsesquioxanes (POSS), a liquid POSS derivative with reactive C=C double bond, is used to modify addition-cured liquid silicone rubber (LSR) as an effective nanofiller for the first time. Significant enhancements on mechanical properties are obtained. With addition of only 1.5 parts per hundred rubbers (phr) of acrylo POSS to fumed silica-strengthened silicones, the Young's modulus and ultimate tensile strength are increased by 432% and 66%, respectively, and the hardness of resulting LSR composites is improved as well. Proton nuclear magnetic resonance and Fourier transform infrared spectroscopies prove the efficient hydrosilylation between Acrylo POSS and hydrosiloxane directly. The thermal stability and morphology investigations also confirm that POSS is covalently incorporated into the network of silicone rubber. The increment of crosslink density is proved by extraction and swelling experiment and dynamic mechanical analysis. It can be envisioned that this simple and effective method could help produce high performance silicone rubber composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46996.     

Structure and Properties of Dynamically Cured Thermoplastic Vulcanizate Based on Poly(vinylidene fluoride), Silicone Rubber,and Fluororubber

Thermoplastic vulcanizates (TPVs) based on poly (vinylidene ?uoride) (PVDF), silicone rubber (SR) and ?uororubber (FKM) were prepared via dynamic vulcanization. Morphology characterization showed that spherical rubber particles were dispersed separately and “connected” by “bridge” in the TPV with 10 wt.% FKM, but agglomerated together with higher FKM content. The mechanical properties of TPVs were improved, especially tear strength and elongation increased from 24 kN.m^?1 and 23% to 103 kN.m^?1 and 306%, respectively, with FKM increased from 10 wt.% to 50 wt.%. Rheology studies and dynamic mechanical properties results showed that the compatibility between PVDF and rubber phase was improved by FKM.     

Microcellular foaming of polypropylene containing low glass transition rubber particles in an injection molding process

Microcellular foams in polypropylene containing rubber particles were produced in an injection molding process. The foams are generated because of the thermodynamic instability and are controlled by formation process. The effect of processing parameters on microcellular foaming was investigated in the injection molding process. Injection speed and pressure are less important factors but packing pressure plays an important role in controlling the foam density. A critical packing pressure, about 5 × 10⁶ Pa, was found to generate microcellular foams in our polypropylene material system. Rubber particles inside the polypropylene seem to stabilize the microcellular foams.     

POSS/硅橡胶复合材料的结构和加工性能研究

采用熔体共混法制备了笼型硅氧烷齐聚物(POSS)/硅橡胶复合材料.利用X射线衍射仪和电子显微镜对复合材料中的POSS分散情况进行了观察,结果表明,熔体共混后,一部分POSS以分子水平分散在硅橡胶中,另一部分POSS则由于自组织结晶以微米颗粒分散在硅橡胶中.采用橡胶加工分析仪对复合材料的加工性能进行了表征,结果表明,某些情况下POSS对硅橡胶产生了增塑效应.POSS对硅橡胶的增强效应、增塑效应取决于其分散结构.     

Low‐κ nanocomposite films based on polyimides with grafted polyhedral oligomeric silsesquioxane

Nanocomposites of polyimides (PI) with covalently grafted polyhedral oligomeric silsesquioxane (R₇R′Si₈O₁₂ or POSS) units were prepared by thermally‐initiated free‐radical graft polymerization of methacrylcyclopentyl‐POSS (MA‐POSS) with the ozone‐pretreated poly[N,N′‐(1,4‐phenylene)‐3,3′,4,4′‐benzophenonetetra‐carboxylic amic acid] (PAA), followed by thermal imidization. The chemical composition and structure of the PI with grafted methacrylcyclopentyl‐POSS side chains (PI‐g‐PMA‐POSS copolymers) were characterized by nuclear magnetic resonance (NMR), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). The POSS molecules in each grafted PMA side chain of the amorphous PI films retained the nanoporous crystalline structure, and formed an aggregate of crystallites. The PI‐g‐PMA‐POSS nanocomposite films had both lower and tunable dielectric constants, in comparison with that of the pristine PI films. Dielectric constants (κ's) of about 3.0–2.2 were obtained. The present approach offers a convenient way for preparing low‐κ materials based on existing PI's. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Role of nanoclay in determining microfibrillar morphology development in PP/PBT blend nanocomposite fibers

In this work, a new and highly efficient method of surface-initiated free radical graft-polymerizations on the surfaces of silica gel particles was put forward, and the graft-polymerization of methacrylic acid (MAA) was conducted. This method was convenient, feasible and highly effective. Coupling agent ??-mercaptopropyltrimethoxysilane(MPTS) was first bonded onto the surfaces of silica gel particles, obtaining the modified particles MPTS-SiO₂, onto which mercapto groups were chemically attached, so a redox initiation system of graft-polymerization was constituted by the mercapto group on the surfaces of MPTS-SiO₂ particles and the cerium (IV) salt in the solution. And then the surface-initiated free radical graft-polymerization of MAA on the surfaces of silica gel particles was carried out, resulting in the grafted particles PMAA/SiO₂ with a very high grafting density (35?g/100?g) of PMAA. The grafted particles PMAA/SiO₂ were characterized by infrared spectrum (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The effects of the main factors on the new surface-initiated graft polymerization were emphatically examined, and the corresponding mechanism of the graft-polymerization was investigated in depth. The experimental results show that the mercapto group-cerium salt system analogous to the hydroxyl group-cerium salt system, can also effectively initiate vinyl monomers to be graft-polymerized on the surfaces of solid particles, and furthermore, it is a highly effective surface-initiated graft-polymerization method. In this graft-polymerization system, several factors such as sulfuric acid concentration, the used amount of cerium salt and the reaction temperature affect the grafting density greatly. For the graft-polymerization of MAA, the appropriate reaction conditions are as follows: reaction time of 3?h, reaction temperature of 50?°C, cerium concentration of 5.0?×?10^?3?M, acid (H⁺ ion) concentration of 0.15?M and MAA concentration of 0.5?M.     

Preparation and thermal degradation behavior of room temperature vulcanized silicone rubber-g-polyhedral oligomeric silsesquioxanes

Room temperature vulcanized (RTV) silicone rubber-g-polyhedral oligomeric silsesquioxanes (POSS) was prepared and its thermal degradation behavior and thermo-oxidative stability were investigated by thermogravimetric analysis (TGA). The results demonstrated that the chemical incorporation of POSS into polydimethylsiloxane (PDMS) chains significantly enhanced thermal stability of RTV silicon rubber in both nitrogen and air atmosphere. The degradation behavior was further monitored by TGA coupled with real time Fourier transform infrared spectra (FTIR), and the residues were characterized by FTIR and X-ray photoelectron spectroscopy (XPS). It was found that the remarkable improvement in thermal stability could be attributed to the following reasons: (1) the branched structure of RTV silicone rubber-g-POSS and interaction between POSS molecules and PDMS chains; (2) POSS traps generated and grafted or cross-linked structure formed; (3) intumescent ceramic protective barrier formed; (4) the perfect distribution of POSS in RTV silicone rubber-g-POSS.     

溶液共混法笼状硅氧烷低聚物/硅橡胶复合材料的分散性

通过溶液共混法制备了笼状硅氧烷低聚物（POSS）／硅橡胶复合材料,用X射线衍射仪和透射电子显微镜研究了该材料的分散状况,考察了POSS质量分数以及烘干温度、溶剂含量对POSS在硅橡胶中分散状况的影响。结果表明,POSS质量分数越低,烘干温度越高,越有利于抑制POSS的结晶．进而有利于制备POSS精细分散的P0ss／硅橡胶复合材料;而溶剂含量越少时,更多的POSS以晶体形式从溶剂中析出,从而使得POSS的结晶程度更显著。     

Finite element simulation of mechanical property evolvement of silicone rubber in the hot vulcanizing process

The technical outline of integrated research on the mechanical properties, the crosslinked structure and the hot vulcanizing technology of silicone rubber materials is formulated. From the statistics of rubber elasticity, the relationship of stored energy function and crosslinked structure parameters is constructed. Following the stress–strain theory of elastomers, related expressions for the mechanical properties and the crosslinked structure are deduced. On the basis of previous research findings, numerical expressions of the mechanical properties of silicone rubber in hot vulcanizing process are obtained. Consequently, the properties of silicone rubber can be predicted and the crosslinked structure can be controlled based on a forward simulation method, or the processing parameters and the initial polymeric material can be optimized on the basis of a backward simulation method Copyright © 2003 Society of Chemical Industry     

Synthesis and characterization of vinyl‐polyhedral oligomeric silsesquioxanes‐reinforced silicone resin with three‐dimensional cross‐linking structure

A novel thermal stability and highly transparent silicone resin‐type material was prepared via hydrosilylation of vinyl‐polyhedral oligomeric silsesquioxanes (POSS)‐grafted methylhydrosilicone oil and vinylmethylsilicone oil in the presence of Karstedt catalyst. The morphology, mechanical property, thermal stability, optical transmittance, thermal‐oxidation resistance of the vinyl‐POSS‐reinforced silicone resins were systematically investigated. Scanning electron microscopy showed that the vinyl‐POSS‐reinforced silicone resins had good compatibility with polydimethylsiloxane (PDMS) systems. The mechanical analysis and thermo gravimetric analysis indicated that the mechanical properties and thermal stability increased with increasing quantity of vinyl‐POSS. However, the optical transmittance increased with the increasing amount of vinyl‐POSS rather than decreased. In addition, the incorporation of vinyl‐POSS did not improve the thermal resistance of the PDMS polymers. The product has the potential application for LED packaging. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42187.     

混炼硅橡胶的配合技术(九)

介绍了用2，4-二氯过氧化苯甲酰作硫化剂的挤出成形用混炼硅橡胶（包括低硬度混炼硅橡胶、不粘连芯线的混炼硅橡胶、高电气强度电线用混炼硅橡胶）的配制方法及改进其加工和表面性能的方法；同时，还介绍了用甲基苯甲酰类过氧化物作硫化剂时改进混炼硅橡胶表面性能的方法（包括添加含氢硅油、硅藻土、二烷基过氧化物或过氧化苯甲酰以及细化硫化剂粒子）。     

Synthesis and self-assembly behavior of POSS tethered amphiphilic polymer based on poly(caprolactone) (PCL) grafted with poly(acrylic acid) (PAA) via ROP,ATRP, and CuAAC reaction

This investigation reports the preparation and self-assembly behavior of polyhedral oligomeric silsesquioxane (POSS) containing poly(caprolactone)-graft-poly(acrylic acid) (POSS-PCL-graft-PAA) polymer. This article focuses on the self-assembly behavior of POSS tethered amphiphilic graft copolymer. In this investigation, POSS tethered alkyne functionalized polycaprolactone (PCL) was prepared by strategic ring opening polymerization (ROP) of ε-caprolactone and α-propargyl-ε-caprolactone using hydroxyl-terminated POSS as an initiator. Azide-terminated poly(tert-butyl acrylate) (P ^t BA) was grafted onto functional PCL via Cu-catalyzed azide-alkyne “click” (CuAAC) reaction. Finally, hydrolysis of the tert-butyl ester group into acid furnished the POSS tethered PCL-graft-PAA polymer. This amphiphilic graft copolymer was characterized by GPC, NMR, and FT-IR analyses and the morphology of the graft copolymer analyzed by HRTEM and FESEM analyses. On changing the graft copolymer concentration (low to high) in water, the morphology of the final graft copolymer changed from micelles to worm-like and core-shell. The structural motif of POSS plays an important role in this morphological transformation. The pH sensitivity was studied using DLS analysis as well as via release profile of rhodamine B as a model compound.