Functional and mechanical properties of acrylate elastomer/expanded graphite nanocomposites

Expanded graphite (EG) is prepared by microwave irradiation to expandable graphite. A stable aqueous suspension of EG is obtained through dispersing EG into deionized water in the presence of surfactant under ultrasonication. Nanocomposites are prepared by compounding EG aqueous suspension with alkyl acrylate elastomer latex. It is showed that, by the latex compounding method (LCM), EG platelets are finely dispersed in the elastomer matrix. The nanocomposites exhibit remarkable improvements in mechanical properties, wear resistance, and gas barrier property. The prepared compound also shows certain electrical conductivity, but soon loses it after milled on a miller. Meanwhile, a dramatic change in EG network is observed corresponding to the loss of electrical conductivity. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal,mechanical, and dielectric properties of polystyrene/expanded graphite nanocomposites

We herewith report the thermal, mechanical (modulus), and dielectric properties of polystyrene (PS)/expanded graphite (EG) nanocomposites fabricated by a simple technique of dispersing EG (up to 2.5 vol %) in PS matrix via solution method followed by hot pressing. The thermal stability and char yield of the nanocomposites are improved marginally. The modulus, electrical conductivity, dielectric constant, and dielectric loss tangent of the nanocomposites are significantly increased with EG content. The modulus of the nanocomposites increases by about twofold at 30°C compared with that of pure PS. The dielectric constant and the loss tangent of nanocomposites are increased up to 13‐fold and 200‐fold compared with that of pure PS, respectively, at 1 MHz and varied with frequency. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The quantitative analysis of nano-clay dispersion in polymer nanocomposites by small angle X-ray scattering combined with electron microscopy

The main objective of this work is to propose a new approach for the quantitative analysis of the degree of dispersion of clay particles in the polymer matrix by small angle X-ray scattering (SAXS) combined with electron microscopy. Due to the low temperature processibility and good thermal stability, poly[(butylene succinate)-co-adipate] (PBSA) was chosen as a model polymer matrix for this study. The nanocomposites of PBSA with four different weight percentages of organically modified montmorillonite (OMMT) loadings were prepared via melt-blending method. The dispersed structure of the clay particles in the PBSA matrix was studied by SAXS. Results show that the clay particles are nicely dispersed in the case of all nanocomposites. However, with a systematic increase in clay loading, the dispersed clay structure of the nanocomposites changes from a highly delaminated to a flocculated and then to a stacked intercalated one. The probability of finding neighboring clay particles in the PBSA matrix as well as their thickness was calculated using the Generalized Indirect Fourier Transformation technique developed by Glatter and the modified Caillé theory proposed by Zhang. The morphology of the nanocomposites was also extensively studied by scanning transmission electron microscopy (STEM). In the case of all nanocomposites, SAXS results were in good agreement with STEM observations. Finally, a correlation between the predicted morphology of nanocomposites and their melt-state rheological properties is reported.     

Application of small angle X-ray scattering to semi-crystalline polymers: 1. Experimental considerations and analysis of data

Experimental problems in studying small angle X-ray scattering from semi-crystalline bulk polymers are discussed and data obtained from slit optics compared, after desmearing, with pin-hole data. Theoretical correlation functions are derived for a model based on alternating layers of crystalline and amorphous phases. Different types of distribution functions for layer thicknesses were employed and compared with experimental correlation functions from polyethylene, poly(trimethylene oxide) and poly(tetramethylene oxide). For the latter polymer with crystallinity ～40%, Gaussian distributions for the thicknesses of both phases gave good agreement, whereas log normal distributions did not. For high crystallinity polymers choice of distribution is not critical. The fraction crystallinity obtained from different X-ray techniques is discussed.     

Morphology and mechanical properties of polypropylene‐POSS hybrid nanocomposites obtained by reactive blending

The polypropylene‐polyhedral oligomeric silsesquioxane (PP‐POSS) organic–inorganic hybrids were obtained and studied. The hybrids were prepared by grafting of POSS on PP chains during a reactive melt‐blending of polypropylene (iPP), maleic anhydride functionalized PP (PP‐g‐MA), and amine‐functionalized POSS (aminopropylheptaisobutyl‐POSS, ambPOSS, aminopropylheptaisooctyl‐POSS, amoPOSS, or aminoethylaminopropylheptaisobutyl‐POSS, am2bPOSS), taking advantage of the high efficiency of amino‐anhydride reaction in the molten state. The structure, morphology, and physical properties of the obtained hybrids and blends were studied by means of wide‐ and small‐angle X‐ray scattering, dynamic scanning calorimetry, scanning electron microscopy, dynamic mechanical thermal analysis, as well as tensile and impact experiments. The influence of POSS chemical structure and grafting degree on the morphological characteristics and mechanical properties was investigated. It was found that grafting of POSS cages on PP chains leads to the POSS dispersion on the molecular level. On contrary, when POSS was mixed with plain iPP any grafting of POSS on iPP chains was impossible, which resulted in phase‐separated blend with crystallites of POSS dispersed in iPP matrix. The mechanical tests revealed that modification of polypropylene by grafting with POSS molecules does not affect significantly its mechanical properties, both static and dynamic, except ultimate strain, which is markedly lower in hybrids and their blends than in plain iPP. Also the impact properties of PP were practically not improved by modification with POSS. POLYM. COMPOS., 34:929–941, 2013. © 2013 Society of Plastics Engineers     

The structure and electro‐mechanical properties of novel hybrid CNT/PANI nanocomposites

Electrically conductive elastomeric nanocomposites containing carbon nanotubes (CNT) and polyaniline (PANI) are reported in the present investigation. The synthesis procedure included an in situ inverse emulsion polymerization of aniline doped with dodecylbenzene sulfonic acid (DBSA) in the presence of CNT and dissolved styrene‐isoprene‐styrene (SIS) block copolymer. The PANI synthesis step was carried out by applying ultrasonic energy. The dispersions obtained were processed by two methods: a recently developed precipitation‐filtration procedure, and a conventional drop‐cast procedure. The techniques developed resulted in homogeneous exfoliated PANI coated nanotubes within the elastomeric matrix. The presence of CNT/PANI in the SIS elastomeric matrix affects thermal, mechanical, and electrical properties of the nanocomposites. The formation of continuous three‐dimensional CNT/PANI networks prepared via the precipitation‐filtration method enhances the nanocomposite properties. Contrarily, the intermittent three‐dimensional network prepared by conventional drop‐cast method leads to inferior properties. Nanocomposites produced by both techniques are observed by HRSEM. The two processing techniques result in different structures, which affect the physical properties of the materials produced. A relatively low percolation threshold for both methods was determined. The Young's modulus of the SIS/CNT/PANI significantly increased in the presence of CNT. The precipitation‐filtration technique yields an improved nanocomposite product compared to the drop‐cast route. POLYM. COMPOS., 35:788–794, 2014. © 2013 Society of Plastics Engineers     

Relationship between pore structure with residual pore and mechanical properties of expanded graphite nanocomposites at varying molding pressures

The main challenges of developing expanded graphite (EG) composites are to improve the diffusion of polymer chains into EG pores and consequently to reduce the residual pore as defects in the final composites. In this paper, composites of unsaturated polyester (UP) resin containing 0.75 wt% EG are prepared at varying molding pressures of 1, 10, 20, and 30 bar. The EG particles are prepared at different exfoliation temperatures in the range of 700 to 900°C to have EGs with different porous structures. The scanning electron microscopy (SEM) micrographs show that residual pores are observed in the composites prepared at a low pressure of 1 bar. However, when the molding pressure increases, the number of the residual pores decreases and consequently the flexural properties improve. The highlighted improvements achieved by increasing the molding pressure from 1 to 30 bar are a decrease in the value of the residual pore from 23% to 3%, an increase in the flexural modulus from 1523 to 1744 MPa, and an increase in the flexural strength from 30.6 to 54.5 MPa. Interestingly, applying higher molding pressure affects the composites containing EGs with the highest degree of porosity, or rather larger pores, more remarkably.     

Physical and mechanical properties of heat‐damaged structural concrete containing expanded polystyrene syntherized particles

Materials recycling for sustainable concrete constructions are favoring the replacement of ordinary aggregate with waste materials, in the form of either solid particles or small void‐formers. This is the case of expanded polystyrene syntherized (EPS) concrete containing EPS particles—or beads—whose high‐temperature residual behavior is investigated in this project. Two EPS mixes and one reference mix (f_c = 25–30 MPa) are tested in compression and tension after a thermal cycle at the reference temperature of 20°C, 150°C, 300°C, 500°C, and 700°C. The thermal diffusivity and the mass loss up to 700°C are investigated as well. The normalized mechanical decay of the two EPS concretes turns out to be slightly higher than that of ordinary concrete, but on the whole, the behaviors are rather close, while the thermal diffusivity of EPS concrete is definitely lower, to the advantage of its insulating capability. Damage indexes are also worked out on the basis of the elastic modulus and of the ultrasonic velocity, in order to have information on the possible void‐induced nonlinear effects. The still open problem, however, is whether the game (polystyrene recycling and mass reduction) is worth the candle (more cement and additives). Copyright © 2014 John Wiley & Sons, Ltd.     

Quantification of organoclay dispersion and lamellar morphology in poly(propylene)-clay nanocomposites with small angle X-ray scattering

Intensity profiles of small angle X-ray scattering (SAXS) curves were analyzed to simultaneously gain quantitative information on nanoclay dispersion as well as lamellar ordering in polypropylene-clay nanocomposites. Different types of PP nanocomposites prepared with PP homopolymer (HPP), random propylene-ethylene copolymer (RCP) and a high impact polypropylene-ethylene propylene rubber (ICP) were analyzed. Various one-dimensional models for stacked structures were applied on Lorentz corrected SAXS spectra to derive long period, thicknesses of alternating high and low electron density layers and their distributions, and the number of stacks for both nanoclay and PP lamellae. We applied a mixed thickness distribution model comprising combined Gaussian and exponential for a simple stack of finite thickness, which was found to explain the experimental data better for both nanoclay tactoids and lamellar stacks, compared to simple Gaussian and exponential thickness distributions. Long period X and number of stacks N were derived as important parameters signifying changes in levels of nanoclay exfoliation in PP. Among the three types of polypropylenes studied, better nanoclay exfoliation was obtained for the high impact ICP grade compared to HPP and RCP. Complete exfoliation of nanoclay was achieved in ICP matrix, employing a masterbatch processing route. Moreover, role of nanoclay as a γ nucleating agent was evident from small and wide angle X-ray analyses, and was seen strongly in RCP. Changes in lamellar structure of PP as a result of nanoclay incorporation, double population consisting of both α and γ polytypes in the nanocomposites from that of a primarily α population in neat polymer matrices, were also analyzed in detail with the mixed thickness distribution model, thereby demonstrating its usefulness.     

SEBS/蒙脱土纳米复合材料结构和性能研究

采用溶液混合方法制备了氢化苯乙烯/丁二烯三元嵌段共聚物(SEBS)/有机蒙脱土(OM-MT)纳米复合材料(NC)。对SEBS/OMMT NC的插层结构和物理力学、动态力学、耐热等性能进行了研究。结果表明,与SEBS复合,OMMT层间距明显增大,制备出具有插层型结构的NC。加入OMMT可明显提高SEBS的拉伸断裂强度、300%定伸强度和断裂伸长率,但永久变形也增大。DMA研究表明,SEBS/OMMT NC的储能模量和损耗模量比纯SEBS显著提高,PEB链段的tanδ降低,而PS链段增加。SEBS/OMMT NC比SEBS的热稳定性明显提高。     

Morphology and mechanical properties of high density polyethylene‐POSS hybrid nanocomposites obtained by reactive blending

The high density polyethylene‐polyhedral oligomeric silsesquioxane (HDPE‐POSS) organic–inorganic hybrids were obtained and their properties studied. The hybrids were prepared by grafting of POSS on polyethylene chains during reactive melt‐blending of HDPE, maleic anhydride functionalized HDPE and amine‐functionalized POSS, taking advantage of the high efficiency of amine‐anhydride reaction in the molten state. The structure, morphology, and physical properties of the obtained hybrids and blends were studied to find the influence of POSS chemical structure and grafting degree on the morphological characteristics and mechanical properties of hybrid nanocomposites. It was found that grafting of POSS cages on HDPE chains leads to the POSS dispersion at the molecular level. On the contrary, when POSS was mixed with plain HDPE any grafting of POSS on polyethylene chains was not possible, which resulted in phase‐separated blend. The mechanical tests revealed that modification of polyethylene by grafting with POSS molecules does not affect significantly its mechanical properties, both static and dynamic, except ultimate strain, which is lower in hybrids and their blends than in plain HDPE. The impact properties (Izod impact strength) were slightly improved by grafting of HDPE with POSS. HDPE‐g‐POSS hybrids demonstrated also much enhanced thermo‐oxidative stability comparing to plain polyethylene. POLYM. ENG. SCI., 55:2058–2072, 2015. © 2014 Society of Plastics Engineers     

Study on thermal enhancement mechanism of POSS‐containing hybrid nanocomposites and relationship between thermal properties and their molecular structure

In this study, a series of poly(4‐acetoxystyrene) (PAS)‐octavinyl polyhedral oligomeric silsesquioxane (POSS) blends and the polystyrene (PS)‐octavinyl POSS blends were prepared by the solution‐blending method and characterized with Fourier transform infrared (FTIR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) techniques. The results show that the glass‐transition temperature (T_g) of the PAS‐POSS blends increases at a relatively low POSS content and then decreases at a relatively high POSS content. POSS can effectively improve the thermal stability of the PAS‐POSS blends at low POSS content, and T_g of PAS‐POSS blends decreases with the increase in POSS content at relatively high POSS content. However, the T_g of the PS‐POSS blends persistently decreases even at very low POSS content. T_g change mechanism was investigated in detail by XRD, TEM, and FTIR spectra. The influence mechanism of POSS content and dispersion in composites, and parent polymer structure on thermal properties of the blends was investigated in detail. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

聚甲基丙烯酸/碳纳米管杂合水凝胶的结构及力学性能研究

利用环境扫描电镜(SEM)和动态粘弹谱仪对制备水凝胶样品分别进行结构形态表征和力学性能测试。结果表明,碳纳米管(MWCNT)和聚甲基丙烯酸水凝胶体系具有很高的兼容性。通过调节MWCNT的含量,可以使得PMAA/MWCNT杂合水凝胶表现出更好的耐压力和形变恢复能力。     

聚甲基丙烯酸/碳纳米管杂合水凝胶的结构及力学性能研究

利用环境扫描电镜(SEM)和动态粘弹谱仪对制备水凝胶样品分别进行结构形态表征和力学性能测试。结果表明,碳纳米管(MWCNT)和聚甲基丙烯酸水凝胶体系具有很高的兼容性。通过调节MWCNT的含量,可以使得PMAA/MWCNT杂合水凝胶表现出更好的耐压力和形变恢复能力。     

Study on glass transition temperature and mechanical properties of cadmium sulfide/polystyrene nanocomposites

The cadmium sulfide/polystyrene (CdS/PS) nanocomposites with concentration (0, 2, 4, 6, and 8) wt% of CdS nanoparticles were prepared by solution casting method and characterized through fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) measurements. The particle size of nanoparticles is found to be around 15 nm. Glass transition and mechanical behavior of CdS/PS nanocomposites were investigated using dynamic mechanical analyzer (DMA). The mechanical properties such as Young's modulus and tensile strength were determined at room, as well as at elevated temperatures through their stress–strain curves. The result shows that glass transition temperature (T_g) is shifted toward the higher temperature after the addition of CdS nanoparticles. The mechanical properties increased at low wt% loading of CdS nanoparticles and decreased for higher wt% loading of CdS nanoparticles. It was also found that mechanical properties decline with increase in the temperature. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Elaboration and mechanical characterization of nanocomposites thin films: Part II. Correlation between structure and mechanical properties of SiO2-PMMA hybrid materials

Mechanical properties of hybrid thin films based on SiO₂-PMMA materials were investigated through nanoindentation tests. We demonstrated in the part I of this paper, that nanoindentation is an appropriate technique to characterize hybrid organic–inorganic thin films. Specific procedures of analysis and the use of appropriate models allows to determine reproductive indentation modulus and hardness of the hybrid layers. The mechanical responses of nanocomposites are not only governed by the composition of the layers but also by the nature and the extent of the hybrid interface. Different layers have been studied, constituted by an inorganic and an organic phase that just be physically mixed or covalently connected. The weak (H bonds) or strong (covalent bonds) interactions generated by the hybrid interface lead to nanocomposites which exhibit different mechanical behaviours. Moreover, comparison between layers obtained by in situ inorganic polymerization in PMMA and layers obtained with preformed silica nano-particles have been also investigated to correlate the morphology of the nanocomposites with the mechanical responses.     

Effect of hybrid reinforcement based on precipitated silica and montmorillonite nanofillers on the mechanical properties of a silicone rubber

Silicone rubber (SR) nanocomposites containing precipitated silica (PS), montmorillonite (MMT), and PS/MMT hybrid fillers were prepared through melt‐mixing technique. In the SR/PS/MMT nanocomposite, the hybrid filler weight ratio was increased progressively from 0.4 to 1.7 while keeping the MMT weight constant. The viscosity, cure characteristics, and mechanical properties of the nanocomposites were subsequently measured. The optimum cure time increased, and the scorch time and rate of cure decreased. Furthermore, when the hybrid filler weight ratio was raised to its optimum, the tensile strength, Young's modulus, modulus at 100 and 300% elongation (M100 and M300), elongation at break, stored energy density at break, and hardness of the nanocomposite improved. The stress–strain properties of the nanocomposite with the hybrid filler improved at high deformation in comparison with those containing the PS and MMT fillers. The MMT filler exfoliated in the SR/MMT nanocomposite but did not in the nanocomposites containing the hybrid filler. Notably, the mechanical properties of the nanocomposite benefitted from the hybrid filler. This was due to the filler–filler and filler–rubber network formation in the rubber by the PS particles. Finally, effect of the PS, MMT, and hybrid fillers on the energy loss or hysteresis of the rubber was measured. POLYM. ENG. SCI., 54:1909–1921, 2014. © 2013 Society of Plastics Engineers     

Polymer/silicate nanocomposites synthesized with potassium persulfate at room temperature: polymerization mechanism, characterization, and mechanical properties of the nanocomposites

Polymer/silicate nanocomposites were synthesized using potassium persulfate (KPS) in the presence of silicate and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) without exterior redox co-catalysts at a room temperature. A mechanism for the room temperature polymerization in the presence of silicate was suggested: AMPS attached on the surface of silicate layers would oxidize Fe⁺² in silicate lattice to become Fe⁺³ and the Fe⁺³ would decompose KPS to form radicals like redox co-catalysts. Poly (acrylonitrile) (PAN)/silicate nanocomposite showed an exfoliated structure, but poly (methyl methacrylate) (PMMA)/silicate nanocomposite showed an intercalated structure. Polymers recovered from the nanocomposites synthesized at a room temperature had high isotactic configurations compared to bulk polymers. The dipole–dipole interaction between monomers and silicate surface might make the lamella of monomers to form on the silicate layer surface and produced polymers with more isotactic configurations. PAN/silicate nanocomposite showed two glass transition temperatures at 113 and 151 °C. The lower temperature might be related to the molecules with low molecular weight. PMMA/silicate nanocomposite had a storage modulus of 4.47×10⁹ Pa at 40 °C.     

Improved mechanical properties and special reinforcement mechanism of natural rubber reinforced by in situ polymerization of zinc dimethacrylate

The peroxide‐cured natural rubber (NR) was reinforced by in situ polymerization of zinc dimethacrylate (ZDMA). The experimental results showed NR could be greatly reinforced by ZDMA. The tensile strength and the hardness of NR/ZDMA composites increased with the content of ZDMA. The reinforcement mechanism was studied further. Both high crosslinking density provided by ionic crosslinking and strain‐induced crystallization improved the mechanical properties. The crosslinking density was determined by an equilibrium swelling method and the crystallization index was measured by Wide‐angle X‐ray diffraction (WXRD). When the amount of ZDMA was high, the ability of strain‐induced crystallization decreased, due to the strong interactions between the rubber phase and the hard poly‐ZDMA (PZDMA) nanodispersions. At the moment, the increasing ionic crosslinking density made up for the effect of the drop of the strain‐induced crystallization, and played a more important role in the reinforcement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of carbon black loading on curing characteristics and mechanical properties of waste tyre dust/carbon black hybrid filler filled natural rubber compounds

Curing characteristics, tensile properties, fatigue life, swelling behavior, and morphology of waste tire dust (WTD)/carbon black (CB) hybrid filler filled natural rubber (NR) compounds were studied. The WTD/CB hybrid filler filled NR compounds were compounded at 30 phr hybrid filler loading with increasing partial replacement of CB at 0, 10, 15, 20, and 30 phr. The curing characteristics such as scorch time, t₂ and cure time, t₉₀ decreased and increased with increment of CB loading in hybrid filler (30 phr content), respectively. Whereas maximum torque (M_HR) and minimum torque (M_L) increased with increasing CB loading. The tensile properties such as tensile strength, elongation at break, and tensile modulus of WTD/CB hybrid filler filled NR compounds showed steady increment as CB loading increased. The fatigue test showed that fatigue life increased with increment of CB loading. Rubber–filler interaction, Q_f/Q_g indicated that the NR compounds with the highest CB loading exhibited the highest rubber–filler interactions. Scanning electron microscopy (SEM) micrographs of tensile and fatigue fractured surfaces and rubber–filler interaction study supported the observed result on tensile properties and fatigue life. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011