Depth-Dependent Indentation Microhardness Studies of Different Polymer Nanocomposites

Continuous depth sensing indentation microhardness measurements were performed to investigate the effect of filler content and dimensionality on the mechanical behaviour of different polymer nanocomposites. In 1D filler reinforced nanocomposites (such as PP/MWCNT system), both the hardness and the indentation modulus were found to appreciably increase up to a filler weight fraction of 1.6 wt.-%. Further addition of the filler changed the properties only insignificantly. In the nanocomposites with 2D filler (such as in PA6/LS) both the hardness and the indentation modulus increase notably with the addition of the filler and showed intense plasticity. In the investigated systems and composition range, the 3D filler (such as PP/OS2) showed no reinforcing effect at all. In was concluded that the 1D and 2D nanofillers play much more effective reinforcing role to improve the mechanical properties than the 3D fillers.     

Effect of Epoxidation of Diene Component of SBS Block Copolymer on Morphology and Mechanical Properties

In this work, the polybutadiene (PB) block of an asymmetric lamellae forming polystyrene/polybutadiene based triblock copolymer was epoxidized to different extent in order to study its effect on morphology and mechanical behaviour of the copolymer. The products were analyzed by means of different microscopic techniques, Fourier transform infrared (FTIR) spectroscopy and microhardness measurements. It was found that the microphase separation behavior and hence the mechanical properties of the materials were drastically altered through epoxidation of the diene block of the styrene/diene triblock copolymer. With the increase in the extent of epoxidation the lamellar structure changed to distorted lamellae and then to disordered domains. Consequently, inhomogeneous mechanical performance of the samples was observed at higher degree of chemical modification.     

Poly(vinyl chloride) Nanocomposites

Poly(vinyl chloride) is one of the major thermoplastics beside other commodities polymers like polyethylene and polystyrene. However, some of its main characteristics such as plasticity, thermal and photo stability are inferior to other commodity polymers. Adding nano scale inorganic fillers to poly(vinyl chloride) or other polymers in view to obtain polymer nanocomposites with superior properties has drawn the attention of many researchers in the last decades. Poly(vinyl chloride) nanocomposites are obtained mainly by in situ polymerization, solution based or mixing techniques. The resulting products show improvement of most important properties of poly(vinyl chloride) such as thermal, mechanical, rheological, flammability, antibacterial, etc. This paper presents preparation ways of poly(vinyl chloride) nanocomposites using different nano fillers and the improved properties compared with those of virgin poly(vinyl chloride).     

Activite de complexes macromoleculaires a base de titane et de lithium,en polymerisation ziegler-natta de l'ethylene

The reaction behaviour of soluble (polydienyllithium or polystyryllithium/TiCl₄/apolar solvents) systems was studied for Ziegler-Natta polymerization of ethylene. The activity and the efficiency of such systems closely depend on the value of the ratio r = [Li]/[Ti] and on the natures of both the organolithium compound and the solvent. For the (polybutadienyllithium/TiCl₄/toluene) system, the optimum activity and efficiency were obtained for r = 2,0. The block copolymer so synthesized is slightly cross-linked; cross-linking could be avoided by using a soluble (polystyrene_DPn=100-butadiene_DPn=2-butadienyllithium/TiCl₄/toluene) system. This behaviour is due to the short length of the polybutadiene block. Moreover, such a system allows measurement of the true efficiency of the initiator complex. Efficiency was found to be 0.44 with respect to titanium concentration; the relatively high value, compared to those of conventional systems, is responsible for the high activity of the studied systems.     

Synthesis of poly(1-vinylimidazole)-block-poly(9-vinylcarbazole) copolymers via RAFT and their use in chemically responsive graphitic composites

This study reports the synthesis of novel poly(1-vinylimidazole)-b-poly(9-vinylcarbazole) (PVI-b-PVK) block copolymers with varying monomer ratios using reversible addition-fragmentation chain-transfer (RAFT) polymerization and their incorporation in responsive composite materials. Specifically, non-covalent exfoliation of two different conductive fillers, multi-walled carbon nanotubes (MWCNTs) or reduced graphene oxide (rGO), was studied. The percolation threshold of the synthesized nanocomposites was dependent on the polymer used for dispersion, showing a better affinity of the fillers for block copolymers with higher relative carbazole content. Resistivity measurements showed selective variation in the resistance signal when the materials were exposed to various organic solvents and acids, providing a good basis for the design of sensing devices.     

REVIEW Polymer Nanocomposites: Flammability

Flame retardation of materials has become a very important issue of concern to researchers and producers. Recently, it has been found that the nano fillers are ecologically friendly and having a high aspect ratio, their dispersion in the polymer matrix leads to significant improvements of many properties. From the point of view of flame retardancy, the nano fillers are able even in small amounts to significantly decrease important flammability characteristics such as heat release rate and increase the oxygen index. This paper covers some recent contributions and progresses to the flammability characteristics of different groups of polymer nanocomposites such as: thermoplastics, thermosettings, elastomers, thermoplastic elastomers and polyblends.     

Unique rheological behavior of rubber based nanocomposites

Montmorillonite clay (N) based nanocomposites were prepared using three different grades of acrylonitrile butadiene rubber (NBR) (19%, 34%, and 50% acrylonitrile contents), styrene butadiene rubber (SBR), and polybutadiene rubber (BR). Rheological study was carried out on these nanocomposites at three different temperatures (110 °C, 120 °C, and 130 °C) over a range of shear rates for comparison. The results showed that the shear viscosity decreased with increasing shear rate and incorporation of the unmodified (N) and the modified (OC) fillers up to a certain loading, when the results were compared with the gum rubber. This effect became more prominent with increasing polarity of the rubber. The die swell, on the other hand, decreased with loading of N and OC. With increasing filler volume fraction, the die swell further decreased. Decrease of viscosity with concomitant decrease of die swell is unique in such systems. Consecutive runs of the same sample over different shear rates increased the viscosity. The results were explained with the help of X‐Ray Diffraction (XRD) data and Transmission Electron Microscopy (TEM).© 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1854–1864, 2005     

丁羟胶型聚氨酯弹性体的水解稳定性

丁羟胶型聚氨酯弹性体的水解稳定性;弹性体;扩链剂     

Deformation and fracture mechanisms in filled polymers

As fillers are traditionally designated those finely divided solids which are added to a polymer matrix in relativly large amounts to modify its properties and/or to reduce the price of the resulting compound. Generally a filler material is stiffer than the matrix and depending on their origin, shape and treatment fillers are reinforcing or not. In this presentation the authors will briefly review the characteristic mechanical effects on small strain behaviour, structure and time‐dependent properties of filled polymers stemming from the addition of more or less “spherical” fillers such as calcium carbonate, quartz flour, silica or glass spheres. The effect of such fillers on yield deformation, the nature of possible damage proceeding fracture and their effect on the toughness of particulate filled thermoplastics and thermosets will be discussed in more detail.     

Rheology of highly filled polypropylene compounds: Measurement and applications

It is common knowledge among rheologists as well as polymer engineers that compounds of thermoplastics with a high volume content of mineral fillers show a viscoelastic behaviour which is significantly different from homogeneous systems. A strong nonlinearity is combined with the development of a second plateau region of the dynamic moduli at lower frequencies. This for one makes the rheological characterization of these materials more complicated, as could be shown in a round robin test, including a PP-compound with talc. The linearity criterion has to be handled carefully to achieve comparable and representative results. However, the viscoelasticity gives access to a quick characterization method regarding dispersion quality in compounds. This can be shown for the case of PP-talc-compounds, where correlations between relaxation spectrum and impact strength could be developed.     

Thermal properties and microhardness of HDPE/clay nanocomposites compatibilized by different functionalized polyethylenes

The calorimetric characteristics, the flammability, the thermal stability and the microhardness of polyethylene high density/clay nanocomposites (HDPE/clay) have been studied by differential scanning calorimetry, thermogravimetry, determination of limiting oxygen index and microhardness tests. The nanocomposites have been compatibilized by ethylene–acrylic acid copolymer (EAA), acrylic acid grafted HDPE (HDAA) and maleic anhydride grafted HDPE (HDMA). The clay was montmorillonite Cloisite 15A. The influence of the presence and the type of the compatibilizers on the properties of the nanocomposites has been evaluated. The results have shown that the thermal stability, the reduction of the flammability and the microhardness of HDPE/clay nanocomposites, compatibilized by HDAA and HDMA are higher than those for nanocomposite compatibilized by EAA. Moreover, the presence and the type of compatibilizer have negligible effect on the characteristics of the HDPE phase transitions. These results have been interpreted by the better clay dispersion and higher level of clay exfoliation in the presence of compatibilizers HDAA and HDMA, than those in the presence of EAA compatibilizer.     

纳米纤维素晶须的表面醋酸酯化改性及复合材料的力学性能

采用硫酸水解法制备纳米纤维素晶须, 再以冰醋酸为分散介质, 浓硫酸为催化剂, 醋酸酐为酯化剂对纳米纤维素晶须进行不同程度醋酸酯化改性, 得到醋酸酯化的纳米纤维素. 采用红外光谱(FTIR)、 X射线光衍射(XRD)、 透射电子显微镜(TEM)和X射线光电子能谱(XPS)等手段对改性产物进行分析和表征. 结果表明, 改性纳米纤维素晶须中醋酸酯基的平均取代度过小或过大时均不适宜用作复合材料的增强相. 当改性纳米纤维素晶须中醋酸酯基的平均取代度为0.05时, 醋酸酯化反应只发生在纳米纤维素晶须的表面. 此时, 晶须能在丙酮中稳定悬浮, 表现出流动双折射现象, 并保持了改性前纳米纤维素晶须的棒状形态和高结晶度. 将这种改性后的纳米纤维素晶须作为增强相与醋酸纤维素通过溶液浇铸法制成纳米复合膜, 结果显示, 与空白醋酸纤维素膜相比, 添加改性纳米纤维素晶须后, 纳米复合膜的拉伸强度、 杨氏模量和断裂伸长率都得到了提高. 在玻璃化转变区间纳米复合膜储能模量的降低幅度小于空白膜.     

Dielectric,mechanical and electro-stimulus response properties studies of polyurethane dielectric elastomer modified by carbon nanotube-graphene nanosheet hybrid fillers

The typical nano-carbon materials, 1D fiber-like carbon nanotubes (CNTs) and 2D platelet-like graphene nanosheets (GRNs), that have attracted tremendous attention in the field of polymer nanocomposites due to their unprecedented properties, are used as conducting filler to induce a considerable improvement in the mechanical, thermal and electrical properties of the resulting graphene/polymer nanocomposites at very low loading contents. This study deals with the preparation and electro-stimulus response properties of polyurethane (PU) dielectric elastomer films with such 1D and 2D nanocarbon fillers embedded in the polymer matrix. The various forms of carbon used in composite preparation include CNT, GRN and CNT-GRN hybrid fillers. Results indicate that the dielectric, mechanical and electromechanical properties depend on the carbon filler type and the carbon filler weight fraction. Here, it has been also established that embedding CNT-GRN hybrid fillers into pristine polyurethane endows somewhat better dispersion of CNTs and GRNs as well as better interfacial adhesion between the carbon fillers and matrix, which results in an improvement in electric-induced strain. Therefore, the nanocomposites seem to be very attractive for microelectromechanical systems applications.     

Mechanochemical synthesis of poly(butadiene-b-acrylic acid)

The preparation of block copolymer with polybutadiene, respectively poly(acrylic acid) sequences, using mechanochemical methods was investigated. The synthesis involves the generating of polybutadiene macroradicals, by ultra-high speed stirring of the polymer in toluene solution. The macroradicals are capable to initiate the polymerization of acrylic acid present in the reaction medium, leading to block copolymer formation. The influence of different parameters, such as temperature, duration, acrylic acid/polybutadiene molar ratio, on the yield and composition of the synthesized copolymer was studied.     

Influence of nanoparticles on elastic and optical properties of a polymeric matrix: Hypersonic studies on ethylene-vinyl alcohol copolymer-titania nanocomposites

High resolution Brillouin spectroscopy (HRBS) backscattering elastic data in nanocomposites of ethylene-vinyl alcohol copolymer (EVOH) and TiO₂ nanoparticles present anomalous dependence with concentration, while Young’s modulus and microhardness data show the expected behaviour. When performing HRBS with the 90A scattering geometry to asses the effective elastic constant, the expected behaviour for low concentration of TiO₂ nanoparticles is again obtained. This unusual disagreement can be solved assuming that the inclusion of TiO₂ nanoparticles induces anomalous refractive index behaviour at the applied laser wavelength for the different EVOH-TiO₂ nanocomposites. Comparison with experimental elastic and optical data obtained in isotactic-polypropylene-TiO₂ nanocomposites proves that EVOH-TiO₂ nanocomposites show an unusual optical behaviour at the laser wavelength, possibly due to a singular bonding between the EVOH polymer and the TiO₂ nanoparticles.     

Infrared spectroscopy on new multiphase thermoplastic elastomers based on hydrogen bond complexes - temperature dependence and orientation behaviour

The structure and deformation behaviour of a new class of thermoplastic elastomers is studied by temperature dependent infrared (IR) spectroscopy and by IR - dichroism spectroscopy. The thermoplastic elastomer is based on polybutadiene with statistically distributed side groups which form an anisotropic supramolecular structure via hydrogen bonds. Changes in the IR spectra at elevated temperatures are related to the melting of the ordered structure. The uniaxial deformation behaviour is studied by linear dichroism Fourier-transform (FT)-IR spectroscopy. A deformation model is developed which accounts for the major experimental results: while the polybutadiene segments behave as flexible chains with characteristic rubberlike elasticity the polar units within the supramolecular structure show an orientation behaviour characteristic for rodlike molecules.     

Thermogravimetric Analysis and Thermal Ageing of Crosslinked Nitrile Rubber/Poly(ethylene-co-vinyl Acetate) Blends

The thermal behaviour of nitrile rubber (NBR)/poly(ethylene-co-vinyl acetate) (EVA) blends was studied by thermogravimetry. The effects of blend ratio, different crosslinking systems (sulphur, peroxide and mixed), various fillers (silica, clay and carbon black) and filler loading on the thermal properties were evaluated. It was found that the initial decomposition temperature increased with the addition of NBR to EVA. Among the various crosslinking systems studied, the peroxide cured system showed the highest initial decomposition temperature. This is associated with the high bond dissociation energy of C–C linkages. The addition of fillers improved the thermal stability of the blend. The mass loss at different temperatures and activation energy of degradation were also studied. The thermal ageing of these blends was carried out at 50 and 100°C for 72 h. It was seen that the properties are not affected by the mild ageing condition. Also, the peroxide cured system was found to exhibit better retention in properties, than other crosslinking systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Polymer nanocomposites based on polyamide 6 modified with fulleroid fillers

Polymer nanocomposites based on polyamide and fulleroid modifiers are synthesized through in situ polymerization, and their mechanical and electric properties are studied. After introduction of 0.001–0.1 wt % fulleroid modifiers, Young’s modulus and the strength of thermoplastic composites increases by 15–20%, practically independently of the amount of filler. This circumstance is due to the fact that the introduction of fulleroid fillers causes selective crystallization of polyamide 6 only in the α form. The introduction of fullerene fillers considerably improves the tribological characteristics of polymer nanocomposites, thereby decreasing the friction coefficient by a factor of 2. The electric properties of nanocomposites are studied also.     

聚丁二烯1,2-结构含量和SBS中聚丁二烯段1,2-结构含量的调节

以正丁基锂为引发剂,环己烷为溶剂,研究了四氢呋喃(THF)对聚丁二烯1,2-结构和丁苯嵌段共聚物SBS中聚丁二烯段1,2-结构含量的影响,指出在一定温度下,聚丁二烯1,2-结构含量与体系中THF的浓度有指数关系。控制体系中THF的浓度和聚合反应温度,可调节聚合产物中聚丁二烯1,2-结构含量。     

Morphology and deformation behaviour of SBS/PS blends: a combined microscopic and spectroscopic study

Correlation between morphology and micromechanical deformation behaviour of blends consisting of a lamellae-forming linear styrene/butadiene block copolymer and polystyrene homopolymer (hPS) was studied by different microscopic techniques (transmission electron microscopy and scanning electron microscopy) and rheo-optical Fourier transformed infrared spectroscopy. Attributable to a change in morphology from well-ordered lamellae to a distorted one, a transition in deformation mechanism from homogeneous plastic flow of the lamellae to formation of local craze-like deformation zones was observed on addition of hPS. The latter led to a drastic reduction in elongation at break. An abrupt depression in the degree of orientation of the polystyrene (PS) and the polybutadiene (PB) phases in the blends suggested that the failure occurs at the interface between the added hPS and PS blocks of the block copolymer.