Synthesis and characterization of novel waterborne polyurethane nanocomposites with magnetic and electrical properties

The novel nanocomposites derived from waterborne polyurethane and nano-Fe₃O₄ (WPU/Fe₃O₄) have been successfully synthesized by in situ polymerization progress. The nano-Fe₃O₄ particles prepared by co-precipitation method were modified by using oleic acid (OA) to improve their compatibility with monomers. The chemical structures, morphology, thermal behavior, mechanical properties, magnetic properties and electrical properties of the WPU/Fe₃O₄ nanocomposites were investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscope (AFM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), vibrating sample magnetometer (VSM) and high resistance meter respectively. The results indicated that the Fe₃O₄ nanoparticles modified by oleic acid could be homogeneously dispersed in the WPU and the introduction of ones was obviously improving the thermal properties, magnetic properties and electrical properties of WPU/Fe₃O₄ nanocomposites. The resulting WPU/Fe₃O₄ nanocomposites would be having the potential applications in microwave absorption.     

From cellulosic waste to nanocomposites. Part 2: synthesis and characterization of polyurethane/cellulose nanocomposites

New polyurethane (PU)-based nanocomposites were synthesized through two-step in situ polymerization by incorporating low loading levels of spherical cellulose nanoparticles (CNs). Structural, mechanical, thermal, and morphological characterization of the nanocomposites was done with infrared spectroscopy, X-ray diffraction, tensile test, dynamic mechanical thermal analysis, thermogravimetry, differential scanning calorimetry, and field emission scanning electron microscopy. The results showed with incorporation of CNs there was no significant change in the structure of PU. However, the addition of 1 % CNs into PU increased the modulus nearly 42 % and tensile strength by 112 %. On the contrary, elongation at break decreased with increasing nanoparticles contents, but the nanocomposites maintained an elongation of greater than 800 %, which was still a large elongation. The thermal stability of PU enhanced with increasing the small amounts of nanoparticles. Also, incorporating of the CNs improved the phase separation between the soft and hard domains which led to an upward shift in melting temperatures and enthalpy of crystalline phase melting. These results were very encouraging in terms of using CNs as an inexpensive nanofiller and improving the mechanical and thermal properties of PU without using solvents in nanocomposite preparation.     

Crystalline morphology and properties of multi-walled carbon nanotube filled isotactic polypropylene nanocomposites: Influence of filler size and loading

Isotactic polypropylene (PP) nanocomposites with multi-walled carbon nanotubes (MWCNTs) of various diameters (10–50 nm) were fabricated by extrusion and compression-molding techniques and characterized by X-ray diffraction measurements, differential scanning calorimetry, scanning electron microscopy, mechanical test and differential thermal analyses. The pure PP exhibits both the a- and b-axes oriented α-crystal, whereas the MWCNTs induce the b-axis orientation of the α-crystal along with the formation of minor γ-phase crystal in nanocomposites. Crystallinity, long period of lamellae, tensile strength, tensile modulus (TM) and microhardness (H) of PP considerably change by different loading and sizes of MWCNTs. The estimated values H/TM = 0.09–0.10 for all samples approach the predicted value of 0.10 for polymers. The increase in crystallinity has been demonstrated by both XRD and DSC studies. Mathematical models have been invoked to explain the changes in mechanical properties. An increase in thermal stability of polymer matrix occurs with increasing MWCNTs size and loading.     

Effects of modified Clay on the morphology and thermal stability of PMMA/clay nanocomposites

The potential to improve the mechanical, thermal, and optical properties of poly(methyl methacrylate) (PMMA)/clay nanocomposites prepared with clay containing an organic modifier was investigated. Pristine sodium montmorillonite clay was modified using cocoamphodipropionate, which absorbs UVB in the 280–320 nm range, via ion exchange to enhance the compatibility between the clay platelets and the methyl methacrylate polymer matrix. PMMA/clay nanocomposites were synthesized via in situ free-radical polymerization. Three types of clay with various cation-exchange capacities (CEC) were used as inorganic layered materials in these organic–inorganic hybrid nanocomposites: CL42, CL120, and CL88 with CEC values of 116, 168, and 200 meq/100 g of clay, respectively. We characterized the effects of the organoclay dispersion on UV resistance, effectiveness as an O₂ gas barrier, thermal stability, and mechanical properties of PMMA/clay nanocomposites. Gas permeability analysis demonstrated the excellent gas barrier properties of the nanocomposites, consistent with the intercalated or exfoliated morphologies observed. The optical properties were assessed using UV–Visible spectroscopy, which revealed that these materials have good optical clarity, UV resistance, and scratch resistance. The effect of the dispersion capability of organoclay on the thermal properties of PMMA/clay nanocomposites was investigated by thermogravimetric analysis and differential scanning calorimetry; these analyses revealed excellent thermal stability of some of the modified clay nanocomposites.     

Fabrication and characterization of OMMt/BMI/CE composites with low dielectric properties and high thermal stability for electronic packaging

Thermostable nanocomposites based on interpenetrating polymer network bismaleimide/cyanate ester (BMI/CE) copolymer, derived from bisphenol A dicyanate, 4,4′-bismaleimidodiphenyl methane, and doped by 1–5 wt% organo-modified 2D montmorillonite (OMMt) nanoparticles were synthesized and characterized using a dielectric strength tester, concept 40 impedance analyzer, scanning electron microscope (SEM), dynamic mechanical analysis, and thermogravimetric analysis techniques. OMMt improves the dispersibility, alignment and interfacial strength of these nanocomposites, the electrical conductivity increase with increasing OMMt loading, and a suitable addition of OMMt can enhance the mechanical properties and dielectric property of BMI/CE copolymer. SEM analysis shows distinct characteristics of a ductile fracture of the blends. In addition, the OMMt/BMI/CE nanocomposites have a better thermal stability and a higher thermal conductivity compared to those of BMI/CE resin with the increasing of OMMt content. All of these changes in properties are closely correlated with the OMMt/BMI/CE nanocomposites, which could form an interaction interface structure in the system.     

Effect of surface modification of Fe3O4 nanoparticles on thermal and mechanical properties of magnetic polyurethane elastomer nanocomposites

Magnetic polyurethane elastomer nanocomposites were prepared by incorporating pure and thiodiglycolic acid (TDGA) surface-modified Fe₃O₄ nanoparticles into polyurethane matrix using in situ polymerization method. Surface modification of Fe₃O₄ nanoparticles was carried out to enhance the dispersion of the nanoparticles in polyurethane matrix. Pure and TDGA surface-modified Fe₃O₄ nanoparticles were synthesized by coprecipitation method and characterized by Fourier Transform Infrared Spectroscopy, X-ray diffraction, and Vibrating Sample Magnetometer. The morphology and dispersion of the nanoparticles in the magnetic polyurethane elastomer nanocomposites were studied by Scanning Electron Microscope. It was observed that surface modification of Fe₃O₄ nanoparticles with TDGA enhanced the dispersion of the nanoparticles in polyurethane matrices. Furthermore, effect of surface modification of Fe₃O₄ nanoparticles on thermal and mechanical properties of magnetic polyurethane elastomer nanocomposite was investigated by thermogravimetric analysis, dynamic mechanical thermal analysis, and an Instron type Tensile Tester. It was concluded that surface modification of Fe₃O₄ nanoparticles allowed preparation of the magnetic nanocomposites with better mechanical properties. Moreover, study of fibroblast cells interaction with magnetic nanocomposites showed that the products can be a good candidate for biomedical application due to their in vitro biocompatibility and non-toxicity.     

Lithium aluminosilicate reinforced with carbon nanofiber and alumina for controlled-thermal-expansion materials

Abstract

Materials with a very low or tailored thermal expansion have many applications ranging from cookware to the aerospace industry. Among others, lithium aluminosilicates (LAS) are the most studied family with low and negative thermal expansion coefficients. However, LAS materials are electrical insulators and have poor mechanical properties. Nanocomposites using LAS as a matrix are promising in many applications where special properties are achieved by the addition of one or two more phases. The main scope of this work is to study the sinterability of carbon nanofiber (CNFs)/LAS and CNFs/alumina/LAS nanocomposites, and to adjust the ratio among components for obtaining a near-zero or tailored thermal expansion. Spark plasma sintering of nanocomposites, consisting of commercial CNFs and alumina powders and an ad hoc synthesized β-eucryptite phase, is proposed as a solution to improving mechanical and electrical properties compared with the LAS ceramics obtained under the same conditions. X-ray diffraction results on phase compositions and microstructure are discussed together with dilatometry data obtained in a wide temperature range (?150 to 450 °C). The use of a ceramic LAS phase makes it possible to design a nanocomposite with a very low or tailored thermal expansion coefficient and exceptional electrical and mechanical properties.     

A detailed thermal analysis of nanocomposites filled with SiO2, AlN or boehmite at varied contents and a review of selected rules of mixture

In order to investigate and compare the thermal and mechanical properties of nanocomposites filled with various nanoparticles multiple experiments have been carried out. The aim of this study was to enhance the thermal and mechanical properties of epoxy resin for fiber reinforces structures by the addition of nanoparticles. These altered properties were analyzed and reconciled with each other as well as compared to data developed from different rules of mixture. A hot curing epoxy system based on bisphenol-A (DGEBA) has been filled with different contents of silicon dioxide (SiO₂), aluminum nitride (AlN) and boehmite nanoparticles to examine the effects in the material’s thermal and mechanical behavior with variable filler materials and contents compared to the unfilled epoxy. The glass transition temperature fluctuates very little with varied filler content. The coefficient of thermal expansion can be reduced with increasing filler content. This improvement recurs also in thermal conductivity and during dynamic mechanical analysis. Several rules of mixture have been applied to be verified on the basis of varied materials and filler contents. The results did not always match the experiments. The deviations are ascribed to the influence of interphases that build up in the vicinity of the nanoparticles during the process of curing.     

Thermal, dynamic mechanical and rheological properties of metallocene-catalyzed cycloolefin copolymers (mCOCs) with high glass transition temperature

We have successfully synthesized and pelletized metallocene-catalyzed cycloolefin copolymers (mCOCs). Furthermore, their thermal oxidation, dynamic mechanical and rheological properties have also been investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and capillary rheometer, respectively. Their decomposition temperature (Td), glass transition temperature (Tg), and maximum damping (tanδ) are 450 °C, 203 °C and 2.6, respectively. The thermal oxidation for lab-made mCOC results from free-radical-induced reaction, causing discoloration, and its b* value (CIE LAB system) is 29.67. With 1,2-bis(3,5-di-tert-butyl-4-hydroxyhydro-cinnamoyl)hydrazine as an antioxidant, its b* value can effectively decrease and reach − 0.48. Experimental results reveal it is a tough and flexible polymer for a variety of applications since it possesses excellent thermal stability and mechanical properties.     

Synthesis and properties of waterborne polyurethane/attapulgite nanocomposites

The novel nanocomposites derived from waterborne polyurethane (WPU)/Attapulgite (AT) nanocomposites have been successfully synthesized by in situ polymerization progress. AT functionalized by chemical modification were incorporated as a crosslinker in prepolymer. The chemical structures, morphology, thermal behavior, and mechanical properties of the WPU/AT nanocomposites were investigated by Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and tensile testing respectively. The experimental results indicated that the organically modified attapulgites were homogeneously dispersed in the WPU and resulted in an improvement of thermal stability, tensile strength and elongation at break of WPU/AT nanocomposites.     

The role of epoxy matrix occlusions within BaTiO3 nanoparticles on the dielectric properties of functionalized BaTiO3/epoxy nanocomposites

In this work, the effects of controlled nanoparticles aggregations of barium titanate (BaTiO₃) on the dielectric properties of epoxy nanocomposites are investigated in detail with respect to different experimental parameters like frequency, ceramic content and temperature. Dispersing silanized BaTiO₃ nanopowder under ultrasonic and stir, nanocomposites of epoxy-amine matrix with different morphologies are obtained. The nanoparticles silane functionalization containing amine end groups effectively improve the compatibility of the nano-BaTiO₃ and the epoxy matrix. Storage modulus, glass transition temperature, tensile and flexural properties of nanocomposites and dielectric properties are increased until 10% by weight of nano-BaTiO₃ loading, well dispersed in the matrix. Above 10 wt.% of nano-BaTiO₃, scanning electronic microscopy and thermal analysis showed that agglomeration of nanoparticles occurs. Rheological and mechanical nanocomposites properties were evaluated and matrix occlusion behaviors were identified. In light of the specific behavior of the occluded polymer, the dielectric properties, especially dielectric loss are discussed.     

表面修饰纳米SiO2与聚丙烯共混制备聚丙烯/SiO2纳米复合材料

二氧化硅纳米粒子经表面修饰将丙烯酸酯键接到SiO2表面制备出丙烯酸酯修饰SiO2纳米粒子.丙烯酸酯修饰SiO2纳米粒子与聚丙烯(PP)熔融共混制备PP/SiO2纳米复合材料.研究了纳米粒子对复合材料力学性能的影响,并对纳米粒子增韧机理进行了研究.研究结果表明:复合材料冲击强度在SiO2含量为3.5 wt%时达到最大值,SiO2纳米粒子对聚丙烯基体材料有很好的增强增韧效果.     

A study of nanocrystalline NiFe2O4 in a silica matrix

The present work deals with the synthesis of nickel ferrite/SiO₂ nanocomposites, obtained by embedding nickel ferrite nanoparticles in a silica matrix, through sol-gel method based on hydrolysis and condensation of a silicon alkoxide and thermal treatment. Methods employed in characterization of the materials obtained at different ferrite concentration and at suitable thermal treatments were differential scanning calorimetry (DSC), X-ray diffraction (XRD), mid-infrared (IR) spectra and transmission electron microscopy (TEM). In purpose to evaluate magnetic properties of these nanocomposites, static magnetic measurements using vibrating sample magnetometer (VSM) were carried out.     

Nickel oxide/polypyrrole/silver nanocomposites with core/shell/shell structure: Synthesis,characterization and their electrochemical behaviour with antimicrobial activities

Magnetic and conducting Nickel oxide–polypyrrole (NiO/PPy) nanoparticles with core–shell structure were prepared in the presence of Nickel oxide (NiO) in aqueous solution containing sodium dodecyl benzenesulfonate (SDBS) as a surfactant as well as dopant. A stable dispersion of silver (Ag) nanoparticles was synthesized by chemical (citrate reduction) method. NiO/PPy nanocomposites were added to the Ag colloid under stirring. Ag nanoparticles could be electrostatically attracted on the surface of NiO/PPy nanocomposites, leading to formation of NiO/PPy/Ag nanocomposites with core/shell/shell structure. The morphology, structure, particle size and composition of the products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV) and current–voltage (I–V) analysis. The resultant nanocomposites have the good conductivity and excellent electrochemical and catalytic properties of PPy and Ag nanoparticles. Furthermore, the nanocomposites showed excellent antibacterial behaviour due to the presence of Ag nanoparticles in the composite. The thermal stability of NiO–PPy as well as NiO/PPy/Ag nanocomposites was higher than that of pristine PPy. Studies of IR spectra suggest that the increased thermal stability may be due to interactions between NiO and Ag nanoparticles with the PPy backbone.     

Preparation and characterization of TiO2–ZrO2 and thiol-acrylate resin nanocomposites with high refractive index via UV-induced crosslinking polymerization

Novel nanocomposites of TiO₂–ZrO₂ nanoparticles and thiol-acrylate resin, with high refractive index, high transparency, good thermal stability and mechanical properties were prepared via UV (Ultraviolet rays)-induced crosslinking polymerization. In this work, TiO₂ nanoparticles were synthesized, and its surface treatment was performed with ZrO₂ to depress the photocatalytic activity of TiO₂. No aggregation of TiO₂–ZrO₂ nanoparticles was found after mixing with photocrosslinkable materials and transparent coatings and blocks were obtained. Thiol-acrylate was used as an organic matrix with high refractive index and as a promoter of UV curing reaction. Transmission electronic microscopic studies (TEM) of nanocomposites showed that the TiO₂–ZrO₂ nanoparticles with a diameter 3–6 nm were dispersed in the organic matrix and maintained their original size before immobilization.     

热塑性聚氨酯弹性体的性质及应用

分析了所制备的4个系列的热塑性聚氨酯弹性体（TPUE）的性能。研究了硝化纤维素（NC）与TPUE共混物的力学性能和热分解性能。此外，还研究了TPUE对硝胺改性双基推进剂力学，工艺能量和燃烧性能的影响。结果表明，这些弹性体是应用于火药粘和剂系统的理想材料。     

Ultra high molecular weight polyethylene/graphene oxide nanocomposites: Thermal,mechanical and wettability characterisation

Numerous carbon nanostructures have been investigated in the last years due to their excellent mechanical properties. In this work, the effect of the addition of graphene oxide (GO) nanoparticles to UHMWPE and the optimal %wt GO addition were investigated. UHMWPE/GO nanocomposites with different GO wt% contents were prepared and their mechanical, thermal, structural and wettability properties were investigated and compared with virgin UHMWPE. The results showed that the thermal stability, oxidative resistance, mechanical properties and wettability properties of UHMWPE were enhanced due to the addition of GO. UHMWPE/GO materials prepared with up to 0.5 wt% GO exhibited improved characteristics compared to virgin UHMWPE and nanocomposites prepared with higher GO contents.     

Cryogenic properties of SiO2/epoxy nanocomposites

SiO₂/epoxy nanocomposites were prepared using diglycidyl ether of bisphenol-F (DGEBF) type epoxy and tetraethylorthosilicate (TEOS) via the sol-gel process. Silica nanoparticles were collected after burning off the matrix resin and the silica nanoparticles were observed using TEM. The cryogenic tensile properties at 77 K and thermal expansion coefficient of the nanocomposites were studied. The tensile properties at room temperature were also given to compare with the cryogenic tensile properties. The fracture surfaces were examined with scanning electron microscopy (SEM). The effects of silica nanoparticle content have been studied on the cryogenic tensile and thermal properties of the nanocomposites. In addition, the dependence of the glass transition temperature on the silica nanoparticle content has also been examined.     

Physical, chemical, and mechanical properties of nanostructured materials

Nanocrystalline materials have special physical, chemical, and mechanical properties. To a significant extent, these properties are attributed to a high density of grain boundaries and other defects in nanocrystalline compounds. We study the microstructure and mechanical properties of nanomaterials (Al, Al-alloys, Cu, Ni, Ti, and stainless steel) and nanocomposites (Al₂O₃/Ni-P) by the methods of transparent and scanning electron microscopy, X-ray diffraction analysis, and microhardness and tensile tests. The experimental methods include the procedures of measuring the electric and corrosion resistances. The materials are prepared by using contemporary methods, namely, by hydrostatic extrusion (nanometals) and by sintering ceramic powders covered with Ni-P nanoparticles under high pressure by using the procedure of nonelectric chemical metallization (Al₂O₃/Ni-P nanocomposites). Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 1, pp. 82–89, January–February, 2006.     

Ductile PLA nanocomposites with improved thermal stability

Polylactide (PLA) is used as a biomedical material because it is biodegradable, but the vast majority of biodegradable polymers in clinical use are composed of rather stiff materials that are unsuitable for use in numerous applications because they exhibit limited extendibility, weak mechanical strength, and poor thermal stability. We modified PLA with 2-methacryloyloxyethyl isocyanate (MOI) to prepare ductile PLA materials. By utilizing a novel sol–gel process, PLA nanocomposites were further prepared with improved mechanical properties and thermal stability. The 10% thermal decomposition temperature for PLA modified with 5% MOI and 5–10% silica was 21–32 °C higher than that of original pristine PLA. Elongation at break increased by 4–13 times when compared to neat PLA while the tensile strength was maintained at 30–40 MPa. These synthesized PLA nanocomposites can be applied as biomaterials with improved mechanical and thermal properties.