Improvement of photo-stability of LLDPE-based nanocomposites

LLDPE-based nanocomposites undergo faster photo-oxidation than the unfilled matrix and the extent of their physical properties deterioration, namely elongation at break and tensile strength, is dependent on the organo-nanoclay loading. The observed acceleration is not due to faster photo-oxidation but rather due to a reduction of the oxidation induction time. The presence in the organoclays of trace amounts of metal ions may be promoting catalytic photodegradation. While UV absorbers provide useful protection, use of a metal deactivator has been found to greatly enhance the photo-stability of the LLDPE-based nanocomposites. Combinations of a metal deactivator and UV absorber yield synergistic effects.     

Influence of organo-clay on electrical and mechanical properties of PP/MWCNT/OC nanocomposites

The electrical, thermal and mechanical properties of nanocomposites, based on polypropylene (PP) filled by multi-walled carbon nanotubes (MWCNTs) and organo-clay (OC), were studied with the purpose of finding out the effect of OC on the microstructure of MWCNTs dispersion and PP/MWCNT/OC composites. It was found that addition of organo-clay nanoparticles improved nanotube dispersion and enhanced electrical properties of PP/MWCNT nanocomposites. Addition of organo-clay (MWCNT/OC ratio was 1/1) reduced the percolation threshold of PP/MWCNT nanocomposites from ?_c = 0.95 vol.% to ?_c = 0.68 vol.% of carbon nanotubes, while the level of conductivity became 2–4 orders of magnitude higher. The DSC and DMA analyses have shown that the influence of organo-clay on the thermal and mechanical properties of material was not significant in composites with both fillers as compared to PP/OC. Such an effect can be caused by stronger interaction of OC with carbon nanotubes than with polymer matrix.     

Transesterification catalysts to improve clay exfoliation in synthetic biodegradable polyester nanocomposites

We report here on the melt intercalation preparation of polymer/clay nanocomposites based on three commercial synthetic biodegradable polyesters: EastarBio Ultra, Ecoflex, and Bionolle, respectively. The montmorillonite clay addition is performed either by direct dispersion of Cloisite 30B in the polyester matrix or by dispersing a “PCL-grafted Cloisite 30B” masterbatch in the biodegradable polyesters. All obtained nanocomposites display an intercalated morphology as attested by X-ray diffraction measurements. The various analyses clearly show that the Bionolle (BIO) matrix gives the best results. Morphological characterization and mechanical properties of these nanocomposites also show that the “masterbatch route” leads to poor results as a consequence of the very low compatibility between the poly(ε-caprolactone) (PCL) of the masterbatch and the three other polyester matrices. In a second part, nanocomposites based on the BIO matrix are prepared by direct dispersion of the organo-clay in the presence of three different metal-based catalysts with the aim to promote transesterification reactions between the nanocomposite constituents. The mechanical properties and morphological characterization of these nanocomposites show that the tin-based catalyst (Sn) is the more efficient. Indeed, the effectiveness of transesterification reactions taking place between the ester functions of the BIO matrix and the hydroxyl groups of the organo-clay and the resulting “grafting” of BIO chains on the organo-clay surface are confirmed by thermogravimetric analyses performed after the extraction procedure. TEM observations show that this catalyst enhances the clay platelets exfoliation within the BIO matrix as a consequence of the transesterification reactions. Nanocomposites prepared in presence of Sn show better clay dispersion and enhanced stiffness with a 60% increase in Young’s modulus.     

Effect of functionalized graphene on the physical properties of linear low density polyethylene nanocomposites

Dodecyl amine-modified graphene (DA-G)/linear low density polyethylene (LLDPE) nanocomposites were prepared through solution mixing. Field emission scanning electron microscopy analysis revealed homogeneous dispersions of graphene layers in the nanocomposites. X-ray diffraction analysis showed that the average crystallite size of the nanocomposites was increased. However, the % crystallinity was found to decrease due to the formation of a random interface. Dynamic mechanical analysis showed that the storage moduli of the nanocomposites were much higher than that of neat LLDPE. The nanocomposites were also more thermally stable than neat LLDPE. Isothermal thermogravimetry showed that homogeneously distributed graphene could act as a good inhibitor during thermal degradation of the nanocomposites. Differential scanning calorimetry showed that the crystallization temperature of the nanocomposites increased with increasing DA-G content. Thermomechanical analysis showed that the dimensional stability of the nanocomposites was significantly increased by the addition of the DA-G. The coefficients of thermal expansion decreased with increasing DA-G content. The oxygen and nitrogen permeability of the nanocomposites was lower than that of neat LLDPE.     

Metal nanoparticle-conjugated polymer nanocomposites

Recent literature describing nanocomposites of metal nanoparticles and conjugated polymers and oligomers are reviewed. Preparation of these nanocomposites by chemical and electrochemical methods are described, and the electronic and optical properties of these materials are discussed. Some initial applications that have been investigated for such nanocomposites are covered.     

Versatile nanocomposites in phosphoproteomics: A review

Protein phosphorylation is one of the most important post-translational modifications. Phosphorylated peptides are present in low abundance in blood serum but play a vital role in regulatory mechanisms and may serve as casual factors in diseases. The enrichment and analysis of phosphorylated peptides directly from human serum and mapping the phosphorylation sites is a challenging task. Versatile nanocomposites of different materials have been synthesized using simple but efficient methodologies for their enrichment. The nanocomposites include magnetic, coated, embedded as well as chemically derivatized materials. Different base materials such as polymers, carbon based and metal oxides are used. The comparison of nanocomposites with respective nanoparticles provides sufficient facts about their efficiency in terms of loading capacity and capture efficiency. The cost for preparing them is low and they hold great promise to be used as chromatographic materials for phosphopeptide enrichment. This review gives an overview of different nanocomposites in phosphoproteomics, discussing the improved efficiency than the individual counterparts and highlighting their significance in phosphopeptide enrichment.     

Linear low‐density polyethylene nanocomposites by in situ polymerization using a zirconium‐nickel tandem catalyst system

A series of linear low‐density polyethylene (LLDPE) nanocomposites containing different types of nanofiller (TiO₂, MWCNT, expanded graphite, and boehmite) were prepared by in situ polymerization using a tandem catalyst system composed of {Tp^Ms}NiCl ( 1 ) and Cp₂ZrCl₂ ( 2 ), and analyzed by differential scanning calorimetry, dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). Based on these analyses, the filler content varied from 1.30 to 1.80 wt %. The melting temperatures and degree of crystallinity of the LLDPE nanocomposites were comparable to those of neat LLDPE. The presence of MWCNT as well as boehmite nucleated the LLDPE crystallization, as indicated by the increased crystallization temperature. The DMA results showed that the presence of TiO₂, EG, and CAM 9080 in the LLDPE matrix yielded nanocomposites with relatively inferior mechanical properties compared to neat LLDPE, suggesting heterogeneous distribution of these nanofillers into the polymer matrix and/or the formation of nanoparticle aggregates, which was confirmed by TEM. However, substantial improvement in the storage modulus was achieved by increasing the sonication time. The highest storage modulus was obtained using MWCNT (1.30 wt %). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3506–3512     

Effect of compatibilizer and Irganox MD 1024 on the thermo-oxidative stability of PP/PP-g-MA/OMMT nanocomposites

The thermo-oxidative stability of polymeric materials reinforced with mineral fillers, such as clays, may be lower than that of pristine polymers, due to the presence of metallic ions and compatibilizing agents. In this paper, an effort was made to understand the influence that a compatibilizing agent and a metal deactivator bonded to a primary stabilizer has on the thermal stability of polypropylene/polypropylene-grafted maleic anhydride/organic montmorillonite (PP/PP-g-MA/OMMT) nanocomposites. At the first stage of this work, the organically modified montmorillonite clay is chemically analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry to quantify the metals present in the clay. TGA, DSC, OIT, and dynamic OIT were used to assess the degradation of the nanocomposites. The results showed that the use of compatibilizing agents has a positive effect on the stability of nanocomposites in the initial steps of degradation, but has a degradative effect at higher temperatures, as indicated by the decreasing T_max for compatibilized nanocomposites. In relation to Irganox MD 1024, an increase in all the parameters for assessing the stability of nanocomposites was observed; however, the most significant change was the delay in the temperature at which the occurrence of exothermal reactions begins. Use of this additive is responsible for delaying the beginning of the exothermic reaction until a higher temperature, as a function of its concentration, as well the differences between the beginning of volatile release and the exothermal reactions. Also was discussed the influence of Irganox MD1024 concentration on T_max, and the difference of temperature between the beginning of heat releasing and the initial weight loss, which decreases as the stabilizer concentration is increased. Thanks to the association of dynamic OIT and TGA results from experiments performed with identical conditions. This complementary use of these techniques is a powerful tool for assessing the stability in the polymeric system.     

Photo‐induced surface transformations of silica nanocomposites

The photo‐induced, physicochemical surface transformations to silica nanoparticle (SiNP) ‐ epoxy composites have been investigated. The silica nanocomposites (SiNCs) were prepared using a two‐part epoxy system with a 10% mass fraction of SiNPs and exposed to varying doses of high intensity, ultraviolet (UV) radiation at wavelengths representative of the solar spectrum at sea level (290 nm to 400 nm) under constant temperature and humidity. Visibly apparent physical modifications to the SiNC surface were imaged with scanning electron microscopy. Surface pitting and cracking became more apparent with increased UV exposure. Elemental and surface chemical characterization of the SiNCs was accomplished through X‐ray energy dispersive spectroscopy and X‐ray photoelectron spectroscopy, while attenuated total reflectance Fourier transform infrared spectroscopy revealed changes to the epoxy's structure. During short UV exposures, there was an increase in the epoxy's overall oxidation, which was accompanied by a slight rise in the silicon and oxygen components and a decrease in overall carbon content. The initial carbon components (e.g. aliphatic, aromatic and alcohol/ether functionalities) decreased and more highly oxidized functional groups increased until sufficiently long exposures at which point the surface composition became nearly constant. At long exposure times, the SiNC's silicon concentration increased to form a surface layer composed of approximately 75% silica (by mass). Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

UV‐curing synthesis of sulfonated polyaniline‐silver nanocomposites by an in situ reduction method

Sulfonated polyaniline‐silver (SPAni‐Ag) hybrid nanocomposites have been synthesized by the in situ reduction using a UV‐curing polymerization method without using any reducing or binding agent. An aqueous solution of aniline and orthoanilinic acid (OA) comonomers, a free‐radical oxidant and silver metal salts were irradiated by UV rays. Reduction of the silver salt in aqueous aniline and OA leads to the formation of silver particles which in turn catalyze the oxidation of comonomers to sulfonated polyaniline (SPAni). The resultant SPAni‐Ag nanocomposites were characterized by using different spectroscopy analyses like UV–visible (UV–Vis), X‐ray diffraction (XRD) and infrared spectroscopy. The absorption bands were revealed to be optically active and the peaks blue‐shifted due to the presence of metallic silver within the SPAni matrix. The XRD patterns displayed both the broad amorphous polymeric and sharp metallic peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposites showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the nanocomposites had a better thermal stability than the bulk SPAni. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of core‐shell silver–polyaniline nanocomposites by gamma radiolysis method

Core‐shell silver (Ag)–polyaniline (PAni) nanocomposites have been synthesized by the in‐situ gamma radiation‐induced chemical polymerization method. Aqueous solution of aniline, a free‐radical oxidant, and/or silver metal salt were irradiated by γ‐rays. Reduction of the silver salt in aqueous aniline leads to the formation of silver nanoparticles which in turn catalyze oxidation of aniline to polyaniline. The resultant Ag‐PAni nanocomposites were characterized by using different spectroscopy analyses like X‐ray photoelectron, UV–visible, and infrared spectroscopy. The optical absorption bands revealed that the bands at about 400 nm are due to the presence of nanosilver and the blue‐shifted peak at ～ 555 nm is due to the presence of metallic silver within the PAni matrix. X‐ray diffraction pattern clearly indicates the broad amorphous polymer and the sharp metal peaks. Scanning electron microscopy and transmission electron microscopy of the nanocomposite showed a uniform size distribution with spherical and granular morphology. Thermogravimetric analysis revealed that the composites have a higher degradation temperature than polyaniline alone. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5741–5747, 2007     

Natural photo-aging degradation of polypropylene nanocomposites

The natural photo-aging degradation of polypropylene (PP), PP/CaCO₃ and PP/SiO₂ nanocomposites were studied outdoor for up to 88 days. The chemical structure characterized by Fourier transform infrared spectroscopy (FTIR) and pyrolysis gas chromatography-mass spectroscopy (PGC-MS) showed that PP nanocomposites are much more susceptible to photo-degradation than unfilled PP. And the oxidation rate is faster with more filler amount. There are lots of chain scissions happened in PP nanocomposites, accompanied with the formation of ketone, alcohol, ester and unsaturated double bond. This severe chain scission led to great decrease of M_n and M_w, and the consequent small fragments would re-crystallize and increase the crystallinity of the nanocomposites. However, these effects do not relate to the ultraviolet character of the two nano fillers.     

Light-responsive nanocomposites combining graphene oxide with POSS based on host-guest chemistry

A facile methodology has been proposed to construct lightresponsive nanocomposites composed of GO and POSS based on host-guest inclusion of CD/Azo. Through manipulating photo-irradiation conditions, GO and POSS moieties in GO-POSS exhibited impressive and reversible supramolecular assembly/disassembly behaviors and had remarkable effect on oxygen barrier property of PVA-coated films, which would have potential application for smart gas barrier materials in packaging.     

Preparation of gold-, gold/silver-dendrimer nanocomposites in the presence of benzoin in ethanol by UV irradiation

Gold- and gold/silver-dendrimer nanocomposites have been synthesized by UV irradiation of their salts dissolved in ethanol containing dendrimers. As dendrimers, poly(amidomaine) PAMAM dendrimers and poly(propyleneimine) PPI dendrimers of various generations were used. The photoreduction of their salts is greatly accelerated by using benzoin as a photoinitiator. The sizes of gold in the nanocomposites are affected by the concentration of benzoin as well as the concentration of dendrimers, but are hardly changed with the kind of dendrimers. For gold/silver-dendrimer nanocomposites, the absorption spectra of gold/silver nanoparticles in the nanocomposites are very similar to the theoretical spectra of gold/silver alloy nanoparticles, suggesting the formation of gold/silver alloy nanoparticles. From the comparison of TEM and DLS measurements, it is found that the metal-dendrimer nanocomposites consist of metal nanoparticles covering by dendrimer molecules.     

负载卤化镍(NiX2/HD)催化MMA的原子转移自由基聚合

以负载卤化镍(NiX2/HD)为催化剂合成聚甲基丙烯酸甲酯(PMMA),具有反应可控、后处理简单且催化剂可以反复使用的优点。研究结果表明:卤原子、催化剂、钝化剂的类型和含量、反应温度等条件对该体系的聚合速率及可控性有重要影响。在相同条件下,NiCl2较NiBr2的催化速率快;钝化剂卤化铜/三-(N,N-二甲基氨基乙基)胺(CuX2/Me6TREN)对聚合产物分子量分布的可控性要优于卤化铁/三-(N,N-二甲基氨基乙基)胺(FeX3/Me6TREN);增大钝化剂的含量,聚合速率降低,且含量为1%时聚合的可控性较好;温度升高聚合速率加快,分子量分布指数(PDI)增大。顺磁共振检测中观察到钝化剂中过渡金属的化合价发生改变。     

Preparation of Isotactic Polypropylene/Organoclay Nanocomposites by Solution Mixing Methodology: Structure and Properties Relationships

Isotactic Polypropylene (iPP) based nanocomposites filled with organo-clay nanoparticles were prepared and the relationships between their structure and properties were investigated. Modified C₁₆-C₁₈ smectite clay nanoparticles were used in order to promote matrix/filler compatibilization and to improve interfacial adhesion. X-Ray analysis performed on the nanocomposites demonstrated that at low organo-clay content (1 and 3% by weight) a nanostructure has been obtained, while in presence of 5% by weight of organoclay cluster regions have been formed. Mechanical tests showed that the elastic modulus increases of about 20% compared to the neat polymeric matrix value when 1 and 3% of nanofiller is added.     

Polyethylene thermal oxidative stabilisation in carbon nanotubes based nanocomposites

Multiwall carbon nanotubes (MWNT)/linear low density polyethylene (LLDPE) nanocomposites were studied in order to understand the stabilisation mechanism for their thermal and oxidative degradation. Thermogravimetry coupled with infrared evolved gas analysis and pyrolysis gas chromatography-mass spectrometry demonstrate that MWNT presence slightly delays thermal volatilisation (15-20 °C) without modification of thermal degradation mechanism. Whereas thermal oxidative degradation in air is delayed by about 100 °C independently from MWNT concentration in the range used here (0.5-3.0 wt.%). The stabilisation is due to formation of a thin protective film of MWNT/carbon char composite generated on the surface of the nanocomposites is shown by SEM and ATR FTIR of degradation residues. The film formation mechanism is discussed.     

Preparation and characterization of metal-chitosan nanocomposites

Various metal-chitosan nanocomposites were synthesized, including silver (Ag), gold (Au), platinum (Pt), and palladium (Pd) in aqueous solutions. Metal nanoparticles were formed by reduction of corresponding metal salts with NaBH4 in the presence of chitosan. And chitosan molecules adsorbing onto the surface of as-prepared metal nanoparticles formed the corresponding metal-chitosan nanocomposites. Transmission electron microscopy (TEM) images and UV-vis spectra of the nanocomposites revealed the presence of metal nanoparticles. Comparison of all the resulting particles size, it shows that silver nanoparticles are much larger than others (Au, Pt and Pd). In addition, the difference in particles size leads to develop different morphologies in the films cast from prepared metal-chitosan nanocomposites. Polarized optical microscopy (POM) images show a batonet-like structure for Ag-chitosan nanocomposites film, while for the films cast from other metal (Au, Pt, and Pd)-chitosan nanocomposites, some branched-like structures with a few differences among them were observed under POM observation.     

Preparation and characterization of poly(vinyl alcohol)/organo-modified cloisite Na+ with chiral L-leucine amino acid/TiO2 nanocomposites

Poly(vinyl alcohol)/organo-clay/TiO₂ nanocamposites films were prepared with 10 wt % of organo-nanoclay and various amount of TiO₂ nanoparticles. Cloisite Na⁺ has been modified via cation exchange reaction using ammonium salt of natural L-leucine amino acid as a cationic surfactant. After that poly(vinyl alcohol)/organo-nanoclay/TiO₂ nanocomposites were synthesized by dispersion of TiO₂ on the surfaces of organo-nanoclay in poly(vinyl alcohol) matrix by using ultrasonic energy. Three nanocomposites with different loading of TiO₂ were prepared and characterized by X-ray diffraction, fourier transform infrared spectroscopy, field emission type scanning electron microscope, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and ultraviolet-visible transmission spectra. The results showed that the organo-nanoclay and TiO₂ were dispersed homogeneously in poly(vinyl alcohol) matrix and also showed improvement in their thermal properties compared with the pure poly(vinyl alcohol).     

Catalytic fire retardant nanocomposites

In this paper the chemical activity of carbon nanotubes and polyhedral oligomeric silsesquioxane during thermal degradation and combustion of polymer nanocomposites is addressed. Indeed, polymer-nanofiller systems may exhibit chemical effects capable of thermal stabilisation of polymers as well as reduction of combustion rate and heat released, owing to catalytic effects induced by the nanofillers at high temperature.Carbon nanotubes in the presence of oxygen are shown to promote oxidative dehydrogenation in polyethylene with production of a stable surface layer of carbon char that provides an effective oxygen barrier effect. A similar action is performed by metal-containing polysilsesquioxanes dispersed in polypropylene.With either carbon nanotubes or metal POSS, partial carbonisation of the polymer matrix occurs during combustion, subtracting part of the organic polymer from combustion, targeting one of the major fire retardancy aim.