Polylactide/graphite nanosheets/MWCNTs nanocomposites with enhanced mechanical, thermal and electrical properties

In this study, we have prepared a series of novel biodegradable polymer [polylactide (PLA)]-based nanocomposites using graphite nanosheets (GNs) and multi-walled carbon nanotubes (MWCNTs) by solution-blending technique and investigated their morphologies, structures, thermal stabilities, mechanical and dielectric properties, and electrical and thermal conductivities. Before preparation of the PLA/GNs/MWCNTs nanocomposites, the raw GNs used were endured a rapid expansion by thermal treatment. Temperature of this treatment had some obvious impacts on morphological changes of graphite nanosheets which were verified by means of scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. Resultant nanocomposites were characterized and evaluated by means of SEM, XRD, thermal conductivity measurements, tensile and impact tests, thermogravimetric analysis and dielectric measurements. Results obtained in this study indicated that thermal-expanded GNs in the presence of MWCNTs facilitate the formation of an appropriate conductive network in PLA matrix which resulted in a relatively low percolation threshold for thermal and electrical conductions of PLA/GNs/MWCNTs nanocomposites. Significant improvements in thermal and electrical conductivities, thermal stability and mechanical properties of PLA/GNs/MWCNTs nanocomposites obtained through the presence of both nanoparticles in PLA matrix were associated with their good co-dispersion and co-reinforcement effects. The macroscopic properties of nanocomposites were found to be strongly dependent on their components, concentrations, dispersion, and the resulted morphological structures.     

Flame retardant performance of a modified aluminum trihydroxide with increased thermal stability

A modified form of aluminum trihydroxide has been synthesized that is thermally stable to approximately 350°C. Flame retardant and smoke generation performance in low melting temperature thermoplastics, such as polyvinyl chloride, polypropylene, and ethylene vinylacetate, are comparable to unmodified ATH. The increased thermal stability also allows this material to be used in thermoplastics with higher melting temperatures, such as polycarbonate, polybutylene terephthalate, and polyphenylene oxide, where ATH cannot be used.     

过渡金属氧化物对苯并恶嗪热稳定性影响研究

将过渡金属氧化物TiO2、MnO2、CuO、Cu2O、ZnO、ZrO2以及Y2O3、CeO2、Sm2O3、Gd2O3分别添加到苯酚/4,4'-二苯甲烷二胺型苯并恶嗪(BB)中间体中,制备了过渡金属氧化物/BB固化物,通过FTIR、TGA和DMA分析研究了过渡金属氧化物对苯并恶嗪热稳定性的影响。结果表明,这些氧化物的添加不改变BB固化物的化学结构;除ZnO外,其他氧化物均使BB的热稳定性和800℃残炭率降低,这是由于过渡金属氧化物与BB中N原子间配位作用的形成削弱了C—N键,使其更易断裂。     

An investigation into the thermal stability of PVC/montmorillonite composites

An effective stabilizing system for poly (vinyl chloride) (PVC)/clay composites was established. Different types of stabilizers, i.e., organotin, calcium/zinc, barium/zinc, and an epoxy costabilizer, were investigated. The combination of the organotin stabilizer and the epoxy costabilizer was the most effective stabilizing system. Different grades of Cloisite nanoclays were investigated. Cloisite Na did not cause premature degradation of PVC. Cloisite 10A strongly accelerated the degradation of PVC because of the presence of excess surfactant, while a PVC/Cloisite 30B system showed much better thermal stability because there was less organic impurity in the Cloisite 30B. Phosphonium‐modified clays were also prepared. They showed better thermal stability than ammonium‐modified clays, but the drying conditions still need to be optimized in order to produce a dispersible clay powder. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Physical,mechanical, and thermal properties of micronized organo‐montmorillonite suspension modified wood flour/poly(lactic acid) composites

In this study, micronized organo‐montmorillonite (OMMT) suspension was prepared with sodium‐montmorillonite (Na‐MMT), didecyl dimethyl ammonium chloride, and dispersant polyethylene glycol 1000 by a ball‐milling process. Then, wood flours (WFs) were impregnated with prepared OMMT suspension at a concentration of 0.5, 1.0, 2.0, or 4.0%. WFs were characterized by X‐ray diffraction and scanning electron microscopy. The hygroscopicity of WF was investigated by a vapor adsorption method. WFs were, respectively, blended with poly (lactic acid) (PLA) to produce WF/PLA composites. Thereafter, physical, mechanical, and thermal properties of the composites were tested. The results showed that a great amount of OMMT attached on the surface of WF, partly penetrating into the microstructure of WF. Owing to the hydrophobicity of OMMT, the vapor adsorption of OMMT‐modified WF decreased. The composite which was produced by WF treated with 0.5% OMMT suspension, showing an increment in the physical, mechanical, and thermal properties. However, OMMT should not be overloaded. Otherwise, the accumulation of OMMT might cause poor interfacial adhesion between WF and PLA matrix. POLYM. COMPOS., 36:731–738, 2015. © 2014 Society of Plastics Engineers     

Morphology,thermal, and mechanical properties of flame‐retardant silicone rubber/montmorillonite nanocomposites

Flame‐retardant methyl vinyl silicone rubber (MVMQ)/montmorillonite nanocomposites were prepared by solution intercalation method, using magnesium hydroxide (MH) and red phosphorus (RP) as synergistic flame‐retardant additives, and aero silica (SiO₂) as synergistic reinforcement filler. The morphologies of the flame‐retardant MVMQ/montmorillonite nanocomposites were characterized by environmental scanning electron microscopy (ESEM), and the interlayer spacings were determined by small‐angle X‐ray scattering (SAXS). In addition to mechanical measurements and limited oxygen index (LOI) test, thermal properties were tested by thermogravimetric analysis (TGA). The decomposition temperature of the nanocomposite that contained 1 wt % montmorillonite can be higher (129°C) than that of MVMQ as basal polymer matrix when 5% weight loss was selected as measuring point. This kind of silicone rubber nanocomposite is a promising flame‐retardant polymeric material. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3275–3280, 2006     

Development of high‐performance epoxy/clay nanocomposites by incorporating novel phosphonium modified montmorillonite

Novel organoclays were synthesized by several kinds of phosphonium cations to improve the dispersibility in matrix resin of composites and accelerate the curing of matrix resin. The possibility of the application for epoxy/clay nanocomposites and the thermal, mechanical, and adhesive properties were investigated. Furthermore, the structures and morphologies of the epoxy/clay nanocomposites were evaluated by transmission electron microscopy. Consequently, the corporation of organoclays with different types of phosphonium cations into the epoxy matrix led to different morphologies of the organoclay particles, and then the distribution changes of silicate layers in the epoxy resin influenced the physical properties of the nanocomposites. When high‐reactive phosphonium cations with epoxy groups were adopted, the clay particles were well exfoliated and dispersed. The epoxy/clay nanocomposite realized the high glass‐transition temperature (T_g) and low coefficient of thermal expansion (CTE) in comparison with those of neat epoxy resin. On the other hand, in the case of low‐reactive phoshonium cations, the dispersion states of clay particles were intercalated but not exfoliated. The intercalated clay did not influence the T_g and CTE of the nanocomposite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of oligomeric‐modified montmorillonite on morphology and properties of polycarbonate/montmorillonite nanocomposites

Low‐molecular‐weight copolymers of styrene and vinylbenzyl ammonium salts (oligomeric surfactant) were used to modify montmorillonite (MMT). The oligomeric‐modified MMT showed good thermal stability, which made it suitable to be used for preparing polycarbonate(PC)/MMT nanocomposites at high temperature. A different series of PC/MMT nanocomposites had been prepared by melt processing using a twin screw extruder. The effect of oligomeric surfactant structure and clay loading on the morphology, mechanical property, thermal stability, and color appearance of the nanocomposites were explored. The results of X‐ray diffraction and transmission electron microscopy analyses indicated that the PC/MMT nanocomposites had partially exfoliated structures. The PC/MMT nanocomposites were found to retain light colored, which was important for optical application. Compared to neat PC, the nanocomposites showed better properties of thermal stability and heat insulation. The mechanical properties of the nanocomposites are significantly enhanced by incorporating clay into the PC matrix. The tensile strength of nanocomposites with 2 wt% clay content was up to 55 MPa, which was much higher than that of the neat PC (37 MPa). The maximum tensile modulus value was 19% higher than that of neat PC. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Electrocatalysis and detection of nitrite on a polyaniline‐Cu nanocomposite‐modified glassy carbon electrode

A polyaniline (PANI)‐Cu nanocomposite‐modified electrode was fabricated by the electrochemical polymerization of aniline and the electrodeposition of copper under constant potentials on a glassy carbon electrode (GCE), respectively. Scanning electron microscope result shows that the PANI‐Cu composite on the surface of the GCE displays the nanofibers having an average diameter of about 80 nm with lengths varying from 1.1 to 1.2 μm. The electrode exhibits enhanced electrocatalytic behavior to the reduction of nitrite compared to the PANI‐modified GCE. The effects of applied potential, pH value of the detection solution, electropolymerization charge, temperature, and nitrite concentration on the current response of the composite‐modified GCE were investigated and discussed. Under optimal conditions, the PANI‐Cu composite‐modified GCE can be used to determine nitrite concentration in a wide linear range (n = 18) of 0.049 and 70.0 μM and a limit of detection of 0.025 μM. The sensitivity of the electrode was 0.312 μA μM^?1 cm^?2. The PANI‐Cu composite‐modified GCE had the good storage stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

FT-IR spectroscopic studies of metal nitrates supported on a modified montmorillonite clay

Diffuse reflectance FT-IR spectra of transition metal nitrates on a modified montmorillonite clay show strong absorptions due to the presence of NO⁺ and NO^– ions. An attempt has been made to explain the mechanism of activation of the metal nitrates by the clay.     

Preparation and characterization of phosphonium montmorillonite with enhanced thermal stability

Quaternary phosphonium cations (hexadecyl tributyphosphonium; tetradecyl tributylphosphonium; tetraphenylphosphonium; methyl triphenylphosphonium; ethyl triphenylphosphonium and propyl triphenylphosphonium) were intercalated into montmorillonite (MMT) rich bentonite of Indian origin, by ion exchange reaction. The phosphonium MMT were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction analysis (PXRD), particle size distribution (PSD) and thermogravimetric analysis (TGA). The phosphonium cations significantly influenced the particle size distribution. With longer alkyl chain finer particles were formed. The tetrabutylphosphonium and tetraphenylphosphonium MMT showed enhanced thermal stability (300–400 °C) and may be potentially useful materials for melt processing of polymer/layered silicates nanocomposites.     

Improvement in voltage,thermal, mechanical stability and ion transport properties in polymer‐clay nanocomposites

We report novel results on optimization of intercalated polymer‐clay nanocomposite endowed with desirable properties like, (i) very high ionic conductivity (～ 10^?3 S cm^?1) at room temperature, (ii) substantial improvement in voltage stability (～ 5.6 V), mechanical stability (25 MPa), and thermal stability (250°C) (iii) t_ion ～ 99% and cation transport number (t_Li+) ～ 67%: Intercalation of polymer salt (PAN)₈LiCF₃SO₃ complex into dodecylamine modified montmorillonite clay (DMMT) nanometric channels has been confirmed by X‐ray diffraction and Transmission electron microscopy analysis. Complex impedance spectroscopy suggests bulk electrical conduction in the high frequency region and electrode polarization effect at the low frequencies. The experimental value of conductivity, voltage, and mechanical stability is observed to be invariably higher in polymer nanocomposite film when compared with clay free polymer‐salt complex film. The same is true for cation transport. The optimized polymer film serves dual purpose of electrolyte and separator in energy storage devices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thiocarbohydrazide‐modified chitosan as anticorrosion and metal ion adsorbent

To explore the application of chitosan (CS) derivatives in anticorrosion and adsorption, thiocarbohydrazide‐modified chitosan (TCHECS) derivative was synthesized and characterized. The preliminary electrochemical measurements of the behaviors of 304 steel and Cu sheets in 2% HAc (v/v) containing TCHECS, chitosan (CS), and hydrazine cross‐linked epoxy‐N‐phthaloylchitosan (HECS) had been performed. The short‐term electrochemical tests show that the new compound can act as a mixed‐type metal anticorrosion inhibitor; its inhibition efficiency is 88% when the concentration was 30 mg/L. The preliminary adsorption studies for sorbents TCHECS and HECS on a metal ion mixture aqueous solution were also performed. The results show that TCHECS can absorb As (V), Ni (II), Cu (II), Cd (II), and Pb (II) efficiently at pH 9; the removal of the As (V), Ni (II), Cu (II), Cd (II), and Pb (II) are around 55.6–99.9%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40671.     

Preparation and characterization of PVC/montmorillonite nanocomposites—A review

This article presents an overview of the preparation and characterization of poly(vinyl chloride)/montmorillonite (PVC/MMT) nanocomposites. Different methods of PVC/MMT nanocomposite preparation are discussed. The incorporation of MMT into the PVC matrix results in an increase of thermal stability and induces changes in the mechanical properties. However, the properties of PVC/MMT nanocomposites depend strongly on the MMT organic modification procedure that governs the extent of MMT penetration by PVC macrochains and plays an important role with regard to the morphology formation. Flammability as well as other properties—barrier, optical, etc.—of PVC/MMT nanomaterials are also described. Finally, a future outlook is given. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Enhanced mechanical and thermal properties of polyimide/organically modified montmorillonite hybrid film based on stable poly(amic acid) ammonium salt

In this study, polyimide/organically modified montmorillonite (PI/OMMT) hybrid film was prepared by in situ polymerization from the stable poly(amic acid) ammonium salt/OMMT (PAAS/OMMT) precursor hybrid. PAAS was obtained by incorporating calculated triethylamine into terpolymer poly(amic acid) (PAA), which was synthesized by pyromellitic dianhydride (PMDA), 4,4′‐oxydianiline and p‐phenylenediamine in dimethylacetamide (DMAc). OMMT as a type of layered clays was prepared through surface treatment of montmorillonite (MMT) with 1‐hexadecylamine. Mechanical property measurements of PI/OMMT hybrid film indicated that the addition of 5 wt% of OMMT increased the Young's modulus of PI film up to 11.24 GPa, which is 58% higher than the pristine PI film from PAAS. Besides, the tensile strength increased to 168.36 MPa, which was higher than that of PI film derived from PAA (164.3 MPa) and PI film derived from PAAS (145.2 MPa). Moreover, the thermal stabilities of PI/OMMT hybrid film with appropriate OMMT content were also better than those of original PI films. POLYM. COMPOS., 34:2076–2081, 2013. © 2013 Society of Plastics Engineers     

Polylactide (PLA)—a new way of production

Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent properties for different polymer applications, has been used mostly in the biomedical field, mainly because of its high price, resulting from expensive polymerization and purification techniques. Although this polymer can play a major role in future markets for biodegradable polymers, the current high price has to be reduced significantly to at least $4 US/kg. Therefore, this paper aims to partially review the polymerization techniques traditionally used in PLA synthesis and to propose new developments that enable us to produce these polymers by an innovative process for just a portion of the costs traditionally charged, using reactive extrusion techniques in a closely intermeshing co-rotating twin screw extruder. This paper gives an overview of attainable mechanical properties and future markets.     

The formation and hydrolytic stability of metal ion— polyacid gels

A wide range of metal oxide—polyacid cements have been studied to determine the influence that the nature of the cation and polymer structure have on their formation and water stability. The formation of water-stable products depends markedly upon the type of oxide and polyacid employed and some typical examples of rapid-setting ionomer cements with varying degrees of water resistance have been listed. Poly(ethylenesulphonic acid) has been found to be a poor cement former compared to polycarboxylic acids. The stability in water of these systems appears to be dependent on a number of factors, including the nature of the metal ion—polyanion bonding, the size of the cation and the presence of other potential ligands on the polymer. To aid a fuller understanding of the influence of the cation—polyanion bonds on the properties of cements made from CaO and CdO with poly(acrylic acid) or ethylene-maleic acid copolymer, stability constants for Ca²⁺ and Cd²⁺ with these polyacids have been determined. Cd²⁺ is bound much more strongly than Ca²⁺ to the macroanions of these polyacids and poly(acrylic acid) appears to be a more effective cation binder than ethylene—maleic acid copolymer.     

Studies on morphologies and thermal properties of poly(lactic acid)/polycaprolactone/organic‐modified montmorillonite nanocomposites

Poly(lactic acid)/organic montmorillonite (PLA/OMMT) nanocomposites were prepared via twin‐screw extrusion. Montmorillonite (MMT) was firstly organically modified to improve the compatibility between polyester and MMT. The effects of ratio between PLA and OMMT and the addition of polycaprolactone (PCL), as a compatilizer, on the properties of PLA/OMMT nanocomposites were studied. The morphology and the properties of the nanocomposites were characterized by XRD, DSC, and TEM. Using OMMT, the intercalated structure was formed during the extrusion process and the OMMT interlayers space was enlarged. More OMMT content was apt to form thicker structure with more stacked individual silicate layers, which led to lower degree of crystallinity of PLA. It showed that 1 phr OMMT could result in the largest interlayers space and the best crystallization state. PCL can effectively increase the binding force between two phases and improve the order of the nanocomposites. In addition, the annealing after treatment can form regular structure and enhance the thermal properties of nanocomposites. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Study of the effects of multi‐walled carbon nanotubes on mechanical performance and thermal stability of polypropylene

Carbon nanotubes (CNTs) have been added to polypropylene (PP) matrix to improve the overall performance of composites. The mixing process has been carried out by melt compounding using a twin screw co‐rotating extruder with different CNTs amounts in the 0.5–10 wt% from a concentrated PP‐CNTs masterbatch (20 wt% CNTs). Results show a remarkable increase in tensile strength and elastic modulus while a decrease in elongation at break is detected. With regard to thermal behavior, a remarkable increase in thermal stability at high temperatures (decomposition process studied by thermogravimetric analysis) is obtained as the CNTs amount increases. In addition to this improvement, a noticeable increase in thermal stability at medium temperatures (degradation onset determined by differential scanning calorimetry, DSC) is also observed. In a similar way, other property related to thermal and mechanical performance, such as Vicat softening temperature (VST) is improved with CNTs content. The optimum balance between cost and properties seems to be in the 1–3 wt% range. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effect of particle morphology on the emulsion stability and mechanical performance of polyolefin modified asphalts

Recent federal regulations concenrning roadbed performance have motivated research in polymer modified asphalt binders. Earlier studies on these binders have shown that many of them are susceptible to gross phase separation when the binder is stored at high temperatures under quiescent conditions. This phase separation, in turn, is affected by the initial morphology and storage conditions. In this effort we investigate the effect of particle morphology on the high-temperature emulsion stability of a low-density polyethylene-modified asphalt binder, as well as the concomitant effects on the mechanical behavior. We show for unstabilized emulsions that the dominant phase separation mechanism shifts from coalescence to creaming at a critical particle radius of 4 μm at 110°C. However, stabilized emulsions showed no evidence of gross phase separation for up to 48 hours at 110°C. Dramatically different morphologies were observed for the unstabilized and stabilized emulsions; unstabilized emulsions having teardrop shaped particles and stabilized emulsions having both spherical particles and long cylindrical domains. The mechanical behavior, including the high-temperature dynamic viscoelastic behavior and low-temperature fracture toughness, increased with polyolefin content, but was insensitive to the particle morphology.