Influence of highly branched poly(amido amine) on the properties of hyperbranched polyurethane/clay nanocomposites

The fascinating architecture of hyperbranched polymer imparts a truck load of novel properties to the material. Epoxy resin modified Mesua ferrea L. seed oil based hyperbranched polyurethane (MHBPU) nanocomposites were prepared by in situ technique using s-triazine based highly branched poly(amido amine) (HBPAA) modified organo-nanoclay. The HBPAA was synthesized by A₂ + B₃ technique with good yield (>75%) using urea and s-triazine. The formation of the polymer was confirmed with the help of ¹H NMR, FTIR, UV spectroscopic, and measurements of solution viscosity with other physical properties. This HBPAA was successfully utilized to swell the montmorillonite organo-nanoclay as the interlayer gallery distance increases up to 8.2 Å, obtained by XRD study. The FTIR further confirmed the presence of interactions of the HBPAA moiety with the organo-clay layers. The formation of nanocomposites was confirmed by FTIR, XRD, SEM, TEM and rheological studies. The improvements of tensile strength (1.7 times) and scratch hardness (2.3 times) along with the dramatic enhancement of thermostability and flame retardancy without compromising impact resistance, bending, and elongation at break of the nanocomposites compared to pristine MHBPU thermoset are the noticeable credits of the present investigation. The results signify the great potential of the studied materials for various advanced applications.     

Polyamide 4,6 nanocomposites with and without the use of a maleated polyolefin elastomer as a toughener

In this study, polyamide 4,6 (PA 4,6)-based nanocomposites were successfully prepared using a twin screw extruder. A commercial organo-montmorillonite (denoted as 30B) and a commercial maleated polyolefin elastomer (denoted as POEMA) served as the reinforcing filler and toughener, respectively. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed the nano-scaled dispersion of 30B in the composites. Nevertheless, the presence of POEMA slightly depreciated the dispersibility of 30B. Polarized light microscope (PLM) observations showed that the inclusions of 30B and POEMA led to the formation of diffused/broken PA 4,6 spherulites. Differential scanning calorimetry (DSC) results indicated that the addition of 30B retarded the crystallization of PA 4,6; the addition of POEMA led to a similar retardation effect on PA 4,6 crystallization. Interesting melting behaviors associated mainly with the crystal annealing of PA 4,6 upon heating were observed for the fast-cooled samples. The presence of POEMA was noted to hamper the annealing process of PA 4,6 crystals. The thermal stability enhancement of PA 4,6 in the presence of 30B was further raised to a higher extent when POEMA was included in the matrix. The rigidity, including the storage/Young's/flexural moduli, of PA 4,6 significantly increased after adding 30B. These properties, however, declined after the additional incorporation of POEMA. The PA 4,6/POEMA/30B nanocomposites basically displayed balanced impact strength between those of the neat PA 4,6 and PA 4,6/POEMA blends.     

Comparisons of phase morphology and physical properties of PVDF nanocomposites filled with organoclay and/or multi-walled carbon nanotubes

Binary and ternary poly(vinylidene fluoride) (PVDF) nanocomposites filled with organoclay (15A) and/or multi-walled carbon nanotubes (MWNTs) were successfully prepared. MWNTs were dispersed more homogeneously than 15A within PVDF matrix, and the presence of MWNTs facilitated the dispersibility of 15A. The 15A addition induced β-form PVDF crystal formation, but MWNTs hardly changed the α-form crystal development. Both nanofillers facilitated the nucleation of PVDF (up to 12.3 °C increase), and the efficiency of enhancing PVDF crystallization followed the sequence MWNT > 15A/MWNT > 15A. The nanocomposites possess higher T_m° than neat PVDF. In particular, adding 15A led to a T_m° (β-form) increase of no less than 11 °C. A rheological percolation threshold at 1 wt.% MWNT loading was determined. The electrical resistivity dropped by more than 13 orders of magnitude at 5 wt.% MWNT loading. The nanocomposites exhibited enhanced tensile modulus (up to 83% increase with MWNTs inclusion) compared with neat PVDF.     

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.     

Structure, thermal properties and mechanical properties of sPS-based nanocomposites with and without styrenic elastomer inclusions

Syndiotactic polystyrene (sPS)-based nanocomposites with and without toughener inclusions were successfully prepared. One organo-montmorillonite (20A) and two styrenic elastomers (SBS and SEBS) served as the reinforcing filler and as tougheners, respectively. XRD and TEM results confirmed the achievement of intercalated and partially exfoliated sPS/20A nanocomposites. The presence of SBS or SEBS slightly depressed the dispersibility of 20A. DSC results indicated that 20A inhibited the crystallization of sPS. The presence of SBS or SEBS further retarded the crystallization of sPS; this effect was more apparent with SEBS. The presences of 20A and SBS/SEBS facilitated the formation of α-form sPS crystals. The thermal stability enhancement of sPS/20A nanocomposites was confirmed, and was further improved with the inclusion of SBS or SEBS. The stiffness of sPS increased with the sole addition of 20A. The addition of SBS or SEBS greatly increased the impact strength of the composites, especially with the addition of SEBS. The achievement of toughened sPS-based nanocomposites was confirmed.     

Preparation and properties of novel epoxy/graphene oxide nanosheets (GON) composites functionalized with flame retardant containing phosphorus and silicon

2-(Diphenylphosphino)ethyltriethoxy silane (DPPES) was grafted onto the surface of graphene oxide nanosheets (GON) via a condensation reaction. X-ray photoelectron spectroscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and Raman spectroscopy verify that DPPES did not only covalently bond to GON as a functionalization moiety, but partly restored its conjugated structure as a reducing agent. DPPES on graphene sheets oxide was observed by transmission electron microscopy, and contributed to the favorable dispersion of DPPES-GON in nonpolar toluene. Additionally, the flame retardancy and thermal stability of epoxy/DPPES-GON nanocomposites that contain various weight fractions of DPPES-GON were studied using the limiting oxygen index test, UL-94 test and by thermogravimetric analysis in nitrogen. The composites containing 10 wt% DPPES-GON can pass V-0 rating in UL-94 test. Adding 10 wt% DPPES-GON in epoxy greatly increased the char yield and LOI by 42% and 80%, respectively. Epoxy/DPPES-GON nanocomposites with phosphorus, silicon and graphene layer structures were found to exhibit much greater flame retardancy than neat epoxy. The synergistic effects among silicon, phosphorus and GON can improve the flame retardancy of epoxy resin.     

Preparation and properties of polyimide nanocomposites with negative thermal expansion nanoparticle filler

Nanocomposites with tunable coefficient of thermal expansion (CTE) were prepared by incorporating cubic zirconium tungstate (ZrW₂O₈) nanoparticles at various volume percentages in a polyimide (PI). Rod-shaped nanoparticles of cubic ZrW₂O₈, which has isotropic negative thermal expansion, were synthesized using a hydrothermal method. The interfacial interaction between the PI and ZrW₂O₈ was enhanced by covalently bonding different organic moieties, including a short aliphatic silane and PI oligomer, to the surface of ZrW₂O₈. Structure–property relationships for the PI–ZrW₂O₈ nanocomposites were investigated for thermal degradation, glass transition, tensile and thermal expansion properties. Addition of ZrW₂O₈ nanoparticles did not alter the thermal degradation and glass transition temperature of the base PI. The addition of ZrW₂O₈ nanoparticles increased the Young's modulus of the polymer, indicating stiffening of the polyimide matrix. The increase was higher for nanocomposites with engineered interfaces due to the efficient load transfer achieved through the presence of linker groups. The addition of ZrW₂O₈ reduced the in-plane CTE of the base PI at all loadings studied. The CTE of the base PI was reduced by around 22% with the addition of ZrW₂O₈ at 15 volume% loading.     

Effects of vacuum thermal cycling on mechanical and physical properties of high performance carbon/bismaleimide composite

The aim of this article was to investigate the effects of vacuum thermal cycling on mechanical and physical properties of high performance carbon/bismaleimide (BMI) composites used in aerospace. The changes in dynamic mechanical properties and thermal stability were characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. The changes in linear coefficient of thermal expansion (CTE) were measured in directions perpendicular and parallel to the fiber direction, respectively. The outgassing behavior of the composites were examined. The evolution of surface morphology and surface roughness were observed by atomic force microscopy (AFM). Changes in mechanical properties including transverse tensile strength, flexural strength and interlaminar shear strength (ILSS) were measured. The results indicated that the vacuum thermal cycling could improve the crosslinking degree and the thermal stability of resin matrix to a certain extent, and induce matrix outgassing and thermal stress, thereby leading to the mass loss and the interfacial debonding of the composite. The degradation in transverse tensile strength was caused by joint effects of the matrix outgassing and the interfacial debonding, while the changes in flexural strength and ILSS were affected by a competing effect between the crosslinking degree of resin matrix and the fiber-matrix debonding.     

P25/graphene nanocomposites as a high-performance anode material for lithium ion batteries

P25/graphene nanocomposites were successful synthesized in a water-ethanol solvent under hydrothermal conditions. During the process of the reduction of GO into graphene (GR), the P25 nanoparticles were decorated on graphene sheets simultaneously. Moreover, the GR content in the as-synthesized nanocomposites can be easily adjusted by changing the dosage of P25. The interesting P25/GR nanocomposites were found to be a promising anode material for lithium-ion batteries and showed significantly enhanced Li-ion insertion/extraction performance. The optimal weight percentage of GR was found to be 29.9%, which resulted in a high capacity of 282.8 mAh g⁻¹ after 50 cycles at a current rate of 0.5 C. The improved capacity may be attributed to the synergetic effect between graphene sheets and P25 nanoparticles.     

Preparation polystyrene/multiwalled carbon nanotubes nanocomposites by copolymerization of styrene and styryl-functionalized multiwalled carbon nanotubes

Styryl-functionalized multiwalled carbon nanotubes (p-MWNTs) were prepared by esterification based on the carboxylate salt of carbon nanotubes and p-chloromethylstyrene in toluene. Then in situ radical copolymerization of p-MWNTs and styrene initiated by 2,2′-azobis(isobutyronitrile) (AIBN) was applied to synthesize composites of styryl-functionalized multiwalled carbon nanotubes and polystyrene (PS) (p-MWNTs/PS). Characterizations carried out by FT-IR, ¹H NMR, UV–vis show that styryl group covalently bond to the surface of MWNTs. The results of UV showed that the solutions of p-MWNTs/PS in chloroform have the hyperchromic effect. Transmission electron microscopy (TEM) images of p-MWNTs/PS composites and scanning electron microscopy (SEM) images of fracture surface of p-MWNTs/PS composites showed the functionalized nanotubes had a better dispersion than that of the unfunctionalized MWNTs in the matrix. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) suggested that the thermal stability of p-MWNTs/PS composites improved in the presence of MWNTs.     

Thermo-mechanical characteristics of thermally aged polyethylene/polypropylene blends

Polyethylene (PE), polypropylene (PP) and their blends have attracted a lot of attention due to their potential industrial applications. Therefore, the current work has been carried out with the main objective of investigating the impact of the thermal aging/treatment and blend ratio (composition range) on the mechanical (tensile and hardness) and thermal characteristics (using thermogravimetric analysis in a dynamic air atmosphere) of PE, PP and PE/PP binary blends. Samples of PE/PP blends containing 100/00, 75/25, 50/50, 25/75 and 0/100 wt.% were prepared via injection moulding technique and thermally treated/aged at 100 °C for 0, 2, 4, 7, 14 days. The tensile measurements indicated that the yield strength and the modulus decrease with increasing PE content. It was also observed that PE, PP and their blends deform in ductile modes. They undergo a uniform yielding over a wide range of deformation, which is followed by strain hardening and then failure. The strain to break for pure PE is found to be much higher than that for pure PP and for their blends, intermediate values have been observed. The hardness measurements have also revealed that increasing PE content in PE/PP blends reduced the hardness value of PP, however, thermal aging at 100 °C has not affected the polymers hardness which holds also true for the tensile properties, showing a good correlation between tested mechanical properties. The thermogravimetric analysis (TGA) in a dynamic air atmosphere and derivative thermogravimetric analysis (DTA) were conducted to study the thermal degradation and stability of thermally unaged and aged PE, PP and PE/PP blends in terms of the initial (T_d and T_d(1%)) and final (T_d(99%)) decomposition temperatures and maximum decomposition rate temperature (T_max). All polymers start to decompose at no less than 365 °C. As for mechanical properties, the blend ratio has affected the thermal properties however, aging time has not.     

The intercalation of poly(methyl methacrylate)/aluminophosphate nanocomposites and the properties improvement

Poly(methyl methacrylate) (PMMA)/dodecylamine templated lamellar aluminophosphate (DDA-LAP) intercalated nanocomposites are prepared by in situ bulk polymerization of MMA. The intercalated structure is characterized. With the intercalation of DDA-LAP in PMMA matrix, the glass-transition temperatures of nanocomposites (T_g) are increased. The nanocomposites obtained keep relatively high transparency in optical property and have a significant improvement in mechanical properties and thermal stability. The mechanism for the properties enhancement is investigated. The strong interfacial interaction between the aluminophosphate layers and the PMMA chains, the homogeneously distribution and the graphitized char formation during heating are three key roles for the properties improvement.     

Polyethyleneimine-loaded bimodal porous silica as low-cost and high-capacity sorbent for CO2 capture

In this work, bimodal (meso-macro) porous silicas with different mesopore diameters synthesized by using rice husk ash as a low-cost silica source and chitosan as a natural template were used as a polyethyleneimine (PEI) support for CO₂ capture. Unimodal porous silica supports with equivalent mesopore diameters to bimodal porous silica supports have been prepared for purpose of comparison. Effects of different PEI contents (10, 20, 30, 40 and 50 wt%) on CO₂ sorption capacity have been systematically investigated. The porous silica supports and the PEI-loaded porous silica supports were characterized by N₂-sorption analysis, scanning electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analysis. CO₂ sorption measurements of all PEI-loaded porous silica supports were performed at different adsorption temperatures (60, 75, 85, 90, 95 and 105 °C). At low PEI contents (10–20 wt%), the CO₂ sorption of all adsorbents was found to decrease as a function of adsorption temperature, which was a characteristic of a thermodynamically-controlled regime. A transition from the thermodynamically-controlled regime to a kinetically-controlled regime was found when the PEI content was increased up to 30 wt% for PEI-loaded unimodal porous silicas and 40 wt% for PEI-loaded bimodal porous silicas. At high PEI contents (40–50 wt%), the CO₂ capturing efficiency of the PEI-loaded bimodal porous silicas was found to be considerably greater than that of the PEI-loaded unimodal porous silicas, indicating that most of the amine groups of PEI molecules loaded on the unimodal porous silica supports was useless, and thus the appeared macroporosity of the bimodal porous silica supports could provide a higher effective amine density to adsorb CO₂.     

Low-cost removal of organic pollutants with nickel nanoparticle loaded ordered macroporous hydrogel as high performance catalyst

A facile route for the in situ preparation of catalytically active Ni nanoparticles (NPs) in ordered macroporous hydrogel (OMH) has been developed. The hydrogel was fabricated based on polystyrene colloid template. The electronegativity of amide and carboxyl groups on the poly(acrylamide-co-acryl acid) chains of the hydrogel caused strong binding of Ni²⁺ ions which made them distribute uniformly inside the hydrogel. When immersed in NaBH₄ aqueous solution, the Ni²⁺ ions on the hydrogel were reduced to Ni NPs. The resultant Ni NPs loaded OMH showed good catalytic activity for the reduction of a common organic pollutant, 4-nitrophenol, with NaBH₄. A kinetic study of the catalytic reaction was carried out. The rate constant per unit weight could reach 0.53 s⁻¹ g⁻¹, which is much better than many common hydrogel loaded nickel catalysts. Moreover, the current catalyst can be easily separated and recovered with stable catalytic activity.     

Electrical and rheological properties of PMMA/LDPE blends filled with carbon black

Conductive immiscible multiphase blends of PMMA/LDPE filled with carbon black (CB) were studied in this work. Thermo-electrical behavior of the blends was compared with the composites made up of individual polymers in the blend, PMMA and LDPE filled with CB. The conductivity of the immiscible binary blend at different CB content was followed and modeled using a model circuit in which resistors resembling different phases and the interface between them present in the blend. Electrical percolation threshold was measured for the blend and compared with the single component polymers in order to judge the preferred phase for CB distribution in it. Rheological network formation by CB particles in the blend was also studied using dynamic rheology. The effect of CB loading on the morphology of the multiphase blend was also studied using FESEM images. Theoretical models were also used to predict the percolation thresholds for electrical and rheological network formation and compared with the experimental values.     

Polyacrolein/mesoporous silica nanocomposite: Synthesis,thermal stability and covalent lipase immobilization

In this work, new polyacrolein/MCM-41 nanocomposites with good phase mixing behavior were prepared through an emulsion polymerization technique. Mesoporous silica was synthesized by in situ assembly of tetraethyl orthosilicate (TEOS) and cetyl trimethyl ammonium bromide (CTAB). The structure and properties of polyacrolein containing nanosized MCM-41 particle (5 and 10 wt%), were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, Dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption techniques, and thermogravimetric (TGA) analyses. The SEM images from the final powder have revealed good dispersion of the MCM-41 nanoparticles throughout polymeric matrix with no distinct voids between two phases. The results indicated that the thermal properties of the nanocomposite were enhanced by addition of MCM-41. Thermomyces lanuginosa lipase (TLL) was used as a model biocatalyst and successfully immobilized with polyacrolein and the nanocomposite via covalent bonds with the aldehyde groups. The activity between free enzyme, polyacrolein, and MCM-41 nanocomposite (10 wt%)-immobilized TLL was compared. The immobilized lipase with the nanocomposite shows better operational stability such as pH tolerance, thermal and storage stability. In addition, the immobilized lipase with the nanocomposite can be easily recovered and retained at 74% of its initial activity after 15 time reuses.     

Facile preparation of poly(vinyl alcohol) nanocomposites with pristine layered double hydroxides

In this paper, nano-sized Mg–Al layered double hydroxide (LDH) was synthesized by a fast nucleation and slow aging method. The structures of LDH were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and photon correlation spectroscopy (PCS). Poly(vinyl alcohol) (PVA) nanocomposites with different LDH loadings were prepared by water solution casting method. TEM observations show that the LDH nanoplatelets are uniformly dispersed in the PVA matrix. Tensile tests indicate that the elastic modulus and the tensile strength of PVA are improved by about 15% and 54%, respectively, when incorporating with 2 wt% LDH. The improvement of mechanical properties of PVA can be attributed to fine dispersion of LDH, good compatibility and strong interaction between PVA and LDH. In addition, the presence of LDH decreases the decomposition rates at the second stage and improves the amount of residues of PVA. Meanwhile, the transparency of the nanocomposite films is maintained compared with neat PVA.     

Preparation and thermal properties of form-stable palmitic acid/active aluminum oxide composites as phase change materials for latent heat storage

Form-stable palmitic acid (PA)/active aluminum oxide composites as phase change materials were prepared by adsorbing liquid palmitic acid into active aluminum oxide. In the composites, the palmitic acid was used as latent heat storage materials, and the active aluminum oxide was used as supporting material. Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) were used to determine the chemical structure, crystalloid phase and microstructure of the composites, respectively. The thermal properties and thermal stability were investigated by a differential scanning calorimeter (DSC) and a thermogravimetry analyzer (TGA). The FT-IR analyses results indicated that there is no chemical interaction between the palmitic acid and active aluminum oxide. The SEM results showed that the palmitic acid was well adsorbed into porous network of the active aluminum oxide. The DSC results indicated that the composites melt at 60.25 °C with a latent heat of 84.48 kJ kg⁻¹ and solidify at 56.86 °C with a latent heat of 78.79 kJ kg⁻¹ when the mass ratio of the PA to active aluminum oxide is 0.9:1. Compared with that of the PA, the melting and solidifying time of the composites CPCM5 was reduced by 20.6% and 21.4% because of the increased heat transfer rate through EG addition. The TGA results showed that the active aluminum oxide can improve the thermal stability of the composites.     

Rapid modification of montmorillonite with novel cationic Gemini surfactants and its adsorption for methyl orange

A rapid method was developed to prepare organic montmorillonite (organo-MMT) using three novel Gemini surfactants by microwave irradiation of 1 h, which was more effective than conventional heating method of 8–48 h. The structure and morphology of organo-MMTs were characterized by XRD, FT-IR, TEM and SEM. The adsorption amount of Gemini surfactants on MMT and the thermal stability of organo-MMTs were investigated by thermogravimetric analysis (TGA). The results indicated that Gemini surfactants were more efficient than cetyltrimethyl ammonium bromide in the modification of MMT, the organoclays obtained by microwave irradiation method had larger layer spacing than those from traditional heating method. And with the increase of the dosage and chain length of Gemini surfactants, the amount of the intercalary or adsorbed surfactant on the organoclay gradually increased, whereas the thermal stability weakened appropriately. Besides, the adsorption results for methyl orange indicated that all organo-MMTs displayed more excellent adsorption capacities than unmodified MMT. The amount of methyl orange adsorbed onto the organo-MMTs increased proportionately with the increase of the amount or the chain length of Gemini surfactants. This study affords a rapid and efficient method to obtain the organoclay with large interlayer distance and strong adsorption capacity.