Polycarbonate/molybdenum disulfide/carbon black composites: Physicomechanical,thermal, wear,and morphological properties

To investigate the influence of molybdenum disulfide (MoS₂) as solid lubricant and filler on the polycarbonate (PC) and carbon black (CB) composites, PC containing one weight percentage of CB powder was compounded and extruded with 0.5, 1.0, 2.0, and 3.0 weight percentage of MoS₂ powder in a co‐rotating twin screw extruder. Thus, the fabricated PC/CB/MoS₂ composites were characterized for physicomechanical properties such as density, void content, surface hardness, tensile behaviors, and impact strength. The thermal characteristics of the composites have been studied by differential scanning calorimetry and dynamic mechanical analysis (DMA). The effect of MoS₂ content, loads and sliding distances on wear characteristics of the composites were evaluated using pin‐on‐disc equipment. It was found that wear, friction, and laser etching resistance of PC/CB/MoS₂ composites increased with increase in MoS₂ content along with improvement in tensile and impact strengths. DMA analysis indicates the storage modulus of PC/CB/MoS₂ composites increased with increase in MoS₂ content below the glass transition temperature (T_g) of PC. Worn surfaces and laser etched surfaces were examined with scanning electron microscopy and optical microcopy respectively to have better insight of the wear and laser etching mechanism. It was observed that the MoS₂ as solid lubricant played major role in improving resistance to wear, friction, and laser etching. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

A study on mechanical,thermal, and wear characteristics of nylon 66/molybdenum disulfide composites reinforced with glass fibers

The influence of silane‐coated short glass fibers (SGF) on the mechanical and wear characteristics of nylon 66 composites was investigated by compounding nylon 66 with 35% SGF as well as with 2% molybdenum disulfide (MoS₂) and without MoS₂ in a co‐rotating twin screw extruder. Thus the resultant material was evaluated for physico‐mechanical, thermal, sliding wear, and morphological characteristics. It was found that the addition of glass fibers as well as MoS₂ has significantly improved the tensile strength, tensile modulus, and impact strength of the nylon 66. Differential scanning calorimetry analysis reveals significant changes in the crystallization behavior of nylon 66 for incorporation of fillers. Thermal stability of the nylon 66 was found to be improved as revealed by the thermogravimetric analysis results. Dynamic mechanical analysis results show drastic improvement in the storage modulus of the nylon 66 both in the glassy region as well as in the rubbery region. Wear analysis shows that the incorporation of glass fibers and MoS₂ filler has reduced the wear loss and specific wear rate of nylon 66. Worn surfaces were examined with scanning electron microscopy to have better insight of the wear mechanism. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Influence of free volume on the mechanical properties of Epoxy/poly (methylmethacrylate) blends

Positron lifetime measurements have been performed to investigate the free volume dependence of the mechanical properties of Epoxy/poly methyl methacrylate (PMMA) blends of varying composition of PMMA (2.5, 5, 7.5, 10, 12.5, 15, and 17.5 wt%). The mechanical properties of the blends have been evaluated according to the (ASTM) standard. The positron results indicate that the mechanical properties like tensile strength and surface hardness have a significant dependence on the free volume of the blends. It is also found that the blends of the present study show positive deviation from the familiar linear additivity rule suggesting the immiscible nature of the blends. Further, up to 5-wt% of PMMA in the blend, an increase in relative fractional free volume correlates well with a decrease of tensile strength.     

Investigation on miscibility behaviors of elastin‐like polypentapeptide blends with polyvinyl alcohol in aqueous and solid state

The polypentapeptide of elastin, poly(GVGVP) has shown remarkable properties and have great potential for biomedical applications. To explore its applications further, the miscibility behaviors of poly(vinyl alcohol) (PVA)/poly(GVGVP) blends have been explored in a very broad composition range. The miscibility behaviors of these blends have been investigated in both solution and solid state using various analytical techniques, including ultrasonic velocity, density, refractive index (RI) and viscosity techniques at 25 °C. The results confirmed the miscibility of the blend up to 40% of the polypeptide. This was further supported by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44624.     

Molecular transport of n‐alkanes through diol chain‐extended polyurethane membranes

Molecular transport of n‐alkanes was investigated by calculating sorption, diffusion, and permeation of liquids through the diol chain‐extended polyurethane (PU) membranes in the temperature interval 25–60°C. Sorption experiments were performed gravimetrically. Diffusion coefficients were calculated from Fick's equation. These results showed a dependency on the nature and size of interacting n‐alkane molecules as well as morphology of the chain‐extended PUs. Transport kinetics followed an anomalous trend. Using the temperature‐dependent transport parameters, activation energies were calculated for diffusion and permeation processes using an Arrhenius equation. The van't Hoff relationship was used to obtain enthalpy and entropy of sorption. Concentration profiles of liquids through PU membranes were computed using Fick's equation, solved under appropriate initial and boundary conditions. A correlation was attempted between transport properties of liquids and physicomechanical properties of PU membranes. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 874–882, 2005     

Structure–property relationship of starch‐filled chain‐extended polyurethanes

Chain‐extended polyurethane (PU) elastomers were prepared using castor oil with 4,4′‐methylene bis (phenyl isocyanate) (MDI) as a crosslinker and 4,4′‐diamino diphenyl sulphone (DDS) as an aromatic diamine chain extender. A series of starch‐filled (from 5 to 25% wt/wt) diamines chain‐extended PUs have been prepared. The starch‐filled PU composites were characterized for physico‐mechanical properties viz, density, surface hardness, tensile strength, and percentage elongation at break. Thermal stability of PU/starch have been carried out by using thermogravimetric analyzer (TGA). Thermal degradation process of PU/starch were found to proceed in three steps. TGA thermograms of PU/starch shows that all systems were stable upto 235°C, and maximum weight loss occur at temperature 558°C. The microcrystalline parameters such as crystal size (〈N〉) and lattice strain (g in %) of PU/starch have been established using wide‐angle X‐ray scattering (WAXS) method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2945–2954, 2003     

Investigation of multi‐walled carbon nanotube‐reinforced high‐density polyethylene/carbon black nanocomposites using electrical,DSC and positron lifetime spectroscopy techniques

BACKGROUND: The positive temperature coefficient (PTC) effect on material properties has attracted much attention in recent years due to the prospects of many applications like temperature sensors, thermistors, self‐regulating heaters, etc. It has been suggested that incorporation of multi‐walled carbon nanotubes (MWNTs) into carbon black (CB)‐filled polymers could improve the electrical properties of composites due to high conductivity and network structure and significantly reduce the required CB loading. RESULTS: We observed no change in melting temperature and crystalline transition temperature on addition of MWNTs. However, the heat of fusion decreases as the amount of conducting carboxylated MWNT (c‐MWNT) filler increases and the resistivity of the composite decreases. The free volume shows an increase up to 1.5 wt% of c‐MWNT content and then decreases. CONCLUSION: Well‐developed crystals could not be formed due to restricted chain mobility as filler content increases. This results in minimum intermolecular interactions, and thus a decreased heat of fusion. A composite with c‐MWNT content of 0.5 wt% showed the highest PTC and higher resistivity at 150 °C possibly due to the formation of flocculated structures at elevated temperature. For filler content greater than 1.5 wt%, the decrease in free volume may be due to restricted chain mobility. Copyright © 2009 Society of Chemical Industry     

The influence of zinc oxide–cerium oxide nanoparticles on the structural characteristics and electrical properties of polyvinyl alcohol films

With the objective to investigate the influence of zinc oxide–cerium oxide (ZnO–Ce₂O₃) nanoparticles on the electrical properties of polyvinyl alcohol (PVA), PVA/ZnO–Ce₂O₃ nanocomposite films were prepared by solution intercalation method with different weight percentage viz., 0.5, 1.0, and 2.0?wt% of ZnO–Ce₂O₃ nanoparticles. The fabricated nanocomposites were characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The effect of ZnO–Ce₂O₃ nanoparticles on the dielectric constant (ε′), dielectric loss (ε″), electric modulus (M′ and M″), ac conductivity (σ _ac), and dielectric loss tangent (tan δ) over a range of frequencies at room temperature of PVA nanocomposites have been studied. FT-IR, XRD, and DSC analysis indicates the nature of ZnO–Ce₂O₃ nanoparticles interaction with the PVA matrix. The morphological behavior of the nanocomposites has been performed using scanning electron microscopy (SEM). The dielectric behaviors such as dielectric constant (ε′) and dielectric loss (ε″) increases with increase in nanoparticle concentration, but decreases with increase in frequency. But, the electric modulus (M′) increases with increase in frequency. Dielectric loss tangent (tan δ) decreases with increase in filler content at lower frequency, but at higher frequencies the tan δ increases with increase in nanoparticles content. AC conductivity (σ _ac) of PVA/ZnO–Ce₂O₃ nanocomposites increases with increasing frequency following the universal dielectric response law.     

Fibre reinforced composites of multifunctional epoxy resins

Glass and carbon fibre reinforced epoxy composites were fabricated for N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) and its formulated systems with tri- and di-functional reactive epoxy diluents using 30% diaminodiphenyl sulphone (DDS) as a curing agent. The epoxy laminates were evaluated for their physical, chemical and mechanical properties [at room (26°C) and high (100°C) temperatures]. A marginal increase (<20%) in the mechanical properties of CFRP was found compared with GFRP laminates. Incorporation of epoxy diluents altered the mechanical properties of the composites significantly. The incorporation of triglycidyl-4-aminophenol diluent to TGDDM systems resulted in an improvement in mechanical properties of about 2–6%.     

Structure-property relationship of castor oil based diol chain extended polyurethanes (PUs)

A series of 1,4-butane diol and 1,6-hexane diol based chain extended polyurethanes (PUs) have been prepared using castor oil with different diisocyanates such as methylene bis (phenyl isocyanate) (MDI), toluene-2,4-diisocyanate (TDI) and hexa methylene diisocyanate (HMDI) as crosslinkers. The prepared aliphatic diol based chain extended PU's have been characterised for physico-mechanical properties such as density, tensile strength, percentage elongation at break, tensile modulus and surface hardness; and optical properties like total transmittance and haze. The properties imparted by the chain extenders and diisocyanates on PUs have been explained on the basis of chemical structure. Effect of heat aging on mechanical properties of PUs have also studied. These changes have been interpreted quantitatively in terms of microcrystalline parameters computed using wide-angle X-ray scattering (WAXS) data.