K. Prashantha

Preparation and properties of novel melt-blended halloysite nanotubes/wheat starch nanocomposites.

Novel bionanocomposites based on halloysite nanotubes as nanofillers and plasticized starch as polymeric matrix were successfully prepared by melt-extrusion for the first time. Both modified and non modified halloysites were added at different weight contents. The structural, morphological, thermal and mechanical properties of plasticized starch/halloysites nanocomposites were investigated. Melt-compounding appears to be a suitable process to uniformly disperse nanotubes in the plasticized starch matrix. Interactions between plasticized starch and halloysites in the nanocomposites and microstructure modifications were monitored using Fourier transfer infrared spectroscopy, X-ray diffraction and dynamic mechanical analysis. Addition of halloysite nanotubes slightly enhances the thermal stability of starch (onset temperature of degradation delayed to higher temperatures). The tensile mechanical properties of starch are also significantly improved (up to +144% for Youngs modulus and up to +29% for strength) upon addition of both modified and unmodified halloysites, interestingly without loss of ductility. Modified halloysites lead to significantly higher Youngs modulus than unmodified halloysites.

Plasticized-starch/poly(ethylene oxide) blends prepared by extrusion

Blends based on plasticized-wheat starch (as matrix or rich phase) and poly(ethylene oxide) (PEO) (as dispersed phase) were prepared by melt processing in a twin-screw extruder. The extrusion of the plasticized-starch is significantly facilitated by blending with PEO. Plasticized-starch and PEO are immiscible in the range of the investigated blend ratios (90/10-50/50). The phase inversion takes place when the PEO content is 50 wt.% in the blend. Both the thermal stability and the tensile properties of plasticized-starch are improved by blending with PEO. Also, a synergistic effect between plasticized-starch and PEO is noticed at 25-40 wt.% PEO content in the blend, the Youngs modulus of the materials obtained being the highest and higher than both neat polymer components at those blending ratios.

Studies on the effect of storage time and plasticizers on the structural variations in thermoplastic starch

Starch was combined with plasticizers such as glycerol, sorbitol, glycerol/sorbitol and urea/ethanolamine blends by means of high shear extrusion process to prepare thermoplastic starch (TPS). Effect of storage time and plasticizers on the structural stability of melt processed TPS was investigated. Morphological observation, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy reveal that melt extrusion process is efficient in transforming granular starch into a plasticized starch for all plasticizer compositions. XRD analysis highlights major changes in the microstructure of plasticized starch, and dependence of crystalline type and degree of crystallinity mainly on the plasticizer composition and storage time. Dynamical mechanical analysis (DMA) yields a decrease of the peak intensity of loss factor with aging time. The effect of ageing on tensile strength also appears to be highly dependent on the plasticizer composition. Thus, through different plasticizer combinations and ageing, starch-based materials with significant differences in tensile properties can be obtained, which may be tuned to meet the requirements of a wide range of applications.

Present Status and Key Challenges of Carbon Nanotubes Reinforced Polyolefins: A Review on Nanocomposites Manufacturing and Performance Issues

Carbon nanotube reinforcement is a key emerging technology to simultaneously impart enhanced mechanical properties while adding multifunctional characteristics to polymer materials and systems. The promise of extraordinary improvement in-end use properties of polyolefin/carbon nanotube hybrid systems has spurred great interest and intensive activity in academics and industries. This review offers a comprehensive discussion of the preparation, compounding, properties and applications of such nanocomposites. The processing, dispersion and orientation of nanotubes, as well as the characterisation of physical and mechanical properties of carbon nanotube filled polyolefins are discussed. In particular the scientific principles and mechanisms in relation to the methods of manufacturing are highlighted, with an outlook towards commercial applications.

Electrical and Dielectric Properties of Multi-Walled Carbon Nanotube Filled Polypropylene Nanocomposites

Different concentrations of multi-wall carbon nanotubes (MWNTs) filled polypropylene (PP) nanocomposites were prepared through PP/MWNT masterbatch dilution process by melt compounding with a twin-screw extruder. Prepared nanocomposites were characterized for their electrical resistivity and dielectric properties. The experimental results revealed that incorporation of MWNTs in PP matrix had decreased the electrical resistivity and increased the dielectric constant at low dielectric loss. The electrical conductivity and dielectric constant of PP/MWNT nanocomposites increased significantly near the percolation thresholds, which is equal to 2 wt.% of MWNTs. The PP nanocomposite containing 5 wt.% MWNT exhibited a high dielectric constant under wide sweep frequencies attended by low dielectric loss. Its dielectric constant is >110 under lower frequency, and remains the same in the entire frequency range. Interestingly, dielectric constant values of the prepared nanocomposite systems have weak or nil frequency dependence in the entire frequency range. Morphological characterization was done using scanning electron microscopy (SEM) and it was observed that nanotubes are distributed reasonably uniformly indicating a good dispersion of nanotubes in the PP matrix. The obtained results indicate that a common commercial plastic with good comprehensive performance, which exhibited the potential for applications in advanced electronics, was obtained by a simple industry benign technique.

Preparation and characterization of carbon nanotube filled poly (2-hydroxyethylmethacrylate) nanocomposites

Poly(2-hydroxyethylmethacrylate) (PHEMA)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared by solvent casting using dimethyl formamide (DMF) solvent via sonication process. Effect of addition of MWNTs on the properties of nanocomposites was investigated at different nanofiller contents. Uniform dispersion and distrubution of nanotubes in PHEMA matrix is obtained within the studied composition range. The electrical resistivity, dielectric permittivity and the loss factor of dry PHEMA and PHEMA/MWNT nanocomposites were studied by varying the MWNT concentration in the frequency range of 30 Hz to 1 MHz. The obtained results indicated that the addition MWNTs to PHEMA matrix decreases the electrical resistivity and increases the dielectric constant at low dielectric loss. The thermal properties of the PHEMA/MWNT nanocomposites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal behavior of these nanocomposites was also compared with PHEMA homopolymer. The glass transition temperature (Tg) of PHEMA homopolymer was found to increase with nanotube concentration. Experimental results also demonstrated that the incorporation of the MWNTs into the PHEMA matrix not only enhanced the mechanical property but also increased and the thermal stability of the PHEMA/MWNT nanocomposites increases with increase in MWNT concentration.

Mechanical, thermal and flame-retardant properties of epoxy-nylon fabric-clay hybrid laminates

Epoxy–nylon fabric laminate composites containing 0.1–0.7 phr clay reinforcements were prepared using a hand layup technique. The fabricated laminates were tested for thermal stability, impact resistance, mechanical properties and flame retardancy. The results indicated an increase in impact resistance, tensile strength, flexural strength and Young’s modulus to an extent and then a decrease as the clay content is increased. Overall results show that a 0.2-phr clay reinforcement into the epoxy–nylon fabric laminate has shown better impact resistance (33.9% more than the neat epoxy–nylon fabric laminate), tensile strength (nearly two times the neat sample), flexural strength (nearly five times the neat sample) and Young’s modulus (39.4% more than the neat sample). Thermal stability is found to decrease slightly upon addition of clay. UL-94 tests conducted on the composite laminate samples have shown a reduction in the burning rate. Also, the tests performed in the present study indicate that the materials under investigation have promising applications in construction, agriculture and decorative purposes.

Processing and Mechanical Behaviour of Halloysite Filled Starch Based Nanocomposites

Bionanocomposites based on halloysite nanotubes (HNT) as nanofillers and starch as polymer matrix were prepared by melt-extrusion process using glycerol as plasticizer and glycerol monostearate as lubricant. Scanning electron microscopic (SEM) images show homogenous dispersion of HNTs in starch matrix. A Fourier transform infrared analysis (FTIR) reveals the interaction between external hydroxyl groups of HNTs with C–O–C groups of starch. Upon halloysite addition, storage modulus, Young modulus and tensile strength increase without loss of ductility.

Qualifying Dispersion and Distribution of Carbon Nanotubes in Polyamide Matrix during Melt-Mixing by Flow Simulation

This work aims at numerically simulating the flow of nanocomposites in a twin-screw mixer so as to develop a prediction tool of nanofiller dispersion and distribution in a polymer matrix during processing. The rheological behaviour of polyamide 6 / carbon nanotubes blends (PA6/MWCNT) containing from 1 to 5 wt.% of MWCNT was investigated over a large range of shear rates (0.1 to 100 s−1) and temperatures (230 to 245 °C). The macroscopic dispersion of the nanotubes was assessed by dynamic rheometry. Viscosity laws of the nanocomposites were characterized and implemented in a finite element software package to compute the velocity, pressure and temperature fields during the mixing process. A good agreement was founded between the calculated and measured torques. The dispersive and distributive capability of the flow was numerically evaluated and compared to the nanotubes dispersion quality experimentally qualified by oscillatory rheometry. Experimental and numerical results are complementary and allow better understanding the mixing capability of the twin-screw mixer used to compound nanocomposites.

Studies on flocculation of clay suspension by polyacrylamide

Abstract The flocculation of dilute pottery clay suspension using polyacrylamide (PAM) was investigated. Different molecular weight PAMs were synthesized by free-radical polymerization initiated with the persulfate-bisulfate redox pair. The synthesized polyelectrolytes (PAM1, PAM2 and PAM3, from low to high molecular weight) and a commercial one (C-492) were used for flocculation studies. The flocculating performance of polyelectrolytes was measured on 3% w/v pottery clay suspension using settling tests and turbidity measurements. PAM2 at pH 5.0 showed the maximum settling rate, which is nearly three times that of C-492, and it also showed a better turbidity reduction. Molecular weight is the key factor in influencing settling and turbidity reduction. In the present study, increasing molecular weight enhanced settling rate and turbidity reduction to a certain level beyond which there is a decrease, suggesting an optimum molecular weight for the given application. PAM2, a medium molecular weight polyelectrolyte (2.0·105 g/mol) has shown better performance than PAM1 (1.3·105 g/mol), PAM3 (6.0·105 g/mol) and the commercial polyelectrolyte C-492 (molecular weight of order 106).