J. Soulestin

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.

Deformation mechanisms of plasticized starch materials.

The aim of this paper is to understand the influence of plasticizer and plasticizer amount on the mechanical and deformation behaviors of plasticized starch. Glycerol, sorbitol and mannitol have been used as plasticizers. After extrusion of the various samples, dynamic mechanical analyses and video-controlled tensile tests have been performed. It was found that the nature of plasticizer, its amount as well as the aging of the material has an impact on the involved deformation mechanism. The variations of volume deformation could be explained by an antiplasticization effect (low plasticizer amount), a phase-separation phenomenon (excess of plasticizer) and/or by the retrogradation of starch.

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.

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.

How does temperature govern mechanisms of starch changes during extrusion

Potato and pea starches were processed on a twin-screw extruder under various moisture and thermomechanical conditions, chosen to keep material temperature Te close to starch melting temperature, Tm, whilst avoiding die expansion. Extruded rods were analysed by asymmetrical flow field flow fractionation coupled with light scattering, X-ray diffraction, DSC, and light microscopy with image analysis. Molar mass of extruded materials decreased more for potato than for pea starch, when specific mechanical energy SME increased, likely because of larger amylopectin sensitivity to shear. No crystallinity was detected when ΔT = (Tm-Te) ≤ 0. Residual gelatinization enthalpy ΔHg decreased with ΔT. As illustrated by larger ΔT values for ΔHg = 0, decreasing moisture favored melting, likely by increasing solid friction. The fraction of granular remnants of potato starch was inversely correlated to SME. These results could be explained by considering starch melting during extrusion as a suspension of solid particles embedded in a continuous amorphous matrix.

Using water to modify the localization of clay in immiscible polymer blends

Bio-based polyamide 11 (PA11) and water-soluble polyethylene oxide (PEO) (80/20 wt/wt) were used to prepare an immiscible polymer blend. Ternary systems containing 1 wt% hydrophilic clay (organomodified or native clay) were elaborated using extrusion with and without injection of water. The cryoscopic effect on PA11 and PEO observed by high pressure differential scanning calorimetry indicated that they were both miscible with water under conditions of water-assisted extrusion. Transmission electron microscopy revealed a selective localization of both types of clay in the matrix (PA11). However, with water-assisted extrusion a part of the organomodified clay platelets was localized into the dispersed phase (PEO). Under rheological tests, the unmodified clay exhibited a different effect compared with the organomodified clay on the modulus and viscosity of the blend. The van Gurp–Palmen plot indicated that clay potentially decreased the interfacial tension between PA11 and PEO, while the weighted relaxation spectra confirmed that water improved the dispersion state of the clay and limited the polymer degradation. Thermogravimetric analyses showed that the presence of clay and water improved the thermal stability of PA11/PEO blends. Our work is the first one which has realized water-assisted extrusion of a clay-filled ternary blend.

Water Diffusion Mechanisms in New Bio-Nanocomposites Based on Polyhydroxyalkanoates/Nanoclays

Nanocomposites based on bacterial semi-crystalline polyhydroxyalkanoates, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) or poly (3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)), and organo-modified montmorillonite nanoclay are prepared by melt processing. All nanocomposites are characterized by X-Ray Diffraction (XRD) and Transmission Electronic Microscopy (TEM) and exhibit a mainly intercalated structure. Concerning water transport properties, a decrease of barrier properties for PHBV/nanoclay films is measured due to the affinity of nanoclay to water; whereas for P(3HB-co-4HB)/nanoclay nanocomposites, a decrease of the water permeability is observed relative to the tortuosity effect. Eventually, as a function of nanoclay content, a competition is evidenced between the tortuosity effect and the water sorption induced by nanoclay.