Patricia Krawczak

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.

Fracture Mechanics Applied to Glass Fibre/Epoxy Matrix Interface Characterization

The possibility of the application of mode I and mode II fracture mechanics to the characterization of the glass fibre/epoxy matrix interface has been studied here. The aim is to find out a method much more sensitive and reliable than the commonly used methods such as single filament tests which could allow a separate analysis of cracks initiation and potion phenomena that are involved in the damage of composite structures. One original contribution of this comparative analysis on materials differing only in their fibre sizing is the attempt to use the whole resistance curve of the materials including the propagation phase by assuming that some differences in the amplitude of the well known fibre bridging phenomenon are directly induced by differences in interface quality, which is the only parameter that is not kept constant. Both mode I and mode II tests have revealed a high sensitivity to the fibre/matrix interface quality: According to the property which is considered, variations are noted in a range of 150% to 300% for a modification of the interface by different sizing and in a range of 150% to 700% for an artificial modification of the interface by hydrothermal aging. Nevertheless mode II tests offered rather limited information (only about cracks initiation). On the other hand the interest of mode I fracture mechanics as fibre/matrix interface characterization method has appeared, in so far as this technique makes it possible to separate cracks initiation and then cracks extension phenomena, on which the fibre/matrix interface quality has a specific incidence, that is translated by variations of cracks initiation and propagation energies, of cracks growth rates and of acoustic emissions.

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.

Polyamide-6/Clay Nanocomposites: A Critical Review

The plastics business is gathering around nanocomposites because of the unusual performance of these materials in some technologically important applications, such as automotive parts, packaging, textiles and flame resistant materials. The use of clay as the reinforcing component of polymers has transformed the properties of the resultant materials. These nanocomposites are regarded as futuristic. However the science of clay-polymer interaction is still a subject of intense investigation. The industrialization of nanocomposites is accelerating and efforts are being made to achieve still better performance by optimising of their compounding and processing conditions. Nanocomposites based on many different polymers have been, or are being developed. The current scenario in relation to polyamide-6/clay nanocomposites is presented in this article. Preparation, processing and application issues are addressed in particular.

Mechanical, Optical and Barrier Properties of PA6/Nanoclay-Based Single-and Multilayer Blown Films

The optimisation of food packaging films requires the films to be designed with excellent barrier properties to gases (usually water vapour and oxygen) and high mechanical and optical performances, without significant cost increase. Polymer nanocomposites may offer an interesting opportunity in this respect. This solution is studied in the present paper for both polyamide-6 (PA6) single-layer films and polyethylene/maleic anhydride grafted polyethylene/polyamide-6 (PE/PEgMAH/PA6) multilayer films. The addition of 2 wt.% of nanoclay in PA6 simultaneously improves the mechanical properties (tensile modulus, yield stress and strength), optical performances (gloss, haze and clarity) and oxygen impermeability. The processing conditions have no major influence on the studied properties, except for the optical properties. The cost increase induced by this solution is balanced by the benefits obtained in terms of overall improvement of film properties.

Prediction of injection-moulded flax fibre reinforced polypropylene tensile properties through a micro-morphology analysis

Micromechanical models usually applied to predict the mechanical properties of short glass fibre reinforced composites were used to evaluate the Young’s modulus and tensile strength of flax fibre reinforced polypropylene. Due to lack of accuracy between the experimental results and the existing models, a new adjustment to the Kelly-Tyson model was proposed. The changes were based on the understanding of the microstructure obtained in polypropylene/flax fibre composites produced by injection moulding with different flax fibre content. The mechanical properties were interpreted based on real fibre loading, fibre orientation, fibre dimension distribution and morphology of the composites. Lack of fibre/matrix adhesion, strong fibre damage and changes on the crystallization behaviour of polypropylene in the presence of flax fibres affect the mechanical strength, stiffness and elongation of the composites. The Kelly-Tyson’s model used for tensile strength prediction was modified to take into consideration the fibre property variability due to the large distribution of fibre shape ratio induced by the process. Finally, matrix modulus has been adjusted to take into account the change of crystallinity with fibre content. A better description of the mechanical properties is obtained using the proposed approach, resulting indeed in an excellent approximation to the modulus of the composite.

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.