Samira Benali

Study of interlayer spacing collapse during polymer/clay nanocomposite melt intercalation.

The influence of the chemical structure of alkylammonium organo-modifying montmorillonite clays on the ability to form nanocomposites by melt blending, depending on the processing temperature and the organoclay thermal treatment, has been investigated. On one side chlorinated polyethylene/Cloisite 30B (nano)composite has been prepared by melt intercalation at 175 degrees C and its wide angle X-ray diffraction pattern revealed that the peak characteristic of the interlayer spacing of the organoclay was shifted to lower d-spacing, indicating a collapse of the organoclay structure. On the other side, (nano)composites based on ethylene-vinyl acetate copolymer/Cloisite 30B have been prepared by melt intercalation at 140 degrees C. At this temperature, exfoliation was observed with the as-received organoclay while the same organo-modified clay, simply dried at 180 degrees C for 2 hours, induced again the formation of a composite with a collapsed structure. The effect of the Cloisite 30B thermal treatment on the morphology and mechanical properties of ethylene-vinyl acetate-based (nano)composites was investigated using wide angle X-ray diffraction and tensile tests. In order to shed some light on the origin of this clay interlayer collapse, organoclay modified with various ammonium cations bearing long alkyl chains with different amounts of unsaturations were studied using wide angle X-ray diffraction and X-ray photoelectron spectroscopy before and after thermal treatment at 180 degrees C for 2 hours. Isothermal thermogravimetric analysis of all organoclays was also investigated. The layers collapse effect is discussed depending upon the level of unsatured hydrocarbon present in the organic surfactant.

Quantifying the degree of nanofiller dispersion by advanced thermal analysis: application to polyester nanocomposites prepared by various elaboration methods

An innovative thermal analysis methodology is applied for the characterization of poly(e-caprolactone) (PCL) nanocomposites containing layered silicates, needle-like sepiolite or polyhedral oligomeric silsesquioxane (POSS) nano-cages, aiming at assessing the key factors affecting nanofiller dispersion and nanocomposite properties. This methodology takes benefit of the fact that—for a given nanofiller aspect ratio—the magnitude of the excess heat capacity recorded during quasi-isothermal crystallization is directly related to the occurrence of pronounced changes to the PCL crystalline morphology. The extent of these changes, in turn, directly depends on the amount of matrix/filler interface and can therefore be considered a reliable measure for the degree of nanofiller dispersion, as supported by complementary morphological characterization. The importance of processing parameters is demonstrated in a comparative study using various melt processing conditions, evidencing the need for high shear to effectively exfoliate and disperse individual nanoparticles throughout the polymer matrix. Furthermore, the choice of the nanocomposite elaboration method is shown to profoundly affect the final morphology, as illustrated in a comparison between nanocomposites prepared by melt mixing, by in situ polymerization and by a masterbatch approach. Grafting PCL onto the filler strongly enhances its dispersion quality as compared to conventional melt mixing; subsequently further dispersing such grafted nanohybrids into the polymer matrix through a masterbatch approach provides a highly efficient method for the elaboration of well-dispersed nanocomposites. Finally, the crucial issue of interfacial compatibility is addressed in a comparison between various surface-treated layered silicates, showing that high degrees of filler dispersion in a PCL matrix can only be achieved upon polar modification of the silicate.

Key factors for tuning hydrolytic degradation of polylactide/zinc oxide nanocomposites

Abstract The hydrolytic degradation of thin films of polylactide/surface treated zinc oxide [poly(lactic acid) (PLA)/ZnOs] nanocomposites was investigated in phosphate buffer solution at the temperature of 37°C for more than 10 months. To produce PLA/ZnOs nanocomposites, the previously silanized metal oxide nanofiller has been dispersed into PLA by melt blending using twin screw extruders and the resulting dried pellets were shaped into thin films of about 70 μm thickness. For sake of comparison, pristine PLA was processed and investigated under similar conditions. The evolution of molecular weights of the PLA matrix, as well as of crystallinity and thermal parameters of interest, with the hydrolysis time, has been recorded by size exclusion chromatography (SEC) and differential scanning calorimetry (DSC), respectively. Accordingly, at longer hydrolysis time, the nanocomposites revealed better resistence to the hydrolytic degradation (lower weight loss, smaller decrease of molecular mass, no dramatic increase in dispersity), data that were also associated with the changes in the morphology of specimens over time as evidenced by visual analysis or by microscopy. The results show the possibility to tune the hydrolytic degradation and prolonging the service life of PLA throught the incorporation of a small amount of hydrophobic silanized nanofiller (ZnOs). A bulk degradation mechanism was assumed, whereas the delayed degradation of nanocomposites was ascribed to a slowdown of the water diffusion into PLA matrix thanks to important increases of the crystallinity and especially to the hydrophobic properties of ZnO nanofiller treated with ∼3 wt-% triethoxycaprylylsilane. Accordingly, the rate of hydrolytic degradation of PLA/ZnOs nanocomposite films can be reduced by increasing the loading of nanofiller and PLA crystallinity.

Microscopic Morphology of Chlorinated Polyethylene-Based Nanocomposites Synthesized from Poly(ε-caprolactone)/Clay Masterbatches

Chlorinated polyethylene (CPE) nanocomposites were synthesized by melt blending clay-rich/poly(epsilon-caprolactone) (PCL) masterbatches to CPE matrices. The masterbatches were prepared following two synthetic routes: either PCL is melt-blended to the clay or it is grafted to the clay platelets by in situ polymerization. The microscopic morphology of the nanocomposites was characterized by X-ray diffraction, atomic force microscopy, transmission electron microscopy, and modulated temperature differential scanning calorimetry. When using free PCL, intercalated composites are formed, with clay aggregates that can have micrometric dimensions and a morphology similar to that of the talc particles used as fillers in commercial CPE. PCL crystallizes as long lamellae dispersed in the polymer matrix. When using grafted PCL, the nanocomposite is intercalated/exfoliated, and the clay stacks are small and homogeneously dispersed. PCL crystallizes as lamellae and smaller crystals, which are localized along the clay layers. Thanks to the grafting of PCL to the clay platelets, these crystalline domains are thought to form a network with the clay sheets, which is responsible for the large improvement of the mechanical properties of these materials.

Fire and Gas Barrier Properties of Poly(styrene-co-acrylonitrile) Nanocomposites Using Polycaprolactone/Clay Nanohybrid Based-Masterbatch

Exfoliated nanocomposites are prepared by dispersion of poly(-caprolactone) (PCL) grafted montmorillonite nanohybrids used as masterbatches in poly(styrene-co-acrylonitrile) (SAN). The PCL-grafted clay nanohybrids with high inorganic content are synthesized by in situ intercalative ring-opening polymerization of -caprolactone between silicate layers organomodified by alkylammonium cations bearing two hydroxyl functions. The polymerization is initiated by tin alcoholate species derived from the exchange reaction of tin(II) bis(2-ethylhexanoate) with the hydroxyl groups borne by the ammonium cations that organomodified the clay. These highly filled PCL nanocomposites (25 wt% in inorganics) are dispersed as masterbatches in commercial poly(styrene-co-acrylonitrile) by melt blending. SAN-based nanocomposites containing 3 wt% of inorganics are accordingly prepared. The direct blend of SAN/organomodified clay is also prepared for sake of comparison. The clay dispersion is characterized by wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM), and solid state NMR spectroscopy measurements. The thermal properties are studied by thermogravimetric analysis. The flame retardancy and gas barrier resistance properties of nanocomposites are discussed both as a function of the clay dispersion and of the matrix/clay interaction.

FT-NIR monitoring of a scattering polyurethane manufactured by reaction injection molding (RIM): Univariate and multivariate analysis versus kinetic predictions

Near InfraRed (NIR) spectroscopy was used to monitor in situ a polyurethane synthesis during a RIM process. Univariate and multivariate analysis of transmittance spectra were used to calculate the reaction extent. A very good agreement was observed between multivariate analysis (PCA), univariate (Beer-Lambert) analysis and kinetic predictions. It was demonstrated that, in this case, PCA methods can provide a good estimation of the reaction extent versus time, without time-consuming calibration. The spectral range of PCA has to be carefully chosen.

In situ monitoring of polyurethane cure using fibre-optical FT-NIR spectroscopy

In-line monitoring of the reaction extent of polyurethane during a reactive injection moulding (RIM) process is carried out using fibre-optic near infrared (NIR) spectroscopy. Up to 250 transmission spectra are recorded during the reaction. Univariate and multivariate analysis of transmittance spectra were used to calculate the chemical conversion. A good agreement is observed between first principal component of principal component analysis (PCA), and univariate (Beer—Lambert) results. It is observed that, in this case, the PCA method can provide a good practical estimation of the time-concentration profile during the reaction, without the need of the time-consuming calibration methods. The scores of PC1 are merely linearly correlated to the level of conversion and contain enough information for the quantitative analysis. As expected interactions and hydrogen-bonding play an important role. Hence the spectral region of PCA analysis has to be carefully selected to obtain a good agreement with the Beer—Lambert law. The NIR spectroscopy and the PCA are easy-to-use techniques for on line monitoring of polyurethane reactions and these results open up a low cost effective opportunity for monitoring the fast RIM process.

Chemeorheology: a new design for simultaneous rheological and Fourier transform near infrared analysis

In this paper we present a new laboratory-made system which allows the combination of rheometer dynamical analysis (RDA) and Fourier transform near infrared (FT-NIR) spectroscopy. Dynamic rheological data and NIR spectra were simultaneously collected. Previous studies of thermosetting systems and, more particularly, polyurethane studies, manufactured by the reaction injection moulding (RIM) process, emphasised the need for simultaneous rheological and kinetic measurements. The rheological measurements, performed using RDA, were obtained using oscillatory shear experiments at variable angular frequencies between two parallel plates. In-situ monitoring of the extent of reaction of the investigated polyurethane was carried out at room temperature using fibre-optic FT-NIR spectroscopy. Multivariate analysis of transmittance spectra was performed to calculate the degree of conversion. The appliance for simultaneous measurement is described and their advantages and limitations are briefly discussed. The viscoelastic behaviour and the extent of reaction were studied during reactive blending of polyurethane formation, especially at the critical moment of gelation. A good agreement is observed, between separate and simultaneous rheological-FT-NIR measurements. Indeed, rheological experiments (up to 100 Hz) are not perturbed by the increase of the weight of the RDA plates. The RDA-FT-NIR technique may provide a powerful tool for studying curing reactions of polymers for both industrial and academic communities.

PCL/Clay Nano-Biocomposites

Poly(e-caprolactone) is a biopolyester synthesized from fossil resources with interesting biodegradable properties. However, for certain applications, this biopolymer cannot be fully competitive with conventional thermoplastics since some of its properties appear too weak. The association of PCL with nano-sized fillers allows for significantly improving a large range of properties. The most reported nano-fillers in poly(e-caprolactone)-based materials are represented by organo-modified clays more likely leading to one of the most widely investigated families of nano-biocomposites. This chapter is dedicated to this novel class of materials with a special focus set on the relationships between the production process, the extent of nano-filler dispersion and the thermo-mechanical properties, e.g., crystallinity and stiffness, of the related nano-biocomposites.

Supramolecular Approach for Efficient Processing of Polylactide/Starch Nanocomposites

All-biobased and biodegradable nanocomposites consisting of poly(l-lactide) (PLLA) and starch nanoplatelets (SNPs) were prepared via a new strategy involving supramolecular chemistry, i.e., stereocomplexation and hydrogen-bonding interactions. For this purpose, a poly(d-lactide)-b-poly(glycidyl methacrylate) block copolymer (PDLA-b-PGMA) was first synthesized via the combination of ring-opening polymerization and atom-transfer radical polymerization. NMR spectroscopy and size-exclusion chromatography analysis confirmed a complete control over the copolymer synthesis. The SNPs were then mixed up with the copolymer for producing a PDLA-b-PGMA/SNPs masterbatch. The masterbatch was processed by solvent casting for which a particular attention was given to the solvent selection to preserve SNPs morphology as evidenced by transmission electron microscopy. Near-infrared spectroscopy was used to highlight the copolymer–SNPs supramolecular interactions mostly via hydrogen bonding. The prepared masterbatch was melt-blended with virgin PLLA and then thin films of PLLA/PDLA-b-PGMA/SNPs nanocomposites (ca. 600 μm) were melt-processed by compression molding. The resulting nanocomposite films were deeply characterized by thermogravimetric analysis and differential scanning calorimetry. Our findings suggest that supramolecular interactions based on stereocomplexation between the PLLA matrix and the PDLA block of the copolymer had a synergetic effect allowing the preservation of SNPs nanoplatelets and their morphology during melt processing. Quartz crystal microbalance and dynamic mechanical thermal analysis suggested a promising potential of the stereocomplex supramolecular approach in tuning PLLA/SNPs water vapor uptake and mechanical properties together with avoiding PLLA/SNPs degradation during melt processing.