Anne-Lise Goffin

Bionanocomposites based on poly(ε-caprolactone)-grafted cellulose nanocrystals by ring-opening polymerization

A ‘grafting from’ approach was used to graft poly(e-caprolactone) (PCL) polymers to cellulose nanocrystals by Sn(Oct)2-catalyzed ring-opening polymerization (ROP). The grafting efficiency was evidenced by the long-term stability of suspension of PCL-grafted cellulose nanocrystals in toluene. These observations were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Extracted nanohybrids were characterized by Differential Scanning Calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The morphology and crystalline structure of the PCL-grafted cellulose nanocrystals was examined by transmission electron microscopy (TEM) and X-Ray diffraction, respectively. Results showed that cellulose nanocrystals kept their initial morphological integrity and their native crystallinity. Nanocomposites with high content of cellulose nanocrystals were prepared using either neat cellulose nanocrystals or PCL-grafted cellulose nanocrystals and high molecular weight PCL as matrix using a casting/evaporation technique. Thermo-mechanical properties of processed nanocomposites were studied by DSC, dynamical mechanical analyses (DMA) and tensile tests. A significant improvement in terms of Youngs modulus and storage modulus was obtained.

From interfacial ring-opening polymerization to melt processing of cellulose nanowhisker-filled polylactide-based nanocomposites.

In the present work, cellulose nanowhiskers (CNWs), extracted from ramie fibers, were incorporated in polylactide (PLA)-based composites. Prior to the blending, PLA chains were chemically grafted on the surface of CNW to enhance the compatibilization between CNW and the hydrophobic polyester matrix. Ring-opening polymerization of l-lactide was initiated from the hydroxyl groups available at the CNW surface to yield CNW-g-PLA nanohybrids. PLA-based nanocomposites were prepared by melt blending to ensure a green concept of the study thereby limiting the use of organic solvents. The influence of PLA-grafted cellulose nanoparticles on the mechanical and thermal properties of the ensuing nanocomposites was deeply investigated. The thermal behavior and mechanical properties of the nanocomposites were determined using differential scanning calorimetry (DSC) and dynamical mechanical and thermal analysis (DMTA), respectively. It was clearly evidenced that the chemical grafting of CNW enhances their compatibility with the polymeric matrix and thus improves the final properties of the nanocomposites. Large modification of the crystalline properties such as the crystallization half-time was evidenced according to the nature of the PLA matrix and the content of nanofillers.

Polyester-Grafted Cellulose Nanowhiskers: A New Approach for Tuning the Microstructure of Immiscible Polyester Blends

Cellulose nanowhiskers (CNW), extracted from ramie fibers by sulfuric acid hydrolysis, were used as substrates to compatibilize binary polyester blends containing 50/50 (w/w) polycaprolactone (PCL) and polylactide (PLA). To tailor their interfacial energy and fine-tune their adhesion with the components of the blend, CNW were subjected to different surface polyester grafting by the means of ring-opening polymerization. PCL and PLA homopolyesters as well as P(CL-b-LA) diblock copolymers were successfully grafted on the surface of CNW and the resulting substrates were loaded into the PCL/PLA blend by melt-blending. Morphological and rheological analyses were conducted in order to evaluate the ability of these nanoparticles to enhance the compatibility of PCL/PLA blends. Our results showed that unmodified CNW as well as (co)polyester-grafted CNW improved, at different levels, the compatibility of PCL/PLA blends by preventing from coalescence the dispersed domains. (co)polyester-grafted CNW also enhance the mechanical properties of the blend, which can be explained by the formation of cocontinuous phase morphology at the interface. Our findings suggest that (co)polyester-grafted CNW, especially CNW-g-P(CL-b-LA) diblock copolymers, can serve as a suitable nanofiller to tune the compatibility of PCL/PLA blends and their related microstructures.

From polyester grafting onto POSS nanocage by ring-opening polymerization to high performance polyester/POSS nanocomposites

Polyester-grafted polyhedral oligomeric silsesquioxane (POSS) nanohybrids selectively produced by ring-opening polymerization of e-caprolactone and L,L-lactide (A.-L. Goffin, E. Duquesne, S. Moins, M. Alexandre, Ph. Dubois, Eur. Polym. Journal, 2007, 43, 4103) were studied as “masterbatches” by melt-blending within their corresponding commercial polymeric matrices, i.e., poly(e-caprolactone) (PCL) and poly(L,L-lactide) (PLA). For the sake of comparison, neat POSS nanoparticles were also dispersed in PCL and PLA. The objective was to prepare aliphatic polyester-based nanocomposites with enhanced crystallization behavior, and therefore, enhanced thermo-mechanical properties. Wide-angle X-ray scattering and transmission electron microscopy attested for the dispersion of individualized POSS nanoparticles in the resulting nanocomposite materials only when the polyester-grafted POSS nanohybrid was used as a masterbatch. The large impact of such finely dispersed (grafted) nanoparticles on the crystallization behavior for the corresponding polyester matrices was noticed, as evidenced by differential scanning calorimetry analysis. Indeed, well-dispersed POSS nanoparticles acted as efficient nucleating sites, significantly increasing the crystallinity degree of both PCL and PLA matrices. As a result, a positive impact on thermo-mechanical properties was highlighted by dynamic mechanical thermal analysis.

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.