Hans E. Miltner

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.

Experimental evidence for reduced chain segment mobility in poly(amide)-6/clay nanocomposites

Poly(amide)-6/clay nanocomposites are investigated by means of modulated temperature differential scanning calorimetry. The importance of polymer–filler interaction is explored by comparing nanocomposites based on untreated and organically modified clay. During quasi-isothermal crystallization experiments, an excess contribution is observed in the recorded heat capacity signal due to reversible melting and crystallization. The magnitude of this excess contribution depends on the nanocomposite investigated. We suggest that it is directly related to the segmental mobility of the polymer chains in the interphase region. As such, the magnitude of this excess contribution can be used to quantify the efficiency of the polymer–clay interaction. Depending on the clay type used, differences in interfacial interaction can be achieved, which is of great importance with respect to the improvement of material properties. Based on thermal analysis results, a simple interphase model is proposed that is able to account for both the thermal and mechanical properties of poly(amide)-6/clay nanocomposites.

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.

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.

RheoDSC: A hyphenated technique for the simultaneous measurement of calorimetric and rheological evolutions

A newly developed hyphenated technique is presented combining an existing rheometer and differential scanning calorimeter into a single experimental setup. Through the development of a fixation accessory for differential scanning calorimeter (DSC) crucibles and a novel rotor, the simultaneous measurement is performed inside the well-controlled thermal environment of a Tzero DSC cell. Hence, the evolution of thermal and flow properties of a material can be simultaneously measured using steady or oscillatory shear measurements and regular or modulated temperature DSC measurements. Along with the construction of a prototype, a validation of the design was performed. The technique offers interesting opportunities for the investigation of flow-induced transitions, for instance, crystallization or phase separation, and provides an asset for high-throughput screening of materials. The potential of the novel technique is demonstrated by two case studies: the chemorheology during the cure of a thermosetting epoxy-amine system and the flow-induced crystallization of syndiotactic polypropylene.