Alejandro J. Müller's Lab
About the lab
Featured projects (8)
New plastic bottles in opaque PET (polyethylene terephtalate) appeared recently on the market. When their waste is mixed to those of transparent-PET-based, the obtained material cannot be recycled anymore because of a loss of properties. The project has been 65% cofinanced by the European Regional Development Fund (ERDF) through the Interreg V-A Spain France Andorra programme (POCTEFA 2014-2020). POCTEFA aims to reinforce the economic and social integration of the French–Spanish–Andorran border. Its support is focused on developing economic, social and environmental cross-border activities through joint strategies favouring sustainable territorial development. The occurrence of these new packagings creates a threat for the recycling industry, very present in the POCTEFA area. In order to maintain and strengthen this sector, new outputs for the recycling of opaque PET bottles are required. This is the challenge that RevalPET proposes to take up. More details on www.poctefa.eu
The project goal is to understand the crystallization behavior of crystallizable polymers as well as the influence of other components in a blend on the crystallization behavior of a particular component.
Featured research (7)
In this work, blends of Poly(ethylene oxide), PEO, and poly(1,6-hexanediol), PHD, were prepared in a wide composition range. They were examined by Differential Scanning Calorimetry (DSC), Polarized Light Optical Microscopy (PLOM) and Wide Angle X-ray Scattering (WAXS). Based on the results obtained, the blends were partially miscible in the melt and their crystallization was a function of miscibility and composition. Crystallization triggered phase separation. In blends with higher PEO contents both phases were able to crystallize due to the limited miscibility in this composition range. On the other hand, the blends with higher PHD contents display higher miscibility and therefore, only the PHD phase could crystallize in them. A nucleation effect of the PHD phase on the PEO phase was detected, probably caused by a transference of impurities mechanism. Since PEO is widely used as electrolyte in lithium batteries, the PEO/PHD blends were studied with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and the effect of Li-salt concentration was studied. We found that the lithium salt preferentially dissolves in the PEO phase without significantly affecting the PHD component. While the Li-salt reduced the spherulite growth rate of the PEO phase within the blends, the overall crystallization rate was enhanced because of the strong nucleating effect of the PHD component. The ionic conductivity was also determined for the blends with Li-salt. At high temperatures (>70 °C), the conductivity is in the order of ~10−3 S cm−1, and as the temperature decreases, the crystallization of PHD was detected. This improved the self-standing character of the blend films at high temperatures as compared to the one of neat PEO.
In this work, we prepare and characterize multiphasic thin films containing poly(ε-caprolactone), PCL, poly(butylene succinate), PBS, and a poly (butylene succinate-ran-ϵ-caprolactone) (PBS-ran-PCL) random copolyester. To that aim, thin films were prepared by sequential dipping of a silicon substrate into chloroform solutions of the respective polymers. The preparation method resulted in films with varying compositions of PCL and PBS components depending on the initial concentration of the dipping solutions and the number of dipping steps employed for the preparation of the samples. Atomic force microscopy (AFM), grazing incidence X-ray scattering at wide angle (GIWAXS) and scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared nanospectroscopy (nano-FTIR) were employed to characterize the films obtained. As chloroform can dissolve all components, the final composition of the film was always rich in the last deposited layer component. The thin films obtained were semicrystalline with a complex axialitic or dendritic morphology of the dominant component (that one deposited last) with traces of the other components, whose presence and location was revealed by s-SNOM/nano-FTIR.
We study the composition-dependent miscibility of polyamide 6 and biobased polyamide 4,10 (PA6/PA410) blends, as triggered by crystallization driven phase segregation. The blends were prepared by extrusion in a wide composition range and studied by X-ray diffraction (both in-situ and ex-situ SAXS/WAXS), Differential Scanning Calorimetry (DSC), and Polarized Light Optical Microscopy (PLOM) during non-isothermal crystallization. The blends were miscible in the amorphous state, as demonstrated by a single Tg that follows the Fox equation as a function of composition. The blends were also considered to be miscible in the melt, as no evidence of phase segregation was found by SAXS or phase contrast microscopy in the melt. Remarkably, the blends can also be miscible in the crystalline state in a limited composition range. When only 10 or 20% PA6 is present in the blends, co-crystallization was evidenced by DSC and WAXS and the blends exhibited a single PA410 rich crystalline phase. On the other hand, as 30% or more PA6 is added to PA410, crystallization driven phase segregation occurs and progressively increased with PA6 content in the blends. Hence double crystalline blends are formed with both PA6 rich and PA410 rich crystalline phases. Clear evidence of the presence of either one or two crystalline phases was obtained by temperature-dependent measurements employing DSC, PLOM, WAXS and SAXS. Both the single and double crystalline PA6/PA410 blends exhibited good mechanical properties in view of the excellent compatibility displayed by the blends. The mechanical properties are in line with those exhibited by miscible blends following a simple rule of mixtures.
The crystallization of heterogeneously nucleated bulk polymers typically occurs in a single exothermic process, within a narrow temperature range, i.e., a single exothermic peak is detected by differential scanning calorimetry when the material is cooled from the melt. However, when a bulk semicrystalline polymer is subdivided or dispersed into a multitude of totally (or partially) isolated microdomains (e.g., droplets or cylinders), in number comparable to that of commonly available nucleating heterogeneities, several separated crystallization events are typically observed, i.e., fractionated crystallization. This situation is often found for the minor crystallizable component in immiscible blends. When the bulk polymer is dispersed into a number of microdomains that is several orders of magnitude higher than the available number of heterogeneities within it, most microdomains will be heterogeneity-free. In these clean microdomains the nucleation can occur by contact with the interfaces (i.e., surface nucleation) or by homogeneous nucleation inside the microdomain volume. These cases can be easily encountered in cylinders or spheres within strongly segregated block copolymers, or in infiltrated polymers within nanopores of alumina templates. In this work, a comprehensive review of the known cases of fractionated crystallization is provided. The changes upon decreasing microdomain sizes from a dominant single heterogeneous nucleation, through fractionated crystallization, to surface or homogeneous nucleation are critically reviewed. Emphasis is placed on the common features of the phenomenon across the different systems, and thus on the general conclusions that can be drawn from the analysis of representative semicrystalline polymers. The origin of the fractionated crystallization effects and their dramatic consequences on the nucleation and crystallization kinetics of semicrystalline polymers are also discussed.
- Polymer Science and Technology
About Alejandro J. Müller
- Follow my group on Twitter: "https://twitter.com/AJ_Muller_Group" Check me out at: https://sites.google.com/site/profalejandromueller/ and https://scholar.google.com/citations?user=KFdB3igAAAAJ&hl=en