In this work, we present the nonlinear shear rheology of low molecular weight polystyrene melts, and unentangled solutions obtained by diluting large polymers in oligomeric solvents. As far as linear melts are concerned, while their linear viscoelastic response is consistent with predictions from the Rouse model, in the nonlinear regime, the Cox-Merz rule does not appear to be strictly obeyed, despite a universal thinning exponent of -0.5. As for the nonlinear response of solutions, shear strain hardening is observed due to the low elasticity and long relaxation times, which allow for the achievement of very large values of the Weissenberg number. [1]. Furthermore, it is demonstrated that longer linear oligomers align better in the flow direction, thereby suppressing strain hardening, similar to the nematic effect observed in the uniaxial extension of long polymer chains.
The modelling of such behaviour requires accurate use of the existing physics with the addition of new ingredients. The experimental results for unentangled melts are analysed using the shear slit model [2] and simulations. Concerning solutions, simulations involving monomeric friction reduction effects demonstrate that mitigating this friction reduction is responsible for shear hardening.
We provide an outlook on the rheological behaviour of more complex unentangled architectures, such as star polymer melts and solutions made by diluting high molecular weight stars in oligomeric counterparts.

The understanding of the effects of branching on the flow behavior of polymer melts and mechanical properties in the solid state is of fundamental interest to polymer science since its beginnings. Next to their quantity and length, their positioning is decisive, as the resulting topology is key in controlling properties.
A new synthetic route is developed to access defined branched model systems. This is realized through grafting onto the pyridine ring of Poly(2-vinylpyridine). A variety of homo and block copolymers can be synthesized with the use of different backbone, i.e. a Poly(2-vinylpyridine-b-styrene-b-2-vinylpyridine) backbone to yield a pom-pom architecture.
We present investigations of nonlinear startup behavior and uniaxial extension of a pom-pom shaped polymer melt. If the arm and backbone relaxation times are sufficiently separated, two stress overshoots can be observed. Additionally, we find that the Cox-Merz Rule is not valid for high branching levels. In uniaxial extension, we identified four characteristic, strain rate dependent regimes of the extensional viscosity. The four regimes enable the prediction over the whole range of strain rates exclusively through the LVE and the molecular topological parameters. We can experimentally confirm simplifications of the pom-pom equations using the Considère criterion to predict the extensional viscosity as a factor of [q²/ln(sqrt(3)q)] above the linear-viscoelastic envelope (LVE) at medium strain rates. Overall, we find that for the Cox-Merz Rule and the Considère criterion the effective backbone entanglements s_b,eff are the decisive quantity. Both rules are obeyed by the pom-poms if s_b,eff > 2 and not hold true below.

The rheological behavior of polymers is often analyzed by experimental studies using high-pressure capillary rheometry. The experimental results are then corrected by applying the method of Bagley [1] to calculate the “true shear stress” and by following the method of Rabinowitsch/Weissenberg [2] to calculate the so called “true shear rate”. This work presents a new method which can replace the method of Rabinowitsch/Weissenberg [2] and enables a more accurate calculation of the true shear rate, especially in the transition region between the Newtonian plateau and the Power law region. The method uses numerical calculations that can be implemented in common calculation programs like Microsoft Excel, Python, Matlab, etc. These numerical calculations are very fast and enable the implementation of rheological models like those of Carreau [3], Yasuda [4], Bingham [5], etc. Therefore, this work enables a more accurate analysis of high-pressure capillary rheometry measurements and can probably be extended for Parallel-Plate Rheometry.

The kinetics of an RMT 6 epoxy resin and the thermo-mechanical properties of the finally cross-linked product were experimentally studied using an Anton Paar MCR 702 MultiDrive rheometer. In order to gain insights in the evolution of macroscopic rheological properties induced by chemical reactions within the sample material, the rheological measurements were coupled with in-situ Raman spectroscopy. The gelation-kinetics was further evaluated with a so-called Multiwave rheometry test. Accordingly, the Winter-Chambon criterion was used to determine the sol/gel transition point [1]. For dynamic mechanical analysis of the cured component a linear drive module was added to the instrument. The combination of linear drive and rotational drive in one device allowed the characterization of thermal transitions using dynamic mechanical analysis (DMA) in two different deformation modes (torsion and bending). Two thermal events could be detected from the DMA test: the main glass transition temperature and a sub-glass transition of the material [2]. Additionally, this unique experimental setup allows determining the complex Young’s modulus as well as shear modulus using a single specimen in a continuous measurement run over a wide temperature and frequency range. The instrument frame and air bearings are designed to provide outstandingly low radial and axial compliance at the same time, thus enabling the measurement of accurate modulus values in all testing modes.

Incorporation of nano-additives in a polymeric matrix, leads to the formation of nanohybrids with innovative physicochemical properties compared to the initial materials and / or the respective conventionally filled systems. In this work, we investigate the rheological response of different series of poly(ethylene oxide) / silica, PEO / SiO2, nanocomposites by shear rheology. More specifically, spherical SiO2 nanoparticles of two different radii are dispersed in PEOs of different molecular weights. The nanoparticles were well dispersed in the polymer matrix as confirmed via Transmission Electron Microscopy (TEM), while their structure and morphology were investigated by X-Ray Diffraction (XRD) and Small Angle X-Ray Scattering (SAXS) [1]. Nanocomposites over a wide range of compositions were developed to investigate both the effect of the nanoparticles size and concentration and the effect of the polymer molecular weight, on the rheological properties of the nanocomposite materials. For all systems, three different concentration regimes are observed with distinctly different rheological response; a ‘polymer-like’ regime, where the behavior resembles the one of the respective polymers, a ‘weak gel-like’ regime at higher nanoparticle content, where enhanced polymer / particle interactions modify the behavior, and a ‘strong gel-like’ one characterized by percolated networks of nanoparticles formed within the polymer matrices [2]. The ‘polymer-like’ regime is especially interesting since a significant reduction of the melt viscosity is observed attributed to a dilution of the entanglement network of the chains due to the nanoadditive presence.
Acknowledgements: This work was supported by the EU Horizon Europe Programme (project WISE, Grant Agreement 101138718).

Halloysite nanotube (HNT)-reinforced biodegradable PLA-based nanocomposite films were successfully fabricated using a blown film extruder with HNT concentrations ranging from 1.5 to 6 wt.%. The biodegradability of these films was evaluated through a soil burial test over 90 days at ~30 °C and 60% RH. Physiological weight loss, water absorption, and post-burial mechanical properties were examined. The results indicated that PLA/HNT films exhibited gradual degradation in the first 15 days, with substantial changes by 90 days. Pristine PLA films showed ~54% weight loss after 15 days, whereas PLA/HNT6 composites exhibited a lower weight loss of 35%. By Day 90, neat PLA films had fully degraded (~108% weight loss), while PLA/HNT6 films retained greater stability (~81% weight loss). SEM micrographs of 15-day soil-buried samples showed fungal growth, confirmed by FTIR analysis. A significant reduction in tensile strength was observed, decreasing from ~68% for pristine PLA to ~22% for PLA/HNT6 within 15 days. After 90 days, pristine PLA films were completely degraded, preventing further tensile testing. Crystallinity reduced from ~27% to ~18% for PLA after 15 days, with a significant drop to ~4% after 90 days. PLA/HNT6 films exhibited a reduction from ~36% to ~18%. These findings indicate that neat PLA degraded faster than PLA/HNT composites, demonstrating HNT’s role in enhancing durability. Thus, the development of such hybrid nanocomposites offers a promising approach for sustainable packaging applications, ensuring improved degradation dynamics and superior physicomechanical properties.