This study[1] provides a detailed picture of how a protein (Lysozyme) complexes with a poly(acrylic acid) polyelectrolyte (PAA) in water at the atomic level using a combination of all-atom molecular dynamics simulations and experiments. The effect of PAA and temperature on the protein's structure is explored. The simulations reveal that Lysozyme's structure is relatively stable except from local conformational changes induced by the presence of PAA and temperature increase. The effect of a specific thermal treatment on the complexation process is investigated revealing both structural and energetic changes. Certain types of secondary structures (i.e, α-helix) are found to undergo a partially irreversible shift upon thermal treatment which aligns qualitatively with experimental observations.[2] This uncovers the origins of thermal aggregation in Lysozyme and points to new PAA/Lysozyme bonds that are formed and potentially enhance the stability in the complexes. As the temperature changes distinct amino acids are found to exhibit the closest proximity to PAA, resulting into different PAA/Lysozyme interactions; consequently, a different complexation pathway is followed. Energy calculations reveal the dominant role of electrostatic interactions. This detailed information can be useful for designing new biopolymer/protein materials and understanding protein function under immobilization of polyelectrolytes and upon mild denaturation processes.

Poly(vinylidene fluoride) (PVDF) and its copolymer P(VDF-co-TrFE) are attracting increasing interest due to their remarkable piezoelectric properties. However, their piezoelectric properties can be affected by annealing or storage at room temperature, due to the formation of secondary crystals that may reduce the mobility of the amorphous fraction. This study aims to deepen the understanding of the mechanisms underlying the formation of secondary crystals in P(VDF-co-TrFE) with VDF/TrFE molar ratios of 80/20 and 55/45, after various annealing durations and temperatures. Differential scanning calorimetry (DSC) analyses revealed the presence of a low-temperature endothermic peak during the heating process, attributed to the melting of secondary crystals. The temperature of this peak and the associated enthalpy variation are directly dependent on the annealing conditions. Subsequently, the impact of secondary crystals on dielectric properties was evaluated using dynamic dielectric spectroscopy (DDS) tests. These analyses revealed that secondary crystals primarily influence the αc relaxation, associated with the mobility of chains in the crystalline phase.

Polyhydroxyalkanoates (PHAs) have gained considerable attention as sustainable alternatives to petrochemical-based polymers. In addition to being biobased, biodegradable, and biocompatible, PHAs exhibit highly versatile physicochemical properties, enabling applications ranging from 3D printing filaments and food packaging to high-value biomedical materials (Koller & Mukherjee, 2022). Among PHAs, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) is of particular interest due to its tunable material properties and superior biocompatibility. However, the widespread industrialization of P(3HB-co-4HB) remains limited (Huong et al., 2021). A key challenge for P(3HB-co-4HB) is its low nucleation density, which leads to slow crystallization during melt processing and poor mechanical properties. While studies on P(3HB-co-4HB) crystallization exist, the effect of thermal history is often neglected (Wang et al., 2022). This work investigates the influence of melt processing temperature on P(3HB-co-4HB) crystallization, focusing on the effects of thermal degradation and melt memory on crystallization rate, nucleation density, and spherulite growth rate. To establish a direct correlation with the crystallization rate observed via differential scanning calorimetry (DSC), nucleation density was assessed by microtome-cutting thin slices from DSC samples, followed by observation under polarized optical microscopy (POM). To enhance crystallization rates, thymine was studied as a biocompatible, biodegradable nucleating agent for P(3HB-co-4HB). Its nucleation efficiency was evaluated by comparison with the P(3HB-co-4HB) self-nucleation potential. All experiments were conducted on in-house microbially synthesized P(3HB-co-4HB) to ensure the absence of additives. This study provides fundamental insights into how the crystallization behavior and material performance of PHAs can be controlled and improved, aiming to contribute to the advancement of sustainable material development.

While crystallization behavior of isotactic polypropylene homopolymers had been subject to a wide range of experimental and modeling studies, this is not the case for propylene-ethylene random copolymers (PPR). This class of polymers offers up to now significant challenges, both from an experimental as well as a modeling perspective. The ethylene incorporation in the propylene chains, as well as the distribution of this comonomer, has a marked effect on the crystallization kinetics and can cause a separation between primary crystallization (i.e. space filling) and subsequent secondary crystallization (increase of crystallinity in filled space) within the spherulitic skeletons. In this work [1], the underlying mechanism is first quantified by means of X-ray and calorimetric measurements. Based on these experiments an extended model framework is presented, capable of predicting multiphase non-isothermal crystallization kinetics as well as the final crystallinity as a function of the applied thermal conditions relevant for processing. The chemical composition distribution (CCD) of the ethylene comonomer serves as critical input to parameterize the model. The good match between experiments and model predictions demonstrates the power of the newly developed framework. The final crystallinity, the amount of α- and γ-phase, and the ratio between primary and secondary crystallization can be predicted as a function of the time-temperature history To the best knowledge of the authors, it is the first time that such a direct connection with the CCD is incorporated in a crystallization model, offering a new tool to bridge the gap between chemical structure and resulting product properties.

Typical packaging materials have a multi-layered structure in which polyethylene (PE) is glued with different materials, making them extremely difficult and costly to recycle.(1) The adoption of mono-material packaging containers entirely based on PE is being explored to improve the circularity of plastic packaging. Biaxially oriented polyethylene films (BOPEs) are promising materials due to their superior me-chanical properties and optical characteristics. Tenter-frame biaxial stretching is a semi-solid state process in which a cast PE sheet is stretched in two perpendicular directions.(2) It has attracted great attention since the resulting BOPEs show significantly improved tensile modulus, strength, impact resistance, and puncture resistance compared to conventional blown films.(3) However, due to the fast crystallization rate of PE crystals and the fast segmental dynamics of chains in the amorphous and melt state, accurate control of the properties upon processing still remains a challenge.
In this project, we developed an apparatus able to apply biaxially orientation of PE while exposing the sample with X-rays (Figure 1a). Thanks to it, we performed an in-situ X-ray investigation during PE biaxial stretching and successive crystallization. In particular, we were able to follow the evolution of the degree of crystallinity and orientation during biaxial stretching of different PE industrial grades. These results helped us to assess the structural configuration before, during and after the stretching at the unit-cell length scale (Figure 1b-c) and contribute to deepen the understanding of BOPE processing, a fundamental step towards single material packaging applications.

DPI is acknowledged for funding this research (Project #847).