Natural fibers are a sustainable alternative to synthetic fibers due to their high weight‐specific Young's moduli and strengths. However, the mechanical properties of natural fibers are very sensitive to their moisture content. Therefore, chemical treatments are often applied to natural fibers to lower their water absorption and enhance fiber‐matrix interaction. The aim is to study the effects of fiber modifications with sodium hydroxide, silane, and siloxane on the water uptake and tensile properties of flax fiber composites produced via prepreg technology. In addition, the effect of moisture on the composites' tensile properties was investigated by conditioning one part of the tensile specimens according to DIN EN 2823 (at 70°C and 85% relative humidity). The NaOH treatment was the only modification that had positive effects on the Young's modulus and tensile strength in the unconditioned and conditioned state. The increase of the tensile modulus and strength are most likely due to changes in flax fiber composition, crystallinity of the cellulose and the rougher fiber surface of NaOH modified fibers. This shows that chemical treatment of natural fibers may improve the performance level of natural fiber composites and prevent a loss in their mechanical properties in humid environments.Highlights: Flax fiber modifications with sodium hydroxide, silane, and siloxane. Flax fiber composite production via prepreg technology. Water uptake after conditioning at 70°C and 85% relative humidity. Tensile tests before and after conditioning. SEM images of modified flax fibers.

In recent years, the development of a circular economy of plastic products in the automotive industry has been pursued by original equipment manufacturers (OEMs) not only due to strategic premises by the European Commission but also due to an increasing demand by customers. To achieve a circular economy, high-quality recyclates are needed. However, in the current situation, there is a discrepancy between the low-quality recyclate that is available on the market and the high-quality recyclate that is demanded by manufacturers. To increase the quality of recyclate on the market, a standardized process to reward a ‘design-for-recycling’ approach at the product development stage is needed. This paper proposes an allocation method that takes into account material compositions and common recycling processes and incentivizes the preservation of high-quality grades of recyclate based on grade purity.

Fibre-reinforced polymers based on natural fibers, such as flax fibers, exhibit pronounced nonlinear orthotropic material behavior. This presents a significant challenge in finite element analysis (FEA) simulations, as the nonlinear constitutive models available in commercial FEA tools are difficult to apply and fail to capture all the material’s specific characteristics. Relying on initial or reduced secant moduli in linear quasi-static analyses of deformations or stress states can result in inaccurate outcomes and overly optimistic strength predictions, particularly in compression-dominated cases. However, with appropriate modifications, classical laminate theory (CLT) can be adapted for nonlinear analysis. This involves iteratively updating the components of the stiffness matrix for the unidirectional (UD) ply during the calculation process based on the current strain state and stress interactions. This study presents and discusses a computational algorithm for the FEA software ABAQUS/CAE 2019, which incorporates material-related orthotropic nonlinearities and stress-dependent interactions within the CLT framework. The algorithm represents a single-scale material model at the meso level (UD ply) and is based on the concept of orthotropic elasto-damage within the framework of continuum damage mechanics (CDM) theory. Numerical implementation is achieved through a user-defined field (USDFLD) subroutine, accompanied by a pre-processing Python script for managing experimental data, computing data fields, and calculating parameters. As shown below, this type of implementation appears justified compared to a user material subroutine (UMAT) subroutine in terms of computational efficiency and practicality.

In Zeiten knapper werdender Ressourcen, steigender Luftverschmutzung, überlasteter Verkehrsinfrastruktur und des Klimawandels wird der Bedarf an effizienten und zugleich differenzierten Mobilitätskonzepten für urbane Umgebung besonders deutlich. Pedelecs und Cargo-Pedelecs bieten hier eine interessante Alternative für persönliche Mobilität und innerstädtische Logistik. Die Vorteile liegen in der emissionsfreien Fortbewegung und den günstigen Anschaffungskosten. Bei den verwendeten Materialien liegt ökologisches Optimierungspotenzial vor.

In this study, the processing of stereocomplex poly(lactic acid) (sc‐PLA) via continuous compounding followed by thermoplastic foam injection molding (FIM) is investigated. Various nucleating agents are compounded with a mixture of poly(L‐lactide) (PLLA) and poly(D‐lactide) (PDLA). The crystalline material structures are greatly influenced by the cooling conditions of the extruded strand. In particular, a controlled two‐stage cooling strategy, consisting of initial air cooling followed by water‐bath cooling, effectively suppresses cold crystallization and promotes a predominantly stereocomplex crystallization behavior of the granulates. PLLA and PDLA are compounded with the aluminum complex NA‐21 and talc as nucleating agents and processed into foamed specimens using FIM with nitrogen as a physical blowing agent. X‐ray diffraction confirms a primarily stereocomplex crystalline structure in the foamed specimens, and scanning electron microscopy reveals a closed‐cell foam morphology within the PLA matrix. The present study thus demonstrates the feasibility of stereocomplex crystallite formation in thermoplastic foam injection molding, establishing a processing route for sc‐dominated PLA foam parts that combines the density reduction of foaming with the elevated melting range of the stereocomplex crystalline structure.