Abstract. Technical natural fibre semi-finished products are mainly used in lightweight automotive components as random fiber mats which are often combined with petrochemical matrix resins for large series production process. However, random fiber arrangement and limited fiber length restrain the complete utilization of the material-inherent strength reserves of natural fibers. With high-levels of petroleum-based plastics (about 20-50 wt -%) in the structure, these applications have a clear potential in terms of eco-friendliness and sustainability. The development of new fully bio-based composites and efficient manufacturing methods suitable for series processing is the purpose of the current sub-project C4 "Flexible textile / plastics processes with renewable raw materials" in the framework of the Excellence Cluster MERGE EXC 1075, funded by DFG (Deutsche Forschungsgemeinschaft). A high-efficiency in terms of massproduction, reproducibility and flexibility requires the performance of successive steps in the manufacture of semifinished and final products. The appropriate process line comprises the steps of the preparation of the thermoplastic matrix sheets (such as from Bio-polyethylene or Bio-polyamide) and a specific chemical modification of the reinforcing materials (wood veneer and unidirectional flax fibers) on the concept of a discontinuous or continuous production of unidirectional reinforced Natural Fibre Composites (NFC) prepregs. Moreover, the shaping of hybrid lightweight structures from NFC prepregs makes possible the incorporation of these innovative technologies into new concepts and potential applications in several fields such as automotive industry or sport equipment. The mechanical properties profile of the flax -natural unidirectional sheet for fibre reinforced bioplastics has been here studied in detail with pressengineered samples and has confirmed their high application potential as an alternative to glass fiber-reinforced composite sheets.

Poly(vinyl amine) (PVAm) reacts with acetone in aqueous solution. It generates imine and aminal moieties along the PVAm backbone. The molecular structure of acetone‐modified PVAm is confirmed by liquid 1H and 13C as well as solid state 13C NMR and ATR‐FTIR spectroscopies. Model compounds produced from 1,3‐diaminopropane with acetone in chloroform are used to assign the solid state 13C NMR signals of the modified polymer. Quantitative elemental analysis of acetone‐modified PVAm samples supports the analytical results. The mechanism of the imine and aminal formation is discussed with regard to the anomeric stabilization of the incipient hemiaminal intermediate. The rapid and unexpectedly favorable formation of PVAm acetone hemiaminal, acetone imine, and aminal formation has implications for the conduct of PVAm research and even the interpretation of prior published results. As acetone was often used in the past to precipitate waterborne PVAm derivatives, this finding has a severe impact on the interpretation of research results. The consequences and the revised interpretation of selected publications are discussed.

Biocomposite materials consisting of biopolyethlylene (bio‐PE) and wood veneer are produced using four structurally different maleic anhydride (MA) copolymers as reactive interfacial components. The respective MA copolymer was dip coated onto the veneer surface and serves as adhesion‐promoting and compatibilizing reagents for the highly polar wood veneer and the weakly polar bio‐PE. Fourier transformation infrared spectroscopy confirms esterification reactions on to the wood veneers. The MA copolymer modified woods show hydrophobic surfaces due to contact angles with water droplets up to 125 °. The adapted surface properties of the materials provide compatible biocomposite material verified by scanning electron microscopy/energy‐dispersive X‐ray spectroscopy images of wood fibers impregnated with the bio‐PE matrix. Furthermore, the tensile properties of the biocomposite materials are greatly improved for all MA copolymer coatings. Compared to the unmodified wood veneer/bio‐PE composites, the polypropylene‐graft‐maleic anhydride modification was found to have the highest improvement of 139% in Young's modulus and 115% in tensile strength. POLYM. COMPOS., 40:1979–1988, 2019. © 2018 Society of Plastics Engineers

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Wood veneer/biopolyethylene (bio-PE) biocomposite materials were produced by using poly(N-vinylformamide-co-vinylamine) (PVFA-co-PVAm) copolymers as a phase-mediating reagent. In a preliminary step, PVFA-co-PVAm was adsorbed onto the wood veneer component from aqueous solution. In its adsorbed form, it served as an adhesion promoter and improved the compatibility between both the highly polar wood veneer and weakly polar bio-PE surface. Structural parameters and their effect on the adsorption process, such as the degree of hydrolysis (DH) of poly(N-vinylformamide) (PVFA) (30, 50, and > 90%), the molecular weight of PVFA-co-PVAm (Mw 10,000, 45,000, or 340,000 g/mol), and the pH value (4, 7, and 11) influenced the resulting wetting behavior of the PVFA-co-PVAm-modified wood veneer surface. Thus, the hydrophobizing effect of the PVFA-co-PVAm was clearly detectable because the contact angle with water was considerably increased up to 116° by adsorption of PVFA-co-PVAm 9095 at pH 11. The adsorbed amount of PVFA-co-PVAm was determined by energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). The PVFA-co-PVAm-coated wood veneers were consolidated with bio-PE in a hot press process. The modified composite materials showed remarkably improved Young’s moduli (552 MPa) and tensile strengths (4.5 MPa) compared to former composite materials produced without PVFA-co-PVAm modification.