No abstract

Lyocell fibers have extraordinary textile properties, but they show a distinct tendency to fibrillate in the wet state. Treatments with crosslinking compounds used for textile finishing could be a practical means of controlling this problem. Some polyfunctional reactive dyestuffs also greatly increase wet abrasion resistance. Fiber tenacity decreases slightly compared to reactive compounds used for easy care finishing.Alternative methods for the dissolution of cellulose have been studied for many years. Cellulose-N-methylmorpholine-N-oxide-water has become a key system and is already used for industrial production of cellulosic fibers. Lyocell fibers have extraordinary dry, wet, and loop strength and low shrinkage compared to viscose fibers, but they show a distinct tendency to fibrillate under mechanical stress in the wet state. Fibrils split lengthwise along the fiber axis and show up, macroscopically, as a fibrous surface with local greying. While this property has some applications, for example, for textiles with particular surface structure, it prevents their wider use in the industry. From fundamental research on the structure of Lyocell fibers, workers concluded that the spinning process causes the formation of a large fraction of highly oriented crystalline regions. The lateral links between the crystallites are weaker than those in viscose or in modal fibers [3, 4, 91. Previous work [6] revealed a good correlation between the results of our wet abrasion test [7] of different fibers and the cluster fraction defined in reference 5.The ekmentary fibrils of solvent spun cellulosic fibers are less aggregated than the fibrils generated by a viscose process, and they also show the lowest wet abrasion numbers.

ZUSAMMENFASSUNG:Flachsfasern konnen auf Grund ihres Eigenschaftsprofils als Verstitrkungsmaterial in Verbundwerkstoffen genutzt werden. Als wichtiger Anwendungsfall bietet sich die Substitution von Glasfasern in Compounds aus Glasfasern und dem Standardkunststoff Polypropylen an. Problematisch fur diesen Einsatz sind die hohe Wasseraufnahme der Naturfaser und deren geringe Haftung zum hydrophoben Polymeren. Es wurde daher versucht, die Adhasion zur Polypropylenmatrk durch Applikation von bifunktionellen Silanen zu erhohen. Wihrend alkylgruppenfunktionalisierteWane nur eine unbedeutende Verbesserung der Faser-Matrix-Haftung bewirken, konnte jedoch eine deutliche Steigerung mit solchen Silanen erzielt werden, deren funktionelle Gruppe unter Verarbeitungsbedingungen des Verbundwerkstoffes radikalisch reagiert. Fur vinyl-und methacrylgruppenfunktionalisierte Silane wurde die Abhangigkeit zwischen dem Hydrolysekatalysator, der die Radikal-Reaktion initiierenden Verbindung, der Silanauflage und dem Adhasionsniveau untersucht und unter optimalen Konzentrationsverhaltnissen die Silanauflage variiert. SUMMARYBecause of their properties, flax fibres can be used as reinforcing material in composites, e. g. as substitute for glass fibres in composites with polypropylene. A major drawback of this application is the high water adsorption of the natural fibre and its low adhesion to the hydrophobic polymer.Therefore, improvement of adhesion to the polypropylene matrix by application of bifunctional silanes was investigated. While silanes with alkyl groups did not significantly improve the fibre-matrix adhesion, it was found that silanes which carry functional groups capable of reacting by formation of free radicals under processing conditions lead to a remarkable improvement. For silanes with vinylic and methacrylic * Korrespondenzautor.

ZUSAMMENFASSUNG SUMMARY:Adhesion of flax fibres to a polypropylene matrix in flax/PP composites was

Flax‐nonwoven reinforced polypropylene has become a competitor to textile glass fabric reinforced polypropylene because of its economic and ecological advantages. Suitable application forms are needle‐punched 100% flax or hybrid fabrics of flax/polypropylene manufactured of rough and fine decorticated flax. The construction of the nonwoven influences the strength, handle, matrix compatibility, and flow of the fabric. In this way, composite properties may be tailored to each end‐use. The main application fields are subassemblies exposed to a medium range of stress. The method of hybrid‐nonwoven manufacturing represents a technological alternative to the existing film‐stacking method. Produced with lower technology, the parameters of composites of hybrid‐nonwovens are comparable to properties of composites manufactured by the film‐stacking method. Adhesion characteristics may be improved by addition of compatibilizers. The compatibilizers may be added to the flax‐fiber surface or may be inserted into the polypropylene. All these methods lead to comparable mechanical parameters for the fiber composites.