A broad variety of regenerated cellulose fibres was subjected to single fibre tensile tests in order to determine the modulus of elasticity, tensile strength, and failure strain. The results were compared to glass fibres and flax fibres, which are considered the most important technical and natural fibres, respectively. With regard to their modulus of elasticity and tensile strength, regenerated cellulose fibres showed clearly lower values than glass fibres, even when their low density was taken into account. The average modulus of elasticity and tensile strength of regenerated cellulose fibres was also lower than the values measured for flax fibres, but when variability was considered, both fibres performed similarly. In terms of interfacial shear strength with polypropylene, lyocell fibres performed significantly less well than sized glass fibre and ramie fibre. The most important difference between regenerated cellulose fibres and both glass and flax fibres is their high failure strain and thus high work to fracture. The high work to fracture of regenerated cellulose fibres makes them particularly useful for composite applications where high fracture toughness is required.

Samples of lyocell fibres were taken in the form of filaments from fibre tow of potentially infinite length and in their final condition of staple fibres. Mechanical testing showed comparable tensile strength, but a 50% lower modulus of elasticity for staple fibres and a higher elongation at break compared to filaments from fibre tow. Structural investigation by means of synchrotron wide angle X-ray scattering and birefringence measurement revealed a significantly lower degree of preferred orientation together with less fibre straightness for staple fibres than for filaments. It is concluded that plastic deformation during the processing of staple fibres from filaments induces permanent changes in the orientation of cellulose chains in the fibres, which in turn is responsible for the observed differences in mechanical performance.

A tensile testing set-up was developed for the determination of the elastic modulus, tensile strength, and failure strain of single regenerated cellulose fibres. Since the accuracy of strain measurement is crucial for the measured elastic modulus and failure strain, strain measurements were performed mechanically and with a non-contacting optical method in parallel. The optical validation of mechanical strain measurement showed an agreement of measured strain >99%, confirming the accuracy and usefulness of the set-up and sample geometry developed for the test series.

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An experimental investigation into the adhesion of regenerated cellulose fiber lyocell, natural cellulose fiber ramie, and E-glass fiber to the polypropylene (PP) and epoxy matrices, by means of the microbond technique, was conducted. Force–displacement plots indicate a brittle failure of the interface, followed by high frictional forces in the PP matrix and low frictional forces in the epoxy matrix. The interfacial shear strength (IFSS) of lyocell–epoxy system was significantly higher than that measured in the lyocell–PP system. Chemical modification of lyocell fiber with maleic anhydride resulted in a two-fold increase in IFSS with PP. Ramie exhibits better adhesion characteristics, due mainly to the rough surface, than lyocell.