The interaction between wood, hemp and viscose fibre with polypropylene matrices was investigated. Hot stage microscopic studies were used to observe the crystallisation of polypropylene in the presence of lignocellulosic fibres. a-form transcrystallinity was observed on chemically pulped wood and hemp fibres, and thermomechanical pulp, and sporadic a -nucleation was observed on viscose and lyocel fibres. Methods of fibre chemical modification and nucleating agents were sought, in order to modify the crystalline form of the interphase to the ~-morphology. A calcium pimellate fibre treatment was used to generate a pseudo-transcrystalline morphology around TMP fibre in thin films of polypropylene. The deformation of this P-form interphase during tensile loading was observed, with visible stress whitening being limited to the interphase region, confirming the action of the interphase as a buffer zone. Composites of unmodified, succinylated and pimellate treated TMP and hemp fibres in polypropylene were formed and tested in tension and impact. Blends with TMP fibres gave lower strength and impact results than hemp blends because of the poor aspect ratio of the TMP fibre, with wide fibre bundles being visible when failure surfaces were observed by scanning electron microscopy. At low fibre loadings, the pimellate treatment gave an improvement in impact resistance and energy at break. Differential scanning calorimetry confirmed that P-a transformation had occurred. The pimellate treatment was not bonded to the fibre surface, so a P-spherulitic morphology was present in these test specimens. Further work was conducted to investigate a more permanent bond between the P-nucleant and the fibre, but this work was not scaled up. Differential scanning calorimetry of unmodified fibre blends revealed that there was a small proportion of P-form cylindritic material present, resulting from shear forces in the melt during pressing. The blends of succinylated fibre, and calcium ion exchanged succinylated fibre, in polypropylene gave a reduced cylindrite population, and demonstrated a reduction in toughness relating to the total absence of P-morphologies.