Abstract: The invention provides a process for aminoarylating cellulosic materials such as cotton and reconstituted fibres and a process for treating the aminoarylated cellulose with an effect chemical such as a dye, flame retardant or cross linking agent. Improved take up of the effect chemical by the modified cellulose means increased efficiency in the process and in the case of dyeing, avoids or reduces the washing off of hydrolysed dye and the resultant production of large volumes of contaminated water requiring to be treated. The cellulosic material may be present in a blend with other types of fibre for example a blend with poly(alkyleneterephthalates) or polyamides.