Characterization of cellulose in post-consumer cotton textiles
Licentiate thesis, 2015
The overall objective of this thesis is to provide a background to the recycling of cotton. Since cotton consists of pure cellulose, it might be possible to include used cotton, in the already existing viscose industry. In this thesis two aspects important to accomplishing this task have been studied; changes that occur in cotton fibres during service life, and comparison between cotton and dissolving pulp in terms of susceptibility to acid hydrolysis.
During the service life of a cotton textile, it is laundered many times, exposing it to numerous drying and rewetting cycles. From research on paper recycling, it is well known that drying and rewetting induce hornification of cellulosic fibres, making the fibres stiff and less porous. However, no increase in the degree of hornification, during the service life of cotton fibres has been measured, probably due to the high initial hornification of cotton fibres. Laundering, however, decreases the mass average molecular mass of cellulose, down to 151 kDa, after more than 50 laundering cycles, from 1323 kDa in a never-laundered sheet.
The second aspect studied was reactivity of different cellulosic fibres towards acid hydrolysis. It was found that laundering had no effect on the levelling off degree of polymerization (LODP). Despite the initial large difference between new sheets and discarded sheets, the molecular mass distributions were quite similar for the sheet samples, after only 60 min of hydrolysis (0.4 M HCl, 80 °C). With textile recycling in mind, this is promising, since textiles sent for recycling will have been though a different number of laundering cycles.
Levelling-off degree of polymerization