Hydroxylamine grafting of periodate oxidized cellulose microfibrils and its impact on fibre adhesion

In this work, dialdehyde cellulose microfibrils (DA-CMFs) were reacted with O-substituted hydroxylamines, demonstrating an effective and versatile method for lateral functionalization of DA-CMFs using mild, aqueous reaction conditions. Depending on the conditions used, partial or complete substitution of the aldehydes could be achieved. The reaction was performed in the presence and absence of the reducing agent α-picoline borane (PB). DA-CMFs were reacted with O-(carboxymethyl) hydroxylamine (HAAA), and the adhesive properties of native and HAAA-conjugated DA-CMFs to fibres were studied. The adhesive properties were shown to depend on charge; while native DA-CMFs aggregate heavily in contact with the fibre surface, HAAA-conjugated DA-CMFs showed significantly improved adhesion. For a degree of substitution of 50% or higher, a sealed layer, without aggregates, could be observed using electron microscopy. Finally, a versatile protocol for co-insertion of HAAA (carboxylate) and aminooxy-PEG3-azide (hydroxylamine azide) was developed and demonstrated, with high yields of insertion. The modified DA-CMFs retained good adhesive properties to fibres, showing that the approach is general, and that the chemistry can be tuned depending on the target application.