Impact of ring-opening chemistry on the local chain mobility of arabinoxylan

Periodate oxidation and borohydride reduction has been put forward as a modification that increases the flexibility of polysaccharide chains, thereby lowering the glass transition temperature. To investigate whether the reaction is able to increase the chain mobility of a branched polysaccharide such as arabinoxylan (AX), ring-opened dialdehyde AX (DAX), and dialcohol AX (DiolAX) were studied with solid-state NMR techniques. For materials equilibrated at 53% relative humidity, it was found that DiolAX exhibits increased chain mobility, observed as a two- and three-fold decrease in the proton relaxation time in the rotating frame (T_1ρH), compared to AX and DAX. From measurements of the proton dipolar linewidth, the narrowest linewidth, thus highest mobility, was observed at the C5/ring-opened C2C3 region of DiolAX. This is expected largely from an increase in mobility of the ring-opened C2C3 environments. When the materials were equilibrated at <10% RH, the dynamics became slower and more similar across AX, DAX and DiolAX.