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 (T1ρH), 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.