Effect of adding a small amount of high molecular weight polyacrylamide on properties of oxidized cassava starch

Oxidized cassava starch (OCS) was blended with small proportions (0.5–3 wt%) of high molecular weight of a polyacrylamide (PAM) to overcome brittleness of the starch material for warp sizing. Properties of the starch-based sizes, blended with the PAM or polyvinyl alcohol (PVA), were compared in order to highlight the specific strengthening and toughening effects of the PAM on the OCS blends. The results showed that blending OCS with 3 wt% PAM resulted in growth of tensile strength and elongation at break by 25.67% and 51.59%, respectively. The viscosity stability and sizing performance were also enhanced. For equivalent performances of the starch sizes, the dosage of the PAM was needed only one-tenth of the PVA. Therefore, it was reasonable to expect a replacement of a large amount of PVA in a starch-based size by adding a small amount of the high molecular weight of PAM. The analyses of the phenomena by means of ATR–FTIR, SEM and XRD confirmed that hydrogen bonding interaction and chain entanglement occurred between PAM and OCS molecules, which could inhibit the crystallization of OCS and reduce the crystallite size in OCS/PAM blend films, and hence strengthen mechanical properties for the blends. While in the OCS/PVA blend, the two polymers had a tendency of self-crystallization, and PVA could increase the crystallite size of OCS and decrease its relative crystallinity.