Moreover, it could be speculated that when relatively low or high content CS was added into compound system, neither of the “bridges” can fully link WF with PVC matrix together as Fig. 2a and b showed. The loose interfacial bonding was insufficient to resist the imposed forces from the tip of test rod, resulting in the low vicat softening temperature. The “bridge” link of biopolymer CS performed excellently (Fig. 2c) when the amount of CS achieved an optimum proportion (30 phr).