From waste to functional additives: thermal stabilization and toughening of PVA with lignin

Blend films of poly(vinyl alcohol) (PVA) and a graft copolymer (GL) of acrylic acid (AA) with eucalypt lignosulfonate calcium (HLS) were prepared by using a solution casting method. The structure of GL/PVA blend films was confirmed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), which indicate that GL/PVA is a homogeneous system due to the strong interactions between PVA and GL. Differential scanning calorimetry (DSC) results indicate that only one glass transition temperature ( T g ) can be seen over the entire blending ratio. Meanwhile, the T g was enhanced and the melting point ( T m ) was depressed when GL was added to PVA. With the addition of 3 wt% GL, the onset decomposition temperature ( T o ) was increased by 102 °C compared to that of PVA. Compared with pure PVA, the GL/PVA exhibited a remarkable improvement in mechanical properties: the tensile strength and Young's modulus of GL/PVA with 5 wt% GL were 39% and 285% higher than that of pure PVA, respectively. These results show that a new melt-processing method of PVA may be developed by the addition of GL in PVA. With the addition of modified lignin, the thermal stability and mechanical properties of PVA can be greatly improved.