Supermolecular structure and thermal properties of poly(ethylene terephthalate)/lignin composites

Poly(ethylene terephthalate) (PET) has been compounded with lignin (L) by a single-screw extruder. The influence of L presence and its content on the thermal properties and crystalline structure of PET has been studied. Morphological analyses evidenced good dispersion of the L particles in the PET matrix. Polarizing optical microscopy (POM) and small-angle X-ray scattering (SAXS) techniques were employed to measure the L particles dimension. The influence of L on the overall isothermal crystallization of PET was investigated by using differential scanning calorimetry (DSC). L particles acting as nucleating agent in the composite increased the crystallization rate. The crystallization process was composed of primary and secondary stages. As the L content was increased in the composite, the primary crystallization progressively proceeded toward higher percentage of the crystallizable PET fraction. As evidenced by SAXS and wide angle X-ray diffraction (WAXD), the L presence produced a noticeable enhancement of PET crystallinity and crystal dimensions.