Influence of the lignin on thermal degradation and melting behaviour of poly(thylene terephthalate) based 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 stability of PET has been studied by using thermogravimetric analysis. The experiments carried out in oxidative conditions evidenced the barrier effect of L that interferes to the diffusion of the volatile degradation products to the gas phase and, at the same time, to the diffusion of the oxygen from the gas phase to the PET matrix. The influence of L on the melting behaviour of PET has been investigated on samples submitted to subsequent annealing steps procedure. X-ray techniques were employed to investigate crystallinity and crystal dimensions of pure PET and PET/L composites. Considering the supermolecular and crystal structure of the annealed samples, their melting behaviour were explained assuming small changes in the melting entropy.