Joining of Poly(Ethylene Terephthalate) PET and its biodegradable derivatives. Granules of PET and biodegradable PETs modified by organic additives by extrusion compounding. Laser Transmission Welding (LTW) with a continuous wave High Power Diode Laser (cw-HPDL). A novel predicting analytical model derived from the mixture rule was developed. Identification of the routes to thermal degradation of PET and biodegradable PET blends.