Structure and properties of isotactic polypropylene functionalized by ultraviolet irradiation

The structural, crystalline, thermal, morphological, and mechanical properties of isotactic polypropylene (iPP) functionalized by lower energy ultraviolet (UV) irradiation are studied by means of infrared spectroscopy (IR), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), thermogravimetry (TG), thermomechanical analysis (TMA), polariscope, and mechanical measurements. After the UV irradiation in less than a few hours, the oxygen containing polar groups have been introduced onto iPP chains. DSC analysis shows that a new melting peak is observed around 150°C for the UV irradiated iPP, indicating that there is a α-phase to β-phase transition during UV irradiation process. Under polariscope, the morphology of the UV irradiated iPP is changed, and the deformed α-phase morphology can be observed. DSC and WAXD analysis reveal for the crystallinity of the UV-irradiated iPP increase with UV time, but the relative level and the order of β-phase increase and then decrease with increasing UV time. Under the controlled UV time, the thermomechanical deformation of iPP decrease, and the initial and final thermal degradation temperature of iPP rises up by 70 to 125°C higher, respectively, indicating that the UV-irradiated iPP has higher thermal stability than the non-UV irradiated iPP. The tensile and impact strength, the elongation at break, and the Young's modulus of the UV-irradiated iPP are enhanced, exhibiting the toughened and strengthened effects.