Vývoj struktury alfa a beta-polypropylénu během UV ozáření: Víceúrovňové porovnání

Abstract

Vliv UV ozáření v průběhu akcelerované fotodegradace na vývoj struktury alfa a beta-polypropylénu je náplní této práce. Strukturní vývoj je sledován pomocí řady experimentálních metod na molekulární, nadmolekulární a mikroskopické úrovni. Byl nalezen výrazný efekt nukleace - pouze 0.03 hm. % nukleantu výrazně zpomalil průběh fotodegradace.

The effects of UV irradiation on neat and ?-nucleated isotactic polypropylenes have been studied at the molecular, morphological and microscopic levels. Commercially available isotactic polypropylene (PP) was modified by a specific ?-nucleating agent based on N,N?-dicyclohexylnaphthalene-2, 6-dicarboxamide. Compression-moulded plates were prepared from both starting (?-PP) and nucleated (?-PP) polypropylenes and exposed to UV irradiation. The exposure time varied from 0 to 240 h. Molecular degradation and the evolution of supermolecular structure were determined using infrared spectroscopy, wide-angle X-ray scattering and differential scanning calorimetry

surface cracking was observed by light microscopy. Lower degradability was found in ?-PP as compared to ?-PP

an increase in crystallinity on short-time exposure followed by crystallinity decrease with prolonged exposure was detected in both samples. The ?-phase content in the crystalline portion of ?-PP remained stable during UV irradiation under given irradiation conditions. Re-melting experiments have shown that the crystallization ability of both ?-PP and ?-PP markedly decreased with exposure time. Lower degradability of ?-PP as compared to ?-PP has been ascribed to higher light absorbance resulting from the specific morphology of ?-PP.