Effect of UV irradiation on poly(vinyl alcohol)

Polimerni materijali su tijekom eksploatacije često izloženi svjetlu. Ultraljubičasto zračenje (UV) je dio vidljivog spektra s najkraćim valnim duljinama i najvećom energijom na koje su polimeri posebno osjetljivi. U radu je uz pomoć dinamičko-mehaničke analize ispitan utjecaj UV zračenja na strukturu i toplinsko-mehanička svojstva poli(vinil-alkohola). Ispitni uzorci izloženi su 10, 30 i 60 min djelovanju UV zračenja iz točkastog izvora. Prigušivanje mehaničkih vibracija izrazito ovisi o strukturi materijala, te su promjene uslijed djelovanja zračenja vidljive u mehaničkom spektru, gdje je prikazana ovisnost faktora prigušivanja o temperaturi. Na temelju eksperimentalnih podataka potvrđeno je da su polimerni materijali osjetljivi na UV zračenje te da je ono utjecalo na toplinsko-mehanička svojstva poli(vinil-alkohola). Nakon zračenja došlo je do promjene u mehaničkom spektru i to u vidu porasta intenziteta vrha u području neposredno prije prijelaza iz staklastog u gumasto stanje, vjerojatno kao posljedica razgradnje molekula u amorfnoj fazi na kratke lance. Osim toga, vrh prijelaza iz staklastog u gumasto stanje pomaknuo se u više temperature, što ukazuje na redukciju pokretljivosti lanaca, vjerojatno uslijed umrežavanja molekula.Polymeric materials are often exposed to light during exploitation. Ultraviolet radiation (UV) is the part of the visible spectrum with the shortest wavelengths and the highest energy that polymers are particularly sensitive to. The influence of UV radiation on the structure and thermal-mechanical properties of poly (vinyl alcohol) was investigated by means of dynamic-mechanical analysis (DMA). The samples were exposed to UV radiation from a spot light source for 10, 30 and 60 min. The damping of mechanical vibrations is highly dependent on the structure of the material, and the effect of the radiation is visible in the mechanical spectrum, where the damping factor vs. temperature is shown. Based on experimental data, it has been confirmed that the polymer materials are sensitive to UV radiation and that it has affected the thermal-mechanical properties of poly (vinyl alcohol). After radiation, there was a change in the mechanical spectrum: (i) an increase in the peak intensity in the temperature range just before the glass to rubber transition, probably as a result of the disintegration of molecules in the amorphous phase into short chains; (ii) the peak attributed to the glass to rubber transition shifted to higher temperatures, indicating a decrease in the motility of the chains, probably due to the crosslinking of the molecules