Effect of aging on structure and properties of polymers

S povećanjem ekološke svijesti, sve je veća težnja za primjenom biorazgradivih polimernih materijala. Međutim, glavni nedostatak polimera kao tehničkih materijala predstavlja podložnost starenju što u velikoj mjeri ograničava njihov životni vijek. U radu je pomoću dinamičko-mehaničke analize (DMA) ispitan utjecaj prirodnog starenja pri skladištenju na uzorcima svježih i skladištenih folija od čistog poli(vinil-alkohola) (PVA) te polimerne mješavine od PVA + 20% hitozana (CS). Na skladištenim folijama utvrđena je viša temperatura staklastog prijelaza te je modul pohrane za oko 1000 MPa niži pri sobnim temperaturama u odnosu na svježe folije. U mehaničkom spektru tan δ vs. T za čisti PVA uslijed starenja se pojavila beta relaksacija, koja je vjerojatno posljedica razgradnje PVA u amorfnoj fazi. S dodatkom CS, krivulja se izraženije pomiče u područje viših temperatura, a beta relaksacija je slabija. Pomicanje prijelaza iz staklastog u gumasto stanje u više temperature je vjerojatno posljedica porasta udjela kristalne faze u polimeru koja djeluje poput fizikalnog umreženja.With environmental awareness on the rise, there is a higher tendency for the application of biodegradable polymer materials. However, the main disadvantage of polymers as technical materials is their susceptibility to aging, what reduces their service life significantly. In this work, the effect of natural aging of polymer films made of pure poly(vinyl-alcohol) (PVA) and a polymer blend composed of PVA + 20% chitosan (CS) is examined by means of dynamic-mechanical analysis (DMA). For the aged samples there is a shift of the glass to rubber transition to higher temperatures and a decrease of the storage modulus for about 1000 MPa at the room temperature compared to that of the freshly prepared films. In the mechanical spectrum tan δ vs. T for the pure PVA, a new relaxation process appears and that is probably the consequence of degradation of PVA in the amorphous phase. By adding chitosan, the α relaxation shifts notably in the higher temperature ranges and the β relaxation is less clear. Glass to rubber transition is shifted in the higher temperature ranges, probably because of the increase in crystalline phase in polymer which acts as a physical crosslinking site in the network