Real-time ageing of polyesters with varying diols

Polyesters are a widely used class of polymer due to their excellent processing, mechanical and recycling properties. However, polyesters are usually not used for durable goods. Thus, further understanding of underlying chemical and physical degradation mechanisms and their changes when changing the chemical composition of the polymer is required. This work presents four polyesters with varying diols (recycled poly (ethylene terephthalate) (PET-R), poly (butylene terephthalate) (PBT), poly (ethylene glycol-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol terephthalate) (PETG) and poly (1,4-cyclohexylenedimethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol terephthalate) PCTT) submitted to a real-time exposure in Southern France for almost two years (16056 h). This environment demonstrated an average temperature of 20.6 °C, relative humidity of 61.4%RH and UV exposure (300–400 nm) of 0.95 MJ/m2. Differential scanning calorimetry showed significant physical ageing of the PET-R. Attenuated total reflectance Fourier transform infrared spectroscopy presented the loss and shift of the ester bond with an increase in hydroxyl species, as a result of significant chain scission of the polyesters. Degradation dominated the mechanical toughness response, resulting in all polyesters to become increasingly brittle with ageing. While the reference (t = 0 h) charpy v-notch toughness was 3.2, 2.6, 5.0 and 104 for PET-R, PBT, PETG and PCTT, respectively, they all decreased to below 1.5 kJ/m2 after 2928 h of ageing. Similar behaviour was observed for charpy weld line toughness with reference between 93 and 290 kJ/m2 and decreased to 1.8–2.2 kJ/m2. PET-R demonstrated the highest tensile elongation after ageing, but despite this PCTT was the last polyester to decrease significantly below the reference, presenting that PCTT was significantly more resistant towards ageing induced embrittlement. [Display omitted] •Four polyesters is submitted a real time exposure behind glass for two years.•Degradation tracked via IR as a loss of ester groups and increased oxidative species.•Embrittlement was found as measured by tensile test, charpy v-notch and weld line toughness.•Decrease in glass transition temperature shows degradation in the polyesters.•All polyesters chemically degraded but PCTT maintained usability longer than the other polyesters.