Early-stage photodegradation of aromatic poly(urethane-urea) elastomers

Abstract

16The photooxidative stability of an aromatic segmented poly(urethane-urea) (PUU) elastomer, 17 stabilised with a range of carbon black fillers, was assessed after very low UVA doses as a means to 18 identify components that are highly susceptible to UV degradation, and suggest better design of such 19 materials. Fourier-transform infrared (FTIR) analysis indicated rapid degradation of the urea bonds 20 in the hard segments, followed by chain scission and photo-Fries reaction of the urethane linkages. In 21 the soft segments, the oxidation of the original ether groups resulted in the formation of large 22 amounts of ester groups, while some crosslinking of the ether groups was also evident. Carbon black 23 provided moderate protection against degradation, with the smallest-sized particles being the most 24 effective. Protection was evidenced by reduced surface cracking as well as an increased resistance to 25 chemical changes in both the soft segments and hard segments. Even so, significant degradation was 26 still evident at low UV doses suggesting that further stabilisation is required to increase the UV 27 durability of these elastomers and improve their long-term performance. 28 29 Keywords: UV ageing; aromatic poly(urethane-urea); carbon black 30 system. PUUs have been found to exhibit better photostability than their polyurea counterparts [19]. 53However, due to limited work in this area, a complete description of the PUU photodegradation 54 process and how the UV irradiation affects the properties of PUU remain unclear. 55 effects of three types of carbon black with different structural characteristics on the UV stability of 77 this PUU were also studied. The photodegradation processes were analysed using Fourier-transform 78 infrared (FTIR) studies of the PUU surface chemistry over the monitoring period, along with other 79 techniques such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), 80 119 2.3 Accelerated UV ageing 120 Samples were cut from 2.5-3.5 mm thick flat sheets and loaded into custom-built extensometers 121 according to ASTM D1149-16 using Method B, Procedure B1 -Straight Specimens (Static 122 Elongation). The accelerated ageing method was adapted from UV Resistance MIL-STD-810G, 123Method 505.5, Procedure II (A2). Briefly, samples were loaded into a QUV accelerated weathering 124 tester (Q-Lab, Ohio, USA) that was equipped with UVA-340 lamps. The samples were held at 50°C 125 143 X-ray photoelectron spectroscopy (XPS) 144Surface analysis was performed on a Kratos Axis ULTRA X-ray photoelectron spectrometer 145 (XPS) using monochromatic Al Kα (hν = 1486.6 eV) radiation. Curve fitting was undertaken using a 146Gaussian-Lorentzian peak shape and Shirley background function. The binding energy was poly (etherurethane urea)

Photochemical weathering of polyurethane microplastics produced complex and dynamic mixtures of dissolved organic chemicals

“…This result is in partial agreement with the literature, 32,33,58 as other studies have reported a decreasing 1597 cm −1 band, attributing it to CC stretching vibrations in aromatic rings. 29,59 Other notable changes in the irradiated samples were the increasing carbonyl peak at 1704 cm −1 wavenumber in all PU microplastics (Fig. S7.8†), a strong indicator of photo-oxidation; 9,19,49 the increasing and broadening 3200–3600 cm −1 wavenumber region in all PU microplastics (Fig.…”

“…† Overall, the results of the ATR-FTIR analysis aligned well with the scientic literature. 29,32,33,35,36,[57][58][59] For all PU microplastics, yellowing via the quinonoid route was supported by the emergence of a band at 814 cm −1 (out-of-plane C-H bending vibration in 1,4-disubstituted aromatic rings) that had decreased by receiving a UV dose of 350 MJ m −2 , indicating that aromatic rings were degraded (Fig. S7.6 †).…”

A colorless, transparent and mechanically robust polyurethane elastomer: synthesis, chemical resistance and adhesive properties

“…Moreover, upon soaking in 40% H 2 SO 4 aqueous solution, the peak intensity of the stretching vibration peak of C–O–C at 1104 cm −1 decreased, inferring that the hydrogen on the α-carbon atom of the PTMEG ether bond may be oxidized by an acid. 52,53 More severe decomposition of the chemical bonds of the elastomer led to the deterioration in the strength of XDI-PUE after soaking in an acid. Therefore, it is believed that the present PUE is more suitable for use under alkali conditions.…”

Experimental study of UV induced tensile properties deterioration and chemical aging of polyurea–POSS composites

“…direct photolysis of C−C and C−H bonds, the presence of residue from the catalyst used in polymerization, Norrish-I and Norrish-II type reactions due to the presence of a carbonyl group, the attack of oxygen on C−C/C=C bond, the presence of hydroperoxide and/or the photo-Fries reaction which leads to the formation of free radicals. 21 In general, UV radiation in ambient sunlight has wavelength in the range of 290 nm–400 nm. Therefore, the polymer degradation due to ambient sunlight exposure is primarily driven by the UV radiation.…”