Preparation And Properties Of LDHs/Antioxidant/Elastomer Modified Bitumen

Elastomer (SBS) modified bitumen (EMB) waterproof membrane has beenwidely used due to the excellent resistance to flowing at high temperature andcracking at low temperature. However, elastomer modified bitumen material is proneto aging after long-term exposure to natural environmental factors, such as ultraviolet(UV) light, heat, oxygen and so on, which would lead to the deterioration of lowtemperature flexibility of bitumen membrane, and then cracking is always happened.Consequently, waterproof layers of building roof are destroyed, resulting in thefailure of waterproof. Therefore, it is of great significance for extending the servicelife of bitumen waterproof membrane by improving the resistance to UV aging andthermal-oxidative aging of elastomer modified bitumen.In this paper, layered double hydroxides (LDHs), antioxidant, reactive assistantpolyphosphoric acid (PPA) and their compounds were used as modifiers to prepareEMB with aging resistance performance, and the effects of modifiers on softeningpoint and low temperature flexibility of EMB were investigated. Accelerated UVaging and thermal-oxidative aging test were implemented on anti-aging EMB toexplore the effects of those modifiers on UV aging resistance and thermal-oxidativeaging resistance of EMB. The chemical structures and phase morphology of EMBbefore and after aging were characterized by Fourier transform infrared (FTIR)spectroscopy and fluorescence microscopy (FM) to study the modification and agingresistance mechanism of EMB added with modifiers. The main results obtained are asfollows:(1) LDHs enhances the softening point and low temperature flexibility of EMB,improving the deformation resistance at high temperatures and crack resistance at lowtemperatures, and both antioxidant1076and antioxidant168further increase thesoftening point of EMB with LDHs. After UV aging and thermal-oxidative aging, theaging degree of LDHs/EMB is significant lower than that of EMB. The antioxidant1076and antioxidant168can further improve the anti-aging performance of3%LDHs/EMB, and antioxidant1076shows better modified effect than antioxidant168.Furthermore, the optimum loading of LDHs, antioxidant1076and antioxidant168 are3%,0.6%and0.6%, respectively, which is based on influence trend of modifierson EMB before and after aging.(2) Composite antioxidant composed of a ratio of1:1antioxidant1076toantioxidant168is applied to modify LDHs/EMB. The results of UV aging andthermal-oxidative aging indicate that antioxidant1076to antioxidant168in thecomposite antioxidant exhibit synergistic effect, the improvement of compositeantioxidant is better than that of either single antioxidant. The further enhancement ofLDHs/EMB is attributed to capturing free radical of antioxidant1076, decomposinghydroperoxide of antioxidant168and shielding UV rays of LDHs. The mutualcomplementation of three additives in improving aging resistance of EMB leads toboth excellent UV aging resistance and thermal-oxidative aging resistance of EMB.(3) The PPA added in LDHs/EMB can react with bitumen and SBS molecules toplay a role of crosslinking, resulting in enhanced high temperature resistance of EMB,as0.8%PPA increase the softening point of EMB by8℃. Meanwhile, the result ofstorage stability test shows that softening point difference between the top section andbottom section of EBM with0.6%PPA decreases from9.5℃that of EBM withoutPPA to1.2℃, implying the storage stability of EMB is evidently improved by PPA.Furthermore, the addition of PPA decreases the softening point increment and lowtemperature flexibility decrement of EBM after UV aging and thermal-oxidativeaging, retarding the performance deterioration rate of EMB.(4) FTIR analysis demonstrates that the characteristic peaks of oxygenicfunctional groups (carbonyl C=O and sulfoxide group S=O) are increased after UVaging, indicating that oxidation reaction has taken place during aging of EMB leadingto the generation of oxygenic functional groups. While the peak’s intensity ofcarbon-carbon double bond C=C in butadienyl is weakened, reflecting thedegradation reaction of SBS has taken place leading to the break of double bond. Theoxidative condensation of bitumen and chain scission degradation of SBS areinhibited due to the introduction of LDHs and antioxidant, resulting in the extents ofoxygenic functional groups increment and double bond decrement are decreased.Additionally, PPA added into LDHs/EMB could restrain the oxidative condensationof bitumen, while it has little influence on degradation of SBS.(5) The morphology observation obtained by FM demonstrates that the network structure formed by SBS in bitumen is gradually destroyed, the heterogeneousstructure consisted of continuous SBS phase and dispersed bitumen phase graduallyshifts to homogeneous one after aging, phase boundary becomes dim and evendisappeared. However, the two separated phase in LDHs/antioxidant/SBS modifiedbitumen after aging can be still observed, which could further illustrate thecombination of LDHs and antioxidant significantly enhances the aging resistance ofEMB. Moreover, PPA changes the morphological structure of EMB, leading toobscure phase separation and increased compatibility between SBS and bitumen. Butafter aging, bitumen phase is observable while SBS phase becomes fuzzy, whichindicates that the aging of bitumen is suppressed while the degradation of SBS is stillremarkable.