Preparation of O-vanillin-based stabilisers and their application in polypropylene
O-vanillin(OVA)is a naturally phenolic compound with a unique phenol-aldehyde structure.Two novel bio-based stabilisers,O-vanillin-purine schiff base compounds(SB1 and SB2)were synthesized via schiff base reaction using OVA,adenine(Ade),and 2,6-diaminopurine(26-DAPY)as raw materials.The samples were then hot-pressed by melt blending with polypropyl-ene(PP)using a closed plastic mixer,respectively.Fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resonance hydrogen spectrum(1H NMR)were used to characterise the chemical structures of SB1 and SB2.The thermal stability of SB1 and SB2 was tested by thermogravimetric analysis.The thermal oxidative stability,initial oxidation temperature(IOT),oxidation induc-tion time(OIT),tensile properties after photo-oxidative aging,and ultraviolet transmittance of the PP films were studied to investi-gate the effects of SB1 and SB2 on the thermal oxidative stability,photo-oxidative stability,and ultraviolet shielding performance of PP.The antioxidant activity was evaluated by theoretical calculation of bond dissociation energy,highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap.The results indicate that the temperatures corresponding to 5%thermal weight loss for SB1 and SB2 are 202℃and 219℃,respectively,higher than OVA(144℃).The addition of SB1 improves the thermal oxida-tive stability of PP.Compared to pure PP,the addition of SB1 increases the initial oxidation temperature(IOT)and oxidation induc-tion time(OIT)by 7-19℃and 2.2-4.9 min,respectively.The addition of 0.1wt%of SB1 or SB2 exhibits photo-oxidative stabiliza-tion effects on PP.In the UV transmittance test of PP films,the transmittance of PP films with the addition of 1.0 wt%of SB1 or SB2 is reduced to less than 6.0%and 6.2%in the range of 250-400 nm,respectively.
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