RESUMO
Antioxidants (AOs) from natural resources are an attractive research area, as petroleum-based products can be replaced in polymer stabilization. Therefore, novel esters based on the p-hydroxycinnamic acids p-coumaric acid, ferulic acid and sinapic acid were synthesized and their structure properties relationships were investigated. The structures of the novel bio-based antioxidants were verified using NMR and Fourier-transform infrared (FTIR) spectrometry. The high thermal stability above 280 °C and, therefore, their suitability as potential plastic stabilizers were shown using thermal gravimetric analysis (TGA). The radical scavenging activity of the synthesized esters was evaluated by using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Stabilization performance was evaluated in polypropylene (PP) using extended extrusion experiments, oxidation induction time (OIT) measurements and accelerated heat aging. In particular, the sinapic acid derivative provides a processing stability of PP being superior to the commercial state-of-the-art stabilizer octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.
RESUMO
In this work, a block copolymer (BCP) consisting of poly((butyl methacrylate-co-benzophenone methacrylate-co-methyl methacrylate)-block-(2-hydroxyethyl methacrylate)) (P(BMA-co-BPMA-co-MMA)-b-P(HEMA)) is prepared by a two-step atom-transfer radical polymerization (ATRP) procedure. BCP membranes are fabricated applying the self-assembly and nonsolvent induced phase separation (SNIPS) process from a ternary solvent mixture of tetrahydrofuran (THF), 1,4-dioxane, and dimethylformamide (DMF). The presence of a porous top layer of the integral asymmetric membrane featuring pores of about 30 nm is confirmed via scanning electron microscopy (SEM). UV-mediated cross-linking protocols for the nanoporous membrane are adjusted to maintain the open and isoporous top layer. The swelling capability of the noncross-linked and cross-linked BCP membranes is investigated in water, water/ethanol mixture (1:1), and pure ethanol using atomic force microscopy, proving a stabilizing effect of the UV cross-linking on the porous structures. Finally, the influence of the herein described cross-linking protocols on water-flux measurements for the obtained membranes is explored. As a result, an increased swelling resistance for all tested solvents is found, leading to an increased water flux compared to the pristine membrane. The herein established UV-mediated cross-linking protocol is expected to pave the way to a new generation of porous and stabilized membranes within the fields of separation technologies.
