UV-Curable Ester/Acrylate Precursors from Oxidized Chemical Recycling Products of HDPE Milk Bottles

A process for synthesizing UV-curable ester/acrylate precursors from dicarboxylic acid mixtures, oxidized chemical recycling products of HDPE milk bottles, has been developed. The behavior and properties of the non-purified oxidized products were compared to its commercial diacid single components in producing the precursors. Two as-received oxidized products obtained at different conditions, i.e., Oxi-1 and Oxi-2, containing molar compositions of succinic acid (C4): glutaric acid (C5): adipic and longer dicarboxylic acids (C6+) of 55: 23: 22 and 67: 9: 24, were employed. The precursors were produced at high yields by end-capping the carboxylic groups with hydroxyethyl acrylate, utilizing p -TSA catalyst and MEHQ radical scavenger. With 5 mol% p -TSA and 3 wt% MEHQ, a reaction at 120 °C for 2 h was effective for synthesizing the precursors from Oxi-1, Oxi-2, and succinic acid. However, the optimal condition for adipic acid was at 140 °C for 4 h, implying lower esterification reactivity due to its longer methylene sequence. All ester/acrylate precursors were fully cured under UV lights within 10 min. DMA results of cured films from neat precursors (100CL-series) indicate that those derived from longer diacids yielded crosslinked networks with relatively lower T g and rubbery plateau. However, when only 10% of the precursors were used as crosslinkers for acrylic acid/ethyl-hexyl acrylate (10CL-series), the influence of the starting material’s diacid composition on the film’s properties was lowered. The oxidized products from the nitric oxidation of HDPE have a high potential as value-added starting materials for UV-crosslinkers comparable to those from pure commercial diacids.