Antonino Leonardo D, Sumerskii Ivan, Potthast Antje, Rosenau Thomas, Felisberti Maria Isabel, Dos Santos Demetrio J
Nanoscience and Advanced Materials Graduate Program (PPG-nano), Federal University of ABC (UFABC), Santo André 09210-580, Brazil.
Department of Chemistry, Division of Chemistry of Renewable Resources, University of Natural Resources and Life Sciences Vienna (BOKU), Konrad-Lorenz-Strasse 24, 3430 Tulln an der Donau, Austria.
ACS Omega. 2023 Jul 18;8(30):27621-27633. doi: 10.1021/acsomega.3c03422. eCollection 2023 Aug 1.
Lignin, the world's second most abundant biopolymer, has been investigated as a precursor of polyurethanes due to its high availability and large amount of hydroxyls present in its structure. Lignin-based polyurethanes (LPUs) are usually synthesized from the reaction between lignin, previously modified or not, and diisocyanates. In the present work, LPUs were prepared, for the first time, using the blocked isocyanate approach. For that, unmodified and hydroxypropylated Kraft lignins were reacted with 4,4'-methylene diphenyl diisocyanate in the presence of diisopropylamine (blocking agent). Castor oil was employed as a second polyol. The chemical modification was confirmed by P nuclear magnetic resonance (P NMR) analysis, and the structure of both lignins was elucidated by a bidimensional NMR technique. The LPUs' prepolymerization kinetics was investigated by temperature-modulated optical refractometry and Fourier-transform infrared spectroscopy. The positive effect of hydroxypropylation on the reactivity of the Kraft lignin was verified. The structure of LPU prepolymers was accessed by bidimensional NMR. The formation of hindered urea-terminated LPU prepolymers was confirmed. From the results, the feasibility of the blocked isocyanate approach to obtain LPUs was proven. Lastly, single-lap shear tests were performed and revealed the potential of LPU prepolymers as monocomponent adhesives.
木质素是世界上第二丰富的生物聚合物，由于其易于获取且结构中存在大量羟基，已被研究作为聚氨酯的前体。木质素基聚氨酯（LPU）通常由木质素（无论是否预先改性）与二异氰酸酯之间的反应合成。在本工作中，首次采用封端异氰酸酯法制备了LPU。为此，未改性和羟丙基化的硫酸盐木质素在二异丙胺（封端剂）存在下与4,4'-二苯基甲烷二异氰酸酯反应。蓖麻油用作第二种多元醇。通过磷核磁共振（P NMR）分析确认了化学改性，并通过二维核磁共振技术阐明了两种木质素的结构。通过温度调制光学折射法和傅里叶变换红外光谱研究了LPU预聚合动力学。验证了羟丙基化对硫酸盐木质素反应活性的积极影响。通过二维核磁共振研究了LPU预聚物的结构。证实了受阻脲封端的LPU预聚物的形成。从结果来看，证明了封端异氰酸酯法获得LPU 的可行性。最后，进行了单搭接剪切试验，揭示了LPU预聚物作为单组分粘合剂的潜力。
