ABSTRACT

During the last years, several efforts were dedicated to the development of lignin-based polyurethane adhesives, in which phase separation and brittleness were the most significant reported limitations. Hydroxypropylation emerged as a feasible method to overcome their restricted performance, since this method generates lignin with higher reactivity and branched molecular structure, at different extends. However, the effect of lignin hydroxypropylation on properties of lignin-based PU adhesives remains unclear. In this work, mixtures of lignins and castor oil were used as renewable raw material polyol in the PU synthesis. First, a pristine kraft lignin (KL) was used as reference, followed by incorporation of two hydroxypropylated lignins: highT_HPL – obtained under high temperature and pressure (150°C, 18 bar) and lowT_HPL – synthesized under milder conditions (40°C, atm). Temperature modulated optical refractometry (TMOR) revealed a slower curing process for than highT_HPL-containing PU. LowT_HPL lignin improved the PU modulus of elasticity and ultimate tensile stress. KL and lowT_HPL incorporation resulted in higher strength of wooden adhesively bonded joints (single lap shear tests – 4.5 MPa). The results elucidated the main effects of hydropropylation on PU and its application on adhesively bonded joints, supporting the development of further lignin-based adhesives.

摘要

在过去的几年中，一些努力致力于开发木质素基聚氨酯粘合剂，其中相分离和脆性是报告的最重要的限制。羟丙基化成为克服其受限性能的可行方法，因为该方法生成的木质素具有更高的反应性和不同程度的支化分子结构。然而，木质素羟丙基化对木质素基聚氨酯粘合剂性能的影响仍不清楚。在这项工作中，木质素和蓖麻油的混合物被用作聚氨酯合成中的可再生原料多元醇。首先，使用原始硫酸盐木质素 (KL) 作为参考，然后加入两种羟丙基化木质素：highT_HPL – 在高温和高压（150°C，18 bar) 和 lowT_HPL – 在较温和的条件 (40°C, atm) 下合成。温度调制光学折光率 (TMOR) 揭示了比含高 T_HPL 的 PU 更慢的固化过程。LowT_HPL 木质素提高了 PU 的弹性模量和极限拉伸应力。KL 和 lowT_HPL 的结合导致木质粘合接头的强度更高（单搭接剪切试验 - 4.5 MPa）。结果阐明了羟丙基化对 PU 的主要影响及其在粘接接头上的应用，支持进一步开发木质素基粘合剂。KL 和 lowT_HPL 的结合导致木质粘合接头的强度更高（单搭接剪切试验 - 4.5 MPa）。结果阐明了羟丙基化对 PU 的主要影响及其在粘接接头上的应用，支持进一步开发木质素基粘合剂。KL 和 lowT_HPL 的结合导致木质粘合接头的强度更高（单搭接剪切试验 - 4.5 MPa）。结果阐明了羟丙基化对 PU 的主要影响及其在粘接接头上的应用，支持进一步开发木质素基粘合剂。