Ribca Iuliana, Sochor Benedikt, Roth Stephan V, Lawoko Martin, Meier Michael A R, Johansson Mats
Wallenberg Wood Science Center (WWSC), Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen 56-58, SE-100 44 Stockholm, Sweden.
Division of Coating Technology, Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen 48, SE-100 44 Stockholm, Sweden.
ACS Omega. 2023 Jul 3;8(28):25478-25486. doi: 10.1021/acsomega.3c03022. eCollection 2023 Jul 18.
In this study, the combination of sequential solvent fractionation of technical Kraft lignin was followed by allylation of most OH functionalities to give highly functional thermoset resins. All lignin fractions were highly functionalized on the phenolic (≥95%) and carboxylic acid OH (≥85%) and to a significant extent on the aliphatic OH moieties (between 43 and 75%). The resins were subsequently cross-linked using thiol-ene chemistry. The high amount of allyl functionalities resulted in a high cross-link density. Dynamic mechanical analysis measurements showed that the thioether content, directly related to the allyl content, strongly affects the performance of these thermosets with a glass transition temperature () between 81 and 95 °C and with a storage modulus between 1.9 and 3.8 GPa for all thermosets. The lignin fractions and lignin-based thermosets' morphology, at the nanoscale, was studied by wide-angle X-ray scattering measurements. Two π-π stacking interactions were observed: sandwich (≈4.1-4.7 Å) and T-shaped (≈5.5-7.2 Å). The introduction of allyl functionalities weakens the T-shaped π-π stacking interactions. A new signal corresponding to a distance of ≈3.5 Å was observed in lignin-based thermosets, which was attributed to a thioether organized structure. At the same time, a lignin superstructure was observed with a distance/size corresponding to 7.9-17.5 Å in all samples.
在本研究中，对工业硫酸盐木质素进行连续溶剂分级，然后将大部分羟基官能团烯丙基化，以得到高官能度热固性树脂。所有木质素级分在酚羟基（≥95%）和羧酸羟基（≥85%）上都实现了高度官能化，在脂肪族羟基部分也有显著程度的官能化（43%至75%）。随后使用硫醇-烯化学对树脂进行交联。大量的烯丙基官能团导致了高交联密度。动态力学分析测量表明，与烯丙基含量直接相关的硫醚含量强烈影响这些热固性材料的性能，所有热固性材料的玻璃化转变温度（）在81至95°C之间，储能模量在1.9至3.8 GPa之间。通过广角X射线散射测量研究了木质素级分和木质素基热固性材料在纳米尺度上的形态。观察到两种π-π堆积相互作用：夹心型（≈4.1 - 4.7 Å）和T型（≈5.5 - 7.2 Å）。烯丙基官能团的引入削弱了T型π-π堆积相互作用。在木质素基热固性材料中观察到一个对应于≈3.5 Å距离的新信号，这归因于硫醚有序结构。同时，在所有样品中都观察到一种距离/尺寸对应于7.9 - 17.5 Å的木质素超结构。
