Structural Modifications of Residual Lignins from Sisal and Flax Pulps during Soda-AQ Pulping and TCF/ECF Bleaching

We have studied the structural modifications of lignins from sisal and flax during their soda-anthraquinone (AQ) pulping and subsequent totally chlorine-free (TCF) and elementary chlorine-free (ECF) bleaching. For this purpose, residual lignins were isolated from pulps, analyzed by Py-GC/MS, 2D-NMR, and GPC, and their characteristics were compared to the “milled-wood” lignin of the raw materials. Soda-AQ pulping caused a preferential removal of S-lignin and cleavage of β–<i>O</i>–4′ linkages, but the structure of the residual lignin remained relatively similar to native lignin. TCF bleaching barely affected the lignin structure, and noticeable amounts of β–<i>O</i>–4′ linkages still occur in these pulps. In contrast, ECF bleaching caused strong modifications in the lignin structure with the complete removal of lignin markers in ECF-bleached sisal pulp. However, residual lignin was still present in ECF-bleached flax pulp, with a predominance of G- and H-lignin units and the presence of β–<i>O</i>–4′ linkages

Synthesis of 4H-SrMnO_3.0 Nanoparticles from a Molecular Precursor and Their Topotactic Reduction Pathway Identified at Atomic Scale

Stoichiometric 4H-SrMnO_3.0 nanoparticles have been synthesized from thermal decomposition of a new molecular heterometallic precursor [SrMn­(edta)­(H₂O)₅]·³/₂H₂O whose crystal structure has been solved by single crystal X-ray diffraction. From this precursor, highly homogeneous 4H-SrMnO_3.0 nanoparticles, with average particle size of 70 nm, are obtained. The agglomeration of these nanoparticles maintains the sheet-assembling morphology of the metal–organic compound. Local structural information, provided by atomically resolved microscopy techniques, shows that 4H-SrMnO_3.0 nanoparticles exhibit the same general structural features as the bulk material, although structural disorder, due to edge dislocations, is observed. The nanometric particle size enables a topotactic reduction process at low temperature stabilizing a metastable 4H-SrMnO_2.82 phase. The oxygen deficiency is accommodated through extra cubic layers breaking the ...chch... 4H-sequence. These defect areas are Mn³⁺ rich, as evidenced by high energy resolution EELS data. Magnetic characterization of nano-SrMnO_3.0 shows significant variations with respect to the bulk material. Besides the dominant antiferromagnetic interactions, a weak ferromagnetic contribution as well as exchange bias and a glassy-like component are present. After the reduction process, the stabilization of Mn³⁺ in the 4H-structure gives rise to magnetic anomalies in the 40–60 K temperature range. The origin of such magnetic features is discussed

Modification of the Lignin Structure during Alkaline Delignification of Eucalyptus Wood by Kraft, Soda-AQ, and Soda‑O₂ Cooking

The modification of the lignin structure of an eucalyptus feedstock during alkaline delignification by kraft, soda-AQ, and soda-O₂ cooking processes has been investigated by different analytical techniques (size exclusion chromatography (SEC), pyrolysis gas chromatography–mass spectroscopy (Py-GC/MS), ¹H–¹³C two-dimensional nuclear magnetic resonance (2D-NMR), and ³¹P NMR). The characteristics of the lignins were compared at different pulp kappa levels, and with the native lignin isolated from the wood. The structural differences between the kraft, soda-AQ, and soda-O₂ residual lignins were more significant at earlier pulping stages. At the final stages, all the lignin characteristics were similar, with the exception of their phenolic content. Strong differences between lignins from pulps and cooking liquors were observed, including enrichment in guaiacyl units in pulp residual lignin and enrichment in syringyl units in black liquor lignin. A comparison of the alkaline cookings indicate that soda-O₂ process produced higher lignin degradation and provided promising results as pretreatment for the deconstruction of eucalyptus feedstocks for subsequent use in lignocellulose biorefineries