Lignopolyurethanic materials based on oxypropylated sodium lignosulfonate and castor oil blends

The rational valorization of lignin and its derivatives is a challenge in biorefinery because this biopolymer is one of the major source of aromatic moieties. Lignosulfonates are used to a lesser extent than lignin to prepare macromolecular materials. In the current study, sodium lignosulfonate (NaLS), which was either blended or not blended with OH-containing vegetable oil (i.e., castor oil (CO)), was reacted with diphenylmethane diisocyanate (MDI) to prepare polyurethane-type materials, such as lignopolyurethanes (i.e., CO/NaLS/MDI and NaLS/MDI, respectively). NaLS was oxypropylated (LS-Oxy) to increase its reactivity towards MDI. LS-Oxy was characterized and then used after being blended or not blended with CO to prepare lignopolyurethanes CO/LS-Oxy/MDI and LS-Oxy/MDI, respectively. These materials were characterized by infrared spectroscopy, thermogravimetry (TG), and dynamic mechanical thermoanalysis (DMA). The T-g values obtained from DMA (loss modulus peak) indicated that the lignopolyurethanes with an intermediate degree of cross-linking were obtained. In a final set of experiments and due to their potential application, the obtained lignopolyurethanes were reinforced with sisal fibers, and the impact strength, flexural properties and scanning electron microscopy (SEM) images of the materials were obtained. The results indicated that the presence of sisal fibers led to a significant improvement in the impact strength of the lignopolyurethanes, especially in those prepared from LS-Oxy [CO/LS-Oxy/MDI: approximately from 40 jm(-1) (without sisal) to 370 jm(-1) (with sisal); LS-Oxy/MDI: from 15 jm(-1) (without sisal) to 459Jm(-1) (with sisal)]. The flexural properties of CO/LS-Oxy/MDI (with or without sisal) corresponded to a less rigid material compared to the other material. The results indicated that the characteristics of the lignopolyurethanes could be tuned by oxypropylation of NaLS and/or blending with CO as well as by the addition of sisal fibers, which enables the production of materials with a wide range of properties. (C) 2015 Elsevier B.V. All rights reserved.