Utilisation de lignines Kraft comme agent de couplage dans des composites à base de polyéthylène de haute densité (HDPE) contenant des fibres d’écorce
|Advisor:||Stevanovic-Janezic, Tatjana; Rodrigue, Denis; Wang, Xiangming|
|Abstract:||This research work is divided into three parts. The first part is dedicated to the review of different approaches discussed in the literature concerning wood-plastic composites (WPC) and different possibilities while highlighting the preliminary results obtained. It also reported the potential of lignin as coupling agent. In the second part, the optimization of the effectiveness of this new type of coupling agent combining modified lignin with a commercial coupling agent (polyethylene maleate: MAPE) is discussed. Finally, the performance of the selected composites upon the freeze-thaw resistance tests and the effect of extractions (water and soda) on the characteristics (flexural and tensile properties) of composites containing bark fibers and modified lignin are presented in the last part. The problem of compatibility between the constituents of WPC is related to the extremely opposite characteristics of natural fibers and the polymer matrix. A multitude of physical or chemical treatments can improve compatibility and the interfacial interactions between components. The environmental and economic impact of the use of petroleum chemicals and the demand to valorize the co-products of wood transformation offers the possibility of using esterified lignin in the production of a new generation of WPC. We have demonstrated the feasibility of composite based on high density polyethylene (HDPE) containing 30% of black spruce bark fibers, with 5% (based on the mass of bark) of Kraft lignin esterified by maleic anhydride. The combination of esterified Kraft lignin with the MAPE (at equal levels) has been demonstrated to improve the compatibility between the bark fibers and the matrix. Given that natural fibers contain lignin, the esterified lignin (with succinic and maleic anhydride) is supposed to create a structure which acts as bond between the bark fibers and the hydrophobic matrix (HDPE). This action is related to the high porosity of esterified lignin as revealed by SEM, which allows for mechanical anchoring due to van der Waals or π–π interactions. The effect of the structure of coupling agent on the mechanical properties of the composites has been determined. A statistical analysis performed on the collected data made it possible to determine the best settings of parameters for optimal mechanical properties of composites, designed through the innovative approach of using esterified Kraft lignin as a coupling agent for WPC. Finally, the effect of water and soda extractions of bark fibers prior to their incorporation into composites was studied, on the mechanical characteristics of the composites. The composites with best mechanical performance were finally tested regarding freeze-thaw resistance since an outside application of the material, is anticipated in the Quebec context. However, the test for resistance to freeze-thaw positively influences the characteristics of WPC. It has been shown that different extractions do not affect the mechanical properties (flexural and tensile). Better behavior was found for formulations with a coupling agent combining lignin esterified with the MAPE.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||20 April 2018|
|Collection:||Thèses et mémoires|
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