Abstract:The purpose of this study was the synthesis of novel low-cost carbon fibers along with the investigation of the optimal parameters of temperature and time for the stabilization of hybrid high-density polyethylene (HDPE) and lignin melt-spun fibers. These fibers were manufactured by physical compounding of HDPE and chemically-modified softwood kraft lignin (SKL) in order to produce green fiber precursors for carbon fiber synthesis. Stabilization tests were performed with respect to thermal treatment (physical method) and sulfonation treatment (chemical method). The results revealed that only chemical methods induce the desired thermal process-ability to the composite fibers in order to manufacture carbon fibers by using a simple method. This investigation shed light on the stabilization techniques of polymeric fibers in the absence of any cyclic groups in terms of environmentally-friendly mass production of carbon fibers using low-cost and green raw materials. This study facilitates incorporation of softwood lignin in homegrown polymeric fibers by a low-cost production process via melt-spinning of composite fibers, which were successfully stabilized using a facile chemical method and carbonized. Additionally, a comprehensive investigation of the thermal behavior of the samples was accomplished, by examining several ways and aspects of fiber thermal treating. The properties of all studied fibers are presented, compared, and discussed.

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Abstract. The quality of high density polyethylene (HDPE) -lignin spun fibers depends on the spinning method and the chemical modification of the raw material. On the other hand, nylon-type polymers are widely known for their simple experimental synthesis and use. The goal of this study was the fabrication of composites containing lignin, nylon and multi-walled carbon nanotubes (MWCNTs) based fibers with enhanced mechanical properties. Therefore, a nylon-type polymer was synthesized, using diethylenetriamine and sebacoyl chloride, and was conjugated with lignin as well as MWCNTs with the aim of determining the materials' compatibility, differences in chemical behavior as well as their ability to be melt spun and be further processed. The materials were compounded with HDPE and melt spun, producing fibers that were characterized in respect of their morphology, structural, chemical and elemental composition. Finally, the HDPE fibers were used for the production of one dimensional composites inside dumb bell type sacrificial templates with an epoxy resin solution. The composites, which contained fibers enriched with oxidized lignin and MWCNTs, presented higher elastic modulus and ultimate tensile strength than the rest of the composites. This is a novel attempt, presenting an innovation concerning durable fibers with low cost materials and procedures.