Thermal Treatment of Melt-Spun Fibers Based on High Density PolyEthylene and Lignin

Panagiotis Goulis,Konstantinos Mpalias,Dimitrios Dragatogiannis,Costas Charitidis,Ioannis Kartsonakis,Stavros Anagnou,Giorgos Konstantopoulos

doi:10.3390/c3040035

Panagiotis Goulis, Konstantinos Mpalias + Show 5 more

Open Access

https://doi.org/10.3390/c3040035

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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.

Highlights

Stabilization of polymeric fibers is an essential step for carbon fiber (CF) synthesis [1,2] in order to prepare the polymer to resist intense thermal processing by enhancing polymer’s intra- and inter-molecular network through extensive crosslinking [3]
The produced samples were characterized in respect of their morphology and elemental analysis via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS)
For the successful stabilization of the fibers, it is required that the sulfur atoms, coming from sulfuric acid, have to form sulfur bridges onto the polymeric chains of high-density polyethylene (HDPE) and lignin

Summary

Introduction

Stabilization of polymeric fibers is an essential step for carbon fiber (CF) synthesis [1,2] in order to prepare the polymer to resist intense thermal processing by enhancing polymer’s intra- and inter-molecular network through extensive crosslinking [3]. The main precursors involved in CF synthesis are polyacrylonitrile (PAN), pitch, and rayon. 80% of the precursors currently used in industrial-scale plants and its stabilization mechanism has been extensively studied throughout the previous century. The major occurring reactions are, namely, summarized to cyclization, dehydrogenation, and oxidation, which lead to a conjugated polymer structure of C=N, C=C, and C=O, respectively [4]. Some secondary crosslinking reactions may occur during the process. The high cost of currently-used precursors demonstrates the urgent need to investigate alternative precursors in order to reduce the cost of production and enable wide commercialization of CF materials [5]

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