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The tensile properties of polyacrylonitrile (PAN)-based and pitch-based single carbon fibers were assessed using Raman scattering. Parameters and ratios related to Raman scattering and stress measurement for the G- and D-bands were analyzed. These include the peak values of Raman shifts (RG, RD), full width at half maximum (FWHMG, FWHMD), peak value slopes (|AG|, |AD|), peak value intercepts (BG, BD), the intensity ratio (ID/IG), the peak value ratio (RD/RG), the full width at half maximum ratio (FWHMD/FWHMG), the slope ratio (AD/AG), and the intercept ratio (BD/BG). These parameters and ratios were determined by analyzing the PAN-based and pitch-based carbon fibers and were correlated to the tensile modulus (E), interlayer spacing (d002), lattice spacing (d10), and crystalline size (Lc and La). In addition, a linear relationship was identified between the Raman scattering, stress measurement parameters, ratios and E, d002, d10, as well as between the Raman scattering, stress measurement parameters, ratios and La and LC on the log–log scale. [ABSTRACT FROM AUTHOR]

While carbon fibers (CFs) are still the most attractive reinforcement material for lightweight structures, they are mostly manufactured using crude oil-based process chains. To achieve a higher eco-efficiency, the partial substitution of polyacrylonitrile (PAN) by renewable materials, such as lignin, is investigated. So far, this investigation has only been carried out for batch manufacturing studies, neglecting the transfer and validation to continuous CF manufacturing. Therefore, this work is the first to investigate the possibility of partial substituting lignin for PAN in a continuous process. Lignin/PAN-blended CFs with up to 15 wt.-% lignin were able to attain mechanical properties comparable to unmodified PAN-based carbon fibers, achieving tensile strengths of up to 2466 MPa and a Young's Modulus of 200 Pa. In summary, this study provides the basis for continuous Lignin/PAN-blended CF manufacturing. [ABSTRACT FROM AUTHOR]

Concrete is the most used construction material in the world; however, its deficiency in shrinkage and low tensile resistance is undeniable. Used as secondary reinforcement, fibers can modify concrete properties in various ways. Carbon-fiber-reinforced concrete is highly suitable to maintain longevity of infrastructure where corrosion of steel can shorten the useful service life of the structure while polypropylene fibers can mostly improve the shrinkage of concrete. However, the biggest challenge with fiber-reinforced concrete is the appearance of the poorly structured interfacial transition zone around the fibers. In this study, environmentally friendly and low-cost attempts were made to coat fibers with fly ash to enhance the structure of mortar around the fibers. Coated carbon and polypropylene fibers were used in mortar in single and hybrid forms to investigate the efficiency of fiber coating methods on mechanical and durability properties of fiber-reinforced cement mortar. A minimal dosage of 0.25% and 0.5% (by volume) PAN-based carbon fiber and polypropylene fiber was added to mortar to make low-cost mixes. Compressive, tensile and three-point bending tests were done after 14 and 28 days of curing, and the results were analyzed. The results showed higher compressive strength in coated fiber-reinforced samples and comparable results in tensile strength, flexural strength, and toughness parameters. Scanning Electron Microscopy (SEM) photos and Energy-Dispersive X-ray (EDX) analysis approved the efficacy of the coating methods.

Concrete is the most used construction material in the world; however, its deficiency in shrinkage and low tensile resistance is undeniable. Used as secondary reinforcement, fibers can modify concrete properties in various ways. Carbon-fiber-reinforced concrete is highly suitable to maintain longevity of infrastructure where corrosion of steel can shorten the useful service life of the structure while polypropylene fibers can mostly improve the shrinkage of concrete. However, the biggest challenge with fiber-reinforced concrete is the appearance of the poorly structured interfacial transition zone around the fibers. In this study, environmentally friendly and low-cost attempts were made to coat fibers with fly ash to enhance the structure of mortar around the fibers. Coated carbon and polypropylene fibers were used in mortar in single and hybrid forms to investigate the efficiency of fiber coating methods on mechanical and durability properties of fiber-reinforced cement mortar. A minimal dosage of 0.25% and 0.5% (by volume) PAN-based carbon fiber and polypropylene fiber was added to mortar to make low-cost mixes. Compressive, tensile and three-point bending tests were done after 14 and 28 days of curing, and the results were analyzed. The results showed higher compressive strength in coated fiber-reinforced samples and comparable results in tensile strength, flexural strength, and toughness parameters. Scanning Electron Microscopy (SEM) photos and Energy-Dispersive X-ray (EDX) analysis approved the efficacy of the coating methods. [ABSTRACT FROM AUTHOR]

The aim of this work is to review a possible correlation of composition, thermal processing, and recent alternative stabilization technologies to the mechanical properties. The chemical microstructure of polyacrylonitrile (PAN) is discussed in detail to understand the influence in thermomechanical properties during stabilization by observing transformation from thermoplastic to ladder polymer. In addition, relevant literature data are used to understand the comonomer composition effect on mechanical properties. Technologies of direct fiber heating by irradiation have been recently involved and hold promise to enhance performance, reduce processing time and energy consumption. Carbon fiber manufacturing can provide benefits by using higher comonomer ratios, similar to textile grade or melt-spun PAN, in order to cut costs derived from an acrylonitrile precursor, without suffering in regard to mechanical properties. Energy intensive processes of stabilization and carbonization remain a challenging field of research in order to reduce both environmental impact and cost of the wide commercialization of carbon fibers (CFs) to enable their broad application. [ABSTRACT FROM AUTHOR]

Carbon concrete polyacrylonitrile (PAN)/lignin-based carbon fiber (CF) composites are a new promising material class for the building industry. The replacement of the traditional heavy and corroding steel reinforcement by carbon fiber (CF)-based reinforcements offers many significant advantages: a higher protection of environmental resources because of lower CO2 consumption during cement production, a longer lifecycle and thus, much less damage to structural components and a higher degree of design freedom because lightweight solutions can be realized. However, due to cost pressure in civil engineering, completely new process chains are required to manufacture CF-based reinforcement structures for concrete. This article describes the necessary process steps in order to develop CF reinforcement: (1) the production of cost-effective CF using novel carbon fiber lines, and (2) the fabrication of CF rebars with different geometry profiles. It was found that PAN/lignin-based CF is currently the promising material with the most promise to meet future market demands. However, significant research needs to be undertaken in order to improve the properties of lignin-based and PAN/lignin-based CF, respectively. The CF can be manufactured to CF-based rebars using different manufacturing technologies which are developed at a prototype level in this study. [ABSTRACT FROM AUTHOR]