Gunnar Henrik Seide

Novel Carbon Nanotube/Cellulose Composite Fibers As Multifunctional Materials

Electroconductive fibers composed of cellulose and carbon nanotubes (CNTs) were spun using aqueous alkaline/urea solution. The microstructure and physical properties of the resulting fibers were investigated by scanning electron microscopy, Raman microscopy, wide-angle X-ray diffraction, tensile tests, and electrical resistance measurements. We found that these flexible composite fibers have sufficient mechanical properties and good electrical conductivity, with volume resistivities in the range of about 230-1 Ohm cm for 2-8 wt % CNT loading. The multifunctional sensing behavior of these fibers to tensile strain, temperature, environmental humidity, and liquid water was investigated comprehensively. The results show that these novel CNT/cellulose composite fibers have impressive multifunctional sensing abilities and are promising to be used as wearable electronics and for the design of various smart materials.

Spinnability and Characteristics of Polyvinylidene Fluoride (PVDF)-based Bicomponent Fibers with a Carbon Nanotube (CNT) Modified Polypropylene Core for Piezoelectric Applications

This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10 wt % carbon nanotubes (CNTs) and 2 wt % sodium stearate (NaSt). The sodium stearate is added to lower the viscosity of the melt. The compound constitutes the fiber core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of an all-trans conformation β phase, caused by draw-winding of the fibers. The core and sheath materials, as well as the bicomponent fibers, are characterized through different analytical methods. These include wide-angle X-ray diffraction (WAXD) to analyze crucial parameters for the development of a crystalline β phase. The distribution of CNTs in the polymer matrix, which affects the conductivity of the core, was investigated by transmission electron microscopy (TEM). Thermal characterization is carried out by conventional differential scanning calorimetry (DSC). Optical microscopy is used to determine the fibers’ diameter regularity (core and sheath). The materials’ viscosity is determined by rheometry. Eventually, an LCR tester is used to determine the core’s specific resistance.

Influence of process parameters on filament distribution and blending quality in commingled yarns used for thermoplastic composites

A prospective method for manufacturing thermoplastic composites involves commingling to produce hybrid yarn consisting of two components: reinforcement fibres and thermoplastic matrix. In this work, various types of commingled hybrid yarns were developed to improve blend uniformity and achieve homogeneous filament distribution in two-component hybrid yarns. An experiment was carried out to examine the distribution of filaments in a series of glass/polypropylene commingled hybrid yarns. The influence of changes in process parameters such as the degree of overfeeding, production speed, and air pressure on the filament distribution in the cross-section of commingled hybrid yarns was investigated. In this study, new technological approaches to achieve blend uniformity in commingled hybrid yarns are developed. The radial distribution index and a new blending coefficient were used to evaluate the blending uniformity of the yarns.

A method for investigating blending quality of commingled yarns

A prospective technology for manufacturing thermoplastic composites is based on hybrid commingled yarns. The hybrid yarns are further processed into semi-impregnated thermoplastic preforms in the form of woven or non-crimped fabrics, which are consolidated and molded in a single processing step. The quality of the component distribution in yarn is known to affect the mechanical properties of the manufactured composites. As part of a quality management system for the manufacturing process of thermoplastic composites based on commingling yarns, a new method for analyzing the blending quality along the length of commingled structures is presented in this work. By using this method, a new blending index (kb,yarn ) is introduced as a measure of the quality of commingled yarns. The blending index combines the existing coefficients of the lateral and radial distribution of fibers in the cross-section of hybrid yarns. Within this paper, the new analysis method is explained in detail using the example of glass fiber/polyamide 6 (GF/PA) commingled yarns. Due to the combination of the yarn analysis along the yarn axis and in its cross section, the new method allows for the first time a reliable comparison of the blending quality in commingled yarns used for the manufacturing of thermoplastic composites.

Modification of the mechanical properties of polyamide 6 multifilaments in high-speed melt spinning with nano silicates

In the last few years research activities have been focused on the modification of fiber properties with nano-scaled additives. One of the most important fields of research is the alteration of mechanical properties such as the tenacity and the specific breaking load. In this study, we determined the influence of nano-phyllosilicates on the drawability of polyamide 6 multifilament yarns. It was first demonstrated that the drawability of the fibers drastically increased in an industrially relevant high-speed melt spinning process. Structural properties of the material are identified by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). Changes in the crystalline properties as well as in the alignment of the silicates are compared with the stress–strain curves of the fibers, and a molecular mechanism for the drawing process is derived from these experiments. In a first step, a significant phase transition in the crystalline structure unaffected by the silicates occurs for low draw ratios (DRs). Beyond this point, where unmodified fibers start to break, a gliding between the silicate layers takes place, which is responsible for an extended drawability of the fibers. This mechanism leads to new possibilities for fiber processing, which can be used to research ultra-fine filaments in future studies.

Process–structure relationship of carbon/ polyphenylene sulfide commingled hybrid yarns used for thermoplastic composites

Commingling is a prospective manufacturing process for the production of hybrid yarn in which a reinforcement material and a thermoplastic matrix in the form of filaments are mixed to form continuous filament yarn. In this work, hybrid two-component carbon/ polyphenylene sulfide (PPS) yarns designed for high-performance thermoplastic composites were developed. Experiments were carried out to investigate the manufacturing process of commingled yarn and quantify the homogeneity of distribution of carbon and PPS fibers in cross section of commingled hybrid yarns. The effect of process parameters in commingling including degree of overfeeding, production speed, and air pressure on the filament distribution in the cross section of commingled hybrid yarns was investigated. The results show that process parameters play a large part in improving blend uniformity and filament distribution in hybrid commingled yarns. A correlation between the observed homogeneity and the process parameters was established.

Poling Effects in Melt-Spun PVDF Bicomponent Fibres

This research shows the successful functionalisation of bicomponent fibres, consisting of a conductive polypropylene (PP) core, doped with carbon nanotubes (CNT) and a piezoelectric sheath (polyvinylidene fluoride, PVDF) by draw winding and poling. These steps lead to the usability of the PVDF’s piezoelectric capabilities. The PP/CNT constitutes the fibre core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of β phase crystals (all-trans conformation), caused by draw-winding of the fibres. This β phase eventually has to be poled for the uniform alignment of polymer chains. The material’s behaviour in high electric field is analysed recording the poling voltage during the poling process. The outcome is hysteresis curves for different β phase contents, which verify a successful material poling.

Fabrication techniques for polymer optical fibres

Abstract There are a lot of different possibilities to manufacture polymer optical fibres. Regarding the final application, such as data transmission, lighting, or sensors, and the requirements concerning the polymer optical fibres, it is distinguished between step-index polymer optical fibres and graded-index polymer optical fibres. This chapter briefly summarizes the existing manufacturing techniques for step-index and graded-index polymer optical fibres and compares the advantages and the disadvantages of each process. At first the discontinuous manufacturing techniques for polymer optical fibres are discussed. These include preform production, heat drawing and batch extrusion. Finally the continuous manufacturing techniques are discussed. These include continuous extrusion, photochemical polymerization, co-extrusion, dry-spinning, melt-spinning and a modified melt-spinning process for the production of graded-index polymer optical fibres.

Carbon fiber production costing: a modular approach

Carbon fiber is expected to increase its importance as a lightweight substitute material. The significant market potential in the automotive industry is strongly dependent on carbon fiber cost. A decrease of about 50% from the present cost level of polyacrylonitrile (PAN)-based carbon fibers is needed. This ambitious target is only achievable with high-cost transparency in the production chain. This paper reviews published cost models and identifies the need for a consistent methodology and transparency over input parameters. A new cost model with a modular structure covering all process steps by cost type and disclosing all process parameter assumptions is introduced. The most cost-intense steps are polymerization, including raw material (25%), carbonization (22%) and fiber washing after coagulation (19%). Most important cost types are energy (34%), raw material (19%) and capital costs for equipment (18%). The high-cost share of 54% for carbon fiber PAN precursor is consistent with most reviewed models.

Extrusion of CNT-modified Polymers with Low Viscosity - Influence of Crystallization and CNT Orientation on the Electrical Properties

Several polymers were modified with multiwalled carbon nanotubes (CNT) to study the influences of the crystallization in the polymeric matrix and of the CNT orientation during extrusion on the electrical conductivity. Experiments were carried out with common semi-crystalline polymers (polypropylene, polyethylene, polyamide 6) and compared to an amorphous polymer (ethylene vinyl acetate). All polymers were grades with low viscosity, so that the CNT could be oriented well during extrusion. For all materials, the percolation threshold was determined, and the lowest value of 3% was found in polypropylene. The percolation threshold was correlated to the degree of crystallinity of the matrix polymers, so that crystallites could be seen as an excluded volume for CNT. The crystallization itself was analyzed by differential scanning calorimetry (DSC), whereby nucleation effects and changes in the crystallization temperature were found. The shear rate during extrusion had a large influence on the electrical conductivity. This effect was analyzed by transmission electron microscopy (TEM), with which the orientation of CNT in the direction of extrusion was visualized and differences between the polymer matrices were explained.