Mechanical and electrical property improvement in CNT/Nylon composites through drawing and stretching
Highlights
► Drawing and stretching significantly improved CNT alignment and straightness. ► We examine the effect of reduced CNT waviness on properties of CNT composites. ► Both mechanical and electrical properties showed substantial increases. ► CNT/nylon composites with a high volume fraction (15%) were achieved.
Introduction
Carbon nanotubes (CNTs) have highly desirable mechanical, thermal and electrical properties. They are promising candidates as reinforcement for the next generation of high performance composites. Significant effort has been focused on developing CNT composites over the last two decades. Methods for fabricating CNT composites include: dispersing short CNTs in polymer matrix [1], [2], [3], infiltrating CNT buckypaper with polymer solutions [4], [5], and reinforcing with CNT fiber assemblies [6], [7], [8].
Studies of CNT composites [9], [10], [11] so far have largely focused on improving the nanotube dispersion quality and the interface with the matrix. To achieve good quality CNT/polymer dispersion, short CNTs in low volume fractions are typically utilized. Although short CNT composites have some advantages in certain low volume fraction applications, such as thermally and electrically conducting materials, their mechanical properties fall far short of traditional high performance structural composites. It results largely from the short CNT length (usually <10 μm), which cannot efficiently transfer a mechanical load across the weakly bonded interface. Chemical modification may improve interfacial shear strength, at the expense of introducing defects in the CNT structures and thus degrading the properties [12]. Achieving high volume fractions of dispersed CNTs in polymer is difficult because the resulting high viscosity complicates further processing.
Another approach is to infiltrate CNT films (also known as buckypapers) with thermoplastic polymers or epoxy resin [4], [13]. The CNTs in the buckypaper sheets have no preferential orientation and each nanotube is curved and wavy. CNT fibers (yarns) can also be used to fabricate composites. They include plied or braided CNT fiber assemblies [6], [7] and long spun fibers infiltrated by polymer [8]. The most significant component in these composites is the CNT fiber. Techniques for making CNT fibers are classified into “liquid” methods [14], where CNTs are dispersed into a liquid and solution-spun into fibers, and “solid” methods [15], [16], where CNTs are directly spun into ropes or yarns. The last 10 years have seen rapid progress in the “solid” fiber spinning approach [17], [18], [19], [20], [21], [22], [23], [24]. While the mechanical properties of these fibers are promising, they both have limitations. The “liquid” method requires short CNTs for solution spinning, which limits the mechanical properties, while the “solid” method involves fiber twisting, which is a slow and expensive process. Scaling-up of these technologies presents a major obstacle for engineering applications.
In a recent work by Cheng et al. [25], a high volume fraction of highly aligned CNTs was homogeneously dispersed in an epoxy matrix. The CNT/epoxy composites were produced by drawing and stacking CNT sheets from aligned CNT arrays, and then infiltrating the stacked CNT sheets with epoxy. This method alleviates many limitations of other CNT processing methods. However, wavy nanotubes are still present, which reduces the mechanical properties of the composites.
Here we report a strategy, mechanical stretching of aligned CNT composites, to address the issue of CNT waviness. This approach involves drawing and winding thin CNT ribbons from free-standing CNT arrays, infusing a nylon 6,6 solution between layers of the CNT ribbon without disturbing the pre-existing alignment and stretching the composite while locally heating it to reduce the CNT waviness. The mechanical and electrical property results of this work identify a new mechanism of maximizing mechanical properties of CNT composites.
Section snippets
Rotational winding CNT ribbons into composites
Vertically aligned CNT arrays with a height of ∼700 μm were synthesized on a quartz substrate with iron chloride (FeCl2) powder using a thermal chemical vapor deposition (CVD) method described in literature [26]. The CNTs were drawn from the arrays onto a rotating cylindrical polytetrafluoroethylene (PTFE) spool (as depicted in Fig. 1a and b). Continuous CNT tows were placed on the rotating spool while tension was applied in order to well pre-align the ribbons. Meanwhile, nylon 6,6 (1.14 g/cm3 at
CNT/nylon 6,6 composites
The CNTs used to fabricate composites in this study were characterized by Raman and TEM (Fig. 2). A sharp G band peak (due to graphitic carbon) at 1583 cm−1 and a weak D band peak (due to disordered carbon) at 1357 cm−1 were observed in the Raman spectrum, indicating that the as-synthesized nanotubes were well-crystallized. The TEM image shows a nanotube having 50 walls and a diameter of 45 nm (inset in Fig. 2). These nanotubes were highly drawable from the array and had a high aspect ratio of
Conclusion
A novel drawing and stretching approach was developed for fabricating CNT/nylon 6,6 composites with good CNT alignment, high CNT volume fraction and straight nanotubes. The winding method created aligned CNT composites, while the local heating and stretching strategy led to further reduction of CNT waviness. Both mechanical and electrical properties showed substantial increases (191%, 294% and 207% for tensile strength, Young’s Modulus and electrical conductivity, respectively) as the stretch
Acknowledgements
This work is financially supported by the North Carolina Space Grant. We thank Yong-Jae Choi and Chi-Kai Chiu, PhD students in Department of Materials Science and Engineering at NC State University, for their help with the materials analysis.
References (44)
- et al.
Processing and property investigation of single-walled carbon nanotube (SWNT) buckypaper/epoxy resin matrix nanocomposites
Compos Part A-Appl Sci Manuf
(2004) - et al.
Carbon nanotube yarn and 3-D braid composites. Part I: Tensile testing and mechanical properties analysis
Compos Part A-Appl Sci Manuf
(2010) - et al.
Carbon nanotube yarn and 3-D braid composites. Part II: Dynamic mechanical analysis
Compos Part A-Appl Sci Manuf
(2010) - et al.
Properties of composites of carbon nanotube fibres
Compos Sci Technol
(2009) - et al.
Study on poly(methyl methacrylate)/carbon nanotube composites
Mater Sci Eng A-Struct Mater Prop Microstruct Process
(1999) - et al.
Carbon nanotube/epoxy composites fabricated by resin transfer molding
Carbon
(2010) - et al.
A novel approach to fabricate high volume fraction nanocomposites with long aligned carbon nanotubes
Compos Sci Technol
(2010) - et al.
Fiber waviness in nanotube-reinforced polymer composites-1: modulus predictions using effective nanotube properties
Compos Sci Technol
(2003) - et al.
Fiber waviness in nanotube-reinforced polymer composites-II: modeling via numerical approximation of the dilute strain concentration tensor
Compos Sci Technol
(2003) - et al.
Elastic properties of composites with fiber waviness
Compos Part A-Appl Sci Manuf
(1996)
Mechanical behavior of self-assembled carbon nanotube reinforced nylon 6,6 fibers
Compos Sci Technol
Multi-walled carbon nanotubes reinforced nylon 6 composites
Polymer
An assessment of the science and technology of carbon nanotube-based fibers and composites
Compos Sci Technol
Spatial statistics of carbon nanotube polymer composites
Polymer
Fluoroelastomer-MWNT nanocomposites-1: dispersion, morphology, physico-mechanical, and thermal properties
Polym Compos
Toward a stretchable, elastic, and electrically conductive nanocomposite: morphology and properties of poly[styrene-b-(ethylene-co-butylene)-b-styrene]/multiwalled carbon nanotube composites fabricated by high-shear processing
Macromolecules
Layer-by-layer assembled composites from multiwall carbon nanotubes with different morphologies
Nano Lett
Mechanical and electrical properties of polycarbonate nanotube buckypaper composite sheets
Nanotechnology
Surfactant-assisted processing of carbon nanotube/polymer composites
Chem Mater
Polymer nanocomposites containing carbon nanotubes
Macromolecules
Noncovalent functionalization as an alternative to oxidative acid treatment of single wall carbon nanotubes with applications for polymer composites
ACS Nano
Reinforcement of macroscopic carbon nanotube structures by polymer intercalation: the role of polymer molecular weight and chain conformation
Phys Rev B
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