Electrospun Nanofiber Reinforced Composites: Fabrication and Properties

This dissertation presents research related to the use of electrospun nanofibers for reinforcement of mechanical properties of polymers, like thermoplastic polyurethane (TPU), melamine-formaldehyde (MF) and polyimide (PI). Nylon-6 and PI electrospun nanofibers are excellent candidates for reinforcement purposes as they possess excellent mechanical properties. Both long and short electrospun nanofiber reinforced composites were prepared and the effects of the fiber contents, the fabricating methods, and use of continuous and/or short nanofibers on the wetting behavior, mechanical properties, thermal and optical properties were investigated in the present work. Chapter 1 provided a general introduction of fiber reinforced polymer composites and electrospinning technology. The classification, the mechanical properties and the fabrication methods of fiber reinforced polymer composites were introduced. Nanofibers as a special kind of fibers have been attracting more and more attention in fiber reinforced polymer composites due to their excellent mechanical properties compared to the traditional fibers. The affecting factors on the properties of fiber reinforced polymer composites were also introduced in Chapter 1. Chapter 2 is the cumulative part of the thesis subdivided into 4 parts. Each part is the summary of the published work in different peer-reviewed journals. In Section 2.1, electrospun nylon-6 nanofiber mats were used to reinforce melamine-formaldehyde (MF) by dip-coating combined with hot-pressing (method 1) and passing the MF solution through nylon-6 nanomats combined with hot-pressing (method 2). The resulted composite films by both methods presented synergistic effects in tensile strength and toughness compared to the pure MF resin. The wetting behavior of the samples (produced by methods 1 and 2) led to quite different effects on the morphology and mechanical properties of the composites. Depending on the loading amount of nylon-6 nanofibers, the effect between MF and nylon-6 could be considered as fiber reinforced MF or MF glued nylon-6 fibers. Section 2.2 highlighted a novel layer-by-layer procedure for making high performance nylon-6 nanofiber reinforced TPU composites. The fast wetting of nylon-6 nanofibers by a TPU/N,N’-dimethylformamide (DMF) solution greatly improved the interfacial interaction between nylon-6 nanofibers and the TPU matrix, and led to a significant improvement in mechanical properties like tensile strength, E modulus, elongation at break and toughness. The enhancement was achieved without sacrificing the transparency of TPU by just using very small amounts (even as small as 0.4 wt%) of nylon-6 nanofibers. Section 2.3 and 2.4 focused on the initial investigations of using short electrospun nanofibers as reinforcement. A liquid processing technique was applied to prepare short electrospun nanofibers and their dispersions. The pre-loaded very small amount of short nanofibers (˂ 5 wt%) gave rise to significant enhancement effects without sacrificing the transparency. In section 2.3, a comparison study by using short nylon-6 nanofibers to reinforce TPU and poly(methyl methacrylate) (PMMA) was provided. The interaction of hydrogen bonding (H-bonding) and the homogeneous distribution of short fibers between nylon-6 nanofibers and the TPU matrix led to a stronger interface compared to nylon-6/PMMA composites and better reinforcement effects were observed in nylon-6/TPU composite than in nylon-6/PMMA composites. Section 2.4 described the self-reinforced PI composites and compared the enhancement in mechanical properties by short PI nanofibers and PI nanofiber mats. The solubility difference between PI and its precursor, polyamic acid (PAA) provided the opportunity to prepare self-reinforced composites. As compared to using PI nanofiber mats as reinforcement, the short PI nanofiber reinforced PI composites showed better mechanical properties due to the much better dispersability of short nanofibers. Quite less amounts of short PI nanofibers than nanofiber mat were required to achieve similar enhancement of the composites, i.e. 38 wt% of PI nanofiber mat compared to 2 wt% of short PI nanofibers were required to achieve almost the same tensile strength. Chapter 3 presents an outlook about the problems and challenges in electrospun nanofiber reinforced polymer composites. Future work about electrospun nanofiber reinforced composites could be focused on (1) how to prepare strong nanofiber with excellent mechanical properties; (2) the effect of diameter and aspect ratio of nanofibers on the properties of nanofiber reinforced polymer composites; (3) how to enhance the nanofiber/matrix interaction and (4) how to prepare super strong electrospun carbon nanofibers as reinforcements.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2014

Author dc:creator

• Jiang, Shaohua

Contributors dc:contributor

• Agarwal, Seema

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/1699/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:1699