The development of sub-micro filler enhanced polymer composites

Li, Y., 2007. The development of sub-micro filler enhanced polymer composites. PhD, Nottingham Trent University.


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Sub-micro silica flakes and graphite reinforced polymer composites have been developed in this research. The sub-micro polymer composites are designed to overcome problems associated with nanocomposite technology. Apart from the high cost of production, the other major problem in nanocomposites is reduced efficiency in mechanical reinforcement at high filler loadings. The surface area of nano-fillers in high filler loaded composites is too high resulting in insufficient polymer molecules to wet the filler surface and hence increased filler agglomeration occurs. Increasing filler dimension into the sub-micro range can avoid such difficulties. The dimension of fillers in the sub-micro range also has the advantage of utilising modern polymer processing technologies.

In this thesis, sub-micro composite reinforcement has been studied through the identification of suitable fillers, modelling of sub-micro composites and experimental validation of model predictions. The processing methodology, effects of filler loading, aspect ratio and compatibility of filler with matrix are also investigated. In addition, rheology, crystallisation, fracture toughness and the thermodynamic behaviour of submicro filler reinforced polymer composites are studied. The investigation was primarily focused on various combinations of single-layered silica flakes and multi-layered graphite sheets reinforced nylon-6 and polypropylene. The predicted Young's modulus and strengths of developed composites are as high as 3.3 GPa and 81 MPa at 5wt% silica flake content as well as 11.75 GPa and 301MPa at 30wt% flake fraction, respectively. Experimental results show that tensile modulus and strengths of the submicro composites produced agree well with modelling data at low filler loading. They are, however, much lower than the predictions in the high filler loading range due to the breakage of silica flakes during composite processing. In spite of filler breakage, the tensile modulus and strength of 5wt% silica flake reinforced N6 improved 68% and 67% respectively, compared to the N6. The tensile strength is also 38% higher than thatof 5wt% clay/N6 nanocomposites. The tensile modulus of 30wt% silica flake reinforced N6 improved over 240% which is similar to the achievement of 30wt% glass fibre/N6 composites. In addition, the fracture toughness and thermal deflection temperature of a silica flake/N6 composite improved by 17% at 5wt% and 20.3 oC at 10wt% filler content respectively.

For multi-layered graphite sheet reinforced polypropylene sub-micro composites, mechanical properties are a function of both filler thickness and filler loading. Over 112% improvement in Young's modulus has been achieved with a composite produced via a multi-extrusion method at 20wt% filler loading, compared with the pure polymer.
The crystallinities of all sub-micro composites produced are either similar to or lower than those of pure polymers. This implies that the major contribution to the improvement of mechanical properties is from sub-micro fillers. In addition, the crystallisation rate and crystallisation temperature of sub-micro composites are increased when compared with base polymers due to the nucleation effect of fillers. The introduction of sub-micro fillers into nylon-6 and polypropylene did not result in significant change in rheology. This may be associated with flake breakage and relatively poor interfacial bonding at the filler/polymer interface.

In summary, this work demonstrates the potential of sub-micro filler enhanced composites in improving major engineering properties. It also proves that the sub-micro approach can fill the gap between nano and fibre reinforcement.

Item Type: Thesis
Creators: Li, Y.
Date: 2007
ISBN: 9781369313598
Rights: This work is the intellectual property of the author, and may also be owned by the research sponsor(s) and/or Nottingham Trent University. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, of if a more substantial copy is required, should be directed in the first instance to the author.
Divisions: Schools > School of Science and Technology
Record created by: EPrints Services
Date Added: 09 Oct 2015 09:34
Last Modified: 17 Sep 2020 13:49

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