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Title: Compatibilisation of 1D/2D graphitic nanomaterials and poly(propylene) via non-covalent functionalisation with poly(acrylate)s
Author: Gupta, Jaipal
ISNI:       0000 0004 7431 7123
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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1D and 2D graphitic materials (carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs)) are of great interest due to their extraordinary electrical, thermal, mechanical and optical properties rarely found in bulk materials. The transfer of such properties to polymers has been limited and the development of scalable, cost-effective, multi-functional composite materials not fully realised. Polymers filled with 1D and 2D graphitic nanomaterials have uses in a wide range of applications and industries ranging from aerospace and automotive to personal care and high-tech products. Growing global economic development has sharply increased the world’s energy needs and in particular, our energy storage needs. In addition, they have potential applications in electronics, sensors and energy conversion. Another application in the area of personal care has shown that CNT-polymer composites can be used to speed up the process of bone-regeneration by being used as tissue scaffold materials. An application of interest is to use graphitic nanomaterials to produce composites with high mechanical performance (stiffness and strength) with low filler quantity providing innovative light-weighting solutions. Further potential applications of 1D and 2D graphitic nanomaterials include; touch screens, capacitors, spintronic devices, fuel cells, conductive films, high frequency circuits and flexible electronics. The development of such innovative materials requires the nanofiller to be homogenously dispersed within the polymer matrix, e.g. poly(propylene)(PP). The formation of an interconnected filler network structure at a low percolation threshold will result in the enhancement of electrical and thermal conductivity. In addition, efficient interfacial adhesion and stress transfer between filler and polymer results in improved mechanical strength and stiffness. However, poor compatibility between filler and the PP matrix prevents efficient homogenous dispersion and network formation. To address this major technical challenge, the use of a polymer compatibiliser which non-covalently functionalised graphitic nanomaterials was explored. By way of example, poly(lauryl acrylate) P[LA] was selected based upon its known compatibility with PP and it was proposed that it would also non-covalently functionalise such fillers via CH-π wrapping. P[LA] was synthesised using controlled living radical polymerisation methods and was shown to both be thermally stable for extrusion and physisorbed onto the surface of MWCNTs. For composites of PP, P[LA] and either MWCNTs or GNPs evidence was obtained confirming that P[LA] improved filler dispersion however, the most notable observation was a significant reduction in Tg of PP which was associated with P[LA] plasticising PP. Further polymer compatibilisers based on copolymers (statistical and block) of P[LA] and poly(2-phenyl ethyl acrylate) P[2PEA] where also synthesised and their potential to non-covalently functionalise CNTs and GNPs via both CH-π wrapping and π-π stacking examined. A range of characterisation techniques were employed to thoroughly understand the behaviour of these compatibilisers when added to composites of MWCNTs/GNPs and PP. Evidence for π-π stacking of P[2PEA] onto the surface of both graphitic fillers was observed from extensive electron microscopy observations. The potential of P[LA-co-2PEA] block copolymers as compatibilisers for 1D and 2D graphitic materials and PP was proven. The use of poly(acrylate)s as compatibilisers to assist the dispersion of 1D and 2D graphitic nanofillers in a PP has proven to be a concept with limited potential to alter the mechanical, electrical and thermal properties of polymers. The excellent thermal stability demonstrated by poly(acrylate)s for the purpose of melt blending with PP provides scope for further work through alternative functionalisation strategies e.g. covalent functionalisation. Throughout the project, the discussion has centred around the use of P[LA] and P[2PEA] due their potential to adsorb onto surface of 1D and 2D graphitic fillers and promote their dispersion in a PP matrix however, further work should investigate a range of poly(acrylate)s with various structures, chemistries, molecular weights and dispersities. For example, the use poly(acrylate)s with longer side chains such as poly(octadecyl acrylate) or poly(acrylate)s containing aromatic side chains with a greater number of benzene rings such as pyrene, for example pyrene acrylate. It is evident that the viscosity of the compatibilising polymer influences the extent of dispersion of the compatibiliser in the PP and matrix and therefore, it would be interesting to investigate if there is a correlation between the viscosity of the polymer compatibiliser and the extent of its dispersion in the PP matrix. GNPs with a greater aspect ratio are predicted to achieve percolation at lower loadings, increase electrical and thermal conductivity as well as improve the mechanical properties. Additionally, it would be interesting to explore what GNP quantity is required to achieve electrical and rheological percolation with the same type of GNPs and correlate those findings with graphenes with different aspect ratios to understand the role of flake dimensions. It is clear, P[LA] is not particularly successful in compatibilising the GNPs used in this study. In addition, it would useful to conduct dynamic cross-polarized optical microscopy and WAXS/SAXS scattering experiments during heating and cooling to investigate transcrystallinity phenomena at the interface between GNPs and the PP matrix.
Supervisor: Not available Sponsor: Warwick Manufacturing Group
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TP Chemical technology