Thermo-electrical and mechanical studies on polymer-organically modified montmorillonite composites / Norhana Abdul Halim

Abdul Halim, Norhana (2010) Thermo-electrical and mechanical studies on polymer-organically modified montmorillonite composites / Norhana Abdul Halim. PhD thesis, University of Malaya.

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Abstract

The field of polymer-nanoclay composite has attracted a lot of attention in materials studies due to the dramatic improvement on polymers characteristics. For example mechanical and thermal properties, chemical resistance as well as the reduced gas permeability. However, structural changes and the mechanisms that may contribute to these improvements are not fully understood. In this work, the study on polymer nanoclay composite concentrates on the effects of OMON inclusion within different polymer matrix systems. The matrixes are a series of natural rubbers (Standard Malaysia Rubber – Latex grade (SMRL); Deproteinized Natural Rubber (DPNR) and Epoxidized Natural Rubber (ENR-50)), plasticized Polyvinyl chloride (pPVC) and Polyethylene (PE). OMON is a renewed Montmorillonite (Mon) clay mineral, where chemical modifications carried out had changed the organophobic property of this mineral into organophylic. XRD analyses demonstrate the intercalation of polymeric chains, showing the increase in OMON basal spacing d001 from 1.840 nm to 3.864 nm. From the FTIR spectra of polymer-OMON composites, matrix-OMON silicates interaction is shown with the appearance of (Si-O-R) band and the changes in SiH (SiH and SiH) vibrations. Investigation on the improved matrix-OMON interactions within polymer-OMON composites concentrates on their thermo-electrical and mechanical responses. TSC measurement is chosen to carry out the thermo-electrical studies, which involves instrumentation of TSC system. The high sensitivity of TSC technique is capable to detect various dipoles and space charges relaxations, as shown with the emergence of ,  and  peaks. Observations and analyses on  and  OMON peaks reveal the effects of matrix-alkyl and matrix-silicate interactions on methylene groups (CH2) and alkyl chains (CH2)n within OMON gallery in the composites. Decomposition on TSC peaks confirm the involvement of various distributed relaxation processes. It also reveals the existence of molecular-ion deep traps with high activation energy E (> 4eV). Analyses on pre-exponential factor n from N-fitting method distinguish a range of dipole relaxations. It gives characteristic relaxation time n that suggest the occurances of dipole (10-10 s to 10-13 s), dipole-segmental (10-14 s to 10-17 s) and segmental (10-18 s to 10-28 s) relaxation modes. Several n (10+1 s to 10-4 s) from experimental TSC peaks also confirm the cooperative relaxation around the glass transition temperature Tg. Abstract Analyses and observations on some basic mechanical properties generated from tensile test demonstrate structural effects on the entire composite system. Various matrix-alkyl chains and matrix-silicate interactions induce interfacial adhesion, interparticle bridging flocculated and stacking layer structure, which influence the elasticity modulus Young Y, Tensile strength max and Maximum elongation max. Polar matrix-silicate interactions within CENR-50 (30%) composite had improved the interfacial adhesion, which contributed to the significant increase in modulus Y (15420 %) compares to that of pristine ENR-50. Similarly, CpPVC (30%) that is a pPVC composite with the improved OMON stacked structure (N 21 layers) also demonstrates the increased modulus Y (2323 %). Polymers intercalation into OMON gallery can promote certain chemical reactions, which affect the inner structure of a composite. For example, chains crosslinking within OMON gallery that creates the interparticle bridging flocculated structure also promotes more slippage on the matrix chain during stress loading. As a result, it improves the Maximum elongation max with the increase of OMON content as shown by the CSMRL (30%) (max 70 %) and CDPNR (30%) (max 125 %) composites.

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