Elsevier

Polymer

Volume 42, Issue 7, March 2001, Pages 3301-3304
Polymer

Polymer Communication
Improvement of tensile properties of nano-SiO2/PP composites in relation to percolation mechanism

https://doi.org/10.1016/S0032-3861(00)00741-2Get rights and content

Abstract

Low nano-silica loaded polypropylene composites are produced by conventional compounding technique in which the nanoparticles are grafted by polystyrene using irradiation beforehand. A high interfacial stress transfer efficiency is demonstrated by both strengthening and toughening effects perceived in tensile tests. The role of the modified nanoparticles in improvement of tensile properties of the nanocomposites is discussed in terms of percolation concept. A double percolation of yielded zones is presented to explain the specific influence generated by the nano-SiO2 particles at low-filler loading regime.

Introduction

Mechanical properties of polymers can be improved by incorporating nanoparticles. In order to reach this improvement, it is generally believed that a homogeneous dispersion of the particles in the polymer matrix is a prerequisite, otherwise the loosely agglomerated nanoparticles would easily result in failure of the composites when they are subjected to force. Therefore, specific techniques (e.g. intercalation polymerization and solution blending) are nowadays used for the preparation of polymer-based nanocomposites [1], [2]. In this way, however, the nanoparticles cannot be compounded with polymers like conventional particulate fillers, which have been employed in plastics industry on a large scale since many years.

To overcome this difficulty, in the work presented here nanoparticles are treated through irradiation grafting so that macromolecular grafting chains are formed onto their surfaces both inside and outside the nanoparticle agglomerates. Then these modified nanoparticles are mechanically mixed with polymers as usual [3]. The significantly increased hydrophobility of the nanoparticles due to the presence of the grafting polymers is beneficial for a good interfacial bonding between the nanoparticles and the matrix, even though a completely uniform distribution of the particles cannot be achieved during this compounding process. Nevertheless, it was found that the deformation habit of the matrix polymer can be improved remarkably already at rather low-filler loading [4], [5]. In this context, it can be of interest to discuss the role of the treated nanoparticles in strengthening and toughening as a result of percolation mechanisms. This will be done in the present work, which reports about the tensile behavior of a polypropylene (PP)-based nanocomposites filled with polystyrene-grafted nano-SiO2 (denoted by SiO2-g-PS).

Section snippets

Experimental

An isotactic PP homopolymer (melting flow index: 6.7 g/10 min) and nanoparticles of SiO2 (diameter: 7 nm) were selected as the matrix polymer and the fillers, respectively. Styrene was used as grafting monomers. Mixture of particles/monomer (100/20) and solvent were irradiated by 60Co γ-ray at a dose rate of 1 Mrad/h in air. During this process, the monomer was polymerized into polystyrene (PS) molecules. Having been exposed to a dose of 30 Mrad, the solvent was recovered and the dried residual

Results and discussion

The tensile strengths of SiO2-g-PS/PP nanocomposites are plotted against their SiO2 volume fraction in Fig. 1. With a rise in filler content, the strength of the nanocomposites increases first and then keeps nearly unchanged. As interfacial interaction in a composite material governs stress transfer efficiency and extent of induced matrix deformation and eventually determines the mechanical performance of the composite, the above filler loading dependence of strength should be analyzed at this

Acknowledgements

The financial support by the National Natural Science Foundation of China (Grant: 59725307), the Deutsche Forschungsgemeinschaft (DFG FR675/34-1), the Foundation for the Excellent Youth Scholars of the Ministry of Education of China, the Key Programs of the Ministry of Education of China (Grants: 98069 and 99198), the Natural Science Foundation of Guangdong (Grant: 990277) and the Talent Training Program Foundation of the Higher Education Department of Guangdong Province are gratefully

References (15)

  • M.Z Rong et al.

    Polymer

    (2001)
  • S Wu

    Polymer

    (1985)
  • K Friedrich

    Compos Sci Technol

    (1985)
  • A Margolina et al.

    Polymer

    (1988)
  • E.P Giannelis

    Adv Mater

    (1996)
  • G Carrotenuto et al.

    Appl Compos Mater

    (1995)
  • Rong MZ, Zhang MQ, Zheng YX, Zeng HM. Chinese Patent (Application No.: CN99116017),...
There are more references available in the full text version of this article.

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