Nanocomposites polyolefin/clay

It is generally accepted that thermal stability of polymer nanocomposites is higher than that of pristine polymers, and that this gain is explained by the presence of anisotropic clay layers hindering diffusion of volatile products through the nanocomposite material. It is important to note that the exfoliated nanocomposites, prepared and investigated in this work, had much lower gas permeability in comparison with that of pristine unfilled PE [12], Thus, the study of purely thermal degradation process of PE nanocomposite seemed to be of interest in terms of estimation of the nanoclay barrier effects on thermal stability of polyolefin/clay nanocomposites. 

There are two basic types of nanocomposites, in which particles are intercalated or exfoliated. In an intercalated composite the nanodispersed filler still consists of ordered structures of smaller individual particles, packed into intercalated structures. Exfoliated particles are those dispersed into practically individual units, randomly distributed in the composite. Layered silicates, such as montmorillonite clays or organoclays, can be used in nanocomposites. Because clays are hydrophilic and polyolefines are hydrophobic, it is not easy to make a nanocomposite based on polyethylene or polypropylene because of their natural incompatibility. 

Synthesizing a Polyolefin-Clay Nanocomposite Using the Polymerization Method... 

Tjong, S. C. and Ruan, Y. H. 2008. Fracture behavior of thermoplastic polyolefin/clay nanocomposites. Journal of Applied Polymer Science 110 864-871. 

Toward Polyolefin-Clay Nanocomposites by In Situ Polymerization.134... 

A viable process for manufacturing polyolefin-clay nanocomposifes by in situ polymerization requires adequate catalytic activity, desirable polymer microstructure, and physical properties including processibility, a high level of clay exfoliation fhaf remains stable under processing conditions and, preferably, inexpensive catalysf components. The work described in the previous two sections focused on achieving in situ polymerization with clay-supported transition metal complexes, and there was less emphasis on optimization of polymer properties and/or clay dispersion. Since 2000, many more comprehensive studies have been undertaken that attempt to characterize and optimize the entire system, from the supported catalyst to the nanocomposite material. The remainder of this chapter covers work published in the past decade on clay-polyolefin nanocomposites of ethylene and propylene homopolymers, as well as their copolymers, made by in situ polymerization. The emphasis is on the catalyst compositions and catalyst-clay interactions that determine the success of one-step methods to synthesize polyolefins with enhanced physical properties. 

The preparation of polyolefin-clay nanocomposites with nanodispersions that remain stable during processing, even at elevated temperatures, remains an important goal. For many potential applications, commercial success will preclude the use of large amounts of expensive compatibilizing agents. A promising approach is the in situ polymerization of... 

Peoples, B. C. 2008. In situ production of polyolefin-clay nanocomposites. PhD thesis. University of California, Santa Barbara. 

Evidences of Polymer/Clay Interaction and Confinement in Polyolefin/Clay Nanocomposites... 

Hasegawa, N. and Usuki, A. 2004. Silicate layer exfoliation in polyolefin/clay nanocomposites based on maleic anhydride modified polyolefins and organophilic clay. 

Polyolefins are a major class of commodity synthetic polymers. The technology for the production of these important polymers is well estabUshed, from catalyst synthesis to polymerization reactor technology. Despite constant advancements in polyolefin production technology, applications of polyolefins are stiU mainly limited to commodity products. The recent interest in the production of polyolefin-clay nanocomposites extends the use of polyolefins to specialty and engineering plastic appHcations. Polyolefin-clay nanocomposites are lighter than conventional composites, but have thermal stability, barrier, and mechanical properties that are comparable to those of engineering plastics. 

As an alternative to melt mixing, in-situ polymerization is an attractive technique for the preparation of polyolefin-clay nanocomposites because it can promote better clay exfoliation and dispersion in the polymer matrix [1]. During in-situ polymerization, a coordination catalyst (such as Ziegler-Natta, metallocene, or late transition metal complex) is supported onto the clay interlayer surface to make polyolefin chains directly between the clay layers, leading to their exfoliation and dispersion into the polymer phase. 

Olefin in-situ polymerization methods for the production of polyolefin-clay nanocomposites still face many challenges before becoming industrially relevant. 

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