Polyolefines polyolefin-clay nanocomposites

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. 

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... 

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. 

In mineralogy, the term clay is used for a variety of polycrystaUine materials that are well described in clay science, mineralogy properties, and characterization textbooks [2-5]. Clays can be present in fibrous, tubular, lath shaped, and planar geometries. In this chapter, however, our focus will be mainly on the planar clay varieties called smectites that include montmorillonites, the most commonly used clay for the produchon of polyolefin-clay nanocomposites. In this section, we wiU focus on clay characteristics that are relevant to catalyst supporting and particle break-up during polymerization clay chemistry, crystalline structure, and geometry. 

Most commercial polyolefins are produced by coordination polymerization catalysts. When compared to free radical processes used to make low-density polyethylene (LDPE), these catalysts work in comparatively gentle conditions, such as lower pressures and temperatures, while providing greater flexibility in controlling the polyolefin molecular structure. An understanding of the polymerization mechanism with coordination catalysts is essential for designing proper systems for the production of polyolefin-clay nanocomposites and wUl be covered in the next section. 

---