Cloisite composites nanocomposites

Lee, S. Y. and Hanna, M. A. 2008. Tapioca starch-poly (lactic acid)-Cloisite 30B nanocomposite foams. Polymer Composites 30 665-672. 

Fig. 4 WAXD patterns of Qoisite SOB clay and SMPU/clay nanocomposites of different clay contents, dooi = l -8nm is the d-spadng of Cloisite SOB and the numbers refer to the different clay contents in the composites. Reprinted from [77], Copyright 2007, with permission from Elsevier...

Noble Polymers supplies a 6% nanoclay-PP composite for the structural seat back of the Honda Accura TL 2004 car. It replaces a 30% glass PP compound in the seat back. Noble Polymers is also targeting the replacement of 20% glass fibre reinforced PP in office furniture parts. Southern Clay Products supplies Cloisite nanocomposite external parts to General Motors for its Impala vehicle, in competition with talc-filled PP. 

As a matrix polymer HDPE with melt flow index of 1.0 g/10 min and crystallinity degree K of 0.72, determined by samples density, manufactured by firm Hrmtsman LLC, was used. As nanofrller organoclay Na" -montmorillonite of industrial production of mark Cloisite 15, supplied by firm Southern Clay (USA), was used. A maleine anhydride (MA) was applied as a coupling agent. Conventional signs and composition of nanocomposites HDPE/MMT are listed in Table 1 [3]. 

To estimate the distance between the layers in clay. X-ray diffraction was used. The nanofiller (Cloisite SOB) possesses a strong maximum with d-spacing equal to 1.96 nm. For the H-BlN(Fig. la) and H-T3N (Fig. Ic) nanocomposites, the absence of diffraction maximum indicates successful exfoliation of the clay in these systems. For the other modified composites, a lower intensity peak is observed at an angle similar to that of OMMT. This suggests that the clay has not been efficiently exfoliated in these systems resulting in a microcomposite structure associated with lower values of the maximum stress obtained in the tensile test experiments. 

The XRD analysis of sodium montmorillonite (Cloisite Na shows that the interlayer spacing remains unchanged, that is to say that a microcomposite is formed rather than a nanocomposite. This structure has been confirmed by TEM where a clear microphase separation is observed. The properties of such a composite (filled with 3 wt% inorganics) remain in the same range as traditional microcomposites and very similar to the properties of the PCL matrix alone, as it will be shown further on. 

The barrier properties of the PCL-based composites were investigated. The transport properties, sorption and diffusion, were measured by a microgravimetric method . The studied model permeants were methylene chloride and water vapour for which the zero concentration diffusion coefficient Dq was determined. The presence of clay (hydrophilic platelets) in the composite gives rise to specific sites on which water molecules can be entrapped and immobilized, thus the water sorption increases on increasing the clay content, particularly for microcomposites containing Cloisite Na It was found out that the microcomposites as well as the intercalated nanocomposites have diffusion parameters for water vapour very near to those of pure PCL. 

In this section, PCL-based nanocomposites have been synthesized by in-situ intercalative polymerization of e-CL in the presence of various organo-modified (Cloisite 25A, Cloisite 30B) or non-modified (Cloisite Na layered silicates . As previously mentioned, this synthetic approach involves dispersion of the aluminosilicate platelets in the liquid monomer followed by polymerization (in bulk or in solution) by either thermal or catalytic activation using organometallic compounds (aluminium or tin alkoxides for instance). Depending on the nature of the filler and/or the activation mode, different composite morphologies can be obtained. 

For the nanocomposites prepared with non-modified clay (Cloisite Na and with Cloisite 25A, it is clear that the clay content does not affect the polymer molar masses and the polydispersity index. For all the composites, the number average molar weights (Mn) of extracted PCL chains are around 20,000 g mol with polydispersity indexes of about 2.0. This range of molecular weight fits well the expected values computed from the initial monomer-to-tin molar ratio by assuming selective and quantitative initiation by the tin alkoxide groups. 

The morphological characterization of the composites has been performed by both XRD and TEM. The XRD patterns of Cloisite Na based materials show an increase of the interlayer spacing from about 1.2 nm (in the native clay) to 1.6 nm for the in-situ polymerized nanocomposites, attesting for the formation of an intercalated structure. Thus, it comes out that in-situ polymerization of e-CL allows to prepare intercalated nanocomposites from non-modified clay. This is a major advantage of this process since it has been observed that the direct melt blending of preformed PCL chains with the same Cloisite Na only leads to conventional microcomposites (without any intercalation). 

The polymerization of e-CL was conducted in bulk at 100 °C by using dibutyltin dimethoxide as catalyst and in the presence of 25 to 50 wt% of (organo)clay. In order to collect PCL composites with high inorganic content, polymerizations were terminated at rather low monomer conversion. In agreement with observations made for PCL layered silicate nanocomposites prepared by the same technique and containing a small amount of clay (1-10 wt%), intercalated nanocomposites are recovered when the nanofiller is Cloisite Na or Cloisite 25A. In contrast, partially exfoliated/partially intercalated structures are formed in the presence of Cloisite 30B this situation results from the grafting of PCL chains on the clay surface as already discussed. Then, the desired PCL-based... 

The obtained composites have been analyzed by XRD and TEM in order to estimate the extent of the nanofiller dispersion in the PCL matrix. In all cases, intercalated nanocomposites were formed as evidenced by the significant increase in the interlayer distance. For instance, the interlayer distance increases from 1.17 nm to 1.79 nm for Cloisite Na -filled PCL composite (Figure 7). The intercalated nanostructures have been confirmed by TEM analysis. 

Aliphatic polyester layered silicate nanocomposites based on poly(e-caprolactone) (PCL) and on plasticized poly(L-lactide) (PLA) have been prepared first by melt blending of the respective polymer matrix with different (organo-modified) montmorillonites. It has been demonstrated that melt blending with organo-modified clay such as Cloisite 20A, 25A or SOB, yields intercalated nanocomposites with the possibility of partial exfoliation. Even at low organoclay content, substantial improvement of thermal stability, gas barrier properties and physical-mechanical performances have been noticed. However, melt blending of natural montmorillonite with PCL or neat (non plasticized) PLA leads to microphase-separated compositions. 

---