Organo-modified clays

Figure 2.2 Schematic illustration of exfoliated organo-modified clays with immobilized enzyme molecules.

Pluta et al. investigated PLA/MMT nanocomposites by studying the dispersions of modified and unmodified MMT prepared by melt blending. XRD showed that the good affinity between the organo-modified clay and the PLA was sufficient to form an intercalated structure in the nanocomposite. TGA showed that... 

Furthermore, the introduction of organo-modified clays in an epoxy resin was found to lead to the formation of a stronger interface with E-glass fibers, with an increase of the interfacial shear strength of around of 30% for a filler content of 5 wt% [11]. 

Lee S, Cho W, Hahn P, Lee M, Lee Y, Kim K (2005) Microstructural changes of reference montmorillonites by cationic surfactants. Appl Clay Sci 30(3-4) 174-180 Lee SM, Tiwari D (2012) Organo and inorgano-organo-modified clays in the remediation of aqueous solutions an overview. Appl Clay Sei 59-60 84—102 Lee S Y, Chen H, Hanna M A (2008) Preparation and eharacterization of tapioca stareh-poly(lactic add) nanocomposite foams by melt intercalation based on elay type. Ind Crops Prod 28(1) 95-106 Lee SY, Hanna MA (2009) Tapioca starch-poly(lactic acid)-Cloisite 30B nanocomposite foams. Polym Compos 30(5) 665-672... 

R. H. Vora, P. K. Pallathadka, S. H. Goh, T. S. Chung, Y. X. Lim, and T. K. Bang, Preparation and characterization of 4,4-bis(4-aminophenoxy)diphenyl sulfone based fluoropoly(ether-imide)/organo-modified clay nanocomposites. Macromolecular Materials and Engineering, 288 (2003), 337-56. 

Morgan et al. also studied the effect of surfactant on ignition delay times in PP/PP-g-MA/clay nanocomposites. In this study, careful extraction of surfactant-treated montmorillonite, which removed excess surfactant, produced 17% longer ignition delay times in the cone calorimeter relative to nanocomposite samples that contained the excess surfactant in organo-modified clay. ... 

In this chapter we considered recent developments that have tried to increase the efficiency of infumescent system for polymeric materials using nanofillers, including organo-modified clays, layered double hydroxides, polyhedral silsesquioxane, and nanoparticles of silica as synergists. Intumescent nanocomposites exhibit superior flammability properties as well as enhancing properties, such as mechanical properties. 

Epoxy-clay nanocomposites are prepared by in situ polymerization with organo-modified clays. In this technique, the prepolymer intercalates between the layered crystals during swelling, a process in which heat, stirring, and/or sonication is applied to favor prepolymer diffusion into the clay gallery. Then polymerization can be initiated between the intercalated sheets either by heat, radiation, or a suitable initiator. A variant of in situ polymerization is the exfoliation-adsorption technique, in which the organo-modified clay is first dispersed in a solvent before starting the standard in situ polymerization. 

Epoxy-clay nanocomposites were studied extensively, but only ordered exfoliated nanocomposites were reported with in situ polymerization. Two recent works showed that disordered and highly exfoliated epoxy-clay nanocomposites can be prepared using an exfoliation-adsorption process." In this method the organo-modified clay is first dispersed in a solvent. It is well known that due to the weak forces that stack the layers together, layered silicates can easily be swelled and eventually delaminated in an adequate solvent. The polymer then adsorbs onto the delaminated sheets, and when the solvent is evaporated, a highly disordered structure is obtained before starting the standard in situ polymerization. 

As far as organo-modified clays are concerned, the XRD patterns show a significant increase in the interlayer distance (Table 2), attesting for the effective polymer chain intercalation in between clay platelets. 

The presence of a tiny amount of filler, i.e., as low as 3 wt% inorganics, allows to increase the elastic modulus from 216 MPa for unfilled PCL to around 280 MPa for intercalated nanocomposites obtained with organo-modified clays. It is worth pointing out that increasing the clay content enhances the material stiffiiess (Figure 1). 

In case of microcomposites, the gain in stability is less important. Thus, the observed increase of the thermal stability of nanocomposites is to be related to the nanodispersion of the clay. The silicate layers are thought to oppose an effective barrier to the permeation of oxygen and combustion gases. However, increasing the amount of clay leads to a continuous decrease in the temperature shift which is only 30 °C for 10 wt% organo-modified clay. 

The preparation of PCL nanocomposites by melt blending leads to microcomposites when Cloisite Na is used whereas intercalated structures are obtained with organo-modified clays such as Cloisite 25A and Cloisite 30B. As expected, the mechanical and barrier properties of the conventional microcomposites are in the same range of unfilled PCL. In contrast, all main properties of the material are improved by intercalating polymer chains between silicate sheets. 

Figure 3. XRD pattern of Cloisite 30B and of PCL-based nanocomposites prepared by in-situ ROP with 1, 3,5 and 10 wt% of this organo-modified clay.

All PCL nanocomposites originated from the masterbatch remain rather ductile, with elongation at break higher than 300%. The stress at break slightly drops when the clay content is increased but remains at an acceptable level. Similar observations have been reported for the two organo-modified clays (Cloisite 25A and Cloisite 30B), that is increased stiffriess and preserved ultimate tensile properties. 

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