Viscosity epoxy nanocomposites

To date only few dielectric relaxation studies have been reported on thermosetting nanocomposite systems. Kanapitsas et al. [109] reported isothermal dielectric relaxation studies of epoxy nanocomposite systems based upon three different clay modifications, a low viscosity epoxy resin based on the diglycidyl ether of bisphenol-A type (Araldite LY556, CIBA) and an amine hardener in a temperature range of 30-140 °C. Whilst details on the epoxy system investigated and the nanocomposite morphology were vague, it was reported that the overall mobility is reduced in the nanocomposite compared to the neat matrix resin. 

Bandyopadhyay et al. [138] have also studied the distribution of nanoclays such as NA and 30B in NR/ENR (containing 50 mol% epoxy) and NR/BR blends and their effect on the overall properties of the resultant nanocomposite blends. They calculated the preferential distribution of clays at various loadings in the blend compounds from the viscoelastic property studies from DMA. The tensile properties of the 50 50 NR/ENR and 50 50 NR/BR blend nanocomposites are shown in Table 5. It is apparent that in both the blends that the mechanical properties increase with increasing clay concentration up to a certain extent and then decrease. These results have been found to depend on matrix polarity and the viscosity of the blend compounds. 

Hence, the stated above results have shown that melt viscosity extreme change of nanocomposites HDPE-EP could be described within the framework of the fractal model. The main structural parameter, controlling this effect, is the change of the fractal dimension of macromolecular coil in melt. The main physical cause, defining the mentioned effect, is a partial interaction of HDPE matrix and epoxy polymer particles. In this case the... 

Loos and co-workers [64] studied the effect of CNT on the mechanical and viscoelastic properties of epoxy matrices. Bisphenol A based epoxy resin nanocomposites were prepared with various small proportions of single-walled carbon nanotubes (SWCNT) and then investigated using acetone as a diluent to reduce the resin viscosity, and the products after removal of the solvent were characterised by FT-IR, Raman spectroscopy, thermogravimetric analysis (TGA), DSC, DMA, tensile, compression, flexural and impact testing, and SEM of the fracture surfaces. The effects of small amounts of SWCNT on mechanical and viscoelastic properties of the nanocomposites are discussed in terms of structural changes in the epoxy matrix. 

Epoxy-clay nanocomposites differ from the polyamide-6-clay system fundamentally, because the epoxy system forms a cross-linked material during polymerization. A study of the mechanism of exfoliation in epoxy-clay nanocomposites (82) showed that the gel time of the epoxy outside of the clay galleries constituted the time Umit available for exfoliation. At that time, of course, the viscosity of the system approaches infinity. 

In situ polymerisation of the polymer matrix is an attractive method of preparing graphene-based composites although often solvents are used to reduce the viscosity of the dispersions. For example, intercalative polymerisation of methyl methacrylate and epoxy resins has been achieved with graphene oxide to produce nanocomposites with enhanced properties. It has also been possible to use in situ polymerization produce polyethylene- and polypropylene-matrix graphene oxide nanocomposites. The technique of grafting poly(methyl methacrylate) chains onto graphene oxide has also been employed to make the filler compatible with the polymer matrix. " ... 

To achieve improved dispersibUity of nanoclay fillers within polymer systems, three familiar methods are commonly used, namely, melt intercalation, solution intercalation, and in situ polymerization. The melt-intercalation method is based on the melting point of polymer matrices and is applied by annealing above the melting point of the polymer (Reddy et al., 2013). This method has been chosen by industrial sectors to produce polymer/clay nanocomposites. However, it is not apphcable to the fabrication of biobased polymer/clay nanocomposites based on thermosetting materials such as epoxy and polyester due to their high viscosities (Wypych and Satyanarayana, 2005 Wang et al., 2014). Therefore, the fabrication of biobased thermosetting polymer/clay nanocomposites is mainly based on solution intercalation or in sim polymerization. 

This lower aspect ratio from self-alignment in the random orientation will result in lower reinforcement. We will explore this possibility when epoxy-montmorillonite nanocomposites are discussed later in chapter 6. Because of the high viscosity of epoxies, it is difficult to align montmor-illonite in the polymer matrix. Alignment is possible with the application of a magnetic field to influence the orientation of montmorillonite through their inherent magnetic properties. 

However, the mentioned model does not explain the causes of extreme reduction of the melt viscosity of HDPE/EP nanocomposites. Therefore for explanation of this effect the authors [11] used another treatment. As it is known [13], the extreme change of properties of blends in the case of their interaction (both chemical and physical) is realised at equimolar (stoichiometric) component contents. Since for the considered nanocomposites the extremum is reached at 2.0-3.0 mass percentage EP, then this means that the polymer matrix interacts not with the entire epoxy polymer, but only a part of it consisting of 4-6 mass percentage HOPE. In this case for estimation of rig (further designated as Tjo) the relationship applied for description of the chemical reaction kinetics of two components can be used [14] ... 

The dependence E c p) adduced in Figure 8.6 compared with the plot of Figure 8.5 demonstrates that the maximum value of the elasticity modulus corresponds to the minimum melt viscosity. Therefore, the epoxy polymer is a plasticiser in melt and an anti-plasticiser in the solid-phase state for HDPE/EP nanocomposites [16]. 

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