Nanoparticles compatibilization effect

Theories that describe the reduction of the size of the dispersed phase in the presence of nanoparticles vary, depending on whether the filler is located in the continuous phase, in the dispersed phase, or at the interphase between the two blend components. Compatibilizing effects due to polymer adsorption on the filler surface, as well as reduction in the interfacial tension between the two phases in the presence of the filler, are the generally accepted mechanisms when the fillers are located at the interface [11,13,26]. Ray et al. [11] showed that upon addition of only 0.5 wt% of organically modified clay, the interfacial tension decreased from 5.1 to 3.4 mN/m for a PS/PP blend and from 4.8 to 1.1 mN/m for PS/PP-g-MA, suggesting a possible interfacial activity of the clay that is localized at the interface in similar fashion to classical compatibilizers. 

W. Li, J. Karger-Kocsis, R. Thomann, Compatibilization effect of Ti02 nanoparticles on the phase structure of PET/PP/Ti02 nanocomposites. Journal of Polymer Science, Part B Polymer Physics 47 (16) (2009) 1616-1624. 

Evolution of the RIT ratio as a function of time was obtained for a 70/30 PDMS/PIB blend containing different amounts of silica at 20 °C. Silica is an Aerosil Rhodorsil R972, R is the volume average diameter of the PIB droplets, is the apparent interfacial tension of the system [89]. To conclude, it seems that the displacement of the nanoparticles in the melted polymer blends and their localization in the final binary blend influences the compatibilization effect especially because it influences the origin of the droplet size reduction. On the other hand, the understanding of the mechanisms responsible... 

So far, the compatibilizing effect of nanoparticles is mostly influenced by their localization in the polymer blends and by extension, by their surface chanistry. In all, the localization of these nanoparticles at the interface is not really accurate and the size and surface chemistry are not well-controlled parameters. It is only very recently that authors have started developing new nanoparticles with highly controlled surface properties and structures, and to control their localization and dispersion in polymer blends. It is on record that many authors have studied the control of nanoparticles dispersion in block copolymers leading to various morphologies [105-111], but not in blends of homopolymers, that are mostly commonly used in industrial application. 

The presence of nanomaterial influences the crystaltization process as it acts as additional heterogeneity creating more interfaces [29]. In some cases, the presence of a nanofiller alters the crystaltization temperature and thus the thermal properties. In the dispersed phase, the presence of nanoparticles increases the occurrence of fractionated crystaltization [17,23,27,29,53-55,61-63,93-95]. Also, the extent of compatibilization effect from the nanomaterial can alter the whole process of crystaltization in the polymer blend. When a nanofiller is organically modified, using compounds with a similar chemical structure to one or both polymers present in the blend, the influence of the nanofillers here on the crystallization behavior is complex. This is because several factors have to be taken in consideration, such as the nucleating effect of the matrix on the dispersed phase or vice-versa, the nucleating effect of the nanofiller compatibitizer on both phases. There are reported cases where modified nanofillers have impeded the crystaltization process and thus retarded crystaltization in the overall material. 

After solving Eq. (7.8), one could obtain spinodal boundaries this analysis, while incomplete, provides a good indication under which conditions nanoparticles can either stabilize or destabilize a homogeneous blend. In particular, it has been found that when the particles are sufficiently small, and polymers have sufficiently high molecular weight, they can have a compatibilizing effect even when they have a strong preference for one of two polymers. 

Nowadays, nanoparticles have been widely used as fillers and compatibilizers. They exert certain effect on the miscibility of blends. Ginzburg applied a simple theory to study the effect of nanoparticles on the miscibility of PVA/PMMA blends and compared theoretical and experimental results for the same system with fillers and without fillers (Ginzburg 2005) when nanoparticle radius is smaller than polymer radius of g5n ation, the addition of nanoparticles increases the critical value of Xn and stabilizes the homogeneity (Fig. 10.38). 

Compatibilization of polymer blends aims to improve the interaction between phases, ascertaining the appropriate, stable morphology and improved performance. Blends have been compatibilized mainly by addition of a compatibilizer, a co-solvent, or in a reactive process, where the compatibilizing molecules are formed within the interphase [1, 73, 302]. About 20 years ago a note in a USSR technological journal reported that the addition of a small amount of PMMA to a PE/PS blend reduced the PS drop diameter by a factor of ten. The effect was later explained by a balance of the three interfacial tension coefficients in the blends, inter-related by Neuman s triangle equation [1,352,353]. In simple terms, the PMMA, immiscible in PE and PS, formed a layer around PS drops, preventing coalescence. In a sense, addition of nanoparticles to polymer blends acts similarly. 

N. Mnif, V. Massardier, T. Kallel, B. Elleuch, New (PP/EPR)/nano-CaC03 based formulations in the perspective of polymer recycling. Effect of nanoparticles properties and compatibilizers. Polymers for Advanced Technologies 21 (12) (2010) 896-903. 

In this chapter, we present a summary of fire retardant nanoclays used in polymer blends based on the authors previous experience and the literature [15-31]. Because the main objective of this work is to study the fire retarding effects of nanoclays on polymer blends, we will focus on the properties affecting the fire performance of polymer blends (a) dispersion of nanoclay, (b) rheology, (c) thermal stability, and (d) flammability (ignition, fire spread, and toxicity), whereas the effects of nanoclays on mechanical properties and compatibilization can be found easily in references listed in Table 8.1 (e.g.. References [16, 17, 19-21] on compatibilization and [16, 18, 21, 25, 26, 29-31] on mechanical properties). A review of the mechanism by which nanoparticles organize in polymer blends is also available in [32]. 

To further bring the positive effects of nanoparticles into play, we introduced reactive compatibilizing into naiioparticles filled PP composites as follows [BOSS]. Firstly, the monomer glycidyl methaciylate (GMA) with reactive epoxide groups was introduced onto Si02 nanoparticles by chemical graft polymerization... 

Chitosan has also been used as reinforcement in nanocomposites. Chitosan nanoparticles were used by Kampeerapappun et al. [204] to produce bionanocomposites with cassava starch and MMT nanocomposites. The authors reported that the addition of chitosan, due to its hydrophilicity and ability to attach to the clay surface, played a role in compatibilizing the interface between starch matrix and MMT. As a result, the starch/MMT composite film at low MMT content exhibited an improvement in tensile properties due to a reinforcement effect It was also found that the surface hydrophobicity of the composite film increased with an increase in chitosan content In association with film hydrophobicity, the water vapor transmission rate and moisture absorption were found to decrease with an increase in chitosan content. 

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