Preparation by melt mixing and characterization of isotactic polypropylene/SiO₂ nanocomposites containing untreated and surface‐treated nanoparticles

Abstract

ABSTRACT:In the present study two series of isotactic polypropylene (iPP)/SiO 2 nanocomposites containing 1, 2.5, 5, 7.5, and 10 wt % SiO 2 nanoparticles were prepared by melt-mixing on a twin-screw corotating extruder. In the first series untreated fumed silica nanoparticles were used, whereas in the second nanoparticles were surface-treated with dimethyldichlorosilane. In both cases, the average size of the primary nanoparticles was 12 nm. Tensile and impact strength were found to increase and to be affected mainly by the type and content of silica nanoparticles. A maximum was observed, corresponding to samples containing 2.5 wt % SiO 2 . These findings are discussed in light of the SEM and TEM observations. By increasing the amount of nanoparticles, large aggregates of fumed silica could be formed, which may explain the reduction of mechanical properties with higher concentrations of SiO 2 . However, it was found that surface-treated nanoparticles produced larger aggregates than did those derived from untreated nanoparticles, despite the increased adhesion of the iPP matrix, as was postulated from yield strength. This behavior negatively affected mechanical properties. In addition, an effort was made to determine if toughening theories, mainly the critical interparticle distance for rubber toughening or composites, also might be applicable in nanocomposites. From DSC measurements it was demonstrated that silica nanoparticles acted as effective nucleating agents, increasing the crystallization rate and the degree of crystallinity of iPP.

Nanocomposites of isotactic polypropylene with carbon nanoparticles exhibiting enhanced stiffness, thermal stability and gas barrier properties

“…Along the screw there were different screw elements [13] in order to induce polymer melting and achieve fine dispersion of the nanoparticles in the polymer melt. Prior to melt processing, carbon nanoparticles were dried for 24 h at 140 o C. Compounding was carried out using a screw rotating speed of 225 rpm and also a temperature profile 175,180,185,190,190,195,190 o C at the sequential heating zones, from the hopper to the die.…”

“…However, as can be seen in Figure 2a tensile strength reduces by increasing the CN content. This behaviour is maybe due to the interactions between the nanoparticles themselves, as more and larger agglomerates are formed, which act as stress concentrators and ultimate failure points of the material [13,17]. Generally, the drop in the tensile strength has been attributed to the reduction of the polymer fraction in the transverse cross-section of the polymer [27], which becomes an even greater issue due to the extremely large surface area of the filler used, and the presence of stress concentration around the filler's particles [28].…”

“…Compared to conventional composites, polymer nanocomposites exhibit a much increased internal interfacial area, resulting in maximized polymer-nanoparticles interactions, since the filler is dispersed on a nanometer scale. Most products require a balance between stiffness and impact strength, and this need has been met using several nanoparticles, at loadings of 10% or less, increasing the range of the material's applications [13][14][15]. Although nanocomposites can be prepared either through melt compounding [16][17][18][19][20] solution blending [21], in situ polymerization techniques [22,23] and sol-gel reactions [24], due to its compatibility with current industrial processes, such as extrusion and injection molding, the absence of organic solvents, and its suitability with most commodity polymers, melt-mixing is 4 probably the most industrially feasible and versatile technique amongst the various strategies used for the preparation of nanocomposites.…”

Nucleation ability of advanced functional silica/lignin hybrid fillers in polypropylene composites

“…The incorporation of silica into polypropylene matrix is an attractive way to significant improvements in the properties of the composites, e.g., mechanical strength and elastic modulus, thermal stability, chemical resistance, heat and flame resistance, and reduction in gas permeability [9][10][11][12][13]. These properties led to the application of silica/polypropylene composites in various industrial fields, e.g., packaging, automotive, medical, and textile industries [14][15][16].…”

Cyclic viscoelastoplasticity of polypropylene/nanoclay composites

“…The fact that some critical concentration χ cr exists (such that enhancement of mechanical properties of nanohybrids is observed at χ < χ cr only) has been reported by several authors (Hsieh et al 2004;Bikiaris et al 2006). It is explained by (i) formation of a stable filler network structure in polymer nanocomposites (Wang et al 2006;Su et al 2011), (ii) development of constrained regions where mobility of chains is severely restricted by surrounding clay platelets and their stacks (Zhang and Loo 2009), and (iii) overlapping of interfacial layers of neighboring nanoparticles (Mortezaei et al 2011).…”