Novel Preparation of Hybrid Polypropylene/Silica Nanocomposites in a Slurry-Phase Polymerization Reactor

Abstract

Polypropylene (PP) composites containing nanosized (φ ∼ 10 nm) spherical silica particles were prepared in situ utilizing a 1-L slurry-phase polymerization reactor containing a MgCl2-supported Ziegler−Natta (fourth-generation) catalyst. Composites were prepared with variable filler sizes ranging from the nano- to microsize domain. The surface of the silica particles was modified with a silane coupling agent to prevent catalyst deactivation and to achieve better polymer/filler synergy by decreasing the hydrophobicity surrounding the bulk particle surface. The feasibility of the process was tested with low loading additions (∼3 wt % for each sample) of (nano)silica. The effect of the filler on the crystal structure and crystallite size of PP was studied with differential scanning calorimetry and wide-angle X-ray diffraction. The reaction kinetics of the nanocomposite (∼10 nm) was studied and compared with samples containing larger microsized particles. It was demonstrated that the former did not decrease the catalyst activity when compared with the latter; comparisons were also made with pure PP. The particle size influenced the reactivity of the catalyst, and the addition of silica influenced the degree of crystallinity of the PP.

Study and evaluation of dispersion of polyhedral oligomeric silsesquioxane and silica filler in polypropylene composites

“…In the case of PP/SiO 2 composites, both χ and the α phase contribution (χ α ) decreased with the increasing wt% content of the silica filler. Garcia et al suggested that the degree of silica dispersion inside the PP matrix influenced the crystallinity. The formation of aggregates of silica particles resulted mainly from the poor compatibility between PP chains and SiO 2 particles and the presence of amorphous SiO 2 aggregates in the PP matrix distorted the polymer structure.…”

Synthesis of polypropylene/clay nanocomposites using bisupported Ziegler‐Natta catalyst

“…The crystallinity of the samples was calculated from the enthalpy evolved during crystallization and melting using the following equations19, 20: or where X1 and X2 are crystallinity of the samples, Δ H c is the apparent enthalpy of crystallization, Δ H f is the heat of the fusion determined by DSC, Δ H ° f is the value of the enthalpy corresponding to the melting of 100% crystalline sample, and φ is the weight fraction of the filler in the nanocomposite. A value of 165 J/g was chosen for Δ H ° f 19–21…”

“…Results from TGA show that by introducing the clay into the PP matrix the thermal stability considerably increase. Enhancement in thermal stability of the polymer/clay nanocomposites is attributed to the lower permeability of oxygen and the diffusibility of the degradation products from the bulk of the polymer caused by the exfoliated clay in the composites 19, 22, 11…”

The Role of CaO in the Ziegler–Natta Catalyst for Propylene Polymerization

“…As seen from figure 4, the particle size of CaO determined by the laser light scattering analysis exhibited a very broad uni-modal particle size distribution ranging from 0.3 to 60 lm with an average particle size of 5 lm. Garcı´a et al [10] studied the in situ polymerization of propylene incorporation with silica employing the forth generation Ziegler-Natta catalyst and observed that SiO 2 had some implications on the catalyst deactivation by its physical deposition on the outer surface of the catalyst.…”

“…The chemical incompatibility of nonpolar propylene around hydrophilic inorganic metal such as surface silanol functionalities of SiO 2 [8] and the catalyst sensitivity toward these oxophilic species [9] cause the process not facile. In order to overcome these problems, modified SiO 2 with hydrophobic chains is used to increase polymer/filler synergy and prevents catalyst deactivation but the addition of microsized filler particles can cause masking or pore blockage thereby obscuring the active sites in the course of polymerization [10].…”