Characterization of Effects of Silica Nanoparticles on (80/20) PP/PS Blends via Nonlinear Rheological Properties from Fourier Transform Rheology

Abstract

Effects of silica nanoparticles with different natures (hydrophilicity and hydrophobicity) on (80/20) PP/PS blends were investigated via linear and nonlinear rheological properties. The hydrophilic silica nanoparticle was fumed silica OX50 while the two hydrophobic ones were precipitated silica D17 and fumed silica R202. SEM images revealed that hydrophilic OX50 could not improve morphological properties of the blends. On the other hand, the two hydrophobic silica nanoparticles (R202 and D17) improved morphological properties. TEM examination showed that OX50 silica nanoparticles aggregated inside PS droplets, thereby making breakup of PS (dispersed) phase into smaller sizes more difficult. D17 and R202 improved morphological properties regardless of the different droplet size reduction mechanisms, and rheological properties improved as a result. Both linear rheological properties from SAOS (small-amplitude oscillatory shear) tests and nonlinear rheological properties from LAOS (large-amplitude oscillatory shear) tests were obtained. The nonlinear−linear viscoelastic ratio (NLR ≡ normalized nonlinear rheological properties/normalized linear rheological properties) was used to quantify the degree of droplet dispersion and distinguish the effects of silica particles on the morphology of PP/PS blends. Previous research has observed an inverse correlation between NLR and droplet size. PP/PS/OX50 blends with no alteration of droplet size showed constant NLR values (≅1) with increasing concentration of OX50 (hydrophilic silica). However, NLR values of PP/PS blends with hydrophobic silica nanoparticles (D17 and R202) were much larger than 1 (NLR > 1) and increased with silica concentration, which is consistent with morphological evolution, i.e., reducing droplet size. However, NLR values of PP/PS/R202 blends were relatively larger than those of PP/PS/D17 blends despite smaller droplet sizes. This can be attributed to a different morphology microstructure, i.e., R202 located in PP matrix phase and D17 at interface between PP and PS. Therefore, the NLR value of PP/PS/silica blend could be due to the combined effects of the interface between droplets (PP/PS blend) and particle−polymer interactions (PP/silica nanocomposites). Especially, R202 showed larger NLR values due to PP/R202 nanocomposites. Based on these findings, relative NLR (= NLR PP/PS/silica /NLR PP/silica ) is proposed as an effective measurement of droplet size information in PP/PS blends by eliminating the effects of PP/silica nanocomposites. Relative NLR matched well with droplet size evolution from the SEM results.

Characterization of polypropylene/polystyrene boehmite alumina nanocomposites: Impact of filler surface modification on the mechanical, thermal, and rheological properties

“…As a result, the rheological properties of the blend changed slightly, most likely because of the hydrodynamic (volumetric) effects of particles rather than them acting as morphology modifiers. Salehiyan et al . reported similar results when hydrophilic particles (Cloisite30B, untreated CNa + clays, and OX50 fumed silica) were added to 80/20 PP/PS blends: they mostly localized inside the PS droplets.…”

Influence of Silica Size on Properties of Poly[(Butylene Succinate)‐Co‐Adipate]/Butyl‐Etherified High‐Amylose Starch Blend Composites

“…As a result, there was a greater interaction between these silica particles and the minor BHAS phase than the PBSA matrix, which lead to limited interactions per unit volume, thereby, slightly increasing the viscosity and storage modulus with increasing silica content, but with no significant improvement with the changes in the screw speed. Similarly, other researchers observed less marked improvement in storage modulus with the addition of hydrophilic silica particles to the PP/PS (80/20) blends; instead observing that the hydrophilic silica particles were jammed inside the dispersed PS phase, which resulted in large particle clusters that led to no significant improvement in morphology, thus, to less effective improvements in rheological properties . Clearly, there was a relationship between the rheological behavior of composites and the localization of silica particles in the PBSA/BHAS blends.…”

“…This indicates that the highly agglomerated microsilica particles in the PBSA matrix result in inefficient improvement of droplet breakup and with the decrease in the size of the agglomerate, dispersion improves, leading to the improvement in droplet breakup. In a similar study, Salehiyan et al studied the effects of silica nanoparticles on PP/PS blends and observed that hydrophilic silica nanoparticles did not improve the morphological properties of PP/PS blends. They also discovered that the aggregated silica nanoparticles were located inside the dispersed PS phase, which led to the formation of irregular droplet shapes as well as coexistence of large and small droplets, indicating inefficient suppression of coalescence by hydrophilic silica particles.…”

“…However, the thermal and mechanical properties of PBSA/butyl‐etherified high amylopectin starch (BWS) blends remained poor in comparison to those with butyl‐etherified high amylose starch (BHAS) (linear structures) . This was attributed to the immiscibility in polymer blends with low mixing entropy (Δ mixS) . Furthermore, the resulting properties of immiscible polymer blends are affected by their phase morphology depending on the processing conditions, molecular characteristics, and interfacial properties .…”

“…[11] This was attributed to the immiscibility in polymer blends with low mixing entropy (Δ mixS). [12][13] Furthermore, the resulting properties of immiscible polymer blends are affected by their phase morphology depending on the processing conditions, molecular characteristics, and interfacial properties. [14] To improve the interfacial properties of immiscible polymer blends, it is important to control and fine-tune the morphology development by the addition of compatibilizers.…”