•Evolution of structure-property correlation of polypropylene (PP) aging under six typical climate scenarios is uncovered.•Principal component analysis (PCA) is proved to be promising in establishing a comprehensive indicator for aging.•The degradation risk map of PP in China is established and the relative importance of weathering factors is evaluated.A full understanding on the relationships between weathering factors and deteriorations in the physical or mechanical properties of polymeric materials as well as their intercorrelations is critically important to forecast the durability of materials. In this work, the outdoor weathering behaviors of isotactic polypropylene (iPP) across a 1.5-year period under six typical climate scenarios in China are investigated. A wide sets of natural exposure conditions and test methods allow the establishment of the substantial correlations between chemical/physical structures and appearance/mechanical properties under simultaneous effects of multiple weathering factors (such as light, heat, oxygen etc.). The results under diverse natural environments suggest that the crystallinity and crack development depend largely on the molecular weight while the yellowing index correlates directly with the carbonyl index irrespective of the exposure conditions. The relationship between tensile strength and molecular weight is found to be in accord with an empirical linear model. Subsequently, using principal component analysis (PCA), a data reduction and visualization method, the degradation risk map of PP materials in China is established and the relative importance of relevant weathering factors is evaluated. Temperature is found to be the most dominant weathering factor on iPP aging under the climate scenarios investigated in the present work.

We study the influence of particle shape on shear-induced droplet deformation in polymeric emulsions. During shearing, droplets become elongated and rotate periodically about their major axes while aligning along the vorticity direction in ellipsoid-filled emulsions, while similar behavior is not observed in the pristine, microsphere-filled or ellipsoid-filled inverse systems. Based on the Jeffery orbit theory, the formation of anisotropic droplets with extremely small Reynolds number due to arrested coalescence in Newtonian matrix and strong confinement effect are suggested to be responsible for the vorticity alignment of droplets during slow shearing.

A new kind of percolation-to-droplet transition (PDT) caused by selective wetting was identified in near-critical polymer blend films. Nanoscale particles proved to possess superior ability in suppressing this morphological transition.

The flow-induced spatial organization of the droplet phase in ternary polymeric emulsions consisting of two Newtonian fluids, namely polyisobutylene (PIB) and polydimethylsiloxane (PDMS), in the presence of a small amount of solid polystyrene (PS) microspheres are explored by direct flow visualization. The results suggest that the asymmetric affinities of interfacially located PS microspheres to two fluid components lead to diverse flow-induced morphologies in PIB/PDMS blends with different compositions. In 10/90 blends where microspheres are preferentially wetted by the PIB droplets, significantly promoted coalescence of PIB droplets is observed. Increasing the loading of microspheres or changing the shear rate will alter the size and spatial distribution of PIB droplets. In contrast, in the inverse 90/10 blends where microspheres are wetted by the continuous PIB phase, bridging of PDMS droplets is found, leading to the generation of string-like or grape-like clusters. These results indicate that the flow-induced morphology of PIB/PDMS blends in the presence of PS microspheres is not only determined by the experimental conditions such as shear rate but also to a large extent by the asymmetric interfacial affinities of microspheres for fluid components.

Silica microrods with aspect ratios (AR) varying from 1 to 16 but similar surface chemical characteristics are synthesized and their potential in preparing stable oil-in-water Pickering emulsions is explored. The stability of hexadecane/water emulsions is found to strongly depend on the AR and concentration of particles. Emulsions stabilized with these silica microrods are quiescently stable for quite a long period of time (over months), while emulsions with spherical particles of similar diameters destabilize after only dozens of hours. The superior stabilization efficiency of microrods with larger ARs is attributed to their higher steric hindrance, interface adsorption energy and capillary forces.

With increasing temperature, a transition from fracture phase separation (FPS) to viscoelastic phase separation (VPS) was found in dynamically asymmetric PS/PVME blends with LCST behavior. Typical morphology formed via VPS disappeared under large quench depths, indicating some other specification might control the morphological evolution during VPS besides the dynamic asymmetry.

The effect of linear triblock copolymer compatibilizer (styrene–ethylene/butylene–styrene, SEBS) with strong viscoelasticity on the stress relaxation behavior of polypropylene (PP)/polystyrene (PS) (20/80) blends under various shear deformations has been investigated. With the addition of SEBS, the initial deformation of dispersed droplets under step shear strains was suppressed, and the following stress relaxation was found to be continuously retarded. The strain sensitivity of the stress relaxation modulus became weaker with the addition of SEBS possibly due to the improved viscoelasticity and interfacial adhesion. But the increase of strain led to more pronounced retardation in the stress relaxation of compatibilized blends. These phenomena were discussed in terms of the competitive effect of morphology refinement and the changes in interfacial and viscoelastic properties brought by compatibilization. The dominant factors determining the relaxation behavior were suggested to rely on the SEBS loading.

Two possible mechanisms of generating core–shell droplets, namely the rupture of blend films and the disintegration of compound threads, were identified in immiscible polymer blends with high viscosity. The deformation and relaxation behavior of the core–shell droplets was shown to be intimately related to the core-to-shell diameter ratio (Rcs).

The efficiency of tin(II) 2-ethylhexanoate catalyst and hydrophilic silica nanoparticles in compatibilizing polycarbonate/poly(methyl methacrylate) (PMMA/PC) blends were compared in terms of the morphological, thermal, and mechanical properties. Both the catalyst and nanoparticles were found to refine the morphology of PMMA/PC blends. Although the blends with catalyst exhibited smaller phase size, they possessed more deteriorated mechanical performance and worse thermal properties than those of nanoparticle-filled ones due to the significant degradation during transesterification reactions. The addition of nanoparticles refined the morphology of PMMA/PC blends kinetically to a lesser extent. However, the thermal and mechanical properties of blends were improved noticeably upon the addition of nanoparticles. Finally, the mechanisms, advantages, and disadvantages of catalyst and nanoparticles in compatibilizing PMMA/PC blends were discussed and compared.

The antioxidative effect of chemically reduced graphene oxide (rGO) on the thermal-oxidative stability of polypropylene (PP) was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). rGO was prepared by reduction of graphene oxide (GO) and characterized by atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. PP/rGO nanocomposites were then prepared without using a compatibilizer by melt blending. It was found that the thermal-oxidative degradation of PP was retarded noticeably by the rGO. The stabilization mechanism of rGO was discussed in terms of the changes in carbonyl bands and oxygen diffusion. It was proposed that the improved thermal-oxidation stability of PP/rGO nanocomposites can be attributed to the decline in both the concentration of peroxy radicals and oxygen permeability. The acceptor-like electronic property afforded by the long conjugated CC bonds and the barrier effect of rGO were suggested to be responsible for the improved thermal-oxidation stability of PP.

Thermal oxidation behavior of isotactic polypropylene (PP) films with and without nucleating agent was investigated at 100 °C in air. The crystal form of PP was modified with a specific aryl amide derivative as β-nucleating agent (β-NA). Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests were performed to determine the extent of chemical degradation and the variations of microstructure of the two kinds of PP films during thermal oxidation. It was found that the mechanism of thermal oxidation of PP films was not changed in the presence of β-NA, but the time to initiation and the rate of oxidation both declined. Moreover, during the thermal oxidation aging, the melting temperature of neat PP significantly decreased while only a slight decrease of the melting temperature occurred for β-PP. Overall, the investigation indicated that the thermal oxidative stability of β-PP was higher than that of neat PP. The underlying mechanism was further analyzed by considering the change in the physical structure, especially the crystalline and the amorphous structure, of PP in the presence of β-NA.

The morphology change and the corresponding molecular mechanism of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends induced by hydrophilic or hydrophobic nanoparticles were studied. It was found that there was a threshold of hydrophilic silica loading for the occurrence of network–droplet morphological transition in PS/PVME blends. On the contrary, the viscoelastic network could sustain for a much longer time in the blends with higher loading of hydrophobic silica. Rheological measurements suggested that the networking of hydrophilic silica nanoparticles in the PVME-rich phase would significantly reduce the dynamic asymmetry of two phases and make the compositional asymmetry the dominant factor in controlling the morphology development during phase separation. However, adding the hydrophobic silica fillers would result in an increase of dynamic asymmetry and a decrease in compositional asymmetry because of their selective dispersion in the PS-rich phase, both stabilizing the continuous network structure.

The fractionated crystallization behavior of polypropylene (PP) droplets in its 20/80 blends with polystyrene (PS) in the presence of hydrophilic or hydrophobic fumed silica nanoparticles was studied by using differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It was found that the fractionated crystallization of PP droplets in the PS matrix was promoted by adding a low content of hydrophobic or hydrophilic nanoparticles due to their morphological refinement effect. However, discrepancies in the fractionated crystallization behavior of PP droplets occurred as the nanoparticle content increased. The crystallization became dominated by the heterogeneous nucleation effect of high content of hydrophilic nanoparticles, which possibly migrated into PP droplets during mixing and significantly suppressed their fractionated crystallization. In contrast, the morphological refinement effect still played a dominated role in promoting the fractionated crystallization of PP droplets in PP/PS blends filled with higher content hydrophobic nanoparticles as a result of the efficiently morphological refinement effect.

Stress relaxation probing on the immiscible blends is an attractive route to reveal the time-dependent morphology–viscoelasticity correlations under/after flow. However, a comprehensive understanding on the stress relaxation of co-continuous blends, especially after subjected to a shear strain, is still lacking. In this work, the stress relaxation behavior of co-continuous polystyrene/poly(methyl methacrylate) (50/50) blends with different annealing times, strain levels, and temperatures was examined under step shear strain and was correlated with the development of their morphologies. It was found that co-continuous blends display a fast relaxation process which corresponded to the relaxation of bulk polymer and a second slower relaxation process due to the recovery of co-continuous morphology. The stress relaxation rates of co-continuous blends tend to decrease due to the coarsening of instable co-continuous structure during annealing. Furthermore, the stress relaxation of the co-continuous blends is strongly affected by the change of viscosity and interfacial tension caused by the temperature. The contribution of morphological coarsening, viscosity, and interfacial tension variation on the stress relaxation behavior of co-continuous blends was discussed based on the Lee–Park model and time–temperature superposition principle, respectively.

The effect of hydrophilic silica nanoparticles (SiO2) on the shape stability of crystallizable polybutylene terephthalate (PBT) fibrils in polystyrene (PS) matrix under quiescent and shear conditions was investigated using optical-shear technique, differential scanning calorimetry (DSC) and rheometry. The contributions of the crystallization and viscoelasticity to the improved stability of molten PBT fibrils with different nanosilica contents were discussed based on their rheology data and polarized microphotographs. Upon the addition of only 0.05 wt.% SiO2 nanoparticles, the shape stability of PBT fibrils during quiescent annealing increased noticeably due to the rapid crystallization in these filled PBT droplets. With increasing nanoparticle content, the enhanced viscoelasticity of PBT droplets due to the addition of nanoparticles also began to play a role in improving the shape stability of droplets. The addition of silica nanoparticles was also found to suppress the development of nodular morphology on PBT fibrils under shear flow caused by heterogeneous crystallization. It has been suggested that the loading of a relative high content of silica nanoparticles, the application of a rapid quenching and low rate shear flow are in favor of the shape stability of PBT fibrils under shear flow.Graphical abstract

The morphological hysteresis behavior of immiscible polymer blend reflects the dependence of their steady-state morphology on the shear protocol applied. In this work, the influences of hydrophobic and hydrophilic fumed silica nanoparticles on the morphology hysteresis behavior of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) (10/90) blends under simple shear flow were investigated by using optical shear technique. Compared with particle-free blend, the morphology hysteresis zone of filled blends was found to be expanded by the addition of hydrophobic or hydrophilic fumed silica nanoparticles. It was found that the expansion of the morphology hysteresis zone in hydrophobic nanoparticle-filled blend stemmed from the suppression of droplet coalescence. However, the expansion in the morphological hysteresis zone for hydrophilic nanoparticle-filled blend, which was less noticeable, might originate from the more difficult breakup of PIB droplets upon the addition of nanoparticles.

The morphology of immiscible fluid mixtures under confined environment usually displays different scenarios compared with those presented in bulk systems. In this work, the influence of confinement and component ratio on the droplet morphology of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) blends in confined steady shear flow was investigated. While increasing the degree of confinement, the morphology of dispersed phase experienced a transition from the bulk behavior toward the confined behavior. Increasing the concentration of PIB phases in confined blends resulted in more coarsened structure under low shear rate and generated pearl necklace or string-like structures under a higher shear rate. The maximum aspect ratio of PIB droplets increased while increasing PIB concentration. The width and the aspect ratio of PIB droplets obtained experimentally were compared to the predictions of a single droplet MM model for bulk flow and an M model considering confinement. The experimental droplet width agreed well with the predictions of these two models only in the small droplet zone, large deviations appeared for the degree of confinement up to 0.36 and higher, whereas constant droplet width was found. The M model decreased the deviation between the experimental aspect ratio and the prediction of MM model in the high Ca zone. Good agreement between the prediction of M model and experiment results was found when the orientation angles of the droplets were corrected by using the M model.Graphical abstractHighlights►The effect of confinement and component ratio on the morphology of PIB/PDMS blends in confined shear flow was investigated. ► The experimental width and aspect ratio of PIB droplets were compared to the predictions of MM model and M model. ► The prediction of M model agreed well with the experiment results when the orientation angles were corrected.

The effect of hydrophilic silica nanoparticles (SiO2) on the relaxation and breakup dynamics of selectively filled polyamide (PA6) droplets with different degrees of deformation in polystyrene (PS) matrix during quiescent annealing were in situ investigated. It was found that, with the increase of silica content, the relaxation process of PA6 droplets was slowed down gradually and the relaxation mode was changed correspondingly. The critical break aspect ratios (ARcr) of PA6 droplets were also improved with the increase in SiO2 nanoparticle contents. Comparisons of the experimental values of ARcr, characteristic relaxation time (τd) and breakup time (tb) of the SiO2-filled PA6 droplets with corresponding theoretical values were made. The results of comparison were discussed in terms of viscoelasticity and interfacial tension. It was proposed that the alternation of the viscoelastic properties of PA6 droplets in stead of the interfacial tension change of the blends was responsible for the phenomena observed.

The influence of surface nature (hydrophobic and hydrophilic) and concentration of silica nanoparticles on the coalescence behavior of immiscible polydimethylsiloxane (PDMS)/polyisobutylene (PIB) (90/10) blends under simple low-rate shear flow were investigated via optical shear technique. It was found that the coalescence of PIB droplets in PDMS matrix was suppressed efficiently by incorporating hydrophobic silica nanoparticles, and a constant droplet size was obtained at high particle contents. The addition of a small amount (<0.4 wt.%) of hydrophilic silica nanoparticles also decreased the size of PIB droplets. Clusters of small PIB droplets were formed at low filler concentration. When the filler concentration exceeded 0.8 wt.%, the clusters of PIB drops disappeared and elongated PIB threads with large size were formed, which suggest that the coalescence of PIB droplets was promoted. The results indicate that the discrepancy in the morphology evolution of PDMS/PIB blends upon the addition of silica nanoparticles is controlled not only by the surface chemistry of nanoparticles but also by their concentration in the blends.

The antioxidative effect of chemically reduced graphene oxide (rGO) on the thermal-oxidative stability of polypropylene (PP) was evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). rGO was prepared by reduction of graphene oxide (GO) and characterized by atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. PP/rGO nanocomposites were then prepared without using a compatibilizer by melt blending. It was found that the thermal-oxidative degradation of PP was retarded noticeably by the rGO. The stabilization mechanism of rGO was discussed in terms of the changes in carbonyl bands and oxygen diffusion. It was proposed that the improved thermal-oxidation stability of PP/rGO nanocomposites can be attributed to the decline in both the concentration of peroxy radicals and oxygen permeability. The acceptor-like electronic property afforded by the long conjugated CC bonds and the barrier effect of rGO were suggested to be responsible for the improved thermal-oxidation stability of PP.

The flow-induced spatial organization of the droplet phase in ternary polymeric emulsions consisting of two Newtonian fluids, namely polyisobutylene (PIB) and polydimethylsiloxane (PDMS), in the presence of a small amount of solid polystyrene (PS) microspheres are explored by direct flow visualization. The results suggest that the asymmetric affinities of interfacially located PS microspheres to two fluid components lead to diverse flow-induced morphologies in PIB/PDMS blends with different compositions. In 10/90 blends where microspheres are preferentially wetted by the PIB droplets, significantly promoted coalescence of PIB droplets is observed. Increasing the loading of microspheres or changing the shear rate will alter the size and spatial distribution of PIB droplets. In contrast, in the inverse 90/10 blends where microspheres are wetted by the continuous PIB phase, bridging of PDMS droplets is found, leading to the generation of string-like or grape-like clusters. These results indicate that the flow-induced morphology of PIB/PDMS blends in the presence of PS microspheres is not only determined by the experimental conditions such as shear rate but also to a large extent by the asymmetric interfacial affinities of microspheres for fluid components.