Effective and fast-screening route to evaluate dynamic elastomer-filler network reversibility for sustainable rubber composite design

.The introduction of self-healing and reprocessability into conventional vulcanized rubbers has been recognized as a promising strategy to promote elastomer circularity. However, the reversibility and recovery of cross-linking polymer networks have often been assessed by static mechanical testing, which highly limits the understanding of the underlying microscale mechanisms. In this work, we investigated the network recovery of natural rubber (NR)/carbon black (CB) nanocomposites using Fourier transform (FT) rheology coupled with large amplitude oscillation shear (LAOS) technology across linear and nonlinear regimes (0.01–500%). The self-healing process of the rubber composite networks was monitored by using a programmed time–temperature oscillation shear measurement. The role of CB particle size in the filler network recovery was also discussed from the perspective of strain-induced crystallization of NR. Coupling FT-rheology and LAOS analysis, two distinct nonlinear enhancement behaviors beyond the linear viscoelastic regime were detected in the rubber nanocomposites, which were ascribed to the filler network disruption followed by the polymer network deformation. The relationship of the nonlinearity parameter I3/1 as a function of strain amplitude was selected to quantify the nonlinear rheological responses, where the role of the filler and polymer on the network recovery can therefore be differentiated. This work provides an efficient method to evaluate the self-healing and reprocessability of cross-linked rubbers and offers a fast-screen route for formulation development and sustainable rubber composite design

Effective and Fast-Screening Route to Evaluate Dynamic Elastomer-Filler Network Reversibility for Sustainable Rubber Composite Design

The introduction of self-healing and reprocessability into conventional vulcanized rubbers has been recognized as a promising strategy to promote elastomer circularity. However, the reversibility and recovery of cross-linking polymer networks have often been assessed by static mechanical testing, which highly limits the understanding of the underlying microscale mechanisms. In this work, we investigated the network recovery of natural rubber (NR)/carbon black (CB) nanocomposites using Fourier transform (FT) rheology coupled with large amplitude oscillation shear (LAOS) technology across linear and nonlinear regimes (0.01–500%). The self-healing process of the rubber composite networks was monitored by using a programmed time–temperature oscillation shear measurement. The role of CB particle size in the filler network recovery was also discussed from the perspective of strain-induced crystallization of NR. Coupling FT-rheology and LAOS analysis, two distinct nonlinear enhancement behaviors beyond the linear viscoelastic regime were detected in the rubber nanocomposites, which were ascribed to the filler network disruption followed by the polymer network deformation. The relationship of the nonlinearity parameter I3/1 as a function of strain amplitude was selected to quantify the nonlinear rheological responses, where the role of the filler and polymer on the network recovery can therefore be differentiated. This work provides an efficient method to evaluate the self-healing and reprocessability of cross-linked rubbers and offers a fast-screen route for formulation development and sustainable rubber composite design

Properties of polylactic aicd/polycaprolactone/montmorillonite (PLA/PCL/MMT) nanocomposites

Polylactid acid/Polycaprolactone (PLA/PCL) nanocomosites consisting of organically modified montmorillonite (organoclay) toughened with Metallocene catalysed Linear Low Density Polyethylene (mLLDPE) was prepared PLA/PLC of composition 70/30 with fixed mLLDPE content of 10 phr while MMT in 1, 2, 4 phr was produced. Correspond toughened nanocomposites were prepared by using a twin screw extruder then injected into typical speciments using an injection molding machine. The effects of mLLDPE and MMT on mechanical, thermal and thermomechanical properties of the PLA/PCL blend were investigated. The mechanical properties of the nanocomposites were studied through tensile, flexural and impact test. The thermal properties were characterized by using differential scanning calorimeter (DSC) and thermogravimetry analysis (TGA). The dynamic mechanical analysis (DMA) was used to investigate the effects of dynamic forces at various temperatures. mLLDPE toughened nanocomposites showed relatively lower tensile strength and flexural modulus compared to PLA/PCL nanocomposites and it was concluded from mechanical test that MMT increased tensile strength and flexural modulus of all nanocomposites at lower contents. On the other hand, impact strength and elongation at break of the mLLDPE toughened nanocomposites was higher than that of PLA/PCL nanocomposites and MMT loadings exhibited a reductive effect on impact strength of nanocomposites. The crystallization temperature and melting temperature of the nanocomposites did not change siginificantly while the thermal stability of the nanocomposites improved with incorporation of MMT. Storage modulus of nanocomposites below glass transition temperature increased with increasing MMT content

Effect of organoclay on non-linear rheological properties of poly(lactic acid)/poly(caprolactone) blends

The nonlinear viscoelastic properties of PLA/PCL blends with and without clay (montmorillonite, MMT) under large amplitude oscillatory shear (LAOS) flow were investigated. The G′ and G″ as a function of strain amplitude, Lissajous plots and FT-rheology methods were used to interpret nonlinear behavior of PLA/PCL blends with and without MMT. Additionally, scanning electron microscopy (SEM) images of PLA/PCL with MMT blends were taken to investigate the effects of clay on the internal structure of the PLA/PCL blends. A relationship between morphological changes and linear and nonlinear rheological properties was observed. SEM image analysis revealed that clay acted as a compatibilizer and then reduced the size of droplets in the PCL domain of the PLA matrix. As a result, nonlinear properties sensitively reflect morphological changes with increasing MMT amount. The nonlinear rheological properties of PLA/PCL/MMT/metallocene-LLDPE (mLLDPE) were also investigated when mLLDPE was used as an impact modifier to improve mechanical properties, and the nonlinear rheological properties of PLA/PCL/MMT and PLA/PCL/MMT/mLLDPE were also compared

Tuning the Conductivity of Nanocomposites through Nanoparticle Migration and Interface Crossing in Immiscible Polymer Blends: A Review on Fundamental Understanding

This article critically reviews the detailed fundamental understanding of the influence of conductive nanoparticle migration on the localization, and hence, electrical conductivity of immiscible polymer blend nanocomposites. Three types of conductive nanoparticles, namely, spherical, tubular, and platelet, are discussed with respect to their migration and electrical conductivity of obtained nanocomposites. A complete migration process consists of bulk migration within one component, contact with the interface, and penetration to the other component. During processing, the wetting coefficient parameter is the main thermodynamically controlling factor for nanoparticle localization. However, kinetic effects, such as mixing sequence and intensity, viscosity ratio, size and shape of the nanoparticles, and mixing time, can play a substantial role in determining the final locations of nanoparticles. Moreover, the rate of migration varies with the surface chemistry of the nanoparticles. It has been reported that nanoparticles in a more viscous phase move slower compared with a low viscous phase. Furthermore, nanoparticles having high aspect ratios and surface polarities compatible with the other component migrating faster. It is established that immiscible polymer blend nanocomposites with a ?double percolation? structure having higher conductivity with nanoparticles are localized at the interface of the co-continuous blends

Nanostructured Immiscible Polymer Blends: Migration and Interface

Nanostructured Immiscible Polymer Blends: Migration and Interface covers a wide range of nanoparticle types, emphasizing the mechanisms and parameters involved in the migration of nanofillers inside immiscible polymer blends. This book explores the influence of nanoparticle migration on the localization, and hence, morphology development, electrical conductivity, and met-rheological properties of blended composite materials. As the influence of solid particles, ranging in size from several hundred nanometers to a few microns in immiscible polymer blends has been extensively studied for use as compatibilizers, morphology stabilizers, and reinforcement agents, this book is a timely resource

Influence of Nanoclay Localization on Structure–Property Relationships of Polylactide-Based Biodegradable Blend Nanocomposites

This article highlights the recent research achievements regarding the development of nanoclay-containing biodegradable composites of polylactide (PLA)-based immiscible blends. The structure?property relationships of particular blends, namely, PLA/poly(ε-caprolactone), PLA/poly(butylene succinate), and PLA/poly[(butylene succinate)-adipate], are studied with respect to the nanoclay incorporations. For different nanoclay types and concentrations, the morphologies of these nanocomposites are probed and correlated to their viscoelastic, mechanical, and thermal properties, along with their crystallization behavior and kinetics and gas permeability. The nanoclay dispersion and distribution characteristics are found to be key parameters influencing the final properties. In particular, nanocomposites with a higher degree of nanoclay dispersion exhibit significant enhancement in their mechanical, thermal, and barrier properties, and some agglomerations are effective as regards favorable crystallization behavior. In terms of the clay localization, the positioning of nanoclays at the interface reduces the minor phase size remarkably, because of the droplet encapsulation that counteracts coalescence. However, for improved understanding of the influence of nanoclay localization on the structure?property relationships of these blends, further systematic study is required. That is, nanocomposites with different localizations but the same nanoclay loads should be compared. This can be achieved by tuning the processing protocols and the nanoclay inclusion orders in the blends

Nonlinear behavior of PP/PS blends with and without clay under large amplitude oscillatory shear (LAOS) flow

Dynamic oscillatory measurement, i.e., small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS) test was used to investigate linear and non-linear viscoelastic properties of Polypropylene (PP)/Polystyrene (PS) blends with and without 5 wt.% clay (C20A). Fourier transform (FT-Rheology), Lissajous curves and stress decomposition methods were used to analyze non-linear responses under LAOS flow. Composition effects of blends were investigated prior to compatibilization effects. Elevated concentrations of dispersed phase (PS) increased the moduli G'(ω) from SAOS test and G*(γ0) from LAOS test of the blends as well as strain thinning behavior. Interestingly, addition of 5 wt.% clay (C20A) boosted moduli of the blends as well as led to similar strain thinning behaviors among the PP/PS/C20A blends, except for the (90/10) PP/PS blend. The latter did not show improved rheological properties despite morphological improvements, as shown by SEM. Results from SEM and improved rheological properties of PP/PS/C20A blends revealed the compatibilization effects of clay (C20A) particles regardless of size reduction mechanisms. Third relative intensities (I3/1) from FT-rheology were found to be sensitive to clay (C20A) additions for the (70/30) and (30/70) PP/PS blends. Similarly, Lissajous curves could detect changes upon clay (C20A) addition, specifically at lower strain amplitudes whereupon addition of 5 wt.% clay resulted in the closed loops of Lissajous curves showing a more ellipsoidal shape due to increased elasticity in the blends. However, detection of these changes at larger strain amplitudes was more challenging. Therefore, stress decomposition (SD) method was applied for more precise characterization as it decomposes the total stress (σ) into elastic stress (σ′) and viscous stress (σ″). Using SD method, elastic stress was more distorted, especially, strain hardening, while the total stress response remained almost unchanged at larger strain amplitudes

Rheology of poly (lactic acid)-based systems

Being commercialized in 1992, poly (lactic acid) (PLA) has been considered for biomedical applications and as a reliable substitute for a wide range of commodity and engineering applications where noncompostable petroleum-based polymers are currently being used. However, PLA suffers from series of drawbacks and it would not be applicable unless these shortcomings resolve somewhat. Besides the PLA’s brittleness and low toughness which originate from its higher glass transition temperature, the major shortcomings which negatively influence the other features of PLA are its low melt strength and slow crystallization kinetics. These weaknesses limit the processability, formability and foamability of PLA, and hence, the manufacturing of PLA based products. In this context, the improvement of rheological and viscoelastic properties of PLA is of a great importance as it enhances the melt strength. To control the PLA’s rheological and viscoelastic properties, various attempts such as varying the D-lactide content in PLA molecules, increasing the PLA’s molecular weight, the use of chain extender and branching, controlling the PLA’s crystallization, compounding with micro-/nano-sized fillers and blending with other polymers have been considered. This article critically reviews these studies that have been conducted so far on rheological investigations of various PLA-based systems

Supramolecular Poly(cyclotriphosphazene) Functionalized Graphene Oxide/Polypropylene Composites with Simultaneously Improved Thermal Stability, Flame Retardancy, and Viscoelastic Properties

A novel crosslinkable supramolecular poly(cyclotriphosphazene) functionalized graphene oxide (FGO) is synthesized and melt-processed with polypropylene (PP), which results in a PP composite with simultaneously improved flame retardancy, smoke-suppression, and thermal and viscoelastic properties. The cone-calorimetry test results reveal that the peak heat-release rate and total heat release of the composite (2 wt% FGO) are reduced by 39.7% and 29.9%, respectively, compared to those of the neat PP. Meanwhile, the total smoke released and total smoke production of PP are significantly (42.7% and 34.9%, respectively) reduced after composite formation with 2 wt% FGO. Similarly, the PP/FGO composite shows an improved maximum weight loss temperature of 392.4 °C, compared to that of neat PP (361.4 °C). Thermogravimetric Fourier-transform infrared spectroscopy (TG-FTIR) analysis further confirms that the composite reduces the evolution of the flammable components and toxic gases, especially CO gas, indicating that the FGO significantly decreases the fire hazards of the PP. The thermomechanical and melt-rheological analyses reveal that the composite has higher mechanical stiffness and viscoelastic properties than the neat polymer. In summary, FGO is shown to have potential as an advanced additive to obtain PP composites with multifunctional properties; however, higher FGO loading would be needed to improve UL-94 rating from V-2 to V-0