Elastomer Research Articles

Wetting-Induced Elastocapillary Deformation of Supported Thin Rubbery Polymer Films

Wetting-Induced Elastocapillary Deformation of Supported Thin Rubbery Polymer Films

Influence of Layer’s Annealing Temperature on Sensing Properties of Spin-Coated SBS Layer Exposed to Alcohol Vapor

QCM-based alcohol vapor sensors have been widely researched, and various materials have been deposited onto the sensor surface to serve as a functional layer. However, non-conductive polymers such as SBS as a functional layer for alcohol sensors are still minimally reported. In this study, the SBS was deposited on 1 side of the QCM using the spin coating technique. After deposition, the layer was annealed for 1 h. The annealing temperatures are 100, 150 and 200 °C. The concentrations of exposed alcohol vapor were 5, 10, 15, 20, 25, 50, 75 and 100 ppm. This study demonstrated that the SBS layer has the potential to be a functional layer of alcohol sensors. SBS 200 °C is an optimum functional layer for alcohol vapor sensors due to its high ∆f and sensitivity. Meanwhile, SBS 100 °C has poor ∆f and sensitivity. This is due to the morphology of 200 °C SBS, which consists of more valleys that perform as interaction sites for SBS and alcohol molecules. However, one of the limitations of SBS as a functional sensor layer for alcohol sensors is its low selectivity, which is a characteristic of rubbery polymers. HIGHLIGHTS The SBS layer annealed at higher temperatures has more valleys than the SBS layer annealed at low temperatures. The valleys in the morphology of the SBS layer act as interaction sites for alcohol molecules, where each site interacts with an alcohol molecule. It is based on the sensor response and proved by fitting the Langmuir model. The SBS layer annealed at 200 ᵒC has a high ∆f, sensitivity, and longer response time. The selectivity of SBS was relatively low, a characteristic of rubbery polymers. The interaction between SBS and methanol is physisorption. GRAPHICAL ABSTRACT

IMMISCIBLE POLYMER–FILLER SYSTEMS FOR TUNABLE MECHANICAL PROPERTIES

ABSTRACT A model system consisting of a 50/50 immiscible mixture of polyethylene glycol (PEG) and polytetrahydrofuran (PTHF), with covalently bound nano silica–reinforcing particles, was used to investigate how the distribution of particles affects viscoelastic properties. The rubbery polymers were generated by chain extending from their respective oligomers through hydroxyl end groups with 1,6-diisocyanato hexane. The viscosity of the resulting PEG and PTHF polymers was 32 and 1000 Pa-s, respectively. Setting the overall SiO2 concentration to 10 phr, we explored three different silica distributions: (1) all-in-PEG, 20 phr in PEG and neat PTHF; (2) uniform, 10 phr in both PEG and PTHF; and (3) all-in-PTHF, neat PEG and 20 phr in PTHF. When compared with the uniform system, the storage and loss shear moduli and the viscosity of the all-in-PTHF system showed a 20-fold increase of the stiffness at low strain, yet nearly the same viscosity at high strain. Similarly, the storage and loss moduli of all-in-PEG mixtures were roughly 1/10 that of the uniform system. The surprisingly high modulus and high viscosity of the all-in-PTHF system can be understood as the entire PTHF regions themselves becoming solid filler.

Enhancing CO2 Transport Across the PEG/PPG-Based Crosslinked Rubbery Polymer Membranes with a Sterically Bulky Carbazole-Based ROMP Comonomer.

A series of poly(ethylene glycol)-block-poly(propylene glycol) (PEG/PPG)- and 5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide)-based crosslinked rubbery polymer membranes, denoted as PEG/PPG-2CZPImide (x:y), are prepared from the norbornene-functionalized PEG/PPG oligomer (NB-PEG/PPG-NB) and 2-(bicyclo[2.2.1]hept-5-en-2-ylmethyl)-5,6-di(9H-carbazol-9-yl)isoindoline-1,3-dione (2CZPImide-NB) via ring-opening metathesis polymerization (ROMP). The molar ratio (x:y) of the NB-PEG/PPG-NB (x) to 2CZPImide-NB (y) monomers is varied from 10:1 to 6:1. X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and pure gas permeability studies reveal that the comonomer 2CZPImide-NB successfully increases the d-spacing among the crystalline PEG/PPG segments, hence enhancing the diffusivity of gases through the membranes. The synthesized membranes exhibit good CO2 separation performance, with CO2 permeabilities ranging from 311.1 to 418.1 Barrer and CO2/N2 and CO2/CH4 selectivities of 39.4-52.0 and 13.4-16.0, respectively, approaching the 2008 Robeson upper bound. Moreover, PEG/PPG-2CZPImide (6:1), displaying optimal CO2 permeability and CO2/N2 and CO2/CH4 selectivities, shows long-term stability against physical aging and plasticization resistance up to 20 days and 10 atm, respectively.

Understanding the Mechanical Behavior of Sulfide Solid Electrolyte Membranes for Practical Applications in All-Solid-State Batteries

All-solid-state batteries (ASSBs) hold great promise as next-generation energy storage systems due to their enhanced stability and high energy density compared to traditional lithium-ion batteries. This improvement stems from the use of a solid electrolyte (SE) instead of a highly volatile liquid electrolyte and the incorporation of a lithium metal anode. In general, sulfide-based SSBs require adequate pressurization conditions to establish an intimate interface between the solid particles, ensuring a continuous electron/ion conduction path. At the cell level, maintaining external stack pressure during operation is crucial to preserve conformal solid-solid contact. Furthermore, when scaling up, fabrication pressure should be carefully considered to enhance electrode densification without causing damage. In particular, the fabrication of thin, robust, and scalable SE membranes faces practical challenges due to a limited amount of polymeric binder and the low intrinsic ductility of SEs after densification. Understanding the mechanical behavior of these SE membranes is essential to ensure their structural stability during manufacturing.In this study, we systematically examined the mechanical properties of SE and SE membranes. The deformability of various types of sulfide SEs was assessed using a powder compaction test, departing from the commonly used indentation method. The yield pressure, which indicates the deformability of the SE powder, is influenced by the composition and synthesis conditions of the SEs. The stress-strain behaviors of the SE membranes were obtained through tensile and flexural tests for both as-prepared and pressed samples, respectively. The tensile and bending behaviors of the SE membranes strongly depend on the combination of the SE and polymeric binder. The utilization of a ductile SE and a rubbery polymer binder can enhance the flexibility and ductility of the membrane, leading to increased densification degree and low interfacial resistance even under lower fabrication pressure. The details of cell configuration, fabrication procedure, and the resulting performances of the cell will be discussed in this talk.

Improved mechanical, magnetic and radiation shielding performance of rubbery polymer magnetic nanocomposites through incorporation of Fe3O4 nanoparticles

The current research investigates the impact of magnetite (Fe3O4) nanoparticles (3–12 wt%) on the properties of rubbery polymer nanocomposites fabricated via melt blending method. The tensile and impact properties were improved at an optimal 6 wt% Fe3O4, revealing a good interfacial interaction. Fe3O4 enhanced the thermal stability, as evidenced by the increased integral procedure decomposition temperature up to 26 %. Fe3O4 increased residual and saturated magnetization the most at 6 wt% loading. The gamma-ray shielding properties were explored with energy ranging from 0.2835 to 2.506 MeV, and effectively at low energies. Increased Fe3O4 content correlated positively with linear attenuation coefficient (LAC), enhancing radiation shielding but reducing neutron shielding. At 0.2835 MeV, the LAC values increased up to 0.12431 cm−1 for 12 wt% Fe3O4, while the fast neutron removal cross-section values decreased from 0.10427 cm−1 to 0.08548 cm−1. These findings highlight the multifunctional potential of Fe3O4-incorporated nanocomposites in radiation shielding applications.

Ductility of a nanocomposite of glassy and rubbery polymers

A brittle glassy polymer can be made ductile by forming a nanocomposite with a rubbery polymer. This paper investigates a nanocomposite of poly(methyl methacrylate) (PMMA) and poly(ethyl acrylate) (PEA). Pure PMMA is a brittle glass, pure PEA is a rubber, and a PEA-PMMA nanocomposite is ductile. We fabricate the nanocomposite by swelling PEA with MMA monomer, followed by polymerizing MMA. We prepare nanocomposites of various weight fractions of PMMA and measure their properties, including modulus, yield strength, fracture strain, fracture strength, work of fracture, and toughness. Whereas bulk PMMA fractures at a strain of ∼0.05 by localizing inelastic deformation in crazes, the PEA-PMMA nanocomposite can be stretched several times its original length with homogeneous deformation. The nanocomposite separates into a glassy phase and a rubbery phase. For a nanocomposite of 45 % weight fraction of PMMA, atomic force microscopy shows that the two phases are bicontinuous and the phase size is at ∼20 nm. For the nanocomposite to undergo large deformation, the continuous glassy phase must accommodate. Our experiments exclude the mechanism that the glassy phase in the nanocomposite breaks into small pieces. Rather, the glassy phase in the nanocomposite is itself ductile. We discuss the molecular picture of this ductility.

Fabrication of high-performance biochar incorporated Pebax®1657 membranes for CO2 separation

This study highlights the utilization of biobased material for developing high-performance membranes for gas separation applications. Biochar was synthesized by the pyrolysis of pine needles and further modified by silane functionalization. Thus obtained biochar was incorporated into a rubbery polymer, poly(ether-blockamide) (Pebax-1657), to synthesize mixed matrix membranes (MMMs). Morphologies of membranes and physio-chemical interactions of the biochar and polymer were evaluated using SEM, FTIR, DSC, and XRD. MMMs exhibit higher gas adsorption properties compared to the neat Pebax-1657 membrane. The effect of biochar incorporation on gas permeation properties was conducted in an indigenously designed setup using pure CH4, CO2, and N2 gases in the pressure range of 5–30 kg/cm2. 20 wt% Biochar loaded MMM achieved a higher CO2 permeability of 114 Barrer, signifying 79% higher permeability over the pristine Pebax membrane. Correspondingly, the highest selectivity values for CO2/CH4 and CO2/N2 achieved were 32 and 94, respectively, with increasing pressure. A regression model was developed to estimate the relation between biochar loading and gas permeability. The data revealed a strong positive correlation (0.7–0.9) between gas permeability and the percentage of biochar loaded. The developed MMMs are stable and exhibit superior performance for CO2 removal from natural gas and power plant off-gases. Pine needles derived MMMs represent a promising new approach for developing high-performance and environmentally sustainable membranes for gas separation applications.

Simple and complex sorption−solution isotherms for membrane polymers: A statistical thermodynamic fluctuation theory

Simple, site-specific adsorption isotherm models, such as GAB and other generalizations of BET, fit strikingly well to experimental isotherms of simple shapes for glassy and rubbery polymers. However, the structures of dense polymers do not necessarily resemble the unrestricted layer-by-layer adsorption mechanism on one type of sorption site assumed by these models. Since polymers contain micropores, sorptive likely (ad)sorbs on the internal surfaces of the free (accessible) volume voids, and dissolves in the polymer phase. While the empirical dual mode sorption model and its variants address this duality, other common models assume chiefly only one of the two mechanisms. Moreover, the simplified models do not fit complex isotherms, such as those for alcohols and poly[(trimethylsilyl)propyne] (PTMSP). The statistical thermodynamic fluctuation theory is adopted here to capture the sorption-solution duality consistently even for the complex isotherms. The statistical thermodynamic ABC isotherm derived from this theory involves the sorbate-sorbent and mono-, di-, and tri-sorbate interactions expressed by sorbate number correlations. This work shows that BET, GAB, dual-mode sorption model, Flory-Huggins, and ENSIC models are special cases of the ABC isotherm. The isotherm multiplicativity principle has been derived from the number fluctuation relationship to model complex isotherms.

Permeance of Condensable Gases in Rubbery Polymer Membranes at High Pressure.

The gas transport properties of thin film composite membranes (TFCMs) with selective layers of PolyActive™, polydimethylsiloxane (PDMS), and polyoctylmethylsiloxane (POMS) were investigated over a range of temperatures (10-34 °C; temperature increments of 2 °C) and pressures (1-65 bar abs; 38 pressure increments). The variation in the feed pressure of condensable gases CO2 and C2H6 enabled the observation of peaks of permeance in dependence on the feed pressure and temperature. For PDMS and POMS, the permeance peak was reproduced at the same feed gas activity as when the feed temperature was changed. PolyActive™ TFCM showed a more complex behaviour, most probably due to a higher CO2 affinity towards the poly(ethylene glycol) domains of this block copolymer. A significant decrease in the permeate temperature associated with the Joule-Thomson effect was observed for all TFCMs. The stepwise permeance drop was observed at a feed gas activity of p/po ≥ 1, clearly indicating that a penetrant transfer through the selective layer occurs only according to the conditions on the feed side of the membrane. The permeate side gas temperature has no influence on the state of the selective layer or penetrant diffusing through it. The most likely cause of the observed TFCM behaviour is capillary condensation of the penetrant in the swollen selective layer material, which can be provoked by the clustering of penetrant molecules.

Adhesion, roughness, wettability, and dielectric strength of elastomers liquid blends for high-density fiberboard wood adhesive

In the present study, the physical characteristics of elastomer (EL) blend with natural polymers such as polyvinyl alcohol (PVA), Dexrin (D), Arabic gum (AG), and corn starch (CS) based on high-density fiberboard wood adhesives were investigated. The EL blends were prepared by dissolving AG, D, PVA, and CS in deionized water at 70 °C for 1 h under magnetic stirring continuously until the solution was clear, and blends were made with a weight of 60/40 (w/w); then were cast into a mold with a 20 cm diameter and left at room temperature for 24 h to ensure complete water removal and drying of the samples. The prepared EL and EL blend structures, adhesion strengths, roughness, wettings, and dielectric strengths, were investigated. The modified EL blend reveals a 144 MPa for pull-off strength and 770.8 N for shear strength for high-density fiberboard (HDF) wood as a substrate to the EL/AG, respectively. The surface roughness and contact angle of the EL/PVA mixture were found to be high, measuring 4.57 µm for roughness and shows the water contact angles for the samples. An increase in the contact angle of the El/AG blend where reached to(83.94˚) was observed due to the decrease in the –COOH and OH groups present in the backbone of the arabic gum. The greatest dielectric strength for EL/AG was reported to be 18.62 kV/mm at 0.5 kV/s and 22.77 kV/mm at 5 kV/s.and optical microscoby image for break down region was shown the carbonization in the break down point as aresult of carashing polymers chains, also micro cracks occuring forspecimens and this cracks extends directly from the breakdown region

Nanocellulose‐Incorporated Composite Membranes of PEO‐Based Rubbery Polymers for Carbon Dioxide Capture

To achieve sustainable and energy‐efficient CO2 capture processes, it is imperative to develop membranes that possess both high CO2 permeability and selectivity. One promising approach involves integrating high‐aspect‐ratio nanoscale fillers into polymer matrices. The high‐aspect‐ratio fillers increase surface area and improve interactions between polymer chains and gas molecules passing through the membrane. This study focuses on the integration of cellulose nanocrystals (CNCs) with an impressive aspect ratio of around 12 into rubbery polymers containing polyethylene oxide (PEO), namely PEBAX MH 1657 (poly[ether‐block‐amide] [PEBA]) and polyurethane (PU), to fabricate mixed‐matrix membranes (MMMs). By exploiting the interfacial interactions between the polymer matrix and CNC nanofillers, combined with the surface functionalities of CNC nanofillers, the rapid and selective CO2 transport is facilitated, even at low filler concentrations. This unique feature enables the development of thin‐film composites (TFCs) with a selective layer around 1 μm. Notably, even at a filling ratio as low as 1 weight percent, the resulting membranes exhibit remarkable CO2 permeability (>90 Barrer) and CO2/N2 selectivity (>70). These findings highlight the potential of integrating CNCs into rubbery polymers as a promising strategy for the design and fabrication of highly efficient CO2 capture membranes.

Physically crosslinked polyacrylates by quadruple hydrogen bonding side chains.

Dynamic polymer materials can be obtained by introducing supramolecular interactions between the polymer chains. Here we report on the preparation and mechanical properties of poly(methyl acrylate) (PMA) and poly(n-butyl acrylate) (PBA) funcionalized with ureidopyrimidinone (UPy) in the side chains. In contrast to the traditional UPy with a methyl group, the selected UPy motif contained a branched alkyl side chain, which enhances solubility, compatibility with the polymer matrix and potentially prevents stacking of UPy dimers. Low molar mass PMA and PBA were synthesized via Cu(0)-mediated radical polymerization and allyl bonds were introduced with different degrees of functionalization by stoichiometrically controlled transesterification with allyl alcohol. The allyl esters served as functional handles for UPy attachment via UV-initiated radical thiol-ene coupling. The PMA-UPy materials displayed a more glassy appearance, in contrast to the rubbery PBA-UPy polymer networks, associated to its higher glass transition temperature. The mechanical properties of the resulting hydrogen bonded polymer networks were assessed by thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis and tensile testing, followed by rheological analysis of the network dynamics. Furthermore, the effect of associative groups on the linear viscoelastic response is discussed based on a modified sticky Rouse model indicating the absence of significant aggregation or phase separation of the UPY units.

Development of broad modulus profile upon polymer-polymer interface formation between immiscible glassy-rubbery domains.

Interfaces of glassy materials such as thin films, blends, and composites create strong unidirectional gradients to the local heterogeneous dynamics that can be used to elucidate the length scales and mechanisms associated with the dynamic heterogeneity of glasses. We focus on bilayer films of two different polymers with very different glass transition temperatures ([Formula: see text]) where previous work has demonstrated a long-range (∼200 nm) profile in local [Formula: see text] is established between immiscible glassy and rubbery polymer domains when the polymer-polymer interface is formed to equilibrium. Here, we demonstrate that an equally long-ranged gradient in local modulus [Formula: see text] is established when the polymer-polymer interface ([Formula: see text]5 nm) is formed between domains of glassy polystyrene (PS) and rubbery poly(butadiene) (PB), consistent with previous reports of a broad [Formula: see text] profile in this system. A continuum physics model for the shear wave propagation caused by a quartz crystal microbalance across a PB/PS bilayer film is used to measure the viscoelastic properties of the bilayer during the evolution of the PB/PS interface showing the development of a broad gradient in local modulus [Formula: see text] spanning [Formula: see text]180 nm between the glassy and rubbery domains of PS and PB. We suggest these broad profiles in [Formula: see text] and [Formula: see text] arise from a coupling of the spectrum of vibrational modes across the polymer-polymer interface as a result of acoustic impedance matching of sound waves with [Formula: see text] nm during interface broadening that can then trigger density fluctuations in the neighboring domain.

Reliability analysis based on load spectrum: A structural improvement of Indian Railways three-piece freight bogie elastomeric pad

Dynamic characteristics and reliability of elastomeric pads are dominant components in the design methodology to satisfy the performance parameters under dynamic operations. The fatigue life of rubber pads fitted with elastomeric pads mainly depends upon elastomers; natural rubber, chloroprene, nitrile butadiene, silicon compounds, etc., additives, accelerators, activators, fillers, anti-degradants, and manufacturing processes. The performance of the elastomeric pad is evaluated based on service operation, simulation, and laboratory testing. New and failed elastomeric (EM) pads have been examined in the Indian Rubber Manufacturer’s Research Association IRMRA laboratory for detailed failure analysis of existing EM pads. Further, chemical and physical properties are also evaluated in M&C (Metallurgical and Chemical) and Testing Directorate of Research Designs and Standards Organization (RDSO), labs respectively. The fatigue life of the EM pad is estimated based on the results extracted from the Finite Element (FE) analysis of the EM pad. An attempt is made to modify the design of the EM pad by considering the results of detailed field trials, lab testing, and FE analysis. The modified design satisfies the dynamic characteristic during FE (Structural and Thermal) analysis and lab testing.

Polyimide blend metal–organic framework‐based mixed matrix membrane for gas separation: A review

AbstractPolyimide (PI), a glassy polymer, suffers from permeability–selectivity trade‐off and plasticization, which restrict its gas separation performance. Instead of exploring new materials, polymer blend and mixed matrix membrane (MMM) emerge as promising approaches in improving membrane gas separation efficiency attributed to their simplicity and cost efficiency. However, polymer immiscibility and polymer‐filler incompatibility are the main challenges encountered in these two approaches, respectively. Thus far, only limited reviews target the comparison between PI/glassy and PI/rubbery polymer blends. Besides, the review on improving the compatibility between polymer and filler in PI‐metal–organic framework (MOF) MMM is also lacking. Hence, this review aims to assess the gas separation characteristics of PI blended with glassy and rubbery polymers, focusing on the blend miscibility. It was discovered that the casting solvent's solubility parameter and solvent volatility play a part in governing the blend miscibility. Meanwhile, the efficiency of surface functionalization and ionic liquid addition in improving the polymer–filler compatibility in MMM is also reviewed. The wet method for filler incorporation demonstrates a more homogeneous filler dispersion within the membrane. Hence, its employment in MOF‐based MMM fabrication can be explored further.

Thermal transitions and foaming of a rubbery polymer, poly(ethylene-co-vinyl acetate-co-carbon monoxide), in carbon dioxide: Temperature scaling as a new approach for rational selection of foaming conditions

The foaming of a thermoplastic elastomer, poly(ethylene-co-vinyl acetate-co-carbon monoxide) with varying copolymer compositions was explored using CO2. Copolymers with 0, 10, and 20 wt% vinyl acetate and 10 wt% carbon monoxide, with the remainder being ethylene, designated as EVACO-0010, EVACO-1010, and EVACO-2010 were evaluated. Melting and crystallization temperatures and their depression in CO2 were determined using high-pressure torsional braid analysis. Sorption and swelling assessments were carried out using a modified magnetic suspension balance. Foaming experiments were conducted at 200 bar near the depressed melting and crystallization temperatures. Foams with low (< 0.2 g/cm3) bulk densities of EVACO-1010 and EVACO-2010 were generated near their crystallization temperatures in CO2. A new concept of scaling the foaming temperature with respect to the melting or the crystallization temperature of the polymer in carbon dioxide was developed which provides an insightful new approach for the rational selection of polymer foaming conditions.

Revisiting experimental techniques and theoretical models for estimating the solubility parameter of rubbery and glassy polymer membranes

Estimation and correlation of the Hildebrand solubility parameter (δ) of polymers and small molecules is a common practice in membrane material science and is accomplished by experimental and numerical routes. In this paper, we revisit, update, and compare both routes to enhance the accuracy in the determination of δ. Best practices for the experimental determination of polymer solubility parameters are provided, and the viability of Dynamic Light Scattering (DLS) was demonstrated as an alternative to conventional time- and material-consuming techniques, such as Ubbelohde viscometry and swelling measurements. Glassy and rubbery polymers, including high fractional free volume (FFV) microporous polymers such as PIM-1 and poly(1-trimethylsilyl-1-propyne) (PTMSP), are among the samples included in this study with great relevance to membrane science. In an attempt to enhance the accuracy of numerical estimate of polymer solubility parameters via the group contribution method, we provide updated group contribution parameters, along with their uncertainty, according to the technique recently reported by Smith et al. These updated group contribution parameters result in a mean absolute relative error of 9.0% in predicting the solubility parameter on a test set of 40 polymers, which is on par with the average 10% error reported previously. We also show, using machine learning techniques, that augmenting the group contribution model with extra parameters or non-linear relationships does not improve its accuracy. Results of the updated group contribution technique and dynamic light scattering measurements were compared to experimental viscometry on four test polymers, and the difference between the three techniques is compared.

Glassy and Rubbery Epoxy Composites with Mesoporous Silica

The reinforcing efficiency of SBA-15-type mesoporous silica, when used as additive in epoxy polymers, was evaluated in this study. The effects of silica loading and its physicochemical characteristics on the thermal, mechanical, and viscoelastic properties of glassy and rubbery epoxy mesocomposites were examined using SBA-15 mesoporous silicas with varying porosities (surface area, pore size, and volume), particle sizes, morphologies, and organo-functionalization. Three types of SBA-15 were used: SBA-15 (10) with 10 nm pore diameters and long particles, SBA-15 (5) with 5 nm pore diameters and short particles, and SBA-15 (sc) with 10 nm pore diameters and short particles (“sc” for short channel). SBA-15 (10) was modified with propyl-, epoxy-, and amino-groups to study the effect of functionalization. The glassy or rubbery epoxy polymers and mesocomposites were produced by the crosslinking of a diglycidyl ether of bisphenol A (DEGBA) epoxy resin with isophorone diamine (IPD) or Jeffaminje D-2000, respectively. Mesoporous silica was uniformly dispersed inside the polymer matrices; however, the opacity levels between the rubbery and glassy samples were different, with completely transparent rubbery composites being prepared with as high as a 9 wt. % addition of SBA-15. The mechanical and thermal performance properties of the mesocomposites were dependent on both the type of the curing agent, which affected the cross-linking density of the pristine polymer matrix, and the characteristics of the mesoporous silica variants, being, in general, improved by the addition of up to 6 wt. % silica for the glassy polymers and up to 9 wt. % for the rubbery polymers.

Phase-field modelling and analysis of rate-dependent fracture phenomena at finite deformation

AbstractFracture of materials with rate-dependent mechanical behaviour, e.g. polymers, is a highly complex process. For an adequate modelling, the coupling between rate-dependent stiffness, dissipative mechanisms present in the bulk material and crack driving force has to be accounted for in an appropriate manner. In addition, the resistance against crack propagation can depend on rate of deformation. In this contribution, an energetic phase-field model of rate-dependent fracture at finite deformation is presented. For the deformation of the bulk material, a formulation of finite viscoelasticity is adopted with strain energy densities of Ogden type assumed. The unified formulation allows to study different expressions for the fracture driving force. Furthermore, a possibly rate-dependent toughness is incorporated. The model is calibrated using experimental results from the literature for an elastomer and predictions are qualitatively and quantitatively validated against experimental data. Predictive capabilities of the model are studied for monotonic loads as well as creep fracture. Symmetrical and asymmetrical crack patterns are discussed and the influence of a dissipative fracture driving force contribution is analysed. It is shown that, different from ductile fracture of metals, such a driving force is not required for an adequate simulation of experimentally observable crack paths and is not favourable for the description of failure in viscoelastic rubbery polymers. Furthermore, the influence of a rate-dependent toughness is discussed by means of a numerical study. From a phenomenological point of view, it is demonstrated that rate-dependency of resistance against crack propagation can be an essential ingredient for the model when specific effects such as rate-dependent brittle-to-ductile transitions shall be described.