Rubber Domains Research Articles

High Impact Toughness ABS/CaCO<sub>3</sub> Nanocomposites Prepared through Pressure Induced Flow Moulding

ABS/CaCO3 nanocomposite with super toughness was processed by pressure induced flow (PIF) moulding. After PIF processing, the impact toughness of ABS/CaCO3 nanocomposite improved remarkably, the average highest Izod impact strength of nanocomposite increased to around 69 kJ/m2, which was 2.3 times higher than that of orignal ABS. Moreover, the relative toughening mechanism was investigated. The disk-like rubber domain and the cavities caused by calcium carbonate were researched by small angle X-ray scattering (SAXS). The synergy of them could prevent the craze becoming a large crack effectively.

Tailored Nanostructured Thermoplastic Elastomers from Polypropylene and Fluoroelastomer: Morphology and Functional Properties

Conventional thermoplastic elastomer from rubber–plastic blends has rubber domains of a few micrometers dispersed in a plastic matrix. Nanotailoring of novel thermoplastic elastomeric blends from polypropylene (PP) and fluoroelastomer (FKM) by a special green technique generated a unique morphology in which FKM was dispersed in the nanometer range (50–70 nm) into the continuous PP matrix. The evolution of the unique nanostructure morphology was explained with the help of a viscoelastic drop breakup mechanism. The nanostructured blends exhibited superior physical properties and outstanding oil swelling resistance and thermal stability, which increased upon vulcanization of the rubber phase in situ. For example, volume swell of nanostructured PP/FKM blends was 8–10% in ASTM oil #3 at 100 °C for 72 h, which was the lowest in this type of thermoplastic elastomer. Insights into how the unique morphology influenced the functional properties of thermoplastic elastomers was provided. These new thermoplastic elastomers can be used in the automotive industry, particularly as a liner material for car hoses where superior flexibility, oil resistance, and heat resistance are desirable properties.

Theoretical and morphological evaluation of dynamic viscoelasticity and thermo-mechanical characteristics of TPV composites

In this work, the regular usage of conventional dynamic mechanical analyzer (DMA) has been extended through the characterization of rubber elasticity and dynamic viscoelasticity of the TPV composites based on natural rubber, ethylene octene copolymer and carbon black (NR/EOC/CB). Two independent theoretical approaches viz. rubber index and damage parameter, have been adopted in order to evaluate the same. Rubber index, which is the function of temperature and entropy, has been utilized here to estimate the elasticity of the rubber networks. On the other hand, a classical damage parameter, which is a measure of dynamic viscoelasticity, has been obtained from initial tangent modulus through cyclic stress softening i.e. Mullins effect. Moreover, the measurement of thread break-up time obtained from the capillary number expression and morphological observations has directed us to revalidate the new mechanism of morphology evolution through the thermodynamic calculations. The reduced interconnectivity between the rubber domains, which has been obtained as a result of uneven filler dispersion into the rubber phase, has resulted in reduced elasticity in the rubber networks, as evident from the experimental results and atomic force micrographs. This study has thus revealed different novel aspects of dynamic mechanical analyzer and provided innovative methods for the characterization of rubber-like materials.

Radiation crosslinked blends based on an ethylene octene copolymer (EOC) and polydimethyl siloxane (PDMS) rubber with special reference to the optimization of processing parameters

Transformation of morphology of EOC : PDMS blends with the change in processing parameters.

Influence of blend ratio on properties of novel thermoplastic vulcanizates based on copolyester/epoxidized natural rubber blends

Novel thermoplastic vulcanizates based on copolyester (COPE) and epoxidized natural rubber with 30 mol% epoxide (ENR-30) were prepared with various blend ratios and their properties were investigated. The main target was to prepare the dynamically cured COPE/ENR-30 blends with low hardness (lower than 80 Shore A) but superior in damping properties. The mixing torque of the blend mixer was captured and it was found that increasing the fraction of rubber increased the final mixing torque. Dynamic mechanical properties of the blends were also determined. It was found that with increasing rubber proportion, storage modulus and complex viscosity were increased but tan δ was decreased. In addition, morphology of the blends shows increasing size of vulcanized rubber domains dispersed in the thermoplastic matrix with increasing of rubber proportion. However, the strength properties decreased in terms of Young’s and 100 % moduli, tensile strength, elongation-at-break, and hardness. This might be attributed to the increasing size of vulcanized rubber domains. Enhanced rubber elasticity and damping properties were observed with increasing rubber content in the blends, as indicated by decreased tension set and tan δ. Furthermore, temperature scanning stress relaxation results show that with increasing rubber content the blends had their relaxation curves shifted upwards and thermal resistance increased. In addition, thermal properties characterized by DSC show the decreasing heat of crystallization (H) of COPE, or decreasing crystallinity, with increasing rubber content.

Novel thermoplastic natural rubber based on polyamide 12 blends

Dynamically cured 60/40 epoxidized natural rubber (ENR)/polyamide 12 (PA-12) and unmodified natural rubber (NR)/PA-12 blends with different types of curing systems (i.e. sulfur- and peroxide-cured systems) were prepared. It was found that mixing torque, shear viscosity, tensile strength, hardness, stress relaxation, thermal, and oil resistance properties of the ENR/PA-12 blends were higher than those of the NR/PA-12 blends. This is attributed to the chemical interaction between polar functional groups in ENR and PA-12 molecules which caused the formation of ENR-grafted PA-12. Smaller vulcanized rubber domains dispersed in the PA-12 matrix was observed in the dynamically sulfur-cured ENR/PA-12 blends. This is attributed to higher shear and elongational viscosities during mixing operation at high temperature. However, the peroxide-cured blends exhibited higher relaxation property, oil resistance, and cross-link density than those of the sulfur-cured blends due to strong reversion effect observed in the sulfur-cured system.

Influence of rubber on the curing kinetics of DGEBA epoxy and the effect on the morphology and hardness of the composites

The influence of the end groups of two liquid rubbers on curing kinetics, morphology, and hardness behavior of diglycidyl ether of bisphenol-A based epoxy resin (DGEBA) has been studied. The rubbers are silyl-dihydroxy terminated (PDMS-co-DPS-OH) and silyl-diglycidyl ether terminated (PDMS-DGE). Crosslinking reactions, investigated by shear rheometry, ranged 90–110 °C, using a constant concentration (5 phr) of liquid rubbers and 1,2-Diamino cyclohexane (1,2-DCH) as hardener agent. The gel time, tgel, of the neat epoxy significantly decreased when adding the elastomers, more so for the silyl-dihydroxy terminated elastomer; at 110 °C the reaction was nearly complete before rheological test started. The results suggest that the elastomers induced a catalytic effect on the curing reaction. Scanning electron microscopy revealed phase separation of the elastomer during the curing reaction with rubber domains about 5 μm size. However, the DGEBA/dihydroxy terminated elastomer composite cured at 110 °C exhibited a homogenous morphology, that is, the rapid reaction time would not allow for phase separation. Water contact angle tests evidenced either more hydrophilic (silyl-diglycidyl ether terminated rubber) or more hydrophobic (silyl-dihydroxy terminated rubber) behavior than the neat epoxy. The latter effect is attributed to the presence of aromatic rings in the backbone structure of PDMS-co-DPS-OH. Microindentation measurements show that the elastomers significantly reduced the hardness of the epoxy resin, the DGEBA/ether terminated composite exhibiting the lowest hardness values. Moreover, hardness increased as reaction temperature did, correlating with a reduction of microdomains size thus enabling the tuning of mechanical properties with reaction temperature.

Effect of NR/ABS Ratio on Mechanical, Dynamical and Morphological Properties of Vulcanized NR/ABS Blends

Dynamically vulcanized NR/ABS blends by phenolic curing were carried out using an internal mixer at 180 °C. The effect of NR/ABS ratio (i.e., 50/50, 60/40, 70/30) on mechanical, dynamical and morphological properties was investigated. It was found that the tensile strength and hardness increased with an increase in ABS loading whilst the elongation at break decreased, indicating that the strength and hardness attributed to thermoplastic component whereas the elasticity of the blends contributed to the vulcanized NR. The results showed that the 60/40 NR/ABS blend provided the well-balanced mechanical properties. The storage modulus of thermoplastic vulcanizates (TPVs) increased with increasing contents of rubber. This is due to that a higher content of vulcanized NR domain was dispersed in the ABS matrix. The results agreed well with the tan δ and complex viscosity of the TPV at various blend ratios. SEM micrographs of 60/40 NR/ABS blend showed that vulcanized rubber domains were dispersed in a continuous ABS phase and it contributed to greater interfacial adhesion between the two phases and thus provided superior properties.

Epoxidized natural rubber/epoxy blends: Phase morphology and thermomechanical properties

ABSTRACTEpoxidized natural rubbers (ENRs) were prepared. ENRs with different concentrations of up to 20 wt % were used as modifiers for epoxy resin. The epoxy monomer was cured with nadic methyl anhydride as a hardener in the presence of N,N‐dimethyl benzyl amine as an accelerator. The addition of ENR to an anhydride hardener/epoxy monomer mixture gave rise to the formation of a phase‐separated structure consisting of rubber domains dispersed in the epoxy‐rich phase. The particle size increased with increasing ENR content. The phase separation was investigated by scanning electron microscopy and dynamic mechanical analysis. The viscoelastic behavior of the liquid‐rubber‐modified epoxy resin was also evaluated with dynamic mechanical analysis. The storage moduli, loss moduli, and tan δ values were determined for the blends of the epoxy resin with ENR. The effect of the addition of rubber on the glass‐transition temperature of the epoxy matrix was followed. The thermal stability of the ENR‐modified epoxy resin was studied with thermogravimetric analysis. Parameters such as the onset of degradation, maximum degradation temperature, and final degradation were not affected by the addition of ENR. The mechanical properties of the liquid‐natural‐rubber‐modified epoxy resin were measured in terms of the fracture toughness and impact strength. The maximum impact strength and fracture toughness were observed with 10 wt % ENR modified epoxy blends. Various toughening mechanisms responsible for the enhancement in toughness of the diglycidyl ether of the bisphenol A/ENR blends were investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39906.

Morphological analysis of high-impact polypropylene using X-ray microCT and AFM

Detailed visualization and understanding of high-impact polypropylene (hiPP) particle morphology and its evolution on the scale of entire particles is important for obtaining the required mechanical and optical properties of this material and for the quantitative description of mass transport in hiPP particles. Shape and size of hiPP particles as well as the spatial distribution of pores, PP homopolymer and ethylene-propylene rubber (EPR) phases in individual particles is visualized by micro-computed tomography (microCT) and atomic force microscopy (AFM) techniques. The morphology of each hiPP particle depends on many factors including catalyst system, the initial pore structure of porous catalyst and homopolymer particles, reactor conditions and particle history. These factors affect the required content, the constitution and the spatial distribution of EPR phase. To understand particle morphology and its evolution in a quantitative way we need a high-quality morphology data. The presented results include the AFM visualization of rubber layer on the surface of hiPP particles, the microCT visualization of not only porous homopolymer PP particles but also of large rubber domains in hiPP particles and the AFM mapping of the fine networked structure of EPR rubber and pores in hiPP particles.

Toughening plastics by crack growth inhibition through unidirectionally deformed soft inclusions

We demonstrate that without changing the filler content mechanical properties of commodity plastics with immiscible soft inclusions can be decisively enhanced, simply by pressure induced flow processing in the solid state. As an example, we have chosen acrylonitrile-butadiene-styrene (ABS), where shape and orientation of the soft fillers were changed by processing, resulting in an array of aligned and oriented nanosize deformed rubber domains. These deformed domains effectively controlled the propagation of cracks inside the solid matrix and were responsible for a multifold increase of tensile and impact toughness. Thus, appropriate processing allows manufacturing plastics with high impact resistance in accordance with engineering needs.

Influence of curing systems on dynamically cured epoxidized natural rubber/thermoplastic polyurethane blends

Dynamically cured 40/60 epoxidized natural rubber (ENR)/thermoplastic polyurethane (TPU) blends with peroxide and three different types of sulfur curing system were prepared using an internal mixer. It was found that the blends with peroxide exhibited higher modulus, mixing torque, mixing temperature, hardness, and shear viscosity than the blends with the sulfur-cured systems (i.e. conventional (CV), semiefficient (semi-EV), and efficient sulfur vulcanization (EV)). This is attributed to peroxide-caused cross-linking reaction in both ENR and TPU phases. Furthermore, it was found that the dynamically CV-cured blends exhibited higher thermal resistance, relaxation behavior, cross-link density, oil resistance, and mechanical strength than those of the semi-EV and EV-cured blends. The dynamically CV-cured blends also exhibited the smallest vulcanized rubber domains dispersed in the TPU matrix. This is due to higher levels of cross-link density in ENR phase and possibly higher interfacial attraction. On the other hand, it is difficult to identify the spherical rubber particle in the peroxide-cured blend due to cross-linking reaction that occurs in the TPU matrix.

Characterisation of Used PP-Based Car Bumpers and Their Recycling Properties

Three used PP-based car bumpers are characterized by many techniques (fractionation, IR, TGA, DSC, DMTA, and SEM). They show different impact and static and dynamic mechanical properties depending on their composition and morphology. It appears that block copolymer compatibilizers constituted by polyethylene-polypropylene sequences allow a better compatibility between the rubber domains and the PP matrix leading to relatively high impact resistance. Indeed if the ethylene sequences of the copolymer are large enough to crystallize, the decreased mobility of the whole system impairs the impact resistance. In addition, a higher amount of rubber in domains regular in shape and of greater dimension (1–3 μm) promotes a more homogeneous dispersion of external force inside the material, decreasing the risk of fracture. The amount of mineral fillers regulates the elastic modulus (the higher the load, the higher the modulus); however, a fairly good interfacial adhesion is required for satisfactory impact strength. All PP-based bumpers have been mechanically recycled in an internal mixer to redistribute oxidized species and to reestablish phase compatibilization. Recycling improves mechanical properties in slow speed test but fails to increase impact strength particularly in filled bumper, in which the quality of the matrix/filler interphase is hard to improve by simple remixing.

Opening and Closing of Nanocavities under Cyclic Loading in a Soft Nanocomposite Probed by Real-Time Small-Angle X-ray Scattering

The opening and closing of nanocavities in a model soft nanocomposite subjected to cyclic uniaxial tension were directly studied by real-time small-angle X-ray scattering (SAXS). The volume fraction and average shape of the nanocavities have been detected by a pronounced increase in the scattering invariant Q/Q0 and a detailed analysis of the scattering patterns. Cavities appear upon loading past an intrinsic stress σint or intrinsic elongation λint. Upon unloading, nanocavities are progressively closed until the volume void fraction ϕvoid reaches 0 for a constant “closure stress” of about 3.5 MPa. As the sample is reloaded, no cavities are observed when the current elongation remains below the maximum elongation of previous cycles λmax(N – 1) (N is the number of the cycles). Above this elongation, the void volume fraction ϕvoid of the sample increases again. In contrast with ϕvoid, the cumulative void volume fraction ϕcum_void appearing in the sample to reach a given maximum historical elongation, λmax, or equivalently maximum historical stress σmax, was found to be independent of loading history. Both results point toward a process of creation of nanovoids in confined rubber domains that have not previously cavitated rather than to the reopening of the previously created cavities. All critical cavitation parameters display a strong memory effect, mostly captured in this uniaxial test by the maximum historical stress or elongation. The closure stress probably results from the Laplace pressure. A mechanism based on the rearrangement of filler agglomerates by strong shear stress after the emergence of nanocavities is proposed to account for the formation and release of the local geometric confinement and the non-reopening of the previously opened nanovoids upon reloading.

Thermoplastic Natural Rubber Based on Blending of Co-Polyester: Effect of Amount of Epoxide Groups in Epoxidized Natural Rubber on Preperties

TPNRs based on blending of co-polyester (i.e., PBT/PC) and epoxidized natural rubber (ENR) with various epoxide content (i.e., 10, 20, 30, 40 and 50 mol% epoxide) were prepared by dynamic vulcanization. It was found that the co-polyester/ENR blends gave better properties (i.e., mechanical, dynamic mechanical, morphological and oil resistant properties) than that of co-polyester/unmodified NR blend. It was also found that co-polyester/ENR with 50 mol% epoxide exhibited the highest tensile strength, elongation at break, modulus at 100% elongation, hardness, storage modulus, complex viscosity and oil resistant properties but showed the lowest tension set value. This indicates the highest elasticity. Moreover, it was found that size of vulcanized rubber domains dispersed in thermoplastic matrix decreased with increasing the epoxide content in ENR molecules.

Effect of Curing System on Morphological, Rheological, Thermal and Mechanical Properties of Thermoplastic Vulcanizates Based on Epoxidized Natural Rubber and Polypropylene

Thermoplastic vulcanizates (TPVs) based on epoxidized natural rubber (ENR) and polypropylene (PP) were prepared in an internal mixer at 180°C. The effects of curing systems (i.e., sulfur and peroxide) on morphological, rheological, thermal and mechanical properties were studied. It is found that the sulfur cured TPVs show higher tensile strength, tear strength and elongation at break than those cured with the DCP systems. The rheological analysis indicates that TPVs cured with DCP system show lower apparent shear viscosity than those with sulfur system. SEM studies show that TPVs vulcanized with DCP system exhibit smaller and finely dispersed rubber domains, which provides it higher thermal stability than sulfur cured TPVs.

PLLA Microalloys Versus PLLA Nanoalloys: Preparation, Morphologies, and Properties

Nanostructured polymer blends have attracted significant attention recently. In this paper, the poly(lactic acid) (PLLA)/ethylene-co-acrylic ester-co-glycidyl methacrylate (E-AE-GMA) rubber (80/20) nanoalloys and microalloys were fabricated by melt blending and the structure-property relationships of the prepared alloys were investigated. In the nanoalloys, the rubber domains are homogeneously dispersed in the PLLA matrix with the overall domain size of <100 nm. Such nanoalloys exhibit not only high transparency in the visible region, but also significantly improved ductility and impact strength, compared with neat PLLA. Moreover, the nanodomains in the PLLA matrix enhance the crystallization rate of PLLA drastically. The overall crystallization rate of the PLLA nanoalloy is even higher than that of the PLLA nucleated by talc. In contrast, the PLLA microalloy has a phase structure with the size of the rubber domains being in the micrometer to submicrometer scale. The microalloy is opaque and displays almost the same tensile strength and modulus as the nanoalloy, but much higher impact strength than the nanoalloy.

Mechanical and rheological properties, and morphology of polyamide‐6/organoclay/elastomer nanocomposites

AbstractThe effects of ethylene‐methyl acrylate‐glycidyl methacrylate (E‐MA‐GMA) terpolymer and three types of organoclays (Cloisite® 15A, 25A, and 30B) on mechanical and rheological properties, and morphology of impact modified polyamide‐6/montmorillonite ternary nanocomposites were investigated by X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), parallel disk rheometry, melt flow index measurements, and tensile and impact tests. The materials were prepared by melt blending using a co‐rotating twin‐screw extruder. XRD and TEM analyses showed that exfoliated‐intercalated nanocomposites were formed in both polyamide‐6/Cloisite® 25A and Cloisite® 30B binary nanocomposites and in ternary systems. SEM micrographs showed that rubber domain sizes were larger in the nanocomposites than in their corresponding polyamide‐6/elastomer blends. Generally, tensile strength, Young's modulus, and elongation at break decreased with the addition of elastomer to polyamide‐6/organoclay binary nanocomposites. In the melt state, liquid‐like behavior of polyamide‐6 slightly turned to pseudo solid‐like in the binary and ternary nanocomposites. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Mechanical and dielectric properties of epoxy resin modified using reactive liquid rubber (HTPB)

AbstractIn the present study, hydroxyl‐terminated polybutadiene (HTPB) liquid rubber was employed to modify epoxy resin using 2,4,6‐tri (dimethylaminomethyl) phenol as a catalyst, and methyl hexahydrophthalic anhydride as a curing agent. The reactions between HTPB and epoxy were monitored by Fourier transform infrared (FTIR); the mechanical and dielectric properties of HTPB modified epoxies were evaluated and the morphology was investigated through scanning electronic microscopy (SEM). The FTIR analysis evidenced the occurrence of a chemical reaction between the two components. The mechanical results indicated that the impact strength of HTPB‐modified epoxy was superior to that of the pure epoxy. As the HTPB content increased up to 10 phr the best mechanical performances in terms of tensile and flexural properties were achieved when compared to the unmodified epoxy. Higher concentration of HTPB resulted in larger particles and gave lower mechanical strength values. The incorporation of HTPB into epoxy decreased the dielectric constant and dissipation factor over a wide frequency range from 1 to 106 Hz, and improved the electrical resistivity. SEM micrographs showed that the modified epoxy exhibited a two‐phase morphology where the spherical rubber domains were dispersed in the epoxy matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thermal degradation and crystallization behavior of blend‐based nanocomposites: Role of clay network formation

AbstractThe main goal of this study is to explicate the exact role of nanoclay particles on thermal degradation mechanism and crystallization behavior of blend‐based nanocomposites. Thermoplastic olefin (TPO) nanocomposites, as a simple model, were prepared via melt mixing in an internal batch mixer. X‐ray diffractometry (XRD) and transmission electron microscopy tests show that a relatively good dispersion of silicate layers was obtained in the system. On the addition of nanoclay, a remarkable reduction in rubber domain size was observed through scanning electron microscopy (SEM). Thermogravimetric analysis shows that nanoclay particles can retard thermal decomposition process. Thermal degradation kinetic studies, using Flynn–Wall–Ozawa method, reveal that addition of nanoclay contents higher than 1 wt % changes the mechanism of thermal degradation. A mechanism was proposed to explain this phenomenon based on SEM images of char residues. Non‐isothermal crystallization behavior of samples was investigated using differential scanning calorimeter. The unexpected reduction in crystallinity of TPO nanocomposites containing 5 wt % nanoclay was explained using rheometry analysis and attributed to the formation of stable percolated clay networks in this sample. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012