Rubber Phase Research Articles

Investigating the High- and Low-Temperature Performance of Warm Crumb Rubber–Modified Bituminous Binders Using Rheological Tests

Rubberized asphaltic materials have been frequently combined with warm-mix asphalt technologies to tackle the issues of high energy consumptions and emissions during construction. Effective and accurate characterization of binder properties is conducive to the improvement of long-term pavement performance. The current study aims to quantify the effects of rubber content and warm-mix additives on rutting and thermal cracking performance of crumb rubber-modified bitumen (CRMB), and explore the rubber and additives modification mechanisms and their impacts on the binder performance. CRMBs containing different rubber contents and warm-mix additives after long-term aging were subject to multiple stress creep and recovery (MSCR) tests and low-temperature frequency sweep tests using a dynamic shear rheometer (DSR) with 4-mm loading plate to investigate the high- and low-temperature performance, respectively. Rheological tests were also conducted on the bitumen and rubber phases of CRMB to understand the rubber modification mechanism. Results show that CRMB binders have superior rutting and thermal cracking resistance due to rubber modification. The improvement of high- or low-temperature performance is more prominent at higher rubber concentrations. The effects of warm-mix additives on the rutting and thermal cracking performance are different. Generally, the wax-based additive improves the rutting resistance but negatively affects the low-temperature performance. In contrast, the chemical-based additive has an opposite effect except for the high-temperature performance of neat bitumen. The stiffening of the bitumen phase and the contribution of swollen rubber particles in the bitumen matrix together contribute to the peculiar viscoelastic response of CRMB, i.e., stiffer/softer and more elastic at high/low temperatures. This modification mechanism explains the superior rutting and thermal cracking performance of CRMB.

Additivity of the mechanical properties for acrylonitrile‐butadiene‐styrene resins

AbstractAcrylonitrile‐butadiene‐styrene (ABS) resins have broad applications in automotive, transportation, and electronic industry attributed from their steadily tunable mechanical properties though varying compositions. It arises a question whether the additivity principle is applicable in their composition‐mechanical properties relationship. Here, we evaluated the applicability of the additivity principle for Young's modulus (YM), tensile strength (TS), and elongation at break (EB), based on a collection of 360 ABS resins from literatures and commercial products. We found that more than 90% of resins satisfy the additivity principle for YM and TS. While for EB, it varied from 14% to 100% depending on the combinations (A + B + S, AB + S, A + BS, or AS + B) and the contributed weights by mass, molar, or volume fractions. The majority of nonadditive resins have EB less than 20%, where the presence of the agglomeration of rubber phases, incompatible internal phases, cracks for those less ductile ABS resins are widely used qualitative and apparent reasons for the non‐predictable EB and the failure for the additivity principle. We then construct a classification model to distinguish the additive from nonadditive resins for EB, the area under the receiver operating characteristic curve (AUC) only achieves a fair value of 0.84. It further reveals that the fraction of acrylonitrile and butadiene, processing temperature, the length of spline, and the strain rate in the tensile test are important factors responsible for the failure of the additivity for EB. This study provides a quantitative reference to manipulate the mechanical properties for ABS resins beyond empirical evaluations.

Elastocaloric effect in vulcanized natural rubber and natural/wastes rubber blends

Vulcanized natural/wastes rubber blends were prepared and their elastocaloric properties were analysed. A thermodynamic frame was used to discriminate the contributions of thermoelastic effects and strain induced crystallization/melting. The substitution of 20 wt% of the natural rubber matrix by waste rubber particles resulted in a maintain and even a slight improvement of heat exchanges (+10%), that we ascribed to a (i) high thermoelastic effect and a (ii) a high ability of the natural rubber matrix to crystallize due to a nucleation ability of the waste particles, both resulting from a strain amplification in the rubber phase due to undeformable carbon black aggregates in the waste particles. The materials coefficient of performance, COPmat, was estimated equal to 4.4 for the neat natural rubber and 3.8 for the blend containing 20 wt% of wastes due to larger mechanical energy originated from reinforcing effect of waste particles. Nonetheless, the elastocaloric (eC) abilities of these materials, especially their wide temperature spans (similar to those in films or polycrystals using rare earth elements) make these natural/waste rubber blends good candidates for application such as heating/cooling machines. Moreover, the partial replacement of natural rubber, a bio-source material showing risks of shortage, by industrial wastes rubber, place these blends as promising eco-friendly materials with high added value.

Phase morphology, mechanical, and thermal properties of fiber-reinforced thermoplastic elastomer: Effects of blend composition and compatibilization.

In this work, recycled high density polyethylene (rHDPE) was compounded with regenerated tire rubber (RR) (35–80 wt.%) and reinforced with recycled tire textile fiber (RTF) (20 wt.%) as a first step. The materials were compounded by melt extrusion, injection molded, and characterized in terms of morphological, mechanical, physical, and thermal properties. Although, replacement of the rubber phase with RTF compensated for tensile/flexural moduli losses of rHDPE/RR/RTF blends because of the more rigid nature of fibers increasing the composites stiffness, the impact strength substantially decreased. So, a new approach is proposed for impact modification by adding a blend of maleic anhydride grafted polyethylene (MAPE)/RR (70/30) into a fiber-reinforced rubberized composite. As in this case, a more homogeneous distribution of the fillers was observed due to better compatibility between MAPE, rHDPE, and RR. The tensile properties were improved as the elongation at break increased up to 173% because of better interfacial adhesion. Impact modification of the resulting thermoplastic elastomer (TPE) composites based on rHDPE/(RR/MAPE)/RTF was successfully performed (improved toughness by 60%) via encapsulation of the rubber phase by MAPE forming a thick/soft interphase decreasing interfacial stress concentration slowing down fracture. Finally, the thermal stability of rubberized fiber-reinforced TPE also revealed the positive effect of MAPE addition on molecular entanglements and strong bonding yielding lower weight loss, while the microstructure and crystallinity degree did not significantly change up to 60 wt.% RR/MAPE (70/30).

Evaluation of mechanical properties of polypropylene – Acrylonitrile butadiene styrene blend reinforced with cowrie shell [Cypraeidae] powder

The urge to produce high-performance engineering products from the characteristic sustainable assets is growing continuously. Composite materials are amongst those versatile materials which combine the miscellaneous properties that can never be accomplished using the monolithic material. Nowadays, distinctive ecological issues are essentially influencing the advancements in material science and technology and there is a trend to investigate the capability of bio-fillers as the reinforcement phase for polymer matrix composites. The main impetus behind the use of natural resources is their renewability, biodegradable nature sometimes and importantly none of them impose any sort of adverse effect on the environment. Whereas sources of the synthetic reinforcing materials are limited and many of them cause environmental problems too. In this work, an attempt has been made to evaluate the potential of one such bio-filler, i.e., Cowrie Shell (CS) as a reinforcing phase for a polymer composite. Polypropylene (PP), Acrylonitrile-Butadiene Styrene (ABS) and CS Powder were used as a polymer, rubber phase copolymer and reinforcing filler respectively to prepare PP/ABS blend (80/20 wt%/wt%) and development of composite material. CS powder (of particle size − 90 µm & 150 µm) was prepared by crushing, grinding and sieving operations and was blended in five different ratios up to 15 wt% with PP/ABS. The characterization of mechanical behavior was done by carrying tensile, flexural, and impact tests. The results showed a steady improvement in the tensile, flexural and impact strength with increasing CS concentration having cost efficient application. The outcome of the Polypropylene-graft-maleic anhydride (PP-g-MA) compatibilizer addition was also studied which has shown a further increase in the mechanical properties.

Cover Image, Volume 139, Issue 3

This image, designed by António Faria in collaboration with the authors of this work (H.P. Diogo and J.J. Moura Ramos), flies over several aspects of poly (ether imide), PEI, from its molecular structure to the most current applications. It also slightly reveals TSDC experimental results that reflect different types of molecular mobility. The present work contains an in-depth TSDC investigation of the slow mobility in PEI in the glassy state, in the glass transformation region, and in the rubber phase. DOI: 10.1002/app.51568

Achieving morphological evolution and interfacial enhancement in fully degradable and supertough polylactide/polyurethane elastomer blends by interfacial stereocomplexation

The degradable polyurethane elastomers containing poly (L-lactide) (L-PU) and poly (D-lactide) (D-PU) were synthesized and incorporated in commercial PLLA as the toughening modifier. The stereocomplexation of PLA (sc-PLA) is successfully achieved at the interface of PU and PLLA domains in a single melt-blending process. The morphology and matrix crystallization in PLLA/D-PU blends is significantly improved by the presence of interfacial sc-PLA, showing morphological evolution to strip-shaped dispersion of PU phase and remarkable acceleration in matrix crystallization kinetics. After incorporating D-PU, the mechanical properties of blends are improved by interfacial sc-PLA, demonstrating that the notched Izod impact strength increases from 11.8 ± 3.1 KJ/m2 of PLLA/L-PU15 to 27.0 ± 5.8 KJ/m2 of PLLA/D-PU15 and even greater enhancement after thermal annealing is achieved. By observing the morphology of the impact fracture surface, the toughening mechanism of D-PU is investigated, revealing that the superior interfacial strength facilitates shear yielding of non-annealed sample and further prohibits de-bonding of rubber phase after thermal annealing. Hydrolysis tests in alkaline environment show that although interfacial sc-PLA can retard the hydrolysis rate, the blends still experience rapid weight loss to achieve full degradation. This work provides a highly effective strategy to toughen PLLA without sacrificing its degradability.

Cover Image, Volume 138, Issue 45

The cover image by Shin Horiuchi and co-authors shows how the distribution of nano-sized silica in binary rubber blends is characterized by scanning transmission electron microscopy (STEM) tomography, combined with energy dispersive X-ray spectrometry (EDX). 3D distribution of silica, is visualized by STEM-EDX tomography. The phase-separated morphologies of polyisoprene rubber (IR) and styrene-butadiene rubber (SBR) meanwhile is visualized by STEM-tomography in high-angleannular-dark field (HAADF) mode. The combination of STEM-EDX and STEM-HAADF tomography determines the distribution of silica between the two rubber phases quantitatively. The silica in IR (light blue) and in SBR (dark blue) phases can be identified as yellow and pink regions, respectively. DOI: 10.1002/app.51443

Effect of multiple extrusion on phase structure and properties of impact copolymerized polypropylene

As a typical multi-component polymer, impact polypropylene copolymer (IPC) experiences the phase structure evolution during repeated processing, and the coarsening of phase domain often occurs. In this work, two IPCs with different molecular weight of rubber phase were compared systemically. The evolution of IPC phase morphology and crystallization behavior after multiple extrusion were studied through scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The materials mechanical properties were tested. Then the influence of rubber phase molecular weight on the phase morphology evolution and the properties after repeated extrusion were discussed in detail. It was found that for the IPC with low molecular weight of rubber phase, the size of rubber phase became smaller and dispersed more evenly with the increase of extrusion times; for the IPC with high molecular weight of rubber phase, the rubber phase size turned to unstable after multiple shearing. The rubber phase size had a complex effect on IPC mechanical properties.

Spatial distribution of silica fillers in phase‐separated rubber blends investigated by three‐dimensional elemental mapping

AbstractThe distribution of nano‐sized silica in binary rubber blends is characterized by scanning transmission electron microscopy (STEM) tomography combined with energy dispersive X‐ray spectrometry (EDX). 3D distribution of silica is visualized by STEM‐EDX tomography with the tilt‐series of silicon elemental maps, while the phase‐separated morphologies of polyisoprene rubber (IR) and styrene‐butadiene rubber (SBR) are visualized by STEM‐tomography in high‐angle‐annular‐dark field (HAADF) mode. The combination of STEM‐EDX and STEM‐HAADF tomography enables us to determine the distribution of silica between the two rubber phases quantitatively even with high contents of silica up to 70 phr (weight parts per hundred rubber). It is found that silica is preferentially distributed in the SBR phase, but it is also distributed in the IR phase when the IR fraction in the total rubber components is higher than 40 wt%. The preferential distribution of silica in the SBR phase improves the dispersion of the IR domains. This is the first use of this technique for a multicomponent polymer system, showing the advantage to characterize the complicated multicomponent polymer composite morphologies.

Payne effect of carbon black filled natural rubber nanocomposites: Influences of extraction, crosslinking, and swelling

Rubber nanocomposites experiencing dynamic shears at large strain amplitudes (γ) exhibit the nonlinear Payne effect featured by decays of storage and loss moduli (G′ and G″) or by G′ decay accompanied with G″ overshoot near a critical strain amplitude. The occurrence of the Payne effect has been assigned to damages of “filler network” and rubber-filler interfacial interactions for a long time and to Rouse dynamics of rubber chains recently. To solve the dispute, influences of extraction, crosslinking, and paraffin swelling on the Payne effect of carbon black filled natural rubber nanocomposites are investigated systematically. Master curves of G′ as a function of γ could be always created, and overshoot of G″ in the filled vulcanizates weakens with increasing filler content and intensifies by dilution via paraffin swelling, suggesting that the Payne effect is not mainly rooted in the “filler network” and rubber-filler interfacial interactions. The filler reduces the onset strain amplitude of the Payne effect by amplifying microscopic strain amplitude of the rubber phase, irrespective of whether the matrix is crosslinked or not and whether the crosslinked matrix is swollen or not. Partial removal of bound rubber by compounding the paraffin swollen compounds could lower modulus and eliminate G″ overshoot of the deswollen vulcanizates without influence on the mechanism of G′ decay accompanying Payne effect. The overshoot is found to be closely related to the overall viscous characteristic of the vulcanizates in the linear viscoelastic regime. Provided herein are new insights for recognizing the important roles of the viscoelastic rubber phase on the Payne effect of the nanocomposites.

Development of Photosensitive Natural Rubber as a Mechanical Modifier for Ultraviolet-Curable Resin Applied in Digital Light Processing-Based Three-Dimensional Printing Technology.

Natural rubber (NR), a natural product from the Hevea brasiliensis tree, has been developed as a photosensitive mechanical modifier utilized in lithography-based three-dimensional (3D) printing technology. Here, we transformed NR to photosensitive NR (PNR) by incorporating acrylate groups via chemical modifications. The acrylated NR was blended with a commercial resin (CR) at various rubber contents (0 to 3 wt %) by a simple mixing approach. The blended resin was solidified to pattern the desired specimen using a digital light processing-based 3D printer. The effect of PNR contents on mechanical properties and thermal performance of the printed specimen compared to the neat CR was studied in this work. A printed sample containing 1.5 wt % PNR can increase the elongation ability and impact strength by approximately 59 and 116%, respectively, compared to the neat CR. The microstructure of the printed objects shows a heterogeneous surface consisting of dispersed rubber droplets and a continuous CR matrix. Two glass transition temperatures belonging to the rubber phase and the resin matrix can be observed. The thermal decomposition of the printed part decreased slightly with the elevation in the rubber content. Consequently, the synthesized photosensitive natural rubber could be used as a toughness modifier employed in ultraviolet-curable resin for the light-based 3D printing technology.

Poly(lactic acid) (PLA)/Poly(butylene succinate-co-adipate) (PBSA) Compatibilized Binary Biobased Blends: Melt Fluidity, Morphological, Thermo-Mechanical and Micromechanical Analysis.

In this work poly(lactic) acid (PLA)/poly(butylene succinate-co-adipate) (PBSA) biobased binary blends were investigated. PLA/PBSA mixtures with different compositions of PBSA (from 15 up to 40 wt.%) were produced by twin screw-extrusion. A first screening study was performed on these blends that were characterized from the melt fluidity, morphological and thermo-mechanical point of view. Starting from the obtained results, the effect of an epoxy oligomer (EO) (added at 2 wt.%) was further investigated. In this case a novel approach was introduced studying the micromechanical deformation processes by dilatometric uniaxial tensile tests, carried out with a videoextensometer. The characterization was then completed adopting the elasto-plastic fracture approach, by the measurement of the capability of the selected blends to absorb energy at a slow rate. The obtained results showed that EO acts as a good compatibilizer, improving the compatibility of the rubber phase into the PLA matrix. Dilatometric results showed different micromechanical responses for the 80–20 and 60–40 blends (probably linked to the different morphology). The 80–20 showed a cavitational behavior while the 60–40 a deviatoric one. It has been observed that while the addition of EO does not alter the micromechanical response of the 60–40 blend, it profoundly changes the response of the 80–20, that passed to a deviatoric behavior with the EO addition.

Investigation on micro-structure of self-compacting concrete modified by recycled grinded tire rubber based on X-ray computed tomography technology

Abstract Micro-structural properties of the cement-based materials are important factors affecting the mechanical behavior. In this investigation, based on the non-destructive testing technology (NDT) of X-ray computed tomography, the micro-structural properties of self-compacting concrete modified by recycled ground tire rubber as partial replacement of fine aggregate are researched. The CT slice images are segmented effectively by a combined method of thresholding and K-means clustering. Based on the segmented slice images, the specimens are 3D reconstructed. The variations of the volume fraction, surface area and distributing characteristic of the pore and rubber phase are investigated. Moreover, a fractal analysis is conducted to characterize the micro-structural properties of RSCC. It provides a uniform criterion to characterize the micro-structural characteristics of pore phase and rubber phase.

Constitutive model for epoxy shape memory polymer with regulable phase transition temperature

ABSTRACT The epoxy shape memory polymer (SMP) with adjustable phase transition temperature is a kind of high-performance shape memory polymer, which can change its phase transition temperature and improve its mechanical properties through the process of photo curing. An epoxy SMP constitutive model combining phase transition and viscoelasticity is established by discretizing the epoxy SMP into several glass phase units and rubbery phase units in this paper. The model includes the viscoelastic constitutive equations of glass phase units and rubber phase units, the parameter expression during shape memory process, and material parameter equation during photocuring process. And the stress relaxation behavior of epoxy SMP at different temperatures and the change of material parameters during the photo-curing process are simulated numerically, and the simulation results perform consistency with the experimental data. The model can not only relate shape memory effect and phase transformation in physics but also better characterize the viscoelastic properties of SMP and predict the shape memory response of SMP.

Modified natural rubber glove with spent coffee grounds for prothesis arm cover

In this research, we developed modified rubber gloves that could cover prosthetic arms manufactured from Fused Deposition Modeling (FDM) 3D printing. FDM can produce customized prosthetic arms that are lightweight and fit the individual needs of patients. Currently, the gloves used to cover prosthetic arms are made from flexible and soft material such as silicone or polyurethane. In these studies, were use natural rubber latex (NR) to produce rubber gloves, that enhance the physical appearance of the prosthetic arm, producing a similar color and detail to the patients arm. The glove color was improved by mixing with spent coffee grounds (SCG) to produce a similar color to that of natural human skin. Moreover, SCG was not only used as a color pigment, it also contains coffee oil that creates a glossy textured on the surface similar to silicone oil. The modification process of NR used a SCG dispersion solution mixed with NR. Rubber gloves were prepared by a dipping process and use sulfur vulcanization at 75 °C, for 2 h in a hot air oven. The specimens were characterization by physical (morphology, color parameter, and %swelling), mechanical (tensile test) and thermal properties. Furthermore, the SCG can be used as a filler in natural rubber due to rubber-filler interactions that improve the tensile strength of the rubber glove with the SCG particles having a good distribution in the rubber phase. The SCG can improve the ageing stability (under 70 °C and Fluorescent light) of the rubber gloves as represented by the color parameter and tensile properties. After ageing showed a small difference in color parameter and a slight decrease in the tensile properties when greater amounts of SCG was presented in the rubber phase. Moreover, this can increase the economic value of natural rubber and spent coffee grounds in Thailand.

Reaction kinetics and properties of MDI base poly (urethane-isocyanurate) network polymers

ABSTRACT Since the trimerization of isocyanate occurs easily and controllably to form a clear trifunctional isocyanate ring, this reaction is an ideal candidate for the synthesis of a clear poly(urethane-isocyanurate) network polymer. Poly(urethane-isocyanurate) network polymer (PUI) was prepared from diphenylmethane diisocyanate (MDI) and propylene glycol (PPG) by cyclotrimerization of isocyanate group (NCO). It was proved that the expected product was successfully prepared by NCO determination, fourier transform infrared (FTIR) and gel permeation chromatography (GPC) characterization. The mechanical and thermal properties were characterized. Through the effects of catalyst dosage, polyurethane prepolymer molecular weight, reaction time, reaction temperature and MDI addition on the reaction process, it is determined that under certain other conditions, the step heating method is better for cyclotrimerization reaction. Generally, the better heating conditions are 60 °C/1 h + 80 °C/4 h + 100 °C/2 h + 120 °C/2 h + 140 °C/2 h + 160 °C/2 h. The results of thermogravimetric analysis (TGA) and mechanical properties showed that with the increase of cross-linking points in the polymer structure, the thermal stability, tensile strength, tensile modulus and hardness of PUI increased, while the elongation at break decreased significantly. The glass transition temperature (Tg) of PUI is around 45 °C, and it can be seen that the elastic modulus of the material can range from 58 to 1980 MPa. X-ray diffraction results show that the rubber phase represented by the flexible segment and the plastic phase represented by the rigid structure are amorphous.

Study on Shape Memory Behavior of Ternary Poly(Lactic Acid)/Poly(Methyl Methacrylate)-grafted Natural Rubber/Natural Rubber Thermoplastic Vulcanizates

ABSTRACT Here, poly(lactic acid) (PLA)/poly(methyl methacrylate)-grafted natural rubber (NR-PMMA)/natural rubber (NR) ternary blends with co-continuous phase structure were prepared via peroxide-induced dynamic vulcanization. The good compatibility between NR-PMMA with PLA and NR and the interfacial grafting reaction during the preparation process ameliorated the interfacial compatibility between the phases. Therefore, the energy stored in the rubber phases could be effectively transferred to PLA, thus achieving an excellent shape-memory effect even under-repeated shape-memory cycles. Furthermore, by adding 10 wt% NR-PMMA, the TPVs exhibited improved impact strength and tensile strength up to 98.05 kJ/m2 and 45.2 MPa, respectively.

NMR Studies on the Phase-Resolved Evolution of Cross-Link Densities in Thermo-Oxidatively Aged Elastomer Blends

A knowledge of the distribution of cross-link densities (CDs) in the constituent rubber phases of an elastomer blend is essential to understand its overall service properties, but phase-resolved CD estimations have so far been limited to qualitative assessments. In a first study of its kind, we demonstrate a phase-resolved quantification of the CDs in sulfur-cured blends of natural rubber (NR) and styrene–butadiene rubber (SBR) using solid-state ¹H homonuclear dipolar double-quantum (DQ) magic-angle spinning (MAS) NMR spectroscopy. The blends were also subjected to prolonged thermo-oxidative aging to monitor the chemical changes in the two phases. Analyses of the residual dipolar coupling constant (Dᵣₑₛ), arising due to spatial restrictions by cross-links to molecular motions, as observed in MAS and static ¹H DQ experiments, suggest that unaged NR and SBR cross-link to similar extents. A minimum in Dᵣₑₛ after around 500 h of aging duration is observed in NR, associated with the formation of highly mobile defect fractions, as seen from free induction decay (FID) combined with transverse relaxometry, with further cross-linking up to 1000 h. SBR appears more stable, with a gradual increase in Dᵣₑₛ over the aging duration. Phase-resolved experiments reveal a somewhat less cross-linked SBR phase in an unaged 50:50 blend. The phase-specific distribution of CDs in the blend phases becomes significant upon aging, which suggests that NR ages more strongly in the blend as compared to the aged single vulcanisates, thus dictating the blend properties.

Melt fracture and wall slip of thermoplastic vulcanizates

AbstractThermoplastic vulcanizates (TPVs) are blends of polypropylene (PP) (thermoplastic phase) and ethylene propylene diene monomer (EPDM) rubber (rubber phase) in which a high content of rubber EPDM is cross‐linked and dispersed in a thermoplastic matrix (PP) in the presence of oil (lubricant) and filler. Depending on the molecular characteristics of the constituent polymers, the level of curing and the amount of cross‐linked rubber, their processing (extrusion) exhibits various difficulties such as melt fracture (extrudate distortions). In this study, a number of different TPVs with various characteristics, including the degree of curing and amount of cross‐linked rubber are examined in capillary extrusion at two different temperatures (190°C and 205°C) relevant to real processing. First, the effect of the temperature on the yield stress is investigated using rheological measurements. Consequently, the flow behavior of the TPVs in capillary flow is studied concluding that TPVs slip massively (nearly plug flow) due to the presence of lubricant and the vulcanized rubber phase. Although there is little slip observed in PP samples, EPDMs themselves exhibit severe slip and melt fracture. As a consequence, the TPV samples essentially follow the slip behavior of EPDMs. Finally, the melt fracture analysis of several TPVs has shown that with increase of temperature and amount of cross‐linked rubber, the severity of TPVs' surface defects increases accordingly.