Ethylene Propylene Diene Monomer Composites Research Articles

Enhancing Thermal Insulation of EPDM Ablators via Constructing Alternating Planar Architectures.

Ethylene–propylene–diene monomer (EPDM) composites were usually enhanced with ablative additives to protect solid rocket motor (SRMs) casings. However, the poor thermal insulation caused by the high thermal conductive ablative fillers can lead to rocket motor failure. Herein, the novel EPDM composites containing alternating layers of ablative EPDM (AM) and heat-insulated EPDM (HM) were prepared through layer-multiplying extrusion. Compared with conventional EPDM ablative material, the multilayer composites showed enhanced thermal insulation and mechanical properties that could be further improved by tuning the number of layers. The ablation and thermal insulation properties possessing in AM and HM layers could be combined by forced assembly during co-extrusion, and the alternating multilayer composite was capable of showing the effect of each component. In particular, compared with AM, the maximum back-face temperature with 40 alternating layers of AM/HM decreased from 96.2 °C to 75.6 °C during oxyacetylene test, while the good ablation properties were preserved in the AM component. This significant improvement was attributed to the planar orientation and densification of ablative additives, and the interruption of conductive pathways in the through-plane direction of AM/HM alternating laminate. The anisotropic EPDM composites featuring mechanical robustness, good ablative resistance and thermal insulation suggest considerable potential application in the aerospace industry.

Study on Thermal-Oxidative Aging Properties of Ethylene-Propylene-Diene Monomer Composites Filled with Silica and Carbon Nanotubes.

In this work, a small amount of carbon nanotubes (CNTs) was used to partially replace the silica in ethylene-propylene-diene monomer (EPDM) to prepare EPDM composites via mechanical blending. The mechanical properties, thermal-oxidative aging properties and thermal stability of the composites were systematically investigated. The results showed that with the increase of CNTs content, the Shore A hardness and stress at 100% strain of the composites increased, while the elongation at break decreased. With the aging time increasing, the aging coefficient and elongation at break of composites decreased while hardness increased due to the raise of crosslinking density. In addition, evidences were found to demonstrate the improved aging resistance by adding CNTs in the EPDM composites, including the less change in Shore A hardness, the smaller change ratio of elongation at break and the lower aging coefficient. When the content of CNTs reached 10 phr, the aging coefficient of the EPDM composite aged for 168 h was nearly twice that of the composite without CNTs, and the thermal stability of the EPDM composite with CNTs was improved as demonstrated by thermal analysis.

Filler Influence on H2 Permeation Properties in Sulfur-CrossLinked Ethylene Propylene Diene Monomer Polymers Blended with Different Concentrations of Carbon Black and Silica Fillers.

Filler effects on H2 permeation properties in sulfur-crosslinked ethylene propylene diene monomer (EPDM) polymers blended with two kinds of carbon black (CB) and silica fillers at different contents of 20 phr–60 phr are investigated by employing volumetric analysis in the pressure exposure range of 1.2 MPa~9.0 MPa. A linear relationship is observed between the sorbed amount and pressure for H2 gas, which is indicative of Henry’s law behavior. The hydrogen solubility of EPDM composites increases linearly with increasing filler content. The magnitude of hydrogen solubility for the filled EPDM composites is dependent on the filler type. The hydrogen solubility is divided into two contributions: hydrogen absorption in the EPDM polymer and hydrogen adsorption at the filler surface. Neat EPDM reveals pressure-dependent bulk diffusion behavior. However, with increasing filler content, the diffusivity for the filled EPDM composites is found to be independent of pressure. The magnitude of filler effects on the hydrogen permeation parameter is measured in the order of high abrasion furnace CB~semireinforcing furnace CB ˃ silica, whose effect is related to the specific surface area of CB particles and interfacial structure. The correlation between the permeation parameters and filler content (or crosslink density) is discussed.

Role of polymer‐filler interaction on Mg(OH)2 and alumina trihydrate‐loaded ethylene propylene diene monomer based polymer composite for high voltage insulation application

AbstractUse of polymer composite as a high voltage insulator material is currently under investigation for its commercial application, longer durability, and cost effectiveness. This work probes the effect of polymer‐filler interaction on mechanical, morphological, thermal and dielectric properties of ethylene propylene diene monomer (EPDM) based polymer composite. EPDM composites were successfully prepared using two roll‐mill and vulcanized in a hot press compression mold. Surface morphology indicates uniform dispersion of filler at lower filler loading, whereas at higher loading cluster/agglomeration was observed. 30 phr magnesium hydroxide (Mg(OH)2) loaded sample showed the highest static contact angle of 102.3°. Mg(OH)2 based samples show higher tensile strength because of strong interfacial interaction between filler and polymer. In addition, alumina trihydrate (ATH) and Mg(OH)2 based composite exhibit high thermal stability with initial thermal degradation temperature of ~200 and ~320°C, respectively. FTIR spectrum reveals the formation of strong –OH bonds between Mg(OH)2 and polymer molecules. A maximum enhancement in dielectric breakdown strength of ~50% and ~30% were recorded for 60 phr ATH and 30 phr Mg(OH)2 loaded EPDM composites respectively. Finally, the results indicate a strong possibility of developing EPDM based polymer composites as an efficient high voltage insulator.

Effects of inorganic nanofibers and high char yield fillers on char layer structure and ablation resistance of ethylene propylene diene monomer composites

Influences of fillers [including multi-walled carbon nanotubes (MWCNTs), SiC nanowires, methyl-polyhedral oligomeric silsesquioxanes (methyl-POSS) and boron phenolic resin] on the characteristics of porous structure in char layers of ethylene propylene diene monomer (EPDM) composites were studied using experimental solid rocket motor (SRM). Comparing to basic formulation (Porosity: 78.25%), char layers of fillers formulation present lower porosity (Ranging from 64.03% to 67.69%) and showed significant trends of overall or local densification. Further analysis revealed different densification mechanisms: CNTs and SiC nanowires can promote chemical vapor deposition (CVD) reaction in char layers and reduce its porosity, which can be referred as “CVD-promotion densification”; boron phenolic resin is relatively high in char yield and char residue would densify the microstructure of char layers, which can be referred as “char residue densification”; methyl-POSS show a combination of both mechanisms, which lead to the lowest mass ablation rate [170.4 g/(m2·s)] and the best ablation performance.

Effects of carbon nanotubes on char structure and heat transfer in ethylene propylene diene monomer composites at high temperature

Owing to their high thermal conductivities, the direct addition of carbon nanotubes (CNTs) as fillers for ablative insulation materials inevitably has a deleterious effect on the performance of the obtained composites. However, this paper found that CNTs could reduce the thermal conductivity of the char layer skeleton of ethylene propylene diene monomer (EPDM) composites at high temperature. In this study, the ablation characteristics of EPDM composites with CNTs were tested using an ablation test motor. The results show that CNTs can reduce the ablation rates and the thermal conductivity of the char layer skeleton of the composites at high temperature. CNTs promote vapor deposition of pyrolysis gases, and a layer of pyrolytic carbon is formed on the surface of CNTs. As a result, the structure of the char layer becomes denser, and the thermal conductivity of the char layer skeleton decreases.

EPDM with Biochar, Carbon Black, Aramid Pulp and Ionic Liquid-compatibilized Aramid Pulp

Carbon black (CB) is a fossil fuel-derived product widely used as reinforcement in the rubber industry despite its pollution potential and its high energy-demanding production. Biochar, on the other hand, is a renewable source of carbon recently studied for the partial substitution of CB in elastomeric materials. Aramid pulp/fibers have also been used in a variety of applications in this sector, usually after a surface treatment. In this work, the use of aramid pulp (AP) and biochar in the preparation of ethylene propylene diene monomer (EPDM) composites and hybrid composites has been studied. The 1-n-butyl-3-methylimidazolium methanesulfonate ionic liquid (IL) was used as compatibilizer in AP, and the rubber-filler interaction was studied via thermal, rheometric, mechanical, and swelling analyses. The biochar-EPDM and the reference CB-EDPM compounds showed similar hardness, modulus at 50 % strain and tear strength results. Among the tested fillers, AP was identified as the most effective to obtain EPDM composites with enhanced properties. A synergistic effect of biochar and IL-treated AP was found, resulting in higher tensile strength for the hybrid formulation (EPDM/Bio05AP05IL) compared to those with just biochar or CB, and reasonable strain at break. In all, the hybrid composites of EPDM reinforced with biochar and AP showed the potential to partially or fully replace CB formulations.

Tuning the Ablation, Thermal and Mechanical Characteristics of Phenolic Resin Reinforced EPDM Ultra-High Temperature Insulation

The present research reports the influences of variant phenolic resin concentrations on the thermo-mechanical and ablation characteristics of ethylene propylene diene monomer (EPDM) elastomer. Backface temperature acclivity (BTA), charring rates, and insulation indexes were executed for the fabricated composite specimens. It was noticed that BTA was enhanced while linear/radial/mass ablation rates were significantly diminished with increasing concentration of phenolic resin (PR) in base matrix (elastomeric polymer). The composite (30wt%PR/EPDM) has 25% high thermal endurance compared to virgin EPDM composite. Thermal conductivity was increased with increasing PR to EPDM ratio. PR incorporation has remarkably enhanced the ultimate tensile strength of the EPDM elastomer. An efficient improvement in elastomeric hardness was also observed with increasing PR contents in EPDM matrix. Scanning Electron Microscopy (SEM) results showed the porosity generation and polymer melting during ablation.

Influence of composite structure design on the ablation performance of ethylene propylene diene monomer composites

Abstract By introducing functional fillers into the ethylene propylene diene monomer matrix, the anti-ablation, thermal insulation, and adhesive layer were prepared, respectively. We have studied the mechanical properties, ablation properties, thermal insulation properties, and bonding properties of different composite structures after design and analyzed the ceramic mechanism. The results showed that the content of ceramic fillers improved the thermal stability and ablation properties of anti-ablation layer composites. The formation of liquid structure can fill the hole defects and ablation pit. The foaming agent improved thermal insulation properties of the thermal insulation layer, and the strength of the bonding layer has been greatly improved. The design of the composite structure can not only reduce the density but also have an excellent thermal insulation effect. And as the thickness of the heat insulation layer increases, the heat blocking effect becomes more excellent.

Ethylene‐propylene diene monomer‐based polymer composite for attenuation of high energy radiations

AbstractRadiation shielding composites of ethylene‐propylene diene monomer (EPDM), reinforced with tungsten (W) and barium sulphate (BaSO4) in different filler weight (wt%) were synthesized. The effects of W and BaSO4 on gamma and neutron attenuation properties of the composites were studied by experimental methods using 137Cs, 60Co and 252Cf radioactive sources. EPDM composites with W and BaSO4 fillers were also investigated for filler dispersion using scanning electron microscopy and X‐ray radiograph. The experimental results revealed that the incorporation of W and BaSO4 significantly improved the radiation attenuation properties of the EPDM composites. It was observed that the attenuation properties of the composite material increases with higher concentration of the filler. The half‐value layer (HVL), tenth value layer thickness and relaxation length of the composites were found to decrease with increasing concentration of the filler. The results also showed that the attenuation behaviour of 50 wt% BaSO4 filled polymer composite is comparable to that of the composite with 25 wt% W. The developed composite with 75 wt% W filler exhibited the maximum radiation attenuation with lowest HVL thicknesses.

Mechanical, flame‐retarding, and creep‐recovery proprieties of ethylene–propylene–diene monomer enhanced with nano‐hydroxide for undersea tunnel sealing gasket

AbstractThis study investigates the mechanical, flame‐retarding, and creep‐recovery proprieties of ethylene–propylene–diene monomer (EPDM) composites. The EPDM composites are filled with different contents of nano‐Mg(OH)2 (NMH) or nano‐Al(OH)3 (NATH). To examine the effect of contents of NMH (or NATH) and seawater immersion, mechanical tests are conducted and the limiting oxygen index (LOI) method was applied. Creep‐recovery tests are then conducted to obtain the creep resistance property of EPDM composites with contents of NMH (or NATH). The microstructure of EPDM composites is investigated by using scanning electron microscopy (SEM). The results indicate that NMH (or NATH) can enhance the flame‐retarding, creep resistance, and hardness properties, whereas tensile strength and elongation at break increase at first and then decrease with increasing content of NMH (or NATH). The Findley power law and the Weibull distribution function show good correspondence with the results of creep‐recovery tests for EPDM composites. Furthermore, SEM results show good interfaces between nanoparticles and the matrix implying the mechanism of the above results.

Carbon nanotube reinforced ablative material for thermal protection system with superior resistance to high-temperature dense particle erosion

The ablation rate of thermal protection system (TPS) material increases significantly in particle erosion environment, which can cause the spacecraft to fail in severe cases. Developing TPS material resistant to particle erosion can improve the performance and reliability of future spacecraft. This paper uses a particle erosion test motor to build the particle erosion environment, and evaluates the particle erosion resistance of ethylene propylene diene monomer composites with carbon nanotubes (CNTs). The structure and properties of char layer after the ablation experiment are studied. The results show that CNT-reinforced composites exhibit superior resistance to high-temperature dense particle erosion, and the charring rate is 68.0% lower than that without CNTs. The superior reinforcement of CNTs in erosion resistance found in this paper points the direction for the research and development of CNT reinforced TPS material.

Silica and modified silica fume waste (mSF) as reinforcing fillers for rubber industry

Purpose The purpose of this paper is to evaluate the efficiency of commercial silica, silica fume-waste (SF) and modified silica fume-waste (mSF) as reinforcing filler in acrylonitrile-butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM) through the mixing process of rubber. The composites were prepared using different loadings of silica fume and commercial silica in EPDM and NBR composites. Structural characterization of silica and SF was done using X-ray fluorescence and scanning electron microscopy (SEM). The surface of silica fume waste was modified using poly methyl methacrylate/butyl acrylate through emulsion polymerization to increase the interaction between silica and rubber, then consequently better dispersion in rubber matrix was obtained. The mSF waste was characterized using FT-IR spectra and transmission electron microscopy. Design/methodology/approach The investigated rubber mixes and vulcanizates were evaluated by measuring the curing characteristics, mechanical testing, thermogravimetric analysis and morphological studies (SEM). The mechanical properties of composites including tensile strength, elongation at break and modulus were estimated and analyzed. Findings The results revealed that the composites (NBR and EPDM) containing mSF as filler exhibited better rheological and mechanical properties compared to unmodified silica waste and commercial silica. The SEM analysis indicated that the mSF was homogeneously dispersed through the surface of NBR and EPDM composites. Also, results showed that (NBR and EPDM) composites exhibited remarkable improvements in tensile strength, elongation at break and hardness in the presence of mSF; they also showed an increase in the thermal stability. This means that the treatment of surface SF can improve its dispersion in rubber. Research limitations/implications Silica cannot be applied in rubber matrix without surface modification because of their incompatibility; their dispersion is not good without surface modification. Practical implications The modified silica surface is considered as effective reinforcing filler which can replace other fillers because of its lower surface energy and enhanced intercalating behavior in rubber. Social implications This study is just a start in establishing rubber projects with wide applications in the industry and providing a cheap local product while preserving the quality and that is the use of factory waste, which helps in protecting the environment from pollution. Originality/value mSF is cheap with relatively high purity, which make rubber/mSF composites appear as new grade of material that can be used in different media rather than rubber.

Improved Self-Supporting and Ceramifiable Properties of Ceramifiable EPDM Composites by Adding Aramid Fiber.

Ceramifiable ethylene propylene diene monomer (EPDM) composites with fiber network structures were prepared by using aramid fiber (AF), ammonium polyphosphate (APP), and silicate glass frits (SGF). The effect of AF on the curing characteristic of the ceramifiable EPDM composites was studied. The morphology of AF in the composites system was observed by optical microscopy (OM) and scanning electron microscope (SEM). The effects of the observed AF network structures on the solvent resistance, mechanical properties, ablative resistance, self-supporting property, and ceramifiable properties of the composites were investigated. Results suggested that the existence of the AF network structure improved the vulcanization properties, solvent resistance, thermal stability, and ablative resistance of the EPDM composites. An excellent self-supporting property of the EPDM composites was obtained by combining the formation of the AF network and the formation of crystalline phases at higher temperature (above 600 °C). The thermal shrinkage performance of AF and the increased thermal stability of the EPDM composites improved the ceramifiable properties of the EPDM composites.

Improved Viscoelastic Damping Properties of Carbon Black Reinforced EPDM Composites by Blending with ENR

EPDM/ENR blends were prepared from saturated nonpolar ethylene propylene diene monomer (EPDM) and unsaturated epoxidized natural rubber (ENR). The dynamic mechanical properties of EPDM/ENR compounds and their vulcanizates were studied by rubber processing analyzer and dynamic mechanical thermal analyzer. The results show that the addition of ENR is helpful to improve EPDM processability. With the increase of ENR content, the tensile strength of EPDM/ENR decreases first and then increases while the elongation at break increases. The lowest tensile strength is still greater than 12.5MPa, which shows the industrial usage. The temperature range for the loss factor being greater than 0.1 becomes wider from -40.1 ˚C ~ 7.7 ˚C for pure EPDM to -40.1 ˚C ~ 80 ˚C for 80 : 20 EPDM/ENR.

Heat dissipative mechanical damping properties of EPDM rubber composites including hybrid fillers of aluminium nitride and boron nitride.

As highly integrated electronic devices and automotive parts are becoming used in high-power and load-bearing systems, thermal conductivity and mechanical damping properties have become critical factors. In this study, we applied two different fillers of aluminium nitride (AlN) and boron nitride (BN), having polygonal and platelet shapes, respectively, into ethylene-propylene-diene monomer (EPDM) rubber to ensure improved thermo-mechanical properties of EPDM composites. These two different shapes are considered advantageous in providing effective pathways of phonon transfer as well as facilitating sliding movement of packed particles. When the volume ratio of AlN : BN was 1 : 1, the thermal conductivity of the hybrid-filler system (EPDM/AlN/BN) increased in comparison to that of the single-filler system (EPDM/AlN) of 3.03 to 4.76 W m-1 K-1. The coefficient of thermal expansion (CTE) and thermal distortion parameter (TDP) substantially decreased from 59.3 ppm °C-1 and 17.5 m K-1 of EPDM/AlN, to 39.7 ppm °C-1 and 8.4 m K-1 of EPDM/AlN/BN, representing reductions of 33 and 52%, respectively. Moreover, the damping coefficient of EPDM/AlN/BN was greatly increased to 0.5 of at 50 °C, compared to 0.03 of neat EPDM. These excellent performances likely stem from the effective packing of AlN/BN hybrid fillers, which could induce facile energy transfer and effective energy dissipation by the sliding movement of the adjacent hybrid fillers in the EPDM matrix.

Effects of multi-walled carbon nanotubes on char residue and carbothermal reduction reaction in ethylene propylene diene monomer composites at high temperature

Mechanistic investigation of the effect of nanofillers on the ablation of composites is essential to meet the demand for high-performance ablative composites. Ethylene propylene diene monomer (EPDM) composites with and without 5 wt% multi-walled carbon nanotubes (MWCNTs) are prepared, and their ablation rates are tested using a solid rocket motor. The carbothermal reduction reaction during ablation is studied using a high-temperature tube furnace. The carbothermal reduction reaction of silica at high temperature results in a large consumption of char, and is an important reaction affecting the ablation process. The addition of MWCNTs increases the char residue of EPDM composites. MWCNTs can enhance the rate-limiting reaction, thereby reducing the released gas and increasing the production of SiC. The network structure of MWCNTs in char has a directional effect on the in-situ formation of SiCw, which can improve the ablation resistance of composite.

A study on dispersions of CB and CNT in PP/EPDM composites and their mechanical reinforcement

Carbon material (carbon black (CB) and carbon nanotube (CNT)-reinforced composites are being studied widely. The content of the reinforcing materials is known as the main influencing factor. However, the dispersion of the reinforcing materials is often neglected or, where it is investigated, not thoroughly evaluated. In this article, the dispersion states of carbon materials in the composite materials were quantitatively analyzed using an image processing method. Meanwhile, the reliability of the image analysis was verified through the testing results of the mechanical and rheological properties of the composites. Both CB and CNTs improved the mechanical properties of maleic anhydride-grafted polypropylene (PP)/ethylene propylene diene monomer composites, wherein their dispersion was the dominant factor instead of their content. The dispersion of the easily agglomerated CNT was significantly poorer than that of CB. Therefore, CB was better in inducing the crystallization of PP.

Effect of micro-nano additives on breakdown, surface tracking and mechanical performance of ethylene propylene diene monomer for high voltage insulation

Ethylene propylene diene monomer (EPDM) is a polymer widely used for insulation in high voltage outdoor insulators and cables. It is well accepted that appropriate addition of micron particles to form a composite can enhance its insulation performance. This work reports improvement on the dielectric breakdown strength, tracking failure time, mechanical properties and volume resistivity of EPDM composites co-filled with boron nitride (BN) micron and nano–particles. Test specimens were fabricated by melt-blending and hot press techniques. AC breakdown tests were performed as per IEC60243-1 Standard. The tracking test was performed following IEC 60587 Standard and volume resistivity measurement as per ASTM D257. Experimental results show improvement in electrical properties with increasing particle loading up to a certain dosage but enhancement in the mechanical properties is observed up to 30 wt% particles addition. The co-filled composite exhibits considerably higher dielectric breakdown strength (89.24 kV/mm) and volume resistivity (~ 5.0 × 1015 Ω cm) relative to Micro-20 wt%. The tracking failure time of the co-filled is much improved due to excellent resistance against dry band arcing and thermal accumulation in the discharge region. Moreover, co-filled composites show improvement in mechanical properties as compared to the micron–filled counterparts. The improved thermal conductivity, better thermal stability and overall higher surface area of the particles are possible factors which impart better performance to the co-filled composites.

Redeposition and densification of pyrolysis products of polymer composites in char layer

Under high temperature and pressure of solid rocket motors (SRMs), the pyrolysis will produce a char layer with non-uniform pore structure of Ethylene propylene diene monomer (EPDM) composites, whose compact structure can improve the ablation resistance of the composites. It is of great theoretical and practical significance to study the formation mechanism of the compact structure of the char layer for further studying the ablation mechanism and guiding the development of EPDM composites. To date, the formation mechanism of the compact structure has not been observed with direct evidence. In this work, the in-situ deposition experiment and the deposition ablation experiment for EPDM composites are designed and carried out. The in-situ deposition experiment results show that the pyrolysis gas produced by EPDM composites can generate chemical vapor deposition reaction in the char. The results of the deposition ablation experiment show that the chemical vapor deposition reaction of pyrolysis gas produced by EPDM composites in carbon skeleton surface of the char layer will lead to the densification of its pore structure in the ablation condition of SRMs.