Cure and scorch in the processing of ethylene‐propylene‐diene terpolymer (EPDM)

The objective of this work is to ascertain the characteristics of desirable (cure) and especially undesirable (scorch) crosslinking when carbon black filled ethylene propylene diene terpolymer (EPDM) is processed using different peroxide initiators. The mixing temperature and the nature of the peroxide initiator are crucial parameters affecting scorch (undesirably premature crosslinking) in this rubber. Processability and properties of EPDM prepared using various mixer set temperatures have been investigated. Dicumyl peroxide (Luperox DC), di(t‐butylperoxy) diisopropylbenzene (Luperox F), and 2,5‐dimethyl‐2,5‐di(t‐butylperoxy) hexane (Luperox 101) were used as crosslinking initiators. Higher mixing temperatures give shorter scorch times, greater scorch magnitudes, greater heterogeneities in crosslink spatial distribution and poorer tensile properties. However, extreme localization of the unwanted crosslinking at the rubber‐filler interface does have a beneficial effect. Luperox DC offers poorer processability and poorer resulting properties than do Luperox F and Luperox 101, due to its shorter half‐life and greater solubility in the rubber phase. This is the first time that the spatial heterogeneity of crosslinking and scorch has been related to the basic thermodynamics of 3‐component 2‐phase systems. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44523.     

Assessment of crosslink network and network defects of unfilled and filled ethylene‐propylene‐diene terpolymer using solid state nuclear magnetic relaxation spectroscopy

Reinforced rubbers are complex compared to unfilled systems. There are differences in the mechanisms affecting network molecular structure as well as properties of the rubber materials. In this article investigation of crosslink network and untied network defects on a molecular level of unfilled and carbon black filled ethylene‐propylene‐diene terpolymer was carried out using proton solid‐state double‐quantum NMR spectroscopy. The results show that the filled system demonstrates lower cure efficiency in conjunction with more noncoupled network defects than the unfilled one. In addition, the filled system yields the greater spatial heterogeneity because of the localization of the free radicals at the rubber–filler boundary. These strongly influence the mechanical properties of the filled rubber. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44224.     

Effect of silane coupling agent on the fatigue crack propagation of silica‐filled natural rubber

Based on the real‐time crack tip morphology monitoring, the influence of silane coupling agent (SCA) on the crack‐growth behavior of silica‐filled natural rubber (NR) was analyzed. By using SCA, silica particles can be well dispersed and a filler–matrix network can be formed, which leads to lower crack‐growth rate. Results indicate that a dosage of 5 wt % (with respect to silica loading) is the optimal content. The real‐time observation and scanning electron microscopy (SEM) analysis proved that thin ligaments and dimples with homogeneous distribution appear on the crack tip. These crack tip morphologies reflect the low crack‐growth rate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41980.     

Adhesion between ethylene-propylene-diene monomer and thermoplastics in two-component injection molding: Effect of dicumylperoxide as curing agent

Strong adhesion at the interface is an important aspect in two-component (2K) injection molding. It was therefore investigated whether dicumylperoxide (DCP) as curing agent in ethylene-propylene-diene monomer (EPDM) could stimulate interdiffusion and/or induce chemical bonding with thermoplastics. EPDM mixtures containing DCP concentrations between 2 to 8 parts per hundred rubber (phr) were combined with polar and non-polar thermoplastics. Changes in EPDM physico-mechanical bulk properties were analyzed, and the adhesion was evaluated by high temperature contact angle measurements and tensile testing. Results showed that DCP concentration did not influence EPDM-thermoplastic compatibility. However, EPDM adhesion with polyethylene (PE) did improve when using up to 6 phr DCP (57% adhesion) as crosslinking is promoted. While with polypropylene (PP), adhesion linearly decreased (from 55% to 35% adhesion) with higher DCP concentrations due to prevailing scission reactions. Adhesion through chemical bonding with acrylonitrile-butadiene-styrene (ABS) caused better adhesion at 4 phr (43% adhesion) compared to polycarbonate (PC) at 4 phr (13% adhesion) where only limited interdiffusion occurs. Thus, selecting the optimal DCP concentration is highly important to boost adhesion between EPDM and thermoplastics. Furthermore, at these optimal DCP concentrations, physico-mechanical properties require consideration as these properties were significantly affected.     

Interplay between key variables of peroxide cured EPDM and evaluation of electromechanical efficiency for MV cables

Extensive work has been done on ethylene‐propylene‐diene monomer (EPDM) vulcanizates and the main factors influencing their cure efficiency. However, very little attention has been given to the evolution of material properties and the interplay between key variables formulation. The effect of ethylene/propylene content and concentration of peroxide and type on viscoelastic and dielectric properties of EPDM elastomers was investigated using dynamic mechanical analysis and electric property measurements at room temperature. In order to compare results, these measurements were obtained by FTIR spectroscopy. Differences between real and imaginary (loss) part of the permittivity of EPDM/ dicumyl peroxide (DCP) composites were more significant than those in EPDM/di(tert‐butylperoxyisopropyl)benzene (DTBPIB) composites. For peroxide DTBPIB, the dielectric percolation limit moves further with the increase of ethylene content of EPDM. The dielectric percolation limit of the peroxide DTBPIB is found to be approximately 60 g at a 75% of ethylene in EPDM. The FTIR analysis showed that a termoxidative degradation was promoted at mixes with peroxide DCP at 45 and 75% of ethylene in EPDM. Therefore, we could interestingly show the decrease in electrical properties particularly associated with termoxidative degradation of peroxide DCP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46139.     

Effect of the elastomer viscosity on the morphology and impact behavior of injection molded foams based on blends of polypropylene and polyolefin elastomers

The impact resistance of injection-molded polypropylene (PP) parts is severely reduced when they are foamed. It is necessary to implement strategies, such as elastomer toughening, to increase the impact behavior of foamed parts. However, the knowledge on the effect of elastomer addition on the morphology, cellular structure, and impact of injection-molded cellular parts is very limited. In this work, foamed parts based on blends of PP and polyolefin elastomers have been produced and characterized. A high and a low viscosity octene-ethylene copolymer (EOC) and a high viscosity butene-ethylene copolymer (EBC) were employed. The blends have been thermally and rheological characterized. Solids materials and foams (relative density 0.76) were injection-molded. The solid phase and cellular structure morphologies were studied using scanning electron microscopy. The results showed that elastomer toughening has been successful to obtain an improvement of the impact behavior in solid and cellular polymers. In this case, EOC materials provide an appropriate interfacial adhesion and optimized cellular structure which results in high impact resistance. The optimum elastomer to improve the properties is the EOC with a higher viscosity which provides impact resistance with n values below 3 due to the toughening of polymer matrix, thick skin thickness, and low cell size.     

Elastic polyaniline with EPDM and dodecylbenzenesulfonic acid as plasticizers

Elastomeric polyaniline was prepared by being mixed with ethylene–propylene–diene (EPDM) rubber in low concentrations (10, 20, or 30 wt %). The mixture was made in an internal mixer coupled to a torque rheometer. The polyaniline was doped with dodecylbenzenesulfonic acid (DBSA) via reactive processing during the mixing. When the EPDM rubber was added to the polyaniline and DBSA, the doping reaction was not interrupted, as demonstrated by an increase in the torque values. We chose the relative DBSA and EPDM concentrations to obtain the highest conductivities (10⁻¹ to 10⁻³ S cm⁻¹) and the best mechanical properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1768–1775, 2001     

Thermally stable bromobutyl rubber with a high crosslinking density based on a 4,4′‐bismaleimidodiphenylmethane curing agent

The development of thermally stable bromobutyl rubbers has been a challenge in rubber chemistry and engineering. In this circumstance, 4,4′‐bismaleimidodiphenylmethane (BMI) was newly applied as a novel crosslinking agent for thermally stable brominated isobutylene–isoprene rubber (BIIR) with a high crosslinking density. With oscillating disk rheometry and differential scanning calorimetry, the curing characteristics of BIIR were systematically investigated with respect to the content of BMI. We found that BMI alone could crosslink BIIR at higher temperature, and a corresponding possible chemical reaction mechanism was proposed. With the introduction of zinc oxide, the curing reaction of BIIR with BMI was significantly accelerated, and the resulting vulcanizate provided a higher state of curing with excellent overcure reversion stability even at a temperature of 190 °C for 2 h. The content of the dicumyl peroxide (DCP) reaction accelerator was also optimized to be BMI/DCP = 1:0.05 on the basis of considerations of the curing rate, scorch safety, maximum rheometric torque, and reversion resistance at 160 °C. Compared with the conventional sulfur‐cured BIIR, the BMI‐cured BIIR exhibited a higher crosslinking density with a superior low compression set property at elevated temperatures and an excellent thermal stability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44092.     

Chemorheological time‐temperature‐transformation‐viscosity diagram: Foamed EPDM rubber compound

Thermal analysis, rheometry, and kinetic modeling are used to generate a comprehensive processability diagram for thermosetting and elastomeric resins. A chemorheological “time‐temperature‐transformation‐viscosity” diagram is proposed to fully characterize curing reactions toward process' on‐line control, optimization, and material design. Differential scanning calorimetry and thermogravimetric techniques are used to measure total reaction heat, degree of vulcanization, and cure kinetics. The viscosity, as a function of temperature and cure degree, is obtained from parallel plate rheometry. The auto‐catalytic Kamal–Sourour model, including a diffusion‐control mechanism, is used to model cure kinetics, while the Castro–Macosko model serves to model the rheological behavior. Non‐linear least‐squares regression and numerical integration are used to find models' parameters and to construct the chemorheological diagram. The usefulness of the proposed methodology is illustrated in the context of an industrial‐like Ethylene Propylene Diene Termononer rubber compound that includes a chemical blowing agent. Even though the rubber formulation contains crosslinking agents, primary and secondary accelerators, promoters, activators, and processing aids, the chemorheological diagram is obtained consistently, validating the proposed methodology to any thermosetting or elastomeric resin. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43966.     

Exploring the role of stearic acid in modified zinc aluminum layered double hydroxides and their acrylonitrile butadiene rubber nanocomposites

The proposed study attempted to explore the role of stearic acid modification on the properties of zinc‐aluminum based layered double hydroxides (LDH) and their composites with acrylonitrile butadiene rubber (NBR). Three distinctive LDH systems were adapted for such comparison; an unmodified LDH and two stearic acid modified LDH. The use of zinc oxide and stearic acid in the rubber formulation was avoided as the modified LDH would be able to deliver the necessary activators for the vulcanization process. Emphasis was predominantly given to reconnoiter the merits of stearic acid modification on the increase in interlayer distance of the LDH. X‐ray diffraction studies and transmission electron microscope morphological investigations of LDH powders indicated that modification with stearic acid increased the interlayer spacing which would favor the intercalation of NBR polymer chains into the layered space. However, stress–strain studies indicated better mechanical properties for composites with unmodified LDH. Composites with LDH showed higher crosslinking densities than conventionally sulfur cured control compounds using zinc oxide/stearic acid as activators. This was evident from equilibrium swelling method as well as statistical theory of rubber elasticity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41539.     

Dynamic mechanical properties of SBR and EPDM vulcanisates filled with cryogenically pulverized flexible polyurethane foam particles

The dynamic mechanical properties of rubber vulcanisates filled with cryogenically pulverized polyurethane foam particles, used as a reinforcing filler, were investigated with respect to storage modulus (E′), loss modulus, and the variation of glass transition temperature. Two rubbers were using styrene–butadiene rubber (SBR) and ethylene–propylene copolymer (EPDM). The effects of filler concentration and filler characteristics (such as particle size and moisture content) were also monitored. It was found that the optimum dynamic mechanical properties of the compounds were obtained when introducing the PU particles of 40–50 parts per hundred (pph) rubber in the SBR and 30 pph in the EPDM, the properties being affected by the size of PU particles and moisture content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1129–1139, 1999     

Crosslinking of unfilled carboxylated nitrile rubber with different systems: Influence on properties

The presence of two functional groups, nitrile and carboxyl, in carboxylated nitrile rubber allows it to be crosslinked with different agents. In this study, we examined the influence of different crosslinking agents on the properties of unfilled carboxylated nitrile rubber. Significant differences were found when different crosslinking agents were used, as shown in the vulcanization curves, especially in the variation of the viscous component with the reaction time. The reaction rate was highest when organic peroxide was used, and it was lowest when metallic peroxide or copper sulfate was used. When the crosslinking agents led to the formation of ionic bonds (metallic oxide and metallic peroxide), the carboxylic groups ? COOH had a greater participation in the crosslinking. However, when copper sulfate was used, coordination bonds were formed, and the main contribution was due to the nitrile groups. Tensile strength, tear strength, and abrasion properties were superior when the crosslinking systems used led to the formation of ionic bonds. On the contrary, the compression set was optimum when covalent bonds were formed. Copper sulfate behaved as an intermediate between the two previous situations. The mechanodynamic response of the compounds also depended on the crosslinking agent used. The correlation between crosslink density by swelling in dichloromethane, maximum damping temperature by dynamic measurements, and glass‐transition temperature by differential scanning calorimetry had to be explained in terms of the crosslink type. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Formulation and curing characteristics of EPDM/NR and EPDM/SBR polyblends used in metallic surfaces rubber lining

In this work, a new elastomeric liner was introduced to protect the metal surfaces of storage tanks against corroding materials in petrochemical industries. This new liner was prepared on the basis of EPDM/NR and EPDM/SBR compounds. The elastomeric compounds were cured by using super‐heated water vapor at atmospheric pressure. To increase the rate of curing in these rubber samples, the optimum curing system contained 15 phr sulfur and 1.5 phr mercaptobenzothiazole, 1.5 phr zinc diethyl dithiocarbamate, and 1.8 phr tetramethylthiuram disulfide accelerators. Mechanical tests showed that ultimate tensile strength, elongation at break, and hardness of both polyblend samples were comparable to the SBR/NR blend, which is widely used in the rubber lining of metallic surfaces. In the next step, the chemical resistance of the samples was measured by placing them in a 30 wt % HCl solution. The tensile strength, elongation at break, and weight loss of the samples were measured before and after immersion in HCl. Also, the chemical resistances for EPDM/NR, EPDM/SBR, and SBR/NR samples were qualitatively measured in caustic solution. The cracking, blistering, permeability, and adhesion of the rubber samples to steel surface were observed. Finally, the results showed that EPDM/SBR (70/30) polyblend can be a suitable substitute for conventionally used SBR/NR (50/50) for a successful rubber used to line metallic surfaces. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of crystalline structure on the cell morphology and mechanical properties of polypropylene foams fabricated by core-back foam injection molding

Foam injection molding (FIM) is an advanced technology for preparing lightweight plastic foams, but its inferior mechanical performance remains a challenge. In this study, microcellular injection-molded β-polypropylene (β-PP) foams with high ductility were successfully prepared by combing the β-nucleating agent with controllable temperature field. Foaming results showed that the microcellular β-PP foams exhibiting a cell size of about 8 μm and cell density over 10⁸ cells/cm³ were prepared with a crystalline diameter approximately 5 μm, while PP foams had a rather large cell size approximately 150 μm and low cell density of 10⁵ cells/cm³ with 30 μm crystalline size. As a result, this significant improvement in cell structure as well as the crystalline size lead to a significant increment of 86% for the ductility of β-PP foams. This work offers a facile strategy to prepare injection-molded foams with desirable mechanical properties for their wide range of applications, such as automotive construction and consumer electronics.     

Thermomechanical properties and water uptake capacity of soy protein‐based bioplastics processed by injection molding

The optimization of the processing conditions in the production of soy protein bioplastics by injection molding has been essential in order to develop materials with a great capacity to absorb water while displaying good mechanical properties. Using a 50/50 (wt/wt) soy protein/glycerol mixture, and 40 °C, 500 bar, and 70 °C as reference values for cylinder temperature, injection pressure, and mold temperature, respectively, the effect of those processing parameters over thermomechanical and hydrophilic properties was studied. Processing parameters did not show a great influence over the thermomechanical bending properties within temperatures ranging from ?30 to 130 °C, as most samples displayed a similar response, independently of the parameter studied. On the other hand, when studying tensile and hydrophilic properties, the main effect corresponded to the cylinder and mold temperature values, as pressure did not exert a clear influence when increased from 300 to 900 bar. Samples with a lower water uptake were obtained when processed at higher temperature, as a result of crosslinking promotion. Moreover, a greater extensibility was observed when bioplastics are processed at high mold temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43524.     

A new microcellular injection molding process for polycarbonate using water as the physical blowing agent

This article presents a new process for producing microcellular injection molded plastic parts using water as the physical blowing agent and micro‐scaled particles as the cell nucleating agents. Distilled water with dissolved salt were fed through the hopper of an injection molding machine at a preset rate and mixed with polycarbonate (PC) in the machine barrel. Microcellular PC tensile bars were then injection molded with different shot volumes, water/salt solution feed rates, and salt concentrations. Tiny salt crystals of 10–20 μm recrystallized during molding acted as nucleating agents in the PC foamed parts. The surface roughness, mechanical properties, and microstructure of the solid and foamed parts were measured and compared with microcellular injection molded parts using supercritical fluid (SCF) nitrogen as the physical blowing agent. At a similar weight reduction of about 10%, the water foamed PC parts have a smooth surface comparable to that of solid injection molded parts. They also possess similar, if not better, mechanical properties compared to SCF nitrogen foamed PC parts. Without the nucleating agent, PC/water foamed parts exhibit much larger and fewer bubbles within the molded parts. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Comparison of cure characteristics and mechanical properties of nano and micro silica‐filled CSM elastomers

In this study, the effect of micro and nano silica and their combination on mechanical and thermal properties of Chlorosulfonated Polyethylene compounds were investigated. Cure characteristics were studied using a Monsanto Moving Die Rheometer at 155°C. Incorporation of nano silica accelerated the vulcanization whereas the micro silica particles decelerated the curing process. Both micro and nano silica increased the crosslink density as evidenced by swelling test. However, this value has been more improved in CSM/nano silica composites. The physico‐mechanical properties of CSM/nano silica are superior compared to CSM/micro silica. Nano silica provided reinforcing efficiency which is not only because of higher specific surface area but also because of various interactions and especially physical interactions which are discussed in the text. Nano silica particles also improved the thermal properties more efficiently. Incorporation of 15 phr (part per hundred) nano and 5 phr micro silica to polymer improved the initial decomposition temperature for about 51°C and 16°C, respectively, using a TGA. The combination of micro and nano silica, showed that by coupling nano and micro fillers, the loading of fillers can be minimized. In other words, the hybrid samples with a lower filler loading behave as efficient as their separate counterpart with higher loading. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42668.     

Mechanical Properties and Antimicrobial Activity of Silicone Rubber Compounds Containing Acrylated Norfloxacin and Its Polymer

Summary: Antibacterial silicone rubbers (SR) were prepared by platinum curing and peroxide curing of a silicone compound containing the synthetic antimicrobial monomer 1‐ethyl‐6‐fluoro‐7‐{4‐[2‐hydroxy‐3‐(2‐methylacryloyloxy)‐propyl]piperazin‐1‐yl}‐4‐oxo‐1,4‐dihyroquinoline‐3‐carboxylic acid (MQ) and its polymer PMQ. The effects of the two curing systems on the mechanical properties were compared. Tensile strength and elongation at break of the platinum‐cured SR decreased with increasing concentrations of MQ and PMQ. For the peroxide curing system, the elongation at break increased with increasing concentrations of the antimicrobial agents. The antibacterial activity of the prepared SR was examined by the shake flask test against Staphylococcus aureus and Escherichia coli, which are representative of Gram‐positive and Gram‐negative bacteria, respectively. All compounds showed excellent antibacterial activities against these two types of bacteria.

Structure of acrylated norfloxacin.     

1,2,3‐triazole crosslinked polymers as binders for solid rocket propellants

In this study, 1,2,3‐triazole crosslinked polymers were synthesized as a new binder for solid rocket propellant systems by reacting the azide groups of the polymer with the ethynyl groups of a dipolarophile curing agent. All the mixtures were cured in an oven at 52°C for 7 days, and the curing reactivity of the products was analyzed using a Fourier transform‐infrared spectrometer. The carbonyl group adjacent to the triple bond, which acts as an electron‐withdrawing group, considerably accelerated the 1,3‐dipolar cycloaddition reaction between the azide and ethynyl functional groups, affording rubbery materials. The modulus of the polymers increased whereas the elongation at the break decreased with increasing ratio of the crosslinker to the prepolymer, resulting in highly crosslinked polymers. The molecular weights between the crosslinking points and interaction parameters of the 1,2,3‐triazole crosslinked polymers were determined from the swelling data, Flory–Rehner equation, and Mooney–Rivlin equation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40594.     

Effects of EPDM‐g‐MAH compatibilizer and internal mixer processing parameters on the properties of NR/EPDM blends: An analysis using response surface methodology

This study evaluates the effects of ethylene‐propylene‐diene‐monomer grafted maleic anhydride (EPDM‐g‐MAH) and internal mixer melt compounding processing parameters on the properties of natural rubber/ethylene‐propylene‐diene rubber (NR/EPDM) blends. Using Response Surface Methodology (RSM) of 2⁵ two‐level fractional factorial, we studied the effects of NR/EPDM ratio, mixing temperature, Banbury rotor speed, mixing period, and EPDM‐g‐MAH contents in NR/EPDM blends. The study found that the presence of EPDM‐g‐MAH in NR/EPDM blends had a predominant role as a compatibilizing agent, which affected the processability and properties of the final material. We also determined the model fitting with constant determination, R² of 99.60% for tensile strength (TS) response with a suggested combination of mixing process input parameters. The reproducibility of the proposed mixing strategy was then confirmed through model validation with a minor deviation at +2.303% and higher desirability of 0.960. This study is essential in providing a process design reference for NR/EPDM blends preparation by melt‐blending and the role of a compatibilizer from the systematic Design of Experiment (DOE) approach. The experimental findings were further supported with swelling and cross‐link density measurements, differential scanning calorimetry analysis, and observation of fracture morphology using a scanning electron microscope. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42199.