Barrier properties of electron‐beam‐modified EPDM rubber

EPDM rubber was surface‐ and bulk‐modified with varying concentrations of trimethylol propane triacrylate (TMPTA) in the presence of a constant electron‐beam irradiation dose of 100 kGy and over a wide range of irradiation doses from 0 to 200 kGy at a fixed TMPTA concentration (10%). The permeation rate and absorption of three homologous nonpolar solvents, namely, n‐hexane, n‐heptane, and n‐octane, along with an aromatic solvent, toluene, and a polar solvent, trichloroethylene, through unirradiated, unmodified control, and modified rubber membranes (≈150 μm) were studied. It was found that both the permeation rate and absorption decrease progressively with increase in the TMPTA concentration up to 10% for both the surface‐ and bulk‐modified rubbers. With increase in the radiation dose, there also is an initial drop in the values up to 50 kGy for the control and surface‐modified rubbers and up to about 100 kGy for the bulk‐modified one. The control rubber shows the highest absorption and permeation for all the solvents except trichloroethylene, followed by the bulk‐modified rubber membrane. Trichloroethylene is, however, absorbed and permeated most by the surface‐modified sample. The observations are explained in terms of the structural modifications of the rubber, crosslinking, changes in the relevant thermodynamic properties such as surface energy, the penetrant size, and the transport mechanism of the penetrants. The influence of temperature on the permeability characteristics of the control and modified rubbers was also studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 784–795, 2000     

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.     

Foaming of EPDM with water as blowing agent in injection molding

Chemical foaming of elastomers is state of the art and preferred to the more complex systems engineering of physical foaming, yet, many commonly used chemical blowing agents often are hazardous. In current investigations, we introduced water bound to carrying substances (silica, carbon black) into elastomer compounds. A stable, reproducible foaming process can be implemented using water as physical blowing agent. In first tests, the average cell diameters in injection molded elastomer parts exceed the average cell diameters of chemically foamed parts. Yet, varied amounts of blowing agent can reduce the cell diameters. Furthermore, nucleating agents and water carriers are being examined to reduce cell diameters and reach cellular structures and mechanical properties of chemically foamed parts. In conclusion, foaming of elastomers with water is a promising. Yet, further examinations have to cover the effect mechanism of foaming and vulcanization as well as continuous processing and compounding. Rear end of an EPDM part foamed with water carried on silica in injection molding process (mold temperature 195 °C, breathing mold opening 2 mm) © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43613.     

Method for time–temperature–transformation diagrams using DSC data: Linseed aliphatic epoxy resin

A novel method to generate time–temperature–transformation (TTT) diagrams from Differential Scanning Calorimetry (DSC) data is presented. The methodology starts with dynamical DSC information to obtain the total transformation heat, followed by an isothermal‐dynamic temperature ramp that allows the inclusion of diffusion‐controlled reaction kinetic. The cure kinetics is modeled using an auto‐catalytic Kamal–Sourour model, complemented with a Kissinger model that allows the direct prediction of one energy of activation, DiBenedetto's equation for the glass transition temperature as a function of the cure degree and adjusted reaction constants to include diffusion mechanisms. The methodology uses a nonlinear least‐squares regression method following J.P. Hernández‐Ortiz and T.A. Osswald's methodology (J. Polym. Eng. 2004, 25, 23). A typical linseed epoxy resin (EP) presents two different kinetics control mechanisms, thereby providing a good model to validate the proposed experimental and theoretical method. TTT diagrams for EPs at two different accelerator concentrations are calculated from direct integration of the kinetic model. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40566.     

Effect of electron-beam irradiation on the thermal vulcanization of a natural rubber compound

The influence of electron-beam irradiation on the thermal vulcanization curing kinetics of a natural rubber compound was investigated by means of rheometric tests [moving die rheometry (MDR)] and differential scanning calorimetry (DSC). Differences in the storage moduli of compounds with different radiation doses were observed and assigned to a plasticizer effect by the zinc stearate mainly formed in the mixing stages; this compound migrated to the interphase region. This fact was confirmed by Fourier transform infrared spectroscopy. From the measurements performed by MDR and DSC testing, the induction time (t_o) was analyzed in the frame of the Claxton–Liska model, whereas the kinetic behavior of the nonirradiated and pre-irradiated compounds were satisfactorily fitted with the Isayev–Deng and Kamal–Ryan models. Additionally, both curing characterization techniques corroborated the fact that the pre-irradiated rubber compound showed an earlier t _o and a lower activation energy in comparison with the nonirradiated compound. These facts were attributed to the effect of irradiation on the free sulfur content present in the rubber compound, which promoted more activated precursor species to crosslink with rubber. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47216.     

Structural determination of ethylene‐propylene‐diene rubber (EPDM) containing high degree of controlled long‐chain branching

This work highlights an attempt to characterize the degree and nature of long‐chain branching (LCB) in an unknown sample of ethylene‐propylene‐diene rubber (EPDM). Two EPDM rubbers selected for this study were comparable in comonomer compositions but significantly different with respect to molar mass and the presence of LCB. Both rubbers contained 5‐ethylidene‐2‐norbornene (ENB) as diene. Solution cast films of pure EPDM samples were used for different characterization techniques. ¹H‐NMR, and ¹³C‐NMR were used for assessing the comonomer ratios and LCB. Size exclusion chromatography (SEC) equipped with triple detector system was used to determine the molar mass (both absolute and relative) and polydispersity index (PDI). Presence of branching was also detected using sec‐viscometry. Rheological analysis has also been used for characterizing LCB. Finally, on the basis of the experimental findings and the available theories, an attempt was made to identify the chemical nature and degree of LCB. This study reveals the possibility of detailed characterization of molecular architecture of EPDM containing LCB by comparing with an essentially linear EPDM in light of an existing theory. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

Sigmoidal Chemorheological Models of Chip‐Underfill Materials Offer Alternative Predictions of Combined Cure and Flow

Prior rheology results on chip‐underfill epoxy resins have been re‐analyzed by a sigmoidal model that contains three variable physical parameters, including the terminal cured viscosity of the gel, an induction or dwell time and a time factor associated with the speed of conversion as viscosity undergoes large dynamic changes during rapid crosslinking. The analyses were conducted with resins that were originally cured between 150 and 180 °C and show obvious non‐linearity, even on a semi‐log plot of dynamic viscosity. The sigmoidal models more accurately represent a wider range of dynamic viscosity than power‐law‐based rheological models, which are both more common and more generally accepted for practical application. If total flow is the critical design parameter in terms of chip underfill, perhaps these alternative sigmoidal models need to be more thoroughly evaluated to gauge their practical use and validity.

     

Influence of sulfenamide accelerators on cure kinetics and properties of natural rubber foam

The effect of types of sulfenamide accelerator, i.e., 2‐morpholinothiobenzotiazole (MBS), N‐t‐butylbenzothiazole‐2‐sulfenamide (TBBS), and N‐cyclohexyl benzothiazole‐2‐sulfenamide (CBS) on the cure kinetics and properties of natural rubber foam was studied. It has been found that the natural rubber compound with CBS accelerator shows the fastest sulfur vulcanization rate and the lowest activation energy (E_a) because CBS accelerator produces higher level of basicity of amine species than other sulfenamide accelerators, further forming a complex structure with zinc ion as ligand in sulfur vulcanization. Because of the fastest cure rate of CBS accelerator, natural rubber foam with CBS accelerator shows the smallest bubble size and narrowest bubble size distribution. Moreover, it exhibits the lowest cell density, thermal conductivity and thermal expansion coefficient, as well as the highest compression set as a result of fast crosslink reaction. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44822.     

Analysis of the foaming mechanisms of materials based on high‐density polyethylene (HDPE) crosslinked with different irradiation doses

Different crosslinked high‐density polyethylene based cellular polymers have been produced by a free foaming process using a chemical blowing agent. The polymer matrix was crosslinked by electron beam irradiation using different doses ranging from 25 to 175 kGy. The main aim of this work is to study the effect of the different irradiation doses on the density, cellular structure, and foaming mechanisms. Results show that irradiation doses as high as 175 kGy have to be used to obtain cellular materials with a low relative density (0.06), cell sizes of around 50 μm, and cell densities of 1.6 × 10⁷ cells cm^?3. The strain hardening of the polymer matrix increases with the irradiation dose leading to an increase of the polymer resistance to be stretched, which helps to avoid undesirable cellular degeneration processes. Irradiation doses lower than 175 kGy are not able to stabilize the cellular structure leading to foams with relative densities higher than 0.1 and degenerated cellular structures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46276.     

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.     

Natural rubber/leather waste composite foam: A new eco‐friendly material and recycling approach

This article describes a new approach of recycling the leather waste (shavings) using it as filler in natural rubber foams composites. The foams were prepared using different amounts of leather waste (0–60 parts per hundred of rubber) and submitted to morphological (SEM microscopy) and mechanical analyses (cyclic stress–strain compression). The increase of leather shavings on the composite causes an increase of viscosity in the mixture, which reflects in the foaming process. This results in smaller and fairly uniform cells. Furthermore, expanded rubber has the biggest cell size, with more than 70% of cell with 1000 µm, while the composite with the higher concentration of leather has around 80% of total number of cells with 100–400 µm. The mechanical parameters were found to depend on the leather dust concentration. Moreover, the stiffness rises with the increase of leather shavings; consequently, the compression force for expanded rubber was 0.126 MPa as well as the composite with higher concentration of leather was 7.55 MPa. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41636.     

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.     

Effects of epoxidized natural rubber (ENR‐50) and processing parameters on the properties of NR/EPDM blends using response surface methodology

The effects of epoxidized natural rubber (ENR‐50) and processing parameters on the properties of natural rubber/ethylene–propylene–diene rubber (NR/EPDM; 70 : 30 phr) blends were studied. The compounds were prepared by melt compounding method. Using response surface methodology of two‐level full factorial, the effects of ENR‐50 contents (?1 : 5 phr; +1 : 10 phr), mixing temperature (?1 : 50°C; +1 : 110°C), rotor speed (?1 : 40 rpm; +1 : 80 rpm), and mixing time (?1 : 5 min; +1 : 9 min) in NR/EPDM blends were evaluated. Cure characteristics and tensile properties were selected as the responses. The significance of factors and its interaction was analyzed using ANOVA and the model's ability to represent the system was confirmed using the constant of determination, R² with values above 0.90. It was found that the presence of ENR‐50 has the predominant role on the properties of NR/EPDM blends. The addition of ENR‐50 significantly improved cure characteristics and tensile strength up to 5.12% and 6.48% compared to neat NR/EPDM blends, respectively. These findings were further supported by swell measurement, differential scanning calorimetry, and scanning electron microscopy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40713.     

Chemorheological study of compatibilized blends of low‐density polyethylene and polydimethyl siloxane rubber

Compatibilization of the blends of polydimethyl siloxane (PDMS) rubber and low‐density polyethylene (LDPE) was achieved through reactive processing during extrusion in a Monsanto Processability Tester (MPT). The chemorheological characteristics of 50 : 50 LDPE : PDMS blends with varying proportions (0–8 wt %) of ethylene comethyl acrylate (EMA) were investigated at three different temperatures (170, 190, and 210°C) and four different shear rates (61.3, 122.6, 306.6, and 613.1 s^?1). It was found that EMA reacts with vinyl groups of PDMS rubber at a temperature of 190°C during extrusion through the capillary of MPT, forming EMA‐grafted‐PDMS rubber (EMA‐g‐PDMS), which acts as the compatibilizer for the blend systems. The results are based on IR spectroscopy, melt rheology, and phase morphology of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2810–2817, 2003     

Rheological properties of ionically and covalently crosslinked polypropylene‐type thermoplastic elastomers

Maleic anhydride was grafted onto a polypropylene‐type thermoplastic elastomer PER by reactive processing with a screw extruder, and a maleated PER (MPER) was prepared. Aiming at ionic crosslinking, magnesium 12‐hydroxy stearate (MgStOH), zinc oxide (ZnO), and zinc sulfide (ZnS), and aiming at covalent crosslinking, melamine as an amino compound, and Epocizer and GRYCI‐ALE as epoxy compounds, were added to the MPER, melt‐mixed by use of the screw extruder, and crosslinked compounds were obtained. The rheological properties such as capillary flow properties and dynamic viscoelasticities of the compounds were measured and their melt processabilities were evaluated. The degree of crosslinking was in the order of epoxy compounds > MgStOH > melamine > ZnO, ZnS > MPER (blank). In the case of the compound with MgStOH of a moderately high degree of crosslinking, the non‐Newtonian behavior is remarkable and the die swell ratio is low and suitable for extrusion. However, in the case of compounds with epoxy compounds of an excessive degree of crosslinking, fine extrudate cannot be obtained due to the lack of fusion and the control of degree of crosslinking is necessary. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 762–773, 2002     

Using a silanized silica nanofiller to reduce excessive amount of rubber curatives in styrene‐butadiene rubber

In recent years, the rubber industry has come under pressure to improve health and safety at work, minimize damage to the environment, reduce costs, and increase competitiveness. Rubber compounds contain additives including curing chemicals, which are hazardous and harmful. Reducing their use or eliminating them altogether will be beneficial to rubber compounders and manufacturers of rubber articles. A styrene‐butadiene rubber (SBR) was cured and reinforced with a high loading of precipitated amorphous white silica nanofiller. The silica surfaces were pretreated with bis(3‐triethoxysilylpropyl) tetrasulfide (TESPT), which is a sulfur‐bearing bifunctional organosilane to chemically adhere silica to the rubber. The chemical bonding between the filler and rubber was optimized via the tetrasulfane groups of TESPT by adding accelerator and activator. The rubbers were subsequently cured and their hardness, tensile strength, elongation at break, stored energy density at break, tearing energy, tensile modulus, Young's modulus, and bound rubber content were measured. This study showed that using the filler in combination with a sulfur‐donor accelerator was the most efficient method for curing and reinforcing the rubber. This led to a significant reduction in the use of the curing chemicals, a faster curing cycle, and very good mechanical properties for the rubber vulcanizate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of functionalization on dispersion of POSS‐silicone rubber nanocomposites

The nanocomposite of PDMS using functionalized fumed silica and nonreactive POSS as fillers were prepared by blend method in a planetary mixer. Fumed silica was functionalized by aliphatic and aromatic groups to study the filler–filler interactions with the aliphatic and aromatic POSS fillers and consequently their influence on the properties in the PDMS matrix. Transmission electron microscope (TEM) showed a good dispersion in the systems having the silica and POSS fillers with similar modifications. However, aliphatic and aromatic filler combinations showed more aggregated structures. Moreover, aliphatic POSS despite of good dispersion at higher loadings, act as lubricant, which is attributed to the disturbance in the PDMS‐ silica filler interaction and also the filler–filler interaction within fumed silica. There is a decrease in complex viscosity with the functionalization of fumed silica and with the aromatic/aliphatic POSS fillers. The thermal stability of aromatic functionalized fillers improves owing to the thermally stable phenyl groups. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dual crosslinking of carboxylated nitrile butadiene rubber latex employing the thiol‐ene photoreaction

At present, the most common used crosslinking process for carboxylated nitrile butadiene rubber (XNBR) latex is an accelerated sulfur curing system with zinc oxide. To avoid allergenic reactions related to residual accelerator levels in dipped XNBR latex articles such as medical gloves, a dual curing process has been developed combining thermal and photochemical crosslinking reactions. The two‐step procedure involves the formation of covalent and ionic bonds to ensure good mechanical properties of the final products. The photochemical thiol‐ene reaction is used to generate covalent crosslinks between the remaining C?C double bonds of the butadiene units whereas the carboxylic moieties are conventionally cured with divalent metal oxides (ZnO) under elevated temperature (formation of ionic crosslinks). The photochemical curing step is carried out both in the latex phase using a falling film photoreactor (prevulcanization) as well as in the solid phase by UV irradiation of dried XNBR films (postvulcanization). The mechanical properties and crosslink densities of the cured XNBR films are determined and the influence of selected curing parameters is assessed. The results give evidence that a combined approach of thermal prevulcanization and photochemical postvulcanization makes the production of latex articles (e.g., gloves) with tailored properties and good skin compatibility feasible. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A New Approach to the Evaluation of Stabilizer Efficiency Under Photo‐Ageing

Summary: Elastomers are very sensitive to oxidative degradation due to the combined effect of light and oxygen. Hence, we investigate the impact of stabilizers on the evolution of molecular structure of elastomers through photo‐oxidation. While a dual processes is generally reported to describe photo‐oxidation of elastomers (oxidation by‐products formation and crosslinking), the aim of the current study is to provide a complete characterization of the efficiency of additives taking into account the dual processes: chemical changes (formation of photoproducts) and molecular structure changes (crosslinking). This work gives new insights about relationships between chemical changes and physical properties evolution of the material through ageing. We conclude that the two phenomenon are correlated to the primary peroxidation reaction and a dual efficiency does not exist for any additive.

Kinetic curves of carbonylated by‐products formation upon photooxidation of stabilized EPDM films comparing with a unstabilized reference.