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Migration and Emission of Plasticizer and Its Degradation Products during Thermal Aging of Nitrile Rubber
Abstract
The behavior of nitrile rubber during long-term thermal aging was evaluated by following the migration of low-molecular-weight additives and additive degradation products from the material. Headspace-GC-MS analysis showed that at 60°C the number of low-molecular-weight compounds released was rather low, but a significant increase in the number and amount of products was observed when the temperature was raised from 60° to 80°C, e.g., several degradation products of tris(2-butoxyethyl)phosphate plasticizer including 2-butoxyethanol and 1-butanol were identified. Oxidation of the plasticizer was also seen in the FTIR spectra. The color of the material changed from light brown to almost black during the aging.
... At an aging temperature of 100 °C, larger aggregates of several microns in size appeared on the surface of the EPDM composites. These observations suggest that small molecular substances, such as plasticizers and antioxidants, migrate onto the surface during thermal oxidative aging, leading to the formation of aggregates on the surface [34][35][36][37]. Therefore, the migration of small molecular substances within the rubber matrix contributed to the deterioration of the mechanical properties of the rubber composites. ...
... At an aging temperature of 100 • C, larger aggregates of several microns in size appeared on the surface of the EPDM composites. These observations suggest that small molecular substances, such as plasticizers and antioxidants, migrate onto the surface during thermal oxidative aging, leading to the formation of aggregates on the surface [34][35][36][37]. Therefore, the migration of small molecular substances within the rubber matrix contributed to the deterioration of the mechanical properties of the rubber composites. ...
The aging behavior and life prediction of rubber composites are crucial for ensuring high-voltage transmission line safety. In this study, commercially available ethylene–propylene–diene monomer (EPDM) spacer composites were chosen and investigated to elucidate the structure and performance changes under various aging conditions. The results showed an increased C=O peak intensity with increasing aging time, suggesting intensified oxidation of ethylene and propylene units. Furthermore, the surface morphology of commercial EPDM composites displayed increased roughness and aggregation after aging. Furthermore, hardness, modulus at 100% elongation, and tensile strength of commercial EPDM composites exhibited a general increase, while elongation at break decreased. Additionally, the damping performance decreased significantly after aging, with a 20.6% reduction in loss factor (20 °C) after aging at 100 °C for 672 h. With increasing aging time and temperature, the compression set gradually rose due to the irreversible movement of the rubber chains under stress. A life prediction model was developed based on a compression set to estimate the lifetime of rubber composites for spacer bars. The results showed that the product’s life was 8.4 years at 20 °C. Therefore, the establishment of a life prediction model for rubber composites can provide valuable technical support for spacer product services.
... Acrylonitrile─butadiene rubber (NBR), the copolymer of acrylonitrile and butadiene, is an important polymer for many applications due to its good oil resistance and low-gas permeability. 1 The polar (CN) groups on polymer backbone are responsible for these characteristics. Many properties of NBR, including tensile strength, abrasion resistance, hardness, and heat resistance are dependent on the acrylonitrile (ACN) content. ...
The increasing environmental and toxic health concerns due to phthalate-based plasticizers are pushing researchers to eliminate these market leader plasticizers and to find nature-friendly bio-based plasticizers with reduced migration. The present study is also an effort in this regard. Herein, the epoxidized monoester of glyc-erol formal based on soybean oil is synthetically modified by carbonation in the presence of a catalyst to increase the polarity of the plasticizer. These modified and pristine plasticizers were incorporated in acrylonitrile─butadiene rubber and their migration analysis during heating the sample for 60 h were performed using fou-rier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) by observing the absorbance of the characteristic carbonyl stretching vibration peak (1736 cm À1) of plasticizer relative to the C H stretching vibration of butadi-ene (968 cm À1). The results of migration kinetics and mechanical testing demonstrated reduction of diffusion coefficients by modification while hardness and tensile strength are hardly affected. In addition to the fact that soybean oil as a natural resource is more sustainable, the additional synthesis step of binding CO 2 is advantageous for a green chemistry approach. K E Y W O R D S mechanical properties, plasticizer, rubber, spectroscopy, structure-property relationships
... Since engineering structural element experiences different environmental conditions in their service life, their behavior under these conditions must be investigated precisely. In this context, thermal properties of composites, and thermal aging of sandwich-structured composites have been documented in [62][63][64][65][66][67][68][69][70][71][72][73][74]. Recently, in [75] accelerated thermal aging was applied to 3D-printed mold insert to determine its effects on behavior and life time of the component. ...
Sandwich-structured composites are in high demand in various industries, and additive manufacturing has proven its ability to meet this demand. As a result of the advances in three-dimensional (3D) printing techniques, 3D-printed polymers have received considerable attention in fabrication of sandwich structures with complex geometries. This paper is concerned with design, manufacturing, and analysis of the 3D-printed sandwich-structured components which experienced various loadings and environmental conditions. The core structure plays a major role in the in-plane behavior of lattice composites, therefore in this study, sandwich specimens with two types of core topologies made of two common and similar 3D printing filaments, acrylonitrile butadiene styrene (ABS) and acrylonitrile styrene acrylate (ASA), were manufactured. Based on the applications of sandwich-structured parts, they might experience different temperatures in their service life. In order to determine effects of thermal environment, we conducted accelerated thermal aging within temperatures of 22-60 °C, which is below glass temperature of the examined materials. Based on a series of three-point bending tests, the failure behavior of the original and aged components are determined, and the effects of temperature change on the bending behavior of 3D-printed sandwich parts are discussed. The experimental practice revealed that ASA with honeycomb core specimens indicated highest stability under bending load after thermal aging. The current study sheds lights on durability of 3D-printed sandwich structural elements, and the obtained results demonstrate feasibility of 3D printing technology in fabrication of thermal-stable sandwich structures.
... NBR is, however, relatively sensitive to thermo-oxidative aging due to the unsaturated backbone of the butadiene part [16] . Several studies have been conducted to study the thermal degradation behavior of nitrile rubber [17] . The increasing environmental and toxic health concerns due to phthalate-based plasticizer have pushed the researchers to eliminate these market leader plasticizers and find nature friendly biobased plasticizers [18] . ...
The migration of plasticizer from a product can restrict the usability of the product as this process affects material properties and shorten their service life. The objective of the present study was to investigate this migration process and observe its dynamics under short-term thermal aging. For this purpose, in situ FTIR-ATR spectra were recorded after every hour for continuous 60 hours, while the plasticized and unplasticized NBR system was mounted and heated on ATR crystal with a heating plate at 70 °C. The band ratio of the corresponding characteristic peak areas from plasticizer carbonyl (1736 cm-1) and reference C-H stretching from butadiene (968 cm-1) was determined after every hour. TGA analysis carried out on similar NBR samples with gradually increasing plasticizer amounts helped to obtain the calibration curve which was used to determine the migrated plasticizer amount. With the obtained data, it was possible to determine the diffusion coefficient and to quantify the migrated plasticizer amount during short-term thermal aging and thus present a universal tool for the comparison of different plasticizers with respect to their migration behavior.
... During aging at 60°C, the amount of 2-butoxyethanol increased slowly, but only a few new low molecular weight products were formed over 224 days of aging. were not detected in an earlier HS-GC-MS study of the same nitrile rubber even though a higher extraction temperature (100°C vs. 80°C) was used during the HS-GC-MS analysis (Hakkarainen et al., 2003). ...
Here we discuss the newly developed micro and solventless sample preparation techniques SPME (Solid Phase Microextraction) and MESI (Membrane Extraction with a Sorbent Interface) as applied to the qualitative and quantitative analysis of thermal oxidative degradation products of polymers and their stabilizers. The coupling of these systems to analytical instruments is also described. Our comprehensive literature search revealed that there is no previously published review article on this topic. It is shown that these extraction techniques are valuable sample preparation tools for identifying complex series of degradation products in polymers. In general, the number of products identified by traditional headspace (HS-GC-MS) is much lower than with SPME-GC-MS. MESI is particularly well suited for the detection of nonpolar compounds, therefore number of products identified by this technique is not also to the same degree of SPME. Its main advantage, however, is its ability of (semi-) continuous monitoring; but it is more expensive and not yet commercialized.
... During aging at 60°C, the amount of 2-butoxyethanol increased slowly, but only a few new low molecular weight products were formed over 224 days of aging. were not detected in an earlier HS-GC-MS study of the same nitrile rubber even though a higher extraction temperature (100°C vs. 80°C) was used during the HS-GC-MS analysis (Hakkarainen et al., 2003). ...
This presentation will focus on both the characterization of new materials for SPME and their use in extracting analytes of interest from complex matrices. Solid phase microextraction (SPME) is an important sampling tool. It consists of placing a coated fiber above a sample (headspace mode) or immersing it in a liquid such that molecules (analytes) of interest can be selectively extracted and concentrated. The captured species are then released by heating or dissolution into a chromatograph for separation and identification. It is a ‘green’ method because no additional solvent is used in this process. We have developed a new class of SPME fibers that offer extraordinary capacity and speed. They are prepared by sputtering a material under conditions that lead to a nanoporous coating on the fiber. When silicon is sputtered under these conditions, its outermost surface can be additionally oxidized, leading to a high density of silanol groups than can be subsequently silanized. For example, the fibers can be derivatized with octadecyldimethylmethoxysilane by chemical vapor deposition (CVD), which creates a hydrophobic extraction medium. The performance of our 2 micron sputtered coatings has been compared to that of thicker (7 micron) commercial coatings. Our fiber consistently outperforms the commercial fiber, showing significantly higher capacity for alcohols, amines, aldehydes, and esters. Real world samples, e.g., hops and PAH from water, have also been analyzed. Different coating thicknesses have been prepared and evaluated. Sputtered coatings have been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and wetting.
This study presents an analysis of plasticizers and other additives in elastomers using several techniques to obtain relevant information for aging investigations. Thermogravimetric quantification of polymeric matrix, polymeric matrix char, carbon black, inorganic substances, plasticizers and other additives is commonly used. However, the thermogravimetric weight loss attributed to plasticizers and other additives contains additional components whose contribution to the weight loss has not been considered. Unreported components include water and carbonyl sulfide, which develop over long-term elastomer aging, and should be separately accounted for. This study employed Karl-Fischer oven techniques for calculating water content and linked thermogravimetric analysis with Fourier-transform infrared spectroscopy to measure carbonyl sulfide. Chromatoprobe-GC/MS was used to determine the ratio between rubber-related substances and JP-8 fuel and its additives, which can diffuse into rubbers. In fuel bladders, this occurrence is frequently observed, and the ratio consistently decreases over time.
The shelf life of MS29513-016 nitrile O-Rings was determined by accelerated heat aging from 40 to 85°C for varying aging times up to 50 weeks. The microhardness, tensile strength and 50% tensile stress all rise as a function of aging time while the elongation at break decreases. The crosslink density by solvent swell followed the development or loss of network chains during the aging process. In this case, the net increase in crosslink density showed a good correlation with the hardness, tensile strength and tensile stress results. Property loss is attributed to the labile nature of the sulfur cure system, the high double bound content of the nitrile rubber and the high level of ester plasticizer in the compound. Activation energies were lower than expected due to the sealed plastic packaging which impeded oxygen migration. Nevertheless, results clearly show that the O-Rings are out-of-specification beyond 7 years of shelf life due to the loss of elasticity (elongation at break < 200%). The nominal 15 year shelf life for nitrile rubber used in aerospace sealing applications according to SAE AS5316 needs to be reconsidered in light of the results.
Thermal aging is possibly the most significant factor affecting the rapid gas decompression (RGD) resistance of rubber. In this study, NBR vulcanizates by different sulfur curing systems such as conventional (CV), semi-efficient (SEV), and efficient (EV) were thermally aged for 7 days at 100 °C. The effect of thermal aging on RGD resistance, and physico-mechanical properties has been evaluated by changes in the rating of RGD and properties before and after aging. The presented results show that thermal aging of NBR vulcanizates strongly depends on crosslink density and mechanical properties. Thermal aging of nitrile rubber samples increased the crosslink density and decreased tensile and tear strength which lead to lower RGD resistance. The significant changes of RGD resistance were in the CV > SEV > EV system order during aging. The results obtained indicate that the SEV system might be a suitable selection for engineering applications with middle physico-mechanical properties and good thermal aging and RGD resistance.
Whitening phenomena of the EPDM composites with different inorganic filler compositions which were aged at 90^{\circ}C for 7 days in air and tap water atmospheres, respectively, were investigated. The aged samples in tap water containing stearic acid exhibited severe whitening phenomena, while all the samples aged in air did not show any whitening. Depending on the filler compositions, there was no big difference in the whitening phenomena. The whitening materials were analyzed using gas chromatography/mass spectrometry (GC/MS), image analysis, energy-dispersive X-ray spectroscopy (EDX), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The whitening materials were identified to be salts of stearic acid. The salts of stearic acid were formed by reaction of metal cation in tap water and stearic acid in the sample.
Polyacrylonitrile (PAN) films were exposed to radiations of long wavelengths (λ ≥ 300 nm) and of short wavelength (λ = 254 nm) under atmospheric oxygen. Changes in the Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectra were followed and compared to those obtained during the thermolysis and the thermooxidation of PAN films at 150°C. The products formed in these four conditions of degradation were identified by coupling FTIR and UV-Vis analysis to chemical derivatisation reactions and physical treatments. An analysis of the gas phase has also been done. A general mechanism accounting for thermolysis, thermooxidation and photooxidation is proposed.
Imaging chemiluminescence measurements on nitrile-butadiene rubber, before and after subjection to accelerated aging, did not give the expected heterogeneous oxidation profile. The results followed the migration and depletion of an easily peroxidised plasticiser. This indicates the usefulness of chemiluminescence as a very sensitive tool in measuring aging phenomena in polymers and also the difficulties in interpreting the origin of the peroxides resulting in the chemiluminescence signal
Infrared and NMR have been used to follow the thermal degration of polyacrylonitrile. Infrared band assignments are made for the degraded material based on comparison with solid state 13C NMR studies and elemental analysis. Solid state 13C NMR studies show that in addition to the previously proposed degradation by cyclization, degradation by unsaturation on the polymer backbone also takes place.
The photo-oxidation of acrylonitrile-butadiene copolymers (NBR) has been investigated for comparison with the photo-oxidation of various polybutadienes (BR) and styrene-butadiene copolymer (SBR) which have been studied recently. Numerous similarities are revealed between these elastomeric materials. Associated hydroperoxides are primarily formed in the allylic position of the butadiene units. Associated unsaturated hydroperoxides are then decomposed into secondary allylic alcohols and αβ unsaturated ketones. The latter absorb at wavelengths longer than 300 nm and are photo-oxidized into saturated acids. The most outstanding feature is associated with the rate of disappearance of double bonds and the rate of formation of photoproducts which becomes zero after 10 h of irradiation. Photo-oxidation stopped after a few hours of irradiation. By the use of micro FTIR analysis, a concentration profile of photoproducts and double bonds has been obtained and a heterogeneous reaction has been revealed. Only two differences have been noticed between the photo-oxidation of BR, SBR and NBR. The first difference is that the presence of acrylonitrile units favours the formation of hydrogen bonds between hydroperoxides and alcohols. The second difference resides in the lower permeability to oxygen of NBR compared with BR and SBR.
The thermal ageing at 100°C of vulcanized acrylonitrile-butadiene copolymer (NBR) is described. Analysis was based both on infrared spectroscopy (surface analysis) and on physical properties analysis (tensile and microhardness tests). Both methods appear to be complementary to describe the two competitive phenomena (oxidation and crosslinking) involved in the elastomer ageing. It is emphasised that the mechanical behaviour of aged NBR is different in comparison with chloroprene rubber.
The thermal and photo-oxidation of various formulations of polychloroprene have been studied. The ATR-FTIR technique has been especially used. The first step in oxidation is an allylic hydrogen abstraction leading to different radicals. Some hydroperoxides are formed and then decomposed into alcohols, ketones, acid chlorides and acids. The influence of crosslinking and carbon black on the oxidative degradation is also reported.
Accelerated thermal degradation of nitrile-butadiene rubber was studied (a) in air, at atmospheric pressure, and temperatures of 90, 105 and 120 °C; (b) in air, at 90 °C and 5 atm, at 105 °C and 3 atm and 5 atm, and at 120 °C and 3 atm and 5 atm. The changes of elongation at break as a result of the accelerated thermooxidative degradation were studied, and the importance of air pressure as a thermooxidative degradation accelerator is pointed out. On the basis of the experimental results, kinetic equations of thermal degradation of nitrile-butadiene rubber in an oven with forced air circulation and in pressurized air are derived.
The intermediate and final degradation products formed in six different low-density polyethylene (LDPE) films modified with either starch and/or pro-oxidants or photosensitizers (Scott−Gilead formulation [SG]) were investigated. We propose that dicarboxylic acids and ketoacids, formed in the materials to varying degrees, are due to both secondary oxidation products and a zip depolymerization mechanism by backbiting through a cyclic transition state. Hydrocarbons, ketones, carboxylic acids and dicarboxylic acids are formed during early stages of photo-oxidation, and the ketones disappeared while several ketoacids appeared and the relative amount of dicarboxylic acids increased in the most severely degraded materials. During prolonged photo-oxidation, additional oxidation of ketones and monocarboxylic acids to dicarboxylic acids explains the high amount of dicarboxylic acids. In the thermo-oxidized samples the amount of ketones and monocarboxylic acids remained high even in the most degraded samples. Mono- and dicarboxylic acids were formed in several micrograms per 100 mg of polymer, while the ketones and ketoacids were formed in fewer micrograms per 100 mg of polymer. LDPE modified with the iron dimethyldithiocarbamate (SG1) was the most susceptible material to photo-oxidation, while LDPE containing starch and pro-oxidants (LDPE-MB) was the most susceptible material to thermo-oxidation. Degraded LDPE-MB demonstrated less formation of degradation products; e.g., only in UV-initiated samples thermally degraded at 80 °C for 5 weeks could degradation products be detected. Larger amounts of ketones and ketoacids were formed in the SG materials than in the starch-filled materials.
Carboxylic acid salts, which are compounds involving strong hydrogen bonds between carboxyl and carboxylate groups, have been largely ignored in previous studies of the microstructure of ionomers. In the vast majority of commerical applications of ionomers that are derived from acrylic or methacrylic acid copolymers, however, the carboxylic acid groups are only partially neutralized and there is a stoichiometric excess of carboxylic acid groups to metal cations present. It is under these circumstances that the formation of acid salts becomes particularly significant. In this work we present infrared studies of anhydrous partially and fully neutralized ethylene-co-methacrylic acid copolymer samples. Zinc ions were introduced into the sample by immersion in a dilute solution of diethylzinc in hexane, which results in a material that resembles a "skin-core" composite of a fully neutralized tetracoordinated zinc carboxylate skin and an essentially pure acid copolymer core. This is a quasi-equilibrium situation, since mixing of the skin and core is prevented by the restricted mobility of the fully neutralized zinc salt. At elevated temperatures, however, the fully neutralized zinc salt and the pure acid copolymer mix and the transformation to hexacoordinated zinc carboxylates and zinc acid salts is observed in the infrared spectrum. Significantly, incorporation of a flexible miscible polymer, poly(vinyl methyl ether), reduces the temperature at which this transition occurs. The results are discussed in terms of a series of equilibria. Acid salts are local structures that need to be considered when developing models of ionomers.
A number of volatile pyrolyzates of large-scale thermolysis of ABS and SAN plastics, which include phenyl substituted aliphatic nitriles and dinitriles, have been tentatively identified by GC-MS. The exact isomers of most of these compounds have, however, not been specified, owing to limitations of 70 eV electron ionization (EI) mass spectrometry and temperature-programmed retention indices in the absence of model compounds. In this study, some of the isomeric forms of these compounds were clarified using chemical ionization (CI) mass spectrometry and capillary gas chromatography (GC) involving model compounds. The presence of phenylacetonitrile, 2-phenylpropanenirile, 3-phenylpropanenitrile, trans-3-phenyl-2-propenenitrile, and 4-phenylbutanenitrile among the pyrolyzates was confirmed by GC. Isobutane and methane CI of the nitriles yielded intense MH+ and adduct ions of low to medium intensity. Most of the smaller phenyl substituted nitriles tended to fragment by loss of 27 mass units, attributed to HCN. Isobutane CI of the larger molecules produced more fragmentation than methane CI which yielded little or no fragmentation. The reliability of the CI spectra was limited to the role of providing molecular formula information and some indirect evidence for the presence of the nitrile group in the molecules.