Multi-walled carbon nanotube reinforced self-crosslinking hydrogenated carboxylated nitrile butadiene rubber latex film with improved properties

A dielectric self-crosslinking hydrogenated carboxylated nitrile butadiene rubber (HXNBR) latex film was prepared by diimide reduction hydrogenation of XNBR latex and the doping of multi-walled carbon nanotube (MWCNT). The structures of the HXNBR and XNBR were characterised by Fourier transform infrared spectroscopy (FTIR) and ¹HNMR, confirming the successful hydrogenation of XNBR. The mechanical, thermal, and electrical properties of the prepared HXNBR latex films were studied, and the HXNBR latex film reinforced by only 3?phr MWCNTs exhibited improved mechanical, thermal, and dielectric properties.     

A study on the crosslink network evolution of nitrile butadiene rubber reinforced by in situ zinc dimethacrylate

In this article, we study the evolution of networks based on nitrile butadiene rubber (NBR) which is reinforced by in situ zinc dimethacrylate (ZDMA) during curing. The crosslink density of the composites cured for different time was evaluated by equilibrium swelling experiments. The curing process was analyzed by using a UR‐2030 Rotorless Rheometer. Mechanical properties of the composites cured for different time were also used to evaluate the evolution of the networks. The results reveal that the covalent crosslinked network of NBR is formed rapidly in the early curing stage while the ionic crosslinks grow gradually during the whole curing process. The ionic crosslinks affect much more on the mechanical properties and make the composite easier to achieve inextensibility limit of the network. A sketch for formation of the NBR/ZDMA network was proposed in the last part of this article. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Reversible crosslinking in epoxy resins. I. Feasibility studies

The objective of the research is to investigate epoxy resins where crosslinks formed in curing reactions can be cleaved and reformed without significant sacrifice in resin properties. In this phase of the investigation, experimental disulfide-containing crosslinking agents have been studied, including dihydrazides of dithiodicarboxylic acids(aliphatic and aromatic) and dithio-aromatic diamines. Conditions for curing reactions and for subsequent cleavage of crosslinks by reduction have been determined in model systems and confirmed for a prototype epoxy resin. A preliminary comparative evaluation of cure kinetics and of crosslink density and thermal and mechanical properties has been carried out for this resin cured with aromatic curing agents (4,4′-dithiodianiline and methylene dianiline) and with aliphatic compounds (3,3′-dithiopropionic acid dihydrazide and hexamethylene diamine). It has been shown that in a resin fully cured with disulfide-containing crosslinking agents, crosslinks could be ruptured by reduction, and reestablished by oxidation under mild conditions.     

Effect of imidazolium ionic liquid type on the properties of nitrile rubber composites

We investigated the influence of hydrophilic and hydrophobic imidazolium ionic liquids on the curing kinetic, mechanical, morphological and ionic conductivity properties of nitrile rubber composites. Two room temperature ionic liquids with a common cation—1‐ethyl‐3‐methylimidazolium thiocyanate (EMIM SCN; hydrophilic) and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI; hydrophobic)—were used. Magnesium–aluminium layered double hydroxide (MgAl‐LDH; also known as hydrotalcite) was added to carboxylated acrylonitrile–butadiene rubber (XNBR) whereas fumed silica Aerosil 380 was used in acrylonitrile–butadiene rubber (NBR) as reinforcing fillers. NBR compounds were vulcanized with a conventional sulfur‐based crosslinking system whereas XNBR compounds were cured with MgAl‐LDH. The optimum cure time reduction and tensile properties improvement were obtained when both ionic liquids were added at 5 parts per hundred rubber (phr). The results revealed that EMIM SCN and EMIM TFSI induced an increase in the AC conductivity of nitrile rubber composites from 10^?10 to 10^?8 and to 10^?7 S cm^?1, respectively (at 15 phr ionic liquid concentration). The presence of ionic liquids in NBR slightly affected the glass transition temperature (T_g) whereas the presence of EMIM TFSI in XNBR contributed to a shift in T_g towards lower temperatures from ?23 to ?31 °C, at 15 phr loading, which can be attributed to the plasticizing behaviour of EMIM TFSI in the XNBR/MgAl‐LDH system. Dynamic mechanical analysis was also carried out and the related parameters, such as the mechanical loss factor and storage modulus, were determined. © 2013 Society of Chemical Industry     

Characteristics of the photochemical prevulcanization in a falling film photoreactor

The photochemical prevulcanization of natural rubber (NR) latex via the thiol‐ene reaction is a new approach aiming at the replacement of noxious processing agents used in conventional sulfur vulcanization processes (e.g., accelerators) together with cost saving options. The crosslinking reaction involves the excitation of a selected photoinitiator with ultraviolet (UV) light which is followed by the formation of thioether links due to the thiol‐ene addition reaction. The photochemical process is carried out in a falling film photoreactor which provides not only a continuous prevulcanization process but also exhibits a technology which is already commercially well established. The main advantage of the falling film process lies in the short prevulcanization time and the mild reaction temperature. Following the idea of the manufacture of low‐allergenic surgical gloves made from NR latex without compromising on the glove quality by means of physical performance, crucial process parameters of the falling film process have been determined and characterized in this study. Surgical gloves were made from the photocured NR latex which was prevulcanized using selected process conditions. The physical properties including tensile strength, elongation, modulus, and crosslink density were examined together with the aging stability and the stability against high‐energy radiation (sterilization with gamma rays). It was found that the UV light intensity, the number of illumination cycles, the choice of photoinitiator, and the thiol crosslinker play an important part in the glove quality. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Novel self‐crosslinking film from hydrogenated carboxylated nitrile rubber latex

A new type of self‐crosslinking latex film was prepared from hydrogenated carboxylated nitrile‐butadiene rubber (HXNBR) latex by diimide reduction. The properties of the HXNBR rubber, including film surface morphology, physical properties, thermal stability and ageing properties, were investigated. FTIR spectroscopy was used to confirm the HXNBR structure, from which the degree of hydrogenation can be obtained. The morphology of the film surface was monitored by atomic force microscopy, which confirmed that HXNBR latex can form a continuous film with good cohesive properties from self‐crosslinking latex particles. The self‐crosslinking provided the latex film with excellent tensile strength. The thermal stability was improved after hydrogenation, as indicated by thermogravimetric methods. The activation energy for degradation was determined by Coats‐Redfern plots. Hot air oven thermal ageing confirmed that the oxidation resistance increased as the degree of hydrogenation increased. All these results showed that HXNBR latex can form a self‐crosslinking film with better mechanical properties, and heat and oxidation resistance than those of XNBR latex film in a wide range of film applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39865.     

Structure-property relations of carboxylated nitrile rubber

The technical properties and the network structure of carboxylated nitrile rubber (XNBR) having a mixed crosslink system of sulfur and metal carboxylate have been studied. XNBR of different carboxyl contents (Krynac 221, Krynac 110C), yielding different concentrations of ionic crosslinks, have been used for this purpose. The amount of ionic crosslinks was also varied by varying the amount of crosslinking agent (zinc peroxide). It has been observed that ionic crosslinks impart high tensile strength, permanent set, and hardness, while sulfur crosslinks introduce high flex crack resistance, elongation at break, and tear strength in the vulcanizate. Heat buildup and resilience could be explained with the help of stress relaxation experiments. Stress decay is more when the amount of ionic crosslinks is higher. Higher stress relaxation gives higher hysteresis. The kinetics of the crosslinking of a mixed crosslink system has also been studied. At overcure times the amount of ionic crosslinks is greater than that of sulfur crosslinks which desulfurizes in this region. The technical properties could be explained on this basis.     

硫化NR胶乳胶膜的结构与性能研究

对不同硫化体系和硫化方式硫化的ＮＲ胶乳胶膜的结构与性能进行研究。结果表明：采用不同硫化体系的硫化胶乳所形成的硫交联键主要的为多硫键,硫化胶乳胶膜的结构对性能的影响因硫化方式不同而有差异。     

Mechanistic approach to the curing of carboxylated nitrile rubber (XNBR) by zinc peroxide/zinc oxide

The crosslinking of carboxylated nitrile rubber (XNBR) with a special preparation based on zinc oxide/zinc peroxide (Struktol ZP1014) is studied. It is shown that ionic species, by metallic salts formation, and covalent crosslinks, by zinc peroxide decomposition, are formed. The complete process can be empirically split in two contributions, with mathematical modeling rendering a satisfactory fit to experimental data. However, infrared and calorimetric analyses support the contribution of at least three mechanisms to the torque build-up: a very fast ionic species formation process by the initial zinc oxide present; covalent crosslinks and additional ionic species formation coming from zinc peroxide decomposition and contributing at all times from the beginning but decaying with time; and a third, not yet determined, contribution that accounts for the torque increment at long times.     

Impact of blend ratio on the properties of graphene oxide‐filled carboxylated acrylonitrile–butadiene rubber/styrene–butadiene rubber blends

Carboxylated acrylonitrile–butadiene rubber (XNBR) and styrene–butadiene rubber (SBR) composites with 3 phr (parts per hundred rubber) graphene oxide (GO) were prepared using a latex mixing method. Effects of XNBR/SBR blend ratios on the mechanical properties, thermal conductivity, solvent resistance and thermal stability of the XNBR/SBR/GO nanocomposites were studied. The tensile strength, tear strength, thermal conductivity and solvent resistance of the XNBR/SBR/GO (75/25/3) nanocomposite were significantly increased by 86, 96, 12 and 21%, respectively, compared to those of the XNBR/SBR (75/25) blend. The thermal stability of the nanocomposite was significantly enhanced; in other words, the temperature for 5% weight loss and the temperature of the maximal rate of degradation process were increased by 26.01 and 14.97 °C, respectively. Theoretical analysis and dynamic mechanical analysis showed that the GO tended to locate in the XNBR phase, which led to better properties of the XNBR/SBR/GO (75/25/3) nanocomposite. © 2017 Society of Chemical Industry     

Effect of prevulcanization on the rheological behavior of natural rubber/styrene butadiene rubber latex blends

The effect of prevulcanization on the rheological behavior of natural rubber (NR), styrene butadiene rubber (SBR) latices, and their blends was studied with special reference to shear rate, blend ratio, vulcanizing systems, prevulcanization time, and accelerator systems. The NR latex showed a sharp increase in viscosity with increase in prevulcanization time due to high extent of crosslinking. However, SBR latex showed marginal effect on viscosity with prevulcanization time due to its low dry rubber content and low degree of unsaturation. Blends showed variations in viscosity according to the change in composition. The use of a single accelerator was found to have marked influence on the viscosity of the blends compared with a combination of accelerators. Swelling experiments were carried out in order to determine the crosslink density of the blends. The viscosity changes have been correlated with the crosslinking density of the latices and their blends. © 1996 John Wiley & Sons, Inc.     

Effect of curing systems on polymer-filler interaction,technical properties and fracture mode of carboxylated nitrile rubber

The effects of carbon black on polymer-filler interaction, technical properties and fracture mode of carboxylated nitrile rubber (XNBR) cured by different curing systems have been studied. Technical properties show improvement in all cases with increase of filler loadings. At lower loadings of filler, a marked difference in physical properties was observed among different curing systems whereas this difference is minimized at higher loadings when polymer-filler interaction overshadows the effect of the crosslinking system. Scanning electron microscope studies of tensile fracture surfaces have been made. While filler has marked effect on fracture mode, crosslinking system seems to have little effect. Unfilled (gum) and carbon-black (N 550) filled XNBR vulcanizates show different fracture patterns irrespective of the curing system. This is true in the case of sulphur, metal oxide and metal oxide-sulphur mixed crosslinking systems. But the dicumyl peroxide cured system shows a different fracture pattern and the difference is more in the case of gum vulcanizates.     

The effect of crosslinking type on the physical properties of carboxylated acrylonitrile butadiene elastomers

Vulcanization of carboxylated nitrile rubber (XNBR) with different vulcanizing agents (i.e., zinc peroxide, sulphur, and a zinc peroxide–sulphur mixed system) was studied. Properties of the vulcanized compounds depend on the type of crosslinking produced (i.e., ionic or covalent) rather than the crosslinking density. Ionic crosslinks gave rise to greater stress relaxation, relaxation rates, and a greater generation of heat. In the relaxation spectra, tan δ versus temperature, two transitions appeared. Those occurring at the lower temperature corresponded to the polymer T_g, while the transition occurring at the higher temperature was associated with ionic structures. The properties of the vulcanized compounds with ionic crosslinks decreased drastically after treatment with ammonia, which acts as a plasticizer of the ionic aggregates formed. The effect of ammonia disappeared on expansion in solvent, which resulted in the recovery of the original crosslinks, producing a value of v_r—volume fraction of swollen rubber in equilibrium—close to the original value and the reappearance of the ionic transition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 927–933, 1999     

Thermal and mechanical behavior of natural rubber latex‐silica aerogel film

A major problem in most natural rubber latex (NRL) commonly encountered like other polymer is susceptibility to mechanical properties and thermal degradation; particularly in thin film due to the presence of double bonds in the main chain. Therefore, it is desirable to seek for ways of improving these properties. Silica aerogel is a material with extraordinary properties was believed to have potential enhance properties in NRL films because of its high specific surface area. Therefore, based on the unique character of silica aerogel, NRL‐silica aerogel film was developed by latex compounding and dry coagulant dipping to form thin film where silica aerogel acts as filler. Silica aerogel, synthesized from rice husk was dispersed in a ball‐mill using distilled water for NRL compounding. Results indicate that increasing silica aerogel loading enhances the mechanical properties of the NRL‐silica aerogel film. Effects of postvulcanization processes were also investigated, whereby the best reinforcing effect was obtained at 4 phr silica aerogel loading with leaching postvulcanization condition. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

硫化体系在丁腈手套制备中的应用

介绍了N-羟甲基丙烯酰胺（N-AM）硫化体系在丁腈手套制备中的应用。实验采用羧基丁腈胶乳（XNBRL）为原料,以N-AM为硫化剂、二丁基二硫代氨基甲酸锌（Bz）为促进剂、ZnO为硫化活性剂,经过预硫化、硫化、干燥等过程制得羧基丁腈胶膜。通过测试胶膜性能,研究了A（N-MA）、B（ZnO）、C（Bz）配比等因素对胶膜物理机械性能的影响,发现C（BZ）是影响胶膜物理性能的主要因素,其次是A（N-MA）和B（ZnO）。研究最终确定了最佳硫化体系配比A：B：C为3．5：2：1。     

Use of sodium and potassium butyl xanthate as accelerator for room temperature prevulcanization of natural rubber latex

Sodium and potassium butyl xanthates (Nabxt and Kbxt) were prepared in the laboratory. Characterization of these xanthates were done using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (¹H NMR) spectroscopy, thermogravimetric analysis (TGA), and differential thermal analysis (DTA) techniques. These xanthates were used as accelerators for the prevulcanization of natural rubber latex (NRL) at room temperature. Optimization of prevulcanization time was done. Films were casted from these prevulcanized NRL. Tensile properties of latex vulcanisates were measured and potassium butyl xanthate gave superior properties to the NRL films compared with sodium butyl xanthate. Effect of thermal ageing on tensile properties of these prevulcanized NRL films was also investigated and these properties were found to be improved after thermal ageing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of temperature on sulfur prevulcanization of natural rubber latex

Sulfur prevulcanization of natural rubber latex was conducted at 60, 70, 80, and 90°C for different periods. The extent of crosslinking was assessed. Tensile properties, water absorption, leaching, and stress-relaxation characteristics of the films were also evaluated. The volume fraction of rubber (Vr), which is a measure of crosslink density of the films, showed a maximum when prevulcanization was conducted at 80°C for 2 h or at 90°C for 1 h. At lower temperatures, the rate of reaction was slow. At each temperature, tensile strength and elongation at break decreased when the prevulcanization time increased, whereas the modulus increased up to a maximum crosslinking and thereafter decreased. Water absorption and leaching were more rapid in prevulcanized film than in postvulcanized film. The rate of stress relaxation slightly increased as the extent of prevulcanization increased. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1913–1920, 1997     

Keratin as a filler for carboxylated acrylonitrile‐butadiene rubber XNBR

The presented investigations concern the distribution and characterization of keratin waste, derived from the processes of cattle skins, and its use as a filler for carboxylated acrylonitrile‐butadiene rubber XNBR. The recovered keratin improves mechanical proprieties such as tensile strength, hardness, resistance to fuel and oil. The addition of keratin in a quantity of five parts per hundred rubber (XNBR) increases the crosslinking density of composites, as testified by the formed ion nodes and the existing mono and disulphide bonds. Electric conductance and water absorption increased with time for elastomers filled with protein. Therefore these composites are biodegradable after their period of use. As a result hydrophilic–hydrophobic protein–elastomeric composites will have usable properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of different types of filler and filler loadings on the properties of carboxylated acrylonitrile–butadiene rubber latex films

The effects of different types of fillers and filler loadings on the properties of carboxylated nitrile rubber (XNBR) latex were identified. Silica, mica, carbon black (CB; N330), and calcium carbonate (CaCO₃) were used as fillers with filler loadings of 10, 15, and 20 parts per hundred rubber. Furnace ashing and Fourier transform infrared analysis proved that interaction existed between the fillers and XNBR latex films. The morphology of the filled XNBR films was significantly different for different types of fillers. Mica and CaCO₃ fillers showed uneven distribution within the XNBR film, whereas other fillers, such as silica and CB, showed homogeneous distribution within the films. In the observation, silica and mica fillers also illustrated some degree of agglomeration. The mechanical properties (e.g., tensile and tear strengths) showed different trends with different types of fillers used. For silica and mica fillers, the mechanical properties increased with filler loadings up to a certain loading, and decreased with higher filler loadings. For CB filler, the mechanical properties increased gradually with increasing filler loadings. CaCO₃ fillers did not increase the mechanical properties. The crosslinking density of the XNBR films increased when they were incorporated with fillers because of the presence of elastomer–filler and filler–filler interactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films were extensively investigated by means of several series of model latexes with varying backbone polymer crosslinking density and interfacial crosslinking functional groups. It was found that the tensile strength of crosslinked model latex films increased with increasing gel content (i.e. crosslinking density) of latex backbone polymers up to about 75% and then decreased with further increase in gel, while their elongation at break steadily decreased with increasing gel content. These findings showed that latex particle coalescence was retarded above a gel content of about 75% so that the limited coalescence of latex particles containing gel contents higher than 75% prevented the tensile strength of crosslinked latex films from increasing by further crosslinking the latex backbone polymers. This was contrary to the theory of rubber elasticity that the tensile strength increases with increasing molecular weight and crosslinking density. This limitation was found to be overcome by the interfacial crosslinking among latex particles during film formation and curing. This paper will discuss the effects of both latex backbone polymer and interfacial crosslinking on latex film properties. It will also discuss the development of self-curable latex blends and structured latexes containing co-reactive groups: oxazoline and carboxylic groups.