Effects of different drying methods on the microstructure and thermal oxidative aging resistance of natural rubber

In this work, the wet natural rubber granules were dried by hot air and by microwave at 115°C, respectively; the morphological structures of dried natural rubber granules were studied by using a scanning electronic microscope, whereas the thermal oxidative properties of dried natural rubber granules were investigated by comparison of variation in properties before and after aging, and the changes in the thermal oxidative decompose temperatures. The results showed that it needed 13.47 min for microwave drying and 210.00 min for hot air drying to reduce the moisture content of wet natural rubber to the required value. The granules of natural rubber dried by microwave were of rough surfaces and the cutting traces produced during the processing of wet natural rubber remained on the natural rubber surface; whereas, the natural rubber granules dried by hot air were of smooth surfaces, and the cutting traces produced during the processing of wet granules disappeared. The thermal oxidative resistance of vulcanized natural rubber dried by microwave improved significantly. The initial plasticity (P₀), plasticity retention index, and thermo‐oxidative decomposition temperature of natural rubber dried by microwave were higher than those of natural rubber dried by hot air. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effects of natural astaxanthin-modified silica on properties of natural rubber

Natural astaxanthin is a natural substance extracted from algae such as Haematococcus pluvialis. Its molecular structure contains conjugated double bonds as well as keto and hydroxyl groups, and therefore it has high activity. In this research, natural astaxanthin was used to modify the surface of the silica, and its effects on natural rubber vulcanization properties, physical and mechanical properties, dynamic properties, and antiaging properties were studied by means of rubber process analyzer, dynamic mechanical anaylsis, and scanning electron microscopy. The results showed that natural astaxanthin-modified silica could reduce the degree of delayed vulcanization. At the same time, the resilience and abrasion resistance of the obtained vulcanizates were increased. The DIN abrasion volume of the vulcanizates modified and reinforced by the second strategy decreased by 19.2% and 23.6%, respectively; the Payne effect of the natural astaxanthin-modified silica/NR composites was weakened, and the dispersibility of the filler and the compatibility with the rubber matrix was significantly improved. Regardless of which strategy was used to modify the silica, the vulcanizates had a lower rolling resistance. Specially, it could greatly improve the hot air aging resistance property of rubber. Natural astaxanthin as being a renewable feedstock is expected to have a quite broad applications in the rubber industry. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 136, 47287.     

Compressive stress relaxation modeling of butadiene rubber under thermo‐oxidative aging

The compressive stress relaxation tests of butadiene rubber (BR) at different thermo‐oxidative aging temperatures were carried out. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR‐ATR) was used to observe the variations of internal groups before and after the thermo‐oxidative aging. Magnetic resonance‐crosslink density (MR‐XLD) spectroscopy was used to measure the crosslink densities. The results showed the compressive stress relaxation of BR during thermo‐oxidative aging was dominated by chemical reactions: crosslinking, chain scission, and oxidation. Then an empirical model and an amendatory standard linear solid (SLS) model were put forward to describe the compressive stress relaxation behavior of BR. Both models fitted the data well. The SLS model, based on the aging mechanism of BR, not only made up the disadvantages of the empirical model, but also considered the changes of intrinsic viscosity (η) during the thermo‐oxidative aging of BR. The SLS model showed that the thermo‐oxidative aging of BR was mainly dominated by the crosslinking and oxidation reactions. This research proposes the amendatory SLS model and has important significance for study the stress relaxation behavior of crosslinked rubbers during thermo‐oxidative aging. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44630.     

DSC valuation of PRI of raw natural rubber

Thermal oxidation of raw natural rubber from Hevea brasiliensis was analyzed by differential scanning calorimetry (DSC) in dynamic mode. The results obtained revealed a linear relation between the PRI and onset temperature obtained by DSC (r² = 0.91), for PRI values <70. On the other hand, when the natural rubber PRI was over 70, DSC was unable to assess that criterion accurately. This was probably because the two techniques were not equivalent regarding the phenomenon measured. Oxidation primarily results in chain scissions during PRI measurement. In DSC, the transition seen during thermal oxidation was associated with crosslinking. In fact, thermo‐oxidation is in the initial phase when PRI is measured, but in the terminal phase at the onset of transition in DSC. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2354–2359, 2001     

天然橡胶光/热氧老化及抗老化性能研究进展

对天然橡胶的老化失效行为，特别是光/热氧老化机理进行了总结，同时综述了自然老化和人工加速老化等常见老化方法及天然橡胶的防老化技术，并展望了天然橡胶防老化技术未来的发展趋势。     

Nanocomposites based on epoxidized poly(styrene-co-butadiene) rubber and graphene nanoplatelets

Nanofillers play as reinforcing agents of the polymer matrix. The reinforcement and dynamic mechanical properties of nanocomposites based on filled epoxidized-poly(styrene-co-butadiene) rubber are investigated. The modification of the polymer matrix allows improvement in polymer–filler interaction, and thus the mechanical properties of the vulcanizates. Here, the rubber was modified by introducing the epoxy functional groups in the matrix. The quantification for epoxidation rate was analyzed by means of NMR and ~8.8% epoxidation was optimized. The nanocomposites were prepared by melt-mixing technique. The influence of rubber epoxidation in enhancing dynamic mechanical and thermal properties was demonstrated. Stable filler networking using exfoliated graphene nanoplatelets (xg C750) and carbon black (CB-N234) in epoxidized rubber is described through multihysteresis measurements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47802.     

Application of computed X-ray tomography scanning in the study of thermo-oxidative degradation of thick-walled filled natural rubber vulcanizates

The aging of five thick-walled natural rubber compounds has been studied by computed X-ray tomography scanning and crosslink density measurements. The compounds were compouded as ordinary carbon-black-filled rubbers with sulfur and peroxide as curing agents. The rubber samples were aged in air at 70, 100, and 150°C for 1000h. The relatively new technique of computed X-ray tomography scanning proved to be a good method for studying the aging procedure, and especially for following the crack propagation in the surface. Antioxidants (TMQ and 6PPD) had a low effect on the resistance toward oxidative degradation and crosslinking under these conditions. Surprisingly, the efficient sulfur-vul-canized material had a poor resistance toward thermal degradation. When the crosslink density and the computed X-ray tomography scanning results were compared, it was assumed that the computed X-ray tomograph detected oxygen in the surface, both as elementary oxygen and as oxygen in degradation products, i.e., in carbonyls. The results agree well with the theory that oxidative aging is limited by the ability of the oxygen to diffuse into the material.     

改善丁苯橡胶老化性能的方法

简单介绍丁苯橡胶老化的原理以及主要因素臭氧,其次热氧。主要综述了改善丁苯橡胶静态制品和动态制品的耐臭氧老化性的物理方法,如微晶蜡和表面涂层,以及化学方法,如γ射线辐射交联、化学防老剂、与耐臭氧老化的聚合物共混。阐述了如何改善其耐热氧老化性的方法,包括增加苯乙烯的含量、填充适量炭黑和使用载硫体。     

Study of local oxidative degradation in polypropylene impact copolymer by energy dispersive X-ray system

Summary In this study, the thermal oxidative degradation of a polypropylene (PP) impact copolymer was examined using a transmission electron microscope equipped with an energy dispersive X-ray system (TEM/EDX). The oxidative behavior was visually captured by oxygen line analysis. The oxidation resistance of the ethylene-propylene rubber (EPR) phase was considerably higher than that of the PP matrix, indicating that the degradation behavior of the PP impact copolymer was heterogeneous. It was found that the higher resistance of the EPR phase originated from its primary structure by ¹³C-NMR measurement.     

2种方式干燥的天然橡胶干燥特性之研究

为探讨微波干燥天然橡胶新技术，分别在温度115℃下，采用电热烘箱产生热空气和微波干燥装置干燥湿天然橡胶胶粒，对二者的干燥特性及硫化胶性能进行对比分析研究。结果表明，微波干燥只需13．467min就可使胶料含水量降至0．791％，热空气干燥则需211min。天然橡胶微波干燥和热空气干燥主要包含失水率加速期、失水率减速期、失水率相对恒速期3个失水阶段。整个干燥过程中，微波干燥失水率较大，而热空气干燥失水率比较小。微波干燥天然橡胶硫化胶的耐热氧老化性能得到显著提高：其老化前后拉断伸长率变化率（-35％）和拉伸强度变化率（-59％）明显高于热风干燥天然橡胶硫化胶的拉断伸长率变化率（-62％）和拉伸强度变化率（-89％）。     

Effects of coupling agents on the properties of an NR/SBR matrix and its adhesion to continuous basalt fiber cords

The effects of various coupling agents on the characteristics and properties of a natural rubber (NR)/styrene–butadiene rubber (SBR) matrix and its adhesion to continuous basalt fiber (CBF) cords were studied. Four types of silane-based and two types of titanate-based coupling agents were added separately to the rubber matrix during the mixing process. The processability of the rubber compounds and the mechanical and tension fatigue properties of the vulcanizates were evaluated. The static and dynamic adhesion between the CBF cord/rubber matrices were investigated using the H pull-out test and an elastomer testing system, respectively. The results showed that the effects of the coupling agent were controlled by its chemical structure, and it was found that the addition of (3-aminopropyl)triethoxysilane was the most effective for enhancing the interfacial fatigue properties, due to the combined improvements of the initial adhesion, interfacial stress states, and the fatigue property of the rubber matrix. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47098.     

Effect of heterogeneous oxidative aging on light absorption by biomass burning organic aerosol

Light-absorbing organic aerosol (brown carbon, BrC) impacts the radiative balance of the earth’s atmosphere; however, the magnitude of this impact is poorly constrained due to uncertainties in BrC sources, composition, and lifetime. In particular, the role of chemical “aging” on the optical properties of BrC particles is poorly understood. Here we carry out laboratory studies aimed at understanding how one such aging process, heterogeneous oxidation, may affect the chemical and optical properties of biomass burning-derived BrC. We generate BrC from smoldering ponderosa pine needles, oxidize the BrC in a flow reactor, and use simultaneous measurements of aerosol optical properties and chemical composition to monitor changes upon oxidation. Under the set of conditions investigated here, we find that with increased oxidant exposure, the aerosol becomes more oxidized and less absorbing, presumably due to oxidative degradation of the chromophores. Both the kinetics and evolution of this process are oxidant dependent. While heterogeneous oxidation by ozone results in a rapid “bleaching” of the BrC (i.e., decrease in absorptivity), a substantial fraction of the BrC is resistant to bleaching by this mechanism. In contrast, bleaching due to heterogeneous oxidation by OH in the presence of ozone remains active over long timescales (timescale of days), suggesting a sustained evolution of BrC optical properties throughout the aerosol atmospheric lifetime.

Copyright © 2019 American Association for Aerosol Research     

Preparation and properties of natural rubber nanocomposites with solid‐state organomodified montmorillonite

A novel organomodified montmorillonite prepared by solid‐state method and its nanocomposites with natural rubber were studied. The nanocomposites were prepared by traditional rubber mixing and vulcanizing process. The properties of solid‐state organomodified montmorillonite were investigated by Fourier‐transform infrared spectroscopy (FITR) and thermogravimetric analysis (TGA). The dispersion of the layered silicate in rubber matrix was characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the nanocomposites consisting of solid‐state organomodified montmorillonite and natural rubber are obtained. The solid‐state organomodified montmorillonite can not only accelerate the curing process, but also improve the mechanical and aging resistance properties of NR. The properties improvement caused by the fillers are attributed to partial intercalation of the organophilic clay by NR macromolecules. In addition, the dynamic mechanical analysis (DMA) results showed a decrease of tanδmax and increase of T_g when the organoclay is added to the rubber matrix, which is due to the confinement of the macromolecular segments into the organoclay nanolayers and the strong interaction between the filler and rubber matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Stress–thermal oxidative aging behavior of hydrogenated nitrile rubber seals

The long-term thermal oxidative aging behavior of uncompressed and compressed hydrogenated nitrile rubber seals was studied in terms of the weight loss, chemical structure, crosslinking density, compression set, fracture morphology, and mechanical properties. It was found that weight loss of the uncompressed seals was more than that of the compressed seals due to restricted mobility of additives and molecular chains under compression. The ATR–FTIR results showed that hydroxyl groups and carbonyl groups both were formed under the uncompressed and compressed states, whereas only the generation of amide groups was observed under the uncompressed state. Additionally, crosslinking reactions dominated throughout the aging process, but stress-induced and oxidation-induced chain scissions occurred and competed with crosslinking during subsequent middle and later stages of aging at 110 °C. Compression set of the compressed seals implied the formation of a denser network structure. The surface damage of the uncompressed seals gradually turned more serious and inhomogeneous than that of the compressed seals. Mechanical properties of the uncompressed and compressed seals showed a similar variation tendency with exposure time and degraded more seriously at higher temperatures. The TGA results indicated that the aging conditions (elevated temperature and compressive stress) did not significantly affect the thermal stability of the rubber seals. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47014.     

天然虾青素改性白炭黑/天然橡胶复合材料的制备与性能

采用天然虾青素对白炭黑表面进行物理改性，并与天然橡胶（NR）制备成复合材料。利用RPA、DMA、SEM等测试手段对天然虾青素改性白炭黑/天然橡胶复合材料的结构与性能进行表征。结果表明，在硫化特性方面，与未采用天然虾青素改性白炭黑相比，采用天然虾青素改性白炭黑所得胶料的焦烧时间和工艺正硫化时间均缩短，促进了橡胶的硫化过程；在物理力学性能方面，所得硫化胶的拉伸强度基本不变，回弹性和耐磨性明显增加，压缩生热降低；在动态黏弹性方面，所得硫化胶的Payne效应明显降低，填料的分散性在一定程度上得到改善；在动态力学性能方面，所得硫化胶的滚动阻力降低，玻璃化转变温度提高。特别地，在耐老化方面，天然虾青素改性白炭黑/天然橡胶复合材料的耐热空气老化性能明显提高。     

Cold Plasma Modification Effects on the Water Flow through Sintered UHMWPE Membranes

Natural rubber latex and various concentration of natural antioxidant were blended in different ratios and irradiated at various absorbed doses by gamma rays from Co-60 source at room temperature. The aqueous extraction of Diospyros peregrina was used as natural antioxidant. It was found that the addition of different concentration of natural antioxidant into natural rubber latex improve the aging property of the film. Decreasing in tensile strength of rubber film with 10 phr natural antioxidant and 15 kGy radiation dose after 24 hours aging at 100°C was 9.34% compared to 13.89% for film without natural antioxidant. The tensile strength, tear resistance and modulus at 500% elongation of the rubber film were found to be optimum at 15 kGy radiation dose and with 10 phr natural antioxidant. Elongation at break, permanent set and swelling ratio decreases with the increasing absorbed radiation dose as well as the concentration of the natural antioxidant.     

Soybean oil induced efficient thermal–oxidative degradation of covalently crosslinked styrene butadiene rubber

It has been a technical challenge of recycling tire rubbers due to the covalently crosslinked polymer network structure. Unlike conventional recombination of crosslinked SBR under thermal oxidation, SBR vulcanizate was efficiently degraded by thermal oxidation at 150 °C in presence of soybean oil, resulting in 47.3% sol fraction by weight. The structural evolution of SBR vulcanizates during thermal oxidation was characterized by sol–gel ratio, chemical structure, molecular weight, and oxidative erosion on the rubber surface. It was found that the continuous oxidation process facilitated main chain scission of SBR vulcanizates, resulting in a decrease of molecular weight of the sol fraction. The concentration of carbonyl groups, sol fraction, and surface erosion continually increased with reaction time. The large amounts of soybean oil significantly affect the thermal stability of SBR vulcanizates. Moreover, soybean oil is more efficient in decomposition of the SBR vulcanizates and results in more homogeneous and efficient oxidation reactions than paraffin oil. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48935.     

Mechanisms of oxidative degradation. I. Oxidation of synthetic rubbers catalyzed by metallic ions

The oxidative stability of rubbers depends on the structure of the rubber and the impurities contaminating the rubber. It is known that the oxidation of natural rubber is accelerated by the presence of metallic impurities. Besides GR-S rubber and nitrile rubber, the effects of metallic impurities on the oxidation of new rubbers, especially those introduced after the discovery of Ziegler-Natta catalyst, have not been reported. In the first part of this paper, the theoretical background on the mechanisms of metalcatalyzed oxidation is given. Most of the early work was carried out for the oxidation of hydrocarbons in the liquid phase. The difficulties in applying the liquid-phase results to the oxidation of high polymers in the solid phase are mentioned. The new rubbers used for this study are polyisoprene, polybutadiene, cis-poly-1,3-butadiene, styrenebutadiene copolymer, butyl rubber, ethylene-propylene terpolymer (EPT), propylene oxide rubber, polyacrylic rubber, and butadiene-acrylonitrile rubber. The effects of stearic acid and various stearates on the oxidation of these rubbers are presented. The number of electrons transferred by the metal ion during redox reactions was found to be related to the effectiveness of the ion as a catalyst. Both the high and low oxidation states of the metal ion were shown to be active catalysts, supporting the accepted theory of metal catalysis through a hydroperoxide decomposition mechanism.     

Effect of ultraviolet-A radiation on surface structure,thermal, and mechanical and electrical properties of liquid silicone rubber

Liquid silicone rubber (LSR) products outdoors are often subjected to high intensity of ultraviolet (UV)-A radiation. However, the influence of UV-A radiation on LSR is rarely studied. To study the influence of UV-A radiation on LSR, the surface of LSR with UV-A aging time was characterized by tests at different detection depths [X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR)]. The operation properties (thermal stability and mechanical and electrical properties) for outdoor insulators were also analyzed. It was found that the porous surface and the loose layer of LSR increased, but the growth rate of them decreased as UV-A aging time increased. SiO₂ fillers were lost in the surface. C H bonds in  CH₃ and  CH₃ in Si CH₃ increased with aging time. The increased crosslinking density increased the thermal stability, hardness, dielectric loss tangent, relative dielectric constant, and volume resistivity and decreased elongation-at-break. The mechanical strength initially increased and then decreased. Based on the proposed aging mechanism, the UV-A resistance of LSR can be improved by reducing the amount of hydrogen-containing silicone oil and by increasing the molecular weight of raw rubber. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47652.