Studies on thermal–oxidative degradation behaviours of raw natural rubber: PRI and thermogravimetry analysis

Abstract

Thermal–oxidative degradation behaviours of raw natural rubber (NR) have been investigated by using thermogravimetry analysis in inert and oxidative atmospheres and the plasticity retention index (PRI). The activation energy E_a, was calculated using Horowitz–Metzger and Coats–Redfern methods and compared with PRI. The E_a values obtained by each method were in good agreement with each other. The June samples are the least stable rubbers among the studied ones, whereas February samples exhibited the highest values of activation energy, therefore in agreement with the PRI behaviour, which indicates that the thermo-oxidative stability of the June samples are the poorest during the thermo-oxidative degradation reaction. Natural rubber is a product of biological origin, and thus these variations in the values of thermal behaviour and PRI might be related to the genetic differences and alterations of climatic conditions that act directly on the synthesis of non-rubber constituents, which are generally reflected in latex and rubber properties.     

不同种植年份橡胶树PR107生胶性能的研究

研究了1981年、1986年、1990年、1996年4种不同种植年份的PR107天然橡胶的生胶性能和混炼胶的硫化特性以及硫化胶的物理机械性能,并对胶样进行TG/DTG分析。结果表明:1986年份的生胶相对分子质量最大,硫化速率最快,硫化胶的物理机械性能最好,热稳定性最好;1996年份的生胶的热稳定性最差。     

Study on effective storage time of raw natural rubber

The effective storage time (i.e., storage life) of raw natural rubber (NR) was investigated with heat‐accelerated storage aging combined with thermogravimetry (TG) and differential thermal analysis (DTA) method, as well as the heat aging life equation. The test results show that the effective storage time of raw NR can be estimated more conveniently in relatively shorter time by this method. It is found that the effective storage time of raw NR is associated with rubber processing technology and with ambient temperature during storage, but it has little relation with P₀ and PRI. At ambient temperature, the effective storage time of the natural‐coagulated and biological‐coagulated NR is obviously higher than the acetic acid‐coagulated NR; the lower the ambient temperature, the longer the effective storage time. The effective storage time of the acetic acid‐coagulated NR is 12.2–13.4 years at ambient temperature of 30°C, 23.8–25 years at 25°C, and 47.4–47.9 years at 20°C. The effective storage time of the natural‐ and biological‐coagulated NR is 13.7–15.2 years at 30°C, 29.6–30.4 years at 25°C, and about 62.5–65.8 years at 20°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4114–4119, 2006     

Extensional rheology of raw natural rubber from new clones of Hevea brasiliensis

Natural rubber (NR) is a biopolymer whose properties depend on the molecular structure of the 1,4‐cis polyisoprene chains, nonrubber constituents, environmental conditions, etc. NR has been characterized by Mooney viscosity, Wallace plasticity, nitrogen content (%N). However, these cannot effectively account for clone's differences. The aim of this work is to use extensional rheology to characterize and differentiate NR samples as for clone type and the season of the year in comparison to the traditional characterizations. Three IAC 300 series and RRIM 600 clones of Hevea brasiliensis tapped between October 2006 (Oct_06) and August 2008 (Aug_08) were investigated. IAC 329 clones showed the least susceptibility to seasonal changes, whereas RRIM 600 was the most influenced. An opposite trend between extensional viscosity (η_E) and %N was established. The former was very sensitive to changes in the molecular structure of NR, being fundamental for monitoring purposes and strategic development of new rubber tree clones. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Study on thermal degradation of sol and gel of natural rubber

The thermal degradation of natural rubber (NR) in air at a constant heating rate was studied by using of the thermogravimetry (TG) and thermogravimetry and differential thermal analysis (TG–DTA) simultaneous techniques. It indicates that the temperature of thermal degradation of gel and sol of NR rises linearly along with the increment of the heating rate, whereas the heating rate has little effect on the degree of thermal degradation. Accompanying other side reactions, the thermal degradation of NR is not a simple random chain scission process, and it is an exothermic reaction. The dynamic variation of molecular structure of NR during the thermal degradation was studied using Fourier transform infrared spectroscopy (FTIR). It shows that the products of the thermal degradation of both sol and gel of NR are hydroperoxide, carbonyl, and hydroxyl compounds. The formation of gel makes the temperature of the thermal degradation of NR decrease and the rate of the thermal degradation increase; thus, the thermal stability of NR is reduced. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1339–1344, 2000     

The thermal behaviour of lignins modified by chlorophosphazenes

The thermal behaviour in air of lignins modified by chlorophosphazenes as well as that of the raw materials of lignins has been investigated using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA). The thermogravimetry and derivative thermogravimetry studies of lignins modified by chlorophosphazenes have shown their thermal resistance to be relatively higher than that of the intital raw materials of lignins in concrete kraft lignin and sodium ligninosulfonate. The differential thermal studies have demonstrated that the thermal degradation of products investigated takes place via exothermic processes. The lignins modified by chlorophosphazenes have been shown to be thermal and flame-resistant materials.     

Comparative study on the technological properties of latex and natural rubber from Hancornia speciosa Gomes and Hevea brasiliensis

This work reports a systematic comparative study of the technological properties of natural lattices and rubbers extracted from Hancornia speciosa Gomes and Hevea brasiliensis [(Willd. ex Adr. de Juss.) Muell.‐Arg.] (clone RRIM 600) trees from 11 collections in Brazil throughout 2004. Natural rubber latex particle sizes and distributions were quite similar with an average diameter around 1 μm. Molecular weight, Wallace plasticity, and Mooney viscosity values were approximately the same for both rubbers. Fourier transform infrared spectroscopy peaks characteristic of natural rubber were observed for both Hancornia and Hevea. The measured differences in technological properties included lower values for Hancornia dry rubber content, % ash, % nitrogen, and plasticity retention index but higher value for acetone extract. Interestingly, nitrogen and protein content were much lower in Hancornia, suggesting that it may have important applications in nonallergic rubber uses. This represents the first report of lacticifer‐produced low‐protein natural rubber. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

原位接枝改性对白炭黑补强NR橡胶结构与性能的影响

研究了原位接枝改性白炭黑补强的天然橡胶力学性能及动态性能,采用红外光谱、热失重、转矩流变仪分别对改性前后的橡胶结构进行了表征。结果表明,白炭黑填充的天然橡胶经原位接枝改性后,拉伸强度和定伸应力均提高,压缩永久变形和阻尼因子(tanδ)均减小;当改性剂用量为9份时,胶料综合性能最好。TG分析及红外光谱分析结果表明,改性剂在混炼阶段与橡胶、炭黑粒子发生了接枝反应,在硫化阶段参与了交联反应。转矩流变仪测试结果表明,改性剂在混炼阶段需要达到一定的温度(约在120℃左右)才能与白炭黑发生接枝反应,且反应为吸热反应。     

氯化石蜡共混改性天然胶乳的研究

分别采用氯化石蜡、氯化石蜡／Sb2O3共混改性天然胶乳．考察了改性胶乳硫化胶膜的力学性能及阻燃性能．并进行了TG·DTG和DSC分析。结果表明：改性胶乳的阻燃效果比未改性天然胶乳的高．且氯化石蜡／Sb2O3共混改性天然胶乳可产生协同阻燃效果；随Sb2O3用量的增加．硫化胶膜撕裂强度增加．而拉伸强度下降。氯化石蜡／Sb2O3改性胶乳的热降解过程为二步反应．且起始热降解温度比天然胶乳的低．玻璃化转变温度提高。     

霉化对天然橡胶组分及其热降解过程的影响

采用红外光谱仪分析了微波干燥未霉化天然橡胶(NR)和霉化天然橡胶(NR—m)的组分。图谱显示,NR在1541.20cm-1处有酰胺Ⅱ吸收峰,而NR—m没有。采用热重分析法分别在氮气和空气气氛中测试了微波干燥的NR和NR—m热降解和热氧降解。TG和DTG曲线显示,NR和NR—m的热降解均为1步反应,热氧降解均为2步反应。在等速升温条件下,NR的热降解温度和热氧降解温度均高于NR—m,NR降解时的活化能明显低于NR—m;2试样的反应级数为:在热降解中n2,在热氧降解中n2;在热降解中NR的相关系数r均大于NR—m;随升温速率的增大,2试样的A值和A1值均增大。     

Study of the effect of natural rubber‐graft‐o‐aminophenol on the thermal stability and mechanical properties of nitrile rubber

The grafting copolymerization of natural rubber and o‐aminophenol was carried out by using two‐roll mill machine. The prepared grafted antioxidant, NR‐graft‐o‐AP, analyzed by using Infrared and ¹H‐NMR Spectroscopy techniques. The thermal stability, mechanical properties, and ultrasonic attenuation coefficient were evaluated for NBR vulcanizates containing the commercial antioxidant, PBN, and the prepared grafted antioxidant, NR‐graft‐o‐AP, and the control vulcanizate. Results of the thermal stability indicate that the prepared NR‐graft‐o‐AP can protect NBR vulcanizate against thermal treatment much better than the commercial antioxidant, PBN, and control mix, respectively. The prepared grafted antioxidant improves the mechanical properties of NBR vulcanizate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of Sol-Gel-Derived Nano-silica on the Properties of Natural Rubber-Poly Butadiene Rubber-Reclaim Rubber Ternary Blends/Silica Nanocomposites

Silica incorporation into natural rubber (NR)-polybutadiene rubber (PBR)-reclaim rubber (RR) ternary blend system was carried out by sol-gel technique at different temperatures. The effect of RR on silica reinforcement was studied for NR-PBR-RR blend systems. The physicochemical properties of sol-gel vulcanizates indicates that the reinforcing efficiency of the nanocomposites increases with increasing RR content. Sol-gel vulcanizates prepared at 50°C shows superior mechanical properties than others. The amount of silica incorporated by sol-gel technique was determined through thermogravimetry analysis, which indicates the increasing trend of thermal stability with silica content. SEM studies indicate the coherency and homogeneity in the NR-PBR-RR/SiO ₂ nanocomposites.     

Study of Resistance of Silicone Resin to Heat and Irradiation

Resistance of silicone resin to heat and irradiation was studied. The chemical structure of silicone resin before and after being heated and irradiated was analyzed by Fourier Transform Infrared Spectroscopy (FT-IR). The thermal stability of silicone resin was investigated by thermogravimetric analysis (TG) and differential thermogravimetry analysis (DTG), and its improvement was indicated by TG and DTG analyses of silicone resin after being irradiated by ⁶⁰Co γ-ray under different fluence. The surface morphology, mechanical properties, corrosion resistance and chemical resistance of silicone resin clear paints before and after being heated and irradiated were studied by SEM, EIS et al.     

三氯溴甲烷改性天然胶乳的力学性能与阻燃性分析

对单用三氯溴甲烷改性天然胶乳和并用三氧化二锑改性胶乳的硫化胶膜的力学性能和阻燃性能进行了研究,并采用TG和DTG进行了热性能的分析。结果表明:三氯溴甲烷与三氧化二锑改性天然胶乳比单用三氯溴甲烷改性胶乳的阻燃性要好;三氯溴甲烷用量增加,改性天然胶乳硫化胶膜的阻燃性提高,而力学性能下降;三氯溴甲烷改性胶乳的起始热降解温度提前,改性胶乳热降解为二步反应。     

Thermal properties of higher molecular weight light stabilizers of the benzophenone type

The thermal properties of some new higher molecular weight UV absorbers of the 2-hydroxy-benzophenone type have been studied using DTA and TG methods, and the obtained results have been compared with the thermal properties of 2-hydroxy-4-n-octyloxybenzophenone. The DTA, TG, and DTG curves and initial and maximum rate temperatures are given. The maximum rates of active decomposition and residues were also evaluated.     

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     

力醇罗热分解特性研究

采用差示扫描量热分析法（DSC）、热重分析法（TG）和微分热重法（DTG）,研究了力醇罗抗菌药的热分解动力学过程,计算了其热分解动力学参数一活化能（E）,分析了其热分解机理,并剖析了其结构特征。     

尼龙1212/SEBS-g-MA/DIDP/BSBA共混体系热行为的研究

利用差示扫描量热(DSC)、热失重(TG)和微分热失重(DTG)，研究了尼龙1212/SEBS-g-MA／DIDP／BSBA共混体系共混物的热行为和降解过程。实验结果表明，共混体系均为单一的熔融行为，加入的SEBS-g-MA使熔点和熔融热下降；热降解为二步降解过程。     

废旧轮胎热解行为的TG/DTA研究

运用热重/差热联用仪（TG/DTA）研究了4种废旧轮胎样品及3种橡胶原料（天然橡胶、丁苯橡胶、顺丁橡胶）的热解行为,通过TG/DTA数据计算了各个降解阶段的热解动力学参数（表观活化能和指前因子）,并确定了轮胎中的橡胶类型（天然胶和合成胶）,得到其基本组成（有机助剂、橡胶、炭黑和无机助剂）的含量,为进行废旧轮胎的转化利用提供基础数据。结果表明:橡胶原料、轮胎样品的热解过程均可划分为两个一级反应阶段,其中轮胎样品的第1段热解活化能比第2段的小,随着反应温度的升高及转化深度的增大,热解对温度的依赖程度增大;废轮胎样品中可热解部分为64％～66％,炭黑为30％～33％,灰分为3％～6％;升温速率可明显地改变轮胎样品的热解历程,但对热解产物的收率影响甚微;天然橡胶的热解失重和合成橡胶的解聚使废旧轮胎的热解表现为一放热过程。