低蛋白天然橡胶在空气和氮气气氛中的热降解行为

采用热重分析法研究了低蛋白天然橡胶(LPNR)在氮气和空气气氛下的热降解和热氧降解行为,并与天然橡胶(NR)在同样条件下的降解行为进行了比较.结果表明,在氮气气氛下,LPNR和NR的热降解都是1步进行,LPNR的起始降解温度(T0)、最大降解温度(Tp)和反应活化能都比NR高,说明其耐热性比NR好;在空气气氛下,LPN...     

氯化天然橡胶的热降解研究

用傅立叶变换红外光谱法和热失重分析法研究了氯化天然橡胶(CNR)的热氧降解和热降解过程。结果表明,CNR的热降解为一步反应,在160～390 ℃时CNR 发生脱氯化氢反应,在390 ℃时CNR 仍有质量分数为0.35的残留物存在,而且较稳定。CNR的热氧降解为两步反应,在160～390 ℃时,产生氯化氢和二氧化碳;在390～575 ℃时分解产物为二氧化碳,且分解彻底。     

溴化天然橡胶的热降解研究

用傅立叶变换红外光谱法和热失重分析法研究了溴质量分数分别为31%、51%和69%的溴化天然橡胶（BNR）的热降解和热氧降解过程。结果表明,BNR热降解为两步反应,第1步BNR发生脱溴化氢反应,失重率近似等于其溴含量;第2步BNR31、BNR51和BNR69在475℃降解时仍有9.7%、15.6%和12.7%的残留物存在,且较稳定。BNR热氧降解分3步进行,第1步反应的温度及降解率与热降解相近,产物主要是溴化氢,此外还有少量二氧化碳;第2步和第3步产物为二氧化碳,且分解彻底。     

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。     

环氧化天然橡胶硫化胶在不同气氛下的热降解行为？

利用热重-微商热重（ TG-DTG-DSC）研究了在氮气、空气氛围中ENR硫化胶的热降解动力学,根据不同升温速率下得到的热重数据,通过Ozawa-Flynn-Wall模型求取热降解过程的活化能E、指前因子A等参数,得到ENR硫化胶在不同气氛下降解反应过程中动力学参数方面的差异。 ENR在氮气气氛中降解时为一步反应,在空气中为复杂多步反应。另外,空气气氛中的活化能E和指前因子A均大于氮气中。     

淀粉加速凝固天然橡胶的热降解研究

采用热重分析法(TGA)和差热分析法(DTA)研究了自然微生物凝固天然橡胶(N-NR)和淀粉微生物凝固天然橡胶(S-NR)在空气气氛中的热降解行为,为探索新的天然胶乳加工工艺提供科学依据。研究结果表明:(1)实验条件下,两种凝固方式的橡胶在空气气氛中的降解均为多步反应。(2)S-NR的抗氧化性能较N-NR好。     

胶乳法溴化天然橡胶的热降解研究

采用胶乳法分别制备了溴质量分数为0.28和0.41的溴化天然橡胶(BNR),并采用傅里叶变换红外光谱法和热重分析法研究其热降解和热氧降解过程.结果表明:胶乳法BNR热降解为2步反应,第1步发生脱溴化氢反应,试样的质量损失率近似等于其溴质量分数;第2步BNR在475℃降解时仍有6.9%～8.8%的残留物存在,且较稳定.胶乳法BNR热氧降解分3步进行,第1步反应的温度及质量损失率与热降解相近,产物主要是溴化氢,此外还有少量二氧化碳;第2步和第3步产物为二氧化碳,且分解彻底.     

环氧化天然橡胶/PVC共混物的热氧降解

采用热重－差示热重分析和差热分析了环氧化天然橡胶（ENR）／PVC共混物的热氧降解过程,结果表明,炭黑补强的ENR／PVC共混物的热氧降解过程分为3个阶段,第1阶段主要是PVC脱氯化氢,而氯化氢引起ENR发生催化氧化反应而放热,且该阶段明显受到ENR／PVC共混比的影响,随着PVC用量的增大,共混物的热氧稳定性下降。     

天然橡胶和胶清橡胶的热氧降解特性研究

采用热重分析法(TGA)研究了胶清胶(NR-s)和天然橡胶(NR)在空气气氛中的热氧降解行为。结果表明:(1)NR-s和NR的TG图中均出现多个平台,对应的DTG图中均出现多个峰,因此其热氧降解均属于多步反应。(2)NR-s的T0.05(质量损失率为5%时的温度)为283℃,NR的T0.05为316℃,说明NR-s的热稳定性较NR有一定的下降。     

气氛对壳聚糖及其铜离子混合物热降解的影响

利用热重分析(TGA)和差热分析(DTA)研究了壳聚糖及其铜离子混合物在氮气气氛和空气气氛中的热降解行为,探讨了气氛对壳聚糖及其铜离子混合物热降解的影响,并采用FTIR、X-射线衍射对壳聚糖铜离子混合物进行了表征.结果显示,壳聚糖及其铜离子混合物的热降解和热氧降解分三个阶段进行:第一阶段为材料失水,为吸热反应;第二阶段为主链脱乙酰和糖苷键的裂解,为放热反应;第三阶段为吡喃环的裂解和炭化残渣的分解,为放热反应.气氛对壳聚糖第一、第二阶段的降解影响较小,对第三阶段的降解影响较大.     

Study on the thermal degradation of epoxidized natural rubber

The thermal degradation and thermooxidative degradation of epoxidized natural rubber (ENR) were studied by thermogravimetry (TG). In the thermal degradation of ENR, the initial temperature of weight loss T₀ = 1.20B + 348, the temperature of maximum weight loss rate T_p = 1.07B + 392, and the final temperature of weight loss T_f = 0.77B + 445. The C_p, which corresponds to the degradation rate at temperature T_p, increases along with the heating rate B and its mean value is 43%, but C_f, which corresponds to the degradation rate at temperature T_f, is not affected by the heating rate, and its average value is close to 100%. As in the thermooxidative degradation, T₀ = 1.84B + 246, T_p = 0.30B + 378, and T_f = 2.27B + 584. The value of C_p increases along with the heating rate B and its mean value is 36%, but C_f is not affected by the heating rate and the average value approximately equals 100%. The thermal degradation in nitrogen could be a one-step reaction, whereas the thermooxidative degradation has a multiple-step reaction. The reactive environment has a great effect on the thermal degradation of ENR and the difference of the mechanisms of the two reaction systems is obvious. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2207–2211, 1998     

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     

蛋白质对天然橡胶硫化动力学的影响

选用与天然胶乳中的d球朊结构类似的牛白蛋白,将其加入到经Alcalase蛋白酶处理得到的低蛋白天然橡胶中,通过硫化仪法研究了蛋白质对胶料硫化动力学的影响。结果表明：各胶样的硫化反应可按一级反应处理;在相同温度条件下,随着蛋白质用量的增加,焦烧时间（t10）和正硫化时间（t90）缩短,硫化反应速率提高,说明牛白蛋白能够提高天然橡胶的硫化速度;硫化速率随着温度的升高而显著提高,且都能很好地符合阿伦尼乌斯方程;反应活化能随着蛋白质用量的增加而提高。     

Thermal degradations of chlorinated natural rubber from latex and chlorinated natural rubber from solution

The thermal degradations of chlorinated natural rubbers from latex (CNR‐L) and from solution (CNR‐S) under nitrogen atmosphere were studied with thermogravimetric analysis (TGA). The thermal degradations of CNR‐L and CNR‐S are one‐step reaction. The shapes of the thermogravimetric and derivative thermogravimetric curves are similar. The degradation temperatures of CNR‐L and CNR‐S increase linearly with the increment of heating rates. The heating rate hardly affects the thermal degradation rates of CNR‐L and CNR‐S at the various degradation stages. The thermal degradations of CNR‐S and CNR‐L are dehydrochlonation reactions. The reaction activation energy (E) of CNR, at the first stage, is around 100 kJ/mol. After that, E remains relatively steady (80–140 kJ/mol). At the last stage, E rises rapidly (130–270 kJ/mol). The variation tendency of frequency factor (A) is similar to that of E. As the initial degradation temperature T₀ of CNR‐L is 10.9°C lower than that of CNR‐S, the thermal stability of CNR‐S is better than that of CNR‐L, which may be caused by the difference of molecular structure between CNR‐L and CNR‐S, as FTIR results indicate that there are more ? OH, ? C?O and ? COO? groups in the CNR‐L molecular chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of atmosphere on the thermal decomposition of chlorinated natural rubber from latex

The kinetics of the thermal decompositions of chlorinated natural rubber (CNR) from latex under both air and nitrogen atmospheres were studied with thermogravimetric analysis (TGA). The thermooxidative decomposition of CNR had two weight-loss step changes in the TGA curves, which occurred at the two distinct temperature ranges of about 160–390 and 390–850°C, respectively. The gaseous products of the first step change were mainly HCl with a little CO₂, and the apparent reaction order (n) was 1.1. The reaction activation energy (E) increased linearly with the increment of heating rate (B), and the apparent activation energy (E₀), calculated by extrapolation back to zero B, was 101.7 kJ/mol. Bs ranging from 5 to 30°C/min were used. The initial temperature of weight loss (T₀) was 1.31B + 252°C, where B is in degrees Celsius per minute. The final temperature of weight loss (T_f) was 0.93B + 310°C, and the temperature of maximum weight-loss rate (T_p) was 1.03B + 287°C. The decomposition weight-loss percentage at T_p (C_p) and that at T_f (C_f) were not affected by B, and the average values were 38 and 60%, respectively. The second weight-loss step change was an oxidative decomposition of the molecular main chain. The value of n was 1.1. E increased linearly with the increment of B, and E₀ was 125.0 kJ/mol. C_f after the second step approached 100%, which indicated complete decomposition. The thermal decomposition of CNR in a N₂ atmosphere had only one weight-loss step change with an n of 1.1. E increased linearly with the increment of B, and E₀ was 98.6 kJ/mol. T₀ was 1.25B + 251°C, T_f was 0.91B + 315°C, and T_p was 1.09B + 286°C. C_p and C_f were not affected by B, and the average values were 37 and 68%, respectively. The weight percentage of more stable, nonthermal decomposed residue was about 30%. The thermal decompositions of CNR in both atmospheres were similar, mainly by dehydrochlorination, at the low temperature range (160–390°C) but were different at the high temperature range (390–850°C). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2590–2598, 2001     

低溴化天然橡胶的研究

对自制的低溴化天然橡胶(BNR)的溴含量、红外谱图、在甲苯中溶解性能、不饱和度及综合力学性能进行研究分析。结果表明:随着反应过程中溴化液用量的增加,制得的低溴BNR的溴含量也增大,且溴含量不与溴化液用量成线性正比关系;溴化天然胶乳的红外光谱分析表明,溴已经接到天然橡胶分子链上,其C-Br键对应的红外光谱位置分别为956 cm-19、08 cm-1;在常温下,低溴BNR在甲苯中溶解性较差,在水浴加热70℃情况下,对低溴BNR在甲苯中的溶解性略有改善,同时随溴含量的增加,溶解性也越差。经塑炼后的低溴BNR在水浴加热70℃的情况下,对低溴BNR能完全溶于甲苯溶剂中;制得的低溴BNR的不饱和度略有降低,不饱和度随溴化液用量的增加变化不大;低溴BNR的加工性能总体较好,经溴化后的天然橡胶较纯胶的综合力学性能都有所下降,其中当硫磺用量为2.7份时,综合力学性能相对较好。     

Thermal degradation and ageing behavior of microcomposites of natural rubber,carboxylated styrene butadiene rubber latices,and their blends

The effect of microfillers on the thermal stability of natural rubber (NR), carboxylated styrene butadiene rubber (XSBR) latices, and their 70/30 NR/XSBR blend were studied using thermogravimetric method. Microcomposites of XSBR and their blend were found to be thermally more stable than unfilled samples. The activation energy needed for the degradation of polymer chain was calculated from Coats‐Redfern plot. Activation energy needed for the thermal degradation of filled samples was higher than unfilled system. It indicated the improved thermal stability of the filled samples. The ageing resistance of the micro‐filled samples was evaluated from the mechanical properties of aged samples. The thermal ageing was carried out by keeping the samples in hot air oven for 7 days at 70°C. The mechanical properties such as tensile strength, modulus at 300% elongation, and strain at break were computed. As compared to unfilled samples, micron‐sized fillers reinforced systems exhibited higher ageing resistance. Finally, an investigation was made on the influence of ion‐beam irradiation on microcomposites of NR, XSBR latices, and their 70/30 blend systems using ²⁸Si⁸⁺ performed at 100 MeV. The surface changes of the samples after irradiation were analyzed using X‐ray photoelectron spectroscopy. The results of XPS measurements revealed that the host elements were redistributed without any change in binding energies of C_1s, O_1s, and Si_2p. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Moisture-sorption properties and studies on the dilute solution behavior of epoxidized natural rubber ENR 50

Studies of the dilute solution capillary viscosity and moisture sorption of commercial samples of epoxidized natural rubber (ENR 50) were carried out. Dilute solution viscometry of ENR 50 solutions was conducted in xylene, tetrahydrofuran, and methyl ethyl ketone solvents and the degradation due to shearing and oxidation for this rubber was followed. At average elevated temperatures and high relative humidities, epoxidized natural rubber ENR 50 shows high moisture sorption. Moisture sorption measurements at 100% RH and 34°C followed by desorption show near equilibrium moisture intake of 3.402–3.661 g H₂O/100 g rubber, which agrees reasonably well with the estimated value of 4.108 g H₂O/100 g ENR 50. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1633–1644, 1999     

液体天然橡胶氧化降解制备工艺的比较

采用了3种新的降解体系硝基苯-过氧化氢、过硫酸钾-丙醛和高碘酸制备液体天然橡胶(LNR),并与传统的降解剂苯肼进行了对比.通过正交实验考察了降解剂用量、温度、时间等对粘均相对分子质量(Mη)的影响,并通过红外光谱对降解后橡胶分子的结构进行了探讨,得到最佳降解体系.结果表明:高碘酸降解所得LNR结构单一稳定,当其用量为干胶质量的0.3％、30℃下反应6h可得到Mη为13 067的LNR,高碘酸是最佳的天然橡胶降解剂.