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％）。     

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。     

自然老化对导电硅橡胶电阻特性的影响

分析了异电硅橡胶的电阻性特自然老化条件下的变化规律,发现自然老化对导电硅橡胶电阻行性的影响与导电粒子的质量分数有关,并确定了最佳的导电粒子质量分数。     

小颗粒“胶乳法”氯化天然橡胶穿透干燥试验

通过氯化天然橡胶(CNR)的穿透干燥试验,探讨风温、风速以及粒径对“胶乳法”CNR干燥速率的影响规律,结果表明,温度和风速对含水量的下降速率影响较大,而粒度对其影响较小。建立了穿透干燥方程,对实验数据进行了拟合,结果显示其吻合性较好。红外光谱分析以及物理性能测试结果表明,“胶乳法”CNR物料的干燥温度应控制在100℃以下。     

液体聚异戊二烯对天然橡胶/聚丁二烯橡胶硫化胶微观结构和性能的影响

研究了液体聚异戊二烯(LIR)作为增塑剂对天然橡胶(NR)/聚丁二烯橡胶(BR)硫化胶微观结构、弯曲疲劳性能、压缩疲劳性能和动态力学性能的影响,并与加入工业用增塑剂芳烃油的硫化胶进行了对比。结果表明,加入LIR较芳烃油有利于炭黑在NR/BR体系中的分散;随着LIR用量的增加,NR/BR硫化胶的耐屈挠疲劳性能基本不变;与芳烃油增塑的NR/BR体系相比,LIR增塑NR/BR体系的耐屈挠疲劳性能较优,压缩疲劳生热和压缩永久变形较低;加入LIR降低了硫化胶滚动阻力的同时减弱了其抗湿滑性。     

Effect of crosslink structures on dynamic mechanical properties of natural rubber vulcanizates under different aging conditions

The effects of crosslink structures on the dynamic mechanical properties (DMPs) of unfilled and carbon black N330‐filled natural rubber (NR) vulcanizates cured with conventional (CV), semiefficient (SEV), and efficient (EV) cure systems and having about the same total crosslink densities were investigated before and after aerobic and anaerobic aging at 100°C. The three unfilled NR vulcanizates cured with the CV, SEV, and EV systems had about the same mechanical loss factor (tan δ) values at about 0°C but showed some apparent differences in the tan δ values in the order EV > SEV > CV at relatively high temperatures of 40–80°C before aging. However, N330‐filled NR vulcanizates gave higher tan δ values than the unfilled vulcanizates and showed little effect of the crosslink types on the tan δ at different temperatures over the glass‐transition temperature (T_g) before aging. Aerobic heat aging increased the T_g and tan δ values of the vulcanizates over a wide range of temperatures from ?80 to 90°C that was mainly due to the changes in the total density and types of crosslinks. The unfilled vulcanizates cured with the CV system showed the greatest change in DMP because of their poor resistance to heat aging. Aerobic heat aging of NR vulcanizates caused a more significant change in the DMP than anaerobic heat aging because of the dominant effect of the oxidative degradation during aerobic heat aging on the main‐chain structure, crosslink structures, and DMPs of the vulcanizates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 710–718, 2001     

Oil and thermal aging resistance in compatibilized and thermally stabilized chlorinated polyethylene/natural rubber blends

Influences of EPDM-g-MA as a compatibilizer and a phenolic antioxidant on oil and thermal aging resistance in 50/50 CPE/NR blends were investigated. It has been found that EPDM-g-MA could decrease phase size of the blend system, indicating compatibilizing effect. The optimal concentration of EPDM-g-MA is 1 phr. Beyond this concentration, phase size starts to increase. The addition of phenolic antioxidant apparently decreases the phase size in blends. This is probably due to the improvement in a thermal stabilization of NR phase in blends provided by the antioxidant, which leads to a reduction in phase coalescence during blending. In addition, the results of oil and thermal aging resistance are in good agreement with the morphological results, indicating that the oil resistance and thermal aging properties based on relative tensile strength in the 50/50 CPE/NR blends are strongly controlled by the size of the NR dispersed phase in CPE matrix. The smaller the dispersed phase size, the higher the resistance to oil and thermal aging.     

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     

配方因素对均聚型/共聚型氯醚橡胶共混物耐热老化性能的影响

采用机械共混方法制备了均聚型/共聚型氯醚橡胶(CO/ECO)共混物,考察了配方因素对共混物耐热老化性能的影响。结果表明,CO和ECO二者的共混比对共混物耐热老化性能影响不大。增强剂的种类对耐热老化性能影响较为显著,以填充沉淀法白炭黑和气相法白炭黑共混物的耐热老化性能较好;以炭黑为增强剂时,其用量以40~50份为佳。以三聚硫氰酸为硫化体系硫化的共混物,其热稳定性优于以1,2-亚乙基硫脲为硫化体系硫化的共混物。添加各种软化剂,均会导致共混物耐热老化性能下降;而各种防老剂中,以防老剂NBC、4010 NA和RD对共混物的防老化效果为最好。     

微波干燥和热风干燥对金萱茶叶品质影响

将微波干燥和热风干燥应用于新鲜金萱茶叶的干燥,在3个不同的微波功率（350 W,470 W,800 W）和4个不同的空气温度（70 ℃,80 ℃,90 ℃,100 ℃）下,研究了干燥参数即微波功率或温度对干燥时间、失水量的影响,同时还考察了茶叶中茶多酚总量和儿茶素含量的变化、干茶叶的复水性。实验得出,与热风干燥相比,微波干燥的时间缩短了76%～95%,而且干燥后的茶叶有很好的复水性,但干燥后茶多酚总量少于热风干燥;同时随着功率增加,微波干燥时间由11 min降为6 min,随着温度升高,热风干燥时间由127 min缩短为45 min。这两种方法的茶叶干燥动力学模型均满足Page’s半经验公式。     

微波加热在纱线烘干中的应用

介绍了微波加热的基本原理、特点以及影响微波加热的因素,与蒸汽烘干、射频烘干相比,微波加热比蒸汽烘干节能40％,比射频烘干节能20％,仅每年运营维护费用比射频烘干节省4．5万元。提出应重点加强微波与物料间相互作用理论、微波场中物料的传热、传质机制,微波加热工艺与设备、微波加热技术与其它技术的有机结合等方面的研究。     

丁基橡胶热氧老化性能的研究

通过改变配方中酚醛树脂的用量和卤素给予体的种类及用量,探讨了各变量下对IIR硫化特性和耐热氧老化性能的影响。实验表明,老化前后,300%定伸应力和硬度均有所提高,而拉伸强度、撕裂强度和拉断伸长率有不同程度下降。在树脂用量为8份、CIIR用量为11份、BIIR用量为9份时,各配方的IIR硫化胶性能最好。     

Mechanical properties,oil resistance,and thermal aging properties in chlorinated polyethylene/natural rubber blends

The use of natural rubber (NR) for partly substituting elastomeric chlorinated polyethylene (CPE) was determined. Mechanical and thermal aging properties as well as oil resistance of the blends were also investigated. The amount of NR in blends significantly affected the properties of the blends. The blends with NR content up to 50 wt % possessed similar tensile strength to that of pure CPE even after oil immersion or thermal aging. Modulus and hardness of the blends appeared to decrease progressively with increasing NR content. These properties also decreased in blends after thermal aging. After oil immersion, hardness decreased significantly for the blends with high NR content, whereas no change in modulus was observed. The dynamic mechanical properties were determined by dynamic mechanical thermal analysis. NR and CPE showed damping peaks at about ?40 and 4 °c, respectively; these values correlate with the glass‐transition temperatures (T_g) of NR and CPE, respectively. The shift in the T_g values was observed after blending, suggesting an interfacial interaction between the two phases probably caused by the co‐vulcanization in CPE/NR blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 22–28, 2002; DOI 10.1002/app.10171     

Red pepper (Capsicum annuum L.) drying: Effects of different drying methods on drying kinetics,physicochemical properties,antioxidant capacity,and microstructure

Results of an experimental study are presented and discussed for pulsed vacuum drying (PVD), infrared-assisted hot air-drying (IR-HAD), and hot air-drying (HAD) on drying kinetics, physicochemical properties (surface color, nonenzyme browning index, red pigments, rehydration ratio, water holding capacity, and ascorbic acid), antioxidant capacity (ferric reducing antioxidant power and 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity), and microstructure of red pepper. As expected, the drying time decreased with an increase in drying air temperature, IR-HAD needed the shortest drying time, followed by HAD and PVD. The effective moisture diffusivity (D_eff) of red pepper under PVD, HAD, and IR-HAD was computed to be in the range 1.33–5.83?×?10^?10, 1.38–6.87?×?10^?10, and 1.75–8.97?×?10^?10 m²/s, respectively. PVD provided superior physicochemical properties of dried red pepper compared to samples dried by HAD and IR-HAD. In detail, PVD yielded higher rehydration ratio, water holding capacity, red pigment and ascorbic acid content, brighter color, lower nonenzyme browning index, and comparable antioxidant capacity compared to samples dried by HAD and IR-HAD at the same drying temperature. Furthermore, PVD promoted the formation of a more porous structure, while HAD and IR-HAD yielded less porous structure. The current findings indicate that PVD drying has the potential to produce high-quality dried red pepper on commercial scale.     

Effect of thermal oxidative ageing on the morphology of natural rubber networks as viewed by ESR

The change of network morphology of unfilled sulfur crosslinked natural rubber exposed to thermal oxidative ageing has been studied. Three model networks with different sulfur contents (efficient network, semi‐efficient and conventional vulcanizate) have been analysed by applying spin probe ESR, equilibrium swelling measurements and mechanical measurements. By combining the density distribution deduced from the complex ESR spectra and the equilibrium swelling density, it is shown that the major network changes occur in the networks with predominantly polysulfidic bonds (conventional network) after 96 h of ageing at 373 K. The effect of ageing on the network with predominantly monosulfidic bonds is much less pronounced. Both effects (main chain scission and additional local crosslinking) have been analysed in the course of prolonged ageing up to 240 h. A correlation between network structure and its mechanical performance is established. © 2000 Society of Chemical Industry     

Hydrogenated natural rubber blends: Aspect on thermal stability and oxidative behavior

Hydrogenated natural rubber (HNR) prepared from natural rubber (NR) is a new sustainable elastomer with excellent thermal properties. This study reports on the effect of vulcanization system and blend ratio on the thermal and oxidative resistance of HNR/NR vulcanizates. The various HNR/NR ratios vulcanized by peroxide and sulfur donor system exhibited the highest retention of tensile strength after thermal aging due to the formation of zinc‐dimethyldithiocarbamate (ZDMDC) which is an efficient antioxidant. The results from thermogravimetric analysis (TGA) indicated that the saturated structure of HNR had higher decomposition temperature and activation energy to enhance the thermal stability of HNR/NR vulcanizates. The initial and maximum decomposition temperatures of NR and HNR phases in vulcanizates were not affected by rubber blend ratio. This suggests that the decomposition pattern of HNR has no influence on another constituent. The increase in HNR content in the blends could retard the ozonolysis resulting in the surface cracking attacked by ozone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on preparation of chlorinated natural rubber from latex and its thermal stability

The effects of pH value of reaction system, reaction time, and reaction temperature on the chlorination reaction in the preparation of chlorinated natural rubber (CNR) from natural rubber latex were discussed. It has been found from the thermal analysis that the thermal degradation of CNR in nitrogen is a one-step reaction, and 30% carbonide with a stable structure remained at 360 to 700°C; whereas the thermo-oxidative degradation of CNR in air is a multistep reaction, and the thermal degradation ratio reaches to 100% at 560°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2863–2867, 1999     

聚丙烯酸酯改性石墨及其对天然橡胶导热性能的影响

采用聚丙烯酸酯改性石墨,然后将其填充到天然橡胶中,研究了改性石墨对复合材料导热性能和力学性能的影响。结果表明,石墨经聚丙烯酸酯改性后降低了自身的聚集作用,同时由于其被包覆,受力时更不易分层滑移;表面粗糙度的提高及有机基团的增多使得石墨与橡胶间的结合作用增强,同时促成了更多导热网链和"桥接"导热通道的形成,从而提高了其填充天然橡胶的热导率和力学性能。石墨在改性时软硬段单体的配比影响其包覆效果,进而影响其填充天然橡胶的导热和力学性能;当石墨与改性单体的质量比为10/1、软硬段单体的质量比接近1/1时,所改性石墨填充天然橡胶的热导率较高,综合力学性能较好。     

天然橡胶干燥气流分布的均匀性研究

借助Fluent软件,建立了不同工况状态、不同胶层厚度和不同流道的天然橡胶干燥模型,模拟了气体的流动状况。根据胶层表面压差和中心面竖向速度的分布情况,分析了相应模型气流分布的均匀性。结果表明：矩形流道模型,胶层表面压差沿流向逐渐增大分布,导致了穿过橡胶层气流分布的不均匀,气流量越大、干燥阶段越往后,气流分布的不均匀性越明显;梯形流道模型,不同胶层厚度的流体分布规律基本一致,在斜面斜率最大时,气流均匀化效果较优;干燥状态一定时,组合模型两段斜面的合理设置,气流分布的均匀性进一步提高;相对整个干燥过程而言,梯形流道⑤模型气流分布的整体均匀化效果比斜面组合②模型的更好。