EPDM/PA配比对硫化胶老化性能及耐油性能的影响

研究了三元乙丙橡胶(EPDM)/三元尼龙(PA)配比对其硫化胶热空气老化前后和油中浸泡后物理机械性能的影响。结果表明,随着PA用量的增大,硫化胶拉伸强度下降后趋于稳定,撕裂强度变化不大,100%定伸应力和DIN磨耗均呈上升趋势,拉断伸长率、浸油后的质量变化率和体积变化率均下降,正硫化时间变长。热空气老化后,硫化胶拉伸强度、硬度、100%定伸应力和拉断伸长率变化趋势同常温下一致。浸油后,硫化胶拉伸强度、100%定伸应力均呈上升趋势,拉断伸长率先是不变然后下降。     

ACM/CM共混胶的老化及耐介质性能研究

研究了丙烯酸酯橡胶(ACM)/氯化聚乙烯(CM)共混比对其硫化胶热空气老化前后的物理机械性能和耐油性能等的影响。结果表明,随着ACM用量的增大,硫化胶撕裂强度和硬度均下降;老化前后的拉伸强度和100%定伸应力均先增大然后减小,拉断伸长率和拉断永久变形与之相反。老化后的拉伸强度和定伸应力均高于老化前的数据,拉断伸长率和拉断永久变形均低于老化前的数据。随着ACM用量的增大,正硫化时间缩短。随着ACM用量的增大,热油浸泡后的硫化胶体积变化率和质量变化率均减小,耐油性能增强。     

丁苯橡胶热空气老化性能变化之间的相关性

通过热空气老化试验,建立了丁苯橡胶(SBR)热空气老化拉伸性能变化率与邵尔A硬度变化值之间的相关性。结果表明,在热空气老化过程中,无论是普通硫化体系还是有效硫化体系,SBR硫化胶老化后的邵尔A硬度变化值随老化时间的延长而呈指数趋势增加,且老化后扯断伸长率变化率与邵尔A硬度变化值之间呈线性关系;在普通硫化体系下,硫化胶表现为老化后扯断伸长率变化率和拉伸强度变化率随老化时间的延长而呈指数趋势下降,而老化后拉伸强度变化率与邵尔A硬度变化值之间以及拉伸强度变化率与扯断伸长率变化率之间呈线性关系。     

共混比对CM／XNBR并用胶性能的影响

研究了不同共混比对氯化聚乙烯橡胶（CM）／羧基丁腈橡胶（XNBR）并用胶在热空气老化前后的力学性能、耐油性的影响。结果表明,随着XNBR用量的增加,焦烧时间缩短,硫化速度加快,拉断伸长率、拉伸强度先减小后增加;100％定伸应力出现极大值;拉伸永久变形、撕裂强度、体积磨耗量和高温下浸油前后的体积和质量变化率均按一定规律减小;常温下体积和质量变化率均很小;硬度明显提高且基本稳定;热空气老化后,拉断伸长率整体下降,拉伸强度,100％定伸应力和撕裂强度均有明显提升,DIN磨耗量除CM纯胶有明显降低外,其他配比的磨耗体积基本维持不变;热油老化后,伸长率、拉伸强度、100％定伸应力均有所下降。     

三元乙丙橡胶耐热配方的优选研究

研究了交联助剂HVA-2和甲基丙烯酸盐用量对EPDM耐热空气老化性能的影响。结果表明,当HVA-2用量为1份,甲基丙烯酸镁用量为15份时,EPDM耐热空气老化性能最好;在175℃×96 h热空气老化后,EPDM硫化胶拉伸强度变化率为-0.9%,拉断伸长率变化率为-37.7%。     

CM与乙烯甲基丙烯酸酯弹性体共混硫化胶性能研究

本文研究了不同共混比对氯化聚乙烯橡胶（CM）/乙烯甲基丙烯酸酯弹性体（EMA）共混硫化胶在热空气老化前后的物理机械性能、耐油等性能的影响规律。结果表明,随着共混硫化胶中EMA含量的增大,硫化时间延长;随着EMA橡胶含量的增大,共混硫化胶的撕裂强度、扯断伸长率基本保持不变,硬度、100%定伸应力增大,拉伸强度降低,老化前后共混硫化胶的各项性能变化趋势跟老化之前大体相同,并且变化不大,所以EMA硫化胶的热空气老化性能好。耐热油老化后,拉伸强度和扯断伸长率是降低的,并且低于耐油之前,100%定伸应力逐渐增大,小于耐油之前相同并用比的值;体积变化率和质量变化率增大。     

NBR并用少量ACM对共混胶耐热油及耐热空气性能的影响

研究了在丁腈橡胶(NBR)中并用少量丙烯酸酯橡胶(ACM),以改善其硫化胶的耐热油老化及耐热空气老化性能。硫化体系为硫磺/三巯基均三嗪(TCY)并用。结果表明,NBR/ACM并用比在95/5至75/25之间,热油和热空气老化后皆有较好的性能保持率。随着ACM并用比的增加,热油浸泡之后的质量变化率和体积变化率下降,拉伸强度下降,撕裂强度上升,拉断伸长率下降;热油老化之后拉断伸长率的保持率上升,定伸应力和硬度基本不变,正硫化时间和焦烧时间缩短。     

环保型增塑剂对羧基型丙烯酸酯橡胶性能的影响

研究4种增塑剂（RS107,RS735,TP95,TP759）对羧基型丙烯酸酯橡胶（ACM）性能的影响。结果表明：添加增塑剂可以明显改善羧基型ACM胶料的加工性能,同时有延迟硫化的效果;当增塑剂用量相同时,4种增塑剂对羧基型ACM硫化胶物理性能的影响差异较小,硫化胶在1^#油中浸泡后体积变化率差异不大;随着增塑剂用量的增大,硫化胶的硬度和拉伸强度降低,拉断伸长率和压缩永久变形增大,热空气老化后的拉伸强度变化率和拉断伸长率变化率均增大,在1^#油中浸泡后体积变化增大,在3^#油中浸泡后体积变化减小,脆性温度降低。增塑剂RS735和TP759因其硫化胶的耐热空气老化性能优异而更适合在油、高温工况下使用。     

过氧化物硫化体系对CM／XNBR共混物性能的影响研究

研究了不同用量过氧化物硫化体系对氯化聚乙烯橡胶（CM）／羧基丁腈橡胶（XNBR）共混硫化胶各相交联密度及热空气老化前后的物理机械性能、耐油性能等的影响规律。结果表明,随硫化体系用量的增加,共混硫化胶两相的交联密度都明显增加,交联密度差值变大;焦烧时间逐渐降低;硬度、拉伸强度、100％定伸应力、体积磨耗量呈上升趋势,永久变形、扯断伸长率明显降低,撕裂强度整体变化不大,常温下体积和质量变化率均很小,高温下体积和质量变化率明显降低后趋于平稳;热空气老化后,硬度、拉伸强度、100％定伸应力、撕裂强度整体上升,扯断伸长率整体下降,体积磨耗量整体变化不大;热油老化后,拉伸强度、100％定伸应力变化不大,扯断伸长率明显降低。     

硫化剂DCP用量对NBR/EVM并用胶交联密度及力学性能的影响

研究了硫化剂DCP(过氧化二异丙苯)用量对丁腈橡胶(NBR)/乙烯-醋酸乙烯酯橡胶(EVM)共混胶的硫化特性、两相交联密度、物理力学性能以及热空气老化性能的影响。结果表明,随着硫化剂DCP用量的增大,NBR/EVM共混胶的硫化速度和交联密度逐渐增大。与老化前相比,经热空气老化后硫化胶的交联密度增大,经125℃热空气老化后硫化胶的交联密度增大速率逐渐变大,且在DCP用量为1.5份时老化后的硫化胶交联密度增大一倍多。随着硫化剂DCP用量的增大,NBR/EVM硫化胶中NBR相的交联密度逐渐增大、EVM相的交联密度微降,在DCP用量为1.5份时两相交联密度相差最大。与老化前相比,经过热空气老化后硫化胶中NBR相的交联密度明显增大,EVM相的交联密度则变化不大。随着硫化剂DCP用量的增大,NBR/EVM硫化胶的拉伸强度基本保持不变,硬度和100%定伸应力均逐渐增大,拉断伸长率和压缩永久变形均逐渐减小。与老化前相比,经70℃、100℃热空气老化后硫化胶的硬度、拉伸强度、100%定伸应力均增大,而拉断伸长率基本保持不变。经125℃热空气老化后硫化胶的100%定伸应力明显变大,拉伸强度和拉断伸长率均明显减小。     

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     

不同初始含水率湿天然橡胶微波干燥特性研究

对不同初始含水率的湿天然橡胶(NR)微波干燥特性进行了研究。结果表明,湿天然橡胶微波干燥的全过程可分为加速、减速、相对恒速干燥三个阶段;湿天然橡胶快速干燥和较快速干燥阶段为物料干燥的主要阶段;不同的初始含水率对湿天然橡胶的干燥过程和产品表观质量影响较大,胶料初始含水率越高,干燥速率越快,但干燥时间较长,且产品表观质量较差,初始含水率越低,干燥时间短,产品表观质量较好;湿天然橡胶微波干燥较佳初始含水率范围为10%～20%。     

Drying characteristics and water dynamics during microwave hot-air flow rolling drying of Pleurotus eryngii

Abstract

The aim of this study was to improve the drying uniformity and quality of Pleurotus eryngii by using the combination of microwave drying and hot-air flow rolling drying. The moisture content, drying uniformity, and water migration of P. eryngii during microwave hot-air flow rolling drying (MARD) were analyzed in detail. The temperature distribution images were obtained via infrared thermal imaging techniques and the relationship between relaxation time and signal amplitude were obtained via low-field nuclear magnetic resonance analysis and imaging (LF-NMR/MRI). The curves of signal amplitude with moisture content changes were fitted by a linear model with good linearity correlation. It was found that the hot-air and rolling bed could improve the drying uniformity of microwave drying. And the free water was found to transform into immobilized water and bound water during the drying process. Only a small amount of water was left in the dried P. eryngii in the final stage. The results could provide supportive information for improving the uniformity and quality of the drying processes of the edible fungi.     

Effect of Microwave-Vacuum Drying on the Carotenoids Retention of Carrot Slices and Chlorophyll Retention of Chinese Chive Leaves

Microwave-vacuum drying, and combined microwave-vacuum with air or vacuum drying were investigated as potential methods for drying green and high-carotenoid vegetables of Chinese chive leaves and carrot slices. The samples were dried by microwave-vacuum until the moisture content reached about 20% (wet basis), and then by conventional air drying at the temperature of 45-50°C or conventional vacuum drying at the temperature of 55-60°C or by continued microwave-vacuum drying at lower power level to final moisture content about 6% (wet basis). The carotenoid retention of carrot slices and chlorophyll retention of Chinese chive leaves, dried by these methods, was evaluated and compared with those dried by freeze-drying and conventional hot-air drying. The comparison showed that the carotenoid retention of carrot slices and chlorophyll retention of chive leaves, dried by the current methods, was very close to or even as much as those dried by freeze-drying and much better than those dried by conventional hot-air. Blanching was not necessary when using microwave-vacuum drying or combined microwave-vacuum with conventional hot-air drying or vacuum drying, because the activity of enzymes which were responsible for the degradation of color was greatly reduced with extremely rapid decreasing of moisture, and because oxygen was absent in microwave-vacuum drying.     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Abstract

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

Effect of drying technique and disintegrant on physical properties and drug release behavior of microcrystalline cellulose-based pellets prepared by extrusion/spheronization

The aim of this study was to investigate the influence of drying technique and disintegrant on physical properties and drug release behavior of microcrystalline cellulose-based pellets prepared by extrusion/spheronization. Formulations of paracetamol (6.7%, w/w), microcrystalline cellulose (66.7%, w/w) and different disintegrants, alginic acid, calcium carbonate, d-mannitol, croscarmellose sodium, sodium starch glycolate, crospovidone, in concentrations of 10% or 20% (w/w) were made and processed to pellets by extrusion/spheronization. Different drying techniques, i.e. hot-air drying, microwave drying and freeze-drying, were applied to each formulation. Physical properties, such as particle size distribution, moisture content, apparent density, pellet morphology, were evaluated. The mechanical properties and drug release behavior of the pellets were also examined. Only small difference in crushing strength between hot-air dried and microwave-dried pellets were found. Freeze-drying process resulted in pellets with larger diameter, weaker and more porous than pellets dried with the other processes. The porous structure promoted a faster drug release while the drug release from hot-air dried pellets and microwave-dried pellets was insignificantly different. Different disintegrants were incorporated in the pellets but none of the pellets disintegrated within 90 min. However, the drug release from pellets containing disintegrant was faster than that of pellets with no disintegrant. The results suggested that the type and amount of disintegrant is less influenced than the drying technique.     

湿法氧化锌种类和用量对天然橡胶性能的影响

研究湿法氧化锌种类和用量对天然橡胶(NR)性能的影响。结果表明:与添加普通氧化锌的胶料相比,对于未填充炭黑NR体系,减半用量的湿法氧化锌混炼胶的焦烧时间和t90较短,Fmax较大;硫化胶的定伸应力、拉伸强度和剪切模量(G′)较大,拉断伸长率、损耗模量(G″)和损耗因子(tanδ)较小。对于填充炭黑NR体系,减半用量的湿法氧化锌混炼胶的门尼粘度、G′和G″较大,tanδ较小,焦烧时间和t90较短,Fmax较大;硫化胶的密度稍低,硬度和定伸应力较大,耐老化性能较好,玻璃化温度较低,tanδ较小,其他物理性能变化不大。湿法氧化锌FF的性能优于湿法氧化锌HR。     

陶瓷坯体不同干燥方式的对比研究

分别采用普通热风、远红外和微波干燥方式对陶瓷坯体的干燥过程进行实验研究,研究不同干燥方法对干燥速度、坯体内外温差的影响。结果表明,热空气干燥主要靠水分浓度差实现,内外温差较大;远红外线干燥的坯体内外温度均匀,恒速阶段的干燥速度是热风干燥恒速阶段速度的1.2倍;微波干燥主要靠温度差实现水分扩散,最大干燥速度可达4.26%/min(干基),约为热风干燥速度的12倍。将含水量为22wt%的陶瓷坯体干燥至恒重,普通电热干燥的运行成本最高,约为远红外干燥的1.5倍和微波干燥的4.2倍。分析了远红外干燥和微波干燥在陶瓷工业应用的可行性,指出了需要解决的技术难题。     

Strawberry drying: Development of a closed-cycle modified atmosphere drying system for food products and the performance evaluation of a case study

In the present study, a closed-cycle modified atmosphere drying (CC-MAD) system was developed as an alternative drying technique to facilitate drying processes for agricultural commodities appropriate to highly humid and sunny regions with a better quality. An absorption dehumidifying system was designed for working pseudo-continuously with the most efficient absorbent in terms of moisture absorption, desorption rate, and capacity. The system, assisted by a solar panel for absorbent regeneration, was tested, while its optimum working condition was determined by strawberry drying. This unique process was comparatively carried out using hot-air and freeze-drying techniques in terms of processing time and final product quality. Strawberry slices (5?mm thickness) were dried successfully using CC-MAD. The optimum drying conditions of CC-MAD were determined as drying temperature of 60°C, drying air/gas velocity of 3?m/s and drying medium oxygen level of 9.47%. The loss of ascorbic acid was significantly reduced by CC-MAD technique. These losses were found to be 2.9, 6.9, 27.2, and 23.8% by freeze-drying, CC-MAD, hot-air drying, and hot-air drying combined with CC-MAD, respectively. The total monomeric anthocyanins loss was also significantly reduced by the CC-MAD technique (20.3%), in a similar way to that of freeze-drying (18.1%) in comparison with hot-air drying (40.4%). In addition, CC-MAD (12,446?kJ/kg fresh product at 4?h drying time) is three times more advantageous in terms of energy cost compared with freeze-drying (30492.8?kJ/kg fresh product at 24?h drying time) and six times faster in terms of drying time. This new drying system can be used as an alternative to freeze-drying in the drying of foods, especially in products sensitive to oxidation.