The dissolution and recrystallization of polyethylene crystals suspended in various solvents

The dissolution and recrystallization of crystals of polyethylene suspended in p-xylene, n-dodecane, and decalin, are described. It is shown that differential thermal analysis (DTA) can be applied to suspensions of polymer crystals to determine the dependence of dissolution temperature on concentration, temperature of crystallization, and solvent. In addition, DTA can be used to follow the course of isothermal recrystallization of a suspension as a function of time and temperature, as well as recrystallization occurring during heating at a constant rate. The results of DTA, coupled with those obtained by electron microscopy and low angle X-ray analysis, make it possible to present a general picture of the behaviour of suspended polyethylene crystals. Recrystallization normally occurs by a dissolution-redeposition mechanism, and evidence for thickening by creep-up is limited to certain special conditions. A detailed discussion of recrystallization is presented which involves both thermodynamic and kinetic arguments.     

Orientation distributions by recovery behaviour in electrodeposited copper layers at room temperature

An X-ray diffraction study of the microstructure parameters of the growth and recrystallization texture arising in electrodeposited copper layers at room temperature has been carried out. It was established that the type of recrystallization texture is dependent on the conditions under which the growth texture has been obtained. The orientation distributions of the effective crystallite size, the elastic stored energy and its release rate, which were observed in low-indexed crystal directions, are discussed in connection with the orientation distribution of crystal volumes of the recrystallization texture in the same directions.     

Effective solvent system selection in the recrystallization purification of pharmaceutical products

This treatment describes the details of a methodical three step algorithm for determining the best operating conditions for the recrystallization separations of solid mixtures for the chosen targeted solvent systems. Our algorithm was applied to effectively separate a representative pharmaceutical product (caffeine) from a related pharmaceutical product (theophylline). The limitations of such calculations with currently available, widely used predictive methods for computing solution thermodynamics without experimental data are directly examined. Also presented here is a novel two stage recrystallization procedure which can potentially dramatically improve the overall recovery yields of the desired products. These systematic selection calculations described herein should enable researchers to quickly screen many potential solvent systems and operating conditions and concentrate experimental efforts only on the most promising candidates for such purifications.     

三甲苯麝香重结晶工艺的研究

测定了三甲苯麝香在ｗ（Ｃ２ Ｈ５ ＯＨ） ＝ ９５％ 乙醇中的溶解度曲线。通过考察乙醇与粗晶的配比、溶解温度、溶解时间、冷却方式、冷却温度等影响因素，确定了重结晶提纯三甲苯麝香的最佳工艺条件如下：溶解温度８０℃，结晶温度４５℃，溶解时间１ｈ，结晶时间１ｈ，３ 次重结晶ｗ（Ｃ２ Ｈ５ ＯＨ）＝ ９５％ 乙醇和粗晶质量比分别为６∶１、８∶１ 和９∶１。     

重结晶法提纯制备尿素方法研究

通过对尿素重结晶温度及提纯次数的优化,建立了一种尿素的重结晶提纯方法。经提纯后的尿素样品采用红外光谱法和核磁共振法对其结构进行定性表征,并与美国国家标准与技术研究院(NIST)的尿素标准物质进行对照验证。样品纯度采用质量平衡法和差示扫描量热法进行测试,结果表明经重结晶后的样品纯度可达到99.9%。方法可有效提纯尿素并应用于尿素纯度标准物质的研制。     

Temperature modulated DSC studies of melting and recrystallization in poly (oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK)

The thermal and crystal morphological properties of amorphous and melt crystallized poly(oxy‐1,4‐phenyleneoxy‐1,4‐phenylenecarbonyl‐1,4‐phenylene) (PEEK) were investigated. Two different molecular weights were studied by Temperature Modulated DSC (TMDSC) over a broad range of annealing times and temperatures. The lower molecular weight PEEK under all crystallization conditions was found to exhibit secondary crystal melting in the low endotherm region, followed by melting of primary crystals melting in the low endotherm region, followed by melting of primary crystals superimposed with a large recrystallization contribution. Primary crystal melting broadly overlapped with melting of the recrystallized species and contributed to the broad highest endotherm. Recrystallization contributions and the interpretation of TMDSC were partially confirmed by independent rapid heating rate melting point determinations and variable heating rate DSC. The higher molecular weight PEEK showed many similarities but generally had smaller levels of reorganization above the annealing temperature under most higher temperature crystallization conditions. TMDSC provides excellent resolution of recrystallization and related events compared to standard DSC. The broad and substantial exothermic recrystallization in amorphous samples was also examined, showing that recrystallization continues through the final melting region.     

多杀菌素A的纯化方法研究

采用柱层析的方法从多杀菌素原料药中提取多杀菌素A和D的混合物(85∶15),然后采用重结晶的方法从多杀菌素A和D的混合物中提取多杀菌素A。多杀菌素A提取的优化条件为:甲醇为重结晶溶剂,多杀菌素A和D混合物质量与甲醇体积比为0.1 g/mL。在该条件下多杀菌素A的重结晶收率为64%,纯度为98.7%。     

Microstructural origin of physical and mechanical properties of ultra high molecular weight polyethylene processed by high velocity compaction

Ultra High Molecular Weight Polyethylene (UHMWPE) is a semi-crystalline polymer with exceptional wear and impact properties, but also a very high melt viscosity, owing to its extremely long chains. Therefore, UHMWPE is non-melt processable and its processing is long and expensive. However, a new process, High Velocity Compaction (HVC), allows processing UHMWPE within short processing times via sintering. Several high velocity impacts are applied to a powder-filled die to provide self-heating. The sintering is then obtained by local fusion/recrystallization. In this study, the physical and mechanical properties of UHMWPE processed by HVC are investigated. Ductile UHMWPE with a high modulus was obtained. The particular microstructure of the material resulting from the sintering by fusion/recrystallization has then been characterized. It appears that mechanical properties of HVC-UHMWPE are governed by the microstructure induced by processing conditions, and hence can be adjusted for a given application.     

获得抑制剂法生产低温高磁感取向硅钢的抑制剂控制研究进展

综述了国内外大钢铁企业与研究机构采用获得抑制剂法生产低温高磁感取向硅钢的开发及应用情况,分析了以该法生产高磁感取向硅钢过程中抑制剂的控制技术,包括固有抑制剂组成方案、气态渗氮方式与工艺及高温退火工艺的制定. 研究表明,固有抑制剂组成方案的设计思路大体一致,化合物抑制剂以AlN为主、硫化物为辅,同时添加少量Sn, Sb等单元素抑制剂,但组成元素含量存在一定差别;在脱碳退火后用NH3进行非平衡渗氮处理已成为气态渗氮的主要方式,但最佳方式仍未明确,具体选择需依据实际生产条件,相应脱碳及渗氮工艺的控制条件差别较大;高温退火工艺中升温制度差别不大,升温阶段退火气氛中N2含量的选择存在差别. 此外,分析了抑制剂控制技术目前存在的关键问题,并指出了进一步的研究方向.     

十二碳二元酸的重结晶精制工艺研究

采用有机溶剂重结晶法对十二碳二元酸粗品进行精制,讨论了溶剂种类、溶剂浓度对重结晶效果的影响;采用正交实验设计方法优选了重结晶工艺。结果表明:二元酸与乙酸粗品的固液比(质量体积比)为1.0:12.5,乙酸体积分数为100%,溶解温度为90℃,脱色剂的加入量为1%,脱色时间为60min时,用毛细气相色谱(GC)测定产品纯度为99.62%,用气质联用测定产品中所含的杂质为十三碳二元酸,用热分析仪(TG-DSC)测定产品熔点为130℃。     

DNS产品中杂质的生成机理及DNS精制工艺

跟踪了对硝基甲苯邻磺酸(NTS)制备4,4′-二硝基二苯乙烯-2,2′-二磺酸(DNS)的过程,推测了4-硝基苯甲醛2-磺酸钠(NBS)与4-硝基苯甲酸2-磺酸钠(NSB)杂质的生成机理。考察了重结晶温度、pH值、结晶次数及光照等因素对DNS产品的纯度及收率的影响,确定了DNS重结晶的优化操作条件。研究结果表明,适宜的重结晶温度约为85℃,优化pH值为9~10,以重结晶后所得精制DNS为原料可制备高品质4,4′-二氨基二苯乙烯-2,2′-二磺酸(DSD酸)。     

Dynamic Recrystallization during the Sliding Wear of Alumina at Elevated Temperatures

In previous studies, a very fine grain size surface layer of several micrometer thickness has been consistently observed in the wear track of alumina couples after wear at elevated temperatures. Detailed microstructural observations have revealed that dynamic recrystallization is the most probable mechanism for the surface layer formation. In this study, grain size and thickness of the surface layer are reported for the samples tested under various wear conditions. Both the grain size and the thickness are dependent on the testing temperature, nominal contact pressure, and the sliding velocity. The strain rate and the local temperature of the wear surface are estimated taking frictional heat into account and the Zener-Hollomon parameter Z = exp( Q/RT ) is calculated. A logarithmic plot of the grain size and Z yields a good linear relationship. This linearity and the slope of –0.21, similar to that previously reported for metals, further substantiate that dynamic recrystallization occurring in the wear surface is responsible for the formation of the fine grain size surface layer     

奥克托今结晶工艺对其撞击感度的影响研究

以结晶机理为指导,硝酸为溶剂,水为稀释剂,采用溶剂-非溶剂法重结晶奥克托今,用立式落锤仪测定其撞击感度。通过工艺条件的改变,寻求奥克托今撞击感度与结晶工艺的关系。实验结果表明,奥克托今晶体的撞击感度与其结晶工艺密切相关。实验较佳工艺条件,在(30±1)℃下,用98%的硝酸35 mL溶解5.0 g奥克托今,加水速率为0.67 mL/min,搅拌速率为220 r/min,测其撞击感度,计算的特性落高值为22.91 cm。     

微波催化合成四苯基卟啉

在有机溶剂体系中,利用微波催化苯甲醛、吡咯合成四苯基卟啉。最佳反应条件为:二甲苯溶剂100ml,对硝基苯甲酸催化剂1.8g,苯甲醛0.02mol、吡咯0.02mol,微波功率210W,辐射时间15min,产率达到52 9%,经重结晶,双组分紫外光谱法测定四苯基卟啉纯度达96%。     

Melting behaviour of poly(butylene succinate) in miscible blends with poly(ethylene oxide)

The melting behavior of poly(butylene succinate) (PBSU) in miscible blends with poly(ethylene oxide) (PEO), which is a newly found polymer blends of two crystalline polymers by our group, has been investigated by conventional differential scanning calorimetry (DSC). It was found that PBSU showed double melting behavior after isothermal crystallization from the melt under certain crystallization conditions, which was explained by the model of melting, recrystallization and remelting. The influence of the blend composition, crystallization temperature and scanning rate on the melting behavior of PBSU has been studied extensively. With increasing any of the PEO composition, crystallization temperature and scanning rate, the recrystallization of PBSU was inhibited. Furthermore, temperature modulated differential scanning calorimetry (TMDSC) was also employed in this work to investigate the melting behavior of PBSU in PBSU/PEO blends due to its advantage in the separation of exotherms (including crystallization and recrystallization) from reversible meltings (including the melting of the crystals originally existed prior to the DSC scan and the melting of the crystals formed through the recrystallization during the DSC scan). The TMDSC experiments gave a direct evidence of this melting, recrystallization and remelting model to explain the multiple melting behavior of PBSU in PBSU/PEO blends.     

Effect of annealing on morphologies and performances of hydroxypropyl methylcellulose/hydroxypropyl starch blends

The morphologies and performances of the blends of hydroxypropyl methylcellulose (HPMC), which is a thermal gel, and hydroxypropyl starch (HPS), which is a cooling gel, provides a scientific model to understand the relationship between the microstructure and performance of the unique thermal/cooling gel system. The films based on these blends have been developed for various applications, such as food packaging and medicine capsules, mainly for improving processibility. The morphologies and performance of the blends strongly depend on annealing or storage conditions and time since they are neither miscible nor compatible. This work focuses on the effects of storage conditions and time on the morphologies and performance of the blend films. It was found that the morphologies of the blend system depend on temperature, moisture, and annealing time. Correspondently, the gas permeability and mechanical properties of the film were also environmentally and time dependent. When HPS is continuous phase, the annealing results in starch recrystallization, which increases rigidity. When HPMC is the continuous phase, the materials showed less moisture sensitivity. Starch recrystallization and phase separation, which resulted in microcracks on the surface of the films, are the main reasons for the reduction in gas barrier and elongation. This work will study these issues using scanning electron microscope, X-ray diffraction, mechanical testing and establish their relationship.     

PP透明剂后处理的研究

本论文基于改善DBS类成核剂在加工中产生臭味及提高PP透明性的设想，采用国内DBS第二代成核剂(CHII)，先后用丙酮、异丙醇(IPO)、乙醇、N，N-二甲基酰胺(DMF)和环醚类溶剂(SA)等对其进行了重结晶提纯；研究了提纯条件(不同溶剂、温度、溶剂用量)对CHII的重结晶收率、熔点、表观密度和热性能的影响，其中用溶剂SA效果最好；确定了以17／1为最佳溶剂／溶质重量比用量。经溶剂后处理的CHII比粗产品的纯度上有了很大的提高。CHII经纯化后。在1700．Ocm^-1处的C=O峰消失。     

N,N’-二硫代二吗啉的无水制备工艺研究

以吗啉和一氯化硫为原料,以固体氢氧化钠为缚酸剂合成了N,N’-二硫代二吗啉(DTDM),考察了反应条件和重结晶条件对产物收率的影响。结果表明,较佳的合成工艺条件为:n(吗啉)∶n(S2Cl2)∶n(NaOH)=2∶1∶2,反应温度30~40℃,反应时间8 h,粗产品收率可达93%;较佳的重结晶工艺条件为:溶剂乙酸乙酯,m(溶剂)∶m(产品)=4∶1,结晶温度0~5℃,重结晶收率可达93%,DTDM总收率可达86%以上,采用FTIR与1H NMR对产物结构进行了表征。     

Recrystallization behaviour of cubic boron nitride under high pressure

The recrystallization behaviour of micron-sized cubic boron nitride (cBN) was studied by analysing the grain size and morphology of samples treated at 8−16 GPa/1500–2200 °C. The results show that the recrystallization temperature of cBN under a pressure of 8 GPa is approximately 1650 °C and increases by approximately 100 °C with every 2 GPa increase in pressure. Once grain recrystallization starts, the grains grow abnormally quickly as the temperature rises, and the strengthening effects of grain refinement and defect structure are greatly weakened. The recrystallization behaviour of cBN at high pressure is helpful to understand the sintering mechanism and control the microstructure and mechanical properties of sintered polycrystalline cBN compacts. In addition, the melting curve for cBN under high pressure is inferred according to the empirical relationship between recrystallization temperature and melting temperature, and the phase diagram for boron nitride is revised based on this new melting curve.     

N-氨甲酰谷氨酸合成研究

以谷氨酸、氰酸钾为原料,脲丙酸为催化剂,经过亲核加成反应,重结晶纯化得到目标化合物N-氨甲酰谷氨酸。考察了物料配比、反应时间及温度对反应收率和产品稳定性的影响。优化反应条件为:n(谷氨酸)∶n(氰酸钾)=1∶1.2,反应温度控制在60~65℃,盐酸浓度为12 mol/L,此条件下产品的总收率达到87.0%,含量≥92.0%,产品结构经过1H NMR确认。