The crystallization characterization of bulk syndiotactic polystyrene sample: immediate evidence from IR spectroscopy

The crystallization characterization of bulk syndiothactic polystyrene (s-PS) sample is thoroughly studied using the Fourier transform infrared spectroscopy (FTIR). The WAXD is further used to identify the s-PS crystal formation to confirm the specific absorbance in FTIR spectra. Both melt and cold-crystallization behavior are quantitatively determined using FTIR spectra ranging from 870 to 820 cm⁻¹ at 264 °C. Fitting curves to IR spectra provides direct evidence of bulk s-PS crystallization behavior in quantification. The melt-crystallization process yields the β-form only; while the cold-crystallization process yields both the α and the β-form crystal in bulk s-PS sample. The β-form crystal is generated from the phase-transformation of the α-form crystal by cold-crystallization process, the α-form crystal is the initial phase. The activity energy of the α-form formation is lower that that of the β-form, suggesting that the α-form crystal is kinetically favorable while the β-form crystal is thermodynamically favorable.     

CaO对CaO-Al2O3-SiO2微晶玻璃晶化过程活化能的影响

CaO对CaO-Al2O3-SiO2系统微晶玻璃的烧结及析晶性能有较大影响,从而影响了微晶玻璃的结构及性能.本文运用DTA、烧结收缩率分别测定了CaO-A12O3-SiO2系统微晶玻璃的烧结活化能及析晶活化能,研究了这两者的变化趋势.     

Separation of 1,3-propanediol from glycerol-based fermentations of Klebsiella pneumoniae by alcohol precipitation and dilution crystallization

The separation of 1,3-propanediol from the glycerol-based fermentation broth of Klebsiella pneumoniae plays an important role during the microbial production of 1,3-propanediol. In this paper, the separation of 1,3-propanediol from fermentative broth by a combination of ultrafiltration and alcohol dilution crystallization was investigated. The broth was first filtered by ultrafiltration, and 99% of cells, 89.4% of proteins and 69% of nucleic acids were removed. The obtained broth was further condensed by vacuum distillation, and then alcohol was added. The macromolecular impurities, such as nucleic acids, polysaccharides and proteins, were precipitated, and inorganic and organic salts were crystallized. The optimal volume ratio of alcohol added to the condensed fermentation broth was determined to be 2:1. As a result, proteins, nucleic acids and electric conductivity decreased by 97.4%, 89.7% and 95.8%, respectively, compared with the fermentative broth. The influences of pH and water content in condensed broth on alcohol precipitation and dilution crystallization were also investigated. The experimental results indicated that alcohol precipitation and dilution crystallization was feasible and effective for the separation of 1,3-propanediol from actual fermentation broth. Translated from The Chinese Journal of Process Engineering, 2006, 6(3): 454–457 [译自: 过程工程学报]     

Self-assembly and crystallization behavior of a double-crystalline polyethylene-block-poly(ethylene oxide) diblock copolymer

The self-assembly and crystallization behavior of a well-defined low molecular weight polyethylene-block-poly(ethylene oxide) (PE-b-PEO) diblock copolymer was studied. The number-average degrees of polymerization for the PE and PEO blocks were 29 and 20, respectively. The molecular weight distribution was 1.04 as determined by size-exclusion chromatography. The PE-b-PEO sample exhibited two melting points at 28.7 and 97.4 °C for the PEO and the PE crystals, respectively. The crystallization of the PE blocks was unconfined, while the crystallization of the PEO blocks was confined between pre-existing PE crystalline lamellae, as demonstrated by simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) studies. In the fully crystalline state, both PE and PEO blocks formed extended-chain crystals with PE chains tilted ∼22° from the lamellar normal and PEO chains parallel to the lamellar normal, as evidenced by two-dimensional WAXD study of shear-oriented samples. Regardless of hydrogen bonding among hydroxyl chain ends in the PEO blocks, interdigitated, single-crystalline layer morphology was observed for both PE and PEO crystals. The partial crystalline morphology, where the PE crystallizes and the PEO is amorphous, had the same overall d-spacing as the fully crystalline morphology. A double-amorphous PEO layer sandwiched between neighboring PE crystalline layers was deduced based on a chain conformation study using Fourier transform infrared. The confined crystallization kinetics for PEO blocks was investigated by differential scanning calorimetry, which could be explained by a heterogeneous nucleation mechanism. The slower crystallization rate in the PEO-block than the same molecular weight homopolymer was attributed to the effects of nanoconfinement and PEO chains tethered to the PE crystals.     

Hydrogen bonding,miscibility, crystallization,and thermal stability in blends of biodegradable polyhydroxyalkanoates and polar small molecules of 4‐tert‐butylphenol

The hydrogen bonding, miscibility, crystallization, and thermal stability of poly(3‐hydroxybutyrate) (PHB)/4‐tert‐butylphenol (BOH) blends and poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐3HHx)]/BOH blends were investigated by Fourier transform infrared (FTIR) spectroscopy, solid‐state¹³C‐NMR, differential scanning calorimetry, wide‐angle X‐ray diffraction (WAXD), and thermogravimetric analysis. The results of FTIR spectroscopy and solid‐state¹³C‐NMR show that intermolecular hydrogen bonds existed between the two components in the blends and that the interaction was caused by the carbonyl groups in the amorphous phase of both polyesters and the hydroxyl groups of BOH. With increasing BOH content, the chain mobility of both the PHB and P(3HB‐3HHx) components was improved. After the samples were quenched, the detected single glass‐transition temperatures decreased with composition, indicating that both PHB/BOH and P(3HB‐3HHx)/BOH were miscible blends in the melt. Moreover, as BOH content increased, the melting temperatures of PHB and P(3HB‐3HHx) clearly decreased, which implied that their crystallization was suppressed by the addition of BOH. Although the crystallinity of PHB and P(3HB‐3HHx) components decreased with increasing BOH content in the blends, their crystal structures were hardly affected after they were blended with BOH, which was further proven by WAXD results. In addition, the thermal stability of PHB was improved by a smaller amount of BOH.     

金属铝诱导法低温制备多晶硅薄膜

以氢气稀释的硅烷（SiH4）和硼烷（B2H6）为气源,利用等离子体增强化学气相沉积法（PECVD）制备出p型a-Si薄膜.采用铝诱导晶化技术对不同厚度的铝膜对a-Si薄膜晶化的影响进行了研究.实验中发现,铝膜溅射为10 s的非晶硅薄膜样品在450℃下退火10 min后,p型a-Si结构仍为非晶态,铝膜溅射为20 s的非晶硅薄膜在450℃下退火20 min后,p型a-Si薄膜开始晶化为polySi薄膜,并且铝膜厚度越厚,则a-Si薄膜晶化程度越强.     

Phase transitions of canola oil sediment

Canola sediment was obtained from an industrial filter cake by solvent extraction. When heated in the differential scanning calorimeter (DSC) (5–100°C), the sediment exhibited a single narrow melting peak at around 74.8°C. No solid-state polymorphic transformation of the material could be detected over this temperature range. The X-ray powder diffraction pattern of canola sediment resembled waxes from other sources with an orthorhombic unit cell. The phase transition behavior of canola sediment in oil was studied by both DSC and polarizing microscopy. With increasing ratio of oil/sediment, a reduction in both melting temperature and transition enthalpy was observed. The shape of the supercooling curve resembled that of the melting curve. The induction time was determined by spectrophotometry and was used to calculate the interfacial free energyσ between sediment and oil; σ=4.71 erg/cm². The effect of temperature and sediment concentration on the clouding time of canola oil was studied; the clouding time was the shortest at 5°C.     

稀土氧化物掺杂ZnO-Bi2O3系压敏陶瓷"软心"现象的研究

掺杂稀土氧化物的大尺寸ZnO压敏陶瓷具有明显的“软心”特征,即内部电位梯度远远低于表层。经过XPS关于Zn结合能的研究、SEM关于杂质分布状况的研究及XRD关于相态的研究表明:试样内部氧和添加剂的匮乏及晶态的不完善是影响内层电位梯度的三大主要因素。     

高含量ZnO对Li2O-Al2O3-SiO2系统微晶玻璃晶化和性能的影响

采用差热分析、X-射线衍射分析和扫描电镜等分析手段研究了高含量ZnO对Li2O-Al2O3-SiO2系统微晶玻璃晶化和性能的影响.结果表明随着ZnO由9wt%增加到11wt%,该系统玻璃转变温度降低,晶化峰值温度降低,最佳成核温度从755±2℃降至745±2℃.通过计算,样品的晶化活化能E和晶化指数n分别为303±3(kJ/mol)、286±3(kJ/mol)、278±3(kJ/mol)和2.9±0.2、3.1±0.2、3.4±0.2.说明了ZnO在能降低玻璃熔融温度的同时能促进玻璃晶化,但ZnO含量达到11wt%时,其热膨胀系数发生突变.     

PA6/1212共聚物的性能研究

用差示扫描量热仪对尼龙6/1212(PA6/1212)共聚物的一次、二次熔融行为及结晶行为进行了研究,分析了组成与熔融峰、结晶峰的关系,发现了冷结晶现象;研究了PA1212单体含量为2%~20%的PA6/1212共聚物的力学性能与组成的关系。结果表明,在此组成范围内可制得刚性优良的共聚物,冲击强度也有所改善,当PA1212单体含量为11%时,可得到综合力学性能相对较好的共聚物。