双峰分子量分布对聚乙烯等温结晶动力学的影响

通过熔融共混制备了一系列分子量分布规律变化的双峰聚乙烯(BPE),并采用高斯拟合对其分子量分布(MWD)曲线进行分峰处理,研究了低/高分子量级分相对含量(AL/H)对BPE的等温结晶动力学的影响。结果表明:BPE的平均分子量、分子量分布宽度及双峰位置均基本不变,只有双峰的相对强度规律性地变化;参数AL/H能够很好地定量BPE双峰特征和低高分子量级分的相对含量;AL/H值的增加,即低分子量级分含量的增大,可以明显提高BPE的结晶速率,但不会改变结晶成核和增长类型。     

PE-HD/PC/POE-g-MAH复合材料断裂性能的研究

采用基本断裂功(EWF)法评价了高密度聚乙烯(PE-HD)/聚碳酸酯(PC)/聚烯烃弹性体接枝马来酸酐(POE-g-MAH)复合材料处于平面应力与平面应变过渡状态下的断裂韧性和塑性功。研究不同PC含量对复合材料断裂行为的影响,并把宏观断裂参数的变化与复合材料的微观结构联系起来,从物质结构上寻求断裂功参数变化的原因。结果表明,随PC含量的增加,复合材料的比基本断裂功增加,比塑性功降低;复合材料的断裂韧性主要取决于屈服后材料抵抗裂纹扩展的能力,复合材料的塑性变形能力也更依赖于屈服后的行为;复合材料的缺口冲击强度随PC含量的增加而降低,缺口冲击强度高的材料比基本断裂功较小。     

双峰聚乙烯膜光稳定性研究

研究了纯双峰聚乙烯(BPE)薄膜和改性BPE薄膜的光稳定性能,用力学性能测试、衰减全反射傅里叶变换红外光谱、差示扫描量热分析和扫描电子显微镜表征样品老化前后的物理化学变化。结果表明,纯BPE薄膜光稳定性较差,其紫外老化寿命200h左右。添加了光屏蔽剂钛白粉等多层BPE薄膜具有较好的光稳定性;受光层即第一层膜紫外老化寿命为4 000h左右,理化性质明显劣化,而其他层薄膜的理化性质只发生了少许变化,说明受光层改性BPE薄膜对其他多层膜起到很好的保护作用。     

PP/POE/硅灰石复合材料性能的研究

用基本断裂功(EWF)方法研究聚丙烯(PP)/聚烯烃弹性体(POE)/硅灰石复合材料的断裂行为,研究不同硅灰石含量对复合材料断裂行为的影响,并把宏观断裂参数的变化与复合材料的微观结构联系起来,从物质结构上寻求断裂参数变化的原因.结果表明,当PP/POE/硅灰石质量比为62/8/30时,PP/POE/硅灰石复合材料的比基本断裂功为83 kJ/m2,PP/POE/硅灰石复合材料的断裂韧性主要取决于复合材料屈服后抵抗裂纹扩展的能力,PP/POE/硅灰石复合材料的塑性变形能力更依赖于屈服前的行为.相同大小的硅灰石制得的PP/POE/硅灰石复合材料的缺口冲击强度随着硅灰石含量的增加而降低.缺口冲击强度高的复合材料,比基本断裂功却较小,耐长期破裂性也较差,说明基本断裂功比缺口冲击强度更能揭示复合材料长期破坏行为的特征.     

PE－HD/硅灰石/POE-g-MAH复合材料的断裂行为

采用基本断裂功法（EWF）评价了高密度聚乙烯（PE－HD）/硅灰石/马来酸酐接枝乙烯－辛烯共聚物（POE-g-MAH）复合材料处于平面应力与平面应变过渡状态下试样的断裂行为,研究了不同硅灰石含量对复合材料断裂行为的影响。对该体系EWF方法的适用效果以及试样所处的应力状态进行了验证,用线性回归法处理数据成功得到了各断裂功参数。结果表明,随着硅灰石含量的增加,PE－HD/硅灰石/POE-g-MAH复合材料的比基本断裂功增加,比塑性功降低;复合材料的断裂韧性主要取决于屈服后材料抵抗裂纹扩展的能力,复合材料的塑性变形能力也更依赖于屈服后的行为;PE－HD/硅灰石/POE-g-MAH复合材料的缺口冲击强度随着硅灰石含量的增加而降低,缺口冲击强度高的材料比基本断裂功却较小。     

超声波与引发剂结合制备高熔体强度聚乙烯

采用超声辐照方法制备了高熔体强度聚乙烯,研究了不同超声条件对相对分子质量分布呈双峰(简称双峰)的高密度聚乙烯(HDPE)分子链结构及性能的影响,并成功制备了高熔体强度聚乙烯。结果表明:延长超声时间可以增加双峰HDPE链缠结程度,但导致部分聚乙烯降解,降低了熔体强度。超声过程中加入微量自由基引发剂过氧化二异丙苯有效地提高了双峰HDPE分子链缠结程度和长链支化结构含量,从而极大提高了双峰HDPE的熔体强度并保留了HDPE优异的力学性能。     

管材专用料HDPE4803T加工性能的研究

在对管材专用料高密度聚乙烯(HDPE)4803T的性能测试和结构表征的基础上,研究了管材加工温度和挤出速度对加工参数的影响情况,并对管材的性能进行了测试.结果表明,HDPE4803T属典型的双峰分布聚乙烯树脂,其性能满足PE80级管材料的指标要求.材料的熔体强度对加工温度变化的敏感性较弱.挤出温度和挤出速度对管材的性能影响很小,采用该管材专用料,可以在较宽的挤出温度和挤出速度范围内制备出性能优良的管材.     

PC／bPE增容共混材料力学性能与阻裂行为研究

通过熔融接枝的方法制备了双峰聚乙烯接枝马来酸酐(bPE-g-MAH)作为PC/bPE(聚碳酸酯/双峰聚乙烯)共混材料的相容剂,提高了共混材料的冲击强度和耐溶剂开裂性能.用扫描电镜(SEM)对PC/bPE共混材料在冲击作用下形成的裂纹尖端结构进行了观测.结果表明,增容共混材料的裂纹尖端存在纤维连结区,这些连结两断裂分离面的纤维对裂纹扩展有钝化和阻碍作用,从而提高了共混材料的抗开裂性和冲击强度.     

全硫化超细粉末橡胶对PVC-U力学性能及形态的影响

研究了未增塑聚氯乙烯／粉末橡胶共混物的力学性能和形态特征。研究发现，随粉末橡胶用量增大，共混物的冲击强度先有所降低然后逐渐上升。实验结果和电镜图像表明：粉末橡胶基本粒子均匀分散的效果是影响共混物冲击韧性高低的重要因素；环氧化天然橡胶有促进粉末橡胶分散、改进增韧效果的作用。基本断裂功方法的研究结果表明，共混物的比基本断裂功随粉末橡胶用量增多而降低，比非基本断裂功则随之而升高，且断裂功的变化主要表现在材料屈服之前。     

相对分子质量分布对双峰聚乙烯薄膜树脂等温结晶动力学的影响

研究了2种双峰聚乙烯薄膜树脂（9455F1 W和9455F1 100）的等温结晶动力学行为,并讨论了相对分子质量分布的双峰相对含量对结晶过程的影响。结果表明,2种样品都呈现双峰分布的特征,且其相对分子质量相差不大,但高/低相对分子质量级分含量不同;其中,9455F1 W样品的高相对分子质量级分的相对含量大,9455F1 100样品的低相对分子质量级分的相对含量大;随低相对分子质量级分含量的增加,样品的结晶速率常数增大,半结晶时间减小,结晶速率增大。     

Structure–Property–Process Relationship for Blown Films of Bimodal HDPE and Its LLDPE Blend

Blown films of bimodal‐high‐density polyethylene (HDPE) (BPE) and its blend containing 40 wt% of linear low‐density polyethylene (LLDPE) are prepared in various neck‐heights (NHs). The crystal structures of both films are investigated in detail using small‐angle X‐ray scattering and wide‐angle x‐ray diffraction techniques. The results show that the blending of LLDPE notably modifies the crystal structure of BPE, including crystal density (ρ_c), crystallite size of the 110 plane (〈L₁₁₀〉), thickness of the lamellar crystal (L_c), and grain widths of the lamellae. The relationships between NH, crystal structure, and the resistance of dart‐drop impact (DDI) are investigated for both BPE and BPE/LLDPE films. The results indicate that the reorientation of lamellae might be a primary factor responsible for the DDI property. However, large values of ρ_c, L_c, and 〈L₁₁₀〉 are required for the film to achieve high DDI.     

Compressive mechanical properties of partially sintered porous alumina of bimodal particle size system

This paper examined theoretically and experimentally packing behavior, sintering behavior and compressive mechanical properties of sintered bodies of the bimodal particle size system of 80 vol% large particles (351 nm diameter)–20 vol% small particles (156 nm diameter). The increased packing density as compared with the mono size system was explained by the packing of small particles in 6-coordinated pore spaces among large particles owing to the similar size relation between 6-coordinated spherical pore and small particle. The sintering between adjacent large particles dominated the whole shrinkage of the powder compact of the bimodal particle size system. However, the bimodal particle size system has a high grain growth rate because of the different curvatures of adjacent small and large particles. The derived theoretical equations for the compressive strengths of both mono size system and bimodal particle size system suggest that the increase in the grain boundary area and relative density by sintering dominate the compressive strength of a sintered porous alumina. The experimental compressive strengths were well explained by the proposed theoretical models. The strength of the bimodal particle size system was high at low sintering temperatures but was low at high sintering temperatures as compared with that of mono size system of large particles. This was explained by mainly the change of grain boundary area with grain growth. The stress–strain relationship of the bimodal particle size system showed an unique pseudo-ductile property. This was well explained by the curved inside stress distribution along the sample height. The inside stress decreases toward the bottom layer. The fracture of one layer of sintered grains over the top surface proceeds continuously with compressive time along the sample height when an applied stress reaches the critical fracture strength.     

Bimodal grain structure effect on the static and dynamic mechanical properties of transparent polycrystalline magnesium aluminate (spinel)

Transparent polycrystalline magnesium aluminate (spinel) with bimodal and unimodal grain structures were prepared. The influence of grain size distribution on static and dynamic mechanical properties were systematically investigated. The results showed that bimodal grain structure spinel has larger flexural strength (236.31 MPa) compared to unimodal grain structure spinel (221.38 MPa). Whereas, their values of hardness are very similar (15.1 vs 14.7 GPa) and fracture toughness remains unchanged (1.1 MPa∙m^1/2 for both spinel). Although static compression strength of bimodal grain structure spinel (1236 MPa) is higher than that of unimodal one (1078 MPa) due to a smaller average grain size in the former, the negative effect of bimodal grain structure reduced the spinel strength compared to theoretically predicted value. Bimodal grain structure spinel shows slightly lower increment (49%) in compression strength from static to dynamic loading compared to that of unimodal one (57%) due to a decreased strain-rate sensitivity ascribed to bimodal grain structure. A brittle mode in inelastic deformation at Hugoniot elastic limit was demonstrated in both bimodal and unimodal grain structures. Bimodal grain structure has an influence on the Hall-Petch-like relation of yield strength under planar impact loading.     

Structure and strength of a polyethylene pipe grade containing glass spheres and low-molar-mass linear polyethylene

The resistance to slow crack growth and to internal over-pressure of pipes based on a commercial polyethylene gas pipe grade (BPE; 0.6 mol% butyl branches and M?_W = 197,000 g/Mol) blended with both an injection molding grade linear polyethylene (LPE;M?_W = 42,000 g/mol) and 0.5 ± 0.1 mm glass spheres was studied. The blends and the pure polymer components were characterized by density measurements, differential scanning calorimetry, small-angle X-ray scattering, and transmission electron microscopy. The fracture properties of extruded pipes were measured using hydrostatic pressure testing and notched uniaxial testing on samples cut from the pipe wall. The polymer components were macroscopically uniformly blended and differential scanning calorimetry indicated the occurrence of partial co-crystallization between the branched and linear components. Transmission electron microscopy showed molar mass segregation on a 100 nm level. Notched uniaxial testing showed that the slow crack growth resistance of pure BPE was considerably higher than that of the LPE/BPE blend with 30% LPE. Fractography indicated that the fracture-initiating particles were larger in pipes failing after shorter period of time in the hydrostatic pressure testing. The lifetimes of hydrostatic pressure tested pipes based on the BPE grade containing glass spheres were similar to those of pipes based on the LPE/BPE blend with 30% LPE.     

Improved recovery of B‐phycoerythrin produced by the red microalga Porphyridium cruentum

A simplified process for the primary recovery and purification of B‐phycoerythrin (BPE) from Porphyridium cruentum exploiting aqueous two‐phase systems (ATPS) and isoelectric precipitation was developed in order to reduce the number of unit operations and benefit from increased purity and yield of the protein product. Evaluation of the partitioning behaviour of BPE in polyethylene glycol (PEG)/sulphate, PEG/dextran and PEG/phosphate ATPS was carried out to determine under what conditions the BPE and contaminants concentrated into opposite phases. An additional stage of isoelectric precipitation at pH 4.0 after cell disruption resulted in an increase in purity of the target protein from the BPE crude extract and enhanced the performance of the subsequent ATPS. PEG1000/phosphate ATPS proved to be suitable after isoelectric precipitation for the recovery of highly purified (defined as absorbance ratio A_{545 nm}/A_{280 nm} > 4.0) BPE with a potential commercial value as high as US$ 50/mg. An ATPS extraction stage comprising 29.5% (w/w) PEG1000, 9.0% (w/w) phosphate, a volume ratio (V_r) equal to 1.0, a system pH of 7.0 and loaded with 40% (w/w) of the BPE extract generated by precipitation allowed BPE recovery with a purity of 4.1±0.2 and an overall product yield of 72% (w/w). The purity of BPE from the crude extract increased 5.9‐fold after isoelectric precipitation and ATPS. The results reported herein demonstrate the benefits of the practical application of isoelectric precipitation together with ATPS for the recovery and purification of BPE produced by P. cruentum as a first step in the development of a commercial purification process. Copyright © 2006 Society of Chemical Industry     

大型中空容器级HDPE树脂的中试聚合研究

采用两段淤浆聚合工艺合成了由低摩尔质量的均聚物和高摩尔质量的共聚物组成的、具有宽峰或双峰摩尔质量分布的高密度聚乙烯大型中空容器级树脂。通过调节第一段和第二段聚合过程中聚合物的熔体质量流动速率来控制摩尔质量的大小及其分布；采用控制第二段共聚物中共聚单体数量来调节聚合物密度；控制第一段小分子数目，增加第二段摩尔质量或调整密度获得最大耐环境应力开裂性（ESCR）。随着共聚单体丁烯-1加入量的增加，反应釜共混物的密度、熔点、结晶度、拉伸屈服应力、断裂伸长率减少。随着高摩尔质量共聚物的含量增加，屈服应力、熔点、密度、结晶度减少，摩尔质量分布的双峰特性也增加，反应釜共混物的均聚物峰的高度减少，共聚物峰的高度增加。流变性能结果表明，通过改变共混物的组分可以获得力学性能和加工性能的平衡。     

Effects of Sodium Benzoate and Sodium Chloride on the Aggregation Behaviors of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEO-PPO at the Air/Water Interface

The effect of sodium benzoate and sodium chloride on the aggregation behavior of PEO-PPO-ph-PPO-PEO (BPE) and PPO-PEO-ph-PEO-PPO (BEP) polyethers at the air/water interface was investigated by measuring the equilibrium surface tension, surface dilational viscoelasticity, and surface tension relaxation. The measurements of surface tension showed that sodium benzoate has a better effect on decreasing the surface tension of BPE and BEP solutions than NaCl, especially when the polyether concentrations are low. According to dilational viscoelasticity measurements, the concentration of BPE required for the maximum dilational modulus is lower than that of BEP, indicating that BPE more easily forms a compact adsorbed layer. The dilational modulus values of BPE solutions in the presence of sodium benzoate and NaCl first increase and then decrease after passing through a maximum, and then they increase again with increasing electrolyte concentration. On the other hand, the dilational modulus values of BEP solutions in the presence of sodium benzoate and NaCl first increase to a maximum and then decrease with increasing electrolyte concentration. The surface tension relaxation results are consistent with those of dilational viscoelasticity. The different effects of sodium benzoate and NaCl on the polyether aggregation behaviors are caused by the strong hydrophobic and π-π interactions between polyethers and sodium benzoate. This work has a great importance for the application and development of polyethers.     

The linear and circular bulk photovoltaic effect in the piezoelectric crystal La3Ga5SiO14 with different impurities

The linear bulk photovoltaic effect (BPE) and photorefractive effect (PR) in La₃Ga₅SiO₁₄ has interesting peculiarities, connected with symmetry of the crystal. Due to the symmetry the both effects depend on the light polarization. The symmetry permits also to observe the circular BPE. The all these effects have extrinsic character and depend on the impurity ions. In the present paper we investigated the linear and circular BPE for different impurities.     

Boesenbergia pandurata Attenuates Diet-Induced Obesity by Activating AMP-Activated Protein Kinase and Regulating Lipid Metabolism

Obesity, a chronic metabolic disorder, is characterized by enlarged fat mass and dysregulation of lipid metabolism. The medicinal plant, Boesenbergia pandurata (Roxb.) Schltr., has been reported to possess anti-oxidative and anti-inflammatory properties; however, its anti-obesity activity is unexplored. The present study was conducted to determine whether B. pandurata extract (BPE), prepared from its rhizome parts, attenuated high-fat diet (HFD)-induced obesity in C57BL/6J mice. The molecular mechanism was investigated in 3T3-L1 adipocytes and HepG2 human hepatoma cells. BPE treatment decreased triglyceride accumulation in both 3T3-L1 adipocytes and HepG2 hepatocytes by activating AMP-activated protein kinase (AMPK) signaling and regulating the expression of lipid metabolism-related proteins. In the animal model, oral administration of BPE (200 mg/kg/day for 8 weeks) significantly reduced HFD-induced body weight gain without altering the amount of food intake. In addition, elevated serum levels of total cholesterol, low-density lipoprotein cholesterol, and triglycerides were suppressed by BPE administration. Fat pad masses were reduced in BPE-treated mice, as evidenced by reduced adipocyte size. Furthermore, BPE protected against the development of nonalcoholic fatty liver by decreasing hepatic triglyceride accumulation. BPE also activated AMPK signaling and altered the expression of lipid metabolism-related proteins in white adipose tissue and liver. Taken together, these findings indicate that BPE attenuates HFD-induced obesity by activating AMPK and regulating lipid metabolism, suggesting a potent anti-obesity agent.     

bPE-g-MAH对PC/bPE共混物力学性能与断面形态结构的影响

利用熔融接枝法制备了双峰聚乙烯接枝马来酸酐(bPE-g-MAH),将其用作聚碳酸酯/双峰聚乙烯(PC/bPE)共混物的增容剂。通过力学性能测试和扫描电镜分析,研究了bPE-g-MAH对共混物相容性和力学性能的影响。结果表明:bPE-g-MAH的加入使得PC和bPE两相的界面黏合作用增强,使PC/bPE共混物的冲击强度显著提高。