等规聚丙烯成核剂的结构和构型分析

成核剂在聚丙烯的结晶过程中作为晶核，参与调节晶体的晶型、大小及其分布，促使形成不同性能的聚丙烯材料．成核剂促进聚合物结晶的机制是聚合物结晶领域的研究热点，但其结构对聚合物结晶的影响尚不清晰；而成核剂通常具有同分异构体，使其结构解析更加困难，但成核剂的结构解析是进一步研究其成核机理的基础．本文综合运用核磁共振（NMR）波谱、傅里叶变换-红外（FT-IR）光谱和扫描电镜能谱分析（SEM-EDS）表征了一种二元羧酸复合物类β晶型聚丙烯成核剂的结构和构型，结果表明该成核剂cis-△4-四氢邻苯二甲酸钙为消旋体，羧酸与钙以桥式螯合方式形成有机羧酸金属盐．     

改善三水醋酸钠固液相变性能的实验研究

三水醋酸钠在凝固过程中存在严重的过冷和相分层。用明胶做其防相分层剂,添加不同的成核剂,来解决其过冷问题。最终找到几种能显著改进三水醋酸钠相变特性的添加剂配方,并发现被加入添加剂的三水醋酸钠混合物被加热到的温度对其过冷度有直接影响,同时从晶体结构方面对有效添加剂的选择原则进行了探讨。     

Synergistic Effects of Polyethylene Glycol and Polyhedral Oligomeric Silsesquioxanes on Crystallization Behavior of Poly(L-lactide)

The synergistic effects of poly(ethylene glycol) (PEG) and polyhedral oligomeric silsesquioxanes (POSS) on the crystallization behavior of semicrystalline poly(L-lactide) (PLLA) were systemically investigated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Initially, the influences of PEG and POSS, individually, on PLLA crystallization were studied. The results indicated that PEG, as an efficient plasticizer, enhanced the mobility of the PLLA chains, resulting in decreasing of the glass transition temperature. The enhanced crystallization capacity of PLLA was strongly dependent on the molecular weight and content of the PEG, increasing with decreasing of the molecular weight and increasing of the PEG content. The experimental results also indicated that POSS was a heterogeneous nucleating agent, promoting the crystallization of PLLA. The synergistic effects of PEG and POSS on PLLA crystallization were then analyzed. The results showed that in the presence of PEG and POSS the crystallinity of PLLA was further enhanced due to their synergistic effects.     

聚丙烯中电树枝生长机理研究

耐电树枝老化特性是表征聚合物绝缘材料介电性能的重要参数之一.聚丙烯(PP)是典型半结晶聚合物,其复杂的非均匀聚集态结构影响电树枝的生长.本文对PP及加入成核剂的PP试样进行了耐电树枝化性能实验,通过偏光显微镜(PLM)及差示扫描量热法(DSC)分析加入成核剂前后PP的结晶形态、结晶度以及结晶结构对电树枝生长特征的影响.以相界面自由能的热驱动作用以及放电雪崩理论为基础,对电树枝生长的热力学和动力学机理进行分析,阐明电场分布对电树枝生长的重要作用.根据半结晶材料的结晶相和非晶相的物理性能,建立材料内部电场分布计算模型,模拟针-板电极条件下聚合物材料内部的局域电场分布情况,分析了电树枝通道的动力学生长特征,探讨了成核剂改变PP的结晶结构抑制电树枝沿电场生长的作用.     

Effect of Metallic Salts of Malonic Acid on the Formation of β Crystalline Form in Isotactic Polypropylene

The effects of malonic acid and the lithium, sodium, potassium, zinc, magnesium, calcium, strontium, and barium salts of malonic acid on the formation of β crystalline form in isotactic polypropylene at the crystallization temperatures 120 and 130°C have been investigated. It was found that malonic acid and the lithium, sodium, and potassium salts of malonic acid inhibit the formation of β crystalline form in polypropylene. Zinc malonate has a limited positive effect on the formation of β crystalline form, while magnesium, calcium, strontium, and barium salts are β nucleating agents, in descending order. The decreased β nucleation abilities of the alkaline earth metallic salts of malonic acid are attributed to the increasing atomic radii of the combined metals and decreasing crystallization temperatures.     

Comparison of Nucleation Effects of Organic Phosphorous and Sorbitol Derivative Nucleating Agents in Isotactic Polypropylene

Organic phosphorous and sorbitol derivatives are two types of very effective nucleating agents for isotactic polypropylene (iPP). The effects of two kinds of organic phosphorous nucleating agents, Irgastab NA-11 and ADK NA-21, and two kinds of sorbitol derivatives, Irgaclear DM and Millad 3988, on mechanical properties and crystallization behaviors of iPP are compared in this paper. The organic phosphorous nucleating agents had better effects on mechanical properties of iPP than sorbitol derivatives, whereas the latter had better effects on transparency of iPP than the former. At the same time, the organic phosphorous nucleating agents and sorbitol derivatives had similar effects on the crystallization peak temperature (Tc) of iPP. When the concentration of nucleating agents was 0.2 wt%, compared to those of virgin iPP, the tensile strength and flexural modulus of iPP nucleated with Irgastab NA-11 and ADK NA-21 were increased by 19.35% and 17.67%, and 29.48% and 24.84%, and the haze value was decreased by 43.58% and 44.01%, respectively. On the other hand, the tensile strength and flexural modulus of iPP nucleated with Irgaclear DM and Millad 3988 were increased by 7.03% and 7.46%, and 7.20% and 11.96%, and the haze value was decreased by 51.03% and 52.23%, respectively. When the cooling rate was 10°C /min, the Tc of iPP nucleated with these four nucleating agents was increased from 118.74°C of virgin iPP to about 130°C. Meanwhile, the morphology study showed that addition of both organic phosphorous and sorbitol derivative type nucleating agents could decrease the spherulite size of iPP significantly and that sorbitol derivatives have greater effects.     

Nucleating Efficiency of Organic Phosphates in Polypropylene

Organic phosphates used as nucleating agents can remarkably promote the stiffness and crystallization rate of polypropylene homopolymer and ethylene–propylene copolymer. In this article, the nucleating activity of 2,2′-methylene-bis(4,6-di-tert-butylphenyl) phosphoric acid and its derivatives for isotactic polypropylene (iPP) were investigated with a differential scanning calorimeter (DSC) and polarized light microscope (PLM), and their influence on mechanical properties of polypropylene was also studied. The results showed that the sodium salt (NA7) and the glyceride ester (NA8) of the organic phosphoric acid were of high nucleating efficiency. If 0.4 wt% of NA7 or NA8 was added to PP, the crystallization peak temperature of PP was raised 15°C or 11°C, respectively, the amount of crystallinity was increased by 3 to 6%, and the crystallization rate was enhanced significantly. The nucleating activity is thermally stable when the mixture of iPP and a nucleating agent was melted and crystallized repeatedly in the DSC. The nucleating agents mentioned above could increase the modulus of the polymer by 20 to about 30% and could increase the flexural strength by 10 to about 20%. However, a number of other organic phosphates tested have little nucleating effect.     

Effects of α/β Compound Nucleating Agents on Mechanical Properties and Crystallization Behaviors of Isotactic Polypropylene

Sodium 2,2’-methylene-bis (4,6-di-tert-butylphenyl) phosphate (commercial name: Irgastab NA-11) and N,N’-dicyclohexylnaphthalene-2,6-dicarboxamide (commercial name: NU-100) are highly effective nucleating agents for α-isotactic polypropylene (iPP) and β-isotactic polypropylene (iPP) respectively. Effects of a total concentration of 0.2 wt% NA-11/NU-100 compound nucleating agents with different ratios of NU-100 on mechanical properties and crystallization behaviors of iPP were studied in this paper. The results showed that good balance between decreased stiffness and increased toughness of iPP was realized when the ratio of NU-100 was 50 wt%. Compared with those of virgin iPP, tensile strength, tensile modulus, flexural strength, and flexural modulus of iPP nucleated by the compound nucleating agent with 50 wt% NU-100 decreased by only 2.9%, 4.8%, 3.8% and 6.1% respectively, while the notched Izod impact strength of the nucleated iPP was increased by 212.8%. In addition, differential scanning calorimetry analysis results showed that addition of the NA-11/NU-100 compound nucleating agent increased the peak crystallization temperature of iPP significantly, but the crystallization rate of the nucleated iPP decreased with increasing ratio of NU-100 in compound nucleating agents.     

Synthesis of Co(II) Complex with Hexamethylenetetramine Using Jet Milling and Its Influence on the Thermal Performance of Poly(l-lactic acid)

Cobalt(II)-hexamethylenetetramine (Co(II)-HMTA) complex was prepared using jet milling. Elemental analysis and thermogravimetric analysis confirmed that the structure of the Co(II)-HMTA complex was Co(HMTA)₂Cl₂·6H₂O (LG). The influence of LG on the thermal performance of poly(l-lactic acid) (PLLA) was investigated. Isothermal crystallization behavior and X-ray diffraction analysis (XRD) results of PLLA/LG showed that LG could improve the crystallization performance of PLLA; 1% LG caused the half time of overall crystallization (t_1/2) of PLLA to decrease from 96.5 min to a minimum value 3.8 min at 100°C. However, the isothermal crystallization kinetics of PLLA/LG described using the Avrami equation and XRD analysis indicated that the isothermal crystallization temperature and the LG concentration significantly affected the isothermal crystallization process of PLLA. In particular, 0.3% LG caused the intensity of the X-ray crystal diffraction peaks of PLLA to decrease with an increase of isothermal crystallization time after increasing for the first 5 min. The thermal decomposition analysis of PLLA/LG showed that the onset decomposition temperature of PLLA with a small amount of LG was higher than that of the neat PLLA and PLLA with a high concentration LG.     

变温FTIR光谱法研究PET/纳米CaCO_3复合材料的固态转变

采用变温FTIR光谱法研究了原料PET和PET/nano-CaCO3(MPET)复合材料体系在40~250℃之间逐渐升温过程中,PET基体的固态转变。通过研究PET内标谱带1 410 cm-1与结晶相关谱带1 342cm-1吸光度之比值随温度变化关系曲线,结合其在同样条件下的差热扫描(DSC)曲线,分析了纳米CaCO3粒子的加入对PET固态转变和结晶相关谱带的影响,表明纳米CaCO3粒子的加入显著改善了PET的结晶和熔融行为。     

三水合醋酸钠纳米成核剂的性能研究

三水合醋酸钠是一种具有较高的储能密度和热导率的储热相变材料,但是在凝固过程中的过冷和相分离现象限制了它的应用,需要寻求有效的成核剂和增稠剂来克服过冷和相分离的问题。本文实验分析了几种纳米材料（AIN、Si₃N₄、ZrB₂、SiO₂、BC₄、SiB₆）的成核效果,结果表明质量分数5%或4%的Si₃N₄、10%ZrB₂、5%AlN在自然分散下就能够消除三水合醋酸钠过冷度,质量分数2%的SiO₂在熔化的三水合醋酸钠中经磁力搅拌和超声分散后能够消除其过冷度。结合纳米材料的粒度分析结果,表明粒度分布在几十纳米到300纳米左右的纳米材料有较好的成核效果。     

High-energy-density pentazolate salts: CaN_(10) and BaN_(10)

The search for high energy density materials(HEDMs)in polymeric nitrogen compounds has gained considerable attention.Previous theoretical predictions and experiments have revealed that metal ions can be used to stabilize the pentazolate(N-5)anion.In this work,by employing a machine learning-accelerated crystal structure searching method and first-principles calculations,we found that the new pentazolate salts,CaN(10)and BaN(10),are energetically favorable at high pressures.Phonon dispersion calculations reveal that they are quenchable at ambient pressure.Ab initio molecular dynamics simulations verify their dynamic stability at finite temperature.Bader charge and electron localization function illustrates that alkaline earth atoms serve as electron donors,contributing to the stability of N5 rings.Bonding calculations reveal covalent bonds between nitrogen atoms and weak interactions between N5 rings.Similar to other pentazolate salts,these polymeric nitrides have high energy densities of approximately 2.35 kJ/g for CaN(10)and 1.32 kJ/g for BaN(10).The predictions of CaN(10)and BaN(10)structures indicate that these salts are potential candidates for green nitrogen-rich HEDMs.     

Thermal Performance of a Blend System Based on Poly(l-lactic acid) and an Aliphatic Multiamide Derivative of 1H-Benzotriazole

An aliphatic multiamide derivative derived from 1H-benzotriazole, N, N'-bis(1H-benzotriazole) sebacic acid acethydrazide (SA), was synthesized to evaluate its effect on the thermal performance, including non-isothermal crystallization and melting behavior as well as thermal stability, of poly(l-lactic acid) (PLLA). The comparative study, by means of DSC measurements, showed that the incorporation of SA caused a non-isothermal crystallization peak to appear and become sharp, showing its advanced crystallization promoting effect for PLLA. The non-isothermal crystallization results further indicated that 2 wt% SA was the saturation concentration for PLLA crystallization, and that the cooling rate was also a crucial determinant for PLLA crystallization. Considering the melting behavior, the difference between the virgin PLLA and PLLA/2%SA further confirmed the crystallization accelerative effect of SA for PLLA, with the increase of crystallization temperature in the temperature zone from 90 to 130°C being beneficial to the crystallization of PLLA during processing. Compared to the virgin PLLA, the trends of thermal decomposition curves were similar, suggesting that the introduction of SA of 0.5–3 wt% did not significantly change the thermal decomposition behavior of PLLA.     

Crystallization Kinetics of Functionalized Fe3O4/Ethylene-vinyl Acetate Copolymer Nanocomposites Adhesives

In the present paper, the crystallization behaviors of six different functional Fe₃O₄/ethylene-vinyl acetate (EVA) copolymer nanocomposite adhesives were studied. Crystal structures of the nanocomposite adhesives were characterized by wide-angle X-ray scattering, and the results showed that both functionalized and non-functionalized Fe₃O₄ nanoparticles had only a small influence on the crystal structure of EVA. The cystallization kinetics was investigated through differential scanning calorimetry. The Ozawa and Mo methods were applied to analyze the crystallization behaviors, and the nucleating effect was estimated through the Dobreva and Gutzow method. Finally, the crystallization energy barrier was studied by the Kissinger method.     

Acoustic spectroscopy and electrical characterization of SiO2/Si structures with ultrathin SiO2 layers formed by nitric acid oxidation

Ultrathin silicon dioxide (SiO₂) layers formed on Si substrate with nitric acid have been investigated using both acoustic deep-level transient spectroscopy (A-DLTS) and electrical methods to characterize the interface states. The set of SiO₂/Si structures formed in different conditions (reaction time, concentrations of nitric acid (HNO₃), and SiO₂ thickness [3–9 nm]) was prepared. The leakage current density was decreased by post-oxidation annealing (POA) treatment at 250°C in pure nitrogen for 1 h and/or post-metallization annealing (PMA) treatment at 250°C in a hydrogen atmosphere for 1 h. All structures of the set, except electrical investigation, current-voltage (I - V), and capacitance — voltage (C - V) measurements, were investigated using A-DLTS to find both the interface states distribution and the role of POA and/or PMA treatment on the interface-state occurrence and distribution. The evident decreases of interface states and shift of their activation energies in the structures with PMA treatment in comparison with POA treatment were observed in most of the investigated structures. The results are analyzed and discussed.      

Temperature and pressure dependencies of the crystal structure of the organic superconductor (TMTSF) 2 ClO 4

The crystal structure of (TMTSF)₂ClO₄ has been determined at (7 K, 1 bar) and at (7 K, 5 kbar) with a high accuracy. For the latter, low temperature and pressure were applied simultaneously using a X-ray diffraction instrumentation designed in our laboratory, these results are the first for molecular compounds. The effects of lowering the temperature are not the same as those produced by increasing the pressure. At (7 K, 1 bar) the anion ordering which occurs in this compound, and which is characterised by the appearance of b ^* /2 superlattice reflections, is well observed. This anion ordering leads to the presence of two independent stacks of TMTSF cations which is the only case found in the Bechgaard salts family. The comparison of the low temperature crystal structures under atmospheric pressure and at 5 kbar shows that the centres of mass are nearly the same, independent of the pressure: the interchain interactions do not depend on the doubling of the unit cell. Under pressure, the ordering (0, 1/2, 0) does not occur at any temperature. These structural data are confirmed by the quantum chemical calculations which show that the difference in the site energy of the two independent cations is 100 meV. Received 10 April 2000 and Received in final form 27 September 2000     

Embedding methods for poly(l-lactic acid) microfiber mesh/human mesenchymal stem cell constructs

Fiber mesh scaffolds were recently investigated in tissue engineering as possible support for stem cell growth and differentiation, in order to repair lesion areas in clinical practice. In particular, the literature is focused on fiber mesh scaffolds constituted of biocompatible and resorbable polymeric structures, like poly(l-lactic acid) (PLLA). However, as regards the study of constructs constituted of PLLA microfibers and cells, only quantitative and SEM analyses were reported, lacking histological analysis. Histological evaluation of these constructs could give important information about cellular distribution in the scaffold, cell–scaffold interactions and extracellular matrix production. The purpose of our study was to find a valid method to analyze PLLA microfiber/cell constructs from both histological and histochemical angles. Biodegradable non-woven fiber meshes were prepared using hollow microfibers, based on PLLA.We first evaluated different embedding methods useable for histological analysis and the results showed that among the paraffin, Killik, and acrylic resin the only suitable medium was the latter. Then we employed the acrylic resin to embed the constructs made up of PLLA microfibers and bone marrow-derived human mesenchymal stromal cells, which we then analyzed with Toluidine Blue, PAS and Alcian Blue staining. These constructs, previously analyzed for cell viability by MTT and CCK-8 tests, showed viable/proliferating cells until 6 weeks of culture. The stainings performed on constructs confirmed viability data obtained with SEM and MTT/CCK-8 and supplied other information on the cell behaviors such as the distribution and organization onto the scaffold and the production of extracellular matrix molecules. In conclusion, this methodological study mainly suggests a suitable method to analyze PLLA microfiber/cell constructs, at the same time confirming and enriching the literature data on the compatibility between PLLA microfibers and hMSCs.     

Preparation and Characterization of Gelatin–Poly(L-lactic) Acid/Poly(hydroxybutyrate-co-hydroxyvalerate) Composite Nanofibrous Scaffolds

Poly(L-lactic) acid (PLLA) scaffolds, prepared by electrospinning technology, have been suggested for use in tissue engineering. They remain a challenge for application in biological fields due to PLLA's slow degradation and hydrophobic nature. We describe PLLA, PLLA/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and PLLA/PHBV/gelatin (Gt) composite nanofiberous scaffolds (Gt–PLLA/PHBV) electrospun by changing the electrospinning technology. The morphologies and hydrophilicity of these fibers were characterized by scanning electron microscopy (SEM) and water contact angle measurement. The results showed that the addition of PHBV and Gt resulted in a decrease in the diameters and their distribution and greatly improved the hydrophilicity. The in-vitro degradation test indicated that GT–PLLA/PHBV composite scaffolds exhibited a faster degradation rate than PLLA and PLLA/PHBV scaffolds. Dermal fibroblasts viabilities on nanofibrous scaffolds were characterized by [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] (MTT) assay and cell morphologies after 7 days culture. Results indicated that the GT–PLLA/PHBV composite nanofibers showed the highest bioactivity among the three scaffolds and increased with increasing time. The SEM images of cells/scaffolds composite materials showed the GT–PLLA/PHBV composite nanofibers enhanced the dermal fibroblasts's adhesion, proliferation, and spreading. It is suggested that the nanofibrous composite scaffolds of GT–PLLA/PHBV composites would be a promising candidate for tissue engineering scaffolds.     

Influence of Bovine Bone Content on In Vitro Degradation of Poly-L-lactic Acid and Bovine Bone Composite Materials

In vitro degradation experiments of poly-L-lactic acid (PLLA) and bovine bone (BB) composites were carried out in a phosphate-buffered solution (PBS) at 37°C with a pH of 7.4. The influence of BB content on pH value of PBS, water uptake, molecular weights, molecular weight distributions, weight losses, mechanical strengths, and morphologies of PLLA/BB was investigated with degradation times. The results indicated that the presence of the BB modified the degradation of the PLLA matrix. The degradation rate of PLLA in the PLLA/BB composite was slower than the degradation rate of the sole PLLA material. Furthermore, the degradation rate of the composites became slower with the increasing content of BB in PLLA/BB composites.     

The Effect of Poly(Ethylene Succinate) on Mechanical Properties of PLLA/PES Blend Prepared by Melt-Blending

Fully biodegradable poly(L-lactide) and poly(ethylene succinate) (PLLA/PES) blends were prepared via melt-blending using PLLA and PES as reactants in a stainless steel chamber. The prepared PLLA/PES blend, as well as neat PLLA and PES, was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) to confirm the structure and the crystallization of PLLA in the blend. The mechanical properties of PLLA/PES blends were determined by bending and tensile tests and the effects of PES content on the mechanical properties of PLLA/PES blends were investigated. It was found that blending some amount of PES could significantly improve the elongation at break while still keeping considerably high strength and modulus. With increasing PES content, both strength and modulus gradually decreased; however the elongation at break significantly increased. SEM was used to examine the morphology of fracture surfaces of PLLA/PES blends.