Interfacial crystallization and its mechanism in in-situ dynamically vulcanized iPP/POE blends

The effect of in-situ crosslinking of poly (ethylene-co-octene) (POE) rubber phase on the interfacial crystallization of isotactic polypropylene (iPP) in dynamically vulcanized iPP/POE blends was studied. The results showed that in situ crosslinking of POE obviously increased the interfacial crystallization of iPP in the dynamically vulcanized blends, comparing with that of pure iPP and the unvulcanized blend. The interfacial crystallization of iPP was further increased with the increase in crosslink degree. After annealing, the obvious interfacial crystallization was still obtained in the blend with high crosslink degree. Based on the fluctuation assisted nucleation mechanism in solution blended iPP/polyolefin block copolymer (OBC) blends, we proposed for the first time the interfacial crystallization mechanism in dynamically vulcanized blends: the oriented chains of iPP formed by concentration fluctuation at the interface during phase separation or shearing stress during melt mixing can be maintained because of the in situ crosslinking of POE phase, resulting in the enhancement of nucleation density at the iPP/POE interface. Our study proposes a new interfacial crystallization mechanism, and provides guidance for the preparation of high performance thermoplastic vulcanizates (TPVs) product by tailoring the interfacial crystallization of TPVs.     

新型热塑性弹性体DVA的制备及性能

研究不同相容剂和橡塑比(溴化丁基橡胶/聚酰胺用量比)对聚酰胺柔性合金(DVA)性能的影响。结果表明:马来酸酐接枝聚丙烯(PP-g-MAH)是理想的相容剂,用其制备的DVA相态精细、物理性能优异,PP-g-MAH的最佳用量是10份;随着橡塑比的增大,DVA的物理性能下降,气密性变差,分散相橡胶粒径变大,未能发生相反转。     

热塑性弹性体的研究与产业化进展

化学合成型和共混型热塑性弹性体类型、市场概况、产业化进展及最新研究发展方向进行了论述。介绍了几种具有市场应用前景的新型热塑性弹性体品种,如聚酰胺类TPE、热可逆共价交联类TPE、茂金属催化聚烯烃类TPE、甲壳型液晶类TPE、生物基TPE、新型热塑性硫化橡胶等,对它们的制备方法、性能特点及市场发展概况进行了详细论述,并对它们的应用领域和产业化方向进行了评述和展望。     

Fabrication of a High-Performance and Reusable Planar Face Mask in Response to the COVID-19 Pandemic

The coronavirus disease 2019(COVID-19)pandemic has caused a surge in demand for face masks,with the massive consumption of masks leading to an increase in resou...     

论学术自由的限度及其实现

学术自由应是一种有限度的自由 ,确立学术自由限度的原则是符合“三个有利于”的要求 ,学术自由限度的标准应该视学术活动的不同方面区别对待。制约学术自由限度的因素包括政治、法律、学者自身、经济和道德等多个方面。学术自由的实现需要内外部环境的共同支持和优化     

工频自动加压装置中的干扰及其抑制

主要对在实验室内进行工频耐压试验,试品击穿放电时所产生的严重干扰现象进行分析研究,提出了抑制干扰的方法。     

动态硫化IIR/PP热塑性弹性体的结构与性能Ⅱ.影响IIR/PP热塑性弹性体弹性性能的因素

研究了影响丁基橡胶／聚丙烯热塑性弹性体弹性性能的因素，分析了高温压缩热塑性弹性体的压缩变形机理。结果表明，提高分散相的交联密度和连续相的结晶度都有助于改善丁基橡胶／聚丙烯热塑性弹性体的弹性；在氯化石蜡和二月桂酸二丁基锡的混合改性剂质量分数为PP总量的10％-20％时，可以大大降低材料的压缩永久变形；橡塑比越高，丁基橡胶／聚丙烯热塑性弹性体的弹性越好；压缩温度对弹性的影响很显著，随着压缩温度的提高，材料的压缩永久变形增大；在高温下，被增容的橡胶在压缩状态下黏性增大，弹性下降，产生压缩永久变形，同时高温条件下聚丙烯分子链运动加剧，部分大分子链发生移位。     

Surface‐initiated ring‐opening polymerization of ϵ‐caprolactone from the surface of PP film

This article presents the ring‐opening polymerization of ε‐caprolactone (ε‐CL) from PP film modified with an initiator layer composed of ? OSn(Oct) groups. This method consists of two steps: (1) Sn(Oct)₂ exchanged with the hydroxyl groups on the surface of PP film, forming the ? OSn(Oct) groups bonded on the surface; (2) surface‐initiated ring‐opening polymerization of ε‐CL with the ? OSn(Oct) groups. The initiator layer is characterized by attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR), contact angles, and X‐ray photoelectron spectroscopy (XPS). The growth of PCL chains from the initiator layer through ring‐opening polymerization is successfully achieved. ATR‐FTIR, XPS, and scanning electron microscope (SEM) are also used to characterize the grafted film. XPS results reveal that the PCL chains cover the surface of PP film after 4 h. The SEM images reveal that the PCL chain clusters grow into regular spheroidal particles, which can be changed into other different morphology by treated with different solvents. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

ATBN/MP复合增容NBR/PP热塑性硫化胶

研究了端氨基液体丁腈橡胶(ATBN)和马来酸酐接枝聚丙烯(MP)对NBR／PP共混体系的增容效果。采用TEM,SEM,DSC分析了NBR／PP共混体系的相态结构及其PP的结晶行为。结果表明,ATBN／MP是NBR／PP共混体系较理想的增容剂,当ATBN用量为5份,MP为10份时,增容效果最佳;增容剂存在一个临界胶束浓度(CMC),当增容剂浓度大于CMC时,增客剂的增容作用变差。增容良好的NBR／PP共混体系经过动态硫化后,可制备相态结构精细、性能优异的NBR／PP热塑性硫化胶;界面结合加强后,其流动性能略有下降。     

Entropy-Enthalpy Compensations Fold Proteins in Precise Ways

Exploring the protein-folding problem has been a longstanding challenge in molecular biology and biophysics. Intramolecular hydrogen (H)-bonds play an extremely important role in stabilizing protein structures. To form these intramolecular H-bonds, nascent unfolded polypeptide chains need to escape from hydrogen bonding with surrounding polar water molecules under the solution conditions that require entropy-enthalpy compensations, according to the Gibbs free energy equation and the change in enthalpy. Here, by analyzing the spatial layout of the side-chains of amino acid residues in experimentally determined protein structures, we reveal a protein-folding mechanism based on the entropy-enthalpy compensations that initially driven by laterally hydrophobic collapse among the side-chains of adjacent residues in the sequences of unfolded protein chains. This hydrophobic collapse promotes the formation of the H-bonds within the polypeptide backbone structures through the entropy-enthalpy compensation mechanism, enabling secondary structures and tertiary structures to fold reproducibly following explicit physical folding codes and forces. The temperature dependence of protein folding is thus attributed to the environment dependence of the conformational Gibbs free energy equation. The folding codes and forces in the amino acid sequence that dictate the formation of β-strands and α-helices can be deciphered with great accuracy through evaluation of the hydrophobic interactions among neighboring side-chains of an unfolded polypeptide from a β-strand-like thermodynamic metastable state. The folding of protein quaternary structures is found to be guided by the entropy-enthalpy compensations in between the docking sites of protein subunits according to the Gibbs free energy equation that is verified by bioinformatics analyses of a dozen structures of dimers. Protein folding is therefore guided by multistage entropy-enthalpy compensations of the system of polypeptide chains and water molecules under the solution conditions.