Preparing iPP/HDPE/CB functionally gradient materials: influence factors of components and processing

In this work, gradient materials with low electrical resistivity were prepared by compounding isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends with carbon black (CB) through extruding and injection molding. Contact angle measurements and morphology measurements showed that the CB particles were selectively located in HDPE phase and the final composites had a gradient structure that the HDPE/CB phase exhibited different morphologies in the skin layer and core layer of the composites under different processing procedures. The main factors influencing the formation of the functional gradient materials (FGM), including screw speed during extruding, iPP types and CB contents were discussed. They affect the phase morphology by shear stress, the restoration of HDPE phase, and the viscosity ratio of polymer blends, respectively. In conclusion, iPP/HDPE/CB FGM could be formed easily in the composites blending with the iPP type with narrow molecular weight distribution (MWD) and higher CB content extruded at higher screw speed. The electrical properties of iPP/HDPE/CB composites were studied and the results showed that screw speed in extrusion significantly influenced the percolation curve and electrical property of the final composites. Copyright © 2011 John Wiley & Sons, Ltd.     

Study of the nanostructure of γ‐irradiated high‐density polyethylene/carbon black composite and its durability as geomembrane

The degradation of the nearby generation of high‐density polyethylene (HDPE) loaded with 2.5% of carbon black (CB) content (ie, HDPE/CB composites) is studied experimentally with the end goal of radiation safety applications. The impact of various γ‐irradiation doses in the air on the nanostructure of free volume and durability has been researched. The free volume was evaluated utilizing the positron annihilation lifetime (PAL) technique while the durability was contemplated by measuring the mechanical properties such as strain, elongation at break, and tear resistance. The electrical conductivity was explored to demonstrate the impact of the irradiation dose on the conductivity of the samples. Surface morphology studies using a scanning electron microscope (SEM) showed the surface fracture of HDPE/CB composites for unirradiated and irradiated samples. The surface roughness of the HDPE/CB GMs increases with increasing the irradiation dose. Among various uses of HDPE/CB composites, sheets are liners of dumps used to dispose of interim storage for Low and Medium Level Waste of NORMs and TENORMs. HDPE Geomembrane liners proved its utilization from the results of present research of electrical, mechanical tests, and SEM morphology to have the required resistance to weather conditions.     

电子束辐照交联CB/HDPE凝胶复合物的阻温特性

对电子束辐照交联并经溶剂抽提得到的炭黑/高密度聚乙烯(CB/HDPE)凝胶复合物的阻温特性进行了研究.结果表明,凝胶复合物与未抽提的交联试样和未交联试样相比,其PTC强度显著增大,并伴有明显的NTC现象.经热冷循环后,表现出很好的阻温特性稳定性,并且NTC现象消失.表明阻温特性的稳定性及NTC现象的消除强烈依赖于CB/HDPE导电复合材料凝聚态结构的稳定性     

Porous product with reduced apparent density keeps good mechanical properties. Extruded composites of poly(vinyl chloride) blown under microwave irradiation

New foaming method, enhanced by microwave irradiation, was elaborated and applied to obtain porous poly(vinyl chloride) and its composites with fine cell structure. The so called “thermal runaway” effect was observed during the heating of poly(vinyl chloride) under microwave irradiation. The temperature of this effect decreases as a result of additives incorporation into polymer matrix. Microwave irradiation allowed effective heating of extruded poly(vinyl chloride) and its composites with carbon black (CB) filler, behind the extruder head and decomposing azodicarbonamide (ADC) to obtain porous products. The use of CB additive to poly(vinyl chloride) significantly increased its ability to be heated under microwave irradiation as well as improved the cell structure and decreased the apparent density of final products.Among additionally used fillers (1 wt%) the montmorillonite caused the apparent density decrease of foamed materials ca. 10%, however beneficially influenced on the quality of cells structure, giving the products with isotropic cells and the highest cell density as well as keeping the tensile strength on similar level as in the case of the materials with CB and ADC only.     

INVESTIGATION OF MICROSTRUCTURE AND CONDUCTIVE MECHANISM OF HIGH DENSITY POLYETHYLENE/CARBON BLACK PARTICLE COMPOSITE BY POSITRON ANNIHILATION LIFETIME SPECTROSCOPY

The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) compositewere investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples,one with various CB contents in the composites and the other with various γ-irradiation doses in HDPE/CB compositecontaining 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value inHDPE/CB composite is about 16.7 wtO/ and the suitable γ-irradiation dose for improving the conductive behavior ofHDPE/CB composite is about 20 Mrad. T'he result observed for the second set of samples suggests that γ-irradiation causesnot only cross-linking in amorphous regions but also destruction of the partial crystalline structure. Therefore, a suitableirradiation dose, about 20 Mrad, can induce sufficient cross-linking in the amorphous regions without enhancing thedecomposition of crystalline structure, so that the positive temperature coefficient (PTC) effect remains while the negativetemperature coefficient (NTC) effect is suppressed. A new interpretation of the conductive mechanism, which might providea more detailed explanation of the PTC effect and the NTC effect has been proposed.     

Molecular orientation,crystallinity, and flexural modulus correlations in injection molded polypropylene/talc composites

In order to promote better understanding of the structure‐mechanical properties relationships of filled thermoplastic compounds, the molecular orientation and the degree of crystallinity of injection molded talc‐filled isotactic polypropylene (PP) composites were investigated by X‐ray pole figures and wide‐angle X‐ray diffraction (WAXD). The usual orientation of the filler particles, where the plate planes of talc particles are oriented parallel to the surface of injection molding and influence the orientation of the α‐PP crystallites was observed. The PP crystallites show bimodal orientation in which the c‐ and a*‐axes are mixed oriented to the longitudinal direction (LD) and the b‐axis is oriented to the normal direction (ND). It was found that the preferential b‐axis orientation of PP crystallites increases significantly in the presence of talc particles up to 20 wt% in the composites and then levels‐off at higher filler content. WAXD measurements of the degree of crystallinity through the thickness of injection molded PP/talc composites indicated an increasing gradient of PP matrix crystallinity content from the core to the skin layers of the molded plaques. Also, the bulk PP crystallinity content of the composites, as determined by DSC measurements, increased with talc filler concentration. The bulk crystallinity content of PP matrix and the orientation behavior of the matrix PP crystallites and that of the talc particles in composites are influenced by the presence of the filler content and these three composite's microstructure modification factors influence significantly the flexural moduli and the mechanical stiffness anisotropy data (E_LD/E_TD) of the analyzed PP/talc composites. Copyright © 2009 John Wiley & Sons, Ltd.     

iPP/HDPE/CB三元导电复合材料的导电与流变行为

利用界面能原理使CB选择性分布于HDPE中成为复合导电相,固定CB在HDPE中的质量分数(20 wt％),控制CB/HDPE导电相在iPP中的含量,制备出一系列三元(iPP/HDPE/CB)导电复合材料,并研究其导电逾渗和流变逾渗行为.结果表明,在复合导电相含量为20 wt％时复合材料内即形成导电网络,在复合导电相含量30 wt％时出现流变网络.只有当复合导电相在材料中形成连续相时(60 wt％),损耗因子在频率扫描中才出现峰值.     

Effect of compounding procedure on morphology and crystallization behavior of isotactic polypropylene/high‐density polyethylene/carbon black ternary composites

The effect of compounding procedure on morphology and crystallization behavior of isotactic polypropylene/high‐density polyethylene/carbon black (iPP/HDPE/CB) composite was investigated. iPP/HDPE/CB composites were prepared by four compounding procedures (A: iPP + HDPE + CB; B: iPP/HDPE + CB; C: HDPE/CB + iPP; D: iPP/CB + HDPE). Scanning electron microscopy observation showed that CB particles are mainly distributed in HDPE in all composites, and the phase morphology of composites was obviously affected by a compounding procedure. The size of the HDPE/CB domains in the composites prepared by procedures A and D decreased with the increase in CB content, whereas that of HDPE/CB in the composites prepared by procedures B and C rarely changed with the increase in CB content. The crystallization behaviors of the composites were significantly affected by their phase morphology, which resulted from the variation of compounding procedure. The isothermal crystallization rate of iPP in the composites prepared by procedures A and D was obviously increased, which may originate from the small HDPE/CB droplets dispersed in the iPP phase. The non‐isothermal crystallization curves of composites prepared by procedure D represented two peaks because the iPP component in these composites had the fastest crystallization rate, whereas the curves of composites prepared by other compounding sequences only exhibited one peak. Moreover, the crystallinity of HDPE almost increased by one time with the incorporation of only 1 phr CB because the CB particles selectively located in the HDPE phase, and the crystallinity of HDPE decreased with the further increase of CB content because of the strong restriction of CB on the HDPE chains. Copyright © 2011 John Wiley & Sons, Ltd.     

PE/CB复合材料的辐照效应

研究了两种炭黑(CB)对PE的影响及PTC功能材料挤出后的特性，发现挤出后粒子和聚合物取向对材料电性能都有较大影响。经γ射线辐照后HDPE／CB功能复合材料稳定性大为提高，初步探讨了辐射对PTC功能材料稳定性的影响。结合辐射交联等方法提高材料的稳定性。用扫描电镜(SEM)观测了一系列PE／CB的形态、CB的分布、链段的分子运动，并结合Fisher的toy model对PE／CB机制做了较系统的解释。     

The effect of shear on mechanical properties and orientation of HDPE/mica composites obtained via dynamic packing injection molding (DPIM)

The interfacial interaction and orientation of filler play important roles in the enhancement of mechanical performances for polymer/inorganic filler composites. Shear has been found to be a very effective way for the enhancement of interfacial interaction and orientation. In this work, we will report our recent efforts on exploring the development of microstructure of high density polyethylene (HDPE)/mica composites in the injection‐molded bars obtained by so‐called dynamic packing injection molding (DPIM), which imposed oscillatory shear on the melt during the solidification stage. The mechanical properties were evaluated by tensile testing and dynamic mechanical analysis (DMA), and the crystal morphology, orientation, and the dispersion of mica were characterized by scanning electron microscopy and two‐dimensional wide‐angle X‐ray scattering. Compared with conventional injection molding, DPIM caused an obvious increase in orientation for both HDPE and mica. More importantly, better dispersion and epitaxial crystallization of HDPE was observed on the edge of the mica in the injection‐molded bar. As a result, increased tensile strength and modulus were obtained, accompanied with a decrease of elongation at break. The obtained data were treated by Halpin–Tsai model, and it turned out that this model could be also used to predict the stiffness of oriented polymer/filler composites. Copyright © 2009 John Wiley & Sons, Ltd.     

Conduction stability of high-density polyethylene/carbon black composites due to electric field action

Conduction stability of high-density polyethylene/carbon black (HDPE/CB) composites with a CB volume fraction slightly above the percolation threshold is studied in relation to electric field action at various ambient temperatures below the melting point of HDPE. It is found that resistance of the composites shows considerable changes after the electric field is switched off. Influence of irradiation crosslinking of HDPE on the conduction stability is also discussed.     

Reduced percolation thresholds of immiscible conductive blends

The DC conductivity of polymer blends composed of poly(ethylene‐co‐vinyl acetate) (EVA) and high density polyethylene (HDPE), where a conductive carbon black (CB) had been preferentially blended into the HDPE, were investigated to establish the percolation characteristics. The blends exhibited reduced percolation thresholds and enhanced conductivities above that of the individually carbon filled HDPE and EVA. The percolation threshold of the EVA/HDPE/CB composites was between 3.6 and 4.2 wt % carbon black, where the volume resistivity changed by 8 orders of magnitude. This threshold is at a significantly lower carbon content than the individually filled HDPE or EVA. At a carbon black loading of 4.8 wt %, the EVA/HDPE/CB composite exhibits a volume resistivity which is approximately 14 and 11 orders of magnitude lower than the HDPE/CB and EVA/CB systems, respectively, at the same level of incorporated carbon black. The dielectric response of the ternary composites, at a temperature of 23°C and frequency of 1 kHz, exhibited an abrupt increase of ca. 252% at a carbon concentration of 4.8 wt %, suggesting that the percolation threshold is somewhat higher than the range predicted from DC conductivity measurements. Percolating composites with increasing levels of carbon black exhibit significantly greater relative permittivity and dielectric loss factors, with the composite containing 6 wt % of carbon black having a value of ϵ′ ≈ 79 and ϵ″ ≈ 14. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1899–1910, 1999     

粒子填充HDPE复合体系动态流变行为研究

研究了炭黑(CB)和石墨(GP)填充高密度聚乙烯(HDPE)复合体系的动态流变行为.发现高填料含量时出现似固体行为,并认为它归因于无机粒子网络逾渗结构的形成.在相同聚合物基体条件下,粒子种类和粒子几何参数(粒子形状、大小、粒径分布)对低频区域流变行为、流变参数的逾渗行为和逾渗阈值(φ_c)有决定性影响,且种类的影响相比于粒子几何参数更为显著.此外,高表面活性及高比表面积(大径厚比、小尺寸)粒子填充体系具有较低的φ_c.     

Evolution in surface morphology during rapid microwave annealing of PS‐b‐PMMA thin films

Microwave annealing enables rapid (60 s) ordering and orientation of block copolymer films. The developed morphology in polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) thin films depends on details of the heating rate that is controlled by microwave output energy as well as the sample location in the microwave. Over a wide heating rate (1.1–2.7 °C/s), perpendicular orientation of the cylindrical mesostructure at the surface is >50% after 60 s, but goes through a maximum at 1.8 °C/s leading to approximately 97% perpendicular cylinders at the surface. The propagation of this perpendicular surface morphology through the film thickness is also dependent upon the microwave annealing conditions. The surface structure evolves with the microwave annealing time from imperfect ordering to perpendicular cylinders to parallel cylinders as the annealing time increases. This work demonstrates the importance of controlling the heating rate during microwave annealing, which will be critical for optimizing microwave conditions for directed self‐assembly. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1499–1506     

电响应聚合物薄膜的表面图案化

研究了炭黑(CB)和石墨(GP)填充高密度聚乙烯(HDPE)复合体系的动态流变行为.发现高填料含量时出现似固体行为,并认为它归因于无机粒子网络逾渗结构的形成.在相同聚合物基体条件下,粒子种类和粒子几何参数(粒子形状、大小、粒径分布)对低频区域流变行为、流变参数的逾渗行为和逾渗阈值(φc)有决定性影响,且种类的影响相比于粒子几何参数更为显著.此外,高表面活性及高比表面积(大径厚比、小尺寸)粒子填充体系具有较低的φc.     

聚乙烯/炭黑复合材料导电体系的结构形态

将导电填料（例如炭黑）加入绝缘的聚合物基体即得到导电复合材料,两组混全物的电阻率随导电填料体积分数的变化而改变,电阻率与导电填料体积分数的关系称为渗流曲线,可分为三个主要区域：低导电填料含量区域,复合材料的电阻率很大,聚合物的电阻率占主导;渗流区域,导电填料含量少量的增加会引起复合材料电阻率很大的提高;高导电填料区域,复合材料电阻率很大的提高;高导电填料区域,复合材料电阻率主要由导电填料的电阻率决定,对于导电复合材料已有大量的实验和理论工作来解释导电复合材料已有大量的实验和理论工作来解释导电填料含量和复合材料各组分的形貌对电性能的影响,其中有效介质普适方程（GEM方程）已经对大量的渗流曲线进行了精确的拟合。聚乙烯／炭黑复合材料中由于炭黑的大量分布很难观测其微观形貌,本文对不同辐照交联程度和不同环境温度下聚乙烯／炭黑复合材料的渗流曲线进行分析,试图找出GEM方程各参数与复合材料各组分形貌的关系,为导电复合材料的设计和制备提供理论基础。     

Studies of modification of HDPE and interfacial interaction of its composites with sericite

Ultraviolet irradiation, which is environment friendly and without any chemical pollution, was used to functionalize high‐density polyethylene (HDPE) and to improve the interfacial interaction of its composites with sericite in this study. The oxygen‐containing groups of C?O, C‐O, and C(?O)O were quickly introduced onto molecular chains of HDPE by ultraviolet irradiation in ozone atmosphere and the contents of the introduced oxygen‐containing groups increased with increasing the modification time. It is important to note that the irradiation time greatly decreased compared to that in air or oxygen atmosphere. After modification, the molecular weight of the irradiated HDPE decreased and its distribution became wider. The irradiated HDPE in ozone was not crosslinked, which is an advantage over the same reaction in air or oxygen atmosphere. With increasing the irradiation time, the melting temperature of the irradiated HDPE lightly decreased, while its crystallinity, hydrophilicity, and fluidity increased. The composites of HDPE/sericite were prepared. The results showed that the dispersion of sericite in the matrix and the interfacial interaction of sericite with the matrix were markedly improved for the irradiated HDPE/sericite composites. As a result, the irradiated HDPE/sericite composites showed significantly increased tensile yield strength and notched impact strength. Copyright © 2010 John Wiley & Sons, Ltd.     

Compacted UHMWPE fiber composites: Morphology and X‐ray microdiffraction experiments

The effect of compaction conditions on UHMWPE fibers is examined by microbeam X‐ray diffraction (WAXS) and scanning electron microscopy (SEM). The morphological observations indicate that melting occurs during compaction both on the surface of the fiber as well as in its internal regions. In addition, the recrystallized phase is nucleated on the fiber surface, possibly epitaxially. The recrystallized phase that originates from the internal regions of the fiber retains the initial highly oriented structure. WAXS microbeam measurements do not show any significant core‐shell structure in compacted single fibers. Considering the overall characteristics of the melting process during compaction, we can conclude that the hexagonal phase that appears upon heating of the fibers under moderate pressure is responsible for good adhesion of the fibers to each other, even more significantly than surface melting, especially because of its ability to retain the high orientation of the chains in the fibers. This information is relevant for understanding the formation and microstructure of the matrix component in the self‐reinforced composites fabricated by compaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1535–1541, 2007     

Epitaxial and graphoepitaxial growth of isotactic polypropylene (iPP) from the melt on highly oriented high density polyethylene (HDPE) substrates

Although under normal conditions only the crystallization behavior of PE on oriented iPP substrates can be studied due to the higher melting point of iPP, the faster crystallization rate of a molten, oriented HDPE film compared to a nonoriented iPP layer was used to study the crystallization of iPP on the oriented HDPE film by means of transmission electron microscopy (TEM) and electron diffraction (ED). Besides the known epitaxial relationship of HDPE/iPP with their chains 50° apart, two new orientation relationships with (a) chains of both polymers parallel and (hk0)_iPP in contact with the HDPE substrate, and (b) the a‐axis of iPP crystals parallel to the chain direction of HDPE but (001)_iPP in contact with the HDPE substrate were observed. Both orientations are assumed as graphoepitaxy. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1893–1898, 1999     

Resistivity-Temperature Behavior of CB-Filled HDPE Foaming Composites

High-density polyethylene/carbon black foaming conductive composites were prepared from acetylene black（ACEY） and super conductive carbon black（HG-1P） as conductive filler, low-density polyethylene（LDPE） as the second component, ethylene-vinyl acetate（EVA） and ethylene propylene rubber（EPR） as the third component, azobisformamide（AC） as foamer, and dicumyl peroxide（DCP） as cross-linker. The structure and resistivity-temperature behavior of high-density polyethylene（HDPE）/CB foaming conductive composites were investigated. Influences of carbon black, LDPE, EVA, EPR, AC, and DCP on the foaming performance and resistivity-temperature behavior of HDPE/CB foaming conductive composites were also studied. The results reveal that HDPE/CB foaming conductive composite exhibits better switching characteristic; ACET-filled HDPE foaming conductive composite displays better positive temperature coefficient（PYC） effect; whereas super conductive carbon black（HG-1P）-filled HDPE foaming conductive composite shows better negative temperature coefficient（NTC） effect.