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.     

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.     

iPP/HDPE/CB复合材料的制备及反常的温度-电阻效应

本文利用普通熔融挤出法制备了iPP/HDPE/CB复合材料, 分别采用注射成型及压制成型方法得到测试试样. 通过研究复合材料体积电阻率随温度的变化, 考察注塑试样和压制试样的PTC特性及复合材料形态结构与试样PTC特性之间的关系.     

应力引发官能化EPDM/HDPE及其对PA66/EPDM/HDPE 共混物相形态和力学性能的影响

通过提高双螺杆挤出机螺杆转速的方法,研究了熔融挤出过程中高剪切应力对马来酸酐(MAH)官能化三元乙丙橡胶(EPDM)与高密度聚乙烯(HDPE)共混物的接枝率、熔体流动速率及凝胶含量的影响.随着双螺杆挤出机螺杆转速的增加,强烈的机械剪切应力引发EPDM/HDPE共混物大分子链的断链反应形成大分子自由基,从而引发接枝反应制...     

Phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene/high density polyethylene blends

The phase morphology, crystallisation behaviour and mechanical properties of isotactic polypropylene (iPP)/high density polyethylene (HDPE) blends were investigated. It was found that the properties are intimately related to each other. The morphology of the blends showed a two phase structure in which the minor phase was dispersed as domains in the major continuous matrix phase. The domain size of the dispersed phase increased with increasing concentration of that phase due to coalescence. It was also found that the domain size of the dispersed phase depends on the viscosity difference between the two phases. For a given HDPE/iPP blend, where HDPE is the matrix and iPP is the dispersed phase, the iPP domains were smaller than HDPE domains of the corresponding iPP/HDPE blend where iPP is the matrix and HDPE is the dispersed phase. A co-continuous morphology was observed at 50/50 PP/HDPE composition. Crystallinity studies revealed that blending has not much effect on the crystalline melting point of polypropylene and high density polyethylene. The crystallisation enthalpy and heat of fusion values of HDPE and PP in the blend were decreased as the amount of the other component increased. The variation in percent crystallinity of HDPE and PP in the blend was found to depend on the morphology of the blend. All the mechanical properties except Young's modulus and hardness showed negative deviation from the additivity line. This is due to the incompatibility of these blends.     

Mechanical properties and characterization of slowly cooled isotactic polypropylene/high‐density polyethylene blends

In previous studies, we found that Young's moduli of quenched isotactic polypropylene/high‐density polyethylene (iPP/HDPE) exceeded the upper bound, calculated from the Voigt model, with the moduli of the quenched homopolymers as those of the two components. We suggested that this might be due to crystallization, as the components crystallized at higher temperatures in the blend than on their own. We repeated the same set of measurements, this time on iPP/HDPE blends that were cooled slowly. We also examined crystallization at various rates of cooling with differential scanning calorimetry. At slow cooling rates, the HDPE and iPP components in the blends crystallize at lower temperatures than in the pure homopolymers, suggesting that the presence of one component inhibits rather than promotes the crystallization of the other. Electron microscopy of slowly cooled blends revealed very different interfacial morphologies depending on whether the HDPE or the iPP crystallizes first. Young's moduli of most of the blends lie on the upper bound; however, some blends with co‐continuous morphologies fall well below the lower bound. The mechanical properties are discussed in terms of the interfacial morphology, the crystallization behavior, and the large‐scale phase separation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1384–1392, 2003     

Preparation of Polylactide/Poly(ether)urethane Blends with Excellent Electro-actuated Shape Memory via Incorporating Carbon Black and Carbon Nanotubes Hybrids Fillers

In this work, hybrid conductive fillers of carbon black(CB) and carbon nanotubes(CNTs) were introduced into polylactide(PLA)/thermoplastic poly(ether)urethane(TPU) blend(70/30 by weight) to tune the phase morphology and realize rapid electrically actuated shape memory effect(SME). Particularly, the dispersion of conductive fillers, the phase morphology, the electrical conductivities and the shape memory properties of the composites containing CB or CB/CNTs were comparatively investigated. The results suggested that both CB and CNTs were selectively localized in TPU phase, and induced the morphological change from the sea-island structure to the co-continuous structure. The presence of CNTs resulted in a denser CB/CNTs network, which enhanced the continuity of TPU phase.Because the formed continuous TPU phase provided stronger recovery driving force, the PLA/TPU/CB/CNTs composites showed better shape recovery properties compared with the PLA/TPU/CB composites at the same CB content. Moreover, the CB and CNTs exerted a synergistic effect on enhancing the electrical conductivities of the composites. As a result, the prepared composites exhibited excellent electrically actuated SME and the shape recovery speed was also greatly enhanced. This work demonstrated a promising strategy to achieve rapid electrically actuated SME via the addition of hybrid nanoparticles with self-networking ability in binary PLA/TPU blends over a much larger composition range.     

Polymeric positive-temperature-coefficient materials: dynamic curing effect

The object of this work was to prepare high-density polyethylene (HDPE)/ethylene–propylene–diene terpolymer (EPDM)/conductive carbon black (CB) composites by dynamic curing and to characterize the positive-temperature-coefficient (PTC) performances of the composites.EPDM and dicumyl peroxide were preblended in a research mill. The roll-milled strands were blended with HDPE and CB in a Haake mixer. The sheet resistivity and morphology of the HDPE/EPDM/CB composites with or without the dynamic curing process were investigated. It was concluded that the dynamically cured blends exhibit better PTC performance than the simple blends without dynamic curing. The effects of shear intensity and dicumyl peroxide content during the dynamic curing process were discussed for the PTC characteristics of the HDPE/EPDM/CB composites.     

Preparation of Polylactide/Poly(ether)urethane Blends with Excellent Electro-actuated Shape Memory <Emphasis Type="Italic">via</Emphasis> Incorporating Carbon Black and Carbon Nanotubes Hybrids Fillers

In this work, hybrid conductive fillers of carbon black (CB) and carbon nanotubes (CNTs) were introduced into polylactide (PLA)/thermoplastic poly(ether)urethane (TPU) blend (70/30 by weight) to tune the phase morphology and realize rapid electrically actuated shape memory effect (SME). Particularly, the dispersion of conductive fillers, the phase morphology, the electrical conductivities and the shape memory properties of the composites containing CB or CB/CNTs were comparatively investigated. The results suggested that both CB and CNTs were selectively localized in TPU phase, and induced the morphological change from the sea-island structure to the co-continuous structure. The presence of CNTs resulted in a denser CB/CNTs network, which enhanced the continuity of TPU phase. Because the formed continuous TPU phase provided stronger recovery driving force, the PLA/TPU/CB/CNTs composites showed better shape recovery properties compared with the PLA/TPU/CB composites at the same CB content. Moreover, the CB and CNTs exerted a synergistic effect on enhancing the electrical conductivities of the composites. As a result, the prepared composites exhibited excellent electrically actuated SME and the shape recovery speed was also greatly enhanced. This work demonstrated a promising strategy to achieve rapid electrically actuated SME via the addition of hybrid nanoparticles with self-networking ability in binary PLA/TPU blends over a much larger composition range.     

纤维状填料/HDPE复合体系的导电渗流与流变渗流行为的关系

研究了纤维状导电材料不锈钢纤维(SSF)填充高密度聚乙烯(HDPE)导电复合体系的导电渗流与流变渗流行为之间的关系,并与颗粒状导电颗粒炭黑(CB)/HDPE导电复合体系进行了比较.发现当SSF含量极低(0.3vol%)时,SSF/HDPE体系即发生导电渗流现象,且导电渗流转变区域极窄;而仅当SSF含量达到4.8vol%时,该复合体系才表现出流变渗流现象,这一结果与CB/HDPE体系及纳米级导电纤维填充体系截然不同.此外,通过正温度系数效应的研究发现SSF形成的导电通路稳定性高于CB/HDPE体系.我们认为,SSF/HDPE体系呈现的这些特点均与SSF较大的直径及长径比且其导电通路及流变渗流网络的形成机理不同有关.     

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.     

Phase morphology of iPP/aPS/SEP blends

Supermolecular structure and phase morphology of the ternary isotactic polypropylene/atactic polystyrene/poly(styrene-b-ethylene-co-propylene) (iPP/aPS/SEP) compression molded blends with 100/0, 90/10, 70/30, and 50/50 iPP/aPS weight ratios and with different amounts of added SEP compatibilizer were studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). SEP significantly reduced the size of dispersed aPS particles that enabled better spherulitization in the iPP matrix. Furthermore, iPP spherulites in ternary blends with 90/10 iPP/aPS weight ratio became larger in comparison with the pure iPP. TEM revealed that the SEP formed continuous interface layer around the dispersed aPS particles even when only 2.5 wt.% of SEP was added. Particle size distribution was distinctly bimodal. When the SEP content was increased to 10 wt.%, joining together smaller and bigger aPS and SEP particles formed dispersed aggregates. Additionally, both amorphous components (aPS and SEP) influenced crystallization process of iPP matrix and so modified, to some extent, its final supermolecular structure. SEP compatibilizer did not significantly affect crystallite orientation. The increase of crystallite sizes, which was more affected by the addition of aPS than by the addition of SEP, seemed to be influenced by the solidification effect rather than by the phase morphology of the blends.     

CRYSTALLIZATION AND MECHANICAL PROPERTIES OF BLENDS OF METALLOCENE SHORT CHAIN BRANCHED POLYETHYLENE WITH CONVENTIONAL POLYOLEFINS

Metallocene-catalyzed short chain branched polyethylene (SCBPE) was blended with LDPE, HDPE, PS, EPDM and iPP in the weight proportions of 80 and 20. The crystallization and mechanical properties of these blends were studied by PLM, DSC and DMA. It has been observed in PLM that SCBPE/LDPE, SCBPE/HDPE and SCBPE/EPDM can form band spherulites whose band width and size are both smaller than that of the pure SCBPE. Tiny crystallites are observed in the completely immiscible SCBPE/PS blend. The crystallites in SCBPE/iPP are very small and only irregular spherulites are seen. The crystallization kinetics and mechanical properties of SCBPE are greatly affected by the second polyolefin, but in a different way, depending on the phase behavior and the modulus of the second components. SCBPE may be phase miscible in the melt with HDPE, LDPE and EPDM and co-crystallize together with HDPE or LDPE during cooling. A big change of crystal morphology and crystallization kinetics is seen in SCBPE/iPP blend compared with pure SCBPE and the lowest tanδ is also seen for this system. DMA results show that the tensile modulus of the blends has nothing to do with phase behavior, but only depends on the modulus of the second component.     

聚烯烃共混物注射制品的形态控制与多层次结构

从注射制品形态控制和结构表征的角度探讨高分子材料加工-形态-性能之间的关系.研究中采用动态保压成型方法来制备注射样品,在注射成型过程中引入剪切应力场的作用,制得的样品表现出明显的多层次结构,从外向里分别为皮层、剪切层、芯层,表现出不同的相形态、结晶形貌以及取向行为.研究发现,剪切应力对聚烯烃的形态发展和结构变化具有重要影响.在剪切应力的作用下,聚烯烃共混物中分散相会发生变形、取向,从而导致共混物的相转变点发生移动;结晶形态从球晶转变为shish-kebab结构;聚烯烃共混物在高剪切应力下相容,低剪切下发生相分离;HDPE/PP共混物的注射制品中出现附生结晶等现象.     

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。     

Capillary extrusion of polypropylene/high-density polyethylene immiscible blends as studied by rheo-particle image velocimetry

The capillary extrusion of polypropylene (PP) and high-density polyethylene (HDPE) immiscible blends was studied in this work by rheo-particle image velocimetry (Rheo-PIV). The PP/HDPE blends were prepared by single screw extrusion and extruded through a transparent capillary die at a temperature of 200 °C and concentrations of 80/20, 60/40, 40/60 and 20/80 wt%, respectively. PIV measurements described accurately the flow behavior of PP/HDPE blends and revealed continuous velocity profiles in the die, without macroscopic phase separation, for all the blends in the resolution range of the PIV technique. The flow behavior of all the blends was shear-thinning (power-law) type and their viscosities laid in between the values corresponding to the neat polymers and increased in an exponential way along with the concentration of the highest viscosity component in the blend (HDPE). Also, it was found that the extruded blends acquired a stratified morphology and that HDPE mitigates extrudate distortions in PP, meanwhile PP eliminates slip and flow instabilities in HDPE by migrating to the region of highest shear stresses in the die. Migration of PP to the capillary wall was corroborated by Raman spectroscopy measurements on the periphery of solid extrudates. Finally, via calculations of the density of the molten blends under flow using the velocity profiles in the die, we show that the homopolymers are compatible in the molten state and follow a simple inverse relation for their density, and an exponential one for their viscosity.     

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     

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。     

Effects of the reduction of PAni-coated oxidized multiwall carbon nanotubes on the positive temperature coefficient behaviors of their carbon black/high density polyethylene composites

Polyaniline (PAni)-coated reduced multiwall carbon nanotubes (PRMWNTs) and carbon black (CB)-filled high-density polyethylene (HDPE) composites (PRMWNTs/CB/HDPE) were prepared through a melt mixing method. Oxidized MWNTs (OMWNTs) were prepared by treating pristine multiwall carbon nanotubes (MWNTs) with an acid mixture (HNO₃:H₂SO₄), and PAni-coated OMWNTs (POMWNTs) were synthesized via in-situ polymerization of aniline monomer in the presence of OMWNTs. POMWNTs were further reduced using hydrazine monohydrate to obtain the PRMWNTs. Fourier transform infrared (FT-IR) spectra and thermogravimetric analysis (TGA) confirmed the formation of PRMWNTs. PRMWNTs showed significantly improved thermal stability and electrical conductivity comparing to POMWNTs. The positive temperature coefficient (PTC) behavior of PRMWNTs/CB/HDPE composites revealed enhanced PTC intensity and electrical conductivity at room temperature compared to POMWNTs/CB/HDPE composites. The PRMWNTs-10/CB/HDPE composite showed high peak resistivity (301.99 MΩ-cm) and low room temperature resistivity compared to the POMWNTs/CB/HDPE composite, and thus showed the highest PTC intensity value of 6.693 as well as very excellent cyclic stability.     

Studies on preparation of HDPE/CB composites including a novel oriented structure by the microwave heating and their characterization

Microwave heating has several advantages over traditional methods of heating, including rapid and uniform heating, greater penetration depth of heat into material, lower power costs and selective heating within the material and so on. In this paper, effects of microwave heating on the properties of high‐density polyethylene/carbon black (HDPE/CB) composites were studied. The results show that the HDPE/CB composites can be heated via microwave irradiation, and composites with different CB concentration exhibit different microwave heatability. The 20 wt% CB composites have the most rapid heating rate, and its temperature reaches 78°C after 10 sec, and 159°C after 150 sec, respectively. Meanwhile, microwave heating improves the mechanical properties of HDPE/CB composites. Scanning Electron Microscopy (SEM) analysis shows a better combination between CB particles and HDPE after microwave irradiation. Furthermore, selective heating of microwave was used to prepare a novel oriented structure, which the core layer has preferential orientation and the surface layer has little orientation. Characterization of the novel oriented structure was also studied. Wide angle X‐ray diffraction (WAXD) analysis of 25 wt% CB composites with the novel oriented structure shows that the diffraction peaks of the surface layer are obviously weaker than those of the core layer, which indicates that orientation in the core layer is more intensive than that in the surface layer. The novel oriented structure is different to the traditional skin‐core structure, in which the surface layer has preferential orientation and the core layer has little orientation. Copyright © 2009 John Wiley & Sons, Ltd.