Impedance spectra of carbon black filled high‐density polyethylene composites

Carbon black (CB) filled high‐density polyethylene (HDPE) composites are prepared by ordinary blending for use as an electrical conductive polymer composite. The composite changes from an electrical insulator to a conductor as the CB content is increased from 10 to 20 wt %, which is called the percolation region. For explanatory purposes, three models, namely, “conduction via nonohmic contacting chain,” “conduction via ohmic contacting chain,” and a mixture of them corresponding to the conductions in the percolation region, high CB loading region, and limiting high CB loading are proposed by the reasonable configurations of aggregate resistance, contact resistance, gap capacitance, and joining aggregates induction. The characters of the impedance spectra based on the three models are theoretically analyzed. In order to find some link between the electrical conductivity and the CB dispersion manner in the composites, the impedance spectra of three samples, HDPE/15 wt % CB (the center of the percolation region), HDPE/25 wt % CB (a typical point in the high CB loading region), and HDPE/19 wt % CB (the limiting high CB loading region), are measured by plotting the impedance modulus and phase angle against the frequency and by drawing the Cole–Cole circle of the imaginary part and real part of the impedance modulus of each sample. The modeled approached spectra and the spectra measured on the three samples are compared and the following results are found: the measured impedance spectrum of HDPE/15 wt % CB (percolation region) is quite close to the model of conduction via nonohmic contacting chain. The character of the measured spectrum of HDPE/25 wt % CB consists of the form of the model of conduction via ohmic contacting chain. The impedance behavior of HDPE/19 wt % CB exhibits a mixture of the two models. From the comparisons, it is concluded that the electrical conducting network in the percolation region of the CB filled HDPE composite is composed of aggregate resistance, nonohmic contact resistance, and gap capacitance, and that of the high CB loading region consists of continuously joined CB aggregate chains, which are possibly wound and assume helix‐like (not straight lines) conductive chains, acting as electrical inductions as the current passes through. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1344–1350, 2005     

Nonisothermal bulk crystallization of high‐density polyethylene via a modified depolarized light microscopy technique: Further analysis

The quiescent nonisothermal bulk crystallization kinetics of high‐density polyethylene was investigated with a modified depolarized light microscopy technique, which allowed for studies at average cooling rates of approximately 5–2500 °C min^?1. All of the samples crystallized at a pseudoisothermal temperature (i.e., the plateau or crystallization temperature), despite the nonisothermal nature of the cooling conditions. The rate of the crystallization process increased monotonically with increasing the cooling rate and decreasing the crystallization temperature. Moreover, the apparent crystallinity content was a certain decreasing function with the cooling rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1009–1022, 2002     

Adhesion between high strength and high modulus polyethylene fibers by use of polyethylene gel as an adhesive

The use of polyethylene gels to adhere high strength and high modulus polyethylene fibers together has been investigated. It was found that the joint strength obtained using high density polyethylene (HDPE) gel in decalin or tetralin depended on the heating temperature and time of the gel. When heated at 100°C for 30 min, the gel showed such a high joint strength that polyethylene fibers were torn, and this should be enough for practical uses. The results of the present study demonstrate that utilization of the polyethylene gel as an adhesive is an extremely effective method when polyethylene fibers are used in composite materials.     

Grafting of multifunctional groups onto the surface of high‐strength polyethylene fibers and the interface of their composites

High‐strength polyethylene (HSPE) fibers were oxidated via chemical reactions in an acidic medium, and the carboxyl group was transferred into the acyl chloride and then reacted with pentaerythritol or diethylene triamine to graft the multifunctional group compounds onto the surface of the HSPE fibers. Subtractive Fourier transform infrared spectroscopy and the methylene blue absorbing method were used to study the functional groups on the surface of the modified fibers and their content. The results show that the polar functional groups, including ? COOH, ? OH, and ? NH₂, were introduced onto the surface of the HSPE fibers, and the polar groups improved the wettability. The interface shear stress (IFSS) of the composites that were made from modified fibers and epoxy was measured by means of the microdebond method. The results show that the IFSS was greatly increased by the grafting of pentaerythritol or diethylene triamine onto the HSPE fiber surface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 449–454, 2005     

Deuteron n.m.r. study of chain motion in solid polyethylene

The chain motion in the amorphous regions in linear polyethylene is studied by exploiting various ²H n.m.r. pulse methods. The experimental techniques employed are described in considerable detail. In particular, the solid echo- and the spin alignment spectra are recorded over a wide range of temperatures (123–393 K) as a function of the pulse spacings. In addition the spin-lattice relaxation times of both polymerization and alignment are given for the crysralline as well as the amorphous regions. The data are analysed in terms of highly constrained conformational motions which generate an exchange of C-H bond directions between 2, 3, or all 4 tetrahedral sites on a diamond lattice. Thus in the temperature interval from the γ-relaxation up to ～200 K only 2 sites are accessible, whereas a third site is appreciably populated at room temperature. Between 330 K and the melting point the number of conformations accessible to the chain must be high enough to lead to an increasingly isotropic 4 site exchange. The motion remains highly constrained and localized, however, up to the melting region as shown by the analysis of the spin-alignment spectra. The intensity ratio of the deuteron n.m.r. signals from the rigid crystalline and the mobile amorphous regions, respectively, yields the crystallinity of the sample as a function of temperature in remarkable agreement with the results obtained by X-rays. Finally, frequency dependent relaxation of spin alignment due to torsional oscillations of the chains in the crystalline regions is observed and analysed.     

Study on the preparation of hyperbranched polyethylene fibers and hyperbranched polyethylene composite fibers via electrospinning

This contribution mainly studied the preparation of hyperbranched polyethylene (HBPE) fibers and HBPE/multiwalled carbon nanotube (MWCNT) composite fibers via electrospinning for the first time. Firstly, the effects of solvents, solution concentration, voltage, and rotating speed of collector on the morphology of HBPE fibers were studied. Among the factors, solvent type, concentration, and voltage showed notable influence on the morphology of HBPE fibers. HBPE has an excellent dispersion effect on CNT in organic solvents. Through ultrasonic dispersion, the HBPE solutions with dispersed MWCNT were obtained. Then HBPE/MWCNT composite fibers were obtained with different contents of MWCNT via electrospinning. The effects of voltage and working distance on the morphology of HBPE/MWCNT composite fibers were investigated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42517.     

A neutron scattering study of slowly crystallized bulk polyethylene

Neutron scattering measurements on polyethylene slowly crystallized from the melt give similar results, in the q range 0.1-0.4 Å^?1, to melt-quenched material. This indicates a similar type of folding, at least as concerns structure on a scale of about 10 Å. It is anticipated that some degree of demixing of isotope species will have occurred during these experiments; this has been minimized by a light crosslinking procedure. Several arguments are advanced to suggest that in this q range any demixing does not affect the scattering: in particular the normalized intensities are independent of the isotope concentration. The samples have been extensively characterized to assess the effects of slow crystallization (as opposed to quenching) and crosslinking, both separately and in combination. Slowly crystallized samples are similar whether crosslinked previously or not, the principal difference being changes in the way different lamellae stack together. In both cases the morphology is completely different from that of quenched material, as indicated by much larger lamellar thicknesses. Hence, in these experiments there is enough molecular mobility for stems (chain traverses of lamellae) to be much longer than in the case of quenching; the fold type (as assessed by stem separation) is however, similar to the quench case. This conclusion is discussed in the light of a new proposal for equilibrium roughness on the crystal growth surfaces.     

Structure-property relationships on uniaxially oriented carbon nanotube/polyethylene composites

Multi walled carbon nanotubes have been incorporated into a linear low density polyethylene matrix through high energy ball milling technique at room temperature, without any chemical modification or physical treatment of the nanotubes. Highly oriented samples, with different draw ratios, were obtained by drawing at 80 °C the composite films. SEM and FTIR results on the drawn PE films demonstrate that the molecular chains in both crystalline and amorphous phases are well oriented along the drawing direction. The effect of different weight percent loadings of nanotubes and draw ratio on the morphology, thermal, mechanical and electrical properties of the composite fibers have been investigated.     

PE改性沥青的几个问题

总结了PE改性沥青储存稳定性,低温性能及耐老化性能方面的问题与研究进展。     

X-Ray photoemission study of plasma modified polyethylene surfaces

X-Ray photoelectron spectroscopy (XPS) was used to determine plasma induced chemical species on the surface of polyethylene (PE). Argon plasmas were found to have no detectable chemical effect on the PE surface, whereas oxygen and nitrogen plasmas created new chemical species which altered the chemical reactivity of the PE surface. Oxygen plasmas were found to react more rapidly with the PE surface than nitrogen plasmas. The degree of incorporation of new chemical species in the near surface region is approximately 20 at. % at the saturation level for both oxygen and nitrogen plasmas. Core level spectra for oxygen and nitrogen plasma treated PE suggest the formation of primarily C-O-C species in the former and C-N species in the latter. Angle-resolved XPS measurements indicate that the depth of incorporation of new chemical species is confined to the top 25 A.     

Mechanical and antibacterial properties of modified nano‐ZnO/high‐density polyethylene composite films with a low doped content of nano‐ZnO

Nano‐ZnO/high‐density polyethylene (HDPE) composite films were prepared via melt blending and a hot compression‐molding process. The properties, including ultraviolet absorption, mechanical and antibacterial properties of the films, and plasticizing behavior of the composites, were investigated. The results show that the absorbance in the ultraviolet region of the HDPE films was enhanced after the addition of modified nano‐ZnO to the HDPE matrix. Also, we found that improvement in the HDPE films of the tensile strength and elongation at break was achieved by the incorporation of modified ZnO nanoparticles up to 0.5 wt % in contrast with the original nano‐ZnO/HDPE composite films. Antibacterial testing was carried out via plate counting, and the results indicate that the HDPE films doped with modified ZnO nanoparticles showed favorable antibacterial activity, especially for Staphylococcus aureus. However, the low doped content of modified nano‐ZnO in the HDPE matrix made the balance torque of the composites increase slightly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ultra‐high enhancement in the toughness of polyethylene by exfoliated natural clay nanosheets

The full exfoliation of inorganic natural clay was engineered in a nonpolar polyethylene following a novel method without the involvement of any chemical modification to the surface of silicate layers. Tensile results showed that the toughening effect was dependent of strain rates, and the toughness of polyethylene was substantially improved by nearly five times with 0.5 wt % natural clay nanosheets at a strain rate of 0.15 s^?1. Toughening mechanism was also discussed based on this new exfoliated system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41314.     

聚乙二醇修饰纳米银的制备研究

研究了巯基乙酸聚乙二醇酯的制备技术,获取足量巯基乙酸聚乙二醇酯,以其作为分散剂,研究纳米银和纳米银聚合物核壳材料的合成方法并获得相应产物。通过FTIR红外光谱仪、紫外-可分光光度计、透射电子显微镜、扫描电子显微镜等仪器对产物的微观结构进行测试与表征,证实了上述结果。     

Film blowing of silane‐modified polyethylene

The grafting of vinyltriethoxysilane (VTES) onto polyethylene (PE) with the help of small amounts of peroxides was investigated to film‐blow these modified materials. The degree of crosslinking was kept very low to achieve good melt processability and improved mechanical properties. The possibility of obtaining modified PE films with improved properties and regularly distributed crosslinking with a single processing step demonstrates the uniqueness of this study. The additive concentration was established through preliminary studies; with a batch mixer, it was possible to process the modified PE in the film‐blowing operation. Water treatment of the modified films after film blowing allowed for improved properties without the processability being affected. The modification of PE was followed with mechanical, rheological, and extraction tests and with calorimetric analyses. The variations of the main mechanical properties of the films were very important from an application point of view. The elastic modulus and tear strength of the films for both extrusion directions (machine and transverse) increased with the VTES concentration increasing and even more with the addition of a small quantity of a peroxide. Some reductions of the tensile strength and elongation at break were observed, but these reductions were not considerable. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and mechanical properties of composite of fibrous cellulose and maleated polyethylene

Fibrous cellulose and maleated polyethylene (FC–MPE) composites were prepared under melt mixing by maleation of polyethylene (PE) to obtain maleic anhydride (MA) grafted PE (MPE) and successive compounding of the resultant MPE with fibrous cellulose (FC). When increasing the content of added MA to 2 wt %, the grafting efficiency of MA decreases gradually to 84% and the grafted MA chains become longer. Scanning electron microscopy (SEM) reveals strong adhesion of MPE to FC in the FC–MPE composite, which is probably due to the increased compatibility between MPE and FC, in contrast to no adhesion of unmaleated PE (UPE) to FC in the FC–UPE composite. This difference in interfacial structure between the FC–MPE and FC–UPE composites results in quite different mechanical properties for them. With an increase in the FC content to 60 wt %, the tensile strength of the FC–MPE composite increases significantly and reaches 125% that of pure PE. Furthermore, the larger Young's modulus, larger bending elastic modulus, and smaller elongation of the FC–MPE composite strongly indicate effective transfer of the high tensile strength and elasticity of FC to the MPE matrix through the strong adhesion between FC and MPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1971–1980, 2002; DOI 10.1002/app.10428     

Insulation performance and microstructure in modified polyethylene by MPE

Electrical measurements have shown to be able to provide useful information on physical, chemical, and microstructural properties of dielectric material. In this article, the depolarization characteristics of low‐density polyethylene blended with a small amount of metallocene catalyzed polyethylene were measured by pulsed electro‐acoustic method under various stresses. According to space charge limited current theory, the derivation of quantities such as mean volume density of space charge, apparent trap‐controlled mobility, trap depth distribution, and threshold stress were discussed. The test results showed that low‐density polyethylene blended with 1 wt % metallocene catalyzed polyethylene could effectively decrease deep trap density, increase shallow trap density, and then improve the mobility of charges. We also measured the breakdown voltage and tensile strength of the blends. It was found that low‐density polyethylene blended with a small amount of metallocene catalyzed polyethylene could effectively improve its breakdown voltage and tensile strength but reduce the material tenacity. Finally, mechanical relax and crystalline morphology of blends were studied by dynamic mechanical measurement, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering experiments. The results showed that the improvement of electrical properties and mechanical strength in the blends were relevant to the crystalline morphology. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Chain conformation of polyethylene in the solid state as studied by 13C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy

High-resolution ¹³C nuclear magnetic resonance (n.m.r.) spectra of melt-quenched polyethylene and polyethylene single crystals are measured by the cross-polarization/magic angle spinning technique. Melt-quenched polyethylene and polyethylene single crystals have four small upfield peaks, a shoulder on the main peak and three small peaks, respectively. Based on the ¹³C n.m.r. resonance lines of cyclic paraffin C₆₄H₁₂₈ reported previously, it is concluded that the main peak and the three upfield peaks arise from the trans zigzag structure region and the folded structure region, respectively. From these peak intensities, it is estimated that the stem length of polyethylene single crystals is approximately 125 Å. Taking into account an error in the estimation of the small peak intensities, the calculated stem length of 125 Å is consistent with the crystal thickness (120–150 Å) observed directly by electron microscopy. It can be concluded, therefore, that polyethylene single crystals mainly contain sharply folded structure. Melt-quenched polyethylene may contain sharply folded structure to some extent in addition to loose loops.     

高氯氯化聚乙烯对CR与MMA接枝共聚合的影响

以甲苯为溶剂,在９０℃条件下,研究了１０份氯含量为５７％的高氯氯化聚乙烯（ＨＣＰＥ）对１００份粘接型氯丁橡胶与７５份甲基丙烯酸甲酯（ＭＭＡ）接枝共聚合的影响。结果表明,该体系与无ＨＣＰＥ体系相比,ＭＭＡ转化率约提高４０％,产物接枝效率约高５０％,接枝度约高９０％。产物含有较高相对分子质量的级分,相对分子质量分布较宽,并且有较好的物理机械性能和较高粘接强度。     

Thermal degradation kinetics of polyethylene and silane‐crosslinked polyethylene

The thermal degradation of linear low‐density polyethylene (LLDPE) and linear low‐density silane‐crosslinked polyethylene (SXLPE) was studied. Kinetic evaluations were performed by model‐free kinetic analysis and multivariate nonlinear regression. Apparent kinetic parameters for the overall degradation were determined. The results show that the thermal stability of SXLPE was higher than that of LLDPE. Their decomposition reaction model was a single‐step process of an nth‐order reaction. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1172–1179, 2005     

Molecular fractionation in melt-crystallized polyethylene: 4. Fracture

The macroscopically brittle fracture of five high-density polyethylenes subjected to different constant uniaxial tensile loads was studied by s.e.m. fractography on both untreated and solvent-etched samples. The low molecular weight systems showed three types of fracture propagation: interspherulitic propagation with and without reorientation and trans-spherulitic interlamellar propagation. There is evidence that the development of fracture is associated with a strength distribution in the structure caused by molecular weight segregation occurring during solidification of the samples.