Structure–properties of electron beam irradiated and dicumyl peroxide cured low density polyethylene blends

Low density polyethylene (LDPE) and its blends with styrene butadiene rubber and ethylene propylene diene monomer were cured, using electron beam irradiation as well as dicumyl peroxide (DCP). The effect of blending was found to change the melt viscosity when compared with the virgin LDPE. Also, the influence of curing system on the various properties was investigated. It was found that either irradiation or DCP curing enhanced the gel content and crosslink density as well as the mechanical and hot set properties. The obtained data showed that the curing greatly influence the stress strain and hot set properties, in which there is a variation in such properties for both curing methods in spite of the gel contents were comparable. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Effects of polyethylene molecular structure on peroxide crosslinking of low density polyethylene

The effects of molecular structure on the dicumyl peroxide crosslinking of two low density polyethylenes have been studied. Peroxide efficiency was determined largely by the content of terminal vinyls in the two polymers. Differences in molecular weight distribution and branch content had comparatively little influence on the gel content but hot creep resistance of the vulcanized materials was affected. Scorching was affected, also, by the presence of vinyl unsaturations in the polymer.     

Wax crosslinking with dicumyl peroxide

A Fischer—Tropsch paraffin wax of high molecular weight, congealing point 205°F (96·1°C), was crosslinked with dicumyl peroxide as initiator. At peroxide/wax molar ratios of less than 1·15 : 1, crosslinked waxes with molecular weights up to approximately double that of the starting material are obtained. These products are characterised by an increase in elasticity. At peroxide/wax ratios greater than 1·15 : 1 insoluble and infusible gels are formed. The efficiency and fate of the initiator and possible side reactions are discussed.     

氯丁橡胶/氯化聚乙烯橡胶共混胶的过氧化二异丙苯共硫化性能

研究了以过氧化二异丙苯（DCP）作共硫化剂的氯丁橡胶（CR）与氯化聚乙烯橡胶（CM）共混胶的性能,并用橡胶加工分析仪和动态热机械分析仪进行了表征。结果表明,与纯CR和CM相比,CR/CM共混胶的加工性能明显改善,焦烧时间缩短,正硫化时间变长,力学性能介于纯CR和纯CM之间。共混胶的储能模量（G＇）大于纯CR和CM,损耗因子（tanδ）介于两者之间。CR与CM具有一定的相容性。当DCP/Zn O/亚乙基硫脲（质量比）为1.80/4.25/0.35时,CR/CM共混胶的G＇更大,tanδ略小,两相的玻璃化转变温度更为靠近,交联程度、相容性、共硫化程度高于三者质量比为0.80/4.25/0.50时的CR/CM共混胶。     

Solubility and diffusivity of cyclohexane in high density polyethylene

The diffusivity and solubility of cyclohexane in a high density polyethylene, HDPE, were studied using a gravimetric, quartz‐spring, sorption balance. Solvent concentrations up to a weight fraction of 0.15 over a temperature range of 90 to 160°C were measured. Diffusion coefficients in the range of 10^?6 to 10^?7 were determined. Two types of polymer samples were used: a commercial bead form and flat sheets prepared by melting the polymer. Within the experimental error no differences were observed between the two forms indicating that there were no significant effects caused by the melting and compression. The solubility of cyclohexane in the HDPE as a function of the activity of the cyclohexane was linear. Above the melt temperature the solubility data were predicted better by the group‐contribution, lattice‐fluid equation of state (GCLF‐EoS) than by the van der Waals free‐volume (UNIFAC‐vdw‐FV) model. Below the melt temperature a correction factor for the elasticity significantly improved the predictions for both models. Although the HDPE has a crystallinity of 77.6%, the experimental data and the Vrentas‐Duda free‐volume theory indicated no significant tortuosity effects. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

过氧化物交联HDPE材料的研究

研究了交联用高密度聚乙烯(HDPE)的种类、交联剂二叔丁基过氧化物(DTBP)、助交联剂T的用量对交联HDPE复合材料结构和性能的影响。选用辛烯为共聚单体和支化度(每1000C中的甲基数)为3.2的HDPE为原料树脂,主交联剂DTBP和助交联剂T的质量分数分别为0.15%,0.20%时,材料的各项性能符合交联HDPE管材的要求。     

Absorption of dicumyl peroxide by extruded polyethylene: Difference between surface and bulk morphology

Under some conditions, the absorption of dicumyl peroxide (DICUP) at 70°C by extruded low density polyethylene (LDPE) displayed features which are characteristic of two-stage sorption. For example, the initial slope of the DICUP absorption curve (plot of M_t/M_∝ against \documentclass {article}\pagestyle{empty}\begin{document}$\sqrt t$\end{document} ) reflecting diffusion in the surface region was 2.5 times higher than the slope of the second stage (reflecting diffusion in the bulk) for 4-mm-diameter LDPE rods extruded at 130°C and 180 rpm (die pressure = 6000 psig). Only a single stage curve was evident in the same rod with its surface removed or in smaller diameter extrudate. Increasing the screw speed from 10 to 45 rpm at nearly constant extrusion pressure (1800–2380 psig) resulted in an approximately 50% decrease in the initial (first stage) slope with a negligible effect on the second stage slope. Increasing the die pressure (4900–6000 psig), by decreasing the extrusion temperature, at constant screw speed (125 rpm) resulted in an almost threefold decrease in the second stage slope without apparent effect on the first stage slope. Photomicrographs demonstrated the presence of distinct surface and bulk morphologies with evidence of a transcrystalline surface layer oriented prependicular to the surface at low screw speeds and larger spherulites in the bulk of the high pressure extrudate. Such morphological features and the observed dependence of the two stage sorption curves on extrusion conditions are consistent with the surface and bulk morphology of the extruded LDPE rod being dependent on the screw speed and die pressure, respectively. These uptake curves were determined by modifying the classical sorption technique to separate the measurement of the equilibrium uptake from the continuous recording of the slow changes in mass during absorption. This technique may be useful in the characterization of the migration process in other plastic/penetrant systems where diffusion is too slow to be measured by conventional means.     

Mechanical and thermal properties of blends of low‐density polyethylene and ethylene vinyl acetate crosslinked by both dicumyl peroxide and ionizing radiation for wire and cable applications

Formulations of chemically crosslinked and radiation‐crosslinked low‐density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with a poly(ethylene vinyl acetate) copolymer (EVA) and the effects of various coadditives, including polyethylene grafted with maleic anhydride (PEgMA), vinyl silane with boric acid, and talc, on the mechanical and thermal properties were investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron‐beam accelerator were both used and compared. Improved mechanical properties were observed by the partial replacement of LDPE with EVA. Similar mechanical or thermal properties were observed with coadditives such as PEgMA and vinyl silane with boric acid. The addition of a small amount of talc improved the tensile strength of the formulations. All crosslinked formulations showed good thermal stability on the basis of the retention of mechanical properties after thermal aging for 168 h at 135°C and a hot‐set test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhanced mechanical and thermal properties of nanodiamond reinforced low density polyethylene nanocomposites

In this study, the reinforcement effects of low-content hydrophilic nanodiamond (ND) on linear low-density polyethylene (PE) nanocomposites were investigated. ND was incorporated in PE via simple solution blending. The obtained PE/ND nanocomposites were characterized using scanning electron microscopy, ultraviolet–visible spectra, X-ray diffraction, tensile test, thermogravimetry, and differential scanning calorimetry. Generally, PE/ND nanocomposites with poor interfacial interaction cause large agglomerates, resulting in brittle and poor mechanical properties. Owing to the different natures of non-polar PE and polar ND, the higher the ND content, the larger the agglomerates formed in the nanocomposites. However, PE/ND nanocomposites show unique mechanical properties, that is, the Young's modulus, tensile strength, elongation at break, and toughness increased upon the incorporation of ND. The Young's modulus of the PE/ND nanocomposites exceeded the theoretical value calculated using the Halpin–Tsai model. In addition, the toughness increased by 18% at only 0.5 wt% ND loading. Furthermore, there was an increase in the thermal degradation temperature, melting temperature, and crystallization temperature.     

Rheological properties of polyethylenes modified with dicumyl peroxide

Low- and high-density polyethylenes were modified using dicumyl peroxide. The modified polyethylenes were subjected to steady and oscillatory shearing flows. The viscous and elastic properties determined with a cone-and-plate rheometer are correlated to the molecular weight of the materials, which was determined with the aid of size exclusion chromatographic analysis. It was found that both the melt viscosity and elasticity increase with the amount of dicumyl peroxide used, and shear-thinning behavior becomes more intense. The Bueche master curve of viscosity is constructed by using a relaxation time based on the weight-average molecular weight for both virgin and modified resins.     

Crystallinity,thermal diffusivity,and electrical conductivity of carbon black filled polyamide 46

Polyamide 46 (PA 46) with carbon black (CB) has been subjected to a heat treatment. Crystallinity, specific heat capacity, crystalline melting peak temperature, thermal diffusivity, and electrical conductivity were measured. The crystallinity increases with duration of thermal treatment. The maximum value is dependent on the filler fraction. A lower CB content leads to a higher crystallinity at maximum tempering time. The crystalline melting peak temperature increases with decreasing filler fraction and duration of thermal treatment due to different crystal types and/or diverging geometric forms of the crystals. Thermal diffusivity and electrical conductivity act positively proportional to each other and increase with CB content and tempering time. The thermal diffusivity decreases with increasing temperature. The volume resistance of PA 46 is lowered by heat treatment. By CB addition in combination with a tempering process, the PA 46 can be transferred into a conductor. CB is moved by PA 46 crystals into amorphous regions forming conductive pathways. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48882.     

Neurotoxic effects of the oxidative thermal degradation products form low density polyethylene

Adult male Wistar rats were exposed for 2–5 weeks, 6 h nightly, 5 nights a week, to oxidative thermal degradation products of low density polyethylene derived by heating (325°C) under an airstream in a tube oven. Chemical analysis of the degradation products in the gaseous fraction revealed a wide variety of potentially toxic molecules which included carbon monoxide (<20 ppm), formaldehyde (1.4 ppm), acrolein (0.5 ppm) and various other aldehydes (total concentration 18 ppm expressed as formaldehyde). The mean oxygen concentration was 20%. The total particulate fraction amounted to 8 mg m^?3. The latter particles might have caused the detected discoloration of the rat fur. Similarly this contamination might have been the cause of a very significant increase in the duration and frequency of preening of the rats. The neurochemical effects associated with the exposure included an increase in the cerebral RNA concentration as well as initial increase in the glycosylation of cerebral protein in vitro. NADPH-diaphorase activity was below the control range throughout the exposure while the superoxide dismutase activity displayed an increasing trend five weeks after the beginning of the experiment. The latter effects were taken as a response to potentially harmful molecules in the brain whereas the effects on the RNA and glycosylation might have resulted from a more peripheral nervous irritation.     

Spherulite nucleation in polypropylene blends with low density polyethylene

Primary nucleation of spherulites in blends of isotactic polypropylene (iPP) with low density polyethylene (LDPE) was investigated by means of differential scanning calorimetry and optical microscopy. The number of iPP spherulites in the blend decreases with increasing LDPE concentration to a much greater extent than follows from the decreasing amount of iPP. The shapes of spherulite size distributions indicate that athermal (heterogeneous) primary nucleation is inhibited. The density of primary nucleation in the blends decreases strongly with increasing mixing time. The same effect was observed in the blends with the nucleating agent which was added to iPP or LDPE. These experiments demonstrate that heterogenoeus nuclei migrate across interphase boundaries from the iPP melt to the LDPE melt during the mixing process. It is suggested that the interfacial energy difference between the nuclei and the molten components of the blend is responsible for the migration of nuclei.     

Electrical properties of natural-fiber-reinforced low density polyethylene composites: A comparison with carbon black and glass-fiber-filled low density polyethylene composites

The electrical properties of sisal fiber-low density polyethylene (LDPE) and coir fiber-LDPE composites have been studied. The dielectric constant progressively increases with increase of fiber loading and decreases with increase of frequency in the case of all composites. The dielectric constant of sisal-LDPE composites has been studied as a function of fiber length. Volume resistivity values decrease with fiber content. The increase of dielectric constant with fiber loading is more predominant at low frequencies in both the sisal fiber-LDPE and coir fiber-LDPE composites. The results of the natural-fiber-filled composites were compared to those of the carbon and glass-fiber-filled LDPE composites. The dielectric constant of carbon-black-loaded LDPE composites increases with carbon content, and the increase is sharper at high carbon content. This is associated with the network formation of carbon black in LDPE matrix. © 1997 John Wiley & Sons, Inc.     

Thermoplastic elastomers based on high‐density polyethylene,ethylene–propylene–diene terpolymer,and ground tire rubber dynamically vulcanized with dicumyl peroxide

Thermoplastic vulcanizates (TPVs) based on high‐density polyethylene (HDPE), ethylene–propylene–diene terpolymer (EPDM), and ground tire rubber (GTR) were dynamically vulcanized with dicumyl peroxide (DCP). The polymer blend was composed of 40% HDPE, 30% EPDM, and 30% GTR, and the concentration of DCP was varied from 0.3 to 3.6 parts per hundred rubber (phr). The properties of the TPVs were determined by evaluation of the gel fraction content and the mechanical properties. In addition, IR spectroscopy and differential scanning calorimetry analysis were performed as a function of the DCP content. Decreases in the Young's modulus of the blends and the crystallinity of HDPE were observed when the content of DCP was greater than 1.8 phr. The results regarding the gel content indicate that the presence of DCP promoted the crosslinking of the thermoplastic matrix, and optimal properties were obtained with 1.5% DCP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39901.     

Mechanical and thermal properties of coal gasification fine slag reinforced low density polyethylene composites

Coal gasification fine slag (CGFS) was processed via a grading technique. The CGFS products (CGFS‐S1, CGFS‐S2, CGFS‐S3) with different sizes were obtained. Effects of particle size and unburned carbon on tensile properties of filled low density polyethylene (LDPE) were studied within the CGFS weight fractions ranging from 10 to 50 wt %. The tensile strength was found to increase with decreasing CGFS size, and the tensile properties exhibited good performance, owing to unburned carbon. The tensile strength of the composites increased with increasing CGFS‐S3 weight fraction. The analysis of mathematical model and SEM revealed that the firm improvement of tensile strength resulted from the strong interactions between LDPE polymer chains and CGFS‐S3 particles, and good dispersion of CGFS‐S3 in resin. Thermogravimetric analysis proved obvious reinforcement in thermal‐oxidative stability by incorporation of CGFS‐S3. The degree of crystallinity of LDPE/CGFS‐S3 showed the first increased and then decreased variation tendency. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46203.     

Mechanical and thermal properties of low density polyethylene composites filled with dye‐loaded shell powder

To achieve reinforcement and coloring in one combined process of polymer production, a dye‐loaded shell powder (DPSP) based on Congo red and pearl shell powder was prepared and used as a versatile bio‐filler in low‐density polyethylene (LDPE). The DPSP was characterized by means of X‐ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. The mechanical, thermal, and colorimetric properties of prepared LDPE/DPSP composites were investigated as well. Adding DPSP could significantly increase the strength and stiffness of LDPE composites while giving an outstanding coloring performance. Moreover, the impact strength of LDPE composites was improved at lower filler loading rate, and the maximum incorporation content could reach 10 wt % with a good balance between toughness and stiffness of LDPE composites. The thermal performance studies confirmed an increase in thermal stability and heat resistance of LDPE composites with the incorporation of DPSP. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44118.     

线性低密度聚乙烯催化剂研究新进展

综述了各种线性低密度聚乙烯(LLDPE)催化剂的国内外发展状况,包括茂金属催化剂、混合催化剂、非茂金属催化剂、双功能催化剂和后过渡金属催化剂等。     

线性低密度聚乙烯催化剂研究进展

综述了各种LLDPE催化剂的国内外发展状况，包括铬系催化剂、齐格勒-纳塔催化剂、茂金属催化剂、非茂金属催化剂、后过渡金属催化剂和复合催化剂等。