Liquid-liquid phase separation in blends of a linear low-density polyethylene with a low-density polyethylene

A linear low-density butene copolymer, of overall branch content 3 mol %, has been blended with a low-density polyethylene. The low-density polyethylene has an overall branch content of 5 mol %, including both long and short branches. The two materials were blended in a wide range of compositions and the phase behavior investigated using indirect experimental methods, the examination of quenched blends by differential scanning calorimetry, and transmission electron microscopy. After quenching from temperatures up to 170°C, blends, of almost all compositions, show two crystal populations, separated on a micron scale. It is argued that this implies that the blends were phase separated in the melt before quenching. This behavior shows good agreement with predictions based on previous extensive studies of binary and ternary blends of linear with lightly branched polyethylenes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1921–1931, 1997     

Secondary relaxation processes in polyethylene terephthalate-additive blends: 1. N.m.r. investigation

High-resolution carbon-13 and deuterium n.m.r. experiments have been used to examine the effects that low-molecular weight additives have on the secondary relaxation processes in polyethylene terephthalate (PET). These experiments have revealed that both the phenyl rings and the carbonyl groups in PET undergo small angle oscillations at temperatures below the glass transition temperature. It would, however, appear from the deuterium n.m.r. experiments that the phenyl rings also undergo rapid 180 flips, which appear to be closely related to the relaxation peak that is observed in dynamic mechanical experiments. Extremely little motion has, however, been observed in the ethylene glycol units and it has therefore been concluded that this group does not contribute to the secondary relaxation processes. Finally it has been observed that by blending low-molecular weight additives into the polymer it is possible to significantly reduce the number of the phenyl ring flips in the polymer and thereby suppress the relaxation peak.     

Mechanical relaxation of medical grade UHMWPE of different crosslink density as prepared by electron beam irradiation

Dynamic mechanical thermal analysis (DMTA) has been applied on medical grade ultra high molecular weight polyethylene of different crosslink density as prepared by electron beam irradiation to probe for contributions from crosslinking as well as crystallization. The crosslinking proceeds at a crystalline structure with a crystallinity about 50%. With increasing irradiation dose from 0 to 110 kGy, the molar mass between adjacent crosslinks decreases significantly to reach 3170 g/mol at lowest, whereas the crystallite thickness changes and new thin lamellae grow at almost constant degree of crystallinity. From DMTA in the entire temperature range from ?150 to +140°C and the angular frequency range from 0.6 to 135.4 Hz, three relaxation processes γ, β, and α of different temperature position and activation energy are distinguished. The corresponding chain mobility has been discussed as a sensitive discriminator for the coexisting crosslinked and lamellar phases showing the same dimension of a couple of 10 of nanometres. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Secondary relaxation processes in polyethylene terephthalate–additive blends: 2. Dynamic mechanical and dielectric investigations

Dynamic mechanical and dielectric analysis have been used to examine the effects that low molecular weight additives have upon the secondary relaxation processes in polyethylene terephthalate. In each of the polymer/additives blends examined one main secondary relaxation peak, known as the β peak has been observed below the glass transition temperature. It would, however, appear from the dielectric and mechanical results that the β peak consists of two different relaxation processes, one on the high temperature side and one on the low temperature side of the peak. A closer examination of these relaxation processes suggests that the high temperature side of the peak is due to phenyl ring flips, whereas the low temperature side is due to the motion of the carbonyl groups. In addition, it would appear that the activation energy and the enthalpy of the phenyl ring flips are both considerably higher than that of the carbonyls. Finally, when low molecular weight additives were blended into the polymer it was observed that only the high temperature side of the peak was suppressed and that the low temperature side remained virtually unaltered. This would indicate that although the additives suppress the motion of the phenyl rings, they have little effect upon the motion of the neighbouring carbonyl groups.     

Microdomain structure and chain orientation in polypropylene/polyethylene blends investigated by micro-Raman confocal imaging spectroscopy

Compositional domain structure of blends of isotactic polypropylene with linear polyethylene and chain orientation of neat polymers and of the blends were assessed by micro-Raman confocal imaging spectroscopy and FT Raman spectroscopy. The results were correlated with polarised photoacoustic FTIR and with DSC. The surface and inner parts of compression-moulded, injection-moulded and drawn specimens were compared. Polymer domains in the blends and domains of different orientation were identified. The larger size of the polymer domains and lower chain orientation in the core of the specimens prepared by injection-moulding were explained by different cooling conditions of the melt. Possibilities and limitations of the micro-Raman confocal spectroscopy method were discussed.     

Space charge behaviors of low-density polyethylene blended with polypropylene copolymer

In this study, the space charge behaviors of the blend polymers of low-density polyethylene (LDPE) and polypropylene copolymer were investigated by the pulsed electro-acoustic method (PEA) with the electrode system of aluminium/specimen/semiconductive layer. The blend specimen composed by 90 wt% LDPE and 10 wt% polypropylene copolymer (B10) showed a larger amount of space charge than pure LDPE (PE) under a DC field of 50 MV m⁻¹ at both 30 and 60 °C. Positive carriers moved more slowly in B10 than in PE under a positive DC voltage applied to the semiconductive electrode at 30 °C. DC currents were also measured under the same experimental condition as the space charge measurement. The DC current of B10 was lower than that of PE at 30 °C, but higher at 60 °C. The experimental results were explained by the introduction of traps by blending.     

Comparative study on matrix resins in two low-density polyethylene based cable insulation materials with different voltage grades

In industry, crosslinked polyethylene (XLPE) cable insulation is usually produced from crosslinkable compounds consisting of low-density polyethylene (LDPE) and additives, which known as “cable materials”. Considering that in addition to additives, the structure of matrix resin is a key factor in determining the property of XLPE, it is worthy to study the structure requirements of matrix resin for the development of cable materials with different voltage grades. In this work, the structure of matrix resins of a high voltage grade and an extra high voltage grade cable material were comparatively investigated. Interestingly, it was found that the matrix resins have no significant difference in chain structure parameters including molecular weight and its distribution and vinyl content between two samples, and their crystalline structure as well as the melt rheology and melting crystallization behavior are also very similar. These results suggest that these matrix resins may not substantially differ. Our work shows that cable materials with different voltage grades are not necessarily diverge in terms of matrix resin structure, and it could be possible to develop higher grade cable materials using the same matrix resin as lower grade counterparts.     

Measurement of solubility and diffusion coefficients of ethylene in solid and molten low-density polyethylene with different melt indices

The diffusion behavior of ethylene in polyethylene is of great importance for the polymerization and degassing of polyethylene (PE) industry. Based on the gravimetric sorption and desorption measurement approach, an intelligent gravimetric analyzer is applied to obtain the solubility and diffusion coefficients of ethylene in solid low-density PE (LDPE) with different melt indices at 30°C to 70°C, 0 to 4 atm and in molten LDPE at 160°C to 230°C, 0 to 4 atm, respectively. Results indicate that both the solubility and diffusion coefficients of ethylene in solid LDPE are smaller than those in molten LDPE, while the dissolution enthalpy and diffusion activation energy of ethylene in solid LDPE are higher. In addition, one- and two-dimensional diffusion models are built and the effects of particle size, polymer properties, and operation conditions are systematically investigated on the diffusion behaviors of ethylene in solid and molten LDPE.     

Epifluorescence studies and secondary relaxation processes in immiscible blends of polybutadiene‐poly(2‐vinyl naphthalene) by fluorescence spectroscopy

The development of the morphology of polybutadiene/poly(2‐vinyl naphthalene) blends in five proportions by mass (5, 10, 50, 90, and 95%, w/w) is studied by epifluorescence and scanning electron microscopy (SEM) techniques. The phase separation process of these immiscible polymers produces a primary morphology that is formed by dispersed droplets in a continuous matrix. In the sequence a secondary phase separation inside the primary domains is detected by epifluorescence microscopy of the intrinsically fluorescent domains. Secondary phase separation is confirmed by SEM fracture surface analysis. The relative size of the droplets and the matrix composition depend on the proportion of the components of the blends. The mechanism of the phase separation process is preferentially by nucleation growth for either primary or secondary phase separation processes. Secondary relaxation processes involving the poly(2‐vinyl naphthalene) phase are studied by fluorescence spectroscopy. The profile of the steady‐state excimer fluorescence of poly(2‐vinyl naphthalene) with the temperature in the blend differs from that of the isolated homopolymer and is explained by the contribution from the interface to the radiationless deactivation. The Arrhenius plot for the temperature dependence exhibits slope changes that are related to the polymer relaxation processes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1637–1649, 2002; DOI 10.1002/app.10389     

交联键类型对硫化丁苯橡胶拉伸应力松弛行为的影响

利用两相模型讨论了不同硫化体系的硫化丁苯橡胶的应力松弛行为。通过平衡溶胀法求得不同硫化体系中存在的几种不同交联网络结构的含量。普通硫化体系(CV)含有较多的多硫交联键,有效硫化体系(EV)含有较多的单硫交联键,而半有效硫化体系(SEV)的单硫、多硫交联键含量在前两者之间。考察了交联键类型、拉伸速率以及应变对应力松弛行为的影响。结果表明,CV体系的拉伸强度、不可松弛分量都要高于其它2种体系。交联键类型对可松弛分量的影响较小。     

Crystallization,structure, morphology,and properties of linear low-density polyethylene blends made with different comonomers

Linear low-density polyethylene (LLDPE) 7042, which has a butene comonomer, is widely used but has poor tear and dart strengths. For practical applications, small amounts of other materials can be blended with 7042 to effectively improve its properties. In this study, four blend resins and films (cast and compressed films) were prepared by blending 7042 with four LLDPEs (2045G, 9030, 23F, and 9085) in 8:2 ratios. The results indicated that after blending 2045G, 23F, or 9030 with 7042, the crystallization ability of the three blends was significantly suppressed and crystal size decreased. Moreover, the molecular chain can pass though more lamellar stacks in the blends, leading to an increased tie-chain concentration. Therefore, the tear and dart impact strength of the blend films improved. In contrast, the crystallization ability of the 7042/9085 blend was only slightly suppressed and did not significantly impact its properties. These findings contribute to our understanding of the relationship between material structures and properties, demonstrating that LLDPE blends can be used to improve the tear and dart strengths of 7042.     

Spin trapping of radicals produced by glow discharge on low-density polyethylene

An electron spin resonance study of radicals produced by glow discharge on low-density polyethylene powder shows three kinds of radicals, depending upon experimental conditions. The first formed, alkyl radicals, are unstable at room temperature and react rapidly with oxygen to form peroxide radicals. If a spin trapping compound, N-tert-butyl--phenyl nitrone, is added to the polyethylene, before discharge, nitroxide radicals are formed in place of peroxide. The interest in forming nitroxide radicals is their stability at room temperature. This simple method can be helpful for the observation and identification of radicals produced in polymers, for example by electrical treeing.     

Comparative study of poly(2,3 and 4 methyl cyclohexyl methacrylate)s. Dielectric relaxation spectroscopy (DRS)

The relaxation properties of poly(methyl cyclohexyl methacrylate)s (P2MCHMA), (P3MCHMA), (P4MCHMA) were analyzed. Dielectric spectroscopy (DS) techniques were used for this purpose. These polymers exhibit prominent α peaks, associated to the dynamic glass transitions, and then poorly defined β-relaxations and two other relaxation zones labelled as γ- and δ-relaxation in order of decreasing temperatures. The α relaxation processes were analyzed by means of the free volume theory, using the Vogel-Fulcher-Tammann-Hesse (VFTH) equation and in terms of the Havriliak-Negami (HN) empirical equation. Previously to these analyses, conductive contributions to the loss permittivity were subtracted. The apparent activation energies for the secondary processes under study have been calculated by means of Arrhenius. Comparison with previous relaxation results of poly(cyclohexyl methacrylate) (PCHMA), i.e. the polymer without substituents in the cyclohexyl ring, has been also carried out. In this way, changes in the glass transition absorptions as well as in the secondary processes have been discussed.     

不同相对分子质量聚乙二醇对白炭黑的改性

在沉淀法制备白炭黑过程中直接对白炭黑进行改性.选用聚乙二醇(PEG)作为改性剂,研究了其加入量对白炭黑产品粒径(d 50)、吸油值及表观密度的影响,利用扫描电镜和红外光谱分析仪对改性前后白炭黑的性能进行了表征.研究结果表明:随着PEG2000加入量的增加,产品的平均粒径和表观密度减小,吸油值增大,PEG2000加入量为产品质量的2%～8%时产品吸油值的变化不大.当PEG相对分子质量大于4 000时,所得白炭黑表现为粒径及表观密度增大.随着PEG相对分子质量的增大,白炭黑的吸油值先增大后减小.红外光谱分析结果显示,PEG在一定程度上影响了二氧化硅特征峰的位置.     

Determination of crosslink densities of carbon black filled natural rubber sulfur vulcanizates by 13C NMR MAS spectroscopy and 1H NMR transversal relaxation

Two NMR spectroscopic methods were applied to carbon black filled NR vulcanizates to determine the chemical crosslink density. Both methods give corresponding results. Addition of carbon black leads to a decrease of crosslink density with increasing filler content. The influence is more pronounced at higher sulfur content.     

Bright two-photon emission and ultra-fast relaxation dynamics in a DNA-templated nanocluster investigated by ultra-fast spectroscopy

Metal nanoclusters have interesting steady state fluorescence emission, two-photon excited emission and ultrafast dynamics. A new subclass of fluorescent silver nanoclusters (Ag NCs) are NanoCluster Beacons. NanoCluster Beacons consist of a weakly emissive Ag NC templated on a single stranded DNA ("Ag NC on ssDNA") that becomes highly fluorescent when a DNA enhancer sequence is brought in proximity to the Ag NC by DNA base pairing ("Ag NC on dsDNA"). Steady state fluorescence was observed at 540 nm for both Ag NC on ssDNA and dsDNA; emission at 650 nm is observed for Ag NC on dsDNA. The emission at 550 nm is eight times weaker than that at 650 nm. Fluorescence up-conversion was used to study the dynamics of the emission. Bi-exponential fluorescence decay was recorded at 550 nm with lifetimes of 1 ps and 17 ps. The emission at 650 nm was not observed at the time scale investigated but has been reported to have a lifetime of 3.48 ns. Two-photon excited fluorescence was detected for Ag NC on dsDNA at 630 nm when excited at 800 nm. The two-photon absorption cross-section was calculated to be ～3000 GM. Femtosecond transient absorption experiments were performed to investigate the excited state dynamics of DNA-Ag NC. An excited state unique to Ag NC on dsDNA was identified at ～580 nm as an excited state bleach that related directly to the emission at 650 nm based on the excitation spectrum. Based on the optical results, a simple four level system is used to describe the emission mechanism for Ag NC on dsDNA.     

Quantification of the complexation of protein with neutral water borne polymer by fluorescence spectroscopy

The complexation of bovine serum albumin (BSA) with poly(N-isopropylacrylamide) (PNIPAM) in an aqueous system (pH 7) has been investigated by means of fluorescence spectroscopy. Through analyzing the change of fluorescence intensity of protein chromophores caused by complexation, a quantitative mathematical equation has been established and the average number of bound proteins per neutral polymer (n_b) can be calculated accurately without destroying the dynamic equilibrium of aqueous complex system. At the same time, with the help of this equation, the extreme value of n_b can also be calculated when PNIPAM concentration is low enough. Compared with traditional calculation methods, this method has the advantages of rapid detectability, high sensitivity, accuracy and extensive applicability. Thus, it is a better way to study the complexation of protein with polymer.     

Plasmonic near-field in the vicinity of a single gold nanoparticle investigated with fluorescence correlation spectroscopy

We proposed the estimation of the plasmonic near-field volume in the vicinity of a single gold nanoparticle, and observed experimentally the near-field variation due to a change in the polarization of the illuminating light. Under total-internal-reflection illumination, the plasmonic near-field volume is varied by tuning the polarization of the excitation light. The variation in the optical near-field around a single gold nanoparticle was simulated theoretically with a finite-difference time domain method, and was characterized experimentally employing a fluorescence correlation spectroscopy technique. The experimental results are in agreement quantitatively with the theoretical analysis. These results are highly relevant to important efforts to clarify the interaction between the emitter and the plasmonic antenna, and should be helpful in developing a plasmonic-enhanced total-internal-reflection fluorescence imaging microscope.     

Photografting of methacrylic acid on low-density polyethylene film in presence of polyfunctional monomers

Photografting (λ > 300 nm) of methacrylic acid (MAA) on low-density polyethylene (PE) film (thickness = 30 and 60 μm), on which xanthone photoinitiator was coated earlier, was investigated at 60°C in the presence of polyfunctional monomers such as N,N′-methylenebisacrylamide (MBAAm) and trimethylol propane triacrylate (TMPTA). Addition of the polyfunctional monomers (0.01 and 0.1 wt %) to the grafting system largely accelerated the photografting, and the magnitude of the enhancement was larger for TMPTA than MBAAm. MBAAm component was incorporated into PE substrate and/or MAA-grafted chains through the grafting reaction. Double bonds of the introduced polyfunctional component seemed to act as a new site for the grafting initiation, leading to the promoted grafting. The polyfunctional monomer did not affect distribution of the grafted chains in the cross section of the resultant MAA-grafted film, which was measured by electron probe microanalysis. Wettability of the MAA-grafted PE film was not influenced by the addition of MBAAm, but water absorbency was reduced by using a higher concentration of MBAAm. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1635–1641, 1997     

Microenvironments in poly(1,4-butylene terephthalate) solids revealed by fluorescence spectroscopy

The relationship between the fluorescence behavior and crystallinity of poly(1,4-butylene terephthalate) (PBT) films, prepared by a spin-casting method, was investigated. Throughout the fluorescence measurements of PBT thin films having different crystallinities, the main-chain phenylene fluorescence near 320 nm and that near 365 nm were assigned to monomer fluorescence mainly from crystalline regions and excimer fluorescence from amorphous regions, respectively. It was found that the ratio of the fluorescence intensity at 320 nm to that at 365 nm can be an effective indicator of PBT crystallinity. The present work should provide a quick and nondestructive method for determining the crystallinity of PBT factory products.