The effect of electric field on the creep characteristics of low-density polyethylene (LDPE)

Summary The effect of electric field on the creep characteristics and the corresponding parameters such as instantaneous strain, strain rate, activation energy, activation volume, stress-sensitivity parameter and viscosity was investigated.     

中相对分子质量PIB对LDPE和PS流变行为影响

利用HAAKE转矩流变仪和毛细管流变仪研究了低密度聚乙烯（LDPE）／q7相对分子质量聚异丁烯（HB）和聚苯乙烯（PS），PIB共混体系的流变行为，讨论了PIB含量对LDPE／PIB和PS／PIB共混体系的扭矩、剪切黏度、剪切应力及非牛顿指数（n）的影响。结果表明，随着w（PIB）的增加，共混体系的扭矩、剪切黏度下降，n增加，但仍为假塑性流体（n小于1）。其中，进入平衡态后LDPE／PIB体系的扭矩从5．6N·m降到4．5N·m；PS／PIB体系的扭矩从3．2N·m降到2．5N·m。     

Natural and artificial weathering of low-density polyethylene (LDPE): Calorimetric analysis

Studies of the thermal and photodegradation of two commercial polymers, stabilized and unstabilized low-density polyethylene (LDPE), show the effects of weathering in differential scanning calorimetry (DSC) curves. The shape and the size of the melting peak vary significantly in thermal aging and in accelerated photoirradiation, but no change was observed in natural weathering implying that the crystallinity remains steady in outdoor exposures. The melting temperatures remain steady for all exposure tests. The fall of mechanical properties and the evolution of chemical structure, followed by IR spectroscopy especially near the carbonyl regions, was also performed. The resistance to UV light irradiation as probed by deformation at break was superior in stabilized LDPE compared to unstabilized LDPE. Simple correlations were not observed between the fall of mechanical properties, the rate of oxidation, and the morphology.     

Natural and artificial weathering of low-density polyethylene (LDPE): Calorimetric analysis

Studies of the thermal and photodegradation of two commercial polymers, stabilized and unstabilized low-density polyethylene, show the effects of weathering on differential scanning calorimetry (DSC) curves. The shape and the size of the melting peak vary significantly in thermal aging and in accelerated photoirradiation, but no change was observed in natural weathering, implying that the crystallinity remains steady in outdoor exposures. The melting temperatures remain steady for all exposure tests. The fall of mechanical properties and the evolution of chemical structure, followed by IR spectroscopy results, especially near the carbonyl regions, were also observed. The resistance to UV light irradiation as probed by deformation at break was superior in stabilized LDPE compared to unstabilized LDPE. Simple correlations observed between the fall of mechanical properties, the rate of oxidation, and morphology. © 1993 John Wiley & Sons, Inc.     

EVA增容改性玉米淀粉／LDPE共混体系的研究

以LDPE和玉米淀粉为主要原料,与EVA熔融共混制备了玉米淀粉／LDPE／EVA共混材料,并对其热学性能和抗张性质进行了研究。DSC分析显示EVA可以明显改善LDPE和淀粉之间的相容性,机械性能也有所改善,在EVA含量为10％时,抗张强度为9．2MPa,断后伸长率为117．4％。     

Physico-chemical modifications of superficial regions of low-density polyethylene (LDPE) film under corona discharge

Using e.s.r., ATR and d.s.c., data on the chemical and structural superficial modifications of LDPE films under corona discharge in the presence of air have been obtained. The results show that the electrical discharge creates superficial ethylenic bonds (1630 cm^?1) and carbonyl groups (1720 cm^?1), the amount of which varies inversely with the main power supply. The treated samples when stored in the presence of light and air undergo marked structural and chemical changes. Formation of a thin waxy layer rich in 〉 CO and 〉 CC 〈 bonds with almost total absence of CH₂CH₂ groups characteristic of LDPE is observed.     

Thermal,dynamic mechanical,and rheological behavior of linear low-density polyethylene/poly(octadecene-co-maleic anhydride) blends

Blends of linear low-density polyethylene (LLDPE) and a 50:50 copolymer of octadecene and maleic anhydride (C₁₈-MAH) were characterized by calorimetry, dynamic mechanical testing, and rheometry. In the solid state, the blends are essentially immiscible. No evidence was obtained for cocrystallization of the LLDPE with the paraf-finic side-chains of the C₁₈-MAH. Interactions between the blend components were observed in three ways. First, presence of the C₁₈-MAH in the LLDPE melt increases the nucleation rate for LLDPE crystallization. Second, side-chain crystallization in a portion of the C₁₈-MAH component equivalent to approximately 15% of the total blend is apparently suppressed in the blends. Third, although the mechanical loss of the blends is essentially a sum of the pure components, the β relaxation of the LLDPE is absent in blends containing more than 20% C₁₈-MAH. The blends are also immiscible in the melt. The steady and dynamic shear rheology is dominated by the immiscibility and mismatch in viscosity, η, between the two polymers. A linear dependence on blend composition was found for log η in dynamic (small strain) tests. Nonlinear behavior with positive and negative deviations from linearity was found for log η in steady shear (large strain) tests.     

LDPE接枝聚氨酯对TPU/LDPE共混物流变行为的影响

以低密度聚乙烯(LDPE)接枝聚氨酯(LDPE-g-PU)为增容剂,利用旋转流变仪研究了热塑性聚氨酯弹性体(TPU)/LDPE/LDPE-g-PU共混物的流变行为,分别以温度和增容剂用量为变量研究了共混物的储能模量、耗能模量、损耗角正切以及复数黏度与剪切速率的关系。结果表明:TPU/LDPE/LDPE-g-PU共混物为假塑性流体;加入LDPE-g-PU后,共混物的复数黏度先降低后升高,当w(LDPE-g-PU)为1%时,共混物的复数黏度降至最低;升高温度对共混物复数黏度的影响根据角频率的不同有所差异,低频率时复数黏度升高,高频率时复数黏度降低。     

Classification of volatile products evolved during temperature-programmed co-pyrolysis of low-density polyethylene (LDPE) with polypropylene (PP)

Temperature programmed co-pyrolysis of low-density polyethylene (LDPE) with polypropylene (PP) was investigated. The aim of this research was to determine the volatile product distribution and product evolution rate of co-processing of LDPE with PP. A series co-pyrolysis operation was performed with LDPE and PP using a 1:3, 1:1, 3:1 total carbon ratio of LDPE to PP. A fixed bed reactor was used to pyrolyse small sample of LDPE and PP mixture under an inert gas flow (argon). A special sampling technique was used for collecting organic products eluted from the reactor at different temperature and time intervals. The co-pyrolysis products were analyzed by capillary gas chromatography and the total product evolution rate was investigated as a function of temperature and time. n-paraffins and 1-olefins in aliphatic fraction of co-pyrolysis products were classified as a carbon number. In addition, the recovery of total organic carbon as an organic volatile product was determined. The assessments were based on incorporating the results on temperature-programmed pyrolysis of LDPE and PP. The effect of co-processing of LDPE with PP was determined by calculating the difference between the experimental and the hypothetical mean value of conversion of total organic carbon into volatile products. Conversion into volatile hydrocarbons was found to be higher, with the increasing PP ratio in the co-pyrolysis operation.     

LDPE分子结构对流变行为的影响

采用流动双折射和动态流变实验方法研究了低密度聚乙烯(LDPE)分子结构对其流变行为的影响.熔体在突变收缩口模中流动时的等差线图显示,两种LDPE的流动特性明显不同.由动态流变实验可知,LDPE 1810D在低频剪切时复数黏度比LDPE 2426K大,拟合得到的离散松弛时间谱范围较窄,表明两者的相对分子质量及其分布差别较...     

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.     

Nonlinear behavior of linear low-density polyethylene

To predict the response of polyethylene thin films subjected to stress for a long time, it is necessary to understand the influence of stress on either the relaxation modulus or creep compliance. Extensive testing has been conducted on 20-micron-thick samples of a particular linear low-density polyethylene film at temperatures from 23°C to −50°C. When reduced to creep compliance and compared with results from dynamic mechanical analysis (DMA), the influence of nonlinearities in the response function is apparent. However, the use of a two-step loading procedure has produced sufficient data to discriminate between the effect of stress on amplitude and time on the creep compliance. It has been found that a master curve of compliance generated by DMA equipment may be used in conjunction with certain nonlinear functions to accurately predict the response of the polyethylene. Perhaps of more importance is the observation that the principles of simple time-temperature superposition, commonly used with linear viscoelastic characterization, are insufficient for use with polyethylene films at most stress levels of interest.     

PA6/LDPE共混物流变性能的研究

研究了聚酰胺6/低密度聚乙烯(PA6/LDPE)共混体系的结构和流变性能。结果表明:共混体系呈现以PA6为分散相,LDPE为连续相的海岛结构;在实验范围内共混体系为非牛顿流体,满足幂律方程;LDPE对温度比较敏感,LDPE的流变行为占主导地位,PA6的粘度主要受剪切力的影响;在剪切速度一定时,PA6与LDPE的粘度比随着温度的升高而增加;在温度一定时,粘度比随着剪切速率的增加而下降;改变温度及剪切力可以调节两组分粘度比。     

Reprocessing and shear modification of polyethylene

Reprocessing of used polyethylene serves as a promising solution to a severe ecological and economical problem. This material, however, has frequently been exposed outdoors and demonstrates poor workability and inferior mechanical properties. In this study, we attempt to explore ways for the improvement of flow and product performance by intensive shear processing. When shearing reclaimed polyethylene (LDPE) containing some degree of crosslinking and oxidation, either by repetitive injection molding, extrusion or roll milling, the fluidity of the recycled polymer is gradually increased, frequently with rising ductility of the product and a decrease in melt elasticity. As a result, a practical way of reclaiming poor-flowing, partially gelled polymer has been found. Additionally, the recycled material can be blended with virgin polyethylene, preferably of the linear low density type. Virgin polyethylene by itself, however, demonstrated an opposite response to intensive shear. There was a drop in fluidity, a rise in melt elasticity, and usually a decrease in ductility. All this is believed to result from the degradation processes that may consist of initiation of microgels and recombination of polymer chains by free radicals, as shown by an actual increase in intrinsic viscosity and in the higher modes of molecular weight averages. It was noted that the controlling mechanism of shear modification of virgin polymer differs from that occurring with a partially crosslinked structure. Results of the shear modification of both virgin and reclaimed polyethylene, by continuous kneading in a Brabender Plastograph, indicate mainly a chain scission mechanism. In all cases the melt viscosity dropped together with the ductility of the final product.     

Effect of bark flour on melt rheological behavior of high density polyethylene

The melt rheological behavior of neem bark flour (BF) filled high density polyethylene (HDPE) has been studied at varying volume fraction (?_f) from 0 to 0.26 at 180, 190, and 200°C in the shear rate range from 100 to 5000 s^?1 using extruded pellets of the composites. The melt viscosity of HDPE increases with ?_f because the BF particles obstruct the flow of HDPE. With the incorporation of the coupling agent HDPE‐g‐MAH, the viscosity decreased compared to the corresponding compositions in the HDPE/BF systems due to a plasticizing/lubricating effect by HDPE‐g‐MAH. The composites obeyed power law behavior in the melt flow. The power law index decreases with increase in the filler content and increases with temperature for the corresponding systems while the consistency index showed the opposite trend. The activation energy for viscous flow exhibited inappreciable change with either ?_f or inclusion of the coupling agent, however, the pre‐exponential factor increased with filler concentration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

多壁碳纳米管对聚胺醚电纺溶液流变性能的影响

通过原位聚合法将酸处理过的多壁碳纳米管(MWNTs)与聚胺醚复合,制备碳管含量不同的电纺溶液。采用应变控制型流变仪研究MWNTs/聚胺醚电纺溶液的流变行为。静态流变结果表明:聚胺醚为切力变稀的非牛顿流体,体系的表观粘度随着碳管含量的增加而增大,非牛顿指数减小;随着碳管含量的增加,聚胺醚电纺溶液的粘流活化能增加。动态流变结果表明:储存模量G′和损耗模量G″均随着MWNTs含量的增加而增加。     

Influence of long‐chain branching on the rheological behavior of polyethylene in shear and extensional flow

In this work, a study of the influence of molecular structure on the viscoelastic behavior of melts of commercial polyethylene (PE) copolymers, particularly in extensional flows, will be performed. To enable this study to be performed, a series of four very low‐density polyethylenes (VLDPEs) (film and blow molding grades) with different parameters of molecular weight (M_W), molecular weight distribution (MWD), and degree of long‐chain branching (LCB) will be used. Experiments in shear flow (steady state and oscillatory regime) are complemented with experiments in uniaxial extension (constant strain rate and stress relaxation after a step strain). It will be shown that a qualitative correlation exists between both types of experiments; the stress relaxation experiments being particularly sensitive to the different molecular features of the polymers. In addition, the failure behavior in extension was also investigated and the results indicate that, within experimental error, the Hencky strain to failure is sensitive to the type of molecular structure but the corresponding tensile stress is not. POLYM. ENG. SCI., 45:984–997, 2005. © 2005 Society of Plastics Engineers     

Flow behavior of partially crosslinked low-density polyethylene

The viscosity of low-density crosslinked polyethylene was studied as a function of gel content and shear rate (3.75–33 sec^?1). A simple model relating viscosity with gel content is suggested. It is shown that sol viscosity decreases with cross-linking propagation. The rheological parameters of the sol fraction are changed as a result, and it is natural that this effect should be utilized for flow calculations. Experimental data indicate a high degree of interaction between the sol molecules and the gel, and an experimental technique is presented for measuring it. The rheological parameters of crosslinked polyethylene are closely dependent on the gel content, viscosity and pseudoplasticity increasing with the latter.