A study of the degradation of polyethylene by high-temperature dynamic light-scattering

After passing throught an extuder, a small amount of degradation normally occurs in the high molecular weight tial of a broadly distrubuted polymer sample. This small amount of degradation counld dramatically affect the polymer viscoelastic properties. It is difficult to detect this type of degradion by using convetional analytical methods, such as hightemperature size exculsion chr omatography. An investisgation of this thype of degradation in a broadly distributed polyethylene sample was accomplished by using high-temperature dynamic light-scattering (HTDLS). We have shown that the measured line-width (or the tsranslatinal diffusion coefficient) distrubuiton in the HTDLS is proportional to M^α with α = 3. 580 ± 0.005 so that the HTDLS is a very sensitive techique for detecting a very small amount of degradation im the high molecular weight tail. Another advantage of using the HTDLS is that the study does not intoduce further stress or perturbation into the sample. In study, we also investigated the thermal degradation of the polyelthylene sample in trichlorobenzene at high temperatures. We found that the polyethylene sample after the extrusion undergoes a thermal degradation more easily. © 1994 John Wiley & Sons, Inc.     

HPLC analysis of phospholipids by evaporative laser light-scattering detection

High-performance liquid chromatography (HPLC) for analysis of phospholipids has traditionally employed ultraviolet detection of the eluted compounds. The evaporative laser light-scattering detector (ELSD) offers new opportunities for quantitative analysis of lipids. Phospholipids were isolated from crude and degummed oils prepared from soybeans subjected to storage at high moisture content. Analytical and preparative separations of phospholipids by normal-phase HPLC were accomplished. Major class fractions were analyzed by transmethylation and capillary collumn chromatography for fatty acid composition, and by reverse-phase C-18 HPLC (RP-HPLC) for molecular species composition. The RP-HPLC-ELSD system was limited to the analysis of phosphatidylcholine and phosphatidylethanolamine.     

Improved accuracy and precision in the light-scattering characterization of homo- and copolymers in THF

A one-point method was developed for the estimation of weight-averaged molecular weights from light-scattering data. The method is based on the calculation of the second virial coefficient from theoretical predictions of the dependence of A₂ on the molecular weight. The second virial coefficient is then regressed for a particular polymer—solvent combination from a series of preexisting measurements over a range of molecular weights. The one-point method is found to yield as accurate molecular weight estimates as obtained from a Debye plot using the conventional dilution technique. The variance in the estimation of the Rayleigh factor has also been found to be highly dependent on the measurement concentration. Therefore, the precision in the estimation of molecular weight can be improved by calculating molecular weights at or near the optimal concentration, which is itself molecular weight-dependent. The one-point method is demonstrated for poly(methyl methacrylate)s of various polydispersities in tetrahydrofuran. The molecular weight of polystyrene and polystyrene-co-acrylic acid were also estimated by the one-point method in THF. In the case of the polystyrene-co-acrylic acid, THF becomes a poorer solvent with increasing levels of acrylic acid in the copolymer, and the parameter (A₂M^0.5) is found to vary with the copolymer composition, as is theoretically predicted. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1303–1316, 1997     

Infrared spectroscopic characterization of plasma-treated polyethylene

Thin polyethylene films cast on copper or gold were treated with low-pressure oxygen plasma. Changes in the chemical structure of these films were investigated by infrared spectroscopy using a reflection method in combination with chemical derivatization (CD) reactions. The potential of the CD is demonstrated for hydroxyl groups and carbonyl groups by the reaction with trifluoroacetic anhydride and hydrazine. The reaction conditions were varied to check for side reactions. The results of the derivatization are discussed in terms of secondary structures. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of ozonized polyethylene

Polyolefins (LDPE and HDPE) can be ozonized with ozone/air gas flow to create peroxide and hydroperoxide groups on polymers. These reactive groups can be used to initiate radical polymerization of vinylic monomers and produce graft copolymers. In this study, the optimization of the experimental conditions and the explanation of the phenomena occurring during the ozonization of polyolefins in a fluidized bed have been studied. The most reproducible methods for placing peroxide and hydroperoxide groups onto polyolefins are the iodometric method and indirect titration by thiol. This work shows that it is necessary to control the temperature of the fluidized bed to avoid the acceleration of the reaction and the degradation of the polymers. Then, we studied the effect of different parameters such as the crystallinity and the granulometry of polymers, the time of ozonization and the effect of the load of the reactor on the quality of ozonization. Infrared spectroscopy and steric exclusion chromatography were used to characterize the ozonized polymers. We show that double bonds of PE, particularly vinyl groups, are very reactive to ozone and that ozonized HDPE leads essentially to the formation of hydroperoxide groups, whereas ozonized LDPE leads to the formation of peroxide groups.     

High-temperature coupling of high-speed GPC with continuous viscometry. I. Long-chain branching in polyethylene

The coupling of a high-temperature liquid chromatograph (Waters 150C) with a home-made continuous capillary viscometer is described. This detector is the only one suitable for high-speed GPC when the small volume of the mobile phase prohibits the coupling with a classical viscometer. The pressure drop of the GPC effluent through the capillary is continuously measured along with the refractive index change. This dual detection leads to the determination of the intrinsic viscosity as a function of the elution volume, thus allowing a precise use of Benoit's universal calibration. The accuracy of our system is demonstrated in the case of the characterization of linear and branched polyethylene samples. The results concerning the average molecular weights as well as the branching factors (structure parameter g′ and long-chain branching frequencyλ) are in close agreement with those obtained by the classical way (coupling traditional GPC and discontinuous viscometry). It is well known that an estimate of the λ coefficient is extremely dependent on several hypotheses. However, for a set of commercial low-density polyethylenes, we obtained λ values about 0.5 × 10_?4, with no marked change along the molecular weight range.     

Coefficients of dynamic friction for low density polyethylene

The coefficient of dynamic friction is often the controlling factor for solids conveying, pressure generation, and thermal decomposition of a resin in the feed section of a single-screw plasticating extruder. The coefficients of friction are, however, very poorly understood, and the interpretation of the measurements are complicated by the dissipation of frictional energy at the sliding interface. A new instrument was recently built to help understand dynamic friction, and a numerical technique was developed to estimate the interface temperature. The coefficients of dynamic friction for a low-density polyethylene resin are presented in this paper as a function of the surface temperature, pressure, and velocity.     

High-temperature carbothermal synthesis and characterization of graphite/h-BN bimaterials

Hexagonal boron nitride (h-BN) and graphite have similar crystal structures, comparable lattice parameters, and coefficients of thermal expansion, but vastly different electrical and thermal transport. Despite their key differences, it is possible to couple h-BN and graphite in a bimaterial system allowing the unique properties of both materials to be utilized in a single component. Through a carbothermal reduction of B₂O₃ in nitrogen, the surface of graphite can be converted to h-BN. This results in a layered system that is electrically insulating on the surface due to h-BN, and more compliant as well as conductive within the substrate due to the graphite structural body. We discuss the high-temperature synthesis and characterization of this layered material, focusing on the processing–microstructure relationship as well as the interface of graphite/h-BN to assess the chemical and mechanical adhesion of the layers, and to establish how such properties are contingent on the reacting phase of B₂O₃. This is achieved by investigating the origin of h-BN formation and the unwanted side reaction of boron carbide formation, through the evaluation of the thermochemistry and kinetics governing the carbothermic reactions. We establish that a reaction temperature and holding time of 1700°C for 18 h produced the thickest h-BN layers which exhibited the highest fracture toughness over all lower temperature synthesis conditions.     

DSC and FTIR characterization of biodegradation of polyethylene

Aspergillus niger, a fungus, was used in the degradation of commercially available thermoplastic polyethylene films. Quantitative calorimetric measurements performed on as-received, abiotic, and biotic treated polyethylene samples, revealed that the amorphocity of the sample decreases during biodegradation. In addition, it was found that the external substrates (sucrose) in the growth medium influenced the biodegradation process of polyethylene. Furthermore, the crystallinity data on different biotreated samples indicated that the adapted microorganisms were able to metabolize a small portion of polyethylene. The significance of the Fourier transform infrared (FTIR) results of polyethylene samples have been discussed.     

Mechanical,dynamic mechanical,and thermal characterization of fly ash and nanostructured fly ash‐waste polyethylene/high‐density polyethylene blend composites

Disposal of polyethylene used as carry bags is the greatest challenge increasing day by day. Composite materials were prepared by mixing Fly ash (FA) and nanostructured fly ash (NFA) from thermal power station as filler and blends of Waste polyethylene (WPE)(carry bags) collected from municipal solid waste (MSW) with virgin high‐density polyethylene (HDPE) as matrix. Different modifications were induced to improve the overall properties of these composites. At first, the WPE/HDPE blend matrix was modified by grafting with maleic anhydride (MA) and the composite prepared with FA/NFA. Then, the WPE/HDPE‐FA/NFA composite as a whole was treated with electron beam irradiation at 250 kGy radiation dose and finally the FA/NFA filler was treated with radiation dose of 250 kGy and the composite prepared. Significant enhancement in tensile strength, flexural strength, flexural modulus, and hardness are observed for MA modified and irradiated composites, the increase being more prominent in irradiated composites. Furthermore, an increase in storage/loss moduli with enhanced thermal stability was observed with the addition of FA/NFA and upon modifications. The analysis of the tensile fractured surfaces by scanning electron microscopy was in well correlation with the mechanical properties obtained. In summary, after analyzing the effects of the three different modifications on mechanical, dynamic mechanical and thermal properties, the irradiation on to the WPE/HDPE‐FA/NFA composites investigated was selected as the most appropriate for future applications. POLYM. COMPOS., 37:3256–3268, 2016. © 2015 Society of Plastics Engineers     

低压高密度聚乙烯装置动态模拟模型开发策略浅谈

讨论了应用通用流程模拟软件AspenPlus、聚合物模拟软件PolymersPlus及动态模拟软件AspenDynamics开发低压高密度聚乙烯装置反应系统动态模型的策略和方法。     

Steady flow and dynamic viscoelastic properties of branched polyethylene

The presentation of viscoelastic properties of molten high polymers in a complex plane makes three characteristic rheologic parameters appear. These are examined for a series of commercial samples of low density polyethylene. For instance, it enables products to be recognized which are very similar as far as the melt index is concerned but have different molecular weight distribution, different long chain branching index and consequently different processing properties.     

Viscoelastic material characterization and modeling for polyethylene

An extensive set of stress relaxation and constant strain rate tests for characterizing the mechanical responses of a medium density polyethylene and a high density polyethylene that are commonly used in natural gas distribution piping is described and analyzed. The development of coherent master curves for the relaxation modulus, maximum stress, and the time-to-failure for pressurized pipes through a combination of both horizontal and vertical shifting is presented. The relaxation data are used to develop a nonlinear Viscoelastic material model. The model is assessed by making comparisons of the predicted stress-strain response with the measured response in the constant strain rate tests.     

双向拉伸聚乙烯的微观结构及热学表征

采用红外光谱、核磁共振波谱和高温凝胶色谱对2个双向拉伸聚乙烯试样(分别记作M1,M2)的链结构进行了表征,确定了试样的共聚单体类型、支化度、相对分子质量及其分布。利用差示扫描量热法(DSC)研究了试样的熔融和结晶行为。通过连续自成核退火热分级法测定了不同共聚物中亚甲基序列长度(MSL)的分布。结果表明:M1以短链支化为主,M2则以长链支化为主;M1的总支化度略高于M2,与红外光谱测试结果一致;MSL分布随MSL的增加呈单调递增趋势,M2的MSL集中在198,其峰面积占总峰面积的52.4%;M1的MSL分布呈现2个峰值,在MSL为61处有小峰,峰面积占总峰面积的8.3%,MSL为273处的峰面积占总峰面积的35.1%,与DSC测试的双熔点相对应。     

Formation and characterization of thiourea encapsulated polyethylene oxide

The structure and dynamics of PEO chains encapsulated in thiourea (TU) channels formed in the PEO-TU-inclusion compound (PEO-TU-IC) were studied by XRD, FTIR and solid state NMR spectroscopy. XRD and FTIR observations clearly show PEO-TU-IC adopts a crystal structure different from neat thiourea, and the usual rhombohedral crystal structure of thiourea small molecule ICs. PEO chains in the channel adopt a conformation similar to bulk PEO, as confirmed by solid state NMR spectroscopy. Contact-time array (VCT) NMR profiles shows that PEO chains in the TU channels are considerably more mobile than in bulk PEO. Infrared bands for the PEO shift in the IC, and these were attributed to changes in the secondary forces.     

端烯基聚醚大分子单体的合成及表征

用三乙胺为催化剂,叔碳酸缩水甘油酯的环氧基与甲基丙烯酸的羧基进行反应,生成的羟基继续与环氧基团反应,得到聚醚大分子单体。研究了反应时间、反应温度、催化剂用量对叔碳酸缩水甘油酯单体转化率的影响,对合成的大分子单体进行了IR1、H-NMR表征。结果表明,反应单体的配比对叔碳酸缩水甘油酯的转化率有较大的影响,且反应过程中,甲基丙烯酸单体的转化率也会因不同的反应条件而有所变化。适宜的反应条件为90℃,反应10 h,催化剂用量为反应单体总质量的5%,叔碳酸缩水甘油酯的转化率可以达到76.83%。     

Size-exclusion chromatography with two-angle laser light-scattering (SEC-TALLS) of high molecular weight and branched polymers

The accuracy and precision of results obtained from light-scattering detection at two angles (TALLS) for size-exclusion chromatography (SEC) are examined for linear narrow molecular weight distribution polystyrenes between 1,290,000 and 20,000,000 MW and for branched polyesters. The ratio of light-scattering intensities at 15° and 90° is used to calculate weight-average molecular weight, M?_w, and an average root-mean-square radius, r?_gu, equivalent to the z-average radius. A shape for the polymer molecule is assumed and an analytical relationship for the particle-scattering function is required. It is shown that analysis of the data using the particle-scattering function for a random coil is valid for both high molecular weight, linear polystyrenes and long-chain branched polyesters. The radius, r?_gu, is determined with high precision by using the ratio of light-scattering signals, which is insensitive to errors in sample concentration and changes in the eluent flow rate. The correct average radius for the whole polymer is obtained despite using low-efficiency, large-particle diameter SEC columns; however, axial dispersion significantly affects molecular weights and radii calculated at each retention volume that can limit the utility of plots used to deduce polymer conformation. © 1995 John Wiley & Sons, Inc.     

Surface characterization of polyethylene films modified by gaseous plasma

Of the several techniques available for surface modification, plasma processing has proved to be very appropriate. The low temperature plasma is a soft radiation source and it affects the material only over a few hundred angstroms deep, the bulk properties remaining unaffected. Plasma surface treatment also offers the advantage of greater chemical flexibility. The improvement in adhesion was studied by measuring T‐peel strength. In addition, printability of plasma‐treated PE films was studied by cross test method. It was found that printability increases considerably for plasma treatment of short duration. It was therefore thought of as interesting to study the surface composition and morphology by contact angle measurement, ESCA, and AFM. Surface energy and surface roughness can be directly correlated to the improvement in above‐mentioned surface‐related properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 449–457, 2007     

Preparation and characterization of microporous polyethylene hollow fiber membranes

Microporous polyethylene (PE) hollow fiber membrane with a porosity of 43% and N₂ permeation of 4.96 cm³ (STP)/cm² s cmHg was prepared by melt‐spinning and cold‐stretching method. It was found that PE with a density higher than 0.96 g/cm³ should be used for the preparation of microporous PE hollow fiber membranes. By increasing the spin–draw ratio, both the porosity and the N₂ permeation of the hollow fiber membranes increased. Annealing the nascent hollow fiber at 115°C for 2 h was suitable for attaining membranes with good performance. By straining the hollow fiber to higher extensions, the amount and size of the micropores in the hollow fiber wall increased, and the N₂ permeation of the membranes increased accordingly. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 203–210, 2002; DOI 10.1002/app.10305