Fractionation of Linear Polyethylene with Gel Permeation Chromatography. Part III

Abstract

Many commercial linear polyethylenes have very broad distributions of molecular weight. The high molecular weight fractions often extend beyond the highest molecular weight calibration standard of GPC. For this reason the reliability of information obtainable from GPC has been examined with attention to the average molecular weights. Calibration range is a serious limitation for the accurate determination of the - weight-average and the higher averages of molecular weight. Uncertainty in the baseline at the high molecular weight region, however, does not produce a significant error. With a four-column GPC having 10³ to 10⁷ A nominal capacity, improved resolution is needed in the high molecular weight range. In order to examine the resolution and to improve the calibration, a polyethylene standard of ca. 3–4 million molecular weight is required. With the present limitation of GPC the greatest amount of information can be obtained by examining and intercomparing the cumulative distribution curves. With this representation ca. 95% or more of the cumulative weight range is free from uncertainty in calibration and resolution. A question is raised as to whether melt index is precisely a function of the weight-average molecular weight. This question is pertinent when significantly different molecular weight distributions are involved. GPC offers an opportunity to resolve the question.     

Room Temperature Curing Epoxy Adhesives for Elevated Temperature Service. Part III. The Effect of Silane Coupling Agents

The effect of silane coupling agents incorporated into the bulk of previously-developed room-temperature-curing epoxy adhesives^8,9,10 was studied. The physical and mechanical properties of corresponding aluminum bonded joints were characterized in ambient and humid-hot environments. Experimental results have demonstrated significant advantages of silane addition to the performance of these epoxy adhesives, especially under exposure to humid atmosphere. Thermal analysis of the polymerization processes, taking place during curing of the various low-temperature-curing formulations containing silane coupling agents, indicates that curing is not complete after seven days at room temperature, showing an exotherm at 80-100°C and a residual small one at 120°C. The basic formulation, comprising a tetra- and trifunctional epoxy resin blend and a multifunctional amine and ATBN cross-linking mixture, developed a three-phase matrix-rubber microstructure when the silane was added to the system.     

Room Temperature Curing Epoxy Adhesives for Elevated Temperature Service. Part III. The Effect of Silane Coupling Agents

The effect of silane coupling agents incorporated into the bulk of previously-developed room-temperature-curing epoxy adhesives^8,9,10 was studied. The physical and mechanical properties of corresponding aluminum bonded joints were characterized in ambient and humid-hot environments. Experimental results have demonstrated significant advantages of silane addition to the performance of these epoxy adhesives, especially under exposure to humid atmosphere. Thermal analysis of the polymerization processes, taking place during curing of the various low-temperature-curing formulations containing silane coupling agents, indicates that curing is not complete after seven days at room temperature, showing an exotherm at 80-100°C and a residual small one at 120°C. The basic formulation, comprising a tetra- and trifunctional epoxy resin blend and a multifunctional amine and ATBN cross-linking mixture, developed a three-phase matrix-rubber microstructure when the silane was added to the system.     

用于中间控制的复混肥中总养分快速测定方法的对比研究

选择合适的方法进行系列条件试验,建立了复混肥总养分的快速测定方法。与国标法相比,该方法操作更加简便,能使复合肥总养分的测定时间由6h缩短至2h以内。通过对比试验、精密度试验和回收率试验,验证了复混肥总养分快速测定方法准确可靠。     

高聚物玻璃化转变温度测定不确定度的评估

根据ISO 11357-2-2020《塑料-差示扫描量热法（DSC）-第2部分:玻璃化转变温度和高度的确定》,对高聚物玻璃化转变温度测定进行了不确定度评估。分析了测试过程中不确定度的主要来源,计算出各分量的不确定度,得出合成不确定度和扩展不确定度。结果表明：影响结果不确定度的主要因素为样品的不同批次和随机采样2个分量;该评估方法可以为测定结果的科学表达提供依据。     

Determination of the Melting Point and Glass Transition Temperature of Polymers with the Lattice Model

The melting point and glass transition temperature of polymers is estimated with the lattice model of the bulk polymer phase. The good agreement of the predictions of the theory and the experimental findings on melting of polyethylene is demonstrated. The dependence between the melting point and glass transition temperature of polymers is obtained with the statistical thermodynamic theory and is in good agreement with the experimental data.__________Translated from Khimicheskie Volokna, No. 1, pp. 33–35, January–February, 2005.     

High Temperature Thermal Field-Flow Fractionation for the Characterization of Polyethylene

Abstract

A thermal field-flow fractionation device has been constructed in which the cold wall can be held above 100°C. The apparatus is described. Preliminary results are given which illustrate the retention of polyethylene and polypropylene. Details are provided of preliminary experiments intended to determine the molecular weight averages and molecular weight distribution of a National Bureau of Standards polyethylene sample, SRM 1484. The lack of monodisperse, well-characterized calibration standards is considered a major problem. Nonetheless, good agreement is found with published values for number average and weight average molecular weight.     

Morphology evolution in polytetrafluoroethylene as a function of melt time and temperature. Part III. Effect of prior deformation

In parts I and II the effect of melt time and temperature on dispersed dispersion particles of various molecular weights was described: substantial molecular motion on the substrate occurs with the development of both planar folded chain single crystals, and single molecule single crystals and banded structures with parallel double-striations oriented along the long axis of the crystal or band. The molecules in the single molecule single crystals and bands are parallel to the substrate, an individual double-striation appearing to consist of a ‘double edge’, folded chain, lamella more or less normal to the substrate. In this paper, the effect of deformation and subsequent heat treatment of the nascent particles is described. Similar to the known effect of deformation of compacted nascent PTFE dispersion particles, large scale shear of dispersed dispersion particles can lead to nano-fibrils of indefinite length for both standard size resins and nano-emulsions, of both high and low molecular weight. Sintering of the nano-fibrils in contact with the substrate leads to the development of shish-kebab structures with the nano-fibril as a core and epitaxially nucleated, ‘double edge’, folded chain single crystal kebabs oriented perpendicular to the fibril axis and the substrate. No change is seen in similar fibrils remaining suspended between the dispersion particles. The molecules forming the ‘kebabs’ have ‘wandered’ individually on the substrate (glass) before attaching to the growing kebabs.     

The Effect of Temperature of Test on the Adhesion of Polyethylene Coatings Applied to Metals as a Hot Melt

The adhesion of polyethylene coatings applied as a hot melt to steel, zinc and copper with various surface pretreatments has been studied over a temperature range from ambient to 70 or 80°C. Tensile properties and tear strength of the polymer itself were measured over the same temperature range. Substrates which give high adhesion at room temperature give a fall in adhesion with temperature. This can be understood in terms of a fall in fracture energy of the polymer as indicated by tensile and tear tests. Substrates which give low adhesion at room temperature show first a significant rise and then a fall in adhesion as temperature is raised. Examination of the fracture surfaces by electron microscopy shows a progressive increase in plastic deformation of the polymer as the adhesion rises. The rise in adhesion and change in failure mode are interpreted in the light of the change in mechanical properties of the polymer. The adhesion maxima are not viscoelastic in origin as time-rate equivalence was not observed.     

谷胱甘肽包覆的碲化镉量子点荧光探针法快速测定多巴胺

利用多巴胺(DA)对谷胱甘肽包覆的碲化镉量子点荧光的猝灭作用,建立了快速测定多巴胺的荧光探针分析法。实验结果表明,在Tris-HCl(p H=7.0)溶液中,多巴胺浓度在0.06~2.1μmol/L范围内,碲化镉量子点荧光强度的猝灭值(ΔF)与多巴胺的浓度呈线性关系,线性方程ΔF=165.43cDA+9.57,相关系数(r)0.998 6,方法检出限0.03μmol/L。将本方法应用于样品中DA的分析,RSD为4.2%,DA的加标回收率为95.2%~104.8%。     

New Aspects of Impact Reactivity of Polynitro Compounds,Part III. Impact Sensitivity as a Function of the Imtermolecular Interactions

Published data of impact sensitivity of 33 polynitro compounds detected by sound were expressed as the drop energy, E_dr, required for 50 percent initiation probability. A logarithmic relationship has been found between the E_dr values and heats of fusion of the said compounds. The relationship has been found to be in accordance with the idea concerning the role of plastic deformations of crystal played in the initiation of energetic materials by impact and shock. An analogous application of heats of sublimation has not given convincing results.     

考虑变比热的平板注塑件非对称冷却瞬态温度场数值模拟

对注塑平板制件非对称冷却过程进行了分析,通过近似假设,建立一维非稳态传热模型。考虑无定形聚合物和结晶型聚合物的比热对温度的依赖性,利用分段线性函数拟合聚合物的比热-温度曲线,通过对空间域和时间域的离散化,运用有限差分数值方法,模拟了无定形聚合物和结晶型聚合物注塑平板制件在模具中非对称冷却的一维瞬态温度场。     

Synthesis of 3,5-Disubstituted Isoxazolines as a Template for Liquid-Crystalline Polymers

Summary The synthesis and mesomorphic properties of new polyacrylate liquid crystals 3,5-disubstituted isoxazolines 8a-d are discussed. 1,3-Dipolar cycloadditions of nitrile oxides generated in situ from oximes 2a-b in the presence of 4-substituted styrene 3 (X = Br, Cl and CH₃) provided 3,5-disubstituted isoxazolines 5a-d. The monomers 7a-d were submitted to AIBN conditions and all the final polymers showed a stable nematic phase. The mesophase stability was dependent on the spacer length and terminal group at mesogenic core. Also, a small molecular weight effect was observed.     

交联聚乙烯的交联度简易测定法

<正> 聚乙烯在工业和民用上有着广阔的前途,但是聚乙烯本身也存在着许多缺陷。交联聚乙烯是利用化学或物理方法,使聚乙烯分子由原来直链状结构变为三度空间网状结构。由于结构的改变,分子量增大了,这使交联聚乙烯保持了聚乙烯所有的优良性能,从而也克服了聚乙烯耐热性差、热变形大、耐药物腐蚀性差、内应力开裂等方面的缺陷(见表1)。     

活性颗粒固定架床层压降的实验测定

设计制作了多种型号活性颗粒规整固定架 ,对是否装填活性颗粒固定架的压降性能进行了测试。结果表明干塔床层压降较小 ,湿床层压降较大。对活性颗粒不同装填方式的流体力学性能测试表明 :活性颗粒散堆在床层中压降最大 ,装填在固定架中床层压降降低比较明显。床层压降也受固定架空隙率、波纹倾角等结构参数的影响     

Porosimeter as a Means to Measure the Compactibility of Powders

Samples of silica fume ponder prepressed in the form of slabs under relatively small pressures and cut in spheres were coated with a thin flexible latex film by dipping them into the water emulsion of the natural latex, and their densification behavior was studied using the common mercury intrusion porosimeter. The samples were compacted at isostatic pressure conditions by increasing the mercury pressure, and the volume changes as a function of pressure were recorded. The recorded pressure/volume changes provided information about the compaction course of the original green powder compacts in a continuous fashion.     

Graphene Oxide as a Prospective Graft in Polyethylene Glycol for Enhancing the Toughness of Epoxy Nanocomposites

Polyethylene glycol (PEG) was successfully grafted onto the surface of graphene oxide (GO) by the “grafting to” technique. PEG, GO as well as the PEG grafted GO (GO-g-PEG) was successfully incorporated into an epoxy matrix and subsequently cured using diethylenetoluenediamine (DETDA) to make epoxy nanocomposites. Mechanical, thermal, and rheological properties of the epoxy nanocomposites were studied to check the effectiveness of these fillers in the epoxy matrix. An improvement of 255% and 334% at a very low filler loading of about 0.1 wt% was observed in the fracture toughness of GO and GO-g-PEG loaded systems versus the neat epoxy. Toughening mechanisms are also explained by analyzing SEM images of the fractured surface. Modeling of rheological properties was carried out by following time-independent Newtonian model. The homogeneity of the epoxy filler systems are explained with the help of Cole–Cole plots. The thermal stability of the filler loaded epoxy composites was examined in detail by TGA. Improvements in mechanical properties reveal the potential benefit of the grafting process in epoxy toughening. POLYM. ENG. SCI., 60:773–781, 2020. © 2020 Society of Plastics Engineers