ON THE ORIGIN OF 628 nm FLUORESCENCE IN CERTAIN CHLOROPHYLL PREPARATIONS

Abstract— A fluorescence band at 628 nm seen in certain preparations of chlorophyll on polyethylene particles swollen with tetradecane comes not from an impurity of protochlorophyll in the original chlorophyll, but from a substance like protochlorophyll formed upon adsorption of chlorophyll to the particles. Much of the chlorophyll is grafted to polyethylene in the same particles by a process that does not affect the chromophore. These and other properties peculiar to the particles are tentatively ascribed to a prior free radical oxidation process in the swollen particles.     

Contact angles of submillimeter particles: connecting wettability to nanoscale surface topography

A method is presented for the measurement of contact angles of particles in the size range 100-1000 microm, using an optical microscope. This method is used to characterize the wettability of polyethylene particles produced in a gas-phase polymerization process. The as-polymerized particles are shown to be significantly more hydrophobic than melt-processed polyethylene materials. The surface structure of the particles is examined with scanning electron microscopy, and the increased hydrophobicity of the as-polymerized particles is attributed to the nanoscale texture of the particle surfaces.     

Reinforcement of Polyethylene by Surface-Modified Kaolins

The tensile and impact strength of kaolin-filled polyethylene was found to be dependant on the modulus of the matrix in the vicinity of the filler surfaces and the strength of the filler-matrix bonds, as well as on the degree of dispersion of the kaolin particles on the polyethylene. Improved reinforcement was obtained by the use of novel fillers consisting of kaolin particles encapsulated with high-modulus, surface-bonded, reactive oxyaluminum acylate polymers.     

SiO2/Cr monolayers and formation of polyethylene films

1,3,5-tribenzylhexahydro-1,3,5-triazine-CrCl3 (TAC-CrCl3) was supported on monodisperse St?ber silica and on commercial silica particles. The monolayers of these catalyst particles were successfully prepared with Langmuir-Blodgett technique. The effect of TAC-CrCl3 molecules on the ordering and film-forming of the silica particles was investigated. The particles arrange in domains of hexagonal ordering, but the ordering of particles in the monolayer decreases with increasing Cr loading. These hybrid monolayers are active polymerization catalysts. After polymerization, a relatively rough layer of polyethylene molecules covers the catalyst monolayer and this layer is hydrophobic. The monolayers and the polymers coating films were characterized by IR, UV-vis-NIR, and SEM. The method provides a way to fabricate polyethylene films on silica monolayers.     

Processability of a metallocene‐catalyzed linear PE improved by blending with a small amount of UHMWPE

The processability of a metallocene‐catalyzed polyethylene blended in the melt with low amounts of ultra‐high molecular weight polyethylene was evaluated. Our morphological and thermal studies revealed that the blends were structurally heterogeneous, formed by a matrix of metallocene polyethylene and homogeneously distributed particles of ultra‐high molecular weight material. The visible particles were smaller than those of the reactor powder. Also observed was some degree of interaction between both phases. Rheological data indicated an intense effect of morphology on viscoelastic functions, beyond that expected for a system composed of noninteractive phases. Collectively, our findings suggest the existence, to some extent, of a homogeneous phase at the molecular level composed of a fraction of ultra‐high molecular weight species and metallocene polyethylene. This gives rise to a striking behavior during processing in that the blends show improved extrusion performance the higher their ultra‐high molecular weight polyethylene content. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2963–2971, 2005     

Crystallization characteristics of polymer blends. I. Polyethylene and polystyrene

Blends of polyethylene and polystyrene have been prepared to study the effect of the morphology on their crystallization characteristics since the polymers are known to phase separate. The polymer component present in least amount formed a dispersed phase of discrete spherical particles whose number and size altered with blend composition. However, close to 50% composition cylindrical rods of polyethylene dispersed in polystyrene were observed. With polyethylene in excess the kinetics of crystallization were insensitive to the morphology, but with polyethylene present as the dispersed phase they became dependent on the size and number of the spheres, and in particular on the nucleation density. When the number of spherical particles exceeded that of heterogeneous nuclei, larger supercoolings, and so presumably homogeneous nucleation, were required for crystallization to develop further. The degree of crystallization of the blends then became dependent on the temperature of crystallization rather than on time, and the isothermal crystallization appearing to be instantaneous.     

聚丙烯接枝马来酸酐/SiO_2复合载体型钛催化剂及其聚乙烯的形态研究

扫描电子显微镜(SEM)是研究材料形态、形貌的强有力工具,并广泛用于载体催化剂的研究[1～4].在工业化的烯烃聚合催化剂中,通常需要首先进行负载化,由于无机和有机载体各自具有特殊的优点并存在一些不利因素,如何利用不同类型载体进行复配获得性能优良的复合载体,已成为烯烃聚合催化剂载体化研究的一个重要方向.本工作合成了聚丙烯接枝马来酸酐(PMA)/SiO2复合载体,负载了TiCl4作为烯烃聚合催化剂,既可以避免由纯无机物为载体而引入过多的无机灰分,又能克服仅用聚合物为载体而造成的负载率不高的缺点,同时保持了无机载体固有的刚性和聚合物载体官能团多分布性的特点.该类复合载体制备工艺简单,原料易得,成本较低.为获得复合载体化催化剂形态及其对聚合产物形态影响的信息,我们采用扫描电子显微镜(SEM)跟踪催化剂和聚合物的形态,本文将报道该研究的初步结果.     

Effect of conductive particles on the mechanical,electrical, and thermal properties of maleated polyethylene

Inclusion of conductive particles is a convenient way for the enhancement of electrical and thermal conductivities of polymers. However, improvement of the mechanical properties of such composites has remained a challenge. In this work, maleated polyethylene is proposed as a novel matrix for the production of conductive metal–thermoplastic composites with enhanced mechanical properties. The effects of two conductive particles (iron and aluminum) on the morphological, mechanical, electrical, and thermal properties of maleated polyethylene were investigated. Morphological observations revealed that the matrix had excellent adhesion with both metal particles. Increase in particle concentration was shown to improve the tensile strength and modulus of the matrix significantly with iron being slightly more effective. Through‐plane electrical conductivity of maleated polyethylene was also substantially improved after adding iron particles, while percolation was observed at particle contents of around 20–30% vol. In the case of aluminum, no percolation was observed for particle contents of up to 50% vol., which was linked to the orientation of the particles in the in‐plane direction due to the squeezing flow. Inclusion of particles led to substantial increase (over 700%) in the thermal conductivities of both composites. The addition of high concentrations of metal particles to matrix led to the creation of two groups of materials: (i) composites with high electrical and thermal conductivities and (ii) composites with low electrical and high thermal conductivities. Such characteristics of the composites are expected to provide a unique opportunity for applications where a thermally conductive/electrically insulating material is desired. Copyright © 2015 John Wiley & Sons, Ltd.     

Thiol-ended polyethylene oxide as reactive stabilizer for dispersion polymerization of styrene

 Radical dispersion polymerization of styrene in aqueous ethanol solutions was performed in the presence of a new reactive polyethylene oxide stabilizer with thiol end groups. This reactive stabilizer was compared to the more conventional poly (N-vinyl pyrrolidone). Particles size distribution, molecular weights and kinetics were investigated. Monodispersed polymer particles with diameter in the range 200–2000 nm were obtained depending on the amount of stabilizer used. In all cases, the polyethylene oxide (PEO) sequence of the dispersant was partly incorporated at the surface of the latex particles, but the grafting yield of polyethylene oxide chains was always limited and did not exceed 15%. Part of the stabilizer being unreacted or reacted with low molecular weight polystyrene remained in the continuous phase. Received: 26 September 1996 Accepted: 4 March 1997     

Compatibilisation of polyethylene/ground tyre rubber blends by γ irradiation

In the present work, γ irradiation is used for the in situ compatibilisation of blends of recycled high density polyethylene (rHDPE) and ground tyre rubber (GTR) powder. The expected compatibilisation mechanism involves the formation of free radicals, leading to chain scission within rubber particles, crosslinking of polyethylene matrix and co-crosslinking between the two blend components at the interface. While uncompatibilised rHDPE/GTR blends show poor mechanical properties, especially for elongation at break and Charpy impact strength, irradiation leads to a significant increase of these mechanical performances. Such behaviour is attributed to the development of an adhesion between GTR particles and the surrounding thermoplastic matrix. This conclusion is supported by in situ scanning electron microscopy observations during microtensile tests, showing strong elongation of GTR particles upon deformation of irradiated blends.     

A new extraction method for the preparation of zinc oxide nanoparticles in aqueous two-phase systems

An extraction method was suggested for the preparation of differently shaped nano- and micrometer- sized zinc oxide particles at the interface boundary of aqueous two-phase systems based on polyethylene glycol (polyethylene oxide) and sodium sulfate using NaOH and aqueous ammonia as precipitating agents.     

Thermal analysis of thermoplastic elastomers based on recycled polyethylenes and ground tyre rubber

Thermal stability and phase structure of thermoplastic elastomers (TPEs) based on post-consumer materials such as recycled lowor high-density polyethylene and ground tyre rubber (GTR) were investigated by using TG, DSC and DMTA analysis. Preliminary reclamation of GTR leads to enhancement of compatibility between polyethylene matrix and dispersed GTR particles.     

Thermal, mechanical and electrical properties of copper powder filled low-density and linear low-density polyethylene composites

Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) with different copper contents were prepared by melt mixing. The copper powder particle distributions were found to be relatively uniform at both low and high copper contents. There was cluster formation of copper particles at higher Cu contents, as well as the formation of percolation paths of copper in the PE matrices. The DSC results show that Cu content has little influence on the melting temperatures of LDPE and LLDPE in these composites. From melting enthalpy results it seems as if copper particles act as nucleating agents, giving rise to increased crystallinities of the polyethylene. The thermal stability of the LDPE filled with Cu powder is better than that for the unfilled polymer. The LLDPE composites show better stability only at lower Cu contents. Generally, the composites show poorer mechanical properties (except Young's modulus) compared to the unfilled polymers. The thermal and electrical conductivities of the composites were higher than that of the pure polyethylene matrix for both the LDPE and LLDPE. From these results the percolation concentration was determined as 18.7 vol.% copper for both polymers.     

一类新型PTC复合材料的制备及性能

一类新型ＰＴＣ复合材料的制备及性能杜伟坊,杜海清（湖南大学材料科学及应用化学研究所,长沙,４１００８２）关键词正温度系数,聚乙烯,ＹＢａ_２Ｃｕ_３Ｏ_（７－ｘ）具有正温度系数（ＰＴＣ）的材料在其转化温度附近具有电阻率大幅度上升的特点,因而在温度检测与?..     

Compatible Polyethylene/Polyvinyl Chloride Particle Hybrids Prepared by in‐situ Polymerization

Polyethylene/polyvinyl chloride (PE/PVC) hybrids were successfully prepared by a polymerization‐filling method. The catalyst for ethylene polymerization was supported on PVC particles, and ethylene was then polymerized in‐situ on the surface of the activated PVC. PVC particles could be well segmented and dispersed during in‐situ polymerization, and the prepared hybrids had an additional tangent peak between the glass transitions of polyethylene and PVC, indicating the formation of a compatible interlayer between nascent polyethylene and PVC during polymerization.     

聚合所得初生聚乙烯的晶型

聚合所得初生聚乙烯的晶型伍青，张启兴，卢泽俭，王海华，欧阳巍，林尚安，张光华（中山大学高分子研究所，广州，５１０２７５）（中国科学院广州化学研究所）关键词聚乙烯，结晶，单斜晶，颗粒形态热力学稳定的聚乙烯晶型为正交晶系［１］．当聚乙烯受一定应力作用时如...     

Transformation of the surface structure of a thermosensitive layer by flash illumination. Electronmicroscopical observations

Summary The transformation of the surface structure of a thermosensitive layer by flash-exposure was studied by electronmicroscopical methods. The heat-sensitive layer consists of a mixture of polyethylene particles, carbon black and wetting agents dispersed in a watersoluble binding agent. The characteristic difference in structure of the exposed layer points to a melting of the polyethylene; drastic changes in the properties of the material are observed.     

Deformation behavior of composites based on low-density polyethylene and hollow glass spheres

The mechanical properties of composites of low-density polyethylene with hard particles were examined.     

NMR relaxation and pulsed-gradient diffusion study of polyethylene nanocomposites

We performed pulsed-gradient spin-echo nuclear-magnetic-resonance (NMR) experiments on zinc oxide filled polyethylene. The molecular weights of the polyethylene samples ranged between 808 and 33,000 gmol, and four different zinc oxide samples were used: 27-, 33-, 51-, and 2500-nm-diameter particles. The results of these experiments showed that the diffusion coefficients of the polyethylene chains did not change with nanofiller content, but a drastic change is observed in the NMR relaxation spectrum in spin-spin-relaxation experiments. At fixed zinc oxide content and polyethylene molecular weight (close to entanglement), the system with the smallest zinc oxide showed the most rigid environment. At high polyethylene molecular weights, this effect was still observable but the difference between the three investigated systems was very small, suggesting that the system was dominated by entanglements.     

Establishment of a novel in vitro test setup exposing adherent cells to wear particles made of polyethylene

Wear debris from endoprostheses leads to osteolysis and causes aseptic loosening. Cellular interactions with ultra-high-molecular-weight polyethylene (UHMW-PE) particles are rarely described because of the difficulty of incubation of adherent cells with floating polyethylene particles in vitro.The aim of this study was to develop a technique for analysing interactions of adherent cells with UHMW-PE particles in vitro. Therefore, different volumes of a wear particle suspension, generated in a standard hip wear simulator, were digested and filtered through polycarbonate filters. The filters were applied to cell culture inserts cultivated with human osteoblasts. Particle analysis resulted in a significant reduction of particle numbers in different suspension volumes.Exposure to the highest particle density resulted in a significant decrease of collagen 1 synthesis as well as a tendency for increasing matrix metalloproteinase-1 (MMP-1) production. Therefore, involvement of osteoblasts in matrix degradation due to wear debris can be assumed.