Filamentary extrusion of microcellular polymers using a rapid decompressive element

An extrusion process for manufacturing microcellular plastics is presented. In the past, microcellular structures have been produced in batch processes by using a thermodynamic instability of a polymer/gas system. In order to utilize such a thermodynamic instability in a continuous extrusion process, a large amount of gas must be dissolved quickly in a molten plastic flowing in the machine, and a rapid drop in the gas solubility must be induced in the flowing polymer/gas solution. Since the solubility of a gas in a polymer is a sensitive function of pressure, a thermodynamic instability for producing a microcellular structure can be induced by rapidly lowering the pressure. This paper presents a means for continuously forming the polymer/gas solution at an industrial processing rate and a means of nucleating microcells in the polymer/gas solution using a nozzle. Finally, a process model for controlling the cell morphology is presented by identifying the key parameters that control microcellular foaming in a continuous process. The experimental results agree with theoretical analyses, confirming the fact that the processing pressure strongly affects the microcellular foaming process through its effects on the amount of gas dissolved in the polymer and the magnitude of the pressure drop in the nucleation device.     

Anisotropy in nanocellular polymers promoted by the addition of needle‐like sepiolites

This work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needle‐like nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a two‐step gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needle‐like sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420 nm and cell nucleation densities of 10¹³–10¹⁴ nuclei cm^?3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of well‐dispersed sepiolites in the solid nanocomposites. © 2019 Society of Chemical Industry     

Amorphous and crystalline morphologies in glycolic acid and lactic acid polymers

This paper describes an investigation of a number of parameters which affect the physical structures of glycolic acid (GA) and lactic acid (LA). It has been found that the cooling rate of a quenching process determines the amorphous-crystalline morphology balance, and that the effect of a similar quenching process will vary with the molecular weight of the polymer. At very high molecular weights, even very rapid quenching does not produce higher degrees of amorphous phase. Copolymerization of PGA or of PLA with poly(ethylene oxide) results in either phase blending or phase separation, depending on the copolymer composition and the segmental chain length. The degree of crystallinity of the PGA or PLA component in the copolymer is mostly affected by copolymerization in a state of phase blending.     

形貌可控的银纳米颗粒合成及应用

银纳米材料具有独特的物理性质,在光学、生物和催化等领域应用潜力巨大,是近年来材料领域的研究热点。银纳米材料的很多性能与其形貌密切相关,如枝状银纳米颗粒局部表面等离子体共振较强,不同形貌的银纳米颗粒裸露不同的晶面,导致其催化选择性不同。因此,控制合成特定形貌和结构的银纳米颗粒一直是该领域的重要研究方向。本工作综述了近年来银纳米颗粒形貌可控的合成方法,包括溶液还原法、晶种法、生物合成法、光诱导法、反应-扩散调控的动力学法和模板法等,比较了不同方法的优缺点,分析了不同合成方法的机理。重点介绍了基于反应和扩散调控的动力学方法,总结了其优点和普适性。调研了不同形貌银纳米颗粒在抑菌、局部等离子体共振和催化等领域的应用研究,分析了不同形貌银纳米颗粒的工业化应用前景,并对银纳米形貌的可控合成和应用进行了展望。     

Effect of the crystallinity and morphology on the microcellular foam structure of semicrystalline polymers

Microcellular foam processing of polymers requires a nucleated cell density greater than 10⁹ cells/cm³ so that the fully grown cells are smaller than 10 μm. A microcellular foam can be developed by first saturating a polymer sample with a volatile blowing agent, followed by rapidly decreasing its solubility in the polymer. In general, the cellular structure of semicrystalline polymer foams is difficult to control, compared to that of amorphous polymer foams. Since the gas does not dissolve in the crystallites (1), the polymer/gas solution formed during the microcellular processing is nonuniform. Moreover, the bubble nucleation is nonhomogeneous because of the heterogeneous nature of the semicrystalline polymer. In this paper, the effects of the crystallinity and morphology of semicrystalline polymers on the microcellular foam processing and on the cellular structure of products are investigated. First, polymer specimens with various crystallinities and morphologies were prepared by varying the cooling rate of the polymer melt. Then, the solubility and diffusivity of the blowing agent in and through specimens were studied. The specimens with differing crystallinities and morphologies were foamed and their cellular structures were compared. The experimental results agree with theoretical predictions, indicating that the crystallinity and morphology of semicrystalline polymers exert a strong influence on the foam processing and the structure of the product.     

Periodic mesoporous silica and organosilica with controlled morphologies as carriers for drug release

In this paper, we report the effects of morphology, wall composition of mesoporous materials and different buffer solutions on drug delivery profiles. Hollow spheres of periodic mesoporous organosilica (PMO) were prepared and used as drug carriers which exhibited higher loading capacity and slower release rate compared to the conventional periodic mesoporous silica (PMS) spheres and solid spheres of PMO. This hollow PMO showed promising properties as a reservoir to encapsulate and store larger quantities of guest molecules within its “empty” core. Moreover, its organic reactive sites allowed stronger interactions to the hydrophobic guest molecules, in contrast to inorganic wall possessed by PMS materials. Antibiotic tetracycline was used as a model drug to study the effect of framework difference between PMO and PMS materials on the loading and release processes. Two kinds of release medium, simulated body fluid (SBF) solution (pH 7.4) and phosphate buffer (PB) solution (pH 1.5) were used in this study, which revealed very different release profiles. A slower delivery rate was observed in SBF solution, attributed to the different ionic interactions between the guest molecule and the host material in the two different pH solutions. Overall, hollow PMO shows the lowest release rate and the highest loading amount compared to the other two materials studied herein. The kinetic study reveals that drug release from host material follows the second order kinetic model better than the first order mass transfer model.     

Effect of the pressure drop rate on cell nucleation in continuous processing of microcellular polymers

Microllular plastics are cellular polymers characterized by cell densities greater than 10⁹ cells/cm³ and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth.     

Enhanced conductivity of polyaniline in the presence of nonionic amphiphilic polymers and their diverse morphologies

Poly(ethylene oxide) (PEO) and its copolymers have excellent affinity for protons and contribute to proton transfer. In the present study, PEO and its copolymers, poly[(ethylene oxide)₂₀‐(propylene oxide)₇₀‐(ethylene oxide)₂₀] (EO₂₀PO₇₀EO₂₀, P123) and poly[(ethylene oxide)₁₀₆‐(propylene oxide)₇₀‐(ethylene oxide)₁₀₆] (EO₁₀₆PO₇₀EO₁₀₆, F127), have been found to significantly enhance the conductivity of polyaniline (PANI). After introducing these polymers, the conductivity of PANI is markedly promoted more than two orders of magnitude compared to that of PANI without additives, from 5.2 to 667 S/m. The molecular weight of PEO affects the conductivity of PANI/PEO. The mechanism by which these amphiphilic polymers are beneficial to the conductivity of PANI is studied experimentally and theoretically. The PANI/P123 prepared in the presence of PEO block copolymer shows gradually varying morphologies containing leaflike sheets, rodlike particles, and uniform chestnutlike sphere particles. This is similar to the morphology change of micelles with surfactant concentration. PEO, P123, and F127 are further found to have a positive effect on PANI as a material for sensors or supercapacitors, since high specific capacity and fast response rate are desired qualities in sensors and supercapacitors. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45547.     

New synthetic strategy for facile synthesis of functional polymers by one‐pot combination of controlled radical polymerization and enzymatic reaction

One‐pot synthesis in organic chemistry is deeply rooted in people's minds due to its huge improvement in efficiency compared with conventional stepwise synthesis. Nowadays, such a concept has also been shifted to polymer chemistry by one‐pot introducing compatible or orthogonal organic reactions with polymerizations for facilely synthesizing or modifying polymers. This review systematically summarizes recent developments in the one‐pot combination of enzymatic reactions with controlled radical polymerization to prepare functional polymers. © 2015 Society of Chemical Industry     

Investigation of the nanocellular foaming of polystyrene in supercritical CO2 by adding a CO2‐philic perfluorinated block copolymer

Nanocellular foaming of polystyrene (PS) and a polystyrene copolymer (PS‐b‐PFDA) with fluorinated block (1,1,2,2‐tetrahydroperfluorodecyl acrylate block, PFDA) was studied in supercritical CO₂ (scCO₂) via a one‐step foaming batch process. Atom Transfer Radical Polymerization (ATRP) was used to synthesize all the polymers. Neat PS and PS‐b‐PFDA copolymer samples were produced by extrusion and solid thick plaques were shaped in a hot‐press, and then subsequently foamed in a single‐step foaming process using scCO₂ to analyze the effect of the addition of the fluorinated block copolymer in the foaming behaviour of neat PS. Samples were saturated under high pressures of CO₂ (30 MPa) at low temperatures (e.g., 0°C) followed by a depressurization at a rate of 5 MPa/min. Foamed materials of neat PS and PS‐b‐PFDA copolymer were produced in the same conditions showing that the presence of high CO₂‐philic perfluoro blocks, in the form of submicrometric separated domains in the PS matrix, acts as nucleating agents during the foaming process. The preponderance of the fluorinated blocks in the foaming behavior is evidenced, leading to PS‐b‐PFDA nanocellular foams with cell sizes in the order of 100 nm, and bulk densities about 0.7 g/cm³. The use of fluorinated blocks improve drastically the foam morphology, leading to ultramicro cellular and possibly nanocellular foams with a great homogeneity of the porous structure directly related to the dispersion of highly CO₂‐philic fluorinated blocks in the PS matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Growth strategy for controlling dislocation densities and crystal morphologies of single crystal diamond by using pyramidal-shape substrates

The growth of millimetre-thick diamond single crystals by plasma assisted CVD is complicated by the formation of unepitaxial defects, particularly at the edges of the crystal. These defects tend to encroach on the top surface hence limiting the maximum thickness to typically a few hundreds of micrometres. Dislocations are another type of defects that are also particularly formed at the edges of the crystal. They thread through the diamond film, strongly affecting its characteristics. The growth on pyramidal-shape substrates having different angles and orientations was carried out in an attempt to solve those issues. It was found that the pyramidal-shape tends to disappear after a certain thickness is grown. The inclined faces of the pyramid not only helped in preserving the crystal morphology over a large thickness but also deviated dislocations towards the edges of the crystal, hence limiting their occurrence at the surface. Using this strategy, millimetre-thick diamond single crystals presenting a reduced dislocation density were successfully grown.     

Sequential flow process for the controlled polymerisation and thermolysis of RAFT-synthesised polymers

The RAFT (Reversible Addition-Fragmentation Chain Transfer) process greatly enhances the control over radical polymerisations, while leaving behind a thiocarbonylthio end-group. Thermolysis presents a convenient and efficient way of removing the thiocarbonylthio end-group from RAFT polymers, without the use of additional reagents. This paper describes a simple two-step flow process for the synthesis of RAFT polymers followed by the subsequent removal of the RAFT end-group via thermolysis, without the need for isolating intermediates. A range of different polymers based on styrene, acrylates, methacrylates and acrylamides were synthesised with different RAFT agents and successfully tested for thermolysis at temperatures between 220 and 250 °C in a stainless steel tube flow reactor, resulting in complete removal of thiocarbonylthio end-groups.     

Investigation on the cell nucleation and cell growth in microcellular foaming by means of temperature quenching

The cell nucleation and real‐time cell growth with increasing cell growth time in microcellular foaming were investigated by means of temperature quenching in a supercritical CO₂ pressure‐quench process. Samples of uniform size and shape were saturated in a vessel under conditions of 100–180°C and 30 MPa, and then depressurized to the atmosphere in 10 s. After depressurization, these samples were removed from the vessel at prescribed intervals, and immediately immersed in an ice‐water slurry to obtain foamed samples with various cell growth times. It was found that the nucleation density is closely correlated to the gas absorption capacity of the polymer matrix, so that the final cell density should not be adopted as the nucleation density, as done commonly. The change of cell structure and mass density with increasing cell growth time was dominated by gas diffusion behavior, which was strongly influenced by the temperature. The final cell structure was mainly determined by the cell growth step, where gas diffusion played a key role. The final cell density was in direct proportion to the gas remaining in the substrate, which ranged from 6.0 × 10⁹ to 4.7 × 10⁶ cells/cm³. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 163–171, 2004     

油井结垢规律及其控制措施

油田进入高含水期,地面及集输系统的结垢问题日趋严重,针对新疆某油田的结垢特点,本文选取3个区块7口典型井,通过XRD测试油井结垢的主要产物,分析了结垢的原因,采用EDTA滴定法考察了时间、温度、pH值、成垢离子浓度对结垢的影响规律,同时用静态阻垢法评价了一种复配型阻垢剂的应用效果。结果表明:该油田结垢以CaCO₃为主;结垢动力学在9h发生突变;随着温度升高,碳酸钙垢在水中的溶解度降低;pH值越高,形成垢的趋势越强;Ca²⁺、Mg²⁺和HCO₃^-浓度增加,结垢均增加,对垢的形成有一个促进作用。添加体积比为1:1的HX-1/WAS复配阻垢剂后,阻垢率达到93.9%以上,使用效果优良。     

Preparation of inorganic and organometallic polymers with controlled structures

Preparative and mechanistic aspects of polysilanes and polyphosphazenes are reviewed based on several synthetic methods developed in the author's laboratories. Various aspects of chemoselectivity, regioselectivity, stereoselectivity, and supramolecular control in these reactions are discussed. Polysilanes and copolysilanes are prepared by sonochemical reductive coupling, modifications, and ring-opening polymerization. Polyphosphazenes are prepared by the anionically catalyzed polycondensation of phosphoranimines.     

Preparation of silica nanospheres and porous polymer membranes with controlled morphologies via nanophase separation

ABSTRACT: We successfully synthesized two different structures, silica nanospheres and porous polymer membranes, via nanophase separation between silica sol and polymer. Silica sol, which was in-situ polymerized from tetraorthosilicate, was used as a precursor. Subsequently, it was mixed with a polymer that was used as a matrix component. It was observed that nanophase separation occurred after the mixing of polymer with silica sol and subsequent evaporation of solvents, resulting in organizing various structures, from random network silica structures to silica spheres. In particular, silica nanospheres were produced by manipulating the mixing ratio of polymer to silica sol. The size of silica beads was gradually changed from micro- to nanoscale, depending on the polymer content. At the same time, porous polymer membranes were generated by removing the silica component with hydrofluoric acid. Furthermore, porous carbon membranes were produced by using carbon source polymer through the carbonization process.     

A physical strategy for the preparation of isotactic polypropylene spheres with microsphere and bead–string spherulite morphologies

This study mainly focuses on the formation of isotactic polypropylene (iPP) blend morphologies with microspheres and distinct bead–string spherulites. iPP microspheres have been prepared by a simple and convenient strategy through either an isothermal or a nonisothermal crystallization process based on the macrophase‐separated structure in molten state of iPP/olefin block copolymer (OBC) blend. The dimension of the iPP spheres can be adjusted easily from about 1 µm to >10 µm by controlling the compatibility and annealing conditions. It was found that any of the following three parameters, the molecular structure of OBC (particularly the octene content), molecular weight of iPP, and annealing condition can be rescaled with others in controlling the dimension of the iPP microspheres. The mechanism of the formation of iPP microspheres was studied in detail. Surprisingly, the typical spinodal decomposition morphology with interconnected or thin sheet structure is the precursor of these microspheres. During the subsequent annealing process, it breaks up and further coarsens into spherical structure. In addition, distinct spherulites with a bead–string substructure have been obtained during the isothermal crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40863.     

Synthesis of polyaniline nanostructures with controlled morphology by a two-phase strategy

Polyaniline nanostructures with tubular, spherical, polyhedral, dendritic and belt-like morphologies were synthesized by simply tuning the preparation conditions in a two-phase medium. SEM, FTIR and UV–vis were applied for the characterization of the products. The results showed that the polarity of the organic solvents, the amount of ammonium peroxydisulfate (APS) and the concentration of the acetic acid influenced the morphologies of the polyaniline nanostructures. The difference in the polyaniline morphologies was attributed to the difference in the relative rate of interfacial nucleation to aqueous nucleation. The route reported here is expected to be applied for the controlled synthesis of various polymer nanostructures.     

Investigation on the crystalline morphologies of polyphenylene sulfide and interfacial effect in its fibre composites

Uncured polyphenylene sulfide (PPS) may form a perfect spherulite structure with a diameter of the spherulites larger than 100 μm. On the free surfaces of uncured PPS samples after isothermal crystallization a variety of spherulite patterns can be observed by means of scanning electron microscopy (SEM). However, the crystalline morphologies of PPS are greatly affected by the curing conditions. Graphite fibres, carbon fibres, and glass fibres possess the ability for inducing the transcrystallization of PPS to a different degree. The corrosive resistance of the PPS resin is not only related to its chemical structure, but also to its aggregation structure, and furthermore to the interfacial effect of carbon fibres in the composites.     

The continuous synthesis of addition polymers with a pricesely controlled average molecular weight and minimum polydispersity

A novel technique for the control of continuous synthesis of addition polymers with precisely controlled average molecular weight and minimum polydispersity has been developed. A control system adjusts the concentration of chain-transfer agent in the reactor feed to compensate for all other upsets, in the reactor inputs: initiator and monomer concentrations, temperature and feed rate. The technique has been evaluated quantitatively on a digital computer using a kinetic model of homogeneous, free-radical solution polymerization. In computational tests, the modeled control system generally held the instantaneous number-average chain length within 1%, and quickly returned it to the desired value in response to a wide variety of upsets. By generalizing the Schulz distributions to include termination by disproportionation, combination and chain-transfer, it is shown that changes in the molecular-weight distribution resulting from the action of the control system are minor.