A review on membrane fabrication: Structure, properties and performance relationship

Polymer nanocomposite foams

Carbon nanofibers prepared via electrospinning and following carbonization are summarized by focusing on the structure and properties in relation to their applications, after a brief review of electrospinning of some polymers. Carbon precursors, pore structure control, improvement in electrical conductivity,and metal loading into carbon nanofibers via electrospinning are discussed from the viewpoint of structure and texture control of carbon.

Carbon Nanofibers Prepared via Electrospinning

Lignocellulosic biomass (LCB) is the most abundantly available bioresource amounting to about a global yield of up to 1.3 billion tons per year. The hydrolysis of LCB results in the release of various reducing sugars which are highly valued in the production of biofuels such as bioethanol and biogas, various organic acids, phenols, and aldehydes. The majority of LCB is composed of biological polymers such as cellulose, hemicellulose and lignin, which are strongly associated with each other by covalent and hydrogen bonds thus forming a highly recalcitrant structure. The presence of lignin renders the bio-polymeric structure highly resistant to solubilization thereby inhibiting the hydrolysis of cellulose and hemicellulose which presents a significant challenge for the isolation of the respective bio-polymeric components. This has led to extensive research in the development of various pretreatment techniques utilizing various physical, chemical, physicochemical and biological approaches which are specifically tailored towards the source biomaterial and its application. The objective of this review is to discuss the various pretreatment strategies currently in use and provide an overview of their utilization for the isolation of high-value bio-polymeric components. The article further discusses the advantages and disadvantages of the various pretreatment methodologies as well as addresses the role of various key factors that are likely to have a significant impact on the pretreatment and digestibility of LCB.

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Recent Trends in the Pretreatment of Lignocellulosic Biomass for Value-Added Products

‘Hierarchy’ is a property which can be attributed to a manifold of different immaterial systems, such as ideas, items and organisations or material ones like biological systems within living organisms or artificial, man-made constructions. The property ‘hierarchy’ is mainly characterised by a certain ordering of individual elements relative to each other, often in combination with a certain degree of branching. Especially mass-flow related systems in the natural environment feature special hierarchically branched patterns. This review is a survey into the world of hierarchical systems with special focus on hierarchically porous zeolite materials. A classification of hierarchical porosity is proposed based on the flow distribution pattern within the respective pore systems. In addition, this review might serve as a toolbox providing several synthetic and post-synthetic strategies to prepare zeolitic or zeolite containing material with tailored hierarchical porosity. Very often, such strategies with their underlying principles were developed for improving the performance of the final materials in different technical applications like adsorptive or catalytic processes. In the present review, besides on the hierarchically porous all-zeolite material, special focus is laid on the preparation of zeolitic composite materials with hierarchical porosity capable to face the demands of industrial application.

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Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

Creating a high-efficiency bubble nucleation agent for a polymer foaming process is essential for increasing bubble density as well as decreasing bubble size. Spherulites (crystalline phase) grown in a semicrystalline poly(L-lactide) (PLLA) matrix enhanced carbon dioxide (CO2) bubble nucleation in a batch foaming process. Several sites for PLLA spherulite formation were observed at a hold-temperature of 110 °C after CO2 saturation in molten PLLA, which was heated to 180 °C at 11 MPa. By depressurizing the system from 11 MPa to atmospheric pressure, the dissolved CO2 in the PLLA matrix became supersaturated, and CO2 bubbles nucleated around growing PLLA spherulites. The number of nucleating bubbles increased as a function of increasing spherulite quantity and area. A faster linear spherulite growth rate and a lower hold-temperature created more bubbles around the spherulites. From these observations, it was concluded that the growing spherulites expelled CO2 from the advancing spherulite−amorphous phase in...

Effect of Growing Crystalline Phase on Bubble Nucleation in Poly(L-Lactide)/CO2 Batch Foaming

Experimental and numerical studies on the effects of pressure release rate on number density of bubbles and bubble growth in a polymeric foaming process

Using a newly developed high-pressure autoclave, which has two sapphire windows on the walls, we visually observed the batch physical foaming of polymer-clay nanocomposites to understand the effect of nano-sized clay on the initial stage of foaming. With CO 2 as a physical foaming agent, polypropylene-montmorillonite clay nanocomposites were foamed at 150°C. A high-speed digital camera with a microscope could observe the bubble nucleation and bubble growth behavior of the early stage of foaming in situ. The series of micrographs was analyzed in order to investigate the effect of clay content on bubble nucleation and growth. The experiments, together with CO 2 -solubility and diffusivity data, show that the clay enhances bubble nucleation as a nucleation agent and retards the growth of bubbles at the early stage of foaming.

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Visual observation of CO2 foaming of polypropylene‐clay nanocomposites

The visual observations of batch and continuous foaming processes were conducted to understand the bubble nucleation and bubble growth behaviors in polymers. The batch foaming was performed using a newly developed high-pressure cell, where two sapphire windows were equipped on the walls so as to observe the early stage of bubble nucleation and growth behaviors with the help of a high-speed digital camera and microscope. In the batch process, homo polypropylene was foamed at different pressure release rates using CO2 as a physical blowing agent to see the effects of operating condition on the bubble nucleation and growth rates. The in situ observation could identify that (1) the bubble nucleation and growth occur simultaneously, (2) the influence region, where the nucleation was suppressed, exists around bubbles, and (3) the nucleation rate and the growth rate increase as the pressure release rate increases. The continuous foaming was performed using a different visualization unit, which consists of an aut...

Visual observations of batch and continuous foaming processes

A nanocellular PS/PMMA polymer blend foam was prepared, where bubble nucleation was localized in the PMMA domains. The blend, which contains dispersed nanoscale PMMA islands, was prepared by polymerizing MMA monomers in a PS matrix to form highly dispersed PMMA domains in the PS matrix by diffusion mixing. The resulting blend was foamed with CO 2 at room temperature. A higher depressurization rate at lower foaming temperature made the bubble diameter smaller and the bubble density larger, and a higher PS composition in the blend resulted in a larger bubble density. A void with 40-50 nm in average diameter and a pore density of 8.5 x 10 14 cm -3 was obtained as for the finest nanocellular foams.

Kentaro Taki

Papers

Effect of Growing Crystalline Phase on Bubble Nucleation in Poly(L-Lactide)/CO2 Batch Foaming

Experimental and numerical studies on the effects of pressure release rate on number density of bubbles and bubble growth in a polymeric foaming process

Visual observation of CO2 foaming of polypropylene‐clay nanocomposites

Visual observations of batch and continuous foaming processes

Nanocellular Foams of PS/PMMA Polymer Blends