• Polymer(Korea)
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• v.25 no.5
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• pp.707-718
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• 2001

Polypropylene (PP) exhibits many beneficial properties such as low density high thermal stability, chemical resistance, good processability and recyclability. However, only limited research has been done on expanded polypropylene (EPP). In this study, we were trying to prepare EPP with chemical blowing agent. Ethylene-octene copolymer (mPE) was melt blended with PP to enhance melt fluidity of PP at processing temperature and to make more flexible foamed material. Prior to foaming, phase morphology of PP/mPE blends were investigated to examine the effect of phase morphology on the foaming ratio and cell structure of foams. Phase morphology of PP/mPE blends were affected by the content of mPE and mixing torque ratio. At the same composition, it was affected by mixing rpm. High blowing ratio and stable cell structure were obtained in the blend which has the continuous PP matrix with dispersed droplets of mPE.

• Journal of Pharmaceutical Investigation
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• v.40 no.spc
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• pp.9-17
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• 2010

Polymorphism has been recognized to be a critical issue throughout the drug product development process. Most of solid phase drugs have polymorphism, which has generated a great deal of interest and the field has been evolving rapidly. Preferably, thermodynamically most stable form of a drug substance is selected to obtain consistent bioavailability over its shelf life and various storage conditions. Moreover, it has the lowest potential for conversion from one polymorphic form to another. However, metastable or amorphous forms may be used intentionally to induce faster dissolution rate for rapid drug absorption and higher efficacy. For pharmaceutical industry, polymorphism is one of the key activities in form selection process together with salt selection. This article introduces the main features in the investigation of solid form selection especially polymorphic behavior with thermodynamic backgrounds, physicochemical properties with solubility, dissolution, and mechanical properties, and characterization techniques for proper analysis. The final form can be recommended based on the physicochemical and biopharmaceutical properties and by the processability, scalability and safety considerations. Pharmaceutical scientists especially in charge of formulation need to be well aware of the above issues to assure product quality.

• Journal of Pharmaceutical Investigation
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• v.41 no.1
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• pp.45-50
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• 2011

Nonclassical pathway of crystallization has been utilized to modify the properties and morphologies of inorganic and organic/inorganic materials. In here, the polymer-directed crystallization method has been applied to the pharmaceutical active ingredient to assess the applicability for as a particle engineering tool. The polymer-directed crystallization was successful to modifying the crystal size, habit and morphology, but it was not effective to discover the novel polymorphs of Sibutramine (SB). SB was selected as a model drug and polyacrylic acid (PAA), polyethylene imine (PEI) and chitosan (CHI) were added as a crystallization pathway modifier. SB was crystallized via drowning crystallization using methanol or ethanol as a solvent and water as a non-solvent. The significant interactions between polymer and the drug were confirmed by measuring the solubility of the drug in presence of polymer during the crystallization. The crystal forms of SB are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope (OM). The polymer-directed crystallization seems to be able to modify the crystal properties of pharmaceutical active ingredient, which is critical in determining the bioavailability, processability, and stability.

• Macromolecular Research
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• v.10 no.2
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• pp.67-74
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• 2002

New immunoprotecting membranes were prepared by spin coating the amphiphilic random multiblock copolymers of poly(ethylene glycol) (PEG) and poly(tetramethylene ether glycol) (PTMEG) or poly(dimethyl siloxane) (PDMS) on porous Durapore(R) membrane. The copolymer coating was intended to make a biocompatible, immunoprotecting diffusional barrier and the supporting porous substrate was for mechanical stability and processability. By filling Durapore(R) membrane pores with water, the penetration of coating solution into the pores was minimized during the spin coating process. A single coating process produced a completely covered thin surface layer (~1 ${\mu}{\textrm}{m}$ in thickness) on the porous substrate membrane. The permselectivity of the coated layer was influenced by PEG block length, polymer composition, and thickness of the coating layer. A composite membrane with the coating layer prepared with PEG 2 K/PTMEG 2 K block copolymer showed that its molecular weight cut-of fat any 40 based on dextran was close to the molecular size of IgG (Mw = 150 kDa). However, IgG permeation was detected from protein permeation test, while glucose oxidase (Mw = 186 kDa) was not permeable through the coated membrane.

• Proceedings of the Membrane Society of Korea Conference
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• 1997.10a
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• pp.39-45
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• 1997

Introduction : Polyimides are one of the most important classes of the high performance polymers due to their excellent electrical, thermal, and high-temperature mechanical properties. But their uses are limited because of their poor solubility. Most polyimide derivatives are processed in the form of polyamic acids, which are subsequently converted into the imide structures.Recently, it has been found that the soluble polyimides with large molecular weight sufficient to application. For enhancing processability, the majority of approaches have involved the following factors. As much as, the separation of the imide ring along the back-bone, that is to say, reducing the density of imide ring in the repeat structure. The introduction of bulky substituents along the back-bone, in order to enhance the free volume of main-chain. The incorporation of flexible or thermally stable linkages in the main-chain, reducing the packing force. The disruption of symmetry or recurrence regularity through copolymerization in order to reduce crystallnity.The objectives of this investigation are the synthesis and characterization of soluble polyimides as membrane materials by the single-step polymerization and the preparation of the asymmetric polyimide membrane by using phase inversion technique. In the present study, three series of polyimide derivatives are synthesized; H series is homopolyimides, A series is prepared from single dianhydride and two diamines, B series is yielded from two dianhydrides and a diamine. The dope solution was directly prepared from the PI solution via one step polymerization from monomers.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.26-31
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• 2017

Environmental problem of the solid propellants is an issue of growing importance in solid rocket. For examples, ammonium perchlorate (AP) as an solid propellants oxidizer could create a poisonous gas and atmospheric pollutions, such as HCl. Among the several oxidizers, N-guanylurea dinitramide (GuDN) is an effective candidate substance for eco-friendly oxidizer, which has high performance, pressure exponent, and eco-friendly smog during combustion for solid propellant of gas generator. In this paper, the theoretical analysis of characteristics as a gas generator propellant, propellant manufacturing processability, propellant hardness properties and combustion characteristics were studied.

• Journal of Radiation Protection and Research
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• v.29 no.1
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• pp.33-39
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• 2004

In order to vitrify the W1 waste (ion-exchange resin(IER), zeolite, and dry active waste(DAW)) generated from Korean Nuclear Power Plants, a glass formulation development based on waste compositions and production rates was performed. A aluminoborosilicate glass, AG8W1, was formulated to vitrify the W1 waste in an induction cold crucible melter(CCM). The processability, product performance, and economics of the candidate glass were calculated using a computer code and were measured experimentally in the laboratory and CCM. The glass viscosity and electrical conductivity as the process parameters were in the desired ranges. Start-up and maintaining glass melt of the candidate glass were favorable in the CCM. The product quality of the glass such as chemical durability, phase stability, etc. was satisfactory. The vitrification process using the candidate glass was also evaluated to be operated as economically as possible.

• Applied Chemistry for Engineering
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• v.5 no.6
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• pp.1030-1035
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• 1994

Curing behavior and glass transition temperatures of epoxy resins into which reactive diluents were added to control processability were investigated. Heat of cure generated of the epoxy resin was reduced with butyl glycidyl ether(BGE) and phenyl glycidyl ether(PGE) contents. $T_g$ of the resin was decreased with the amount of reactive diluents and it was attributed to increased molecular weight between crosslink points. Cure kinetics of the resins was studied employing autocatalytic reaction model and found that reaction constants decreased as the contents of reactive diluent was increased.

• Proceedings of the KSPS conference
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• 1996.10a
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• pp.430-431
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• 1996

Among the scholars of second language (L2) acquisition who have used prosodic considerations in syntactic analyses, pausing and intonation contours have been used to define utterances in the speech of second language learners (e.g., Sato, 1990). In recent research on conversational analysis, it has been found that lexically marked causal clause combining in the discourse of native speakers can be distinguished as "intonational subordination" and "intonational coordination(Couper-Kuhlen, Elizabeth, forthcoming.)". This study uses Pienemann's Processability Theory (1995) for an analysis of the speech of native speakers of Japanese (L1) learning English. In order to accurately assess the psycholinguistic stages of syntactic development, it is shown that pitch, loudness, and timing must all be considered together with the syntactic analysis of interlanguage speech production. Twelve Japanese subjects participated in eight fifteen minute interviews, ninety-six dyads. The speech analyzed in this report is limited to the twelve subjects interacting with two different non-native speaker interviews for a total of twenty-four dyads. Within each of the interviews, four different tasks are analyzed to determine the stage of acquisition of English for each subject. Initially the speech is segmented according to intonation contour arid pauses. It is then classified accoding to specific syntactic units and further analysed for pitch, loudness and timing. Results indicate that the speech must be first claasified prosodic ally and lexically, prior to beginning syntactic analysis. This analysis stinguishes three interlanguage lexical categories: discourse markers, coordinator $s_ordinators, and transfer from Japanese. After these lexical categories have been determined, the psycholinguistic stages of syntactic development can be more accurately assessed.d.

• Carbon letters
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• v.13 no.4
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• pp.243-247
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• 2012

A fabrication method to improve the processability of thermoplastic carbon nanotube (CNT) mat composites was investigated by using in-situ polymerizable and low viscous cyclic butylene terephthalate oligomers. The electrical conductivity of the CNT mat composites strongly depended on the compression pressure, and the trend can be explained in terms of two cases, low and high compression pressure, respectively. High CNT mat content in the CNT mat composites and the surface of the CNT mat composites with fully contacted CNTs was achieved under high compression pressure, and direct contact between four probes and the surface of the CNT mat composites with fully contacted CNTs gave resistance of $2.1{\Omega}$. In this study the maximum electrical conductivity of the CNT mat composites, obtained under a maximum applied compression pressure of 27 MPa, was 11 904 S $m^{-1}$, where the weight fraction of the CNT mat was 36.5%.