Bumjae Lee

Rice-husk flour filled polypropylene composites; mechanical and morphological study

Abstract To determine the possibility of using lignocellulosic materials as reinforcing fillers in the thermoplastic polymer composite, polypropylene as the matrix and rice-husk flour as the reinforcing filler were used to prepare a particle-reinforced composite in order to determine testing data for the physical, mechanical and morphological properties of the composite according to the filler loading in respect to thermoplastic polymer. In the sample preparation, four levels of filler loading (10, 20, 30 and 40 wt.%) were designed. In the tensile test, six levels of test temperature (−30, 0, 20, 50, 80 and 110 °C) and five levels of crosshead speed (2, 10, 100, 500 and 1500 mm/min) were designed. Tensile strengths of the composites slightly decreased as the filler loading increased. Tensile modulus improved with increasing filler loading. Notched and unnotched Izod impact strengths were lowered by the addition of rice-husk flour. The composite became brittle at higher crosshead speed, and showed plastic deformation with increasing test temperature.

Applications of 1,1-Diphenylethylene Chemistry in Anionic Synthesis of Polymers with Controlled Structures

The use of 1,1-diphenylethylenes in anionic polymerization is reviewed. The structure and reactivity of 1,1-diphenylethylenes and the corresponding simple and polymeric 1,1-diphenylalkyllithiums are described. The applications of 1,1-diphenylethylene chemistry include: 1. Their use to form initiators 2. End-capping agents to attenuate reactivity for crossover to reactive, polar monomers or for functionalization reactions 3. For chain-end and in-chain functionalization using substituted 1,1-diphenylethylenes and 1,1-diarylethylenes 4. The preparation and applications of non-homopolymerizable 1,1-diphenylethylene-functionalized macromonomers 5. The use of bis(1,1-diphenylethylenes) and tris(1,1-diphenylethylenes) as precursors for hydrocarbon-soluble dilithium and trilithium initiators, respectively 6. The use of bis(1,1-diphenylethylenes) and tris(1,1-diphenylethylenes) as living linking agents to prepare heteroarm (miktoarm) star-branched polymers

Zirconium Hydroxide‐coated Nanofiber Mats for Nerve Agent Decontamination

Diverse innovative fabrics with specific functionalities have been developed for requirements such as self-decontamination of chemical/biological pollutants and toxic nerve agents. In this work, Zr(OH)4 -coated nylon-6,6 nanofiber mats were fabricated for the decontamination of nerve agents. Nylon-6,6 fabric was prepared via the electrospinning process, followed by coating with Zr(OH)4 , which was obtained by the hydrolysis of Zr(OBu)4 by a sol-gel reaction on nanofiber surfaces. The reaction conditions were optimized by varying the amounts of Zr(OBu)4 ,the reaction time, and the temperature of the sol-gel reaction. The composite nanofibers show high decontamination efficiency against diisopropylfluorophosphate, which is a nerve agent analogue, due to its high nucleophilicity that aids in the catalysis of the hydrolysis of the phosphonate ester bonds. Composite nanofiber mats have a large potential and can be applied in specific fields such as military and medical markets.

Toward a detoxification fabric against nerve gas agents: guanidine-functionalized poly[2-(3-butenyl)-2-oxazoline]/Nylon-6,6 nanofibers

A novel guanidine-functionalized polymer, poly[2-(3-butenyl)-2-oxazoline] (PBuOxz), has been co-electrospun with Nylon-6,6 to form fibers that could be used for the decontamination of chemical warfare agents (CWAs). PBuOxz was obtained from the living cationic polymerization of 2-(3-butenyl)-2-oxazoline, which was synthesized starting from 4-pentenoic acid. This clickable PBuOxz polymer could be easily functionalized through the introduction of amine groups via thiol–ene click chemistry, followed by guanidinylation to form guanidine-functionalized PBuOxz (G-PBuOxz). The synthesized G-PBuOxz/Nylon-6,6 fibers are an active hydrolysis species for diisopropyl fluorophosphate (DFP), an organophosphate mimic of nerve agents. The decontamination efficiency for DFP could be as high as 100% under trace aqueous solution conditions using this G-PBuOxz/Nylon-6,6 fiber as the decontamination agent at the ratio of [guanidine]/[DFP] = 100/1 in 2 hours. The hydrolysis occurs via a general SN2 mechanism for this G-PBuOxz-based catalysis. Furthermore, the kinetics of decontamination were also investigated based on time and guanidine concentration. Hence, this G-PBuOxz/Nylon-6,6 fiber is effective as a hydrolyzing agent against toxic organophosphates, and thus exhibits potential as a material for protecting against chemical warfare agents.

Synthesis of novel telechelic fluoropolyols based on vinylidene fluoride/hexafluoropropylene copolymers by iodine transfer polymerization

Well-defined α,ω-diiodo-poly(vinylidene fluoride (VDF)-co-hexafluoropropylene (HFP)) with a narrow unimodal molecular weight distribution (polydispersity index < 1.3) was subjected to iodine transfer polymerization, which allows controlled “pseudo-living” free radical telomerization. The molecular weight of the obtained polymer increased linearly with polymerization time, and the molecular weight distribution was determined by size exclusion chromatography. The prepared α,ω-diiodo-poly(VDF-co-HFP) was converted to α,ω-bis(hydroxyethyl)-poly(VDF-co-HFP) as a novel telechelic fluoropolyol by incorporation of ethylene units and subsequent hydrolysis with aqueous bicarbonate (acting as a nucleophile and phasetransfer reagent) in hexamethylphosphoramide, a polar aprotic solvent. The obtained fluorinated polyol was characterized by 1H, 13C, and 19F NMR and exhibited a molecular weight below 3,000 Da, making it a suitable telechelic fluorinated prepolymer for the synthesis of fluorinated polyurethanes or their acrylate oligomers.