Dae Young Lim

Mechanical and thermal properties of long carbon fiber-reinforced polyamide 6 composites

The purpose of this study is to elucidate the influence of carbon fiber (CF) content on the mechanical and thermal properties of long carbon fiber (LCF)-reinforced polyamide 6 (PA6) thermoplastic composites. PA6/LCF composites were manufactured by a twin-screw extruder. The average length of the carbon fibers in the composites was approximately 13–15 mm. We found that the interfacial adhesion between the PA6 matrix and the carbon fibers was very good. The mechanical properties, such as the tensile strength, the tensile modulus, and the flexural strength of the PA6/LCF composites, increased as the CF content increased and were higher than those of short carbon fiber reinforced PA6 composites. The melting temperature (Tm) and thermal degradation temperature of the composites were not affected by the addition of CF, whereas the crystallization temperature (Tc) was affected by the addition of CFs.

Effects of binder fibers and bonding processes on PET hollow fiber nonwovens for automotive cushion materials

In this study, nonwoven fabrics were developed for the replacement of polyurethane foams in car interiors, in particular, cushioning materials for car seats. Polyethylene terephthalate (PET) hollow fibers and two types of bicomponent binder fibers were used to manufacture automotive nonwovens by carding processes and then post-bonding processes, such as needle punching or thermal bonding. The physical and mechanical properties of nonwovens were thoroughly investigated with respect to the effects of binder fibers and bonding processes. The tensile strength and elongation for nonwovens were found to be significantly improved by combined needle punching and thermal bonding processes. In addition, the nonwoven cushioning materials were characterized in terms of hardness, support factors, and compressive and ball rebound resilience. The nonwovens showed greater hardness than the flexible PU foam. However, support factors over 2.8 for the nonwovens indicated improved seating comfort, along with better seating characteristics of greater resilience and air permeability in comparison with the PU foam.

Manufacturing and analyses of wet-laid nonwoven consisting of carboxymethyl cellulose fibers

Carboxymethyl cellulose (CMC) is a cellulose derivative having water-soluble property, biodegradability, and biocompatibility. It has been used in various medical applications as forms of gel, film, membrane, or powder. In this study, composite CMC nonwovens were produced, by a wet-laid nonwoven process, to improve the wet strength of carboxymethyl cellulose nonwovens. Followed by preparing the CMC fibers from cotton fiber, the composite CMC nonwovens composed of CMC fibers and PE/PP bicomponent fibers were manufactured by using 85/15 % v/v of ethanol/water solution as a dispersion medium. Structural analyses of CMC fibers, such as XRD, TGA, FT-IR, and degree of substitution indicated that CMC fibers were successfully produced. The wet strength of CMC nonwoven was dramatically increased by blending with the PE/PP fibers without sacrificing the key properties for wound dressing materials such as liquid absorption, gel blocking and liquid retention. It is expected that the composite CMC nonwovens will be a good candidate for wound dressing materials for mild exudate condition.

Reflective composite sheet design for LCD backlight recycling

We have designed a reflective composite sheet consisting of a birefringent polymer matrix and isolated isotropic or minimally birefringent fibers. The optical properties of the sheet have been investigated in terms of the width, spacing, and thickness of the individual fibers. Commercial software (FDTD Solution) was used to simulate the reflectance of the proposed sheet, and conventional processes such as cast-film extrusion in combination with solid-state drawing were used to manufacture the multilayer composite sheet. The measured and simulated reflectance spectra confirm the feasibility of employing the sheet as a reflective polarizer.

Composites of Polyolefin Elastomer Reinforced with Short Carbon Fiber and Its Copolymerization Conditions

To study the effects of short carbon fiber (SCF) on the properties of the polyolefin elastomers (POEs), we prepared the poly(ethylene-co-1-hexene) (PEH)/SCF composites at different percentages of SCF. We also prepared polyethylene (PE)/SCF composites to compare with PEH/SCF composites. PEH was synthesized by the copolymerization of ethylene and 1-hexene using metallocene catalyst/cocatalyst system. Optimum stirring speed, Al/Zr feeding molar ratio, polymerization time, and polymerization temperature were 700 rpm, 600, 30 min, and 60 °C, respectively. We investigated the morphology of the composites using scanning electron microscopy (SEM) and found that the wettability of SCF in PEH/SCF composites was fairly better than that of SCF in PE/SCF composites. It was observed from mechanical tests that the ultimate tensile strength and tensile modulus of PEH/SCF composites were remarkably enhanced as the SCF content increased, whereas those of PE/SCF composites were a little increased. PEH/SCF composites exhibited lower crystallinity than PE/SCF ones. Thermal stability of the composites was enhanced by the addition of SCF.

Preparation of Polypropylene Composites Reinforced with Long Carbon Fibers and Their Properties

Long carbon fiber reinforced polypropylene (LCFP) composites were prepared at different fiber/resin input ratios and fiber lengths by extrusion and compression molding techniques. Fiber contents and fiber lengths were controlled by the carbon fiber/resin input ratio and screw extruder speed, respectively. The effects of the fiber content and fiber length on the mechanical properties of LCFP were investigated. The fiber length of the composites with the same fiber content decreased with an increase in screw speed. Further, the mechanical properties of the composites improved with an increase in the fiber content and mean fiber length. The fracture surfaces of the composites were investigated by scanning electron microscopy (SEM).

Compatibilizing effects of polypropylene-g-itaconic acid on the polypropylene composites

We prepared long carbon fiber (LCF)-reinforced thermoplastic composites using a compatibilizer of itaconic acid grafted polypropylene (PP-g-IA). We confirmed the structure of PP-g-IA and investigated the compatibilizing effects of PPg- IA on LCF/polypropylene composites. The tensile strength, tensile moduli, flexural strength, and flexural moduli of the composites increased with increasing PP-g-IA content in the thermoplastic composites. Using single pull-out analyzing system, we found PP-g-IA improved interfacial strength between the carbon fiber and PP matrix. The thermal properties of the composites were measured by thermogravimetric analysis (TGA). We could observe that LCF enhanced the mechanical properties and thermal decomposition temperature of the polypropylene (PP) composites, compared with neat PP. The fractured surfaces of PP/PP-g-IA/LCF composites showed that PP-g-IA was effective for improving the interfacial adhesion between LCF and PP matrix.

Fiber-based Diffuser Sheet for Liquid Crystal Display Backlight Unit

A fiber diffuser sheet based on poly (ethylene naphthalate) (PEN) and poly (methylpentene) (PMP) has shown potential for liquid crystal display backlight units, but these materials have an interfacial adhesion problem. To improve the interfacial adhesion between the fibers and matrix components, we have proposed the use of amorphous poly (cyclohexane-1,4-dimethylene terephthalate) (Tritan) instead of PEN. Furthermore, the fabrication processes have been optimized and simplified to improve the optical and mechanical properties of the sheet. As a result, the most effective fiber content for achieving the best haze characteristics of a sample consisting of Tritan and PMP has been identified.

Electrical Properties of Novel Polyolefin Based Thermoplastic Elastomer and Graphene Nanocomposites

Numerous efforts to prepare useful graphene-based nanocomposites have been made and important improvements achieved. In our studies, novel structured polyolefin-based thermoplastic elastomer, poly(ethylene-ter-1-hexene-ter-divinylbenzene) (PEHV) was designed and synthesized. And high quality graphene was manufactured via the exfoliation of graphite. PEHV/graphene nanocomposites were fabricated using solution casting method as the amount of graphene added. The morphologies of nanocomposites were observed using scanning electron microscopy. And density, mechanical properties and electrical properties were also measured. Electrical properties and mechanical properties were improved with the increase of graphene added in nanocomposites. It is expected that PEHV/graphene nanocomposites could be applied to lightweight EMI shielding materials.

Studies on the improvement of compatibility in reinforced polypropylene composites using polypropylene-g-anhydride itaconate

We prepared long carbon fiber (LCF)-reinforced thermoplastic composites using a new compatibilizer, anhydride itaconate-grafted polypropylene (PP-g-AI). For a good grafting ratio of anhydride itaconate (AI) onto polypropylene (PP), we found optimum mixing conditions such as mixing temperature, monomer content, and initiator type. The initiator, 2,5-dimethyl-2,5-di(tert-butyl peroxy)-hexane (Luperox 101), showed the best graft ratio. The optimum reaction temperature, initiator content, and monomer content were found to be approximately 190°C, 1 phr, and 5 wt%, respectively. We characterized the structure of PP-g-AI using Fourier transform infrared spectroscopy. The ultimate tensile strength of LCF/PP-g-AI/PP composites increased by approximately 15% as the PP-g-AI content increased up to 5 wt%, compared with that of the PP/LCF composites. The fractured surfaces of PP/PP-g-AI/LCF composites showed that PP-g-AI was effective in improving the interfacial adhesion between LCF and the PP matrix.