Seung Han

Curing reaction of biphenyl epoxy resin with different phenolic functional hardeners

The investigation of cure kinetics and relationships between glass transition temperature and conversion of biphenyl epoxy resin (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl) with different phenolic hardeners was performed by differential scanning calorimeter using an isothermal approach over the temperature range 120–150°C. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of formulations using xylok and dicyclopentadiene type phenolic resins (DCPDP) as hardeners proceeds through a first-order kinetic mechanism, whereas the curing reaction of formulations using phenol novolac as a hardener goes through an autocatalytic kinetic mechanism. The differences of curing reaction with the change of hardener in biphenyl epoxy resin systems were explained with the relationships between Tg and reaction conversion using the DiBenedetto equation. A detailed cure mechanism in biphenyl-type epoxy resin with the different hardeners has been suggested.

Cure Kinetics of Biphenyl Epoxy-Phenol Novolac Resin System Using Triphenylphosphine as Catalyst

The effects of the concentration of triphenylphosphine as a catalyst on the cure reaction of the biphenyl epoxy/phenol novolac resin system were studied. The kinetic study was carried out by means of the analysis of isothermal experiments using a differential scanning calorimeter. All kinetic parameters including the reaction or- ders, activation energy and kinetic rate constants were evaluated. To describe the cure reaction with the catalyst concentration, the normalized kinetic model was developed. The suggested kinetic model with a diffusion term was successfully able to describe and predict the cure reaction of epoxy resin compositions as functions of the catalyst content and temperature.

Kinetic study of the effect of catalysts on the curing of biphenyl epoxy resin

The investigation of cure kinetics of biphenyl epoxy (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl)dicyclopentadiene type phenolic resin system with different kinds of catalysts was performed by a differential scanning calorimeter using an isothermal approach. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of the formulations using triphenylphosphine (TPP), 1-benzyl-2-methylimidazole (1B2MI), and tris(4-methoxyphenyl)phosphine (TPAP) as a catalyst proceeds through an nth-order kinetic mechanism, whereas thatof the formulations using diazabicycloundecene (DBU) and tetraphenyl phosphonium tetraphenyl borate (TPP–TPB) proceeds by an autocatalytic kinetic mechanism. To describe the cure reaction in the latter stage, we have used semiempirical relationship proposed by Chern and Poehlein. By combining an nth-order kinetic model or an auto-catalytic model with a diffusion factor, it is possible to predict the cure kinetics of each catalytic system over the whole range of conversion.

The Role of Transforming Growth Factor-β and Bone Morphogenetic Protein with Fibrin Glue in Healing of Bone-Tendon Junction Injury

Bone-tendon junction injuries have poor healing potential. This study evaluated the role of TGF-β and BMP-2 in a fibrin glue carrier in healing of injuries at bone-tendon junction. Seventy-two skeletally mature male rabbits were divided into 4 groups. The tendo-Achilles was surgically transected at its insertion and reattached with a pullout suture. Group 1 served as a control. In groups 2, 3, and 4, fibrin glue, a mixture of TGF-β and fibrin glue, and a mixture of BMP-2 and fibrin glue were injected into the bone-tendon junction. The animals were sacrificed at 2, 4 and 8 weeks after surgical procedure. The addition of TGF-β to fibrin glue did not significantly improve the biomechanical properties of repair tissue. BMP-2 in combination with fibrin glue accelerates healing in a bone-tendon injury and also improves the histological and biomechanical properties of the repair tissue so formed.

Stress fractures of the femoral diaphysis in children : A report of 5 cases and review of literature

The authors report five new cases of the stress fracture of the femoral diaphysis in children. These injuries usually occurred without a history of recent increase of activity. Recently regained normal activity after long-term immobilization and a fibrous cortical defect were predisposing factors. The periosteal reactions were usually identified in the initial radiograph and were not confined to the medial cortex of the distal femur; they might occur in any part of the femoral diaphysis, and also concomitantly on the multiple cortex. The atypical radiographic presentations frequently required MRI for differential diagnosis. Even though the MRI may be confusing to the inexperienced observer, it can lead to the diagnosis of a stress fracture with confidence, negating the need for biopsy. Clinicians should be aware of this diagnostic entity in the differential diagnosis of femoral diaphyseal lesions in children because the occurrence might be more common than reported. Serial simple radiographic examinations taken at intervals to look for the evidence of progressive fracture healing and the restriction of activity or immobilization may be an adequate approach for management.

Frequency dispersion characteristics of the complex permittivity of the epoxy-carbon black composites

The effects of frequency, volume fraction of carbon black, and porosity on the complex permittivity of the epoxy-carbon black composites were investigated and the frequency dispersion behavior model for the complex permittivity was proposed. In the epoxy-carbon black composites, the frequency dispersion behaviors of the complex permittivity changed from relaxation spectrum to resonance spectrum with increasing the amount of carbon black. The complex permittivity of the composites increased with decreasing the porosity. Comparing the complex permittivity of the composites filled with 2 vol % of carbon black with the values obtained from three types of previously reported model equations, the relaxation behavior coincided with the Havriliak-Negami model. The damping and asymmetrical factor values were increased with increasing porosity in the composites. The empirical equation proposed here was useful in describing the complex permittivity of the composites of >3 vol % carbon black with resonance type. The damping factor (γ) decreased as the filler content increased, but the asymmetrical factor (κ) increased reversely.

Composition dependence of rheological properties of polymer blends

Abstract A semi-empirical rheological equation of state was developed to described temperature, shear rate and composition dependence of the steady-state shear viscosity of poly( l -lactic acid)(PLA)/poly(e-caprolactone)(PCL) systems. The composition dependent rheological equation of state proposed here has a very simple algebraic form with a few adjustable parameters. Its simplicity is a great advantage for practical application and it appears to be suitable for describing the rheological behaviour of PLA/PCL blends.

Differences in Bone Mineral Density between the Right and Left Hips in Postmenopausal Women

Bone mineral density (BMD) using dual energy radiography absorptiometry are commonly used for the diagnosis of osteoporosis. It is usually measured at the spine and also at one hip joint. Controversy still exists regarding the use of bilateral hip scanning. We analyzed the difference of BMD at bilateral hips in 384 postmenopausal women, retrospectively. The concordance and discordance rates of the lowest T-score and BMD between both hips were evaluated. The BMDs of the femoral neck and trochanter were significantly different between both hips (P < 0.05). There were also discrepancies between the lowest T-scores of both hips (P < 0.05). The discordance rates were about 30%. Due to significant differences in BMD between both hips at the femoral neck and trochanter and high discordance rate, bilateral hip measurements using DEXA are recommended to avoid underestimating osteoporosis.

Diagnostic Value of Synovial White Blood Cell Count and Serum C-Reactive Protein for Acute Periprosthetic Joint Infection After Knee Arthroplasty

BACKGROUND The diagnosis of periprosthetic joint infection (PJI) remains difficult, particularly in acute postoperative stage. The purpose of this study was to investigate the optimal cutoff value of synovial white blood cell (WBC) count, percentage of polymorphonuclear cells, erythrocyte sedimentation rate, and C-reactive protein (CRP) for diagnosing early postoperative infection after knee joint arthroplasty. METHODS We retrospectively reviewed primary total knee arthroplasties and unicompartmental knee arthroplasties, with a knee aspiration within 3 weeks of surgery, from January 2006 to November 2016. Twelve infected cases and 185 uninfected cases met the inclusion criteria of our study. We compared the laboratory parameters (synovial WBC count, percentage of polymorphonuclear cells, erythrocyte sedimentation rate, and CRP levels) between the 2 groups. Receiver operating characteristic curves were constructed to determine the optimal cutoff values for each parameter. Each parameter was studied to determine its sensitivity, specificity, and positive and negative predictive values (PPV and NPV) in diagnosing acute PJI. RESULTS There were 2 optimal cutoff values for synovial WBC count and CRP levels. With the cutoff value of synovial WBC set at 11,200 cells/μL, acute PJI could be diagnosed with the highest sensitivity (100%) and specificity (98.9%); with the cutoff value set at 16,000 cells/μL, the best PPV and NPV were found (100% and 99.5%, respectively). Similarly, the CRP level >34.9 mg/L had the best sensitivity (100%) and specificity (90.3%), whereas the CRP level >74.5 mg/L had the best PPV (100%) and NPV (99.2%). CONCLUSION Synovial WBC count and CRP levels are useful in diagnosing acute PJI between 1 and 3 weeks after primary knee arthroplasty.

Recurrent Inflammation on the Hand due to a High Pressure Injection of Urethane : A Case Report

We describe a case of a high-pressure polyurethane injection injury to the hand, and discuss how its management differs from other injection injuries. A male patient was transferred to our hospital due to persistent purulent discharge from the 2nd finger, which began 15 days after the injury. The injected foreign body, polyurethane, could not be recognized by the patient and was not indicated radiographically. During surgery, the polyurethane foam was removed. The patient had no functional impairment 24 months after surgery.