Shin-Shing Shyu

Kinetic study of chitosan-tripolyphosphate complex reaction and acid-resistive properties of the chitosan-tripolyphosphate gel beads prepared by in-liquid curing method

Chitosan gel beads were prepared using an in-liquid curing method by the ionotropic crosslinking with sodium tripolyphosphate. Crosslinking characteristics of the chitosan-TPP beads were improved by the modification of in-liquid curing mechanism of the beads in TPP solution. Chitosan gel beads cured in pH value lower than 6 were really ionic-crosslinking controlled, whereas chitosan gel beads cured in pH values higher than 7 were coacervation-phase inversion controlled accompanied with slightly ionic-crosslinking dependence. According to the result, significantly increasing the ionic-crosslinking density of chitosan beads could be achieved by transferring the pH value of the curing agent, TPP, from basic to acidic. The swelling behavior of various chitosan beads in acid appeared to depend on the ionic-crosslinking density of the chitosan-TPP beads that were deeply affected by the curing mechanism of the beads. The mechanism of chitosan-TPP beads swollen in weak acid was chain-relaxation controlled, while the mechanism of chitosan-TPP beads swollen in strong acid seem to be not only chain-relaxation but also chain-scission controlled. Chitosan-TPP beads prepared in acidic TPP solution decreased the chain-scission ability due to the increase of ionic crosslinking density of the beads. By the transition of curing mechanism, the swelling degree of chitosan-TPP beads was depressed, and the disintegration of chitosan-TPP beads would not occur in strong acid. The mechanism of ionic-crosslinking reaction of chitosan beads could be investigated by an unreacted core model, and the curing mechanism of the chitosan beads is mainly diffusion controlled when higher than 5% of chitosan was employed.

The Effect of chemical treatment on reinforcement/matrix interaction in Kevlar-fiber/bismaleimide composites

Abstract The thermal properties of all the bismaleimides have been examined by differential scanning calorimetry, thermogravimetry and thermomechanical analysis. Both 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane (BMPP) and 2,2-bis[4-(4-maleimidophenoxy)phenyl]hexafluoropropane (BMIF) showed a large processing temperature range between their melting points and initial polymerization temperature, which decreased the cross-link density of the cured resins without significant reduction in their thermal resistance. The introduction of flexible groups to BMI structure improved the interfacial shear strength of the Kevlar/bismaleimide composites measured by means of the microbond pull-out test. The results of the pull-out tests show that both BMPP and BMIF have larger interfacial shear strength values than 4, 4′-bismaleimidodiphenylmethane (BMI-DMA). The surface modification with reactive functional groups can enhance both the interlaminar shear strength and T-peel strength of the Kevlar-fiber/BMPP resin system. The ILSS was markedly improved by chlorosulfonic-acid treatment. But higher concentrations of chlorosulfonic acid and longer reaction times caused a lower ILSS. From the ILSS and T-peel strength values, it can be concluded that treatment with 0.2% chlorosulfonic acid for 150 s is the optimum chlorosulfonation condition. In this study, the chlorosulfonation/allylamine treatment produced the best ILSS and T-peel strength. The fracture surfaces of the T-peel specimens were examined by SEM.

Development of biodegradable co-poly(d,l-lactic/glycolic acid) microspheres for the controlled release of 5-FU by the spray drying method

Abstract The water-soluble anti-cancer drug, 5-fluorouracil (5-fluoro-2,4-pyrimidinedione) (5-FU) is encapsulated into biodegradable co-poly ( d,l -lactic/glycolic acid) (PLGA) using the spray drying method for the development of long-lasting controlled release systems. In this study, the effects of both polymeric composition and technological parameters on release profiles of 5-FU were investigated. The degradation of various microspheres was also investigated. The mixture of dichloromethane/chloroform/methanol (1:1:2 v/v) instead of dichloromethane/chloroform (1:1 v/v) resulted in the modification of morphology, while the physical structure of the microsphere varied from a porous PLGA microsphere to a dense PLGA microsphere. The results show that the average diameter was 2 μm and the anti-cancer drug loading of microspheres approached approximately 8% (w/w). In addition, the lactide/glycolide ratio of the polymer is an important parameter for controlling the release profile of the entrapped anticancer drug. Our results indicate that the mixture solvent using the spray drying method was more efficient than emulsification solvent diffusion.

Cure behavior, morphology, and mechanical properties of the melt blends of epoxy with polyphenylene oxide

Cure behavior, miscibility, and phase separation have been studied in blends of polyphenylene oxide (PPO) with diglycidyl ether of bisphenol A (DGEBA) resin and cyanate ester hardener. An autocatalytic mechanism was observed for the epoxy/PPO blends and the neat epoxy. It was also found that the epoxy/PPO blends react faster than the neat epoxy. During cure, the epoxy resin is polymerized, and the reaction-induced phase separation is accompanied by phase inversion upon the concentration of PPO greater than 50 phr. The dynamic mechanical measurements indicate that the two-phase character and partial mixing existed in all the mixtures. However, the two-phase particulate morphology was not uniform especially at a low PPO content. In order to improve the uniformity and miscibility, triallylisocyanurate (TAIC) was evaluated as an in situ compatibilizer for epoxy/PPO blends. TAIC is miscible in epoxy, and the PPO chains are bound to TAIC network. SEM observations show that adding TAIC improves the miscibility and solvent resistance of the epoxy/PPO blends.

Kevlar fiber-epoxy adhesion and its effect on composite mechanical and fracture properties by plasma and chemical treatment

Kevlar 49 fibers were surface-modified by NH3-, O2-, and H2O-plasma etching and chlo-rosulfonation and subsequent reaction with some reagents (glycine, deionized water, eth-ylendeiamine, and 1-butanol) to improve the adhesion to epoxy resin. After these treatments, the changes in fiber topography, chemical compositions of the fiber surfaces, and the surface functional groups introduced to the surface of fibers were identified by SEM, XPS, and static SIMS. Interlaminar shear strength (ILSS) and T-peel strenght between the fiber and opoxy resin, as measured by the short-beam test and T-peel test, were remarkedly improved by gas plasma and chlorosulfonation (0.1% and 0.25% CISO3H at 30 s). However, from the results of similar GIC values of the treated and untreated fiber composites, it is clear that the fiber/matrix interfacial bond strength is only a minor contributor to GIC. SEM was also used to study the surface topography of the fracture surfaces of composites in T-peel test. It could be seen from SEM observations that the improvement of fiber/matrix interfacial bond strength often accompanied a change in fracture mode from the interface of fiber/epoxy resins to the fiber fibrillation and the resins.

Characteristic and controlled release of anticancer drug loaded poly (D,L-lactide) microparticles prepared by spray drying technique.

Anticancer drug release from polylactic acid microspheres prepared by the spray-drying process was studied. Several process parameters and properties of the polymer solution have been investigated. Normal size distributions with diameters ranging from 5-10 #119 m were obtained by the spray drying technique. The yield of microspheres recovered depended on polymer solution and process conditions employed. Results show that the yield of microspheres could reach 50%, and the experimental drug loading approached the theoretical drug loading. Scanning electron microscopy indicated that microspheres were composed of a dense thin skin layer and porous core. The magnitude of this effect depended on the inlet temperature, feed polymer concentration and airflow rate. Increasing inlet temperature and polymer concentration resulted in an intact particle shape and a slower drug dissolution rate. The in-vitro release of anticancer drug from microspheres was sustained over 7 days. The drug release behaviour depended on inlet temperature, air flow rate, PLA concentration and drug loading. The anticancer drug release rate from polylactic acid microspheres prepared by the spray-drying method was depressed, and the long-acting release could be achieved by appropriate operating parameters.Anticancer drug release from polylactic acid microspheres prepared by the spray-drying process was studied. Several process parameters and properties of the polymer solution have been investigated. Normal size distributions with diameters ranging from 5-10 microm were obtained by the spray drying technique. The yield of microspheres recovered depended on polymer solution and process conditions employed. Results show that the yield of microspheres could reach 50%, and the experimental drug loading approached the theoretical drug loading. Scanning electron microscopy indicated that microspheres were composed of a dense thin skin layer and porous core. The magnitude of this effect depended on the inlet temperature, feed polymer concentration and air flow rate. Increasing inlet temperature and polymer concentration resulted in an intact particle shape and a slower drug dissolution rate. The in-vitro release of anticancer drug from microspheres was sustained over 7 days. The drug release behaviour depended on inlet temperature, air flow rate, PLA concentration and drug loading. The anticancer drug release rate from polylactic acid microspheres prepared by the spray-drying method was depressed, and the long-acting release could be achieved by appropriate operating parameters.

Surface properties and interfacial adhesion studies of aramid fibres modified by gas plasmas

The surface of aramid (Kevlar 49) fibre was modified by NH3, O2 or H2O plasmas in order to improve the adhesion to epoxy resin. Electron spectroscopy for chemical analysis (ESCA) and static secondary ion mass spectroscopy (SSIMS) were used to identify the chemical compositions and functional groups of the plasma-treated fibre surface, respectively. The surface topography and mechanical properties of plasma-treated fibres were also investigated. After plasma treatments, the interfacial shear strength (IFSS) of aramid-fibre/epoxy-resin composites, as measured by the microbond pull-out technique, was markedly improved (43–83% improvement) and the fibre strength was only little affected (less than 10% loss). Significant improvement in the IFSS principally resulted from forming the covalent bonds between the newly reactive functionalities at the modified fibre surfaces and the epoxides of the resin.

Plasma surface treatment on carbon fibers. Part 1: Morphology and surface analysis of plasma etched fibers

Abstract High modulus (M40) and high strength (T300) carbon fibers have been surface treated by argon and oxygen plasma to modify the fibre surfaces. The etching process and the effects of plasma gases on the carbon fibers are discussed. ESCA analyses of treated fiber surfaces show abnormal functionality changes during the plasma treatments. A clear picture of the removal of the outermost structure by plasma etching is given by the coupled evidence of SEM and ESCA analysis.

Thermal and mechanical properties of PPO filled epoxy resins compatibilized by triallylisocyanurate

A series of blends has been prepared by adding a poly(phenylene oxide) (PPO), in varying proportions, to an epoxy resin cured with dicyandiamide. All the materials show two-phase morphology when characterized by SEM and DMA. SEM and DMA indicate that partial mixing exists in all the blends especially with high PPO content. This implies that the epoxy oligomer or low crosslinking density epoxy exists in the PPO phase after curing. The tensile strength and modulus of these blends are nearly independent of the PPO content, while the fracture toughness (GIC) is improved by PPO. However, the two-phase particulate morphology is not uniform. In order to improve the uniformity and miscibility, triallylisocyanurate (TAIC) has been used as an in situ compatibilizer for the polymer blends of epoxy and PPO. SEM and DMA reveal improvement of miscibility and solvent resistance for this system. The fracture toughness of these TAIC-modified systems are also improved by adding TAIC (0–20 phr). © 2000 Society of Chemical Industry

Plasma surface treatments of carbon fibers. Part 2: Interfacial adhesion with poly(phenylene sulfide)

Abstract Type I and type II carbon fibers were covered with a thin plasma polymer film and etched by an oxygen or an argon plasma to reinforce the interfacial adhesion with poly(phenylene sulfide). Plasma etching of the fibers increased the interfacial shear strength up to 2·5 times which is much better than plasma polyacrylonitrile deposited fibers. Electron spectroscopy for chemical analysis surface analyses show different mechanisms of adhesion enhancement. Film deposited fibers which possess more abundant oxygen functionalities and aromatics show improved adhesion. On the other hand, increased adhesion with etched fibers occurs as a result of a larger area of unoxidized carbon structure. Surface nitrogen atoms also play a role in the interfacial adhesion.