Taweechai Amornsakchai

Kevlar reinforcement of polyolefin-based thermoplastic elastomer

Composite systems of Kevlar, poly(p-phenylene terephthalamide), and Santoprene, a polyolefin-based thermoplastic elastomer, were studied. Kevlar pulp was used as-received in one system, and modified in the other. The as-received Kevlar pulp was found to reinforce Santoprene to a certain degree. It was found that with increasing amount of Kevlar in the composite, low-strain modulus and tensile strength increased, while the elongation at break decreased sharply. To improve mechanical properties of the composite, hydrolysis of Kevlar pulp surface was employed in conjunction with maleic anhydride-grafted-polypropylene (MA-g-PP), a reactive compatibiliser. It was found that the treated Kevlar pulp greatly improved the low-strain modulus, tensile strength, and elongation at break of the composite. Dynamic mechanical analysis showed that the storage modulus of the Kevlar/MA-g-PP/Santoprene composite was significantly higher than the as-received Kevlar composite. A slight increase in transition temperatures of polypropylene matrix was also observed. As a result of the fact that low-strain modulus and tensile strength of the composite were improved when hydrolysed Kevlar pulp and MA-g-PP were used, it is suggested that such a combination might have increased the interfacial adhesion of the fibre and the matrix, and effective fibre volume fraction, resulting in a better distribution of stress along the reinforcing fibre.

Composite of aramid fibre (poly-m-phenylene isophthalamide)-thermoplastic elastomers (SEBS): enhancement of tensile properties by maleated-SEBS compatibiliser

Aramid fibre, poly-m-phenylene isophthalamide (Teijin-Conex), was used to reinforce thermoplastic elastomer, styrene (ethylene butylene) styrene (SEBS). It was found that the moduli at 100 and 300% elongation of the composite increased linearly with increasing fibre loading. On the other hand, tensile strength of the composites decreased as the fibre content was increased. Improvement of interfacial adhesion was carried out by, first, slightly hydrolysing the fibre with sodium hydroxide solution to increase the number of reactive amino end groups and then mixing with the matrix and compatibiliser, maleic anhydride grafted SEBS (MA-g-SEBS), at various concentrations. Tensile strength of the compatibilised composite was found to increase and then level-off at 5 wt% compatibiliser. Fractured surface of composite containing compatibiliser showed more fibre breakage than the uncompatibilised one. Examination of the extracted fibre revealed that some fraction of rubber was chemically bonded to the fibre surface. These results suggest good compatibilising performance of MA-g-SEBS for the system studied.

Improvement of interfacial adhesion of poly(m-phenylene isophthalamide) short fiber–thermoplastic elastomer (SEBS) composites by N-alkylation on fiber surface

A composite of short-fiber, poly(m-phenylene isophthalamide), and thermoplastic elastomer styrene (ethylene–butylene) styrene (SEBS), was investigated. The fiber surface was modified by N-alkylation (heptylation and dodecylation) to improve their compatibility with a less polar SEBS matrix. Observation of fiber-surface morphology by SEM revealed surface roughness after N-alkylation. Nearly complete coating of the polymer matrix on the fiber was observed on a fractured surface of the composite, which is evidence for the improvement of fiber–matrix adhesion. It was found that the modulus of the composites grew with increasing fiber loading to approximately the same extent for both unmodified and modified fiber composites. Tensile strength of the modified fiber composites was found to improve significantly over that of the unmodified fiber composite. This suggests that the presence of the alkyl group on the fiber surface is responsible for an improvement of interfacial adhesion.

Antimicrobial effects of silver zeolite, silver zirconium phosphate silicate and silver zirconium phosphate against oral microorganisms

OBJECTIVE To evaluate the antimicrobial activities of silver inorganic materials, including silver zeolite (AgZ), silver zirconium phosphate silicate (AgZrPSi) and silver zirconium phosphate (AgZrP), against oral microorganisms. In line with this objective, the morphology and structure of each type of silver based powders were also investigated. METHODS The antimicrobial activities of AgZ, AgZrPSi and AgZrP were tested against Streptococcus mutans, Lactobacillus casei, Candida albicans and Staphylococcus aureus using disk diffusion assay as a screening test. The minimum inhibitory concentration (MIC) and minimum lethal concentration (MLC) were determined using the modified membrane method. Scanning electron microscope and X-ray diffraction were used to investigate the morphology and structure of these silver materials. RESULTS All forms of silver inorganic materials could inhibit the growth of all test microorganisms. The MIC of AgZ, AgZrPSi and AgZrP was 10.0 g/L whereas MLC ranged between 10.0-60.0 g/L. In terms of morphology and structure, AgZrPSi and AgZrP had smaller sized particles (1.5-3.0 µm) and more uniformly shaped than AgZ. CONCLUSIONS Silver inorganic materials in the form of AgZ, AgZrPSi and AgZrP had antimicrobial effects against all test oral microorganisms and those activities may be influenced by the crystal structure of carriers. These results suggest that these silver materials may be useful metals applied to oral hygiene products to provide antimicrobial activity against oral infection.

The effects of silane-SiO2 nanocomposite films on Candida albicans adhesion and the surface and physical properties of acrylic resin denture base material

STATEMENT OF PROBLEM Polysiloxane has been used as a coupling material in restorative dental materials for several decades. However, few studies are available on the application of polysiloxane in other dental prosthesis functions. PURPOSE The purpose of this study was to investigate the effects of silane-SiO2 nanocomposite films on Candida albicans adhesion and the surface and physical properties of acrylic resin denture base materials. MATERIAL AND METHODS Specimens were separated into 2 groups, uncoated and coated. They were coated with a film by using the dip-coating method. Specimens were incubated with Candida albicans 10(7) cells/mL for 1 hour, and the adherent cells were counted under an optical microscope. The following surface properties were measured: surface chemical composition with Fourier-transform infrared spectrometry, surface roughness with a surface profiler, surface energy with the sessile drop method, and surface hardness with a microhardness tester. The physical properties, including water sorption, water solubility, ultimate flexural strength, and flexural modulus, were evaluated according to International Organization for Standardization 20795-1 requirements. The adhesion of Candida albicans and the surface properties of the specimens were investigated after cleaning with effervescent tablets and brushing. An MTT assay was used to evaluate the coated specimens. The results were statistically analyzed with the Mann-Whitney U test (α=.05). RESULTS A significant reduction in Candida albicans adhesion (P=.002) was observed before cleaning. In addition, the surface energy was comparable (P=.100), the surface hardness increased significantly (P=.008), and the surface roughness remained unchanged (P=.310). After cleaning with effervescent tablets, a significant decrease in Candida albicans adhesion (P=.002) and in surface roughness (P=.008) was observed; however, similar surface energies were measured (P=.100). After cleaning with a toothbrush, the adhesion of Candida albicans was significantly higher on the coated specimen than on the uncoated specimen (P=.004). The surface roughness values were significantly different (P=.008), and the surface energies could not be determined. The coated specimen had a silicon-oxygen-silicon peak instead of an ester bond in the polymethyl methacrylate structure. The coating film reduced the water sorption (P=.008) and water solubility (P=.032), and increased the ultimate flexural strength (P=.008) and flexural modulus (P=.032) of the specimen. The coated specimen also had satisfactory toxicity results. CONCLUSIONS Reduced Candida albicans adhesion was observed on the coated specimens. The polymeric film did not change the surface roughness of the acrylic resin specimen; however, it did slightly reduce the surface energy. The physical properties of the acrylic resin did not decrease after it was coated with the film.

Reinforcing performance of recycled PET microfibrils in comparison with liquid crystalline polymer for polypropylene based composite fibers

Recycled polyethylene terephthalate (rPET) used as an alternative reinforcing additive for polypropylene (PP) based composite fibers, compared with liquid crystalline polymer (LCP), was investigated. Both PP-LCP and PP-rPET composites were prepared as fiber using hot drawing process. The effects of draw ratios and compatibilizer dosages on morphology in relation to tensile properties of both types of the composite systems were studied. The variation of draw ratios resulted in much change of stress–strain behavior in compatibilized rPET composite system owing to the obvious difference in morphological change of rPET dispersed phase upon drawing. Tensile strength and extensibility of both composites system were significantly improved with compatibilizer loading. The tensile strength of compatibilized rPET-composite fibers was higher than that of the compatibilized LCP system. The obtained results demonstrated the high potential of rPET as a well-defined reinforcing material for PP based composite fiber under the improved interfacial adhesion promoted by compatibilizer.

Rheology, morphology and tensile properties of thermotropic liquid crystalline polymer/polypropylene in-situ composites

Blends of various grades of polypropylene (PP) with a thermotropic liquid crystalline polymer (TLCP), namely a copolymer of p-benzoic acid and ethylene terephthalate (60/40 mole ratio) were prepared as extruded films. A thermoplastic elastomer styrene (ethylene-butylene) styrene (SEBS) was used as a compatibilizer. Melt viscosities of all specimens were measured using a plate-and-plate rheometer with oscillating mode in the shear rate region of 1 - 200 rad/s. Addition of SEBS compatibilizer resulted in an increase of the blend viscosity. Observation of the blend morphology revealed an improvement of TLCP dispersion. The TLCP fiber aspect ratio (length to diameter) in the extruded film also increased after addition of SEBS. As a result, the film modulus in extrusion direction was enhanced. The tensile strength of the film specimen was also increased due to an improvement of interfacial adhesion.

Photoinitiated grafting of methyl methacrylate on highly oriented polyethylene: Effect of draw ratio on grafting

Modification of highly oriented polyethylene was performed using a photoinitiated grafting technique. The samples were first coated with photoinitiator and then exposed to methyl methacrylate vapor under UV light (A > 290 nm) at 60°C. The extent of grafting was studied as a function of draw ratio. It was found that the extent of grafting decreased significantly as the draw ratio was increased. Control samples of undrawn samples with different thermal histories suggested that there was another factor in addition to crystallinity that influences the extent of grafting. It is proposed that amorphous orientation or taut-tie molecules reduce the photoinitiation process. Gravimetric and attenuated total reflectance-IR measurements indicated that the grafting reaction can occur below the sample surface (or internal grafting) and that the proportion of surface grafting increases with increasing draw ratio.

Potential Use of Recycled PET in Comparison with Liquid Crystalline Polyester as a Dual Functional Additive for Enhancing Heat Stability and Reinforcement for High Density Polyethylene Composite Fibers

The recycle poly(ethylene terephthalate) (rPET) used as an alternative reinforcing material for in situ microfibrillar-reinforced composite, compared with liquid crystalline polymer (LCP), was investigated. The PE-LCP and PE-rPET composites were prepared as fiber using hot drawing process. The effects of draw ratios and compatibilizer (styrene-ethylene butylene-styrene-grafted maleic anhydride, SEBS-g-MA) loading on morphology, tensile properties, thermal stability and dynamic mechanical characteristics of the LCP- and rPET-composite systems were studied. In as-spun samples containing compatibilizer, the fibrillation of LCP domains was observed whereas rPET domains appeared as droplets. After drawing, good fibrillation of LCP and rPET domains is remarkably observed especially in the composite fibers with compatibilizer loading. The mechanical properties of the composite fibers were strongly depended on the fibrillation of the dispersed phases which directly related the levels of draw ratio and compatibilizer loading. The mechanical properties enhanced by SEBS-g-MA were more pronounced in the rPET than LCP systems. The presence of rPET in the composite fibers alone or with the compatibilizer clearly improved the thermal resistance of PE whereas no significant change in thermal stability for the LCP-containing composite fibers with and without compatibilizer loading. The results from dynamic mechanical analysis revealed that an improvement in dynamic mechanical properties of the composite fibers could be achieved by drawing with optimum draw ratio together with optimum compatibilizer dosage. All obtained results suggested the high potential of rPET minor blend-component as a good reinforcing and thermal resistant materials for the thermoplastic composite fiber, in replacing the more expensive LCP.

Substitution of Iron in Preparation of Enhanced Thermal Property and Bioactivity of Hydroxyapatite

Incorporation of Iron into hydroxyapatite (HAp) has generated a novel material for which their properties differ from those of conventional HAp. Although XRD indicated that the as-prepared iron-substituted hydroxyapatite (HApFe) is of a single crystalline phase similar to that of HAp, we found that carbonate ions can incorporate in the HApFe structure 3 times better than in HAp. As results, HApFe possesses the Vickers microhardness about 1.5 times higher than that of HAp. Thermal behaviors and bioactivity of HApFe are discussed in comparison to those of HAp. Various experimental methods have been employed in this work including powder XRD, IR, SEM, DSC/TGA and Vickers Hardness testing.