W. L. Tham

Water Absorption and Hygrothermal Aging Behaviors of SEBS-g-MAH Toughened Poly(lactic acid)/Halloysite Nanocomposites

Poly(lactic acid)/halloysite nanoclay composites (PLA/HNC) containing maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH) were exposed to hygrothermal aging at three different temperatures, i.e., 30, 40 and 50°C. The analysis was focused on the water diffusion kinetics and physical changes induced by the hygrothermal degradation. The water absorption kinetics of the PLA/HNC composites at immersion temperature of 30 and 40°C conforms to Ficks law. The equilibrium water absorption (Mm ) and diffusion coefficient (D) values are dependent on the SEBS-g-MAH content and immersion temperatures. Hydrolytic chain scission provoked significant molecular weight reduction. Nevertheless, adding SEBS-g-MAH improved hygrothermal stability of the PLA/HNC nanocomposites.

Effects of titanate coupling agent on the mechanical, thermal, and morphological properties of poly(methyl methacrylate)/hydroxyapatite denture base composites

Poly(methyl methacrylate) (PMMA)/hydroxyapatite (HA) denture base composites were prepared using heat-processing polymers powder–liquid method, according to dental laboratory practice. The HA was pre-treated by isopropyl triisostearoyl titanate coupling agent (TCA) in order to improve the interfacial bonding between HA and PMMA. The effects of different concentration of titanate coupling agent (i.e., 2–8%) on the mechanical and morphological properties of PMMA were investigated. It was found that PMMA/2% TCA-treated HA composites exhibited higher flexural modulus and strength compared to PMMA/untreated HA composites. This is attributed to the enhanced interfacial interaction between PMMA and HA by the titanate coupling agent. However, for the PMMA/HA treated with 6% and 8% of TCA, the flexural properties was slightly reduced, which may associated to the plasticizing effects caused by excessive concentration of coupling agent. In addition, the fracture toughness properties of PMMA/5HA composites were influenced by the different concentration of TCA. The thermal properties of the PMMA/HA composites were enhanced by the treatment of titanate coupling agent.

Flexural and Morphological Properties of Poly(Methyl Methacrylate)/ Hydroxyapatite Composites: Effects of Planetary Ball Mill Grinding Time

Poly(methyl methacrylate) (PMMA)/hydroxyapatite (HA) composites have potential applications in bone cement, prosthesis, and dental implant. In this study, PMMA containing 5 wt% of HA is prepared using polymerization followed by compression molding. PMMA and HA powder are ground using planetary ball milling. The grinding time takes from 30 to 120 min. The effects of the grinding time and particle size of the PMMA/HA powder on the flexural properties and morphology of the composites are investigated. The structure patterns of PMMA/5HA are characterized using X-Ray diffraction (XRD). No new phase is observed in the XRD pattern with the different sizes of PMMA/HA powder. This indicates that planetary milling solely reduces the size of PMMA/ HA powder. However, it does not modify the structure of PMMA and HA. A reduction of ~40% in the particle diameter is observed in both PMMA and PMMA/5HA powder after subjected to planetary milling for 60 min. For the planetary ball mill-ground PMMA/HA powder, the flexural modulus of the respective PMMA composites is slightly increased. Planetary milling can increase the volume of fine particles in the composites specimens, which results in a more homogeneous distribution of HA and a reduction of void contents in PMMA matrix. The reduction in void content is observed on the fractured surface of PMMA composites through field emission scanning electron microscopy.

Mechanical and Thermal Properties Enhancement of Poly(Lactic Acid)/Halloysite Nanocomposites by Maleic-Anhydride Functionalized Rubber

Poly(lactic acid) (PLA)/halloysite composites were prepared using melt compounding followed by compression molding. Maleic anhydride grafted styrene-ethylene/butylene-styrene (SEBS-g-MAH) was used to toughen the PLA composites. The mechanical properties of the PLA composites were studied through tensile, flexural, and impact tests. The thermal properties were characterized by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The fracture surfaces of the composites were assessed by using field emission scanning electron microscopy (FESEM). The impact strength and thermal properties of the PLA/halloysite composites were increased by addition of SEBS-g-MAH.

Improvement of Microstructure and Properties of Poly(methyl methacrylate)/Hydroxyapatite Composites Treated with Zirconate Coupling Agent

Poly(methyl methacrylate) (PMMA)/hydroxyapatite (HA) composite has potential application in denture base materials. Surface treatment of HA using zirconate coupling agent (ZCA) has been carried out to improve the interfacial bonding between the PMMA matrix and HA filler. The effects of different concentration of ZCA (i.e., 2–8%) on the mechanical properties of PMMA/HA composites was investigated using tensile and three-point bending flexural tests. The morphological properties of the PMMA/HA composites was characterized using field emission scanning electron microscopy (FESEM). It was found that PMMA/5HA-2% ZCA composites exhibited higher flexural strength compared to that of untreated PMMA/HA composites. This is attributed to the enhancement of interfacial interaction between PMMA and HA, which can be evidenced by the FESEM and EDX technique. The kinetics of simulated body fluid (SBF) absorption of PMMA/HA composites were studied at 37°C for immersion duration of 2 months. The mathematical treatment used in analyzing the data was the Fickian diffusion and utilized Ficks second law of diffusion. It is worth mentioning that the kinetics of SBF absorption of the PMMA/HA composites conformed to Fickian law behavior, whereby the initial SBF absorption follows a linear relationship between the percentage gain at any time t and t1/2, followed by saturation. It was found that the equilibrium SBF content of PMMA/HA composite was reduced by the ZCA treatment.

Mechanical and Thermal Oxidation Behavior of Poly(Lactic Acid)/Halloysite Nanotube Nanocomposites Containing N,N ′-Ethylenebis(Stearamide) and SEBS-g-MA

Poly(lactic acid) (PLA)/halloysite nanotube (HNT) nanocomposites were prepared using melt compounding followed by compression molding. Maleic anhydride grafted styrene–ethylene/butylene–styrene copolymer (SEBS-g-MA) and N,N′-ethylenebis(stearamide) (EBS) were used to improve the impact properties of PLA nanocomposites. The properties of PLA/HNT nanocomposites were characterized by tensile and impact tests, Fourier transform infrared spectroscopy, thermal analysis (DSC and TGA), and morphological analysis (FESEM and TEM). In addition, the oxidation onset temperature (OOT) was determined using DSC. The PLA/HNT6/EBS5 nanocomposites gives higher impact strength improvement (98%) compared to that of PLA/HNT6/SEBS-g-MA5 (77%). Also, the PLA/HNT6/EBS5 exhibited higher OOT compared to that of PLA/HNT6/SEBS-g-MA5 nanocomposites.

Effect of N,N′-ethylenebis(stearamide) on the water absorption and hydrolytic degradation of poly(lactic acid)/halloysite nanocomposites

Poly(lactic acid)/halloysite nanoclay (PLA/HNC) nanocomposites with N,N′-ethylenebis(stearamide) (EBS) were produced by melt mixing. Water absorption behaviors of the PLA nanocomposites were studied at three different temperatures, that is, 30, 40, and 50°C. The water absorption kinetics of PLA/HNC nanocomposites conform to Fickian diffusion behavior at immersion temperatures of 30 and 40°C due to the diffusional exponent (n) values that were close to 0.5 for all specimens. However, the hydrolysis of PLA occurred for longer time deviations at 50°C. Activation energy of water diffusion (E a) for PLA nanocomposites were found to be affected by the HNC and EBS contents. The glass transition temperature (T g), cold crystallization temperature (T cc), and melting temperature (T m) of the PLA sample were shifted to lower temperature after subjected to immersion temperature of 50°C. The carbonyl index of all PLA specimens increased after water absorption at 40 and 50°C due to the formation of higher amount of carboxylic acid end groups during the hydrolysis process.