Yottha Srithep

Nanofibrillated cellulose (NFC) reinforced polyvinyl alcohol (PVOH) nanocomposites: properties, solubility of carbon dioxide, and foaming

Polyvinyl alcohol (PVOH) and its nanofibrillated cellulose (NFC) reinforced nanocomposites were produced and foamed and its properties—such as the dynamic mechanical properties, crystallization behavior, and solubility of carbon dioxide (CO2)—were evaluated. PVOH was mixed with an NFC fiber suspension in water followed by casting. Transmission electron microscopy (TEM) images, as well as the optical transparency of the films, revealed that the NFC fibers dispersed well in the resulting PVOH/NFC nanocomposites. Adding NFC increased the tensile modulus of the PVOH/NFC nanocomposites nearly threefold. Differential scanning calorimetry (DSC) analysis showed that the NFC served as a nucleating agent, promoting the early onset of crystallization. However, high NFC content also led to greater thermal degradation of the PVOH matrix. PVOH/NFC nanocomposites were sensitive to moisture content and dynamic mechanical analysis (DMA) tests showed that, at room temperature, the storage modulus increased with decreasing moisture content. The solubility of CO2 in the PVOH/NFC nanocomposites depended on their moisture content and decreased with the addition of NFC. Moreover, the desorption diffusivity increased as more NFC was added. Finally, the foaming behavior of the PVOH/NFC nanocomposites was studied using CO2 and/or water as the physical foaming agent(s) in a batch foaming process. Only samples with a high moisture content were able to foam with CO2. Furthermore, the PVOH/NFC nanocomposites exhibited finer and more anisotropic cell morphologies than the neat PVOH films. In the absence of moisture, no foaming was observed in the CO2-saturated neat PVOH or PVOH/NFC nanocomposite samples.

Comparisons of microcellular polylactic acid parts injection molded with supercritical nitrogen and expandable thermoplastic microspheres: Surface roughness, tensile properties, and morphology

Microcellular injection molding is capable of fabricating light weight, dimensionally stable plastic parts while using less material and energy. Two kinds of blowing agents, namely, supercritical nitrogen and expandable thermoplastic microspheres, were employed to produce foamed polylactic acid parts. The surface characteristics were evaluated with a 2D surface roughness analyzer and a 3D white-light interferometer surface profiler. Through surface roughness comparisons, injection molded ASTM tensile test bars with expandable thermoplastic microspheres exhibited better surface quality than their supercritical nitrogen counterparts. The tensile properties of injection molded polylactic acid tensile bars with nitrogen and expandable thermoplastic microspheres at various weight concentrations were investigated. The results showed that the polylactic acid/nitrogen parts possessed a better Young’s modulus and tensile strength. The microstructure on the fractured cross-sectional surfaces was characterized using a scanning electron microscope. As reflected by the testing results, the cell microstructure—such as cell size and cell density, and multi-layered structure with a foamed core sandwiched by skin layers—played an important role in the surface quality and mechanical properties. In addition, while an appropriate expandable thermoplastic microsphere content had a positive effect on the cell microstructure and weight reduction, too high of a concentration of expandable thermoplastic microsphere adversely affected the tensile properties and surface roughness of the microcellular polylactic acid tensile test bars.

Processing and characterization of poly(lactic acid) blended with polycarbonate and chain extender

Abstract Currently, use of poly(lactic acid) (PLA) is limited for commercial applications because it has a low heat resistance. In this research, an increase of over 40°C heat distortion temperature (HDT) of PLA alloy was obtained by blending PLA with polycarbonate (PC) and a chain extender (CE). Molecular weight, thermal, mechanical and morphological properties of PLA and PC blend with different CE contents were investigated. Gel permeation chromatography (GPC) results showed that some PLA-PC copolymers were produced and the compatibility of the PLA phase and in the PC phase was improved via the chain extension reaction. In addition, the reaction induced by CE also affected the crystallization behaviors of PLA, as observed from differential scanning calorimetry (DSC) results and the enthalpy of melting of PLA decreased with increasing CE content. The combined effects of the CE increasing molecular weight, improving compatibility and limiting the crystallization behavior of PLA/PC alloy greatly improved the HDT.

Microcellular injection molding of recycled poly(ethylene terephthalate) blends with chain extenders and nanoclay

Abstract Poly(ethylene terephthalate) (PET) resin is one of the most widely used thermoplastics, especially in packaging. Due to thermal and hydrolytic degradations, recycled PET (RPET) exhibits poor mechanical properties and lacks moldability. The effects of adding chain extender (CE) and nanoclay to RPET were investigated. Melt blending of RPET with CE was performed in a thermokinetic mixer (K-mixer). The blended materials were then prepared via solid and microcellular injection molding processes. The effects of CE loading levels and the simultaneous addition of nanoclay on the thermal and mechanical properties and cell morphology of the microcellular components were noted. The addition of 1.3% CE enhanced the tensile properties and viscosity of RPET. The higher amount of CE (at 3%) enhanced the viscosity, but the margin of improvement in mechanical properties diminished. While the solid RPET and CE blends were fairly ductile, the samples with nanoclay and all microcellular specimens showed brittle fractural behavior. Finally, nanoclay and the increase of CE content decreased the average cell size and enlarged the cell density of the microcellular samples.

Effects of nucleation and stereocomplex formation of poly(lactic acid)

Abstract The effects of poly(d-lactide) (PDLA), nanoclay, talc, and stereocomplex formation were investigated in blends where these materials were added as a minor phase in a major phase of poly(l-lactide) (PLLA). Blends containing 2% PDLA, nanoclay, or talc as nucleants were prepared via melt blending and showed a strong increase in the crystallization rate as revealed by isothermal and nonisothermal crystallization measurements. The blending of 2% PDLA with PLLA led to the highest crystallization rate. Moreover, a stereocomplex formation was observed in a PLLA/PDLA blend (50:50). Wide-angle X-ray diffraction and differential scanning calorimetry verified that complete stereocomplex crystallites that do not form homocrystallites can be achieved. Compared with pure PLLA, the stereocomplex had a higher melting temperature and a higher crystallization temperature, by more than 50°C and 25°C, respectively.

Plasticizer effect on melt blending of polylactide stereocomplex

Abstract Poly(l-lactide) (PLLA)/poly(d-lactide) (50/50) with plasticizer contents ranging from 2% to 16% w/w were prepared by melt blending using an internal mixer. Wide-angle X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry results confirmed that complete stereocomplex polylactide crystallites without any homocrystallites were produced. Compared to neat PLLA, the melting temperature of the stereocomplex polylactide and its plasticized samples was approximately 55°C higher. Higher plasticizer contents decreased glass transition temperature of the stereocomplex, which implied higher flexibility and enhanced the crystallization rate. However, the plasticizer in the stereocomplex reduced the thermal stability.

Fabrication of highly porous interconnected three-dimensional scaffolds with micro-channels

A novel highly porous 3-D poly(ɛ-caprolactone) (PCL) scaffold with micro-channels was fabricated by injection molding and diluent acetic acids leaching technologies. In this study, the chitosan fiber was employed to form the microchannel in PCL matrix. The morphology, porosity and mechanical properties of the scaffolds were studied and calculated. It was found that the larger the content of chitosan fiber is, the higher the porosity would be, due to the volumetric expansion of chitosan fiber in PCL matrix during it being leached. In addition, the less the content of chitosan fiber is, the higher the compressive modulus would be.

Effect of banana fibers and plasticizer on melt processing of poly(vinyl alcohol)

Abstract Poly(vinyl alcohol) (PVOH) resin is one of the most widely used water-soluble biodegradable polymer. Because of thermal degradation, PVOH exhibits limited melt processing and lacks moldability. The effects of adding glycerol as plasticizer and banana fibers (BF) to PVOH on its moldability and mechanical property were investigated. Melt blending of PVOH with glycerol and/or BF was performed in an internal mixer. The blended materials were then compression molded to produce tensile specimens. Various characterization techniques were employed to study the mechanical properties, compatibility, and crystallization behavior of the PVOH blends. By melt blending with glycerol, PVOH could be processed but decreased the tensile modulus, tensile strength, and crystallization temperature. Furthermore, the addition of BF enhanced the mechanical and thermal properties and crystallization temperature of plasticized PVOH due to compatibility between the two components. Apart from enhancing the mechanical properties and thermal stability, the incorporation of BF can reduce the production cost.