Key Engineering Materials Vol. 751

Abstract: The concept of smart blender to form a multilayer structure of PLA/EVOH has been developed. Unlike conventional mixing, smart blending provides a formation of multilayer structure by dictating the motion of stir rod to agitate melts. The PLA and EVOH are supplied separately by a single-screw extruder. An experimental rig is assembled at the end of a co-extruder, and melt from an extruder entered an experimental rig via a cylindrical port. The molten EVOH is recursively stretched and folded in an experimental rig of PLA major phase to give an alternating layer structure. The rod is rotated by variable speed motor that is independently controllable. The rod rotational speed and volumetric flow rates of EVOH and PLA are of our interest. Careful design of stir rod in smart blending is necessary for effective performance. The computational model provided the visualization of flow profile inside an experimental rig. The simulation determined the geometry of the stir rod required to achieve the spiral flow developed of the melt. The experimental results suggest that the injected streams of EVOH are stretched and folded to multiple and distributed layers ranging thickness from 10 to 200 um. The characteristic folding of EVOH melt depends on the volumetric flow rate of the screw extruder and rod rotational speed. However, the coalescence of EVOH layers is observed for high rod rotational speed.

Abstract: The effects of microcrystalline cellulose (MCC) on mechanical, thermal and morphological properties of polyoxymethylene (POM)/polypropylene (PP) blends at different compositions were investigated. The blends and composites were prepared by melt mixing using an internal mixer at 200°C. Scanning electron microscopy (SEM) analysis revealed phase separation between POM and PP phases due to the difference in polarity of POM and PP. When adding the MCC in the blends the morphology slightly changed due to the weak interaction between MCC and polymer phases. Incorporation of MCC at 5 phr could improve Young’s modulus of POM/PP blends. The storage modulus of the blends was improved after adding MCC 5 phr due to reinforcing effect of the MCC. The thermal properties found that the addition of MCC had no effect on the melting temperature of the blends. The blends exhibited higher decomposition temperature than pure POM. The blends showed the decomposition temperatures increased when increasing amount of PP content, which were higher than pure POM. Therefore, it may be inferred that the addition of PP could enhance the thermal stability of the POM/PP blends, but the addition of MCC did not improve the thermal stability.

Abstract: Ag-natural rubber (Ag-NR) hybrid sheets were successfully prepared with a very simple and low cost method. In this method, silver nanoparticles (AgNPs) were firstly synthesized by a rapid and green microwave-assisted using polyvinylpyrroridone (PVP) media. The effect of PVP weight ratios towards the size of AgNPs was also investigated. Then, Ag-NR hybrid sheet samples were prepared by latex mixing-casting method using concentrated natural rubber (NR) latex with the synthesized AgNPs colloids. The characteristic absorption, particles sizes and shapes of the obtained AgNPs were examined through UV-vis, TEM and SAED. Also, the prepared Ag-NR sheet samples were characterized using XRD, FT-IR, SEM and EDS techniques. It was found that the particles sizes of all the synthesized AgNPs had spherical-like shape, and the mean sizes were increased from 29.7 to 90.4 nm upon increasing PVP contents. EDS results showed the AgNPs were well-dispersed and impregnated into the rubber matrix. Moreover, the antibacterial properties of the prepared Ag-NR sheets were tested by agar disk-diffusion method with Gram-positive and Gram-negative bacteria as Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), respectively. The results showed that the hybrid sheets exhibited excellent antibacterial properties against these bacteria, in which the zones of inhibition were also dependent on the synthesized AgNPs by utilizing the different amounts of PVP.

Abstract: Sawdust is a waste from furnitureindustry which is mostly left in the garbage or burn for landfill in hugequantities every year. Efforts to find utilization of this material haveresulted mostly in low value. However, sawdust waste can be considered as analternative to fabricate fiber reinforced polymer composites for furniturefunction. This study was undertaken to determine the physical and mechanicalproperties of wood plastic composites, which were made under laboratoryconditions by hot pressing of high-density polyethylene (HDPE) with teakwoodsawdust as filler. Seven levels of mixed flour, 10, 20, 30, 40, 50, 60 and 70%,based on the composition by weight was added to the HDPE powder with palm oilas coupling agent. A flat pressing technology, the simplest method for capableof large dimension wood plastic panel production, was used to manufacturetesting specimens in dimensions 5.8 x 7.3 cm². Investigation of themechanical property of the composites material, according to the Americansociety for testing and materials (ASTM) method, was done by impact strengthtester. The measurement results were found that impact strength was decreased uponthe increasing of the sawdust up to 30 % mixing then gradually increased. However,by increasing mixed flour content, water resistance of the panels wasnegatively influenced. The best appearance of composites material in comparisonwith the natural woods was ~30% sawdust powder mixing. The woodplastic panels were utilized for construction of a Thai spirithouse as an outdoor decoration.

Abstract: Poly (lactic acid) (PLA) is a biopolymer derived from renewable resources and can be disposed of without creating harm to the environment. PLA can be formed by thermoplastic processes and has good mechanical properties. However, its disadvantages are a high crystallization temperature, slow crystallization rate, poor heat stability and low ductility. In the past, it was found that poly (D-lactic acid) (PDLA) can form complexes with poly (L-lactic acid) (PLLA) and the complexes could accelerate the crystallization and increase the degree of crystallinity of the PLA, but decrease the ductility. It is known that polyethylene glycol (PEG) can improve the ductility of PLLA. In this research, PDLA was copolymerized with PEG in an attempt to improve both crystallization behavior and ductility of PLLA. Poly (D-lactic acid)-co-polyethylene glycol (PDEG) was synthesized by ring opening polymerization using D-lactide and PEG at a D-lactide:PEG weight ratio of 10:3. The PDEG was blended with PLLA with a PDEG content of 0wt% to 50wt% by melt blending process. Fourier transform infrared spectrometry (FT-IR) and X-Ray diffractometry (XRD) confirmed the stereocomplex formation between PDEG and PLLA. Characterization by differential scanning calorimetry (DSC) revealed that crystallization temperatures of the blends were decreased in the presence of PDEG. Storage moduli and tan of the blends obtained from dynamic mechanical analysis (DMA) decreased as PDEG content increased. Polarized optical microscopy (POM) micrographs of blends with PDEG content of 1wt% to 5wt% obviously showed that crystallization rate was increased. PDEG has the potential to be an effective nucleating agent and efficient plasticizer for PLLA.

Abstract: Water resistant is drawback property of thermoplastic starch. Blending of hydrophobic starch to natural one is another solution. Different blending ratio of tapioca/octenyl succinate starch (OSA) at 0/100, 25/75, 50/50, 75/25, 100/0 were prepared using internal mixer, and molded by compression molding at 135-140°C, 1000-1500 MPa for 9 minutes. Density of the blend was decreased, due to lower density of OSA starch. There was mechanical properties improvement in 25% OSA blended tapioca starch i.e. tensile strength, Young’s modulus & elongation at break, due to synergy effect of OSA & tapioca starch. There was improvement in degradation temperature of the blend studying by TGA technique. Water resistance of the blend is improved related to the content of OSA starch in the blend on short time contact (10 min), but no impact at longer time exposure (1hr). The blend had a better resistant to degradation with a-amylase, which OSA starch could retard the degradation.

Abstract: Preparation of cellulose acetate (CA)/TiO₂/WO₃ composite nanofibers via sol-gel with electrospinning process for improving the photocatalytic efficiency was conducted. CA was removed from fibers by a heat treatment. Microstructure and elemental composition of TiO₂/WO₃ nanofibers were evaluated by scanning electron microscope (SEM) and energy dispersive microscopy (EDX), respectively. The results showed that the nanofibers of TiO₂ and WO₃ were achieved with the average diameter range of ca. 310-701 nm and both TiO₂ and WO₃ are well dispersed along fiber length, confirmed by an EDX analysis. The results also showed that the smoothness of fiber surface decreased with decreasing WO₃ contents. The photocatalytic activity of the materials were also tested for methylene blue degradation. TiO₂/WO₃ exhibited the highest activity comparing to pure TiO₂ and WO₃. Moreover, it was found that a TiO₂/WO₃ specimen possessed the energy storage ability as a result, it showed the photocatalytic activity in the absence of light.

Abstract: Poly(L-lactic acid) (PLA) has good mechanical properties and is biodegradable. However, its crystallization rate is slow, crystallization period long, and its crystallization temperature high at 116 °C. Consequently, long processing cycles are required for the production of high crystallinity poly (L-lactic acid). Addition of nucleating agents is an efficient way to solve this problem. Aliphatic amide such as N,N-ethylenebis(12-hydroxystearamide) and ethylenebis-stearamide are reported as nucleating agents for poly (L-lactic acid). In this study, the effect of the aliphatic polyamide, poly (hexamethylene succinamide) on the crystallization behavior of PLA was investigated. Poly (hexamethylene succinamide) was synthesized by melt polymerization. Between one and ten weight percent poly (hexamethylene succinamide) was blended with poly (L-lactic acid) by melt extrusion. The crystallization temperature and crystallization period decreased with increasing poly (hexamethylene succinamide) content. The degree of crystallinity increased with the addition of poly (hexamethylene succinamide). A poly (hexamethylene succinamide) content of 5%wt provides optimum conditions for production of poly (L-lactic acid)-poly (hexamethylene succinamide) blend with good mechanical properties. The polymers obtained are entirely from renewable resources.

Abstract: Polystyrene-grafted natural rubber (PS-GNR) at various graft levels was evaluated to improve mechanical properties of natural rubber (NR). PS-GNR was synthesized by emulsion copolymerization at 60°C at different reaction times between 15 and 360 mins to control the grafting levels of PS in the PS-GNR co-polymer. The resultant PS-GNR co-polymers were then blended into NR latex. The vulcanized NR compounds were investigated for the effect of PS grafting percentage in PS-GNR/NR compounds on mechanical properties, including tensile, tear strength and hardness. A core-shell structure was revealed with PS encapsulating the NR core via transmission electron microscopy. The polystyrene grafting percentage was determined to be 12.7%, 17.1%, 22.1% and 23.6% for polymerization times of 15 min, 60min, 120min, and 360 min, respectively. Addition of PS-GNR into NR exhibited biphasic behavior, resulting in a decrease in the tensile strength and tear strength. With further increase in grafting percentage of PS, the tensile strength and tear strength continues to decrease. The rigid chain of PS grafted onto NR surface reduced the elasticity of NR chain resulting in lower tear strength and the tensile strength. Fracture surface revealed a decrease in ductility of material with increasing grafting percentage of PS. On the other hand, modulus and hardness of PS-GNR/NR compounds were found to increase with increasing grafting percentage of PS. The addition of PS-GNR to rubber compound had shown an impact on dynamic behavior. With further increase in grafting percentage of PS in PS-GNR, an enhancement of storage modulus of rubber compound was clearly observed.

Abstract: In this research study, the degradation of natural rubber was applied for applications in agriculture products such as rubber mulch. This work included the synthesis of 20% wt silica/ natural rubber composites from high ammonia concentrate latex (HA) and fresh latex (FL). They were casted by film casting. The experimental study of rubber composite degradation was done by putting the samples underground and above the soil surface under accelerated degradation test box equipped with a solar simulator lamp for a period of 50 days. Samples were characterized by scanning electron microscopy (SEM) to examine the dispersion on cross-sectional area between natural rubber and silica. Thermogravimetric analysis (TGA) was used to analyze the thermal stability of the composites. Tensile strength (MPa), modulus at 100% elongation (MPa), and elongation at break (%) of the samples after aging were tested by focusing on. It was found that thermal degradation of natural rubber compounds consisted of one step of mass loss between 341°C and 455°C. The SEM result showed good dispersion of Si in the rubber samples. Moreover, it was found that before aging, the composite samples had higher tensile strength than that of the rubber. After aging, the composite samples had lower tensile strength than that of the rubber. Elongation @ break value of HA/Si and FL/Si after aging were decreased obviously.