Biocomposites of poly(lactic acid) and lactic acid oligomer-grafted bacterial cellulose: It's preparation and characterization

This work demonstrates the synthesis of lactic acid oligomer-grafted-untreated bacterial cellulose (OLLA-g-BC) by in situ condensation polymerization which increased compatibilization between hydrophobic poly(lactic acid) (PLA) and hydrophilic BC, thus enhancing various properties of PLA-based bionanocomposites, indispensable for stringent food-packaging applications. During the synthesis of OLLA-g-BC, hydrophilic BC is converted into hydrophobic due to structural grafting of OLLA chains with BC molecules. Subsequently, bionanocomposites films are fabricated using solution casting technique and characterized for structural, thermal, mechanical, optical, and gas-barrier properties. Morphological images showed uniform dispersion of BC nanospheres in the PLA matrix, which shows strong filler–matrix interaction. The degradation temperatures for bionanocomposites films were above PLA processing temperature indicating that bionanocomposite processing can be industrially viable. Bionanocomposites films displayed decrease in glass transition (T g ) and ~20% improvement in elongation with 10 wt % fillers indicating towards plasticization of PLA. PLA/OLLA-g-BC films showed a slight reduction in optical transparency but had excellent UV-blocking characteristics. Moreover, dispersed BC act as blocking agents within PLA matrix, reducing the diffusion through the bionanocomposite films which showed ~40% improvement in water-vapor barrier by 5 wt % filler addition, which is significant. The reduced T g , improved elongation combined with improved hydrophobicity and water-vapor barrier make them suitable candidate for flexible food-packaging applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47903. © 2019 Wiley Periodicals, Inc

Pengaruh Model Pembelajaran Guided Inquiry dengan Mind Map terhadap Hasil Belajar dan Motivasi Siswa pada Materi Redoks di Kelas X SMA Negeri 5 Palu

This study aimed to investigate the effect of guided inquiry learning model with mind map toward learning achievement and motivation of students on Reduction-Oxidation in Class X at SMA 5 Palu. This study was a quasi-experimental design with a non-randomized pretest-posttest control group design. This study was carried out by holding two groups of Class X Sciences 1 as the experimental group (n = 31) and Class X Sciences2 as the control group (n = 32). Testing of learning achievement data of students used t-test statistical analysis of two parties with the prerequisite tests: normality and homogeneity tests of written test given after learning (posttest). Results of the data analysis showed the average value (i) of the experimental class was 56.48 with a standard deviation of 11.07, and (ii) of the control class was 46.25 with a standard deviation of 11.98. Based on the hypothesis test results with t-test statistical of two parties obtained -ttable ≤ tcountt≥ + ttable (tcount = 2.43 and ttable= 1.67) with a significance level of α = 0.05 and degrees of freedom of 61, then H0 is rejected and Ha is accepted. Results of the data analysis of students motivation by using descriptive statistical analysis from the questionnaire of students motivation showed that the experimental class was currently on attitudes agree with the positive category of 82.58%, and the control class was on attitudes agree with the positive category of 83.78%.It can be concluded that there was an effect of guided inquiry learning model with mind map toward learning achievement of students, but it had no effect on the motivation of students in Class X at SMA 5 Palu on Reduction-Oxidation

Aerodynamic Performances of MAV Wing Shapes / N. I. Ismail...[et al.]

In general, there are four common Low Reynolds Number wing’s designs for fixed wing Micro Air Vehicle (MAV) which known as Rectangular, Zimmerman, Inverse Zimmerman and Ellipse wing. However, each wing design produces diverse performance and in fact the aerodynamic comparison study among the wings is still lack. Thus, the objective of this study is to evaluate the basic aerodynamic performance found on Rectangular, Zimmerman, Inverse Zimmerman and Ellipse wing designs with view to find the optimal wing shape for Micro Air Vehicle (MAV) configuration. Here, each design was analysed based on simulation works. The results show that at stall angle, the Ellipse wing has maximum lift coefficient ( ) recorded at 1.12 which is at least 4.33% higher than the other wing designs. Based on drag coefficient ( ) analysis, the Inverse Zimmerman Wing exhibited the lowest minimum drag value at 0.033 which is 8.45% lower than the other wing’s designs. In moment coefficient analysis, the results reveal that the Inverse Zimmerman Wing has produced the steepest curve slope value at -0.36 which is 17.39% higher than the other wings. The aerodynamic efficiency ( ⁄) study has also revealed that Zimmerman Wing recorded the highest ⁄value at 6.80 and at least 1.35% higher than to the other wing. Based on these results, it was concluded that Zimmerman wing has the highest potential to be adopted as MAV wing due to its optimal aerodynamic efficiency

Melting behaviour of poly(lactic acid)-hemp-silica composites by modulated temperature differential scanning calorimetry

Abstract too long

Multiple melting behavior of poly(lactic acid)-hemp-silica composites using modulated-temperature differential scanning calorimetry

Poly(lactic acid) (PLA)-hemp-nanosilica (PHS) composites were prepared by impregnation of hemp woven fabric with PLA solution. Nanosilica was dispersed in the PLA solution to introduce a matrix reinforcing nanophase within the composite. The melting behavior of PLA composites was obtained by using differential scanning calorimetry (DSC) and modulated-temperature DSC (mT-DSC). Multiple melting which appeared in the non-isothermal heating curve showed that the temperature of a low melting peak increased when using a slower scanning rate. The incorporation of nanosilica in PLA composites affected the melting temperature (Tm) and sufficiently formed nucleation sites that promoted the growth of PLA crystals. Composites analyzed by a temperature-modulated program showed a broad exothermic peak before the melting peak in the non-reversing heat capacity and endothermic melting in the reversing heat capacity curve. This behavior was explained by a process of partial melting, recrystallization and remelting (mrr). The mT-DSC resolved that hemp fiber induced recrystallization and nanosilica acted as an effective nucleating agent, which promoted small and imperfect crystals that changed successively into more stable crystals through a melt-recrystallization process

Mechanical properties of self-reinforced poly(lactic acid) composites prepared by compression moulding of non-woven precursors

A hot compaction method has been used to form all-PLA composites by partial melting and fusion of fibres in non-woven mats where the matrix phase is formed from partially melted fibres and the reinforcement phase is the original PLA fibres that remain. Compaction required a minimum of 10 min heating at temperature range 172°C to 176°C under a load of 2.4 MPa. An advantage is that the oriented high tensile strength fibre properties are retained, while matrix adhesion is strong because melt adhesion is provided by the same polymer. The all-PLA composite structure was confirmed using scanning electron microscopy (SEM) and wide-angle X-ray scattering. Mechanical properties were evaluated from modulated force thermo-mechanical analysis. The temperature window below melting temperature of PLA of about at 172°C to 176°C was found as the optimum temperature for all-PLA composites with optimum properties. SEM study also shown the gaps between the fibers are filled with recrystallised material that has melted from the original fibre

Melting behaviour and dynamic mechanical properties of poly (lactic acid) - hemp - nanosilica

Poly(lactic acid)-hemp-nanosilica composites were prepared with a film stacking method. Melting behaviour of PLA composites was obtained using differential scanning calorimetry (DSC) and modulated-temperature DSC (mT-DSC). Crystallization and melting behaviour of the composites was studied in the range of 60-170 C at various heating rates with non-isothermal DSC. DSC results confirmed that the cold crystallization enthalpy gradually decreased corresponding with an increase in filler content. Multiple melting endotherms observed through mT-DSC were explained by a process of partial melting, recrystallization and remelting (mrr). The dynamic mechanical properties were determined via modulated force thermomechanometry. Better interfacial bonding was evidenced by an increased storage modulus with nanosilica addition, while the damping factor decreased respectively

Poly(lactic acid)-hemp-nanosilica hybrid composites: Thermomechanical, thermal behavior and morphological properties

PLA-hemp-nanosilica composites were prepared by a film stacking method, using hot compaction in a heated press with interspersed layers of hemp fibre. Dynamic mechanical properties measured with modulated force thermomechanometry (mf-TM) showed that the storage modulus increased with increase in filler loading due to increasing restriction to mobility of polymer molecule. The loss modulus and tan(?) in contrast showed an opposite trend. Thermal property of the composites was assessed using differential scanning calorimetry (DSC). DSC results were determined with increasing scanning rate, the temperature of a low melting peak increased. Double melting behaviour appeared in the heating curve when using a slower scanning rate. Nano-silica promoted small and imperfect crystals that changed successively into more stable crystals through a melt-recrystallization process

Poly(lactic acid) hemp composites combined with nano-silica

An important issue for all composites is reduction of creep. The reinforcing fibers dramatically reduce creep, however nano-composites can improve tensile properties and toughness. The aim of this work is to prepare and characterize PLA combined hemp-fiber and nano-silica composites