Proton Nuclear Magnetic Resonance (1 H-NMR) Spectroscopy 1 HNMR spectra were obtained with a Varian Gemini 300 MHz NMR spectrometer. Solid samples were solubilised in deuterated dimethyl sulfoxide (DMSO-d6) and placed in 5 mm NMR tube. The spectra were collected at 25 oC over a spectra width of 4796 Hz using a 90o pulse. The acquisition time was 1.98 s, the relaxation delay (d1) was 5 s (the relaxation time (T1) of anomeric proton was measured to be 0.9 s), and 16 scans were accumulated. Data were processed with 0.5 Hz exponential line broadening and zero filled to 131,072 points before Fourier transformation.
- Synthesis of Chemically Modified Starch
- Preparation of Blends and Nanocomposites based on Modified Starch
Differential Scanning Calorimetry (DSC) The thermal transition temperatures of a modified starch, EVOH, blends, and nanocomposites prepared in the present research were determined by differential scanning calorimetry (DSC) (TA instruments). All DSC runs were made under a nitrogen atmosphere with heating rates of 10 oC/min. Indium and zinc were used to calibrate the temperature and the heat of fusion.
Optical Microscopy The phase separation of blends of modified starch and EVOH was observed by an optical microscope equipped with a hot stage (Instec) and a digital camera (Spot insight 2, Diagnostic Instrument). Specimens were cast from 1 wt % solution of polymer mixtures on a slide glass to obtain a film of about 2－3 μm in thickness, which was then first dried in a fume hood and subsequently in a vacuum oven. The heating rates employed were 0.5 oC/min. Images of single phase and separated phase were obtained by digital camera. At each weight fraction of EVOH, at least 5 samples were measured for determining the cloud point of the mixture, and an average value was obtained from the repeated measurements.
Fourier Transform Infrared (FTIR) Spectroscopy Using a Fourier transform infrared spectrometer (Perkin Elmer), FTIR spectra were obtained at room temperature for modified starches, blends of a modified starch and EVOH, and nanocomposites based on a modified starch with mode of attenuated total reflectance (ATR). Spectral resolution was maintained at 4 cm−1. Specimens were grinded into fine powders and slowly dried for 24 h in a fume hood until the solvent and moisture evaporated, and they were then stored in a vacuum oven until use.
Wide Angle X-ray Diffraction (WAXD) WAXD experiments were conducted at room temperature on the films, which were hot pressed by compression molding, using a General Electric X-ray generator (Model XRD-6) operated at 30 kV and 30 mA (Nifiltered Cu Kα radiation). For annealed specimens, the films were first heated at 200 oC for 5 min and then immediately transferred to a vacuum oven in which the temperature was regulated at an annealing temperature. The samples were annealed for at least 3 h and quenched by liquid nitrogen before the WAXD measurements began.
X-ray Diffraction (XRD) Using a Rigaku X-ray generator operated at 40 kV and 150 mA, X-ray diffraction patterns were obtained to determine the mean interlayer spacing of the (001) plane (d001) for the natural clay or organoclays, and their nanocomposites. The X-ray beam was monochromatized to Cu Kα with a graphite crystal. The range of 2θ scanning of X-ray intensity employed was 1.5–10 degrees.
Transmission Electron Microscopy (TEM) TEM images of specimens were taken at room temperature. The ultrathin sectioning (around 100 nm) was performed by ultramicrotomy at room temperature for the clay (or organoclay) nanocomposites. A transmission electron microscope (JEM1200EX 11, JEOL) operated at 120 kV was used to obtain images of nanocomposite specimens.
Thermogravometric Analysis (TGA) The thermal degradation temperature of polymers was determined by a thermogravometric analyzer (TGA 2050, TA Instrument). All TGA data was obtained under a nitrongen atmosphere at a heating rate of 10 oC/min, and the thermal degradation temperature was determined at the point of 90 wt % of the original weight.
Tensile Test The tensile test of the blends and nanocomposites based on a modified starch was performed by a tensile tester (Instron, Model 5567), following the ASTM standard, D638-00. The load cell used for the tensile test was an Instron static load cell with a 10 kN capacity. A cross-head speed of 5 mm/min was used for the test. The upper yield stress on the stress-strain curve was considered as the tensile strength. For all the results reported in this dissertation, at least 3 replicates of specimens were tested, and an average value of the measured values was used. All specimens for tensile testing were compounded by a twin-screw mini compounder (Haake Instruments) and hot compressed into films with uniform thickness. Then the films were cut into dumbbell shape for the tensile test. The thickness and length of the specimens were accurately measured before use.
Hydrophilicity Test Saturated aqueous sodium chloride solution was prepared, and it was put into a sealable chamber. The ambient temperature of this chamber was kept around 20 °C. In this way, the constant relative humidity (74%) was obtained in the chamber. Dried, chemically modified starch samples were put into the chamber after being accurately weighed. Then the samples were weighed every two days until the weight did not change further.
Biodegradability Test Materials that were to be characterized for their biodegradability include NS (the positive control), modified starches employed in the present study, and LDPE (the negative control). Since dry natural starch is not processable, it was premixed with 10 wt % of glycerol (acting as plasticizer) by mini twin-screw compounder. All materials were molded between two Teflon sheets into thin films (25×50×1 mm ) by applying a 250 kg/cm2 pressure using a preheated hydraulic press, and accurately weighted by digital balance. Every sample had 10 duplicates with the same size and weight. The compost was offered by KB Compost Services, Inc. The composition of the compost was (approximate dry weight): 5% animal dung; 10% sawdust; 10% shredded paper; 10% food waste; 20% shredded leaves; and 45% garden soil. The compost was fully shredded and sifted to remove large clumps. The moisture content of the compost was maintained by periodic spraying of water. To avoid anaerobic condition, the compost was aerated by turning at least 3 times a week. All samples were buried inside the compost at a depth of at least 1.5 feet. One duplicate of each sample was dug out every two weeks and weighed after thorough washing with water and drying in a vacuum oven until it reached a constant weight. The weight loss (Wloss) was calculated by:
Wloss = ((Winitial – Wweighted)/Winitial)x100%