8/13/2019 Posible aplicacin de acido esterico en plsticos biodegradables

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Abstract

Most plastics, at present, are petroleum-based and do not degrade over many decades under

normal environmental conditions. As a result, efforts towards developing environment-friendly and

biodegradable green plastics for various commercial applications have gained significant

momentum in recent years. Soy protein isolate (SPI)-based green plastics have been shown to

suffer from high moisture sensitivity and low strength. These properties have limited their use in

most commercial applications. They are also difficult to process into sheets without any plasticizer.

The commonly used plasticizer, glycerol, tends to leach out over time producing time-dependent

properties, which is highly undesirable for commercial applications. The objectives of the current

research are to reduce the moisture sensitivity and simultaneously improve the tensile properties of

SPI by incorporation of stearic acid without affecting its biodegradability. The effect of stearic acid

and glycerol on the tensile and thermal properties of SPI has been characterized using various

techniques to determine the interaction mechanisms between stearic acid and soy protein.

Mechanical properties were characterized using Instron tensile tester. Attenuated total reflectance-

Fourier transform infrared (ATR-FTIR) spectroscopy, differential scanning calorimetry (DSC),

thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) techniques have been used to

determine the effects of stearic acid and glycerol on the surface chemistry, thermal transitions and

thermal degradation of the stearic acid modified SPI plastic (resin). The tensile test results show

that Youngs modulus increased on increasing the stearic acid content, reaching the maximum

value at about 25% (by weight of SPI powder) stearic acid. Further increase in stearic acid content

from 25 to 30% led to a reduction in Youngs modulus. The moisture content, fracture stress, strain,

and energy at break decreased steadily on increasing the stearic acid from 0 to 30% for SPI

containing 30% glycerol. At 25% stearic acid content, the modulus and the fracture stress increased

significantly, whereas the fracture strain, energy at break and the moisture content decreased on

reducing glycerol content. Scanning electron microscopy photomicrographs of fractured surfaces

showed a layered structure for stearic acid modified-SPI resin. TGA measurements showed that the

thermal degradation of stearic acid modified-SPI resin initiated at higher temperature than the SPI

resin. DSC scans indicated that stearic acid modified-SPI resin had a small degree of crystallinity,

which was confirmed by X-ray diffraction patterns. Modifying SPI resin with stearic acid has been

successful in obtaining better tensile and thermal properties as well as reduced moisture sensitivity

without any processing problems.