The Studies On Preparation And Properties Of Soy Protein Isolate/Starch Biodegradable Material

In this paper, a kind of biodegradable material was made of soy protein isolate (SPI) andstarch, also its relevant processes and parameters were studied systematically. The bestpressing conditions of preparing the SPI/starch biodegradable material were as follows:pressing temperature120℃, hot pressure15MPa, pressing time15min. In the conditionwhich the content of starch was15%, using five-factors orthogonal rotation experiment, themodified conditions of SPI/starch biodegradable material were optimized. The optimumconditions were as follows: the addition of succinic anhydride30%, ultrasonic power240W,reaction time30min, the addition of glycerol20.27%, the added amount of water6%. Underthese conditions, the properties of the obtained SPI/starch biodegradable material were asfollows: elongation301.82%, tensile strength6.84MPa, water absorption46.74%. Thedegradation results showed: when the SPI/starch biodegradable material was buried in49days,in the aqueous soil solution environment, the rate of weight loss was62.14%weight; while inthe natural soil environment, the rate of weight loss was67.72%.The structure, composition and properties of SPI/starch biodegradable materials wereinvestigated with fourier transform infrared spectroscopy (FTIR), amino acid analyzer, X-raydiffraction (XRD), scanning electron microscopy (SEM), integrated thermal analysisinstrument (TG-DTA/DSC), and HAAKE torque rheometer. FTIR results showed that: in theSPI/starch biodegradable material, the emergence of new N-H bond meant it had reactionsbetween SPI and the starch molecules. In the secondary structure of SPI/starch biodegradablematerial, the content of α-helical was more than SPI’s, the content of β-sheet and β-turn wasless than SPI’s, the content of unordered structure was more than SPI’s. The spatial structureof SPI/starch complex molecules was changed. The results of amino acid analysis showed that:compared with the SPI, the total content of amino acid of the SPI/starch biodegradablematerial was decreased, and various contents of amino acids were decreased, while thecontents of arginine and lysine were reduced more. The results of X-ray diffraction analysisshowed that: the crystallinity of SPI was52.34%, the crystallinity of SPI material was56.51%,the crystallinity of SPI/starch biodegradable material was54.38%, the crystallinity ofSPI/starch biodegradable material was less than SPI material’s. The results of SEM analysisshowed that: in the SPI/starch biodegradable material, SPI and starch molecules combinedwith covalent binding, then the volume of molecular complexes increased and spread which reducing the aggregation of molecular. In thermodynamic performance test, the resultsshowed that: the glass transition temperature of raw SPI, SPI materials and SPI/starchbiodegradable materials were56.52℃,43.22℃and40.12℃respectively. In the SPI/starchbiodegradable materials, the thermal weight loss process could be divided into three processes:water volatilized when the temperature was100℃or so; glycerol volatilized when thetemperature was100～242.68℃; the degradation of SPI/starch molecules was happenedwhen the temperature followed by242.68℃. When the temperature was440.50℃, theresidual mass percentage of SPI/starch biodegradable material was34.04%.In HAAKE torquerheometer study, the results showed that: in the SPI/starch biodegradable material, SPI and thestarch molecules had complex reactions to form a new interaction, which causing changes inthe rheological properties of material. The torque trend of SPI/starch system showed abimodal, which meant increased.